WO2020095221A1 - Urea production method and device - Google Patents

Urea production method and device Download PDF

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Publication number
WO2020095221A1
WO2020095221A1 PCT/IB2019/059527 IB2019059527W WO2020095221A1 WO 2020095221 A1 WO2020095221 A1 WO 2020095221A1 IB 2019059527 W IB2019059527 W IB 2019059527W WO 2020095221 A1 WO2020095221 A1 WO 2020095221A1
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Prior art keywords
low
pressure
pressure steam
urea
steam condensate
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PCT/IB2019/059527
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French (fr)
Japanese (ja)
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小嶋保彦
佐々木啓伍
柳川貴弘
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東洋エンジニアリング株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
    • C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
    • C07C273/04—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds from carbon dioxide and ammonia
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
    • C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
    • C07C273/14—Separation; Purification; Stabilisation; Use of additives
    • C07C273/16—Separation; Purification
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C275/00—Derivatives of urea, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/141—Feedstock
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals

Definitions

  • the present invention relates to a method and an apparatus for producing urea from ammonia and carbon dioxide.
  • the urea production method typically includes a synthesis step, a high-pressure decomposition step, a condensation step, and a purification step and a concentration step.
  • urea is generated from ammonia (NH 3 ) and carbon dioxide (CO 2 ).
  • ammonium carbamate (NH 2 COONH 4 ) is produced by the reaction of ammonia (NH 3 ) and carbon dioxide (CO 2 ).
  • urea (NH 2 CONH 2 ) and water (H 2 O) are produced by the dehydration reaction of ammonium carbamate.
  • Both reactions are equilibrium reactions, but the reaction of (2) is slower and rate-determining than the reaction of (1).
  • the urea synthesis solution obtained in the synthesis step is heated to decompose ammonium carbamate contained in the urea synthesis solution into ammonia and carbon dioxide, a mixed gas containing ammonia and carbon dioxide, and a higher concentration. To obtain a urea synthesis solution.
  • the condensation step the mixed gas obtained in the high pressure decomposition step is condensed.
  • the urea synthesis liquid after being treated in the high-pressure decomposition process is heated at a pressure lower than the pressure in the high-pressure decomposition process and higher than atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. By doing so, a urea synthesis solution having an increased urea concentration is obtained.
  • the urea synthesis liquid that has been treated in the purification step is heated at a pressure lower than the pressure in the purification step and at an atmospheric pressure or a pressure lower than atmospheric pressure to generate a gas phase and a liquid phase.
  • a urea synthesis solution having a further increased urea concentration is obtained.
  • Non-Patent Document 1 Such a urea production method is disclosed in Non-Patent Document 1 and Patent Document 1.
  • the steam condensate generated when the low-pressure steam is consumed (that is, used as a heating source) in the refining process and the concentration process is decompressed, and the resulting steam condensate at 100 ° C. is supplied to the condensation process. Used as a condensate.
  • This steam condensate is at 100 ° C., so its pressure is atmospheric pressure.
  • the steam condensate generated when low-pressure steam is consumed in the refining process and the concentration process is depressurized to about atmospheric pressure (1.2 bar) and then flushed to generate steam at about atmospheric pressure. Is used to heat the ammonia.
  • Patent Document 1 describes a method in which steam condensate generated in the refining process and / or the concentrating process is used as a heating source of raw material ammonia supplied to the synthesis process.
  • Non-Patent Document 1 the low-pressure steam condensate generated when low-pressure steam is consumed in the refining process and the concentration process is decompressed to generate atmospheric pressure steam condensate.
  • the atmospheric pressure steam condensate has a low temperature
  • the amount of low-pressure steam generated in the condensation process is reduced. That is, the amount of heat that can be recovered by the steam condensate at atmospheric pressure is small. Further, the head of the pump required to raise the pressure of the steam condensate supplied to the condensation step becomes high.
  • Non-Patent Document 1 has a low temperature, and therefore, the applications in which this steam can be used as a heating source are limited, and the heat transfer area of the heat exchanger when used as a heating source is limited. Will become bigger. Thus, the utility value of atmospheric steam condensate and steam is not high.
  • Patent Document 1 does not describe the pressure level of the steam condensate used for heating the raw material ammonia.
  • An object of the present invention is to provide a urea production method and apparatus capable of obtaining relatively useful steam condensate and steam from low-pressure steam condensate generated when low-pressure steam is consumed in a purification step and / or a concentration step. It is to be.
  • a synthesis step of synthesizing urea from ammonia and carbon dioxide to produce a urea synthesis solution By heating the urea synthesis solution generated in the synthesis step, to decompose ammonium carbamate, and a high-pressure decomposition step of separating a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution, At least a part of the mixed gas obtained in the high-pressure decomposition step is absorbed into an absorption medium and condensed, and a condensation step of generating low-pressure steam using heat generated during this condensation, Heating the urea synthesis liquid after being treated in the high-pressure decomposition step at a pressure lower than the pressure in the high-pressure decomposition step and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase.
  • the condensing step A part of the low-pressure steam generated in, a refining step,
  • the urea synthesis liquid that has been treated in the purification step is heated at a pressure lower than the pressure in the purification step and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated.
  • Fluid generation process A method for producing urea is provided, which comprises:
  • a synthesizer configured to synthesize urea from ammonia and carbon dioxide to produce a urea synthesis solution; By heating the urea synthesis solution generated in the synthesizer, to decompose ammonium carbamate, and a high-pressure decomposer configured to separate a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution, A condenser configured to absorb and condense at least a part of the mixed gas obtained in the high-pressure decomposer with an absorption medium, and to generate low-pressure steam using heat generated during the condensation, Heating the urea synthesis liquid after being treated in the high-pressure decomposer at a pressure lower than the pressure of the high-pressure decomposer and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase A purification device configured to obtain a urea synthetic solution having an increased urea concentration and to generate low-pressure steam condensate, wherein the urea synthetic solution after
  • a refining apparatus including a heat exchange structure for heating using a part of the low-pressure steam that has been made,
  • the urea synthesis liquid after being treated in the purification device is heated at a pressure lower than the pressure of the purification device and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated.
  • the concentration device is configured to generate a low pressure steam condensate as well as to obtain a urea synthesis liquid having a further increased urea concentration, and the urea synthesis liquid after being treated by the purification device is treated by the condensation device.
  • a concentrating device comprising a heat exchange structure for heating with another part of the generated low pressure steam, At least a part of the low-pressure steam condensate obtained from one or both of the refining device and the concentrating device is decompressed to a pressure higher than atmospheric pressure to generate low-low pressure steam condensate and low-low pressure steam.
  • Low and low pressure fluid generator There is provided a urea production apparatus including:
  • the urea manufacturing method and apparatus which can obtain a steam condensate and steam with comparatively high utility from the low pressure steam condensate produced when low pressure steam is consumed in a refinement
  • the urea production method according to the present invention includes a synthesis step, a high pressure decomposition step, a condensation step, a purification step, a concentration step, and a low / low pressure fluid generation step.
  • the urea production method according to the present invention can further include a step of recovering the raw material in the gas (recovery step). Ammonia and carbon dioxide as raw materials can be externally supplied to one or more of the synthesis process, the high-pressure decomposition process, the condensation process, the purification process, and the recovery process.
  • urea is synthesized from ammonia and carbon dioxide to produce a urea synthesis solution.
  • urea is also synthesized from ammonium carbamate contained in the circulating liquid from the condensation step described later.
  • the operating pressure in the synthesis step is generally from 130 bar (absolute pressure; also below) to 250 bar, preferably from 140 bar to 200 bar, the temperature generally from 160 ° C to 200 ° C, preferably from 170 ° C. It is 190 ° C.
  • High-pressure decomposition process In the high-pressure decomposition step, medium pressure steam is typically used as a heating source to heat the urea synthesis liquid produced in the synthesis step. As a result, ammonium carbamate contained in the urea synthesis liquid obtained from the synthesis step is decomposed, and the mixed gas containing ammonia and carbon dioxide is separated from the urea synthesis liquid.
  • this mixed gas obtained from the high-pressure decomposition step may be referred to as “high-pressure decomposition outlet gas”. Further, the intermediate-pressure steam condensate is generated by the condensation of the intermediate-pressure steam used as the heating source.
  • -A high-temperature heating medium is required for heating in the high-pressure decomposition process.
  • medium-pressure steam having a higher pressure than low-pressure steam is used because the temperature of the low-pressure steam recovered in the condensation step described later is insufficient.
  • the pressure of medium pressure steam is generally 12 to 40 bar, preferably 14 to 25 bar.
  • the pressure of medium-pressure steam condensate is similar.
  • Medium pressure steam is often generated as appropriate as back pressure steam of the steam turbine in the urea manufacturing plant. Alternatively, it can be supplied from outside the urea production plant.
  • the operating temperature of the high-pressure decomposition step is generally 150 ° C to 220 ° C, preferably 160 ° C to 200 ° C.
  • the urea synthesis solution obtained in the synthesis process contains urea, ammonia, carbon dioxide, ammonium carbamate and water.
  • the urea synthesis solution is usually heated under a pressure substantially equal to the pressure of the synthesis step, whereby the ammonium carbamate is decomposed into ammonia and carbon dioxide.
  • the obtained ammonia and carbon dioxide, unreacted ammonia, unreacted carbon dioxide, and water are separated as a mixed gas containing ammonia, carbon dioxide, and water.
  • condensation step At least a part of the mixed gas (high pressure decomposition outlet gas) obtained in the high pressure decomposition step is absorbed by the absorption medium and condensed. The heat generated during this condensation is used to generate low pressure steam.
  • the low pressure steam is used as a heating source for heating another fluid, the low pressure steam is condensed to generate a low pressure steam condensate.
  • the pressure of the low pressure steam is generally 3 to 9 bar, preferably 5 to 7 bar.
  • the pressure of low pressure steam condensate is similar.
  • water which may contain urea, ammonia, carbon dioxide and ammonium carbamate
  • the like known in the field of the urea production method can be appropriately used.
  • the temperature of the liquid (process fluid) obtained in the condensation step is generally 100 ° C to 210 ° C, preferably 160 ° C to 190 ° C.
  • the high pressure process including the synthesis process, the high pressure decomposition process and the condensation process
  • the high-pressure decomposition step and the condensation step have almost the same pressure.
  • the mixed gas separated in the high-pressure decomposition process (high-pressure decomposition outlet gas) is introduced into the condensation process and comes into contact with the absorption medium containing water under cooling, and this mixed gas is condensed.
  • this mixed gas is condensed.
  • a part of ammonia and carbon dioxide becomes ammonium carbamate (see the above formula (1)), and the urea synthesis reaction (see the above formula (2)) also proceeds by keeping the condensation temperature high.
  • a large amount of heat is generated when the mixed gas condenses in the condensation process, but heat is recovered to make effective use of this heat.
  • a method of heat recovery there is a method of exchanging heat between the urea synthesis liquid after being treated in the high-pressure decomposition step and the internal fluid (process fluid) of the condenser.
  • a method of exchanging heat between the internal fluid (process fluid) of the condenser and the steam condensate (particularly low pressure steam condensate) to generate low pressure steam is adopted.
  • this method can be combined with at least one of the above two methods.
  • the condensation process it is necessary to supply steam condensate in order to generate low-pressure steam by heat recovery.
  • the low-pressure steam condensate can be supplied to the vessel and the low-pressure steam condensate can be transferred from the vessel to the condenser.
  • the steam condensate supplied to the condensation process (condenser) in order to generate the low-pressure steam may be referred to as “condensation process supply steam condensate”.
  • the medium-pressure steam condensate generated in the high-pressure decomposition process is often decompressed and used as the steam condensate for the condensation process supply.
  • the medium-pressure steam condensate may be used as a steam condensate for supplying the condensing process after the temperature is lowered by being used as a heating source for another process.
  • the amount of low-pressure steam generated in the condensation step is large, it is general that the amount of steam condensate supplied to the condensation step is insufficient only with the medium-pressure steam condensate generated in the high-pressure decomposition step.
  • At least a part of the low and low pressure steam condensate which will be described in detail later (usually a part of the low and low pressure steam condensate), is used as a steam condensate for the condensation process supply for increasing the pressure by a pump to generate low pressure steam in the condensation process. Can be used.
  • Vertical or horizontal shell and tube heat exchangers can be used for heat exchange between the condenser internal fluid (process fluid) and steam condensate.
  • a method of condensing the mixed gas on the tube side can also be adopted, but a method of condensing the mixed gas on the shell side can also be adopted so that the residence time in the condensation step can be extended for condensation and reaction. ..
  • the gas not condensed in the condensation step may be appropriately decompressed, and then the absorption medium may be cooled while being absorbed and condensed in the absorption medium (liquid) to obtain a recovery liquid containing ammonia and carbon dioxide. Yes (collection process). Unreacted ammonia and unreacted carbon dioxide can be recovered by returning the recovered liquid to a high-pressure process (including a synthesis process, a high-pressure decomposition process and a condensation process), usually a condensation process, after appropriately increasing the pressure.
  • a high-pressure process including a synthesis process, a high-pressure decomposition process and a condensation process
  • water which may contain urea, ammonia, carbon dioxide and ammonium carbamate
  • the like known in the field of the urea production method can be appropriately used.
  • a synthesizer performing the synthesizing process
  • a condenser performing the condensing process
  • the condensate is gravity-generated
  • a circulation method there is a method in which the raw material ammonia supplied to the synthesizer is used as a driving fluid and the condensate obtained in the condensation step is pressurized by an ejector and circulated. Further, the method of circulating using gravity and the method of circulating using an ejector may be combined.
  • This mixed gas can be collected in the absorption medium (cooling process) by cooling the absorption medium while absorbing and condensing it in the absorption medium (liquid). Unreacted ammonia and unreacted carbon dioxide can be recovered by returning this recovered liquid to the high-pressure process, usually the condensation step.
  • the absorption medium water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
  • the urea synthesis liquid after being treated in the high-pressure decomposition process is efficiently reduced in content of ammonia, carbon dioxide, ammonium carbamate and water by performing treatment by decompression and heating in multiple stages. , High concentration product urea can be obtained. Therefore, a purification process and a concentration process are performed.
  • the low pressure steam generated in the condensing process can be used as a heating source.
  • This low-pressure steam has a lower temperature than the medium-pressure steam used as a heating source in the high-pressure decomposition process.
  • medium-pressure steam condensate in addition to low-pressure steam, can be used in combination as a heating source, and / or steam generated by decompressing medium-pressure steam condensate is used in combination. be able to.
  • the medium-pressure steam condensate is a steam condensate generated by consuming medium-pressure steam as a heating source.
  • the urea synthesis liquid after being treated in the high pressure decomposition step is used as a heating source at a pressure lower than the high pressure decomposition step and higher than the atmospheric pressure, using a part of the low pressure steam generated in the condensation step. Heating produces a gas phase and a liquid phase. At this time, ammonium carbamate contained in the urea synthesis liquid after being treated in the high-pressure decomposition step can be decomposed. By separating this gas phase from the liquid phase, a urea synthesis solution having an increased urea concentration is obtained. In addition, low pressure steam condensate is generated from the low pressure steam used as a heating source.
  • depressurization is performed at least once and heating is performed at least once in the purification process.
  • the purification process can be performed in one step or in multiple steps.
  • the refining process can be performed in two steps, a medium pressure decomposition process and a low pressure decomposition process.
  • the urea synthesis liquid immediately after being treated in the high-pressure decomposition step is decompressed to a pressure exceeding atmospheric pressure, and heated if necessary to generate a gas phase (mixed gas) and a liquid phase, This is the step of separating the gas phase.
  • heat may be recovered in the condensation step by heat exchange between the urea synthesis liquid immediately after being treated in the high-pressure decomposition step and the internal fluid (process fluid) of the condenser.
  • the step of heating the urea synthesis solution after being heated by the heat recovery at a pressure lower than that in the high pressure decomposition step to separate the mixed gas corresponds to the intermediate pressure decomposition step.
  • low pressure steam can be used as a heating source.
  • ammonium carbamate contained in the urea synthesis solution after being treated in the high pressure decomposition step is decomposed.
  • a mixed gas containing ammonia and carbon dioxide hereinafter, also referred to as “medium-pressure decomposition outlet gas”
  • a urea synthesis solution having a reduced ammonium carbamate concentration can be obtained.
  • the operating pressure of the medium-pressure decomposition process depends on how many stages of pressure reduction and heat treatment are performed, but in the case of two stages (medium-pressure decomposition process and low-pressure decomposition process), it is generally 3 bar to 130 bar, It is preferably from 6 bar to 70 bar, more preferably from 10 bar to 20 bar.
  • the operating temperature of the medium pressure decomposition step depends on the operating pressure, but is generally 100 ° C to 180 ° C, preferably about 130 ° C to 170 ° C.
  • the urea synthesis liquid after being treated in the intermediate-pressure decomposition step can be decompressed and / or heated at a pressure lower than the intermediate-pressure decomposition step (however, atmospheric pressure or higher).
  • a mixed gas containing ammonia and carbon dioxide hereinafter, also referred to as “low-pressure decomposition outlet gas”
  • a urea synthesis solution having a further reduced ammonium carbamate concentration can be obtained.
  • the operating pressure of the low-pressure decomposition process is generally 1.5 bar to 6 bar, preferably 2 bar to 4 bar.
  • the operating temperature of the low-pressure decomposition step depends on the operating pressure, but is generally about 90 ° C to 170 ° C, preferably about 110 ° C to 150 ° C.
  • the refining device that performs the refining process can include a pressure reducing valve for depressurizing, a heat exchange structure for heating, and a gas-liquid separation structure.
  • the intermediate-pressure decomposer that performs the intermediate-pressure decomposition step can have a heat exchange structure between steam as a heating source and the process fluid (urea synthesis solution).
  • a pressure reducing valve for reducing the pressure can be arranged upstream of the intermediate pressure decomposer with reference to the flow of the process fluid (urea synthesis liquid).
  • the urea synthesis liquid after being treated in the purification step is subjected to the condensation step at a pressure lower than the pressure of the purification step (pressure after the last depressurization operation in the purification step) and at atmospheric pressure or pressure lower than atmospheric pressure.
  • Another part of the generated low-pressure steam is used as a heating source to heat the gas to generate a gas phase and a liquid phase.
  • a urea synthesis liquid having a further increased urea concentration is obtained.
  • low pressure steam condensate is generated from the low pressure steam used as a heating source.
  • the concentration step the content of water contained in the urea synthesis solution is reduced by heating under atmospheric pressure or under vacuum.
  • the depressurizing operation is performed at least once, and the heating operation is performed at least once.
  • the concentration step can be performed in one step or in multiple steps.
  • the concentration step can be performed in two steps.
  • the prilled solid urea can be produced by performing the two-stage concentration under the following conditions.
  • First stage Urea concentration 80-98% by mass
  • Pressure 100 mmHg (0.13 bar) to 500 mmHg (0.67 bar), preferably 150 mmHg (0.20 bar) to 350 mmHg (0.47 bar)
  • Temperature 125-140 ° C.
  • Second stage Urea concentration 94-99.9% by mass
  • Temperature 130-145 ° C.
  • the concentrating device that performs the concentrating step can include a pressure reducing valve for reducing the pressure, a heat exchange structure for performing heating, and a gas-liquid separation structure.
  • the urea obtained from the concentration step can be used as the product urea, or the granulation step can be performed after the concentration step to obtain the granular product urea.
  • Low and low pressure fluid generation process In the low-low pressure fluid generation process, at least a part of the low-pressure steam condensate obtained from one or both of the purification process and the concentration process is depressurized to a pressure higher than the atmospheric pressure to reduce the low-pressure steam condensate and the low-pressure steam. Generate.
  • the low and low pressure steam condensates and the low and low pressure steam have a pressure above atmospheric pressure and lower than the low pressure steam condensate obtained from one or both of the refining and concentration steps.
  • the low and low pressure steam condensate and the low and low pressure steam have a lower pressure than the low pressure steam generated in the condensation process.
  • Low and low pressure steam condensate and low and low pressure steam are more useful than atmospheric pressure steam condensate and steam, respectively.
  • the low / low pressure fluid generation device used for performing the low / low pressure fluid generation step may include a pressure reducing valve and may further include a gas-liquid separator (vessel).
  • the pressure of the low and low pressure steam and the low and low pressure steam condensate is preferably 2 bar or more, more preferably 3 bar or more.
  • the pressure difference between the low and low pressure steam and the pressure of the low and low pressure steam condensate and the low pressure steam generated in the condensation step is preferably 1 bar or more, more preferably 2 bar or more.
  • the low and low pressure steam can be used as a heating source in the urea production apparatus.
  • the usage destination as a heating source is preheating of raw material ammonia, heating of air supplied to the granulation process, and heating in the low-pressure decomposition process and concentration process (decomposition and concentration of synthetic solution, concentration of urea aqueous solution). ..
  • their use as heating sources for low and low pressure steam is effective in that order. For example, it is most effective to use low and low pressure steam for preheating the feedstock ammonia.
  • the flow of low and low pressure steam can be appropriately branched and each branched flow can be used as each heating source.
  • the urea synthesis liquid that has been treated in the purification step can be heated using at least a part of the low and low pressure steam, and then can be heated using the low pressure steam.
  • the concentrator is configured to heat the urea synthesis liquid after it has been treated in the refiner with at least a portion of the low and low pressure steam, and this heat exchange structure provided downstream thereof.
  • a heat exchange structure configured to heat the structure-heated urea synthesis liquid with low pressure steam.
  • Ammonia preheating process with low and low pressure steam At least a part of the low and low pressure steam can be used as a heating source to heat the raw material ammonia.
  • a device ammonia preheater
  • an appropriate heat exchange structure heat exchange between the raw material ammonia and the low and low pressure steam
  • At least a part of the low- and low-pressure steam condensate can be used as a steam condensate for supplying the condensation process for generating low-pressure steam in the condensation process. Therefore, the pressurization process (low-low pressure steam condensate pressurization process) which pressurizes at least one part of low-low pressure steam condensate can be performed. Therefore, a line for introducing the low and low pressure steam condensate from the low and low pressure fluid generator to the condenser can be provided, and a booster such as a pump can be provided in the line.
  • the temperature of the steam condensate for supplying the condensation process is higher than that when using steam condensate at atmospheric pressure as the steam condensate for supplying the condensation process. Therefore, the amount of low-pressure steam generated in the condensation step can be increased. Further, the head of the pump for boosting the pressure of the steam condensate can be lowered.
  • At least a portion of the low and low pressure steam condensate can be used as a heat source in the urea production apparatus.
  • Examples of preferable uses as a heating source include preheating of raw material ammonia, heating in the granulating step, and heating in the concentrating step.
  • the flow of the low and low pressure steam condensate can be appropriately branched and each branched flow can be used as each heating source.
  • a pressure increasing step of increasing at least a part of the low pressure low pressure steam condensate may be performed.
  • non-pressurized or pressurized low-low pressure steam condensate can be used as the heating source.
  • the design pressure of the device used for the heating for example, the raw material ammonia preheater
  • the urea synthesis liquid after being treated in the purification step is heated with at least a part of low-low pressure steam condensate, and then with low-low pressure steam or low-pressure steam or both.
  • the concentrator is configured with a heat exchange structure configured to heat the urea synthesis liquid after being treated in the refiner with at least a part of the low and low pressure steam condensate, and the heat exchange structure provided downstream thereof.
  • a heat exchange structure configured to heat the urea synthesis liquid heated by the exchange structure with low pressure steam.
  • At least a part of the low and low pressure steam condensate can be used as a heating source to heat the raw material ammonia.
  • the temperature of the synthesis step can be raised by using the low- and low-pressure steam condensate, which has a lower utility value than the low-pressure steam.
  • the amount of low pressure steam generated in the condensation step can be increased.
  • the temperature of the raw material ammonia is usually low, even if the temperature of the low and low pressure steam condensate is lowered by heating the raw material ammonia, it is easy to effectively utilize the heat of the low and low pressure steam condensate.
  • the raw material ammonia may be further heated by low pressure steam, or may be further heated by using another high temperature heating source. It is also possible to heat the feedstock ammonia with low and low pressure steam condensate, then with low and low pressure steam, and then with low pressure steam.
  • a device (ammonia preheater) provided with an appropriate heat exchange structure (for exchanging heat between the raw material ammonia and the low and low pressure steam condensate) can be used in the ammonia preheating process using the low and low pressure steam condensate.
  • the urea production method may include a granulation step of producing granular solid urea using air from the urea synthesis liquid treated in the concentration step.
  • the granulating step can include heating the air with a portion of the low and low pressure steam condensate. The heating of the air is performed, for example, to raise the temperature and / or dry the air from the outside.
  • Atmospheric temperature is usually sufficiently low compared to low and low pressure steam condensate. Therefore, if at least a part of the low and low pressure steam condensate is used for heating the air used in the granulation step, it is easy to effectively use the heat of the low and low pressure steam condensate. Additionally, low and low pressure steam and / or low pressure steam and / or another high temperature heating source may be utilized to further heat the air.
  • an appropriate heat exchange structure (a heat exchange structure for performing heat exchange between at least a part of low and low pressure steam condensate and air, a low A device provided with a heat exchange structure for exchanging heat between at least a part of the low pressure steam and air can be used.
  • the condensation step and the synthesis step can be performed in a single pressure vessel. That is, it is possible to use a single pressure vessel in which the condenser and the synthesizer are integrated.
  • the low pressure steam condensate is depressurized to a pressure higher than the atmospheric pressure to generate low and low pressure steam and low and low pressure steam condensate. Therefore, compared with the case where the low-pressure steam condensate is depressurized to the atmospheric pressure, the temperature of the generated steam is higher, and these can be used as a heating source in many applications. Moreover, the heat transfer area of the heat exchanger for using these as a heat source can be made small.
  • the low- and low-pressure steam condensate can be used as a heat source at a pressure higher than the atmospheric pressure, the amount of heat that can be recovered increases, which is advantageous for the heat transfer area of the heat exchanger for heat recovery. is there.
  • the low-pressure steam condensate in line 1 is heated by the process fluid in the condenser A (used to recover the heat of condensation) and becomes low-pressure steam.
  • the low-pressure steam condensate in line 1 comes from the medium-pressure steam condensate in which the medium-pressure steam is condensed in the high-pressure decomposer.
  • the medium-pressure steam condensate from the high-pressure decomposer is decompressed by, for example, a pressure reducing valve (not shown) to become low-pressure steam and low-pressure steam condensate, which are gas-liquid separated in a vessel (not shown) to obtain low-pressure steam condensate.
  • the low-pressure steam extracted from the condenser A to the line 2 is partially sent to the refining device B via the line 3 and used as a heating source. Another part of the low-pressure steam in line 2 is sent to the concentrator C via line 4 and used as a heating source. The rest of the low-pressure steam in line 2 can be appropriately used as a heating source other than these, but it is not shown in FIG.
  • low-pressure steam condensate in which low-pressure steam is condensed is extracted into line 5 and line 6, respectively.
  • These low-pressure steam condensates merge and are sent to the low-low pressure fluid generator D via the line 7.
  • the low pressure steam condensate is decompressed to generate low and low pressure steam condensate and low and low pressure steam, and these are separated into gas and liquid in a vessel to obtain low and low pressure steam in line 8 and line 9.
  • Gain low and low pressure steam condensate The low and low pressure steam is sent to the ammonia preheater E to heat the raw material ammonia.
  • the low pressure steam condensate is branched into lines 10 and 11.
  • the low / low pressure steam condensate in the line 10 is sent to the ammonia preheater F to heat the raw material ammonia, and is extracted as the low / low pressure steam condensate in the line 12.
  • the ammonia preheater F can be arranged upstream of the ammonia preheater E based on the flow of the raw material ammonia.
  • the low and low pressure steam condensate in the line 12 is stored in, for example, a steam condensate holding tank (not shown) placed under atmospheric pressure.
  • the low and low pressure steam condensate in the line 11 is pressurized and sent to the condenser A as a steam condensate for supplying the condensation process.
  • the low and low pressure steam condensate in the line 11 is supplied to a vessel (not shown), and the low and low pressure steam condensate is sent to the condenser A from this vessel. It should be understood that in FIG. 1 this vessel is included in the block showing condenser A.
  • the booster for this boosting is not shown in FIG. In FIG. 1 it should be understood that this booster is provided in line 9 or 11. Further, even if the pressure of the steam condensate boosted by the booster becomes equal to that of the low pressure steam condensate, the temperature does not substantially change before and after the booster, and is the same as that of the low pressure steam condensate. In order to distinguish it from the low-pressure steam condensate generated by the condensation of low-pressure steam, the steam condensate boosted by the booster will be referred to as low-low pressure steam condensate. For example, the low and low pressure steam condensate (line 11) can be boosted to the same pressure as the low pressure steam condensate (line 1) and these steam condensates (lines 1 and 11) can be combined and used in condenser A.
  • raw material ammonia which is appropriately pressurized by a pump (not shown), is supplied to the synthesizer H via lines 101, 102, 103, and 104.
  • Raw carbon dioxide is supplied to the synthesizer H via lines 105 and 106.
  • the raw material ammonia (line 101) is heated in a heat exchanger (ammonia preheater) F by heat exchange with low- and low-pressure steam condensate.
  • the heated raw material ammonia (line 102) is heated in a heat exchanger (ammonia preheater) E by heat exchange with low-pressure low-pressure steam.
  • the low and low pressure steam is condensed into a low and low pressure steam condensate.
  • the heated feedstock ammonia (line 103) can then be utilized as the drive fluid for ejector I.
  • a heat exchanger to the line 103 to further heat the raw material ammonia by heat exchange with the low pressure steam.
  • the urea synthesis solution is sent from the synthesizer H to the high-pressure decomposer G via the line 110.
  • the urea synthesis liquid is heated in the heating section (heat exchange structure) by the medium-pressure steam.
  • the medium-pressure steam becomes a medium-pressure steam condensate and is extracted from the heating section.
  • Carbon dioxide is supplied as stripping gas to the bottom of the high-pressure decomposer G via lines 105 and 107.
  • the high-pressure decomposition outlet gas is introduced into the condenser A via the line 112. Further, the urea synthesis liquid from which the high-pressure decomposition outlet gas has been separated is sent to the purification apparatus B via the line 111.
  • the high-pressure decomposition outlet gas introduced into the condenser A is absorbed and condensed by the absorbing liquid (absorption medium) introduced through the line 120.
  • the obtained condensate is pressurized by the ejector I through the line 121 and circulated from the line 104 to the synthesizer H.
  • the gas that has not condensed (condenser outlet gas) is extracted from the line 122 and decompressed by the decompression valve J.
  • Low-pressure steam condensate is introduced into the condenser A as a cooling source.
  • the low pressure steam condensate is heated by the internal fluid (process fluid) of the condenser A to generate low pressure steam.
  • the refining device B includes a pressure reducing valve B1, a medium pressure decomposer B2, a pressure reducing valve B3, and a low pressure decomposer B4.
  • the urea synthetic solution from the line 111 is decompressed by the decompression valve B1, and is sent to the intermediate pressure decomposing unit B2 for performing the intermediate pressure decomposing step via the line 113.
  • the urea synthesis liquid (which may be a gas-liquid two-phase flow) introduced from the line 113 to the intermediate pressure decomposer B2 is heated in the heating section (heat exchange structure) by the low pressure steam of the intermediate pressure decomposer B2.
  • the low-pressure steam becomes a low-pressure steam condensate and is extracted from the heating section.
  • the medium pressure decomposition outlet gas is extracted from the line 132.
  • the urea synthesis liquid from which the medium-pressure decomposition outlet gas has been separated is extracted from the line 131, decompressed by the decompression valve B3, and introduced from the line 134 to the low-pressure decomposition device B4 that performs the low-pressure decomposition step.
  • carbon dioxide is supplied from the line 144 to the low-pressure decomposer B4 in order to accelerate the decomposition of the carbamate.
  • the urea synthesis liquid (which may be a gas-liquid two-phase flow) introduced into the low-pressure decomposer B4 from the line 134 is heated in the heating unit (heat exchange structure) of the low-pressure decomposer B4 by the low-pressure steam.
  • the low pressure decomposition outlet gas is withdrawn from line 142.
  • the urea synthesis liquid from which the low-pressure decomposition outlet gas has been separated is extracted from the line 141 and sent to the concentrator C.
  • the concentrator C includes a pressure reducing valve C1, a heater C2, a gas-liquid separator C3, a heater C4, and a gas-liquid separator C5.
  • the urea synthesis liquid from the line 141 is decompressed by the pressure reducing valve C1 and introduced into the heater C2 from the line 145.
  • this heater in particular, its heat exchange structure
  • the low-pressure steam heats the urea synthesis liquid, and low-pressure steam condensate is generated.
  • the heated urea synthesis liquid becomes a gas-liquid two-phase flow and is introduced into the gas-liquid separator C3 from the line 151, the gas phase is in the line 153, and the liquid phase (the urea synthesis liquid in which urea is concentrated) is in the line. It is extracted to 152.
  • the urea synthesis solution in line 152 is introduced into the heater C4.
  • the low-pressure steam heats the urea synthesis liquid, and low-pressure steam condensate is generated.
  • the heated urea synthesis solution becomes a gas-liquid two-phase flow and is introduced into the gas-liquid separator C5 from the line 161, and the gas phase is in the line 163 and the liquid phase (the urea synthesis solution in which urea is concentrated) is in the line. It is extracted in 162 and sent to the granulation process.
  • Ammonia, carbon dioxide and water contained in the gas extracted from the condenser A, the medium pressure decomposer B2 and the low pressure decomposer B4 can be recovered. Further, water contained in the gas extracted from the gas-liquid separator C3 and the gas-liquid separator C5 can be recovered. In such a recovery process, the absorption medium can be cooled while absorbing and condensing the gas in the absorption medium.
  • the absorption medium water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
  • a mixed gas (line 133) is obtained by mixing the medium pressure decomposition outlet gas (line 132) with the condenser outlet gas (line 123) whose pressure is reduced by the pressure reducing valve J.
  • the mixed gas is cooled in the medium pressure absorber K1 while being absorbed and condensed in the liquid from the line 173 to obtain a recovered liquid in the line 171.
  • the recovered liquid is pressurized by the pump P1 and supplied to the condenser A from the line 120.
  • the low pressure decomposition outlet gas (line 142) is cooled in the low pressure absorber K2 while being absorbed and condensed in the liquid from the line 175 to obtain a recovered liquid in the line 172.
  • the pressure of the recovered liquid is increased by the pump P2 and is sent from the line 173 to the medium pressure absorber K1 as an absorption medium.
  • the gas in line 153 extracted from the gas-liquid separator C3 is sent to the heat exchanger K3, and the gas in line 163 extracted from the gas-liquid separator C5 is sent to the heat exchanger K4.
  • the gas is cooled and condensed in each heat exchanger.
  • the condensed water (line 174) is pressurized by the pump P3 and sent from the line 175 to the low pressure absorber K2 as an absorption medium.
  • An appropriate cooling medium such as cooling water can be used for cooling the absorbers K1 and K2 and the heat exchangers K3 and K4.
  • MP STM Medium pressure steam LP STM: Low pressure steam LLP STM: Low and low pressure steam MP SC: Medium pressure steam condensate LP SC: Low pressure steam condensate LLP SC: Low and low pressure steam condensate

Abstract

The present invention involves obtaining steam and steam condensate having relatively high utility value from low-pressure steam condensate generated when low-pressure steam is consumed in a purification step and/or a concentration step. A urea production method of the present invention comprises: a synthesis step; a high-pressure decomposition step; a condensation step; a purification step in which a urea synthesis solution is heated after the high-pressure decomposition step by using a portion of low-pressure steam generated in the condensation step as a heating source, thereby obtaining a low-pressure steam condensate and a urea synthesis solution having an increased urea concentration; a concentration step in which the urea synthesis solution is heated after the purification step using a separate portion of the low-pressure steam as a heating source, thereby obtaining a low-pressure steam condensate and a urea synthesis solution having an even greater urea concentration; and a step in which at least a portion of the low-pressure steam condensate obtained in the purification step and/or the concentration step is reduced in pressure, thereby generating a low-pressure steam condensate and a low-pressure steam.

Description

尿素製造方法および装置Urea production method and device
　本発明は、アンモニアと二酸化炭素から尿素を製造する方法および装置に関する。 The present invention relates to a method and an apparatus for producing urea from ammonia and carbon dioxide.
　尿素製造方法は、典型的には、合成工程、高圧分解工程、凝縮工程を含み、また、精製工程および濃縮工程を含む。合成工程では、アンモニア(ＮＨ 3)と二酸化炭素(ＣＯ 2)とから、尿素を生成させる。詳しくは、式（１）で示すように、アンモニア(ＮＨ 3)と二酸化炭素(ＣＯ 2）との反応により、アンモニウムカーバメイト(ＮＨ 2ＣＯＯＮＨ 4)が生成される。さらに、式（２）で示すように、アンモニウムカーバメイトの脱水反応により尿素(ＮＨ 2ＣＯＮＨ 2)と水(Ｈ 2Ｏ)とが生成される。
２ＮＨ ３＋ＣＯ ２　→　ＮＨ ２ＣＯＯＮＨ ４　　（１）
ＮＨ ２ＣＯＯＮＨ ４　→　ＮＨ ２ＣＯＮＨ ２＋Ｈ ２Ｏ　　（２）
いずれの反応も平衡反応であるが、（１）の反応に比べて、（２）の反応が遅く、律速となる。 The urea production method typically includes a synthesis step, a high-pressure decomposition step, a condensation step, and a purification step and a concentration step. In the synthesis step, urea is generated from ammonia (NH 3 ) and carbon dioxide (CO 2 ). Specifically, as shown by the formula (1), ammonium carbamate (NH 2 COONH 4 ) is produced by the reaction of ammonia (NH 3 ) and carbon dioxide (CO 2 ). Further, as shown by the formula (2), urea (NH 2 CONH 2 ) and water (H 2 O) are produced by the dehydration reaction of ammonium carbamate.
2NH 3 + CO 2 → NH 2 COONH 4 (1)
NH 2 COONH 4 → NH 2 CONH 2 + H 2 O (2)
Both reactions are equilibrium reactions, but the reaction of (2) is slower and rate-determining than the reaction of (1).
　高圧分解工程では、合成工程で得られた尿素合成液を加熱して、当該尿素合成液に含まれるアンモニウムカーバメイトをアンモニアと二酸化炭素に分解し、アンモニアと二酸化炭素を含む混合ガスと、より高濃度の尿素合成液を得る。凝縮工程では、高圧分解工程で得られた混合ガスを凝縮させる。 In the high-pressure decomposition step, the urea synthesis solution obtained in the synthesis step is heated to decompose ammonium carbamate contained in the urea synthesis solution into ammonia and carbon dioxide, a mixed gas containing ammonia and carbon dioxide, and a higher concentration. To obtain a urea synthesis solution. In the condensation step, the mixed gas obtained in the high pressure decomposition step is condensed.
　精製工程では、高圧分解工程で処理された後の尿素合成液を、高圧分解工程の圧力より低く且つ大気圧より高い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度が高められた尿素合成液を得る。 In the purification process, the urea synthesis liquid after being treated in the high-pressure decomposition process is heated at a pressure lower than the pressure in the high-pressure decomposition process and higher than atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. By doing so, a urea synthesis solution having an increased urea concentration is obtained.
　濃縮工程では、精製工程で処理された後の尿素合成液を、精製工程の圧力より低く且つ大気圧もしくは大気圧より低い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度がさらに高められた尿素合成液を得る。 In the concentration step, the urea synthesis liquid that has been treated in the purification step is heated at a pressure lower than the pressure in the purification step and at an atmospheric pressure or a pressure lower than atmospheric pressure to generate a gas phase and a liquid phase. By separating, a urea synthesis solution having a further increased urea concentration is obtained.
　このような尿素製造方法が非特許文献１及び特許文献１に開示される。非特許文献１によれば、精製工程や濃縮工程で低圧スチームを消費（すなわち加熱源として使用）した際に生じるスチームコンデンセートを減圧し、得られる１００℃のスチームコンデンセートを、凝縮工程に供給するスチームコンデンセートとして使用する。このスチームコンデンセートは１００℃であるので、その圧力は大気圧である。また、同文献によれば、精製工程や濃縮工程で低圧スチームを消費した際に生じるスチームコンデンセートを、ほぼ大気圧（１．２バール）まで減圧した後にフラッシュし、それによって生じるほぼ大気圧のスチームを、アンモニアの加熱に用いている。 Such a urea production method is disclosed in Non-Patent Document 1 and Patent Document 1. According to Non-Patent Document 1, the steam condensate generated when the low-pressure steam is consumed (that is, used as a heating source) in the refining process and the concentration process is decompressed, and the resulting steam condensate at 100 ° C. is supplied to the condensation process. Used as a condensate. This steam condensate is at 100 ° C., so its pressure is atmospheric pressure. According to the same document, the steam condensate generated when low-pressure steam is consumed in the refining process and the concentration process is depressurized to about atmospheric pressure (1.2 bar) and then flushed to generate steam at about atmospheric pressure. Is used to heat the ammonia.
　特許文献１には、精製工程及び／又は濃縮工程で発生したスチームコンデンセートを、合成工程に供給する原料アンモニアの加熱源として用いる方法が記載されている。 [Patent Document 1] describes a method in which steam condensate generated in the refining process and / or the concentrating process is used as a heating source of raw material ammonia supplied to the synthesis process.
国際公開第２０１７／０４３３９１号International Publication No. 2017/043391
　非特許文献１によれば、精製工程や濃縮工程で低圧スチームを消費した際に生じる低圧スチームコンデンセートを減圧して、大気圧のスチームコンデンセートを生じさせている。しかし、大気圧のスチームコンデンセートは温度が低いので、凝縮工程に供給するスチームコンデンセートとして使用すると、凝縮工程における低圧スチームの発生量が少なくなってしまう。すなわち大気圧のスチームコンデンセートで回収できる熱量は小さい。また、凝縮工程に供給するスチームコンデンセートを昇圧するために必要な、ポンプの水頭が高くなる。さらに、非特許文献１に示されるほぼ大気圧のスチームは温度が低く、したがって、このスチームを加熱源として使用できる用途は限られ、また、加熱源として使用する際の熱交換器の伝熱面積が大きくなってしまう。このように、大気圧のスチームコンデンセートおよびスチームの利用価値は、高いとは言えない。 According to Non-Patent Document 1, the low-pressure steam condensate generated when low-pressure steam is consumed in the refining process and the concentration process is decompressed to generate atmospheric pressure steam condensate. However, since the atmospheric pressure steam condensate has a low temperature, when used as a steam condensate supplied to the condensation process, the amount of low-pressure steam generated in the condensation process is reduced. That is, the amount of heat that can be recovered by the steam condensate at atmospheric pressure is small. Further, the head of the pump required to raise the pressure of the steam condensate supplied to the condensation step becomes high. Further, the steam at almost atmospheric pressure shown in Non-Patent Document 1 has a low temperature, and therefore, the applications in which this steam can be used as a heating source are limited, and the heat transfer area of the heat exchanger when used as a heating source is limited. Will become bigger. Thus, the utility value of atmospheric steam condensate and steam is not high.
　特許文献１には、原料アンモニアの加熱に用いるスチームコンデンセートの圧力レベルに関する記載はない。 Patent Document 1 does not describe the pressure level of the steam condensate used for heating the raw material ammonia.
　本発明の目的は、精製工程および／または濃縮工程で低圧スチームを消費した際に生じる低圧スチームコンデンセートから、比較的利用価値の高いスチームコンデンセートおよびスチームを得ることが可能な尿素製造方法および装置を提供することである。 An object of the present invention is to provide a urea production method and apparatus capable of obtaining relatively useful steam condensate and steam from low-pressure steam condensate generated when low-pressure steam is consumed in a purification step and / or a concentration step. It is to be.
　本発明の一態様によれば、
　アンモニアと二酸化炭素から尿素を合成し、尿素合成液を生成する合成工程と、
　前記合成工程で生成した尿素合成液を加熱することによって、アンモニウムカーバメイトを分解し、かつアンモニアと二酸化炭素を含む混合ガスを前記尿素合成液から分離する高圧分解工程と、
　前記高圧分解工程で得られる前記混合ガスの少なくとも一部を吸収媒体に吸収させて凝縮させ、この凝縮の際に生じる熱を用いて低圧スチームを発生させる凝縮工程と、
　前記高圧分解工程で処理された後の尿素合成液を、前記高圧分解工程の圧力より低く且つ大気圧より高い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度が高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせる工程であって、前記高圧分解工程で処理された後の尿素合成液を加熱するための加熱源として、前記凝縮工程で発生させた前記低圧スチームの一部を用いる、精製工程と、
　前記精製工程で処理された後の尿素合成液を、前記精製工程の圧力より低く且つ大気圧もしくは大気圧より低い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度がさらに高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせる工程であって、前記精製工程で処理された後の尿素合成液を加熱するための加熱源として、前記凝縮工程で発生させた前記低圧スチームの別の一部を用いる、濃縮工程と、
　前記精製工程および前記濃縮工程のうちの一方もしくは両方から得られた低圧スチームコンデンセートの少なくとも一部を、大気圧より高い圧力に減圧することによって、低低圧スチームコンデンセートと低低圧スチームを発生させる低低圧流体発生工程と
を含む、尿素製造方法が提供される。 According to one aspect of the invention,
A synthesis step of synthesizing urea from ammonia and carbon dioxide to produce a urea synthesis solution;
By heating the urea synthesis solution generated in the synthesis step, to decompose ammonium carbamate, and a high-pressure decomposition step of separating a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution,
At least a part of the mixed gas obtained in the high-pressure decomposition step is absorbed into an absorption medium and condensed, and a condensation step of generating low-pressure steam using heat generated during this condensation,
Heating the urea synthesis liquid after being treated in the high-pressure decomposition step at a pressure lower than the pressure in the high-pressure decomposition step and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase. By the step of obtaining a urea synthesis solution having an increased urea concentration and generating low-pressure steam condensate, as a heating source for heating the urea synthesis solution after being treated in the high-pressure decomposition step, the condensing step A part of the low-pressure steam generated in, a refining step,
The urea synthesis liquid that has been treated in the purification step is heated at a pressure lower than the pressure in the purification step and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. Thereby, in the step of producing a low-pressure steam condensate together with obtaining a urea synthesis solution having a further increased urea concentration, the condensation as a heating source for heating the urea synthesis solution after being treated in the purification step. A concentrating step using another portion of the low pressure steam generated in the step;
At least a part of the low-pressure steam condensate obtained from one or both of the purification step and the concentration step is depressurized to a pressure higher than atmospheric pressure to generate low-low pressure steam condensate and low-low pressure steam. Fluid generation process
A method for producing urea is provided, which comprises:
　本発明の別の態様によれば、
　アンモニアと二酸化炭素から尿素を合成し、尿素合成液を生成するよう構成された合成器と、
　前記合成器で生成した尿素合成液を加熱することによって、アンモニウムカーバメイトを分解し、かつアンモニアと二酸化炭素を含む混合ガスを前記尿素合成液から分離するよう構成された高圧分解器と、
　前記高圧分解器で得られる前記混合ガスの少なくとも一部を吸収媒体に吸収させて凝縮させ、この凝縮の際に生じる熱を用いて低圧スチームを発生させるよう構成された凝縮器と、
　前記高圧分解器で処理された後の尿素合成液を、前記高圧分解器の圧力より低く且つ大気圧より高い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度が高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせるよう構成された精製装置であって、前記高圧分解器で処理された後の尿素合成液を、前記凝縮器で発生させた前記低圧スチームの一部を用いて加熱する熱交換構造を含む精製装置と、
　前記精製装置で処理された後の尿素合成液を、前記精製装置の圧力より低く且つ大気圧もしくは大気圧より低い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度がさらに高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせるよう構成された濃縮装置であって、前記精製装置で処理された後の尿素合成液を、前記凝縮装置で発生させた前記低圧スチームの別の一部を用いて加熱する熱交換構造を含む濃縮装置と、
　前記精製装置および前記濃縮装置のうちの一方もしくは両方から得られた低圧スチームコンデンセートの少なくとも一部を、大気圧より高い圧力に減圧することによって、低低圧スチームコンデンセートと低低圧スチームを発生させるよう構成された低低圧流体発生装置と
を含む、尿素製造装置が提供される。 According to another aspect of the invention,
A synthesizer configured to synthesize urea from ammonia and carbon dioxide to produce a urea synthesis solution;
By heating the urea synthesis solution generated in the synthesizer, to decompose ammonium carbamate, and a high-pressure decomposer configured to separate a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution,
A condenser configured to absorb and condense at least a part of the mixed gas obtained in the high-pressure decomposer with an absorption medium, and to generate low-pressure steam using heat generated during the condensation,
Heating the urea synthesis liquid after being treated in the high-pressure decomposer at a pressure lower than the pressure of the high-pressure decomposer and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase A purification device configured to obtain a urea synthetic solution having an increased urea concentration and to generate low-pressure steam condensate, wherein the urea synthetic solution after being treated in the high-pressure decomposer is generated in the condenser. A refining apparatus including a heat exchange structure for heating using a part of the low-pressure steam that has been made,
The urea synthesis liquid after being treated in the purification device is heated at a pressure lower than the pressure of the purification device and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. The concentration device is configured to generate a low pressure steam condensate as well as to obtain a urea synthesis liquid having a further increased urea concentration, and the urea synthesis liquid after being treated by the purification device is treated by the condensation device. A concentrating device comprising a heat exchange structure for heating with another part of the generated low pressure steam,
At least a part of the low-pressure steam condensate obtained from one or both of the refining device and the concentrating device is decompressed to a pressure higher than atmospheric pressure to generate low-low pressure steam condensate and low-low pressure steam. Low and low pressure fluid generator
There is provided a urea production apparatus including:
　本発明によれば、精製工程および／または濃縮工程で低圧スチームを消費した際に生じる低圧スチームコンデンセートから、比較的利用価値の高いスチームコンデンセートおよびスチームを得ることが可能な尿素製造方法および装置が提供される。 ADVANTAGE OF THE INVENTION According to this invention, the urea manufacturing method and apparatus which can obtain a steam condensate and steam with comparatively high utility from the low pressure steam condensate produced when low pressure steam is consumed in a refinement | purification process and / or a concentration process are provided. To be done.
低低圧スチームコンデンセートおよび低低圧スチームの製造と利用の例を説明するための模式図である。It is a schematic diagram for demonstrating the example of manufacture and utilization of low-low pressure steam condensate and low-low pressure steam. 尿素製造プラントの概略構成例を示すプロセスフローダイアグラムである。It is a process flow diagram which shows the schematic structural example of a urea manufacturing plant. ガス中の原料（アンモニアおよび二酸化炭素）を回収する工程の概略構成例を示すプロセスフローダイアグラムである。It is a process flow diagram which shows the schematic structural example of the process of collect | recovering the raw materials (ammonia and carbon dioxide) in gas.
　本発明に係る尿素製造方法は、合成工程、高圧分解工程、凝縮工程、精製工程、濃縮工程、および低低圧流体発生工程を含む。本発明に係る尿素製造方法は、さらに、ガス中の原料を回収する工程（回収工程）を含むことができる。原料としてのアンモニアおよび二酸化炭素は、合成工程、高圧分解工程、凝縮工程、精製工程、回収工程のうちの一つもしくは複数の工程に、外部から供給することができる。 The urea production method according to the present invention includes a synthesis step, a high pressure decomposition step, a condensation step, a purification step, a concentration step, and a low / low pressure fluid generation step. The urea production method according to the present invention can further include a step of recovering the raw material in the gas (recovery step). Ammonia and carbon dioxide as raw materials can be externally supplied to one or more of the synthesis process, the high-pressure decomposition process, the condensation process, the purification process, and the recovery process.
　〔合成工程〕
　合成工程において、アンモニアと二酸化炭素から尿素を合成し、尿素合成液を生成する。合成工程において、後述する凝縮工程からの循環液に含まれるアンモニウムカーバメイトからも、尿素が合成される。 [Synthesis process]
In the synthesis step, urea is synthesized from ammonia and carbon dioxide to produce a urea synthesis solution. In the synthesis step, urea is also synthesized from ammonium carbamate contained in the circulating liquid from the condensation step described later.
　合成工程の運転圧力は一般的に１３０バール（絶対圧。以下においても同様）から２５０バール、好ましくは１４０バールから２００バールであり、温度は一般的に１６０℃から２００℃、好ましくは１７０℃から１９０℃である。 The operating pressure in the synthesis step is generally from 130 bar (absolute pressure; also below) to 250 bar, preferably from 140 bar to 200 bar, the temperature generally from 160 ° C to 200 ° C, preferably from 170 ° C. It is 190 ° C.
　〔高圧分解工程〕
　高圧分解工程では、典型的には中圧スチームを加熱源として用いて、合成工程で生成した尿素合成液を加熱する。これによって、合成工程から得られる尿素合成液に含まれるアンモニウムカーバメイトを分解し、アンモニアと二酸化炭素を含む混合ガスを尿素合成液から分離する。高圧分解工程から得られるこの混合ガスを、以下、「高圧分解出口ガス」と呼ぶことがある。また、加熱源として用いた中圧スチームが凝縮することによって、中圧スチームコンデンセートが生じる。 [High-pressure decomposition process]
In the high-pressure decomposition step, medium pressure steam is typically used as a heating source to heat the urea synthesis liquid produced in the synthesis step. As a result, ammonium carbamate contained in the urea synthesis liquid obtained from the synthesis step is decomposed, and the mixed gas containing ammonia and carbon dioxide is separated from the urea synthesis liquid. Hereinafter, this mixed gas obtained from the high-pressure decomposition step may be referred to as “high-pressure decomposition outlet gas”. Further, the intermediate-pressure steam condensate is generated by the condensation of the intermediate-pressure steam used as the heating source.
　高圧分解工程における加熱には、高温の加熱媒体が必要である。典型的には、当該加熱において、後述する凝縮工程で回収される低圧スチームでは温度が不十分であり、低圧スチームより圧力が高い中圧スチームが利用される。 -A high-temperature heating medium is required for heating in the high-pressure decomposition process. Typically, in the heating, medium-pressure steam having a higher pressure than low-pressure steam is used because the temperature of the low-pressure steam recovered in the condensation step described later is insufficient.
　中圧スチームの圧力は一般的に１２バールから４０バール、好ましくは１４バールから２５バールである。中圧スチームコンデンセートの圧力も同程度である。中圧スチームは、尿素製造プラント内でスチームタービンの背圧スチームとして適宜発生させる場合が多い。あるいは、尿素製造プラントの外部から供給することができる。 The pressure of medium pressure steam is generally 12 to 40 bar, preferably 14 to 25 bar. The pressure of medium-pressure steam condensate is similar. Medium pressure steam is often generated as appropriate as back pressure steam of the steam turbine in the urea manufacturing plant. Alternatively, it can be supplied from outside the urea production plant.
　高圧分解工程の運転温度は一般的に１５０℃から２２０℃、好ましくは１６０℃から２００℃である。 The operating temperature of the high-pressure decomposition step is generally 150 ° C to 220 ° C, preferably 160 ° C to 200 ° C.
　詳しくは、合成工程で得られた尿素合成液は、尿素、アンモニア、二酸化炭素、アンモニウムカーバメイトおよび水を含む。この尿素合成液は、通常、合成工程の圧力と実質的にほぼ等しい圧力下で加熱され、これにより、アンモニウムカーバメイトがアンモニアと二酸化炭素に分解される。得られたアンモニアおよび二酸化炭素、未反応アンモニア、未反応二酸化炭素、ならびに水が、アンモニア、二酸化炭素および水を含む混合ガスとして分離される。 Specifically, the urea synthesis solution obtained in the synthesis process contains urea, ammonia, carbon dioxide, ammonium carbamate and water. The urea synthesis solution is usually heated under a pressure substantially equal to the pressure of the synthesis step, whereby the ammonium carbamate is decomposed into ammonia and carbon dioxide. The obtained ammonia and carbon dioxide, unreacted ammonia, unreacted carbon dioxide, and water are separated as a mixed gas containing ammonia, carbon dioxide, and water.
　高圧分解工程として、加熱のみによる分解法を採用することができる。しかし、分解を促進するために、加熱に加えて、二酸化炭素ガスを供給して尿素合成液と接触させるストリッピング法を採用することもできる。  As a high-pressure decomposition process, it is possible to adopt a decomposition method that involves only heating. However, in order to accelerate the decomposition, a stripping method in which carbon dioxide gas is supplied and brought into contact with the urea synthesis solution in addition to heating can also be adopted.
　〔凝縮工程〕
　凝縮工程では、高圧分解工程で得られる混合ガス（高圧分解出口ガス）の少なくとも一部を吸収媒体に吸収させて凝縮させる。この凝縮の際に生じる熱を用いて、低圧スチームを発生させる。なお、低圧スチームを、他の流体を加熱する加熱源として用いたとき、低圧スチームが凝縮することによって、低圧スチームコンデンセートが生じる。 [Condensing process]
In the condensation step, at least a part of the mixed gas (high pressure decomposition outlet gas) obtained in the high pressure decomposition step is absorbed by the absorption medium and condensed. The heat generated during this condensation is used to generate low pressure steam. When the low pressure steam is used as a heating source for heating another fluid, the low pressure steam is condensed to generate a low pressure steam condensate.
　低圧スチームの圧力は一般的に３バールから９バール、好ましくは５バールから７バールである。低圧スチームコンデンセートの圧力も同程度である。 The pressure of the low pressure steam is generally 3 to 9 bar, preferably 5 to 7 bar. The pressure of low pressure steam condensate is similar.
　吸収媒体としては、水（尿素、アンモニア、二酸化炭素及びアンモニウムカーバメイトを含んでいてもよい）など、尿素製造方法の分野で公知の吸収媒体を適宜使用できる。 As the absorption medium, water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
　凝縮工程で得られる液（プロセス流体）の温度は一般的に１００℃から２１０℃、好ましくは１６０℃から１９０℃である。なお、尿素製造における高圧プロセス（合成工程、高圧分解工程及び凝縮工程を含む）には、圧力損失以外に圧力を減じるものが無いので（後述する循環のためにエジェクターによる昇圧は行う）、合成工程、高圧分解工程及び凝縮工程は、ほぼ同等の圧力となる。 The temperature of the liquid (process fluid) obtained in the condensation step is generally 100 ° C to 210 ° C, preferably 160 ° C to 190 ° C. In the high pressure process (including the synthesis process, the high pressure decomposition process and the condensation process) in the urea production, there is nothing to reduce the pressure other than the pressure loss (the pressure is increased by the ejector for circulation to be described later). The high-pressure decomposition step and the condensation step have almost the same pressure.
　詳しくは、高圧分解工程において分離された混合ガス（高圧分解出口ガス）は、凝縮工程に導入されて、水を含む吸収媒体と冷却下に接触し、この混合ガスが凝縮する。凝縮の際に、一部のアンモニアと二酸化炭素はアンモニウムカーバメイトとなり（上記式（１）参照）、凝縮温度を高く保つことによって尿素合成反応（上記式（２）参照）も進む。 Specifically, the mixed gas separated in the high-pressure decomposition process (high-pressure decomposition outlet gas) is introduced into the condensation process and comes into contact with the absorption medium containing water under cooling, and this mixed gas is condensed. During the condensation, a part of ammonia and carbon dioxide becomes ammonium carbamate (see the above formula (1)), and the urea synthesis reaction (see the above formula (2)) also proceeds by keeping the condensation temperature high.
　凝縮工程で混合ガスが凝縮する際には大量の熱を発生するが、この熱を有効活用するために熱回収を行う。熱回収の方法としては、高圧分解工程で処理された後の尿素合成液と、凝縮器の内部流体（プロセス流体）との熱交換による方法がある。あるいは、凝縮器の内部流体（プロセス流体）と温水（加圧水を用いる場合が多い）とを熱交換して、より高温となった温水を得る方法がある。しかし、多くの場合、凝縮器の内部流体（プロセス流体）とスチームコンデンセート（特には低圧スチームコンデンセート）とを熱交換して、低圧スチームを発生させる方法が採用される。あるいは、この方法に前述の２つの方法の少なくとも一方を組み合わせることもできる。 A large amount of heat is generated when the mixed gas condenses in the condensation process, but heat is recovered to make effective use of this heat. As a method of heat recovery, there is a method of exchanging heat between the urea synthesis liquid after being treated in the high-pressure decomposition step and the internal fluid (process fluid) of the condenser. Alternatively, there is a method of exchanging heat between the internal fluid (process fluid) of the condenser and hot water (pressurized water is often used) to obtain hot water having a higher temperature. However, in many cases, a method of exchanging heat between the internal fluid (process fluid) of the condenser and the steam condensate (particularly low pressure steam condensate) to generate low pressure steam is adopted. Alternatively, this method can be combined with at least one of the above two methods.
　このように、凝縮工程では、熱回収によって低圧スチームを発生させるために、スチームコンデンセートの供給が必要である。例えば、凝縮工程において、凝縮器とは別に、低圧スチームコンデンセートを貯めるためのベッセルを用いる場合、このベッセルに低圧スチームコンデンセートを供給し、そのベッセルから凝縮器に低圧スチームコンデンセートを移送することができる。本明細書では、この低圧スチームを発生させるために、凝縮工程（凝縮器）に供給するスチームコンデンセートを「凝縮工程供給用スチームコンデンセート」ということがある。 In this way, in the condensation process, it is necessary to supply steam condensate in order to generate low-pressure steam by heat recovery. For example, when a vessel for storing low-pressure steam condensate is used separately from the condenser in the condensation step, the low-pressure steam condensate can be supplied to the vessel and the low-pressure steam condensate can be transferred from the vessel to the condenser. In this specification, the steam condensate supplied to the condensation process (condenser) in order to generate the low-pressure steam may be referred to as “condensation process supply steam condensate”.
　高圧分解工程で発生する中圧スチームコンデンセートを減圧して、凝縮工程供給用スチームコンデンセートに使うことが多い。この際、中圧スチームコンデンセートが、別の工程の加熱源として使われて温度が低下した後に、凝縮工程供給用スチームコンデンセートとして使われることもある。いずれにしても、凝縮工程で発生する低圧スチーム量が多いので、高圧分解工程で発生した中圧スチームコンデンセートだけでは、凝縮工程供給用スチームコンデンセートの量が不十分であることが一般的である。そこで、後に詳述する低低圧スチームコンデンセートの少なくとも一部（通常は、低低圧スチームコンデンセートの一部）を、ポンプで昇圧して凝縮工程において低圧スチームを発生させるための凝縮工程供給用スチームコンデンセートとして利用することができる。 The medium-pressure steam condensate generated in the high-pressure decomposition process is often decompressed and used as the steam condensate for the condensation process supply. At this time, the medium-pressure steam condensate may be used as a steam condensate for supplying the condensing process after the temperature is lowered by being used as a heating source for another process. In any case, since the amount of low-pressure steam generated in the condensation step is large, it is general that the amount of steam condensate supplied to the condensation step is insufficient only with the medium-pressure steam condensate generated in the high-pressure decomposition step. Therefore, at least a part of the low and low pressure steam condensate, which will be described in detail later (usually a part of the low and low pressure steam condensate), is used as a steam condensate for the condensation process supply for increasing the pressure by a pump to generate low pressure steam in the condensation process. Can be used.
　凝縮器の内部流体（プロセス流体）とスチームコンデンセートとの熱交換のために、縦型もしくは横型のシェル＆チューブ型の熱交換器を採用できる。チューブ側で混合ガスを凝縮する方法も採用できるが、凝縮工程の滞留時間を、凝縮と反応のために長くとることができるように、シェル側で混合ガスを凝縮する方法を採用することもできる。 Vertical or horizontal shell and tube heat exchangers can be used for heat exchange between the condenser internal fluid (process fluid) and steam condensate. A method of condensing the mixed gas on the tube side can also be adopted, but a method of condensing the mixed gas on the shell side can also be adopted so that the residence time in the condensation step can be extended for condensation and reaction. ..
　なお、凝縮工程で凝縮しなかったガスは、適宜減圧した後に、吸収媒体（液体）中に吸収および凝縮させながらその吸収媒体を冷却することによって、アンモニアおよび二酸化炭素を含む回収液を得ることができる（回収工程）。この回収液を、適宜昇圧した後に、再度高圧プロセス（合成工程、高圧分解工程及び凝縮工程を含む）、通常は凝縮工程に返送することによって、未反応アンモニアおよび未反応二酸化炭素を回収できる。吸収媒体としては、水（尿素、アンモニア、二酸化炭素及びアンモニウムカーバメイトを含んでいてもよい）など、尿素製造方法の分野で公知の吸収媒体を適宜使用できる。 The gas not condensed in the condensation step may be appropriately decompressed, and then the absorption medium may be cooled while being absorbed and condensed in the absorption medium (liquid) to obtain a recovery liquid containing ammonia and carbon dioxide. Yes (collection process). Unreacted ammonia and unreacted carbon dioxide can be recovered by returning the recovered liquid to a high-pressure process (including a synthesis process, a high-pressure decomposition process and a condensation process), usually a condensation process, after appropriately increasing the pressure. As the absorption medium, water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
　〔循環〕
　凝縮工程で得られた凝縮液（高圧分解出口ガスの少なくとも一部を吸収した吸収媒体）が再度合成工程に送られる。このようにして、尿素に転化しなかった未反応アンモニアと未反応二酸化炭素に、合成工程、高圧分解工程および凝縮工程の間を循環させる方法を採用することができる。凝縮工程で得られた凝縮液を循環させる方法としては下方に合成器（合成工程を行う）を配置し、その上方に凝縮器（凝縮工程を行う）を設置して、重力を用いて凝縮液を循環させる方法がある。また、別の循環方法として、合成器に供給する原料アンモニアを駆動流体として、凝縮工程で得られた凝縮液をエジェクターによって昇圧して循環させる方法がある。また、重力を用いて循環する方法とエジェクターを用いて循環する方法を組み合わせてもよい。 〔Circulation〕
The condensate obtained in the condensation step (absorption medium that has absorbed at least a part of the high-pressure decomposition outlet gas) is sent to the synthesis step again. In this way, it is possible to employ a method in which unreacted ammonia and unreacted carbon dioxide that have not been converted to urea are circulated between the synthesis step, the high-pressure decomposition step and the condensation step. As a method of circulating the condensate obtained in the condensing process, a synthesizer (performing the synthesizing process) is arranged below, and a condenser (performing the condensing process) is installed above the condensing liquid, and the condensate is gravity-generated There is a way to circulate. As another circulation method, there is a method in which the raw material ammonia supplied to the synthesizer is used as a driving fluid and the condensate obtained in the condensation step is pressurized by an ejector and circulated. Further, the method of circulating using gravity and the method of circulating using an ejector may be combined.
　〔精製工程および濃縮工程〕
　高圧分解工程で処理された後の尿素合成液に対して減圧と加熱の処理を行うことによって、未分離のアンモニア、二酸化炭素およびアンモニウムカーバメイト、ならびに水を、アンモニア、二酸化炭素および水を含む混合ガス（気相）として分離する。これによって尿素濃度が高められた尿素合成液（液相）が得られる。 [Purification step and concentration step]
By decompressing and heating the urea synthesis liquid that has been treated in the high-pressure decomposition step, the unseparated ammonia, carbon dioxide and ammonium carbamate, and water are mixed gas containing ammonia, carbon dioxide and water. Separate as (gas phase). As a result, a urea synthesis liquid (liquid phase) having an increased urea concentration is obtained.
　この混合ガスは、通常吸収媒体（液体）中に吸収および凝縮させながらその吸収媒体を冷却することによって、吸収媒体中に回収し、回収液を得ることができる（回収工程）。この回収液を、再度高圧プロセス、通常は凝縮工程に返送することによって、未反応アンモニアおよび未反応二酸化炭素を回収できる。吸収媒体としては、水（尿素、アンモニア、二酸化炭素及びアンモニウムカーバメイトを含んでいてもよい）など、尿素製造方法の分野で公知の吸収媒体を適宜使用できる。 -This mixed gas can be collected in the absorption medium (cooling process) by cooling the absorption medium while absorbing and condensing it in the absorption medium (liquid). Unreacted ammonia and unreacted carbon dioxide can be recovered by returning this recovered liquid to the high-pressure process, usually the condensation step. As the absorption medium, water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
　このような減圧と加熱の処理において、高圧分解工程で処理された後の尿素合成液を可能な限り減圧したほうが、未分離のアンモニア、二酸化炭素、アンモニウムカーバメイトおよび水を、加熱によって混合ガスとして分離しやすい。一方、分離した混合ガスを冷却しながら吸収媒体に吸収させ、得られた回収液を再度高圧プロセスに返送するためには、減圧と加熱の処理において尿素合成液は可能な限り高圧である方が有利である。そのため、高圧分解工程で処理された後の尿素合成液に対して、減圧と加熱による処理を複数段階に分けて行うことにより、効率的にアンモニア、二酸化炭素、アンモニウムカーバメイトおよび水の含有量を減らし、高濃度の製品尿素を得ることができる。そのために、精製工程と、濃縮工程とを行う。 In such pressure reduction and heating treatments, it is better to reduce the pressure of the urea synthesis solution after it has been treated in the high pressure decomposition step as much as possible to separate unseparated ammonia, carbon dioxide, ammonium carbamate and water as a mixed gas by heating. It's easy to do. On the other hand, in order to allow the separated mixed gas to be absorbed in the absorbing medium while being cooled and to return the obtained recovered liquid to the high pressure process again, it is preferable that the urea synthesis liquid has a high pressure as much as possible in the pressure reduction and heating treatments. It is advantageous. Therefore, the urea synthesis liquid after being treated in the high-pressure decomposition process is efficiently reduced in content of ammonia, carbon dioxide, ammonium carbamate and water by performing treatment by decompression and heating in multiple stages. , High concentration product urea can be obtained. Therefore, a purification process and a concentration process are performed.
　精製工程および濃縮工程のいずれにおいても、凝縮工程において発生する低圧スチームを加熱源として用いることができる。この低圧スチームは、高圧分解工程で加熱源として用いられる中圧スチームと比べて、低温である。 In both the refining process and the concentrating process, the low pressure steam generated in the condensing process can be used as a heating source. This low-pressure steam has a lower temperature than the medium-pressure steam used as a heating source in the high-pressure decomposition process.
　なお、精製工程および濃縮工程のいずれにおいても、加熱源として、低圧スチームに加えて、中圧スチームコンデンセートを併用することができ、且つ／または、中圧スチームコンデンセートを減圧して生じるスチームを併用することができる。中圧スチームコンデンセートは、中圧スチームが加熱源として消費されて生じるスチームコンデンセートである。中圧スチームコンデンセートを減圧することにより、中圧スチームよりも低圧のスチームおよびスチームコンデンセートが得られる。 In addition, in both the purification step and the concentration step, in addition to low-pressure steam, medium-pressure steam condensate can be used in combination as a heating source, and / or steam generated by decompressing medium-pressure steam condensate is used in combination. be able to. The medium-pressure steam condensate is a steam condensate generated by consuming medium-pressure steam as a heating source. By decompressing the medium pressure steam condensate, steam and steam condensate at a pressure lower than that of the medium pressure steam are obtained.
　〔精製工程〕
　精製工程では、高圧分解工程で処理された後の尿素合成液を、高圧分解工程の圧力より低く且つ大気圧より高い圧力において、凝縮工程で発生させた低圧スチームの一部を加熱源に用いて加熱することによって、気相と液相を生じさせる。このとき、高圧分解工程で処理された後の尿素合成液に含まれるアンモニウムカーバメイトを分解することができる。この気相を液相から分離することによって、尿素濃度が高められた尿素合成液を得る。また、加熱源として使用した低圧スチームから、低圧スチームコンデンセートが生じる。 [Refining process]
In the purification step, the urea synthesis liquid after being treated in the high pressure decomposition step is used as a heating source at a pressure lower than the high pressure decomposition step and higher than the atmospheric pressure, using a part of the low pressure steam generated in the condensation step. Heating produces a gas phase and a liquid phase. At this time, ammonium carbamate contained in the urea synthesis liquid after being treated in the high-pressure decomposition step can be decomposed. By separating this gas phase from the liquid phase, a urea synthesis solution having an increased urea concentration is obtained. In addition, low pressure steam condensate is generated from the low pressure steam used as a heating source.
　このために、精製工程において、減圧操作を少なくとも一回行い、また、加熱操作を少なくとも一回行う。精製工程を一段階で行うことができ、あるいは複数段階で行うことができる。例えば精製工程を、中圧分解工程と、低圧分解工程の二段階で行うことができる。 For this reason, depressurization is performed at least once and heating is performed at least once in the purification process. The purification process can be performed in one step or in multiple steps. For example, the refining process can be performed in two steps, a medium pressure decomposition process and a low pressure decomposition process.
　中圧分解工程は、高圧分解工程で処理された直後の尿素合成液を、大気圧を超える圧力に減圧し、必要に応じて加熱して、気相（混合ガス）と液相を生じさせ、気相を分離する工程である。ただし、前述のように、高圧分解工程で処理された直後の尿素合成液と、凝縮器の内部流体（プロセス流体）との熱交換によって、凝縮工程で熱回収する場合がある。この場合は、当該熱回収によって加熱された後の尿素合成液を、高圧分解工程より低い圧力で加熱して混合ガスを分離する工程が、中圧分解工程に該当する。 In the medium-pressure decomposition step, the urea synthesis liquid immediately after being treated in the high-pressure decomposition step is decompressed to a pressure exceeding atmospheric pressure, and heated if necessary to generate a gas phase (mixed gas) and a liquid phase, This is the step of separating the gas phase. However, as described above, heat may be recovered in the condensation step by heat exchange between the urea synthesis liquid immediately after being treated in the high-pressure decomposition step and the internal fluid (process fluid) of the condenser. In this case, the step of heating the urea synthesis solution after being heated by the heat recovery at a pressure lower than that in the high pressure decomposition step to separate the mixed gas corresponds to the intermediate pressure decomposition step.
　中圧分解工程では、低圧スチームを加熱源として用いることができる。中圧分解工程では、高圧分解工程で処理された後の尿素合成液に含まれるアンモニウムカーバメイトが分解される。中圧分解工程から、アンモニア及び二酸化炭素を含む混合ガス（以下、「中圧分解出口ガス」ということがある）と、アンモニウムカーバメイト濃度が低下した尿素合成液が得られる。 ▽ In the medium pressure decomposition process, low pressure steam can be used as a heating source. In the medium pressure decomposition step, ammonium carbamate contained in the urea synthesis solution after being treated in the high pressure decomposition step is decomposed. From the medium-pressure decomposition step, a mixed gas containing ammonia and carbon dioxide (hereinafter, also referred to as “medium-pressure decomposition outlet gas”) and a urea synthesis solution having a reduced ammonium carbamate concentration can be obtained.
　中圧分解工程の運転圧力は、減圧と加熱による処理を何段階行うかにもよるが、例えば、２段階（中圧分解工程と低圧分解工程）の場合、一般的に３バールから１３０バール、好ましくは６バールから７０バール、より好ましくは１０バールから２０バールである。中圧分解工程の運転温度は運転圧力にもよるが、一般的に１００℃から１８０℃、好ましくは１３０℃から１７０℃程度である。 The operating pressure of the medium-pressure decomposition process depends on how many stages of pressure reduction and heat treatment are performed, but in the case of two stages (medium-pressure decomposition process and low-pressure decomposition process), it is generally 3 bar to 130 bar, It is preferably from 6 bar to 70 bar, more preferably from 10 bar to 20 bar. The operating temperature of the medium pressure decomposition step depends on the operating pressure, but is generally 100 ° C to 180 ° C, preferably about 130 ° C to 170 ° C.
　低圧分解工程では、中圧分解工程の後に、中圧分解工程より低い圧力（ただし大気圧以上）において、中圧分解工程で処理された後の尿素合成液を減圧および／または加熱することができる。低圧分解工程から、アンモニア及び二酸化炭素を含む混合ガス（以下、「低圧分解出口ガス」ということがある）と、アンモニウムカーバメイト濃度がさらに低下した尿素合成液が得られる。 In the low-pressure decomposition step, after the intermediate-pressure decomposition step, the urea synthesis liquid after being treated in the intermediate-pressure decomposition step can be decompressed and / or heated at a pressure lower than the intermediate-pressure decomposition step (however, atmospheric pressure or higher). .. From the low-pressure decomposition step, a mixed gas containing ammonia and carbon dioxide (hereinafter, also referred to as “low-pressure decomposition outlet gas”) and a urea synthesis solution having a further reduced ammonium carbamate concentration can be obtained.
　低圧分解工程の運転圧力は、一般的に１．５バールから６バール、好ましくは２バールから４バールである。低圧分解工程の運転温度は運転圧力にもよるが、一般的に９０℃から１７０℃、好ましくは１１０℃から１５０℃程度である。 The operating pressure of the low-pressure decomposition process is generally 1.5 bar to 6 bar, preferably 2 bar to 4 bar. The operating temperature of the low-pressure decomposition step depends on the operating pressure, but is generally about 90 ° C to 170 ° C, preferably about 110 ° C to 150 ° C.
　精製工程を行う精製装置は、減圧を行うための減圧弁、加熱を行うための熱交換構造、および気液分離構造を含むことができる。例えば、中圧分解工程を行う中圧分解器は、加熱源としてのスチームとプロセス流体（尿素合成液）との熱交換構造を有することができる。また、プロセス流体（尿素合成液）の流れを基準として、中圧分解器の上流に、減圧を行うための減圧弁を配することができる。 The refining device that performs the refining process can include a pressure reducing valve for depressurizing, a heat exchange structure for heating, and a gas-liquid separation structure. For example, the intermediate-pressure decomposer that performs the intermediate-pressure decomposition step can have a heat exchange structure between steam as a heating source and the process fluid (urea synthesis solution). Further, a pressure reducing valve for reducing the pressure can be arranged upstream of the intermediate pressure decomposer with reference to the flow of the process fluid (urea synthesis liquid).
　〔濃縮工程〕
　濃縮工程では、精製工程で処理された後の尿素合成液を、精製工程の圧力（精製工程における最後の減圧操作の後の圧力）より低く且つ大気圧もしくは大気圧より低い圧力において、凝縮工程で発生させた低圧スチームの別の一部を加熱源に用いて加熱することによって、気相と液相を生じさせる。この気相を液相から分離することによって、尿素濃度がさらに高められた尿素合成液を得る。また、加熱源として使用した低圧スチームから、低圧スチームコンデンセートが生じる。濃縮工程では、大気圧下もしくは真空下で加熱を行うことにより、尿素合成液に含まれる水の含有量を減らす。 [Concentration process]
In the concentration step, the urea synthesis liquid after being treated in the purification step is subjected to the condensation step at a pressure lower than the pressure of the purification step (pressure after the last depressurization operation in the purification step) and at atmospheric pressure or pressure lower than atmospheric pressure. Another part of the generated low-pressure steam is used as a heating source to heat the gas to generate a gas phase and a liquid phase. By separating this gas phase from the liquid phase, a urea synthesis liquid having a further increased urea concentration is obtained. In addition, low pressure steam condensate is generated from the low pressure steam used as a heating source. In the concentration step, the content of water contained in the urea synthesis solution is reduced by heating under atmospheric pressure or under vacuum.
　このために、濃縮工程において、減圧操作を少なくとも一回行い、また、加熱操作を少なくとも一回行う。濃縮工程を一段階で行うことができ、あるいは複数段階で行うことができる。例えば濃縮工程を、二段階で行うことができる。 Therefore, in the concentration step, the depressurizing operation is performed at least once, and the heating operation is performed at least once. The concentration step can be performed in one step or in multiple steps. For example, the concentration step can be performed in two steps.
　濃縮工程の条件は造粒方法にも依存するが、例えば、二段階の濃縮を以下に示す条件で行い、プリル状固体尿素を製造することができる。
・１段目
尿素濃度：８０〜９８質量％、
圧力：１００ｍｍＨｇ（０．１３バール）〜５００ｍｍＨｇ（０．６７バール）、好適には１５０ｍｍＨｇ（０．２０バール）〜３５０ｍｍＨｇ（０．４７バール）、
温度：１２５〜１４０℃。
・２段目
尿素濃度：９４〜９９．９質量％、
圧力：１０ｍｍＨｇ（０．０１３バール）〜１００ｍｍＨｇ（０．１３バール）、好適には１５ｍｍＨｇ（０．０２０バール）〜５０ｍｍＨｇ（０．０６７バール）、
温度：１３０〜１４５℃。 Although the conditions of the concentration step depend on the granulation method, for example, the prilled solid urea can be produced by performing the two-stage concentration under the following conditions.
・ First stage
Urea concentration: 80-98% by mass,
Pressure: 100 mmHg (0.13 bar) to 500 mmHg (0.67 bar), preferably 150 mmHg (0.20 bar) to 350 mmHg (0.47 bar),
Temperature: 125-140 ° C.
・ Second stage
Urea concentration: 94-99.9% by mass,
Pressure: 10 mmHg (0.013 bar) to 100 mmHg (0.13 bar), preferably 15 mmHg (0.020 bar) to 50 mmHg (0.067 bar),
Temperature: 130-145 ° C.
　濃縮工程を行う濃縮装置は、減圧を行うための減圧弁、加熱を行うための熱交換構造、および気液分離構造を含むことができる。濃縮工程から得られる尿素を製品尿素とすることができ、あるいは濃縮工程に続いて造粒工程を行い、粒状の製品尿素を得ることもできる。 The concentrating device that performs the concentrating step can include a pressure reducing valve for reducing the pressure, a heat exchange structure for performing heating, and a gas-liquid separation structure. The urea obtained from the concentration step can be used as the product urea, or the granulation step can be performed after the concentration step to obtain the granular product urea.
　〔低低圧流体発生工程〕
　低低圧流体発生工程において、精製工程および濃縮工程のうちの一方もしくは両方から得られた低圧スチームコンデンセートの少なくとも一部を、大気圧より高い圧力に減圧することによって、低低圧スチームコンデンセートと低低圧スチームを発生させる。低低圧スチームコンデンセートおよび低低圧スチームは、大気圧より高く、かつ精製工程および濃縮工程のうちの一方もしくは両方から得られた低圧スチームコンデンセートよりも低い圧力を有する。したがって、低低圧スチームコンデンセートおよび低低圧スチームは、凝縮工程で発生させる低圧スチームよりも低い圧力を有する。低低圧スチームコンデンセートおよび低低圧スチームは、それぞれ大気圧のスチームコンデンセートおよびスチームと比べて、利用価値が高い。 [Low and low pressure fluid generation process]
In the low-low pressure fluid generation process, at least a part of the low-pressure steam condensate obtained from one or both of the purification process and the concentration process is depressurized to a pressure higher than the atmospheric pressure to reduce the low-pressure steam condensate and the low-pressure steam. Generate. The low and low pressure steam condensates and the low and low pressure steam have a pressure above atmospheric pressure and lower than the low pressure steam condensate obtained from one or both of the refining and concentration steps. Thus, the low and low pressure steam condensate and the low and low pressure steam have a lower pressure than the low pressure steam generated in the condensation process. Low and low pressure steam condensate and low and low pressure steam are more useful than atmospheric pressure steam condensate and steam, respectively.
　低低圧流体発生工程を行うために用いる低低圧流体発生装置は、減圧弁を含むことができ、さらに気液分離器（ベッセル）を含むことができる。 The low / low pressure fluid generation device used for performing the low / low pressure fluid generation step may include a pressure reducing valve and may further include a gas-liquid separator (vessel).
　低低圧スチームおよび低低圧スチームコンデンセートの温度を比較的高くする観点から、低低圧スチームおよび低低圧スチームコンデンセートの圧力は２バール以上が好ましく、３バール以上がより好ましい。低低圧スチームおよび低低圧スチームコンデンセートの圧力と、凝縮工程で生じる低圧スチームとの圧力差は１バール以上が好ましく、２バール以上がより好ましい。圧力差がこのような範囲にあると、低圧スチームコンデンセートを低低圧流体発生装置に流入させて、低低圧流体を発生させることが容易である。 From the viewpoint of making the temperature of the low and low pressure steam and the low and low pressure steam condensate relatively high, the pressure of the low and low pressure steam and the low and low pressure steam condensate is preferably 2 bar or more, more preferably 3 bar or more. The pressure difference between the low and low pressure steam and the pressure of the low and low pressure steam condensate and the low pressure steam generated in the condensation step is preferably 1 bar or more, more preferably 2 bar or more. When the pressure difference is in such a range, it is easy to cause the low pressure steam condensate to flow into the low and low pressure fluid generating device to generate the low and low pressure fluid.
　〔低低圧スチームの利用〕
　低低圧スチームを、尿素製造装置内で、加熱源として利用することができる。加熱源としての利用先は、原料アンモニアの予熱、造粒工程に供給する空気の加熱、ならびに、低圧分解工程および濃縮工程での加熱（合成液の分解および濃縮、尿素水溶液の濃縮）が考えられる。典型的には、低低圧スチームの加熱源としてのこれらの利用は、この順に効果的である。例えば、低低圧スチームを原料アンモニアの予熱に利用することが最も効果的である。低低圧スチームのこれらの利用を二以上実施する場合、低低圧スチームの流れを宜分岐して、各分岐流を各加熱源として利用することができる。 [Use of low and low pressure steam]
The low and low pressure steam can be used as a heating source in the urea production apparatus. The usage destination as a heating source is preheating of raw material ammonia, heating of air supplied to the granulation process, and heating in the low-pressure decomposition process and concentration process (decomposition and concentration of synthetic solution, concentration of urea aqueous solution). .. Typically, their use as heating sources for low and low pressure steam is effective in that order. For example, it is most effective to use low and low pressure steam for preheating the feedstock ammonia. When two or more of these uses of low and low pressure steam are carried out, the flow of low and low pressure steam can be appropriately branched and each branched flow can be used as each heating source.
　例えば、濃縮工程において、精製工程で処理された後の尿素合成液を、低低圧スチームの少なくとも一部を用いて加熱し、その後、低圧スチームを用いて加熱することができる。そのために、濃縮装置が、低低圧スチームの少なくとも一部を用いて精製装置で処理された後の尿素合成液を加熱するよう構成された熱交換構造と、その下流に設けられた、この熱交換構造で加熱された尿素合成液を、低圧スチームを用いて加熱するよう構成された熱交換構造とを含むことができる。 For example, in the concentration step, the urea synthesis liquid that has been treated in the purification step can be heated using at least a part of the low and low pressure steam, and then can be heated using the low pressure steam. To that end, the concentrator is configured to heat the urea synthesis liquid after it has been treated in the refiner with at least a portion of the low and low pressure steam, and this heat exchange structure provided downstream thereof. A heat exchange structure configured to heat the structure-heated urea synthesis liquid with low pressure steam.
　〔低低圧スチームによるアンモニア予熱工程〕
　低低圧スチームの少なくとも一部を加熱源として用いて、原料アンモニアを加熱することができる。この工程には、適宜の熱交換構造（原料アンモニアと、低低圧スチームとの間の熱交換を行う）を設けた装置（アンモニア予熱器）を使用することができる。この工程によって、低圧スチームより利用価値が低い低低圧スチームを用いて、合成工程の温度を高めることができる。 [Ammonia preheating process with low and low pressure steam]
At least a part of the low and low pressure steam can be used as a heating source to heat the raw material ammonia. In this step, a device (ammonia preheater) provided with an appropriate heat exchange structure (heat exchange between the raw material ammonia and the low and low pressure steam) can be used. By this process, the temperature of the synthesis process can be increased by using the low-pressure low-pressure steam which has a lower utility value than the low-pressure steam.
　〔低低圧スチームコンデンセートの、凝縮工程への供給水としての利用〕
　低低圧スチームコンデンセートの少なくとも一部を、凝縮工程において低圧スチームを発生させるための凝縮工程供給用スチームコンデンセートとして利用することができる。そのために、低低圧スチームコンデンセートの少なくとも一部を昇圧する昇圧工程（低低圧スチームコンデンセート昇圧工程）を行うことができる。このために、低低圧流体発生装置から凝縮器に低低圧スチームコンデンセートを導くラインを設け、そのラインにポンプなどの昇圧機を設けることができる。 [Use of low and low pressure steam condensate as feed water for the condensation process]
At least a part of the low- and low-pressure steam condensate can be used as a steam condensate for supplying the condensation process for generating low-pressure steam in the condensation process. Therefore, the pressurization process (low-low pressure steam condensate pressurization process) which pressurizes at least one part of low-low pressure steam condensate can be performed. Therefore, a line for introducing the low and low pressure steam condensate from the low and low pressure fluid generator to the condenser can be provided, and a booster such as a pump can be provided in the line.
　このような構成によれば、凝縮工程供給用スチームコンデンセートとして大気圧のスチームコンデンセートを用いる場合と比較して、凝縮工程供給用スチームコンデンセートの温度が高くなる。したがって、凝縮工程で発生する低圧スチームの発生量を増やすことができる。また、スチームコンデンセートの昇圧用のポンプの水頭を低くすることができる。 With such a configuration, the temperature of the steam condensate for supplying the condensation process is higher than that when using steam condensate at atmospheric pressure as the steam condensate for supplying the condensation process. Therefore, the amount of low-pressure steam generated in the condensation step can be increased. Further, the head of the pump for boosting the pressure of the steam condensate can be lowered.
　〔低低圧スチームコンデンセートの加熱源としての利用〕
　低低圧スチームコンデンセートの少なくとも一部を、尿素製造装置内で、加熱源として利用することができる。加熱源としての好ましい利用先の例として、原料アンモニアの予熱、造粒工程における加熱、および濃縮工程における加熱を挙げることができる。低低圧スチームコンデンセートのこれらの利用を二以上実施する場合、低低圧スチームコンデンセートの流れを適宜分岐して、各分岐流を各加熱源として利用することができる。また、前述のように、凝縮工程において低圧スチームを発生させるためのスチームコンデンセートとして利用するために、低低圧スチームコンデンセートの少なくとも一部を昇圧する昇圧工程を行うことがある。この昇圧工程を行うとき、上記加熱源として、昇圧していないもしくは昇圧した低低圧スチームコンデンセートを用いることができる。前者の場合、当該加熱に使用する機器（例えば原料アンモニア予熱器）の設計圧力を低くすることができる。後者の場合、当該加熱に利用した後のスチームコンデンセートを、高圧な機器もしくは高い場所に位置する機器に送ることが容易である。また、後者の場合、前者の場合と比較して、配管等による圧力損失に起因して低低圧スチームコンデンセートの圧力が低下した後でも、低低圧スチームコンデンセートが低温になることを防ぐことが容易である。 [Use of low and low pressure steam condensate as a heating source]
At least a portion of the low and low pressure steam condensate can be used as a heat source in the urea production apparatus. Examples of preferable uses as a heating source include preheating of raw material ammonia, heating in the granulating step, and heating in the concentrating step. When two or more of these uses of the low and low pressure steam condensate are carried out, the flow of the low and low pressure steam condensate can be appropriately branched and each branched flow can be used as each heating source. Further, as described above, in order to use as a steam condensate for generating low pressure steam in the condensation step, a pressure increasing step of increasing at least a part of the low pressure low pressure steam condensate may be performed. When performing this pressurizing step, non-pressurized or pressurized low-low pressure steam condensate can be used as the heating source. In the former case, the design pressure of the device used for the heating (for example, the raw material ammonia preheater) can be lowered. In the latter case, it is easy to send the steam condensate used for the heating to a high-pressure device or a device located at a high place. Also, in the latter case, compared to the former case, it is easier to prevent the low-low pressure steam condensate from becoming low in temperature even after the pressure of the low-low pressure steam condensate decreases due to the pressure loss due to piping, etc. is there.
　例えば、濃縮工程において、精製工程で処理された後の尿素合成液を、低低圧スチームコンデンセートの少なくとも一部を用いて加熱し、その後、低低圧スチームまたは低圧スチームまたはその両方を用いて加熱することができる。そのために、濃縮装置が、低低圧スチームコンデンセートの少なくとも一部を用いて精製装置で処理された後の尿素合成液を加熱するよう構成された熱交換構造と、その下流に設けられた、この熱交換構造で加熱された尿素合成液を、低圧スチームを用いて加熱するよう構成された熱交換構造とを含むことができる。 For example, in the concentration step, the urea synthesis liquid after being treated in the purification step is heated with at least a part of low-low pressure steam condensate, and then with low-low pressure steam or low-pressure steam or both. You can To this end, the concentrator is configured with a heat exchange structure configured to heat the urea synthesis liquid after being treated in the refiner with at least a part of the low and low pressure steam condensate, and the heat exchange structure provided downstream thereof. A heat exchange structure configured to heat the urea synthesis liquid heated by the exchange structure with low pressure steam.
　〔低低圧スチームコンデンセートによるアンモニア予熱工程〕
　低低圧スチームコンデンセートの少なくとも一部を加熱源として用いて、原料アンモニアを加熱することができる。特には、合成工程および／または凝縮工程に供給する原料アンモニアを、低低圧スチームコンデンセートによって加熱することが好ましい。ただし、合成工程と凝縮工程の両方に原料アンモニアを供給する場合は、合成工程に供給する原料アンモニアの加熱を、凝縮工程に供給する原料アンモニアの加熱よりも優先することが好ましい。この工程において、合成工程に供給する原料アンモニアを加熱すれば、低圧スチームより利用価値が低い低低圧スチームコンデンセートを用いて、合成工程の温度を高めることができる。この工程において、凝縮工程に供給する原料アンモニアを加熱すれば、凝縮工程において発生する低圧スチームの量を増やすことができる。 [Ammonia preheating process using low and low pressure steam condensate]
At least a part of the low and low pressure steam condensate can be used as a heating source to heat the raw material ammonia. In particular, it is preferable to heat the raw material ammonia supplied to the synthesis step and / or the condensation step by low pressure steam condensate. However, when the raw material ammonia is supplied to both the synthesis step and the condensation step, it is preferable to give priority to the heating of the raw material ammonia supplied to the synthesis step over the heating of the raw material ammonia supplied to the condensation step. In this step, if the raw material ammonia supplied to the synthesis step is heated, the temperature of the synthesis step can be raised by using the low- and low-pressure steam condensate, which has a lower utility value than the low-pressure steam. In this step, if the raw material ammonia supplied to the condensation step is heated, the amount of low pressure steam generated in the condensation step can be increased.
　原料アンモニアの温度は通常低温であるため、原料アンモニアの加熱によって低低圧スチームコンデンセートの温度が低下しても、低低圧スチームコンデンセートが持つ熱を有効に活用しやすい。原料アンモニアは低圧スチームでさらに加熱してもよいし、さらに別の高温の加熱源を利用して加熱してもよい。原料アンモニアを、低低圧スチームコンデンセートで加熱し、次いで低低圧スチームで加熱し、次いで低圧スチームで加熱することもできる。 Since the temperature of the raw material ammonia is usually low, even if the temperature of the low and low pressure steam condensate is lowered by heating the raw material ammonia, it is easy to effectively utilize the heat of the low and low pressure steam condensate. The raw material ammonia may be further heated by low pressure steam, or may be further heated by using another high temperature heating source. It is also possible to heat the feedstock ammonia with low and low pressure steam condensate, then with low and low pressure steam, and then with low pressure steam.
　低低圧スチームコンデンセートによるアンモニア予熱工程には、適宜の熱交換構造（原料アンモニアと、低低圧スチームコンデンセートとの間の熱交換を行う）を設けた装置（アンモニア予熱器）を使用することができる。 A device (ammonia preheater) provided with an appropriate heat exchange structure (for exchanging heat between the raw material ammonia and the low and low pressure steam condensate) can be used in the ammonia preheating process using the low and low pressure steam condensate.
　〔造粒工程〕
　尿素製造方法は、濃縮工程で処理された尿素合成液から空気を用いて粒状固体尿素を製造する造粒工程を含むことができる。造粒工程が、低低圧スチームコンデンセートの一部を用いて空気を加熱する工程を含むことができる。空気の加熱は、例えば、外部からの空気を昇温および／または乾燥させるために行う。 [Granulation process]
The urea production method may include a granulation step of producing granular solid urea using air from the urea synthesis liquid treated in the concentration step. The granulating step can include heating the air with a portion of the low and low pressure steam condensate. The heating of the air is performed, for example, to raise the temperature and / or dry the air from the outside.
　大気温度は通常低低圧スチームコンデンセートに比べて十分に低温である。そのため、低低圧スチームコンデンセートの少なくとも一部を造粒工程で用いる空気の加熱に利用すれば、低低圧スチームコンデンセートが持つ熱を有効に活用しやすい。さらに、低低圧スチームおよび／または低圧スチームおよび／または別の高温の加熱源を利用して、空気をさらに加熱してもよい。 ▽ Atmospheric temperature is usually sufficiently low compared to low and low pressure steam condensate. Therefore, if at least a part of the low and low pressure steam condensate is used for heating the air used in the granulation step, it is easy to effectively use the heat of the low and low pressure steam condensate. Additionally, low and low pressure steam and / or low pressure steam and / or another high temperature heating source may be utilized to further heat the air.
　上記造粒工程を行うために、尿素製造の分野で公知の造粒装置に、適宜の熱交換構造（低低圧スチームコンデンセートの少なくとも一部と空気との間の熱交換を行う熱交換構造、低低圧スチームの少なくとも一部と空気との間の熱交換を行う熱交換構造）を設けた装置を使用することができる。 In order to carry out the above-mentioned granulation step, in a granulating apparatus known in the field of urea production, an appropriate heat exchange structure (a heat exchange structure for performing heat exchange between at least a part of low and low pressure steam condensate and air, a low A device provided with a heat exchange structure for exchanging heat between at least a part of the low pressure steam and air can be used.
　〔その他〕
　凝縮工程でも尿素合成反応は進行するため、凝縮工程と合成工程を単一の圧力容器の中で行うことができる。つまり、凝縮器と合成器とが一体化された単一の圧力容器を用いることができる。 [Other]
Since the urea synthesis reaction proceeds even in the condensation step, the condensation step and the synthesis step can be performed in a single pressure vessel. That is, it is possible to use a single pressure vessel in which the condenser and the synthesizer are integrated.
　本発明によれば、大気圧よりも高い圧力に低圧スチームコンデンセートを減圧させて、低低圧スチームおよび低低圧スチームコンデンセートを発生させる。したがって、低圧スチームコンデンセートを大気圧まで減圧する場合と比べて、発生したスチームの温度が高く、これらを加熱源として使用できる用途が多い。また、これらを加熱源として使用するための熱交換器の伝熱面積を小さくできる。 According to the present invention, the low pressure steam condensate is depressurized to a pressure higher than the atmospheric pressure to generate low and low pressure steam and low and low pressure steam condensate. Therefore, compared with the case where the low-pressure steam condensate is depressurized to the atmospheric pressure, the temperature of the generated steam is higher, and these can be used as a heating source in many applications. Moreover, the heat transfer area of the heat exchanger for using these as a heat source can be made small.
　また、低低圧スチームコンデンセートは、大気圧より高い圧力で加熱源として利用することを可能にするので、回収できる熱量が増え、熱回収のための熱交換器の伝熱面積に対しても有利である。 In addition, since the low- and low-pressure steam condensate can be used as a heat source at a pressure higher than the atmospheric pressure, the amount of heat that can be recovered increases, which is advantageous for the heat transfer area of the heat exchanger for heat recovery. is there.
　〔プロセス例〕
　以下、図面を用いて本発明を詳細に説明するが、本発明はこれによって限定されない。図１、２において、「ＭＰ　ＳＴＭ」は中圧スチームを、「ＬＰ　ＳＴＭ」は低圧スチームを、「ＬＬＰ　ＳＴＭ」は低低圧スチームを、「ＭＰ　ＳＣ」は中圧スチームコンデンセートを、「ＬＰ　ＳＣ」は低圧スチームコンデンセートを、「ＬＬＰ　ＳＣ」は低低圧スチームコンデンセートを、それぞれ意味する。図１において、実線はスチームを、破線はスチームコンデンセートを表す。より厳密には、圧力の高いスチームコンデンセートを減圧すると、スチームとスチームコンデンセートの２相流になるが、ここではこのような２相流も破線で示す。 [Process example]
Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. 1 and 2, "MP STM" indicates medium pressure steam, "LP STM" indicates low pressure steam, "LLP STM" indicates low and low pressure steam, "MP SC" indicates medium pressure steam condensate, and "LP SC". Means low pressure steam condensate, and “LLP SC” means low pressure steam condensate. In FIG. 1, the solid line represents steam and the broken line represents steam condensate. More strictly speaking, when the steam condensate having a high pressure is decompressed, it becomes a two-phase flow of steam and steam condensate. Here, such a two-phase flow is also shown by a broken line.
　図１に示すように、ライン１の低圧スチームコンデンセートは、凝縮器Ａでプロセス流体によって加熱され（凝縮熱の回収に利用され）、低圧スチームとなる。ライン１の低圧スチームコンデンセートは、高圧分解器で中圧スチームが凝縮した中圧スチームコンデンセートに由来する。高圧分解器からの中圧スチームコンデンセートは、例えば減圧弁（不図示）によって減圧されて低圧スチームと低圧スチームコンデンセートとなり、これらがベッセル（不図示）で気液分離され、低圧スチームコンデンセートが得られる。 As shown in FIG. 1, the low-pressure steam condensate in line 1 is heated by the process fluid in the condenser A (used to recover the heat of condensation) and becomes low-pressure steam. The low-pressure steam condensate in line 1 comes from the medium-pressure steam condensate in which the medium-pressure steam is condensed in the high-pressure decomposer. The medium-pressure steam condensate from the high-pressure decomposer is decompressed by, for example, a pressure reducing valve (not shown) to become low-pressure steam and low-pressure steam condensate, which are gas-liquid separated in a vessel (not shown) to obtain low-pressure steam condensate.
　凝縮器Ａからライン２に抜き出された低圧スチームは、一部がライン３を経て精製装置Ｂに送られ、加熱源として利用される。ライン２の低圧スチームの別の一部が、ライン４を経て濃縮装置Ｃに送られ、加熱源として利用される。ライン２の低圧スチームの残部は、これら以外の加熱源として適宜利用できるが、図１には示していない。 The low-pressure steam extracted from the condenser A to the line 2 is partially sent to the refining device B via the line 3 and used as a heating source. Another part of the low-pressure steam in line 2 is sent to the concentrator C via line 4 and used as a heating source. The rest of the low-pressure steam in line 2 can be appropriately used as a heating source other than these, but it is not shown in FIG.
　精製装置Ｂおよび濃縮装置Ｃから、低圧スチームが凝縮した低圧スチームコンデンセートが、それぞれライン５およびライン６に抜き出される。これら低圧スチームコンデンセートは、合流し、ライン７を経て低低圧流体発生装置Ｄに送られる。 From the refiner B and the concentrator C, low-pressure steam condensate in which low-pressure steam is condensed is extracted into line 5 and line 6, respectively. These low-pressure steam condensates merge and are sent to the low-low pressure fluid generator D via the line 7.
　低低圧流体発生装置Ｄでは、低圧スチームコンデンセートを減圧させて低低圧スチームコンデンセートと低低圧スチームとを発生させ、これらをベッセルで気液分離して、ライン８に低低圧スチームを得、ライン９に低低圧スチームコンデンセートを得る。低低圧スチームは、アンモニア予熱器Ｅに送られて、原料アンモニアを加熱する。低低圧スチームコンデンセートは、ライン１０と１１に分岐される。ライン１０の低低圧スチームコンデンセートは、アンモニア予熱器Ｆに送られて原料アンモニアを加熱し、ライン１２に低低圧スチームコンデンセートとして抜き出される。原料アンモニアの流れを基準として、アンモニア予熱器Ｅよりも、アンモニア予熱器Ｆを上流に配することができる。ライン１２の低低圧スチームコンデンセートは、例えば、大気圧下に置かれたスチームコンデンセート保持タンク（不図示）に蓄えられる。ライン１１の低低圧スチームコンデンセートは、昇圧されて、凝縮器Ａに凝縮工程供給用スチームコンデンセートとして送られる。ただし、ライン１１の低低圧スチームコンデンセートは不図示のベッセルに供給され、このベッセルから低低圧スチームコンデンセートが凝縮器Ａに送られる。図１においてこのベッセルは凝縮器Ａを示すブロックに含まれると理解されたい。また、この昇圧のための昇圧機は図１に示していない。図１においては、この昇圧機は、ライン９もしくは１１に設けられていると理解されたい。また、当該昇圧機で昇圧されたスチームコンデンセートは低圧スチームコンデンセートと同等の圧力となっても、温度は昇圧機前後で実質的な変化はなく、低低圧スチームコンデンセートと同程度である。低圧スチームが凝縮して発生した低圧スチームコンデンセートと区別するために、当該昇圧機で昇圧されたスチームコンデンセートを低低圧スチームコンデンセートと表記することとする。例えば、低低圧スチームコンデンセート（ライン１１）を、低圧スチームコンデンセート（ライン１）と同じ圧力まで昇圧し、これらのスチームコンデンセート（ライン１および１１）を合流させて、凝縮器Ａで用いることができる。 In the low and low pressure fluid generator D, the low pressure steam condensate is decompressed to generate low and low pressure steam condensate and low and low pressure steam, and these are separated into gas and liquid in a vessel to obtain low and low pressure steam in line 8 and line 9. Gain low and low pressure steam condensate. The low and low pressure steam is sent to the ammonia preheater E to heat the raw material ammonia. The low pressure steam condensate is branched into lines 10 and 11. The low / low pressure steam condensate in the line 10 is sent to the ammonia preheater F to heat the raw material ammonia, and is extracted as the low / low pressure steam condensate in the line 12. The ammonia preheater F can be arranged upstream of the ammonia preheater E based on the flow of the raw material ammonia. The low and low pressure steam condensate in the line 12 is stored in, for example, a steam condensate holding tank (not shown) placed under atmospheric pressure. The low and low pressure steam condensate in the line 11 is pressurized and sent to the condenser A as a steam condensate for supplying the condensation process. However, the low and low pressure steam condensate in the line 11 is supplied to a vessel (not shown), and the low and low pressure steam condensate is sent to the condenser A from this vessel. It should be understood that in FIG. 1 this vessel is included in the block showing condenser A. Moreover, the booster for this boosting is not shown in FIG. In FIG. 1 it should be understood that this booster is provided in line 9 or 11. Further, even if the pressure of the steam condensate boosted by the booster becomes equal to that of the low pressure steam condensate, the temperature does not substantially change before and after the booster, and is the same as that of the low pressure steam condensate. In order to distinguish it from the low-pressure steam condensate generated by the condensation of low-pressure steam, the steam condensate boosted by the booster will be referred to as low-low pressure steam condensate. For example, the low and low pressure steam condensate (line 11) can be boosted to the same pressure as the low pressure steam condensate (line 1) and these steam condensates (lines 1 and 11) can be combined and used in condenser A.
　図２に示すように、不図示のポンプにより適宜昇圧された原料アンモニアが、ライン１０１、１０２、１０３及びライン１０４を経て、合成器Ｈに供給される。原料二酸化炭素がライン１０５、１０６を経て合成器Ｈに供給される。原料アンモニア（ライン１０１）を、熱交換器（アンモニア予熱器）Ｆにおいて、低低圧スチームコンデンセートとの熱交換によって加熱する。次いで、加熱した原料アンモニア（ライン１０２）を、熱交換器（アンモニア予熱器）Ｅにおいて低低圧スチームとの熱交換によって加熱する。熱交換器Ｅで低低圧スチームは凝縮して低低圧スチームコンデンセートとなる。その後、加熱した原料アンモニア（ライン１０３）を、エジェクターＩの駆動流体として利用することができる。図示はしないが、ライン１０３にさらに熱交換器を追加して、低圧スチームとの熱交換によって原料アンモニアをさらに加熱することもできる。 As shown in FIG. 2, raw material ammonia, which is appropriately pressurized by a pump (not shown), is supplied to the synthesizer H via lines 101, 102, 103, and 104. Raw carbon dioxide is supplied to the synthesizer H via lines 105 and 106. The raw material ammonia (line 101) is heated in a heat exchanger (ammonia preheater) F by heat exchange with low- and low-pressure steam condensate. Next, the heated raw material ammonia (line 102) is heated in a heat exchanger (ammonia preheater) E by heat exchange with low-pressure low-pressure steam. In the heat exchanger E, the low and low pressure steam is condensed into a low and low pressure steam condensate. The heated feedstock ammonia (line 103) can then be utilized as the drive fluid for ejector I. Although not shown, it is possible to further add a heat exchanger to the line 103 to further heat the raw material ammonia by heat exchange with the low pressure steam.
　合成器Ｈから、尿素合成液がライン１１０を経て、高圧分解器Ｇに送られる。高圧分解器Ｇでは、尿素合成液が、中圧スチームによる加熱部（熱交換構造）において加熱される。中圧スチームは、中圧スチームコンデンセートとなって当該加熱部から抜き出される。高圧分解器Ｇの底部には、ライン１０５および１０７を経て二酸化炭素がストリッピングガスとして供給される。 The urea synthesis solution is sent from the synthesizer H to the high-pressure decomposer G via the line 110. In the high-pressure decomposer G, the urea synthesis liquid is heated in the heating section (heat exchange structure) by the medium-pressure steam. The medium-pressure steam becomes a medium-pressure steam condensate and is extracted from the heating section. Carbon dioxide is supplied as stripping gas to the bottom of the high-pressure decomposer G via lines 105 and 107.
　高圧分解器Ｇから、ライン１１２を経て、高圧分解出口ガスが凝縮器Ａに導入される。また、高圧分解出口ガスが分離された尿素合成液が、ライン１１１を経て精製装置Ｂに送られる。 From the high-pressure decomposer G, the high-pressure decomposition outlet gas is introduced into the condenser A via the line 112. Further, the urea synthesis liquid from which the high-pressure decomposition outlet gas has been separated is sent to the purification apparatus B via the line 111.
　凝縮器Ａに導入された高圧分解出口ガスは、ライン１２０から導入される吸収液（吸収媒体）によって吸収されて凝縮する。得られた凝縮液はライン１２１を経て、エジェクターＩで昇圧され、ライン１０４から合成器Ｈに循環される。凝縮しなかったガス（凝縮器出口ガス）は、ライン１２２から抜き出され、減圧弁Ｊで減圧される。凝縮器Ａには、冷却源として低圧スチームコンデンセートが導入される。低圧スチームコンデンセートが、凝縮器Ａの内部流体（プロセス流体）によって加熱されて、低圧スチームが発生する。 The high-pressure decomposition outlet gas introduced into the condenser A is absorbed and condensed by the absorbing liquid (absorption medium) introduced through the line 120. The obtained condensate is pressurized by the ejector I through the line 121 and circulated from the line 104 to the synthesizer H. The gas that has not condensed (condenser outlet gas) is extracted from the line 122 and decompressed by the decompression valve J. Low-pressure steam condensate is introduced into the condenser A as a cooling source. The low pressure steam condensate is heated by the internal fluid (process fluid) of the condenser A to generate low pressure steam.
　精製装置Ｂは、減圧弁Ｂ１、中圧分解器Ｂ２、減圧弁Ｂ３、および低圧分解器Ｂ４を含む。ライン１１１からの尿素合成液は、減圧弁Ｂ１で減圧され、ライン１１３を経て、中圧分解工程を行う中圧分解器Ｂ２に送られる。ライン１１３から中圧分解器Ｂ２に導入された尿素合成液（気液二相流でもよい）は、中圧分解器Ｂ２の低圧スチームによる加熱部（熱交換構造）で加熱される。低圧スチームは、低圧スチームコンデンセートとなって当該加熱部から抜き出される。 The refining device B includes a pressure reducing valve B1, a medium pressure decomposer B2, a pressure reducing valve B3, and a low pressure decomposer B4. The urea synthetic solution from the line 111 is decompressed by the decompression valve B1, and is sent to the intermediate pressure decomposing unit B2 for performing the intermediate pressure decomposing step via the line 113. The urea synthesis liquid (which may be a gas-liquid two-phase flow) introduced from the line 113 to the intermediate pressure decomposer B2 is heated in the heating section (heat exchange structure) by the low pressure steam of the intermediate pressure decomposer B2. The low-pressure steam becomes a low-pressure steam condensate and is extracted from the heating section.
　中圧分解出口ガスがライン１３２から抜き出される。中圧分解出口ガスが分離された尿素合成液がライン１３１から抜き出され、減圧弁Ｂ３で減圧され、ライン１３４から、低圧分解工程を行う低圧分解器Ｂ４に導入される。なお、カーバメートの分解を促進するために、ライン１４４から低圧分解器Ｂ４に二酸化炭素が供給される。 The medium pressure decomposition outlet gas is extracted from the line 132. The urea synthesis liquid from which the medium-pressure decomposition outlet gas has been separated is extracted from the line 131, decompressed by the decompression valve B3, and introduced from the line 134 to the low-pressure decomposition device B4 that performs the low-pressure decomposition step. Note that carbon dioxide is supplied from the line 144 to the low-pressure decomposer B4 in order to accelerate the decomposition of the carbamate.
　ライン１３４から低圧分解器Ｂ４に導入された尿素合成液（気液二相流でもよい）は、低圧分解器Ｂ４の低圧スチームによる加熱部（熱交換構造）で加熱される。低圧分解出口ガスがライン１４２から抜き出される。低圧分解出口ガスが分離された尿素合成液がライン１４１から抜き出され、濃縮装置Ｃに送られる。 The urea synthesis liquid (which may be a gas-liquid two-phase flow) introduced into the low-pressure decomposer B4 from the line 134 is heated in the heating unit (heat exchange structure) of the low-pressure decomposer B4 by the low-pressure steam. The low pressure decomposition outlet gas is withdrawn from line 142. The urea synthesis liquid from which the low-pressure decomposition outlet gas has been separated is extracted from the line 141 and sent to the concentrator C.
　濃縮装置Ｃは、減圧弁Ｃ１、加熱器Ｃ２、気液分離器Ｃ３、加熱器Ｃ４、および気液分離器Ｃ５を含む。ライン１４１からの尿素合成液は減圧弁Ｃ１で減圧され、ライン１４５から、加熱器Ｃ２に導入される。この加熱器（特にはその熱交換構造）では、低圧スチームによって尿素合成液が加熱され、低圧スチームコンデンセートが発生する。加熱された尿素合成液は、気液二相流となってライン１５１から気液分離器Ｃ３に導入され、気相がライン１５３に、液相（さらに尿素が濃縮された尿素合成液）がライン１５２に抜き出される。 The concentrator C includes a pressure reducing valve C1, a heater C2, a gas-liquid separator C3, a heater C4, and a gas-liquid separator C5. The urea synthesis liquid from the line 141 is decompressed by the pressure reducing valve C1 and introduced into the heater C2 from the line 145. In this heater (in particular, its heat exchange structure), the low-pressure steam heats the urea synthesis liquid, and low-pressure steam condensate is generated. The heated urea synthesis liquid becomes a gas-liquid two-phase flow and is introduced into the gas-liquid separator C3 from the line 151, the gas phase is in the line 153, and the liquid phase (the urea synthesis liquid in which urea is concentrated) is in the line. It is extracted to 152.
　ライン１５２の尿素合成液は、加熱器Ｃ４に導入される。この加熱器（特にはその熱交換構造）では、低圧スチームによって尿素合成液が加熱され、低圧スチームコンデンセートが発生する。加熱された尿素合成液は、気液二相流となってライン１６１から気液分離器Ｃ５に導入され、気相がライン１６３に、液相（さらに尿素が濃縮された尿素合成液）がライン１６２に抜き出され、造粒工程に送られる。 The urea synthesis solution in line 152 is introduced into the heater C4. In this heater (in particular, its heat exchange structure), the low-pressure steam heats the urea synthesis liquid, and low-pressure steam condensate is generated. The heated urea synthesis solution becomes a gas-liquid two-phase flow and is introduced into the gas-liquid separator C5 from the line 161, and the gas phase is in the line 163 and the liquid phase (the urea synthesis solution in which urea is concentrated) is in the line. It is extracted in 162 and sent to the granulation process.
　凝縮器Ａ、中圧分解器Ｂ２および低圧分解器Ｂ４から抜き出されるガスに含まれるアンモニア、二酸化炭素および水を回収することができる。また、気液分離器Ｃ３および気液分離器Ｃ５から抜き出されるガスに含まれる水を回収することができる。このような回収処理においては、ガスを吸収媒体中に吸収および凝縮させながらその吸収媒体を冷却することができる。吸収媒体としては、水（尿素、アンモニア、二酸化炭素及びアンモニウムカーバメイトを含んでいてもよい）など、尿素製造方法の分野で公知の吸収媒体を適宜使用できる。 Ammonia, carbon dioxide and water contained in the gas extracted from the condenser A, the medium pressure decomposer B2 and the low pressure decomposer B4 can be recovered. Further, water contained in the gas extracted from the gas-liquid separator C3 and the gas-liquid separator C5 can be recovered. In such a recovery process, the absorption medium can be cooled while absorbing and condensing the gas in the absorption medium. As the absorption medium, water (which may contain urea, ammonia, carbon dioxide and ammonium carbamate) and the like known in the field of the urea production method can be appropriately used.
　以下、このような処理の例について説明する。図２に示したように、中圧分解出口ガス（ライン１３２）を、減圧弁Ｊで減圧された凝縮器出口ガス（ライン１２３）と混合した混合ガス（ライン１３３）を得る。この混合ガスを、図３に示すように、中圧吸収器Ｋ１において、ライン１７３からの液体中に吸収および凝縮させながらその液体を冷却して、ライン１７１に回収液を得る。この回収液をポンプＰ１で昇圧して、ライン１２０から凝縮器Ａに供給する。 Below, an example of such processing is explained. As shown in FIG. 2, a mixed gas (line 133) is obtained by mixing the medium pressure decomposition outlet gas (line 132) with the condenser outlet gas (line 123) whose pressure is reduced by the pressure reducing valve J. As shown in FIG. 3, the mixed gas is cooled in the medium pressure absorber K1 while being absorbed and condensed in the liquid from the line 173 to obtain a recovered liquid in the line 171. The recovered liquid is pressurized by the pump P1 and supplied to the condenser A from the line 120.
　低圧分解出口ガス（ライン１４２）を、低圧吸収器Ｋ２において、ライン１７５からの液体中に吸収および凝縮させながらその液体を冷却して、ライン１７２に回収液を得る。この回収液をポンプＰ２で昇圧して、ライン１７３から中圧吸収器Ｋ１に吸収媒体として送る。 The low pressure decomposition outlet gas (line 142) is cooled in the low pressure absorber K2 while being absorbed and condensed in the liquid from the line 175 to obtain a recovered liquid in the line 172. The pressure of the recovered liquid is increased by the pump P2 and is sent from the line 173 to the medium pressure absorber K1 as an absorption medium.
　気液分離器Ｃ３から抜き出されたライン１５３のガスが、熱交換器Ｋ３に送られ、気液分離器Ｃ５から抜き出されたライン１６３のガスが、熱交換器Ｋ４に送られ、それぞれのガスが各熱交換器で冷却されて凝縮する。凝縮した水（ライン１７４）をポンプＰ３で昇圧して、ライン１７５から低圧吸収器Ｋ２に吸収媒体として送る。 The gas in line 153 extracted from the gas-liquid separator C3 is sent to the heat exchanger K3, and the gas in line 163 extracted from the gas-liquid separator C5 is sent to the heat exchanger K4. The gas is cooled and condensed in each heat exchanger. The condensed water (line 174) is pressurized by the pump P3 and sent from the line 175 to the low pressure absorber K2 as an absorption medium.
　吸収器Ｋ１およびＫ２、ならびに熱交換器Ｋ３およびＫ４における冷却のために、冷却水などの適宜の冷却媒体を用いることができる。 An appropriate cooling medium such as cooling water can be used for cooling the absorbers K1 and K2 and the heat exchangers K3 and K4.
ＭＰ　ＳＴＭ　：中圧スチーム
ＬＰ　ＳＴＭ　：低圧スチーム
ＬＬＰ　ＳＴＭ：低低圧スチーム
ＭＰ　ＳＣ　　：中圧スチームコンデンセート
ＬＰ　ＳＣ　　：低圧スチームコンデンセート
ＬＬＰ　ＳＣ　：低低圧スチームコンデンセート
Ａ　：凝縮器
Ｂ　：精製装置
Ｂ１、Ｂ３、Ｃ１、Ｊ：減圧弁
Ｂ２：中圧分解器
Ｂ４：低圧分解器
Ｃ　：濃縮装置
Ｃ２：加熱器
Ｃ３：気液分離器
Ｃ４：加熱器
Ｃ５：気液分離器
Ｄ　：低低圧流体発生装置
Ｅ　：熱交換器（アンモニア予熱器）
Ｆ　：熱交換器（アンモニア予熱器）
Ｇ　：高圧分解器
Ｈ　：合成器
Ｉ　：エジェクター
Ｋ１：中圧吸収器
Ｋ２：低圧吸収器
Ｋ３、Ｋ４：熱交換器
Ｐ１、Ｐ２、Ｐ３：ポンプ
  MP STM: Medium pressure steam
LP STM: Low pressure steam
LLP STM: Low and low pressure steam
MP SC: Medium pressure steam condensate
LP SC: Low pressure steam condensate
LLP SC: Low and low pressure steam condensate
A: Condenser
B: Refining equipment
B1, B3, C1, J: Pressure reducing valve
B2: Medium pressure decomposer
B4: Low pressure decomposer
C: Concentrator
C2: heater
C3: Gas-liquid separator
C4: heater
C5: Gas-liquid separator
D: Low and low pressure fluid generator
E: Heat exchanger (ammonia preheater)
F: Heat exchanger (ammonia preheater)
G: High-pressure decomposer
H: synthesizer
I: Ejector
K1: Medium pressure absorber
K2: Low pressure absorber
K3, K4: Heat exchanger
P1, P2, P3: Pump

Claims (20)

  1. 　アンモニアと二酸化炭素から尿素を合成し、尿素合成液を生成する合成工程と、
    　前記合成工程で生成した尿素合成液を加熱することによって、アンモニウムカーバメイトを分解し、かつアンモニアと二酸化炭素を含む混合ガスを前記尿素合成液から分離する高圧分解工程と、
    　前記高圧分解工程で得られる前記混合ガスの少なくとも一部を吸収媒体に吸収させて凝縮させ、この凝縮の際に生じる熱を用いて低圧スチームを発生させる凝縮工程と、
    　前記高圧分解工程で処理された後の尿素合成液を、前記高圧分解工程の圧力より低く且つ大気圧より高い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度が高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせる工程であって、前記高圧分解工程で処理された後の尿素合成液を加熱するための加熱源として、前記凝縮工程で発生させた前記低圧スチームの一部を用いる、精製工程と、
    　前記精製工程で処理された後の尿素合成液を、前記精製工程の圧力より低く且つ大気圧もしくは大気圧より低い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度がさらに高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせる工程であって、前記精製工程で処理された後の尿素合成液を加熱するための加熱源として、前記凝縮工程で発生させた前記低圧スチームの別の一部を用いる、濃縮工程と、
    　前記精製工程および前記濃縮工程のうちの一方もしくは両方から得られた低圧スチームコンデンセートの少なくとも一部を、大気圧より高い圧力に減圧することによって、低低圧スチームコンデンセートと低低圧スチームを発生させる低低圧流体発生工程と
    を含む、尿素製造方法。     A synthesis step of synthesizing urea from ammonia and carbon dioxide to produce a urea synthesis solution;
    By heating the urea synthesis solution generated in the synthesis step, to decompose ammonium carbamate, and a high-pressure decomposition step of separating a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution,
    At least a part of the mixed gas obtained in the high-pressure decomposition step is absorbed into an absorption medium and condensed, and a condensation step of generating low-pressure steam using heat generated during this condensation,
    Heating the urea synthesis liquid after being treated in the high-pressure decomposition step at a pressure lower than the pressure in the high-pressure decomposition step and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase. By the step of obtaining a urea synthesis solution having an increased urea concentration and generating low-pressure steam condensate, as a heating source for heating the urea synthesis solution after being treated in the high-pressure decomposition step, the condensing step A part of the low-pressure steam generated in, a refining step,
    The urea synthesis liquid that has been treated in the purification step is heated at a pressure lower than the pressure in the purification step and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. Thereby, in the step of producing a low-pressure steam condensate together with obtaining a urea synthesis solution having a further increased urea concentration, the condensation as a heating source for heating the urea synthesis solution after being treated in the purification step. A concentrating step using another portion of the low pressure steam generated in the step;
    At least a part of the low-pressure steam condensate obtained from one or both of the purification step and the concentration step is depressurized to a pressure higher than atmospheric pressure to generate low-low pressure steam condensate and low-low pressure steam. Fluid generation process
    A method for producing urea, comprising:
  2. 　前記低低圧スチームコンデンセートおよび低低圧スチームが、３バール以上の圧力を有する、請求項１に記載の尿素製造方法。 The method for producing urea according to claim 1, wherein the low-low pressure steam condensate and the low-low pressure steam have a pressure of 3 bar or more.
  3. 　前記低低圧スチームコンデンセートおよび低低圧スチームの圧力と、前記凝縮工程で発生させる低圧スチームの圧力との差が、２バール以上である、請求項１または２に記載の尿素製造方法。 The urea production method according to claim 1 or 2, wherein a difference between the pressure of the low- and low-pressure steam condensate and the low- and low-pressure steam and the pressure of the low-pressure steam generated in the condensation step is 2 bar or more.
  4. 　前記低低圧スチームコンデンセートの少なくとも一部を、前記凝縮工程において前記低圧スチームを発生させるためのスチームコンデンセートとして利用するために、昇圧する昇圧工程を含む請求項１〜３のいずれか一項に記載の尿素製造方法。 At least a part of the low- and low-pressure steam condensate is used as a steam condensate for generating the low-pressure steam in the condensing step, and includes a pressurizing step for pressurizing. Urea production method.
  5. 　前記合成工程、前記高圧分解工程及び前記凝縮工程から選ばれる少なくとも一つの工程に供給される原料アンモニアを、前記低低圧スチームコンデンセートの少なくとも一部を加熱源として用いて加熱するアンモニア予熱工程を含む請求項１〜４のいずれか一項に記載の尿素製造方法。 A step of preheating ammonia, which comprises heating the raw material ammonia supplied to at least one step selected from the synthesis step, the high-pressure decomposition step and the condensation step by using at least a part of the low-low pressure steam condensate as a heating source. Item 5. The method for producing urea according to any one of Items 1 to 4.
  6. 　前記合成工程、前記高圧分解工程及び前記凝縮工程から選ばれる少なくとも一つの工程に供給される原料アンモニアを、前記低低圧スチームの少なくとも一部を加熱源として用いて加熱するアンモニア予熱工程を含む請求項１〜５のいずれか一項に記載の尿素製造方法。 A method comprising: an ammonia preheating step of heating the raw material ammonia supplied to at least one step selected from the synthesis step, the high pressure decomposition step and the condensation step, by using at least a part of the low and low pressure steam as a heating source. The method for producing urea according to any one of 1 to 5.
  7. 　前記濃縮工程において、前記精製工程で処理された後の尿素合成液を加熱するための加熱源として、前記低低圧スチームコンデンセートの少なくとも一部を用いる、請求項１〜６のいずれか一項に記載の尿素製造方法。 7. In the concentrating step, at least a part of the low and low pressure steam condensate is used as a heating source for heating the urea synthesis liquid after being treated in the refining step. Urea production method.
  8. 　前記濃縮工程において、前記精製工程で処理された後の尿素合成液を加熱するための加熱源として、前記低低圧スチームの少なくとも一部を用いる、請求項１〜７のいずれか一項に記載の尿素製造方法。 The at least a part of the low and low pressure steam is used as a heating source for heating the urea synthesis liquid after being treated in the purification step in the concentration step, The method according to claim 1. Urea production method.
  9. 　前記濃縮工程で処理された尿素合成液から空気を用いて粒状固体尿素を製造する造粒工程を含み、
    　前記造粒工程が、
    前記低低圧スチームコンデンセートの少なくとも一部を用いて前記空気を加熱する工程、
    および、
    前記低低圧スチームの少なくとも一部を用いて前記空気を加熱する工程
    のうちの一方もしくは両方を含む請求項１〜８のいずれか一項に記載の尿素製造方法。     Including a granulation step of producing a granular solid urea using air from the urea synthesis liquid treated in the concentration step,
    The granulation step,
    Heating the air with at least a portion of the low and low pressure steam condensate,
    and,
    Heating the air using at least a portion of the low and low pressure steam
    The urea production method according to claim 1, comprising one or both of the above.
  10. 　前記合成工程と前記凝縮工程を単一の圧力容器の中で行う、請求項１〜９のいずれか一項に記載の尿素製造方法。 The urea production method according to any one of claims 1 to 9, wherein the synthesis step and the condensation step are performed in a single pressure vessel.
  11. 　アンモニアと二酸化炭素から尿素を合成し、尿素合成液を生成するよう構成された合成器と、
    　前記合成器で生成した尿素合成液を加熱することによって、アンモニウムカーバメイトを分解し、かつアンモニアと二酸化炭素を含む混合ガスを前記尿素合成液から分離するよう構成された高圧分解器と、
    　前記高圧分解器で得られる前記混合ガスの少なくとも一部を吸収媒体に吸収させて凝縮させ、この凝縮の際に生じる熱を用いて低圧スチームを発生させるよう構成された凝縮器と、
    　前記高圧分解器で処理された後の尿素合成液を、前記高圧分解器の圧力より低く且つ大気圧より高い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度が高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせるよう構成された精製装置であって、前記高圧分解器で処理された後の尿素合成液を、前記凝縮器で発生させた前記低圧スチームの一部を用いて加熱する熱交換構造を含む精製装置と、
    　前記精製装置で処理された後の尿素合成液を、前記精製装置の圧力より低く且つ大気圧もしくは大気圧より低い圧力において加熱して、気相と液相を生じさせ、この気相を分離することによって、尿素濃度がさらに高められた尿素合成液を得るとともに低圧スチームコンデンセートを生じさせるよう構成された濃縮装置であって、前記精製装置で処理された後の尿素合成液を、前記凝縮装置で発生させた前記低圧スチームの別の一部を用いて加熱する熱交換構造を含む濃縮装置と、
    　前記精製装置および前記濃縮装置のうちの一方もしくは両方から得られた低圧スチームコンデンセートの少なくとも一部を、大気圧より高い圧力に減圧することによって、低低圧スチームコンデンセートと低低圧スチームを発生させるよう構成された低低圧流体発生装置と
    を含む、尿素製造装置。     A synthesizer configured to synthesize urea from ammonia and carbon dioxide to produce a urea synthesis solution;
    By heating the urea synthesis solution generated in the synthesizer, to decompose ammonium carbamate, and a high-pressure decomposer configured to separate a mixed gas containing ammonia and carbon dioxide from the urea synthesis solution,
    A condenser configured to absorb and condense at least a part of the mixed gas obtained in the high-pressure decomposer with an absorption medium, and to generate low-pressure steam using heat generated during the condensation,
    Heating the urea synthesis liquid after being treated in the high-pressure decomposer at a pressure lower than the pressure of the high-pressure decomposer and higher than atmospheric pressure to generate a gas phase and a liquid phase, and separating the gas phase A purification device configured to obtain a urea synthetic solution having an increased urea concentration and to generate low-pressure steam condensate, wherein the urea synthetic solution after being treated in the high-pressure decomposer is generated in the condenser. A refining apparatus including a heat exchange structure for heating using a part of the low-pressure steam that has been made,
    The urea synthesis liquid after being treated in the purification device is heated at a pressure lower than the pressure of the purification device and at an atmospheric pressure or a pressure lower than the atmospheric pressure to generate a gas phase and a liquid phase, and the gas phase is separated. The concentration device is configured to generate a low pressure steam condensate as well as to obtain a urea synthesis liquid having a further increased urea concentration, and the urea synthesis liquid after being treated by the purification device is treated by the condensation device. A concentrating device comprising a heat exchange structure for heating with another part of the generated low pressure steam,
    At least a part of the low-pressure steam condensate obtained from one or both of the refining device and the concentrating device is decompressed to a pressure higher than atmospheric pressure to generate low-low pressure steam condensate and low-low pressure steam. Low and low pressure fluid generator
    A urea production apparatus including:
  12. 　前記低低圧スチームコンデンセートおよび低低圧スチームが、３バール以上の圧力を有する、請求項１１に記載の尿素製造装置。 The urea production apparatus according to claim 11, wherein the low and low pressure steam condensate and the low and low pressure steam have a pressure of 3 bar or more.
  13. 　前記低低圧スチームコンデンセートおよび低低圧スチームの圧力と、前記凝縮器で発生させる低圧スチームの圧力との差が、２バール以上である、請求項１１または１２に記載の尿素製造装置。 The urea production apparatus according to claim 11 or 12, wherein a difference between the pressures of the low and low pressure steam condensate and the low and low pressure steam and the pressure of the low pressure steam generated in the condenser is 2 bar or more.
  14. 　前記低低圧スチームコンデンセートの少なくとも一部を、前記凝縮器において前記低圧スチームを発生させるためのスチームコンデンセートとして利用するために、昇圧する昇圧機を含む請求項１１〜１３のいずれか一項に記載の尿素製造装置。 14. The booster for boosting pressure is used in order to utilize at least a part of the low- and low-pressure steam condensate as a steam condensate for generating the low-pressure steam in the condenser. Urea production equipment.
  15. 　前記合成器、前記高圧分解器及び前記凝縮器から選ばれる少なくとも一つに供給される原料アンモニアを、前記低低圧スチームコンデンセートの少なくとも一部を加熱源として用いて加熱するよう構成されたアンモニア予熱器を含む請求項１１〜１４のいずれか一項に記載の尿素製造装置。 An ammonia preheater configured to heat the raw material ammonia supplied to at least one selected from the synthesizer, the high-pressure decomposer, and the condenser by using at least a part of the low-low pressure steam condensate as a heating source. The urea production apparatus according to claim 11, further comprising:
  16. 　前記合成器、前記高圧分解器及び前記凝縮器から選ばれる少なくとも一つに供給される原料アンモニアを、前記低低圧スチームの少なくとも一部を加熱源として用いて加熱するよう構成されたアンモニア予熱器を含む請求項１１〜１５のいずれか一項に記載の尿素製造装置。 A raw material ammonia supplied to at least one selected from the synthesizer, the high-pressure decomposer and the condenser, an ammonia preheater configured to heat using at least a part of the low-low pressure steam as a heating source. The urea production apparatus according to any one of claims 11 to 15, comprising.
  17. 　前記濃縮装置が、前記精製装置で処理された後の尿素合成液を、前記低低圧スチームコンデンセートの少なくとも一部を用いて加熱する熱交換構造を含む請求項１１〜１６のいずれか一項に記載の尿素製造装置。 The said concentrator contains the heat exchange structure which heats the urea synthetic liquid after processed by the said refinement | purification device using at least one part of the said low-pressure low-pressure steam condensate. Urea production equipment.
  18. 　前記濃縮装置が、前記精製装置で処理された後の尿素合成液を、前記低低圧スチームの少なくとも一部を用いて加熱する熱交換構造を含む請求項１１〜１７のいずれか一項に記載の尿素製造装置。 18. The concentrating device according to claim 11, wherein the condensing device includes a heat exchange structure that heats the urea synthesis liquid that has been treated by the purifying device by using at least a part of the low and low pressure steam. Urea production equipment.
  19. 　前記濃縮装置で処理された尿素合成液から空気を用いて粒状固体尿素を製造する造粒装置を含み、
    　前記造粒装置が、
    前記低低圧スチームコンデンセートの少なくとも一部を用いて前記空気を加熱する熱交換構造、および、
    前記低低圧スチームの少なくとも一部を用いて前記空気を加熱する熱交換構造
    のうちの一方もしくは両方を含む請求項１１〜１８のいずれか一項に記載の尿素製造装置。     Including a granulating device for producing granular solid urea using air from the urea synthesis liquid treated in the concentrating device,
    The granulating device,
    A heat exchange structure for heating the air using at least a part of the low and low pressure steam condensate, and
    Heat exchange structure for heating the air using at least a part of the low and low pressure steam
    The urea production apparatus according to any one of claims 11 to 18, comprising one or both of the above.
  20. 　前記合成器と前記凝縮器が一体化された単一の圧力容器を含む請求項１１〜１９のいずれか一項に記載の尿素製造装置。 The urea production apparatus according to any one of claims 11 to 19, including a single pressure vessel in which the synthesizer and the condenser are integrated.
PCT/IB2019/059527 2018-11-05 2019-11-06 Urea production method and device WO2020095221A1 (en)

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JPS61138794A (en) * 1984-12-10 1986-06-26 加茂　栄一 Wet paper dryer
JPH10182587A (en) * 1996-10-07 1998-07-07 Toyo Eng Corp Improved synthesis of urea and apparatus therefor
JP2007022934A (en) * 2005-07-13 2007-02-01 Toyo Eng Corp Manufacturing method of granular urea product
JP2012017942A (en) * 2010-07-09 2012-01-26 Ihi Corp Drain recovery equipment
WO2017043391A1 (en) * 2015-09-08 2017-03-16 東洋エンジニアリング株式会社 Urea production method and urea production device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5666602A (en) * 1979-10-31 1981-06-05 Haabii Kogyo Kk Condensing recovery
JPS61138794A (en) * 1984-12-10 1986-06-26 加茂　栄一 Wet paper dryer
JPH10182587A (en) * 1996-10-07 1998-07-07 Toyo Eng Corp Improved synthesis of urea and apparatus therefor
JP2007022934A (en) * 2005-07-13 2007-02-01 Toyo Eng Corp Manufacturing method of granular urea product
JP2012017942A (en) * 2010-07-09 2012-01-26 Ihi Corp Drain recovery equipment
WO2017043391A1 (en) * 2015-09-08 2017-03-16 東洋エンジニアリング株式会社 Urea production method and urea production device

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