RU2608766C2 - Method for increasing capacity of ammonia plant - Google Patents

Method for increasing capacity of ammonia plant Download PDF

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RU2608766C2
RU2608766C2 RU2015106809A RU2015106809A RU2608766C2 RU 2608766 C2 RU2608766 C2 RU 2608766C2 RU 2015106809 A RU2015106809 A RU 2015106809A RU 2015106809 A RU2015106809 A RU 2015106809A RU 2608766 C2 RU2608766 C2 RU 2608766C2
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ammonia
synthesis
compressor
reformer
air
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RU2015106809A
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RU2015106809A (en
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Эрманно Филиппи
Серджо ПАНЦА
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Касале Са
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/06Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds in tube reactors; the solid particles being arranged in tubes
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    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/025Preparation or purification of gas mixtures for ammonia synthesis
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    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/382Multi-step processes
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01CAMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00Ammonia; Compounds thereof
    • C01C1/02Preparation, purification or separation of ammonia
    • C01C1/04Preparation of ammonia by synthesis in the gas phase
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    • C01INORGANIC CHEMISTRY
    • C01CAMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00Ammonia; Compounds thereof
    • C01C1/02Preparation, purification or separation of ammonia
    • C01C1/04Preparation of ammonia by synthesis in the gas phase
    • C01C1/0405Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst
    • C01C1/0417Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst characterised by the synthesis reactor, e.g. arrangement of catalyst beds and heat exchangers in the reactor
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00002Chemical plants
    • B01J2219/00004Scale aspects
    • B01J2219/00006Large-scale industrial plants
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00002Chemical plants
    • B01J2219/00018Construction aspects
    • B01J2219/00024Revamping, retrofitting or modernisation of existing plants
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    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0205Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0205Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0244Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being an autothermal reforming step, e.g. secondary reforming processes
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0283Processes for making hydrogen or synthesis gas containing a CO-shift step, i.e. a water gas shift step
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    • C01INORGANIC CHEMISTRY
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0415Purification by absorption in liquids
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    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435Catalytic purification
    • C01B2203/0445Selective methanation
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465Composition of the impurity
    • C01B2203/0475Composition of the impurity the impurity being carbon dioxide
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06Integration with other chemical processes
    • C01B2203/068Ammonia synthesis
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    • C01INORGANIC CHEMISTRY
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14Details of the flowsheet
    • C01B2203/142At least two reforming, decomposition or partial oxidation steps in series
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14Details of the flowsheet
    • C01B2203/146At least two purification steps in series
    • C01B2203/147Three or more purification steps in series
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    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00Technologies relating to chemical industry
    • Y02P20/50Improvements relating to the production of products other than chlorine, adipic acid, caprolactam, or chlorodifluoromethane, e.g. bulk or fine chemicals or pharmaceuticals
    • Y02P20/52Improvements relating to the production of products other than chlorine, adipic acid, caprolactam, or chlorodifluoromethane, e.g. bulk or fine chemicals or pharmaceuticals using catalysts, e.g. selective catalysts

Abstract

FIELD: chemistry.
SUBSTANCE: invention relates to production of ammonia based on reforming hydrocarbons, in particular, to a method of increasing capacity of an ammonia plant. Method comprises increasing amount of hydrogen produced by a reforming section, by replacement of pipes of primary reformer with new pipes having smaller thickness, to increase inner diameter of pipes, and installing an oxygen source for enrichment with oxygen, provided said source, of air fed into secondary reformer, upgrading air compressor by installing new stator and rotor parts, to increase flow rate of air supplied into secondary reformer, while maintaining previous output pressure, as well as upgrading section for removal of CO2, of synthesis gas compressor, drying unit of synthesis gas and ammonia synthesis loop.
EFFECT: higher efficiency of apparatus for producing ammonia.
8 cl, 1 dwg

Description

Technical field

The invention relates to the field of production of ammonia based on hydrocarbon reforming. The invention discloses a method for increasing the productivity of existing ammonia plants.

State of the art

Ammonia requires synthesis gas containing hydrogen (H 2 ) and nitrogen (N 2 ) in an appropriate ratio of 3: 1. Suitable synthesis gas for producing ammonia is also called "ammonia synthesis gas".

It is known to produce ammonia synthesis gas by reforming a hydrocarbon (HC) feed. Such HC raw materials are usually an untreated source of hydrogen and carbon, for example methane, natural gas, naphtha (the first wide fraction of oil distillation), liquefied associated gas or oil gas, or mixtures thereof. Typically, the feed is natural gas or methane.

In a well-known technology, sulfur-free hydrocarbons are mixed with steam in the desired ratio, and the resulting mixture is fed to a primary steam reformer in which most of the hydrocarbons in the feed are converted to a mixture of carbon monoxide, carbon dioxide and hydrogen, while passing through an appropriate catalyst at moderate pressures, in the range of 15-35 bar, and high temperatures, in the range from 780 to 820 ° C.

As you know, this conversion occurs with the absorption of heat. The catalyst is in a plurality of catalytic tubes heated externally by the heat of combustion of gaseous fuels in air. The pressure outside the tubes is usually close to atmospheric.

The gaseous product exiting the primary reformer is fed to the secondary reformer, usually containing a suitable catalytic layer and a reaction space lying above this layer. The secondary reformer also receives the required amount of air to supply the nitrogen necessary for the subsequent synthesis of ammonia. This air is usually supplied by an air compressor driven by a steam turbine or electric motor; alternatively, in some installations an air separation unit is used to supply enriched air to the secondary reformer.

In the reaction space above the catalyst bed, oxygen reacts with the combustible components of the gas obtained at the outlet of the primary reformer, after which the mixed produced gas enters the catalyst bed at elevated temperature.

During the passage through the catalyst, the remaining methane reacts with steam to absorb heat, as a result of which the gas temperature at the outlet of the secondary reformer is usually about 1000 ° C, and over 99% of the supplied hydrocarbons are converted to carbon oxides and hydrogen.

The converted gas coming out of the secondary reformer is then usually processed in devices located sequentially downstream to remove carbon oxides and produce a gas mixture suitable for the synthesis of ammonia (i.e., having a molar ratio of H 2 / N 2 close to 3: 1). These devices include at least shear converters (CO converters), a CO 2 wash column, and a methanization reactor.

Shear converters typically contain a high temperature CO converter, followed by a low temperature CO converter, in which most of the carbon monoxide (CO) converted gas, together with unreacted steam, is catalytically converted to carbon dioxide and additional hydrogen. In a CO 2 wash column, carbon dioxide is removed by wet gas purification with an appropriate solvent, for example, an aqueous solution of amine or potassium carbonate, to obtain a gas stream containing nitrogen and hydrogen in a molar ratio of H 2 to N 2 of about 3: 1, and residues of methane, carbon oxides and nitrogen. In a methanization reactor, the residual carbon oxides are catalytically converted to methane in order to prevent poisoning of the ammonia synthesis catalyst, which is further down the processing cycle of the catalyst, with oxygen-containing compounds.

Then, at low pressure, usually 15-30 bar, synthesis gas is produced for the production of ammonia, which is then compressed to the pressure of the ammonia synthesis loop (cycle), which is usually from 80 to 300 bar, usually about 150 bar. This compression is performed by the main synthesis gas compressor.

The capacity of the ammonia plant is determined by the amount of ammonia produced, or which can be produced, and is measured, for example, in metric tons per day (mt / d). Productivity is related to the hydrocarbon feed used.

In the process of improving the existing ammonia plant, efforts are directed at increasing productivity from the existing level to a much higher predetermined level, with the same or equivalent raw materials. However, a number of so-called bottlenecks are usually found in existing installations. Bottlenecks represent limitations in an existing installation that do not allow achieving the desired performance. The bottleneck could be, for example, the performance of any part of the installation, or a machine, such as a compressor. The bottlenecks of a complex system, however, are not obvious. In existing systems, modernization (refinement) is mainly carried out by replacing individual existing equipment with new, more powerful, and bottlenecks are overcome alternately, as they become apparent. In other words, the installation is first upgraded to eliminate the first bottleneck, then it is put into operation with increased productivity until a new bottleneck is detected.

In most cases, the primary reformer is upgraded by installing more pipes. The air supply to the secondary reformer is usually increased by installing a new air compressor parallel to the existing one, or, in some cases, installing a booster compressor after the existing air compressor. Such an approach, however, is often more expensive than necessary, and therefore inefficient and unacceptable. Therefore, there remains a need to find a suitable way to increase plant productivity for ammonia production.

SUMMARY OF THE INVENTION

The present invention provides a method for increasing the productivity of a plant for producing ammonia, comprising a head section for producing make-up synthesis gas and a synthesis section for converting this make-up synthesis gas to ammonia. The synthesis section includes at least an ammonia converter. The head section mainly includes: a primary reformer containing a group of tubes filled with a catalyst; a secondary reformer, into which a stream exiting the primary reformer, and an oxidizer stream enter; a first compressor for supplying this oxidizing agent to the secondary reformer; a series of sequentially arranged devices for processing a stream exiting the secondary reformer, including a CO oxidation converter (shear reaction), a carbon dioxide removal section and a methanizer; synthesis gas dehumidification unit; the main synthesis gas compressor to increase the pressure of the synthesis gas to the pressure of the synthesis section, containing a number of stators and rotors.

The method of modernization (refinement / modification) of the described installation includes at least the steps described in paragraph 1 of the attached formula. The first step is to increase the productivity of the reforming section. By productivity is meant the flow rate of the hydrogen stream that is produced or which can be obtained from the reforming section. This increase is achieved by one or more of the following:

- replace the primary reformer pipes with new pipes with improved structural material, while the new pipes have the same outer diameter and smaller thickness than existing ones to increase the inner diameter of the pipes; and / or

- set the oxygen source and the oxygen enrichment device of the supplied air sent to the secondary reformer, with the oxygen supply from this source.

Other steps according to the invention include:

- modernization of the aforementioned first compressor by installing new parts of the stator and rotor so that the upgraded compressor unit provides greater air flow for the secondary reformer at the same outlet pressure;

- modernization of the CO 2 removal section;

- modernization of the synthesis gas compressor by replacing at least the rotors of this compressor and reducing the number of stages;

- improvement of the synthesis gas drainage unit;

- modernization of the ammonia synthesis loop.

The authors found that the described method can achieve a significant increase in productivity, for example, at least 40%, with a relatively small number of improvements. In particular, the present invention proposes a way to increase efficiency in different sections of the installation without the need to increase the size of the equipment being upgraded. The invention proposes a combination of steps that can significantly (more than 40%) increase the productivity of the installation.

Some preferred embodiments are described in the dependent claims and will be discussed below.

In some cases, the existing CO 2 removal section is equipped with two absorbers and two regenerators. Thus, the modernization of this CO 2 removal section preferably assumes that these two regenerators must operate at different pressures so that the first generator operates at the first pressure and the second generator operates at the second pressure. More preferably, a jet pump is installed to connect the two regenerators.

In other cases, the existing CO 2 removal section is equipped with only one absorber and only one regenerator. Thus, the modernization of the CO 2 removal section preferably includes the installation of one or more additional reboiler (s) and condenser (s) and the internal re-equipment of these absorber and regenerator. According to another embodiment, said CO 2 removal section with one absorber and one regenerator is modified by installing a new low pressure stripper together with internal refitting of the existing absorber and regenerator.

In some embodiments, the synthesis gas drying unit is a molecular sieve device, and an improvement of this drying unit includes the use of a new absorber with a higher drying capacity than the existing absorber unit, or the installation of an ammonia washing unit capable of removing oxygen-containing compounds.

The step of upgrading the ammonia synthesis loop preferably includes the installation of either radial-axial or radial inner shell parts in an existing converter of this loop. In other embodiments, upgrading the synthesis loop involves upgrading an existing ammonia converter using any of the following technical solutions: a multilayer catalyst, radial or radial-axial design, adiabatic or isothermal designs. These technical solutions will be discussed in more detail in the description below.

In accordance with other embodiments, upgrading the ammonia synthesis loop involves using an additional converter in parallel or in series with the existing one. In the event that the ammonia synthesis loop contains a hydrogen recovery unit, upgrading the ammonia synthesis loop may include an improvement to this hydrogen recovery unit.

The production of hydrogen by the head section can be improved by any of the following methods: installing a preliminary reformer in front of the primary reformer, or lengthening the radiation heat exchanger of the primary reformer, or using an air separation unit to produce oxygen to enrich the air supplied to the secondary reformer. In some embodiments, the secondary reformer burner is also replaced. The introduction of an air separation unit also has the advantage of increasing hydrogen production without reconstructing the air compressor, since the air compressor is already part of the air separation unit.

In some embodiments, the steam / carbon ratio in the head section is reduced, preferably to a value in the range of 2.7-3.1.

Ancillary improvements affecting, for example, heat exchangers, separators, and other equipment are not mentioned, since they have a negligible effect on the growth of the ammonia production plant.

According to other embodiments:

- can also be upgraded section conversion of CO;

- a water chiller can be used to provide the necessary cooling for the plant to produce ammonia;

- ammonia absorption sections can be reconstructed, or new ones can be installed to provide the required cooling ability of the ammonia plant.

Further, the features and advantages of the invention are described in more detail with reference to preferred embodiments and the figure. Detailed Description of the Invention

The figure shows a particular example of a plant setup for producing ammonia. The installation includes a head section that produces make-up gas for the circuit (cycle) 6 of the synthesis of ammonia. The main elements of the head section are: the reforming section, including the primary reformer 1 and the secondary reformer 2; one or more 3 CO converters, a 4 CO 2 wash column, and a methanization reactor 5 (a converter for converting carbon oxides to methane).

The pressure of the feed synthesis gas 42 rises through the main compressor 33 of the synthesis gas to a high pressure in the synthesis loop. This compressor supplies high pressure synthesis gas 31 to synthesis circuit 6.

Circulation in circuit 6 is provided by another compressor (not shown), also called a circulation pump.

The operation of the installation, in more detail, is as follows. In the preheater 10, a mixture of water vapor 8 and a suitable hydrocarbon feedstock 7, for example natural gas, is preheated to about 500 ° C., after which the preheated gas 11 undergoes a catalytic reaction in the tubes of the primary reformer 1.

The resulting gas 13 exiting the tubes of the primary reformer 1 is then oxidized in the secondary reformer 2 by means of the supplied air 14. This air is supplied by an appropriate air compressor. Secondary reformer 2 has a reaction zone 2b and a catalytic zone 2a located below it. In the upper reaction zone 2b, gas 13 reacts with the oxygen contained in the supply air 14. To carry out the reaction, the secondary reformer 2 has a burner.

The resulting gas 17 exiting the secondary reformer 2 is processed in CO converters 3, a carbon dioxide wash column 4 and a methanization reactor 5, with intermediate cooling of the gas in heat exchangers 16, 19 and 26, and heated in a heater 23, which is located in the flow direction after 5 methanization reactor. The liquid is separated in the separators 21, 28.

Rectangle 40 denotes the removal of water in the synthesis gas. This may include a drainage unit, which is either a unit with a molecular sieve selectively absorbing water, or an ammonia washing unit. In many existing installations, part 40 is missing.

Circuit 6 may also include a hydrogen recovery section. This section allows the recovery of a hydrogen-rich stream from purge gas taken from the circuit itself. This hydrogen enriched stream is preferably recycled back to the circuit at the suction end of the circulation pump to minimize the energy required for compression.

Next, with reference to a preferred embodiment, a more detailed description of the method of the invention is provided.

Reforming Performance

The first step of the invention is to increase the performance of primary reforming, i.e. hydrogen production in the primary reformer 1. This is achieved by installing new pipes with a reduced thickness, while the number of catalytic pipes remains unchanged. New pipes have, on the whole, the same diameter but smaller thickness, and, as a result, the inner diameter is larger than that of existing pipes. Preferably, pipes with improved metallurgical properties are used, for example, newly installed pipes are pipes of microalloyed metals that can reliably work at the required pressure and temperature, despite the reduced thickness.

This approach differs from the usual modernization methodology, according to which the number of catalytic pipes is increased to ensure greater productivity. The present invention increases the productivity of each individual pipe by reducing its thickness, with a corresponding increase in flow rate through it.

The performance of the primary reformer is desirable to further increase by reducing the ratio of "steam / carbon" (S / C - from the English Steam / Carbon). Preferably, the vapor / carbon ratio is reduced to 2.7 ÷ 3.1 (mol / mol). By reducing this ratio, a greater amount of natural gas is subjected to steam conversion to hydrogen and carbon oxides. The applicant found that this decrease in S / C gives a gain, despite the deterioration of the balance.

With the conversion commonly used in the prior art, the steam / carbon ratio is left unchanged or is reduced slightly to avoid problems in operation of the CO 2 removal section located further down the processing circuit. In the invention, as will be shown below, a synergistic effect of reducing the S / C ratio and the operation of the carbon dioxide removal section is achieved.

Nitrogen source

Nitrogen typically comes with air supplied to the secondary reformer, for example, with an air stream 14 in the figure. To supply this air, you must use the appropriate unit of the air compressor. In accordance with a feature of the invention, this air compressor unit (compressor and turbine) is being finalized by the installation of new internals (rotor and stator parts). If desired, the secondary reformer 2 is equipped with a new burner.

As shown in the diagram, the secondary reformer 2 has a burner in the reaction stage 2b, providing combustion of the feed gas 13 (from the primary reformer) and air 14. The design of the new burner of the secondary reformer, in accordance with a feature of the invention, will reduce the pressure drop on the air side and shift balance to a higher concentration of hydrogen and carbon oxides.

In some embodiments of the invention, an air separation unit (ASU) is used to produce oxygen to enrich the feed air 14 directed to the secondary reformer 2. This ASU can be used as a source of nitrogen.

Carbon dioxide removal section

Another feature of the invention is to increase the productivity of the CO 2 removal section (element 4 in the diagram), which usually does not work with a significant increase in productivity.

Necessary improvements depend on the method of CO 2 removal used in the modified installation. The most common method is based on the use of an amine solution (especially activated methyldiethylamine MDEA) or potassium carbonate. The carbon dioxide removal section mainly includes absorption subsection and regeneration subsection. Each of these subsections can have one column or several columns, for example two columns.

In some cases, the existing CO 2 removal section is equipped with two absorbers and two regenerators. In this case, according to a feature of the invention, these two regenerators must operate at different pressures so that the first stage operates at the first pressure, and the second stage operates at the second, lower pressure.

More preferably, a suitable device, such as a jet pump, is installed to connect the two regenerators. The required upgrades will be reduced to another pipe connection to ensure the operation of two regenerators at different pressures, and to the installation of simple equipment, such as a jet pump, to connect two regenerators in this section.

In other cases, the existing carbon dioxide removal section is equipped with only one absorption column and only one regeneration column. Thus, modernization essentially increases the heat input to existing columns and includes the installation of additional reboilers and condensers, and the internal re-equipment of these columns. In this case, deeper improvements are required than in the embodiment described above, and preferably include: internal re-equipment of the columns to avoid possible overflow; increasing the productivity of regenerative enrichment; increasing the performance of reboilers and (or) installing a solution / solution heat exchanger.

In another embodiment, a low pressure stripper is installed. This low pressure stripper reduces the performance of the reboiler section and the enrichment section.

It should be noted that the above-described change in the working steam / carbon ratio (reduction to the level of 2.7 ÷ 3.1) has important consequences with respect to the energy consumption for evaporation in the CO 2 removal section. Indeed, reducing the steam / carbon ratio (S / C) significantly reduces the amount of heat used, which has served as an obstacle in existing plants to reduce the S / C ratio. In the present invention, in contrast, the specific energy consumption of the CO 2 removal section is reduced (in other words, the efficiency of the CO 2 removal section is increased), which allows a lower S / C ratio, which, as shown above, has the advantage of generating hydrogen.

Synthesis gas compression

The synthesis gas compressor (element 33 in the circuit) usually has insufficient reserve power and therefore requires modernization. A syngas compressor can have several stages and several rotors (also called impellers) for each stage, in accordance with the compression ratio. In preferred embodiments, this compressor is further developed by reducing the number of rotors (impellers) per stage; the size of the new wheels increases compared to the previous wheels, due to which the compression ratio of the compressor stages is reduced, but the flow rate of the compressed stream increases. A reduction in the number of stages will also lead to an increase in compressor efficiency by reducing leakage past the impellers.

The additional features mentioned above, such as reducing the S / C ratio and installing a new burner, also have a positive effect on the synthesis gas compressor.

Indeed, an increase in productivity usually causes an additional pressure drop in the head section. In this case, the productivity of the synthesis gas compressor is reduced due to a larger pressure drop in the head section. In the present invention, this problem is solved by a modification in which the suction pressure of the synthesis gas compressor is kept almost constant. More precisely, reducing the steam / carbon ratio reduces the pressure drop in the head section, since less water flows into the head section equipment and, as a result, the load on the main synthesis gas compressor is reduced. Installing a new secondary reformer burner can also help to reduce compressor load, since the new burner will be designed to improve steam reforming of hydrocarbons in order to reduce the specific consumption of natural gas (the ratio of the consumption of natural gas to the generated ammonia).

Syngas purification unit

In order to achieve a given performance, in addition to the synthesis gas compressor unit, another device must be installed (if it was not originally installed), namely the synthesis gas purification unit (box 40 in the diagram).

This equipment is introduced to remove the water contained in the synthesis gas and to supply the reacting gas directly to the ammonia converter. The drying procedure can be performed by ammonia washing, in which the synthesis gas is washed with liquid ammonia, or using a molecular sieve, which allows you to selectively remove water from the gas stream.

If there is already a molecular sieve drainage unit, then the first possible option proposed in the invention is to replace the absorber in this drainage unit with a new one with a higher drying capacity (replacing the absorbent layer with another type of layer). Another possible alternative to replacing the type of absorbent layer is to replace the existing section with a completely new ammonia rinse unit.

If there is no drainage unit, then new equipment is introduced to remove oxygen-containing compounds from the synthesis gas. This newly installed equipment is either a molecular sieve-based synthesis gas dehumidification unit or an ammonia washing unit.

Dehumidification units can be introduced into the intermediate stage of the synthesis gas compressor, or at the suction end of this device.

Synthesis loop

As a rule, the synthesis loop (element 6 in the diagram) can withstand only a limited increase in productivity, i.e. does not allow to handle a significantly larger stream of make-up gas coming from the upgraded head section. The elimination of the corresponding bottleneck requires modernization to improve the performance of the synthesis loop.

The main bottleneck for a significant (> 40%) increase in productivity is the ammonia synthesis converter. If the conversion in the converter is not enough, there is a large increase in the circulation in the synthesis loop and the associated working pressure; on the other hand, the pressure in the synthesis loop should not exceed the calculated value.

To address the shortcomings of existing equipment, the invention proposes the modernization of an existing ammonia synthesis converter or, alternatively, the installation of an additional ammonia converter in parallel or in series with an existing converter.

Preferably, the modernization of the existing converter is carried out according to an adiabatic or isothermal scheme.

Advantageously, the adiabatic modernized converter has a radial or radial-axial multilayer structure, i.e. has several catalyst layers intersected by an axial or radial-axial mixed flow of reagents. Mutual cooling between catalyst beds is also used.

The isothermally upgraded converter comprises a heat exchanger (e.g. pipes or plates) immersed in the catalyst bed (s). In this case, a single layer construction is also convenient, since the temperature can be controlled over the catalyst bed.

Other upgrade options

In some cases, the unit of the supply and exhaust fan and (or) the unit of the blower fan are modernized. The supply and exhaust fan unit, in particular, is used to remove flue gases from the primary reformer. The blower fan assembly is used to supply, by injection, combustion air to the burners of the primary reformer. In both cases, the upgrade may concern both the supercharger and the turbine of the fan assembly.

In accordance with some embodiments, high temperature and / or low temperature CO converters are also being upgraded. This is appropriate in cases where it turns out that CO converters are a bottleneck to increase the load. The preferred way to upgrade such CO converters is to use devices with a radial or radial-axial construction principle.

In order to increase hydrogen production in the head section, another solution used is oxygen enrichment of the air supplied to the secondary reformer. This upgrade requires an oxygen source; An example of such a source is an air separation unit, and in this case it may turn out that upgrading an existing air compressor is no longer necessary, since additional air is supplied by a new air compressor belonging to the unit of the air separation unit.

An increase in the oxygen concentration in the process air supplied to the secondary reformer will cause a lack of nitrogen in the synthesis gas, therefore, the air separation unit must also supply nitrogen at the required pressure to the synthesis loop in order to ensure that the ammonia synthesis loop operates with the optimum hydrogen / nitrogen ratio equal to 3: 1.

In some embodiments, the hydrogen recovery unit of the synthesis loop is enlarged or modified. This unit should mainly separate hydrogen from other gases in order to reduce the amount of inert components in the synthesis loop. Hydrogen regeneration can be performed using a molecular sieve or cryogenic unit; if the productivity of these devices is significantly increased, then upgrading the ammonia converter can be avoided, although the energy characteristics of the ammonia plant are not necessarily improved.

For plants where all the ammonia produced must be cooled, a significant increase in productivity requires the modernization of the cooler compressor assembly so that its performance meets the new requirements. As an alternative to upgrading this compressor, an embodiment of the invention proposes the introduction of water cooling units, for example, operating with a lithium bromide refrigeration machine. For a plant equipped with ammonia absorption sections, instead of a refrigerant compressor, consider upgrading these devices (or installing additional sections) to provide the ammonia unit with the necessary cooling means.

The present invention, in particular, is suitable for the modernization of the Russian ammonia production facility of the State Institute of Nitrogen Industry (GIAP) and the Toyo Engineering Corp.

The performance of Russian GIAP plants for ammonia production is 1360 mt / d. These units were designed according to the classic scheme of a primary reformer and had some major differences: CO 2 removal section operates with solutions methylethylamine (IEA) or methyldiethylamine (MDEA) with a high degree of carbonization and using proprietary equipment (an absorber, a regenerator); for cooling ammonia and in the separation stages, absorption-cooling units are used instead of an ammonia compressor. These blocks use low-grade process heat.

Russian TOYO plants are based on the Kellogg classic scheme for the synthesis of ammonia from natural gas and use two stages of reformers, two stages of a CO converter, a CO 2 removal section (Karsol or Benfield process), and ammonia synthesis is performed at 320 kg / cm. 2 The productivity of these plants is 1360 mt / d.

In the plants for the production of GIAP and TOYO ammonia, a four-stage synthesis gas circulation pump is used to ensure the synthesis circuit operates at an overpressure in the range of 200 + 300 bar.

Example

The following example relates to the modernization of a Russian installation made according to the TOYO scheme mentioned above.

The existing primary reformer tubes based on the NK-40 material with an inner diameter of 85 mm were replaced with catalytic tubes made of microalloyed metal with an inner diameter of 92 mm. The volume of the catalyst increased by 15 ÷ 20%. To provide the backup reformer with the primary reformer, the steam / carbon ratio was reduced from 3.8 to 3.0 mol / mol.

The secondary reformer was modernized by replacing the internal burner with a new burner having a truncated-conical end section with a diverging open end (funnel-shaped), as disclosed in EP 1531147. This burner reduces the pressure drop in the process air (for example, the pressure drop drops by 1 bar) and improve gas distribution in the catalyst bed to increase hydrogen production and reduce methane leakage.

The existing air compressor was modernized by replacing the stator and rotor parts, which allows obtaining a polytropic efficiency of about 81% for the low-pressure compressor part and about 77% for the high-pressure compressor part, compared to the previous efficiency of 70% and 65%, respectively.

Similar upgrades were made in the turbine of the air compressor.

The CO 2 removal section using a potassium carbonate solution initially had two absorbers and two regenerators. The modernization of this section was achieved by the sequential inclusion of two regenerators and their operation at two different pressures, namely, the first regenerator was used at a pressure of 1.4 bar abs., And the second regenerator was used at a pressure of 2.1 bar abs.

Wet CO 2 vapors exiting the low pressure regenerator are compressed by means of a jet pump using vapors exiting the high pressure column as entrainment flow. The final outlet pressure of this jet pump is 1.55 bar abs.

The specific energy consumption of the CO 2 removal section was reduced from 950 kcal to 700 kcal for each nm 3 (normal cubic meter, i.e. measured under normal conditions) of CO 2 .

The installation is already equipped with a synthesis gas drainage unit. To provide a 40% increase in the capacity of this section, the old molecular sieve was replaced with Z4-01, supplied by Zeochem, which has a large moisture absorption capacity, without any structural changes being required.

The synthesis gas compressor and associated turbine have been upgraded by replacing the stator and rotor parts. In particular, compressor modernization was carried out by installing fewer impellers in each compressor stage. On the other hand, these impellers made it possible to obtain a higher polytropic efficiency of the compressor. A reduced number of stage impellers reduces the pressure at the compressor outlet and reduces internal leakage / leakage between the impellers (the fewer the wheels, the less leakage between them).

After modernization, the polytropic efficiency of the low-pressure compressor part is about 80%, the high-pressure compressor part is -76%, and the polytropic efficiency of the circulation part is about 78%. The former average polytropic efficiency was less than 70%.

The synthesis loop, which initially had two axial adiabatic ammonia converters, was refitted by replacing the internals in both reactors. Reactors with new internal parts operate with a radial-axial flow, which improves the process of ammonia conversion in the reactor and reduces the pressure drop across the converter. The working pressure of the circuit (at the outlet of the circulation pump) is 240 bar abs. (initially, the working pressure of the circuit was close to 300 bar), and the average concentration of ammonia in the synthesis gas after the converters is 16.4 molar percent. The pressure drop across the converters is less than 5 bar.

After the upgrade, the plant's capacity is about 2000 mt / d.

Claims (28)

1. A method of increasing the productivity of a plant for producing ammonia, having a head section for generating makeup syngas and a synthesis section (6) for converting makeup syngas into ammonia, wherein
head section includes:
a primary reformer (1) containing a group of pipes filled with a catalyst;
secondary reformer (2), which receives the output stream of the primary reformer and the air stream (14);
an air compressor supplying air (14) to the secondary reformer;
sequentially connected devices for processing the stream from the output of the secondary reformer, including at least a CO shift converter (3), a carbon dioxide (CO 2 ) removal section (4) and a methanizer (5);
synthesis gas drainage unit;
a synthesis gas main compressor (33) for increasing the pressure of the synthesis gas to a pressure level in the synthesis section containing a predetermined number of stators and rotors;
wherein the synthesis section includes an ammonia converter,
and when implementing the method:
provide an increase in the amount of hydrogen that is generated or can be generated by the reforming section, by:
replacing the primary reformer tubes with new tubes having substantially the same outer diameter but less thickness than the previous ones to increase the inner diameter of the tubes; and / or
installation of an oxygen source for enrichment with oxygen supplied by this source, air supplied to the secondary reformer;
upgrade (modify) the air compressor by installing new stator and rotor parts so that the upgraded compressor unit provides an increase in the air flow supplied to the secondary reformer, while maintaining the same output pressure;
upgrade the CO 2 removal section;
upgrade the synthesis gas compressor by replacing at least the rotors of this compressor and reducing the number of stages;
modernize the synthesis gas drainage unit;
modernize the synthesis of ammonia,
moreover, the modernization of the CO 2 removal section is carried out by equipping it with two absorbers and two regenerators and ensuring the operation of the regenerators at different pressures so that the first generator operates at the first pressure and the second generator operates at the second pressure, or by equipping it with one absorber and one regenerator and installing one or more additional reboilers and condensers and internal conversion of the absorber and regenerator, or by equipping it with one absorber and ne regenerator and install new stripping the low pressure column and internal conversion absorber and regenerator;
the synthesis gas dehumidification unit is upgraded by using a molecular sieve device with a new absorber with a higher drying capacity compared to the existing absorbent, or by installing an ammonia washing unit that removes oxygen-containing compounds;
and the modernization of the ammonia synthesis loop is carried out by installing radial-axial or radial internal parts in an existing loop converter, either by using several catalyst layers in the converter or a radial or radial-axial structure, or by an adiabatic or isothermal circuit, or by installing an additional converter in parallel or in series with the available converter.
2. The method according to p. 1, in which to connect the two regenerators install a jet pump.
3. The method according to p. 1, in which the ammonia synthesis circuit includes a hydrogen regeneration unit, which is modified during the modernization of the ammonia synthesis circuit.
4. The method according to p. 1, in which the production of hydrogen is increased by installing a pre-reformer before the primary reformer or by lengthening the radiation heat exchanger of the primary reformer.
5. The method according to p. 1, in which the production of hydrogen in the head section is increased due to the installation of an air separation unit for enrichment with oxygen supplied by this unit, the air supplied to the secondary reformer.
6. The method of claim 1, wherein the secondary reformer burner is replaced.
7. The method of claim 1, wherein the vapor / carbon ratio in the head section is reduced, preferably to a value in the range of 2.7 to 3.1.
8. The method according to p. 1, in which the productivity of the installation is increased by at least 40% compared with the previous performance.
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RU2385289C2 (en) * 2003-11-06 2010-03-27 Казале Кемикэлз С.А. Reactor and method of secondary catalytic reforming
EP2284125A1 (en) * 2009-08-13 2011-02-16 Ammonia Casale S.A. Process for revamping an ammonia plant with nitrogen-based washing of a purge stream
EP2404869A1 (en) * 2010-07-06 2012-01-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas

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Publication number Priority date Publication date Assignee Title
RU2385289C2 (en) * 2003-11-06 2010-03-27 Казале Кемикэлз С.А. Reactor and method of secondary catalytic reforming
EP2284125A1 (en) * 2009-08-13 2011-02-16 Ammonia Casale S.A. Process for revamping an ammonia plant with nitrogen-based washing of a purge stream
EP2404869A1 (en) * 2010-07-06 2012-01-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas

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