WO2018206154A1 - Process and apparatus for separating accompanying gases from a crude synthesis gas - Google Patents

Process and apparatus for separating accompanying gases from a crude synthesis gas Download PDF

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Publication number
WO2018206154A1
WO2018206154A1 PCT/EP2018/025130 EP2018025130W WO2018206154A1 WO 2018206154 A1 WO2018206154 A1 WO 2018206154A1 EP 2018025130 W EP2018025130 W EP 2018025130W WO 2018206154 A1 WO2018206154 A1 WO 2018206154A1
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Prior art keywords
absorption medium
synthesis gas
methanol
crude synthesis
scrubbing
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Application number
PCT/EP2018/025130
Other languages
French (fr)
Inventor
Matthias Linicus
Sandra Jensen
Original Assignee
L'air Liquide, Société Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
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Application filed by L'air Liquide, Société Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude filed Critical L'air Liquide, Société Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Publication of WO2018206154A1 publication Critical patent/WO2018206154A1/en

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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
    • B01D53/1425—Regeneration of liquid absorbents
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
    • 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
    • B01D53/1456—Removing acid components
    • B01D53/1462—Removing mixtures of hydrogen sulfide and carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/52—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with liquids; Regeneration of used liquids
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
    • C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
    • C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
    • B01D2252/20—Organic absorbents
    • B01D2252/202—Alcohols or their derivatives
    • B01D2252/2021—Methanol
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/16—Hydrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/20—Carbon monoxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/30—Sulfur compounds
    • B01D2257/306—Organic sulfur compounds, e.g. mercaptans
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/406—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/408—Cyanides, e.g. hydrogen cyanide (HCH)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/0485—Composition of the impurity the impurity being a sulfur compound
    • 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
    • Y02P20/151—Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Definitions

  • the Invention relates to a process for separating accompanying gases from a crude synthesis gas stream by scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, with the absorption medium being conveyed in a circular process in which it is loaded with accompanying gases during scrubbing, subsequently desorbed by lowering the pressure, flashing and/or heating and then reused for scrubbing the crude synthesis gas stream.
  • the invention likewise relates to a plant for carrying out the process.
  • Rectisol process Processes for separating undesirable accompanying materials from a crude synthesis gas stream, e.g. the Rectisol process, are known.
  • the Rectisol process is described fundamentally in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, vol. 15, p. 399 ff.
  • This process serves to purify a crude synthesis gas which has been produced from coal or coke by the fixed-bed pressure gasification process and consists mainly of CO and H 2 by absorption of the accompanying gases.
  • the fixed-bed pressure gasification process is described fundamentally in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, vol. 15, p. 367ff.
  • the Rectisol process uses methanol as absorption medium, exploiting the property of methanol that its absorption capability for the accompanying materials increases greatly with decreasing temperature, while that for CO and H 2 remains virtually constant.
  • the undesirable accompanying materials are mainly the accompanying gases carbonyl sulfide (COS), hydrogen sulfide (H 2 S) and carbon dioxide (CO2).
  • the methanol used as absorption medium is circulated via regeneration plants in this process.
  • the loaded methanol is freed of the absorbed gases by physical means.
  • CO2 is preferentially removed from the loaded methanol absorption medium by depressurization and/or stripping with a gas, for example nitrogen.
  • a gas for example nitrogen.
  • the sulfide-containing gases, COS and H 2 S are driven off by heating. It is desirable to produce a COS/H 2 S gas which is very low in CO2 since the further processing of these gases, which is of economic interest, is impaired by mixing with CO2.
  • the sulfur-containing accompanying gases COS/H 2 S and the CO2 are separated off from the crude synthesis gas in separate, successive absorption steps.
  • This selective absorption is made possible by suitable setting of the process parameters, in particular of the ratio of absorption medium to gas being absorbed.
  • the advantage of selective absorption is that the COS/H 2 S gas and the CO2 gas are very largely kept separate during the absorption and only the minor part has to be separated off in the regeneration of the methanol.
  • the crude synthesis gas also contains further accompanying gases in addition to the abovementioned components COS, H 2 S and CO2.
  • the first publication DE 10 2006 056 1 17 A1 describes a corresponding process in which the absorption steps for separating off the sulfur components and the CO2 are preceded by a further absorption step in order to separate metal carbonyls selectively from the synthesis gas.
  • the synthesis gas stream contains an excessively large amount of mercaptans (C1 -C4) and other undesirable sulfur components which are volatile but very readily soluble in the absorption medium methanol, e.g. thioethers and/or thiophenes, these can accumulate in the methanol and, owing to their low vapour pressure and their high solubility in the methanol, are not removed sufficiently from the methanol in the hot regenerator.
  • An excessively high content of these trace materials makes the methanol unusable for the scrubbing operation since it can lead to contamination of the scrubbed synthesis gas stream.
  • a known possible way of avoiding accumulation of the undesirable components in the absorption medium is to replace a correspondingly large part of the absorption medium continuously, with the discharged part being disposed of. Description of the invention
  • Plant of the invention Plant of the invention:
  • Plant for separating accompanying gases from a crude synthesis gas stream comprising: a column for scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, a container for driving off mainly carbon dioxide from the loaded methanol by flashing,
  • a column for driving off mainly hydrogen sulfide from the loaded methanol by heating comprising a heat exchanger for heating the absorption medium
  • At least one adsorption vessel containing a solid state bed comprising a solid adsorbent at least one adsorption vessel containing a solid state bed comprising a solid adsorbent
  • fluidic communication between two regions of the reactor of the invention is any type of connection which enables a fluid, for example the feed gas stream or the synthesis gas product stream, to flow from one of the two regions to the other, regardless of any regions or components in between.
  • the invention makes it possible to prolong the operating life of the absorption medium. This saves costs for fresh absorption medium and for disposal of the contaminated absorption medium.
  • the size of the proportion of the absorption medium which is conveyed through a solid state bed containing an adsorbent is set so that the content of undesirable components is kept so low that accumulation of the undesirable sulfur component is avoided and the absorption medium can perform its scrubbing function.
  • the adsorption plant prefferably configured with two parallel lines of which one is alternately in operation while the other is being regenerated.
  • the process and a plant operating according to it are particularly suitable for use for scrubbing crude synthesis gas which has been produced by gasification of coal or petroleum and comprises H 2 S, COS, HCN, NH 3 and thiols such as mercaptans, thioethers and/or thiophenes as accompanying gases.
  • the scrubbing of synthesis gas containing volatile accompanying gases by means of a liquid, physically acting absorption medium has been tried and tested for a long time since the absorption medium can readily be regenerated by lowering the pressure, flashing and/or heating.
  • the inventive, additional treatment of the absorption medium with a solid adsorbent expands the usability of the process even to synthesis gases which comprise relatively large proportions of relatively nonvolatile sulfur-containing accompanying gases.
  • the loaded bed When the adsorption capacity of the activated carbon bed is exhausted, the loaded bed is taken out of operation and the loaded activated carbon is replaced by fresh carbon.
  • the loaded bed can be regenerated by means of methanol vapour which is produced by heating the methanol.
  • the contaminated methanol vapour can be added at a suitable place to the accompanying gas stream driven off from the methanol.
  • the desorption is preferably effected by heating in a specially configured column, known as a hot regenerator, and the solid state bed containing the adsorbent is arranged downstream of the hot regenerator and is in fluidic communication with the latter.
  • a hot regenerator a specially configured column
  • the absorption medium discharged from the hot regenerator is particularly preferably cooled by indirect heat exchange with the loaded absorption medium fed to the hot regenerator before being fed to the solid state bed containing the adsorbent. More complete removal of interfering components by means of absorption is possible by lowering the temperature.
  • the heat given off can be transferred to the still loaded absorption medium entering the hot regenerator in the sense of heat integration, as a result of which heat energy is saved here.
  • a preferred embodiment of the invention is characterized in that low-temperature methanol is used as absorption medium. This procedure is known as the Rectisol process and is proven. Here, the high absorption capability of methanol at low temperatures is exploited. The plant therefore has to be equipped with an apparatus for cooling the methanol and with appropriate insulation.
  • Further preferred embodiments of the invention are characterized in that activated carbon or a molecular sieve, i.e. a pelletized material composed of synthetically produced zeolites, is used as adsorbent. The adsorbent used depends on local availability and market prices and on the suitability for the respective synthesis gas to be purified and the accompanying gases present therein.
  • the plant comprises a heat exchanger which is in fluidic communication with the hot regenerator and the adsorption vessel.
  • the absorption medium is low- temperature methanol and the plant is equipped with a cooling apparatus for cooling the methanol and the pieces of equipment containing low-temperature methanol are protected by means of insulating material to reduce losses of cold.
  • the solid adsorbent is activated carbon or a molecular sieve.
  • the adsorbent which is used depends on local availability and market prices and on the suitability for the respective synthesis gas to be purified and the accompanying gases present therein.
  • Fig. 1 a flow diagram of an illustrative embodiment of the plant of the invention
  • a plant according to an illustrative embodiment of the invention shall be described with the aid of Fig. 1 .
  • Crude synthesis gas 1 is cooled in the heat exchanger 2 against the treated synthesis gas 3.
  • condensate separator 4 the condensate 5 formed is separated off.
  • the crude synthesis gas is introduced into the scrubbing column 7.
  • the column is divided into three scrubbing stages each comprising a trickle bed. In the first stage 7a, a prescrub is carried out, in the second 7b mainly H 2 S is scrubbed out and in the third stage 7c mainly CO2 is scrubbed out.
  • the synthesis gas 3 which has been treated in this way then leaves the scrubbing column 7, is used in the heat exchangers 2 and 6 for cooling the crude synthesis gas 1 and is then discharged from the plant for further treatment.
  • the now only lightly loaded methanol 8, 9 is introduced into the flash vessel 10.
  • the carbon dioxide 12 is driven off from the methanol by lowering the pressure and by flashing with nitrogen 1 1 and discharged from the plant for further treatment.
  • the methanol 13 which has been prepurified in this way is then introduced into the column 14 in which mainly sulfur-containing accompanying gases 14 are driven off by heating the methanol.
  • the methanol 15 which has gone through the third scrubbing stage and the first scrubbing stage of the scrubbing column 7 is treated in the column 14.
  • the sulfur-containing accompanying gases 16 driven off from the methanol are discharged from the plant for further treatment, e.g. in a Claus plant.
  • the methanol 17 which has been desorbed in the column 14 is recirculated via heat exchanger 18 into the scrubbing column 7 for reuse.
  • the streams 19 and 20 represent the methanol running from the top downwards through the scrubbing stages.
  • heat exchanger 18 heat exchange between the methanol 13 which has been pretreated in the flash vessel 10 and the methanol 17 which has been regenerated further is carried out.
  • a substream 21 of the methanol 17 is taken off downstream of the heat exchanger 18 and treated in the adsorption plant 22 in which the methanol is passed through an activated carbon bed.
  • the adsorption plant 22 consists of two parallel lines in this example, so that when the activated carbon is replaced or regenerated in one of the lines, the operation of the adsorption plant 22 can continue. This substream 21 is subsequently fed back into the methanol stream 17.
  • the invention provides an advantageous process which increases the operating life of the absorption medium and thus the economics of the absorption process.
  • the invention is therefore industrially applicable in an advantageous way.

Abstract

Process and plant for separating accompanying gases from a crude synthesis gas stream by scrubbing with an absorption medium, with the absorption medium being conveyed in a circular process, wherein the absorption medium is also passed through a solid state bed containing an adsorbent to effect regeneration.

Description

Process and apparatus for separating accompanying gases from a crude
synthesis gas
Field of the invention
The Invention relates to a process for separating accompanying gases from a crude synthesis gas stream by scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, with the absorption medium being conveyed in a circular process in which it is loaded with accompanying gases during scrubbing, subsequently desorbed by lowering the pressure, flashing and/or heating and then reused for scrubbing the crude synthesis gas stream.
The invention likewise relates to a plant for carrying out the process. Prior art
Processes for separating undesirable accompanying materials from a crude synthesis gas stream, e.g. the Rectisol process, are known. The Rectisol process is described fundamentally in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, vol. 15, p. 399 ff. This process serves to purify a crude synthesis gas which has been produced from coal or coke by the fixed-bed pressure gasification process and consists mainly of CO and H2 by absorption of the accompanying gases. The fixed-bed pressure gasification process is described fundamentally in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, vol. 15, p. 367ff. The Rectisol process uses methanol as absorption medium, exploiting the property of methanol that its absorption capability for the accompanying materials increases greatly with decreasing temperature, while that for CO and H2 remains virtually constant. The undesirable accompanying materials are mainly the accompanying gases carbonyl sulfide (COS), hydrogen sulfide (H2S) and carbon dioxide (CO2).
The methanol used as absorption medium is circulated via regeneration plants in this process. In the regeneration plants, the loaded methanol is freed of the absorbed gases by physical means. In a first regeneration step, CO2 is preferentially removed from the loaded methanol absorption medium by depressurization and/or stripping with a gas, for example nitrogen. In a second regeneration step, the sulfide-containing gases, COS and H2S, are driven off by heating. It is desirable to produce a COS/H2S gas which is very low in CO2 since the further processing of these gases, which is of economic interest, is impaired by mixing with CO2.
In the Rectisol process, a distinction is made between the standard Rectisol process and the selective Rectisol process.
In the standard Rectisol process, the accompanying gases COS/H2S and the CO2 are separated off together from the crude synthesis gas in one absorption step.
In the selective Rectisol process, the sulfur-containing accompanying gases COS/H2S and the CO2 are separated off from the crude synthesis gas in separate, successive absorption steps. This selective absorption is made possible by suitable setting of the process parameters, in particular of the ratio of absorption medium to gas being absorbed. The advantage of selective absorption is that the COS/H2S gas and the CO2 gas are very largely kept separate during the absorption and only the minor part has to be separated off in the regeneration of the methanol.
However, the crude synthesis gas also contains further accompanying gases in addition to the abovementioned components COS, H2S and CO2. The first publication DE 10 2006 056 1 17 A1 describes a corresponding process in which the absorption steps for separating off the sulfur components and the CO2 are preceded by a further absorption step in order to separate metal carbonyls selectively from the synthesis gas.
If the synthesis gas stream contains an excessively large amount of mercaptans (C1 -C4) and other undesirable sulfur components which are volatile but very readily soluble in the absorption medium methanol, e.g. thioethers and/or thiophenes, these can accumulate in the methanol and, owing to their low vapour pressure and their high solubility in the methanol, are not removed sufficiently from the methanol in the hot regenerator. An excessively high content of these trace materials makes the methanol unusable for the scrubbing operation since it can lead to contamination of the scrubbed synthesis gas stream. A known possible way of avoiding accumulation of the undesirable components in the absorption medium is to replace a correspondingly large part of the absorption medium continuously, with the discharged part being disposed of. Description of the invention
It is an object of the invention to provide a process which avoids the above-described disadvantages of the prior art. The object is achieved by a process according to Claim 1 and by a plant according to Claim 7. Process of the invention:
Process for separating accompanying gases from a crude synthesis gas stream by scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, with the absorption medium being conveyed in a circular process in which it is loaded with accompanying gases during scrubbing, separately desorbed by lowering the pressure, flashing and/or heating and then reused for scrubbing the crude synthesis gas stream, characterized in that at least part of the absorption medium is passed through a solid state bed containing an adsorbent as further measure in addition to desorption.
Plant of the invention:
Plant for separating accompanying gases from a crude synthesis gas stream, comprising: a column for scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, a container for driving off mainly carbon dioxide from the loaded methanol by flashing,
a column for driving off mainly hydrogen sulfide from the loaded methanol by heating (hot regenerator), comprising a heat exchanger for heating the absorption medium,
at least one adsorption vessel containing a solid state bed comprising a solid adsorbent,
where the hot regenerator and the adsorption vessel are in fluidic communication. For the purposes of the present invention, fluidic communication between two regions of the reactor of the invention is any type of connection which enables a fluid, for example the feed gas stream or the synthesis gas product stream, to flow from one of the two regions to the other, regardless of any regions or components in between. The invention makes it possible to prolong the operating life of the absorption medium. This saves costs for fresh absorption medium and for disposal of the contaminated absorption medium.
The size of the proportion of the absorption medium which is conveyed through a solid state bed containing an adsorbent is set so that the content of undesirable components is kept so low that accumulation of the undesirable sulfur component is avoided and the absorption medium can perform its scrubbing function.
It is advantageous for the adsorption plant to be configured with two parallel lines of which one is alternately in operation while the other is being regenerated.
The process and a plant operating according to it are particularly suitable for use for scrubbing crude synthesis gas which has been produced by gasification of coal or petroleum and comprises H2S, COS, HCN, NH3 and thiols such as mercaptans, thioethers and/or thiophenes as accompanying gases. The scrubbing of synthesis gas containing volatile accompanying gases by means of a liquid, physically acting absorption medium has been tried and tested for a long time since the absorption medium can readily be regenerated by lowering the pressure, flashing and/or heating. The inventive, additional treatment of the absorption medium with a solid adsorbent expands the usability of the process even to synthesis gases which comprise relatively large proportions of relatively nonvolatile sulfur-containing accompanying gases.
When the adsorption capacity of the activated carbon bed is exhausted, the loaded bed is taken out of operation and the loaded activated carbon is replaced by fresh carbon. As an alternative thereto, the loaded bed can be regenerated by means of methanol vapour which is produced by heating the methanol. The contaminated methanol vapour can be added at a suitable place to the accompanying gas stream driven off from the methanol.
Preferred embodiments of the invention
The desorption is preferably effected by heating in a specially configured column, known as a hot regenerator, and the solid state bed containing the adsorbent is arranged downstream of the hot regenerator and is in fluidic communication with the latter. In this way, components which could not be removed, or removed only insufficiently, in the hot regenerator can be removed from the regenerated absorption medium in a targeted manner by binding to the adsorbent. The absorption medium discharged from the hot regenerator is particularly preferably cooled by indirect heat exchange with the loaded absorption medium fed to the hot regenerator before being fed to the solid state bed containing the adsorbent. More complete removal of interfering components by means of absorption is possible by lowering the temperature. The heat given off can be transferred to the still loaded absorption medium entering the hot regenerator in the sense of heat integration, as a result of which heat energy is saved here.
A preferred embodiment of the invention is characterized in that low-temperature methanol is used as absorption medium. This procedure is known as the Rectisol process and is proven. Here, the high absorption capability of methanol at low temperatures is exploited. The plant therefore has to be equipped with an apparatus for cooling the methanol and with appropriate insulation. Further preferred embodiments of the invention are characterized in that activated carbon or a molecular sieve, i.e. a pelletized material composed of synthetically produced zeolites, is used as adsorbent. The adsorbent used depends on local availability and market prices and on the suitability for the respective synthesis gas to be purified and the accompanying gases present therein.
In a further preferred embodiment of the invention, the plant comprises a heat exchanger which is in fluidic communication with the hot regenerator and the adsorption vessel. By this means, heat exchange between the absorption medium transferred from the flash vessel into the hot regenerator and the absorption medium transferred from the hot regenerator into the scrubbing column is carried out.
In a further preferred embodiment of the invention, the absorption medium is low- temperature methanol and the plant is equipped with a cooling apparatus for cooling the methanol and the pieces of equipment containing low-temperature methanol are protected by means of insulating material to reduce losses of cold.
In a further preferred embodiment of the invention, the solid adsorbent is activated carbon or a molecular sieve. The adsorbent which is used depends on local availability and market prices and on the suitability for the respective synthesis gas to be purified and the accompanying gases present therein.
Working example
Further features, advantages and possible uses of the invention can also be derived from the following description of a working example and the drawing. Here, all features described and/or depicted form, on their own or in any combination, the subject matter of the invention, regardless of the way they are summarized in the claims or their back- reference.
The single figure shows: Fig. 1 a flow diagram of an illustrative embodiment of the plant of the invention
In the following, a plant according to an illustrative embodiment of the invention shall be described with the aid of Fig. 1 . Crude synthesis gas 1 is cooled in the heat exchanger 2 against the treated synthesis gas 3. In condensate separator 4, the condensate 5 formed is separated off. After having been cooled further in the heat exchanger 6, the crude synthesis gas is introduced into the scrubbing column 7. The column is divided into three scrubbing stages each comprising a trickle bed. In the first stage 7a, a prescrub is carried out, in the second 7b mainly H2S is scrubbed out and in the third stage 7c mainly CO2 is scrubbed out. The synthesis gas 3 which has been treated in this way then leaves the scrubbing column 7, is used in the heat exchangers 2 and 6 for cooling the crude synthesis gas 1 and is then discharged from the plant for further treatment. The now only lightly loaded methanol 8, 9 is introduced into the flash vessel 10. There, the carbon dioxide 12 is driven off from the methanol by lowering the pressure and by flashing with nitrogen 1 1 and discharged from the plant for further treatment. The methanol 13 which has been prepurified in this way is then introduced into the column 14 in which mainly sulfur-containing accompanying gases 14 are driven off by heating the methanol. Likewise, the methanol 15 which has gone through the third scrubbing stage and the first scrubbing stage of the scrubbing column 7 is treated in the column 14. The sulfur-containing accompanying gases 16 driven off from the methanol are discharged from the plant for further treatment, e.g. in a Claus plant. The methanol 17 which has been desorbed in the column 14 is recirculated via heat exchanger 18 into the scrubbing column 7 for reuse. The streams 19 and 20 represent the methanol running from the top downwards through the scrubbing stages. In the heat exchanger 18, heat exchange between the methanol 13 which has been pretreated in the flash vessel 10 and the methanol 17 which has been regenerated further is carried out. In this embodiment of the invention, a substream 21 of the methanol 17 is taken off downstream of the heat exchanger 18 and treated in the adsorption plant 22 in which the methanol is passed through an activated carbon bed. The adsorption plant 22 consists of two parallel lines in this example, so that when the activated carbon is replaced or regenerated in one of the lines, the operation of the adsorption plant 22 can continue. This substream 21 is subsequently fed back into the methanol stream 17.
Industrial applicability
The invention provides an advantageous process which increases the operating life of the absorption medium and thus the economics of the absorption process. The invention is therefore industrially applicable in an advantageous way.
List of reference numerals
1 Crude synthesis gas
2 Heat exchanger
3 Synthesis gas, treated
4 Condensate separator
5 Condensate
6 Heat exchanger
7 Scrubbing column, a, b, c scrubbing stages
8 Methanol, loaded
9 Methanol, loaded
10 Flash vessel
1 1 Nitrogen
12 Carbon dioxide
13 Methanol, prepurified
14 Column (hot regenerator)
15 Methanol
16 Accompanying gases
17 Methanol
18 Heat exchanger
19 Methanol
20 Methanol
21 Methanol
22 Adsorption plant

Claims

Claims:
1 . Process for separating accompanying gases from a crude synthesis gas stream by scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium, with the absorption medium being conveyed in a circular process in which it is loaded with accompanying gases during scrubbing, separately desorbed by lowering the pressure, flashing and/or heating and then reused for scrubbing the crude synthesis gas stream, characterized in that at least part of the absorption medium is passed through a solid state bed containing an adsorbent as further measure in addition to desorption.
2. Process according to Claim 1 , characterized in that desorption is carried out by heating in a hot regenerator and the solid state bed containing the adsorbent is arranged downstream of the hot regenerator and is in fluidic communication with the latter.
3. Process according to Claim 2, characterized in that the absorption medium discharged from the hot regenerator is, before being fed to the solid state bed containing the adsorbent, cooled by indirect heat exchange against the loaded absorption medium fed to the hot regenerator.
4. Process according to any of the preceding claims, characterized in that low- temperature methanol is used as absorption medium.
5. Process according to any of the preceding claims, characterized in that activated carbon or a molecular sieve is used as adsorbent.
6. Use of the process according to any of the preceding claims for scrubbing crude synthesis gas which has been produced by gasification of coal or petroleum and comprises H2S, COS, HCN, NH3 and thiols such as mercaptans, thioethers and/or thiophenes as accompanying gases.
7. Plant for separating accompanying gases from a crude synthesis gas stream, comprising: a column for scrubbing the crude synthesis gas stream with a liquid, physically acting absorption medium,
a container for driving off mainly carbon dioxide from the loaded methanol by flashing,
- a column for driving off mainly hydrogen sulfide from the loaded methanol by heating (hot regenerator), comprising a heat exchanger for heating the absorption medium,
at least one adsorption vessel containing a solid state bed comprising a solid adsorbent,
- where the hot regenerator and the adsorption vessel are in fluidic communication.
8. Plant according to Claim 7, further comprising a heat exchanger which is in fluidic communication with the hot regenerator and the adsorption vessel.
9. Plant according to either of the preceding claims, characterized in that the absorption medium is low-temperature methanol and the plant is equipped with a cooling apparatus for cooling the methanol and the pieces of equipment containing the low- temperature methanol are protected by insulating material to reduce losses of cold.
10. Plant according to any of the preceding claims, characterized in that the solid adsorbent is activated carbon or a molecular sieve.
PCT/EP2018/025130 2017-05-12 2018-04-26 Process and apparatus for separating accompanying gases from a crude synthesis gas WO2018206154A1 (en)

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