WO2012089776A1 - Process for removing sulphur-containing contaminants from a gas stream - Google Patents

Process for removing sulphur-containing contaminants from a gas stream Download PDF

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Publication number
WO2012089776A1
WO2012089776A1 PCT/EP2011/074179 EP2011074179W WO2012089776A1 WO 2012089776 A1 WO2012089776 A1 WO 2012089776A1 EP 2011074179 W EP2011074179 W EP 2011074179W WO 2012089776 A1 WO2012089776 A1 WO 2012089776A1
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WIPO (PCT)
Prior art keywords
gas stream
sulphur
sulphur dioxide
dioxide
enriched
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PCT/EP2011/074179
Other languages
French (fr)
Inventor
Diego Patricio VALENZUELA
Original Assignee
Shell Internationale Research Maatschappij B.V.
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Publication date
Application filed by Shell Internationale Research Maatschappij B.V. filed Critical Shell Internationale Research Maatschappij B.V.
Priority to EP11802961.0A priority Critical patent/EP2658632A1/en
Priority to EA201300779A priority patent/EA201300779A1/en
Priority to CA2823228A priority patent/CA2823228A1/en
Publication of WO2012089776A1 publication Critical patent/WO2012089776A1/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
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8603—Removing sulfur compounds
    • B01D53/8612—Hydrogen sulfide
    • B01D53/8615—Mixtures of hydrogen sulfide and sulfur oxides
    • 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
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8603—Removing sulfur compounds
    • B01D53/8612—Hydrogen sulfide
    • B01D53/8618—Mixtures of hydrogen sulfide and carbon dioxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
    • C01B17/0426—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process characterised by the catalytic conversion
    • C01B17/0434—Catalyst compositions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
    • C01B17/0456—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process the hydrogen sulfide-containing gas being a Claus process tail gas
    • 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
    • B01D2257/304—Hydrogen sulfide
    • 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
    • B01D2257/30—Sulfur compounds
    • B01D2257/308—Carbonoxysulfide COS
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/504—Carbon dioxide
    • 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
    • B01D53/1475—Removing carbon dioxide
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2
    • 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 present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from a gas stream.
  • the Claus process is a two-step process that includes a burner (oxidation) step followed by a catalytic step wherein use is made of one or more catalytic stages.
  • oxidation step the hydrogen sulphide of a feed stream is partially oxidized by combustion with oxygen to form a gas stream containing sulphur dioxide.
  • the un-reacted hydrogen sulphide and the formed sulphur dioxide contained in the combustion gas can undergo the Claus reaction whereby they are reacted to form elemental sulphur.
  • Claus tail gas still contains appreciable amounts of sulphur compounds such as hydrogen sulphide, carbonyl sulphide and sulphur dioxide. This does not only apply to sulphur recovery with a two-bed catalytic Claus plant, but also to Claus plants with three or more catalytic beds.
  • the tail gas from a Claus process therefore is usually subjected to a hydrogenation treatment to further reduce the amounts of sulphur dioxide, COS, CS2, and mercaptants by converting them into hydrogen sulphide, followed by a treatment wherein use is made of an amine that selectively absorbs hydrogen sulphide.
  • TGT Tail gas Treating
  • the present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from a gas stream comprising the steps of:
  • step (b) extracting heat from the gas stream as obtained in step (a) ;
  • step (c) reacting hydrogen sulphide present in the cooled gas stream as obtained in step (b) with sulphur dioxide at elevated temperature and in the presence of a catalyst to obtain a gas stream which comprises sulphur and water;
  • step (d) separating sulphur from the gas stream obtained in step (c) , thereby obtaining a hydrogen sulphide-lean gas stream;
  • step (e) subjecting at least part of the hydrogen sulphide- lean gas stream as obtained in step (d) to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream;
  • step (h) extracting heat from the gas stream which comprises sulphur dioxide as obtained in step (g) ;
  • step (i) subjecting at least part of the cooled sulphur dioxide-enriched gas stream as obtained in step (f) and at least part of the cooled gas stream which comprises sulphur dioxide as obtained in step (h) to a quench process ;
  • step (j) contacting at least part of the quenched gas stream as obtained in step (i) with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide- enriched absorption solvent and a sulphur dioxide- depleted gas stream;
  • step (k) removing sulphur dioxide from at least part of the sulphur dioxide-enriched absorption solvent as obtained in step (j) to obtain a sulphur dioxide-depleted
  • step (k) absorption solvent and a sulphur dioxide-enriched gas stream; and (1) recycling at least part of the sulphur dioxide- enriched gas stream as obtained in step (k) to step (c) .
  • gas streams can be obtained that contain such small amounts of sulphur-containing contaminants that they can
  • the present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from an acid gas stream.
  • the acid gas stream to be treated in accordance with the present invention can be any gas stream comprising sulphur- containing contaminants.
  • the process according to the invention is especially suitable for gas streams
  • the total gas stream to be treated comprises in the range of from 30 to 100 vol% hydrogen sulphide and from 0 to 60 vol% carbon dioxide, based on the total gas stream.
  • the gas stream to be treated comprises from 55 to 100 vol% hydrogen sulphide and from 0 to 45 vol% carbon dioxide, based on the total gas stream.
  • step (a) the oxidation treatment is carried at a temperature in the range of from 980-2000 °C, preferably in the range of from 1090-1540 °C, and a pressure in the range of from 1.29-2.05 bara, preferably in the range of from 1.56-2.05 bara.
  • the molar ratio of hydrogen sulphide to oxide in step (a) is in the range of from 2 : 1-3 : 1.
  • Step (a) can suitably be carried out in a burner.
  • the gas stream Prior to such an oxidation treatment in step (a) the gas stream can suitably be subjected to a hydrogen sulphide enrichment treatment.
  • a hydrogen sulphide enrichment treatment carbon dioxide and hydrocarbons can be removed from the gas stream, whereas hydrogen sulphide can be retained in the gas stream which is to be subjected to (a) by using a particular absorbent that selectively absorbs hydrogen sulphide.
  • the gas stream to be subjected to the oxidation treatment in step (a) contains hydrogen sulphide in an amount in the range of 40-100 mole %, based on total gas stream.
  • step (b) heat is extracted from the gas stream as obtained in step (a) .
  • This can suitably be done by cooling the gas stream in a two-step heat recovery unit to a temperature range of from 163-177 °C, preferable to a temperature range of from 168-174 °C.
  • a Waste Heat Boiler can suitably be used to
  • low pressure steam can suitably be generated by cooling the gas stream to a temperature range of from 260-370 °C, preferable in the range of from to 315-343 °C.
  • low pressure steam can suitably be generated by cooling the gas stream to a temperature range of from 260-370 °C, preferable in the range of from to 315-343 °C.
  • step (c) use can be made of one or more catalytic stages, whereby after each respective catalytic stage sulphur can be separated from the gas stream as described in step (d) .
  • step (d) the separation of sulphur from the gas stream can suitably be carried out by means of a sulphur condensation unit.
  • step (c) hydrogen sulphide present in the gas stream can be reacted with sulphur dioxide at elevated temperature in a first catalytic stage to obtain a gas stream which comprises sulphur and water.
  • step (c) comprises a catalytic step of a Claus process as described hereinabove.
  • the first catalytic stage is carried out in a catalytic zone where hydrogen sulphide reacts with sulphur dioxide to produce more sulphur.
  • the reaction in the first catalytic stage is carried out with a Claus conversion catalyst at a temperature in the range of from 204-371 °C, preferably in the range of from 260-343 °C, and a pressure in the range of from 1.29-2.05 bara, preferably in the range of from 1.56-2.05 bara.
  • a second and a third catalytic stage can be used in step (c) in which stages use is made of a Claus conversion catalyst.
  • the reaction is carried out at a temperature which is 5 to 20 °C above the sulphur dew point, preferable at a temperature which is 6 to 15 °C above the sulphur dew point, and a pressure in the range of from 1.1-2.0 bara, preferably in the range of from 1.4-1.7 bara.
  • the molar ratio of hydrogen sulphide to sulphur dioxide in step (c) is in the range of from 2:1-3:1.
  • Sulphur condensation units can suitably be applied after each catalytic stage in step (c) , which
  • condensation units can suitably be operated at
  • Claus tail gases The remaining gases as obtained after condensation of sulphur from the gases leaving the final catalytic zone are usually referred to as "Claus tail gases". These gases contain nitrogen, water vapour, some hydrogen sulphide, sulphur dioxide and usually also carbon
  • a suitable Claus catalyst has for instance been described in European patent application No. 0038741, which catalyst substantially consists of titanium oxide.
  • Other suitable catalysts include activated alumina and bauxite catalysts.
  • step (d) sulphur is separated from the gas stream obtained in step (c) , thereby obtaining a hydrogen sulphide-lean gas stream.
  • the gas stream as obtained in step (c) can be cooled below the sulphur dew point to condense and subsequently most of the sulphur obtained can be separated from the gas stream.
  • step (d) can suitably be carried out by cooling the effluent obtained in step (c) to condense and separate sulphur, thereby obtaining the hydrogen sulphide-depleted gas stream.
  • step (e) at least part of the hydrogen sulphide- lean gas stream as obtained in step (d) is subjected to an oxidation treatment to obtain a sulphur dioxide- enriched gas stream. At least part, but preferably the entire hydrogen sulphide-lean gas stream as obtained in step (d) is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide.
  • the oxidation treatment is preferably carried at a temperature in the range of from 538-1038 °C, preferably in the range of from 648-982 °C, and a pressure in the range of from 1.1-2 bara, preferably in the range of from 1.4-1.7. bara .
  • step (f) heat is extracted from the gas stream which comprises sulphur dioxide as obtained in step (e) .
  • the heat extraction in step (f) can be carried out in a similar way as the heat extraction in step (b) as
  • step (g) a sulphur-containing residual hydrocarbon product is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide.
  • the oxidation treatment is preferably carried at a temperature in the range of from 538-1038 °C, preferably in the range of from 648-982 °C, and a pressure in the range of from 1.1-2 bara, preferably in the range of from 1.4-1.7 bara.
  • step (g) any sulphur-containing residual
  • the sulphur-containing residual hydrocarbon product to be used in step (g) is preferably a product from a thermal gasoil unit having a V50 (viscosity at 50 °C) in the range of from 30-50 cSt, a product from a catalytic cracking unit, suitably in slurry form, having a V50 in the range of from 20-50 cSt, or a heavy residue containing up to 10 wt% organic sulphur, based on total heavy residue. More preferably, the residual hydrocarbon product comprises a product from a thermal gasoil unit having a V50 in the range of from 35-45 cSt.
  • the integration of step (e) advantageously ensures that the size of the Claus unit to be used can be reduced or that the capacity of the Claus unit can be increased.
  • steps (e) and (g) can be carried out in the same oxidation unit.
  • steps (e) and (g) are carried out in the same oxidation unit.
  • step (h) heat is extracted from the gas stream which comprises sulphur dioxide as obtained in step (g) .
  • the heat extraction in step (h) can be carried out in a similar way as the heat extraction in step (b) as described hereinbefore.
  • the steps (e) and (gO are carried out in the same oxidation unit, also the steps (f) and (h) are carried out in the same unit.
  • step (i) at least part of the cooled sulphur dioxide-enriched gas stream as obtained in step (f) and at least part of the cooled gas stream comprising sulphur dioxide as obtained in step (h) are subjected to a quenching process before they are contacted with the absorption solvent in step (j) .
  • the respective gas streams are suitably cooled by means of water quenching.
  • the entire cooled sulphur dioxide-enriched gas stream as obtained in step (f) and the entire cooled gas stream comprising sulphur dioxide as obtained in step (h) are subjected to the quenching process before they are contacted with the absorption solvent in step (j) .
  • these gas streams are cooled to a temperature in the range of from 40-60 °C in the quenching process.
  • step (j) at least part of the sulphur dioxide-enriched gas stream as obtained in step (i) is contacted with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream.
  • step (j) use is made of an aqueous solution of the absorption solvent.
  • step (i) 10-90 vol.% of the gas stream as obtained in step (i) can be contacted with the absorption solvent in step (j) .
  • the entire gas stream as obtained in step (i) is contacted with the absorption solvent in step (j) .
  • the absorption solvent in step (j) comprises water and a water-soluble amine absorbent having at least one amine group with a pKa value greater than about 7 and at least one other amine group with a pKa value less than 6.5, wherein the at least one amine group with a pKa value greater than about 7 irreversibly absorbs sulphur dioxide in salt form to render the amine absorbent non-volatile, and wherein the at least one other amine group with a pKa value less than 6.5
  • the water-soluble amine absorbent is a diamine having the general formula:
  • Ri is an alkylene group having 1 to 3 carbon atoms
  • R 2 , R 3 , R and R5 are the same or different and each represent a hydrogen atom, a lower alkyl group having 1 to 8 carbon atoms or a lower hydroxy-alkyl group having 2 to 8 carbon atoms, or any of R 2 , R 3 , R and R5 form together with the nitrogen atoms to which they are attached a 6-membered ring.
  • the diamine is selected from the group consisting of N, N ' , N ' - ( trimethyl ) -N- ( 2- hydroxyethyl ) -ethylenediamine ;
  • step (j) N-methyl-piperazine ; and piperazine.
  • the sulphur dioxide- enriched absorption solvent as obtained in step (j) will need to be regenerated in order to ensure that the absorption solvent can be used again in step (j) .
  • the sulphur dioxide-enriched absorption solvent as obtained in step (j) will normally be passed to a regeneration unit step (k) where the absorption solvent will be freed from sulphur dioxide and the sulphur dioxide-depleted absorption solvent so obtained can suitably be recycled to step (j) .
  • Step (j) can suitably be carried at a temperature in the range of from 20-80 °C, preferably in the range of from 30-60 °C, and a pressure in the range of from 1.1- 2.0 bara, preferably in the range of from 1.4-1.7 bara.
  • a temperature in the range of from 20-80 °C preferably in the range of from 30-60 °C
  • a pressure in the range of from 1.1- 2.0 bara preferably in the range of from 1.4-1.7 bara.
  • At least part of the sulphur dioxide-depleted gas stream as obtained in step (j) is contacted with an absorption solvent to absorb carbon dioxide to obtain a carbon dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream which is lean in carbon dioxide, and carbon dioxide is removed from at least part of the carbon dioxide-enriched adsorption solvent to obtain a carbon dioxide-depleted absorption solvent and a carbon dioxide-enriched gas stream.
  • the entire sulphur dioxide-depleted gas stream as obtained in step (j) is contacted with an absorption solvent to absorb carbon dioxide to obtain a carbon dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream which is lean in carbon dioxide, and carbon dioxide is removed from at least part of the carbon dioxide-enriched adsorption solvent to obtain a carbon dioxide-depleted absorption solvent and a carbon dioxide- enriched gas stream.
  • the sulphur dioxide-depleted gas stream as obtained in step (j) is highly attractive since it is lean in respect of sulphur-containing contaminants.
  • the sulphur dioxide-depleted gas stream as obtained in step (j) contains no hydrogen sulphide and less than 50 ppmv sulphur dioxide.
  • said gas stream contains less than 30 ppmv sulphur dioxide.
  • step (k) sulphur dioxide is removed from at least part of the sulphur dioxide-enriched absorption solvent as obtained in step (j) to obtain a sulphur dioxide-depleted absorption solvent and a sulphur dioxide-enriched gas stream.
  • Step (k) can suitably be carried at a temperature in the range of from 110-150 °C, preferably in the range of from 120-140 °C, and a pressure in the range of from 1.1-1.9 bara, preferably in the range of from 1.2-1.7 bara .
  • step (m) at least part of the sulphur dioxide-depleted absorption solvent as obtained in step (k) is recycled to step (j) .
  • step (j) the entire sulphur dioxide-depleted absorption solvent as obtained in step (k) is recycled to step (j) .
  • step (1) at least part of the sulphur dioxide- enriched gas stream as obtained in step (k) is recycled to step (c) .
  • the entire sulphur dioxide- enriched gas stream as obtained in step (k) is recycled to step (c) .
  • part of the sulphur dioxide- enriched gas stream as obtained in step (k) is not recycled to step (c) , a part of that stream might
  • step (a) suitably be recycled to step (a) .
  • at least part of the sulphur dioxide- depleted absorption solvent as obtained in step (k) is recycled to step (j) .
  • a gas stream comprising sulphur- containing contaminants, including hydrogen sulphide is led via line 1 to an oxidation and heat recovery unit 2 (e.g. a combined burner and heat recovery unit) wherein the gas stream is oxidized and cooled while producing steam which is removed via line 3. Liquid sulphur which is condensed at the low temperature range is also removed via line 3. From unit 2 the gas stream obtained is passed via line 4 to a catalyst and sulphur separation unit 5, the hydrogen sulphide in the gas stream is reacted with sulphur dioxide in the presence of a
  • oxidation unit 8 the hydrogen sulphide-lean gas stream (tail gas) so obtained is passed via line 7 into oxidation unit 8. However a fraction of this gas is passed via line 9 to oxidation and recovery unit 10 (e.g. combine oxidation and heat recovery unit) .
  • oxidation unit 8 the hydrogen sulphide-lean gas stream (tail gas) so obtained is passed via line 7 into oxidation unit 8. However a fraction of this gas is passed via line 9 to oxidation and recovery unit 10 (e.g. combine oxidation and heat recovery unit) .
  • oxidation unit 8 the hydrogen
  • sulphide-lean gas stream is subjected to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream. Heat can be removed via line 14.
  • a residual hydrocarbon product is introduced via line 11 into oxidation and heat recovery unit 10.
  • the residual hydrocarbon product is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide.
  • Heat recovered in the oxidation and heat recovery unit 10 is then removed via line 12.
  • the gas stream obtained in oxidation and heat recovery unit 10 is passed via line 13 into a quenching unit 16, whereas the gas stream obtained in the unit 8 is introduced via line 15 into the quenching unit 16.
  • the quenching medium e.g. water, can be withdrawn from the quenching unit 16 via line 17.
  • the gas stream obtained in the quenching unit 16 is subsequently passed via line 18 to absorption/regeneration unit 19 where it is contacted with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream.
  • the sulphur dioxide-enriched absorption solvent is then regenerated and sulphur dioxide-enriched gas stream thereby obtained is separated from the absorption solvent and recycled via line 20 to the oxidation unit 2.
  • the treated gas stream is recovered via line 21.
  • an acid gas comprising 60 % (v/v) hydrogen sulphide, 40 % (v/v) carbon dioxide, 0 % (v/v) sulphur dioxide, 50 ppmv carbonyl sulphide (COS), 200 ppmv mercaptans and 20 ppmv carbon disulphide is routed via line 1 to a burner unit 2 with a flow rate of 6.74 Nm 3 /s.
  • COS ppmv carbonyl sulphide
  • the acid gas is oxidized at a temperature of 980 °C and a pressure of 1.5 bara.
  • oxidation and heat recovery unit 2 is 2:1.
  • the gas stream so obtained is reacted in the catalyst unit 5 with sulphur oxide at a temperature of 300 °C in a first stage and 220 °C in a second and a third stage, and a pressure of 1.4 bara using a Claus process catalyst which
  • oxidation unit 8 comprises activated alumina. Sulphur and steam are withdrawn from the catalyst unit via line 6. The molar ratio of hydrogen sulphide to sulphur dioxide in the catalyst unit 5 is 2:1. The hydrogen sulphide-lean gas stream (tail gas) so obtained is passed via line 7 into oxidation unit 8. In oxidation unit 8 the hydrogen sulphide-lean gas stream is subjected to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream.
  • a residual hydrocarbon product is introduced via line 11 into oxidation and heat recovery unit 10.
  • the residual hydrocarbon product is subjected to an oxidation treatment which is carried out at a temperature of 900°C and a pressure of 1.3 bara to obtain a sulphur dioxide-enriched gas stream which contains no hydrogen sulphide nor organic sulphur compounds.
  • the gas stream obtained in oxidation and heat recovery unit 10 is passed via line 13 into quenching unit 16 and the gas stream obtained in the oxidation unit 8 is introduced via line 15 into quenching unit 16.
  • the quenching unit 16 the gas stream is cooled with water to a temperature of 50°C, and the water is withdrawn from the quenching unit via line 17.
  • the gas stream obtained in the quenching unit 16 is subsequently contacted at a temperature of 50 °C and a pressure of 1.3 bara in absorption/regeneration unit 19 with a Cansolv SO 2 solvent that selectively absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a gas stream depleted in sulphur dioxide.
  • the sulphur dioxide-enriched absorption solvent is then regenerated and sulphur dioxide-enriched gas stream thereby obtained is separated from the absorption solvent and recycled via line 20 to the oxidation unit 2.
  • the gas stream which is lean in sulphur-containing contaminants is eventually obtained from the absorption/regeneration unit 19 via line 21 comprises 0 ppmv hydrogen sulphide, 50 % (v/v) carbon dioxide, 45 % (v/v) nitrogen, 0 ppmv carbonyl sulphide (COS), 0 ppmv mercaptans, 0 ppmv carbon
  • oxidation and heat recovery unit 2 is operated at a temperature of 1040 °C, a pressure of 1.5 bara, and a molar ratio of hydrogen sulphide to oxide of 2:1.
  • the gas stream so obtained gas is reacted in the catalyst unit 5 with sulphur oxide at a temperature of 280 °C and a pressure of 1.4 bara.
  • absorption/regeneration unit 19 comprises 200 ppmv hydrogen sulphide, 50 % (v/v) carbon dioxide, 45 % (v/v) nitrogen, 20 ppmv carbonyl sulphide (COS), 0 ppmv
  • Example 1 constitutes an improvement in terms of efficient removal of sulphur-containing contaminants when compared to comparative Example 2.

Abstract

A process for removing sulphur-containing contaminants including hydrogen sulphide, from a gas stream, comprising the steps of subjecting the gas stream to an oxidation treatment, extracting heat from the resulting gas stream, reacting catalytically H2 S from said cooled gas stream with sulphur dioxide at elevated temperature to obtain a gas stream which comprises sulphur and water, separating sulphur thereby obtaining a H2 S-lean gas stream, subjecting it to an oxidation treatment, extracting heat from the S02-enriched gas stream obtained therein; subjecting a sulphur-containing residual hydrocarbon product to an oxidation treatment to obtain a gas stream which contains S02, extracting heat from said gas stream which comprises S02, subjecting both streams containing S02 to a quench process, absorbing S02 from the resulting gas stream to obtain a S02-enriched absorption solvent which is regenerated and using the S02-enriched gas stream produced therein as S02 source for Claus Process.

Description

PROCESS FOR REMOVING SULPHUR-CONTAINING CONTAMINANTS FROM
A GAS STREAM
Field of the invention
The present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from a gas stream.
Background of the invention
The removal of sulphur-containing compounds from gas streams comprising such compounds has always been of considerable importance in the past and is even more so today in view of continuously tightening environmental regulations. This holds for hydrogen sulphide-containing gases that have become available in for example oil refineries and combustion gases obtained from a coke- oven. Sulphur contaminants in such gases include apart from hydrogen sulphide, carbonyl sulphide, carbon
disulphide and mercaptans . Considerable effort has been spent to find effective and cost-efficient means to remove these undesired compounds. In addition, such gas streams may also contain varying amounts of carbon dioxide which depending on the use of the gas stream often have to be removed at least partly.
One well-known method that is used to treat certain process streams that contain hydrogen sulphide to recover elemental sulphur is the Claus process. The Claus process is a two-step process that includes a burner (oxidation) step followed by a catalytic step wherein use is made of one or more catalytic stages. In the oxidation step, the hydrogen sulphide of a feed stream is partially oxidized by combustion with oxygen to form a gas stream containing sulphur dioxide. The un-reacted hydrogen sulphide and the formed sulphur dioxide contained in the combustion gas can undergo the Claus reaction whereby they are reacted to form elemental sulphur. Further in the Claus process, un-reacted hydrogen sulphide and sulphur dioxide in the combustion gas are catalytically reacted in accordance with the Claus reaction by passing the combustion gas over a Claus catalyst which provides for a lower Claus reaction temperature. While the Claus process is very effective at providing for the recovery of a major portion of the sulphur in its feed stream, conversion is limited by equilibrium in the Claus process, and so the
Claus tail gas still contains appreciable amounts of sulphur compounds such as hydrogen sulphide, carbonyl sulphide and sulphur dioxide. This does not only apply to sulphur recovery with a two-bed catalytic Claus plant, but also to Claus plants with three or more catalytic beds. The tail gas from a Claus process therefore is usually subjected to a hydrogenation treatment to further reduce the amounts of sulphur dioxide, COS, CS2, and mercaptants by converting them into hydrogen sulphide, followed by a treatment wherein use is made of an amine that selectively absorbs hydrogen sulphide. Upon
regeneration of the hydrogen sulphide-rich amine stream a gas stream enriched in hydrogen sulphide can be recovered which can subsequently be recycled to the Claus unit. The combination of the hydrogenation and amine treatments can be a so-called Tail gas Treating (TGT) process. The tail gas treated in such a TGT process still contains
noticeable amounts of hydrogen sulphide (in the order of 100 ppm sulphur) and other sulphur species such as carbonyl sulfide. For that reason the tail gas will need to be oxidized in an incinerator before it can be
discarded into the air as vent gas or used for other purposes . Hence, there is an ongoing need for improved sulphur recovery processes that provide for high sulphur recovery and better operating efficiencies, preferably with lower capital costs. With increasingly more stringent sulphur emission standards, there is also a need for sulphur recovery processes that provide for even greater sulphur recoveries from process streams containing sulphur compounds than are provided by conventional sulphur recovery systems. Simultaneously refineries are under increasing regulatory pressure to find outlet to high sulphur residual streams such as heavy residue and FCC slurries. Some of these are currently used to produce bunker fuel as maritime fuel. However, future regulatory pressure, notably MARPOL IV, will limit the use of these high sulphur fuels for maritime fuel use. Current use for these high sulphur residual stream is as feed for gasification units. However, these are complex and expensive units.
Summary of the invention
It has now been found that an improved removal of sulphur-containing contaminants from a gas stream can be established, as well as a decrease in hardware and an increase in energy efficiency, when a Claus process is part of a particularly integrated multi-step process for removing sulphur-containing contaminants from a gas stream.
Accordingly, the present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from a gas stream comprising the steps of:
(a) subjecting the gas stream to an oxidation treatment;
(b) extracting heat from the gas stream as obtained in step (a) ; (c) reacting hydrogen sulphide present in the cooled gas stream as obtained in step (b) with sulphur dioxide at elevated temperature and in the presence of a catalyst to obtain a gas stream which comprises sulphur and water; (d) separating sulphur from the gas stream obtained in step (c) , thereby obtaining a hydrogen sulphide-lean gas stream;
(e) subjecting at least part of the hydrogen sulphide- lean gas stream as obtained in step (d) to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream;
(f) extracting heat from the sulphur dioxide-enriched gas stream as obtained instep (e) ;
(g) subjecting a sulphur-containing residual hydrocarbon product to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide;
(h) extracting heat from the gas stream which comprises sulphur dioxide as obtained in step (g) ;
(i) subjecting at least part of the cooled sulphur dioxide-enriched gas stream as obtained in step (f) and at least part of the cooled gas stream which comprises sulphur dioxide as obtained in step (h) to a quench process ;
(j) contacting at least part of the quenched gas stream as obtained in step (i) with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide- enriched absorption solvent and a sulphur dioxide- depleted gas stream;
(k) removing sulphur dioxide from at least part of the sulphur dioxide-enriched absorption solvent as obtained in step (j) to obtain a sulphur dioxide-depleted
absorption solvent and a sulphur dioxide-enriched gas stream; and (1) recycling at least part of the sulphur dioxide- enriched gas stream as obtained in step (k) to step (c) .
In accordance with the present invention gas streams can be obtained that contain such small amounts of sulphur-containing contaminants that they can
advantageously directly be vented into the air or used for different purposes.
Detailed description of the invention
The present invention relates to a process for removing sulphur-containing contaminants, including hydrogen sulphide, from an acid gas stream. The acid gas stream to be treated in accordance with the present invention can be any gas stream comprising sulphur- containing contaminants. The process according to the invention is especially suitable for gas streams
comprising sulphur-containing contaminants and optionally also various amounts of carbon dioxide. Suitably the total gas stream to be treated comprises in the range of from 30 to 100 vol% hydrogen sulphide and from 0 to 60 vol% carbon dioxide, based on the total gas stream.
Preferably, the gas stream to be treated comprises from 55 to 100 vol% hydrogen sulphide and from 0 to 45 vol% carbon dioxide, based on the total gas stream.
In step (a) the oxidation treatment is carried at a temperature in the range of from 980-2000 °C, preferably in the range of from 1090-1540 °C, and a pressure in the range of from 1.29-2.05 bara, preferably in the range of from 1.56-2.05 bara. Preferably, the molar ratio of hydrogen sulphide to oxide in step (a) is in the range of from 2 : 1-3 : 1.
Step (a) can suitably be carried out in a burner. Prior to such an oxidation treatment in step (a) the gas stream can suitably be subjected to a hydrogen sulphide enrichment treatment. In such an enrichment treatment carbon dioxide and hydrocarbons can be removed from the gas stream, whereas hydrogen sulphide can be retained in the gas stream which is to be subjected to (a) by using a particular absorbent that selectively absorbs hydrogen sulphide. Preferably, the gas stream to be subjected to the oxidation treatment in step (a) contains hydrogen sulphide in an amount in the range of 40-100 mole %, based on total gas stream.
In step (b) heat is extracted from the gas stream as obtained in step (a) . This can suitably be done by cooling the gas stream in a two-step heat recovery unit to a temperature range of from 163-177 °C, preferable to a temperature range of from 168-174 °C. In the first step, a Waste Heat Boiler can suitably be used to
generate high to medium pressure steam by cooling the gases to a temperature in the range of from 260-370 °C, preferable in the range of from to 315-343 °C. In the second step low pressure steam can suitably be generated by cooling the gas stream to a temperature range of from
163-177 °C, preferable to a temperature in the range of from 168-174 °C. It is believed that at these
temperatures the sulphur dew point will be reached and the heat exchanger should to be designed for removal of condensed liquid sulphur.
In step (c) use can be made of one or more catalytic stages, whereby after each respective catalytic stage sulphur can be separated from the gas stream as described in step (d) . In step (d) the separation of sulphur from the gas stream can suitably be carried out by means of a sulphur condensation unit.
In step (c) hydrogen sulphide present in the gas stream can be reacted with sulphur dioxide at elevated temperature in a first catalytic stage to obtain a gas stream which comprises sulphur and water. Suitably step (c) comprises a catalytic step of a Claus process as described hereinabove. Suitably, the first catalytic stage is carried out in a catalytic zone where hydrogen sulphide reacts with sulphur dioxide to produce more sulphur. Suitably, the reaction in the first catalytic stage is carried out with a Claus conversion catalyst at a temperature in the range of from 204-371 °C, preferably in the range of from 260-343 °C, and a pressure in the range of from 1.29-2.05 bara, preferably in the range of from 1.56-2.05 bara. Suitably, a second and a third catalytic stage can be used in step (c) in which stages use is made of a Claus conversion catalyst. Suitably, in such a second and third catalytic stage the reaction is carried out at a temperature which is 5 to 20 °C above the sulphur dew point, preferable at a temperature which is 6 to 15 °C above the sulphur dew point, and a pressure in the range of from 1.1-2.0 bara, preferably in the range of from 1.4-1.7 bara. Preferably, the molar ratio of hydrogen sulphide to sulphur dioxide in step (c) is in the range of from 2:1-3:1.
Sulphur condensation units can suitably be applied after each catalytic stage in step (c) , which
condensation units can suitably be operated at
temperature in the range of from 160-171 °C, preferable in the range of from 163-168 °C.
The remaining gases as obtained after condensation of sulphur from the gases leaving the final catalytic zone are usually referred to as "Claus tail gases". These gases contain nitrogen, water vapour, some hydrogen sulphide, sulphur dioxide and usually also carbon
dioxide, carbon monoxide, carbonyl sulphide and carbon disulphide, hydrogen, and small amounts of elemental sulphur .
A suitable Claus catalyst has for instance been described in European patent application No. 0038741, which catalyst substantially consists of titanium oxide. Other suitable catalysts include activated alumina and bauxite catalysts.
In step (d) sulphur is separated from the gas stream obtained in step (c) , thereby obtaining a hydrogen sulphide-lean gas stream. To that end the gas stream as obtained in step (c) can be cooled below the sulphur dew point to condense and subsequently most of the sulphur obtained can be separated from the gas stream. Hence, step (d) can suitably be carried out by cooling the effluent obtained in step (c) to condense and separate sulphur, thereby obtaining the hydrogen sulphide-depleted gas stream.
In step (e) at least part of the hydrogen sulphide- lean gas stream as obtained in step (d) is subjected to an oxidation treatment to obtain a sulphur dioxide- enriched gas stream. At least part, but preferably the entire hydrogen sulphide-lean gas stream as obtained in step (d) is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide. In step (e) the oxidation treatment is preferably carried at a temperature in the range of from 538-1038 °C, preferably in the range of from 648-982 °C, and a pressure in the range of from 1.1-2 bara, preferably in the range of from 1.4-1.7. bara .
In step (f) heat is extracted from the gas stream which comprises sulphur dioxide as obtained in step (e) . The heat extraction in step (f) can be carried out in a similar way as the heat extraction in step (b) as
previously described.
In step (g) a sulphur-containing residual hydrocarbon product is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide. In step (g) the oxidation treatment is preferably carried at a temperature in the range of from 538-1038 °C, preferably in the range of from 648-982 °C, and a pressure in the range of from 1.1-2 bara, preferably in the range of from 1.4-1.7 bara.
In step (g) any sulphur-containing residual
hydrocarbon product can be used. The sulphur-containing residual hydrocarbon product to be used in step (g) is preferably a product from a thermal gasoil unit having a V50 (viscosity at 50 °C) in the range of from 30-50 cSt, a product from a catalytic cracking unit, suitably in slurry form, having a V50 in the range of from 20-50 cSt, or a heavy residue containing up to 10 wt% organic sulphur, based on total heavy residue. More preferably, the residual hydrocarbon product comprises a product from a thermal gasoil unit having a V50 in the range of from 35-45 cSt. The integration of step (e) advantageously ensures that the size of the Claus unit to be used can be reduced or that the capacity of the Claus unit can be increased.
As the conditions of the steps (e) and (g) are similar, if desired, steps (e) and (g) can be carried out in the same oxidation unit. Preferably, steps (e) and (g) are carried out in the same oxidation unit.
In step (h) heat is extracted from the gas stream which comprises sulphur dioxide as obtained in step (g) . The heat extraction in step (h) can be carried out in a similar way as the heat extraction in step (b) as described hereinbefore. Preferably, if the steps (e) and (gO are carried out in the same oxidation unit, also the steps (f) and (h) are carried out in the same unit.
In step (i) at least part of the cooled sulphur dioxide-enriched gas stream as obtained in step (f) and at least part of the cooled gas stream comprising sulphur dioxide as obtained in step (h) are subjected to a quenching process before they are contacted with the absorption solvent in step (j) . In such a quenching process the respective gas streams are suitably cooled by means of water quenching. Preferably, the entire cooled sulphur dioxide-enriched gas stream as obtained in step (f) and the entire cooled gas stream comprising sulphur dioxide as obtained in step (h) are subjected to the quenching process before they are contacted with the absorption solvent in step (j) . Suitably, these gas streams are cooled to a temperature in the range of from 40-60 °C in the quenching process.
In step (j) at least part of the sulphur dioxide-enriched gas stream as obtained in step (i) is contacted with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream.
Preferably, in step (j) use is made of an aqueous solution of the absorption solvent.
Suitably, 10-90 vol.% of the gas stream as obtained in step (i) can be contacted with the absorption solvent in step (j) . Preferably, the entire gas stream as obtained in step (i) is contacted with the absorption solvent in step (j) .
Preferably, the absorption solvent in step (j) comprises water and a water-soluble amine absorbent having at least one amine group with a pKa value greater than about 7 and at least one other amine group with a pKa value less than 6.5, wherein the at least one amine group with a pKa value greater than about 7 irreversibly absorbs sulphur dioxide in salt form to render the amine absorbent non-volatile, and wherein the at least one other amine group with a pKa value less than 6.5
reversibly absorbs sulphur dioxide to saturate the absorption solvent with sulphur dioxide against a partial pressure of sulphur dioxide of no more than 1 atmosphere at 25 °C.
Preferably, the water-soluble amine absorbent is a diamine having the general formula:
R2R5NR1NR3R4
wherein Ri is an alkylene group having 1 to 3 carbon atoms, R2, R3, R and R5 are the same or different and each represent a hydrogen atom, a lower alkyl group having 1 to 8 carbon atoms or a lower hydroxy-alkyl group having 2 to 8 carbon atoms, or any of R2, R3, R and R5 form together with the nitrogen atoms to which they are attached a 6-membered ring.
More preferably, the diamine is selected from the group consisting of N, N ' , N ' - ( trimethyl ) -N- ( 2- hydroxyethyl ) -ethylenediamine ;
N, N, N ' , N ' -tetramethyl-ethylenediamine ;
N, N, N ' , N ' -tetramethyl-diaminomethane ;
Ν,Ν,Ν' ,Ν'-tetrakis- ( 2 -hydroxyethyl ) -ethylenediamine ;
N, N ' -dimethylpiperazine ;
Ν,Ν,Ν' ,Ν'-tetrakis- ( 2 -hydroxyethyl ) -1 , 3-diaminopropane ; N ' , N ' -dimethyl-N, N-bis- ( 2 -hydroxyethyl ) -ethylenediamine ; N-methyl N '-( 2-hydroxyethyl ) -piperazine ;
N- (2-hydroxyethyl) -piperazine;
N, N ' -bis (2-hydroxyethyl ) -piperazine ;
N-methyl-piperazine ; and piperazine. It will be understood that the sulphur dioxide- enriched absorption solvent as obtained in step (j) will need to be regenerated in order to ensure that the absorption solvent can be used again in step (j) . For that purpose the sulphur dioxide-enriched absorption solvent as obtained in step (j) will normally be passed to a regeneration unit step (k) where the absorption solvent will be freed from sulphur dioxide and the sulphur dioxide-depleted absorption solvent so obtained can suitably be recycled to step (j) .
Step (j) can suitably be carried at a temperature in the range of from 20-80 °C, preferably in the range of from 30-60 °C, and a pressure in the range of from 1.1- 2.0 bara, preferably in the range of from 1.4-1.7 bara. Suitably, use is made in step (j) of an aqueous solution that comprises the absorption solvent in a concentration in the range of from 30-55 wt%.
In a particular attractive embodiment of the present invention at least part of the sulphur dioxide-depleted gas stream as obtained in step (j) is contacted with an absorption solvent to absorb carbon dioxide to obtain a carbon dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream which is lean in carbon dioxide, and carbon dioxide is removed from at least part of the carbon dioxide-enriched adsorption solvent to obtain a carbon dioxide-depleted absorption solvent and a carbon dioxide-enriched gas stream. Preferably, the entire sulphur dioxide-depleted gas stream as obtained in step (j) is contacted with an absorption solvent to absorb carbon dioxide to obtain a carbon dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream which is lean in carbon dioxide, and carbon dioxide is removed from at least part of the carbon dioxide-enriched adsorption solvent to obtain a carbon dioxide-depleted absorption solvent and a carbon dioxide- enriched gas stream.
The sulphur dioxide-depleted gas stream as obtained in step (j) is highly attractive since it is lean in respect of sulphur-containing contaminants. Suitably, the sulphur dioxide-depleted gas stream as obtained in step (j) contains no hydrogen sulphide and less than 50 ppmv sulphur dioxide. Preferably, said gas stream contains less than 30 ppmv sulphur dioxide.
In step (k) sulphur dioxide is removed from at least part of the sulphur dioxide-enriched absorption solvent as obtained in step (j) to obtain a sulphur dioxide-depleted absorption solvent and a sulphur dioxide-enriched gas stream. Step (k) can suitably be carried at a temperature in the range of from 110-150 °C, preferably in the range of from 120-140 °C, and a pressure in the range of from 1.1-1.9 bara, preferably in the range of from 1.2-1.7 bara .
Suitably, in a step (m) at least part of the sulphur dioxide-depleted absorption solvent as obtained in step (k) is recycled to step (j) . Preferably, the entire sulphur dioxide-depleted absorption solvent as obtained in step (k) is recycled to step (j) .
In step (1) at least part of the sulphur dioxide- enriched gas stream as obtained in step (k) is recycled to step (c) . Preferably, the entire sulphur dioxide- enriched gas stream as obtained in step (k) is recycled to step (c) . However, if part of the sulphur dioxide- enriched gas stream as obtained in step (k) is not recycled to step (c) , a part of that stream might
suitably be recycled to step (a) . Suitably, at least part of the sulphur dioxide- depleted absorption solvent as obtained in step (k) is recycled to step (j) .
One embodiment of the present invention is
illustrated in Figure 1.
In Figure 1, a gas stream comprising sulphur- containing contaminants, including hydrogen sulphide is led via line 1 to an oxidation and heat recovery unit 2 (e.g. a combined burner and heat recovery unit) wherein the gas stream is oxidized and cooled while producing steam which is removed via line 3. Liquid sulphur which is condensed at the low temperature range is also removed via line 3. From unit 2 the gas stream obtained is passed via line 4 to a catalyst and sulphur separation unit 5, the hydrogen sulphide in the gas stream is reacted with sulphur dioxide in the presence of a
catalyst to obtain a gas stream which comprises sulphur and water, whereby sulphur is withdrawn via line 6. The hydrogen sulphide-lean gas stream (tail gas) so obtained is passed via line 7 into oxidation unit 8. However a fraction of this gas is passed via line 9 to oxidation and recovery unit 10 (e.g. combine oxidation and heat recovery unit) . In oxidation unit 8 the hydrogen
sulphide-lean gas stream is subjected to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream. Heat can be removed via line 14. A residual hydrocarbon product is introduced via line 11 into oxidation and heat recovery unit 10. In oxidation and heat recovery unit 10 the residual hydrocarbon product is subjected to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide. Heat recovered in the oxidation and heat recovery unit 10 is then removed via line 12. The gas stream obtained in oxidation and heat recovery unit 10 is passed via line 13 into a quenching unit 16, whereas the gas stream obtained in the unit 8 is introduced via line 15 into the quenching unit 16. The quenching medium, e.g. water, can be withdrawn from the quenching unit 16 via line 17. The gas stream obtained in the quenching unit 16 is subsequently passed via line 18 to absorption/regeneration unit 19 where it is contacted with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream. The sulphur dioxide-enriched absorption solvent is then regenerated and sulphur dioxide-enriched gas stream thereby obtained is separated from the absorption solvent and recycled via line 20 to the oxidation unit 2. The treated gas stream is recovered via line 21.
The invention is illustrated using the following non- limiting Examples.
Example 1 (according to the invention)
In a process as described in Figure 1, an acid gas comprising 60 % (v/v) hydrogen sulphide, 40 % (v/v) carbon dioxide, 0 % (v/v) sulphur dioxide, 50 ppmv carbonyl sulphide (COS), 200 ppmv mercaptans and 20 ppmv carbon disulphide is routed via line 1 to a burner unit 2 with a flow rate of 6.74 Nm3/s. In the oxidation and heat recovery unit 2 the acid gas is oxidized at a temperature of 980 °C and a pressure of 1.5 bara. The molar ratio of hydrogen sulphide to oxide in the
oxidation and heat recovery unit 2 is 2:1. The gas stream so obtained is reacted in the catalyst unit 5 with sulphur oxide at a temperature of 300 °C in a first stage and 220 °C in a second and a third stage, and a pressure of 1.4 bara using a Claus process catalyst which
comprises activated alumina. Sulphur and steam are withdrawn from the catalyst unit via line 6. The molar ratio of hydrogen sulphide to sulphur dioxide in the catalyst unit 5 is 2:1. The hydrogen sulphide-lean gas stream (tail gas) so obtained is passed via line 7 into oxidation unit 8. In oxidation unit 8 the hydrogen sulphide-lean gas stream is subjected to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream.
A residual hydrocarbon product is introduced via line 11 into oxidation and heat recovery unit 10. In oxidation and heat recovery unit 10 the residual hydrocarbon product is subjected to an oxidation treatment which is carried out at a temperature of 900°C and a pressure of 1.3 bara to obtain a sulphur dioxide-enriched gas stream which contains no hydrogen sulphide nor organic sulphur compounds. The gas stream obtained in oxidation and heat recovery unit 10 is passed via line 13 into quenching unit 16 and the gas stream obtained in the oxidation unit 8 is introduced via line 15 into quenching unit 16. In the quenching unit 16 the gas stream is cooled with water to a temperature of 50°C, and the water is withdrawn from the quenching unit via line 17. The gas stream obtained in the quenching unit 16 is subsequently contacted at a temperature of 50 °C and a pressure of 1.3 bara in absorption/regeneration unit 19 with a Cansolv SO2 solvent that selectively absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a gas stream depleted in sulphur dioxide. The sulphur dioxide-enriched absorption solvent is then regenerated and sulphur dioxide-enriched gas stream thereby obtained is separated from the absorption solvent and recycled via line 20 to the oxidation unit 2. The gas stream which is lean in sulphur-containing contaminants is eventually obtained from the absorption/regeneration unit 19 via line 21 comprises 0 ppmv hydrogen sulphide, 50 % (v/v) carbon dioxide, 45 % (v/v) nitrogen, 0 ppmv carbonyl sulphide (COS), 0 ppmv mercaptans, 0 ppmv carbon
disulphide, and 40 ppmv sulphur dioxide.
Example 2 (comparative Example)
A similar process as described in Example 1 was carried out, except that (a) oxidation unit 8 is replaced by a hydrogenation unit wherein the gas stream is
contacted at a temperature of 320 °C and a pressure of
1.2 bara with a reducing agent hydrogen and a SCOT catalyst, and that (b) no use is made of an integrated oxidation unit 10 wherein a residual hydrocarbon product is subjected to a oxidation treatment and heat recovery. The oxidation and heat recovery unit 2 is operated at a temperature of 1040 °C, a pressure of 1.5 bara, and a molar ratio of hydrogen sulphide to oxide of 2:1. The gas stream so obtained gas is reacted in the catalyst unit 5 with sulphur oxide at a temperature of 280 °C and a pressure of 1.4 bara. The molar ratio of hydrogen
sulphide to sulphur dioxide in catalyst unit 5 is 2:1 The gas stream eventually obtained from the
absorption/regeneration unit 19 comprises 200 ppmv hydrogen sulphide, 50 % (v/v) carbon dioxide, 45 % (v/v) nitrogen, 20 ppmv carbonyl sulphide (COS), 0 ppmv
mercaptans, 0 ppmv carbon disulphide, and 0 ppmv sulphur dioxide .
From the above, it will be clear that the process in accordance with the present invention (Example 1) constitutes an improvement in terms of efficient removal of sulphur-containing contaminants when compared to comparative Example 2.

Claims

C L A I M S
1. A process for removing sulphur-containing
contaminants, including hydrogen sulphide, from a gas stream comprising the steps of:
(a) subjecting the gas stream to an oxidation treatment; (b) extracting heat from the gas stream as obtained in step (a) ;
(c) reacting hydrogen sulphide present in the cooled gas stream as obtained in step (b) with sulphur dioxide at elevated temperature and in the presence of a catalyst to obtain a gas stream which comprises sulphur and water;
(d) separating sulphur from the gas stream obtained in step (c) , thereby obtaining a hydrogen sulphide-lean gas stream;
(e) subjecting at least part of the hydrogen sulphide- lean gas stream as obtained in step (d) to an oxidation treatment to obtain a sulphur dioxide-enriched gas stream;
(f) extracting heat from the sulphur dioxide-enriched gas stream as obtained in step (e) ;
(g) subjecting a sulphur-containing residual hydrocarbon product to an oxidation treatment to obtain a gas stream which comprises sulphur dioxide;
(h) extracting heat from the gas stream which comprises sulphur dioxide as obtained in step (g) ;
(i) subjecting at least part of the cooled sulphur dioxide-enriched gas stream as obtained in step (f) and at least part of the cooled gas stream which comprises sulphur dioxide as obtained in step (h) to a quench process ;
(j) contacting the quenched gas stream as obtained in step (i) with an absorption solvent that absorbs sulphur dioxide to obtain a sulphur dioxide-enriched absorption solvent and a sulphur dioxide-depleted gas stream;
(k) removing sulphur dioxide from at least part of the sulphur dioxide-enriched absorption solvent as obtained in step (j) to obtain a sulphur dioxide-depleted
absorption solvent and a sulphur dioxide-enriched gas stream; and
(1) recycling at least part of the sulphur dioxide- enriched gas stream as obtained in step (k) to step (c) .
2. A process according to claim 1, wherein at least part of the sulphur dioxide-depleted absorption solvent as obtained in step (k) is recycled to step (j) .
3. A process according to claim 1 or 2, wherein in step (1) the entire sulphur dioxide- enriched gas stream as obtained in step (k) is recycled to step (c) .
4. A process according to any one of claims 1-3, wherein the oxidation treatment in steps (e) and (g) are carried out in the same oxidation unit.
5. A process according to claims 1, 2 or 4, wherein a part of the sulphur dioxide-enriched gas stream as obtained in step (k) is recycled to step (a) .
6. A process according to any one of claims 1-5, wherein prior to the oxidation treatment of step (a) the gas stream has been subjected to a hydrogen sulphide
enrichment treatment.
7. A process according to any one of claims 1-6, wherein at least part of the sulphur dioxide-depleted gas stream as obtained in step (j) is contacted with an absorption solvent to absorb carbon dioxide to obtain a carbon dioxide-enriched absorption solvent and a sulphur
dioxide-depleted gas stream which is lean in carbon dioxide, and carbon dioxide is removed from at least part of the carbon dioxide-enriched absorption solvent to obtain a carbon dioxide-depleted absorption solvent and a carbon dioxide-enriched gas stream.
8. A process according to any one of claims 1-7, wherein step (d) is carried out by cooling the effluent obtained in step (c) to condense and separate sulphur, thereby obtaining the hydrogen sulphide-depleted gas stream.
9. A process according to any one of claims 1-8, wherein the sulphur-containing residual hydrocarbon product in step (g) is a product from a thermal gasoil unit having a V50 (viscosity at 50 °C) in the range of from 30-50 cSt, a product from a catalytic cracking unit, suitably in slurry form, having a V50 in the range of from 20-50 cSt, or a heavy residue containing up to 10 wt% organic sulphur, based on total heavy residue.
10. A process according to any one of claims 1-9, wherein the entire gas stream as obtained in step (h) is quenched in step ( i ) .
11. A process according to any one of claims 1-10, wherein the molar ratio of hydrogen sulphide to sulphur dioxide in step (c) is in the range of from 2:1-5:1.
12. A process according to any one of claims 1-11, wherein the adsorption solvent in step (j) comprises water and a water-soluble amine absorbent having at least one amine group with a pKa value greater than about 7 and at least one other amine group with a pKa value less than
6.5, wherein the at least one amine group with a pKa value greater than about 7 irreversibly absorbs sulphur dioxide in salt form to render the amine absorbent non¬ volatile, and wherein the at least one other amine group with a pKa value less than 6.5 reversibly absorbs sulphur dioxide to saturate the absorption solvent with sulphur dioxide against a partial pressure of sulphur dioxide of no more than about 1 atmosphere at 25 °C.
13. A process according to claim 12, wherein the amine absorbent is a diamine having the general formula:
R2R5NR1NR3R4 wherein Ri is an alkylene group having 1 to 3 carbon atoms, R2, R3, R and R5 are the same or different and each represent a hydrogen atom, a lower alkyl group having 1 to 8 carbon atoms or a lower
hydroxy-alkyl group having 2 to 8 carbon atoms, or any of R2, R3, R and R5 form together with the nitrogen atoms to which they are attached a 6-membered ring.
PCT/EP2011/074179 2010-12-31 2011-12-28 Process for removing sulphur-containing contaminants from a gas stream WO2012089776A1 (en)

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