Classifications

• • 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
  • B01D53/75—Multi-step processes
• • 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
• • 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
  • B01D53/1406—Multiple stage absorption
• • 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
• • 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
• • 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
  • C01B17/0408—Pretreatment of the hydrogen sulfide containing gases

Definitions

• This invention relates to a method for purifying gas, more particularly hydrocarbon gas, such as natural gas, which is contaminated with sulfur compounds in the form of H 2 S and mercaptans, as well as with CO 2 . More particularly, the invention comprises a method for converting mercaptans to H2S in, and removing CO2, absorbed hydrocarbons and aromatics from H2S containing gas to form elemental sulfur from H2S.
• H2S sulfur-containing gases
• SO2 sulfur-containing gases
• the H2S content should be reduced to a value lower than 5 mg/Nm3. Requirements are also set with regard to the maximum content of other sulfur compounds. From the prior art a large number of methods are known by which the amount of sulfur compounds in a gas, such as natural gas, can be reduced.
• the following process route is usually employed.
• a first step the gas to be treated is purified, whereby sulfur- containing components are removed from the gas, followed by a recovery of sulfur from these sulfur-containing components, whereafter a sulfur purification step of the residual gas ensues.
• this sulfur purification step it is attempted to recover the last percents of sulfur before the residual gas is emitted via the stack into the atmosphere.
• aqueous solvents absorption agents
• chemical solvent processes include the so-called amine processes in which use is made of aqueous solutions of alkanolamines or of potassium carbonate solutions.
• DMPEG polyethylene glycol
• NMP N-Methyl-Pyrrolidone
• Rectisol methanol
• the Sulfinol process is well-known. In this process, use is made of a mixture of an alkanolamine with sulfolane dissolved in a small amount of water.
• an absorbing device and a regenerator are used.
• the sulfur-containing components are chemically or physically bound to the solvent.
• pressure reduction and/or temperature increase in the regenerator the sulfur-containing components are desorbed from the solvent, whereafter the solvent can be re-used.
• CO2 is wholly or partly removed, depending on the solvent chosen. The removed sulfur compounds together with the CO2 are routed from the regenerator to a sulfur recovery plant in order to recover the sulfur from H2S and other sulfur compounds .
• a frequently used process for recovering sulfur from the thus obtained sulfur compounds, in particular H2S, is the Claus process. This process is described in detail in H.G. Paskall, "Capability of the modified Claus process", Western Research Development, Calgary, Alberta, Canada, 1979.
• the Claus process consists of a thermal step followed by typically 2 or 3 reactor steps. In the thermal step one-third of the H2S is combusted to SO2 according to the reaction
• the efficiency of the Claus process is dependent on a number of factors. For instance, the equilibrium of the Claus reaction shifts in the direction of H2S with an increasing water content in the gas.
• the efficiency of the sulfur recovery plant can be increased by the use of a tail gas sulfur recovery plant; known processes are the SUPERCLAUSTM process and the SCOT process.
• the SUPERCLAUSTM process use is made of a catalyst as described in European patent applications nos. 242.920 and 409.353, as well as in international patent application WO-A 95.07856, where this catalyst is employed in a third or fourth reactor stage as described inter alia in "Hydrocarbon Processing" April 1989, pp. 40-42.
• the last residues of H2S present in the process gas stream are selectively oxidized to elemental sulfur according to the reaction
• the gas fed to the Claus plant may sometimes contain large amounts of CO2, for instance up to 98.5%, which has a highly adverse effect on the flame temperature in the thermal step.
• a large amount of CO2 can give rise to instability of the flame and moreover the efficiency in the thermal step will decrease, so that the total efficiency of the Claus plant decreases.
• the gas may contain large amounts of hydrocarbons. When sulfur-containing gas is processed in an oil refinery gas the hydrocarbon content will generally be low, mostly ⁇ 2% by volume.
• Soot formation gives rise to clogging problems in the catalytic reactors of a Claus plant, in particular the first reactor. Also, the ratio between the oxygen requirement for the conversion of H2S to sulfur and the oxygen requirement for the combustion of the hydrocarbons and aromatics can take such values that the Claus process can no longer be properly controlled. These problems are known in the industry.
• An object of the present invention is inter alia to provide a method for the removal of sulfur-containing contaminants in the form of mercaptans and H 2 S from hydrocarbon gas, such as natural gas, which may also contain CO 2 and higher aliphatic and aromatic hydrocarbons, and the recovery of elemental sulfur, in which method the disadvantages outlined above do not occur. More particularly, it is an object of the invention to provide a method whereby the tail gases contain no or only very few harmful substances, so that these can be discharged into the atmosphere without any objection. It is also an object of the invention to provide a method whereby the sulfur-containing contaminants are recovered to a large extent as elemental sulfur, for instance up to an amount of more than 90%, more particularly more than 95%.
• the present invention provides a simple method for purifying contaminated hydrocarbon gas with recovery of sulfur, according to which method in a first absorption step the sulfur-containing contaminants are removed from the gas, to form on the one hand a purified gas stream and on the other a sour gas, which sour gas is hydrogenated in order to convert the greater part of the mercaptans to H 2 S, whereafter the hydrogenated sour gas is fed to a second absorption step in which the sour gas is separated into an H 2 S-enriched first gas stream, which is fed to a Claus plant, followed by a selective oxidation step of H S to elemental sulfur in the tail gas, and an H 2 S-reduced second gas stream, which second gas stream is combusted.
• the sour gas is first passed through a hydrogenation reactor, whereby the mercaptans in the gas are converted to H2S with the aid of supplied hydrogen. Thereafter the sour gas is separated in a so-called enrichment unit in two other gases, viz. an H2S-rich gas and a C ⁇ 2-rich gas, which contains the greater part of the CO2, hydrocarbons and aromatics.
• the C02 ⁇ rich gas with the hydrocarbons and aromatics present allows of proper burning in an afterburning plant.
• the heat released in this afterburning can be employed very usefully, for instance for generating steam.
• the H2S-rich gas is passed to the sulfur recovery plant.
• the H2S concentration can easily be increased 2 to 6 times.
• This H2S-rich gas can be processed very well in a Claus plant, the great advantage being that the absence of a large part of the CO2, hydrocarbons and aromatics does not cause any additional gas throughput in the plant upon combustion.
• the Claus plant can be made of much smaller design, while moreover much higher sulfur recovery efficiencies are achieved.
• the tail gas obtained from the Claus plant is further processed in a tail gas recovery plant on the basis of selective oxidation of the sulfur compounds to elemental sulfur.
• the tail gas recovery plant is preferably the SUPERCLAUS reactor stage.
• the off-gases from this tail gas desulfurization unit are burned in an afterburner.
• the heat released can be employed usefully for generating steam.
• the sour gas is passed with hydrogen over a hydrogenation reactor containing a sulfided group 6 and/or group 8 metal catalyst supported on a carrier.
• alumina is used with this kind of catalysts, since this material, in addition to the desired thermal stability, also enables a good dispersion of the active component.
• catalytically active material preferably a combination of cobalt and molybdenum is used.
• An alternative method of preventing COS formation, but without water vapor being supplied is the installation of a pre-absorber before the hydrogenation stage, whereby the H 2 S concentration in the gas is reduced to less than a quarter.
• the gas from this pre-absorber is then passed through a hydrogenation reactor, whereby all mercaptans are converted to H 2 S with the aid of the added hydrogen.
• the residual H S is then selectively absorbed in a second absorber, of the second absorption step. On balance, the same H 2 S enrichment is then obtained as with a single absorber.
• the first absorption step is carried out using a chemical, physical or chemical/physical absorption agent which removes all contaminants from the natural gas.
• this is an absorption agent which is based on sulfolane, in combination with a secondary and/or tertiary amine.
• absorption agent which is based on sulfolane, in combination with a secondary and/or tertiary amine.
• the absorption is based on a system whereby the contaminants are absorbed in the solvent in a first column, whereafter, when the solvent is loaded with contaminants, this solvent is regenerated in a second column, for instance through heating and/or through pressure reduction.
• the temperature at which the absorption takes place is to a large extent dependent on the solvent and the pressure used. At the current pressures for natural gas of 2 to 100 bar, the absorption temperature is generally 15 to 50°C, although outside these ranges good results can be obtained as well.
• the natural gas is preferably purified so as to meet the pipeline specifications, which means that in general not more than 10, more particularly not more than 5 ppm of H 2 S may be present.
• the gas stream emanating from the first absorption/desorption which contains the greater part of the contaminants such as H 2 S, aromatics, hydrocarbons and mercaptans, as well as CO 2 , is then hydrogenated in the presence of a suitable catalyst such as Co/Mo on alumina, and hydrogen.
• a suitable catalyst such as Co/Mo on alumina, and hydrogen.
• the gas stream should be heated from the absorption/desorption temperature of about 40°C to the temperature of 200 to 300°C required for the hydrogenation.
• This heating preferably occurs indirectly and not with a burner arranged in the gas stream, as is conventional.
• the disadvantage of direct heating is that direct heating in this case gives rise to substantial soot formation, which can lead to fouling and clogging in the hydrogenation.
• measures can be taken to reduce COS formation.
• the hydrogenated gas is split into an H 2 S-enriched gas and an H2S-reduced gas.
• This absorption preferably occurs using a solvent based on a secondary or tertiary amine, more particularly with an aqueous solution of methyldiethylamine, optionally in combination with an activator therefor, or with a hindered tertiary amine.
• a solvent based on a secondary or tertiary amine more particularly with an aqueous solution of methyldiethylamine, optionally in combination with an activator therefor, or with a hindered tertiary amine.
• MDEA process UCARSOL
• FLEXSORB-SE a hindered tertiary amine
• the manner of operating such processes is comparable to the first absorption stage.
• the extent of enrichment is preferably at least 2 to 6 times or more, which is partly dependent on the initial concentration of H 2 S.
• the extent of enrichment can be set through an appropriate choice of the
• the H 2 S-enriched gas is fed to the thermal stage of a
• the tail gas from the Claus plant which still contains residual sulfur compounds is fed, if desired after supplemental hydrogenation, to a tail gas processing apparatus wherein through selective oxidation of the sulfur compounds, elemental sulfur is formed, which is separated in a plant suitable for that purpose, for instance as described in
• the selective oxidation is preferably carried out in the presence of a catalyst which selectively converts sulfur compounds to elemental sulfur, for instance the catalysts described in the European and international patent applications mentioned earlier.
• a catalyst which selectively converts sulfur compounds to elemental sulfur for instance the catalysts described in the European and international patent applications mentioned earlier.
• These publications, whose content is incorporated herein by reference, also indicate the most suitable process conditions, such as temperature and pressure. In general, however, the pressure is not critical, and temperatures may be between the dew point of sulfur and about 300°C, more particularly less than 250°C.
• the invention will now be elucidated with reference to two drawings in which in the form of a block diagram the method according to the invention is described.
• the sour gas emanating from a first absorption unit (not drawn), in which contaminated natural gas has been separated into, on the one hand, a gas stream with the desired specification and, on the other, the sour gas, is brought in line 1 to the desired hydrogenation temperature, under addition of hydrogen and/or carbon monoxide via line 2, before being passed into the hydrogenation reactor 3. Also, via line 6 water vapor is fed into line 1 to suppress the formation of carbonyl sulfide in the hydrogenation reactor 3.
• the mercaptans and other organic sulfur compounds present in the gas are converted to H2S.
• the gas from the hydrogenation reactor 3, after cooling, is passed via line 7 to an absorber of a selective absorption/regeneration plant. In this cooling, the water vapor supplied is condensed and via an evaporator 5 recirculated to the hydrogenation reactor 3.
• the unabsorbed components of the gas consisting of principally carbon dioxide, hydrocarbons (including aromatics) and a low content of H2S, are directed via line 8 to an afterburner 18 before the gas is discharged via stack 19.
• the H2S-rich gas mixture coming from the regeneration section of the absorption/regeneration plant 9 is supplied via line 10 to the Claus plant 11, in which the greater part of the sulfur compounds is converted to elemental sulfur which is discharged via line 12.
• the tail gas is often passed via line 13 to a tail gas sulfur removal stage 14.
• This sulfur removal stage can be a known sulfur removal process, such as, for instance, a dry bed oxidation stage, an absorption stage, or a liquid oxidation stage.
• the required air for the oxidation is supplied via line 15.
• the sulfur formed is discharged via line 16.
• the gas is then passed via line 17 to the afterburner 18 before the gas is discharged via stack 19.
• the sour gas coming from a first absorption unit (not drawn) in which contaminated natural gas has been split into, on the one hand, a gas stream with the desired specification and, on the other, the sour gas, is passed via line 1 to a pre-absorber 2 of an absorption/regeneration plant, further consisting of a second absorber and a regenerator 9.
• the gas coming from the pre-absorber 2 is passed via line 3 to the hydrogenation reactor 5 and brought to the desired hydrogenation temperature under addition of hydrogen and/or carbon monoxide via line 4.
• the mercaptans and other organic sulfur compounds present in the gas are converted to H 2 S.
• the gas from the hydrogenation reactor after cooling, is passed via line 6 to a second absorber.
• the unabsorbed components of the gas substantially consisting of carbon dioxide, hydrocarbons (including aromatics) and a minimal amount of H 2 S, are routed via line 8 to the afterburner 21 before the gas is discharged via stack 22.
• the regenerated absorption agent is recirculated over the second absorber 7 and then returned via line 11 to the pre-absorber 2. From the pre-absorber 2 the absorbent loaded with H 2 S and CO 2 is returned via line 12 to regenerator 9.
• the tail gas is passed via line 16 to a tail gas sulfur removal stage 18.
• This sulfur removal stage can be a known sulfur removal process such as a dry bed oxidation stage, an absorption stage or a liquid oxidation stage.
• the required air for the oxidation is supplied via line 17.
• the sulfur formed is discharged via line 19.
• the gas is then passed via line 20 to the afterburner 21 before the gas is discharged via stack 22.
• the invention is elucidated in and by the following non-limiting example.
• An amount of sour gas of 15545 Nm 3 /h coming from the regenerator of a gas purification plant had the following composition at 40°C and a pressure of 1.70 bar abs.
• Aromatics (Benzene, Toluene, Xylene)
• sour gas was supplied 3000 Nm ⁇ /h reducing gas containing hydrogen and carbon monoxide and then heated to 205°C to hydrogenate all mercaptans present to H2S in the hydrogenation reactor which contains a sulfided group 6 and/or group 8 metal catalyst, in this case a Co-Mo catalyst. Also supplied to this sour gas was 7000 Nm 3 /h water vapor to suppress COS formation in the hydrogenation reactor.
• the temperature of the gas from the reactor was 226°C.
• the sour gas was then cooled to 46°C and the water vapor contained therein was condensed. This condensation was recirculated, via an evaporator, to the sour gas which is passed to the hydrogenation reactor.
• the amount of the gas coming from the hydrogenation reactor, after condensation of the water vapor supplied, was 18545 Nm 3 /h and had the following composition
• Aromatics (Benzene, Toluene, Xylene)
• the amount of product gas (C02 _ rich gas) from the absorber was 15680 Nm 3 /h with the following composition:
• Aromatics (Benzene, Toluene, Xylene)
• this gas was passed to the stack.
• H2S/CO2 gas mixture H2S-rich gas
• This H2S/CO2 gas mixture amounted to 2870 Nm 3 /h and had the following composition at 40°C and 1.7 bar abs.
• the inlet temperature of the selective oxidation reactor was 220 °C and the outlet temperature was 292 °C.
• the selective oxidation reactor was filled with catalyst as described in European patents 242.920 and 409.353 and in the International patent application WO-A 95/07856.
• the sulfur formed in the sulfur recovery plant was condensed after each stage and discharged.
• the exiting inert gas was passed via an afterburning to the stack.
• the amount of sulfur was 2094 kg/h.
• the total desulfurization efficiency based on the original sour gas, which contained 9.0 vol.% H2S, was 97.7%.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Environmental & Geological Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Analytical Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Treating Waste Gases (AREA)
• Industrial Gases (AREA)
• Gas Separation By Absorption (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19762183

Family Applications (1)

Country Status (10)

Cited By (5)

Families Citing this family (6)

Citations (4)

• 1996
  • 1996-01-19 NL NL1002134A patent/NL1002134C2/nl not_active IP Right Cessation
• 1997
  • 1997-01-16 ZA ZA97370A patent/ZA97370B/xx unknown
  • 1997-01-17 TW TW086100467A patent/TW381043B/zh not_active IP Right Cessation
  • 1997-01-20 CA CA002241790A patent/CA2241790A1/en not_active Abandoned
  • 1997-01-20 KR KR1019980705510A patent/KR19990077361A/ko not_active Application Discontinuation
  • 1997-01-20 JP JP9525885A patent/JP2000503293A/ja active Pending
  • 1997-01-20 EP EP97900807A patent/EP0880395A1/en not_active Ceased
  • 1997-01-20 CN CN97191710A patent/CN1208360A/zh active Pending
  • 1997-01-20 WO PCT/NL1997/000018 patent/WO1997026069A1/en not_active Application Discontinuation
  • 1997-01-20 AU AU13213/97A patent/AU1321397A/en not_active Abandoned

Patent Citations (4)

Also Published As

Similar Documents

Legal Events