Patent Application
20240001288
The present invention is in the field of carbon dioxide (CO2) recovery and purification. In particular, the invention relates to methods and apparatus for desulfurization of CO2-containing streams for carbon capture and storage (“CCS”).
There are many examples in the art of methods for removing sulfur-based compounds such as hydrogen sulfide (H2S), carbonyl sulfide (COS), mercaptans (i.e., thiols), carbon disulfide (CS2) and/or sulfur oxides (SOx), from crude CO2 or other CO2-containing gases.
GB871750 is concerned with methods in which H2S is removed from CO2-containing gases generated either by combustion of hydrocarbons or in blast furnaces. Such gases usually contain up to 400 ppm H2S. Since the CO2 is intended primarily for use in the synthesis of urea, the amount of H2S must be reduced to no more than 2 ppm. The reference teaches that the amount of H2S in the CO2 gas is reduced to the necessary levels by passing the gas through a layer of zeolite that has been activated by heating to remove water of crystallization. Activation of the zeolite by driving off this water creates interstitial voids having dimensions that enable adsorption of H2S. The gas feed to the zeolite can be dried or undried and the zeolite may be regenerated thermally using a heated regeneration gas.
U.S. Pat. No. 5,674,463A is concerned with methods for purifying CO2 obtained from natural sources, such as natural gas, or produced in industry, particularly by the combustion of hydrocarbon products, for use in applications requiring high purity CO2 such as the manufacture of foodstuffs or medical products. The reference teaches that COS and H2S are removed from CO2 gas by first contacting the CO2 with water vapor in the presence of a hydrolysis catalyst such as activated alumina to convert COS in the gas to H2S, and then converting H2S in the resultant gas using an oxidation catalyst such as iron oxide to form elemental sulfur and metal sulfides which are then removed from the gas. Any residual sulfur compounds may be removed by contacting the remaining gas with copper oxide, zinc oxide or mixed copper-zinc oxides.
US2012/0012000A is concerned primarily with separating a sour (i.e., sulfur-containing) syngas comprising hydrogen (H2) and carbon monoxide (CO), together with H2S and CO2, obtained from gasification of a solid or liquid carbonaceous feedstock into at least a CO2 product stream suitable for geological storage, a syngas (H2/CO) product stream suitable for use in a chemical plant or refinery or as a fuel for a gas turbine, and a H2S-enriched stream which can be further processed in, for example, a Claus plant or other suitable sulfur recovery system. The reference teaches introducing the sour synthesis gas into pressure swing adsorption (PSA) system which separates the feed gas into the syngas product stream and a stream enriched in CO2 and H2S, or separates a H2S-depleted feed gas (produced in sour-PSA system) into the syngas product stream and a CO2-enriched gas stream. The sour-PSA system contains an H2S-selective adsorbent such silica gel, activated carbon or molecular sieve.
WO2016/075109A discloses a process for removing H2S equivalents such as COS and/or CS2 by adsorption from Claus tail gas comprising CO2. The tail gas comprising H2S equivalents and CO2 is fed to an adsorption system where it is contacted with an alumina-based adsorbent material to produce a first product gas that is CO2-rich. The adsorbent material is regenerated with a purge gas containing steam to recover the adsorbed impurities in the form of H2S and obtain a second product gas comprising H2S which is recycled to the Claus unit. Optionally, the purged adsorbent material is then dried.
However, there remains a need for a new methods and apparatus for the desulfurization of CO2-containing streams, particularly where the CO2 is intended for CCS in view of the low maximum limit (e.g. no more than 100 ppm in total) for sulfur-containing compounds.
The present invention concerns a method for desulfurization of CO2-containing gas streams.
Such streams are often by-products of crude oil refining or other industrial processes involving physical and chemical gas treatment units used in refineries, natural gas processing plants and gasification or synthesis gas plants, and may be referred to as “acid” gas streams. These “acid” gases will comprise H2S as an impurity, often (but not always) together with one or more of CS2, COS and mercaptans.
Such gases are typically treated in a Claus process which recovers elemental sulfur from gaseous H2S in the presence of O2 according to the following overall reactions:
2H2S+3O2→2SO2+2H2O
4H2S+2SO2→3S2+4H2O
The Claus process may involve either a thermal process or a catalytic process but usually involves a combination of both thermal and catalytic processes to boost overall yields of sulfur. In the thermal process, gaseous H2S reacts in a sub-stoichiometric combustion at temperatures above 850° C. to produce elemental sulfur and water. In the catalytic process, gaseous H2S reacts with SO2 over a catalyst such as activated aluminum (Ill) or titanium (IV) oxide to produce further elemental sulfur and water.
Most commercial Claus processes will involve a thermal stage followed by one or more catalytic stages, with sulfur removed between stages by condenser(s). The first stage usually operates at about 315° C. to about 330° C. to help hydrolyze COS and CS2. Subsequent stages typically operate at lower temperatures to increase catalytic conversion although above the dew point of sulfur. Thus, a second stage may operate at about 240° C., while a third stage may operate at about 200° C. The O2 may be provided to the Claus process in the form of air, i.e., an “air-Claus” process, or in the form of pure O2 or O2-enriched air, i.e., an “oxy-Claus” process.
The inventors have realized that any sulfur-containing compounds that are not H2S such as COS, CS2 and mercaptans from the original “acid” gas, together with SO2 from the Claus process, may be removed from the tail gas by hydrogenation to form H2S which may then then removed together with the residual H2S from the Claus process, either by physical separation or by chemical reaction with at least one solid metal oxide to form metal sulfide(s) and subsequent oxidative regeneration to produce purified CO2 and a recycle gas comprising at least one sulfur-containing compound which is recycled to the Claus process.
Physical separation of H2S and any other sulfur-containing compounds from CO2 may be achieved either by:
The H2S and any other sulfur-containing compounds may alternatively be removed from impure CO2 gas by reaction with a bed comprising at least one solid metal oxide, e.g., zinc oxide (ZnO), to convert the metal oxide(s) into metal sulfide(s), e.g., zinc sulfide (ZnS). The metal oxide(s) may be regenerated by oxidation using a regeneration gas comprising O2 to drive the sulfur from the bed as sulfur dioxide (SO2).
Thus, according to a first aspect of the present invention, there is provided a method for desulfurization of crude carbon dioxide (CO2) gas comprising hydrogen sulfide (H2S) and optionally at least one other sulfur-containing impurity, said method comprising:
According to a second aspect of the present invention, there is provided apparatus for desulfurizing crude CO2 gas comprising H2S and optionally at least one other sulfur-containing impurity, said apparatus comprising:
and
wherein the second outlet of said purification unit is in fluid communication with said Claus unit.
The term “crude CO2” refers to a gas mixture comprising at least about 50 mol. % CO2, e.g., from about 50 mol. % to about 80 mol. % CO2. The crude CO2 is a gaseous mixture comprising H2S and typically water but, in some embodiments, other components, e.g., one or more other sulfur-containing compounds, may be present.
The term “sulfur-containing compound” refers to a compound containing at least one sulfur atom. Examples of sulfur-containing compounds include H2S, COS, CS2, SO2 and mercaptans (or thiols). H2S will normally be present in the crude CO2 feed and is also produced in the hydrogenation step of the present invention. COS and/or CS2 may be present in the crude CO2 feed but may also be produced in the Claus process. SO2 will not typically be present in the crude CO2 feed but is produced in the Claus process. Mercaptans are not produced in the process of the present invention so, if present in the CO2, would come in with the crude CO2 feed gas.
The term “sulfur-containing impurity” refers to an individual sulfur-containing compound present in a gas at an impurity level, e.g., no more than 5 mol. % (or 50000 ppm), and usually no more than 3 mol. % (or 30000 ppm).
The term “impure CO2” refers to a CO2-containing gas having a higher proportion (in terms of mole fraction) of CO2 than the crude CO2 from which it is derived. Such gases typically comprise at least about 80 mol. % CO2, e.g., from 80 mol. % to about 95 mol. % CO2.
The term “physical separation” refers to a process in which at least one sulfur-containing component of a fluid mixture is removed from the other component(s) of the mixture without chemical change, reaction or conversion. In other words, the component(s) is/are separated from the mixture “as is”, i.e., in the form that they are present in the fluid mixture.
The term “oxidative regeneration” refers to a process in which solid metal oxide(s) are regenerated from solid metal sulfide(s) by oxidation, typically using a regeneration gas comprising O2.
The term “purified CO2” refers to a CO2-containing gas that has a higher proportion (in terms of mole fraction) of CO2 than the impure CO2 from which it is derived. Such gases typically comprise at least about 95 mol. % CO2, e.g., from about 95 mol. % to 100 mol. % CO2, and typically no more than 500 ppm, and possibly no more than 100 ppm in total of the sulfur-containing compound(s).
The term “further purified CO2” refers to a CO2-containing gas that has a higher proportion (in terms of mole fraction) of CO2 than the purified CO2 from which it is derived. Such gases typically comprise at least about 99 mol. % CO2, e.g., from about 99 mol. % to 100 mol. % CO2, and typically no more than 100 ppm in total of the sulfur-containing compound(s).
An “H2S-enriched” gas is a gas that contains a higher proportion (in terms of mole fraction) of H2S than the H2S-containing gas from which it is derived.
An “H2S-depleted” gas is a gas that contains a lower proportion (in terms of mole fraction) of H2S than the H2S-containing gas from which it is derived. The term embraces (although is not limited to) gases that contain no H2S.
A “sulfur-selective adsorbent material” is a material that adsorbs sulfur-containing compounds in preference to at least one other component in a gas mixture, i.e., has a higher affinity for sulfur-containing compounds than for the other component(s) of the gas mixture.
“Selective adsorption” is a process in which the sulfur-containing component(s) being removed from the impure CO2 are adsorbed selectively on to an adsorbent and subsequently recovered (in the same chemical form) by desorption using a regeneration gas.
A “water-selective adsorbent material” is a material that adsorbs water in preference to at least one other component in a gas mixture, i.e., has a higher affinity for water than the other component(s).
A “bed” contains particles of either selectively adsorbent material or solid metal oxide(s), or both types of particles. The bed of particles is typically a packed bed but may be a fluidized bed. In a packed bed comprising both types of particles, the particles are typically in separate layers.
The term “downstream” in the context of a selective adsorption unit or reactor refers to a relative location when the unit or reactor is on-feed. The term “upstream” should be interpreted accordingly.
The term “selective amine absorption” refer to a separation or purification process using an amine that selectively (although not necessarily exclusively) absorbs a particular acid gas component, e.g., H2S, in a gas mixture, e.g., H2S-enriched CO2 tail gas.
The term “non-selective amine absorption” refers to a separation or purification process using an amine that absorbs a particular acid gas component, e.g., H2S, in a gas mixture, e.g., H2S-depleted CO2 tail gas, possibly in combination with another acid gas component, e.g., CO2.
The term “non-condensable gas” refers to a gas that is not condensable under the conditions of the present invention. Examples of non-condensable gases include H2, N2 and O2 and noble gases.
A “CO2 purification unit” (i.e., a “CPU”) is a unit which purifies (or further purifies) CO2 by partial condensation with phase separation. Such a unit typically comprises a heat exchanger to cool and partially condense the gas to be purified and one or more, e.g., two, phase separators in series to separate a condensed phase from a vapour phase.
A “distillation unit” is a unit which purifies (or further purifies) CO2 by distillation. Such a unit typically comprises a heat exchanger to cool and optionally at least partially condense the gas to be purified and at least one distillation column. The column may contain trays or may be packed with loose and/or structured packing to increase the vapour/liquid contact surface area within the column.
Preferred embodiments of the present invention will now be described with reference to the drawings in which:
The first aspect of the present invention is a method for desulfurization of crude CO2 gas comprising H2S and optionally at least one other sulfur-containing impurity. The method comprises feeding crude CO2 gas comprising H2S to a Claus process to convert H2S in the presence of O2 gas into elemental sulfur and produce Claus tail-gas comprising CO2, residual H2S and at least one sulfur-containing impurity. The Claus tail-gas is fed to a hydrogenation process to convert the other sulfur-containing impurity (or impurities) into H2S in the presence of H2 and produce H2S-enriched CO2 tail-gas. The H2S-enriched CO2 tail-gas is cooled to knock-out water and the resultant cooled H2S-enriched tail gas (or an impure CO2 gas comprising H2S derived therefrom) is compressed to produce compressed impure CO2 gas comprising H2S. H2S and any other sulfur-containing impurities are removed from the compressed gas by physical separation or by chemical reaction with solid metal oxide(s) to form solid metal sulfide(s) which are converted back to the metal oxide(s) by oxidative regeneration to produce purified CO2 and a first recycle gas comprising at least one sulfur-containing compound. The first recycle gas is recycled to said Claus process to convert the at least one sulfur-containing compound into elemental sulfur.
Embodiments of the present invention improve the recovery and/or purity of CO2 from crude CO2 comprising H2S and optionally any other sulfur-containing impurities.
The Claus process may be a conventional “air-Claus” process or an “oxy-Claus” process as described above but in either case typically comprises a thermal stage and at least one, e.g., from one to four, preferably two or three, catalytic stages. Recycle gas(es) may be recycled either to the feed to the Claus process or to an interstage location, i.e., between two stages within the process, or both.
The Claus process may alternatively be a SUPERCLAUS® process or a EUROCLAUS® process, or a combination of the two Claus processes.
The SUPERCLAUS® process consists of a thermal stage followed by a minimum three catalytic reaction stages, with sulfur removed between stages by condensers. The first reactors are filled with standard Claus catalyst such as activated alumina, promoted alumina and/or titania (TiO2), while the final reactor is filled with a selective oxidation catalyst such as iron oxide and/or chromium oxide (or other metal oxides) on alpha alumina or silica. In the thermal stage, the acid gas is burned with a sub-stoichiometric amount of controlled combustion air (or pure O2 or O2-enriched air), such that the tail gas leaving the last Claus reactor contains typically 0.8 to 1.0 vol. % H2S. The selective oxidation catalyst in the final reactor oxidizes the H2S to sulfur at an efficiency of more than 85%. A third Claus reactor stage could be installed upstream of the selective oxidation reactor if a sulfur recovery rate of more than 99% is required.
The EUROCLAUS® process consists of a thermal stage followed by three or four catalytic reaction stages, with sulfur removed between stages by condensers. The final Claus reactor is filled with a layer of hydrogenation catalyst such as CoMo catalyst (cobalt & molybdenum oxides on alumina), followed by a reactor filled with selective oxidation catalyst such as iron oxide and/or chromium oxide (or other metal oxides) on alpha alumina or silica. In the thermal stage, the acid gas is burned with a sub-stoichiometric amount of controlled combustion air, and the tail gas leaving the last Claus reaction typically contains 0.8 to 1.0 vol. % H2S and 100 to 200 ppmv SO2. This low SO2 content is obtained with a hydrogenation catalyst that converts SO2 to H2S in the last Claus reactor. The selective oxidation catalyst in the final reactor oxidizes the H2S to sulfur at an efficiency of more than 85%. Total sulfur recovery efficiency up to 99.3% can be obtained with three reactor stages, and up to 99.5% can be achieved with four stages.
The crude CO2 gas may be fed to the Claus process at a temperature from about 10° C. to about 70° C., e.g., about 45° C., and at a pressure in a range from about 0.3 bar gauge (g) to about 30 bar g, e.g., from about 0.3 bar g to about 1.8 bar g, e.g., about 0.9 bar g.
The hydrogenation process requires H2 as the reducing gas. The H2 may generated in a H2 generation process such as the partial oxidation of natural gas with sub-stoichiometric air/oxygen in a reducing gas generator, and then fed to the hydrogenation process. However, the demand for fresh H2, or “make-up” H2, from the H2 generation process may be reduced or even eliminated entirely by recycling H2 from another point in the process (see below).
The Claus tail-gas may be fed to the hydrogenation process at a temperature in a range from about 120° C. to about 200° C., e.g., about 130° C., and at a pressure in a range from about 0.2 bar g to about 30 bar g, e.g., from about 0.2 bar g to about 1.8 bar g, e.g., about 0.3 bar g. The pressure and/or temperature of the Claus tail gas may be adjusted as required using conventional means prior to being fed to the hydrogenation process although, in preferred embodiments, the tail gas is fed to the hydrogenation process without adjustment in this way.
The H2S-enriched CO2 tail gas from the hydrogenation process is cooled. Any suitable cooling process may be used but, in preferred embodiments, the H2S-enriched CO2 tail gas is quenched by direct contact with liquid water. After removal of condensed water, the cooled H2S-enriched CO2 tail gas is compressed to form compressed impure CO2 gas comprising H2S.
The cooled H2S-enriched CO2 tail gas may be fed to a compression unit at a temperature in a range from about 10° C. to about 70° C., e.g., about 45° C., and at a pressure in a range from about 0.3 bar g to about 1.8 bar g, e.g., about 1 bar g. The compression unit compresses the gas to a pressure in a range from about 1 bar g to about 120 bar g, e.g., about 30 bar g.
The content of H2S and any other sulfur-containing impurities in the compressed impure CO2 gas is reduced significantly, in some embodiments to a level below 100 ppm, either by physical separation or by chemical reaction with at least one solid metal oxide to form solid metal sulfide(s) and subsequent oxidative regeneration to produce purified CO2, together with a first recycle gas comprising at least one sulfur-containing compound which is recycled to the Claus process.
Physical separation may be by selective adsorption or by distillation and/or partial condensation with phase separation.
In embodiments using selective adsorption, the method involves removing H2S and any other sulfur-containing compounds in the compressed impure CO2 gas by adsorption on a bed of at least one adsorbent material selective for sulfur-compounds in a selective adsorption unit to produce the purified CO2 and, after desorption, a spent regeneration gas comprising H2S and any other sulfur-containing compounds from the compressed impure CO2 gas as the first recycle gas.
Such adsorbent materials include silica gel, molecular sieves (e.g., 4A or 5A zeolites), activated alumina and activated carbons (e.g., Calgon Cu material and Cu-impregnated carbons). The sulfur-containing compounds are adsorbed reversibly on a bed of the solid selective adsorbent(s) and then desorbed, preferably once the solid adsorbent is saturated with the sulfur-containing compound(s). The adsorption process may operate any suitable cycle including PSA, vacuum swing adsorption (VSA) or temperature swing adsorption (TSA). Specific examples include TSA with silica gel; PSA or VSA with silica gel; TSA with zeolites (e.g., 4A, 5A); and TSA with Cu-impregnated carbons.
Compressed impure CO2 gas may be fed to a selective adsorption unit at a temperature in a range from about 10° C. to about 70° C., e.g., about 50° C.
The adsorbent bed of the selective adsorption unit is suitably regenerated using purified (or further purified) CO2 generated in the process. The temperature and/or pressure of the regeneration gas may be adjusted as required using conventional means depending on the temperature and/or pressure of the CO2 gas at the location at which it is removed from the process and the type of cycle being used, e.g., TSA, VSA or PSA, etc. In embodiments using solid metal oxide(s) to purify the compressed impure CO2 gas, the method comprises passing the compressed gas through a bed comprising at least one solid metal oxide in a reactor. The H2S and any other sulfur-containing impurities in the gas convert the metal oxide(s) in the bed to the corresponding metal sulfide(s), thereby removing the impurities from the gas and producing the purified CO2. The metal oxide(s) in the bed is/are regenerated oxidatively by passing a regeneration gas comprising O2 through the bed, usually in a direction countercurrent to the gas when the bed is “on feed”, which drives off the sulfur from the bed in the form of SO2. The spent regeneration gas comprising SO2 is then recycled to the Claus process as the first recycle gas.
In embodiments in which H2S is removed by chemical reaction with at least one solid metal oxide, suitable solid metal oxides include zinc (II) oxide (ZnO), iron (Ill) oxide (Fe2O3), aluminum (Ill) oxide (Al2O3) and Group II metal oxides such as calcium oxide (CaO), magnesium oxide (MgO) and barium oxide (BaO). A single metal oxide may be used but, in some embodiments, a mixture of metal oxides (i.e., a mixed metal oxide) is used. In some embodiments, the mixture of solid metal oxides comprises from about 40 wt % to about 60 wt %, e.g., about 50 wt %, of ZnO.
An example of a suitable mixed metal oxide is disclosed in U.S. Pat. No. 4,044,114 and comprises from about 20 wt % to about 85 wt %, preferably from about 25 wt % to about 80 wt %, of zinc oxide (calculated as ZnO), from about 0.9 wt % to about 50 wt % of alumina (calculated as Al2O3), and from about 2 wt % to about 45 wt % of an oxide of a Group II metal, preferably calcium (calculated as oxide) with or without additional elements.
Compressed impure CO2 gas may be fed to the reactor at a temperature in a range from about 300° C. to about 800° C., or from about 300° C. to about 700° C., e.g., from about 400 to about 550° C.
After compression, the temperature of the compressed gas may be adjusted as required using conventional means prior to being fed to the reactor containing the solid metal oxide(s).
The mixed metal oxide bed of the reactor is suitably regenerated using an oxygen-containing gas, such as purified (or further purified) CO2 generated in the process to which O2 is added in an amount in a range from about 1 to about 5 mol. %, e.g., about 2 mol. %, oxygen. The temperature and/or pressure of the regeneration gas may be adjusted as required using conventional means depending on the temperature and/or pressure of the CO2 gas at the location at which it is removed from the process.
The first recycle gas may be recycled to the Claus process at a temperature in a range from about 10° C. to about 70° C., e.g., about 50° C. and at a pressure in a range from about 0.3 bar g to 30 bar g, or from about 0.3 bar g to about 1.8 bar g, e.g., about 1 bar g. In embodiments in which the temperature and/or pressure of the first recycle gas leaving the purification process is not appropriate in view of the operating conditions of the Claus unit, then the temperature and/or the pressure of the first recycle gas will be adjusted by conventional means as appropriate.
The compressed impure CO2 gas being fed to the selective adsorption unit or to the reactor containing the solid metal oxide(s) will typically contain water. In such cases, the water may be removed by adsorption on at least one adsorbent material selective for water located downstream of either the adsorbent material(s) selective for sulfur-containing compounds or the solid metal oxides. Suitable water selective adsorbent materials include those materials identified above as sulfur-selective adsorbent materials. The water selective adsorbent material(s) may be located in the same vessel as the sulfur-selective adsorbent material(s) or metal oxides, e.g., in a separate layer, or in a separate vessel.
Alternatively, the water may be removed by absorption in a separate vessel, e.g. a glycol unit, located downstream of either the selective adsorption unit or the reactor.
Whether the sulfur-containing impurities are removed by selective adsorption or chemical reaction with solid metal oxide(s), the regeneration gas may contain a small amount of water. However, if water is present, the amount of water is not sufficient to hydrolyze any sulfur-containing compounds being driven off the bed that is being regenerated. In this regard, the regeneration gas typically comprises less than 5 mol. %, preferably less than 2 mol. %, more preferably less than 1 mol. % water. Such an amount of water would be considered in the art to be a de minimis amount.
The H2S-enriched tail gas may be fed directly to a compression unit for compression to produce the compressed impure CO2. However, in some embodiments, the method comprises recovering H2S from the H2S-enriched CO2 tail-gas by selective amine absorption to produce H2S-depleted CO2 tail-gas and recovered H2S; and recycling the recovered H2S to the Claus process to convert the recovered H2S to elemental sulfur.
The H2S-enriched CO2 tail-gas may be fed to a selective amine absorption unit at a temperature from about 10° C. to about 70° C., e.g., about 50° C. and at a pressure from about 0.05 bar g to about 30 bar g, e.g., from about 0.05 bar g to about 1.8 bar g, e.g., about 0.1 bar g.
Conventional selective amine absorption processes using, for example, methyldiethanolamine (MDEA) as the selective amine, are suitable for use in these embodiments of the present invention.
The H2S-depleted CO2 tail gas may be fed directly to a compression unit for compression to produce the compressed impure CO2. However, in some embodiments, the method comprises recovering CO2 and residual H2S from the H2S-depleted CO2 tail-gas by non-selective amine absorption to produce the impure CO2 gas comprising H2S, together with waste gas comprising CO2 and at least one non-condensable gas.
The H2S-depleted CO2 tail gas may be fed to a non-selective amine absorption unit at a temperature from about 10° C. to about 70° C., e.g., about 50° C. and at a pressure from about 0.01 bar g to about 30 bar g, e.g., from about 0.01 bar g to about 1.8 bar g, e.g., about 0.1 bar g.
Conventional non-selective amine absorption processes using, for example, monoethanolamine (MEA), activated methyldiethanolamine (aMDEA) or diethanolamine (DEA) as the non-selective amine, are suitable for use in these embodiments of the present invention.
Depending on the composition, any waste gas produced in the present invention may be vented or fed to a thermal oxidizer where it is combusted to produce a flue gas conforming to local emissions standards, and optionally steam. If the waste gas contains a significant amount of H2, then the waste gas itself may be used as a fuel or H2 may be recovered from the waste gas.
As indicated above, the purified CO2 may contain less than 100 ppm of sulfur-containing impurities in which case further purification is typically not required for CCS. However, in embodiments in which the amount of the impurities exceeds this threshold, further purification is typically required.
In embodiments where further purification is required, the method may comprise feeding the purified CO2 to a further purification process to produce further purified CO2 and a second recycle gas comprising CO2 and H2; and recycling the second recycle gas, or a H2-enriched gas derived therefrom, to the hydrogenation process. A portion of the second recycle gas, or of said H2-enriched gas derived therefrom, is typically purged to prevent a build-up of H2 (if it is in excess), or N2 and/or Ar non-condensable contaminants gas within the process.
The further purification process for further purifying CO2 may involve distillation such as the process disclosed in U.S. Ser. No. 10/254,042 and/or partial condensation with phase separation such as the process disclosed in U.S. Pat. No. 7,819,951, both of which the inventors have realized may be adapted as appropriate for integration with the present invention.
Both distillation and partial condensation of CO2 require a temperature in a range from the critical temperature of CO2 (i.e., about +31° C.) to the triple point temperature of CO2 (i.e., about −57° C.). In some embodiments, the distillation and/or partial condensation with phase separation take(s) place at a “low” (or sub-ambient) temperatures, typically in the range from about +15° C. to about −55° C. In other embodiments, the distillation and/or partial condensation with phase separation take(s) place at a temperature in the range from about 0° C. to −30° C., particularly for H2S distillation from CO2.
The purified CO2 is typically at a temperature from about 10° C. to about 70° C., e.g., about 50° C. and at a pressure from about 10 bar g to about 120 bar g, e.g., about 30 bar g. Thus, in embodiments in which further purification is required, the purified CO2 is typically cooled, e.g., by heat exchange with a refrigerant, to a suitable temperature as described above before being further purified. Additionally or alternatively, the purified CO2 would be further compressed if the pressure of the gas is not sufficient for the further purification.
Recycling H2 to the hydrogenation process enables a reduction in the amount of additional H2 that needs to be generated to meet demand in that process, thereby reducing the size of or even eliminating the hydrogenation unit required which in turn saves capital and operational costs. Where demand is only partially met by the recycled H2, additional H2 can be produced in a H2 generation process as discussed above. However, in some embodiments, the amount of H2 recycled to the hydrogenation process is sufficient to meet the demand for H2 in that process, eliminating the need for a H2 generation process entirely.
Recycling CO2 to the hydrogenation process enables an increase in overall CO2 recovery. It may however be desirable or advantageous to reduce the amount of CO2 being recycled to the hydrogenation unit in the second recycle gas, for example to reduce the size of the hydrogenation unit. In such cases, the method may comprise recovering H2 gas from a recycle gas being fed to the hydrogenation process in a membrane separation process to produce a H2-enriched gas which is recycled to the hydrogenation unit, together with a waste gas comprising CO2 and at least one non-condensable gas.
Conventional membrane separation units may be used to recover H2 gas from recycle gas being recycled to the hydrogenation process. The membranes may be spiral wound, hollow fiber membranes made from polymers such as polysulfone, polyimide or cellulose acetate. An example of a suitable membrane separation process is disclosed in US2010/126180A which the Inventors have realized may be adapted as appropriate for integration with the present invention.
In embodiments in which H2S-enriched CO2 tail-gas is compressed directly to produce the compressed impure CO2 gas comprising H2S, the method may comprise feeding the purified CO2 to a further purification process as described above to produce further purified CO2 and a second recycle gas comprising CO2 and H2; and recycling the second recycle gas, or a H2-enriched gas derived therefrom, to the hydrogenation process. A portion of the second recycle gas, or of said H2-enriched gas derived therefrom, is typically purged to prevent the build-up of H2 (if it is in excess), or N2 and/or Ar in the process.
As mentioned above, purification by physical separation may be by distillation and/or partial condensation with phase separation.
In these embodiments, the method typically comprises removing H2 and any non-condensable gases from the compressed impure CO2 by distillation and/or partial condensation with phase separation to produce H2S-enriched CO2 fluid (which may be a liquid, a gas or two-phase) and H2-enriched CO2 gas, recycling the H2-enriched CO2 gas, or a further H2-enriched CO2 gas derived therefrom, as a second recycle gas to the hydrogenation process; separating the H2S-enriched CO2 fluid by distillation and/or partial condensation with phase separation to produce the purified CO2 as overhead gas and a H2S-enriched bottoms liquid; and vaporizing the H2S-enriched bottoms liquid to produce H2S-enriched gas as the first recycle gas. A portion of the second recycle gas, or of said H2-enriched gas derived therefrom, is usually purged to avoid a build-up of H2 (if it is in excess), or N2 and/or Ar in the process.
As mentioned above, suitable CO2 purification processes in this context are disclosed in U.S. Ser. No. 10/254,042 and U.S. Pat. No. 7,819,951 which the Inventors have realized may be adapted as appropriate for integration with the present invention.
In embodiments in which the purified CO2 comprises at least one residual sulfur-containing impurity, said method may comprise further purifying said purified CO2 by selective adsorption or by chemical reaction with at least one solid metal oxide to form solid metal sulfide(s) and subsequent oxidative regeneration, to produce further purified CO2 and a further recycle gas comprising at least one sulfur-containing compound; and recycling said further recycle gas to said Claus process to convert said sulfur-containing compound(s) into elemental sulfur.
Alternatively, in embodiments in which the purified CO2 overhead gas comprises one or more residual sulfur-containing compounds as impurities, the method may comprise removing H2S and any other sulfur-containing impurities from said purified CO2 overhead gas by selective adsorption or by chemical reaction with at least one solid metal oxide to form solid metal sulfide(s) and subsequent oxidative regeneration, to produce further purified CO2 and a third recycle gas comprising at least one sulfur-containing compound. The third recycle gas may be recycled to the Claus process to convert the sulfur-containing compound(s) into elemental sulfur.
The second aspect of the present invention is apparatus for desulfurizing crude CO2 gas comprising H2S and optionally at least one other sulfur-containing impurity, typically in accordance with the method of the first aspect.
The apparatus comprises a Claus unit for removing H2S from crude CO2 gas. The Claus unit comprises a first inlet for oxidant gas comprising O2, a second inlet for the crude CO2 gas, a first outlet for Claus tail-gas comprising CO2, residual H2S and at least one sulfur-containing impurity; and a second outlet for elemental sulfur. An example of a suitable Claus unit is described in US2010/0126180A.
The apparatus also comprises a source of oxidant gas comprising O2 in fluid flow communication with the first inlet of the Claus unit. For units operating an “air-Claus” process, the source may simply be a blower with a small filter whereas, for units operating an “oxy-Claus” process, the source may be a vacuum swing adsorption (VSA) unit or an air separation unit (ASU), optionally in combination with a back-up system such as a liquid oxygen tank and vaporizer.
In addition, the apparatus comprises a source of crude CO2 gas in fluid flow communication with the second inlet of the Claus unit. Such sources include natural gas “sweetening” units which use amine absorption processes/units, membrane separation systems/units and/or low temperature purification processes/units to generate acid gas streams.
The apparatus further comprises a hydrogenation unit for converting the at least one sulfur-containing impurity in the Claus tail-gas into H2S. The hydrogenation unit comprises a first inlet in fluid flow communication with the first outlet of the Claus unit, a second inlet for H2 and a first outlet for H2S-enriched CO2 tail-gas. An example of a suitable hydrogenation unit is described in US2010/0126180A.
The apparatus also comprises a source of H2 in fluid flow communication with the second inlet of the hydrogenation unit. The source may be a unit generating H2 as described above.
In addition, the apparatus comprises a cooling unit for cooling H2S-enriched CO2 tail gas which is either separate from or integrated with the hydrogenation unit. The cooling unit comprises a first inlet in fluid communication with the first outlet of the hydrogenation unit, a first outlet for cooled H2S-enriched CO2 tail gas, and a second outlet for condensed water. The cooling unit may be a heat exchanger using indirect heat exchange with a coolant but is usually a direct contact cooler comprising a second inlet for cooling water. The cooling unit may be a separate unit or may be integrated with the hydrogenation unit.
Further, the apparatus comprises a compression unit for compressing H2S-enriched CO2 tail-gas or impure CO2 gas comprising H2S derived therefrom. The compression unit must therefore be inherently suitable for handling “sour” gases.
The compression unit comprises an inlet in fluid flow communication with the outlet of the first outlet of the cooling unit; and an outlet for compressed impure CO2 gas. The compression unit may comprise one or more centrifugal or reciprocating compressor and/or may be a multistage compressor with associated intercooler(s) and aftercooler(s). In particular, the compression unit may be an integrally geared or inline centrifugal compressor.
Furthermore, the apparatus comprises a purification unit for removing H2S and any other sulfur-containing impurities from compressed impure CO2 gas by physical separation or chemical reaction with solid metal oxide(s). The purification unit comprises a first inlet in fluid flow communication with the outlet of said compression unit, a first outlet for purified CO2; and a second outlet for a first recycle gas comprising at least one sulfur-containing compound. The second outlet of the purification unit is in fluid communication with the Claus unit. In this regard, the second outlet may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas.
Throughout the specification, the term “in fluid flow communication” is used to refer to different units (or parts of units such as inlets/outlets) being connected by conduits, pipes and/or ducting as appropriate in such a manner to allow the flow of fluid, e.g., gas, between units. The term is intended to include associated flow control devices such as the necessary sensors and/or valves to ensure operational control of the apparatus. Unless stated otherwise, the term is intended to cover both direct and indirect fluid flow communication. “Direct” fluid (or gas) flow communication means that no other fluid (or gas) processing unit (not including flow control apparatus) is provided in the line between the units so connected. “Indirect” fluid (or gas) flow communication is to be interpreted accordingly, i.e., one or more other fluid (or gas) processing units are provided in the line between the units so connected.
In some embodiments, the apparatus comprises a H2 generation unit comprising an outlet for H2 in fluid communication with the second inlet of the hydrogenation unit.
The purification unit in some embodiments is or comprises a selective adsorption unit comprising at least one vessel having an upstream end and a downstream end, and the or each vessel comprises an adsorbent bed comprising at least one layer of adsorbent material(s) selective for sulfur-containing compounds, a first inlet for compressed impure CO2 gas at the upstream end of the or each vessel, a first outlet for purified CO2 at the downstream end of the or each vessel, a second inlet for regeneration gas at the downstream end of the or each vessel; and a second outlet for spent regeneration gas at the upstream end of the or each vessel. The first inlet is in fluid flow communication with the outlet of the compression unit and the second outlet is in fluid flow communication with the Claus unit. In this regard, the second outlet may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas.
In other embodiments, the purification unit comprises a reactor comprising at least one vessel having an upstream end and a downstream end. The or each vessel comprises a bed comprising at least one solid metal oxide, a first inlet for compressed impure CO2 gas at the upstream end of the or each vessel, a first outlet for purified CO2 at the downstream end of the or each vessel; a second inlet for regeneration gas at the downstream end of the or each vessel; and a second outlet for spent regeneration gas at the upstream end of the or each vessel. The first inlet is in fluid flow communication with the outlet of the compression device and the second outlet is in fluid flow communication with the Claus unit. In this regard, the second outlet may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas.
The Inventors have realized that an example of a suitable reactor that may be adapted for integration with these embodiments is disclosed in U.S. Pat. No. 4,797,268.
The bed in the or each vessel of the selective adsorption unit or the reactor may comprise at least one layer of adsorbent material(s) selective for water downstream of at least one layer of adsorbent material(s) selective for sulfur-containing compound(s) or the solid metal oxide(s) respectively.
Alternatively, the purification unit may comprise a separate drier unit downstream of either the selective adsorption unit of the reactor. The drier unit may be a further selective adsorption unit or an absorption unit such as a glycol unit. Either way, the drier unit typically comprises an inlet in fluid communication with the first outlet of the selective adsorption unit or the reactor as appropriate, and an outlet for dried and purified CO2.
In some embodiments, the apparatus comprises a selective amine absorption unit for recovering H2S from H2S-enriched CO2 tail gas. The selective amine absorption unit typically comprises an inlet in fluid flow communication with the first outlet of the cooling unit, a first outlet for H2S-depleted CO2 tail-gas and a second outlet for recovered gas comprising H2S in fluid flow communication with the Claus unit. In this regard, the second outlet may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas. An example of a suitable selective amine absorption unit which the Inventors have realized may be adapted for use in this context is disclosed in WO93/10883A.
In some embodiments, the first outlet of the selective amine adsorption unit is in direct fluid flow communication with the inlet of the compression unit.
In other embodiments, the apparatus may further comprise a non-selective amine absorption unit for recovering CO2 and residual H2S from H2S-depleted CO2 tail-gas. The non-selective amine absorption unit typically comprises an inlet in fluid flow communication with the first outlet of the selective amine absorption unit, a first outlet for impure CO2 gas, and a second outlet for waste gas comprising CO2 and at least one non-condensable gas. The apparatus usually includes a vent for the waste gas, optionally with a thermal oxidizer comprising an inlet in fluid flow communication with the second outlet of the non-selective amine absorption unit, and an outlet for vent gas in fluid communication with the atmosphere via the vent.
In embodiments of the present invention in which the content of the sulfur-containing impurities in the purified CO2 gas even after passage through a selective adsorption unit or a reactor as described above is still above the required threshold, e.g., above 100 ppm, then the apparatus may further comprise a further purification unit, such as a distillation unit and/or a partial condensation with phase separation unit (or CPU), for further purifying purified CO2.
In these embodiments, the further purification unit comprises an inlet for purified CO2 in fluid flow communication with the first outlet of the purification unit, a first outlet for further purified CO2, and a second outlet for a second recycle gas comprising CO2 and H2 in fluid flow communication with either the hydrogenation unit and/or the Claus unit, and a purge line in fluid flow communication with the second outlet of said further purification unit.
For these and other embodiments involving the use of a further purification unit, the second outlet of the further purification unit may be in fluid flow communication with the first or second inlet of the hydrogenation unit or with a third inlet on the hydrogenation unit which is typically dedicated for recycle gas. The second outlet of the CPU may additionally or alternatively be in fluid communication with the first or second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas. Further, the purge line may be in direct fluid communication with a vent to the atmosphere, or with a thermal oxidizer. Alternatively, fluid from the purge line could be used as a fuel or for H2 recovery.
The inventors have realized that the CPU described in FIG. 1B of U.S. Ser. No. 10/254,042 may be used (after suitable adaptation as appropriate) as the further purification unit of the present invention.
These embodiments may further comprise a membrane separation unit for recovering H2 gas from second recycle gas. The membrane separation unit typically comprises an inlet for second recycle gas in fluid flow communication with the second outlet of the further purification unit, a first outlet for H2-enriched gas in direct fluid flow communication with the hydrogenation unit and/or the Claus unit, and a second outlet for waste gas comprising CO2 and at least one non-condensable gas.
These embodiments of the apparatus usually include a vent for the waste gas, optionally with a thermal oxidizer comprising an inlet in fluid flow communication with the second outlet of the membrane separation unit, and an outlet for vent gas in fluid communication with the vent.
In addition, the second outlet of the membrane separation unit may be in fluid flow communication with the second inlet(s) of the hydrogenation unit and/or the Claus unit or with a third inlet(s) on the hydrogenation unit and/or Claus unit which is typically dedicated for recycle gas. In this regard, extra H2 can be fed to the Claus unit for combustion/disposal if not required elsewhere.
In other embodiments, the first outlet of the hydrogenation unit is in direct fluid flow communication with the inlet of the compression unit.
In these embodiments, the apparatus may comprise a further purification unit for further purifying purified CO2. The further purification unit typically comprises an inlet for purified CO2 in fluid flow communication with the first outlet of the purification unit, a first outlet for further purified CO2, and a second outlet for a second recycle gas comprising CO2 and H2 in fluid flow communication with the hydrogenation unit, and a purge line in fluid flow communication with the second outlet of the further purification unit. The second outlet of the further purification unit may be in fluid flow communication with an inlet of the hydrogenation unit (and/or the Claus unit), or with an inlet on the hydrogenation unit (and/or the Claus unit) which is typically dedicated for recycle gas.
These embodiments may further comprise a membrane separation unit for recovering H2 gas from second recycle gas. The membrane separation unit typically comprises an inlet for second recycle gas in fluid flow communication with the second outlet of the further purification unit, a first outlet for H2-enriched gas in direct fluid flow communication with the hydrogenation unit, and a second outlet for waste gas comprising CO2 and at least one non-condensable gas. The H2-enriched gas is typically taken from the permeate side of the membrane(s) and the waste gas is typically taken from the retentate side of the membrane(s).
These embodiments of the apparatus usually include a vent for the waste gas, optionally with a thermal oxidizer comprising an inlet in fluid flow communication with the second outlet of the membrane separation unit, and an outlet for vent gas in fluid communication with the vent.
In addition, the second outlet of the membrane separation unit may be in fluid flow communication with the second inlet(s) of the hydrogenation unit and/or the Claus unit or with a third inlet(s) on the hydrogenation unit and/or on the Claus unit which is typically dedicated for recycle gas.
In some embodiments, the apparatus comprises a non-selective amine absorption unit for recovering CO2 and H2S from H2S-enriched CO2 tail-gas. The non-selective amine absorption unit comprises an inlet in direct fluid flow communication with the outlet of the cooling unit, a first outlet for impure CO2 gas in direct fluid flow communication with the inlet of the compression unit, and a second outlet for waste gas comprising CO2 and at least one non-condensable gas. These embodiments of the apparatus usually include a vent for the waste retentate gas, optionally with a thermal oxidizer comprising an inlet in fluid flow communication with the second outlet of the membrane separation unit, and an outlet for vent gas in fluid communication with the vent.
The purification unit may be a single stage unit. In these embodiments, the purification unit comprises an inlet for compressed impure CO2 in fluid flow communication with the outlet of said compression unit; a first outlet for H2S-enriched CO2 fluid; and a second outlet for H2-enriched CO2 gas in fluid flow communication with an inlet of the hydrogenation unit (and/or with an inlet of the Claus unit).
In these embodiments, the apparatus may further comprise a selective adsorption unit comprising at least one vessel having an upstream end and a downstream end in which the or each vessel comprises an adsorbent bed, said adsorbent bed comprising at least one layer of adsorbent material(s) selective for sulfur-containing compound(s); a first inlet for H2S-enriched CO2 fluid at said upstream end of the or each vessel; a first outlet for purified CO2 at said downstream end of the or each vessel; a second inlet for regeneration gas at said downstream end of the or each vessel; and a second outlet for spent regeneration gas at said upstream end of the or each vessel. The first inlet of the selective adsorption vessel is in fluid flow communication with the first outlet of the single stage purification unit and the second outlet is in fluid flow communication with the Claus unit.
Alternatively, the apparatus may comprise a reactor comprising at least one vessel having an upstream end and a downstream end in which the or each vessel comprises a bed comprising at least one solid metal oxide; a first inlet for H2S-enriched CO2 fluid at said upstream end of the or each vessel; a first outlet for purified CO2 at said downstream end of the or each vessel; a second inlet for regeneration gas at said downstream end of the or each vessel; and a second outlet for spent regeneration gas at said upstream end of the or each vessel. The first inlet of the reactor is in fluid flow communication with the first outlet of the single stage purification unit and the second outlet is in fluid flow communication with the Claus unit.
In still further embodiments of the apparatus, the purification unit comprises a first stage, e.g., a CPU, and a second stage, e.g., a distillation unit.
The first stage comprises an inlet for compressed impure CO2 in fluid flow communication with the outlet of compression unit, a first outlet for H2S-enriched CO2 fluid, and a second outlet for H2-enriched CO2 gas in fluid flow communication with an inlet of the hydrogenation unit (and/or with an inlet of the Claus unit).
The second stage comprises an inlet for H2S-enriched CO2 fluid in fluid flow communication with the first outlet of first stage, a first outlet for purified CO2 gas, and a second outlet for H2S-enriched gas in fluid flow communication with the third inlet of the Claus unit. These embodiments of the apparatus further comprise a purge line in fluid flow communication with the second outlet of the first stage of the purification unit.
The Inventors have realized that FIG. 2 of U.S. Ser. No. 10/254,042 depicts an arrangement of integrated first and second stages that would be suitable for use as the purification unit according to these embodiments of the present invention.
These embodiments may further comprise a membrane separation unit for recovering H2 gas from H2-enriched CO2 gas. The membrane separation unit typically comprises an inlet for H2-enriched CO2 gas in fluid flow communication with the second outlet of the first stage of the purification unit, a first outlet for H2-enriched gas in direct fluid flow communication with an inlet of hydrogenation unit (and/or with an inlet of the Claus unit) and a second outlet for waste gas comprising CO2 and at least one non-condensable gas.
These embodiments of the apparatus usually include a vent for the waste gas, optionally with a thermal oxidizer comprising an inlet in fluid flow communication with the second outlet of the membrane separation unit, and an outlet for vent gas in fluid communication with the vent.
In addition, the second outlet of the membrane separation unit may be in fluid flow communication with the second inlet(s) of the hydrogenation unit and/or of the Claus unit, or with a third inlet(s) on the hydrogenation unit and/or on the Claus unit which is typically dedicated for recycle gas.
If the amount of sulfur-containing components in the purified CO2 gas is still above the required threshold, e.g. above 100 ppm, then these embodiments may further comprise a further purification unit selected from a selective adsorption unit and a reactor comprising a bed of solid metal oxide(s) as described above.
A selective adsorption unit in this context typically comprises at least one vessel having an upstream end and a downstream end. The or each vessel comprises an adsorbent bed comprising at least one layer of adsorbent material(s) selective for sulfur-containing compound(s), a first inlet for purified CO2 at the upstream end of the or each vessel, a first outlet for further purified CO2 at the downstream end of the or each vessel, a second inlet for regeneration gas at the downstream end of the or each vessel, and a second outlet for spent regeneration gas at the upstream end of the or each vessel. In these embodiments, the first inlet of the further purification unit is in fluid flow communication with the first outlet of the second stage of the purification unit and the second outlet is in fluid flow communication with the Claus unit. In this regard, the second outlet of the or each vessel may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas.
A reactor in this context typically comprises at least one vessel having an upstream end and a downstream end. The or each vessel comprises at least one solid metal oxide, a first inlet for purified CO2 at the upstream end of the or each vessel, a first outlet for further purified CO2 at the downstream end of the or each vessel, a second inlet for regeneration gas at the downstream end of the or each vessel, and a second outlet for spent regeneration gas at the upstream end of the or each vessel. In addition, the first inlet of the further purification unit is in fluid flow communication with the first outlet of the second stage of the purification unit and the second outlet is in fluid flow communication with the Claus unit. In this regard, the second outlet of the or each vessel may be in fluid flow communication with the second inlet of the Claus unit or with a third inlet on the Claus unit which is typically dedicated for recycle gas.
Turning now to the figures, in
The residual sulfur compounds are converted in the hydrogenation unit 16 in the presence of H2 gas produced in a reducing gas generation unit 18, into H2S to produce a stream 104 of H2S-enriched CO2 tail-gas which, after quenching with water in a direct contact cooler (shown as integrated with the hydrogenation unit—see stream (of water) leaving hydrogenation unit 16), is then fed to the selective amine absorption unit 20 which selectively absorbs H2S to produce a stream 105 of H2S-depleted CO2 tail-gas and recovered H2S which is recycled back to the Claus unit 6 as part of stream 110. The H2S-depleted CO2 tail-gas from the tail-gas treatment unit 14 contains mainly CO2, N2, H2 and small quantities of sulfur compounds, and is saturated with water.
In the absence of a CO2 capture unit, stream 105 would typically be oxidized in a thermal oxidizer. In this case, however, the CO2 is intended for capture and storage.
The H2S-depleted CO2 tail-gas 105 from tail gas treatment unit 14 is fed to a non-selective amine absorption unit 26 in which most of the CO2 and sulfur compounds are captured and recovered non-selectively to produce a stream 107 of impure CO2 gas, together with a stream 115 of waste gas comprising CO2 and the non-condensable gases, N2 and H2, together with water which is either vented directly or fed to a thermal oxidizer 42 before being vented, depending on its composition.
Stream 107 is mostly CO2 but contains sulfur compounds which may not be acceptable for CO2 sequestration or further use. Stream 107 is therefore fed to compression device 32 where it is compressed to form a stream 108 of compressed impure CO2 gas which is then purified using a selective adsorption unit (or reactor) 36 according to the present invention to remove the sulfur compounds and produce a stream 111 of purified CO2 for sequestration and a stream 109 of spent regeneration gas (or purge gas) comprising desorbed sulfur compound(s) which is recycled to the Claus unit 6.
Water may be removed from the compressed impure CO2 gas in the selective adsorption unit (or reactor) 36 by including at least one layer of water adsorbent material downstream of the layer(s) of sulfur-selective adsorbent material(s) or of the solid metal oxide(s), e.g., ZnO. Alternatively, the stream 111 of purified CO2 may be fed to a drier unit (not shown) prior to sequestration.
The flowsheet depicted in
Instead of air as used in
In addition, stream 105 of H2S-depleted CO2 tail-gas is taken from the tail gas treatment unit 14 and fed directly to a compression device 46 where it is compressed. Water is knocked out of the compressed gas in one or more intercoolers and/or an aftercooler (not shown). A stream 106 of compressed impure CO2 gas is then purified using a selective adsorption unit (or reactor) 50 according to the present invention to remove the sulfur-containing compound(s) and produce a stream 107 of purified CO2 gas and a stream 109 of spent regeneration gas (or purge gas) comprising sulfur-containing compound(s) which is recycled to the Claus unit 6.
Water may be removed from the compressed impure CO2 gas in the selective adsorption unit (or reactor) 50 by including at least one layer of water-adsorbent material downstream of the layer(s) of sulfur-selective adsorbent material(s) or of the solid metal oxide(s), e.g., ZnO. Alternatively, the stream 111 of purified CO2 may be fed to a drier unit (not shown) prior to sequestration.
Stream 107 of purified CO2 gas is then fed to a further purification unit 56 where CO2 is further purified by distillation and/or by partial condensation and phase separation to produce a stream 111 of further purified CO2 for sequestration or other use, and a stream 108 of a waste gas comprising CO2 and H2.
Stream 108 can be recycled directly to the hydrogenation unit 16. However, it may be desirable to reduce the amount of CO2 that is recycled to the hydrogenation unit 16. In such cases, stream 108 may be fed to a membrane unit 62 for H2 recovery to produce a stream 112 of H2-enriched gas and a stream 115 of waste gas.
Stream 112 is recycled to the hydrogenation unit 16. Recycling of this stream in this way has the benefit of reducing or even eliminating the need for fresh H2 from a reducing gas generation unit (not shown) to feed the hydrogenation unit 16.
The stream 115 of waste gas may be vented directly or fed to a thermal oxidizer 70 before being vented, depending on its composition.
The flowsheet depicted in
Stream 104 of H2S-enriched CO2 tail-gas is fed directly from the hydrogenation unit 16 to the non-selective amine absorption unit 26 in which most of the CO2 and sulfur-containing compounds are captured and recovered non-selectively to produce stream 107 of impure CO2 gas, together with a stream 115 of waste gas which is either vented directly or fed to a thermal oxidizer 42 before being vented, depending on its composition.
The flowsheet depicted in
In this arrangement, the stream 101 of O2 or O2-rich air for the Claus unit 6 is generated in an air separation unit 72 either by vacuum swing adsorption (VSA) or cryogenic air separation (in an air separation unit or ASU).
Stream 104 of impure CO2 tail-gas is fed directly from the hydrogenation unit 16 to the compression device 46 where it is compressed to form stream 106 of compressed impure CO2 gas which is then fed to the selective adsorption unit (or reactor) 50 where H2S (optionally, together with water) is removed from the gas.
In this arrangement, sufficient H2 may be recovered in the membrane separation unit 62 and recycled to the hydrogenator 16 that a reducing gas generator (not shown) is not required to provide additional H2.
The flowsheet depicted in
The purification unit has a first stage and a second stage. Regarding the first stage, stream 106 of compressed impure CO2 gas is fed to a first stage 56 where CO2 is purified, e.g., by partial condensation with phase separation, to produce H2S-enriched CO2 liquid, and a stream 108 of a waste gas comprising CO2 and H2 for recycling to the hydrogenation unit 16, optionally after passage through a membrane separation unit 62 to recover H2.
A stream 107 of H2S-enriched CO2 liquid (or gas if vaporised) is fed to a distillation column system 74 where CO2 and H2S are separated in the second stage to generate purified CO2 as overhead gas and H2S-enriched bottoms liquid which is vaporised prior to recycling to the Claus unit 6 in stream 110.
The stream 111 of purified CO2 may be suitable for sequestration. However, if the total amount of sulfur-containing compounds in the purified CO2 is too high, e.g., over 100 ppm, then the purified CO2 may be further purified in a selective adsorption unit (or reactor) 50 to produce a stream 120 of further purified CO2 for sequestration or further use, and a stream 118 of spent regeneration gas (or purge gas) comprising desorbed sulfur-containing compounds which is recycled to the Claus unit 6.
The flowsheets depicted in
The flowsheet depicted in
The purification unit has a single stage (unit 56). Stream 106 of compressed impure CO2 gas is fed to unit 56 where CO2 is purified, e.g., by partial condensation with phase separation or distillation, to produce H2S-enriched CO2 liquid, and a stream 108 of a waste gas comprising CO2 and H2 for recycling to the hydrogenation unit 16, optionally after passage through a membrane separation unit 62 to recover H2.
The level of sulfur-containing compounds in stream 107 of H2S-enriched CO2 gas, typically over 2 mol. %, is far too high for CCS. However, rather than purifying the CO2 by distillation (as in
The flowsheet in
#1. A method for desulfurization of crude CO2 gas comprising H2S and optionally at least one other sulfur-containing impurity, said method comprising:
#2. A method according to #1 comprising:
#3. A method according to #1 or #2 wherein said H2S-enriched CO2 tail gas is cooled by direct contact with water.
#4. A method according to any of #1 to #3 wherein H2S and any other sulfur-containing impurities are removed from said compressed impure CO2 gas by selective adsorption as said physical separation.
#5. A method according to #4 wherein said selective adsorption involves removing H2S and any other sulfur-containing compounds in the compressed impure CO2 gas by adsorption on a bed comprising at least one adsorbent material selective for sulfur-containing compound(s) in a selective adsorption unit to produce said purified CO2 and, after desorption with a regeneration gas, a spent regeneration gas comprising said H2S and any other sulfur-containing compounds from the compressed impure CO2 gas as said first recycle gas.
#6. A method according to #5, wherein said regeneration gas comprises water in an amount that is insufficient to hydrolyze the other sulfur-containing compounds.
#7. A method according to #5 or #6, wherein said compressed impure CO2 gas feed to the selective adsorption unit comprises water, said method comprising drying the purified CO2 gas downstream of said adsorbent material(s) selective for sulfur-containing compound(s).
#8. A method according to #1 to #3 wherein H2S and any other sulfur-containing impurities are removed from said compressed impure CO2 gas by said chemical reaction with at least one solid metal oxide to form solid metal sulfide(s) and subsequent oxidative regeneration.
#9. A method according to #8 comprising:
#10. A method according to #9 wherein said regeneration gas comprises water in an amount that is insufficient to hydrolyze the other sulfur-containing compounds.
#11. A method according to #9 or #10, wherein said compressed impure CO2 gas feed to said reactor comprises water, said method comprising drying the purified CO2 gas downstream of the bed comprising said solid metal oxide(s).
#12. A method according to any of #1 to #11 comprising:
#13. A method according to #12 comprising recovering CO2 and residual H2S from said H2S-depleted CO2 tail-gas by non-selective amine absorption to produce said impure CO2 gas for compression, together with waste gas comprising CO2 and at least one non-condensable gas.
#14. A method according to #12, wherein said H2S-depleted CO2 tail-gas is compressed directly to produce said compressed impure CO2 gas.
#15. A method according to #14 comprising:
wherein a portion of said second recycle gas, or of said H2-enriched gas derived therefrom, is purged.
#16. A method according to #15 wherein the amount of H2 recycled to said hydrogenation process is sufficient to meet demand in that process.
#17. A method according to #15 or #16 comprising recovering H2 gas from said second recycle gas in a membrane separation process to produce said H2-enriched gas, together with a waste gas comprising CO2 and at least one non-condensable gas.
#18. A method according to any of #1 to #3 wherein said H2S-enriched CO2 tail-gas is compressed directly to produce said compressed impure CO2 gas comprising H2S.
#19. A method according to any of #1 to #18 comprising:
wherein a portion of said second recycle gas, or of said H2-enriched gas derived therefrom, is purged.
#20. A method according to #19 wherein the amount of H2 recycled to said hydrogenation process is sufficient to meet demand in that process.
#21. A method according to #19 or #20 comprising recovering H2 gas from said second recycle gas in a membrane separation process to produce said H2-enriched gas for recycle, together with a waste gas comprising CO2 and at least one non-condensable gas.
#22. A method according to any of #1 to #3 comprising recovering CO2 and H2S from said H2S-enriched CO2 tail-gas by non-selective amine absorption to produce said impure CO2 gas for compression, together with a waste gas comprising CO2 and at least one non-condensable gas.
#24. A method according to #1 to #3, wherein said H2S and any other sulfur-containing impurities are removed from said compressed impure CO2 gas by distillation and/or partial condensation with phase separation as said physical separation.
#25. A method according to #24, wherein said purified CO2 comprises at least one residual sulfur-containing impurity, said method comprising:
#26. A method according to #25, comprising:
wherein a portion of said second recycle gas, or of said H2-enriched gas derived therefrom, is purged.
#27. A method according to #26 wherein the amount of H2 recycled to said hydrogenation process is sufficient to meet demand in that process.
#28. A method according to #26 or #27 comprising recovering H2 gas from said second recycle gas in a membrane separation process to produce said further H2-enriched CO2 gas for recycle, together with a waste gas comprising CO2 and at least one non-condensable gas.
#29. A method according to #26 to #28, wherein said purified CO2 overhead gas comprises one or more residual sulfur-containing compounds, said method comprises:
#30. Apparatus for desulfurizing crude CO2 gas comprising H2S and optionally at least one other sulfur-containing impurity, said apparatus comprising:
and
wherein the second outlet of said purification unit is in fluid communication with said Claus unit.
#31. Apparatus according to #30 wherein said source of H2 is an H2 generation unit comprising an outlet for H2 in fluid communication with said second inlet of said hydrogenation unit.
#32. Apparatus according to #30 or #31 wherein said cooling unit is a direct contact cooler further comprising a second inlet for cooling water.
#33. Apparatus according to #30 wherein said purification unit comprises a selective adsorption unit comprising:
wherein said first inlet of said selective adsorption unit is in fluid flow communication with the outlet of said compression unit and wherein said second outlet is in fluid flow communication with said Claus unit.
#34. Apparatus according to #33 wherein said adsorbent bed in the or each vessel comprises at least one layer of adsorbent material(s) selective for water downstream of said at least one layer of adsorbent material(s) selective for sulfur-containing compound(s).
#35. Apparatus according to #33 or #34 comprising a drier unit downstream of said selective adsorption unit, said drier unit comprising:
#36. Apparatus according to Claim #30 wherein said purification unit comprises a reactor comprising:
wherein said first inlet of said reactor is in fluid flow communication with the outlet of said compression device and wherein said second outlet is in fluid flow communication with said Claus unit.
#37. Apparatus according to #36 wherein the or each vessel comprises at least one layer of adsorbent material(s) selective for water downstream of the bed comprising said solid metal oxide(s).
#38. Apparatus according to #36 or #37 comprising a drier unit downstream of said reactor, said drier unit comprising:
#39. Apparatus according to any of #30 to #38 comprising:
#40. Apparatus according to #39 comprising:
#41. Apparatus according to #39 wherein the first outlet of said selective amine adsorption unit is in direct fluid flow communication with the inlet of said compression unit.
#42. Apparatus according to #41 wherein said purification unit is a selective adsorption unit or a reactor, said apparatus further comprising:
and
#43. Apparatus according to #42 comprising:
#44. Apparatus according to any of #30 to #32 wherein the first outlet of said hydrogenation unit is in direct fluid flow communication with the inlet of said compression unit.
#45. Apparatus according to #44 wherein said purification unit is a selective adsorption unit or a reactor, said apparatus further comprising:
and
#46. Apparatus according to #45 comprising:
#47. Apparatus according to any of #30 to #32 comprising:
#48. Apparatus according to any of #30 to #32 wherein said purification unit is a single stage purification unit comprising:
said apparatus comprising a selective adsorption unit comprising:
wherein said first inlet of said selective adsorption vessel is in fluid flow communication with the first outlet of said single stage purification unit and wherein said second outlet is in fluid flow communication with said Claus unit.
#49. Apparatus according to any of #30 to #32 wherein said purification unit is a single stage purification unit comprising:
said apparatus comprising a reactor comprising:
wherein said first inlet of said reactor is in fluid flow communication with the first outlet of said single stage purification unit and wherein said second outlet is in fluid flow communication with said Claus unit.
#50. Apparatus according to any of #30 to #32 wherein said purification unit comprises a purification unit comprising a first stage and a second stage;
and
#51. Apparatus according to #50 comprising:
#52. Apparatus according to #51 comprising a selective adsorption unit comprising:
wherein said first inlet of said selective adsorption unit is in fluid flow communication with the first outlet of said second stage of said purification unit and wherein said second outlet is in fluid flow communication with said Claus unit.
#53. Apparatus according to #51 comprising a reactor comprising:
wherein said first inlet of said reactor is in fluid flow communication with the first outlet of said second stage of said purification unit and wherein said second outlet is in fluid flow communication with said Claus unit.
Particular embodiments of the invention will now be illustrated by computer modelling in the following examples.
The process depicted in the flow sheet of
O
0
84
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 92.5 mol. % at a purity of 100 mol. %, i.e., complete removal of residual H2S (and water) from impure CO2.
The process depicted in the flow sheet of
3.5
O
.0000
.0000
7.2
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 95.8 mol. % at a purity of 99.5 mol. % with the remainder being H2, i.e., complete removal of residual H2S (and water) from impure CO2.
The process depicted in the flow sheet of
3.7
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 91.5 mol. % at 100 mol. % purity, i.e., complete removal of residual H2S (and water) from impure CO2.
The process depicted in the flow sheet of
O
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 95.8 mol. % at a purity of 99.5 mol. % with the remainder being H2, i.e., complete removal of residual H2S (and water) from impure CO2.
The process depicted in the flow sheet of
3.3
O
21
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 95.6 mol. % at a purity of 99.5 mol. %. The product CO2 also contains about 0.5 mol. % H2 and no more than 100 ppm H2S which meets the required specification of H2S for sequestration.
The process depicted in the flow sheet of
O
.5
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 91.6 mol. % at a purity of 100 mol. %, i.e., complete removal of residual H2S (and water) from impure CO2 using a selective adsorbent unit 36 (including the layer of water-adsorbent material).
The process depicted in the flow sheet of
O
O
indicates data missing or illegible when filed
This example illustrates an overall 002 recovery of 95.3 mol % at a purity of 99.5 mol. %. The product CO2 also contains less than 0.5 mol. % H2 and no H2S which meets the required specification of H2S for sequestration.
The process depicted in the flow sheet of
O
indicates data missing or illegible when filed
This example illustrates an overall CO2 recovery of 91.6 mol. % at a purity of 1005 mol. %. Thus, while CO2 recovery is less than in other embodiments, the purity of the 002 is higher in this embodiment.
It will be appreciated that the invention is not restricted to the details described above with reference to the preferred embodiments but that numerous modifications and variations can be made without departing from the spirit and scope of the invention as defined in the following claims.
In this specification, unless expressly otherwise indicated, the word “or” is used in the sense of an operator that returns a true value when either or both of the stated conditions are met, as opposed to the operator “exclusive or” which requires only that one of the conditions is met. The word “comprising” is used in the sense of “including” rather than to mean “consisting of”.
All prior teachings above are hereby incorporated herein by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date thereof.
