SOURCE GAS PURIFICATION APPARATUS AND PURIFICATION METHOD

Abstract

This source gas purification apparatus includes: a first H.sub.2S removing device 2 which removes H.sub.2S from a source gas that includes at least a hydrocarbon, H.sub.2S, and a sulfur compound other than H.sub.2S; a sulfur compound conversion device 3 which converts the sulfur compound other than H.sub.2S into H.sub.2S; and a second H.sub.2S removing device 4 which removes the converted H.sub.2S.

Claims

1-18. (canceled)

19. A source gas purification device comprising: a first H.sub.2S removing device which removes H.sub.2S from source gas at least including hydrocarbon, H.sub.2S, and a sulfur compound other than H.sub.2S; a sulfur compound conversion device which converts the sulfur compound other than H.sub.2S to H.sub.2 S ; and a second H.sub.2S removing device which removes the converted H.sub.2S. wherein the sulfur compound conversion device is a COS.RSH conversion catalyst device including a COS conversion catalyst device and an RSH conversion catalyst device, and wherein the COS conversion catalyst device and the RSH conversion catalyst device are consecutively arranged such that one of COS and RSH which has a smaller abundance ratio primarily becomes a treatment target.

20. The source gas purification device according to claim 19, wherein the sulfur compound other than H.sub.2S is COS and RSH.

21. The source gas purification device according to claim 19, wherein the first H.sub.2S removing device is a chemical absorption device.

22. The source gas purification device according to claim 19, wherein the second H.sub.2S removing device is an adsorption and desorption device using an adsorbent.

23. The source gas purification device according to claim 19, further comprising: a H.sub.2S combustion device; and a lime gypsum-type desulfurization apparatus which treats flue gas from the H.sub.2S combustion device.

24. The source gas purification device according to claim 19, wherein the first H.sub.2S removing device is a H.sub.2S separation device including a H.sub.2S separation membrane or a H.sub.2S adsorbent, and wherein the second H.sub.2S removing device is a chemical absorption device.

25. The source gas purification device according to claim 19, wherein the first H.sub.2S removing device is a H.sub.2S separation device including a H.sub.2S separation membrane or a H.sub.2S adsorbent, and wherein the second H.sub.2S removing device is an adsorption and desorption device.

26. The source gas purification device according to claim 19, further comprising: a mercury removing device provided immediately before the sulfur compound conversion device.

27. A source gas purification method, comprising: a first H.sub.2S removal step of removing H.sub.2S from source gas at least including hydrocarbon, H.sub.2S, and a sulfur compound other than H.sub.2S; a sulfur compound conversion step of converting the sulfur compound other than H.sub.2S to H.sub.2 S ; and a second H.sub.2S removal step of removing the converted H.sub.2S, wherein the sulfur compound conversion step is a COS.RSH conversion step performing a COS conversion step and a RSH conversion step, and wherein the COS conversion step and the RSH conversion step are consecutively performed such that one of COS and RSH which has a smaller abundance ratio primarily becomes a treatment target.

28. The source gas purification method according to claim 27, wherein the sulfur compound other than H.sub.2S is COS and RSH.

29. The source gas purification method according to claim 27, wherein the first H.sub.2S removal step is a step of absorbing and removing H.sub.2S by a chemical absorption device.

30. The source gas purification method according to claim 27, wherein the second H.sub.2S removal step is a H.sub.2S removal step by an adsorption and desorption device using an adsorbent.

31. The source gas purification method according to claim 27, further comprising: a H.sub.2S combustion step; and a lime gypsum-type desulfurization step of treating flue gas from the H.sub.2S combustion step.

32. The source gas purification method according to claim 27, wherein the first H.sub.2S removal step is a step performed by using a H.sub.2S separation device including a H.sub.2S separation membrane or a H.sub.2S adsorbent, and wherein the second H.sub.2S removal step is an absorption step performed by a chemical absorption device.

33. The source gas purification method according to claim 27, wherein the first H.sub.2S removal step is a step performed by using a H.sub.2S separation device including a H.sub.2S separation membrane or a H.sub.2S adsorbent, and wherein the second H.sub.2S removal step is an adsorption step performed by using an adsorption and desorption device.

34. The source gas purification method according claim 27, further comprising: a mercury removal step provided immediately before the sulfur compound conversion step.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a conceptual diagram illustrating a first embodiment of a source gas purification apparatus according to the present invention.

[0036] FIG. 2 is a conceptual diagram illustrating a second embodiment of the source gas purification apparatus according to the present invention.

[0037] FIG. 3 is a conceptual diagram illustrating a third embodiment of the source gas purification apparatus according to the present invention.

[0038] FIG. 4 is a conceptual diagram illustrating a fourth embodiment of the source gas purification apparatus according to the present invention.

DESCRIPTION OF EMBODIMENTS

[0039] Hereinafter, embodiments of a source gas purification apparatus and a source gas purification method according to the present invention are described with reference to the accompanied drawings.

[0040] Source gas purification apparatus (first embodiment)

[0041] A first embodiment of a source gas purification apparatus according to the present invention is conceptually illustrated in FIG. 1.

[0042] The source gas purification apparatus according to the present embodiment includes a CO.sub.2 separation device 1, a chemical absorption device 2, a sulfur compound conversion catalyst device 3, and an adsorption and desorption device 4, as main components.

[0043] According to the present embodiment, natural gas including CO.sub.2, H.sub.2S, a sulfur compound other than H.sub.2S (mainly COS or RSH), and H.sub.2O, as impurities is used as source gas of a treatment target, in addition to hydrocarbon such as methane.

[0044] The source gas that is a treatment target of the present invention is not limited to natural gas, and examples thereof include coal gasification gas, synthesized gas, coke oven gas, petroleum gas (such as associated gas accompanied by crude oil production). However, the present invention is not limited thereto, and gas including acid gas such as H.sub.2S becomes an application target. That is, targets of the present embodiment and another embodiment of the present invention are not limited to natural gas.

[0045] The CO.sub.2 separation device 1 is provided as a form of a CO.sub.2 removing device. The CO.sub.2 separation device 1 is a device that removes CO.sub.2 and other gas components by using a difference between mobility of CO.sub.2 and the other gas components in the film. As the CO.sub.2 separation device 1, a CO.sub.2 separation membrane is mainly used, and a well-known device including a polymer material such as cellulose, polysulfone, and polyimide and inorganic materials such as zeolite and carbon can be employed.

[0046] The chemical absorption device 2 is provided as a form of a first H.sub.2S removing device. The chemical absorption device 2 removes residual CO.sub.2 that is not completely removed by the CO.sub.2 separation device 1, in addition to H.sub.2S removal.

[0047] The chemical adsorption device 2 absorbs and removes residual CO.sub.2 and H.sub.2S by bringing an amine absorbent including an amine compound and source gas into contact with each other. After this absorption and removal, the amine absorbent is heated, so as to dissipate CO.sub.2 and H.sub.2S, and regenerate the amine absorbent.

[0048] Amine is a compound having weak basicity, and has a feature of adsorbing acidic substances such as CO.sub.2 and H.sub.2S and dissipating the acidic substances by heating. According to this feature, amine can be used as an absorbent of acid gas. As the amine absorbent, an absorbent based on N-methyl diethanolamine (MDEA) can be used.

[0049] The source gas from which CO.sub.2 and H.sub.2S are removed is sent to the sulfur compound conversion catalyst device 3. In addition to hydrocarbon such as methane, COS, RSH, and H.sub.2O are included in the source gas from which CO.sub.2 and H.sub.2S are removed.

[0050] The sulfur compound conversion catalyst device 3 is provided as a form of the sulfur compound conversion device. The sulfur compound conversion catalyst device 3 according to the present embodiment is a COS.RSH conversion catalyst device including a front flow COS conversion catalyst device 3A and a back flow RSH conversion catalyst device 3B. The COS conversion catalyst device 3A converts COS to H.sub.2S, and the RSH conversion catalyst device 3B converts RSH to H.sub.2S.

[0051] Examples of a COS conversion catalyst used in the COS conversion catalyst device 3A include a catalyst including a carrier of Al.sub.2O.sub.3 and/or TiO.sub.2 and an active ingredient of at least one kind of metal selected from the group consisting of calcium, magnesium, strontium, zinc, iron, copper, manganese, chromium, barium, nickel, ruthenium, cobalt, and molybdenum as a main component.

[0052] Examples of the RSH conversion catalyst used in the RSH conversion catalyst device 3B include at least one solid acid catalyst selected from silica-alumina and zeolite.

[0053] It is preferable that the COS conversion catalyst device 3A and the RSH conversion catalyst device 3B are consecutively arranged such that one of COS and RSH that has a smaller abundance ratio primarily becomes a treatment target. Possibly, this is because, in a case where the amount of H.sub.2S to be produced increases, the amount of existing H.sub.2S increases in the production system, and thus the reaction hardly progresses in the direction of producing H.sub.2S on chemical equilibrium. In a case where the one having a smaller abundance ratio is first processed, the subsequent conversion target can be easily converted in a state in which an amount of H.sub.2S is smaller.

[0054] In the general natural gas, the abundance ratio of RSH is greater, it is preferable that the COS conversion catalyst device 3A is primarily arranged, and the conversion of COS is first performed.

[0055] The COS conversion catalyst device 3A and the RSH conversion catalyst device 3B may simultaneously convert both COS and RSH by using a catalyst such as CMo/alumina, which is a catalyst integrated in the same reaction vessel and causing an inorganic oxide carrier to support at least one kind of metal belonging to Group V, Group VI and Group VII.

[0056] Any one of the COS conversion catalyst device 3A and the RSH conversion catalyst device 3B can be caused to be driven, according to the properties of source gas of treatment handling. Otherwise, any one of the COS conversion catalyst device 3A and the RSH conversion catalyst device 3B can be provided.

[0057] The adsorption and desorption device 4 is provided as a form of the second H.sub.2S removing device. A material forming the adsorption and desorption device 4 may be an adsorbent such as zinc oxide or a molecular sieve in which a well-known material such as artificial zeolite is employed. The adsorption and desorption device 4 adsorbs and removes H.sub.2S and H.sub.2O from the sulfur compound conversion catalyst device 3. The adsorption and desorption device 4 performs regeneration by desorbing H.sub.2S and H.sub.2O by heating and decompression.

[0058] As illustrated in FIG. 1, the source gas purification apparatus according to the present embodiment includes an NGL recovery device 5, a H.sub.2S combustion device 6, and a lime gypsum-type desulfurization apparatus 7, as other components.

[0059] The NGL recovery device 5 is a device that separates hydrocarbon obtained by causing the adsorption and desorption device 4 to remove H.sub.2S and H.sub.2O into C1 hydrocarbon (methane), C2-4 hydrocarbon (hydrocarbon having 2 to 4 carbon atoms), and C5+ (hydrocarbon having 5 or more carbon atoms). The NGL recovery device 5 separates hydrocarbon by a well-known method such as a cryogenic separation process using a turboexpander.

[0060] The H.sub.2S combustion device 6 is a device that performs combustion treatment on H.sub.2S and COS can be configured with a well-known combustion device such as a combustion burner.

[0061] The lime gypsum-type desulfurization apparatus 7 is an apparatus of recovering SO.sub.2 (sulfurous acid gas) produced by combusting H.sub.2S and COS as gypsum (CaSO.sub.4.2H.sub.2O). A well-known desulfurization apparatus can be employed as the lime gypsum-type desulfurization apparatus 7, the apparatus 7 generally suspends limestone (CaCO.sub.3) in water so as to form a limestone slurry, brings this slurry into contact with flue gas in an absorption tower, absorbs and removes SO.sub.2 in the flue gas, and forms gypsum by oxygen in the flue gas and oxygen in the air introduced into the absorption tower.

Source Gas Purification Method (First Embodiment)

[0062] Subsequently, an embodiment of the source gas purification method according to the present invention is described by describing a mechanism of actions of the source gas purification apparatus according to the present embodiment including a device configuration of FIG. 1.

[0063] First, according to the present embodiment, the source gas is introduced to the CO.sub.2 separation device 1. The CO.sub.2 separation device 1 separates and removes CO.sub.2 included in the source gas from the other gas component by a separation membrane.

[0064] Subsequently, the source gas from which CO.sub.2 is removed is introduced to the chemical absorption device 2. In the chemical absorption device 2, H.sub.2S is removed by chemical absorption. Residual CO.sub.2 that is not completely removed by the CO.sub.2 separation device 1 can be removed in the chemical absorption device 2, in addition to the removal of H.sub.2S. A portion of COS can also be absorbed and removed. In a case where CO.sub.2 concentration in the source gas is low, only the chemical absorption device 2 is used for separation and removal of CO.sub.2, and the CO.sub.2 separation device 1 may be omitted.

[0065] The source gas from which CO.sub.2 and H.sub.2S are removed is sent to the sulfur compound conversion catalyst device 3. Sulfur compounds other than H.sub.2S (described as COS and RSH in FIG. 1) and H.sub.2O are included in the source gas from which CO.sub.2 and H.sub.2S are removed, in addition to hydrocarbon such as methane.

[0066] Vapor is introduced to each of the front flow COS conversion catalyst device 3A and the RSH conversion catalyst device 3B included in the sulfur compound conversion catalyst device 3, COS is converted to H.sub.2S, by the above COS conversion catalyst device 3A, and RSH is converted to H.sub.2S by the back flow RSH conversion catalyst device 3B. The temperature of the introduced vapor is preferably 100 C. to 700 C. and more preferably a temperature greater than 300 C.

[0067] Gas including hydrocarbon, H.sub.2S, and H.sub.2O which can be obtained by converting COS and RSH to H.sub.2S by the sulfur compound conversion catalyst device 3 is introduced to the adsorption and desorption device 4 via a cooler 8. The adsorption and desorption device 4 adsorbs and removes H.sub.2S and H.sub.2O included in the gas.

[0068] The gas from which H.sub.2S and H.sub.2O are removed becomes highly pure hydrocarbon and is sent to the NGL recovery device 5.

[0069] The adsorption and desorption device 4 is regenerated by desorbing H.sub.2S and H.sub.2O by heating and decompression. The desorbed H.sub.2S and H.sub.2O is transported by C1 hydrocarbon (methane) supplied from the NGL recovery device 5, is confluent with the source gas from the CO.sub.2 separation device 1 (illustrated as * in FIG. 1), and is introduced to the chemical absorption device 2.

[0070] The gas sent to the NGL recovery device 5 is separated into C1 hydrocarbon (methane), C2-4 hydrocarbon (hydrocarbon having 2 to 4 carbon atoms), and C5+ hydrocarbon (hydrocarbon having 5 carbon atoms).

[0071] Independently from the C1 hydrocarbon after NGL recovery that is recovered as deliverables, a portion thereof is sent to the H.sub.2S combustion device 6 as auxiliary fuel.

[0072] C2-4 hydrocarbon and C5+ hydrocarbon are recovered as deliverables.

[0073] Meanwhile, the chemical absorption device 2 dissipates H.sub.2S, COS, and CO.sub.2 by performing a heating operation on an amine absorbent. H.sub.2S, COS, and CO.sub.2 are sent to the H.sub.2S combustion device 6.

[0074] C1 hydrocarbon from the NGL recovery device 5 is also sent to the H.sub.2S combustion device 6. C1 hydrocarbon, H.sub.2S, and COS are combusted by the H.sub.2S combustion device 6.

[0075] The flue gas obtained after combusting C1 hydrocarbon, H.sub.2S, and COS is sent to the lime gypsum-type desulfurization apparatus 7 via a heat exchanger 9.

[0076] Heat obtained from the heat exchanger 9 can be used in the production of vapor in the temperature greater than 300 C. supplied to the sulfur compound conversion catalyst device 3.

[0077] The lime gypsum-type desulfurization apparatus 7 recovers SO.sub.2 (sulfurous acid gas) obtained by combusting H.sub.2S and COS, as gypsum (CaSO.sub.4.2H.sub.2O). The lime gypsum-type desulfurization apparatus 7 forms a limestone slurry by suspending limestone (CaCO.sub.3) in water, brings this slurry into contact with flue gas by the absorption tower, absorbs and removes SO.sub.2 in the flue gas, and forms gypsum by oxygen in the flue gas and oxygen in the air introduced to the absorption tower.

[0078] According to the source gas purification apparatus and source gas purification method according to this first embodiment, the absorption step called the chemical absorption step is completed in one step, so as to aim at reducing a burden such as cost and labor in a process. The system is also simple. The S component is recovered as gypsum (CaSO.sub.4.2H.sub.2O), and thus burden in terms of storage is small.

Source Gas Purification Apparatus and Source Gas Purification Method (Second Embodiment)

[0079] A second embodiment of the source gas purification apparatus according to the present invention is conceptually illustrated in FIG. 2.

[0080] In the second embodiment, the first embodiment is provided in a specific level. However, those illustrated in the second embodiment in FIG. 2 are visually different from the first embodiment in appearance, and thus is described as the second embodiment for easier description.

[0081] In the second embodiment, a CO.sub.2 separation device 21 corresponds to the CO.sub.2 separation device 1, a chemical absorption device 22 corresponds to the chemical absorption device 2, a COS conversion catalyst device 23A corresponds to the COS conversion catalyst device 3A, an RSH conversion catalyst device 23B corresponds to the RSH conversion catalyst device 3B, adsorption and desorption devices 24A and 24B correspond to the adsorption and desorption device 4, and the contents described as the first embodiment with respect to the component equipment are incorporated in the present embodiment.

[0082] In FIG. 2, the H.sub.2S combustion device, the NGL recovery device, the lime gypsum-type desulfurization apparatus are not illustrated.

[0083] Subsequently, the present embodiment is described by describing a mechanism of actions of the component equipment according to this second embodiment. This description of the mechanism of actions is the description of the second embodiment of the source gas purification method according to the present invention.

[0084] First, as illustrated in FIG. 2, the source gas is introduced to the CO.sub.2 separation device 21. The CO.sub.2 separation device 21 separates and removes CO.sub.2 included in the source gas from the other gas components by a separation membrane.

[0085] In a case where the source gas which is the target of the present invention is subjected to membrane separation, with respect to a CO.sub.2 proportion in the source gas, gas in which a CO.sub.2 proportion is reduced can be obtained in an outlet on a primary side of the film, and gas in which a CO.sub.2 proportion is increased can be obtained in an outlet on a secondary side thereof.

[0086] In a case where a target CO.sub.2 proportion in the outlet gas on the primary side of the film is not achieved, an absorption method is combined. That is, the chemical absorption device 22 takes this role. Meanwhile, since a portion of the flammable gas such as methane is also included in gas on the secondary side, heat recovery can be performed by burning off gas (OFG in FIG. 2) on the secondary side and using the off gas as a heat source. Otherwise, an operation of repressurizing the off gas, recycling the off gas to the primary side, and recovering the off gas as a product may be performed.

[0087] According to the present embodiment, off gas (OFG in FIG. 2) on the secondary side is combusted to perform heat recovery.

[0088] Subsequently, the source gas from which CO.sub.2 is removed is introduced to the chemical absorption device 22. The chemical absorption device 22 removes H.sub.2S by chemical absorption. The chemical absorption device 22 can also remove residual CO.sub.2 that is not completely removed by the CO.sub.2 separation device 1 in addition to the removal of H.sub.2S. In addition, a portion of COS is absorbed and removed.

[0089] The chemical absorption device 22 dissipates H.sub.2S, COS, and CO.sub.2 by performing a heating operation on the amine absorbent. H.sub.2S, COS, and CO.sub.2 are sent to the H.sub.2S combustion device.

[0090] In a case where a CO.sub.2 concentration in the source gas is low, only the chemical absorption device 2 is used for separation and removal of CO.sub.2, and the CO.sub.2 separation device 1 may be omitted.

[0091] The source gas from which CO.sub.2 and H.sub.2S are removed is heated gas from the RSH conversion catalyst device 23B by a heat exchanger 25 and heated by H.sub.2S combustion gas and combustion gas obtained by combusting off gas with a heat exchanger 26, such that the temperature thereof preferably becomes a temperature greater than 300 C.

[0092] The source gas from which CO.sub.2 and H.sub.2S are removed is sent to the COS conversion catalyst device 23A and subsequently sent to the RSH conversion catalyst device 23B. The source gas becomes a temperature greater than 300 C., COS is converted to H.sub.2S by the front flow COS conversion catalyst device 23A, and RSH is converted to H.sub.2S by the back flow RSH conversion catalyst device 23B.

[0093] The COS conversion catalyst device 23A and the RSH conversion catalyst device 23B are consecutively arranged such that one of COS and RSH that has a smaller abundance ratio primarily becomes a treatment target. This is because, in a case where the amount of H.sub.2S to be produced increases, the amount of existing H.sub.2S increases in the production system, and thus the reaction hardly progresses in the direction of producing H.sub.2S on chemical equilibrium. In a case where the one having a smaller abundance ratio is first processed, the subsequent conversion target can be easily converted in a state in which an amount of H.sub.2S is smaller.

[0094] According to the present embodiment, it is assumed that an abundance ratio of RSH is greater, the COS conversion catalyst device 23A is primarily arranged, and thus COS conversion is first performed.

[0095] Gas including hydrocarbon, H.sub.2S, and H.sub.2O which can be obtained by converting COS and RSH to H.sub.2S is introduced to the adsorption and desorption devices 24A and 24B via a cooler 27. The cooler 27 cools the gas by cooling water. The adsorption and desorption devices 24A and 24B adsorb and remove H.sub.2S and H.sub.2O included in the gas.

[0096] The gas from which H.sub.2S and H.sub.2O are removed becomes highly pure hydrocarbon and is sent to an NGL recovery device (not illustrated).

[0097] The adsorption and desorption devices 24A and 24B are regenerated by desorbing H.sub.2S and H.sub.2O by heating or decompression. Desorbed H.sub.2S and H.sub.2O are transported by C1 hydrocarbon (methane) supplied from the NGL recovery device, is confluent with the source gas from the CO.sub.2 separation device 21, and is introduced to the chemical absorption device 22.

[0098] In the illustrated state, an adsorption and desorption device 24B is closed, and H.sub.2S and H.sub.2O are adsorbed by an adsorption and desorption device 24A. A valve (not shown) is opened, the adsorption and desorption device 24B is heated and decompressed, so as to desorb H.sub.2S and H.sub.2O.

[0099] In this manner, the adsorption and desorption devices 24A and 24B alternatively repeat adsorption and desorption so as to perform a continuous operation of the entire device.

[0100] As described above, this second embodiment is an embodiment describing the first embodiment in a specific level. Accordingly, this second embodiment has the same effect as the first embodiment. In addition to this basic effect, in this second embodiment, it is understood that an effect of enhancing thermal efficiency of a system by combustion of the off gas is exhibited. In this second embodiment, it is understood that two absorption towers included in the adsorption and desorption device alternatively repeat adsorption and desorption, such that an effect of causing the entire device to be continuously driven is exhibited.

Source Gas Purification Apparatus and Source Gas Purification Method (Third Embodiment)

[0101] The third embodiment of the source gas purification apparatus according to the present invention is conceptually illustrated in FIG. 3.

[0102] In this third embodiment, a H.sub.2S separation device 31 is employed as a first H.sub.2S removing device, a sulfur compound conversion catalyst device 32 which is the same as the first embodiment is employed as a sulfur compound conversion device that converts a sulfur compound other than H.sub.2S to H.sub.2S, and a chemical absorption device 33 that is the same as the first embodiment is employed as a second H.sub.2S removing device.

[0103] A CO.sub.2 separation device 34, an adsorption and desorption device 35, an NGL recovery device 36, a H.sub.2S combustion device 37, and a lime gypsum-type desulfurization apparatus 38 basically have the same configuration as the first embodiment.

[0104] The contents of the component equipment having the same names other than the H.sub.2S separation device 31 are the same as those provided in the first embodiment, and thus are basically applied to the present embodiment.

[0105] The H.sub.2S separation device 31 is a device that selectively removes H.sub.2S from natural gas including CO.sub.2, H.sub.2S, a sulfur compound other than H.sub.2S (mainly COS or RSH), and H.sub.2O, in addition to hydrocarbon such as methane, as impurities by a H.sub.2S separation membrane.

[0106] As the H.sub.2S separation membrane, materials through which H.sub.2S or carbon dioxide gas easily pass, and methane or the like hardly passes, which are disclosed in Japanese Unexamined Patent Application Publication No. H07-155787 can be used. As such a H.sub.2S separation membrane, a membrane including silicon, polyimide, and cellulose acetate can be exemplified.

[0107] In addition to the membrane separation using such a H.sub.2S separation membrane, a configuration in which H.sub.2S adsorption is performed by a molecular sieve or zinc oxide is possible.

[0108] Subsequently, the present embodiment is described by describing a mechanism of actions of the component equipment according to this third embodiment. This description of the mechanism of actions is the description of the third embodiment of the source gas purification method according to the present invention.

[0109] First, in the present embodiment, the source gas is introduced to the CO.sub.2 separation device 34. The CO.sub.2 separation device 34 separates and removes CO.sub.2 included in the source gas from other gas components by a separation membrane.

[0110] Subsequently, the source gas from which CO.sub.2 is removed is introduced to the H.sub.2S separation device 31. In the H.sub.2S separation device 31, H.sub.2S is removed by a H.sub.2S separation membrane or an adsorbent. The removed H.sub.2S is combusted by the H.sub.2S combustion device 37. In addition to the removal of H.sub.2S, the H.sub.2S separation device 31 can remove residual CO.sub.2 that is not completely removed by the CO.sub.2 separation device 34.

[0111] The source gas from which CO.sub.2 and H.sub.2S are removed is sent to the sulfur compound conversion catalyst device 32. In addition to hydrocarbon such as methane, a sulfur compound other than H.sub.2S (described as COS and RSH in FIG. 3), and H.sub.2O are included in the source gas from which CO.sub.2 and H.sub.2S are removed.

[0112] Vapor preferably in a temperature of greater than 300 C. is introduced respectively to a COS conversion catalyst device 32A and a RSH conversion catalyst device 32B included in the sulfur compound conversion catalyst device 32, COS is converted to H.sub.2S by the front flow COS conversion catalyst device 32A, and RSH is converted to H.sub.2S by the back flow RSH conversion catalyst device 32B.

[0113] The sulfur compound conversion catalyst device 32 introduces gas including hydrocarbon, H.sub.2S, CO.sub.2 (byproduct), and H.sub.2O which is obtained by converting COS and RSH to H.sub.2S, to the chemical absorption device 33. The chemical absorption device 33 adsorbs and removes H.sub.2S and CO.sub.2 included in the gas.

[0114] The gas from which H.sub.2S and CO.sub.2 are removed includes hydrocarbon and H.sub.2O, and is sent to the adsorption and desorption device 35 via a cooler 39.

[0115] H.sub.2O is adsorbed and removed from the adsorption and desorption device 35.

[0116] The adsorption and desorption device 35 is regenerated by desorbing H.sub.2O by heating and decompression. Desorbed H.sub.2O is transported by C1 hydrocarbon (methane) supplied from the NGL recovery device 5 and is confluent with an outgoing line of C1 hydrocarbon (illustrated as * in the drawing).

[0117] Gas sent to the NGL recovery device 36 is separated into C1 hydrocarbon (methane), C2-4 hydrocarbon (hydrocarbon having 2 to 4 carbon atoms), and C5+ hydrocarbon (hydrocarbon having 5 or greater carbon atoms).

[0118] Independently from C1 hydrocarbon recovered as deliverables, a portion thereof is sent to the adsorption and desorption device 35 as described above, and another portion thereof is sent to the H.sub.2S combustion device 37.

[0119] C2-4 hydrocarbon and C5+ hydrocarbon are recovered as deliverables.

[0120] Meanwhile, the chemical absorption device 33 dissipates H.sub.2S and CO.sub.2 by performing a heating operation on the amine absorbent. H.sub.2S and CO.sub.2 are sent to the H.sub.2S combustion device 37.

[0121] C1 hydrocarbon is also sent to the H.sub.2S combustion device 37 from the NGL recovery device 36 as described above. C1 hydrocarbon and H.sub.2S are combusted by the H.sub.2S combustion device 37.

[0122] The flue gas obtained by combusting C1 hydrocarbon and H.sub.2S is sent to the lime gypsum-type desulfurization apparatus 38 via a heat exchanger 40.

[0123] Heat obtained by the heat exchanger 40 can be used in the production of the vapor in the temperature greater than 300 C. which is supplied to the sulfur compound conversion catalyst device 32.

[0124] The lime gypsum-type desulfurization apparatus 38 recovers SO.sub.2 (sulfurous acid gas) obtained by combusting H.sub.2S and COS as gypsum (CaSO.sub.4.2H.sub.2O). The lime gypsum-type desulfurization apparatus 38 forms limestone slurry by suspending limestone (CaCO.sub.3) in water, brings this slurry into contact with flue gas by the absorption tower, absorbs and removes SO.sub.2 in the flue gas, and forms gypsum by oxygen in the flue gas and oxygen in the air introduced to the absorption tower.

[0125] In addition to the effect that can be expected in the first embodiment, an effect in which a burden of the adsorption and desorption device 35 is reduced such that the size thereof is caused to be compact can be expected in this third embodiment.

[0126] In the third embodiment, the chemical absorption device 33 may not be provided. In this case, the entire gas including hydrocarbon, H.sub.2S, and H.sub.2O is sent from the sulfur compound conversion catalyst device 32 to the adsorption and desorption device 35, so as to adsorb H.sub.2S and H.sub.2O. Accordingly, highly pure hydrocarbon is obtained and sent to the NGL recovery device 36. H.sub.2S and H.sub.2O are desorbed from the adsorption and desorption device 35 by C1 hydrocarbon from the NGL recovery device 36 and sent to the H.sub.2S separation device 31. Other treatments can be performed in the same manner as the above third embodiment.

Source Gas Purification Apparatus and Source Gas Purification Method (Fourth Embodiment)

[0127] The source gas purification apparatus according to the present invention is provided in FIG. 4, and the fourth embodiment is conceptually provided.

[0128] This fourth embodiment is a form in which the mercury removing device 10 is provided immediately before the sulfur compound conversion catalyst device 3 according to the first embodiment.

[0129] According to the present embodiment, in addition to hydrocarbon such as methane, natural gas including CO.sub.2, H.sub.2S, a sulfur compound other than H.sub.2S (mainly COS or RSH), H.sub.2O, and Hg as impurities is provided as the source gas of the treatment target.

[0130] According to the present embodiment, the components indicated by the same reference numerals provided in FIG. 1 have substantially the same configurations as in FIG. 1, and substantially takes the same role.

[0131] The mechanism of actions of the present embodiment, that is, one embodiment of the source gas purification method according to the present invention, is substantially the same as those illustrated in FIG. 1. However, the present embodiment is different from the first embodiment in that a mercury removal step in which a mercury removing device 10 is operated is added.

[0132] The mercury removing device 10 is provided for the purpose of removing mercury (single substance of Hg, or organic mercury), which is a trace component.

[0133] As the mercury removing device 10 that can be employed, activated carbon may be used as a physical adsorbent, or a molecular sieve may be used. However, this method by physical adsorption tends to cause the device to have large capacity. Accordingly, it is preferable to include a mercury adsorbent (chemical adsorbent) as a guard reactor of the sulfur compound conversion catalyst device 3.

[0134] As the included mercury adsorbent, sulfide (such as CuS and/or MoS.sub.3) is preferable. In this form of employing such a mercury adsorbent, due to the chemical adsorption, an adsorption amount is great, and thus space can be saved. In order to cause mercury to be fixed and adsorbed as sulfide, fixation can be performed regardless of the kinds of mercury. The heating temperature of the mercury adsorbent is near 100 C. to 300 C., and a heat source which is the same heat source that heats the sulfur compound conversion catalyst device 3 can be employed.

[0135] According to this fourth embodiment, in addition to the effect exhibited by the first embodiment, an effect of effectively removing mercury included in the source gas can be expected. An effect of preventing poisoning of the conversion catalyst used in the sulfur compound conversion catalyst device 3 existing on the back flow can be expected.

REFERENCE SIGNS LIST

[0136] 1, 34 CO.sub.2 separation device [0137] 2, 33 Chemical absorption device [0138] 3, 32 Sulfur compound conversion catalyst device [0139] 4, 35 Adsorption and desorption device [0140] 5, 36 NGL recovery device [0141] 6, 37 H.sub.2S combustion device [0142] 7, 38 Lime gypsum-type desulfurization apparatus [0143] 8, 39 Cooler [0144] 9, 40 Heat exchanger [0145] 10 Mercury removing device [0146] 31 H.sub.2S separation device