FR2983209A1 - Producing desulfurized natural gas, comprises performing adsorption of sulfur by reacting metal sulfide and hydrogen sulfide to obtain metal disulfide and hydrogen, and regenerating metal sulfide by heating metal disulfide - Google Patents

Abstract

The method comprises, utilizing an amines scrubbing unit (A1), producing a desulfurized natural gas without carbon dioxide (CO 2) (11) at first and a concentrated gas effluent (3) comprising CO 2and H 2S, introducing effluent into a hydrogen sulfide (H 2S) collection unit using a solid adsorbent in a form of a metal sulfide (MeS) for performing adsorption of sulfur by reacting the MeS and H 2S to obtain metal disulfide (MeS 2) and hydrogen, and entering to a methanation unit (M1) that allows collection of CO 2and formation of an additional hot methane flow (7). The method comprises, utilizing an amines scrubbing unit (A1), producing a desulfurized natural gas without carbon dioxide (CO 2) (11) at first and a concentrated gas effluent (3) comprising CO 2and H 2S, introducing effluent into a hydrogen sulfide (H 2S) collection unit using a solid adsorbent in a form of a metal sulfide (MeS) for performing adsorption of sulfur by reacting the MeS and H 2S to obtain metal disulfide (MeS 2) and hydrogen, entering to a methanation unit (M1) that allows collection of CO 2and formation of an additional hot methane flow (7) that is obtained by transferring calories of the methanation unit to a regeneration zone of an H 2S adsorption unit using solid absorbent to obtain methane flow for allowing the regeneration of MeS by heating the MeS 2to obtain the MeS and gaseous sulfur, where the methane flow is used for setting a temperature of the gas effluent after heating at a temperature of 250-350[deg] C, introducing hot methane flow the H 2S collecting unit, and mixing the methane flow with the desulfurized natural gas output from the amines scrubbing unit to deliver desulfurized natural gas. The regeneration phase of the solid adsorbent implemented in the adsorption unit is operated at a temperature of 200-300[deg] C. A molar relationship of hydrogen/CO 2of the effluent of the adsorption unit is 4-4.2. The regeneration zone of the H 2S adsorption unit comprises an exchanger in which the methane hot flow is circulated inside tubes and MeS 2to be regenerated is located inside a grill. A methanation reactor has an annular form, and functions in a radial bed such that a flow runs out from a periphery of the methanation reactor to a central collector.

Description

FIELD OF THE INVENTION The invention relates to a method for purifying a natural gas (mainly consisting of methane) and which may contain significant levels of CO2 and H2S. The process simultaneously allows the production of high purity sulfur.

It also makes it possible to increase the amount of natural gas purified by adding methane, in a proportion of the order of 20%. This proportion is of course a function of the content of H2S in the natural gas to be treated. EXAMINATION OF THE PRIOR ART It is known in the prior art to remove H2S from natural gas by washing with an amine solvent to achieve commercial specifications. Natural gas can also contain CO2, which can also be removed by amine scrubbing at the same time as H2S. The solvent after the regeneration step, generally by heating, produces an acidic gas which may contain H2S contents generally ranging from 30% to 90%. This acid gas is generally sent to a CLAUS unit allowing the conversion of H2S into elemental sulfur. The CLAUS process allows a sulfur recovery rate of the order of 95 to 97%. This sulfur recovery rate in many cases does not allow for compliance with SO2 emissions legislation. Therefore, a tail gas treatment step (T1) is required to transform the residual SO2 into H2S. The tail gas treatment units are of very different types and are generally very expensive in terms of investment and energy consumption. It consists in most cases in a hydrogenation step according to the following reactions: (d) S + H2 H 2 S (e) SO 2 + 3 H 2 -> H 2 S + 2H 2 O (f) CO + H 2 O -> CO 2 + H 2 reactions (d), (e) and (f) have hydrogen and CO requirements. Partial combustion of methane produces CO for the production of hydrogen (f). The H2S formed must then be captured in an amine wash unit for recycling to the CLAUS process inlet. In the case of a weakly concentrated acid gas in H2S (that is to say with a concentration of less than 45-50% vol.), The latter is sent to a unit called enrichment unit. Such an enrichment unit makes it possible to pass the acid gas of a content 45-50% volume, at contents greater than 50% volume allowing direct shipment to a conventional CLAUS unit. The acid gas from the amine washing unit is sent to the enrichment unit from which emerges a gas rich in H2S and highly concentrated in CO2 which is sent to an incinerator. The CLAUS unit and the tail gas treatment unit remain unchanged from the first case. The present process avoids the CLAUS unit, enrichment unit and tail gas treatment sequence, by carrying out the removal of CO2 by amine treatment, but also the removal of H2S in a unit. adsorption using a metal sulphide (MeS) whose regeneration is ensured by a supply of calories from a methanation unit. This methanation unit therefore has a twofold purpose, on the one hand to ensure the complete conversion of CO2 into CH4 which will enrich the methane content of the natural gas treated, and on the other hand to generate calories supplied by the reaction effluent. said methanation unit, which will be used for the regeneration of the adsorbent mass (MeS2) at the level of the H2S uptake unit. SUMMARY DESCRIPTION OF THE FIGURES FIG. 1 represents a diagram of the process according to the present invention in which the amine treatment unit (A1), the regenerative recovery unit of H2S (AH1 / RH1), and the methanation unit (M1). SUMMARY DESCRIPTION OF THE INVENTION The present invention can be defined as a process for producing a desulfurized and CO2-free natural gas using a three-unit process, a) an amine washing unit (A1) which allows part of producing a desulfurized and CO2-free natural gas (11), and secondly a gaseous effluent (3) concentrated in H2S and CO2 which enters b) an H2S capture unit (AH1 / RH1) using a solid adsorbent in the form of a metal sulphide (MeS), carrying out the adsorption of sulfur according to the reaction: MeS + H 2S ---> MeS 2 + H 2 (g) the effluent (5) the H2S capture unit, essentially composed of hydrogen and CO2, which is introduced into c) a methanation unit (M1) that allows the capture of CO2 and the formation of an additional hot flow of CH4 (7), said additional hot methane stream (7) from the methanation unit (M1) transferring its calories to the regeneration zone from the adsorption unit (AH1 / RH1) and becoming a stream (9), to allow the regeneration of the adsorbent solid (MeS2) by return to the sulphide form (MeS), according to the reaction MeS2 MeS + -81 S8 (g) (h) The flow of methane (9) at the outlet of the regeneration zone (RH1) allows the temperature of the gaseous effluent (3) coming from the amine treatment unit (A1) to become 4) after it has been heated to a temperature level of between 250 ° C. and 350 ° C., before its introduction into the H2S (AH1) capture unit, said flow of methane (10) joining the desulfurized natural gas (2) at the outlet of the amine treatment unit (A1) for delivering the desulfurized and CO2-free natural gas with an increased content of methane (11). According to a preferred variant of the process for producing a natural gas desulfurized and non-CO2 enriched in methane according to the invention, the H2S capture unit (AH1 / RH1) uses an adsorbent solid chosen from sulphides. the following metals: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Even more preferably, the adsorbent solid used in the adsorption unit (AH1 / RH1) is of iron sulphide type alternating between a Fei_xS form, x being greater than or equal to 0, and strictly less than 0.5, and a FeS2 form. According to another variant of the process according to the present invention, the molar ratio H2 / CO2 of the effluent (5) of the adsorption unit (AH1 / RH1) of the H 2 S is between 4 and 4.5 and preferably between 4 and 4.2. According to another preferred variant of the process according to the present invention, the regeneration zone RH1 of the adsorption unit of H2S consists of a shell-type heat exchanger, in which the additional hot flow of CH4 (7) circulates at inside the tubes, and the solid to be regenerated (MeS2) is located inside the shell. According to another preferred variant of the process according to the present invention, the reactor used in the methanation unit is a ring-shaped reactor with radial-type flow, the incoming stream (6) being introduced at the periphery of the reactor and the reaction effluent. being collected in a central collector. DETAILED DESCRIPTION OF THE INVENTION The following description is made with reference to FIG. 1 which represents the method according to the invention in its preferred version. The natural gas (1), which is preferably rich in acid gas (typically the contents of CO2 + H2S are greater than 20% by volume) passes through a washing unit (A1) with a thermally regenerable solvent allowing the absorption of the acidic species, generally an alkanolamine amine solvent, such as DEA, or MDEA. At the outlet of the unit A1, there emerges a gas (2) with commercial specifications, and a gas (3) rich in H2S + CO2 at low pressure generally close to the atmosphere. This gas (3) is brought to a temperature close to that of the process, preferably between 250 ° C. and 350 ° C., via an effluent feed exchanger E1. In the reactor AH1 the adsorption takes place. sulfur mainly from H 2 S using an adsorbent solid (101), generally a metal sulfide, denoted MeS. This results in a gaseous effluent depleted of sulfur (5), but rich in H2 and CO2, and a solid loaded with sulfur (100). The gaseous flow rich in H2 and CO2 (5) is at the outlet of the adsorption reactor (AH1) under conditions of temperatures generally between 250 ° C. and 300 ° C., and in H2 / CO2 proportions close to 4 ° C. so that CO2 can be converted to methane. In the case where the proportion H2 / CO2 is greater than 4 (excess of hydrogen), which is the most general case, the excess hydrogen is sent into the natural gas, as shown in the example which follows. The sulfur-filled solid (100) is heated in the exchanger reactor RH1 at a temperature above 550 ° C, and preferably between 550 ° C and 700 ° C. The solid (MeS2) is thus regenerated, that is to say returns to its least sulfurized form (MeS), and is returned to the adsorption section AH1. This results in a stream (8) of elemental sulfur S8 which is then condensed, typically at a temperature below 220 ° C, and preferably at a temperature of between 150 ° C and 200 ° C, to become the liquid sulfur stream. (8a). In this temperature range, the sulfur remains in the liquid state and does not solidify. The gas rich in H2 and CO2 (5) is then compressed in the compressor K1 at a pressure equal to the pressure of the outgoing natural gas (11) to promote the thermodynamics of the reaction. The catalyst present in the methanation reactor (M1) may consist of nickel oxides deposited on an alumina support. The reactor (M1) can operate in fixed bed, and preferably with a radial type flow, the flow to be treated (6) entering the periphery of the reactor and being collected in a central collector.

It remains within the scope of the present invention by disposing several methanation reactors (M1) in series, with intermediate cooling then re-compression so as to improve the overall conversion rate of CO2 to methane. The remainder of the description gives some details of the 3 units involved in the process according to the invention. The amine treatment unit is well known to those skilled in the art and will not be described more precisely. The preferred solvents in the context of the present invention are the alkanolamine-based solvents (MDEA, DEA). The unit for capturing H2S by adsorption on a regenerable solid consists of an adsorption section on a capture mass which changes from a monosulfide form to a disulfide form. By way of example, it may be iron sulphide (FeS) which converts to iron disulfide (FeS2), depending on the sulfur capture reaction: FeS + H2 S FeS2 + H2 (g) Dissociation of the Hydrogen sulfide (H2S) in hydrogen (H2) and sulfur (S) in the form of metal disulfide (FeS2) is exothermic and preferably occurs between 250 ° C and 350 ° C. Regeneration of metal disulfide to metal monosulfide and sulfur gas is endothermic and occurs at temperatures of at least 550 ° C to 600 ° C, preferably greater than 600 ° C. The regeneration reaction of the disulphide takes the form of a thermal regeneration: FeS 2 - → FeS + -8S 8 (g) (h) The method according to the invention therefore implements in the capture unit of the H2S a pair of metal sulphides whose nature allows spontaneous sulphurization at temperatures of the order of 200 ° C. to 500 ° C., preferably between 250 ° C. and 350 ° C., and regeneration by spontaneous release of the sulfur absorbed during a heat treatment carried out between 100 ° C and 400 ° C above the adsorption temperature, preferably between 200 ° C and 300 ° C above the adsorption temperature. The metals that can be used to carry out these disulfide-form sulphide-type transitions can be chosen from the transition metals of the first period such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn. Among these, preference will be given to iron sulphides alternating between a Fe 1-x S form, x being greater than or equal to 0 and strictly less than 0.5, and a FeS 2 form. The methanation unit M1 implements the following methanation reaction: (i) CO2 + 4H 2 CH 4 + 2H 2 O The methanation reaction (i) is highly exothermic and produces a gaseous effluent at a temperature close to 700 ° C. The heat thus provided by the effluent (7) of the methanation unit (M1) provides the calories necessary for the regeneration step 15 of the H2S uptake solid (regeneration reaction h in the unit RH1) . The present invention therefore makes it possible to increase the production of methane by means of the methane produced in the methanation unit (M1) which, after having given up its calories in the regeneration stage of the adsorption solid (RH1), and then at the level of the charge / effluent exchanger (El) joins the treated natural gas (11) at the outlet of the amine treatment unit (A1). The extensive thermal integration of the process according to the invention carried out thanks to the hot effluent of the methanation unit (M1) thus allows both the uptake of H2S at the AH1 capture unit, then the regeneration of the adsorbent solid 25 at the RH1 regeneration. EXAMPLE ACCORDING TO THE INVENTION The following example illustrates the effects of the process according to the present invention.

It is presented as a material balance by following the flow numbers in Figure 1. 1 2 3 4 5 6 7 Flow (Nm3 / h) 200 000 104 000 105 494 105 105 105 105 494 494 494 494 Pressure ( bar) 50 50 2 2 2 50 50 Temperature (° C) 45 45 50 250 250 350 800 vol% CH4 50 98 0.1 0.1 0.1 0.1 21.5 vol% CO2 10 2 15.2 15.2 15.2 15.2 <0.2 vol% H2S 40 <0.001 75.8 75.8 0.1 0.1 0 vol% H2O 0 0.1 9 9 9 9 55.9 vol% H2 0 0 0 0 75.7 75.7 22.3 11 Flow rate 136 (Nm3 / h) 578 Pressure (bar) 50 Temperature (° C) 45 vol% CH4 86.2 vol% CO2 1.6 vol% H2S <0.001 vol% H2O 0.2 vol% H2 12 The amine treatment unit Al works with a solvent which is the MDEA.

The adsorption unit of H.sub.2S works with a solid adsorbent of the Fe.sub.1.sup.xS type, x being equal to 0.4 and in adsorption phase at a temperature of 250.degree. Regeneration of the adsorbent solid is carried out at a temperature of 700 ° C. The methanation unit M1 operates at a temperature of 350 ° C with a catalyst which is a nickel oxide supported on alumina. The H2 / CO2 ratio of the feed stream into the methanation reactor (M1) is 4.2. The process according to the invention makes it possible to produce: 1) a desulphurized and CO2-free natural gas stream (11) 2) a pure solid sulfur stream (8a), 3) the calories necessary for the regeneration of the adsorbent solid are brought by the effluent from the methanation reactor (M1). 4) to increase the amount of methane relative to the natural gas to be treated, since the methane (10) produced in the methanation reactor (M1) is added to the methane of the incoming natural gas (1) so as to produce the treated natural gas stream 15 (11). The volume gain of the product natural gas (11) is 25% relative to the incoming natural gas (1). 20 25 30

Claims (8)

REVENDICATIONS1. A process for producing a desulfurized and CO2-free natural gas using a three-unit process, an amine washing unit (A1) which on the one hand produces a desulfurized and CO2-free natural gas (11), and on the other hand a gaseous effluent (3) concentrated in H2S and CO2 which enters the H2S capture unit (AH1 / RH1) using an adsorbent solid in the form of a metal sulphide (MeS), carrying out the adsorption of sulfur according to the reaction: MeS + H2 S ----> MeS2 + H2 (g) the effluent (5) of the H2S capture unit, consisting essentially of hydrogen and CO2, entering the methanation unit (M1) which allows the capture of CO2 and the formation of an additional hot flow of CH4 (7), said hot flow of methane (7) from the methanation unit (M1) transferring its calories at the regeneration zone of the adsorption unit (AH1 / RH1) and becoming stream (9), to allow the regeneration of the adsorbent solid (MeS2) by return with the sulphide form (MeS), according to the MeS2 MeS + -81 S8 reaction (g) (h) and the flow of methane (9) at the outlet of the regeneration zone (RH1) being used for the heating up of the effluent gas (3) becoming (4) after heating to a temperature level of between 250 ° C and 350 ° C, said hot gaseous effluent (4) being introduced into the H2S collection unit (AH1 ), and said flow of methane (10) joining the desulphurized natural gas (2) at the outlet of the amine treatment unit (A1) to deliver the desulfurized and CO2-free natural gas with increased content of methane (11). 2. Process for producing a methane-enriched, natural gas-free desulfurized natural gas according to claim 1, in which the H2S capture unit (AH1 / RH1) uses an adsorbent solid selected from metal sulphides. following: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. The process for producing a methane-enriched, natural gas-free desulfurized natural gas according to claim 1, wherein the H2S capture unit (AH1 / RH1) uses an alternating iron sulphide adsorbent solid. between a form Fei_ xS, x being greater than or equal to 0 and strictly less than 0.5, and a form FeS2. 4. A process for producing a methane-enriched, methane-free, desulfurized natural gas according to claim 1, wherein the regeneration phase of the adsorbent solid used in the adsorption unit (AH1 / RH1) is operated at a rate of temperature between 200 ° C and 300 ° C above the adsorption temperature. The process for producing a methane-enriched, methane-free, desulfurized natural gas according to claim 1, wherein the H 2 / CO 2 molar ratio of the effluent (5) of the H 2 S adsorption unit is included between 4 and 4.5 and preferably between 4 and 4.2. The process for producing a methane-enriched, natural gas-free desulfurized natural gas according to claim 1, wherein the regeneration zone RH1 of the H2S adsorption unit consists of a shell-type exchanger in which the hot flow of additional CH4 (7) circulates inside the tubes, and the solid to be regenerated (MeS2) is located inside the shell. A process for producing a methane-enriched, methane-free, desulfurized natural gas according to claim 1, wherein the solvent used at the amine treatment unit (A1) is DEA or MDEA. A process for producing a methane-enriched, natural gas-free desulfurized natural gas according to claim 1, wherein the methanation reactor M1 has an annular shape and operates in a radial bed, ie the flow (6). flows from the periphery of the reactor to a central collector.