Absorption gas processing process with thermally optimized hot flash solvent regeneration.

Abstract

The present invention relates to a system and method for treating gases by chemical, physical or hybrid absorption of the compounds to be removed, comprising at least: a) a step of absorption by contacting the gas to be treated and the depleted solvent, thereby obtaining a treated gas and a rich solvent; b) an optional medium-pressure flash separation step; c) a step of heat exchange between a fraction of the cold rich solvent and a hot depleted solvent in a first exchanger; d) a step of heat exchange between a complementary fraction of the cold rich solvent and a hot gaseous effluent in a second exchanger; e) an optional low-pressure flash separation step; f) a step of regenerating the rich solvent by heating in a reboiler; g) a low-pressure flash separation step; h) cooling the depleted solvent.

Description

[Technical Field]

[0001] The present invention relates to the field of gas processing, and more particularly to a method for processing gases by absorption (chemical, physical or hybrid) with hot flash solvent regeneration. This type of regeneration is generally limited to applications where partial regeneration of the solvent is deemed sufficient to meet specifications for the gas being processed.

[0002] Therefore, the target area is essentially the case of decarbonization (capture of CO2 from natural gas, biogas, syngas, industrial flue gases from incinerators, coal power plants, melting furnaces, etc.).

[0003] Cases involving what are called strict specifications (H2S, COS, thiols, SO x , NO x etc.) generally require provision for higher levels of solvent regeneration by steam entrainment (more commonly called steam stripping; i.e., a method for extracting volatile compounds by entrainment with an inert gas) to achieve the required quality of depleted solvent in the regenerator. Hot flash regeneration modes have generally proven unsuitable in these cases. [Background technology]

[0004] Plants for treating gases by absorption with a solvent, preferably an amine, traditionally consist of two chemical reactors: an absorber and a regenerator. In the absorber, the downward flow of the solvent meets the upward flow of the gaseous mixture and combines with the acid gases contained therein. The "sweetened" gaseous mixture leaves the absorber free of its compounds for removal, while the "rich" solvent carries with it the acid gases. In the regenerator, the rich solvent can be regenerated by stripping, i.e., by successive heating in a stripper (evaporator) and boiler to discharge acid-rich vapors, or by hot flashing, i.e., by passing it directly through a reboiler and then through a hot flash to free it from the desorbed gaseous compounds. The solvent "depleted" of acid gases is cooled by the rich solvent from the absorber. The cold depleted solvent can then be returned to the absorber to scrub the gas.

[0005] As with any process, the challenges for a process for treating gases by absorption are the capital expenditure (CAPEX) and operating costs (OPEX) for the plant. Absorption processes using simple hot flash regeneration are known to those skilled in the art and have made some progress in meeting these challenges: by comparison with processes requiring regeneration by stripping, capital expenditure is limited (no regeneration column to begin with) and the energy consumed by the process (reboiler power) can be significantly reduced (this is a major item in the operating costs for the process).

[0006] Hot flash regeneration modes are generally limited to areas of application where lower levels of solvent regeneration are sufficient. Alternatively expressed, very low residual amounts of acid gases (CO2, H2S) in the depleted solvent are not required to meet target specifications in the gas being treated (for low specification decarbonation: natural gas, biogas, CO2 capture from industrial flue gas, etc.).

[0007] The heat integration associated with this hot flash regeneration mode is generally limited. It takes the form of a feed / effluent heat exchanger installation that allows the cold rich solvent from the absorption section to be reheated from the hot depleted solvent exiting the regeneration section. An example is given in Figure 2 (described in more detail later in this specification) for a natural gas decarbonation scenario for gas pipeline specification purposes (typically 2.5% CO2 by volume). In this example, the thermal energy in the hot water-saturated CO2 effluent from the regeneration section is not effectively utilized. Heat from the cooling process of the gaseous effluent is generally not dissipated using cooling towers or water chillers.

[0008] For biogas scrubbing applications, Hitachi Zosen Inova (HZI) proposes recovering heat from the CO2 effluent and also from the hot depleted solvent (see Figure 3; described in detail later in this specification). However, the proposed arrangement of exchangers does not appear to be optimal. The reason is that the seating of the CO2 / rich solvent exchanger as described (i.e., upstream of the rich solvent / depleted solvent exchanger) reduces heat recovery from the depleted solvent and is therefore detrimental to the heat integration of the process.

[0009] In the literature (Patent Document 1; Air Liquide), the use of heat pumps (HP) has been proposed to reduce the heat consumption in this process, also for biogas scrubbing applications. However, there is a considerable increase in the power consumption of this process and in the capital expenditure (due to the heat pump compressor) for the plant.

[0010] It can therefore be seen that at present there is no satisfactory solution to the following problem: to sufficiently reduce the heat consumption in the absorption process without increasing the power consumption of the process and the capital expenditure for the plant.

[0011] The present invention meets this technical challenge by proposing to carry out a hot flash process for solvent regeneration in combination with modified heat integration, which will be described in detail hereinafter.

[0012] In the following description, the term "heat exchanger" or more simply "exchanger" refers to any device that allows the transfer of thermal energy from one fluid to another without the fluids being mixed. The heat exchange may be indirect, via an exchange surface separating the two fluids. In this case, the heat flow crosses the exchange surface separating the two fluids.

[0013] In the following description, unless otherwise indicated, pressures are absolute pressures expressed in bar. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2019 / 053367 Summary of the Invention [Means for solving the problem]

[0015] (Summary of the Invention) The present invention relates to a method for treating gases by chemical, physical or hybrid absorption of removal compounds, comprising at least: a) absorption of the removal compounds in an absorber (1) by contacting a treated gas stream (101) with a solvent stream (117), preferably at a temperature between 20 and 60°C, called "depleted solvent", to give a treated gas (102) and a solvent (103) enriched in the removal compounds, called "rich solvent"; b) optional separation of the rich solvent (103) in a medium pressure flash vessel (2) to desorb the co-absorbed compounds (106) and give a cold rich solvent (104), preferably at a temperature between 40 and 80°C; c) carrying out heat exchange in a heat exchanger (3A) between a fraction (104A) of the cold rich solvent stream (104) and a hot depleted solvent stream (110) to give a reheated rich solvent stream (105A) preferably at a temperature of 60-170°C, highly preferably at a temperature of 100-130°C, and a cooled depleted solvent stream (115) preferably at a temperature of 45-90°C, highly preferably at a temperature of 60-90°C; d) heat exchange in a heat exchanger (3B) between a complementary fraction (104B) of the cold rich solvent stream (104) and a hot desorbed gas effluent (112), which corresponds to the desorbed gas stream (111) from the flash separation in step g) and the gaseous compounds stream (107) optionally from the flash separation in step e), to give a reheated rich solvent stream (105B) preferably at a temperature between 60 and 170°C, highly preferably between 100 and 130°C, and a cooled desorbed gas stream (113), preferably at a temperature between 45 and 90°C, highly preferably between 60 and 90°C; e) optional separation of the reheated rich solvent streams (105A) and (105B) at the outlet of the heat integration step in a low-pressure flash vessel (4), allowing separation of gaseous compounds (107), preferably at a temperature between 60 and 170°C, highly preferably between 100 and 130°C, and a rich solvent stream (108), preferably at a temperature between 60 and 170°C, highly preferably between 100 and 130°C; f) regenerating the rich solvent (108) by heating in a reboiler (5) preferably at a temperature of 70-180°C to give a biphasic regenerated solvent (109); g) separation of the biphasic regenerated solvent (109) in the low-pressure flash vessel (6) allowing separation of a hot depleted solvent stream (110), preferably at a temperature of 70-180°C, highly preferably 110-140°C, from a gaseous stream (111) containing the removal compound in the form of a desorbed gas, preferably at a temperature of 70-180°C, highly preferably 110-140°C; h) final cooling of the cooled depleted solvent (115) to give a fully cooled depleted solvent stream (116) at a temperature between 20 and 60°C, said depleted solvent stream (116) being ready to be fed back to the absorber (1) in the form of a depleted solvent stream (117). The present invention relates to a method including:

[0016] The fraction (104A) of the cold rich solvent stream sent to the heat exchanger (3A) may represent between 0.5% and 50% by weight, preferably between 5% and 40% by weight, of the total rich solvent stream.

[0017] The separation in the medium pressure flash vessel in step b) may be carried out at a higher pressure than the separation in the low pressure flash vessel, at 3 to 10 bar, preferably 5 to 10 bar, highly preferably 5 to 7 bar.

[0018] The separation in the low pressure flash vessel in steps e) and g) may be carried out at a pressure of 0 to 9 bar, preferably 1 to 4 bar.

[0019] In one embodiment, the separation in the low pressure flash vessel in steps e) and g) is carried out at the same pressure of 1 to 4 bar, and the separation in the medium pressure flash vessel in step b) is carried out at a pressure of 5 to 10 bar.

[0020] In one embodiment, the pressure at which the heating in the reboiler in step f) and the separation in the low-pressure flash vessel in step g) are carried out is strictly 0 to 1 bar, and the temperature in the reboiler in this case is 70 to 100°C.

[0021] In another embodiment, the operating pressure in the reboiler is 1-9 bar, preferably 1-4 bar, and the temperature in the reboiler is 100-140°C, preferably 110-140°C.

[0022] The solvent may be a chemical solvent that includes at least one amine.

[0023] The solvent preferably comprises a mixture of tertiary and secondary amines.

[0024] The process may include step i) of final condensation of the desorbed gas stream (113) with the aim of limiting water losses in the process, to give a cooled desorbed compound stream (114), preferably at a temperature of 20-60°C.

[0025] The operating pressure in the absorption step a) may be between 1 and 80 bar.

[0026] The process gas may be selected from biogas, natural gas, synthetic gas (syngas), or industrial flue gas, for example the flue gas of a coal-fired power plant, an incinerator or a melter.

[0027] The invention relates to a gas processing plant which allows the implementation of the method according to the invention, at least: an absorber (1) that makes it possible to contact the treated gas with a solvent called "depleted solvent" to give a solvent rich in the treated gas and the removed compounds called "rich solvent", - an optional vessel (2) for a medium pressure flushing treatment of the rich solvent to desorb the co-absorbed compounds, - Cold rich solvent / hot depleted solvent heat exchanger (3A), - cold rich solvent / hot gas effluent heat exchanger (3B), a conduit for short-circuiting the fraction of cold rich solvent fed to the cold rich solvent / hot depleted solvent heat exchanger (3A) to the cold rich solvent / hot gas effluent heat exchanger (3B); an optional low-pressure flash vessel (4) at the outlet of the heat-integrated step, allowing degassing of the rich solvent; - a reboiler (5) that allows heating of the rich solvent, - a low-pressure flash vessel (6) that allows the separation of the regenerated solvent and the removed compounds in the form of desorbed gases; an optional final condenser (7) for the desorbed gases, with the aim of limiting the losses of water and solvent in the process; - Final cooler for depleted solvent (8), - a set of pumps (9) for the solvent (depleted and / or rich) that allow the solvent to flow through; It also relates to gas processing plants, including

[0028] The heat exchanger (3A) and the heat exchanger (3B) may consist of one and the same device. DETAILED DESCRIPTION OF THE INVENTION

[0029] (List of drawings) Other characteristics and advantages of the method and plant according to the invention will become apparent from the following description of non-limiting exemplary embodiments, with reference to the accompanying figures 1 to 4.

[0030] FIG. 1 shows a schematic diagram of the method according to the invention (using the example of natural gas decarbonation).

[0031] The method proposed by the present invention (FIG. 1) comprises the treatment of gases by absorption in physical, chemical or hybrid solvents (hybrid means a mixture of physical and chemical solvents) utilizing hot flash solvent regeneration, and comprises at least the following steps: - absorption of the removal compound in an absorber (1), allowing contact between the treatment gas and the depleted solvent; - optional separation of the rich solvent in the vessel (2) by a medium pressure flash process MP aimed at desorbing the co-absorbed compounds (typically hydrocarbons in natural gas processing applications), - Heat integration process using a cold rich solvent / hot depleted solvent heat exchanger (3A) - Heat integration process employing a cold rich solvent / hot gas effluent heat exchanger (3B) - Sampling of cold rich solvent stream fractions from cold rich solvent / hot depleted solvent heat exchangers Separation in an optional low-pressure flash LP vessel (4) at the outlet of the heat integration step, allowing degassing of the rich solvent - a step of regeneration by passing the rich solvent through a reboiler (5) with the aim of heating the solvent to regenerate it to the required quality, followed by a step of separation in a low-pressure flash LP vessel (6) allowing the separation of the regenerated solvent and the removed compounds in the form of desorbed gases. - an optional final condensation of the desorbed gases in a final condenser (7) aimed at limiting the losses of water and solvent in the process. - Final cooling of the depleted solvent in the cooler (8) - circulation of solvent between the absorption and regeneration sections by a set of (depleted and / or rich) solvent pumps (9); the number and position of pumps in the solvent loop may vary depending on the type of application (depending on the operating pressures of the absorption and regeneration sections); Contains:

[0032] FIG. 2 shows an absorption process with hot flash regeneration as conventionally used to decarbonate natural gas using a rich solvent / lean solvent exchanger.

[0033] The prior art process comprises the steps of: absorbing the removed compounds from the natural gas in an absorber (1) by contacting the natural gas stream (201) for treatment with a solvent stream (217) called "depleted solvent" to give a treated gas (202) and a solvent (203) rich in the removed compounds, called "rich solvent"; flashing the rich solvent (203) in a medium pressure vessel (2) to desorb the co-absorbed compounds (206) and to give a cold rich solvent (204); heat exchange between the cold rich solvent (204) and a hot depleted solvent stream (210) in an exchanger (3) to give a reheated rich solvent stream (205) and a cooled depleted solvent stream (215). an optional flash separation (4) allowing the separation of gaseous compounds (207) and a rich solvent stream (208); a regeneration of the rich solvent (208) in a reboiler (5) giving a regenerated solvent (209) in biphasic form; a low-pressure flash separation (6) on the regenerated solvent allowing the separation of a regenerated solvent stream free of desorbed gases, or "hot depleted solvent" (210), from a desorbed gas stream (211); the "hot depleted solvent" (210) enters a heat exchanger (8) to be cooled, forming a cold depleted solvent (216); a pump (9) may be used to deliver the solvent (217), referred to as "depleted solvent", to the inlet of the absorber (1).

[0034] Final condensation of gaseous compounds (207) and (211) to form stream (212) which is sent to condenser (7) to form gas stream (214); final cooling of cooled depleted solvent (215) to give a fully cooled depleted solvent stream (216) ready to be fed back to absorber (1), in the form of depleted solvent stream (217), by solvent distribution pump (9).

[0035] Figure 3 shows a prior art absorption process with hot flash regeneration as proposed by Hitachi Zosen Inova (HZI) for biogas scrubbing (CO2 removal).

[0036] The method proposed by the prior art therefore comprises a step of absorption of the removal compounds from said biogas in an absorber (1), said absorption being by contacting the biogas stream (301) for treatment with a solvent stream (316) called "depleted solvent", to give a treated gas (302) (biomethane) and a solvent (303) rich in the removal compounds, called "rich solvent". The rich solvent stream (303) is sent by the solvent distribution pump (9) to the rich solvent / gas effluent heat exchanger (2), where it exchanges heat with a gas stream (312) consisting of the gaseous stream (311) from the low-pressure flash vessel and the optional gaseous stream (307) from the low-pressure flash step (4), to give a cooled gaseous effluent (313) and a reheated rich solvent stream (305). The cooled gaseous effluent (313) is sent to the condenser (7) to form a gas outlet stream (314) (CO2 effluent), and the reheated rich solvent stream (305) is sent to the rich solvent / depleted solvent heat exchanger (3). The resulting stream is a hot rich solvent stream (306), which is sent to flash separation (4). Flash separation (4) allows for the separation of gaseous compounds (307) and a rich solvent stream (308).

[0037] The rich solvent stream (308) is sent to a reboiler (5) which allows the rich solvent to be regenerated by heating, giving a biphasic regenerated solvent (309).

[0038] The regenerated solvent (309) is then sent to a low-pressure flash separation (6), which allows for the separation of a regenerated solvent or "hot depleted solvent" stream (310) and a desorbed gas stream (311).

[0039] Gaseous compounds (307) and (311) form stream (312), which feeds the rich solvent / gas effluent heat exchanger (2).

[0040] Final cooling of the cooled depleted solvent (315) takes place in the cooler (8) to give a fully cooled depleted solvent stream (316) which is ready to be fed back to the absorber (1).

[0041] FIG. 4 shows the hot and cold temperature estimation concept in a rich solvent / depleted solvent exchanger (1) with (A) and without (B) sampling of the solvent fraction on the cold side (bypass).

[0042] (Description of the embodiment) The invention relates to a gas processing plant (FIG. 1) which allows the implementation of the method according to the invention, comprising at least: - an absorber (1) that allows the treated gas to come into contact with a solvent called a "depleted solvent" to give a solvent rich in the treated gas and the removed compounds called a "rich solvent"; - optional vessel (2) for medium pressure flushing of the rich solvent to desorb the co-absorbed compounds; - Cold rich solvent / hot depleted solvent heat exchanger (3A) - Cold rich solvent / hot gas effluent heat exchanger (3B) a conduit (bypass) for short-circuiting the fraction of cold rich solvent feeding the cold rich solvent / hot depleted solvent heat exchanger (3A) to the cold rich solvent / hot gas effluent heat exchanger (3B); - an optional low-pressure flash vessel (4) at the outlet of the heat-integrated step, allowing degassing of the rich solvent; - Reboiler (5) for heating and regenerating the solvent to the required quality - a low-pressure flash vessel (6) that allows the separation of the regenerated solvent and the removed compounds in the form of desorbed gases. - an optional final condenser (7) for the desorbed gases, with the aim of limiting the losses of water and solvent in the process; - Final cooler for depleted solvent (8) - a set of pumps (9) for the solvent (depleted and / or rich), allowing the circulation of the solvent between the absorption and regeneration sections; This also relates to treatment plants containing

[0043] The hot flash regeneration section of the present invention comprises at least a reboiler (5) and a low pressure flash vessel (6), and is thermally integrated with the absorption section containing the absorber (1) by heat exchangers (3A) and (3B).

[0044] The gas treatment method according to the invention (FIG. 1) employs a step a) of absorbing removal compounds from the gas in an absorber (1) by contacting a treated gas stream (101) with a solvent stream (117) completely or highly depleted in removal compounds, called "depleted solvent," to give a treated gas (102) and a solvent (103) rich in removal compounds, called "rich solvent." The operating conditions in the absorption step are typically as follows: pressures are typically 1-80 bar; typically 30-80 bar for natural gas treatment applications, and typically 1-2 bar for flue gas CO2 capture or biogas scrubbing applications.

[0045] The temperature of the depleted solvent may depend on the temperature of the process gas and available cold bodies, but is typically between 20 and 60°C.

[0046] Optionally, step b) of medium-pressure flash separation of the rich solvent (103) in vessel (2) (advantageously carried out at a pressure of 5-10 bar depending on the end use of the gas from the medium-pressure flash) may allow desorption of the co-absorbed compounds (106) and generation of a cold rich solvent stream (104). Without this step, the cold rich solvent stream (104) is identical to the rich solvent stream (103). The temperature of the cold rich solvent (104) may advantageously be between 40 and 80°C, depending on the amount of gas absorbed and the temperature of the depleted solvent and the gas to be treated.

[0047] Then, by heat exchange c) between a fraction (104A) of the cold rich solvent stream (104) and a hot depleted solvent stream (110) in an exchanger (3A), a reheated rich solvent stream (105A) and a cooled depleted solvent stream (115) can be obtained. The reheated rich solvent (105A) generally has a temperature of 60 to 170°C, preferably 100 to 130°C; the cooled depleted solvent (115) generally has a temperature of 45 to 90°C, preferably 60 to 90°C.

[0048] At the same time, there is a step d) of heat exchange in a heat exchanger (3B) between a complementary fraction (104B) of the cold rich solvent stream and a hot desorbed gas effluent (112) which corresponds to the desorbed gas stream (111) from the flash separation in step g) and the gaseous compound stream (107) optionally from the flash separation in step e), to give a reheated rich solvent stream (105B) (the reheated rich solvent (105B) has a temperature generally between 60 and 170°C, preferably between 100 and 130°C) and a cooled desorbed gas stream (113) which has a temperature generally between 45 and 90°C, preferably between 60 and 90°C.

[0049] A low pressure flash separation step e)(4) may be carried out at the outlet from the heat integration step, allowing a first separation of the removed compounds.

[0050] Without this step, the rich solvent stream (108) sent to the reboiler (5) would be the sum of the reheated rich solvent streams (105A) and (105B).

[0051] The process also includes a step f) of regeneration of the rich solvent (108) by heating in the reboiler (5) at a temperature generally between 70 and 180°C, preferably between 100 and 140°C, highly preferably between 110 and 140°C, depending on the operating pressure selected, to give a biphasic regenerated solvent (109) containing the removed compounds in desorbed gas form, followed by a step g) of separation by low-pressure flash (6) allowing the separation of a "hot depleted solvent" stream (110), generally at a temperature between 70 and 180°C, preferably between 110 and 140°C, and a desorbed gas stream (111), generally at the same temperature, generally between 70 and 180°C, preferably between 110 and 140°C. Steps f) and g) allow the hot flash regeneration of the solvent.

[0052] The process also includes a step h) of final cooling of the cooled depleted solvent (115) to provide a fully cooled depleted solvent stream (116) ready to be fed back to the absorber (1) in the form of a depleted solvent stream (117) generally at a temperature of 20-60° C. depending on the temperature of the process gas (101) and the available cold body. The process may also include a step i) of final condensation of the desorbed gas stream (113) from the rich solvent / gas effluent exchanger (3B) in order to limit water losses in the process, allowing a cooled desorbed removal compound stream (114) generally at a temperature of 20-60° C. depending on the available cold body.

[0053] At the heart of the present invention is therefore the practice of sampling a fraction (104B) of the rich solvent stream in combination with a modified heat integration using the thermal energy of the desorbed gas streams ((107) and (111)) on the cold side of the cold rich solvent / hot depleted solvent heat exchanger (3A).

[0054] Without this sampling of the cold rich solvent stream (bypass) fraction, a rich solvent (cold RF, hot RC) / depleted solvent (hot PC, cold RF) exchanger (3A) (Figure 4) would exhibit a temperature constriction on the cold side: the estimated temperature on the cold side (called ΔTf) would typically be 5-20°C smaller than the estimated temperature on the hot side (called ΔTc), depending on the application and exchanger technology. This is easily explained by a change in phase of the rich solvent flowing in the cold leg of the exchanger (desorption of absorbed gases and evaporation of solvent). The depleted solvent flowing in the hot leg of the exchanger is cooled and gives up only its significant heat to the cold rich solvent (no change in state). In Figure 4, the difference in temperature on the cold side (ΔTf) is much lower than the temperature difference on the hot side, and there is no heat integration due to the short-circuit conduit (ΔTc, see curve S). This imbalance between the cold side and the hot side can be reduced due to the presence of a short-circuit conduit that sends a fraction of the cold rich solvent to the exchanger (3B) (see curve A).

[0055] The reason is that the only means of rebalancing the cold and hot temperature estimates in the rich / depleted solvent exchanger (3A) is to divert (bypass) a fraction of the volumetric flow of cold solvent sent to said exchanger. This fraction of the cold rich solvent stream (104B) can be counterheated by the hot desorbed gas (111) and optionally (107) obtained from the flash separation steps (4) and (6), respectively. The use of stream (111) and optionally stream (107) allows for the heat integration of the process.

[0056] The assumed heat integration therefore allows a significant increase in the temperature of the rich solvent at the outlet of exchangers (3A) and (3B). This temperature increase translates into greater evaporation of the rich solvent, the direct consequence of which is a reduction in the energy consumption of the reboiler (5). In accordance with this scenario, a significant gain in energy consumption of the order of 20-40% can be made.

[0057] The volumetric flow fraction of rich solvent (104B) may represent 0.5-50%, preferably 5-40%, of the total volumetric flow of rich solvent depending on the application, the loading of the rich solvent (expressed as moles of acid gas / mole of solvent) and the technology of the exchangers (3A) and (3B). The fraction diverted is adjusted to balance the temperatures of the two rich solvent streams (105A) and (105B) leaving the exchangers (3A) and (3B).

[0058] From a technical standpoint, the heat exchangers (3A) and (3B) may be two physically separate exchangers or a single exchanger (of the plate exchanger type) with multiple inlets and outlets.

[0059] The pressure at which the separation by low-pressure flash treatment in steps e) and g) is carried out is generally 0 to 9 bar, preferably 1 to 4 bar.

[0060] The separation by medium pressure flash treatment in step b) is carried out at a higher pressure than the low pressure separation, generally at a pressure of 3 to 10 bar, preferably 5 to 10 bar, highly preferably 5 to 7 bar.

[0061] According to one preferred device mode, the flash vessels (4) and (6) are operated at the same pressure (excluding load losses in the circuit). The operating pressure of the LP flash vessels (4) and (6) is advantageously 1 to 4 bar. The upper limit is generally determined by the thermal degradation of the solvents used. The operating pressure of the MP flash vessel (2) is advantageously 5 to 10 bar.

[0062] The temperature required in the reboiler (5) is generally between 70 and 180° C., depending on the operating pressure. Advantageously, when the pressure is above 1 bar, the temperature in the reboiler is between 100 and 180° C., preferably between 100 and 140° C., highly preferably between 110 and 140° C.

[0063] The operating pressure in the reboiler (5) is generally between 0 and 9 bar.

[0064] In one embodiment, the hot flash separation step may be carried out under vacuum, which means that the operating pressure in the reboiler (5) in step f) and the pressure of the flash separation in step g) are strictly between 0 and 1 bar. In this case, the temperature of the heat treatment in the reboiler (5) may be below 100°C, preferably between 70 and 90°C.

[0065] In another embodiment, the operating pressure in the reboiler (5) may be 1-4 bar, and the temperature in the reboiler (5) is 100-140°C, preferably 110-140°C.

[0066] In still further embodiments, temperature and pressure are directly related via thermodynamic equilibrium, and such consideration may be given to higher pressures (e.g., pressures above 4 bar, especially 6-8 bar) in the flash vessel and reboiler if the solvent is thermally stable or solvent depletion is secondary (it is not economically compelling to replace stored solvent in the plant more frequently).

[0067] It should be noted that the capital expenditure for the plant according to the invention is also limited or even reduced; - Compared to the conventional flash regeneration scheme (without heat integration), some additional equipment should be considered (one exchanger and one vessel) In contrast to schemes involving regeneration by steam stripping, the regeneration column is replaced by a simple vessel.

[0068] (Example) To illustrate the advantages of the present invention in terms of energy consumption, an example is given below for a biogas cleaning scenario.

[0069] Table 1 below illustrates the benefits of the present invention for scrubbing (decarbonating) biogas to biomethane with a chemical solvent called AE Amine, which consists of a tertiary polyamine, a mixture of tertiary and secondary polyamines, and specifically contains 25% by weight PMDPTA, 11% by weight MDEA, and 4% by weight piperazine. For this type of application, given the specification for the target CO content (typically 2.5% by volume), high levels of regeneration by steam stripping are not required.

[0070] The consequence of partial regeneration of the solvent is an increase in the volumetric flow of solvent required to guarantee specifications (+23% in the inventive scenario relative to high-level regeneration by steam stripping). Capital expenditure nevertheless remains limited because the stripping tower is replaced by a simple vessel and the biogas washing unit is small in size.

[0071] The hot flash regeneration mode and associated heat integration according to the present invention allows for a significant reduction in the reboiler power required to regenerate the solvent: - 44% compared to traditional hot flash regeneration methods, - 30% relative to regeneration by steam stripping mode.

[0072] This reduction in energy consumption allows an increase in the biomethane productivity of the methanation site, as regulations ensure that the heat requirements of the washing process are met by self-consumption of the produced biogas.

[0073] [Table 1] [Brief explanation of the drawings]

[0074] [Figure 1] 1 shows a schematic diagram of the method according to the present invention. [Figure 2]1 illustrates an absorption process with hot flash regeneration as conventionally used to decarbonate natural gas using a rich solvent / depleted solvent exchanger. [Figure 3] A prior art absorption method with hot flash regeneration as proposed by Hitachi Zosen Inova (HZI) for biogas scrubbing (CO2 removal) is shown. [Figure 4] Figure 1 shows the hot and cold temperature estimation concept in a rich solvent / depleted solvent exchanger (1) with (A) and without (B) sampling of the solvent fraction on the cold side (bypass).

Claims

1. 1. A method for treating gases by chemical, physical or hybrid absorption of removal compounds, comprising at least: a) absorption of said removal compounds in an absorber (1) by contacting a treatment gas stream (101) selected from biogas, natural gas, synthetic gas (syngas) or industrial flue gas with a solvent stream (117) called "depleted solvent" at a temperature between 20 and 60°C, to give a treated gas (102) and a solvent (103) enriched in removal compounds, called "rich solvent"; c) exchanging heat between a fraction (104A) of the rich solvent stream (103) and a hot depleted solvent stream (110) in a heat exchanger (3A) to provide a reheated rich solvent stream (105A) at a temperature between 60 and 170°C and a cooled depleted solvent stream (115) at a temperature between 45 and 90°C; d) heat exchange in a heat exchanger (3B) between a complementary fraction (104B) of the rich solvent stream (103) and a hot desorbed gas effluent (112), which corresponds to the desorbed gas stream (111) from the flash separation in step g), to give a reheated rich solvent stream (105B) at a temperature between 60 and 170°C and a cooled desorbed gas stream (113) at a temperature between 45 and 90°C; f) regenerating the sum of the first reheated rich solvent stream (105A) and the second reheated rich solvent stream (105B) by heating in a reboiler (5) at a temperature of 70-180°C to give a biphasic regenerated solvent (109) having a hot depleted solvent stream and a gaseous stream; g) carrying out a separation of the biphasic regenerated solvent (109) in a low-pressure flash vessel (6) making it possible to separate a hot depleted solvent stream (110) at a temperature of 70-180°C and a gaseous stream (111) containing the removal compound in the form of a desorbed gas at a temperature of 70-180°C; h) final cooling of the cooled depleted solvent (115) to give a fully cooled depleted solvent stream (116) at a temperature between 20 and 60° C., said depleted solvent stream (116) being ready to be fed back to the absorber (1) in the form of a depleted solvent stream (117). A method including:

2. The method of claim 1, comprising the steps of: a) absorption of said removal compounds in an absorber (1) by contacting a treatment gas stream (101) selected from biogas, natural gas, synthetic gas (syngas) or industrial flue gas with a solvent stream (117) called "depleted solvent" at a temperature between 20 and 60°C, to give a treated gas (102) and a solvent (103) enriched in removal compounds, called "rich solvent"; b) carrying out the separation of the rich solvent (103) in a medium pressure flash vessel (2) to desorb the co-absorbed compounds (106) and to give a cold rich solvent (104) at a temperature between 40 and 80°C; c) exchanging heat in a heat exchanger (3A) between a fraction (104A) of the cold rich solvent stream (104) and a hot depleted solvent stream (110) to provide a reheated rich solvent stream (105A) at a temperature between 60 and 170°C and a cooled depleted solvent stream (115) at a temperature between 45 and 90°C; d) heat exchange in a heat exchanger (3B) between a complementary fraction (104B) of the cold rich solvent stream (104) and a hot desorbed gas effluent (112), which corresponds to the desorbed gas stream (111) from the flash separation in step g) and to the gaseous removed compound stream (107) from the flash separation in step e), to provide a reheated rich solvent stream (105B) at a temperature between 60 and 170°C and a cooled desorbed gas stream (113) at a temperature between 45 and 90°C; e) separating the reheated rich solvent streams (105A) and (105B) leaving the heat exchangers (3A, 3B) in a low-pressure flash vessel (4) making it possible to separate the gaseous removal compound (107) at a temperature between 60 and 170°C and the rich solvent stream (108) at a temperature between 60 and 170°C; f) regenerating the rich solvent (108) by heating in a reboiler (5) at a temperature of 70-180°C to give a biphasic regenerated solvent (109) having a hot depleted solvent stream and a gaseous stream; g) separation of the biphasic regenerated solvent (109) in a low-pressure flash vessel (6) making it possible to separate a hot depleted solvent stream (110) at a temperature of 70-180°C and a gaseous stream (111) containing the removal compound in the form of a desorbed gas at a temperature of 70-180°C; and h) final cooling of the cooled depleted solvent (115) to give a fully cooled depleted solvent stream (116) at a temperature between 20 and 60° C., said depleted solvent stream (116) being ready to be fed back to the absorber (1) in the form of a depleted solvent stream (117). A method including:

3. 3. The method according to claim 1 or 2, wherein the fraction (104A) of the cold rich solvent stream sent to the heat exchanger (3A) represents between 0.5% and 50% by weight of the total rich solvent stream.

4. 4. The process according to claim 2 or 3, wherein the separation in the medium-pressure flash vessel in step b) is carried out at a higher pressure of 3 to 10 bar than the separation in the low-pressure flash vessel.

5. 5. The process according to claim 2, wherein the separation in the low-pressure flash vessel in steps e) and g) is carried out at a pressure of 0 to 9 bar.

6. 6. The process according to claim 5, wherein the separations in the low-pressure flash vessels in steps e) and g) are carried out at the same pressure of 1 to 4 bar, and the separation in the medium-pressure flash vessel in step b) is carried out at a pressure of 5 to 10 bar.

7. 6. The process according to claim 5, wherein the pressure during heating in the reboiler in step f) and during separation in the low-pressure flash vessel in step g) is strictly 0 to 1 bar.

8. The process according to claim 7, wherein the temperature in the reboiler is from 70 to 100°C.

9. 7. The process according to claim 5 or 6, wherein the operating pressure in the reboiler is from 1 to 9 bar and the temperature in the reboiler is from 100 to 140°C.

10. The method according to any one of claims 1 to 9, wherein the solvent is a chemical solvent comprising at least one amine.

11. 11. The method of claim 10, wherein the solvent comprises a mixture of tertiary and secondary amines.

12. 12. The process according to any one of claims 1 to 11, comprising a step i) of final condensation of the desorbed gas stream (113) with the aim of limiting water losses in the process, providing a cooled desorbed compound stream (114) at a temperature between 20 and 60°C.

13. 13. The process according to any one of claims 1 to 12, wherein the operating pressure in absorption step a) is from 1 to 80 bar.

14. The method of claim 1, wherein the industrial flue gas is the flue gas of a coal-fired power plant, an incinerator or a melting furnace.

15. A gas processing plant allowing the implementation of the method according to any one of claims 1 to 14, comprising at least: an absorber (1) that makes it possible to contact the treated gas with a solvent called "depleted solvent" to give a solvent rich in the treated gas and the removed compounds, called "rich solvent"; - cold rich solvent / hot depleted solvent heat exchanger (3A); - Cold rich solvent / hot gas effluent heat exchanger (3B); a conduit for short-circuiting the fraction of cold rich solvent feeding the cold rich solvent / hot depleted solvent heat exchanger (3A) to the cold rich solvent / hot gas effluent heat exchanger (3B); - a reboiler (5) that allows heating of the rich solvent; a low-pressure flash vessel (6) allowing the separation of the removed compounds in the form of regenerated solvent and desorbed gas; - final cooler (8) for the depleted solvent; - a set of pumps (9) for the solvent (depleted and / or rich) that allow the solvent to flow through; A gas processing plant comprising:

16. 16. A plant according to claim 15, wherein the heat exchanger (3A) and the heat exchanger (3B) consist of one and the same device.

17. The plant of claim 15 or 16, further comprising: a vessel (2) for a medium pressure flushing treatment with a rich solvent to desorb the co-absorbed compounds; a low-pressure flash vessel (4) at the outlet of the heat exchanger (3A, 3B) that allows degassing of the rich solvent; and A final condenser (7) for the desorbed gases, intended to limit the losses of water and solvent in the process.

Images