FR2944217A1 - Method for collecting carbon dioxide in flue gases from e.g. power station, involves recycling heated refrigerant to constitute part of purging gas introduced into adsorbing solid loaded with carbon dioxide to regenerate solid - Google Patents

Abstract

The method involves making flue gases to contact with solid adsorbing carbon dioxide (CO2). Purging gas is introduced into adsorbing solid loaded with carbon dioxide to regenerate a solid for obtaining a gas flow rich in carbon dioxide. The gas flow rich in carbon dioxide compressed to obtain a compressed gas flow. The compressed gas flow is cooled by transferring heat to refrigerant for obtaining heated refrigerant. The heated refrigerant is recycled to constitute a part of the purging gas selected from water and alcohol. The solid adsorbing carbon dioxide is selected from solids obtained by immobilization of amine on a support, zeolite and metal oxide framework (MOF).

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a process for capturing CO2 in combustion fumes by adsorption and compression of purified CO2 for its transport and storage.

BACKGROUND Much of the energy is produced by burning fossil fuels that release CO2 into the atmosphere. These emissions increase the concentration of CO2 in the atmosphere and cause global warming. To limit the magnitude of this warming, it is necessary to reduce the emissions of 002 related to the production of energy. One solution is to capture and store the CO2 emitted by combustion, especially in power plants. A CO2 capture process separates CO2 from the other components of the fumes from the combustion of fossil fuels and thus allows CO2 to be transported in concentrated form to an underground storage facility. In this way, CO2 is sequestered in the underground reservoir instead of being released into the atmosphere. A disadvantage of CO2 capture processes is that they themselves consume energy. In a power plant, the installation of a capture process then reduces the energy efficiency in the plant: part of the energy produced by the combustion of fossil resources is consumed by the capture unit. To avoid the production of CO2 by the process whose object is to avoid the release of CO2, it is essential to minimize the energy consumption, especially the consumption of fossil resources, the capture process. To capture CO2, the reference process is currently absorption of CO2 by a basic solution, for example by an aqueous solution of monoethanolamine. This method has several disadvantages: the energy consumption for the regeneration of the amine is important and the degradation of the amine causes corrosion problems. There are several alternatives to the solvent absorption process, for example, the separation of CO2 by membrane or the separation of CO2 by adsorption. Adsorption on a solid avoids corrosion problems and can potentially reduce the energy cost of regeneration. STATE OF THE PRIOR ART

An adsorption process is a cyclic process in which a CO2 adsorption step is carried out alternately with a regeneration step of the adsorbent. There are two possibilities for regenerating the adsorbent: by modulating the temperature or by modulating the partial pressure of the compound to be adsorbed or desorbed.

Methods using temperature modulation are commonly referred to as "TSA" or "Temperature Swing Adsorption". The adsorbent is heated by an external heat source or, more often, by a hot gas passing through the bed containing the adsorbent solid. Because of thermal inertia, "TSA" is characterized by a relatively long cycle time. Processes using pressure modulation, more precisely partial pressure, are commonly referred to as "PSA" or "Pressure Swing Adsorption". To regenerate the adsorbent, the pressure in the adsorber is lowered. If the desorption pressure is lower than the atmospheric pressure, the term "VSA" or "Vacuum Swing Adsorption" is also used. The pressure reduction can be used in combination with a purge gas that assists desorption. "PSA" processes are well known for purifying H 2 -compound but are rarely used for CO2 capture in combustion fumes. JP 7080246 A2 discloses the use of a "VSA" to treat fumes from a coal-fired power plant. The fumes are first dehumidified (by adsorption), the CO2 is then adsorbed in a second column. The adsorbent is regenerated under vacuum. The document proposes a solution to reduce the gas consumption necessary to regenerate the dehumidification column. Nevertheless the dehumidifier upstream of the CO2 adsorber penalizes the efficiency of the process because some of the energy is spent to adsorb and desorb the water in the dehumidifier. An adsorption process that does not require a dry charge would therefore be greatly preferable. US 6,755,892 B2 describes the use of solids in a process for adsorptive CO2 capture, alternating between adsorption and desorption steps. Three desorption modes are proposed: (i) temperature desorption via an external heat source, (ii) temperature desorption by direct heating with water vapor, (iii) vacuum desorption. No preference is given between these three modes of desorption. However, the energy consumption of a regeneration temperature or vacuum is not at all equivalent. The present invention proposes to optimize the desorption step in order to minimize the energy cost of the capture process. A CO2 capture unit is composed of a capture section and a captured CO2 compression section. CO2 is usually compressed to 110 bar to be transported in supercritical form to a storage site. The CO2 compression chain generates heat at a relatively low temperature.

The method according to the invention proposes to recover the heat generated by the compression of the CO2 and to adapt the regeneration conditions of the adsorbent solid in order to be able to use the available heat to carry out the regeneration of the adsorbent. The challenge is to adapt the operating conditions of adsorption and desorption in order to optimize thermal integration with the CO2 compression chain.

SUMMARY OF THE INVENTION

Process for capturing the CO2 contained in combustion fumes, in which the following steps are carried out: a) the combustion fumes are brought into contact with a solid that adsorbs CO2 so as to obtain a gas depleted in 002 and an adsorbent solid charged at 002, then b) a purge gas is introduced into the adsorbent solid charged with CO2 to regenerate the solid and obtain a gaseous flow rich in CO2, c) at least one compression of the gas stream rich in 002 to obtain a compressed gaseous stream, then d) cooling of the compressed gas stream by heat exchange with a refrigerant to condense a liquid portion of said compressed gas stream and obtain a heated refrigerant, e) recycle the heated refrigerant to form at least a portion of said purge gas in step b). According to the invention, after step d), the liquid portion of said compressed gas stream can be separated and in which at least a first portion of said liquid portion can be recycled to constitute at least a portion of said refrigerant. At least a second portion of said condensed liquid portion in step b) may be recycled to form a portion of said purge gas. The second portion of said condensed liquid portion may be vaporized. Step a) can be carried out at a pressure of between 1 bar absolute and 3 bar absolute and at a temperature of between 50 ° C. and 90 ° C., step b) at a pressure of between 0.05 bar. absolute and 0.8 bar absolute and at a temperature of between 50 ° C and 110 ° C.

The purge gas may be selected from water and an alcohol. The adsorbent solid may be selected from a solid obtained by immobilizing an amine on a support, a zeolite or an MOF.

Combustion fumes can be produced by one of the following facilities: a power plant, a refinery, a cement plant, a steel plant.

The thermal integration with the compression chain, according to the invention, makes it possible to heat the purge gas to the necessary temperature, while minimizing the supply of external energy. In addition, since the purge gas causes the desorption of CO2, the pressure in the adsorber during the desorption phase can be increased compared to a vacuum regeneration mode without purge gas. The fact of being able to increase the pressure of the absorber during desorption makes it possible to reduce the electrical energy consumption of the compressors. It is also possible to reduce the number of stages of compression and thus reduce investment costs.

DETAILED DESCRIPTION OF THE INVENTION Other advantages of the invention will be better understood and will appear more clearly on reading the description given below with reference to the figures, in which: FIG. 1 represents an embodiment of the method according to the invention, Figure 2 an adsorption process devoid of thermal integration according to the present invention.

With reference to FIG. 1, the adsorption CO2 capture method uses at least two columns of adsorbent solid, represented by the columns C1 and C2. According to the invention, the adsorbent solids are used according to a "PSA" type process. One column is in adsorption mode while the other column is in regeneration or desorption mode. The columns work alternately and successively between the adsorption mode and the regeneration mode. "PSA" processes are well known to those skilled in the art and there is obviously the possibility of building more complex cycles with more than two columns, to improve the efficiency and / or purity of CO2. The object of the present invention does not depend on the choice of cycle, nor the number of columns used.

The gas to be decarbonated arrives via line 1. The gas is a combustion smoke comprising CO 2, for example in a content of between 5% and 30%. Combustion fumes can be produced by a thermal power plant for the generation of electricity. The capture process according to the invention can also be applied to all combustion fumes, produced for example in a refinery, in a cement plant, in a steel plant.

Adsorption step: In the description below, the column C1 operates in adsorption mode, while column C2 operates in regeneration mode. The gas to be treated arriving via line 1 at the adsorption temperature is introduced via line 1a into the adsorption column Cl. The CO2 is adsorbed on the solid in the column and a purified gas leaves the column Cl for The duration of the adsorption stage, that is to say the time during which the fumes circulate through the adsorbent solid in the Cl column, depends in particular on the recovery rate of 002, the purity of the required 002, the nature of the cycle chosen, etc. Preferably, the flue gas temperature entering the Cl column is regulated at a temperature close to the regeneration temperature described below to limit the energy consumption that would be necessary to change the temperature of the adsorbent between the adsorption step and the regeneration step. For example, the fumes arriving via line 1 are at a temperature of between 50 ° C. and 90 ° C. Thus, during the adsorption step, the solid in column Cl is at a temperature of between 50 ° C. and 90 ° C. During adsorption, the pressure of the fumes arriving via line 1 and introduced into Cl is between 1 bar and 3 bars absolute. Thus, the CO2 partial pressure of the fumes passing through the adsorbent solid in Cl is sufficient to cause the adsorption of 002 by the solid.

At the end of the adsorption stage the flue gas flow flowing through the duct is stopped. The adsorbent solid in Cl is charged with CO2 and is at a pressure between 1 bar and 3 bar.

Regeneration step: In the following description, the operating mode of C1 is reversed with that of C2 and vice-versa: column C1 operates in regeneration mode, while column C2 operates in adsorption mode. Column C1 is evacuated using a vacuum pump. Optionally, before carrying out the evacuation of the column Cl, one can perform a pressure equalization step with another column. For example the column Cl is connected to another column whose pressure is lower than the pressure in Cl.

A purge gas arriving via the ducts 3 and 3a is introduced into the column C1. During the regeneration, the purge gas circulates in the countercurrent column with respect to the direction of flow of the fumes during the step of flushing. adsorption. The purge gas causes the desorption of CO2 and leads the 002 to the outlet of the column through the ducts 4a and 4.

The effluent from the column Cl during the regeneration step is essentially composed of a mixture of 002 and purge gas. The 002 must be separated from the purge gas. According to the invention, to facilitate the separation, the purge gas is preferably a condensable compound, for example water vapor or an alcohol. The conditions of pressure and temperature in the column C1 during the desorption stage are chosen as a function of the solid used, so as to optimize the thermal integration between the desorption stage and the compression step of 002. The pressure is chosen sufficiently low so that the purge fluid is in vapor form as it circulates in the adsorbent solid during regeneration. For example, the pressure may be between 0.05 bar and 0.8 bar absolute, preferably between 0.1 bar and 0.5 bar absolute. The flow rate is adjusted by means of the valve VE1 which regulates the arrival of purge gas in Cl, as well as the compressor K1 and the pump P1 which act on the evacuation of the purge gas via the ducts 4a and 4. temperature is chosen so as to obtain the best compromise between the performance of the solid in terms of adsorption / desorption and the thermal integration described below. For example, the purge gas is at a temperature between 50 ° C and 110 ° C, so that the adsorbent solid is at a temperature between 50 ° C and 110 ° C. Preferably, the temperature of the adsorbent solid during the regeneration step is between + 20 ° C and -10 ° C relative to the temperature of this solid during the adsorption step.

Compression step: The effluent resulting from the purge of one of the columns C1 or C2 through line 4 is condensed, between 5 ° C. and 50 ° C., preferably at room temperature, by cooling in the heat exchanger El The partially condensed effluent is sent to a separator tank B1 via line 5. The condensates recovered at the bottom of the flask B1 are discharged through line 7. The rich flow 002 leaving B1 through line 61 is then successively compressed by several compressors K1 to K6 arranged in stages, up to a pressure of between 20 and 150 bars, preferably between 50 and 110 bars. Between two compressors, the flow rich in 002 is cooled by one of the heat exchangers E11 to E15, at a temperature between 5 and 50 ° C, preferably at room temperature.

Part of the purge fluid contained in the CO2-rich stream is condensed by cooling in the heat exchangers E11 to E15. After cooling in one of the exchangers E11 to E15, the CO2-rich stream containing a condensed portion is introduced into one of the separator balloons B2 to B6. The condensates are respectively recovered at the bottom of the balloons B2 to B6 and the liquid fraction is discharged through the conduit 7. The pumps P1 to p6 are used to withdraw the liquid in the bottom of the balloons B1 to B6.

After compression in the compressors KI to K6, the CO2-rich stream obtained at high pressure is cooled by the exchanger E16 between 5 ° C. and 50 ° C., preferably at room temperature, before being sent via the pipe 76 to the transport network. The CO2-rich stream can then be transported and injected into an underground reservoir for sequestration.

The liquid obtained by condensation and recovered at the bottom of the balloons BI to B6 is evacuated via line 7.

Thermal Integration According to one embodiment, the present invention proposes to reuse the liquid recovered through line 7 to produce the purge gas. Part of the liquid flowing in the duct 7 can be sent via the duct 8 into the device CH in order to be vaporized therein. The liquid is vaporized in CH by heat exchange, for example a boiler. The steam produced in CH is used as a purge gas to effect the regeneration of the adsorbent solid in one of the columns C1 or C2. The steam generated by CH is sent through line 3 to one of columns C1 or C2.

According to the invention, the heat produced by the compression of the CO2-rich stream is recovered in the compressors K1 to K6 for heating, and possibly vaporizing, the purge fluid. For example, another portion of the liquid flowing in the conduit 7 is used as a coolant in the compression section to recover heat and use it for the regeneration of the adsorbent solids in Cl and C2. Part of the liquid flowing in the duct 7 is withdrawn through the duct 10, optionally subcooled in the exchanger E2 at a temperature between 0 and 50 ° C, preferably between 20 and 40 ° C. Then the liquid flow discharged from E2 through line 100 is used to cool one of the compressed CO2-rich streams 30 from one of the compressors K1 to K6 by heat exchange with respectively one of the streams 111, 121 , 131, 141, 151 and 161 in the exchangers E11 to E16. Optionally, a part of the liquid flow discharged from E2 is sent via line 101 to cool the gas leaving the desorption stage via line 4 in exchanger E1. As a result of this thermal integration, all or part of the liquid purge stream is thus heated, and possibly vaporized, in the exchangers E1 and E11 to E16, and then discharged respectively through the conduits 130 to 136 into the separator tank B10. The liquid part is discharged at the bottom of the flask B10 into the vaporization unit CH via the duct 12, while the vapor fraction discharged at the top of the flask B10 is sent directly to the desorption stage via the duct 13. thermal integration, the thermal energy consumed by CH is reduced, allowing a significant improvement in the 002 balance of the method according to the invention. Optionally, an additional purge fluid is optionally introduced into the conduit 8 through the conduit 9 to compensate for losses of the system.

The adsorbent solids that can be used in the process of the invention can be selected so as to satisfy the following criteria: a) a sufficient cyclic CO2 adsorption capacity in the temperature range that is most favorable to thermal integration. The adsorption capacity in cyclic mode is measured in the laboratory, alternating adsorption and desorption steps by a purge gas. The adsorption capacity is defined here as the adsorbed amount of CO2 in steady state, reached after several cycles of adsorption and desorption. The adsorbent solid must have a cyclic mode adsorption capacity of 002 of at least 0.3 mol / kg, preferably greater than 0.5 mol / kg, very preferably greater than 1 mol / kg. B) a high selectivity with respect to CO2 compared to the non-condensable compounds in the gas to be treated, that is to say, with respect to nitrogen, oxygen, etc. The α (CO2 / N2) selectivity between CO2 and N2, for example, is defined as: a (CO2 / N2) = aads, co2 / gads, N2 I (Pco2 / PN2), with gads, CO2 = adsorbed amount of 002 gads, N2 = adsorbed amount of N2 Pco2 = partial pressure of CO2 PN2 = partial pressure of N2. The α (002 / N2) selectivity may be greater than 10, more preferably greater than 20, most preferably greater than 100. c) The adsorbent solid may be capable of adsorbing CO2 even in the presence of water vapor, to avoid a step of drying the gas to be treated upstream of the adsorption process.

For example, it is possible to use an adsorbent solid prepared by immobilization, for example by a technique for impregnating or grafting amines onto a support. The preparation of these adsorbent solids is, for example, taught in US 4,810,266; US 5,492,683; US 5,876,488; US 7,288,136 B1; WO 20081021700 A1. These solids have the advantage of being as a rule, little affected by the presence of moisture in the gas. In some cases, moisture even improves the performance of these solids for CO2 capture. According to the invention, it is also possible to use other types of solids, such as zeolites, for example mordenite, beta, dealuminated faujasite, ZSM-5, or MOFs (Metal Organic Frameworks) for example, the Cu-Btc or HKUST-1, the ZIF-8, the MIL-91. In a preferred embodiment of the invention, an adsorbent solid is chosen which makes it possible to minimize the flow of purge gas arriving via the pipe 3 necessary for the regeneration.

The numerical examples presented below make it possible to illustrate the operation and advantages of the method according to the invention.

EXAMPLE 1 Example 1 illustrates the operation of the process of FIG. 2. The process shown schematically in FIG. 2 is identical to the process according to the invention of FIG. 1, except for the recycle of the condensates obtained in the bottom of the B1 flasks. at B6 and with the exception of thermal integration proposing to recover the heat in the exchangers El and El 1 to E 16 to produce purge gas. Indeed, in the process of FIG. 2, the stream rich in CO2 is cooled by an external fluid in the exchangers E1 and E1 to E16 and the purge fluid is fed via line 9 into the boiler CH to be vaporized before to be sent through the conduit 3 in one of the columns C1 or C2.

The characteristics of the gas to be treated arriving via line 1 are summarized in Table 1: Flux 1 Pressure (bar) 1.75 Flow (Nm3lh) 1 750 000 CO2 content (%) 13.5 Temperature (° C) 70 Table 1 Adsorption CO2 contained in the fumes is produced by a solid composed of a polyamine impregnated on a silica solid. A removal rate of 90% is considered in the examples for the adsorption part. The desorption of CO2 is carried out at 0.3 bar and 70 ° C. and under steam. Table 2 shows the flow of water required for desorption under these conditions. Flow 4 8 9 3 76 Temperature (° C) 70 37 18 70 25 Pressure (bar) 0.3 0.3 0.3 0.3 State VAP LIQ LIQ VAP Flow rate (tlh) 683 263.1 263.8 263, 8 419.9 Composition (% mol) CO2 39 0 0 0 99 H2O 61 100 100 100 1 Table 2

In this example, it is considered that the energy for the vaporization of the purge water is provided by a coal-fired thermal power station (PCI = 25,000kJ / kg, 65% wt. Carbon) with a yield of 90%. Re-vaporization of the condensed water to effect the desorption will therefore generate CO2. Table 3 shows the CO2 balance associated with the capture operation under these conditions by specifying the amount of CO2 in the flows flowing in the ducts 1, 2 and 76, as well as the CO2 production in the CH boiler. The CO2 removal rate corresponds to the ratio of CO2 emitted overall by the process (amount of CO2 at the outlet of the columns C1 and C2 through the duct 2 and CO2 production by the boiler CH) and the total CO2 treated by the process excluding capture (amount of CO2 contained in the gas to be treated arriving via line 1 and CO2 production by boiler CH). Flux 1 2 76 CH CO2 (t / h) 466.1 46.6 419.5 62.9 Removal rate 76.5% Table 3

Example 2 according to the invention Example 2 refers to Figure 1. The gas to be treated, the removal rate, the adsorption and desorption conditions are identical to those of Example 1. The table 4 shows the effect of thermal integration on reducing the flow of water to be sprayed (stream 8). 4217 11 Flow 4 3 8 9 10 12 13 76 100 Temperature (° C) 70 70 37 18 37 70 70 25 25 Pressure (bar) 0.3 0.3 0.3 0.3 0.3 0.3 0, 3 0.3 Status VAP VAP LIQ LIQ LIQ LIQ VAP LIQ Flow rate (t / h) 683 263.8 152.5 0.7 110.6 0 110.6 419.9 110.6 Composition (% mol) CO2 39 0 0 0 0 0 0 99 0 H20 61 100 100 100 100 100 100 1 100 Table 4

Table 5 shows the effect of the invention on the process 002 balance, expressed as overall removal rate: Flux 1 2 76 CH CO2 (th) 466.1 46.6 419.5 36.75 In Example 2, the liquid flowing in the duct 10 makes it possible to cool the flow rich in 002 in the exchangers El1 to E15. The exchangers E1 and E16 are not used to achieve thermal integration. The cooling is carried out by an external fluid, for example cooling water. The flow 9 corresponds here only to a makeup of water to compensate for the losses of the system since the water condensed in E11 to E15 is recycled in majority by the flow 8. The flow 10 is undercooled at 25 ° C by the intermediate of the exchanger E2.

The example clearly shows the advantage of the invention: a gain of 5.6 points on the removal rate of 002 is obtained.

Claims (8)

1) A method for capturing the 002 contained in combustion fumes, wherein the following steps are carried out: a) the combustion fumes are brought into contact with a solid adsorbing the CO2 so as to obtain a gas depleted in CO2 and a solid adsorbent charged with CO2, then b) a purge gas is introduced into the adsorbent solid loaded at 002 to regenerate the solid and obtain a gas stream rich in 002, c) at least one compression of the CO2-rich gas stream is carried out in order to obtain a compressed gaseous flow, then d) the compressed gas stream is cooled by exchanging heat with a refrigerant to condense a liquid portion of said compressed gas stream and obtain a heated refrigerant, e) the refrigerant is recirculated heated to form at least a portion of said purge gas in step b). 2) The method of claim 1, wherein, after step d), separates the liquid portion of said compressed gas stream and wherein at least a first portion of said liquid portion is recycled to form at least a portion of said fluid 25 refrigerant. 3) Method according to one of claims 1 or 2, wherein recycling at least a second portion of said condensed liquid portion in step b) to form a portion of said purge gas. 4) Process according to claim 3, wherein said second portion of said liquid portion is vaporized. 5) Method according to one of the preceding claims, wherein is carried out: step a) at a pressure between 1 bar absolute and 3 bar absolute and at a temperature between 50 ° C and 90 ° C, Step b) at a pressure of between 0.05 bar absolute and 0.8 bar absolute and at a temperature between 50 ° C and 110 ° C. 6. Process according to one of the preceding claims, wherein the purge gas is selected from water and an alcohol. 7) Method according to one of the preceding claims, wherein the adsorbent solid is selected from a solid obtained by immobilization of an amine on a support, a zeolite, an MOF. 8) Method according to one of the preceding claims, characterized in that the combustion fumes are produced by one of the following facilities: a power plant, a refinery, a cement plant, a steel plant.