Method and apparatus for separating co2 from fumes

Abstract

The invention relates to a method for separating CO2 from fumes which includes cooling the fumes, which contain water and CO2, causing at least partial condensation of the water contained therein generating an aqueous liquid (W) and water-depleted cooled fumes (1), separating (A) the CO2 from the water-depleted fumes forming a CO2-rich gas containing at least 90 mol% of CO2, condensing (D) the CO2-rich gas at a first pressure greater than 50 bara and at least partially evaporating the aqueous liquid to provide part of the cold required for condensing the CO2-rich gas.

Description

[0001] Description

[0002] Title of the invention: Method and apparatus for separating CO2 from fumes

[0003] The present invention relates to a method and apparatus for separating CO2.

[0004] CO2 capture processes using water-containing flue gases include a first cooling and / or compression stage followed by a flue gas drying stage. These stages generate significant quantities of aqueous liquids. The object of this invention is to use these aqueous liquids in the process to generate cooling through their evaporation.

[0005] To produce CO2 in liquid form, a cycle is used, often employing CO2 itself. For acceptable efficiency, the CO2 must be compressed to a pressure sufficient for condensation (or densification if the pressure exceeds the critical pressure) at ambient temperature. The ambient temperature source is typically the cooling water circuit or ambient air. The lower this temperature, the lower the required pressure, resulting in lower energy consumption and fewer stages for the cycle compressor.

[0006] Similarly, when CO2 is produced in supercritical form, one possibility is to proceed in two stages: compression followed by pumping. For the same pressure ratio, pumping consumes less energy than compression. At a given production pressure, it is important to minimize the pressure from which the CO2 is pumped in order to minimize overall energy consumption. In order to pump CO2, a sufficient density must be reached (typically greater than 500 kg / m³). 3 The lower the temperature of the cold source, the more this minimum density can be reached at low pressure.

[0007] State of the art

[0008] It is known from WO24 / 006442 and WO23 / 222637 to condense water contained in fumes.

[0009] Problem solved by the invention

[0010] The invention allows for the recovery of the aqueous liquid from a flue gas treatment unit by using the cold generated by the vaporization of the aqueous liquid to condense a flow of CO2 produced by separating the flue gases. For example, the aqueous liquid can be used in a dedicated evaporative system for CO2 condensation / densification. In the absence of available cooling water, using this aqueous liquid in the CO2 condenser / densifier maximizes energy consumption reduction. Description of the invention: The invention mainly consists of using flue gas condensate as a water source for evaporation in a CO2 condenser. Depending on environmental constraints and the quality of the condensate, it may be necessary to treat the condensate before using it in an evaporative system.The treatment level must be compatible with the release of these condensates into the atmosphere after evaporation, with the presence of operators, with the choice of materials used for the CO2 condenser, and finally with the optimal concentration level within the evaporator itself. When a closed-loop cooling circuit is necessary for the capture unit because no makeup water is available, utilizing the aqueous liquid to produce cooling by evaporation reduces the capture unit's electrical consumption. The point in the process where a reduction in the cooling water temperature has the greatest impact on energy consumption is the high-pressure CO2 condensation / densification.

[0011] Indeed, the pressure at which CO2 condenses depends directly on the temperature reached at the condenser outlet: the higher the temperature, the higher the pressure required. When the temperature at the condenser outlet exceeds 31°C (the critical temperature of CO2), the CO2 becomes supercritical and the pressure exceeds the critical pressure (73 bar). This is referred to as a densifier.

[0012] In the supercritical case, there is no longer a change of state, but the density becomes dependent on pressure and temperature. To achieve the required density at the lowest possible pressure, the temperature must be as low as possible.

[0013] In these different cases, the lower the temperature, the lower the pressure required for densification or condensation, and therefore the lower the electricity consumption. The invention is relevant in two different configurations:

[0014] • Production of CO2 in liquid form ([FIG.1]). To produce CO2 in liquid form, a CO2 refrigeration cycle can be used. This refrigeration cycle can be closed, open, or semi-open. To achieve sufficient efficiency, this CO2 refrigeration cycle requires densifying or condensing the CO2 at ambient temperature. This temperature depends on the available cold source (ambient air, available cooling water). For example, a typical configuration would use cooling water for the interstage coolers of the CO2 cycle compressor and for CO2 condensation. Using the aqueous liquid condensed by cooling and / or compressing the flue gases to cool the CO2 compressor will allow for a reduction in electrical consumption typically between 0% and 5%, depending on the approach of the system used to vaporize the condensate and cool the CO2.However, using the aqueous liquid condensed during CO2 condensation or densification allows for a reduction in the electrical consumption of the CO2 cycle compressor, typically between 5% and 20%. The compressor discharge pressure is lowered from 30 bar to 10 bar. Therefore, there can also be savings in terms of cycle compressor sizing: lowering the compressor discharge pressure can allow for a reduction in the number of compression stages required.

[0015] • Production of supercritical CO2 ([FIG.2]). To produce supercritical CO2, one possible configuration involves compressing the CO2 using a compressor to a pressure sufficient for condensation / densification. Once the CO2 is in a dense phase (liquid or supercritical), it can be pumped. Pumping efficiency is much higher than compression efficiency: the lower the transition pressure between the compressor and the pump, the lower the overall compression energy (compressor + pumping). The gain in overall compression energy (by reducing the compression ratio in the compressor) when using the condensed aqueous liquid is typically between 5% and 20%. Reducing the discharge pressure of the CO2 compressor can also allow for a reduction in compressor size by reducing the number of compression stages. This results in a smaller capital investment.According to one aspect of the invention, a process for separating CO2 from flue gases is provided, comprising at least the following steps: i. Cooling and / or compression of the flue gases, containing water, CO2, and at least one component lighter or heavier than CO2, leading to at least partial condensation of the water they contain, generating an aqueous liquid and cooled and / or compressed flue gases depleted in water content; ii. Separation of the CO2 from the cooled and / or compressed flue gases depleted in water content, forming a CO2-rich gas containing at least 90 mol% CO2; iii. Condensation of the CO2-rich gas at a first pressure greater than 50 bar or densification of the CO2-rich gas at a first pressure greater than 73 bar; and iv. At least partial evaporation of the aqueous liquid to provide at least part of the cooling necessary for the condensation or densification of the CO2-rich gas of step iii).

[0016] According to other optional characteristics that can be combined in any way compatible with science and logic:

[0017] • the aqueous liquid undergoes treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated.

[0018] • the CO2-rich gas of step iii) is the CO2-rich gas from a closed or semi-open refrigeration cycle.

[0019] • the CO2-rich gas condensed in step iii) is subsequently pumped to a second pressure higher than the first pressure and at least greater than 73 bara.

[0020] • a cooling circuit includes a heat exchanger where the aqueous liquid evaporates, as well as water from a water source other than the aqueous liquid.

[0021] • The heat exchanger is an evaporation tower in which aqueous liquid and water from another water source evaporate by direct heat exchange.

[0022] • Chilled water is drawn from the tower at a temperature between 5 and 30°C, or even between 10 and 25°C, or even between 15 and 20°C, and is sent as water in a cooling circuit to condense or densify the CO2-rich gas. • The percentage of aqueous liquid sent to condense the CO2-rich gas decreases if the ambient temperature falls below a threshold.

[0023] • the aqueous liquid generated in step i) makes it possible to generate cold used for the condensation of the refrigerant fluid of a refrigeration cycle whose refrigerant fluid is a gas other than CO2, for example ammonia and the refrigeration cycle serves to condense the gas rich in CO2.

[0024] • the fumes contain at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, argon.

[0025] • the aqueous liquid contains water as well as at least one acid.

[0026] • CO2-rich gas condenses or densifies through indirect heat exchange with an aqueous liquid that evaporates, for example in an air cooler

[0027] • CO2-rich gas condenses or densifies through indirect heat exchange with cooling water by treating the aqueous liquid in an evaporative tower to form cooling water

[0028] • at least partial evaporation of the aqueous liquid to provide all the necessary cooling for the condensation or densification of the CO2-rich gas in step iii), particularly if the gas flow rate is reduced

[0029] The methods according to the invention will be described in more detail with reference to the figures where:

[0030] [FIG.1] represents a process for separating CO2 from fumes according to the invention with production of CO2 in liquid form.

[0031] [FIG.2] represents another method for separating CO2 from fumes according to the invention with production in supercritical form.

[0032] [FIG.3] represents a detail of one of the two preceding figures.

[0033] [FIG.4] represents a detail of one of the two previous figures [FIG.1] and [FIG.2], [FIG.5] represents part of the separation process of one of the two previous figures [FIG.1] and [FIG.2],

[0034] A process for separating CO2 from flue gases according to the invention uses a separation unit A by partial condensation and / or distillation and / or solidification to separate a gas 1 containing less than 90 mol% CO2 and at least one component lighter or heavier than CO2. The gas 1 may comprise at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, argon. The gas 1 was produced by treating water-containing flue gases first by cooling and / or compression to produce an aqueous liquid W and a water-depleted gas. The water-depleted gas is sent directly to the separation unit or, alternatively, treated to enrich it with CO2 upstream of the separation unit A.

[0035] Unit A produces at least one gaseous CO2 stream 3 containing at least 90 mol% CO2, which is compressed by a multi-stage compressor C to a pressure of at least 50 bar, forming a compressed flow 7. The compressed flow 7 is condensed or pseudo-condensed in a condenser D, forming a liquid or supercritical flow 9, which is returned to Unit A for subcooling. Unit A then produces subcooled liquid CO2 5 at the required pressure (typically between 7 and 20 bar).

[0036] The cooling capacity for condensation in the condenser D comes partly from the vaporization of the aqueous liquid W sent to the condenser D. The aqueous liquid W may undergo treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated.

[0037] Fig. 2 illustrates a process for separating CO2 from flue gases according to the invention, using a separation unit A by partial condensation and / or distillation and / or solidification to separate a gas 1 containing CO2 and at least one component lighter or heavier than CO2. The gas 1 may comprise at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, or argon. The gas 1 was produced by treating water-containing flue gases first by cooling and / or compression to produce an aqueous liquid W and a water-depleted gas. The water-depleted gas is sent directly to the separation unit A or, alternatively, treated to enrich it with CO2 upstream of the separation unit A.

[0038] Unit A produces at least one gaseous CO2 stream 3 containing at least 90 mol% CO2, which is compressed by a compressor C, forming a compressed flow 7. The compressed flow 7 is condensed or pseudo-condensed in a condenser D, forming a liquid or supercritical flow 9, which serves as the product after being pumped to a pressure at least greater than 73 bar in a pump P. For example, the stream 3 could be compressed to 80 bar abs in the compressor C, densified, and then pumped to 130 bar abs, or the stream 3 could be compressed to 60 bar abs in the compressor C, condensed, and then pumped to 130 bar abs.

[0039] The cooling capacity for condensation in the condenser D comes from the aqueous liquid W. The aqueous liquid W may undergo treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated.

[0040] Several ways of transferring the cooling capacity of the liquid W to the gaseous CO2 to be condensed 7 can be considered.

[0041] Several other technical configurations are possible for the W liquid evaporation system:

[0042] In Fig. 3, the evaporation of aqueous liquid W takes place in an evaporative tower T, which produces cooling water (at a temperature lower than that of liquid W). The cooling water 10, at a temperature between 5 and 30°C, or even between 10 and 25°C, produced at the bottom of the evaporative tower T, is pumped by a pump PW. A portion 13 is sent to the condenser D. Another portion 11 is discharged to reduce the concentration of the water circuit. The cooling water 13 is heated in the condenser D. In this case, the condenser D is typically a shell-and-tube heat exchanger or a plate-and-fin heat exchanger. The water heated in the condenser D is returned to the evaporative tower T to be cooled again. The condenser D is used in this case for the condensation / densification of CO2 7.

[0043] In Fig 4, the condensation / densification of the CO2-rich gas 7 takes place in the tubes of an ACF air cooler with a water spray system consisting at least partly of liquid W. An adiabatic air cooling system using membranes is also possible.

[0044] The condensation / densification of CO2-rich gas 7 in the pipes of a hybrid cooler partially using water evaporation (in English, "Wet Surface Air Coder, Adiabatic Coolers") to condense or densify the CO2. Finally, the last advantage of the invention is to allow the disposal of the aqueous liquid formed by condensing the water present in the flue gases. It is not necessary to provide a means of discharging this liquid since it is discharged by evaporation. [FIG. 5] shows flue gases 2 containing water, CO2, and preferably at least one SOx and / or at least one NOx, which are cooled in a heat exchanger by indirect heat exchange with a fluid 4, for example, a fluid from separation A. Alternatively, the flue gases can simply be compressed or compressed and cooled. The water in the flue gases 2 condenses, forming an aqueous liquid W and water-depleted flue gases 4.The presence of SOx and / or NOx will make liquid W slightly acidic, and this acidity helps reduce limescale buildup where liquid W is sent. The water-depleted gas 6 is sent directly to the separation unit or, alternatively, treated to enrich it with CO2 upstream of separation unit A. This treatment could, for example, be a TSA adsorption separation, producing a gas 1 enriched with CO2 and depleted in water, and a gas 8 enriched with water and depleted in CO2.

[0045] Preferably, all the aqueous liquid W is sent to be evaporated, thus providing cooling to the CO2-rich gas 7, which condenses or densifies. According to another variant, the aqueous liquid (W) generated by cooling and / or compressing the flue gases generates cooling used to condense the refrigerant in a refrigeration cycle where the refrigerant is a gas other than CO2, for example, ammonia, and the refrigeration cycle serves to condense or densify the CO2-rich gas 7.

Claims

Demands 1. A process for separating CO2 from flue gases comprising at least the following steps: i. Cooling (E) and / or compression of the flue gases (2), containing water, CO2 and at least one component lighter or heavier than CO2, leading to at least partial condensation of the water they contain, generating an aqueous liquid and cooled and / or compressed water-depleted flue gases (6, 8, 1) ii. Separation (A) of the CO2 from the cooled and / or compressed water-depleted flue gases (6, 8, 1) forming a CO2-rich gas (3, 7) containing at least 90 mol% CO2 iii. Condensation (D) of the CO2-rich gas at a first pressure above 50 bara or densification of the CO2-rich gas at a first pressure above 73 bara and iv. At least partial evaporation of the aqueous liquid (W) to provide at least part of the cold needed for the condensation or densification of the CO2-rich gas in step iii).

2. A process according to claim 1 wherein the aqueous liquid (W) undergoes treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated.

3. A method according to any one of the preceding claims wherein the CO2-rich gas (3) of step iii) is the CO2-rich gas from a closed or semi-open refrigeration cycle.

4. A process according to any one of the preceding claims wherein the CO2-rich gas (7) condensed in step iii) is subsequently pumped (P) to a second pressure higher than the first pressure and at least greater than 73 bara.

5. A method according to any one of the preceding claims in which a cooling circuit includes a heat exchanger (T) where the aqueous liquid (W) and water (13) from a water source other than the aqueous liquid evaporate.

6. Method according to claim 5 wherein the heat exchanger is an evaporation tower (T) in which aqueous liquid (W) and water (13) from another water source evaporate by direct heat exchange.

7. A method according to claim 6, wherein chilled water (10) is drawn from the tower (T) at a temperature between 5 and 30°C and is sent as water in a cooling circuit to condense or densify the CO2-rich gas (7).

8. A method as described in any one of the preceding claims, wherein the percentage of aqueous liquid (W) sent to condense the CO2-rich gas (7) decreases if the ambient temperature falls below a threshold.

9. A process as described in one of the preceding claims wherein the aqueous liquid (W) generated in step i) is used to generate cold for the condensation of the refrigerant fluid in a refrigeration cycle where the refrigerant fluid is a gas other than CO2, for example ammonia, and the refrigeration cycle is used to condense the CO2-rich gas.

10. A process according to any one of the preceding claims in which the fumes contain at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, argon.

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