Method and apparatus for separating CO2 from fumes

Abstract

Title: CO2 Separation Process from Flue Gases A process for separating CO2 from flue gases comprises cooling the water-containing flue gases, causing at least partial condensation of the water they contain to generate an aqueous liquid (W) and cooled, water-depleted flue gases (1); separating (A) the CO2 from the water-depleted flue gas to form a CO2-rich gas containing at least 90 mol% CO2; condensing (D) the CO2-rich gas to a first pressure above 50 bar; and at least partially evaporating the aqueous liquid to provide some of the cooling required for the condensation of the CO2-rich gas. Fig. 1

Description

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

[0001] The present invention relates to a method and apparatus for separating CO2.

[0002] CO2 capture processes on water-containing flue gases include a first cooling and / or compression step followed by a flue gas drying step. These steps 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.

[0003] To produce CO2 in liquid form, a cycle can be used, often employing CO2 itself. To achieve 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 generally the cooling water circuit or ambient air. The lower this temperature, the lower the required pressure, and the lower the energy consumption and number of stages of the cycle compressor.

[0004] 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 the CO2, it is necessary to reach a sufficient density (typically greater than 500 kg / m³). The lower the temperature of the cold source, the lower this minimum density can be achieved at a lower pressure.

[0005] State of the art

[0006] It is known from WO24 / 006442 and WO23 / 222637 to condense water contained in fumes.

[0007] Problem solved by the invention

[0008] The invention makes it possible to utilize 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.

[0009] Description of the invention

[0010] The invention mainly consists of using flue gas condensate as a water source to perform evaporation at the level of a CO2 condenser.

[0011] Depending on environmental constraints and the quality of the condensate, it may be necessary to treat this condensate before using it in an evaporation system. The level of treatment must be compatible with the release of this condensate 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.

[0012] When a closed-loop cooling circuit is required for the capture unit because no makeup water is available, utilizing the aqueous liquid to produce cooling by evaporation reduces the 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.

[0013] 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 that must be reached. When the temperature reached at the condenser outlet is above 31°C (the critical temperature of CO2), the CO2 becomes supercritical and the pressure exceeds the critical pressure (73 bar). In this case, it is referred to as a densifier.

[0014] 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.

[0015] In these different cases, the lower the temperature, the lower the pressure to be reached to densify or condense and therefore the lower the electrical consumption.

[0016] The invention is of interest in two different configurations: • 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 involve using cooling water for the interstage coolers of the CO2 cycle compressor and for CO2 condensation. The aqueous liquid condensed by cooling and / or compressing the flue gases can also be used. Cooling the CO2 compressor will typically reduce electrical consumption by between 0% and 5%, depending on the system used to vaporize the condensate and cool the CO2. Conversely, using the aqueous liquid condensed from the CO2 condensation or densification process allows for a reduction in the CO2 cycle compressor's electrical consumption 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 compressor cycle sizing: lowering the compressor discharge pressure can reduce the number of compression stages required. • 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 smaller compressor size by reducing the number of compression stages. This results in a lower capital investment.

[0017] According to one object of the invention, a process for separating CO2 from fumes is provided, comprising at least the following steps: i. Cooling and / or compression of 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 CO2-rich gas at a first pressure above 50 bara or densification of CO2-rich gas at a first pressure above 73 bara and iv. At least partial evaporation of the aqueous liquid to provide some of the cold needed for the condensation or densification of the CO2-rich gas in step iii).

[0018] According to other optional features which can be combined in any way compatible with science and logic: • the aqueous liquid undergoes treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated. • the CO2-rich gas of step iii) is the CO2-rich gas from a closed or semi-open refrigeration cycle. • 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. • 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. • The heat exchanger is an evaporation tower in which aqueous liquid and water from another water source evaporate by direct heat exchange. • Cooled 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 cooling circuit water 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. • 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. • the fumes contain at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, argon. • the aqueous liquid contains water as well as at least one acid.

[0019] The methods according to the invention will be described in more detail with reference to the figures where:

[0020] [Fig. 1] represents a process for separating CO2 from fumes according to the invention with production of CO2 in liquid form.

[0021] [Fig.2] represents another method of separating CO2 from fumes according to the invention with production in supercritical form.

[0022] [Fig.3] represents a detail of one of the two preceding figures.

[0023] [Fig.4] represents a detail of one of the two preceding figures.

[0024] [Fig.1] and [Fig.2],

[0025] [Fig. 5] represents part of the process for separating one of the two figures previous ones.

[0026] [Fig.1] and [Fig.2],

[0027] 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.

[0028] 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).

[0029] The cooling for condensation in the condenser D comes partly from the vaporization of the aqueous liquid W. The aqueous liquid W can undergo treatment to remove solid particles and / or to reduce its acidity before being at least partially evaporated.

[0030] [Fig.2] represents a process for separating CO2 from fumes according to The invention utilizes 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, 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.

[0031] Unit A produces at least one stream of gaseous CO2 3 containing at least 90 mol% CO2 which is compressed by a compressor C forming a compressed flow rate 7. The compressed flow rate 7 is condensed or pseudo-condensed in a condenser D forming a liquid or supercritical flow 9 which serves as product after pumping up to a pressure at least greater than 73 bara in a pump P.

[0032] For example, the flow 3 could be compressed up to 80 bar abs in the compressor C, densified and then pumped up to 130 bar abs or the flow 3 could be compressed up to 60 bar abs in the compressor C, condensed and then pumped up to 130 bar abs

[0033] 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.

[0034] Several ways of transferring the cooling from the liquid W to the gaseous CO2 to be condensed 7 can be envisaged.

[0035] Several other technical configurations are possible for the evaporative system of liquid W: • 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. • 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. • Condensation / densification of CO2-rich gas 7 in the pipes of a hybrid cooler partially using water evaporation (in English “Wet Surface Air Cooler, Adiabatic Coolers”) to condense or densify CO2.

[0036] Finally, the last advantage of the invention is that it allows the aqueous liquid formed by condensing the water present in the fumes to be disposed of. It is not necessary to provide a means of evacuating this liquid because it is evacuated by evaporation.

[0037] [Fig.5] shows fumes 2 containing water, CO2 and preferably at least SOx and / or at least one NOx component 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 be simply 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 the liquid W slightly acidic, and this acidity helps reduce limescale buildup to the location where the 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 with water, and a gas 8 enriched with water and depleted with CO2.

[0038] Preferably, all the aqueous liquid W is sent to be evaporated and thus provide cooling to the CO2-rich gas 7 which condenses or densifies.

[0039] According to another variant, the aqueous liquid (W) generated by cooling and / or compression of the fumes 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 or densify the gas rich in CO2 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 part of the cold needed for the condensation or densification of the CO2-rich gas in step iii).

2. A method 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. A 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 in which cooled water (10) is drawn from the tower (T) at a temperature between 5 and 30°C and is sent as cooling circuit water 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 wherein the fumes contain at least one of the following components: hydrogen, methane, NOx, SOX, carbon monoxide, oxygen, argon.

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