Process and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation and / or solidification

Abstract

Title: Method and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation An apparatus for separating a gas containing CO2, at least one air gas and mercury (1,5) comprises a turbocharger (C), a turbine (T) coupled to the turbocharger, a demercurization unit (D), a cooler (G), a heater (R), a separation unit (CC) operating at temperatures below 10°C, means for sending the gas containing CO2, at least one air gas and mercury (1,5) to the turbocharger, means for sending the compressed gas (7) in the turbocharger to the demercurization unit to form a demercurized gas after heating in the heater,means for sending the demercurized gas (9) to the cooler and from the cooler to the separation unit to produce at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 (13) and a pressurized stream of CO2-depleted gas (15) and means for sending at least a portion of the CO2-depleted gas to expand in the turbine coupled to the turbocharger. Figure 1,

Description

Title of the invention: Method and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation and / or solidification

[0001] The present invention relates to a method and apparatus for separating a gas containing carbon dioxide, at least one air gas, and mercury and possibly NO2 by partial condensation and / or distillation and / or solidification.

[0002] Air gases include nitrogen, oxygen, or argon.

[0003] The invention relates to the integration of a demercurizer in a unit for capturing CO2 from a gas containing CO2, which may for example be fumes from combustion processes.

[0004] According to an object of the invention, there is provided a method for separating a gas containing CO2, at least one gas from air and mercury containing the following steps: i. Compression of the gas in a turbocharger coupled to a turbine forming a compressed gas, ii. Heating of the compressed gas upstream or downstream of the compressor, and demercurization of the heated compressed gas in one or more non-regenerative mercury adsorption reactors producing a demercurized gas, iii. Cooling of the demercurized gas, iv. Separation of the cooled gas in a unit operating at temperatures below 10°C, or even below -50°C, by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of CO2-depleted gas and v. At least part of the CO2-depleted gas is expanded in the turbine coupled to the turbocharger, possibly after being reheated to a temperature above 10°C.

[0005] According to other optional objects: • the compressed gas is heated to a temperature between 50 and 150°C, or even between 100°C and 150°C upstream of the demercurizer. • the demercurized gas is cooled by indirect heat exchange with a refrigerant, the refrigerant, preferably water, having been used to cool the demercurized gas, is used to heat the compressed gas in the heater. • the compressed gas is heated by an electric heater and / or by a heat-transfer fluid. the compressed gas or the gas to be compressed is heated by indirect heat exchange with the gas treated in the demercurizer. Indirect heat exchange takes place in a heat exchanger in which the compressed gas or the gas to be compressed is heated and in which the gas treated in the demercurizer is cooled. the demercurized gas is cooled by indirect heat exchange with a refrigerant. the refrigerant, preferably water, used to cool the demercurized gas is then used to heat a regeneration gas from a gas dryer containing CO2, at least one air gas and mercury. a refrigerant fluid used to cool the demercurized gas is then used to reheat at least part of the CO2-depleted gas to be expanded in the turbine. the refrigerant, preferably water, used to cool the demercurized gas is used to heat the compressed gas. the refrigerant, preferably water, used to cool the demercurized gas, is used for heating and / or cooling at least one building. the refrigerant is water and, having been used to cool the demercurized gas, is heated to generate water vapor. the refrigerant, preferably water, used to cool the demercurized gas, is used to vaporize a liquid for purging the separation operating at less than 10°C. the refrigerant, preferably water, used to cool the demercurized gas, is used to superheat a humid gas. the refrigerant, preferably water, having served to cool the demercurized gas, is used to heat a flow intended to be expanded in a turbine the gas depleted in CO2 is enriched in at least one air gas, for example nitrogen and / or oxygen and / or argon. the gas containing CO2, at least one air gas and mercury contains NO2 and is treated to remove the NO2 in a unit capable of removing the NO2 to a concentration below 5 ppm, or even below 1 ppm in NO2 producing a gas lean in NO2 upstream of compression in the turbocharger. The treatment to remove NO2 is a separation process by partial condensation and / or distillation. gas containing CO2, at least one air gas and mercury and possibly Actually, N02 is composed of combustion fumes. • the gas containing CO2, at least one air gas and mercury and possibly NO2 is composed of combustion fumes separated by adsorption to reduce their content of at least one air gas.

[0006] According to another object of the invention, there is provided an apparatus for separating a gas containing CO2, at least one air gas and mercury comprising a turbocharger, a turbine coupled to the turbocharger, a demercurization unit, a cooler, a heater, a separation unit (CC) by partial condensation in one or more stages and / or by distillation operating at temperatures below 10°C, or even below -50°C, means for sending the gas containing CO2, at least one air gas and mercury to the turbocharger, the heater being connected to heat the gas upstream or downstream of the turbocharger, means for sending the compressed and heated gas to the demercurization unit to form a demercurized gas,means for sending the demercurized gas to the cooler and from the cooler to the separation unit to produce at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of CO2-depleted gas and means for sending at least part of the CO2-depleted gas to expand in the turbine coupled to the turbocharger.

[0007] Flue gases from combustion processes contain large amounts of CO2. Capturing the CO2 contained in these fumes is one of the ways being considered to reduce the effects of climate change.

[0008] These fumes contain many pollutants, including mercury. Mercury can be particularly damaging to aluminum equipment, as it forms a liquid metal complex with it, leading to gradual destruction.

[0009] As a result, processes using aluminum equipment (such as cryogenic processes) are removing mercury, or moving toward more expensive stainless steel equipment.

[0010] Mercury removal is a well-known process, and is typically done by adsorption on sulfidic metals or sulfidic activated carbon. It may require heating to limit the amount of NO2 adsorbed (if present) and therefore to eliminate the risk of auto-ignition of the adsorbent bed. A heat exchanger can recover some of the heat from the treated gas and minimize heating requirements.

[0011] However, the use of conventional adsorbents can be hampered by the presence of nitrogen oxides (NOX), and in particular NO2. Consequently, when these combustion products are present in the fumes, they must be removed before demercurization.

[0012] An aim of the invention is to minimize the heating energy required for the de- mercurization, while preferably recovering some of this heat for other uses in the capture process.

[0013] The invention proposes an integrated scheme making it possible to minimize the need for heat and to recover the heat used for other consumers of the process.

[0014] The invention proposes to treat a gas containing CO2, mercury, nitrogen or another air component, as well as possibly NO2. For example, this gas could be composed of the fumes from a combustion unit, or of fumes pre-concentrated by a first treatment, such as a pressure swing adsorption (PSA) unit.

[0015] These fumes are first treated to remove NO2 if they contain any, typically up to 5 ppm or even 1 ppm of NO2. This treatment can, for example, be a low-temperature treatment such as partial condensation and / or distillation (with possible drying of the gas upstream).

[0016] The gas, freed from its NO2 (if present), is then compressed in a turbocharger. The gas leaving the machine is hot, and is further heated to reach the conditions necessary for demercurization. The temperature required at the inlet of the demercurizer can typically be greater than 100°C while the temperature at the outlet of the turbocharger is typically less than 80°C.

[0017] The gas then passes into a demercurizer operating by adsorption, and the demercurized gas is cooled in an exchanger against a refrigerant fluid (for example water). The outlet temperature of this water is maximized, and the heat it contains can be reused elsewhere in the process (regeneration of dryers, preheating of gas, heating of buildings, production of cold, production of water vapor, etc.).

[0018] The compressed and demercurized gas is then treated in a unit operating by partial condensation and / or distillation, with one or more stages. This unit produces CO2, while the incondensable fraction of the fumes leaving the unit is expanded in the turbine coupled to the aforementioned compressor.

[0019] These non-condensables can possibly be overheated before expansion, for example against all or part of the heat transfer fluid recovering the heat upstream of the demercurizer.

[0020] The method may comprise the following features: • NO2 (if present) is removed before demercurization • the gas is compressed before demercurization • we take advantage of the heat of compression to minimize the need for heating before demercurization • residual heat is recovered and reused • the compressor is driven by the expansion of the non-condensable gases in the partial condensation.

[0021] The invention will be described in more detail with reference to the figures:

[0022] [Fig.l] schematically represents a method according to the invention.

[0023] [Fig.2] represents a variant of the heating means of the method according to [Fig.l].

[0024] [Fig.3] represents a variant of the heating means of the method according to [Fig.l].

[0025] [Fig.4] represents a variant of the heating means of the method according to [Fig.l].

[0026] A gas 1 contains CO2, NO2, at least one air gas and mercury and can be fumes from combustion.

[0027] Gas 1 is treated in a unit 3 making it possible to remove the NO2 down to a concentration of less than 5 ppm, or even 1 ppm of NO2, producing a gas low in NO2 5. Unit 3 can be a separation unit by partial condensation and / or distillation.

[0028] The gas low in NO2 5 is compressed in a turbocharger C coupled to a turbine T and produces a compressed gas 7. The turbocharger C may not have an end refrigerant or may be an adiabatic compressor to maximize the temperature of the gas 7. The compressed gas is reheated in a heater R at the outlet of the compressor to reach a temperature between 50 and 150°C. The first configuration consists of using an electric heater R to heat the gas between typically 60°C and 130°C. This configuration has the disadvantage of consuming a significant amount of electrical energy. The fact that the outlet of the compressor is hot nevertheless makes it possible to limit the power of this heater: the reduction in electrical power of the heater can be between 100% and 20%.

[0029] A second configuration consists of using a heat transfer fluid (for example water vapor or hot water) available in the unit. If the heat transfer fluid is available at a temperature T1 higher than the required temperature T2 at the inlet of the demercurizer, the heater R is constituted by a heat exchanger allowing an indirect heat exchange between the heat transfer fluid and the gas containing mercury. This exchanger is placed between the turbocharger C (without final cooler) and the demercurizer D. In this case, the fact that the compressed gas is hot at the outlet of the turbocharger also makes it possible to save on the consumption of heat transfer fluid.

[0030] Then the gas 7 is demercurized in one or more mercury adsorption reactors D producing a demercurized gas 9.

[0031] The demercurized gas 9 is cooled in a cooler G using a flow of refrigerant fluid W, for example water.

[0032] The cooled gas 11 in the cooler G is separated in a CC unit operating at temperatures below 10°C, or even below -50°C by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least a fluid 13 containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of gas 15 depleted in CO2 and enriched in at least one air gas.

[0033] At least a portion of the CO2-depleted gas 15 is expanded in the turbine T coupled to the turbocharger C, possibly after having been reheated in a heater H to a temperature above 10°C.

[0034] The expanded gas 17 is evacuated from the process.

[0035] The fluid W used to cool the demercurized gas 9 can be used to heat the gas 15 in the heater H.

[0036] This fluid W can also be used to heat the gas 7 in the heater R upstream or downstream of the compressor C, to heat a regeneration gas for a dryer, for example a gas dryer 1 upstream of the unit 3.

[0037] It will be understood that gas 1 does not necessarily contain NO2. In this case, unit 3 is not necessarily present.

[0038] As illustrated in [Fig.2], the heater R can be arranged upstream of the turbocharger C. If the heat transfer fluid is available at a temperature T1 lower than the required temperature T2 at the inlet of the demercurizer D, it is then necessary to place the heat exchanger R upstream of the turbocharger C. The heat transfer fluid is then used over the available temperature range and the temperature increase up to the temperature T2 is ensured by the turbocharger. If the heat transfer fluid has a lower cost than electricity, or is even free, this configuration makes it possible to avoid consuming electricity in an electric heater.

[0039] In the previous configurations, the heat is recovered at a cooler G located after the demercurizer D. A heat exchanger can transfer the heat from the demercurized gas to the heat transfer fluid. This heat transfer fluid can be the same as that used in the configuration of [Fig.2].

[0040] To avoid using an intermediate heat transfer fluid, it is possible to use a gas / gas heat exchanger.

[0041] A first configuration consists of using a gas / gas exchanger EC as illustrated in [Fig.3] upstream of the turbocharger C. The gas entering the turbocharger C is heated using the heat of the gas leaving the demercurizer D. This configuration has the advantage of avoiding the use of an intermediate fluid. The heat produced by the turbocharger C makes it possible to compensate for the thermal losses at the level of the demercurizer D. It also makes it possible to reduce the size of the heat exchanger by having an approach greater than 10°C at the hot end of the exchanger. The gas at 30°C is heated in the heat exchanger EC up to 105°C, then compressed in the compressor C from which it leaves at 130°C, demercurized at 130°C and then sent to cool in the heat exchanger EC to cool it down to 58°C, a cooling step in cooler G cooling it down to 32°C.

[0042] A second configuration, illustrated in [Fig.4], consists of placing the turbocharger C upstream of the gas / gas heat exchanger EC. The compressed gas in C enters the gas / gas heat exchanger EC and the final heating is carried out by a final heater R (electric or using a heat transfer fluid at a sufficiently high temperature). This final heater R is necessary to compensate for the thermal losses and the approach to the hot end of the exchanger EC. It is in this configuration that the heat produced by the turbocharger is least well used. Indeed, the turbocharger C only makes it possible to reduce the size of the gas / gas heat exchanger EC.

Claims

Claims

1. A method of separating a gas containing CO2, at least one gas from air and mercury comprising the following steps: i. Compression of the gas (1.5) in a turbocharger (C) coupled to a turbine (T) forming a compressed gas (7), ii. Reheating (R, EC) of the compressed gas upstream or downstream of the compressor, and demercurization (D) of the reheated compressed gas in one or more non-regenerative mercury adsorption reactors producing a demercurized gas (9), iii. Cooling (G) of the demercurized gas, iv. Separation (CC) of the cooled gas (11) in a unit operating at temperatures below 10°C, or even below -50°C by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 (13) and a pressurized stream of CO2-depleted gas (15) and v. At least part of the CO2-depleted gas is expanded in the turbine coupled to the turbocharger, possibly after having been reheated (H) to a temperature above 10°C.

2. Method according to claim 1 in which the compressed gas is heated to a temperature between 50 and 150°C upstream of the demercurizer (D).

3. Method according to claim 1 or 2 wherein the demercurized gas (9) is cooled by indirect heat exchange with a refrigerant (W) and the refrigerant (W), preferably water, having served to cool the demercurized gas (9), is used to heat the compressed gas (7) in the heater (R).

4. Method according to one of the preceding claims in which the compressed gas is heated by an electric heater (R) and / or by a heat-transfer fluid.

5. Method according to one of the preceding claims in which the compressed gas or the gas to be compressed is heated by indirect heat exchange with the treated gas (9) in the demercurizer.

6. A method according to claim 5 wherein the indirect heat exchange takes place in a heat exchanger (EC) in which the compressed gas or the gas to be compressed is heated and in which the gas treated (9) in the demercurizer (D) cools.

7. Method according to one of the preceding claims in which the CO2-depleted gas (15) is enriched with at least one air gas, for example nitrogen and / or oxygen and / or argon.

8. Method according to one of the preceding claims in which the gas containing CO2, at least one air gas and mercury (1) contains NO2 and is treated to remove the NO2 in a unit (3) making it possible to remove the NO2 down to a concentration of less than 5 ppm, or even less than 1 ppm in NO2 producing a gas lean in NO2 (5) upstream of the compression in the turbocharger.

9. A method according to claim 8 wherein the treatment for removing NO2 is a separation process by partial condensation and / or distillation.

10. Method according to one of the preceding claims in which the gas containing CO2, at least one air gas and mercury and optionally NO2 (1) is composed of combustion fumes.

11. Apparatus for separating a gas containing CO2, at least one air gas and mercury (1,5) comprising a turbocharger (C), a turbine (T) coupled to the turbocharger, a demercurization unit (D), a cooler (G), a heater (R, EC), a separation unit (CC) by partial condensation in one or more stages and / or by distillation and / or solidification operating at temperatures below 10°C, or even below -50°C, means for sending the gas containing CO2, at least one air gas and mercury (1,5) to the turbocharger, the heater being connected to heat the gas upstream or downstream of the turbocharger, means for sending the compressed and heated gas to the demercurization unit to form a demercurized gas,means for sending the demercurized gas (9) to the cooler and from the cooler to the separation unit to produce at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 (13) and a pressurized stream of CO2-depleted gas (15) and means for sending at least part of the CO2-depleted gas to expand in the turbine coupled to the turbocharger.,

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