Method and apparatus for separating a mixture of CO2 and nitrogen by adsorption and partial condensation and / or distillation and / or solidification

Abstract

Title of the invention; Process for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification. In a process for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification, the mixture of CO2 and nitrogen is separated by adsorption forming a nitrogen-enriched and CO2-depleted gas stream (NRI) and a CO2-enriched and nitrogen-depleted gas stream. The nitrogen-enriched stream is heated by sending it to the bottom of a tower (T) fed at an inlet level above the outlet level of the nitrogen-enriched stream by a water stream (CWI). The CO2-enriched stream is separated by partial condensation and / or distillation and / or solidification to form a CO2-enriched stream, and a stream containing nitrogen and water vapor rising in the tower is heated by a heat exchanger (E).The heat exchanger is heated by a fluid flow (F1) which is itself heated by a heat source (I) generated by the separation process. Fig. 3,

Description

Title of the invention: Method and apparatus for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification

[0001] The present invention relates to a method and apparatus for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification, the mixture preferably containing at least 10% mol of CO2, or even at least 30% of CO2.

[0002] FR2884307A is known to separate a mixture of CO2 and nitrogen by PSA or VPSA type adsorption, forming a nitrogen-enriched, CO2-depleted flow and a nitrogen-depleted, CO2-enriched flow. The CO2-enriched flow is separated to form a CO2-rich fluid, while the nitrogen-enriched flow is sent to a mass and heat exchanger tower to cool a water flow. Water-saturated gas exits from the top of the tower. In one example, the nitrogen-enriched flow is expanded in a turbine and then reheated in a heat exchanger of a low-temperature CO2 separation unit upstream of the tower. This requires a more complex heat exchanger and does not allow the nitrogen-enriched flow to exit at a high temperature, since it must cool the water in the tower.

[0003] In industry, it has long been known that releasing water-saturated fumes into the atmosphere can cause a large condensation cloud called a plume. In order to limit the visibility of this plume and also to promote the flow of these fumes towards the top of the tower, processes have been implemented, notably to heat these fumes to raise them away from the dew point.

[0004] The invention described below proposes a new scheme allowing the integration of the heating of residual gases released into the atmosphere on a CO2 capture unit by cryogenic means.

[0005] State of the art

[0006] Numerous techniques exist for heating a water-saturated gas before it is released into the atmosphere. However, suitable techniques do not exist for cryogenic CO2 capture processes on industrial flue gases.

[0007] [Fig. 1] illustrates a known process for releasing into the atmosphere a relatively cold (10-12°C) and water-saturated nitrogen-rich gas (NRI) residual from CO2 capture on flue gases in a tower T. The values ​​given in this example are intended to help the reader better understand this existing process, but it is not assumed that these temperature values ​​are known to those skilled in the art. The nitrogen (NRI) sent to the bottom of the tower T is preferably first expanded to a pressure close to atmospheric pressure in a turbine. The residual nitrogen NRI, cooled by expansion, is sent to the tower T at a temperature between 2 and 6°C and cools by direct heat exchange the water CWI sent to the top of the tower, the cooled water CWO exiting in the tank of the tower T and the slightly warmed nitrogen NRO at the top.

[0008] This final step slightly heats the residual NRI gas to 10-12°C but also saturates the NRO gas with water just before releasing it into the atmosphere. In this case, the nitrogen mixed with water vapor exits tower T and is released into the air, potentially generating a plume.

[0009] Problems solved by the invention

[0010] The current process releases a water-saturated gas at ambient temperature into the atmosphere. This creates a significant risk of plume formation upon contact with the ambient air due to condensation of the water contained in the gas. For regulatory reasons or to avoid disturbing the immediate environment of the unit, it may be necessary to severely limit the presence of these plumes. Furthermore, the heating of these fumes, according to the invention, can, in certain cases and depending on the temperature difference with the ambient air, facilitate the flow of nitrogen-enriched gas from the bottom of the tower to the top of the tower, which in some cases can reach a height of over one hundred meters.

[0011] Description of the invention

[0012] The principle of the invention consists of heating the nitrogen-rich gas using heat from a heat source present in the separation process. The heat is transferred to a heat exchanger by a fluid, for example, water or oil, which heats the nitrogen-rich gas containing water vapor. The heat may, for example, be heat from a heat transfer circuit, for example, a heat transfer loop, using a fluid, for example, water, circulating in a circuit including a heat source. The circuit may be used, for example, to cool and / or heat another element of the separation process, either in the adsorption separation section or in the partial condensation and / or distillation and / or solidification separation section.

[0013] [Fig. 2] shows that in an example, which does not correspond to the invention, a heat transfer loop using a circulating fluid F, which is water or oil, for example. The loop is in fact partially cooled by cooling water CW in a heat exchanger E in order to have a temperature of around 20-30°C. This heat transfer loop is incorporated into a process for separating CO2 from a nitrogen-CO2 mixture similar to that described in FR2884307A, in which the mixture is first separated by adsorption, forming a gas stream enriched in nitrogen and depleted in CO2 and a gas stream enriched in CO2 and depleted in nitrogen. The CO2-enriched stream is compressed in a compressor, cooled, and then separated by partial condensation and / or distillation and / or solidification to form a CO2-enriched stream. In this example, to cool, for instance, the gas from the CO2-enriched gas compressor produced by adsorption, for example in a CO2 PSA intended for separation by partial condensation and / or distillation, the heat transfer loop serves to remove the heat generated by compression. To do this, the fluid circulating in the loop, here water from the loop pressurized by a pump P, passes through the heat source, here the intercooler or final cooler I of a CO2-enriched gas compressor, to be heated. The fluid is divided in two, partly sent to a consumer C to supply heat to consumer C while being cooled itself, and partly to a consumer H to supply heat to consumer H while being cooled itself.Consumer H is used to heat the nitrogen-enriched gas produced by the adsorption process, for example in a CO2 PSA, upstream of its expansion in at least one turbine. The nitrogen-enriched gas can be the NRI gas from [Fig. 1]. The portion of the fluid heated by consumer C is sent to cool in the heat exchanger E against the cooling water CW. It is then mixed with the portion of the fluid used to heat consumer H, and the mixed flow is sent to the heat source I.

[0014] An expansion tower X allows the absorption of variations in the volume of circulating fluid due to varying ambient temperatures.

[0015] It is not admitted that a circuit identical to that of [Fig.2] is known to a person skilled in the art.

[0016] According to one object of the invention, a process is provided for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification in which the mixture of CO2 and nitrogen is separated by adsorption forming a gaseous flow enriched in nitrogen and depleted in CO2 and a gaseous flow enriched in CO2 and depleted in nitrogen, the nitrogen-enriched flow is heated by sending it to the bottom of a tower fed at an inlet level above the outlet level of the nitrogen-enriched flow by a water flow at a temperature higher than that of the nitrogen-enriched flow arriving in the tower, the tower containing means for bringing the water and the nitrogen-enriched flow into direct contact to form a flow containing nitrogen and water vapor rising in the tower,The CO2-enriched flow is separated by partial condensation and / or distillation and / or solidification to form a CO2-enriched stream characterized in that the flow containing nitrogen and water vapor is heated above the water inlet level by a heat exchanger arranged to indirectly heat the flow containing nitrogen and water vapor, the heat exchanger being heated by at least a portion of a fluid flow, for example water or oil, itself heated by a heat source generated by the separation process.

[0017] According to other optional objects of the invention: • The heat exchanger consists of a coil. • The heat exchanger consists of a pipe that passes through an area of ​​the tower and which is connected to a plate heat exchanger. • The heat exchanger is located in the tower. • The heat source is an interstage or final cooler of a compressor of the CO2 enriched flow which compresses the flow intended for separation by partial condensation and / or distillation and / or solidification and / or of a compressor of the CO2 enriched flow and / or of a compressor of the mixture to be separated. • the heat source is ambient air or oil at ambient temperature and the temperature of the nitrogen-enriched flow entering the tower is lower than the ambient temperature. • The temperature of the flow containing nitrogen and water vapor is regulated by varying the flow rate of the fluid sent to the heat exchanger by means of a bypass circuit. • The flow rate of fluid sent to the heat exchanger is varied by means of the bypass circuit according to the ambient temperature. • The flow containing nitrogen and water vapor is heated by the heat exchanger to at least 40°C. • the nitrogen-enriched flow is expanded in at least one turbine upstream of the tower and possibly the flow of fluid heated by the heat source generated by the separation process is also used to heat the nitrogen-enriched flow upstream of the expansion in at least one turbine, preferably upstream of the heat exchanger. • The flow of fluid heated by the heat source generated by the separation process is also used to heat a purge liquid produced by the separation by distillation. • The fluid flow that is sent to the heat exchanger is returned to the heat source to be reheated. • The nitrogen-enriched flow is not cooled upstream of the tower • The nitrogen-enriched flow is not cooled upstream of the tower except by the expansion in at least one turbine if present • The flow of fluid heated by the heat source generated by the separation process is divided into at least two parts, each of which is used to heat a consumer, and only the hottest of the at least two parts that have been used to heat their respective consumer is sent to the heat exchanger.

[0018] According to another object of the invention, an apparatus for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification is provided, comprising an adsorption separation unit for separating the mixture of CO2 and nitrogen by adsorption, forming a gaseous flow enriched in nitrogen and depleted in CO2 and a gaseous flow enriched in CO2 and depleted in nitrogen, a water cooling tower, a conduit for sending the nitrogen-enriched flow to be heated by sending it to the bottom of the tower, a conduit for sending a water flow, at a temperature higher than that of the nitrogen-enriched flow arriving in the tower, to supply the tower at an inlet level above the outlet level of the nitrogen-enriched flow, the tower containing means for bringing the water and the nitrogen-enriched flow into direct contact to form a flow containing nitrogen and water vapor rising in the tower,a partial condensation and / or distillation and / or solidification separation unit, a conduit for sending the CO2-enriched flow to be separated in the partial condensation and / or distillation and / or solidification separation unit to form a CO2-enriched stream characterized in that it comprises a heat exchanger arranged to heat, by indirect heat exchange, the flow containing nitrogen and water vapor before it is vented to the atmosphere, a conduit for sending at least part of a fluid flow, for example water or oil, to the heat exchanger to heat it, the fluid flow itself being connected to be heated by a heat source generated by the separation process upstream of the tower.

[0019] The fluid flow is preferably connected to be heated by the heat source downstream of the tower.

[0020] The portion of fluid sent to the heat exchanger can be cooled upstream of the tower and downstream of the heat source, for example to heat an element of the separation process, for example the nitrogen-enriched flow upstream of a turbine and / or a purge flow from the partial condensation and / or distillation and / or solidification separation unit.

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

[0022] [Fig. 3] illustrates a method for evacuating a residual nitrogen flow from a separation process by adsorption of a mixture of CO2 and nitrogen.

[0023] [Fig.4] illustrates a process for separating a mixture of nitrogen and CO2 by adsorption and by partial condensation and / or distillation and / or solidification with evacuation of a residual nitrogen flow.

[0024] The idea is therefore, according to an illustrated variant, to transmit the heat dissipated by this heat exchanger E corresponding to that of [Fig.2] to the gas containing nitrogen and water vapor which rises in the tower T, before it is released into the atmosphere. Thus, tower T of [Fig.1] is integrated into [Fig.2] and heat exchanger E is added.

[0025] [Fig. 3] illustrates the case in which only one of the portions Fl, F2 of fluid F cooled by the two consumers C, H of [Fig. 2] circulates through an upper zone of the water-nitrogen tower T in a coil-type heat exchanger E, which replaces the heat exchanger E of [Fig. 2]. This device allows the nitrogen mixed with water vapor rising in the tower T to be heated to temperatures of around 40°C and thus cools the water sent to the heat exchanger E. In some cases and depending on the configuration, the temperature of the heated nitrogen can also exceed 40°C.

[0026] Nitrogen mixed with water vapor exits tower T and is released into the atmosphere as a flow NRO, without generating a plume. The heat is thus recovered by the heat source, here element I, an intercooler or aftercooler I of a compressor. The compressor can be a compressor for CO2-enriched gas produced by the adsorption process and intended for the separation process by partial condensation and / or distillation and / or solidification, or a compressor for a CO2-enriched stream produced by the separation process by partial condensation and / or distillation and / or solidification. The fluid, for example water, heated by element I, is split in two and used to heat the consumer H, which can be the heat exchanger that heats the nitrogen-enriched flow from adsorption and intended for a turbine upstream of tower T. It can also heat another consumer C.For example, it can be used to heat a purge liquid from the distillation process, such as a NOx-enriched liquid produced by a scrubbing column. In this example, only the portion of fluid Fl used to heat consumer C is used to heat the gas rising in tower T through exchanger E, and the portion F2 used to heat consumer H is not used to heat exchanger E but is mixed with the portion cooled in exchanger E. The mixed flow is returned to the heat source I. The water heated by element I can only heat heat exchanger E and then be returned to element I.

[0027] In this example, the portion Fl of fluid sent to the exchanger E after passing through to heat the consumer C is hotter than the portion F2 of fluid used to heat the consumer H. It is therefore the hotter portion of fluid that is used to heat the exchanger E.

[0028] This scheme thus makes it possible to propose a solution for heating the gases released into the atmosphere with the same equipment (or even with one less piece of equipment if the coil can be directly integrated into the water-nitrogen tower T). However, the presence of the heat exchanger E in the tower T induces a slight pressure drop (approximately 50 mbar) which must be compensated for by a smaller expansion in the turbine that expands the nitrogen-enriched flow to be evacuated by the tower T, resulting in a given energy loss. to the machine shaft consisting of the turbine coupled to a compressor. However, removing the heat exchanger E from the cooling water CW on the hot water loop (see [Fig. 2]) also reduces the cooling water flow rate and therefore the energy consumption of this loop. At an average outside temperature of 10°C, the overall energy consumption of the unit, taking these two aspects into account, would increase by 0.5%.

[0029] A bypass device B of this heat exchanger E can be installed on either the hot water or gas side in order to regulate the temperature of the hot water returned to the cooler I of the gas compressor and / or of the gas discharged to the atmosphere NRO.

[0030] Thus, the temperature of the water and / or the residual nitrogen gas containing water vapor is regulated by varying the flow rate of water sent to the heat exchanger by means of a bypass circuit. Therefore, when the ambient temperature is warmer, the flow rate of water sent to the heat exchanger can be reduced. Similarly, when the ambient temperature is colder, the flow rate of water sent to the heat exchanger can be increased.

[0031] The bypass duct B of the heat exchanger allows the temperature at the outlet of this heat exchanger E to be regulated in order to compensate for variations in ambient temperature. This bypass can be placed either on the hot fluid side or on the cold fluid side.

[0032] It will be understood that the fluid supplying the heat exchanger does not necessarily circulate in a closed loop and that the circuit can send fluid as a product and / or receive fluid from a fluid source.

[0033] [Fig. 4] illustrates a process for separating a mixture of CO2 and nitrogen by adsorption and partial condensation and / or distillation and / or solidification, in which the mixture of CO2 and nitrogen is separated by adsorption in a PSA unit, forming a nitrogen-enriched, CO2-depleted gas flow NRI and a CO2-enriched, nitrogen-depleted gas flow. The nitrogen-enriched flow is fed at the bottom of a tower at an inlet level above the outlet level of the nitrogen-enriched flow by a water flow at a temperature higher than that of the nitrogen-enriched flow entering the tower, as described previously. The CO2-enriched flow is compressed by a compressor V, cooled in a heat exchanger BAHX, and then separated by partial condensation and / or distillation and / or solidification in a CC unit to form a CO2-enriched stream and optionally a NOx-enriched purge flow P. The purge flow P can be heated to C by the fluid F.The compressor cooler I (here the aftercooler) is used to heat the fluid F as illustrated in the other figures. Alternatively, the heat source can be a compressor of the CO2-enriched flow or of the mixture to be separated upstream of the adsorption unit. The nitrogen-enriched and CO2-depleted flow NRI can, for example, be... relaxed in at least one TD turbine upstream of tower T after preheating in H by fluid F.

Claims

Demands

1. A method for separating a mixture of CO2 and nitrogen by adsorption and partial condensation and / or distillation and / or solidification, wherein the mixture of CO2 and nitrogen is separated by adsorption (PSA) forming a nitrogen-enriched and CO2-depleted (NRI) gas stream and a CO2-enriched and nitrogen-depleted gas stream, the nitrogen-enriched stream is heated by sending it down a tower (T) fed at an inlet level above the outlet level of the nitrogen-enriched stream by a water stream (CWI) at a temperature higher than that of the nitrogen-enriched stream arriving at the tower, the tower containing means for bringing the water and the nitrogen-enriched stream into direct contact to form a stream containing nitrogen and water vapor rising in the tower,The CO2-enriched flow is separated by partial condensation and / or distillation and / or solidification (CC) to form a CO2-enriched flow characterized in that the flow containing nitrogen and water vapor is heated above the water introduction level by a heat exchanger (E) arranged to indirectly heat the flow containing nitrogen and water vapor, the heat exchanger being heated by at least a portion (Fl) of a fluid flow (F), for example water or oil, itself heated by a heat source (I) generated by the separation process.

2. Method according to claim 1 wherein the heat exchanger (E) is constituted by a coil.

3. Method according to claim 1 wherein the heat exchanger (E) is constituted by a pipe which passes through an area of ​​the tower (T) and which is connected to a plate heat exchanger (E).

4. A method according to any one of the preceding claims wherein the heat exchanger (E) is located in the tower (T).

5. A method according to any one of the preceding claims wherein the heat source is an interstage or final cooler (I) of a compressor (V) of the CO2-enriched flow which compresses the flow intended for separation (CC) by partial condensation and / or distillation and / or solidification and / or of a compressor of the CO2-enriched flow and / or of a compressor of the mixture to be separated.

6. A method according to any one of the preceding claims 1 to 4 wherein the heat source is ambient air or oil at ambient temperature and the temperature of the nitrogen-enriched flow entering the tower is lower than the ambient temperature.

7. A method according to any one of the preceding claims wherein the temperature of the flow (NRI) containing nitrogen and water vapor is regulated by varying the flow rate of the fluid sent to the heat exchanger by means of a bypass circuit (B).

8. A method according to claim 7 wherein the flow rate of fluid sent to the heat exchanger is varied by means of the bypass circuit (B) as a function of the ambient temperature.

9. A method according to any one of the preceding claims wherein the flow containing nitrogen and water vapor is heated by the heat exchanger (E) to at least 40°C.

10. A method according to any one of the preceding claims wherein the nitrogen-enriched flow is expanded in at least one turbine (TD) upstream of the tower (T) and optionally the flow of fluid heated by the heat source (I) generated by the separation process also serves to heat the nitrogen-enriched flow upstream of the expansion in the at least one turbine, preferably upstream of the heat exchanger (E).

11. Apparatus for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification comprising an adsorption separation unit (PSA) for separating the mixture of CO2 and nitrogen by adsorption forming a nitrogen-enriched and CO2-depleted gaseous flow (NRI) and a CO2-enriched and nitrogen-depleted gaseous flow, a water cooling tower (T), a conduit for sending the nitrogen-enriched flow to be heated by sending it to the bottom of the tower, a conduit for sending a water flow (CWI), at a temperature higher than that of the nitrogen-enriched flow arriving at the tower, to supply the tower at an inlet level above the outlet level of the nitrogen-enriched flow, the tower containing means for bringing the water and the nitrogen-enriched flow into direct contact to form a flow containing nitrogen and water vapor rising in the tower,a separation unit (CC) by partial condensation and / or distillation and / or solidification, a conduit to send the CO2-enriched flow to be separated in the condensation separation unit, partial and / or distillation and / or solidification to form a CO2-enriched stream characterized in that it comprises a heat exchanger (E) arranged to heat by indirect heat exchange the flow containing nitrogen and water vapor before it is released to the air, a conduit for sending at least a part (Fl) of a fluid flow (F), for example water or oil, to the heat exchanger to heat it, the fluid flow itself being connected to be heated by a heat source (I) generated by the separation process upstream of the tower.

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