Method and apparatus for reducing the cold energy consumption of carbon dioxide liquefaction

Abstract

The present application relates to the technical field of carbon dioxide liquefaction, and particularly relates to a method and device for reducing carbon dioxide liquefaction cold consumption. The method comprises the following steps: sequentially performing n-stage heat exchange cooling and carbon dioxide liquefaction on carbon dioxide compressed gas to obtain liquefied carbon dioxide and separate out non-condensable gas; wherein the non-condensable gas is returned to contact with the carbon dioxide compressed gas in countercurrent to perform the n-stage heat exchange cooling; the n-stage heat exchange cooling process comprises the following steps: gradually reducing the pressure of the non-condensable gas and performing gradual flow separation; wherein n is a positive integer not less than 3. The method can efficiently recover the cold energy of the non-condensable gas, thereby significantly reducing the cold consumption of the carbon dioxide liquefaction process and improving the economic efficiency of the carbon dioxide liquefaction process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide liquefaction, and particularly relates to a method and device for reducing carbon dioxide liquefaction cold consumption. BACKGROUND

[0002] The massive emission of carbon dioxide is one of the main reasons for global warming. With the increasing attention of countries around the world to climate problems, more and more countries have begun to pay attention to carbon dioxide emissions. As the largest carbon dioxide emitter in the world, China's carbon dioxide emissions account for more than 30% of the global total. In the face of the "3060" target of carbon peak and carbon neutrality, the situation of carbon dioxide emission reduction is extremely severe.

[0003] The main ways of carbon dioxide emission reduction include improving energy use efficiency, adjusting energy structure, and carbon dioxide capture, utilization and storage (CCUS). Among them, CCUS is the most direct means to reduce carbon dioxide emissions, and is the only way to solve the carbon emissions of industries such as cement, steel and chemical industry that are difficult to solve by new energy methods.

[0004] Carbon dioxide liquefaction is an important step of CCUS technology. According to the physical and chemical properties of carbon dioxide, the current carbon dioxide liquefaction process mainly includes low-temperature low-pressure liquefaction and normal-temperature high-pressure liquefaction processes. Among them, the low-temperature low-pressure liquefaction process is the carbon dioxide liquefaction process universally adopted at home and abroad. Generally, the process first pressurizes the gaseous carbon dioxide at normal pressure to about 2 MPa, and then absorbs its latent heat by using a refrigeration unit to liquefy it.

[0005] CN201811197226.X discloses a carbon dioxide liquefaction device and process, which includes a carbon dioxide integrated liquefier. The carbon dioxide integrated liquefier includes, from bottom to top, a liquid collection pipe box, a first-stage cooler, a pipe passage intermediate pipe box, and a second-stage cooler. The first-stage cooler and the second-stage cooler are both shell-and-tube heat exchanger structures. The tubes in the first-stage cooler and the second-stage cooler are connected through the pipe passage intermediate pipe box. The tubes of the first-stage cooler are connected to the liquid collection pipe box. The shell passages of the first-stage cooler and the second-stage cooler are connected through U-shaped pipes. The pipe passage intermediate pipe box is provided with a carbon dioxide gas inlet connected to the three-stage outlet of a carbon dioxide compressor through a carbon dioxide gas inlet pipeline. The lower part of the first-stage cooler is provided with a shell passage inlet, and the upper part of the shell passage of the second-stage cooler is provided with a shell passage outlet. The shell passage inlet is connected to the low-temperature methanol outlet of a methanol washing device.

[0006] CN201820491382.6 discloses a carbon dioxide liquefaction recovery device, in the process of operation of the recovery device, the gas flow sensor detects the flow of the gas flowing out of the raw material gas tank in real time and feeds back the flow information to the main controller, the main controller controls the rotating speed of the variable frequency liquid pump according to the flow change of the gas, and controls the flow of the flow regulating electric control valve, so that the delivery amount of the liquid ammonia is adjusted, so that the delivery amount of the liquid ammonia is matched with the flow of the gas, the utilization of the liquid ammonia is more reasonable, the heat absorption in the external environment of the liquid ammonia is reduced, and therefore the power consumption of the subsequent reliquefied ammonia gas is effectively reduced, and the energy consumption of the carbon dioxide recovery device is reduced.

[0007] CN201380070412.6 discloses a carbon dioxide liquefaction device, the carbon dioxide liquefaction device has: a carbon dioxide liquefaction part, which liquefies carbon dioxide recovered from a gas containing carbon dioxide by heat exchange with part of a cold heat source in a gas state used in and manufactured in a cold heat source generating device as a refrigerant; and an energy recovery part, which outputs energy by expanding a gas refrigerant that has been heat-exchanged with carbon dioxide in the carbon dioxide liquefaction part, and lowers the temperature of the gas refrigerant, and returns the gas refrigerant with lowered temperature to the cold heat source generating device.

[0008] However, since the liquefied raw gas usually contains a certain amount of non-condensable gas, during the liquefaction process, this part of non-condensable gas needs to be discharged. At the same time, in order to ensure the concentration of the product carbon dioxide, a certain amount of carbon dioxide will be discharged during the discharge of non-condensable gas. The above three applications do not focus on recovering the cold energy in the non-condensable gas. Although the industry will use a waste heat recovery device to recover the cold energy contained in the non-condensable gas, the efficiency of the cold energy recovery is often low, and the cold consumption required in the liquefaction process cannot be significantly reduced. Based on the above reasons, the existing carbon dioxide liquefaction process has high cold consumption, which causes the operating cost of carbon dioxide liquefaction to rise.

[0009] Therefore, it is urgent to develop a device that can significantly reduce the cold consumption required in the carbon dioxide liquefaction process and improve the economy of the carbon dioxide liquefaction process. SUMMARY

[0010] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide a method and device for reducing the cold consumption of carbon dioxide liquefaction, which can efficiently recover the cold energy of non-condensable gas, thereby significantly reducing the cold consumption of the carbon dioxide liquefaction process and improving the economy of the carbon dioxide liquefaction process.

[0011] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a method for reducing the cold consumption of carbon dioxide liquefaction, which comprises:

[0012] The carbon dioxide compressed gas is sequentially subjected to n-stage heat exchange cooling and carbon dioxide liquefaction to obtain liquefied carbon dioxide and separate out non-condensable gas;

[0013] The non-condensable gas is returned to contact with the carbon dioxide compressed gas in counterflow to perform the n-stage heat exchange cooling; the n-stage heat exchange cooling process comprises: step-by-step depressurization of the non-condensable gas and step-by-step shunting of the non-condensable gas;

[0014] The n is a positive integer not less than 3.

[0015] The second aspect of the present application provides a device for reducing the cold consumption of carbon dioxide liquefaction, which comprises: n-stage heat exchange cooling units connected in sequence, a liquefier, and a pipeline for returning the non-condensable gas separated from the liquefier to the nth heat exchange cooling unit;

[0016] Each heat exchange cooling unit comprises a heat exchanger, a pipeline for passing the non-condensable gas into the heat exchanger as a refrigerant, a pipeline for passing the non-condensable gas through the heat exchange cooling unit with or without shunting, and a pipeline for passing the non-condensable gas into an adjacent heat exchange cooling unit or into the atmosphere or a downstream process section; in addition to the first heat exchange unit, each heat exchange cooling unit further comprises a gas interception device.

[0017] The heat exchanger is used for counterflow contact of the non-condensable gas as a refrigerant with carbon dioxide to perform heat exchange cooling of the carbon dioxide, and the gas interception device is used for depressurization of the non-condensable gas.

[0018] The n is a positive integer not less than 3.

[0019] The present application can achieve the following beneficial effects:

[0020] (1) By the method of the present application, the cold energy in the non-condensable gas can be recovered, so that a part of the cold energy is obtained before the carbon dioxide compressor enters the liquefier, thereby reducing the cold energy consumption in the carbon dioxide liquefaction process.

[0021] (2) By the method of the present application, not only the cold energy in the condensing gas can be recovered, but also the cold energy generated in the step-by-step depressurization process of the condensing gas can be recovered. The step-by-step recovery of the residual cold energy and the combination of the series flow and parallel flow of the condensing gas can make the temperature difference distribution in the entire heat exchange process more reasonable and improve the efficiency of the residual cold energy recovery.

[0022] (3) By the method of the present application, the shunting ratio of the non-condensable gas stream and the pressure of the step-by-step depressurization are easy to adjust, i.e. they can be easily adjusted according to the actual working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The present application provides a device for reducing the cold consumption of carbon dioxide liquefaction.

[0024] Reference Signs List

[0025] 1 - first heat exchange cooling unit, 2 - second heat exchange cooling unit, 3 - third heat exchange cooling unit, 4 - fourth heat exchange cooling unit, 5 - fifth heat exchange cooling unit, 6 - liquefier;

[0026] L1 - first gas trapping device, L2 - second gas trapping device, L3 - third gas trapping device, L4 - fourth gas trapping device, L5 - fifth gas trapping device;

[0027] S1 - first heat exchanger, S2 - second heat exchanger, S3 - third heat exchanger, S4 - fourth heat exchanger, S5 - fifth heat exchanger. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within common

[0029] In a first aspect, the present application provides a method for reducing the cold consumption of carbon dioxide liquefaction, comprising:

[0030] The carbon dioxide compressed gas is sequentially subjected to n-stage heat exchange cooling and carbon dioxide liquefaction to obtain liquefied carbon dioxide, and non-condensable gas is separated out;

[0031] The non-condensable gas is returned to contact with the carbon dioxide compressed gas in countercurrent flow to perform the n-stage heat exchange cooling; the process of the n-stage heat exchange cooling comprises: the non-condensable gas is subjected to stepwise pressure reduction and stepwise flow splitting;

[0032] Wherein, n is a positive integer not less than 3.

[0033] It can be understood that in the general process of carbon dioxide liquefaction, the carbon dioxide is first compressed and cooled by cooling water to obtain carbon dioxide compressed gas, the pressure is generally 2-2.5 MPa, and the temperature is generally 35-45℃. After carbon dioxide liquefaction, the temperature is generally -23℃.

[0034] And, it can be understood that, in the process of returning the liquefied non-condensable gas to contact with the carbon dioxide compressed gas in countercurrent and performing the n-stage heat exchange cooling, the non-condensable gas acts as the refrigerant. And, since the non-condensable gas is in countercurrent contact with the carbon dioxide compressed gas, when the non-condensable gas is in first countercurrent contact with the carbon dioxide compressed gas, the carbon dioxide compressed gas is in n-stage countercurrent heat exchange; when the non-condensable gas is in second countercurrent contact with the carbon dioxide compressed gas, the carbon dioxide compressed gas is in n-1-stage countercurrent heat exchange, and so on. And, since the non-condensable gas is in countercurrent contact with the carbon dioxide compressed gas, the next heat exchange cooling stage in the flow direction of the non-condensable gas and the next heat exchange cooling stage in the flow direction of the carbon dioxide compressed gas have different meanings.

[0035] And, in the process of gradually reducing the pressure, the pressure ratio before and after the interception is small, so that the interception process is closer to a reversible process, and a higher cooling efficiency can be obtained.

[0036] According to the present application, when n is large, the non-condensable gas can be in more countercurrent contact with the carbon dioxide compressed gas, so that the cold energy of the non-condensable gas can be recovered as much as possible. However, in order to simultaneously consider the process saving and the efficiency of recovering the cold energy of the non-condensable gas, preferably, n is a positive integer not less than 3 and not more than 10 (for example, n can be 3, 4, 5, 6, 7, 8, 9, 10), and more preferably, n is a positive integer not less than 3 and not more than 6.

[0037] The n-stage heat exchange cooling process includes corresponding heat exchange cooling stages S1-Sn. n For example, when n is 3, the 3-stage heat exchange cooling process includes heat exchange cooling stages S1, S2 and S3.

[0038] According to the present application, in order to further efficiently recover the cold energy of the non-condensable gas, preferably, in the heat exchange cooling stage S m , it includes sequentially performing heat exchange cooling and pressure reduction on the carbon dioxide compressed gas by the non-condensable gas flowing through the heat exchange cooling stage S m , and then sending the non-condensable gas into the next heat exchange cooling stage S m-1 ; in the heat exchange cooling stage S1, it includes sequentially performing heat exchange cooling and pressure reduction on the carbon dioxide compressed gas by the non-condensable gas flowing through the heat exchange cooling stage S1, and then discharging the non-condensable gas into the atmosphere or a downstream process section.

[0039] Wherein, 2≤m≤n.

[0040] Wherein, the non-condensable gas flowing through the heat exchange cooling stage S m refers to all the non-condensable gas flowing through the heat exchange cooling stage S m .

[0041] It can be understood that the non-condensable gas flowing through is depressurized, and then enters the next heat exchange cooling stage S m-1 . Therefore, in the same heat exchange cooling stage S m , the pressure of the non-condensable gas flowing through is consistent, and the pressure of the non-condensable gas flowing through in different heat exchange cooling stages is different, so that one heat exchange cooling stage corresponds to one pressure.

[0042] According to the present application, in order to further efficiently recover the cold energy of the non-condensable gas, preferably, the pressure ratio (P m-1 / P m ) of the non-condensable gas flowing through in adjacent two-stage heat exchange cooling stages is 0.1-0.8 (for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8). It can be understood that, as described above, one heat exchange cooling stage corresponds to one pressure, P m , which represents the pressure of the non-condensable gas flowing through in the heat exchange cooling stage S m .

[0043] According to the present application, in order to further efficiently recover the cold energy of the non-condensable gas, preferably, when m>2, the non-condensable gas flowing through is divided in the heat exchange cooling stage S m . It can be understood that, in the heat exchange cooling stage S m , the non-condensable gas flowing through is divided, so that the non-condensable gas presents a combination of series flow and parallel flow in the entire heat exchange cooling process, which can make the temperature difference distribution of the non-condensable gas and the carbon dioxide raw material gas at each place in the entire heat exchange cooling process more reasonable, and can more efficiently recover the heat. In the heat exchange cooling stage S2, the non-condensable gas flowing through goes to the heat exchange cooling stage S1; in the heat exchange cooling stage S1, the non-condensable gas flowing through is directly discharged into the atmosphere or a downstream process section, so that the non-condensable gas flowing through does not need to be divided again in the heat exchange cooling stage S1 and the heat exchange cooling stage S2.

[0044] According to the present application, in order to further efficiently recover the cold energy of the non-condensable gas, preferably, the dividing process is to divide the non-condensable gas flowing through into a depressurization flow and a heat exchange flow, the depressurization flow is directly depressurized and then enters the next heat exchange cooling stage S m-1 , and the heat exchange flow is used to sequentially perform heat exchange cooling and depressurization on the carbon dioxide compressed gas. For example, when n is 6, the non-condensable gas returns from the liquefier and enters S6 to become the non-condensable gas flowing through the heat exchange cooling stage S6, and then is divided into a depressurization flow and a heat exchange flow, the depressurization flow is directly depressurized and then enters the next heat exchange cooling stage S5, and the heat exchange flow is used to sequentially perform heat exchange cooling and depressurization on the carbon dioxide compressed gas, and then enters the heat exchange cooling stage S5.

[0045] According to the present invention, in order to further efficiently recover the cold energy of the non-condensable gas, preferably, the volume ratio of the pressure-reducing flow to the heat-exchanging flow is 1:1.5 - 9 (for example, it can be 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9).

[0046] According to the present invention, preferably, the method further includes: when m < n, in the heat-exchanging cooling stage S m in which, the heat-exchanging flow that has experienced the heat-exchanging cooling is combined with the pressure-reducing flow from the previous heat-exchanging cooling stage S m+1 to form a combined flow, and the combined flow is depressurized and then enters the next heat-exchanging cooling stage S m-1 . For example, when n is 6, in the heat-exchanging cooling stage S5, the non-condensable gas flowing through is shunted to form a pressure-reducing flow and a heat-exchanging flow. After the heat-exchanging flow exchanges heat with the carbon dioxide compressed gas, it is combined with the pressure-reducing flow from the heat-exchanging cooling stage S6 to form a combined flow, and the combined flow is depressurized and then enters the heat-exchanging cooling stage S4.

[0047] According to the present invention, preferably, the pressure of the non-condensable gas flowing through in the heat-exchanging cooling stage S1 is 0.1 - 0.2 MPa. It can be understood that after experiencing step-by-step pressure reduction, the non-condensable gas flowing through in S1 is reduced from the same pressure as the carbon dioxide compressed gas to 0.1 - 0.2 MPa, that is, reduced to a pressure close to the atmospheric pressure, so as to fully recover the cold energy in the non-condensable gas.

[0048] According to the present invention, preferably, the carbon dioxide compressed gas flows in series during the process of flowing through the n-stage heat-exchanging cooling stage. [[ID=​​​​​​​​​​​​

[0053] Where n is a positive integer not less than 3.

[0054] It is understandable that before entering the device, carbon dioxide is generally compressed to obtain compressed carbon dioxide gas. Then, the compressed carbon dioxide gas enters the device and passes through n-stage heat exchange and cooling units in sequence, reaching the liquefaction unit for liquefaction. During this process, non-condensable gases are separated and returned to the pipeline entering the n-stage heat exchange and cooling unit, then to the (n-1)-stage heat exchange and cooling unit, then to the (n-2)-stage heat exchange and cooling unit, until it enters the 1-stage heat exchange and cooling unit, and is then discharged into the atmosphere or downstream process section.

[0055] According to the present invention, in order to further and more efficiently recover the cold energy of non-condensable gases, thereby reducing the cold consumption of carbon dioxide liquefaction, the heat exchanger is preferably a plate heat exchanger or a shell-and-tube heat exchanger.

[0056] According to the present invention, preferably, the apparatus can be part of a low-temperature, low-pressure process for producing liquid carbon dioxide, and can be combined with different types of compression, purification, dehydration or refining devices to achieve further functions.

[0057] Hereinafter, E1, E2, E3, E4, and E5 can be used to represent the 1st, 2nd, 3rd, 4th, and 5th stage heat exchange and cooling units, respectively. This description is only for the convenience of illustrating the present invention and is not intended to limit the present invention.

[0058] like Figure 1 The apparatus shown is for reducing the cooling loss of carbon dioxide liquefaction, wherein the apparatus includes five heat exchange units (i.e., n=5) connected in sequence, a liquefier, and a pipeline that returns the non-condensable gas separated from the liquefier to the fifth heat exchange cooling unit E5. E1 includes heat exchanger S1, a pipeline for introducing non-condensable gas as refrigerant into the heat exchanger, and a pipeline for discharging the non-condensable gas into the atmosphere; E2 includes a first gas trapping device L1 and a second heat exchanger S2; E3 includes a second gas trapping device L2, a third gas trapping device L3, and a third heat exchanger S3; E4 includes a fourth gas trapping device L4, a fifth gas trapping device L5, and a fourth heat exchanger S4; E5 includes a sixth gas trapping device L6, a seventh gas trapping device L7, and a fifth heat exchanger S5. Furthermore, each of E2-E5 includes a pipeline for introducing non-condensable gas as refrigerant into the heat exchanger, a pipeline for diverting or not diverting the non-condensable gas flowing through the heat exchange / cooling unit of this stage, and a pipeline for introducing the non-condensable gas into an adjacent heat exchange / cooling unit; and S1-S5 are all shell-and-tube heat exchangers. See below for reference. Figure 1 The apparatus shown illustrates the operation process of the present invention in reducing the cooling consumption of carbon dioxide liquefaction as follows.

[0059] (1) Obtain compressed carbon dioxide gas;

[0060] (2) The carbon dioxide compressed gas is sequentially introduced into the five-stage heat exchange cooling units (E1-E5) for heat exchange cooling, and finally introduced into the liquefier for carbon dioxide liquefaction, and the non-condensable gas is separated out; the non-condensable gas discharged from the top of the liquefier is returned to contact with the carbon dioxide compressed gas in countercurrent, and subjected to the five-stage heat exchange cooling, and the non-condensable gas is subjected to step-by-step pressure reduction and step-by-step flow separation according to (3)-(7);

[0061] (3) The non-condensable gas is first subjected to flow separation after entering E5, 60-63% of which is introduced into the heat exchanger of E5 as a heat exchange flow for cooling the carbon dioxide compressed gas introduced into the heat exchanger of E5, and the rest is used as a pressure reduction flow to reduce the pressure to 1.5-1.9 MPa (P4) by using a trap device, and introduced into E4 to be combined with the heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E4;

[0062] (4) The heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E5 is reduced in pressure to P4 by using a trap device, and then introduced into E4 to be subjected to flow separation, 78-82% of which is introduced into the heat exchanger of E4 as a heat exchange flow for cooling the carbon dioxide compressed gas introduced into the heat exchanger of E4, and the rest is used as a pressure reduction flow to reduce the pressure to 1.1-1.3 MPa (P3) by using a trap device, and introduced into E3 to be combined with the heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E3;

[0063] (5) The heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E4 is combined with the pressure reduction flow of E5, and then reduced in pressure to P3 by using a trap device, and then introduced into E3 to be subjected to flow separation, 78-82% of which is introduced into the heat exchanger of E3 as a heat exchange flow for cooling the carbon dioxide raw material gas introduced into the heat exchanger of E3, and the rest is used as a pressure reduction flow to reduce the pressure to 0.6-0.8 MPa (P2) by using a trap device, and introduced into E2 to be combined with the heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E2;

[0064] (6) The heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E3 is combined with the pressure reduction flow of E4, and then reduced in pressure to P2 by using a trap device, and then introduced into E2 and the heat exchanger of E2 for cooling the carbon dioxide compressed gas introduced into the heat exchanger of E2;

[0065] (7) The heat exchange flow which has undergone heat exchange cooling and flows out from the heat exchanger of E2 is combined with the pressure reduction flow of E3, and then reduced in pressure to 0.1-0.2 MPa (P1) by using a trap device, and then introduced into E1 and the heat exchanger of E1 for cooling the carbon dioxide raw material gas introduced into the heat exchanger of E1, and finally discharged to the atmosphere or a downstream recovery section.

[0066] The present application will be described in detail by way of examples. In the following, E1, E2, E3, E4 and E5 can represent the first, second, third, fourth and fifth heat exchange cooling units, respectively. Such description is only for the convenience of illustrating the present application and does not limit the present application.

[0067] Example 1

[0068] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in Fig. 1, the operation process of reducing the cold consumption of carbon dioxide liquefaction is as follows. Figure 1

[0069] (1) The carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0070] (2) The carbon dioxide compressed gas enters the five-stage heat exchange cooling units (E1-E5) in turn and finally enters the liquefier, and is cooled to -23°C in the liquefier;

[0071] (3) The non-condensable gas discharged from the top of the liquefier is split after entering E5, 80% of which is used as the heat exchange stream entering the heat exchanger of E5 to cool the carbon dioxide compressed gas entering the heat exchanger of E5, and 20% of which is used as the pressure reduction stream to be reduced to 1.6 MPa (P4) using the intercepting device, enters E4, and is combined with the heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E4;

[0072] (4) The heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E5 is reduced to 1.6 MPa (P4) using the intercepting device, and after entering E4, it is split, 90% of which is used as the heat exchange stream entering the heat exchanger of E4 to cool the carbon dioxide compressed gas entering the heat exchanger of E4, and 10% of which is used as the pressure reduction stream to be reduced to 0.8 MPa (P3) using the intercepting device, enters E3, and is combined with the heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E3;

[0073] (5) The heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E4 is combined with the pressure reduction stream of E5, and after being reduced to 0.8 MPa (P3) again using the intercepting device, it enters E3 and is split, 75% of which is used as the heat exchange stream entering the heat exchanger of E3 to cool the carbon dioxide raw material gas entering the heat exchanger of E3, and 25% of which is used as the pressure reduction stream to be reduced to 0.5 MPa (P2) using the intercepting device, enters E2, and is combined with the heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E2;

[0074] (6) The heat exchange stream that has undergone heat exchange cooling flowing out from the heat exchanger of E3 is combined with the pressure reduction stream of E4, and after being reduced to 0.5 MPa (P2) again using the intercepting device, it enters E2 and enters the heat exchanger of E2 to cool the carbon dioxide compressed gas entering the heat exchanger of E2; ​

[0075] (7) The heat exchange cooled heat exchange stream from the heat exchanger in E2 is mixed with the pressure reduction stream from E3, and then is reduced to 0.2 MPa (P1) by the intercepting device, and then enters E1 and the heat exchanger in E1, and cools the carbon dioxide raw material gas entering the heat exchanger in E1, and is finally discharged to the atmosphere or a downstream recovery section.

[0076] Example 2

[0077] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in FIG. Figure 1 The operation process of the device for reducing the cold consumption of carbon dioxide liquefaction is as follows.

[0078] (1) The carbon dioxide with a purity of 98% is compressed to 2.2 MPa first, and is cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0079] (2) The carbon dioxide compressed gas enters the five-stage heat exchange cooling units (E1-E5) in turn, and finally enters the liquefier and is cooled to -23°C in the liquefier;

[0080] (3) The non-condensable gas discharged from the top of the liquefier is split after entering E5, 60% of which is used as the heat exchange stream entering the heat exchanger of E5 to cool the carbon dioxide compressed gas entering the heat exchanger of E5, and 40% of which is reduced to 1.6 MPa (P4) by the intercepting device and enters E4, and is mixed with the heat exchange cooled heat exchange stream from the heat exchanger of E4;

[0081] (4) The heat exchange cooled heat exchange stream from the heat exchanger of E5 is reduced to 1.6 MPa (P4) by the intercepting device, and then enters E4 and is split, 80% of which is used as the heat exchange stream entering the heat exchanger of E4 to cool the carbon dioxide compressed gas entering the heat exchanger of E4, and 20% of which is reduced to 0.8 MPa (P3) by the intercepting device and enters E3, and is mixed with the heat exchange cooled heat exchange stream from the heat exchanger of E3;

[0082] (5) The heat exchange cooled heat exchange stream from the heat exchanger of E4 is mixed with the pressure reduction stream from E5, and then is reduced to 0.8 MPa (P3) by the intercepting device, and then enters E3 and is split, 60% of which is used as the heat exchange stream entering the heat exchanger of E3 to cool the carbon dioxide raw material gas entering the heat exchanger of E3, and 40% of which is reduced to 0.5 MPa (P2) by the intercepting device and enters E2 and is mixed with the heat exchange cooled heat exchange stream from the heat exchanger of E2;

[0083] (6) The heat exchange flow after heat exchange and cooling from the heat exchanger of E3 is combined with the pressure reduction flow of E4 and then reduced to 0.5MPa (P2) by the interception device before entering E2 and the heat exchanger in E2 to cool the carbon dioxide compressed gas entering the heat exchanger in E2.

[0084] (7) The heat exchange flow that has been cooled after heat exchange from the heat exchanger in E2 is combined with the pressure reduction flow in E3. After being depressurized to 0.2MPa (P1) by the interception device, it enters E1 and enters the heat exchanger in E1 to cool the carbon dioxide raw gas entering the heat exchanger in E1. Finally, it is discharged into the atmosphere or downstream recovery section.

[0085] Example 3

[0086] For reference Figure 1 The device shown reduces the cooling loss during carbon dioxide liquefaction. The operation process for reducing the cooling loss during carbon dioxide liquefaction is as follows.

[0087] (1) Carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and then cooled to 40°C with cooling water to obtain carbon dioxide compressed gas;

[0088] (2) The compressed carbon dioxide gas enters the five-stage heat exchange and cooling unit (E1-E5) in sequence, and finally enters the liquefier, where it is cooled to -23°C.

[0089] (3) The non-condensable gas discharged from the top of the liquefier enters E5 and is split. 60% enters the heat exchanger of E5 as a heat exchange flow to cool the carbon dioxide compressed gas entering the heat exchanger of E5. 40% is used as a pressure reduction flow to be reduced to 1.7MPa (P4) by the interception device and enters E4, and merges with the heat exchange flow that has undergone heat exchange and cooling from the heat exchanger of E4.

[0090] (4) The heat exchange flow after heat exchange cooling from the heat exchanger of E5 is depressurized to 1.7MPa (P4) by the interception device and then enters E4 for splitting. 80% of it is used as heat exchange flow to enter the heat exchanger of E4 to cool the carbon dioxide compressed gas entering the heat exchanger of E4, and 20% is used as depressurized flow to be depressurized to 1.2MPa (P3) by the interception device and enters E3, where it is merged with the heat exchange flow after heat exchange cooling from the heat exchanger of E3.

[0091] (5) The heat exchange cooled heat exchange stream from the heat exchanger of E4 is collected with the pressure reduction stream of E5, and then is reduced to 1.2 MPa (P3) by the intercepting device again, and then enters E3 and is divided, 80% of which is used as the heat exchange stream to enter the heat exchanger of E3 to cool the carbon dioxide raw material gas entering the heat exchanger of E3, and 20% of which is used as the pressure reduction stream to be reduced to 0.7 MPa (P2) by the intercepting device and then enters E2 and is collected with the heat exchange cooled heat exchange stream from the heat exchanger of E2;

[0092] (6) The heat exchange cooled heat exchange stream from the heat exchanger of E3 is collected with the pressure reduction stream of E4, and then is reduced to 0.7 MPa (P2) by the intercepting device again, and then enters E2 and enters the heat exchanger of E2 to cool the carbon dioxide compressed gas entering the heat exchanger of E2;

[0093] (7) The heat exchange cooled heat exchange stream from the heat exchanger of E2 is collected with the pressure reduction stream of E3, and then is reduced to 0.2 MPa (P1) by the intercepting device again, and then enters E1 and enters the heat exchanger of E1 to cool the carbon dioxide raw material gas entering the heat exchanger of E1, and is finally discharged to the atmosphere or a downstream recovery section.

[0094] Example 4

[0095] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in Figure 1 , except that E5 is removed, the operation process of the device for reducing the cold consumption of carbon dioxide liquefaction is as follows.

[0096] (1) The carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0097] (2) The carbon dioxide compressed gas enters the four-stage heat exchange cooling unit (E1-E4) in turn, and finally enters the liquefier and is cooled to -23°C in the liquefier;

[0098] (3) The non-condensable gas discharged from the top of the liquefier is divided after entering E4, 90% of which is used as the heat exchange stream to enter the heat exchanger of E4 to cool the carbon dioxide compressed gas entering the heat exchanger of E4, and 10% of which is used as the pressure reduction stream to be reduced to 1.1 MPa (P3) by the intercepting device and then enters E3 and is collected with the heat exchange stream from the heat exchanger of E3 which has undergone heat exchange cooling;

[0099] (4) The heat exchange flow after heat exchange cooling from the heat exchanger of E4 is depressurized to 1.1MPa (P3) by the interception device and then enters E4 for splitting. 70% of it is used as heat exchange flow to enter the heat exchanger of E3 to cool the carbon dioxide compressed gas entering the heat exchanger of E3. 30% of it is used as depressurization flow to be depressurized to 0.5MPa (P2) by the interception device and enters E2, where it is combined with the heat exchange flow after heat exchange cooling from the heat exchanger of E2.

[0100] (5) The heat exchange flow that has been cooled after heat exchange from the heat exchanger of E3 is combined with the pressure reduction flow of E4 and then reduced to 0.5MPa (P2) by the interception device before entering E2 and the heat exchanger in E2 to cool the carbon dioxide compressed gas entering the heat exchanger in E2.

[0101] (6) The heat exchange flow that has been cooled after heat exchange from the heat exchanger in E2 is combined with the pressure reduction flow in E3. After being depressurized to 0.2MPa (P1) by the interception device, it enters E1 and enters the heat exchanger in E1 to cool the carbon dioxide raw gas entering the heat exchanger in E1. Finally, it is discharged into the atmosphere or downstream recovery section.

[0102] Example 5

[0103] For reference Figure 1 The device shown is for reducing the cooling loss of carbon dioxide liquefaction. The difference is that E5 is removed. The operation process for reducing the cooling loss of carbon dioxide liquefaction is as follows.

[0104] (1) Carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and then cooled to 40°C with cooling water to obtain carbon dioxide compressed gas;

[0105] (2) The compressed carbon dioxide gas enters the four-stage heat exchange and cooling unit (E1-E4) in sequence, and finally enters the liquefier, where it is cooled to -23°C.

[0106] (3) The non-condensable gas discharged from the top of the liquefier enters E4 and is split. 60% enters the heat exchanger of E4 as a heat exchange flow to cool the carbon dioxide compressed gas entering the heat exchanger of E4. 40% is used as a pressure reduction flow to be reduced to 1.4MPa (P3) by the interception device and enters E3, and merges with the heat exchange flow that has undergone heat exchange and cooling from the heat exchanger of E3.

[0107] (4) The heat exchange flow after heat exchange cooling from the heat exchanger of E4 is depressurized to 1.4MPa (P3) by the interception device and then enters E4 for splitting. 90% of it is used as heat exchange flow to enter the heat exchanger of E3 to cool the carbon dioxide compressed gas entering the heat exchanger of E3. 10% is used as depressurization flow to be depressurized to 0.6MPa (P2) by the interception device and enters E2, where it is merged with the heat exchange flow after heat exchange cooling from the heat exchanger of E2.

[0108] (5) The heat exchange stream from the heat exchanger of E3 is mixed with the pressure reduction stream of E4, and then is reduced to 0.6 MPa (P2) by the intercepting device, and then enters E2 and the heat exchanger in E2 to cool the carbon dioxide compressed gas entering the heat exchanger in E2;

[0109] (6) The heat exchange stream from the heat exchanger in E2 is mixed with the pressure reduction stream of E3, and then is reduced to 0.2 MPa (P1) by the intercepting device, and then enters E1 and the heat exchanger in E1 to cool the carbon dioxide raw gas entering the heat exchanger in E1, and finally is discharged to the atmosphere or the downstream recovery section.

[0110] Example 6

[0111] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in FIG. 6, except that E5 is removed, the operation process for reducing the cold consumption of carbon dioxide liquefaction is as follows. Figure 1

[0112] (1) The carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa, and is cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0113] (2) The carbon dioxide compressed gas enters the four-stage heat exchange cooling unit (E1-E4) in sequence, and finally enters the liquefier and is cooled to -23°C in the liquefier;

[0114] (3) The non-condensable gas discharged from the top of the liquefier is split after entering E4, 80% of which is used as a heat exchange stream to enter the heat exchanger of E4 to cool the carbon dioxide compressed gas entering the heat exchanger of E4, and 20% of which is used as a pressure reduction stream to be reduced to 1.0 MPa (P3) by the intercepting device, and then enters E3 and is mixed with the heat exchange stream from the heat exchanger of E3 which has undergone heat exchange cooling;

[0115] (4) The heat exchange stream from the heat exchanger of E4 which has undergone heat exchange cooling is reduced to 1.0 MPa (P3) by the intercepting device, and then enters E4 and is split, 80% of which is used as a heat exchange stream to enter the heat exchanger of E3 to cool the carbon dioxide compressed gas entering the heat exchanger of E3, and 20% of which is used as a pressure reduction stream to be reduced to 0.5 MPa (P2) by the intercepting device, and then enters E2 and is mixed with the heat exchange stream from the heat exchanger of E2 which has undergone heat exchange cooling;

[0116] (5) The heat exchange stream from the heat exchanger of E3 which has undergone heat exchange cooling is mixed with the pressure reduction stream of E4, and then is reduced to 0.5 MPa (P2) by the intercepting device, and then enters E2 and the heat exchanger in E2 to cool the carbon dioxide compressed gas entering the heat exchanger in E2;

[0117] ​(6) The heat exchange flow that has been cooled after heat exchange from the heat exchanger in E2 is combined with the pressure reduction flow in E3. After being depressurized to 0.2MPa (P1) by the interception device, it enters E1 and enters the heat exchanger in E1 to cool the carbon dioxide raw gas entering the heat exchanger in E1. Finally, it is discharged into the atmosphere or downstream recovery section.

[0118] Example 7

[0119] For reference Figure 1 The device shown is for reducing the cooling loss of carbon dioxide liquefaction. The difference is that E5 is removed. The operation process for reducing the cooling loss of carbon dioxide liquefaction is as follows.

[0120] (1) Carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and then cooled to 40°C with cooling water to obtain carbon dioxide compressed gas;

[0121] (2) The compressed carbon dioxide gas enters the four-stage heat exchange and cooling unit (E1-E4) in sequence, and finally enters the liquefier, where it is cooled to -23°C.

[0122] (3) The non-condensable gas discharged from the top of the liquefier enters E4 and is split. 70% enters the heat exchanger of E4 as a heat exchange flow to cool the carbon dioxide compressed gas entering the heat exchanger of E4. 30% is used as a pressure reduction flow to be reduced to 0.8MPa (P3) by the interception device and enters E3, and merges with the heat exchange flow that has undergone heat exchange and cooling from the heat exchanger of E3.

[0123] (4) The heat exchange flow after heat exchange cooling from the heat exchanger of E4 is depressurized to 0.8MPa (P3) by the interception device and then enters E4 for splitting. 70% of it is used as heat exchange flow to enter the heat exchanger of E3 to cool the carbon dioxide compressed gas entering the heat exchanger of E3. 30% of it is used as depressurization flow to be depressurized to 0.4MPa (P2) by the interception device and enters E2, where it is merged with the heat exchange flow after heat exchange cooling from the heat exchanger of E2.

[0124] (5) The heat exchange flow after heat exchange and cooling from the heat exchanger of E3 is combined with the pressure reduction flow of E4 and then reduced to 0.4MPa (P2) by the interception device before entering E2 and the heat exchanger in E2 to cool the carbon dioxide compressed gas entering the heat exchanger in E2.

[0125] (6) The heat exchange flow that has been cooled after heat exchange from the heat exchanger in E2 is combined with the pressure reduction flow in E3. After being depressurized to 0.2MPa (P1) by the interception device, it enters E1 and enters the heat exchanger in E1 to cool the carbon dioxide feed gas entering the heat exchanger in E1. Finally, it is discharged into the atmosphere or downstream recovery section.

[0126] Example 8

[0127] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in Figure 1 the difference is that E5 and E4 are removed, the operation process of reducing the cold consumption of carbon dioxide liquefaction is as follows.

[0128] (1) The carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0129] (2) The carbon dioxide raw gas enters the three-stage heat exchange cooling unit (E1-E3) in turn, and finally enters the liquefier and is cooled to -23°C in the liquefier;

[0130] (3) The non-condensable gas discharged from the top of the liquefier is divided into two streams after entering E3, 70% of which is used as a heat exchange stream to enter the heat exchanger of E3 for cooling the carbon dioxide compressed gas entering the heat exchanger of E3, and 30% of which is used as a pressure reduction stream to be reduced to 0.4 MPa (P2) using a trap device, enter E2, and converge with the heat exchange stream that has undergone heat exchange cooling from the heat exchanger of E2;

[0131] (4) The heat exchange stream that has undergone heat exchange cooling from the heat exchanger of E3 is reduced to 0.4 MPa (P2) using a trap device, enters E2 and enters the heat exchanger of E2, and is used to cool the carbon dioxide compressed gas entering the heat exchanger of E2;

[0132] (5) The heat exchange stream that has undergone heat exchange cooling from the heat exchanger of E2 is mixed with the pressure reduction stream of E3, and then reduced to 0.2 MPa (P1) again using a trap device, enters E1, and enters the heat exchanger of E1 to cool the carbon dioxide raw gas entering the heat exchanger of E1, and is finally discharged to the atmosphere or the downstream recovery section.

[0133] Example 9

[0134] Referring to the device for reducing the cold consumption of carbon dioxide liquefaction as shown in Figure 1 the difference is that E5 and E4 are removed, the operation process of reducing the cold consumption of carbon dioxide liquefaction is as follows.

[0135] (1) The carbon dioxide compressed gas with a purity of 98% is first compressed to 2.2 MPa and cooled to 40°C using cooling water to obtain carbon dioxide compressed gas;

[0136] (2) The carbon dioxide raw gas enters the three-stage heat exchange cooling unit (E1-E3) in turn, and finally enters the liquefier and is cooled to -23°C in the liquefier;

[0137] (3) The non-condensable gas discharged from the top of the liquefier is divided into two streams after entering E3. 60% of the non-condensable gas is used as the heat exchange stream to enter the heat exchanger of E3 to cool the carbon dioxide compressed gas entering the heat exchanger of E3. 40% of the non-condensable gas is used as the pressure reduction stream to be reduced to 0.6 MPa (P2) by using a trap device, to enter E2, and to be combined with the heat exchange stream that has been cooled by heat exchange and flows out of the heat exchanger of E2;

[0138] (4) The heat exchange stream that has been cooled by heat exchange and flows out of the heat exchanger of E3 is reduced to 0.6 MPa (P2) by using a trap device, to enter E2, and to enter the heat exchanger of E2 to cool the carbon dioxide compressed gas entering the heat exchanger of E2.

[0139] (5) The heat exchange stream that has been cooled by heat exchange and flows out of the heat exchanger of E2 is combined with the pressure reduction stream of E3, and is reduced to 0.2 MPa (P1) by using a trap device again, to enter E1, and to enter the heat exchanger of E1 to cool the carbon dioxide raw material gas entering the heat exchanger of E1, and is finally discharged to the atmosphere or a downstream recovery section.

[0140] Example 10

[0141] The method and device of Example 3 are used to reduce the cold consumption of carbon dioxide liquefaction, except that the volume ratio of the pressure reduction stream and the heat exchange stream is 1:1 (i.e. 50% of the stream is used as the pressure reduction stream and 50% of the stream is used as the heat exchange stream) each time the stream is divided.

[0142] Example 11

[0143] The method and device of Example 3 are used to reduce the cold consumption of carbon dioxide liquefaction, except that the pressure in E4 is 2 MPa (P4 / P5=0.91), the pressure in E3 is 1.8 MPa (P3 / P4=0.9), the pressure in E2 is 1.6 MPa (P2 / P3=0.89), and the pressure in E1 is 1.4 MPa (P1 / P2=0.88).

[0144] Comparative Example 1

[0145] According to the prior art, the carbon dioxide compressed gas is cooled by heat exchange in a first heat exchange cooling unit, and then is liquefied in a liquefier, and non-condensable gas is separated out. The non-condensable gas is returned to the first heat exchange cooling unit to be in countercurrent contact with the carbon dioxide to be cooled by heat exchange, and then is discharged into the atmosphere. In this process, since only the first heat exchange cooling unit is involved, there is no pressure reduction operation and no stream division operation.

[0146] Test Example

[0147] The methods and devices of Examples 1-11 and Comparative Example 1 are used to liquefy 100 L of carbon dioxide compressed gas with a purity of 98% respectively, and the cold consumption is recorded. The results are shown in Table 1.

[0148] Table 1

[0149]

[0150]

[0151] From the results of Table 1, it can be seen that, relative to Comparative Example 1 using a 1-stage heat exchange cooling unit, Examples 1-9 using the technical solution of the present application can efficiently recover the cold energy of non-condensable gas, thereby significantly reducing the cold consumption of liquefied carbon dioxide and improving the economic efficiency of the carbon dioxide liquefaction process.

[0152] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method of reducing the cold energy consumption for liquefying carbon dioxide, characterized by, The method comprises: The carbon dioxide compressed gas is sequentially subjected to n-stage heat exchange cooling and carbon dioxide liquefaction to obtain liquefied carbon dioxide and separate out non-condensable gas; The non-condensable gas is returned to contact with the carbon dioxide compressed gas in countercurrent to perform the n-stage heat exchange cooling; the n-stage heat exchange cooling process comprises: stepwise depressurization of the non-condensable gas and stepwise shunting of the non-condensable gas; Wherein, n is a positive integer not less than 3; In the heat exchange cooling stage S m , it includes sequentially heat exchanging and cooling the non-condensable gas flowing through the heat exchange cooling stage S m , and then sending the carbon dioxide compressed gas into the next heat exchange cooling stage S m-1 ; in the heat exchange cooling stage S1, it includes sequentially heat exchanging and cooling the non-condensable gas flowing through the heat exchange cooling stage S1, and then discharging the carbon dioxide compressed gas into the atmosphere or downstream process section; Wherein, 2≤m≤n; wherein, when m > 2, during the heat exchange cooling phase S m the non-condensable gas is split off from the flow before the heat exchange cooling.

2. The method of claim 1, wherein, The pressure ratio (P m-1 / P m ) of the non-condensable gas flowing through the adjacent two-stage heat exchange cooling stages is 0.1-0.

8.

3. The method of claim 1, wherein, The process of the flow splitting is to divide the flow through the non-condensable gas into a pressure reducing flow and a heat exchange flow, the pressure reducing flow directly enters the next heat exchange cooling stage S after pressure reduction m-1 , and the heat exchange flow is used for sequentially performing heat exchange cooling and pressure reduction on the carbon dioxide compressed gas.

4. The method of claim 3, wherein, The volume ratio of the depressurized flow and the heat exchange flow is 1:1.5-9.

5. The method of claim 4, wherein, The method further comprises: when m < n, in the heat exchange cooling stage S m , the heat exchange flow after the heat exchange cooling is collected with the pressure reduction flow from the previous heat exchange cooling stage S m+1 to form a converged flow, and the converged flow is subjected to pressure reduction and then enters the next heat exchange cooling stage S m-1 .

6. The method of claim 1, wherein, The pressure of the non-condensable gas flowing through the heat exchange cooling stage S1 is 0.1-0.2 MPa.

7. The method of any of claims 1-6, wherein, The carbon dioxide compressed gas flows in series during the n-stage heat exchange cooling process.

8. An apparatus for use in the method of reducing the cold energy consumption of carbon dioxide liquefaction according to any one of claims 1 to 7, characterized in that, The device comprises: n-stage heat exchange cooling units, a liquefier, and a pipeline for returning the non-condensable gas separated from the liquefier to the nth-stage heat exchange cooling unit, which are sequentially connected; Each heat exchange cooling unit comprises a heat exchanger, a pipeline for introducing the non-condensable gas as a coolant into the heat exchanger, a pipeline for shunting or not shunting the non-condensable gas flowing through the heat exchange cooling unit, and a pipeline for introducing the non-condensable gas flowing through the heat exchange cooling unit into an adjacent heat exchange cooling unit or into the atmosphere or a downstream process section; each heat exchange cooling unit further comprises a gas interception device, except for the first-stage heat exchange unit; The heat exchanger is used for countercurrent contact of the non-condensable gas as a coolant with carbon dioxide to perform heat exchange cooling of the carbon dioxide, and the gas interception device is used for depressurization of the non-condensable gas; n is a positive integer not less than 3.

9. The apparatus of claim 8, wherein, The heat exchanger is a plate heat exchanger or a shell-and-tube heat exchanger.

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