System and method for recovering cold from tail gas of a low-temperature methanol wash unit

Abstract

The application relates to the technical field of heat recovery, in particular to a system and method for recycling cold energy of tail gas of a low-temperature methanol washing unit. The system comprises a tail gas washing tower group, a communication pipe, a first venting drum and a heat exchange assembly. The circulating water and the tail gas are subjected to heat exchange through the heat exchange assembly, the temperature of the circulating water is reduced, the temperature of the tail gas is increased, and the cold energy of the tail gas is fully utilized. After the circulating water is cooled by the tail gas, first, a small amount of circulating water can achieve a cooling effect, and the energy consumption of the air cooling fan is also reduced; second, the cooling effect of each device in the methanol production center is good, and the operation temperature is low; third, the operation pump temperature is reduced. After the low-temperature tail gas is heated by the circulating water, heating is not needed, or the energy consumption required for heating is greatly reduced. Only through the heat exchange between the circulating water and the tail gas, different problems caused by high-temperature circulating water and low-temperature tail gas can be solved at the same time, and the effect is good.

Description

Technical Field

[0001] This application relates to the field of heat recovery technology, and in particular to a system and method for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit. Background Technology

[0002] In the utilities production center of a chemical plant, there is a circulating water station. The circulating water in this station supplies cooling water to various units in the methanol production center. When the chemical plant is located in a high-temperature region during the summer, the consistently high ambient temperature causes the circulating water temperature in the utilities production center to be excessively high, reaching up to approximately 38.5℃. Even with all the air-cooled fans in the cooling towers of the circulating water station operating at full capacity, the circulating water temperature can only be cooled to around 30℃. This high circulating water temperature has several consequences: First, to achieve the desired cooling effect, more circulating water is needed, increasing the power consumption of the air-cooled fans and keeping the entire system under high temperature, thus increasing the load. Second, the poor cooling effect and high operating temperature of the various units in the methanol production center lead to increased system energy consumption, especially for the compressors, which may result in the system operating at reduced load in severe cases. Third, most of the pumps and compressors in the methanol production center use circulating water for sealing; the high temperature of this circulating water causes the operating pumps and compressors to overheat, affecting their long-term operation.

[0003] In addition, the low-temperature methanol washing unit of the chemical plant contains low-temperature tail gas with a temperature of about 15°C and a flow rate of about 330,000 Nm³ / h. This tail gas is low in temperature and corrosive. Before being released into the atmosphere, it needs to be heated, which will increase energy consumption. Summary of the Invention

[0004] This application provides a system for recovering and utilizing the cold energy of the exhaust gas from a low-temperature methanol washing unit, in order to solve the problems caused by high circulating water temperature and low exhaust gas temperature in the prior art.

[0005] On one hand, this application provides a system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit, comprising: a tail gas scrubbing tower group configured to scrub the tail gas introduced into it; a connecting pipe; a first vent cylinder connected to the tail gas scrubbing tower group via the connecting pipe; and a heat exchange assembly disposed between the tail gas scrubbing tower group and the first vent cylinder. The heat exchange assembly includes a heat exchange tube connected to the connecting pipe, a heat exchanger connected to the heat exchange tube, and an inlet pipe and an outlet pipe connected to the heat exchanger. The inlet and outlet of the heat exchange tube are both connected to the connecting pipe. The inlet pipe is configured to allow circulating water to flow in, and the outlet pipe is configured to allow circulating water to be discharged after heat exchange with the tail gas.

[0006] Preferably, the shell side of the heat exchanger is used for circulating water, and the tube side is used for exhaust gas.

[0007] Preferably, the heat exchange assembly further includes an output valve, an inlet valve disposed on the inlet pipe, and an outlet valve disposed on the outlet pipe, wherein the output valve is disposed on the heat exchange tube connected to the outlet of the heat exchanger.

[0008] Preferably, the heat exchange assembly further includes a circulation pipe connecting the inlet pipe and the outlet pipe, and a circulation valve disposed on the circulation pipe.

[0009] Preferably, the heat exchange assembly further includes a first connecting valve, which is disposed on the heat exchange tube connected to the inlet of the heat exchanger. The system for recovering and utilizing the cold energy of the tail gas of the low-temperature methanol washing unit further includes a second connecting valve disposed on the connecting pipe, which is located between the inlet and outlet of the heat exchange tube.

[0010] Preferably, the system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit further includes a first flow limiting valve installed on the connecting pipe, the first flow limiting valve being located downstream of the connection point between the outlet of the heat exchange tube and the connecting pipe.

[0011] Preferably, the system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit further includes a heating component connected to the connecting pipe, the heating component being located downstream of the connection point between the outlet of the heat exchange tube and the connecting pipe.

[0012] Preferably, the heating assembly includes a branch pipe connected to the connecting pipe and a second flow-limiting valve disposed on the branch pipe.

[0013] Preferably, the heating assembly further includes a heater connected to the distributor pipe and a separatory tank connected to the heater.

[0014] On the other hand, this application also provides a method for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit. Using the above-mentioned system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit, the method includes the following steps: The exhaust gas, after being washed by the exhaust gas scrubbing tower group, is introduced into the heat exchanger of the heat exchange component through a connecting pipe. The circulating water is introduced into the heat exchanger of the heat exchange component through the inlet pipe, so that the circulating water and the exhaust gas can exchange heat. The exhaust gas after heat exchange is discharged into the atmosphere through the first vent pipe, and the circulating water after heat exchange is discharged through the outlet pipe.

[0015] The beneficial effects of this application are as follows: The circulating water has a high temperature and needs to be cooled, while the exhaust gas has a low temperature and needs to be heated. Therefore, the circulating water and exhaust gas are exchanged through heat exchange components to lower the temperature of the circulating water and raise the temperature of the exhaust gas, thereby making full use of the cooling capacity of the exhaust gas. After the circulating water is cooled by the exhaust gas, firstly, a small amount of circulating water can achieve a cooling effect. Even if the circulating water needs to be cooled again by an air-cooled fan, the energy consumption of the air-cooled fan will be reduced. A system with good cooling effect can operate at a normal temperature, reducing the load. Secondly, the good cooling effect and low operating temperature of each unit in the methanol production center reduce the system's energy consumption and avoid system load reduction. Thirdly, the sealing water of the pumps in each unit of the methanol production center is cooled to a normal temperature, which lowers the operating temperature of the pumps and promotes long-term operation of the pumps. After the low-temperature exhaust gas is heated by the circulating water, it does not need to be reheated, or the energy consumption required for heating is significantly reduced. The different problems caused by high-temperature circulating water and low-temperature exhaust gas can be solved simultaneously through heat exchange between circulating water and exhaust gas, with excellent results.

[0016] The method for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit provided in this application, since it is implemented using the system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit as described in this application, simultaneously includes all the advantages of the system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a system for recovering and utilizing the cooling capacity of the tail gas from a low-temperature methanol washing unit, provided in an embodiment of this application. Figure label: 10. Exhaust gas scrubbing tower assembly; 11. First scrubbing tower; 12. Second scrubbing tower; 20. Connecting pipe; 30. First vent cylinder; 40. Heat exchange assembly; 41. Heat exchange tube; 42. Heat exchanger; 43. Water inlet pipe; 44. Water outlet pipe; 45. Output valve; 46. Water inlet valve; 47. Water outlet valve; 48. Circulation pipe; 49. Circulation valve; 410. First connecting valve; 50. Second connecting valve; 60. First flow limiting valve; 70. Heating assembly; 71. Diverter pipe; 72. Second flow limiting valve; 73. Heater; 74. Separator; 80. Second vent cylinder. Detailed Implementation

[0019] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that the high-temperature region where the chemical enterprise in the background technology of this application is located can be Xinjiang, and the circulating water is the circulating water of the second circulating water station of the public works production center.

[0021] The following is combined Figure 1 This application describes a system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit, as provided in the embodiments of the present application. The system includes: a tail gas washing tower group 10, configured to wash the tail gas introduced into it; a connecting pipe 20; a first vent cylinder 30, connected to the tail gas washing tower group 10 via the connecting pipe 20; and a heat exchange assembly 40, disposed between the tail gas washing tower group 10 and the first vent cylinder 30. The heat exchange assembly 40 includes a heat exchange pipe 41 connected to the connecting pipe 20, a heat exchanger 42 connected to the heat exchange pipe 41, and a water inlet pipe 43 and a water outlet pipe 44 connected to the heat exchanger 42. The inlet and outlet of the heat exchange pipe 41 are both connected to the connecting pipe 20. The water inlet pipe 43 is configured to allow circulating water to flow in, and the water outlet pipe 44 is configured to allow circulating water that has exchanged heat with the tail gas to output.

[0022] After being washed by the exhaust gas scrubbing tower group 10, the low-temperature exhaust gas enters the connecting pipe 20 and then enters the heat exchanger 42 of the heat exchange assembly 40. At the same time, circulating water enters the heat exchanger 42 from the water inlet pipe 43. The low-temperature exhaust gas exchanges heat with the high-temperature circulating water, which causes the temperature of the exhaust gas to rise and the temperature of the circulating water to drop.

[0023] The heated exhaust gas is discharged into the atmosphere through the first venting cylinder 30. Because the temperature of the exhaust gas is increased, there is no need to heat it up again or the energy required for heating it up again is reduced. The exhaust gas contains water and carbon dioxide, which can cause corrosion of the first venting cylinder 30, especially in winter. Heating the exhaust gas can not only reduce energy consumption, but also prevent corrosion of the pipes it flows through and the first venting cylinder 30.

[0024] Cooled circulating water is supplied to various units in the methanol production center through outlet pipe 44 to achieve a cooling function. Because the circulating water temperature is already lowered, firstly, a small amount of circulating water is sufficient to achieve the required cooling effect, and the air-cooled fans do not need to consume more electricity to cool the circulating water, reducing resource consumption. This also keeps the entire cooled system at a normal temperature, reducing the load. Secondly, the good cooling effect and low operating temperature of each unit in the methanol production center reduce the overall system energy consumption, preventing the system from operating at reduced load. Furthermore, the lower temperature of the sealing water in the pumps of each unit in the methanol production center lowers the operating temperature of the pumps, thereby reducing their energy and electricity consumption, allowing them to operate for longer periods, contributing to energy conservation and promoting green and low-carbon development. Moreover, excessively high circulating water temperature will cause evaporation; the cooled circulating water reduces evaporation, conserving water resources.

[0025] Specifically, the exhaust gas scrubbing tower group 10 includes a first scrubbing tower 11 and a second scrubbing tower 12 connected in sequence, and the two are connected in parallel to the connecting pipe 20.

[0026] In some embodiments provided in this application, the shell side of the heat exchanger 42 is supplied with circulating water, and the tube side is supplied with exhaust gas.

[0027] The heat exchanger 42 includes a shell and heat exchange tubes 41 disposed within the shell. The space between the inside of the shell and the outside of the heat exchange tubes 41 forms the shell side, and the space inside the heat exchange tubes 41 forms the tube side. Since the exhaust gas is corrosive, if it flows along the shell side, it will stagnate in the corners of the shell, causing corrosion. However, the heat exchange tubes 41 are circular straight tubes without dead corners. Therefore, the exhaust gas flows along the tube side of the heat exchange tubes 41 without stagnation, thus preventing corrosion. Furthermore, the circulating water itself is not corrosive. Therefore, the circulating water flows along the shell side, and the exhaust gas flows along the tube side.

[0028] In some embodiments provided in this application, the heat exchange assembly 40 further includes an output valve 45, an inlet valve 46 disposed on the inlet pipe 43, and an outlet valve 47 disposed on the outlet pipe 44. The output valve 45 is disposed on the heat exchange tube 41 connected to the outlet of the heat exchanger 42.

[0029] After the circulating water and exhaust gas have undergone one heat exchange, if the cooling capacity of the exhaust gas is not fully utilized, the output valve 45 can be closed and the inlet valve 46 and outlet valve 47 can be opened, so that the circulating water continuously flowing into the shell side of the heat exchanger 42 can exchange heat with a fixed amount of exhaust gas in the tube side, making full use of the cooling capacity of the exhaust gas. If the cooling range of the circulating water is small, that is, the exhaust gas after one heat exchange cannot effectively cool the circulating water, the output valve 45 can be opened and the inlet valve 46 and outlet valve 47 can be closed, so that the exhaust gas continuously flowing into the tube side of the heat exchanger 42 can exchange heat with a fixed amount of circulating water in the shell side until the temperature of the circulating water drops to the required temperature.

[0030] In some embodiments provided in this application, the heat exchange assembly 40 further includes a circulation pipe 48 connected to the inlet pipe 43 and the outlet pipe 44, and a circulation valve 49 disposed on the circulation pipe 48.

[0031] After the circulating water and exhaust gas exchange heat once, if the temperature drop of the circulating water is small, the inlet valve 46, outlet valve 47 and circulation valve 49 can be opened, so that the inlet pipe 43, circulation pipe 48, outlet pipe 44 and the shell of heat exchanger 42 form a closed loop flow path. The circulating water circulates in this closed loop flow path and continuously exchanges heat with the exhaust gas until the circulating water temperature drops to the required temperature.

[0032] In some embodiments provided in this application, the heat exchange assembly 40 further includes a first connecting valve 410, which is disposed on the heat exchange tube 41 connected to the inlet of the heat exchanger 42. The system for recovering and utilizing the cold energy of the tail gas of the low-temperature methanol washing unit also includes a second connecting valve 50 disposed on the connecting pipe 20, which is located between the two connecting points of the connecting pipe 20 and the inlet and outlet of the heat exchange tube 41.

[0033] When the cooling capacity of the exhaust gas needs to be recovered and reused, the first connecting valve 410 is opened and the second connecting valve 50 is closed, so that the exhaust gas is passed from the heat exchange tube 41 into the heat exchanger 42 to exchange heat with the circulating water; when the cooling capacity of the exhaust gas does not need to be recovered and reused, the second connecting valve 50 is opened and the first connecting valve 410 is closed, so that the exhaust gas avoids the heat exchange component 40.

[0034] In some embodiments provided in this application, the system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit further includes a first flow limiting valve 60 disposed on the connecting pipe 20, the first flow limiting valve 60 being located downstream of the connection point between the outlet of the heat exchange tube 41 and the connecting pipe 20.

[0035] The first flow limiting valve 60 is used to control the flow rate of exhaust gas into the first vent cylinder 30, and is used in conjunction with the second flow limiting valve 72 of the heating assembly 70 (described in detail later) to allow the exhaust gas to flow into the first vent cylinder 30 and the heating assembly 70 at a selectable flow rate.

[0036] In some embodiments provided in this application, the system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit further includes a heating component 70 connected to the connecting pipe 20, the heating component 70 being located downstream of the connection point between the outlet of the heat exchange pipe 41 and the connecting pipe 20.

[0037] Part of the exhaust gas can be heated by exchanging heat with circulating water through heat exchange component 40, and another part can be heated by heating component 70 to ensure that the exhaust gas discharged into the atmosphere is at a suitable temperature.

[0038] It should be noted that in actual working conditions, the heating component 70 and the second venting cylinder 80 are far from the circulating water station. If the heating component 70 is replaced with another heat exchange component 40, a longer pipeline needs to be installed, which will consume more materials and costs. Therefore, the heating component 70 is installed before the second venting cylinder 80 to minimize costs.

[0039] In some embodiments provided in this application, the heating assembly 70 includes a branch pipe 71 connected to the connecting pipe 20 and a second flow limiting valve 72 disposed on the branch pipe 71.

[0040] After heat exchange through heat exchange component 40, the exhaust gas, heated to a suitable temperature, can be discharged through the first vent cylinder 30. At this time, the first flow limiting valve 60 opens and the second flow limiting valve 72 closes. If the exhaust gas, after heat exchange through heat exchange component 40, is still below the suitable temperature, it enters the heating component 70 through the diverter pipe 71 for heating. At this time, the second flow limiting valve 72 opens and the first flow limiting valve 62 closes. This ensures that the exhaust gas discharged through the first vent cylinder 30 and the second vent cylinder 80 (described in detail later) is at a suitable temperature and will not corrode the first vent cylinder 30 and the second vent cylinder 80.

[0041] In addition, the exhaust gas heater 73 heats the exhaust gas with steam. When the exhaust gas, which has already been heated by the heat exchange component 40, re-enters the exhaust gas heater 73, it requires less steam and reduces energy consumption.

[0042] In some embodiments provided in this application, the heating assembly 70 further includes a heater 73 connected to the diversion pipe 71 and a liquid separator 74 connected to the heater 73.

[0043] The exhaust gas contains water, which can be separated into gas and liquid by the separator 74, further reducing the corrosiveness of the exhaust gas.

[0044] Specifically, the system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit also includes a second vent cylinder 80 connected to the separator 74. The tail gas, after being heated by the heating component 70, is discharged through the second vent cylinder 80.

[0045] This application embodiment also provides a method for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit. Using the above-mentioned system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit, the method includes the following steps: The exhaust gas, after being washed by the exhaust gas scrubbing tower group 10, is introduced into the heat exchanger 42 of the heat exchange assembly 40 through the connecting pipe 20. The circulating water is introduced into the heat exchanger 42 of the heat exchange assembly 40 through the water inlet pipe 43, so that the circulating water and the exhaust gas can exchange heat. The exhaust gas after heat exchange is discharged into the atmosphere through the first vent pipe 30, and the circulating water after heat exchange is discharged through the outlet pipe 44.

[0046] It should be noted that the method of recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit is implemented using a system that recovers and utilizes the cold energy of the tail gas from the low-temperature methanol washing unit, which includes all the advantages of the system mentioned above, and will not be elaborated here.

[0047] The system and method for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit, as provided in this application, are illustrated using Guoneng Xinjiang Chemical Co., Ltd. as an example: According to the data, the specific heat capacity of carbon dioxide in the exhaust gas is 0.84 kJ / (kg·℃), and the specific heat capacity of the circulating water is 4.179 kJ / (kg·℃). Assuming that the temperature of the exhaust gas rises to 30℃ after heat exchange with the circulating water, the calculated cold energy contained in the exhaust gas is 8,167,499.85 kJ / h. Therefore, the temperature of the circulating water can be reduced to 20℃ after heat exchange.

[0048] According to statistics, the daily evaporation of circulating water is expected to be reduced by 3,000 tons, and the cost per ton of circulating water is 0.16 yuan. Based on 300 days of operation per year, the estimated annual savings are 144,000 yuan.

[0049] The compressor in the refrigeration unit of the purification device, which is a propylene compressor, has its speed reduced from about 8650 r / min to about 8300 r / min, and its exhaust pressure reduced from about 35 kPa to about 25 kPa. The steam consumption of the turbine power unit has been reduced from about 35 t / h to about 30 t / h, saving about 5 t of 4.1 MPa superheated steam per hour. Each ton of 4.1 MPa superheated steam costs 108.6 yuan. Based on 8000 hours of operation per year, the estimated annual savings are 4.344 million yuan.

[0050] The cooling system using circulating water also includes a purification unit. After cooling to normal temperature, the load can be increased, leading to increased methanol production in the downstream synthesis unit and increased MTO-grade methanol production. Based on an increase of 1.5 tons per hour, a price of 1256.49 yuan per ton of methanol, and 8000 hours of operation per year, the estimated annual benefit is 15,077,880 yuan. The energy consumption of the thermal regeneration tower in the low-temperature methanol washing unit of the purification unit is reduced. It is estimated that the heating steam of the thermal regeneration tower will be reduced from about 11 tons / hour to about 9 tons / hour, saving about 2 tons of 0.46 MPa saturated steam per hour.

[0051] It is estimated that the exhaust gas heater 73 will save approximately 4 tons of saturated steam per hour (0.46 MPa).

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0053] In this application, the term "some embodiments," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0054] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A system for recovering and utilizing the cooling capacity of tail gas from a low-temperature methanol washing unit, characterized in that, include: The exhaust gas scrubbing tower assembly is designed to scrub the exhaust gas introduced into it. Connecting pipe; The first vent cylinder is connected to the tail gas scrubbing tower group through the connecting pipe; as well as A heat exchange assembly is disposed between the exhaust gas scrubbing tower group and the first venting cylinder. The heat exchange assembly includes a heat exchange tube connected to the connecting pipe, a heat exchanger connected to the heat exchange tube, and an inlet pipe and an outlet pipe connected to the heat exchanger. The inlet and outlet of the heat exchange tube are both connected to the connecting pipe. The inlet pipe is configured to allow circulating water to flow in, and the outlet pipe is configured to allow circulating water to be discharged after heat exchange with the exhaust gas.

2. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 1, characterized in that, The shell side of the heat exchanger is for circulating water, and the tube side is for exhaust gas.

3. The system for recovering and utilizing the cooling capacity of the low-temperature methanol washing unit tail gas according to claim 1, characterized in that, The heat exchange assembly further includes an output valve, an inlet valve disposed on the inlet pipe, and an outlet valve disposed on the outlet pipe. The output valve is disposed on the heat exchange pipe connected to the outlet of the heat exchanger.

4. The system for recovering and utilizing the cooling capacity of the low-temperature methanol washing unit tail gas according to claim 3, characterized in that, The heat exchange assembly also includes a circulation pipe connecting the inlet pipe and the outlet pipe, and a circulation valve disposed on the circulation pipe.

5. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 4, characterized in that, The heat exchange assembly further includes a first connecting valve, which is disposed on the heat exchange tube connected to the inlet of the heat exchanger. The system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit further includes a second connecting valve disposed on the connecting pipe, which is located between the inlet and outlet of the heat exchange tube.

6. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 5, characterized in that, The system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit also includes a first flow limiting valve installed on the connecting pipe, the first flow limiting valve being located downstream of the connection point between the outlet of the heat exchange tube and the connecting pipe.

7. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 1, characterized in that, The system for recovering and utilizing the cold energy of the tail gas from the low-temperature methanol washing unit also includes a heating component connected to the connecting pipe, the heating component being located downstream of the connection point between the outlet of the heat exchange tube and the connecting pipe.

8. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 7, characterized in that, The heating assembly includes a branch pipe connected to the connecting pipe and a second flow-limiting valve disposed on the branch pipe.

9. The system for recovering and utilizing the cooling capacity of the tail gas from the low-temperature methanol washing unit according to claim 8, characterized in that, The heating assembly also includes a heater connected to the distributor pipe and a liquid separator connected to the heater.

10. A method for recovering and utilizing the cooling capacity of tail gas from a low-temperature methanol washing unit, characterized in that, The system for recovering and utilizing the cold energy of the tail gas from a low-temperature methanol washing unit according to any one of claims 1 to 9, the method comprising the following steps: The exhaust gas, after being washed by the exhaust gas scrubbing tower group, is introduced into the heat exchanger of the heat exchange assembly through a connecting pipe. Circulating water is introduced into the heat exchanger of the heat exchange assembly through the inlet pipe, so that the circulating water and the exhaust gas can exchange heat. The exhaust gas after heat exchange is discharged into the atmosphere through the first vent pipe, and the circulating water after heat exchange is discharged through the outlet pipe.

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