CN-122015312-A - Liquid carbon dioxide discharging method

CN122015312ACN 122015312 ACN122015312 ACN 122015312ACN-122015312-A

Abstract

The invention discloses a liquid carbon dioxide discharging method in the technical field of high-pressure pipeline safety discharging, which is used for a refrigerating system and comprises the following steps of reducing the well entering flow of carbon dioxide and discharging well ascending carbon dioxide based on the liquid level of a gas-liquid separation tank and the inlet pressure of a throttling pressure reducing device, reducing compression power along with the reduction of the air return port pressure of a cold-heat combined supply device, reducing the well ascending carbon dioxide discharging rate and stopping air return after the device is stopped, stopping discharging when the carbon dioxide outlet pressure of a heat exchanger is reduced to a threshold value, and discharging well ascending and well entering carbon dioxide when the pressure of the system is balanced. According to the invention, the flow rate of carbon dioxide entering a well is reduced based on the liquid level of the gas-liquid separation tank and the pressure of the throttling pressure reducing device, the carbon dioxide of the well is discharged, the compression power of the cold-heat combined supply device is coupled with the pressure of the air return port, then the discharging is stopped, the global discharging is carried out after the pressure of the system is balanced, the risks of freeze blocking and freeze valve of dry ice are eliminated, and the discharging safety and the system stability are improved.

Inventors

Zhan deqing
PAN XINYU
WANG LI
XU XIANG
ZHONG KAI
Hui Xiangchao

Assignees

中国化学工程第三建设有限公司
淮南矿业(集团)有限责任公司

Dates

Publication Date: 20260512
Application Date: 20260120

Claims (10)

1. The method is used for a refrigerating system, the refrigerating system comprises an overground transcritical carbon dioxide cold and hot combined supply device, a gas-liquid separation tank, a downhole throttling pressure reducing device and a heat exchanger, wherein the cold and hot combined supply device separates carbon dioxide through the gas-liquid separation tank, the gas-liquid separation tank enables liquid-phase carbon dioxide to enter a well, and the liquid-phase carbon dioxide is gasified and lifted after passing through the throttling pressure reducing device and the heat exchanger, compressed to a heat utilization equipment end by the cold and hot combined supply device and then flows back to the cold and hot combined supply device; the method is characterized by comprising the following steps of: reducing the well inflow rate of liquid-phase carbon dioxide based on the liquid level of the gas-liquid separation tank and the pressure before the inlet of the throttling pressure reducing device, and discharging the well-lifting carbon dioxide based on the well inflow rate; Reducing the compression power of the cold and hot combined supply device along with the reduction of the pressure of the air return port of the cold and hot combined supply device, and returning air to the cold and hot combined supply device by the gas-liquid separation tank when the pressure of the air return port is reduced to the threshold value of the air return pressure; after the compression power of the cold and hot combined supply device is reduced to be stopped, the release rate of the carbon dioxide of the lifting well is reduced, and the gas-liquid separation tank stops returning gas; Stopping discharging the carbon dioxide when the pressure of the carbon dioxide outlet of the heat exchanger is reduced to the lower pressure limit; When the refrigeration system pressure is balanced, the carbon dioxide of the lifting well and the entering well is discharged simultaneously until the carbon dioxide is completely emptied.
2. The method for discharging liquid carbon dioxide according to claim 1, wherein when the rising carbon dioxide starts to discharge, the flow of the heat exchange working medium of the heat exchanger is controlled, so that the pressure of the carbon dioxide outlet of the heat exchanger is within a pressure setting range, and the temperature is within a temperature setting range.
3. The method for discharging liquid carbon dioxide according to claim 1, wherein the number of operating stages of the compressor is reduced when the pressure of the air return port of the cold and hot combined supply device reaches a preset pressure in the process of reducing the compression power of the cold and hot combined supply device, the air is returned to the cold and hot combined supply device by the gas-liquid separation tank when the pressure of the air return port of the cold and hot combined supply device reaches a threshold value of the air return pressure, the number of operating stages of the compressor is continuously reduced if the pressure of the air return port of the cold and hot combined supply device is continuously reduced, and the cold and hot combined supply device is stopped when the pressure of the air return port of the cold and hot combined supply device does not meet the threshold value of the preset operating parameters.
4. The method for discharging liquid carbon dioxide according to claim 3, wherein when the gas-liquid separation tank returns gas to the cold and hot combined supply device, the gas-phase carbon dioxide is conveyed to the cold and hot combined supply device through a gas return pipeline, and the liquid-phase carbon dioxide enters a well through a well inlet pipeline and sequentially enters a throttling pressure reducing device and a heat exchange device, is gasified to form gas-phase carbon dioxide, and then enters a gas return port of the cold and hot combined supply device through a well lifting pipeline.
5. The method for discharging liquid carbon dioxide according to claim 4, wherein the inflow rate is regulated by providing an injection control valve on the inflow pipe, the ascending carbon dioxide is discharged by providing a first discharge valve on the ascending pipe, the return air is controlled by providing a return air control valve on the return pipe, and the inflow carbon dioxide is discharged by providing a second discharge valve on the inflow pipe.
6. The method for bleeding liquid carbon dioxide as recited in claim 5, wherein the opening of the first bleeding valve is adjusted to a first preset value when the flow rate of the pipe line is in a set flow rate range, the opening of the first bleeding valve is adjusted to a second preset value when the combined cooling and heating device is turned off, and the first bleeding valve and the second bleeding valve are simultaneously opened when the pressure of the refrigeration system is balanced.
7. The method for discharging liquid carbon dioxide according to claim 1, wherein when the carbon dioxide in the well is discharged simultaneously with the rising well, outside air of the refrigerating system is introduced into the refrigerating system to replace residual carbon dioxide in the refrigerating system.
8. The method for discharging liquid carbon dioxide according to claim 1, wherein the combined cooling and heating device outputs carbon dioxide to the heat utilization equipment end through the high heat pipe, and the heat utilization equipment end returns carbon dioxide to the combined cooling and heating device through the low heat pipe.
9. The method for discharging liquid carbon dioxide according to claim 8, wherein the high heat pipeline, the low heat pipeline, the air return port of the cold and hot combined supply device, the inlet and outlet of the throttling and decompressing device and the carbon dioxide outlet of the heat exchanger are respectively provided with a pressure sensor and a temperature sensor, the gas-liquid separation tank is further provided with a liquid level meter, and the well inlet pipeline is provided with a flow monitoring device.
10. The method for discharging liquid carbon dioxide according to claim 1, wherein the pressure of the well-entering carbon dioxide is within the range of 3.5-8.5 MPa, the temperature is within the range of 0-20 ℃ and the pressure of the carbon dioxide outlet of the heat exchanger is within the range of 2.8-3.6 MPa and the temperature is within the range of 15-29 ℃ before the well-entering carbon dioxide is discharged.

Description

Liquid carbon dioxide discharging method Technical Field The invention relates to the field of safety discharge of high-pressure pipelines, in particular to a deep long-distance high-pressure liquid carbon dioxide discharge method for a transcritical carbon dioxide cold-hot combined refrigeration system. Background The transcritical carbon dioxide cold and hot combined supply refrigerating system has the remarkable advantages of high efficiency, environmental protection, extremely low GWP (global warming potential) value of the refrigerant and the like, and is widely applied to the fields of industrial heat and cold supply, regional energy stations, cold chain transportation and the like. In the operation process of the system, the high-pressure carbon dioxide is liquid-phase CO 2, which is usually maintained under the high-pressure working condition of 3.5-8.5 MPa, and the pipe stock is large. In the operation and maintenance process of the system, the scenes such as pipeline maintenance, transformation, equipment maintenance and the like are inevitably met, and the high-pressure carbon dioxide in the system is subjected to planned emptying operation at the moment. In the decompression and release process, the CO 2 medium can undergo severe phase change, so that the risks of ultralow-temperature cooling, ice freezing and blocking and the like are caused. During the pipeline depressurization vent, the process absorbs a lot of heat due to the phase change of liquid phase CO 2 and gas expanded char Shang Xiaoying, and the CO 2 temperature drops dramatically. The valve and pipeline materials toughness can be reduced due to ultralow temperature, so that the pipeline is invalid, and meanwhile, dry ice particles formed in the low-temperature environment can be gradually deposited in the valve and the pipeline, so that the risk of freezing and blocking is further caused. In the prior art, a method aiming at carbon dioxide release focuses on a short-distance and small-flow scene, a deep long-distance and large-flow phase transformation rule of a transcritical cold-hot combined refrigeration system is not fully considered, a cooperative regulation and control mechanism among all modules of the system in the release process is lacked, the risks of dry freezing blockage and freezing valves are difficult to effectively inhibit, the safety and stability of the emptying operation of a multi-phase multi-system high-pressure CO 2 system cannot be ensured, and the large-scale popularization and the safe operation and maintenance of the transcritical carbon dioxide cold-hot combined refrigeration system are restricted. Therefore, the development of the high-pressure multi-phase carbon dioxide discharging method which is suitable for the long-distance, high-pressure and large-pipe stock working conditions of the transcritical carbon dioxide cold-heat combined refrigeration system, can accurately inhibit the dry ice from freezing and blocking, avoids the risk of a freezing valve and ensures the safety and stability of the discharging process becomes a key technical problem to be solved in the current field. Disclosure of Invention The invention aims to provide a liquid carbon dioxide discharging method, which solves the problem that the existing carbon dioxide discharging method is easy to cause dry ice blockage and freeze valve risks when discharging deep long-distance and large-flow liquid carbon dioxide. The invention realizes the above purpose through the following technical scheme: The method is used for a refrigerating system, the refrigerating system comprises an overground transcritical carbon dioxide cold and hot combined supply device, a gas-liquid separation tank, a downhole throttling pressure reducing device and a heat exchanger, wherein the cold and hot combined supply device separates carbon dioxide through the gas-liquid separation tank, the gas-liquid separation tank enables liquid-phase carbon dioxide to enter a well, and the liquid-phase carbon dioxide is gasified and lifted after passing through the throttling pressure reducing device and the heat exchanger, compressed to a heat utilization equipment end by the cold and hot combined supply device and then flows back to the cold and hot combined supply device; the bleeding method comprises the following steps: reducing the well inflow rate of liquid-phase carbon dioxide based on the liquid level of the gas-liquid separation tank and the pressure before the inlet of the throttling pressure reducing device, and discharging the well-lifting carbon dioxide based on the well inflow rate; Reducing the compression power of the cold and hot combined supply device along with the reduction of the pressure of the air return port of the cold and hot combined supply device, and returning air to the cold and hot combined supply device by the gas-liquid separation tank when the pressure of the air return port is reduced to the threshold value of the air return pressure; af