A system and method for recovering and utilizing cryogenic liquid nitrogen from air separation

Abstract

The application relates to a system and a method for recycling and utilizing cold energy of air separation liquid nitrogen. The system comprises a water bath type gasifier, an air bath type gasifier and a liquid nitrogen gasifier connected in parallel. A first liquid nitrogen branch pipe, a second liquid nitrogen branch pipe and a third liquid nitrogen branch pipe are led out from a liquid nitrogen main pipe and connected with the water bath type gasifier, the air bath type gasifier and the liquid nitrogen gasifier respectively. The water bath type gasifier is connected with a nitrogen storage tank through a first nitrogen gas pipeline. The air bath type gasifier is connected with the first nitrogen gas pipeline through a second nitrogen gas pipeline. The liquid nitrogen gasifier is connected with the second liquid nitrogen branch pipe through a third nitrogen gas pipeline. The water outlet of the liquid nitrogen gasifier is connected with a water cooling tower. The method comprises the following steps: the production water before entering the water cooling tower is heated in the liquid nitrogen gasifier. The liquid nitrogen is gasified, and the production water is cooled at the same time. The cooled production water enters the water cooling tower. The nitrogen gas after being warmed is warmed again in the air bath type gasifier and then sent to the nitrogen storage tank for storage. The application can reduce the overall energy consumption of the air separation system.

Description

Technical Field

[0001] This application relates to the recovery of cold energy in the vaporization process of liquid nitrogen, and more particularly to a system and method for recovering and utilizing the cold energy of air-separated liquid nitrogen. Background Technology

[0002] The air separation unit includes a water bath vaporizer or an air bath vaporizer, and an air separation precooling system that washes and cools the compressed air at the air compressor outlet. This system includes an air-cooled tower and a water-cooled tower. The water bath vaporizer requires a continuous supply of low-pressure superheated steam as a heat source and a continuously operating water bath circulating pump to maintain constant water flow within the vaporizer and prevent freezing. The air bath vaporizer uses ambient air as a heat source for heat exchange with liquid nitrogen. A medium-pressure nitrogen electric heater is installed after the air bath vaporizer, with variable frequency automatic temperature control. When the ambient temperature is low and the medium-pressure nitrogen outlet temperature is low, the electric heater is activated to reheat the medium-pressure nitrogen. The cooling water source for the upper part of the air-cooled tower is chilled water from the bottom of the water-cooled tower, while the water source for the middle part of the air-cooled tower is circulating water. In air separation units, it is desirable to keep the temperature of the compressed air exiting the precooling system as low as possible in order to reduce the content of saturated water and carbon dioxide in the compressed air, extend the service life of the molecular sieve purification system, reduce the cold end temperature difference of the heat exchanger in the separation system, and reduce the overall energy consumption of the air separation system.

[0003] In existing technologies, air separation units have at least the following two drawbacks: 1. Water bath or air bath vaporizers that use low-pressure superheated steam as a heat source not only fail to recover and utilize a large amount of cooling energy during the vaporization process of liquid nitrogen, but also consume a significant amount of steam and electrical energy. 2. The refrigeration equipment in the pre-cooling system is an energy-consuming device. Although it can achieve the purpose of cooling the chilled water in the pre-cooling system, it increases the overall energy consumption level of the air separation unit. Summary of the Invention

[0004] This application provides an air separation liquid nitrogen cold energy recovery and utilization system that can recover and utilize the cold energy of liquid nitrogen vaporization, further reduce the chilled water temperature of the precooling system, and improve the cooling effect of the precooling system; based on this objective, another objective of this application is to propose a method for recovering and utilizing the cold energy of air separation liquid nitrogen.

[0005] The objective of this application is achieved as follows: A liquid nitrogen cooling capacity recovery and utilization system for air separation includes a water bath vaporizer, an air bath vaporizer, and a liquid nitrogen vaporizer connected in parallel. A first liquid nitrogen branch pipe, a second liquid nitrogen branch pipe, and a third liquid nitrogen branch pipe are respectively led out from the main liquid nitrogen pipe. The first liquid nitrogen branch pipe is connected to the inlet pipe of the water bath vaporizer, the second liquid nitrogen branch pipe is connected to the inlet pipe of the air bath vaporizer, and the third liquid nitrogen branch pipe is connected to the liquid nitrogen inlet pipe of the liquid nitrogen vaporizer. The exhaust end of the water bath vaporizer is connected to the first liquid nitrogen branch pipe. The gas pipeline is connected, and the end of the first nitrogen pipeline is connected to the nitrogen storage tank; the exhaust end of the air bath vaporizer is connected to the second nitrogen pipeline, an electric heater is installed on the second nitrogen pipeline, and the end of the second nitrogen pipeline is connected to the first nitrogen pipeline; the nitrogen outlet of the liquid nitrogen vaporizer is connected to the third nitrogen pipeline, the end of the third nitrogen pipeline is connected to the second liquid nitrogen branch pipe, the water inlet of the liquid nitrogen vaporizer is connected to the water supply pipe, the water outlet is connected to the low-temperature water pipeline, and the low-temperature water pipeline is connected to the water inlet pipeline of the water cooling tower.

[0006] The liquid nitrogen vaporizer includes a closed shell with a water inlet on one side and a water outlet on the opposite side. The shell contains a cavity that can hold injected water. Heat exchange tubes are arranged in the cavity. The inlet end of the heat exchange tube is connected to the liquid nitrogen inlet pipe. The first end of the liquid nitrogen inlet pipe extends out of the shell and is connected to the third liquid nitrogen branch pipe. The outlet end of the heat exchange tube is connected to the nitrogen exhaust pipe. The tail end of the nitrogen exhaust pipe extends out of the shell and is connected to the third nitrogen pipeline.

[0007] A water supply valve is installed on the water supply pipe, and production water is transported in the water supply pipe. A liquid nitrogen vaporizer bypass pipeline is led out from the water supply pipe after the water supply valve. The end of the liquid nitrogen vaporizer bypass pipeline is connected to the water inlet pipeline of the water cooling tower. A bypass valve is installed on the liquid nitrogen vaporizer bypass pipeline.

[0008] An electric heater inlet valve and an electric heater outlet valve are installed on the inlet and outlet pipelines of the electric heater, respectively. An electric heater bypass pipeline is set on the side of the electric heater, with one end connected to the inlet pipeline and the other end connected to the outlet pipeline. A bypass valve is installed on the electric heater bypass pipeline.

[0009] A method for recovering and utilizing the cooling capacity of liquid nitrogen in air separation includes the following steps:

[0010] Step 1: When the ambient temperature rises and the temperature of the production water entering the water cooling tower is higher than 15°C, or the temperature of the water outlet at the bottom of the water cooling tower is higher than 10°C, the liquid nitrogen vaporizer is put into operation to recover and utilize the cold energy. The production water before entering the water cooling tower exchanges heat in the liquid nitrogen vaporizer. While the liquid nitrogen is vaporized, the production water is cooled down. The cooled production water then enters the water cooling tower to participate in the pre-cooling of the water cooling tower.

[0011] Step 2: After being reheated, the nitrogen gas is reheated a second time in an air-bath vaporizer and then sent to a nitrogen storage tank for storage.

[0012] Step 3: When the demand for medium-pressure nitrogen increases and the reheating by liquid nitrogen vaporizer and air bath vaporizer is insufficient to meet the demand for medium-pressure nitrogen, the water bath vaporizer is activated for parallel operation.

[0013] This application utilizes a liquid nitrogen vaporizer to allow the cooling energy of the liquid nitrogen vaporization to be absorbed by the production water. After the production water is introduced into the water cooling tower, the temperature of the chilled water in the precooling system is reduced, thereby improving the cooling effect of the precooling system. Meanwhile, the heated nitrogen can reduce the energy consumption of the electric heater. When the nitrogen demand is low, the water bath vaporizer can be shut down, which not only saves the amount of low-pressure superheated steam used, but also extends the service life of the molecular sieve purification system, reduces the cold end temperature difference of the heat exchanger in the separation system, and reduces the overall energy consumption of the air separation system. Attached Figure Description

[0014] The specific structure of this application is given by the following figures and embodiments:

[0015] Appendix Figure 1 This is a schematic diagram of the structure of this application;

[0016] Appendix Figure 2 This is a schematic diagram of a liquid nitrogen vaporizer.

[0017] Legend: 1. Liquid nitrogen main pipe, 2. Water supply pipe, 3. Second liquid nitrogen branch pipe, 4. Air bath vaporizer, 4-1. Second nitrogen pipeline, 5. Steam pipeline, 6. First liquid nitrogen branch pipe, 7. Water bath vaporizer, 7-1. First nitrogen pipeline, 8. Nitrogen storage tank, 8-1. Nitrogen main pipe, 9. Nitrogen pipeline network, 10. Electric heater, 10-1. Electric heater bypass pipeline, 11. Water inlet pipeline, 12. Water cooling tower, 13. Liquid nitrogen vaporizer, 13-1. Liquid nitrogen vaporizer bypass pipeline, 13-2. Low temperature water pipeline, 13-3. Third nitrogen pipeline, 13-4. Nitrogen manifold, 13-5. Shell, 13-6. Water outlet, 13-7. Liquid nitrogen inlet pipe, 13-8. Heat exchanger tube, 13-9. Water inlet, 14. Third liquid nitrogen branch pipe. Detailed Implementation

[0018] This application is not limited to the following embodiments, and the specific implementation method can be determined according to the technical solution of this application and the actual situation.

[0019] In this application, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as the positional relationships of top, bottom, left, and right, which are based on the instructions attached. Figure 1 The orientation of the layout is determined by the direction of the map.

[0020] The present application will be explained and described below with reference to the accompanying drawings and embodiments: Embodiments, such as Figure 1As shown, an air separation liquid nitrogen cooling capacity recovery and utilization system includes a water bath vaporizer 7, an air bath vaporizer 4, and a liquid nitrogen vaporizer 13 connected in parallel. A first liquid nitrogen branch pipe 6, a second liquid nitrogen branch pipe 3, and a third liquid nitrogen branch pipe 14 are respectively led out from the liquid nitrogen main pipe 1. The first liquid nitrogen branch pipe 6 is connected to the liquid inlet pipe of the water bath vaporizer 7, the second liquid nitrogen branch pipe 3 is connected to the liquid inlet pipe of the air bath vaporizer 4, and the third liquid nitrogen branch pipe 14 is connected to the liquid nitrogen inlet pipe 13-7 of the liquid nitrogen vaporizer 13. The exhaust end of the water bath vaporizer 7 is connected to the first nitrogen pipeline 7-1, and the end of the first nitrogen pipeline 7-1 is connected to a nitrogen storage tank. 8. The exhaust end of the air bath vaporizer 4 is connected to the second nitrogen pipeline 4-1. An electric heater 10 is installed on the second nitrogen pipeline 4-1. The end of the second nitrogen pipeline 4-1 is connected to the first nitrogen pipeline 7-1. The nitrogen outlet pipe 13-4 of the liquid nitrogen vaporizer 13 is connected to the third nitrogen pipeline 13-3. The end of the third nitrogen pipeline 13-3 is connected to the second liquid nitrogen branch pipe 3. The water inlet 13-9 of the liquid nitrogen vaporizer 13 is connected to the water supply pipe 2. The water outlet 13-6 is connected to the low temperature water pipeline 13-2. The low temperature water pipeline 13-2 is connected to the water inlet pipe 11 of the water cooling tower 12.

[0021] like Figure 2 As shown, the liquid nitrogen vaporizer 13 includes a closed shell 13-5. A water inlet 13-9 is provided on one side of the shell 13-5, and a water outlet 13-6 is provided on the opposite side. The shell 13-5 is a cavity that can accommodate injected water. A heat exchange tube 13-8 is arranged in the cavity. The inlet end of the heat exchange tube 13-8 is connected to the liquid nitrogen inlet pipe 13-7. The first end of the liquid nitrogen inlet pipe 13-7 extends out of the shell 13-5 and is connected to the third liquid nitrogen branch pipe 14. The outlet end of the heat exchange tube 13-8 is connected to the nitrogen exhaust pipe 13-4. The tail end of the nitrogen exhaust pipe 13-4 extends out of the shell 13-5 and is connected to the third nitrogen pipeline 13-3.

[0022] Furthermore, a water supply valve is installed on the water supply pipe 2, and production water is transported in the water supply pipe 2. A liquid nitrogen vaporizer bypass pipeline 13-1 is led out from the water supply pipe 2 after the water supply valve. The end of the liquid nitrogen vaporizer bypass pipeline 13-1 is connected to the water inlet pipeline 11 of the water cooling tower 12. A bypass valve is installed on the liquid nitrogen vaporizer bypass pipeline 13-1.

[0023] like Figure 1As shown, the water bath vaporizer 7, air bath vaporizer 4, and electric heater 10 involved in this application are prior art, and their specific structures are not the inventive point of this application, so they will not be described in detail here. In this application, low-pressure superheated steam is introduced into the bath of the water bath vaporizer 7 to heat the liquid in the bath. The liquid nitrogen delivered by the first liquid nitrogen branch pipe 6 enters the coil set in the bath and exchanges heat with the heated liquid in the bath, thereby completing the vaporization of liquid nitrogen. The air bath vaporizer 4 uses the flow of surrounding air to heat the liquid nitrogen entering its finned tubes, completing the initial liquid nitrogen temperature rise, and then the liquid nitrogen is vaporized by the electric heater 10 set thereafter.

[0024] An electric heater inlet valve and an electric heater outlet valve are installed on the inlet and outlet pipelines of the electric heater 10, respectively. An electric heater bypass pipeline 10-1 is provided on the side of the electric heater 10. One end of the electric heater bypass pipeline 10-1 is connected to the inlet pipeline, and the other end is connected to the outlet pipeline. A bypass valve is installed on the electric heater bypass pipeline 10-1.

[0025] In this application, control valves can be installed on each pipeline as needed. For example, corresponding flow control valves can be installed on the first liquid nitrogen branch pipe 6, the second liquid nitrogen branch pipe 3, and the third liquid nitrogen branch pipe 14. The installation of these valves is a conventional setup in this field, so this application will not describe them one by one. Similarly, thermometers, pressure gauges, and flow meters can be installed on each pipeline and on each piece of equipment as needed to observe the temperature inside the equipment and pipelines, and make corresponding adjustments. For example, a pressure gauge can be installed on the first nitrogen pipeline 7-1 to observe whether the pressure inside the first nitrogen pipeline 7-1 is at a normal level, and a flow meter can be installed to observe the flow rate of medium-pressure nitrogen entering the nitrogen storage tank 8. Thermometers are installed at the high and low liquid levels of the bath in the water bath vaporizer 7 to observe the liquid temperature inside the bath. When the temperature difference between the upper and lower liquid levels is large, the input of low-pressure superheated steam can be increased to raise the liquid temperature. The remaining temperature measuring instruments, pressure measuring instruments, flow measuring instruments, etc., shown in the figures will not be described one by one in this application.

[0026] In use, the production water before entering the water-cooling tower 12 flows through the liquid nitrogen vaporizer 13. While the liquid nitrogen is vaporized, the production water is cooled down. The cooled production water then enters the water-cooling tower 12 to improve the cooling effect of the pre-cooling system. The reheated nitrogen is connected to the inlet of the air-bath vaporizer 4. After being reheated again in the air-bath vaporizer 4, it is sent out. The heated medium-pressure nitrogen will reduce the energy consumption of the heater, prevent condensation on the outer wall of the pipeline caused by the large temperature difference between the medium-pressure nitrogen pipeline and the surrounding environment, and prevent liquid nitrogen from entering the nitrogen pipeline after a sudden interruption of production water.

[0027] A method for recovering and utilizing the cooling capacity of liquid nitrogen in air separation includes the following steps:

[0028] Step 1: When the ambient temperature rises and the temperature of the production water entering the water cooling tower 12 is higher than 15°C, or the temperature of the water exiting the bottom of the water cooling tower 12 is higher than 10°C, the liquid nitrogen vaporizer 13 is put into operation to recover and utilize the cold energy. The production water before entering the water cooling tower 12 first exchanges heat in the liquid nitrogen vaporizer 13. While the liquid nitrogen is vaporized, the production water is cooled down. The cooled production water then enters the water cooling tower 12 to participate in the pre-cooling of the water cooling tower 12.

[0029] Step 2: After being reheated, the nitrogen gas is reheated a second time in the air bath vaporizer 4 and then sent to the nitrogen storage tank 8 for storage.

[0030] Step 3: When the demand for medium-pressure nitrogen increases and the reheating by liquid nitrogen vaporizer 13 and air bath vaporizer 4 is insufficient to meet the demand for medium-pressure nitrogen, water bath vaporizer 7 is activated for parallel operation.

[0031] The above description is merely an example for clearly illustrating this application and is not intended to limit the implementation of this application. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.

Claims

1. A system for recovering and utilizing the cooling capacity of air-separated liquid nitrogen, characterized in that: The system includes a water bath vaporizer, an air bath vaporizer, and a liquid nitrogen vaporizer connected in parallel. A first liquid nitrogen branch pipe, a second liquid nitrogen branch pipe, and a third liquid nitrogen branch pipe are respectively led out from the main liquid nitrogen pipe. The first liquid nitrogen branch pipe is connected to the liquid inlet pipe of the water bath vaporizer, the second liquid nitrogen branch pipe is connected to the liquid inlet pipe of the air bath vaporizer, and the third liquid nitrogen branch pipe is connected to the liquid nitrogen inlet pipe of the liquid nitrogen vaporizer. The exhaust end of the water bath vaporizer is connected to the first nitrogen pipeline, and the end of the first nitrogen pipeline is connected to a nitrogen storage tank. The exhaust end of the air bath vaporizer is connected to the second nitrogen pipeline, which is equipped with an electric heater. The end of the second nitrogen pipeline is connected to the first nitrogen pipeline. The nitrogen outlet pipe of the liquid nitrogen vaporizer is connected to the third nitrogen pipeline, and the end of the third nitrogen pipeline is connected to the second liquid nitrogen branch pipe. The water inlet of the liquid nitrogen vaporizer is connected to a water supply pipe, and the water outlet is connected to a low-temperature water pipeline. The low-temperature water pipeline is connected to the water inlet pipe of the water-cooling tower. Valves for controlling flow rate are installed on both the second liquid nitrogen branch pipe and the third nitrogen gas pipeline.

2. The air separation liquid nitrogen cooling capacity recovery and utilization system as described in claim 1, characterized in that: The liquid nitrogen vaporizer includes a closed shell with a water inlet on one side and a water outlet on the opposite side. The shell contains a cavity that can hold injected water. Heat exchange tubes are arranged in the cavity. The inlet end of the heat exchange tube is connected to the liquid nitrogen inlet pipe. The first end of the liquid nitrogen inlet pipe extends out of the shell and is connected to the third liquid nitrogen branch pipe. The outlet end of the heat exchange tube is connected to the nitrogen exhaust pipe. The tail end of the nitrogen exhaust pipe extends out of the shell and is connected to the third nitrogen pipeline.

3. The air separation liquid nitrogen cooling capacity recovery and utilization system as described in claim 1, characterized in that: A water supply valve is installed on the water supply pipe, and production water is transported in the water supply pipe. A liquid nitrogen vaporizer bypass pipeline is led out from the water supply pipe after the water supply valve. The end of the liquid nitrogen vaporizer bypass pipeline is connected to the water inlet pipeline of the water cooling tower. A bypass valve is installed on the liquid nitrogen vaporizer bypass pipeline.

4. The air separation liquid nitrogen cooling capacity recovery and utilization system as described in claim 1, characterized in that: An electric heater inlet valve and an electric heater outlet valve are installed on the inlet and outlet pipelines of the electric heater, respectively. An electric heater bypass pipeline is set on the side of the electric heater, with one end connected to the inlet pipeline and the other end connected to the outlet pipeline. A bypass valve is installed on the electric heater bypass pipeline.

5. A method for recovering and utilizing the cooling capacity of an air separation liquid nitrogen cooling capacity system as described in claim 1, characterized in that: Includes the following steps: Step 1: When the ambient temperature rises and the temperature of the production water entering the water cooling tower is higher than 15°C, or the temperature of the water outlet at the bottom of the water cooling tower is higher than 10°C, the liquid nitrogen vaporizer is put into operation to recover and utilize the cold energy. The production water before entering the water cooling tower exchanges heat in the liquid nitrogen vaporizer. While the liquid nitrogen is vaporized, the production water is cooled down. The cooled production water then enters the water cooling tower to participate in the pre-cooling of the water cooling tower. Step 2: After being reheated, the nitrogen gas is reheated a second time in an air-bath vaporizer and then sent to a nitrogen storage tank for storage. Step 3: When the demand for medium-pressure nitrogen increases and the reheating by liquid nitrogen vaporizer and air bath vaporizer is insufficient to meet the demand for medium-pressure nitrogen, the water bath vaporizer is activated for parallel operation.

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