Shutdown pressure relief protection system and method for cascade unit

Abstract

The invention belongs to the technical field of low-temperature unit pressure relief protection, and particularly relates to a shutdown pressure relief protection system and method.The shutdown pressure relief protection system of the cascade unit comprises a system high-pressure side pipeline and a system low-pressure side pipeline, and a pressure relief pipe set is arranged on the system high-pressure side pipeline; the pressure relief pipe set comprises a first valve and a second valve, the first valve and the second valve are arranged in parallel, the system low-pressure side pipeline is communicated with an air storage tank, the system low-pressure side pipeline is provided with a suction pressure relief pipe set, the suction pressure relief pipe set comprises a third valve and a fourth valve, the third valve and the fourth valve are arranged in parallel, and the fourth valve is a stop check valve. The flow direction of the working medium in the fourth valve is from the gas storage tank side to the system low-pressure side, and the flow direction of the working medium in the third valve is opposite to the flow direction of the working medium in the fourth valve. The stability and safety of the unit are improved; and the pipeline design is optimized, so that the system is simple, the cost is reduced, and the pipeline arrangement difficulty is reduced.

Description

Technical Field

[0001] The invention relates to a shutdown pressure relief protection system and method for a cascade unit, belonging to the technical field of pressure relief protection for low-temperature units. Background Art

[0002] R23 (trifluoromethane) is a low-temperature working fluid and is often used as the working medium of the cascade unit system. During the operation of the unit, the saturated pressure of R23 does not exceed the design pressure of the container and pipeline, and the unit operates normally; when the unit is shut down, the system temperature rises, and the saturated pressure of R23 at room temperature exceeds 4MPa. This pressure exceeds the design pressure of the container and pipeline. The R23 working fluid in the system needs to be discharged into the gas tank to maintain the system pressure within the design pressure range, thereby ensuring the safety of the system. After shutdown, the working fluid is discharged into the gas tank, and the working fluid needs to be re-pumped into the system when it is restarted. In addition, during the operation of the unit, abnormal conditions such as temperature rise and excessive pressure may occur. The working fluid needs to be discharged in time to maintain the system pressure within the design pressure range. In the prior art, a solenoid valve is generally used to control the pressure relief of the unit, and the opening pressure of the solenoid valve is set for the operating condition and the shutdown condition respectively. When the system is shut down and restarted, the system also needs to be additionally provided with a working fluid suction pipeline. When the working fluid needs to be re-sucked into the system, the working fluid is re-sucked into the system through the suction pipeline.

[0003] When using a solenoid valve for pressure relief, the solenoid valve has a high probability of failure, and once a failure occurs, it is easy to cause serious safety problems; the additional setting of a working fluid suction pipeline increases the complexity of the system, increases the cost and manufacturing difficulty, and increases the difficulty of pipeline layout for units with limited space. Summary of the invention

[0004] In view of the above technical problems in the prior art, the present invention provides a shutdown pressure relief protection system and method for a cascade unit.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] One of the objects of the present invention is to provide a shutdown pressure relief protection system for a cascade unit, comprising a system high-pressure side pipeline and a system low-pressure side pipeline, wherein a pressure relief pipe group is arranged on the system high-pressure side pipeline, and the pressure relief pipe group comprises valve one and valve two, and the valve one and valve two are arranged in parallel, the system low-pressure side pipeline is connected to an air storage tank, and a suction pressure relief pipe group is arranged on the system low-pressure side pipeline, and the suction pressure relief pipe group comprises valve three and valve four, and the valve three and valve four are arranged in parallel, and the valve four is a stop check valve, and the flow direction of the working medium in the valve four is from the air storage tank side to the system low-pressure side, and the flow direction of the working medium in the valve three is opposite to the flow direction in the valve four.

[0007] The beneficial effects of the present invention are as follows: the present invention arranges a pressure relief pipe group in which valves one and two are connected in parallel on the high-pressure side pipeline of the system, and the use of the two valves in parallel improves the stability and safety of the unit; at the same time, the present invention arranges valve three on the low-pressure side pipeline of the system, and connects a stop check valve branch in parallel with valve three in the opposite flow direction, when the unit is shut down or the pressure is too high, valve three is opened to relieve the system pressure; when the unit is restarted, the working medium is sucked back into the refrigeration system by the compressor through the stop check valve under the suction action of the compressor, valve four of the present invention adopts a stop check valve, which is a one-way valve, when the unit is operating normally, the gas in the unit pipeline cannot enter the gas storage tank through valve four, but can only enter the unit from the gas storage tank in one direction when the unit is restarted, avoiding the problem that valve four adopts an electromagnetic valve or a mechanical valve and needs to set the opening pressure, and the opening pressure is difficult to determine; the present invention optimizes the pipeline design, and the high-pressure side and low-pressure side pressure relief pipelines are aggregated to the gas storage tank, so that the system is simple, the cost is reduced, and the difficulty of pipeline layout is reduced.

[0008] On the basis of the above technical solution, the present invention can also make the following improvements:

[0009] Furthermore, the valve 1 is a solenoid valve.

[0010] Furthermore, the second valve is a constant pressure mechanical valve.

[0011] The beneficial effects of adopting the above-mentioned further technical scheme are as follows: Valve 2 of the present invention adopts a constant pressure mechanical valve as a pressure relief valve, which is mainly aimed at the pressure relief demand after the unit is shut down. At the same time, Valve 2 can also relieve pressure when the pressure is too high when the unit is running; Valve 1 of the present invention adopts an electromagnetic valve, which is mainly aimed at the pressure relief demand when the pressure is too high when the unit is running. At the same time, Valve 1 can also relieve pressure when the system is shut down for pressure relief. The combination of the two valves improves the stability and safety of the unit.

[0012] Furthermore, at least two cut-off inspection valves are provided on the high-pressure side pipeline of the system, and the cut-off inspection valves are arranged at the front and rear ends of the pressure relief pipe group.

[0013] The beneficial effect of adopting the above further technical solution is that the setting of the cut-off inspection valve facilitates the inspection of valves one and two, avoiding the inspection process from affecting the system.

[0014] Furthermore, the valve three is a constant pressure mechanical valve.

[0015] The beneficial effect of adopting the above further technical solution is: using a constant pressure mechanical valve to release pressure improves the stability and safety of the system. In addition, the low-pressure side pressure release and working fluid return of the system of the present invention use the same pipeline, which makes the system simple, reduces costs, and reduces the difficulty of pipeline layout.

[0016] Furthermore, at least two cut-off inspection valves are provided on the low-pressure side pipeline of the system, and the cut-off inspection valves are arranged at the front and rear ends of the valve three and the valve four.

[0017] The beneficial effect of adopting the above further technical solution is that the setting of the cut-off inspection valve facilitates the inspection of valves three and four, avoiding the inspection process from affecting the system.

[0018] A second object of the present invention is to provide a shutdown pressure relief protection method for a cascade unit, using the shutdown pressure relief protection system for the cascade unit as described above, comprising:

[0019] 1. When the unit is running, when the unit pressure is too high:

[0020] (1) When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2. Valve 1 is in the open state and valve 2 is closed. The working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1.

[0021] (2) When valve 1 fails or has insufficient pressure relief capacity, the opening pressure of valve 2 is less than the system pressure, valve 2 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 2;

[0022] (3) When valve 2 fails or has insufficient pressure relief capacity, at this time, the opening pressure of valve 1 is less than the opening pressure of valve 2 and less than the system pressure, valve 1 is in the open state, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1;

[0023] 2. After the unit is shut down, the unit needs to be depressurized:

[0024] (1) System high pressure side pipeline:

[0025] ① When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2. Valve 1 is in the open state, valve 2 is closed, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1;

[0026] ② When valve 1 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 2 is less than the system pressure, valve 2 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 2;

[0027] ③ When valve 2 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 1 is less than the system pressure, valve 1 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1;

[0028] (2) System low-pressure pipeline: When the opening pressure of valve 3 is less than the system pressure, valve 3 is opened, and the working fluid enters the gas storage tank from the system low-pressure pipeline through valve 3;

[0029] 3. When the unit is restarted,

[0030] Under the suction action of the compressor, the working fluid flows out of the gas storage tank and returns to the compressor from the low-pressure side pipeline of the system through valve four.

[0031] The beneficial effects of the present invention are as follows: the present invention utilizes valve one and valve two in parallel to relieve pressure on the system when the operating pressure of the unit is too high and after the unit is shut down, in response to different operating conditions of the unit. The installation of the two valves in parallel improves the safety and stability of the system. When one of the valves fails or has insufficient pressure relief capacity, the pressure relief demand of the system can be met by the other valve. Valve three is utilized to assist in relieving pressure on the system when the operating pressure of the unit is too high and after the unit is shut down. When the unit is restarted, the working fluid is sucked back into the refrigeration system through valve four under the suction action of the compressor. The low-pressure side pressure relief of the system and the working fluid reflux use the same pipeline, which makes the system simple, reduces costs, and reduces the difficulty of pipeline layout. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of the present invention.

[0033] The accompanying drawings are marked as follows: 1. Valve one; 2. Valve two; 3. Valve three; 4. Valve four; 5. System high-pressure side pipeline; 6. System low-pressure side pipeline; 7. Gas tank. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0035] Example 1

[0036] See also Figure 1 A shutdown pressure relief protection system for a cascade unit includes a system high-pressure side pipeline 5 and a system low-pressure side pipeline 6. The system high-pressure side pipeline 5 is provided with a pressure relief pipe group, and the pressure relief pipe group includes a valve 1 and a valve 2 2. The valve 1 and the valve 2 2 are arranged in parallel. The valve 1 is a solenoid valve, and the valve 2 is a constant pressure mechanical valve. The system high-pressure side pipeline 5 is provided with at least two stop inspection valves, and the stop inspection valves are arranged at the front and rear ends of the pressure relief pipe group. The system low-pressure side pipeline 6 is connected to the gas storage tank 7. The system low-pressure side pipeline 6 is provided with a suction pressure relief pipe group, and the suction pressure relief pipe group includes a valve 3 3 and a valve 4 4. The valve 3 3 and the valve 4 4 ​​are arranged in parallel. The valve 4 4 ​​is a stop check valve. The flow direction of the working medium in the valve 4 4 ​​is from the gas storage tank 7 side to the system low-pressure side. The flow direction of the working medium in the valve 3 3 is opposite to the flow direction in the valve 4 4. The valve 3 3 is a constant pressure mechanical valve. At least two shut-off inspection valves are provided on the low-pressure side pipeline 6 of the system, and the shut-off inspection valves are arranged at the front and rear ends of the valve three 3 and the valve four 4.

[0037] Example 2

[0038] A shutdown pressure relief protection method for a cascade unit, using the shutdown pressure relief protection system for the cascade unit of the above-mentioned embodiment 1, includes the following working conditions and operation processes:

[0039] 1. When the unit is running, when the unit pressure is too high:

[0040] (1) When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2. Valve 1 is open and valve 2 is closed. The working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 1.

[0041] (2) When valve 1 fails or the pressure relief capacity is insufficient, the opening pressure of valve 2 is less than the system pressure, valve 2 opens, and the working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 2.

[0042] (3) When valve 2 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 1 is less than the opening pressure of valve 2 and less than the system pressure, valve 1 is in the open state, and the working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 1;

[0043] 2. After the unit is shut down, the unit needs to be depressurized:

[0044] (1) System high pressure side pipeline 5:

[0045] ① When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2, valve 1 is in the open state, valve 2 is closed, and the working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 1;

[0046] ② When valve 1 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 2 1 is less than the system pressure, valve 2 2 opens, and the working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 2 2;

[0047] ③ When valve 2 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 1 is less than the system pressure, valve 1 opens, and the working fluid enters the gas storage tank 7 from the system high-pressure side pipeline 5 through valve 1;

[0048] (2) System low-pressure side pipeline 6: The opening pressure of valve 3 3 is less than the system pressure, valve 3 3 is opened, and the working fluid enters the gas storage tank 7 from the system low-pressure side pipeline 6 through valve 3 3;

[0049] 3. When the unit is restarted,

[0050] Under the suction action of the compressor, the working medium flows out of the gas storage tank 7, passes through the valve 44 and returns to the compressor from the system low-pressure side pipeline 6.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A shutdown pressure relief protection system for a cascade unit, comprising a system high-pressure side pipeline and a system low-pressure side pipeline, characterized in that: A pressure relief pipe group is provided on the high-pressure side pipeline of the system, and the pressure relief pipe group includes valve one and valve two, and the valve one and valve two are arranged in parallel. The low-pressure side pipeline of the system is connected to the gas storage tank. A suction pressure relief pipe group is provided on the low-pressure side pipeline of the system, and the suction pressure relief pipe group includes valve three and valve four, and the valve three and valve four are arranged in parallel. The valve four is a stop check valve, and the flow direction of the working medium in the valve four is from the gas storage tank side to the low-pressure side of the system, and the flow direction of the working medium in the valve three is opposite to the flow direction in the valve four.

2. The shutdown pressure relief protection system of the cascade unit according to claim 1, characterized in that: The first valve is a solenoid valve.

3. The shutdown pressure relief protection system of the cascade unit according to claim 1 or 2, characterized in that: The second valve is a constant pressure mechanical valve.

4. The shutdown pressure relief protection system of the cascade unit according to claim 3 is characterized in that: At least two cut-off inspection valves are arranged on the high-pressure side pipeline of the system, and the cut-off inspection valves are arranged at the front and rear ends of the pressure relief pipe group.

5. The shutdown pressure relief protection system of the cascade unit according to claim 1, characterized in that: The valve three is a constant pressure mechanical valve.

6. The shutdown pressure relief protection system of the cascade unit according to claim 5, characterized in that: At least two cut-off inspection valves are arranged on the low-pressure side pipeline of the system, and the cut-off inspection valves are arranged at the front and rear ends of the valve three and the valve four.

7. A shutdown pressure relief protection method for a cascade unit, characterized in that: A shutdown pressure relief protection system for a cascade unit as described in any one of claims 1 to 6 is used.

8. The shutdown pressure relief protection method for a cascade unit according to claim 7, characterized in that: include:

1. When the unit is running, when the unit pressure is too high: (1) When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2. Valve 1 is in the open state and valve 2 is closed. The working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1. (2) When valve 1 fails or has insufficient pressure relief capacity, the opening pressure of valve 2 is less than the system pressure, valve 2 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 2; (3) When valve 2 fails or has insufficient pressure relief capacity, at this time, the opening pressure of valve 1 is less than the opening pressure of valve 2 and less than the system pressure, valve 1 is in the open state, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1; 2. After the unit is shut down, the unit needs to be depressurized: (1) System high pressure side pipeline: ① When both valve 1 and valve 2 are normal, the opening pressure of valve 1 is less than the system pressure and less than the opening pressure of valve 2. Valve 1 is in the open state, valve 2 is closed, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1; ② When valve 1 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 2 is less than the system pressure, valve 2 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 2; ③ When valve 2 fails or the pressure relief capacity is insufficient, at this time, the opening pressure of valve 1 is less than the system pressure, valve 1 opens, and the working fluid enters the gas storage tank from the high-pressure side pipeline of the system through valve 1; (2) System low-pressure pipeline: When the opening pressure of valve 3 is less than the system pressure, valve 3 is opened, and the working fluid enters the gas storage tank from the system low-pressure pipeline through valve 3; 3. When the unit is restarted, Under the suction action of the compressor, the working fluid flows out of the gas storage tank and returns to the compressor from the low-pressure side pipeline of the system through valve four.

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