Differential pressure and temperature control system and method for seawater plate heat exchanger of nuclear power plant

Abstract

The invention belongs to the technical field of nuclear power plant operation control, and particularly relates to a nuclear power plant seawater plate heat exchanger pressure difference and temperature control system and method. An equipment cooling water outlet of the plate heat exchanger is provided with an equipment cooling water thermometer, and a plate heat exchanger bypass pneumatic control valve and a plate heat exchanger differential pressure gauge are arranged between a seawater inlet and a seawater outlet of the plate heat exchanger in parallel. A seawater inlet of the plate heat exchanger is respectively connected with the plate heat exchanger positive flushing inlet pneumatic isolating valve and the plate heat exchanger back flushing outlet pneumatic isolating valve, and a seawater outlet of the plate heat exchanger is respectively connected with the plate heat exchanger positive flushing outlet pneumatic isolating valve and the plate heat exchanger back flushing inlet pneumatic isolating valve. Automatic backwashing of the plate heat exchanger can be achieved, impurities on the seawater side in the plate heat exchanger can be washed away, and the temperature of cooling water of equipment can be controlled to be not lower than the temperature limit value required by design in winter.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant operation and control technology, specifically relating to a differential pressure and temperature control system and method for a seawater plate heat exchanger in a nuclear power plant. Background Technology

[0002] Currently, all nuclear power plants in China are located on coastal sites. The heat load generated by the equipment operating within the nuclear island, apart from natural heat dissipation, is discharged into the final heat sink seawater via plate heat exchangers through the equipment cooling water system. This ensures the safe operation of the equipment within the nuclear island within the design temperature limits. Based on nuclear power plant operating experience, two long-standing problems exist: 1. The seawater side of the plate heat exchanger experiences high differential pressure alarms approximately 2-3 times every 24 hours due to blockage. This requires nuclear power plant staff to manually operate valves to backflush the seawater side of the plate heat exchanger to remove impurities. This increases the workload of nuclear power plant staff and poses a risk of human error. 2. The plate heat exchanger lacks cooling capacity regulation. In winter, low seawater temperatures cause the equipment cooling water temperature to fall below the design temperature limits. Summary of the Invention

[0003] The purpose of this invention is to provide a differential pressure and temperature control system and method for a seawater plate heat exchanger in a nuclear power plant, which can realize automatic backwashing of the plate heat exchanger to wash away impurities on the seawater side of the plate heat exchanger, and can control the equipment cooling water temperature to not be lower than the design temperature limit in winter.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A differential pressure and temperature control system for a seawater plate heat exchanger in a nuclear power plant includes a plate heat exchanger, a pneumatic isolation valve for the plate heat exchanger's forward flush inlet, a pneumatic isolation valve for the plate heat exchanger's forward flush outlet, a pneumatic isolation valve for the plate heat exchanger's backflushing inlet, a pneumatic isolation valve for the plate heat exchanger's backflushing outlet, a bypass pneumatic regulating valve for the plate heat exchanger, a differential pressure gauge for the plate heat exchanger, and a cooling water thermometer. A cooling water thermometer is installed at the cooling water outlet of the plate heat exchanger. A bypass pneumatic regulating valve and a differential pressure gauge are connected in parallel between the seawater inlet and outlet of the plate heat exchanger. The seawater inlet of the plate heat exchanger is connected to both the pneumatic isolation valve for the plate heat exchanger's forward flush inlet and the pneumatic isolation valve for the plate heat exchanger's backflushing outlet. The seawater outlet of the plate heat exchanger is connected to both the pneumatic isolation valve for the plate heat exchanger's forward flush outlet and the pneumatic isolation valve for the plate heat exchanger's backflushing inlet.

[0005] A method for controlling differential pressure and temperature in a seawater plate heat exchanger for a nuclear power plant: a differential pressure gauge monitors the differential pressure of the plate heat exchanger; a cooling water thermometer monitors the temperature of the cooling water after it has been cooled by the plate heat exchanger.

[0006] When the differential pressure of the plate heat exchanger reaches the high differential pressure setting value, the logic action of switching the plate heat exchanger from forward flushing to backflushing is triggered. The pneumatic isolation valves at the backflushing inlet and outlet of the plate heat exchanger slowly open to 50%. Then, the pneumatic isolation valves at the forward flushing inlet and outlet of the plate heat exchanger slowly close to 50%. Next, the pneumatic isolation valves at the backflushing inlet and outlet of the plate heat exchanger slowly open to 100%. Finally, the pneumatic isolation valves at the forward flushing inlet and outlet of the plate heat exchanger slowly close to 0%, and the plate heat exchanger begins backflushing.

[0007] When the differential pressure of the plate heat exchanger returns to the low differential pressure set value, the logic action of switching the plate heat exchanger from backflushing to forward flushing is triggered. The pneumatic isolation valves at the inlet and outlet of the plate heat exchanger for forward flushing slowly open to 50%. Then, the pneumatic isolation valves at the inlet and outlet of the plate heat exchanger for backflushing slowly close to 50%. Next, the pneumatic isolation valves at the inlet and outlet of the plate heat exchanger for forward flushing slowly open to 100%. Finally, the pneumatic isolation valves at the inlet and outlet of the plate heat exchanger for backflushing slowly close to 0%, and the plate heat exchanger begins forward flushing.

[0008] During the period of lowest winter temperatures, when the equipment cooling water temperature reaches the low set temperature value, the logic action of opening the bypass pneumatic regulating valve of the plate heat exchanger is triggered, and the bypass pneumatic regulating valve of the plate heat exchanger slowly opens from 0% to 10%.

[0009] If the equipment cooling water temperature is still lower than the low temperature set value, the bypass pneumatic regulating valve of the plate heat exchanger will no longer be triggered to continue opening. In this case, the main control room will trigger an alarm, and the nuclear power plant staff will organize an investigation to check whether the equipment cooling water thermometer is faulty.

[0010] If extreme low temperature conditions occur, and the plate heat exchanger bypass pneumatic regulating valve is slowly opened from 0% to 10%, but the equipment cooling water temperature is still lower than the low temperature setpoint, nuclear power plant personnel will manually control the opening of the plate heat exchanger bypass pneumatic regulating valve on the PLC logic control cabinet to continue increasing the opening until the equipment cooling water temperature is higher than the low temperature setpoint.

[0011] As the temperature rises, when the equipment cooling water temperature reaches the high set value, the logic action of closing the bypass pneumatic regulating valve of the plate heat exchanger is triggered, and the plate heat exchanger bypass pneumatic regulating valve slowly closes to 0%.

[0012] The beneficial effects achieved by this invention are as follows: This invention enables automatic backwashing of heat exchangers, promptly removing impurities without requiring manual valve operation by nuclear power plant staff, thus reducing their workload and avoiding the risk of human error. Furthermore, this invention can automatically control the equipment's cooling water temperature to maintain it above the designed limit during winter. Attached Figure Description

[0013] Figure 1 A schematic diagram of the differential pressure and temperature control system for a seawater plate heat exchanger in a nuclear power plant. In the diagram: 1. Plate heat exchanger; 2. Pneumatic isolation valve at the inlet of the plate heat exchanger for forward flushing; 3. Pneumatic isolation valve at the outlet of the plate heat exchanger for forward flushing; 4. Pneumatic isolation valve at the inlet of the plate heat exchanger for backflushing; 5. Pneumatic isolation valve at the outlet of the plate heat exchanger for backflushing; 6. Pneumatic regulating valve for the bypass of the plate heat exchanger; 7. Differential pressure gauge for the plate heat exchanger; 8. Cooling water thermometer. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0015] like Figure 1 As shown, a differential pressure and temperature control system for a seawater plate heat exchanger in a nuclear power plant includes a plate heat exchanger 1, a pneumatic isolation valve 2 for the plate heat exchanger forward flush inlet, a pneumatic isolation valve 3 for the plate heat exchanger forward flush outlet, a pneumatic isolation valve 4 for the plate heat exchanger backflushing inlet, a pneumatic isolation valve 5 for the plate heat exchanger backflushing outlet, a pneumatic regulating valve 6 for the plate heat exchanger bypass, a differential pressure gauge 7 for the plate heat exchanger, and a cooling water thermometer 8. The cooling water outlet of the plate heat exchanger 1 is equipped with a device... A cooling water thermometer 8 is provided. A plate heat exchanger bypass pneumatic regulating valve 6 and a plate heat exchanger differential pressure gauge 7 are connected in parallel between the seawater inlet and seawater outlet of the plate heat exchanger 1. The seawater inlet of the plate heat exchanger 1 is connected to the plate heat exchanger forward flushing inlet pneumatic isolation valve 2 and the plate heat exchanger backflushing outlet pneumatic isolation valve 5, respectively. The seawater outlet of the plate heat exchanger 1 is connected to the plate heat exchanger forward flushing outlet pneumatic isolation valve 3 and the plate heat exchanger backflushing inlet pneumatic isolation valve 4, respectively.

[0016] A method for controlling differential pressure in a seawater plate heat exchanger in a nuclear power plant: a differential pressure gauge 7 monitors the differential pressure in the plate heat exchanger 1.

[0017] When the differential pressure of plate heat exchanger 1 reaches the high differential pressure setting value, the logic action of switching the plate heat exchanger from forward flushing to backflushing is triggered. The backflushing inlet pneumatic isolation valve 4 and the backflushing outlet pneumatic isolation valve 5 of the plate heat exchanger slowly open to 50%. Then, the forward flushing inlet pneumatic isolation valve 2 and the forward flushing outlet pneumatic isolation valve 3 of the plate heat exchanger slowly close to 50%. Next, the backflushing inlet pneumatic isolation valve 4 and the backflushing outlet pneumatic isolation valve 5 of the plate heat exchanger slowly open to 100%. Finally, the forward flushing inlet pneumatic isolation valve 2 and the forward flushing outlet pneumatic isolation valve 3 of the plate heat exchanger slowly close to 0%. Plate heat exchanger 1 begins backflushing.

[0018] When the differential pressure of plate heat exchanger 1 returns to the low differential pressure set value, the logic action of switching the plate heat exchanger from backflushing to forward flushing is triggered. The pneumatic isolation valves 2 and 3 at the plate heat exchanger's forward flushing inlet and outlet slowly open to 50%, then the pneumatic isolation valves 4 and 5 at the plate heat exchanger's backflushing inlet and outlet slowly close to 50%, then the pneumatic isolation valves 2 and 3 at the plate heat exchanger's forward flushing outlet slowly open to 100%, and finally the pneumatic isolation valves 4 and 5 at the plate heat exchanger's backflushing inlet and outlet slowly close to 0%. Plate heat exchanger 1 then begins forward flushing.

[0019] The above logic is implemented by the PLC logic control cabinet.

[0020] A method for temperature control of a seawater plate heat exchanger in a nuclear power plant: Equipment cooling water thermometer 8 monitors the temperature of the equipment cooling water after it has been cooled by the plate heat exchanger.

[0021] During periods of lowest winter temperatures, when the equipment's cooling water temperature reaches the minimum set temperature, the logic triggers the opening of the plate heat exchanger bypass pneumatic regulating valve 6. The plate heat exchanger bypass pneumatic regulating valve 6 slowly opens from 0% to 10%.

[0022] Under non-extreme low-temperature conditions, a 10% bypass flow rate is sufficient to raise the equipment cooling water temperature above the low-temperature setpoint. If the equipment cooling water temperature remains below the low-temperature setpoint, the plate heat exchanger bypass pneumatic regulating valve 6 will not be triggered to continue opening, preventing a malfunction in the equipment cooling water thermometer 8 from causing excessive seawater bypass flow to the plate heat exchanger 1, which would then lead to an increase in the actual equipment cooling water temperature. In this situation, an alarm is triggered in the main control room, and nuclear power plant personnel organize a check to determine if the equipment cooling water thermometer 8 is malfunctioning.

[0023] If extreme low temperature conditions occur, and the plate heat exchanger bypass pneumatic regulating valve 6 is slowly opened from 0% to 10%, but the equipment cooling water temperature is still lower than the low temperature setpoint, nuclear power plant personnel can manually control the opening of the plate heat exchanger bypass pneumatic regulating valve 6 on the PLC logic control cabinet to continue increasing the opening until the equipment cooling water temperature is higher than the low temperature setpoint.

[0024] As the air temperature rises, when the equipment's cooling water temperature reaches the high setpoint, the logic triggers the closure of the plate heat exchanger bypass pneumatic regulating valve 6. The plate heat exchanger bypass pneumatic regulating valve 6 then slowly closes to 0%.

[0025] The above logic is implemented by the PLC logic control cabinet.

[0026] Example: 1. During normal operation: Plate heat exchanger 1 is in the forward flushing state, plate heat exchanger forward flushing inlet pneumatic isolation valve 2 and plate heat exchanger forward flushing outlet pneumatic isolation valve 3 are fully open, and plate heat exchanger backflushing inlet pneumatic isolation valve 4 and plate heat exchanger backflushing outlet pneumatic isolation valve 5 are fully closed.

[0027] Seawater and equipment cooling water flow in opposite directions within the plate heat exchanger 1, separated by heat transfer plates, with the seawater cooling the equipment cooling water.

[0028] 2. When the differential pressure of the plate heat exchanger reaches the high differential pressure setting value: the logic action of switching the plate heat exchanger from forward flushing to backflushing is triggered. The pneumatic isolation valve 4 at the backflushing inlet and the pneumatic isolation valve 5 at the backflushing outlet of the plate heat exchanger slowly open to 50%. Then, the pneumatic isolation valve 2 at the forward flushing inlet and the pneumatic isolation valve 3 at the forward flushing outlet of the plate heat exchanger slowly close to 50%. Next, the pneumatic isolation valve 4 at the backflushing inlet and the pneumatic isolation valve 5 at the backflushing outlet of the plate heat exchanger slowly open to 100%. Finally, the pneumatic isolation valve 2 at the forward flushing inlet and the pneumatic isolation valve 3 at the forward flushing outlet of the plate heat exchanger slowly close to 0%. Plate heat exchanger 1 begins backflushing.

[0029] 3. When the pressure of the plate heat exchanger recovers to the low differential pressure set value: the logic action of switching the plate heat exchanger from backflushing to forward flushing is triggered. The pneumatic isolation valves 2 and 3 at the plate heat exchanger forward flushing inlet and outlet slowly open to 50%. Then, the pneumatic isolation valves 4 and 5 at the plate heat exchanger backflushing inlet and outlet slowly close to 50%. Next, the pneumatic isolation valves 2 and 3 at the plate heat exchanger forward flushing inlet and outlet slowly open to 100%. Finally, the pneumatic isolation valves 4 and 5 at the plate heat exchanger backflushing inlet and outlet slowly close to 0%. Plate heat exchanger 1 begins forward flushing.

[0030] 4. During the period of lowest winter temperatures, when the equipment cooling water temperature remains below the low setpoint: the logic action triggers the opening of the plate heat exchanger bypass pneumatic regulating valve 6. The plate heat exchanger bypass pneumatic regulating valve 6 slowly opens from 0% to 10%.

[0031] 5. When the plate heat exchanger bypass pneumatic regulating valve 6 has reached 10% opening, but the equipment cooling water temperature is still lower than the low temperature setpoint: an alarm is triggered in the main control room. Nuclear power plant staff organize a check to see if the equipment cooling water thermometer 8 is faulty. If the equipment cooling water thermometer 8 is not faulty, and the extreme low temperature condition truly exists, nuclear power plant staff manually control the opening of the plate heat exchanger bypass pneumatic regulating valve 6 on the PLC logic control cabinet to continue increasing it until the equipment cooling water temperature is higher than the low temperature setpoint.

[0032] 6. When the equipment cooling water temperature reaches the high set value: the logic action of closing the plate heat exchanger bypass pneumatic regulating valve 6 is triggered. The plate heat exchanger bypass pneumatic regulating valve 6 slowly closes to 0%.

Claims

1. A differential pressure and temperature control system for a nuclear power plant seawater plate heat exchanger, characterized by: The plate heat exchanger includes a plate heat exchanger, a plate heat exchanger positive flushing inlet pneumatic isolation valve, a plate heat exchanger positive flushing outlet pneumatic isolation valve, a plate heat exchanger back flushing inlet pneumatic isolation valve, a plate heat exchanger back flushing outlet pneumatic isolation valve, a plate heat exchanger bypass pneumatic regulating valve, a plate heat exchanger differential pressure gauge, and a device cooling water temperature gauge; the device cooling water outlet of the plate heat exchanger is provided with the device cooling water temperature gauge; the seawater inlet and the seawater outlet of the plate heat exchanger are connected in parallel with the plate heat exchanger bypass pneumatic regulating valve and the plate heat exchanger differential pressure gauge; the seawater inlet of the plate heat exchanger is connected with the plate heat exchanger positive flushing inlet pneumatic isolation valve and the plate heat exchanger back flushing outlet pneumatic isolation valve; and the seawater outlet of the plate heat exchanger is connected with the plate heat exchanger positive flushing outlet pneumatic isolation valve and the plate heat exchanger back flushing inlet pneumatic isolation valve.

2. A nuclear power plant seawater plate heat exchanger differential pressure and temperature control method based on the nuclear power plant seawater plate heat exchanger differential pressure and temperature control system of claim 1, characterized by: The plate heat exchanger differential pressure gauge monitors the differential pressure of the plate heat exchanger; and the device cooling water temperature gauge monitors the temperature of the device cooling water after being cooled by the plate heat exchanger.

3. The method of claim 2, wherein: When the differential pressure of the plate heat exchanger reaches a high differential pressure set value, a logic action of switching the plate heat exchanger from positive flushing to back flushing is triggered; the plate heat exchanger back flushing inlet pneumatic isolation valve and the plate heat exchanger back flushing outlet pneumatic isolation valve are slowly opened to 50%; then the plate heat exchanger positive flushing inlet pneumatic isolation valve and the plate heat exchanger positive flushing outlet pneumatic isolation valve are slowly closed to 50%; then the plate heat exchanger back flushing inlet pneumatic isolation valve and the plate heat exchanger back flushing outlet pneumatic isolation valve are slowly opened to 100%; finally, the plate heat exchanger positive flushing inlet pneumatic isolation valve and the plate heat exchanger positive flushing outlet pneumatic isolation valve are slowly closed to 0%, and the plate heat exchanger starts back flushing.

4. The method of claim 2, wherein: When the differential pressure of the plate heat exchanger returns to a low differential pressure set value, a logic action of switching the plate heat exchanger from back flushing to positive flushing is triggered; the plate heat exchanger positive flushing inlet pneumatic isolation valve and the plate heat exchanger positive flushing outlet pneumatic isolation valve are slowly opened to 50%; then the plate heat exchanger back flushing inlet pneumatic isolation valve and the plate heat exchanger back flushing outlet pneumatic isolation valve are slowly closed to 50%; then the plate heat exchanger positive flushing inlet pneumatic isolation valve and the plate heat exchanger positive flushing outlet pneumatic isolation valve are slowly opened to 100%; finally, the plate heat exchanger back flushing inlet pneumatic isolation valve and the plate heat exchanger back flushing outlet pneumatic isolation valve are slowly closed to 0%, and the plate heat exchanger starts positive flushing.

5. The method of claim 2, wherein: During the period of the lowest air temperature in winter, when the device cooling water temperature reaches a low temperature set value, a logic action of opening the plate heat exchanger bypass pneumatic regulating valve is triggered; the plate heat exchanger bypass pneumatic regulating valve is slowly opened from 0% to 10%.

6. The method of claim 5, wherein: If the device cooling water temperature is still lower than the low temperature set value, the plate heat exchanger bypass pneumatic regulating valve is not opened any more; in this case, the main control room triggers an alarm, and the nuclear power plant staff organizes to check whether the device cooling water temperature gauge is faulty.

7. The method of claim 5, wherein: If the extreme low temperature condition occurs, the plate heat exchanger bypass pneumatic control valve slowly opens from 0% to 10%, and the equipment cooling water temperature is still lower than the low temperature set value, the nuclear power plant personnel manually controls the opening of the plate heat exchanger bypass pneumatic control valve on the PLC logic control cabinet until the equipment cooling water temperature is higher than the low temperature set value.

8. The method of claim 5, wherein: With the rise of air temperature, when the equipment cooling water temperature reaches the high temperature set value, the logic action of closing the plate heat exchanger bypass pneumatic control valve is triggered, and the plate heat exchanger bypass pneumatic control valve slowly closes to 0%.

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