A condensate water system with a shutdown condensate water pump for a gas-steam combined cycle unit and a shutdown water supply method

Abstract

This invention belongs to the technical field of condensate systems and discloses a condensate system and shutdown water supply method for a gas-steam combined cycle unit with a shutdown condensate pump. It includes a branch line connected in parallel to the condenser hot well outlet, consisting of a small-capacity shutdown pump, a vacuum shut-off valve, a filter screen, and a pressure relief safety valve. The safety valve is located downstream of the main condensate pump and connected back to the condenser hot well. After a planned unit shutdown and the main pump stops operating, this shutdown pump starts running, providing an independent cooling water source for equipment such as the desuperheating water in the expansion tank and the low-pressure cylinder spray. This invention achieves flow rate and head matching by setting up a dedicated small-power shutdown condensate pump, thereby significantly reducing power consumption during shutdown. By setting up a vacuum shut-off valve, a check valve, an electrically operated shut-off valve, and a pressure relief safety valve, it effectively prevents high-pressure water from flowing back into the shutdown condensate pump and its suction pipe system during main condensate pump operation, avoiding the risk of overpressure damage.

Description

Technical Field

[0001] This invention relates to the field of condensate systems for gas-steam combined cycle units, and in particular to a condensate system for a gas-steam combined cycle unit with a shutdown condensate pump and a shutdown water supply method. Background Technology

[0002] In thermal power plants, condensate pumps are mainly used to pump out the condensate formed in the condenser. They extract the condensate formed from the cooled steam after the turbine has done its work and transport it to the deaerator or boiler feedwater system as a supplementary water source for the circulating working fluid, ensuring the continuous operation of the thermal cycle. Currently, condensate pumps are typically positioned low to ensure sufficient net positive suction head at the inlet side.

[0003] Condensate systems typically employ a modular design. This system also provides desuperheating water, sealing water, and cooling water to related equipment and systems such as medium and low-pressure bypass depressurizers, shaft seal steam supply stations, and low-pressure cylinder water sprayers. In existing systems, when the unit is shut down, the main condensate pump operates at reduced power thanks to frequency conversion regulation. During shutdown, it continues to supply water to users such as desuperheating water sprayers in the condensate expansion tank, water curtain sprayers, and low-pressure cylinder sprayers. Because the unit is operating at reduced load or shut down, the desuperheating water, sprayers, and sealing water required by equipment such as the condensate expansion tank and low-pressure cylinder are only used to cool residual steam or maintain equipment safety. Their required water supply pressure is far lower than the condensate system pressure during normal unit operation; that is, the pressure required for the desuperheating water is far lower than the head of the selected main condensate pump.

[0004] However, this existing technology has significant drawbacks: the design capacity (100% capacity) of the main condensate pump is far greater than the actual water supply required during shutdown. Currently, most gas turbine power plants are positioned as daily peak-shaving units, starting early and shutting down late each day. The time between shutdown and coasting is frequent and lengthy. Even if the condensate pump speed is reduced through frequency conversion regulation, its power consumption remains high, resulting in unnecessary energy consumption during shutdown. This, in turn, increases the plant's overall power consumption and reduces the economic efficiency of the unit during downtime. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a condensate system and a shutdown water supply method for a gas-steam combined cycle unit with a shutdown condensate pump, thereby reducing the energy consumption of the condensate pump during unit shutdown and decreasing the plant power consumption rate.

[0006] This invention is achieved through the following scheme: A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump includes a condenser hot well, a main condensate pump branch connected to the condenser hot well, and a shutdown condensate pump branch. The shutdown condensate pump branch and the main condensate pump branch are connected in parallel to the outlet of the condenser hot well. The main condensate pump branch is equipped with a main condensate pump set to supply water to the outlet main pipe. The shutdown condensate pump branch is composed of a suction pipe, a shutdown condensate pump, and a discharge pipe connected in series, with the discharge pipe flowing into the outlet main pipe; During normal operation of the unit, the shutdown condensate pump remains in a stopped state, and the vacuum shut-off valve in its suction line and the electric shut-off valve in its discharge line are both in a closed and isolated state. When the unit is shut down, the condenser vacuum is destroyed, and the main condensate pump stops operating, the shutdown condensate pump starts running, drawing water from the condenser hot well and supplying water to the outlet main pipe, providing independent cooling water for the desuperheating and cooling equipment required during the unit shutdown phase.

[0007] Furthermore, the main condensate pump set includes two main condensate pumps, A and B, installed in parallel with a capacity of 100%, one in operation and one on standby. During normal unit operation, the pumps pressurize the condensate in the condenser hot well and then deliver it out.

[0008] Furthermore, a vacuum shut-off valve and a filter screen are sequentially installed along the water flow direction on the suction pipe of the shutdown condensate pump branch. A branch pipe is led out from the pipe section between the vacuum shut-off valve and the filter screen, and a pressure relief safety valve is connected to this branch pipe. The outlet end of the pressure relief safety valve is connected back to the condenser hot well. This pressure relief safety valve is used to release the overpressurized condensate back to the hot well to protect the branch equipment when the shutdown condensate pump is started and the electric shut-off valve fails to open, causing pressure buildup in the pipeline.

[0009] Furthermore, a check valve and an electrically operated shut-off valve are sequentially installed along the water flow direction on the discharge pipe of the shutdown condensate pump branch. When the shutdown condensate pump is started, the electrically operated shut-off valve is in the open state to connect to the outlet main pipe.

[0010] Furthermore, the rated flow rate and head of the shutdown condensate pump are lower than the rated parameters of a single pump in the main condensate pump group; the cooling equipment supplied by the shutdown condensate pump through the outlet main pipe includes at least a turbine low-pressure cylinder water spray cooling device, a water curtain sealing water spray device, and a condensate expansion tank cooling water spray device.

[0011] Furthermore, the design flow rate of the shut-down condensate pump is 15% to 30% of the flow rate of a single main condensate pump, and its design head is lower than the delivery pressure of the main condensate pump set during normal operation.

[0012] A method for shutting down a gas-fired combined cycle turbine unit using a condensate system with a shutdown condensate pump includes the following steps: During normal operation of the unit, the main condensate pump set is responsible for condensate delivery, and the condensate pump branch is kept isolated when the unit is shut down; during the shutdown water supply phase, a planned shutdown operation is performed, and the control system issues a command to shut down the main condensate pump set; Open the vacuum shut-off valve and the electric shut-off valve on the branch of the shut-down condensate pump; Start the shut-down condensate pump so that it draws condensate from the condenser hot well and pumps it through the discharge pipeline to the outlet main pipe to provide cooling water to one or more types of equipment, including at least the desuperheating water spray of the condensate expansion tank, the water spray of the low-pressure cylinder, and the water curtain spray.

[0013] Furthermore, the triggering condition for executing the planned shutdown operation is as follows: after the generator is disconnected, the turbine stops running, and the condenser vacuum is broken, the system determines that the main condensate pump is unusable and then issues a command to start the shutdown condensate pump.

[0014] Furthermore, the operating sequence for opening the vacuum shut-off valve and the electric shut-off valve is as follows: first open the vacuum shut-off valve located in the suction line, and then open the electric shut-off valve located in the discharge line; the start-up timing of the shut-down condensate pump is set after the electric shut-off valve is opened.

[0015] Furthermore, when the exhaust temperature of the low-pressure cylinder of the steam turbine or the internal temperature of the condensate expansion tank drops to a preset safety threshold, the control system issues a command to stop the shutdown condensate pump and close the vacuum shut-off valve and the electric shut-off valve, so that the system returns to standby status.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: (1) Significantly reduce power consumption during shutdown: The required condensate flow rate and head during shutdown are much smaller than those during normal operation. Based on the relationship that the pump shaft power is proportional to the product of flow rate and head, this invention achieves the matching of flow rate and head by setting up a dedicated low-power shutdown condensate pump, thereby significantly reducing power consumption during shutdown.

[0017] (2) Improve system reliability: By setting up vacuum shut-off valve, check valve, electric shut-off valve and pressure relief safety valve, the high pressure water backflow into the shut-down condensate pump and its suction pipe system during the operation of the main condensate pump is effectively prevented, thus avoiding the risk of overpressure damage.

[0018] (3) Optimize equipment utilization: Reduce the inefficient operation time of the main condensate pump during shutdown, which is conducive to extending the maintenance cycle and service life of the main condensate pump. Attached Figure Description

[0019] Figure 1 This is a system diagram of the present invention.

[0020] Attached reference numerals: 1-Condenser hot well; 2-Main condensate pump A; 3-Main condensate pump B; 4-Shutdown condensate pump; 5-Vacuum shut-off valve; 6-Filter screen; 7-Pressure relief safety valve; 8-Check valve; 9-Electric shut-off valve; 10-Outlet main pipe. Detailed Implementation

[0021] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0022] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0023] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] Furthermore, the terms "first," "second," etc., 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. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0025] like Figure 1 As shown, this embodiment provides a condensate system for a gas-steam combined cycle unit with a shutdown condensate pump. The system mainly includes: a condenser hot well 1, a main condensate pump A2, a main condensate pump B3, and a shutdown condensate pump 4.

[0026] Each unit is equipped with two 100% capacity condensate pumps, with one pump in operation and the other on standby. Condensate is drawn from the condenser hot well, pressurized by the main condensate pump, and then combined into one stream. It passes through the condensate polishing unit and shaft seal cooler in sequence, and finally enters the condensate heating inlet of the waste heat boiler.

[0027] During normal operation of the unit, condensate is drawn from the condenser hot well 1, pressurized by the main condensate pump, and sent to the outlet main pipe 10. Then it passes through the condensate polishing device and shaft seal cooler in sequence to the condensate heating inlet of the waste heat boiler.

[0028] The improvement of this invention lies in the addition of a shutdown condensate pump branch line at the outlet of the condenser hot well 1, connected in parallel with the suction lines of the two main condensate pumps. This branch line consists of the shutdown condensate pump 4, the vacuum shut-off valve 5, the filter screen 6, the pressure relief safety valve 7, the check valve 8, and the electric shut-off valve 9.

[0029] The specific connection relationship is as follows: A branch pipe is drawn from the outlet of the condenser hot well 1 as the suction pipe for the shut-down condensate pump 4. Along the water flow direction, from the hot well to the pump inlet, a vacuum shut-off valve 5 and a filter screen 6 are installed sequentially. A branch pipe is drawn from after the vacuum shut-off valve 5 and before the filter screen 6, connecting to a pressure relief safety valve 7. The end of the suction pipe is connected to the inlet of the shut-down condensate pump 4; this safety valve prevents pressurized condensate from flowing back into the shut-down condensate pump during operation, causing overpressure in the piping system. Simultaneously, this safety valve, located before the filter screen, prevents backpressure at the positive outlet of the shut-down pump due to impurities, and also intercepts overpressure on the reverse suction side caused by high-pressure water leaking from the outlet main pipe through the check valve. The outlet of the shut-down condensate pump 4 is connected to the discharge pipe, with a check valve 8 and an electrically operated shut-off valve 9 installed sequentially along the water flow direction. Finally, the discharge pipe is connected to the outlet main pipe 10 of the main condensate pump.

[0030] The water supply shutdown procedure is as follows: Normal operation phase: During normal power generation, the condenser maintains a high vacuum. At this time, the shut-down condensate pump 4 remains shut down, with its inlet vacuum shut-off valve 5 and outlet electric shut-off valve 9 both closed. One of the main condensate pumps, A2 or B3, is put into operation, pressurizing the condensate and sending it to the outlet main pipe 10 to supply water to users at all levels. In this state, even if a very small leak occurs due to the high-pressure water at the main condensate pump outlet through the outlet main pipe 10, the reverse cut-off of the check valve 8, and the closure of the electric shut-off valve 9, the presence of the pressure relief safety valve 7 ensures that if the pressure in the pump's suction line abnormally rises above the set value, the safety valve will immediately open to relieve pressure, effectively protecting the shut-down condensate pump 4 and its suction line from overpressure damage.

[0031] Shutdown Water Supply Phase: When the unit is scheduled to shut down, after the generator is disconnected, the turbine stops, and the condenser vacuum is broken, the control system issues the following commands: First, stop the running main condensate pump; then, open the inlet vacuum shut-off valve 5 and the outlet electric shut-off valve 9 of the shutdown condensate pump 4; finally, start the shutdown condensate pump 4. The shutdown condensate pump 4 begins to draw condensate from the condenser hot well 1, filters it through the filter screen 6, and then sends it to the outlet main pipe 10 through the check valve 8 and the electric shut-off valve 9, specifically supplying water to equipment such as the desuperheating water spray in the condensate expansion tank, the water curtain spray, and the low-pressure cylinder spray.

[0032] Shutdown complete: When the entire shutdown process is finished and the system no longer needs to supply water, stop the shutdown condensate pump 4 and close its inlet and outlet valves. The system will then return to standby status.

[0033] During the coasting phase of the turbine, the water spray in the low-pressure cylinder, the water curtain seal, and the desuperheating water in the condensate expansion tank require high levels of water quality continuity and stable water supply pressure. This system's independent branch design achieves hydraulic isolation between the shutdown cooling water source and the main condensate system, avoiding the risk of water supply interruptions due to main pump shutdown or fluctuations in the condenser hot well water level. This ensures a stable decrease in the metal temperature of the low-pressure cylinder, meeting the peak-shaving operation requirements of the unit's rapid start-up and shutdown.

[0034] Since the required water pressure and flow rate during shutdown are much lower than under normal operating conditions, this small-power pump can fully meet the demand, while the main condensate pump can be completely shut down. This avoids the sudden drop in efficiency, motor overheating, and wear caused by prolonged variable frequency operation of the main pump during low load or shutdown phases.

[0035] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump, characterized in that: It includes a condenser hot well (1), a main condensate pump branch connected to the condenser hot well (1), and a shutdown condensate pump (4) branch. The shutdown condensate pump (4) branch and the main condensate pump branch are connected in parallel to the outlet of the condenser hot well (1). The main condensate pump branch is equipped with a main condensate pump set to supply water to the outlet main pipe (10). The shutdown condensate pump (4) branch is composed of a suction pipe, a shutdown condensate pump (4) and a discharge pipe connected in series, and the discharge pipe merges into the outlet main pipe (10). During normal operation of the unit, the shutdown condensate pump (4) remains in a shutdown state, and the vacuum shut-off valve (5) in its suction line and the electric shut-off valve (9) in its discharge line are both in a closed and isolated state. When the unit is shut down, the condenser vacuum is destroyed and the main condensate pump stops operating, the shutdown condensate pump (4) starts to operate, pumps water from the condenser hot well (1) and supplies water to the outlet main pipe (10), providing independent cooling water for the desuperheating and cooling equipment required during the unit shutdown phase.

2. The condensate system of a gas-steam combined cycle unit with a shutdown condensate pump according to claim 1, characterized in that: The main condensate pump set includes two main condensate pumps A (2) and B (3) with 100% capacity, which are set up in parallel. One pump is in operation and the other is on standby. When the unit is running normally, the pumps pressurize the condensate in the condenser hot well (1) and send it out.

3. A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump according to claim 1 or 2, characterized in that: A vacuum shut-off valve (5) and a filter screen (6) are sequentially installed along the water flow direction on the suction pipe of the branch of the shut-off condensate pump (4); a branch pipe is led out from the pipe section between the vacuum shut-off valve (5) and the filter screen (6), and a pressure relief safety valve (7) is connected to the branch pipe. The outlet end of the pressure relief safety valve (7) is connected back to the condenser hot well (1).

4. A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump according to claim 3, characterized in that: A check valve (8) and an electric shut-off valve (9) are sequentially installed along the water flow direction on the discharge pipe of the shutdown condensate pump (4). When the shutdown condensate pump (4) is started, the electric shut-off valve (9) is in the open state to connect to the outlet main pipe (10).

5. A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump according to claim 4, characterized in that: The rated flow rate and head of the shutdown condensate pump (4) are lower than the rated parameters of a single pump in the main condensate pump group; the cooling equipment supplied by the shutdown condensate pump (4) through the outlet manifold (10) includes at least a turbine low-pressure cylinder water spray cooling device, a water curtain sealing water spray device and a condensate expansion container cooling water spray device.

6. A condensate system for a gas-steam combined cycle unit with a shutdown condensate pump according to claim 5, characterized in that: The design flow rate of the shut-down condensate pump (4) is 15% to 30% of the flow rate of a single main condensate pump, and its design head is lower than the conveying pressure of the main condensate pump set during normal operation.

7. A method for shutting down and supplying water to a gas-steam combined cycle unit using the system described in any one of claims 1 to 6, characterized in that, Includes the following steps: During normal operation of the unit, the main condensate pump set is responsible for condensate delivery, and the condensate pump (4) branch is kept isolated when the unit is shut down; during the shutdown water supply phase, the planned shutdown operation is performed, and the control system issues an instruction to shut down the main condensate pump set; Open the vacuum shut-off valve (5) and the electric shut-off valve (9) on the branch of the shut-down condensate pump (4); Start the shutdown condensate pump (4) to draw condensate from the condenser hot well (1) and pump it through the discharge pipeline to the outlet main pipe (10) to provide cooling water to one or more types of equipment, including at least the desuperheating water spray of the condensate expansion container, the water spray of the low-pressure cylinder and the water curtain spray.

8. A method for shutting down and supplying water to a gas-steam combined cycle unit according to claim 7, characterized in that: The triggering condition for the scheduled shutdown operation is as follows: after the generator is disconnected, the turbine stops running and the condenser vacuum is destroyed, the system determines that the main condensate pump is no longer usable and then issues an instruction to start the shutdown condensate pump (4).

9. A method for shutting down and supplying water to a gas-steam combined cycle unit according to claim 7, characterized in that: The operation sequence of opening the vacuum shut-off valve (5) and the electric shut-off valve (9) is as follows: first open the vacuum shut-off valve (5) located in the suction pipeline, and then open the electric shut-off valve (9) located in the discharge pipeline; the start-up timing of the shutdown condensate pump (4) is set after the electric shut-off valve (9) is opened.

10. A method for shutting down and supplying water to a gas-steam combined cycle unit according to claim 7, characterized in that: When the exhaust temperature of the low-pressure cylinder of the steam turbine or the internal temperature of the condensate expansion tank drops to a preset safety threshold, the control system issues a command to stop the shutdown condensate pump (4) and close the vacuum shut-off valve (5) and the electric shut-off valve (9) to restore the system to standby state.

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