In addition to the steam turbine, the equipment of the steam turbine system is a variety of pumps (feed water pumps, condensate pumps, circulating water pumps, vacuum pumps, lubricating oil pumps, EH oil pumps, etc.), and various heating condensers (high and low additions, deaerators, condensers, etc.). SO~ Let's talk about some things about water pumps.
The water pump has been called by some people as a water pump, but it has been corrected by Sogou input method to give (ji) water pump, Whatever~ no matter what it is, it is a pump used to water the boiler.
The main ones used in power plants are electric feed pumps and steam feed pumps. The electric feed water pump is driven by the power of the plant to drive the motor to rotate, so as to drive the rotation of the feed pump to send the feed water to the boiler side. The steam feed pump is driven by a small steam turbine to drive the steam turbine to drive the feed pump. Generally, two 100% load electric feed pumps (one transport and one backup) or two 50% steam feed pumps (operational) and one 30% electric feed pump (standby) are installed in the power plant to meet the load demand of the power plant.
It feels like a psychological test (clockwise, counterclockwise?)
Fluid couplings
In addition to the pump body and motor, another important device of the electric feed pump is the hydraulic coupler, to put it bluntly, that is, the coupling, which is used to connect the motor and the feed pump to transmit energy, but through the liquid (lubricating oil) as the transmission medium, it can be continuously changed.
The fluid coupling is mainly composed of pump wheels, turbines, rotating inner sleeves, spoon tubes and other components. The pump wheel and the turbine have the same shape and the same effective diameter, in order to avoid resonance, the number of blades is different, generally 1~4 pieces.
(The picture above shows the clear separation of the pump wheel and the turbine)
Principle of fluid coupling adjustment
The transmission of the fluid coupling is mainly carried out by the interaction between the pump wheel and the turbine. The pump wheel is mounted on the input shaft and the turbine is mounted on the output shaft.
The prime mover (motor) drives the pump wheel to rotate at a certain speed, and the working oil in the pump wheel flows to the periphery of the pump wheel from close to the shaft under the drive of the blades, and in the process of flowing, the working oil obtains energy from the pump wheel, and the working oil rushes into the turbine along the direction of absolute speed at the outlet of the pump wheel. The working oil rushed into the turbine first acts on the peripheral blades to drive the rotation of the turbine, and then slowly flows out of the turbine outlet and re-enters the pump wheel, thus continuously circulating.
How is the legendary stepless speed change realized, there is a magic device is the spoon tube, the operator can change the speed of the feed pump by adjusting the opening of the spoon tube in the DCS, so as to change the amount of water supply. The ultimate goal of changing the opening of the scoop tube is to change the working oil flow in the fluid coupler, thereby changing the torque and slip of the transmission (the difference in speed between the pump wheel and the turbine), and finally drive the electric feed pump according to the requirements of the working conditions. When the scoop tube is deep to the bottom of the working chamber (0% position), the working chamber has the least working oil, and the output speed is the lowest. When the scoop tube is removed (100% position), the cavity has the most working oil, and the output speed is maximum.
1 actuator 2 cam 3 spoon tube 4 positioning cylinder 5 control valve 6 control spool 7 control guide sleeve 8 spoon tube position 9 cavity 1 10 cavity 2
The oil circuit of the working oil
The working oil enters the coupler through the flow control valve, and due to the centrifugal force acting on the coupler as it rotates, an oil ring is formed in the working chamber. The position of the scoop tube determines the thickness of the oil ring in the working chamber. The scoop tube delivers the working oil directly to the oil cooler for cooling, which is then returned to the coupler through the flow control valve.
The actuator controls the cam in the direction of the maximum output speed (100%), the control valve core moves to the direction of the spoon tube and the control oil enters the cavity 1 of the oil cylinder, the piston drives the spoon tube to move in the direction of 100%, the working oil pump supplies oil to the working oil circuit, the control guide sleeve moves along the chute of the spoon tube, and the control oil is turned off when the spoon tube reaches 100% position.
(After converting to GIF format, the speed display is not obvious)
Fusible plugs
When the fluid coupling is operating, the circulating circle formed by the pump wheel and the turbine is mostly working oil (and a little air). Due to the existence of slip in the energy transfer process, the temperature of the working oil will rise (so the presence of an oil cooler is required). At the gear ratio i = 0.666 (the ratio of the output to the input), the power loss of the fluid coupling is large and the oil temperature is the highest. Due to the increase in oil temperature, the air expands by heating, which may cause damage to the pump wheel and turbine explosion. For this purpose, a fusible plug is installed on the rotating inner sleeve, and when the oil temperature in the phantom circle rises to 160 °C, the fusible plug melts, and the working oil in the circulating circle is discharged from the plug hole together with the air, and the turbine stops rotating. In normal operation, the oil pump feeds oil to the hydraulic coupler, and the spoon tube continuously discharges the oil to the oil cooler, so ~ without accidents, it will not let you see the phenomenon of the fusible plug melting.
Feed pump cavitation
When the feed pump is running, when the inlet pressure is lower than or equal to the vaporization pressure at the current temperature, the liquid will vaporize, resulting in the water containing bubbles, and the bubbles will burst due to condensation during the continuous pressurization of the water pump, and the active gas in the bubbles will cause impact on the impeller blades and cause chemical corrosion to the metal. The surrounding water rushes into the space of the original bubble at a very high velocity, forming a high-frequency local water hammer. This water hammer will cause repeated impacts on the metal surface of the pump, causing metal fatigue and metal erosion.
In addition to causing damage to metal equipment (impellers, etc.), cavitation will reduce the head and efficiency of the pump, and will also generate vibration and noise and even resonance. Therefore, it is necessary to avoid cavitation during operation. Therefore, in order to prevent the occurrence of cavitation in power plants, it is generally equipped with a pre-pump (to increase the pressure) and the feed water flow is circulating (to prevent the water temperature from rising and vaporizing when the load is low).
The steam feed pump adjusts the speed of the feed pump through the load of the small steam turbine to adjust the feed water flow, which can save a large part of the power plant electricity for the power plant, thereby improving economic benefits. For small units, the power saved in the plant is not as efficient as this part of the pumping work, or the electric feed pump is more cost-effective.