1 Causes and harms of the cavitation erosion of the feed pump The cavitation occurs when the liquid pressure at the inlet of the centrifugal feed pump impeller is equal to or lower than the saturation pressure of the liquid at this temperature. Cavitation is mainly caused by the combination of mechanical erosion and chemical corrosion. As a result, the performance of the feed water pump is reduced, vibration and noise are generated, and the service life of the pump is shortened. As cavitation aggravates, it will cause a cut off, the pressure will drop sharply, and normal work cannot be maintained. Especially after turbine load rejection, the feed pump loses pressure due to steam erosion, resulting in boiler water shortage, burning of the water wall and shutdown of the furnace.
The most dangerous condition of the feed pump is when the turbine throws a full load, the heated extraction steam entering the deaerator falls to zero, and the pressure drop rate in the deaerator is the maximum, so that the rich pressure head at the inlet of the feed pump is reduced to a minimum value. Even less than zero, causing serious cavitation, causing boiler accidents.
2 Prevent the cavitation condition of the feed pump during the load rejection process of the turbine If the cavitation of the feed pump does not occur, the effective NPSH at the inlet should be greater than the required NPSH of the pump, ie: Hg-static inlet of the feed pump Suction head (MPa);hw* Resistance loss of the suction pipe of the water pump (MPa); *Saturation pressure (MPa) corresponding to the inlet of the water pump; Requires NPSH of the pump (MPa) NPSH* Rich pressure of the water pump head.
In the Journal of Jiangxi University of Electric Power Workers (2):! A means to prevent the cavitation of the feedwater pump when the deaerator is in a stable condition; (2) Characterizes the conditions for the cavitation erosion of the feedwater pump in the transient process of the deaerator when the load is removed from the turbine. When the deaerator is in stable operation, Ps=Pd,=0, Anpsh>0, so the feed pump is not cavitation; but when the load is dumped, the pressure of the deaerator falls instantaneously, although the feedwater temperature in the deaerator tank is reduced accordingly. However, the water temperature at the inlet of the feedwater pump cannot be reduced in time. It is only after the pump's suction tube changes its water for the first time that it begins to fall. Obviously, in this transient process, the temperature of the two waters is not equal at the same time and the corresponding saturation pressure is not equal. It can be seen that during the transient process of the deaerator, in order to prevent cavitation at the inlet of the feedwater pump, its rich head must not only be greater than zero, but also have a certain margin to compensate for the dynamic landing of the NPSH at the pump inlet during transients. The operation of the deaerator is a transient process when the unit is under load dump. For each unit, the dynamic drop value of the NPSH in the feedwater pump under transient conditions is different. To ensure the feed pump is under the most dangerous conditions Cavitation does not occur and the condition of Anpsh=Ai-Ah>0 should be satisfied.
The dynamic maximum value AHmax of the feedwater pump NPSH is determined using the formula AHm*K=dynamic value in the process. It is determined to apply the transient process of the water supply in the deaerator tank in the transient process. Ps, Pd, and Ps are checked on the steam property chart. Vs, Vd. 3 General Procedure for Determining Cavitation of Feedwater Pump in Turbine Load Rejection Process 1Ah Calculation (1) Obtain the following instantaneous parameters for full load rejection: M deaerator tank water storage (kg); Ma——vehicle Condenser hot well outlet to deaerator inlet condensate water capacity (kg) Mb--low inlet to deaerator condensate water capacity (kg); Mc* deaerator to feed pump inlet suction Water capacity (kg h0 a - condenser water wells in water wells (kj / kg); hH condensate water drop rate a = (2) using the following formula to calculate hH ten Mmax * at the time accumulated into the deaerator coagulation Water quantity (kg); hs one--water supply inlet (kj/kg) hd(3) of the feed pump inlet According to hs, hd, check the water vapor nature chart, calculate Ps, Pd, Vs, Vd. 3.2 Calculate deaerator Ai hw, a pressure head in stable conditions - the resistance loss of the feed pump suction pipe, calculated according to the pipe resistance formula (M Pa); Air* pump must evaporate excess, see feed pump instructions.
3.3 Calculate the ANPSH when full load is thrown off, and discriminate whether the feed pump evaporates Cheng Shaobing, Wang Xiaoling: prevent the cavitation of the feed pump during the load rejection process of the turbine and measure the cavitation.
4 Prevention of Cavitation Erosion of Feedwater Pumps in Turbine Load Rejection Process The principle of preventing cavitation erosion of feed-water pumps during full-load rejection is to make NPSO 0, and to seek to reduce the situation where it is not possible to increase the elevation of the deaerator to increase the head of the feed pump. , The following methods can be used to prevent and improve the cavitation of the feed pump: (1) Do a good job of management. In a thermal power plant, since saturated water is delivered, the feedwater pump is liable to generate cavitation during operation. Therefore, during low-load operation, the recirculation gate must be opened to increase the flow in the pump, thereby improving its anti-cavitation performance.
(2) Add steam source for equipment. The back pressure from the neighboring machine is decompressed and connected to the deaerator to extract the steam. When the unit suddenly dumps the load, it quickly cuts the steam for the neighboring steam source and reduces the pressure drop in the deaerator.
(3) Improve the condensate system. The condensate of the main condensate system is injected into the suction pipe at the inlet of the water pump. When the load is dumped, the condensate enters the inlet, accelerating the drop of the temperature of the feed water, shortening the lag time of the water temperature reduction in the transient process, and reducing the pressure corresponding to the temperature below The cavitation time and cavitation amount occur due to the saturation pressure, thereby improving the anti-cavitation performance of the feed pump.
(4) Transform the feed pump suction pipe to minimize the suction pipe hw. Reasonably increase the diameter of the suction pipe, while shortening the pipe as much as possible to reduce the flow rate and improve the anti-cavitation performance. Straighten and straighten the suction pipe of the feed pump to reduce the elbow and horizontal pipe section and reduce the resistance loss.
Increase deaerator tank volume. The volume of the feedwater tank is increased. When the load is dumped, the water in the water in the tank is flashed. On the one hand, some heat storage is absorbed, and on the other hand, the pressure of the deaerator is further prevented from decreasing, thereby improving and preventing further cavitation of the feedwater pump.
(6) Device front pump. Before the power plant's feed pump is generally set to the front pump, composed of a pre-pump centrifugal pump series system. After the liquid is pressurized by the front pump, the pressure of the liquid at the inlet of the main pump is increased, thereby improving its anti-cavitation performance.
5 Conclusions (1) When calculating the dynamic maximum value of NPSH at the inlet of the deaerator transient process, the maximum inlet steam quantity of the unit and full load rejection shall be the conditions to ensure that the feed pump can still be guaranteed under the most dangerous conditions. The normal operation.
The principle of preventing cavitation in feed pumps should be maximized and minimized
This tester can test the trailer socket on the
vehicle. It is used to directly test whether the
trailer power supply wiring is normal or not. With LED indicators, it can indicate
any fault on the wiring of the car or the trailer.
How to test the connection of a Trailer (can also be a caravan or bicycle
carrier)
1. Put the plug in the connection of the tester.
2. Press the yellow button on the side of the tester.
3. If the wiring is good, all the LEDs light up. the function of each LED is
(acc iso 1724):
left hand indicator (yellow);
fog light or 12V (blue);
mass (white);
right hand indicator (green);
right rear light (brown);
left brake light (red);
left rear light (black).
Attention: The pin no 2 can be used either for a warning fog lamp or a
permanent 12V connection.
4. If a LED doesn't light up, it is because the corresponding wire is
defective. If all the LEDs don't light up.
1. Put the tester in the socket of the car.
2. Press the yellow button on the side of the tester.
3. If the wiring is good, all the LEDs light up. Do again steps 4 as previous.
You can also test the functions of each pin of the socket.
1. Switch on the left hand indicator (after switching on the ignition key).
2. The corresponding LED must flash with the same frequency. If not, left hand
indicator wiring is defective/broken.
3. Repeat steps 1 and 2 for the right hand indicator, rear light, fog light and
stoplights.
Note: Light shooting and different displays may cause the color of the item in
the picture a little different from the real thing. The measurement allowed
error is +/- 1-3 cm.
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