Functions of boiler feed pumps
The main function of the boiler feed pump in the power plant is to regulate and stabilize the pressure and flow of the feed water. The boiler resistance and the regenerative system cycle need to overcome the system resistance, and the feed pump also provides power protection for the hydrodynamic cycle. In the whole unit, the outlet corresponds to the highest pressure, so the safe operation of the boiler feed pump cannot be ignored.
The task of the feed water pump is to supply the water in the deaerator storage tank with a certain temperature and to remove the oxygen, and then increase the pressure to the boiler to meet the needs of the boiler water. Cavitation is the biggest safety hazard to the feed pump. If the deaerated water enters the feed pump, its temperature will exceed the vaporization temperature of the water under normal pressure. When the inlet pressure of the feed pump is too low, the feed water will vaporize and a large number of bubbles will be generated. When these bubbles enter the high pressure zone, they will be rapidly deformed and collapsed due to compression, and this phenomenon will be blocked. The flow path causes local shock pressure fluctuations. The huge dynamic impact pressure will cause the metal material to cause sponge or honeycomb damage due to fatigue erosion, causing cavitation of the pump body and causing pressure fluctuations in the feed water.
In general, an additional pre-pump can be used to prevent cavitation by increasing the inlet pressure of the feed water. At the same time, it is also possible to combine the pipeline characteristics and reasonably select the operating conditions to ensure the safe operation of the feed pump.
Features of boiler feed pumps
Power plant boiler feed pumps are horizontal, single-suction, multi-stage segmental centrifugal pumps. Since the deaerator is a hybrid heating device, a pump must be used to increase the pressure into the boiler. This pump becomes a feed pump. The motor is easy to operate, flexible, and small in footprint. The steam turbine is dragged. It has steam lines and operating valves. It is troublesome to operate and has a large footprint, but it can be operated at variable speed without "throttle" loss. Therefore, in small and medium-sized thermal power plants, when the grid is connected, electric mode is generally adopted.
Only the isolated thermal power plant (when there is no grid) and the first phase of the project, in order to start the boiler for the first time, the boiler must be equipped with a starter boiler and a steam turbine. Drag the feed pump for the first start. The electric feed pump consumes the power generated by the power plant (factory power), which is converted from coal through a series of energy conversion, while the steam feed pump is the heat energy of the steam consumed, which is converted into coal by the boiler.
After the steam is doing work or not, the small steam turbine of the feed pump is directly dragged to the water pump. That is to say, there are two possibilities for the drag steam of the feed water pump small steam turbine. One is the new steam of the boiler, and the other is the steam extraction of the partial steam after entering the main steam turbine. The latter is to achieve the cascade utilization of energy and increase the amount of steam extraction.
There are two exhaust steamers, one is a deaerator that is discharged into the regenerative system, used as a heat recovery, and the other is discharged into the heating system as part of the heat supply. Therefore, the feed water pump steam turbine of the thermal power plant is a back pressure unit, and there is no cold. Source loss, high energy efficiency.
Case of 300MW Large Generators
Large generator sets (above 300MW units) generally adopt one electric feed water pump, two steam feed water pump, electric feed water pump as start-stop and emergent backup, and the electric feed water pump adjustment mainly relies on the hydraulic coupler spoon adjustment. Cooperate with the boiler water regulating valve.
After the steam feed pump is rushed and warmed up to 3000 rpm, it is transferred to the "remote control" mode, and the water supply is controlled by the speed adjustment. The steam source that drives the small steam turbine is the auxiliary steam and the four-way, cold-end reheat steam three-way steam source, and the exhaust gas is discharged into the condenser.
Since the deaerator is a hybrid heating device, a pump must be used to increase the pressure into the boiler. This pump becomes a feed pump. The motor is easy to operate, flexible, and small in footprint.
The steam turbine is dragged. It has steam lines and operating valves. It is troublesome to operate and has a large footprint, but it can be operated at variable speed without "throttle" loss. Therefore, in small and medium-sized thermal power plants, when the grid is connected, electric mode is generally adopted.
Only the isolated thermal power plant (when there is no grid) and the first phase of the project, in order to start the boiler for the first time, the boiler must be equipped with a starter boiler and a steam turbine. Drag the feed pump for the first start.
