A. Function
The feed pump recirculation system is an automatic protection device for the feed pump.
When the boiler feed pump is under the condition of startup and low load, when the flow rate is lower than the minimum allowable flow rate of the boiler feed pump, in order to prevent the boiler feed pump from vaporizing and protect the boiler feed pump, part of the water needs to be returned to the deaerator through the recirculation valve.
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B. Several typical recirculation systems for feed pumps
1. Boiler feed pump minimum flow valve + pressure reducing device
This control method adopts a specially designed parallel gate valve (minimum flow valve) + pressure reducing device, and implements switch control. When the output flow of the feed pump is less than its minimum flow, the minimum flow valve opening signal is output, and the minimum flow valve opens; when the feed pump output When the flow rate increases to a certain flow rate, the output minimum flow valve closing signal is output, and the minimum flow valve is closed. The minimum flow valve control method adopts a non-adjustable actuator, which has reliable switching, tight closing and low cost.
2. The minimum flow valve (with throttling device) of the boiler feed pump, that is, the regulating recirculation valve.
This control method adopts a regulating recirculation valve (minimum flow valve) with a throttling device, and implements switch control. When the output flow of the feed pump is less than its minimum flow, the minimum flow valve opening signal is output, and the minimum flow valve is opened; when the feed pump When the output flow increases to a certain flow, the output minimum flow valve close signal, the minimum flow valve closes. The minimum flow valve control method adopts a regulating type actuator to realize continuous regulation.