When the recirculation pipeline is running, the vibration amplitude of the outlet pipeline of the boiler water pump is large, and the minimum flow valve recirculation port is fully opened but the vibration cannot be eliminated, which affects the stable operation of the entire unit. The outlet valve of the boiler feed water pump is slightly adjusted, and the pipeline vibration is reduced. On-site investigation of the operating conditions, the unit added a frequency converter and changed to a speed-regulated operation, the operating conditions of the boiler water pump changed, and the pump pipeline fluctuated greatly.
Analysis of Causes of Vibration of Outlet Pipes of Boiler Water Pump
Drawing on the experience of pipe vibration in the past, the possible reasons for the pipeline when the boiler water pump is operating can be roughly considered from the following aspects.
1. Pipeline vibration caused by the two flows of vapor and liquid
Due to poor design and installation or improper operation and operation, a large amount of gas is generated inside the pipeline when the equipment is running. If it cannot be discharged in time, a two-phase flow of vapor and liquid will be generated. When the two-phase flow is flowing, the vapor and water will impact the pipeline and cause vibration.
2. Vibration caused by the vaporization of the water pump
When the inlet pressure of the water filling pump is lower than the saturation pressure corresponding to the inlet water temperature, and when the outlet flow rate is less than the minimum flow rate of the pump, vaporization will occur. When the feedwater pump is vaporized, the outlet pressure and flow rate of the feedwater pump drop or shake, the pump body and pipes produce noise and abnormal vibration, and the current of the water pump motor drops and shakes.
3. Changes in equipment operating conditions
The boiler water pump of unit 1# and 3# on site was changed to frequency conversion speed regulation operation, and the operating conditions changed. When the speed is adjusted to 2000 rpm, the flow rate drops to 2/3 of the full load flow rate, and the head pressure drops to 4/9 of the full load pressure. The pressure drop trend is faster than the flow rate. When the pressure drops by a certain value, the flow rate drops less, and the water flow is blocked at the minimum flow recirculation port, which causes the water flow to be unsmooth, and then causes the pipeline to vibrate.
Solutions to the Vibration of the Outlet Piping of Boiler Water Pump
According to the analysis of the cause of the pipe vibration of the boiler water pump, the following two options are considered
(1) A bypass pipeline is added to the recirculation pipeline, and a stop valve is installed on the bypass pipeline to control the flow. This method can make the water flow smoothly, and solve the problem of pipe movement. However, because the shut-off valve needs to be manually opened and closed, quantitative control cannot be achieved, resulting in low efficiency. If an electric shut-off valve is added to the bypass pipeline, an additional set of data lines needs to be added to connect the electric shut-off valve data signal back to the main control room. To achieve on-site control
(2) According to the actual operating conditions of the site, according to the performance curve of the water pump, find out the operating point when the speed is 2000 rpm, and calculate the minimum flow rate and the pressure value of the pump inlet and outlet under the operating condition. The actual parameters are compared. The valve factory redesigned and calculated the flow area, flow size and throttling form, and increased the flow aperture and flow area of the minimum flow valve to match the unit speed regulation and stable operation.
The program must repurchase the minimum flow recirculation and comprehensively consider the conditions that may be implemented on site and the economics of the program. In order to ensure the long-term stable operation of the unit, after negotiation, the minimum flow valve was selected to be repurchased to achieve automatic control and adjustment in the main control room.
