Fault Analysis and Disposal Technology of Feed Pump Speed ​​Regulation System
Boiler feed pumps are generally equipped with speed control devices, such as hydraulic couplings, the role is based on changes in unit load to adjust the flow to the pump to reduce throttling losses, thereby saving energy.
Hydraulic coupling speed control feed pump (hereinafter referred to as liquid-controlled pump) operation, should be able to put into automatic adjustment to reduce the operation of personnel operations, the speed range should reach 25% to 100%. However, some liquid-phase pumps have a large rate of change of speed, which causes large fluctuations in the flow rate, which may lead to the occurrence of a broken shaft accident.
A power plant pump by the front pump, the main feed pump, hydraulic coupling and growth gear composition. Front pump driven by the motor spindle, the main feed pump by the motor through the growth gear, hydraulic coupling drag. The front pump model is QG50080, the main pump model is DG480180, the hydraulic coupling model is C046, which is the product of Shanghai Electric Power Plant.
1, fault conditions
When the liquid pump is put into operation after a maintenance, it is found that the automatic adjustment of the water supply is deteriorated. When cast automatically, there is a large flow fluctuation, sometimes up to about 80t / h, seriously affecting the normal operation of the unit. To analyze this problem, switching the control system of a normal pump to a failed pump presents the same problem of failure, thereby essentially eliminating the causes of thermal control.
2, to the pump hydraulic coupling adjustment
In the 90s of last century, the hydraulic coupling developed rapidly in China, which solved the throttling regulation problem of the constant speed feed pump and effectively saved the power consumption of the factory.
Hydraulic coupling adjustment is through the spoon pipe turbo drain to regulate the pump speed, so as to achieve the purpose of regulating the flow. The change in flow rate Q is proportional to the speed n.
According to the characteristic curve of the pump, a curve of the relative value g of the flow rate and the relative angular displacement L of the spoon pipe can be made.
g = G / Gmax (1)
Where: G is the pump output flow, t / h; Gmax is the maximum pump output flow, t / h.
μ = α / αmax (2)
Where: A is the spoon tube angular displacement; Amax spoon tube maximum angular displacement.
K = dg / dμ = αmax / Gmax · dG / dα (3)
K is the slope of the curve, which is the amplification factor or adjustment coefficient.
In the ideal state, K = 1, that is, the inclination angle is 45b. During the process of speed adjustment, the hydraulic flow changes smoothly and does not cause the mismatch between the adjustment amount and the flow rate.
K "1, the flow changes slowly, is not conducive to tracking the need for load adjustment.
K "1, the flow rate changes too fast, easily lead to fluctuations in the flow up and down, resulting in drum water level instability, frequent adjustment of the pump may cause shaft rupture.
3, liquid-controlled pump performance test
To find the cause of the malfunction, the pump was tested for its properties using conventional test methods. Check the relevant meter before the test.
Test, the load in each case in Table 1. Through the liquid pump to enhance the pressure after the feed water through the orifice as much as possible to reduce test error. Minimize the use of water, and give the appropriate amendments. On this basis, copy the relevant data.
The test results of the relevant curves shown in Figure 1,2. Figure 1 opening for the terminal opening.
4, failure analysis
During the test, the spoon pipe was manually operated, the flow did not fluctuate, the current was stable and the balance pressure was normal, indicating that there was no movement of the pump shaft. The motor is working properly and the hydraulic coupling can operate normally at each load point. According to the needs of load regulation, when operating the Communicator, the flow has undergone great changes, it is more difficult to control the required flow (Figure 2). Spoon tube stroke changes from 61mm to 71mm, the flow changes from 284t / h to 430t / h. It can be seen from Fig. 1 that the whole speed regulation system has a good linearity but a steeper curve, and the opening degree changes by 1%. The flow rate changes to 11.23t / h and the flow rate of the feed water pump depends on the speed of the feed water pump. The pump shaft is mounted on the turbine of a fluid coupling, and the turbine speed depends on the amount of oil returned to the scoop. If the return stroke unit within the amount of change is too large, will seriously affect the stability of the flow to the pump. To this end, should reduce the rate of change of spoon pipe back to the amount of oil.
4.1 Magnification factor K
Spoon tube maximum travel of 110mm, the maximum flow of 440t / h According to Table 1, the flow from 284t / h to 430t / h, stroke from 61mm to 71mm.
K = dg / dμ = αmax / Gmax · dG / dα = (110/440) · [(430-284) / (71-61)] = 3.65
The inclination of the curve is 74.7b, indicating that the curve is steep, which is the main reason that causes the instability of the speed governing performance of the hydraulic coupling. To improve the performance of hydraulic coupling adjustment, it is necessary to solve the change of the amount of oil return to the spoon tube, so that the amount of return oil decreases with the same opening degree of change.
4.2 Cam
The demolition of the old cam re-install, put into operation, found that the hydraulic coupling to improve the regulatory performance is not obvious. To this end, plus the cam at the same time, change the cam profile, to adapt to the needs of load regulation. That is, under 50% load, the cam profile is steeper. In the region where the load is adjusted constantly, the cam profile is relatively flat and the profile line in the other load regions is also steeper.
4.3 reduce rack and gear ratio
When the hydraulic coupling is adjusted, the cam drives the rack to move up and down, and the rack drives the gear, which in turn drives the sector gear, thereby causing the change of the spoon opening and regulating the feed water flow. The adjustment of the spoon tube is driven by the rotation of the sector gear, which drives the gear coaxial with the sector gear. Reduce the ratio of gear rack and gear, that is, increase the gear diameter, extend the rack length, to ensure spoon tube open and closed strict. Which reduces the gear ratio of the rack and the gear, that is, the cam of the same stroke, the opening of the sector gear becomes smaller, and the return oil regulation of the spoon pipe becomes smaller, thereby reducing the fluctuation of the feed water flow.
5, treatment and results
Based on the above analysis, take corresponding measures. First consider increasing the cam, if you increase the cam is invalid, then consider the use of computer regulation and other measures. Increasing the difficulty of the cam is relatively small, easy to implement, and the profile of the cam has been improved. According to the unit load range of normal operation, taking into account the load below 50%, the cam profile steep; at 50% to 100% load, the corresponding profile is relatively flat. At low loads or during startup, the pump can also maintain a high flow rate due to the need to turn on the feed pump recirculation valve. Increase the cam and improve the line after the flow and related parameters in Table 2.
Increase the cam after the entire governor system characteristic curve shown in Figure 3,4.
As can be seen from Fig. 4, the return of the original cam has little effect on the spoon tube itself. The spoon tube stroke is at (60-70 mm) with a slope of 3.45. According to Table 2, after the improvement of the cam profile, the slope of the whole speed control system (including the hand terminal) is 100/440 · [(416-274) / (71-48)] = 1.4, the inclination is 540, Amplitude decreases, basically meet the needs of load regulation, as shown in Figure 3. Unit through the above transformation after normal operation.
5, concluding remarks
Hydraulic couplings are generally equipped with a cam, and sometimes in order to prevent the cam jams and cancel the cam, because of regulatory characteristics of the scoop tube is not clear, put into operation before the speed governing system has not been static, dynamic flow curve test , Put into operation may occur after the adjustment performance is not good, but also may cause fatigue fracture shaft. Once found to pump fluctuations in flow, it is necessary to find out the cause of the malfunction, take appropriate precautionary measures.
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