1. Fault condition When the liquid regulating pump was put into operation after an overhaul, it was found that the automatic adjustment characteristic of the oil supply deteriorated. When the injection is automatic, there is a large flow fluctuation, sometimes reaching about 80t/h, which seriously affects the normal operation of the unit. In order to analyze this problem, the control system of the normal pump was switched to the faulty pump, and the same fault problem occurred, thereby basically eliminating the cause of thermal control.
2. Adjustment of the oil pump hydraulic coupling
In the 1990s, the hydraulic coupling was rapidly developed in China, which solved the problem of throttle regulation of the fixed speed fuel pump and effectively saved the power consumption of the plant.
The adjustment of the hydraulic coupling is to adjust the speed of the oil pump by adjusting the amount of oil discharged from the turbine through the spoon tube, so as to adjust the flow rate. The 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 scoop tube can be made.
g=G/Gmax(1)
Where: G is the output flow of the pump, t/h; Gmax is the maximum output flow of the pump, t/h.
μ=α/αmax(2)
Where: A is the angular displacement of the spoon tube; Amax is the maximum angular displacement of the spoon tube.
K=dg/dμ=αmax/Gmax·dG/dα(3)
K is the slope of the curve, which is the amplification factor or the adjustment characteristic coefficient.
In the ideal state, K=1, that is, the inclination angle is 45b. During the speed adjustment process of the hydraulic coupling, the flow rate changes smoothly, and does not cause a mismatch between the adjustment amount and the flow rate.
K "1, the flow changes slowly, which is not conducive to tracking the need for load adjustment.
When K"1, the flow rate changes too fast, which may cause the flow to fluctuate greatly, causing the oil level of the steam drum to be unstable, and the oil pump is frequently adjusted, which may cause the pump shaft to break.
3. Performance test of liquid regulating pump
In order to find the cause of the failure, the pump was subjected to a characteristic test using a conventional test method. Check the relevant meter before the test.
During the test, the load of each working condition is shown in Table 1. The oil after the pressure is raised by the liquid pump is passed through the flow orifice as much as possible to reduce the test error. Each desuperheating oil should be used as little as possible and corrected accordingly. On this basis, the relevant data is copied.
4, failure analysis
During the test, the spoon was manually operated, the flow rate did not fluctuate, the current was stable, and the balance pressure was normal, indicating that there was no turbulence in the pump shaft. The motor works normally and the hydraulic coupling can operate normally at each load point. According to the needs of load regulation, the asphalt pump has a great change in flow rate whenever the hand-held device is operated. It is difficult to control the flow rate required. When the stroke of the spoon changes from 61 mm to 71 mm, the flow rate changes from 284 t/h to 430 t/h. The linearity of the whole speed control system is good but the curve is steep. The change of the opening degree is 1%, and the flow rate changes by 11.23t/h. The flow rate of the oil pump is determined by the speed of the oil pump. The pump shaft is mounted on the turbine of the hydraulic coupling, and the speed of the turbine is determined by the amount of oil returned by the spoon. If the amount of oil change in the unit stroke is too large, it will seriously affect the stability of the pump flow. To this end, the rate of change in the amount of oil returned by the spoon should be reduced.
4.1 Magnification factor K
The maximum stroke of the spoon tube is 110mm, and the maximum flow rate is 440t/h. According to Table 1, the flow rate changes from 284t/h to 430t/h, and the stroke changes from 61mm to 71mm.
K=dg/dμ=αmax/Gmax·dG/dα=(110/440)·[(430-284)/(71-61)]=3.65
Then the inclination angle of the curve is 74.7b, which indicates that the curve is steep, which is the main reason for the instability of the hydraulic coupling. In order to improve the adjustment performance of the hydraulic coupling, it is necessary to solve the change amount of the oil return amount of the spoon tube, so that the oil return amount is reduced under the condition of the same opening degree variation.
4.2 The cam reinstalled the removed old cam. After the operation, the asphalt pump found that the improvement of the hydraulic coupling adjustment performance was not obvious. To this end, the cam profile is changed at the same time as the cam is added, so that it is adapted to the needs of load regulation. That is, below 50% load, the cam profile is steep; in the interval where the load is often adjusted, the cam profile is relatively flat; the profile of the remaining load zone is also steep. Botou Taibang Pump & Valve Manufacturing Co., Ltd. 4.3 Reduce the rack and pinion ratio When the hydraulic coupling is adjusted, the cam drives the rack up and down, the rack drives the gear, and the gear then drives the fan gear, causing the spoon to open. The change in degree adjusts the flow rate of the oil. The adjustment of the spoon tube is driven by the rotation of the sector gear, and the rack gear is driven coaxially with the sector gear. Reduce the rack-to-gear ratio, that is, increase the gear diameter, extend the length of the rack, and ensure the opening and closing of the spoon. The asphalt pump reduces the rack-to-gear ratio, that is, the cam of the same stroke, the opening degree of the sector gear becomes smaller, and the oil return adjustment amount of the spoon tube becomes smaller, thereby reducing the fluctuation of the oil supply flow rate.
5, processing methods and results
According to the above analysis, the asphalt pump has taken corresponding measures. First consider adding a cam. If the cam is not effective, consider using computer adjustments. The difficulty of adding a cam is relatively small, easy to implement, and the profile of the cam is improved. According to the load interval of the normal operation of the unit, it is considered that the cam profile is steeper than 50% load; under 50%~100% load, the corresponding profile line is relatively flat. At low loads or during start-up, the pump can maintain a high flow rate due to the need to open the feed pump recirculation valve.
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Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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