Sewage pumping station power saving problem?

What are the specifics of the sewage pumping station power saving problem, the following Zhongda consulting for you to answer.　

0. Preface As the water in the sewage network comes from precipitation and various types of user wastewater, it is affected by the complexity of timing, crowd behavior and pipeline damage and leakage and other factors. Its flow is uncertain and difficult to predict, if the drainage is poor or untimely, will directly lead to the sewage outside the nuisance, the consequences of which are **** know.　　Municipal departments in order to meet the daily drainage needs, generally in the same pumping station are equipped with multiple pumps for drainage configuration. Specific project implementation due to the uncertainty of the actual flow of the network, difficult to predict, the machine pump simple configuration is difficult to do the flow of the inverted pumping station Qλ = Q out (pump flow) the best flow control situation. The resulting adverse effects are analyzed as follows.

1. Two typical configuration analysis 1.1 Qλ> Q out of the work When the flow of the pumping station flow Q & gt; Q out, will lead to the pumping station inlet sewage wells and pipeline network in the sewage level rises, with the water level rises, the actual head of the pumps become smaller, because △ H for the loss of pipe resistance, H pumps = H0 + △ H (1) formula (l): H0 is the difference between the water level of the water inlet and outlet of the pump Axial pumps are low-head sewage pumping station. Is a low head sewage pumping station commonly used pumps. When the head is reduced, the pump discharge flow rate increases; but each pump in the constant speed state to regulate the flow rate is limited. At the same time, a single too large displacement flow will also cause some other problems. Such as cofferdam structure pumping station due to a substantial increase in the pump discharge will make the cofferdam gate stagnation impact enhancement; that is, the machine pump outlet due to stagnation will form additional water column △ H, which is equivalent to an increase in the actual head of sewage pumping machine △ H, which produces pressure can also be regarded as an increase in the pump pipe resistance; and the increase in the pump resistance torque, so that the motor accelerated the effective output torque changes, so that △ n speed difference increases, so that pumping flow rate △ Q changes increase, which is not conducive to the stable operation of the pump system. This periodic change of pipe resistance △ H makes the pump machine working point swing, not only increases the drainage energy loss and will bring machine pump system vibration and noise due to changes in liquid flow, but also cause cavitation phenomenon tends to be heavy, the machine and pump efficiency decline; too high water level operation will cause the pipe network sewage flow rate is too slow and stagnant, reducing the ability of the pipe network to absorb the peak flow, which is one of the direct causes of overflow of sewage at low elevation section and overpressure pipe breakage.　　1.2 Qλ In this condition, the pumping station intake well and the pipe network in the water level drops rapidly, by the formula (l) know: the actual operating head of the pumping machine rises; with the rise in head, the pump pumping machine per minute pumping flow Q will be reduced, the machine and pump the corresponding efficiency is reduced. When the flow rate is small to about 40% of the design flow rate, axial pumps may be into the Q-H saddle-shaped characteristics of the operation of the area, then the pipe resistance characteristics and Q-H characteristics will lose the fixed intersection. Under certain conditions, due to the head H can be seen as proportional to the flow and time of the integral, flow, head instability brought about by the vibration and noise intensification, it is difficult to normal operation of the pump. If the head of the further increase into the small flow area, the axial pump inlet flow angle of attack becomes positive, resulting in reflux and vortex, pump corrosion phenomenon is aggravated and may produce wheezing. Therefore, when entering the critical submerged water depth, the regulations must stop. In addition, it should be noted that the number of frequent starts and stops shall not exceed the permitted number of starts and stops of the pump. In Qλ

2. Frequency conversion speed regulation drainage power-saving principle Simply put, in the ideal target water level, liquid level, flow sensors to the current water level and pipe network sewage flow rate into an electrical control signal, adjust the frequency converter VVVF output frequency f, change the pump motor speed n and pump discharge flow Q. By changing the speed to achieve the regulation of the discharge flow rate, so that the Qλ = Q out of the sewage pumping station to control the sewage pumping station effectively. The water level of the inlet well and pipe network. As the ideal target water level is selected, the pump head is reduced and the pump runs in the high efficiency area, so the power saving effect is good. Frequency control sewage pumping station drainage power saving control system, usually consists of VVVF frequency converter, PLC programmable controller, sensors, PID regulator, switching contactor KMI-KM3 and thermal protection relay KH1-KH3 and so on. It can track the sewage pumping station inlet sewage flow to meet the discharge requirements and can achieve good power savings.　　As we all know, constant pressure frequency conversion water supply system regulates the flow mainly by reducing the valve and pipe resistance energy consumption. System to regulate the pressure at the outlet of the network for the control volume constitutes a closed-loop system; and in the sewage pumping station frequency control drainage system, there is no obvious valve pipe resistance, and its energy saving lies mainly in the pump into the well (or network) ideal target water level selection, as well as outlet weir hysteresis additional head control, that is: (1) a reasonable choice of control pumping station pump into the well water level, reduce the head; the head of the pump is the best working head, and try to avoid high head "to avoid high head". Try to avoid high head "deep well" water consumption.　　(2) the control of the pump running point; in particular, the flow rate Q adjustment range selection, the flow rate should not be too small.　　(3) control the pump outlet cofferdam stagnation additional head △ H, according to the actual situation to reduce the cofferdam gate position.

3. Conclusion Sewage pumping station sewage impurity content and a certain degree of corrosiveness, therefore, should be selected to have good anti-corrosion and impact performance of the level flow sensor, if necessary, can be added to the PTFE corrosion sheath. The appearance of the best smooth and have a good anti-leakage layer, both to prevent impurity deposition, but also to facilitate routine cleaning and maintenance; of course, the stability of the level indicator should be good; flow response linearity is good. Variable frequency speed regulation sewage pump variable flow drainage, not only to improve the operating efficiency of the pump, but also to take full advantage of the pump inlet reasonable water level to reduce the head of power savings, but also to avoid blindly raising the water level operation and the impact of the network to absorb the peak flow of the ability to avoid the high head of the pump to take the water brought about by the deep wells to take the water energy consumption. This frequency conversion speed control drainage device by a pumping station in Hangzhou City, nearly two years of actual operation proved that: frequency conversion speed control variable flow drainage and industrial frequency power supply direct operation of drainage compared to the power-saving effect is extremely obvious, an average of 1,000 tons of water power savings amounted to more than 25kw-h, power saving rate of 53.6%. Frequency word speed drainage control system operation, generally no cofferdam gate stagnation caused by △ H impact, pump flow is smooth, the pump inlet pressure pulsation phenomenon is also significantly improved, machine vibration noise than the frequency operation of more than 15-20dB reduction. This is to improve the surrounding environmental noise has obvious benefits, so the urban sewage pumping station using frequency control drainage can achieve significant economic and social benefits.

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