Regulation mode and energy consumption analysis of centrifugal pump
Through the centrifugal pump and piping system characteristic curve analysis of the centrifugal pump flow regulation of several main ways: export valve regulation, pump speed adjustment and the pump string, parallel regulation. With the characteristic graph analysis of exit valve and pump variable speed regulating the energy loss of the two ways, and makes a comparison and pointed out centrifugal pump speed regulating the flow than outlet valve regulating the flow can better save energy, and energy-saving efficiency and flow rate changes in the size of about. In practical application, it should pay attention to the range of variable speed regulation, in order to better use of centrifugal pump speed adjustment.
Centrifugal pump is a kind of general fluid machine widely used in chemical industry system. It has a wide range of performance (including flow, pressure head and the nature of the transmission medium), small size, simple structure, easy operation, low operating cost and many other advantages. Usually selected centrifugal pump flow, pressure head may and piping requirements, inconsistent, or because the production task, process requirements change, this time require the pump flow adjustment, essence is to change the operating point of the centrifugal pump. The working point of the centrifugal pump is determined by the characteristic curve of the pump and the characteristic curve of the pipeline system. So, the change of the characteristic curve of any one can achieve the purpose of flow regulation. At present, the main flow of the centrifugal pump control valve control, variable speed control, and the pump and, in series, and so on. The principle of regulating a variety of different, in addition to their own advantages and disadvantages, the energy loss caused by are not the same, in order to seek the best, the minimum energy consumption, the energy saving flow regulation must be comprehensive understanding of centrifugal pump flow regulating the relationship between mode and energy consumption.
1. Main ways of pump flow regulation
(1) Change the line characteristic curve
Change the flow of centrifugal pump is the most simple method is to use the pump outlet valve opening to control, its essence is to change the position of the pipeline characteristic curve to change the working point of the pump.
(2) Change the characteristic curve of centrifugal pump
According to the laws and cutting the proportion of law and to change the pump speed, change pump structure (such as cutting impeller diameter method), the two methods can change the characteristic curve of centrifugal pump, so as to achieve the flow adjustment (change in pressure head at the same time). But work has been for pump, change pump structure is not very convenient, and due to the change of the structure of the pump, reducing pump versatility, although it at some time adjusting economic flows [1] is convenient, in the production are rarely used. The method of changing the speed regulating flow of the centrifugal pump is analyzed here. From Figure 1 analysis, when to change the pump speed control traffic declined from Q1 to Q2, the pump speed (or motor speed) from N1 decreased to N2 and speed for N2 pump characteristics of Q-H curve and the pipeline characteristic curve He=H0+G1Qe2 (Banlut curve does not change over to point A3 (Q2, H3), A3 to regulate traffic flow through the speed operating point. This adjustment method regulation effect is obvious, fast, safe and reliable, can prolong the service life of the pump, energy saving, in addition to a reduction in speed operation can effectively reduce the centrifugal pump NPSH NPSHr, away from the pump cavitation area, reduces the possibility of cavitation [2] centrifugal pump generation the. The disadvantage is to change the speed of the pump needs to have a frequency conversion technology to change the original motivation (usually motor) speed, the principle of complex, large investment, and a small flow regulation.
(3) Pump string, and even the way to adjust
When the single centrifugal pump can not meet the transport task, the centrifugal pump can be used in parallel or in series operation. Two same types of centrifugal pumps in parallel, although the pressure head changed little, but increase the total transport flow, the overall efficiency of the pump in parallel and single pump efficiency is the same; centrifugal pumps in series increase the total pressure head, flow changed little, the overall efficiency of the tandem pump and single pump efficiency.
2. Energy consumption analysis of pump under different regulation mode
In the analysis of energy consumption under different regulation methods, the article is only aimed at the current widely used valve regulation and pump variable speed regulation of the two ways to analyze. Because of the centrifugal pump and the series operation is to improve the pressure head or flow, in the chemical field of application is not much, its energy consumption can be combined with figure 2 analysis, the method is basically the same.
(1) Valve regulating flow power consumption
When the centrifugal pump is running, the motor input pump shaft power N is:
N = vQH / ETA
N - axis power, w;
Q -- the effective head of the pump, m;
H - the actual flow of the pump, m3/s;
V - fluid specific gravity, N/m3;
Efficiency of pump.
When the valve is used to adjust the flow rate from Q1 to Q2, the shaft power at the operating point A2 is:
NA2 = vQ2H2 / ETA
VQ2H3 - the actual useful power, W;
VQ2 (H2H3) - valve power loss, W;
VQ2H2 (1 / N - 1) - centrifugal pump power loss, W.
(2) Variable speed regulation of the power flow
In analysis of transmission to use centrifugal pump scaling laws, according to the application condition, the following analysis means of centrifugal pump speed range within + / - 20% and the efficiency of the centrifugal pump itself little change in [3]. With motor speed regulation flow to flow Q2, at the operating point of A3 pump shaft power consumption is:
NA3 = vQ2H3 / ETA
The same can be got by the transformation:
NA3 = VQ2H3vQ2H3 (1 / N - 1) (2)
Type of vQ2H3 - the actual useful power, W;
VQ2H3 (1 / N - 1) - centrifugal pump power loss.
3. Conclusions
For the common centrifugal pump outlet valve pump control and variable speed regulation two main flow regulation and pump variable speed regulation of saving energy consumption than the valve outlet regulating much larger, this can be from both the power analysis and power comparison analysis shows. The relationship between flow and head of centrifugal pump, can be more intuitive to reflect the two types of regulation of the relationship between energy consumption. By adjusting the pump speed to reduce traffic and to reduce the possibility of pump cavitation. When the flow decreases, variable speed regulation of the greater energy efficiency, the valve regulating power loss is, however, variable speed pump too large will result in lower efficiency of pump, pump proportionality law beyond the scope. Therefore, in the practical application should be considered from many aspects, in between the two integrated optimum flow rate adjusting method.
