Discussion on power consumption of secondary booster pump station for urban water supply in operation mode

0 Introduction

The process operation mode and reasonable configuration of equipment of urban secondary booster pumping stations determine the energy consumption of pumping stations. Under the same pump equipment configuration, the energy consumption of pumping stations using different process operation modes is different. So, what process operation mode is the best?

How to calculate its power consumption? The following is a study on the operation mode and energy consumption of the secondary booster pump station, and the best process control method is given at present.

1 Energy consumption of several common operating modes of secondary booster pump stations

At present, the process equipment configuration and process operation status of secondary booster pump stations in northern cities and towns are generally divided into four types:

1) Mode 1: Water pump full speed direct connection water supply mode;

2) Mode 2——Microcomputer controlled water pump variable frequency speed regulation constant pressure water supply mode;

3) Mode 3 - Microcomputer controlled water pump variable frequency speed regulation variable current and variable pressure water supply mode;

4) Mode 4 - Fully automatic pipe network direct connection without negative pressure secondary pressurized water supply.

1.1 Mode 1: Water pump full speed direct connection water supply mode

This water supply method is a booster pump of a secondary booster pump station. It directly supplies water from the water storage tank to users without any intermediate process equipment. It is a simple, practical and economical secondary booster water supply method. Assuming that there are two pumps in the pump station (one for use and one for backup), the water volume during the high day is qa, the daily minimum water volume is 0, the water volume range is 0~qa, the head loss at the most unfavorable point of the pipe network in the community is h0, the maximum pressure of the pipe network is hmax, the characteristic curve of the pump is f1, and the pipeline characteristic curve is f2. The working condition of the pump under the full-speed direct-connected water supply mode is shown in Figure 1.

As can be seen from Figure 1:

1) The water supply regulation of this pumping station is achieved by changing the characteristic curve f2 of the pipeline. The water supply pressure changes between ha and hmax with the flow rate q;

2) The electric power value when the water supply is qa is the area of ​​the graph enclosed by the characteristic curve f1 and the coordinate system (h, 0, q) Pa (1 hmaxAqa0);

3) When the water supply volume is qa, the actual required water supply electric power value is the graphical area P (h0Aqa0) enclosed by the pipeline characteristic curve f2 and the coordinate system (h, 0, q).

In the above calculation results, both formula (2) and formula (4) are accurate values, while formula (2) and formula (4) are engineering approximate values. When analyzing and calculating practical problems, the latter can generally meet the needs of engineering. In all the following analysis and calculation, the engineering approximate method is used.

1.2 Mode 2 - Microcomputer controlled water pump variable frequency speed regulation constant pressure water supply mode

Microcomputer-controlled water pump variable frequency speed regulation constant pressure operation is currently a widely used operation mode in the secondary booster pump station water supply process. This method changes the speed of the water pump to meet the changes in the water supply demand in the community, which not only maintains constant pressure water supply, but also greatly reduces the power consumption of the pump station, thereby reducing the power loss rate of the pump station. Its working condition is shown in Figure 2.

1.3 Mode 3 - Microcomputer controlled water pump variable frequency speed regulation variable current and variable pressure water supply mode

When the water supply pump station is at a low flow rate or zero flow rate, the head loss is large, the pump efficiency is greatly reduced, the power loss rate will increase, and the pump station cannot achieve the best energy-saving effect. In this case, the speed, flow rate and water supply pressure of the water pump unit are usually adjusted according to the water volume and pressure change law of the pipe network in the community, and the above problems are overcome. The operating characteristic curve of the pump station under this mode is shown in Figure 3.

1.4 Mode 4 - Fully automatic pipe network direct connection without negative pressure secondary pressurization water supply mode

This method is to connect the fully automatic network direct connection non-negative pressure water supply equipment directly to the tap water network, use a sealed water tank and a negative pressure suppression and compensation system, automatically adjust the water volume and pressure, and realize the function of no negative pressure in the external tap water pipeline and automatic constant pressure water supply in the internal network. This water supply method makes full use of the primary pressure hj of the public water supply network in the city. The booster pump station only compensates the difference between the inlet pressure hj of the public water supply network and the required water supply pressure ha, so the energy saving effect is significant. The process operation condition of the pump station is shown in Figure 4.

It can be seen from formula (19) that when the pump station is operated in the fully automatic network direct connection non-negative pressure secondary pressurized water supply mode, the power saving rate of the water supply system is proportional to the public network water supply pressure hj; it is inversely proportional to the pressure ha of the internal network, and has nothing to do with the water volume q of the pump station.

2 Comparison of power consumption indicators of pump station operation modes

The above analysis and research are conducted on the operation modes of four urban secondary booster pump stations. The power consumption of the four pump station operation modes is compared and listed in Table 1.

Based on the process water supply parameters of a pumping station in the north, we calculated the actual values ​​of the power consumption indicators of the pumping station using different operating modes under the same process water supply parameters, see Table 2.

As can be seen from Tables 1 and 2, the water supply method described in Section 1.4 is the most energy-efficient pump station process operation method. The actual power consumption of this operation method is much lower than the power consumption of the ideal state of the secondary booster pump station (in this calculation, the actual power consumption is 20.6% lower than the power consumption of the ideal state of the secondary booster pump station); in terms of power saving effect, the former saves more than 70% of power than the latter, and saves more than 10% of power than the constant pressure water supply method.

28.6%~43%. The operating diagrams of the four operating modes of the pump station are shown in Figure 5.

At present, in the water supply process of urban secondary booster pump stations, mode 2 is generally used, and only a small number of them use mode 3. However, the use of mode 4 in urban secondary booster pump stations has great energy-saving space.

3 Conclusion

The microcomputer-controlled variable frequency speed regulation, current conversion and voltage conversion and fully automatic network direct connection without negative pressure water supply operation mode in urban secondary booster pump stations are currently the two most energy-saving process operation methods; in particular, the fully automatic network direct connection without negative pressure water supply has significant energy-saving effects and broad market prospects.