Design and Application of Distributed Variable Frequency Pump System
1. The principle of distributed variable frequency pump system
In the traditional heating branch pipe network system, a set of circulating pumps are generally installed at the heat source or in the heat exchange station, and the flow, head and number of circulating pumps are selected according to the flow of the pipe network system and the resistance of the most unfavorable loop; The end of each user of the pipe network system is equipped with manual control valves or self-operated flow control valves and other adjustment equipment to consume the remaining pressure head of the user and achieve the hydraulic balance between the users in the system; individual existing heating networks are due to the user’s thermal load Due to the change of the pressure head, the capital pressure head is not enough, and the water supply or return water pressure pump is added. However, because it is not easy to adjust, it often has an adverse effect on upstream or downstream users.
With the emergence of new regulating equipment and control methods, digital control of water pumps has become possible. In this way, the regulating equipment in the pipe network can be eliminated in theory, and the water pump with adjustable speed can be replaced by the appropriate node of the pipe network. Meet the requirements of subsequent hydraulic conditions. If the pressure difference of the appropriate node in the pipe network is controlled, this point is called the pressure difference control point. For the choice of the main circulating pump, as long as the resistance of the flow and heat source to the pressure difference control point can be met, this can greatly reduce the circulation pump. The power of the main circulating pump motor drops a lot; each user after the economic control point sets the corresponding distributed variable frequency pump to become a distributed variable frequency pump system, so that the energy of the original valve throttling is no longer lost in vain, because the pump can be variable frequency The speed of the main circulating pump can be adjusted greatly, and the power consumption can be greatly reduced by the main circulating pump. In theory, the adjustment equipment can be omitted. At the same time, the heating system can work at a lower pressure level, and the system is safer. The China Urban Heating Association has also listed the research and development of the distributed variable frequency pump system as the “Tenth Five-Year Plan”.
2. Design of distributed variable frequency pump system
In the distributed variable frequency pump system, the design should be carried out according to the following steps:
1. Pipe network system design, calculate the resistance of the pipe network.
2. Select the differential pressure control point. Different differential pressure control points correspond to different initial equipment investment and pipe network operating costs. The selection should be based on technical and economic analysis.
3. When choosing the main circulating pump, the choice of the main circulating pump considers two aspects:
A: Flow requirements, should be able to provide all the circulating flow of the pipe network;
B: The head requirements should meet the resistance of the pipe network from the heat source to the pressure difference control point.
4. The choice of distributed pumps mainly considers meeting the resistance and flow of users in this branch.
Third, the realization of distributed variable frequency pump system
In accordance with the above thoughts, Tangshan City Heating Power Corporation reformed the heating system of its Longdong boiler room. This article uses this as an example to illustrate the realization process of the distributed variable frequency pump system.
1. The Longdong heating system is composed of a 4×10t/h hot water boiler room and two intermediate supply stations. The basic parameters are as follows:
(1) Heating building area:
Longnan Station: 181814.31m2
Longbei Station: 139891.62m2
(2) Equipment: Two main circulation pumps, one open and one standby, ISR200-150-400, power N is 90KW, flow Q is 400m3/h, and head H is 50m water column.
(3) Pipe network:
1-2 pipe diameter DN300, groove length L=500m
2-3 pipe diameter DN250, groove length L=536m
3-4 pipe diameter DN250, groove length L=650m
2龙南站一次供水加一台变频泵，H=12.5m Q=200m3/h N=15KW
3龙北站一次供水加一台变频泵，H=24m Q=240m3/h N=22KW
2. The constant pressure value of water at the water replenishment point should be recalculated. As it is generally difficult to arrange the distributed pump at the economic control point of the pipe network, when the distributed pump is arranged in the station, for the long branch line, It may cause the drift of the replenishment point. For this working condition, one method is to set the water replenishment point at the lowest point of the pipe network pressure, and the other method is to concentrate the water replenishment at the total return water of the heat source, and appropriately increase the constant pressure value of the water replenishment.
3. In the selection of equipment, the technical parameters of the main circulating pump should have a proper margin.
4. The control of the pressure difference at the pressure difference control point: due to the long distance of the heating pipe network, the signal transmission is not easy to realize or the realization cost is high, the calculated value is converted to the inlet and outlet of the main circulating pump; or the pressure difference control point is used for return Install a pressure gauge on the water pipe, and adjust the pressure difference between the inlet and outlet of the main circulation pump by referring to the value of the pressure gauge.
5. In the distributed variable frequency pump system, because the technical parameters of the water pump product are not continuous, it is impossible to meet the actual needs. Even if the frequency conversion adjustment is performed, it is impossible to meet the requirements. The valve adjustment of individual points in the system is still necessary. .
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