Technical and economic analysis of water supply of

Technical and economic analysis of constant speed pump and variable speed pump water supply (Part I)

1 working principle and characteristics of constant speed pump and variable speed pump

when the pump is installed in a certain pipeline, the actual working state depends not only on the performance curve of the pump itself, but also on the characteristic curve of the whole pipeline. The intersection of these two curves determines the operating condition of the pump in the pipeline system. In the device system with the same pipeline characteristic curve, the working points of different pumps are different. The working points of constant speed pump and variable speed pump are very different, so that the flow, head and efficiency are different

constant speed feed water pump is generally centrifugal in the water supply system, and its working principle is to use the centrifugal force generated by better rotation to make the fluid obtain energy. It uses a certain power motor to drive the pump to rotate at a certain speed, so that the fluid can obtain a certain amount of pressure energy and kinetic energy. The variable speed feed pump (taking yt62 hydraulic coupling as an example) has a special hydraulic coupling. It is a rotating part installed between the prime mover (motor, etc.) and the feed pump, which is transmitted by the kinetic energy of the liquid, so it is used to produce high-performance lightweight thermoplastic honeycomb core materials and sandwich panels. Its working principle is: there is a pump wheel at the end of the driving shaft, and a turbine at the end opposite to the driving shaft on the driven shaft. There is a certain gap between the pump wheel and the turbine, and the two form a cavity, which is called a circular circle. When the prime mover drives the driving shaft to rotate, the working fluid will obtain energy in the pump wheel, throw it out of the pump wheel at a certain speed, rush to the turbine, and transfer the energy to the turbine, so as to drive the driven shaft to rotate, realizing the transmission of power

the circulation of working oil in the circulation circle can be maintained only when the pump wheel and turbine are at different speeds (there is slip), that is, there is a centrifugal force difference. With a slip of 3% under rated operating conditions, as long as the oil volume in the circulating circle is changed, that is, the oil filling volume is changed, the speed and transmission power of the driven shaft can be adjusted to realize stepless speed regulation

2 constant speed pump 1 generally speaking, the gap between the trapezoidal screw is relatively large, and the technical and economic comparison of the variable speed pump

the eighth phase technical transformation project of Hebei Thermal Power Co., Ltd. is two 200 MW double extraction heating units and four 410 t/h circulating fluidized bed boilers, with one unit for each two boilers. It is planned to set two variable speed pumps and one constant speed pump with a nameplate output of 440 t/h and a head of 1400 m for each unit. The following compares the conditions when the constant speed pump (or speed regulating pump) operates alone, two constant speed pumps (or two speed regulating pumps) operate in parallel, and one constant speed pump and one speed regulating pump operate in parallel in the system

2.1 the constant speed pump (or speed regulating pump) operates alone

the methods to change the performance curve of the pump itself include variable speed regulation, moving blade regulation and cavitation regulation. The methods to change the pipeline characteristic curve mainly include outlet throttling regulation and inlet throttling regulation, and the most commonly used regulation method is outlet throttling regulation, which uses changing the valve opening to adjust. Generally, the constant speed pump is regulated by throttling at the outlet, and the variable speed pump is regulated by variable speed

the start-up time of the boiler is long, and the whole pressure raising process of bringing the boiler load to 410 t/h is gradually achieved according to the requirements of the machine side, that is to say, if the speed regulating pump is used in this process, the start-up requirements of the boiler can be met only by changing the speed. From the characteristic curve of the speed regulating pump, it can be seen that the corresponding head when the flow is 120 ~ 450t/h can be increased from 800m (or less) to 1400m according to the gradual temperature rise and pressure rise of the furnace, without the need to adjust the feed water regulating valve. In this case, if the constant speed pump is used for hardness, conductivity, porosity, etc., it takes a long time to throttle the feed water regulating valve to meet the required flow, so it costs a high energy head