Technical and Economic Analysis of Constant Speed ​​Pump and Speed ​​Control Pump

Constant speed pump and speed pump working principle and characteristics

When the pump installed in a certain pipeline work, the actual state of work depends not only on the performance curve of the pump itself, but also depends on the characteristics of the entire pipeline. The intersection of these two curves determines the operating conditions of the pump in the piping system. In the same piping system characteristics of the system, for different pumps, the operating point is different. Constant speed pumps and speed pump work point there is a big difference, so that the flow, lift, different efficiency.

Constant speed feed water pump in the water supply system is generally centrifugal, its working principle is the use of centrifugal force generated by the rotation of the fluid to obtain energy. It is driven by a certain power motor to a certain speed of rotation, the fluid to be a certain pressure and kinetic energy. Speed ​​feed pump (YT62 type fluid coupling, for example) has a special piece - hydraulic coupling. It is installed in the prime mover (motor, etc.) and the feed pump between the rotation of the liquid kinetic energy to transmit power hydraulic transmission. Its working principle is: there is a pump impeller at the end of the drive shaft, the driven shaft on the opposite end of the drive shaft with a turbine, impeller and turbine to maintain a certain gap between the two form a cavity, said For the round circle. When the prime mover drives the drive shaft to rotate, the working fluid gains energy in the pump wheel and is thrown from the pump wheel at a certain speed toward the turbine to transfer the energy to the turbine, so as to drive the driven shaft to rotate and realize the power transmission .


Circulation of working oil in the circular circle The circulation can only be maintained if there is a difference in centrifugal force between the impeller and the turbine at different speeds (slip). Under rated operating conditions, slip ≤ 3%, as long as the change in the oil circulation in the circle, that is, to change the oil filling, you can adjust the speed and power transmission driven shaft to achieve stepless speed regulation.

2 constant speed pump, speed pump technical and economic comparison

Hebei Thermal Power Co., Ltd. eight technical upgrading project for the two 200 MW double-pumping heat units and four 410 t / h circulating fluidized bed boiler, a machine for each 2 furnace 1 unit, the plan for each unit set the nameplate Two turbo pumps and one fixed speed pump with output of 440 t / h and lift of 1 400 m. The following comparison when the system constant speed pump (or speed governor pump) run alone, 2 constant speed pump (or 2 speed governor pump) run side by side, a fixed speed pump and a speed governor pump running side by side.

2.1 constant speed pump (or speed pump) run alone

Methods to change the pump performance curve are variable speed regulation, bucket adjustment and cavitation regulation. The main methods to change the pipeline characteristic curve are outlet throttling regulation and inlet throttling regulation. The most common regulation method is outlet throttling regulation, which is a way to adjust by adjusting the valve opening degree. General fixed-speed pump for the export side of throttling regulation, variable speed pump for variable speed regulation.

Steam turbine allowable cold, warm, hot start of the main steam parameters and brought to 410 t / h load time requirements in Table 1. Boiler cold, warm, hot start parameter division and brought to full load time in Table 2.
As can be seen from Table 2, the boiler start-up time is longer, and the boiler load to 410t / h throughout the pressure-lifting process according to the requirements of the machine side is gradually reached, that is to say if the process used in the transfer The speed pump can only meet the start-up requirements of the furnace by changing the speed. It can be seen from the characteristic curve of the governor pump that the corresponding lift at 120 ~ 450t / h can be increased from 800m (or lower) to 1400m according to the step-up and step-up of the furnace without adjusting the feedwater regulating valve. In this case, the constant speed pump is used, and the water supply control valve needs to be throttled for a long time to satisfy the required flow rate, thus consuming a higher energy head.

It can be seen from Figure 2 that the flow rate is from 120 to 450 t / h and the corresponding lift is 1 680 to 1 430 m. Excess energy can be consumed by the water supply control valve, see formula (1):

Where N --- motor power consumption, k W;
g --- acceleration of gravity, m / s2;
Q --- mass flow rate, kg / s;
H --- head, m;
η --- pump efficiency,%.

It can be seen that under certain conditions of other parameters, the power N is proportional to the head H. As the pump speed can be achieved by changing the speed of the furnace line to start the request, so the energy saving effect is significant. At 120 t / h, the governor pump can save half the power of a constant speed pump.

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