Centrifugal pump common conditioning
Baihengte centrifugal pump is widely used in water conservancy and chemical industry, and its selection of working conditions and analysis of energy consumption are also receiving more and more attention. The so-called operating point refers to the actual water output, head, shaft power, efficiency, and vacuum height of the pump unit at a certain moment. It indicates the working capacity of the pump. Generally, the flow rate and pressure head of the centrifugal pump may be inconsistent with the pipeline system, or the flow rate of the pump needs to be adjusted due to changes in production tasks and process requirements. The essence is to change the operating point of the centrifugal pump. In addition to the correctness of the centrifugal pump selection during the engineering design phase, the choice of the operating point of the centrifugal pump will directly affect the user's energy consumption and cost. Therefore, how to reasonably change the operating point of the centrifugal pump is particularly important.
The working principle of the Baihengte centrifugal pump is to convert the mechanical energy of the high-speed rotation of the motor into the kinetic energy and potential energy of the lifted liquid, which is a process of energy transfer and conversion. According to this feature, the operating point of the Baihengte centrifugal pump is based on the balance between the energy supply and demand of the pump and the pipeline system. As long as the situation of one of the two changes, the operating point will shift. The change of the operating point is caused by two aspects: 1. The characteristic curve of the pipeline system changes, such as valve throttling; 2. The characteristic curve of the pump itself changes, such as variable frequency speed regulation, cutting impeller, water pump series or parallel.
Here are some ways to analyze and compare:
First, the valve throttle
The easiest way to change the flow rate of the centrifugal pump is to adjust the opening of the pump outlet valve, while the pump speed remains the same (typically rated speed), which essentially changes the position of the pipeline characteristic curve to change the operating point of the pump. As shown in Fig. 1, the intersection point A of the pump characteristic curve QH and the pipeline characteristic curve Q-∑h is the limit operating point of the pump when the valve is fully open. When the small valve is closed, the local resistance of the pipeline increases, and the pump operating point moves to the left to point B, and the corresponding flow rate decreases. When the valve is fully closed, it is equivalent to an infinite resistance and the flow rate is zero. At this time, the pipeline characteristic curve coincides with the ordinate. It can be seen from Fig. 1 that when the flow rate is controlled by closing the small valve, the water supply capacity of the water pump itself is unchanged, the lift characteristic is unchanged, and the pipe resistance characteristic will change with the change of the valve opening degree. This method is easy to operate, continuous flow, and can be adjusted freely between a certain maximum flow rate and zero, and no additional investment is required. However, the throttling adjustment is to maintain a certain amount of supply by consuming the excess energy of the centrifugal pump (shaded portion in the figure), and the efficiency of the centrifugal pump will also decrease, which is not economically reasonable.
Second, frequency control
Deviation from the high efficiency zone is the basic condition for the pump to adjust speed. When the speed of the pump changes, the valve opening remains the same (usually the maximum opening), the piping system characteristics remain unchanged, and the water supply capacity and head characteristics change. As shown in Figure 2, A is the pump balance operating point (also called the operating point), corresponding to the efficiency ηa. To reduce the flow rate, the speed can be reduced. At this time, the operating point is B, and the pump is still in the high efficiency zone corresponding to the efficiency ηb. If the valve throttling method is used to adjust, the operating point is C, the corresponding efficiency is ηc, and the efficiency of the pump is lowered. It can be seen that in the case that the required flow rate is less than the rated flow rate, the head of the variable frequency speed regulation is smaller than the throttle of the valve, so the water supply power required for the frequency conversion speed regulation is also smaller than the throttle of the valve, and the shaded part in FIG. 2 indicates The water supply power saved by the frequency conversion speed regulation. Obviously, compared with valve throttling, the energy-saving effect of frequency conversion speed regulation is very prominent, and the centrifugal pump works more efficiently. In addition, the use of variable frequency speed control not only helps to reduce the possibility of cavitation in the centrifugal pump, but also can extend the start/stop process by presetting the up/down time to greatly reduce the dynamic torque. This greatly eliminates the highly damaging water hammer effect and greatly extends the life of the pump and piping system.
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Label: Commonly used conditioning methods for centrifugal pumps
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