DG type high pressure boiler feed water pump flow control of the three methods

DG type high pressure boiler feed water pump for high pressure boiler water supply or other high pressure fresh water pump. High pressure boiler feed water pump are widely used in industry, water conservancy, and other industries, the choice of the point and the analysis of energy consumption is increasingly attention. Point, refers to the boiler feed water pump device in the actual water yield of a transient, head, shaft power and efficiency as well as on the vacuum suction height, it says the feed water pump working ability. Usually, DG type high pressure boiler feed water pump flow rate and pressure head may be inconsistent with the piping system, or because the production task change, technological requirements, it is necessary to regulate the flow of feed water pump, its essence is to change the operation condition of the feed water pump. In addition to the engineering design phase of feed water pump selection is correct or not, the boiler feed water pump are actually used in the choice of point will directly affect the user's energy consumption and cost. Therefore, how to change the operation condition of the boiler feed pump reasonably point is particularly important.

DG type high pressure boiler feed water pump working principle is to put the motor high speed rotating mechanical energy into kinetic energy and potential energy of liquid was promoted, is a process of energy transfer and conversion. According to this characteristic, the operation condition of the boiler feed pump is set up in the feed water pump and pipeline system on the balance between energy supply and demand, the situation changes, as long as either of the two will transfer its point. Piping system characteristic curve changes, such as throttle valve; Feed water pump itself characteristic curve changes, such as frequency control of motor speed, cutting impeller.

here are the three type DG high pressure boiler feed water pump flow control method is analyzed and compared:

1) Throttle valve

change the simplest method is to adjust the pump flow pump discharge valve opening, the feed water pump speed stays the same, Are generally rated speed) , its essence is to change the position of the pipeline characteristic curve to change the point of the pump. Turn down the valve, pipe local resistance increases, feed water pump working condition point moves to the left, the corresponding flow decreases. Valve fitted, equivalent resistance is infinite, flow is zero, the pipeline characteristic curve and the vertical overlap. When turn down the valve to control the flow capacity of feed water pump itself remains unchanged, lift characteristics unchanged, pipe resistance characteristic will change along with the change of valve opening. This method is simple, continuous flow, can be in one of the maximum flow between zero and adjust at will, and no additional investment, applicable occasions is very wide. But the throttle to adjust in the boiler feed water pump spare energy consumption, to maintain a certain supply, the efficiency of the boiler feed water pump will also fall, economically reasonable.

        2） Frequency control of motor speed

point deviates from the high efficiency area is the basic conditions of feed water pump need speed. When the feed water pump speed change, valve opening unchanged ( Usually for the biggest opening) Characteristics, pipeline system unchanged, while water supply capacity and lift characteristics change.

at the required flow rate is less than the rated flow, under the condition of frequency control of motor speed when the head is smaller than the throttle valve, so the water power of the frequency control of motor speed required is smaller than the throttle valve. Obviously, compared with the throttle valve, the energy saving effect of variable frequency speed regulation is very outstanding, the working efficiency of the boiler feed pump is higher. In addition, using variable frequency speed regulation, is not only beneficial to reduce the possibility of boiler feed water pump cavitation occurred, but also by the acc/dec time to extend the preset starting/stopping process, thus greatly reducing the dynamic torque, thus eliminated very greatly and destructive water hammer effect, greatly extend the life span of the feed water pump and pipeline system.

in fact, frequency control of motor speed also have limitations, in addition to larger investment and maintenance cost is higher, will cause the loss of efficiency when the feed water pump speed is too high, is beyond the scope pump proportion law, could not have unlimited speed regulation.

        3）

when cutting impeller rotating speed is constant, pressure head and flow of the pump are related to the impeller diameter. For the same type of pump, the characteristic curve of cutting method to change the pump can be used.

cutting law is established on the basis of a large number of testing data, it thinks if the amount of cutting impeller control within limits ( The cutting limit associated with the than revolutions of feed water pump) Before and after, the cutting feed water pump efficiency can be treated as the same accordingly. Cutting impeller is a simple change of feed water pump performance, the so-called variable diameter adjustment, to some extent, it solved the feed water pump type and the limitation of specification and the contradiction between the diversity of the object requirements of water supply, enlarge the using range of the multistage pump. Cutting impeller is the irreversible process, of course, the user must go through precise calculation and measure the economic rationality of rear can implement.

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