Economic analysis and application of the hottest f

Economic analysis of the application of frequency converter in the condensate pump of power plant and the analysis and solution of problems

1 introduction

Guangzhou power plant is located in Guangzhou City, Guangdong Province. It was founded in 1935 and has been transformed for many times. At present, the plant has four 60MW extraction heating units (#1 ~ #4 units) and one 25MW waste heat comprehensive utilization unit (#0 units). It is the main heating power plant in Guangzhou. The centralized steam supply has not only made great contributions to the environmental protection of Guangzhou, but also created certain economic benefits. In the current bidding and the severe form of rising coal prices, in order to improve their competitiveness and create better economic benefits. We must vigorously promote the transformation of energy conservation and consumption reduction, and strive for safe and frequent occurrence. Since 2003, the plant has carried out a series of energy-saving and consumption reduction transformation projects, in which the frequency control of condensate pump motor is changed, and Kaifeng Longyu Chemical Co., Ltd. of ABB Electric Drive System Co., Ltd. is an ACS800 frequency converter, a new material manufacturer mainly based on POM, with remarkable energy-saving effect. There are also some problems in the operation. Finally, we put forward targeted solutions through analysis, research and summing up experience and lessons. At present, the frequency conversion operation of each condensate pump is good

2 operating conditions of condensate pump

the steam that has done work in the turbine is concentrated in the hot water well after the condenser is cooled and condensed, and the function of the condensate pump is to send the condensate to the deaerator in time. During normal operation, the water level in the condenser shall not be too high or too low. Adjusting the water level in the condenser is a major work in the operation of the condensate pump. Before using the frequency converter, adjust the water level in the condenser by 1 The force value is measured by changing the opening of the outlet valve of the condensate pump for throttling adjustment. In the throttling process, the characteristic curve of the condensate pump remains unchanged, and the blade speed remains unchanged. By turning down the gate valve, the pipe resistance is artificially increased to reduce the flow. Therefore, a lot of energy is lost on the valve. At the same time, the long-term operation of the motor and water pump under high speed and heavy load, as well as the frequent operation of the valve, result in a large maintenance workload, reduce the service life of the equipment, and affect the stable operation of the unit

3 economic benefits of changing frequency control of condensate pump

the #1 ~ #4 units of the plant are c.83/1.27 steam turbines, which are equipped with two 12NL-125 condensate pumps, with a head of 125m, a flow of 320t/h, a motor power of 180km and a voltage of 380V. The speed formula of asynchronous induction motor is n=n1 (1-s) =60f/p (1- (N1-N)/n1). It can be seen that the speed can be changed as long as any one of the parameters is changed. The frequency converter changes the motor speed by changing the power frequency f. For a certain motor, the speed and frequency are linear, as shown in Figure 1

it can be seen that the linearity of variable frequency speed regulation is very good, so the power loss due to throttling regulation can be eliminated, and the purpose of energy saving can be achieved. According to the hydrodynamics theory and the characteristic curve of the water pump, the relationship between the flow, speed, torque and power of the water pump is as follows:

q/qe=n/ne, h/he= (n/ne), p/pe= (n/ne) (1)

where: QE - the rated flow of the pump, he - the rated torque of the pump, PE - the rated power of the pump,

ne - the rated speed of the pump

according to formula (1), when the flow decreases by 20%, the speed decreases by 20%. Therefore, we usually adopt 10kN microcomputer controlled electronic universal experimental machine to meet this condition, and the power decreases by 40%, that is, 40% of electric energy is saved. It can be seen that the energy-saving effect of frequency converter speed regulation is very significant

the following is a group of data recorded before and after the frequency control of the condensate pump in the plant, as shown in Table 1

Table 1 comparison table of data before and after the transformation of condensate pump of unit 1

it can be seen from table 1 that the average current of condensate pump is reduced from 219a to 166a. Based on the annual operation time of unit 1 of the plant t=6800 hours, the annual power savings are:

W savings = w original - W modified =205000 kW · h

based on the power supply price of the plant 0.36 yuan/kw · h, the power savings are equivalent to:

20.5 × The notched side faces the edge of the pendulum 0.36 = 73800 yuan

the cost of the frequency converter transformation is about 120000 yuan. It can be seen that the cost can be recovered in only about 18 months, so the economic benefit is considerable

4 analysis and treatment of problems

4.1 failure shutdown due to high temperature of frequency converter

from September to October 2004, the failure shutdown of frequency converter of condensate pump of unit #2 B occurred three times due to high temperature of working environment. It poses a hidden danger to our energy conservation and consumption reduction and safe operation. Through on-site analysis and inspection, we found that the original cooling fan in the inverter control cabinet provided by the supplier was a 38W small fan, which was installed on the side wall, and the ventilation and heat dissipation effect was poor. As shown in figure 2:

in addition, the control cabinet is installed in the enclosed 380V bus room. In summer, the ambient temperature of the bus room is up to about 40 ℃, and the ventilation is poor. We recorded that the temperature in the control cabinet during fault shutdown was 85 ℃, and the temperature of the inverter body was as high as 98 ℃. The normal working environment of ACS800 frequency converter requires that the temperature is - 40 ~ 70 ℃, dry and clean air

after our analysis and calculation, the fan is installed on the top of the inverter cabinet, and two 100W fans are used for ventilation and heat dissipation. As shown in Figure 3

according to the hydrodynamics, the hot air is discharged upward through the cabinet top, and the cooling air is sucked in from the ventilation at the bottom of the cabinet side, so as to achieve good ventilation and heat dissipation repeatedly