Energy Saving Analysis of Frequency Control Technology in Pump Application

I. Introduction

In industrial production and product processing and manufacturing industries, fan and pump equipment have a wide range of applications; their energy consumption and throttling losses such as valves and baffle-related equipment as well as maintenance and repair costs account for 7% to 25% of production costs, It is not a small overhead costs. With the continuous deepening of economic reform, market competition continues to intensify; energy saving has become an important means to reduce production costs and improve product quality and the development of the early eighties of the frequency control technology is in line with the industry Production automation requirements, creating a new era of intelligent motor. A change of ordinary motor can only run at a fixed speed of the old model, making the motor and its drag load without any changes in the case that can be adjusted according to the requirements of the production speed, thus reducing the motor power to achieve the purpose of efficient operation of the system . In the late 1980s, this technology was introduced into our country and was promoted. Now in electric power, metallurgy, petroleum, chemical, paper, food, textile and other industries in the motor drive equipment has been practical application. At present, the frequency control technology has become a major development direction of modern electric drive technology. Excellent speed performance, significant energy-saving effect, to improve the operating conditions of existing equipment, improve system safety and reliability and equipment utilization, extend the life of the equipment, etc. With the continuous expansion of applications are fully reflected .

Second, review

Usually in industrial production, product processing and manufacturing fan equipment is mainly used for boiler combustion system, drying system, cooling system, ventilation system and other occasions, according to the production needs of the furnace pressure, wind speed, air volume, temperature and other indicators to control and adjust Adapt to process requirements and operating conditions. The most commonly used control method is to adjust the damper, baffle opening size to adjust the controlled object. In this way, regardless of the size of the demand for production, the fan must be running at full speed, and changes in operating conditions make energy throttling loss of throttle, baffle consumed. In the production process, not only control accuracy is limited, but also caused a lot of energy waste and equipment loss. Resulting in increased production costs, shortened equipment life, equipment maintenance, high maintenance costs. Pump equipment also has a wide range of applications in the field of production, pumping pumping station, tank storage tank supply and drainage system, industrial water (oil) recycling system, heat exchange systems are used centrifugal pump, axial pump, gear pump, plunger Pumps and other equipment. Moreover, according to different production needs are often used to adjust the valve, return valve, cut-off valve throttling equipment such as flow, pressure, water level signal control. This will not only cause a lot of energy waste, piping, valves and other sealing performance damage; also accelerated pump chamber, valve body wear and cavitation, serious damage to equipment, affecting production, endangering product quality. Fan, pump equipment most of the asynchronous motor direct drive mode of operation, there is a large start-up current, mechanical shock, poor electrical protection and other shortcomings. Not only affect the service life of the equipment, but also when the load appears mechanical failure can not be instantaneous action to protect the equipment, pump damage often occurs at the same time the motor is also burned phenomenon. In recent years, out of the urgent need for energy saving and the continuous improvement of product quality requirements, combined with the use of frequency converter (inverter) easy operation, maintenance-free, high control accuracy, and can be achieved high-functional features; thus using Drive-driven program began to gradually replace the damper, baffle, valve control program. The basic principle of frequency control technology is based on the motor speed and the power supply input frequency is proportional to the relationship: n = 60f (1-s) / p, (where n, f, s, p, respectively, Slip, motor pole pairs); by changing the motor power frequency to achieve the purpose of changing the motor speed. Inverter is based on the above principles using AC - DC - AC power conversion technology, power electronics, microcomputer control technology in a comprehensive electrical products.

Third, energy-saving analysis

Through the basic laws of fluid mechanics we can see: fan, pump equipment are square torque load, the speed n and flow Q, pressure H and shaft power P has the following relationship: Qαn, Hαn2, Pαn3; that , Flow and speed is proportional to the square of the pressure and speed is proportional to the shaft power and speed is proportional to the cube. Taking a water pump as an example, its outlet pressure head is H0 (outlet pressure head is the static pressure difference between the pump inlet and the outlet of the pipe), the rated speed is n0, the valve resistance characteristic when the valve is fully open is r0, the rated working condition The corresponding pressure is H1, and the outlet flow is Q1. Flow - speed - pressure curve as shown below. In the field of control, the pump is usually used to run the outlet valve to control the flow rate. When the flow rate decreases from Q1 to Q2, the valve opening decreases and the resistance of the pipe network changes from r0 to r1. The system operating point moves from point A to point B along the direction I. By the throttle effect pressure H1 becomes H2. Pump shaft power actual value (kW) can be obtained by the formula: P = Q · H / (ηc · ηb) × 10-3. Among them, P, Q, H, ηc, ηb, respectively, power, flow, pressure, pump efficiency, transmission efficiency, direct drive to 1. Assuming that the total efficiency (ηc · ηb) is 1, when the pump moves from point A to point B, the power consumption saved by the motor is the area difference between AQ1OH1 and BQ2OH2. If the governor is used to change the pump speed n, when the flow rate is reduced by 50% from Q1 to Q2, then the pipe network resistance characteristic is the same curve r0. The system operating point will move along the direction II from point A to point C, Pump operation is more reasonable. In the valve is fully open, only the case of pipe network resistance, the system to meet the flow requirements of the scene, energy consumption is bound to reduce. In this case, the motor consumes less power than the area of ​​AQ1OH1 and CQ2OH3. Compared with the valve opening adjustment and pump speed control, it is clear that the use of pump speed control more effective and reasonable, with significant energy savings. In addition, it can also be seen from the figure that when the valve is adjusted, the system pressure H will increase, which will threaten and damage the sealing performance of the pipeline and the valve. When the speed is adjusted, the system pressure H will vary with the pump speed n Lower and lower, so will not have a negative impact on the system. From the above comparison is not difficult to draw: When the demand for pump flow from the scene down to 50% from 100%, the use of speed regulation than the original valve to save the corresponding power BCH3H2 size, energy saving rate of 75%.

Similarly, if you use frequency control technology to change the pump, fan speed to control the scene pressure, temperature, water level and other process control parameters, the same can be based on the system control characteristics of the relationship curve drawn the above comparison results . That is, using frequency control technology to change the motor speed than the use of valves, baffles more economical and economical regulation, equipment operating conditions will also be significantly improved.

Fourth, energy-saving calculation

For fan, pump equipment using frequency control after the energy-saving effect, usually in the following two ways to calculate:

1, according to the known fan, pump under different control modes of flow - load curve and on-site operation load changes.

Taking an IS150-125-400 centrifugal pump as an example, the rated flow 200.16m3 / h, lift 50m; equipped with Y225M-4 motor, rated power 45kW. Pump in the valve adjustment and speed adjustment flow - load curve as shown below. According to operational requirements, the pump runs continuously for 24 hours, of which 11 hours a day runs at 90% load,

13 hours running at 50% load; annual running time at 300 days. The annual electricity savings are:

W1 = 45 × 11 (100% -69%) × 300 = 46035 kW · h

W2 = 45 × 13 × (95% -20%) × 300 = 131625 kW · h

W = W1 + W2 = 46035 + 131625 = 177660 kW · h

0.5 yuan per kilowatt-hour calculation, the annual electricity savings of 888300 yuan.

2, according to the fan, square pump torque load relationship: P / P0 = (n / n0) 3 calculation, where P0 rated speed n0 power; P is the speed n power. Take an example of a 22kW blower used in an industrial boiler. Operating conditions are still running continuously for 24 hours, of which 11 hours a day running at 90% load (46Hz frequency calculation, the motor power consumption adjustment baffle 98%), 13 hours running at 50% load (20Hz frequency calculation , Baffle motor power consumption adjusted by 70%); the annual running time in 300 days as the basis for the calculation. The frequency of annual energy-saving speed when:

W1 = 22 × 11 × [1- (46/50) 3] × 300 = 16067 kW · h

W2 = 22 × 13 × [1- (20/50) 3] × 300 = 80309 kW · h

Wb = W1 + W2 = 16067 + 80309 = 96376 kW · h

Baffle opening when the power saving is:

W1 = 22 × (1-98%) × 11 × 300 = 1452 kW · h

W2 = 22 × (1-70%) × 11 × 300 = 21780 kW · h

? Wd = W1 + W2 = 1452 + 21780 = 23232kW · h

In comparison, the power saving amount is: W = Wb-Wd = = 73144kW · h

0.5 yuan per kilowatt-hour calculation, the use of frequency control can save electricity 36,500 yuan per year.

A factory centrifugal pump parameters: Centrifugal pump model 6SA-8, rated flow 53.5L / s, lift 50m; with the motor Y200L2-2 type 37kW. Measured data recorded under the valve throttle control and motor speed control of the pump are as follows:

Flow rate L / s Time (h) Consumption of electricity output from the grid (kW · h) Valve throttling adjustment Frequency control of the motor

47233.2 × 2 = 66.428.39 × 2 = 56.8

40830 × 8 = 24021.16 × 8 = 169.3

30427 × 4 = 10813.88 × 4 = 55.5

201023.9 ​​× 10 = 2399.67 × 10 = 96.7

Total 24653.4378.3

In contrast, frequency control in a day can save 275.1kW · h compared to valve throttling control, saving 42.1%.

Five, concluding remarks

Fans, pumps and other equipment using frequency conversion technology to achieve energy-saving operation of energy-saving is a key promotion of energy technology in China by the national government's universal attention, "People's Republic of China Energy Conservation Law," Article 39 put it as a common technology to be Promotion. Practice has proved that the inverter used in fan, pump equipment drive control achieved significant energy-saving effect of the occasion, is an ideal speed control. Not only improve the equipment efficiency, but also to meet the production process requirements, and thus greatly reduce the equipment maintenance and repair costs, but also reduce the shutdown cycle. Direct and indirect economic benefits are evident, and one-time investment in equipment can usually be fully recovered from 9 months to 16 months of production.