Energy Saving Analysis of Frequency Control Technology in Fans and Pumps

I. INTRODUCTION In the field of industrial production and product processing and manufacturing, fan and pump equipment have a wide range of applications. Their power consumption and throttling losses such as valves and baffle-related equipment as well as maintenance and repair costs account for 7% of production costs. % ~ 25%, is not a small overhead costs. With the continuous deepening of economic reform and increasing market competition, energy conservation and consumption reduction have become one of the important measures to reduce production costs and improve product quality. In the early 1980s, the frequency control technology developed in response to the requirements of industrial automation development created a new era of intelligent motors. 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, the 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 .                  usually in industrial production, product processing and manufacturing fan equipment is mainly used for boiler combustion system, drying system, cooling system, ventilation systems and other occasions, according to the production needs of the furnace pressure, wind speed, , Temperature and other indicators to control and adjust to meet the 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 in the field of production also has a vast application space, to pump stations, tank storage tank system, industrial water (oil) recycling systems, heat exchange systems are used centrifugal pumps, axial pumps, gear pumps, Piston 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.   fans, pumps most of the equipment used 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, due to the urgent need of energy conservation 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 achieve high functionality; Therefore, the use of inverter-driven program began to gradually replace the damper, baffle, valve control program.   frequency conversion technology is based on the basic principle of the motor speed and the power input frequency is proportional to the relationship: n = 60 f (1-s) / p, (where n, f, s, p, respectively, Frequency, motor slip, motor pole pairs); by changing the motor operating 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   By the basic laws of fluid dynamics can be seen: fans, pumps are square torque load, the speed n and flow Q, pressure H and shaft power P has the following relationship: Qαn , Hαn2, Pαn3; ie, the flow rate is proportional to the speed, the pressure is proportional to the square of the speed, and the shaft power is proportional to the cube of the speed.   To a pump, for example, its export pressure head for the H0 (outlet pressure that is, the pump inlet and outlet pipe static pressure difference), the rated speed of n0, the valve is fully open when the pipe resistance characteristics r0, rated The pressure corresponding to the condition is H1 and the outlet flow is Q1. Flow - speed - pressure curve as shown below.                                                   ? 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. The pump shaft power actual value (kW) can be calculated from the formula: P = Q · H / (η c · η b) × 10-3. Among them, P, Q, H, η c, η b, respectively, said power, flow, pressure, pump efficiency, transmission efficiency, direct drive to 1. Assuming that the total efficiency (η c · η b) is 1, the power consumption saved by the motor when moving the pump from point A to point B 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 be increased, which will threaten and destroy 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 there will be no adverse effects on the system.   comparison from the above is not difficult to come to that: when the demand for the 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 the use of frequency control technology to change the pump, fan speed to control the site pressure, temperature, water and other process control parameters, the same can be based on the system control characteristics of the relationship drawn from the curve drawn above Comparing 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, the energy-saving calculation   for fans, pumps, energy-saving effect of frequency control after the device is usually used in the following two ways to calculate:   1, according to the known fans, pumps in different control modes Traffic-load curve and load changes in field operation.   To an IS150-125-400 centrifugal pump, for example, the rated flow 200.16m3 / h, lift 50m; equipped with Y225M-4-type 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 and 13 hours runs at 50% load; the annual running time is 300 days.     The annual electricity savings for: W1 = 45 × 11 × (100% -69%) × 300 = 46035kW · h   W2 = 45 × 13 × (95% -20%) × 300 = 131625kW · h   W = W1 + W2 = 46035 +131625 = 177660kW · h   0.5 yuan per kilowatt-hour calculation, the annual electricity savings of 88,830 yuan.   2, according to 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 a 22 kW blower used in an industrial boiler as an example. 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 annual energy-saving frequency control when: W1 = 22 × 11 × [1- (46/50) 3] × 300 = 16067kW · h   W2 = 22 × 13 × [1- (20/50 ) 3] × 300 = 80309kW · h   Wb = W1 + W2 = 16067 + 80309 = 96376 kW · h   The amount of electricity saving when the baffle is opened is: W1 = 22 × (1-98%) × 11 × 300 = 1452kW · h   W2 = 22 × (1-70%) × 11 × 300 = 21780kW · h   Wd = W1 + W2 = 1452 +21780 = 23232 kW · h   compared with the amount of savings: W = Wb-Wd = 96376-23232 = 73144 kW · h   0.5 yuan per kWh basis, 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 of 53.5 L / s, lift 50m; with the motor Y200L2-2 type 37 kW. The measured data of the pump under the valve throttling control and the motor speed control are recorded as follows: Flow rate L / s Time (h) Electricity output from power grid (kW · h) Valve throttling adjustment Motor frequency Speed ​​  47 2 33.2 × 2 = 66.4 28.39 × 2 = 56.8   40 8 30 × 8 = 240 21.16 × 8 = 169.3   30 4 27 × 4 = 108 13.88 × 4 = 55.5   20 10 23.9 × 10 = 239 9.67 × 10 = 96.7   Total 24 653.4 378.3   In contrast, frequency control in a day can save 275.1 kW · h compared with valve throttling control, saving electricity rate of 42.1%.     V. Conclusion   fans, pumps and other equipment using frequency control technology to achieve energy-saving operation is a key promotion of energy-saving technologies in China by the national government's universal attention, "People's Republic of China Energy Conservation Law" Article 39 Article put it as a universal technology to promote. Practice has proved that the inverter used in fan, pump equipment drive control achieved significant energy-saving effect occasions, is an ideal speed control