I. Introduction î ‹
In industrial production and product processing and manufacturing, fans 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's a big production expense. With the continuous deepening of economic reforms, market competition continues to intensify; energy conservation and consumption reduction has become one of the important means to reduce production costs and improve product quality. î ‹î ‹
The frequency control technology developed in the early 1980s conforms to the requirements of the automation of industrial production and created a new era of smart motors. It can change the old mode that the ordinary motor can only run at constant speed, so that the motor and its dragging load can be adjusted according to the production process requirements without any changes, thereby reducing the motor power consumption and achieving the purpose of efficient system operation. . î ‹î ‹
In the late 1980s, the technology was introduced into China and promoted. Now it has been practically applied in the motor transmission equipment of various industries such as electric power, metallurgy, petroleum, chemical industry, papermaking, food, textile and so on. At present, frequency control technology has become a major development direction of modern electric drive technology. Excellent speed control performance, significant power saving effect, improvement of operating conditions of existing equipment, improvement of system safety and reliability, and utilization of equipment, and prolongation of service life of equipment, etc. are fully reflected with the continuous expansion of application fields. . î ‹î ‹ î ‹î ‹
Second, review î ‹î ‹
Usually in the industrial production, product processing and manufacturing industries, the fan equipment is mainly used in the boiler combustion system, drying system, cooling system, ventilation system and other occasions. According to the production needs, the furnace pressure, wind speed, air volume, temperature and other indicators are controlled and adjusted to Adapt to process requirements and operating conditions. The most commonly used control method is to adjust the size of the damper and baffle opening to adjust the controlled object. In this way, regardless of the size of the production needs, the fan must run at full speed, and the change of the operating conditions will cause the energy to be consumed by the throttling loss of the damper and damper. In the production process, not only the control accuracy is limited, but also a lot of energy waste and equipment losses. This leads to increased production costs, shortened equipment life, and high equipment maintenance and repair costs. î ‹î ‹
Pump equipment also has a wide application space in the production area. Pumps, tank storage and discharge systems, industrial water (oil) circulation systems, and heat exchange systems use centrifugal pumps, axial pumps, gear pumps, and plungers. Pumps and other equipment. Moreover, according to different production needs, throttling devices such as regulating valves, return valves, and globe valves are often used to control the flow, pressure, and water level signals. In this way, not only does it cause a lot of energy waste, damage to the sealing performance of pipelines, valves, etc. It also accelerates the wear and cavitation of pump chambers and valve bodies, and severely damages equipment, affects production, and endangers product quality. î ‹î ‹
Most of the fans and pumps are operated by asynchronous motor direct drive, which has the disadvantages of large starting current, mechanical shock, and poor electrical protection characteristics. It not only affects the service life of the equipment, but also cannot instantaneously protect the equipment when the load is mechanically faulted, and often the pump is damaged and the motor is also burned.
In recent years, due to the urgent need for energy saving and the requirement for ever-increasing product quality, the use of frequency conversion governors (referred to as inverters) is easy to operate, maintenance-free, and has high control accuracy, and can achieve high-functionality; Inverter-driven solutions began to gradually replace damper, baffle, and valve control solutions. î ‹î ‹
The basic principle of frequency conversion speed regulation technology is based on the relationship between the motor speed and the input frequency of the working power supply: n = 60 f(1-s)/p, (where n, f, s, and p represent the speed, input frequency, Motor slip ratio, number of poles of the motor pole; the purpose of changing the motor speed by changing the frequency of the motor power supply. Inverter is based on the above principle using AC-DC-AC power conversion technology, power electronics, microcomputer control and other technologies in a comprehensive electrical products. î ‹î ‹ î ‹î ‹
Third, energy-saving analysis Through the basic laws of fluid mechanics we can see: fans, pumps and equipment are a square torque load, its speed n and flow Q, pressure H and shaft power P has the following relationship: Qâˆn, Hâˆn2, P âˆn3; that is, the flow 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. î ‹î ‹
Taking a water pump as an example, its outlet pressure head is H0 (the static pressure difference between the outlet pressure and the inlet of the pump and the outlet of the pipeline), the rated speed is n0, the resistance of the valve when the valve is fully opened is r0, and the rated operating condition The corresponding pressure is H1, and the outlet flow is Q1. The flow rate-speed-pressure curve is shown in the figure below. î ‹î ‹ î ‹î ‹
In field control, the outlet valve is usually used to control the flow rate of the pump. When the flow rate is reduced by 50% from Q1 to Q2, the valve opening decreases so that the resistance of the pipe network changes from r0 to r1, and the system operating point moves from point A to point B in the direction I. The pressure is affected by the throttling pressure. H1 becomes H2. The actual value of the water pump shaft power (kW) can be derived from the formula: P = Q·H/(η c·η b)×10-3. Among them, P, Q, H, η c, and η b represent power, flow, pressure, pump efficiency, and transmission efficiency, respectively, and the direct drive is 1. Assuming that the total efficiency (η c·η b) is 1, the power consumption saved by the motor when the pump moves from point A to point B is the area difference between AQ1OH1 and BQ2OH2. If the speed of the pump is changed by the speed control method, when the flow rate is reduced by 50% from Q1 to Q2, the pipe network resistance characteristic is the same curve r0, and the system operating point will move from point A to point C along the direction II. The operation of the pump is also more reasonable. When the valve is fully open and only the resistance of the pipe network is satisfied, the system meets the flow requirements at the site and the energy consumption is bound to decrease. At this time, the power consumption saved by the motor is the area difference between AQ1OH1 and CQ2OH3. Compared with the valve opening adjustment and the pump speed control, it is obvious that the use of the pump speed control is more effective and reasonable, with significant energy saving effect. î ‹î ‹
In addition, it can be seen from the figure that when the valve is adjusted, the system pressure H will increase, which will threaten and destroy the sealing performance of the pipeline and the valve; while the speed adjustment, the system pressure H will follow the pump speed n. Lower and lower, so it will not have an adverse effect on the system. î ‹î ‹
It is not difficult to draw from the above comparison: When the demand for the pump flow rate from the site is reduced from 100% to 50%, the use of speed adjustment will save the power corresponding to BCH3H2 compared to the original valve adjustment, and the energy saving rate is above 75%. î ‹î ‹ Similar to this, if frequency conversion speed control technology is used to change the rotational speed of pumps and fans to control other process control parameters such as on-site pressure, temperature, water level, etc., the relationship curve can also be drawn based on the system control characteristics to obtain the above Comparing results. That is, the method of changing the speed of the motor using the variable frequency speed control technology is more energy-saving and economical than the valve and baffle adjustment, and the equipment operating conditions will also be significantly improved. î ‹î ‹ î ‹î ‹
Fourth, energy-saving calculation
For the energy saving effect of frequency conversion speed regulation for fans and pump equipment, the following two methods are usually used for calculation:
1. Calculate the flow-load relationship curves of the known fans and pumps in different control modes and the load changes in the field. î ‹î ‹
Taking an IS150-125-400 centrifugal pump as an example, the rated flow is 200.16m3/h and the head is 50m. It is equipped with a Y225M-4 motor and the rated power is 45kW. The flow-load curve of the pump during valve adjustment and speed regulation is shown below. According to the operating requirements, the pump runs for 24 hours in a row, 11% of which runs at 90% load every day, and 13% runs at 50% load; the whole year runs at 300 days. î ‹î ‹ î ‹î ‹
The annual power saving is: W1=45×11×(100%-69%)×300=46035kW·h î ‹î ‹
W2=45×13×(95%-20%)×300=131625kW·h î ‹î ‹
W = W1+W2=46035+131625=177660kW·h î ‹î ‹
Calculated by 0.5 yuan per kilowatt hour, the electricity savings of 88.83 million yuan per year. î ‹î ‹
2, according to the fan, pump square torque load relationship: P / P0 = (n / n0) 3 calculation, where the power of P0 rated speed n0; P for the speed n power. î ‹î ‹
Take the 22 kW blower used in an industrial boiler as an example. Operating conditions are still running continuously for 24 hours, of which 11 hours per day runs at 90% load (frequency is calculated as 46Hz, motor power consumption is calculated as 98% when damper is adjusted), 13 hours is operated at 50% load (frequency is calculated as 20Hz) The power consumption of the motor is calculated as 70% when the damper is adjusted; the operating time of the year is calculated based on 300 days. î ‹î ‹
The annual power saving during frequency conversion speed regulation is: W1=22×11×[1-(46/50)3]×300=16067kW·h
W2=22×13×[1-(20/50)3]×300=80309kW·h î ‹î ‹
Wb = W1+W2=16067+80309=96376 kW·h î ‹î ‹
The power saving when the baffle opening degree is: W1=22×(1-98%)×11×300=1452kW·h î ‹î ‹
W2=22×(1-70%)×11×300=21780kW·h î ‹î ‹
Wd = W1+W2=1452+21780=23232 kW·h î ‹î ‹
The relative power saving is: W= Wb-Wd=96376-23232=73144 kW·h î ‹î ‹
Calculated by 0.5 yuan per degree of electricity, the use of frequency control can save electricity 36.57 million yuan per year. The parameters of the Centrifugal pump of a certain factory are: Centrifugal pump model 6SA-8, rated flow 53. 5 L/s, head 50m; equipped with motor Y200L2-2 type 37 kW. The actual measured data of the pump in the case of valve throttling control and motor speed control are recorded as follows:
Flow L/s Time (h) Electricity consumed by the grid (kW·h) î ‹î ‹
Valve throttling adjustment Motor frequency control î ‹î ‹
47 2 33.2×2=66.4 28.39×2=56.8 î ‹î ‹
40 8 30×8=240 21.16×8=169.3 î ‹î ‹
30 4 27×4=108 13.88×4=55.5 î ‹î ‹
20 10 23.9×10=239 9.67×10=96.7 î ‹î ‹
Total 24 653.4 378.3 î ‹î ‹
In contrast, in one day, the frequency conversion speed regulation can save 275.1 kW·h of power compared with the valve throttling control, and the energy saving rate is 42.1%.
V. Conclusion î ‹î ‹
The use of variable frequency speed control technology for energy-saving operation of fans, pumps, and other equipment is a key promotion technology for China's energy conservation and has received widespread attention from the national government. Article 39 of the “Law of the People's Republic of China on Energy Conservation†classifies it as a general technology. Promotion. Practice has proved that the inverter has been used in the drive control of wind turbines and pumps and has achieved significant power-saving effects. It is an ideal speed control method. It not only improves the equipment efficiency, but also meets the production process requirements, and thus greatly reduces equipment maintenance and maintenance costs, and also reduces the production cycle. The direct and indirect economic benefits are obvious. One-time investment in equipment can usually be recovered in production from 9 months to 16 months.
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