Application of Frequency Control Technology in Energy Saving Analysis of Fans and Pumps
In industrial production and product processing manufacturing, wind turbines and pump equipment are widely used; their power 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 production expense. With the deepening of economic reforms, market competition has intensified; energy conservation and consumption reduction has become one of the important means to reduce production costs and improve product quality.
The frequency conversion speed regulation technology developed in the early 1980s is in line with the requirements of the development of industrial production automation, creating a new era of intelligent motors. The old mode that the ordinary motor can only run at a fixed speed mode can make the motor and its drag load adjust the speed output according to the production process requirements without any modification, thereby reducing the power consumption of the motor and achieving the purpose of efficient operation of the system. .
In the late 1980s, the technology was introduced to China and promoted. It has been applied in motor drive equipment in various industries such as power, metallurgy, petroleum, chemical, paper, food, textile and so on. At present, frequency conversion speed control technology has become a major development direction of modern electric drive technology. Excellent speed control performance, remarkable power saving effect, improvement of operating conditions of existing equipment, improvement of system safety and reliability, equipment utilization, and extension of equipment service life are fully reflected in the application field .
2. Overview Generally, in industrial production and product processing manufacturing, fan equipment is mainly used in boiler combustion systems, drying systems, cooling systems, ventilation systems, etc., and control of furnace pressure, wind speed, air volume, temperature and other indicators according to production needs. And adjustment to adapt to process requirements and operating conditions. The most common control method is to adjust the size of the damper and the opening of the baffle to adjust the controlled object. In this way, regardless of the demand for production, the fan must run at full speed, and the change of operating conditions causes the energy to be consumed by the throttling loss of the damper and the baffle. In the production process, not only the control accuracy is limited, but also a large amount of energy waste and equipment loss. As a result, the production cost increases, the service life of the equipment is shortened, and the equipment maintenance and maintenance costs are high.
Pump equipment also has a wide application space in the production field. Pumping stations, pool storage tanks, 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 requirements, control devices such as regulating valves, return valves, and shut-off valves are often used to control the flow, pressure, water level and other signals. In this way, not only a large amount of energy is wasted, but also the sealing performance of pipelines and valves is destroyed; the wear and cavitation of the pump chamber and the valve body are accelerated, and the equipment is seriously damaged, the production is affected, and the product quality is endangered.
Fans and pumps are mostly driven by asynchronous motors, which have shortcomings such as large starting current, mechanical shock, and poor electrical protection. It not only affects the service life of the equipment, but also does not instantaneously protect the equipment when there is a mechanical failure in the load. The pump is often damaged and the motor is burned.
In recent years, due to the urgent need for energy saving and the continuous improvement of product quality, coupled with the use of frequency converter (referred to as frequency converter) easy to operate, maintenance-free, high control accuracy, and can achieve high functionality, etc.; The inverter-driven solution began to gradually replace the control scheme of the damper, baffle and valve.
The basic principle of the 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, p represent the speed, input frequency, Motor slip rate, motor pole pair number); to change the motor power frequency to achieve the purpose of changing the motor speed. The frequency converter is a comprehensive electrical product based on the above principle using AC-DC-AC power conversion technology, power electronics, and microcomputer control.
III. Energy-saving analysis According to the basic laws of fluid mechanics, fans and pump equipment are square torque loads. The speed n and flow rate Q, pressure H and shaft power P have the following relationship: Qâˆn, Hâˆn2, P âˆn3; that is, the flow rate is proportional to the rotational speed, the pressure is proportional to the square of the rotational speed, and the axial power is proportional to the cube of the rotational speed.
Taking a water pump as an example, its outlet pressure head is H0 (the outlet pressure head is the static pressure difference between the pump inlet and the pipeline outlet), the rated speed is n0, and the tube resistance characteristic when the valve is fully open is r0, the rated working condition. The corresponding pressure is H1 and the outlet flow rate is Q1. The flow-speed-pressure relationship curve is shown below.
In the field control, the outlet valve is usually used to control the flow rate at the fixed speed of the pump. When the flow rate is reduced from Q1 by 50% to Q2, the valve opening is reduced to change the pipe network resistance characteristic from r0 to r1, and the system operating point is moved from the original point A to point B along the direction I; H1 becomes H2. The actual pump power value (kW) can be calculated by the formula: P = Q? H/(η c?η b)×10-3 is obtained. Among them, P, Q, H, η c , η b represent power, flow, pressure, pump efficiency, transmission efficiency, and direct drive is 1. Assuming that the total efficiency (η c? η b) is 1, the power saved by the motor is the difference in area between AQ1OH1 and BQ2OH2 when the pump is moved from point A to point B. If the speed control method is used to change the speed n of the water pump, when the flow rate is reduced by 50% from Q1 to Q2, then the pipe network resistance characteristic is the same curve r0, and the system working point will move from the original point A to point C along the direction II. The operation of the pump is also more reasonable. When the valve is fully open, only the pipe network resistance, the system meets the flow requirements of the site, and the energy consumption is bound to decrease. At this time, the power consumption saved by the motor is the difference in area between AQ1OH1 and CQ2OH3. Comparing the valve opening adjustment and the pump speed control, it is obvious that the pump speed control is more effective and reasonable, and has significant energy saving effect.
In addition, it can be seen from the figure that the valve pressure will increase the system pressure H, which will pose a threat and damage to the sealing performance of the pipeline and the valve; when the speed is adjusted, the system pressure H will follow the pump speed n. Reduced and reduced, so there is no adverse effect on the system.
It is not difficult to draw from the above comparison: When the demand for pump flow from the site is reduced from 100% to 50%, the speed adjustment will save the power corresponding to BCH3H2 compared with the original valve adjustment, and the energy saving rate is above 75%.
Similarly, if the variable speed control technology is used to change the speed of the pump and fan equipment to control other process control parameters such as pressure, temperature, water level, etc., the relationship curve can also be drawn according to the system control characteristics to obtain the above comparison result. . That is to say, the method of changing the motor speed by using the frequency conversion speed regulation technology is more energy-saving and economical than the adjustment of the valve and the baffle plate, and the operating conditions of the equipment will also be significantly improved.
4. Energy-saving calculation For the energy-saving effect of the frequency conversion and speed regulation of the fan and pump equipment, the following two methods are usually used for calculation:
1. Calculate according to the flow-load relationship curve of known fans and pumps in different control modes and the load changes in the field operation.
Take an IS150-125-400 centrifugal pump as an example, with a rated flow of 200.16m3/h and a head of 50m; equipped with a Y225M-4 motor with a rated power of 45kW. The flow-load curve of the pump during valve regulation and speed regulation is shown below. According to the operation requirements, the pump runs continuously for 24 hours, with 90% load running at 11 hours per day and 50% load at 13 hours; the running time is 300 days throughout the year.
Then the annual electricity saving is: W1=45×11×(100%-69%)×300=46035kW? h
W2=45×13×(95%-20%)×300=131625kW? h
W = W1+W2=46035+131625=177660kW? h
Calculated by 0.5 yuan per kilowatt hour, the annual electricity cost can be saved by 88,800 yuan.
2, according to the fan, pump type square torque load relationship: P / P0 = (n / n0) 3 calculation, where the power is P0 rated speed n0; P is the power at the speed n.
Take a 22 kW blower used in an industrial boiler as an example. The operating conditions are still running continuously for 24 hours, with 11% of the load running at 90% per day (frequency is calculated at 46 Hz, motor power consumption is calculated at 98% when the baffle is adjusted), and running at 50% load for 13 hours (frequency is calculated at 20 Hz) When the baffle is adjusted, the motor power consumption is calculated as 70%); the annual running time is calculated based on 300 days.
Then the annual electricity saving during variable frequency speed regulation is: 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 power saving when the opening of the bezel 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 power saving: W = Wb-Wd = 96376-23232 = 73144 kW? h
Calculated by 0.5 yuan per kilowatt hour, the frequency conversion speed can be used to save electricity costs of 36.57 million yuan per year.
The centrifugal pump parameters of a factory are: centrifugal pump type 6SA-8, rated flow rate 53.5 L / s, head 50m; equipped with motor Y200L2-2 type 37 kW. The measured data recorded under the condition of valve throttling control and motor speed control of the pump are as follows:
Flow rate L/s time (h) Consumption of power output from the grid (kW?h)
Valve throttling adjustment motor frequency control 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, variable frequency speed regulation in one day can save 275.1 kW compared to valve throttling control? The power of h has a power saving rate of 42.1%.
V. Concluding remarks Fans, pumps and other equipment using frequency conversion speed regulation technology to achieve energy-saving operation is a key promotion technology for energy conservation in China. It is widely recognized by the national government. Article 39 of the Energy Conservation Law of the People's Republic of China lists it as General technology is promoted. Practice has proved that the frequency converter has achieved remarkable power saving effect in the driving control occasions of fans and pumps, and it is an ideal speed control method. It not only improves the efficiency of the equipment, but also meets the requirements of the production process, and thus greatly reduces the maintenance and repair costs of the equipment, and reduces the production cycle. The direct and indirect economic benefits are obvious, and one-time investment in equipment can usually be recovered in production from 9 months to 16 months.
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