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.
Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.
Tungsten carbide roller material design
Pre-finishing all vehicles roller should ensure its high toughness, strength, rigidity and thermal conductivity, followed before considering its wear resistance. When designing each vehicles roller, pre-finishing materials should choose carbide grades of Co, Co- Ni- Cr binder content is high (greater than or equal to 25wt%) , requiring an average WC grain size of coarse (5μm ~ 6μm), to obtain a higher shock toughness, proper strength and hardness. For the finishing of the roller movements, particularly the last two rollers of the finish rolling, which suffered load is small, and high relative velocity of the material to be pressed (80 m / min ~ 120 m / min). In this case, the wear resistance of the roller to be the most important requirements, and must ensure the strength , timpact toughness and hardness of a reasonable match, so the binder of Co / Ni content ratio and the average grain WC control of particle size and other factors must have greater control in front of different pre-finishing rolling roll.
Tungsten carbide roller category
According to the structure of tungsten carbide rollers, it can be divided into solid tungsten carbide roller and composite tungsten carbide roller. Solid tungsten carbide rollers have been widely used in pre-finishing and finishing stands high speed wire rod mill (including fixed reducing the rack, pinch roller rack). Composite tungsten carbide roller is made of cemented carbide and other materials, and it can be divided into tungsten carbide composite roll rings and solid tungsten carbide composite roller. Tungsten carbide composite roll rings mounted on the roller shaft; solid tungsten carbide composite roller will be directly cast in the roll axis to form a whole, a large load is applied to the rolling mill.
Tungsten carbide roller production process control
Tungsten carbide rollers produced by powder metallurgy method, the key to its process control is the chemical composition of the material and the mixture was prepared, pressed molding, sintering and deep processing and other preparation process parameters.
1. Preparation of starting material (WC focus quality): As the WC raw material and quality control of the use of different levels of quality may fluctuate, resulting in adverse effects on microstructure.
2. Preparation of the mixture: Mixture preparation is the key to the production process of the roller, the roller of failure modes - trachoma, mainly generated by this procedure.
3. Pressing: roller pressing is an important process of the roller mill.
4. Sintering: roller sintering is to determine the final quality of the roller production processes, use of advanced low-pressure sintering technology, HIP sintering technology can greatly improve the performance of roller.
5. Deep processing: deep processing rollers have a greater impact on the quality and accuracy of the roller surface.
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