Fan is an essential supporting equipment of boiler, which has been widely used in thermal power plant, but the electronic loss of traditional fan is very serious in the process of use. Taking the boiler fan of thermal power plant as the research goal, this paper discusses the demand, principle and scheme of high-voltage frequency energy-saving technology transformation of boiler fan of thermal power plant
With the economic growth, the demand for energy is gradually increasing. In the process of energy use, the phenomenon of loss is becoming more and more serious. The main reason is that the relevant equipment and technology are backward, resulting in low power factor and high energy consumption. This paper analyzes the technical transformation of high voltage frequency conversion and energy saving of boiler fan in thermal power plant.
1.Requirements for technical transformation of high voltage frequency conversion and energy saving of boiler fan in thermal power plant
1.1 principle of boiler fan in thermal power plant
The boiler fans of thermal power plant generally adopt centrifugal high-pressure fans, which are divided into induced draft fan and forced draft fan according to their purposes. The forced draft fan is also divided into primary fan and secondary fan. The primary fan is to convey pulverized coal and air to the boiler, and the secondary fan is to strengthen the stirring of pulverized coal in the boiler and supplement air, so as to fully burn pulverized coal and adjust the boiler load. The induced draft fan sucks out the waste gas to maintain the air pressure balance in the boiler, and maintains the temperature stability in the boiler by sucking out hot air. When the load of the boiler needs to be increased, the control program is to increase the air supply volume of the secondary fan first, and then increase the output of pulverized coal; When the load of the boiler needs to be reduced, the control program is to reduce the output of pulverized coal first, and then reduce the supply air volume of the secondary fan.
1.2 current situation of boiler fan in thermal power plant
It can be seen from the analysis that the load of the secondary fan of the boiler changes frequently. Nowadays, most boiler fans operate in full frequency mode, that is, the operating power of the fan cannot be changed. The baffle is set at the fan outlet. When the air volume needs to be adjusted, it can be realized by adjusting the opening and closing degree of the baffle. This operation mode leads to a large part of the wind power being consumed by the baffle when the secondary fan is adjusted, and even the generated return wind offsets part of the wind power again, resulting in a large waste of power. According to statistics, the power consumption of boiler fans accounts for about 45 percent of the total power consumption of thermal power plant, and the way of baffle adjustment makes the power wasted by fans at high load of boiler about 25 percent , and that wasted by fans at low load of boiler reaches 75 percent .
2. Technical transformation principle of high voltage frequency conversion and energy saving of boiler fan in thermal power plant
2.1 principle of high voltage frequency conversion energy saving technology
The so-called high-voltage frequency conversion technology controls the actual power of the fan by adjusting the output of voltage, so as to further control the speed of the fan and adjust the air volume of the fan. The application of high-voltage frequency conversion technology in the fan can fully open the baffle of the air outlet, and use frequency conversion technology to adjust the air volume output of the fan from the source.
The motor speed formula of the fan is: n {{0}} (1-s) N0, N0 = 60F / P. Where n is the actual speed, N0 is the theoretical speed, s is the slip rate, f is the operating frequency of the motor (60 is 60 s), and P is the number of poles of the motor. It can be seen from the speed formula that without considering the slip rate s (s = 0 0.05), the actual speed of the motor n = 60F / P, that is, n is positively proportional to F, and the value of n will increase with the increase of F and decrease with the decrease of F. therefore, the motor speed n can be adjusted by controlling the output of power to adjust the value of F.
2.2 advantages of high voltage frequency conversion energy saving technology
The application of high-voltage frequency conversion energy-saving technology can avoid the loss of air volume due to baffle, improve the working efficiency of fan and reduce power consumption. Compared with the baffle to adjust the air volume, the high-voltage frequency conversion technology is used to adjust the air volume, which is more accurate in conveying the air volume and can realize the accurate control of the boiler load. Moreover, the application of high-voltage frequency conversion technology can effectively protect the fan when the fan is started. The traditional full pressure starting mode will have a great impact on the engine and fan, which is easy to cause failure and even equipment damage. The high-voltage frequency conversion technology makes the engine start slowly, which effectively avoids this problem and greatly reduces the equipment failure rate.
3.1 selection of high voltage frequency converter
The selection of high-voltage frequency converter needs to consider the voltage level and investment cost. For example, for a 1120 kW fan, the selection of high-voltage frequency converter with 60 kV voltage level is obviously unreasonable, which can not make full use of the high-voltage frequency converter and increases the investment cost. In addition, attention should be paid to the problem of harmonic pollution during external selection. By comprehensively analyzing the actual demand of thermal power plant and comparing several types of high-voltage frequency converter on the market (two-level type, multi-level type, unit series type, etc.), it is more appropriate to select unit series type high-voltage frequency converter. It adopts a new topology circuit in recent years, which has the advantages of high power factor, strong anti-interference ability, low harmonic pollution, low cost, non-stop failure and so on.
3.2 main system transformation scheme
QF is a vacuum circuit breaker, QS1 and QS2 are high-voltage disconnectors, and KM1, km2 and KM3 are high-voltage vacuum contactors. When the high-voltage frequency converter is put into use, first close the vacuum circuit breaker QF, then close the high-voltage disconnectors QS1 and QS2, then close the high-voltage vacuum contactors KM1 and km2 and disconnect the high-voltage vacuum contactor KM3. When the high-voltage frequency converter fails, the control and protection system of the high-voltage frequency converter will automatically disconnect the high-voltage vacuum contactors KM1 and km2 and close the high-voltage vacuum contactor KM3 to switch the high-voltage motor from the frequency conversion state to the power frequency state. In order to ensure the safety and reliability when switching the operation state, it is necessary to design the electrical interlock function, that is, when KM1 and km2 are closed, KM3 cannot be closed; When KM3 is closed, KM1 and km2 cannot be closed again.
3.3 precautions for technical transformation scheme of high voltage frequency conversion and energy saving
1) When connecting the high-voltage frequency converter, pay attention to the difference between the input end and the output end, and do not connect it reversely, so as to avoid accidents when the fan is used.
2) Accurately calculate the critical speed of the rotor and take necessary technical protection measures to avoid distortion resonance.
3) After installation, check whether the inverter cabinet is properly grounded.
4) Put the technology of precharge power supply into operation and fan start-up mode to avoid excessive load on the equipment caused by full voltage start-up.
To sum up, in order to respond to the basic national policy of "energy conservation and emission reduction", it is urgent to carry out energy-saving technical transformation of boiler fans in thermal power plants. The energy-saving transformation uses high-voltage frequency conversion technology. Its principle is to use the input voltage to change the speed of the motor, so as to adjust and control the output air volume of the motor.
