Yuxi Xinxing Iron & Steel Co., Ltd. is an iron and steel conglomerate in which Kunming Iron & Steel Group implemented a provincial multiplication plan and made full use of the Yuxi region's resource advantages in the expansion of the Hongta District. The company was completed and put into operation on March 15, 2005. The main products are:
I. Overview
Yuxi Xinxing Iron & Steel Co., Ltd. is an iron and steel conglomerate in which Kunming Iron & Steel Group implemented a provincial multiplication plan and made full use of the Yuxi region's resource advantages in the expansion of the Hongta District. The company was completed and put into operation on March 15, 2005. The main products include square rectangular continuous casting slabs, slabs, hot-rolled ribbed steel bars, medium-wide broadband, etc. The products sell well in such markets as Yunnan, Sichuan, Chongqing and Guangdong. In the excellent situation of the country’s continuous improvement of the market economy system, the acceleration of reform and opening up, and the development of the western region, Yugang has seized the opportunity to accelerate its development, widely absorbed the successful experience of excellent domestic and foreign iron and steel enterprises, optimized the technological structure, and vigorously promoted technological progress and energy saving. The work of reducing consumption and cleaner production has made the structure of steel products more reasonable and the market competitiveness has been significantly enhanced. It has achieved a qualitative leap in the industrial process of modernization, intensification, and high efficiency, and has achieved sustainable development for the company and the Yuxi area. Energy conservation and environmental protection cause and economic development have made great contributions.
Second, the working principle
In the broadband operation area, a three-section beam heating furnace is adopted, and the amount of air supply is adjusted by an air intake valve. The blower is designed for one-use, one-ready, and 24-hour operation.
In the normal production of cold steel heating, the blower inlet valve opening is 70 ~ 80%, the air supply pressure is maintained at about 4.5kPa, to ensure that the furnace heating temperature.
When the heating hot steel bad blower inlet valve opening is 50 ~ 60%, the air supply pressure is maintained at about 4.5kPa, when the heating furnace insulation blowing air demand is less, the inlet valve opening is reduced accordingly, send The wind pressure remains around 4.2 kPa.
Gas exhaust and air exhaust air volume adjustment by the inlet valve. In the normal production of heating cold steel, gas exhaust fan air exhaust intake valve opening is 70 ~ 85%, in the normal production of heating steel is bad, the gas exhaust fan air exhaust fan air inlet valve opening degree is 50~60%, in the heating furnace, the two fan inlet valve opening is 30%.
Air exhaust fan gas exhaust fan inlet valve opening according to the rolling speed of steel rolling size to ensure that the furnace temperature is constant, the two exhaust temperature control within 100 °C, over 180 °C alarm, heating furnace fan technology The figure is as follows:
Third, the system configuration
The three-section beam furnace blower, gas induced draft fan, and air induced draft fan are selected by the maximum production capacity of the heating furnace because of the selection of the motor and the fan. Since the actual production capacity has not reached the maximum production capacity, the gate has been adjusted for a long time. The method of increasing the fluid resistance of the pipe network is used to achieve the flow control, so the system has low efficiency, large power consumption, and serious waste of electric energy.
Due to the requirement of continuous and stable supply of air during normal production, the air volume and air pressure change little. At this time, throttling loss can be eliminated through the adjustment of the speed of the fan by the inverter, and at the same time, the operating efficiency of the fan is improved, although the load rate of the motor is The decrease will reduce the operating efficiency, but the decrease in the operating power of the fan will greatly reduce the loss of the motor and eventually reduce the operating power of the motor. This will save energy.
1 Variable speed control principle:
In accordance with the basic principles of electrical engineering, the motor speed principle satisfies the following relationship:
n=(1-s)60f/p
Where: P-motor pole pairs
F-motor operating frequency
S-slip
From the formula, it can be seen that the synchronous speed N1 of the motor is proportional to the operating frequency N of the motor. Since the slip S is generally smaller <0.05, the actual speed N of the motor is equal to the synchronous speed N1 of the motor, so the power supply of the motor is adjusted. Frequency F can change the actual speed of the motor.
And changing the frequency must change the supply voltage, the electromagnetic relationship produced by the AC motor:
E=4.44fw?
Where: E-motor electromotive force
F-stator frequency
W-winding factor
?-Air gap main flux
When regulating the speed of a different-frequency motor, it is desirable that the main flux is constant and the u/f curve is kept constant. Therefore, when the frequency is changed, the power supply voltage also changes.
2 fan speed-regulating principle:
Due to the complexity of the fluid inside the fan, the theory alone cannot accurately calculate their performance. Only the similar theory in fluid mechanics can be used to calculate the operating conditions of the fan through experiments and simulations. When similar laws are applied to the same fan running at different speeds, the following equation can be obtained:
When changing the speed of the fan, the relationship between the speed n, flow Q, pressure (head) H, and shaft power P is:
It can be seen from the above equation that the flow rate is proportional to the rotational speed, the pressure is proportional to the square of the rotational speed, and the shaft power is proportional to the cube of the rotational speed, so reducing the rotational speed can significantly reduce the power consumption. The energy-saving principle of a fan is to use a speed control device instead of a damper to regulate the flow, reduce the loss of the section, and save energy. A fan is a mechanical device used to transfer gas. A fan is a type of machine that converts the shaft power of a motor into mechanical energy. Their starting torques are small, the load is light, and they have great potential for energy saving.
3 Renovation plan:
The current control mode of the heating furnace blower is mainly based on the demand of the combustion air volume of the heating furnace. The air induced draft fan and the gas induced draft fan are mainly realized according to the induced air temperature and the furnace temperature by adjusting the opening degree of the valve. As the combustion air blower and induced draft fan process is relatively simple, there is no need to do closed-loop control. The retrofit program considers keeping the air intake valve fully open after using the frequency converter, and manually adjusting the fan speed according to the production needs. The system can freely change the amount of induced draft at any time to adapt to changes, maintain the normal economic operation of the wind turbine, and achieve the purpose of stable control, convenient operation, and energy conservation.
In addition, in order to ensure the reliability of the system, the existing control equipment and operation mode of the blower induced draft fan will remain, the design frequency/inverter operation switching selection on the control loop, and the manual/inverter selection will be manually switched to achieve the combustion-supported centrifugal fan. Power frequency or variable frequency operation. Since the heating furnace blower is used for one use and one preparation, the frequency conversion transformation adopts a one-to-two frequency conversion control mode, and the manual switching function of the 1# and 2# fans is set.
Main circuit diagram
In order to reduce the labor intensity of on-duty workers, the start/stop, work/change and speed control of the combustion air blower and induced draft fan after transformation are implemented in both centralized and remote operations, and the existing PLC computer control system is used to use the existing PLC. Module standby point, through the computer control system in the combustion control system to modify the program to increase the blower and induced draft fan speed control operating function and inverter output frequency, output current display.
4 wiring diagram:
Fourth, the transformation of income
Take the gas induced draft fan as an example
Fig.: Frequency converter in operation
The operating parameters of the gas induced draft fan motor after transformation are:
Based on the above actual use results indicate:
The average energy saving rate is over 40%, and the cost can be recovered in about one year.
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