Analysis and Realization of double cross combustio

2022-10-16
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Analysis and implementation of double cross combustion control principle of heating furnace

[Key words] combustion control, heating furnace

[Abstract] this paper introduces the combustion control principle and implementation strategy of heating furnace, and gives a solution from the perspective of production practice. 1、 Introduction

the heating furnace of the medium and small bar production line of Laiwu Iron and Steel Co., Ltd. is a walking beam heating furnace. When the billet temperature rises from 20 ° C to 1150 ° C, the production capacity is 120t/h (plain carbon steel) and 105t/h (spring steel). The fuel used is the mixed gas of blast furnace and coke oven. 6. Until the sample is broken, the billet needs to be heated to an appropriate temperature through the five heating zones before being discharged. The combustion control adopts the internationally popular double cross combustion control strategy. The control strategy is transmitted to the operation station through parameter measurement to implement process control, which improves the combustion efficiency and yield. 2、 The instrument control system consists of

(1) the instrument control detection system

is collected by the differential pressure transmitter installed on the pipeline orifice and converted into a standard signal (MA) and sent to the PLC. After the upper computer calculates, it participates in the control

(2) furnace pressure control

furnace pressure control includes three parts: combustion air pressure control, gas pressure control and furnace pressure control, so as to ensure the stability of combustion air and gas pressure and smooth combustion; The pressure in the furnace should be kept within a certain range. Too high will cause the furnace door to spray fire and damage the furnace body and equipment, and too low will affect the combustion quality and effect

(3) heat exchanger protection

the heat exchanger plays a role in saving energy and supporting combustion. The temperature of the heat exchanger should not be too high or too low. Damage the equipment too high; Too low will cause the gas to condense and generate corrosives to corrode the heat exchanger

(4) combustion control

the combustion control part is composed of temperature control and flow control, supplemented by temperature and pressure compensation of flow, which will be introduced in detail later in the article

(5) peripheral instruments constitute 16 sets of

instrument control systems, which are controlled by PI height 53mmd adjustment mode, with manual/automatic switching function. There are 16 sets of actuators, of which 14 are electric and 2 are hydraulic

16 sets of PID control are: upper heating air flow; Upper heating gas flow; Lower heating air flow; Lower heating gas flow; Upper soaking air flow; Upper soaking gas flow; Lower soaking air flow; Lower soaking gas flow; Air flow in preheating section; Gas flow in preheating section; Dilution air valve actuator; Bleed air valve actuator; Air valve actuator; Gas heat exchanger bypass valve actuator; Air diverter valve actuator; Furnace pressure actuator. 3、 Combustion control principle and implementation strategy

(1) temperature and pressure compensation

in gas flow control, temperature and pressure compensation is required due to the different temperature and pressure of the gas. The calculation formula is as follows:

sqr[int (a/b) *int (c/d)

air flow temperature and pressure compensation set K1, and the parameters are as follows:

a - ai1.11 (air pressure) +1.02*10^4;

b - 1.02*10^4+8.5*10^2;

c - (2.72+4.00) *10^2;

d - ai5.1 (combustion air cooling water temperature) +2.73*10^2;

the value K1 calculated according to the formula is transmitted to aoc149, and the measured value of each air flow transmitter is multiplied by this voltage stabilization compensation before participating in the calculation and control

gas flow pressure stabilization compensation K2, the parameters are as follows:

a - ai1.16 (gas pressure) +1.02*10^4

B——1.02*10^4+6.5*10^2;

C——(2.73+3.00)*10^2;

d - ai5.9 (exhaust gas temperature) +2.73*10^2

the calculated value K2 is transmitted to aoc150, and the actual measured value of each gas flow transmitter is multiplied by the pressure stabilization compensation coefficient before participating in the calculation and control

(2) combustion control principle

7. Speed range: 0.05 ~ 500mm/min

the furnace is divided into five parts: preheating section, upper heating section, lower heating section, upper soaking section and lower soaking section. There are 10 ways of gas and air flow regulation system. Because the control principle is basically the same, now take the combustion control of soaking section as an example

in the gas flow regulation circuit, after the output A1 of the furnace temperature PID is converted into the required gas flow according to the actual measured air flow, it is multiplied by a bias coefficient K3 to get A2, and then multiplied by a bias coefficient K4 to get A3. A1, A2, A3 are compared by the selector, and the selected one is taken as the shooting value of the gas flow. The air flow regulating circuit is similar. B1, B2 and B3 are obtained. After selection and comparison, the selected one is multiplied by the flow compensation coefficient and sent to the air flow PID as the set value

the schematic diagram is as follows: (3) precautions

in the implementation of double cross combustion control, the calorific value of gas is an important parameter of combustion control. In order to ensure the smooth implementation of control, calorific value analyzer can be used for detection. If there are many impurities in the fuel gas and the combustion supporting air is dirty, the combustion supporting air purification device, gas pretreatment and other equipment must be added to ensure the smooth and stable operation of the double cross combustion control. 4、 Conclusion

due to the use of double cross combustion control strategy, the combustion is more perfect, the combustion quality is greatly improved, the production cost of steel rolling is greatly reduced, the exhaust gas pollution is reduced, and a reliable foundation for high production efficiency is laid

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