Application of Gas Analysis Technology in Combustion Control of Heating Furnace

 The heating furnace is the key equipment in the steel rolling production line. To make its oxidation loss rate low and the energy consumption of the heating process low, it is necessary to control the heating furnace. The calorific value of the gas medium of the heating furnace is an important parameter directly related to the heating quality and process consumption.

      Taking the heating furnace of a wide-thick plate production line of an iron and steel as an example, the fuel used in the heating furnace is a mixed gas of blast furnace gas, coke oven gas and converter gas. Problems such as accurate calorific value parameters bring great difficulties to the combustion control of the heating furnace, which directly affects the heating quality of the slab and the oxidation burning rate, resulting in high gas consumption indicators.

      Therefore, the calorific value of the furnace gas medium is an important parameter directly related to the heating quality and process consumption. At present, there are two common heating value test methods: manual analysis and combustion calorimeter.

1. Manual analysis

      The manual analysis method is that the austenitic gas analyzer analyzes the gas composition. The full analysis items are CO2, CnHm, O2, CO, CH4, H2 and N2. The first four items are measured by absorption method, CH4 and H2 are measured by combustion method, and the remaining gas is regarded as the volume of N2. Finally, the calorific value of the gas calculated by the empirical formula Q = K1 * V (CO) + K2 * (H2) + K3 * V (CH4) (K1, K2, K3 are empirical parameters)

      In this way, artificial sampling error, time lag operation error, manual reading visual error and manual calculation error are produced in the testing process. Secondly, it is analyzed that the sampling interval is 2h or longer, which cannot meet the real-time adjustment requirements of the furnace's online combustion control.

2. Combustion calorimeter

      The combustion method calorimeter can realize continuous automatic analysis of the calorific value of coal gas, but the use and maintenance requirements are relatively high, the cost is relatively expensive, and there are still the following problems in practical applications:

(1) Because there are many impurities in the gas, such as dust in blast furnace gas, tar in coke oven gas, etc., it is often caused (the pressure reducing valve and the fine filter in the pretreatment device are blocked), the intake pressure is too low, and eventually As a result, the analysis value is low, or even a flameout, and the analysis is terminated;

(2) In addition, when the humidity in the gas is high, condensate may easily be generated in the pipeline during the analysis process, resulting in blockage of the pipeline and seriously affecting the analysis;

(3) The measured value of the calorimeter has a little lag, and often differs from the calculated value by about 1MJ, resulting in the combustion control cannot respond to the control in time when the calorific value fluctuates greatly.

(4) The exhaust gas generated after the combustion in the calorific value analysis chamber is flooded in the entire analysis room, and there is no lack of effective emissions, which affects the thermal balance during the analysis and also causes errors in the measurement.

In order to optimize the gas analysis process, the infrared gas analyzer newly developed by Tianyu Intelligent Control Co., Ltd. overcomes the disadvantages of the manual analysis method and the combustion method calorimeter. It uses infrared sensors to measure CO For the concentration of CO2, CH4, and CnHm, the thermal conductivity sensor is used to measure the H2 concentration, and the electrochemical sensor is used to measure the O2 concentration. At the same time, the theoretical heating value of the gas is calculated based on the concentration of the measured components. The calculation method of the mixed gas calorific value is as follows:

Q = 126 [CO] +108 [H2) +359 [CH4] +652 [CnHm] MJ / m3

In the formula: [CO], [H2], [CH4], [CnHm] respectively represent the volume concentration of combustible components in the gas.

      The infrared gas analyzer replaces the manual sampling and manual analysis of the austenitic gas analyzer, which can realize automatic measurement and avoid artificial errors. At the same time, the pretreatment system and the instrument have the characteristics of simple structure and convenient operation and maintenance compared with the combustion method calorimeter , More suitable for real-time online analysis requirements of the furnace combustion system.

      The online infrared gas analyzer is also provided with a data transmission interface, which can be transmitted to the superior heating furnace centralized control system through the RS-232 or RS-485, 4-20mA output interface. This provides remote monitoring parameters and automatic control setting parameters for the heating furnace combustion system control.

Prospects of optimizing combustion control after using gas analyzer

      The infrared gas analyzer can be used to guide the operator to accurately adjust the air-fuel ratio, length and length of the flame control of each burner and each temperature control zone according to the gas composition and calorific value of a steel thick plate heating furnace. Improve the combustion efficiency of fuel, which has significant significance for the improvement of the comprehensive benefits of the production lines of iron and steel enterprises. At the same time, the precise control of the air-fuel ratio of each burner and partition can also reduce the generation of NOX and other pollutants, which meets the actual requirements of energy saving and emission reduction and environmental protection.

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