Automatic Control To The Pulse Regenerative Heating Furnace

Improving secondary energy source efficiency is the focus of reducing energy consumption in the steel industry, and also the key point for an enterprise to implement low-cost business strategy, increase profitability and benefit the society. In the past over a long period of time, China's steel industry used coal, heavy oil and other high calorific value, non-renewable energy as the main fuel of the steel rolling furnace. With the continuous development of heating furnace technology, gas heating furnace that takes gas as its main fuel is promoted to use continuously. Especially in the nineties of last century, with the application of high temperature combustion technology, regenerative heating furnace that takes blast furnace gas with low calorific value as its fuel becomes the mainstream.High temperature combustion—HTC, also called high temperature regenerative combustion technology, is a totally new combustion technology that has the widespread application in the developed countries since 1990s. It injects the high temperature air into the furnace, maintained at a low oxygen condition, while delivers fuel to the gas flow, resulting in combustion. The air temperature is heated to above 800℃-1000℃and the oxygen content of air in the combustion zone is 21%-22%. Compared with the conventional combustion process, the most important feature of high temperature combustion is saving fuel, reducing CO2and NOx emissions and lowering combustion noise, which is known as one of the key combustion technology in the 21st century.As regenerative heating furnace uses reversing operation to achieve regenerative heat storage-preheat cycle, during the reversing period, the gas can not enter the furnace, which causes a large disturbance on the combustion process, increasing the difficulty of automatic control. Different from the focused reversing heating furnace, pulse heating furnace increases the groups of reversing valve. Generally speaking,10-20 group of reversing valves are used based on the length of furnace. Each group of reversing valve controls the combustion of one section and every group of reversing valve changes intermittently in a sequence according to the production situation. As pulse heating furnace uses small reversing valve, the speed for reversing is very fast. It does not use the purging process, and the gas in the process of reversing has almost no interruption, at the same time, the function of segmentation due to the increase of the group of reversing valve greatly reduces the disturbance in the combustion process.This project starts from the process characteristics of pulse combustion regenerative heating furnace, adopts the theory of fuzzy control and PID control, combines the study method of classical control theory, focuses on the study of the reversing control, furnace temperature control, air gas pressure control, residual oxygen and the strategies of air coal ratio. Based on the characteristics of pulse combustion and actual situation that air gas flow can not be measured accurately, pulse combustion furnace temperature discrete optimization model and air gas pressure control model. The implementation of the pulse combustion furnace temperature discretized optimization model cleans up the influence of reversing control to combustion process, while ensuring a uniform temperature field under different conditions. The implementation of air gas pressure control model solves the long-troubled technical problem of the inaccurate testing of the gas flow in furnace combustion control and linear feature, ensuring the hit rate of the excess air ratio, improving the combustion efficiency and reducing NOX emissions. At the same time, this model also raises the theoretical point of view that residual oxygen pressure control guides air gas control to achieve the air-gas ratio.The study result of this project is applied to the 2nd heating furnace in middle mill in Hebei Hong Rong Iron and Steel Co. Ltd. which achieves automatic reversing combustion control. Fluctuations of furnace temperature control is less than 5℃, while the realization of air gas pressure automatic control finds a new program for solving the long-term problem of regenerative heating furnace flow measurement and control.