Abstract: Using advanced information technology, computer technology and network communication technology, a secondary process control system for a large plate field heating furnace was established, which realized automatic tracking of the entire heating furnace production process and unified logistics, information flow and slag contact effects. On the premise of ensuring rolling performance, the discharge temperature of the slag is closest to the target value, the temperature difference and fuel consumption of the slag are minimized, the oxidation loss when the slag is burned is minimized, the production of the heating furnace is balanced, and the work intensity is reduced, etc. It plays a role in protecting the slag of the heating furnace equipment and is the biggest environmental protection measure.
In steel rolling production, the heating furnace needs to uniformly heat various billets to the corresponding rolling temperatures to meet the production requirements of rolled steel products. Only by controlling the heating well and ensuring the heating temperature can we produce rolled steel products with accurate cross-sectional dimensions and up-to-standard performance and quality. Therefore, in steel rolling production, it is necessary to strengthen the temperature control of heating furnaces, actively research and innovate furnace temperature control methods, continuously improve the accuracy of furnace temperature control, and make effective contributions to the improvement of economic benefits and market competitiveness of steel rolling enterprises.
1. Research on improvement measures for temperature control of rolling mill reheating furnaces
2.1 Improve the heat conversion efficiency of the heating furnace
The conversion efficiency of the heating furnace is not only directly related to the cost and production efficiency of steel rolling, but also directly related to the sustainable development of the steel rolling mill. Especially at this stage, the country’s environmental protection requirements for steel companies are becoming increasingly strict. Only by continuously improving the heat conversion efficiency can the heat loss be reduced. and pollution can meet the requirements of sustainable development. Therefore, in temperature control, we must start with both equipment and technology to improve conversion efficiency.
For example, double closed-loop ratio control and double cross-width control are commonly used temperature control methods in temperature control. Both methods can effectively promote the improvement of the thermal efficiency of heating furnaces, but double-closed-loop ratio control is not suitable for extremely rapid temperature changes. In this case, problems such as overoxygen or hypoxia are prone to occur. However, double cross-width control can effectively make up for this shortcoming, effectively control the excess air rate, and ensure combustion efficiency.
At the same time, the response speed of double-cross limiting is slow and cannot meet all production scenarios. Therefore, in specific applications, the two control systems should be jointly used, using double closed-loop ratio control to improve the functionality of double-cross width control, and then using double-cross limiting to improve the dynamic management and control deficiencies of double closed-loop wallpaper control. In addition, we can also start from aspects such as the material structure of the heating furnace to optimize the structure of the heating furnace and apply new materials to improve the insulation performance of the heating furnace and reduce heat loss.
2.2 Optimize the furnace temperature preset system
To better control the furnace temperature, we can start with the furnace temperature preset system, optimize the furnace temperature setting value through corresponding methods, and conduct real-time online monitoring of the billet temperature and furnace temperature. First, furnace temperature fitting. The steel blank needs to move in the heating furnace, so when determining and calculating the temperature of the steel blank, it is necessary to combine the furnace temperature and thermocouple value of the position of the steel billet to measure the thread, and then obtain the furnace temperature distribution curve through the linear fitting. Secondly, the billet tracking model is mainly used to analyze and predict the temperature of the steel billet at various locations, track the position of the billet, and can also predict the surface, steel core temperature and cross-section temperature difference when the steel billet comes out of the furnace based on the furnace temperature distribution curve.
3. Optimized control of each loop of the heating furnace
3.1 Smoke temperature control loop
The action of the smoke temperature valve is feedforward controlled according to the corresponding branch pipe flow rate. At the same time, advanced control algorithms such as soft servo technology, disturbance observer, and overlapping control technology are used to improve the control accuracy of smoke temperature; the disturbance observer model intelligently calculates the changing trend, amplitude, and interference sources of the controlled variables as an intelligent controller. The feedforward input greatly improves the control quality; due to the complexity of the control system of the combustion device, serious coupling, time variability and nonlinearity, and poor actuator performance, the conventional PID algorithm is unsatisfactory. The design of the intelligent controller takes these factors into full consideration and combines human operating experience with modern control theory to achieve ideal control effects.
3.2 Design of safe operation control function of heating furnace
(1) Intelligent voice alarm function
The optimized control system incorporates the main operating faults of the heating furnace into the intelligent voice alarm model. When a certain fault occurs or is about to occur, the optimized control system will alarm with different imitated real-person voices to directly locate the point. If the optimization control system is in a fully automatic optimization state, the operator will only intervene when an alarm occurs. This is what we call a “quasi-unmanned operation.”
(2) Automatic switching function for communication failure
When the DB communication between the optimization control system and the PLC system is abnormal and does not automatically recover within a certain period, the optimization control system will automatically switch control rights to the PLC side without interruption or alarm.
(3) Soft sensor model
There are three main situations for automatic processing of some instrument faults:
First, the measuring instrument is inaccurate, and the optimization control system will implement effective optimization operations based on its changing trend;
Second, the optimized control system can automatically eliminate damaged instruments, such as gas flow, and automatically eliminate the sudden changes caused by this or switch to a soft measurement model;
The third is to design an intelligent controller to deal with valves or hydraulic couplings with poor characteristics.
(4) Optimization of automatic processing of some process faults
The control system has completed the following automatic processing models for process failures: the incomplete combustion prevention control model and the furnace temperature gradient imbalance processing model.
4. Optimize control system applications
(1) The circuits that are put into automatic mode include:
Furnace temperature control loop for each section, soot temperature control loop for each heating section, air smoke temperature control loop for each heating section, furnace pressure control loop, combustion air pressure control loop, operating data statistics technology and assessment function, safety control function (voice alarm, safety limiter), HeroRTS remote service function; heating furnace secondary system (predicting the furnace temperature settings of each section based on the furnace entry temperature and tapping temperature).
(2) Based on the above-mentioned automatic control loop, three-dimensional optimization of gas, combustion air and control points is realized. Under the same working conditions, the optimized control system operation reduces gas consumption by 5.8% compared with the manual operation of the original system.
After the newly opened L2 process control system of the new wide and heavy plate rolling mill was put into production, the heating furnace equipment reached a high level of automation. This system can automatically complete the processes of plate feeding, rolling, data tracking, steel loading, tapping, etc., improving production efficiency. Experimental results show that after adopting the secondary system, the blast furnace temperature control has high precision and strong response-ability, which can effectively ensure the stable operation of the blast furnace and improve the billet heating uniformity and target accuracy. Ultimately, we achieve the goal of improving billet heating quality, increasing furnace output, reducing furnace fuel consumption, and saving more than 2% of energy.