I. the basis of system design
According to the general drawings of a new 10M2 shaft furnace project of a company, the system is designed on the basis of the successful experience of the similar system and the technological requirements, system structure and main functions of shaft furnace production. Yes.
The system includes four parts: high voltage, low voltage, instrument and automation. Here, we mainly introduce the automatic control system of shaft furnace.
2.System overview
A. main function description and equipment
A large number of instruments and sensors are used to collect temperature, pressure, flow and other data. Our company integrates a variety of signals into the computer automatic control system to achieve real-time monitoring and control of process parameters in the production process.
Shaft furnace automation system adopts the whole network, full digital structure, using Siemens S7-300 PLC and Uygur UniMAT I/O module, Yanhua ADAM module and the upper computer to form an electronic control, instrument control, computer control "three electricity" system structure.
The main equipments of shaft furnace production technology are: batching, drying, pelleting, raw sieve, cloth, baking, unloading, finished product winch, etc. Auxiliary equipment: blower, circulating water pump, soft water pump, gas pressurization, drum cooling, electrostatic precipitation, thin oil lubrication, electrical automation system and instrumentation system.
B. Process Overview
Shaft furnace pellet production is a complex process which integrates gas making, grinding, batching, drying, pelletizing, distribution, sintering and discharging. First of all, the powder iron concentrate and bentonite from the raw material factory, according to a certain proportion, form a mixture after the batching system, from the belt machine to the dryer, after the dryer dehumidification and mixing evenly into the disc pelletizer, so that raw materials form a certain size of ball (green ball). Then the raw balls pass through the distributor and enter the shaft furnace. The raw balls are sintered according to certain rules. The finished balls are exported to the finished pellet yard as the burden for iron-making.
The main control link in production is the shaft furnace section, and its technological process is shown in Figure 1. The raw balls from the pelletizing section are sent to the drying bed through a distributor; after being dried, the raw balls are fed into the shaft furnace, which undergo preheating, sintering and even tropics. The heat exchanged in the three temperature zones comes from the two combustion chambers of the shaft furnace itself; after being cooled, the high-temperature cooked balls are discharged to the shaft furnace through the rotation of the tooth rolls. Finally, the vibrating feeder sends the cooked balls to the discharging car to transport to the stock yard.
Three, system requirements
From a functional point of view, the shaft furnace system consists of four links. The technological process and influencing factors in each link are as follows:
3.1 temperature control links:
Temperature distribution in shaft furnace is one of the determinants of pellet quality. It is generally believed that there are five zones in shaft furnace roasting pellet, which are dry zone, pretropical zone, roasting zone, even tropical zone and cooling zone. The ideal temperature distribution curve is roughly shown in Fig. 2.
In fact, the temperature distribution of shaft furnace is often difficult to form an obvious temperature zone, so it is not desirable to control its temperature directly and accurately. The temperature in the shaft furnace is usually indirectly controlled by controlling the temperature of the combustion chamber. The main factors affecting the temperature of combustion chamber are the flow rate of gas and combustion-supporting air, so in the temperature control link, the flow rate of gas and combustion-supporting air is mainly controlled.
3.2 air control links:
It is very important, not only the combustion-supporting air in the temperature control link, but also the research and application show that changing the composition and distribution of air flow (mainly cooling air) can change the temperature distribution in the furnace to a certain extent.
3.3 cloth control links:
Uniform distribution is very important for optimizing roasting and furnace conditions. The main factors leading to uneven cloth distribution are uneven raw balls, uneven working mechanism and so on. In this system, it is assumed that the raw ball feeding is uniform. In view of the working mechanism of the cloth truck, our company introduces PLC logic control to achieve the action requirements of the cloth truck.
3.4 unloading control:
Four, system configuration and function realization
Based on the above analysis of the design concept and process of shaft furnace system, the control scheme is as follows:
4.1. Automation system composition
The automatic control system is set up according to its functions as follows: raw material system, drying system, pelleting system, raw sieve material distribution system and shaft furnace body system. The electrical and instrumentation parameters in the system are monitored and controlled separately. The belt scale control system composed of single chip microcomputer and the raw sieve material distribution system are controlled by PLC respectively. The main system of shaft furnace is controlled by Yanhua data module. The above systems are equipped with network communication module to ensure the normal communication between the upper computer and PLC and facilitate on-line monitoring and online modification. The upper computer monitors and issues instructions to complete the control of the whole process of shaft furnace production.
4.2 control function
The system mainly performs the following four functions:
4.2.1 data acquisition
ADAM data acquisition module is responsible for collecting gas, combustion-supporting air, cooling air flow, pressure and temperature of each part of the shaft furnace. After processing, the corresponding effective process parameters are transmitted to the industrial control computer of the shaft furnace section through the communication module, and the upper computer automatically adjusts according to the set algorithm.
Example: The pressure measurement conversion unit adopts capacitive pressure transmitter with accuracy of 0.2. The transmitter generates a 4-20 mA signal corresponding to the actual pressure, which is then received by Yanhua analog acquisition module. The real-time pressure value is displayed on the configuration screen.
4.2.2 valve control
Valve control is mainly to control the opening and measuring of each electric control valve. The input control signal of the valve controller is 4-20 mA current signal, and the electric control valve generates 4-20 mA valve position feedback signal output. The valve control system is composed of servo regulator and ADAM module. The control signal is sent to the control module through the industrial computer. The control module outputs the control signal to the operator. The operator outputs the control signal to drive the actuator to make the electric regulating valve reach the specified opening. The valve position opening signal is feedback and transmitted to the industrial computer through the data acquisition module. .
4.2.3 production process control
The main control objects are the distributor and unloader, the disc feeder in the pelletizing section, the disc pelletizing machine in the pelletizing section, the belt and so on. Considering the coordination and interlock between the equipments in the production process and the safety, stability and reliability requirements of the control system, Siemens 300 CPU and 100 million-dimensional distributed I/O series modules are adopted to control the system.
4.2.4 user interface
User interface functions mainly include: processing process parameters from data acquisition system, forming user interface in production; adopting corresponding control strategies and algorithms according to process parameters, forming a reasonable control output to the valve control system or production process control system; displaying the process flow chart of each production process; important process; Real-time display of parameters, historical trend chart display, fault alarm and event record display, gas consumption report display, etc.
4.3, the composition of control system
Control of 4.3.1 shaft furnace system
Shaft furnace system control mainly includes: raw material control system, pelletizing chamber system, drying control system, raw sieve cloth, baking system, finished product system; auxiliary system: circulating water pump room, soft water station system, blower station system, electrostatic precipitation system, gas pressurization system and other major systems. elaborate
4.3.2 raw material control system
The raw material system is mainly composed of disc feeder and belt weigher. The equipment adopts frequency conversion to control the disc and can adjust the material flow at any time according to the need. Control mode: centralized control and manual beside the machine, the machine can be adjusted according to the needs of manual speed, and with the speed display on the box to achieve speed requirements, centralized in the upper computer through the configuration screen speed setting, input the corresponding parameters in the screen, the system can be root The matching speed between the disc feeder and the belt scale is adjusted automatically according to the set parameters, and the matched raw materials are sent from the 1# belt to the dryer. This system is mainly accomplished by the logic process of automatic control by single chip microcomputer.
4.3.3 drier control system
The raw material delivered by the 1# belt conveyor is fed to the dryer through vibrating feed hopper. The dryer system consists of a dryer, a combustion-supporting fan, a feeding belt, a wall vibrator and an instrument. It is used to mix the powder iron concentrate and bentonite in a certain proportion in the raw material factory, and remove the excess water by the dryer to make the raw material mix evenly. The drier is controlled by soft start to reduce the impact of current.
The interlocking conditions controlled by the drier are: 2# belt running, dryer, 1# belt.
Instrument monitoring points are as follows
Temperature measurement: there are two points: the outlet temperature of the combustion furnace is 1, the temperature of the drying hood is 1.
Pressure measurement: there are two points, which are combustion supporting manifold pressure and gas main pressure.
Flow measurement: a total of 1 points, gas main flow.
The instrument cabinet is equipped with a manual/automatic regulator to regulate the pressure of the main gas pipe and the outlet temperature of the combustion furnace.
4.3.4 ball making system
The disc pelletizer makes a raw ball with a certain size (raw balls). In the system, the disc feeder is controlled by frequency conversion, and the pelletizer is controlled by soft start. Because the water in the raw material is difficult to control and the size of the ball is uniform in the production, the operator needs to observe the disc feeder in real time and take corresponding measures. Therefore, the automatic PID control method is not suitable for each disc, and it is mostly manual. The pelletizing machine is equipped with an operation box beside the machine. The speed of the disc feeder, the electric vibration and the start and stop of the pelletizing machine are controlled by adjusting the potentiometer. The produced pellets are transported from the 4# belt to the screening machine.
4.3.5 screening roasting system:
The raw balls from the pelletizing machine are screened and distributed into the shaft furnace. The raw balls are fired. The interlocking between the equipments is as follows:
4.3.6 body baking system:
The main objects to be controlled include: gas main pipe, branch electric regulating valve, combustion-supporting air main pipe, branch electric regulating valve, cooling air main pipe flow electric regulating valve, distributor and unloader. In order to give full play to the performance of the equipment and ensure the safety and reliability of the whole production process, the automatic control system adopts two-stage computer control scheme, the upper computer adopts industrial control computer, the lower computer adopts Siemens PLC and the I/O module of UNIMAT.
For the automatic distribution system, mainly open-loop control, control the speed of the distribution truck to and fro to achieve uniform distribution. The control method of PID and neural network is adopted in the temperature control of shaft furnace.
Temperature control of shaft furnace is mainly to control the temperature of combustion chamber within the range of technological requirements. Two closed-loop PID control loops can be used to form a gas and combustion-supporting air proportional control system to control the temperature of combustion chamber. Its system control block diagram is shown in Figure 3
The PID controller is designed as a single neuron adaptive PID controller, which can dynamically adjust the three parameters of the PID controller to meet the requirements of real-time control.
4.4 control system monitoring screen is as follows
The 4.4.1 roasting system is shown below.
The temperature, pressure, flow rate and valve opening can be monitored and adjusted by this screen. The picture also includes the drum level, the start and stop of the soft water pump, and the running state.
4.4.2 The amount of gas used in the production should be recorded in the report form, so as to facilitate the regular statistics of the use of gas and bring convenience to the production scheduling. The gas cumulative flow chart is as follows:
4.4.4 alarm screen: including all the points in the main screen, by setting the upper limit, lower limit or state can effectively alarm the collected parameters, remind the operator to find the problem early so as to deal with the problem in time. Can also be in the event of failure through alarm records to analyze the problem, to prevent similar problems in the future recurrence.
4.4.5 gas flow curve: we can observe the flow at different time points and monitor in real time.
4.5 the high-pressure system is not explained here.
5., use effect analysis
Under the condition of meeting the technical requirement and according to the working requirement of each equipment, this automatic control system chooses the PLC-300 series CPU of SIEMENS Company and the I/O module of Uygur dimension, which improves the stability of the system and saves the cost of the system to a certain extent. The system is in good condition after being put into operation.
