Boilers are the main heating equipment in industrial production. Electricity, machinery, metallurgy, chemicals, and civil use all require boilers to provide heat, but depending on the industry, the size of the boilers varies. As an important industrial equipment, in the case of ensuring its safe and stable operation, it should consider its automatic production, improve the automatic operation ability and work efficiency.

Boiler production plays an important role in the industry. The early boiler automation is very low, the monitoring system is imperfect, resulting in continuous system failure, but the boiler is still widely used because it is suitable for various industries. The extensive use of boilers makes the boiler modernized. Be inevitable. The management of boiler modernization requires not only safe and highly automated control schemes, but also factors such as high efficiency, energy saving and environmental protection. Therefore, for the automatic operation of the boiler, we need continuous research and exploration by the people who control it, and strive to achieve a safe and efficient height for the actual operation of the boiler.

There are many temperature control methods for forming a boiler, but basically it is determined based on the relationship between the heat supply and heat dissipation of the boiler. When the heat and heat are balanced, the furnace temperature is kept within a given range. When a certain factor changes, the actual temperature collected from the temperature sensor is compared with a given temperature to obtain the difference between the two, that is, the deviation. The controller sends a corresponding signal according to the specific conditions of the actual deviation value according to the specified law, controls the size of the controlled quantity, and restores the temperature to the range of the given value, thereby realizing automatic control of the temperature.

There are different control methods depending on the type of boiler and the specific conditions on site. From the use, it can be divided into domestic boilers, industrial boilers, and power station boilers. The domestic boiler is mainly operated under low pressure and provides hot water for daily life. It can also be called hot water boiler. This design is the epitome of such boiler; industrial boiler is basically produced under high pressure, which needs to provide a large amount of heat; The power station boiler mainly heats the water to a high-temperature and high-pressure steam state, thereby driving the steam turbine to generate electricity, and can also be a steam boiler. On the other hand, the boiler is mainly divided from the perspective of fuel, mainly including coal-fired boilers, oil-fired boilers, gas-fired boilers, and electric heating boilers. Three types of boilers based on coal, fuel and gas require air as a combustion improver. When the ratio of fuel to air is suitable, the maximum energy efficiency can be achieved. Therefore, such control systems will inevitably use complex algorithms such as ratio control, while burning. The process is complicated and the interference is too much. It is also necessary to monitor the oxygen content of the flue gas and the flame of the furnace. Therefore, most of the boilers of this type of combustion need complex, accurate design, commissioning verification and trial operation before they can be put into the on-site production; Electric heating boilers can control the furnace temperature because of the single mode of energy supply, adjusting the current or voltage of the heater, and the delay is small, the energy utilization rate is high, etc., but it can provide less energy. Therefore, the scale of use is small.

Based on the actual conditions and control requirements, this design selects the electric heating type hot water boiler under the AE2000B type experimental device as the object.

The AE2000B process control experimental device is based on the characteristics of industrial automation and related professional teaching. It draws on the characteristics and strengths of similar experimental devices abroad, and is closely related to the current large industrial automation site. It is widely used in industry and is leading. AI intelligent instrument plus configuration software control system, DCS (Distributed Distributed Control System), after careful design, repeated experiments and repeated argumentation, launched a set of experimental equipment based on undergraduate, focusing on postgraduate teaching and subject base construction. The detection signal, control signal and controlled signal of the AE2000 process experiment device are all ICE standard, that is, the voltage is 1~5V and the current is 4~20mA.

Due to the complicated situation of the actual industrial site and the interference, the controller selects the Siemens S7-200 PLC as the controller because of the selection of the controller with strong anti-interference ability and stable operation, and the characteristics of integrated microcontroller and PLC. Controller. The commonly used Siemens S7-200 series PLC has 224 or 226. This design uses 224 as the controller. As a small PLC introduced by Siemens, Siemens S7-200 series PLC has the characteristics of small size, open communication, large program and data memory, integrated RS485 interface, good expandability and powerful command functions. It is widely used in industrial production sites. Small-scale control system.

The configuration software is a convention in the country, and there is no clear definition. It can be understood as “configuration monitoring software”. It means that the user completes the software functions he needs in a simple way like “building blocks” without having to write a computer program, which is called “configuration”.

Configuration software, also known as configuration monitoring software system software. It refers to some specialized software for data acquisition and process control. They are located in the software platform and development environment at the level of the monitoring layer of the automatic control system. They use flexible configuration methods to provide users with a common level of software tools for quickly building monitoring functions of industrial automatic control systems. The configuration software has a wide application field and can be applied to data acquisition and monitoring control and process control in power systems, water supply systems, petroleum, chemical and other fields.

At present, the commonly used configuration software includes Siemens WINCC, Beijing Kunlun MCGS, Asian Control Kingview, and Beijing 3D force control. Most of the foreign configuration software is only for its own PLC, and the domestic configuration software can basically Several major PLCs are used together.

This design selects the configuration software MCGS of Beijing Kunlun as the upper computer. MCGS is a configuration software for quickly constructing and generating computer monitoring system. It can run on various Microsoft-based 32-bit Windows platforms. It provides users with solutions to solve practical engineering problems in a variety of ways, including animation display, alarm processing, process control and report output. The field of automation has a wide range of applications.

This design uses Siemens S7-200 PLC as the controller, Beijing Kunlun configuration software MCGS as the upper computer, through the on-site temperature sensor for temperature acquisition, using thyristor to adjust the temperature across the heater and other methods to control the heating effect, to achieve The required process requirements for control. The purpose is to understand how the S7-200 PLC is used in the actual industrial production process during the design process, and to solve the problem of instability of most controllers in the case of industrial interference and complicated conditions. Through hands-on operation and observation on the host computer, the specific conditions of the water temperature in the boiler are remotely monitored in real time, and a complete real-time curve of the furnace temperature is obtained. At the same time, it is normal to monitor whether the process is running and achieve the purpose of safe production.

The selected controlled object is a common electric heating boiler, which directly transfers heat to the liquid to be heated through an electric heating rod, and heats a certain amount of liquid to the temperature required by the process.

The liquid to be heated is directly pumped into the boiler by the Danish pump. At the same time, there is an electric regulating valve on the conveying pipe. There is also a liquid level sensor inside the boiler. The sensor and the electric regulating valve form a closed-loop control circuit to ensure the liquid inside the boiler is stable and set in the program. The upper and lower limits of the liquid level ensure safe operation in the boiler. There is an electric heating rod in the boiler and its output voltage is controlled by a single-phase SCR controllable voltage regulating device. At the same time, there is a temperature detecting device in the boiler, and the two and the controller PLC form a closed-loop control loop to achieve the purpose of adjusting the temperature.

In this design, it is required to control the boiler temperature. Therefore, for the liquid level part, only the liquid in the boiler is detected. This liquid level is used as the reference value, and it is used as the alarm value of the upper and lower limits of the liquid level in terms of safety control.

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