Gas is a clean and efficient secondary energy source. However, due to the fact that gasifier stations are auxiliary production equipment in industrial enterprises, their technological progress has not received enough attention. As a result, the industrial gas industry remains largely at the level of 50s and 60s in terms of equipment and technology. The outdated status of gas technology and equipment severely restricts the widespread application of gas in industrial settings.
A gasifier is a device that produces gas by using coal and air or steam as gasification agents. Anthracite and the gasification agent are fed into the furnace through the coal feeding system and the bottom of the furnace, respectively. In the furnace, an oxidation-reduction reaction occurs, producing gas. The material layer inside the furnace is distributed from bottom to top as follows: ash layer, oxidation layer, reduction layer, pyrolysis layer, and drying layer. For normal gasification of coal in the furnace, a properly distributed and stable material layer, along with a high reaction temperature, is essential.
The automation of gasifier control involves several key areas. One of them is online monitoring of furnace conditions. Gasifier production is a complex chemical process involving solid-gas phase reactions. The internal reactions change with variations in raw materials, equipment status, user demand, and human factors. Parameters such as reaction temperature, material layer thickness, position, and distribution are critical for determining furnace conditions. These parameters cannot be directly measured, so they are typically analyzed based on external data and manual inspection.
With a furnace condition monitoring system, operators can obtain accurate and visual information about the furnace state without manually checking it. The key technologies involved in online detection include sensing, signal analysis, and modeling. Typically, some ash barriers are installed around the lower part of the furnace. Their temperatures reflect the furnace conditions. Instead of manually touching these barriers, thermocouples can be used to measure their temperatures accurately. By analyzing the relationship between temperature and ash layer height and position, operators can determine the location of the fire layer and assess the furnace condition.
However, this method has limitations. When the material layer is uneven, the measured temperature may not be accurate, as it also includes the temperature of the gasification agent and water jacket. Additionally, wear on the ash barriers limits the depth of insertion, leading to delayed temperature responses. To improve accuracy, more measurement points should be added, and the installation positions adjusted. Advanced signal separation techniques can help isolate the true material layer temperature. Comparing the detected temperature data with actual manual measurements will help establish a correlation between temperature and material layer height. This data can then be converted into height signals, allowing an industrial computer to visually display the material layer distribution, position, and temperature, enabling real-time furnace condition monitoring.
Despite its advantages, the monitoring system still depends on stable furnace operation. The sensors installed on the inner wall of the furnace only reflect the temperature near the wall, not the entire material layer. Temperatures within the material layer are estimated theoretically under the assumption of uniform and stable conditions. When the furnace is unstable, the monitoring results may be inaccurate. Therefore, further improvements, such as adding a central ash detection device, are needed to enhance the system's adaptability.
Another important aspect is online detection of gas composition. Replacing traditional manual analysis with a high-quality gas analyzer enables real-time monitoring of gas components. Combined with the furnace condition monitoring system, this forms a complete online monitoring system for the gasifier.
Saturation temperature is another critical parameter that determines the reaction temperature. Automatic control of saturation temperature is essential for gasifier operation. A simple PID loop can achieve this. However, the implementation depends on the specific process. For example, gasifiers with built-in steam collection systems, like the TG-3mA model, can easily implement automatic control. Others, like the TG-3m, lack such systems and must control the saturation temperature by adjusting the amount of external steam added.
In cases where the self-generated steam exceeds the required amount, automatic control becomes difficult. This is common in small-scale soft water stations, especially during hot summer months when the incoming water temperature is high. Similarly, when furnace conditions deteriorate, such as when fires or air holes occur, controlling the saturation temperature becomes challenging. Installing a steam collection system can help overcome these issues.
Emergency power failure handling is another critical area. During a power outage, furnace operators must quickly open steam valves at the bottom of each furnace to prevent gas backflow. However, in large gas stations with multiple furnaces, manual operations are impractical. Automating this process ensures rapid and effective response. By replacing the electromagnetic control valve in the saturation temperature system with a pneumatic diaphragm valve, the system can automatically supply steam to the furnace bottom during a power failure, reducing the risk of explosion caused by negative pressure.
Automated coal feeding and ash removal also play a vital role in maintaining proper material layer distribution. These operations directly affect the height and position of the material layer. Manual operations are prone to human error, especially in shift-based systems. Implementing automated coal feeding and ash removal can significantly reduce these issues. Using temperature data from the furnace outlet, coal feeding can be controlled. Under stable conditions, the temperature fluctuates predictably, making it a reliable control parameter. Additionally, by correlating coal input with ash output, the system can automate both processes. This approach allows for small, frequent coal additions and cyclic ash removal, which is scientifically sound but difficult to achieve manually.
Load regulation is also important for large gas stations with multiple users and complex distribution systems. Adjusting the load by regulating the air flow to each furnace is a common practice. However, this can be costly and complex. An alternative is to adjust the blower speed instead of individual air valves, simplifying the control process. Using a simple PID loop, the system can automatically regulate the load based on pressure changes.
Steam collection tank water level and coal bunker level controls are relatively straightforward and well-established. These systems are easy to implement and maintain.
Finally, integrating all these systems into a computerized control system is essential. By combining online monitoring, temperature control, coal and ash management, and load regulation, a comprehensive computer control system can be established. This system uses Siemens technology and custom monitoring tools, with multiple operator stations forming a centralized control center. Operators can monitor and manage the entire system remotely, improving efficiency and safety.
In conclusion, the automation of gasifiers involves various industrial control technologies. It is essentially a process of optimizing and upgrading existing processes and equipment to meet the requirements of automation. The success of such projects depends on the involvement of experienced personnel who understand the gas production process. The computerized control system for gasifiers represents a significant achievement in applying information technology to traditional industries, contributing to improved technology, equipment, and management in the gas industry.
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