In the complex systems of coal‑fired thermal power plants, pulverized coal delivery pipes bear the critical task of transporting pulverized fuel safely and efficiently into the furnace. The temperature within these pipes is a core parameter that directly affects the safety and economic performance of the boiler. It must not be too high, lest it trigger an explosion; nor too low, as that would impair combustion efficiency or even cause pipe blockages.
1. Temperature Profile of the Delivery Pipe: A Dynamic Range
The temperature inside a pulverized coal delivery pipe is not a fixed value but a range that varies dynamically with operating conditions. Based on a comprehensive review of available information, the typical working temperature primarily falls between 100 °C and 270 °C.
Typical operating temperature: Under conventional design, the pipe is required to withstand temperatures of 100–200 °C. In actual operation, systems using hot‑air conveying exhibit higher temperatures-for example, in plants burning anthracite, the medium temperature can reach 250–270 °C.
Design safety threshold: To prevent premature combustion of pulverized coal within the pipe, relevant codes stipulate that the temperature of the air‑fuel mixture before the burner shall not exceed 160 °C. Therefore, equipment design temperatures often account for more extreme conditions; many delivery pipes and their components are designed for 350 °C or even 450 °C.
2. Influencing Factors Behind the Temperature: An Interplay of Multiple Variables
The temperature of the delivery pipe is determined by several interconnected factors, not by any single one alone.
Conveying method: This is the most dominant factor. Hot‑air conveying systems use approximately 300 °C hot air as the transport medium, resulting in higher pipe temperatures. In contrast, dried‑flue‑gas conveying or direct‑fired pulverizing systems operate at relatively lower temperatures.
Coal properties: Different coals have varying volatile matter and moisture contents, which impose different drying and transport temperature requirements. Coals with high volatile matter are more prone to explosion and therefore demand stricter control over the upper temperature limit.
Outlet temperature of the pulverizing system: The pulverized coal exits the mill at a certain temperature-this serves as the "starting point" for the pipe temperature. This outlet temperature is influenced by coal type, mill type, and other factors, and typically ranges from 65 °C to 100 °C.
Ambient conditions and pipe heat loss: During transport, the pipe exchanges heat with the surroundings, causing a gradual temperature drop along the route. Studies indicate that when the temperature difference between the powder and the ambient environment exceeds 100 °C, a 100‑meter pipe may experience a temperature reduction of 10–15 °C.
3. Why Precise Control Matters: Three Key Objectives
Accurately controlling the temperature of pulverized coal delivery pipes is one of the core tasks in power‑plant operation management, and its significance is threefold.
Ensuring safety and preventing explosions: This is the primary and most important reason. Excessive temperatures can cause the pulverized coal to ignite spontaneously or even explode during transport, leading to severe accidents. Hence, the temperature of the air‑fuel mixture must be strictly maintained below the safety limit (e.g., 160 °C).
Ensuring flow and preventing pipe blockages: If the temperature is too low, the moisture in the coal may not fully evaporate, causing the coal to stick to the pipe wall and form blockages. Maintaining an adequate temperature is essential for good flowability of the pulverized fuel.
Improving efficiency and optimising combustion: An appropriate delivery temperature helps the pulverized coal ignite rapidly upon entering the furnace, thereby enhancing combustion efficiency and overall boiler thermal efficiency. Moreover, temperature is a key input for adjusting combustion air distribution.
4. How to Measure Temperature Accurately: From Contact to Remote Sensing
To monitor pipe temperature in real time, power plants employ a variety of measurement techniques.
Traditional contact measurement: The most common method is to insert a thermocouple with a protective sheath directly into the pipe. However, this approach has drawbacks, including flow disturbance, susceptibility to erosion by coal particles, and the fact that the reading only represents a local temperature.
Advanced non‑contact / indirect measurement: To overcome these limitations, the industry has developed new methods. For example, measuring the outer wall temperature of the pipe and then calculating the average internal medium temperature using mathematical models. In addition, some systems collect temperature data from both the upper and lower sections of the pipe wall to determine whether coal deposition has occurred inside.
5. Summary
The temperature of the pulverized coal delivery pipe is a critical parameter that affects the entire pulverizing system in a thermal power plant. It is not an isolated number but the result of a complex interplay among conveying method, coal properties, pulverizer operating conditions, ambient environment, and more. Accurate monitoring and strict control of this temperature are the embodiment of balancing the three major objectives of safety, efficiency, and economy-truly serving as the "thermometer" for safe plant operation.
If you have a more specific focus-such as the temperature at a particular point (e.g., mill outlet or burner inlet) or a particular temperature‑related issue you are encountering-please feel free to provide additional details, and I will be happy to offer more targeted insights.
