How to Improve the Thermal Efficiency of Coal-Fired Boilers
How to Improve the Thermal Efficiency of Coal-Fired Boilers
Improving the thermal efficiency of coal-fired boilers is indeed a subject that requires expertise. The following aspects can be addressed to achieve this:
1. Rational Air Supply and Air Volume Adjustment in Coal-Fired Boilers:
Rational air supply is crucial for enhancing combustion. In mechanized combustion boilers, such as chain-grate, vibrating, and reciprocating boilers, it is important to provide air reasonably based on the unique characteristics of the combustion process to promote efficient burning within the furnace.
2. Control of Furnace Excess Air Ratio:
Controlling the furnace excess air ratio is a measure to improve the completeness of fuel combustion and reduce heat loss. An excessively high excess air ratio can lower the furnace temperature, leading to a decrease in combustion speed, which in turn increases gas incomplete combustion loss and solid incomplete combustion loss. This manifests as thick black smoke, high carbon content in ash residue, increased fuel consumption by the boiler, and a significant drop in output. Conversely, an excessively low excess air ratio often results in incomplete combustion due to insufficient oxygen for combustibles. This also leads to increased gas and solid incomplete combustion losses. Therefore, there exists an economically optimal value for the furnace excess air ratio, which minimizes the sum of q2, q3, and q4, known as the optimal excess air coefficient. This value can be determined through combustion adjustment tests.
3. Maintaining High Furnace Temperatures:
Maintaining high furnace temperatures is a prerequisite for rapid fuel combustion. In stratified combustion boilers, pulverized coal boilers, oil, and gas boilers, under normal combustion conditions, furnace temperatures can reach 1300-1600 degrees Celsius, with furnace outlet flue gas temperatures around 1000 degrees Celsius.
4. Purpose of Maintaining High Temperatures in the Furnace:
1. To increase the chemical reaction rate of combustion, reducing losses from q3 and q4.
2. To enhance radiant heat transfer intensity.
Measures to maintain high furnace temperatures may lead to a noticeable decrease in furnace temperature when using inferior coal. In such cases, one approach is to use refractory bricks or refractory concrete to shield part of the radiant heating surface, reducing water cooling within the furnace. Another option is to install an air preheater to preheat cold air before sending it into the furnace, thereby increasing the heat input and raising the furnace temperature while lowering the exhaust gas temperature.