Why are soot and ash considered undesirable on tube surfaces in a boiler?

Soot and ash accumulating on tube surfaces in a boiler are indeed undesirable primarily because they reduce boiler efficiency. The presence of these deposits acts as an insulating layer between the combustion gases and the boiler tubes, diminishing the transfer of heat. This means that more fuel must be burned to achieve the same level of heating or steam production, leading to higher fuel consumption and operating costs.

In addition to increasing fuel usage, reduced heat transfer can also lead to higher flue gas temperatures, which can further affect overall performance and may lead to unsafe operating conditions. The accumulation of soot and ash can also result in hot spots on the tubes, which may distort or damage them over time. Consequently, maintaining clean tube surfaces is crucial for the optimal performance of a boiler.