A badly soothed HRT boiler under coal firing will typically show a ________ compared to a clean boiler.

• A. Lower stack temperature
• B. Higher stack temperature
• C. Normal stack temperature
• D. Reduced smoke output

Answer: (B)

When a boiler is poorly soothed, specifically under coal firing, it impacts the efficiency of combustion and heat transfer processes. A badly soothed boiler has a buildup of soot and other combustion byproducts on its heat exchange surfaces. This buildup acts as an insulator, reducing the heat transfer efficiency of the boiler.

As a result, more heat is retained in the combustion gases, which leads to a higher stack temperature compared to a clean boiler. A clean boiler allows for more effective heat transfer, leading to cooler flue gases and lower stack temperatures. Thus, the correlation between the state of the boiler and the stack temperature is clear: a poorly maintained boiler with soot will exhibit a higher stack temperature due to reduced thermal efficiency and heat accumulation in the exhaust gases.