What characteristic ensures that slag is deposited prior to entering the superheater in a solid fuel boiler?

The characteristic that ensures slag is deposited prior to entering the superheater in a solid fuel boiler is controlled gas temperatures below the ash fusion temperature. When the gas temperatures remain below the ash fusion temperature, the ash produced from the combustion of solid fuels does not melt and instead stays in a solid state. This allows the ash particles to accumulate and form slag in the boiler before they reach the superheater.

Maintaining these lower temperatures is critical because, if the gas temperature exceeds the ash fusion temperature, the ash can melt and adhere to surfaces, creating operational challenges such as corrosion, fouling, and reduced heat transfer efficiency in the superheater. By effectively managing the gas temperatures, operators can ensure that the undesirable formation of molten ash is minimized, promoting better operational reliability and efficiency of the boiler system.

Other factors, such as the design of the burners or the pressure of the flue gas, do not directly control the behavior of the ash in relation to the temperatures encountered prior to the superheater. Similarly, the insulation of the superheater may help in maintaining its desired operational temperatures but does not influence slag formation upstream in the boiler.