Soot and slag are two different problems. Slag is formation of layers of agglomerated molten ash on the tubes resulting from low melting point ash content in some fuel. Whereas soot is a layer of Pyroletic carbon on the tubes, resulting from improper combustion of aromatic hydrocarbons that are part of the volatile matters in coal. Though the gas temperature in the furnace is very hot, the water wall and super heater metal temperatures are quite cold in comparison. If the volatile hydrocarbons come in contact with this cold metal before combustion due to improper turbulence, these would not burn. A slow pyroletic degradation process would result in to soot formation.

We need to understand two things from this. One, the soot formation mechanism is a slow process and therefore it would take much more than 3-4 hours to build up. The tube surface of any solid fuel fired boiler will be always covered with a layer of dust. Soot blowing operation removes this dust and heat pick up in the water wall increases immediately. But if the spray quantity increases again within 3-4 hours, then it clearly indicates the reason behind attemperation spray increasing would be more likely due to delayed combustion and not soot formation. Secondly, soot formation is an indication of improper combustion. Routine soot blowing operation would not give us the chance of identify if the problem is occurring at all, or, not. Unnecessary soot blowing operation increases the possibility of tube erosion too.

Smart blower can be a good option but then, if we are acting a little smart, we may not need to install the costly hardware at all.

Routine wall blowing could be justified only if we are using coal with high slagging characteristics, which again can be identified.