What Causes Clinkers in CoalFired Boilers? | Hunker
Clinkers, also known as slag, are the parts of the coal that won't burn. The act of burning coal at high heat causes the minerals to melt instead of burn, resulting in ashes that often contain hard lumps. These lavalike lumps then meld together to form even larger lumps that, if not removed, will make the boiler much less efficient.