For the shapes used in stoking chambers with a primary air supply, it is important to avoid damaging the doors when loading wood. Cracks not only cause progressive degradation of these shapes, but also disrupt airflow towards the nozzle. This then prevents the uniform mixing of the primary air with gases, influencing the burning process itself and preventing the combustion chamber from reaching operational temperatures. This reduces the boiler’s overall efficiency.
But equally important is resistance to the alkalis produced during wood combustion. Alkalis can chemically disrupt a block’s structure, causing its gradual degradation.
Here’s a look at the properties of the mixtures that we typically use when manufacturing shaped blocks for stoking chamber doors: