Ash is a complex product with very erratic flow properties. Primarily very wet the ash tends to hang on to vertical faces - especially if it is allowed to impact against them.

Ash will react to produce a multitude of flow conditions - which vary with moisture content and lump size.

You are mixing fly with coarse, or bottom, ash. It is difficult to obtain reasonable mixtures, so the burden will contain lenses of different characteristics. This can cause severe blockages.

For those reasons pumping is a preferred option. Alternatively you may need water cannon to wash out the wagons. ■