Wet bottom furnace
A Wet-bottom furnace or wet-bottom boiler is boiler that contains a wet bottom furnace. It is a kind of boiler used for pulverised fuel firing. In wet bottom boiler the bottom ash is kept in a molten state and tapped off as a liquid. Wet bottom boiler slag is the molten condition ash as it is drawn from the bottom of the slag-tap or cyclone furnaces. An advantage is the fact that the end product in this process has a higher value compared to that of a dry bottom boiler. Wet bottom boilers are  preferred for low volatile coals that produce a lot of ash. But it has higher investment costs and higher maintenance costs, so it is built less often. Wet-bottom boilers. If the ash fusion temperature is less than the furnace temperature then that type of furnace is called a wet bottom furnace.