What is a Slag Screen ? What is its function in the boiler ?

The Slag Screen is a bank of specialized Boiler tubes which is fitted at the entrance of the convection passes in a boiler furnace.  The slag screen cools the hot gases and the ash before the entry to the convection shaft.  This minimizes the risk of slag. 

The slag screen can be arranged in an inline arrangement where the slag screen tubes are parallel to the boiler tubes or a staggered arrangement where the tubes are at an angle to the boiler tubes.