They can be summarized as three kinds: Screw cylinder, shutter cylinder and the multi-tube cylinder. The structure characteristics of the spiral cylinder are that the spiral blades are welded inside the cylinder wall. The structure characteristics of shutter cylinder is that the spiral blades are arranged intensively, so the blades are crisscrossed and in omasum shape. The structure characteristics of multi-tube cylinder (it is also called honeycomb cylinder) looks like simple shell-type heat exchanger, the slag in the tube and the water is outside the tube. The multi-tube cylinders are horizontal type (its axis is level) and inclined type (its axis is inclined with the horizontal ).