Drum-type chip washing machine is one of important equipment in the TSMP process. It is used to remove foreign matters like gravel and metallic substance, and wash away chemical materials which are not good for pulping and bleaching in the wood chips, facilitating separation, bleaching and refining.

The main body of wood chip washer comprises a shell and a wash drum. There are many flushing pipes on the shell and fins on the wash drum. After being pre-steamed, the wood chips enter the chip washing machine which is infused with *0° C hot water via metering screw uniformly. The wash drum in the chip washing machine mixes the water and wood chips so that the foreign matters like gravel and metallic substance mixed in the wood chips sink since the density is greater than that of water, and then they are discharged through the slag-running-off opening at the bottom of the machine while part of the soluble matters in the wood chips dissolve in the water. The mixture of water and wood overflows into the inclined helix dehydrator for dehydration.