Patent ID: 7749354

Claim:
A method for washing co-current downflow wood chips in a hot liquor in a digester having an upper zone and a lower wash zone, the co-current downflow wood chips and hot liquid defining a chip mass which flows from the upper zone through the wash zone of the digester, the method comprising: maintaining outflow of co-current downflow hot liquor from the digester through a plurality of screens disposed about the inner circumference of the digester at a location intermediate the upper zone and the wash zone of the digester; monitoring temperature of the outflow of co-current down flow hot liquor through each of the plurality of screens; measuring the temperature of the outflow of co-current down flow hot liquor through each of the plurality of screens with the temperature of the outflow of hot liquor through each other of the plurality of screens; and adjusting a corresponding flow rate of the outflow of co-current downflow hot liquor through one or more of the screens bringing the rate of outflow of hot liquor from each of the screens to substantially the same rate of outflow of hot liquor as others of the screens or reducing the rate of outflow of hot liquor through one or more of the screens to a value which permits downflow of hot liquor past the one or more of the screens to sweep the one or more of the screens substantially free of solid material wherein the solid material having a tendency to plug the one or more of the screens from permitting the outflow or hot liquor flow through said one or more screens.