Abstract: A method for washing pulp in a batch digester modified pulping process wherein black cooking liquor used for cooking the chips is partially displaced by pumping a first stage wash effluent into the bottom of the digester, additional amounts of the cooking liquor are displaced by pumping a second stage wash effluent, and so on, until sufficient increments of wash effluent have been pumped to displace the cooking liquor. A wash filtrate water is then pumped into the digester from a final pulp washing operation to displace the hot black liquor until all of the hot black liquor is sent to an accumulator, and the various wash effluents have been replenished in their respective stages.

Abstract: A multi-stage wood chip cooking process performed in a single digester in a batch type operation. The wood chips to be cooked are introduced into the digester and soaked with a warm black liquor to remove most of the air from the digester and the chips. This warm black liquor is thereafter displaced from the digester with a mixture of a first stage hot black liquor and hot white liquor, the proportionate amount of hot white liquor being relatively high. The temperature of the digester contents is then raised to a cooking temperature for a predetermined amount of time. The original cooking liquor is then displaced with a mixture of a second hot black liquor and hot white liquor, the proportiionate amount of hot white liquor in this second cooking liquor being less than in the first. Again, the temperature of the digester is raised to a cooking temperature and the cooking is carried out for a shorter period of time than in the first cooking stage.