Abstract:
In a continuous digester which has a boiler with a rotatable bottom scraper and a chip and lye inflow at the top as well as a wash inflow into and a pulp outflow from the boiler, the concentration at the pulp outflow is measured and is used to control the rotation of the scraper so as to maintain a constant concentration of the outgoing pulp. A flow meter at the pulp outflow controls a throttle valve to regulate the outflow. The liquid in the top of the digester is measured and is used to control the devices which feed chips to the digester. Measurement of the pressure in the digester is used to control the flow of black liquor at the chip and lye inflow. The chips are fed in by a chip screw which in turn is fed by a segmental wheel, and the speeds of the chip screw and segmental wheel are maintained proportional to each other.