Abstract: The present invention relates to a digester for continuous cooking, under elevated pressure and temperature, of fibre material in a vertical digester (1), where fibre material and cooking liquid are fed into the top of the digester, used cooking liquor is drawn off from at least one digester screen arrangement (1D) between the top and the bottom of the digester, and fibre material is fed out from the bottom of the digester, it being possible to maintain the temperature in the cooking zone immediately above the digester screen arrangement (1B) at essentially the same temperature level as the remaining cooking zone or cooking zones of the digester.

Abstract: The present invention relates to a method for producing pulp cooked under alkaline conditions, in which method cellulose-containing material is brought into contact, in a digester, with an alkaline cooking liquor containing dissolved potassium and sodium compounds, with used spent cooking liquor being separated off from the cellulose-containing material and withdrawn for the recovery of energy and chemicals, wherein:a) The molar ratio, calculated as K/K+Na, between potassium and sodium in a withdrawn spent cooking liquor exceeds 0.25.b) The withdrawn spent cooking liquor is concentrated with respect to its content of solid material and is subjected to partial oxidation in a reactor, resulting in the formation of a, combustible gas which is withdrawn from the reactor.c) oxygen-containing gas is supplied to the reactor in order to support the partial oxidation.d) The operating temperature in the reactor is adjusted to between 400.degree.-1200.degree. C.