Abstract: A process is provided for heating up wood chips in one or more stages at progressively higher temperatures prior to steaming and pulping in an economical manner at a considerable cost saving; heating the chips in at least a first preheating stage directly with moisture-saturated hot air, optionally admixed with inert gas, having a temperature within the range from about 55.degree. to about 99.degree. C., preferably from 70.degree. to 90.degree. C., having been brought to that temperature in a heat exchanger with hot water or air heaters with waste gases, such as gases drawn at different levels from an evaporator, for example, a Lockman pre-evaporator column.

Abstract: A method for improving heat economy in the batchwise digestion of lignocellulosic material especially when using a batch digester with a digestion or cooking liquor in which the digestion or cooking chemicals are dissolved, such as in sulphate, sulphite, bisulphite, oxygen, peroxide and ammonium hydroxide digestion processes, and also in the manufacture of high yield semichemical pulps.A superatmospheric gas pressure is applied above the level of the liquor in a batch digester; the level of the digester liquor is determined after the liquor has been absorbed by a batch lignocellulosic material; the level of free digestion liquor is then adjusted to that level providing an amount including the absorbed liquor to digest the lignocellulosic material; and then the material is digested under the superatmospheric pressure to form cellulose pulp.