Patent ID: 8273212
Filing Date: 2012-09-25
Classification: D21C

Abstract:
1. A method for the manufacture of sulphate or kraft pulp from disintegrated wood material, comprising: impregnating a wood material in an impregnation zone of a cooking process with an impregnation liquor at a temperature which is above 80° C. but below a cooking temperature by at least 20° C., cooking the wood material in a cooking zone of the cooking process at a cooking temperature, the cooking process comprising the impregnation zone and the cooking zone, the wood material being downwardly moving in the cooking process, allowing the wood material a first retention time in the cooking process, the first retention time starting at a start of the cooking process and terminating when the wood material reaches a first position of the cooking process, the first position being located where a proportion of from the wood material dissolved hemicellulose per unit of time starts to decrease, withdrawing a first cooking liquor at the first position, the first cooking liquor comprising a first amount of a first hemicellulose dissolved from the wood material, reintroducing the first cooking liquor to a last phase of the cooking process at the cooking temperature of the first cooking liquor, the last phase being at a lower portion of the cooking process downstream of the first position and a second position, the second position being downstream of the first position, allowing the wood material a second retention time in the cooking process, the second retention time starting at the start of the cooking process and terminating when the wood material reaches the second position of the cooking process, withdrawing a second cooking liquor at the second position, the second cooking liquor comprising a second amount of a second hemicellulose dissolved from the wood material, the second retention time being longer than the first retention time in the cooking process, and reintroducing the second cooking liquor to the last phase of the cooking process.