Patent ID: 6176971
Filing Date: 2001-01-23
Classification: D21C

Abstract:
A method of producing chemical cellulose pulp in an energy efficient manner using a treatment vessel in a digester system, comprising:(a) introducing a slurry of comminuted cellulosic fibrous material and liquid to a treatment vessel to produce cellulose pulp;(b) treating the material in the vessel with treatment chemical at a temperature greater than 140.degree. C. and a pressure greater than 5 bar gage to produce a treated material and a spent treatment liquor, including sulphur compounds;(c) removing the spent treatment liquid from the vessel at a first temperature;(d) passing the spent liquor in indirect heat exchange relationship with a cooler liquor having a second temperature lower than the first temperature to produce steam at a first pressure, and at a third temperature higher than the second temperature;(e) increasing the pressure of the steam to a second pressure by at least about 0.2 bar more than the first pressure; and(f) using the steam at the second pressure in the digester system.