Converting a kraft pulp mill into a multi-product biorefinery – Part 1: Energy aspects

Abstract

Conversion from kraft pulp into dissolving pulp production is an interesting development since it allows the production of a pulp with higher market value, as well as the production of valuable by-products, for example, hemicellulose, lignin, electricity, and/or heat. In this paper the major energy consequences of converting a modern kraft pulp mill into dissolving pulp production were investigated. Three critical choices for process configuration were examined: a) export the hydrolysate (extracted hemicellulose liquor) to an upgrading plant vs. combustion of the hydrolysate b) level of heat integration c) type of by-products produced (electricity or lignin) The results show that conversion into dissolving pulp production affects the energy balance of the mill considerably and can drastically affect the pulp production capacity of the mill, e.g. if the recovery boiler is the bottleneck. Sending the hydrolysate to combustion decreases the pulp production capacity, whereas lignin separation can debottleneck the recovery boiler and allow for higher pulp production. A higher level of heat integration increases the possibilities for debottlenecking and/or producing by-products. The conclusion is that an economic assessment is necessary in order to identify the most attractive process configuration. This assessment will be presented in the second part of this study.