Biorefinery implementation for recovery debottlenecking at existing pulp mills - Part I: Potential for debottlenecking

Depending on the process strategy employed, implementation of the biorefinery into an existing pulp and paper mill can often help with process debottlenecking, and enable increased pulp and paper production capacity. Many biorefinery process options also offer the opportunity for bioproducts manufacturing and/or fossil fuel replacement. In this paper, the implementation of two biorefinery processes is examined from the perspective of process debottlenecking at a sodium carbonate-based semichemical pulp and paper mill: (a) lignin precipitation from black liquor by acidification with CO2, and (b) the near-neutral hemicellulose pre-extraction process. The recovery cycle, which includes a Copeland fluidized bed reactor, is the main pulp production bottleneck. Also, pulp quality improvements are possible, which would be achieved by lowering pulp yield. In Part I of this paper, biorefinery implementation uncertainties were identified and the potential for recovery debottlenecking and maximum paper production attainable were evaluated. In Part II, the economic evaluation and comparison of the selected biorefinery process options in the context of process debottlenecking are presented. The results show that for the case study mill, the hemicellulose pre-extraction process gives opportunity for higher paper production and paper quality improvement. It allows for a production increase of about 20%, as well as lowering the pulp yield from 85% to 79%. With lignin precipitation, it was found that a 15% paper production increase could be possible if the pulp yield is kept constant.