http://www.che.com Chemical Engineering en-us 2013 Fri, 24 May 2013 6:40:49 EDT Recovery boilers, in which pulp and paper companies burn spent black liquor from the kraft pulping process to recover and recycle sodium and sulfur, are a bottleneck in many paper mills. The reason is that they operate at their upper limit of heat flux into the boiler tubes, thus preventing an increase in... http://www.che.com/chementator/pulp_and_paper/9302.html Tue, 1 May 2012 0:00:00 EDT