The effect of dead load chemicals in the kraft pulping and recovery system

The primary dead load chemicals are sodium carbonate from incomplete conversion during causti - cizing, and sodium sulfate from low reduction efficiency in the recovery boiler, but thiosulfate and chloride also are potentially important. The difference between a low and high dead load operation might amount to as much as 125 kg/metric tons of pulp (mtp). A 1% increase in causticizing efficiency reduces dead load by 6-7 kg/mtp, and a 1% increase in reduction efficiency decreases dead load by 2-3 kg/mtp. Costs associated with dead load include increased internal energy use, greater chemical losses, reduced equipment capacity, and operating problems. The differences in energy use between a low and high dead load operation can be as much as 0.7 GJ/mtp. Evaporators are likely to be affected most, but the green and white liquor system and recovery boiler also could be affected. This paper provides some guidelines for minimizing the effects of dead load.This work was conducted as part of the research program on “Increasing energy and chemical recovery efficiency in the kraft process,” jointly sponsored by the Natural Sciences and Engineering Research Council of Canada (NSERC) and a consortium of the following companies: Alstom Power, Andritz, Aracruz Celulose, Babcock & Wilcox, Boise Paper Solutions, Bowater Canadian Forest Products, Carter Holt Harvey, Celulose Nipo-Brasileira, Clyde-Bergemann, Dia - mond Power International, Domtar, DMI Peace River Pulp, Georgia-Pacific, International Paper, Irving Pulp & Paper, Jammbco, Metso Power, MeadWestvaco, Stora-Enso Re - search, Tembec, and Votorantim Celulose e Papel