Chapter 6: Prehydrolysis Pulping with Fermentation Coproducts

Although the term “integrateed biorefinery” is new, the concept has long been familiar to the pulp and paper industry, where processes include biomass boilers providing combined heat and power, and byproducts of pulping include turpentine, fatty acids and resin acids. In the dominant kraft (or sulfate) pulping process, dissolved lignin and chemicals from the pulp digester are concentrated by evaporation and burned in a recovery boiler to generate steam and to recover the inorganic chemicals that are recausticized and reused as fresh pulping chemicals. In addition, prior to pulping, bark is remived from pulpwood and fed to waste fuel boilers that raise additional steam. High-pressure steam is used in a cogeration process to generate electricity for the plant, while lover-pressure steam is used for pulping process heat and paper drying. In recent years, many paper companies have added wood-fired boiler capacity and used slash from logging or wood residues from lumber mills to replace fossil fuels, typically requiring only natural gas to operate the lime kilns that are part of the recausticizing process.