TECHNICAL ECONOMIC EVUALATION OF A NORTHERN HARDWOOD BIOREFINERY USING THE "NEAR-NEUTRAL" HEMICELLULOSE PRE-EXTRACTION PROCESS

The "near neutral hemicellulose extraction process", involves the extraction of wood hemicellulose using green liquor prior to conventional Kraft pulping. Ancillary unit operations in the process include hydrolysis of the extracted carbohydrates using sulfuric acid, filtration of the extract to remove lignin that was extracted with the carbohydrates, liquid-liquid extraction of acetic acid and by-product furfural, liming of the hydrolyzed extract, separation of gypsum which is the product of the liming reaction, fermentation of C5 and C6 sugars and upgrading of the acetic acid and ethanol products by distillation. Experimental data are presented for the extraction of northeast hardwood chips using green liquor. These data were used to perform a technical economic analysis for a Kraft mill located in the Northeastern U.S. An economic analysis was performed as a function of the size of the pulp mill being retrofitted to accommodate the hemicellulose extraction process. Discounted cash flow rate of return was used to judge the economic merits of the new process. Important cases include whether the extraction vessel is available at the mill site or must be purchased, and whether the utilities and waste treatment facilities are sufficiently large to handle the additional requirements for the new process or must be upgrades. Advantages and disadvantages of the process are discussed.