Technical economic evaluation of a hardwood biorefinery using the "Near-Neutral" hemicellulose pre-extraction process

Forest products companies may increase revenue by producing biofuels and chemicals in addition to wood, pulp and paper products in a so called Integrated Forest Biorefinery (IFBR). One form of such a biorefinery is where the hemicelluloses, which normally end up in the black liquor of a hardwood Kraft mill, are extracted prior to pulping and used for the production of ethanol and acetic acid. The extracted liquor undergoes hydrolysis, separation, fermentation and distillation for the production of acetic acid and ethanol. A computer model was developed for this process using WinGEMS and ASPEN Plus software. The capital and operating cost for the process were estimated by standard methods. The amounts of ethanol and acetic acid produced are relatively small compared to current corn to ethanol and commercial acetic acid plants. This situation results because of the small amount of hemicelluloses extracted which is dictated by pulp quality and pulp yield considerations. The rate of return on investment varies between 7.1% and 13.0% depending upon the size of the pulp mill (750 to 1500 tonne per day) for the case where the utilities and waste treatment facilities are sufficiently large to handle the additional requirements for the process and a suitable vessel is available for upgrading to handle the extraction process. If the utilities and waste treatment system have to be upgraded, then the rate of return on investment decreases to 1.1% to 6.5% depending upon the size of the pulp mill (750 to 1500 tonne per day). In making the capital cost estimates 20% of the cost of a new installed digester was included as the cost of upgrading the extraction vessel and tying it in to the existing pulping process. Installing a new extraction vessel causes the discounted cash flow rates of return to be negative however because of the added capital cost.