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Further development of kraft-based dissolving pulp production
University of New Brunswick
AV Nackawic is currently using prehydrolysis Kraft process (PHK) to manufacture dissolving grade (DG) pulp with a purity around 95%. The PHK process helps to remove the hemicelluloses and other wood constituents. However, selective removal of hemicelluloses in the PHK process is not very high and it is not energy efficient. In this project, the main purposes are to raise the purity of DG pulp to greater than 95%, at the same time produce fine pulp and xylitol. The new proposed process will replace the prehydrolysis stage with pulp fractionation, enzymatic treatments and pulp purification process. The inlet stream contains 800 air dry tonnes per day (ADTPD) of brownstock. This pulp is fractionated into fibers and fines streams with 9: 1 splits. The fine pulp will undergo drying process and produce at 54 ADTPD. The fiber pulp will be treated with xylanase to remove hemicelluloses. Cellulase and xylanase enzymes are used to replace the hypochlorite chemicals, aiming to reduce the viscosity of the pulp. Both enzymes can be recycled up to 60%. The pulp will be purified by cold caustic extraction (CCE) to remove the hemicelluloses. A total of 530 ADTPD of DG pulp will be produced at 96% purity. Hemicelluloses removed during the treatments will be sent to the xylitol production unit and produce 46 TPD of xylitol. The total capital cost is estimated to be CAD $103,200,000, whereas the total annual operating cost corresponds to CAD $75,000,000. A total net annual revenue of CAD $109,000,000 will be expected for this project. The profitability analysis over a 15-year plant life shows that the non-discounted payback period (PBP) is around 3.52 years, approximately 26.47% of the rate of return on investment (ROI) and the internal rate of return (IRR) is estimated to be 20.23%. Based on the sensitivity analysis, the product price, the operating cost and the capital cost are varied by ± 30%. Analysis shows that the optimal investment will be to increase the production capacity of DG pulp and xylitol by 30%.