(467e) A Techno-Economic Simulation of Alternative Feedstock Strategies for An Integrated Forest Biorefinery

Economic pressures and more stringent legislation on environmental issues have enforced the renewal of the forest industry. The pulp and paper making (P&P) companies are pursuing new revenues from the emerging lignocellulosic biorefining industry by producing biofuels simultaneously with their conventional products. Also, the development of sustainable wood-based non-fuel products is widely investigated. However, the multitude of process and product options, combined with the raw material base in the mill region, makes the industry renewal a difficult task. The current integrated biorefineries are mainly utilizing the P&P side streams or by-products as feedstock. However, it is anticipated that in the future multiple volumes of feedstock will be needed to meet the increasing supply of bioproducts.

Finnish P&P industry, especially mechanical pulp production consumes much energy. In thermomechanical pulping (TMP) wood chips are refined into fibrous pulp. Major part (25-40%) of the pulp is refined twice, at main and post/reject refining to reach a proper quality set by the paper properties. The pulp fraction conducted to post refining is characterized as the TMP reject. Because of the high specific energy consumption in post refining it might be appropriate to utilize this raw material fraction for other purposes than papermaking in order to increase the profitability of the production site. Conducting the TMP reject pulp out of the process would also simplify the process as the post refining stage would then not be needed. An average production of TMP reject pulp in a modern TMP department is in the range of 100-200 tons/day. From the biorefining point of view, this can be considered as high volume of mechanically pre-treated feedstock.

The aim of the present study was to evaluate the techno-economic feasibility of a paper mill producing simultaneously light weight coated printing paper and pulp/feedstock for biorefining. The study was done using a steady state process simulation combined with computation of the variable costs. The potential products refined from the TMP reject pulp were yet excluded from this study.

A process model of a modern paper mill consisting of a TMP department, recycled fiber deinking process, paper machine, power plant, and effluent treatment served as a reference. Unit prices for the variable costs (raw materials, electricity, oil etc.) were obtained from public databases. Five different process concepts without the post refining stage were simulated ? i.e. the TMP reject pulp was removed from each option. In three cases the per ton based paper production was equal with the reference and the fiber lost (proportion of TMP reject pulp) was compensated either with deinked pulp, kraft, or increased wood intake to the mill. In the remaining two cases the paper production was lower than in the reference as the paper machine was producing thinner paper or the production was adjusted according the decreased TMP pulp proportion. A unit cost for the TMP reject pulp i.e. biorefinery feedstock was obtained for each process option. True feedstock cost in the value chain is higher due to the fixed costs and required profit margin. The simulation method developed can be utilized for the early evaluation of alternative concepts of process renewal.