A detailed technical economic model was used to develop and determine the kraft cooking targets that optimize mill financial output, given mill production constraints and a range of raw material prices. Traditionally kraft linerboard producers have attempted to achieve the highest pulp kappa number possible, consistent with product strength and appearance. Because kraft linerboard has a high ratio of power consumption to process steam demand, higher pulp yield aggravates the ratio, since more refining is required, and less black liquor is produced. With old corrugated containers (OCC) in common use throughout the containerboard industry, and with the extreme price volatility of this commodity, this study investigated the impact of kappa number target over the range 90-110 under nine different conditions whereby the purchased power cost ranged from $45-$70 per MWh, and OCC price varied from $88-$ 138 per "as purchased ton" (APT). The linerboard mill model was built to constrain both production limitation (machine dryer capacity) and recovery boiler (solids loading), a common condition among USA producers. The model is a comprehensive user-configurable spreadsheet calculator that derives every mill cost (including major costs such as wood fiber, down to the annual cost of safety glasses at the mill). This model, named Carolina Pulp and Paper (CPP), has been used for more than 12 years to teach seniors in the Paper Science and Engineering program at North Carolina State University about mill costs, economics and strategies. This study is entirely based on hypothetical mill model where the simulations used inputs taken from past economic data (fourth quarter of 2019 (USA)), which are publicly available [1].
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