Lignin extraction from kraft black liquor on the commercial scale is a new strategy being employed by existing kraft pulp mills operating at recovery boiler capacity. Lignin extraction has demonstrated the potential to ⅰ) increase pulp mill throughput by removing black liquor solids prior to the recovery boiler to reduce loading, and ⅱ) create a new lignin co-product for increased mill revenue. This research explores the effects of integrating a commercial scale lignin extraction process on steam usage, chemical recovery, and mill operations utilizing WinGEMS process simulation software. It was determined that, for a kraft pulp mill producing 440,000 admt/year southern bleached softwood kraft pulp with the recovery boiler operating at a solids limiting capacity, extracting 5.22% black liquor solids as lignin product from the recovery process allowed for an approximate 5.22% increase in pulp production. In the case of the recovery boiler operating at maximum steam production, extracting 5.22% black liquor solids allowed for a 9.6% increase in pulp production. After the lignin is precipitated, the dilute black liquor is returned to the evaporators resulting in an evaporator economy decrease of 2.5%. For the recovery boiler operating at a solids limiting capacity, the minimum product revenue (MPR) required for the sale of lignin product to achieve 15% internal rate of return (IRR) was calculated at $244/mt.
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