Techno economic evaluation of lignin extraction in a dissolving pulp biorefinery

A simulation model for dissolving pulp production using prehydrolysis kraft process has been developed at Innventia, which reflects a greenfield dissolving softwood kraft pulp mill producing 1,000tpd. The fibrelines comprised a separate prehydrolysis stage before the impregnation stage, with condensate from black liquor evaporation and steam being added to the prehydrolysis stage. The liquor was then removed from the chips and fed to the evaporation plant. The prehydrolysed chips were subjected to impregnation, cooking and oxygen delignification in double stages, with the oxygen delignified pulp being bleached in a four stage sequence D1(EOP)D2P. The simulation program WinGEMS 5.0 was used to establish material and energy balances. A lignin production of 0.2t/t increased pulp production by 8.5%. The heat value of the black liquor decreased but would still be high enough for stable and favourable combustion properties in the recovery boiler. It was found that the lignin price had the largest impact on the economic performance. Lignin removal increased the pulp production and was economically viable, especially if the possibility to produce electricity was low.