Black liquor gasification—consequences for both industry and society

The pulp and paper industry consumes large quantities of biofuels to satisfy process requirements. Biomass is however a limited resource, to be used as effectively as possible. Modern pulping operations have excess internal fuels compared to the amounts needed to satisfy process steam demands. The excess fuel is often used for cogeneration of electric power. If market biofuel availability at a reasonable price is limited, import/export to/from a mill however changes the amount of such biofuel available for alternative users. This work compares different mill powerhouse technologies and CHP plant configurations (including conventional recovery boiler technology and black liquor gasification technology) with respect to electric power output from a given fuel resource. Different process steam demand levels for different representative mill types are considered. The comparison accounts for decreased/increased electricity production in an alternative energy system when biofuel is imported/exported to/from the mill. The results show that black liquor gasification is in all cases considered an attractive powerhouse recovery cycle technology. For moderate values of the marginal electric power generation efficiency for biofuel exported to the reference alternative energy system, excess mill internal biofuel should be used on mill site for gas turbine based CHP power generation. The remaining excess biofuels in market pulp mills should be exported and used in the reference alternative energy system in this case. For integrated pulp and paper mills, biofuel should be imported, but only for cogeneration usage (i.e. condensing power units should be avoided). If biofuel can be used elsewhere for high efficiency CHP power generation, mill internal biofuel should be used exclusively for process heating, and the remainder should be exported.