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Mitigation of climate change and energy security are major driving forces for increased biomass energy utilization. The pulp and paper industry consumes a large proportion of biomass worldwide that include bark, wood residues, and black liquor. Due to the fact that modern pulp and paper industries have established infrastructure for handling and processing biomass, it is possible to lay foundation for future gasification based bio-refineries to co-produce electricity, chemicals or bio-fuels together with pulp and paper products. There is a potential to export electricity or bio-fuels by improving today’s existing chemical pulp and paper mills integrating gasification technology.

The present study evaluates the energy conversion performance of integrated black liquor gasification (BLG) within the chemical pulp mills in comparison with conventional pulp mill energy system. The objective is to investigate and compare various BLG technologies and bio-fuel production routes. The comparison is performed to identify the advantageous route based on system performance indicators e.g. bio-fuel production potential, fuel to product efficiency (FTPE), biomass import, overall system thermal energy efficiency, on-site CO₂ reduction using carbon capture, and potential CO₂ offsets from bio-fuel use in transport sector.

The study on a variety of BLG configurations shows promising results for potential bio-fuel production offering significant contributions toward fossil fuel savings, emission reductions, and improved energy security. Methanol, synthetic natural gas (SNG) and dimethyl ether (DME) show promising features as potential fuel candidates. The comparative results show significantly larger bio-fuel production potential of black liquor conversion to SNG from catalytic hydrothermal gasification than DME, methanol or SNG production from the dry BLG (DBLG) and Chemrec BLG (CBLG) systems. The energy ratio of SNG production from the CHG system is higher than DME and methanol in the CBLG and the DBLG systems. When considering consequences of incremental biomass import, the DBLG system is far better than the CBLG and the CHG systems mainly due to the elimination of the lime kiln. Considerable reduction of on-site CO₂ emissions could be achieved using CO₂ capture and storage in the pulp mills. The CHG and the CBLG systems shows better performance results than the DBLG system comparing potential CO₂ emissions offset from bio-fuels replacing fossil fuels.