Techno-economic feasibility of supercritical water gasification of black liquor

The objective of this study is to investigate the techno-economic feasibility of supercritical water gasification (SCWG) of black liquor integrated to a Kraft pulp mill. The process simulations have been performed through Aspen Plus software. The assessment includes five integration scenarios: stainless steel 316 or Inconel 625 as the reactor materials and hydrogen or combined heat and power (CHP) as the target products. The results illustrates that Inconel reactor is more profitable for CHP production than stainless steel as well as providing lower production cost of hydrogen. Inconel is also more robust against loss of pulping chemicals and changes in the energy price. However, the assessment uses the experimental yields even though surface-to-volume ratio of the reactor will reduce in the industrial scale. Therefore, the results should be validated in pilot scale as well before implementation. Nevertheless, a special reactor configuration can increase surface area. The techno-economic results can be improved by comprehensive investigations of process conditions including also residence time, the concentration of reactor inlet and heterogeneous catalyst. In addition, the SCWG process integrated to a pulp mill can also receive feedstocks from other biomass sectors. This would improve the economic and environmental performances of those sectors as well.