Potential of hydrothermal black liquor gasification integrated in pulp production plant

Greenhouse gas emission mitigation is one of the main motivations for increasing the use of biomass in providing environmentally friendly value-added products. The pulp and paper industry is a promising sector for the integration of biorefinery pathways. Among different technologies to produce pulp, the Kraft process accounts for 60% of the worldwide pulp production. The by-products of the Kraft process are major resources of biomass that can further be exploited. In the conventional Kraft process, black liquor is concentrated and burned in recovery boilers in order to satisfy the process heat demands and to recover the chemicals. Almost 40% of the heating demand of the process accounts for evaporators in which the black liquor is concentrated for utilization in the recovery boilers. The aim of this work is to investigate the potential of replacing conventional recovery boilers with a hydrothermal black liquor gasification unit. Hydrothermal gasification allows for having high water content black liquor (near 80%). This leads to an increase in energy efficiency of the process by reducing the overall heating demand (via eliminating the energy-intensive evaporation and concentrations stages) and simultaneously generating syngas that can be further processed into biofuels. In order to evaluate this potential, related process flow sheets are built and thermo-economic optimization of the integrated process is conducted. Furthermore, heat integration among the mill and the biorefinery is performed in order to identify the optimal operating conditions of the process. This work is a necessary preliminary step to provide incentives to further analyze the potential of the integration of the two.