System analysis of pulping process coupled with supercritical water gasification of black liquor for combined hydrogen, heat and power production

Supercritical water gasification is an innovative black liquor treatment method for hydrogen production. In the present study, an integrated system of pulping and SCWG of black liquor was simulated. Combined hydrogen, power, MP and LP steam are produced for pulping process. The gas product after H2 extraction was burned with imported natural gas to supply more heat. For a reference pulp mill producing 1000 ADt pulp/day, potentially 37126 Nm3/h hydrogen can be produced. The generated MP and LP steam can fully meet the requirement of pulping process. Using air as oxidant in gas combustion is more energy-efficient than using oxygen for being free of oxygen production process. In the case of using air, 22604 kW power can be exported after balancing the consumptions and 219 kgce energy can be produced with 1t pulp production. While using oxygen, 10723 kW power needs be imported and 288 kgce energy can be consumed to produce 1t pulp. However, using air as oxidant may bring N2 and NOx in the exhaust gas, posing a challenge to the subsequent processing. Scaling-up of the system improved the energy efficiency, but the influence is very small when the capacity is above 250ADt/day.