Evaluation of black liquor gasification intended for synthetic fuel or power production

• Global thermodynamic equilibrium calculations can be used to assess the performance of black liquor gasification.
• Heat losses from the gasifier significant influence the performance of the gasifier.
• Optimal performance of the gasifier depends on the application (synthetic fuel or power production).

The performance of a high-temperature pressurized black liquor gasifier intended for fuel or power production was evaluated both by thermochemical equilibrium calculations and with experiments performed in a development plant with a maximum capacity corresponding to 3 MWth. The aim of this paper was to investigate how the energy efficiency and the performance of the gasifier change with desired use of the syngas and to provide an accurate process analysis which can be used in future work for process optimization and understanding. Experiments in the plant were performed for an oxygen equivalence ratio (λ) between 0.414–0.462 at two system pressures, 24.6 and 28.7 bar, respectively. The thermal load on the gasifier was 2.7 MWth during the experiments.The experimentally verified cold gas efficiency taking into account all gaseous species varied between 59.0–62.4%. However, if only CO and H2 (which are the effective molecules for synthetic fuel production) were taken into account; the cold gas efficiency decreased considerably to 53.7–55.4% due to the presence of CH4 in the gas. The results indicate that optimal performance for synthetic fuel production occurs at a higher λ compared to power production. There is also a potential to further improve the performance for an optimal operated commercial plant in the future since the theoretical results indicate that the cold gas efficiency could be as high as 68.8% (λ = 0.35) for fuel production and 81.7% (λ = 0.27) for power production.