Steam gasification of biomass generates a hydrogen-rich product gas that is diluted in unreacted steam and contaminated with tar. In this study, a novel heat integration alternative is conceptualized through syngas cooling to near-ambient temperature via an indirect water condenser downstream of a bubbling fluidized bed gasifier. The steam generated from heat recovery is used for biomass gasification, whereas the condensed bio-oil (unreacted tar and steam) is collected and recycled to the gasifier for further conversion. A one-dimensional kinetic model is developed and tested against experimental data from the literature on steam gasification of bio-oil and steam gasification of biomass in two separate bubbling fluidized bed gasifiers. The average absolute deviation of model predictions for CO2, CO, CH4 and H2 mole fractions are 60.85%, 14.25%, 30.17% and 10.75% for bio-oil steam gasification and 80.63%, 27.70%, 67.28% and 4.71% for biomass steam gasification, respectively. Based on the agreement observed between the model predictions and experimental data over substantial ranges of operating conditions, the same approach is adopted for modeling integrated biomass and recycled bio-oil gasification. Increasing bio-oil recycle ratio increases water conversion and chemical efficiency at the cost of decreasing carbon conversion and thermal efficiency of biomass gasification process. In addition to reactor temperature and steam-to-biomass ratio, tar recycle ratio can be utilized as an optimization variable to compromise between process chemical and thermal efficiencies, as well as wastewater production. Finally, an economic analysis shows that an incremental return on investment of >33% is achievable for the integrated process.

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