Modelling of biomass pyrolysis with ex-situ catalytic upgrading for biocrude production

This study presents a techno-economic assessment of slow pyrolysis of pine sawdust continued by ex-situ catalytic upgrading. The overall process consists of six sections: feed drying, pyrolysis, vapor filtration, ex-situ catalytic upgrading, vapor quenching, and combustion of permanent gas. In the process simulation, biomass is objected to slow pyrolysis at 450ºC in an electrically-heated screw reactor and pyrolysis vapors is upgraded in fixed catalytic bed reactor at 425 ºC (using HZSM-5). The model is then used to investigate effects of feed moisture variation and type of heating source in pyrolysis unit, i.e. thermal vs. electrical heating, to oil energy efficiency. According to the simulation model, the endothermic pyrolysis step requires 1.46 MJ/kg dry-feed. On the other hand, ex-situ upgrading is slightly exothermic and releases 50kJ/kg dry-feed. Overall, the conversion of biomass to bio-oil demonstrates a mass efficiency of 19.65%wt and an energy efficiency of 29.10%. The energy efficiency raises to 32.81% if direct thermal source is applied instead of electrical heating. The bio-oil energy efficiency increases by 1.38% if the moisture content of the biomass decreases by 10%wt. In average, bio-oil and char production in ex-situ catalytic upgrading generates profit 1.47 SEK/kg dry-feed. The uncertainty of bio-oil price causes the highest profit variation