Thermodynamic analysis of polygeneration systems based on catalytic hydropyrolysis for the production of bio-oil and fuels

Novel polygeneration concepts based on catalytic hydropyrolysis and hydrodeoxygenation are presented and compared via process simulation and thermodynamic analysis. These systems process and convert biomass into high-quality bio-oil and fuels such as synthetic natural gas (SNG), molecular hydrogen (H2) and methanol (MeOH).

Twelve system layouts were evaluated and compared with regards to their energy demands and performances. Detailed thermodynamic models were developed, considering the different technological alternatives for the valorisation of bio-char, removal of carbon dioxide, fuel upgrading and water electrolysis, as well as the opportunities for energy integration.

The results show that the standard system, which produces only bio-oil, reaches an energy efficiency of 61% (LHV). This value can be increased by 7–28%-points when co-producing SNG, 10–21%-points when producing H2, and 10–19%-points when producing MeOH. The highest values are achieved by co-production of SNG as light hydrocarbons are produced in the hydropyrolysis, and limited processing is therefore required to reach the desired product quality.

High system efficiencies are possible mainly because of the high efficiency of the core hydropyrolysis process. Carbon conversion efficiencies are highest when generating SNG or MeOH and reach a maximum when electrolysis and char gasification are implemented (98% and 95%). The performance of these polygeneration systems is strongly impacted by the type of CO2-separation process and electrolyser - these processes have a strong influence on the power and heating demands, as well as on the potential energy savings and waste heat valorisation.