Production of Hydrogen for Oil Refining by Thermal Gasification of Biomass: Process Design, Integration and Evaluation
Hydrogen is an important part of crude oil refining operations since it is required in several units for the desulphurization and upgrading of various oil fractions. At present, most of the refineries meet their hydrogen demand through methane steam reforming, a refinery unit that can represent up to 25% of the plant’s fossil CO2 emissions. Processes based on thermochemical gasification of biomass are promising alternatives for hydrogen production. This thesis presents a process integration study of two distinct biomass-to-hydrogen concepts. The focus is put on the
integration of these processes with an existing refinery used as a case study for the identification of promising configurations.
The first biomass-to-hydrogen concept is based on indirect, atmospheric steam gasification and proven technologies for gas cleaning and upgrade (IG concept) while the second concept relies on direct, pressurized oxygen-steam blown gasification and more advanced cleaning and upgrading technologies (DG concept). Mass and energy balances for the biorefinery concepts are obtained by process simulation while actual refinery data is used. Simulation results show that based on Higher Heating Values (HHV), the conversion efficiency from biomass to hydrogen is 67% for the IG concept and 65% for the DG concept.
Process integration tools are then used to identify promising integration and heat recovery opportunities. The identified process configurations differ in terms of coproducts: in addition to hydrogen, the production of HP steam and/or electricity is investigated. All configurations are compared in terms of energy and exergy efficiency and their environmental impact is assessed by
means of a fossil CO2 balance.
Results highlight the potential for improvement of process performances by performing biomass drying with low quality refinery excess heat instead of biorefinery excess heat. This integration allows the export of additional HP steam to the refinery or electricity generation through an
integrated steam cycle, which increase the efficiency of the biorefinery. The IG concept is found to consistently outperform the DG concept according to both thermodynamic efficiencies. For both concepts, the configuration where HP steam is exported to the refinery appears most promising in a context of decreasing emissions from the European power sector.