Despite reducing costs associated with the production of green hydrogen, the production of blue hydrogen remains cheaper and is frequently considered as a transitional hydrogen production option as part of establishing a hydrogen economy. Blue hydrogen production is conventionally executed via steam methane reforming (SMR) coupled with CO2 sequestration. SMR is however an endothermic reaction, hence it requires supplementary heat provision and consequently produces two substantial sources of CO2 (one at comparatively low concentrations and pressures) which collectively results in poor overall sequestration efficiency. An alternative to SMR is the use of autothermal reforming (ATR), this effectively involves the co-injection of oxygen and steam as reactants, eliminating the requirement for supplementary reactor heating ). A single comparatively high concentration and pressure CO2 production stream results which is imminently more suitable for sequestration. The reason ATR is not currently widely used for hydrogen production is (partially) the cost of producing the require oxygen via air separation or the parasitic nitrogen load if air injection is used instead of oxygen (this is considered in the provision of hydrogen for ammonia production for example).
Researchers at the University of Western Australia have completed the final milestone report for the “Bridging Blue and Green Hydrogen” project undertaken in collaboration with INPEX and the Victorian Government. The project focused on addressing the economic and emissions challenges associated with the production of H2 through process integration. The goal of the project was to determine an integrated plant scheme for producing both blue and green H2 so to minimise both the Levelised Cost of Hydrogen (LCOH) and CO2e emissions.
The separate blue and green H2 production processes and the integrated process designs were simulated in Aspen. Economic and emissions analyses were conducted for H2 production via (i) autothermal reforming (ATR) of methane with carbon capture and storage (CCS), (ii) coal gasification (CG) of lignite with CCS, (iii) Polymer Electrolyte Membrane (PEM) electrolysis using renewable energy, and the integrated cases of (iv) ATR w/ CCS + PEM electrolysis and (v) CG w/ CCS + PEM electrolysis for combined blue and green H2 production. The key to the process integration was the use of the oxygen by-product produced by electrolysis during green H2 production to feed the reforming process (ATR or CG).
The results of the study indicate that combined blue and green H2 integration did produce reductions in LCOH (relative to green H2 production) and a reduction in CO2e emissions (relative to blue H2 production) . A primary factor limiting the benefits of process integration however was the scale disparity between the H2 production technologies; ATR and CG with CCS are economically viable at significantly larger production capacities than the scale at which a PEM electrolyser can currently be operated. In addition, ensuring the required continuous supply of oxygen to the reforming process was problematic. Efficient integration of inherently intermittent processes with those requiring continuous operation will be a major focus of future research.
Partners: INPEX Holdings Australia Pty Ltd, Victorian Government Department of Jobs, Precincts and Regions, The University of Western Australia
Project Researchers: Professor Michael Johns, Dr Keelan O’Neill, Dr Saif Al Ghafri
Duration: 12 months