On the cost of zero residual CO2 emission hydrogen: A techno-economic analysis of steam methane reforming with carbon capture and storage

In a net zero economy compliant with the emission targets implicit in the Paris Climate Change Agreement any residual greenhouse gas emissions from hydrogen produced via steam methane reforming (SMR) of natural gas will require reduction to zero. The initial step to achieving this is the capture and storage of 100% of the fossil carbon from both the natural gas feedstock and the natural gas used for combustion, hereafter referred to as zero residual CO2 emission production. For an SMR this means achieving an overall CO2 capture fraction of 99.8% from the flue gases. The remaining 0.2% of stack CO2 emissions are then equal to the atmospheric CO2 from the combustion air used in the steam methane reformer furnace. Via the process modelling of a steam methane reformer integrated with post-combustion CO2 capture (using the CCSI MEA steady state model [1]), we predict that, for an open-art solvent of 35%wt aqueous MEA, a capture fraction of 99.8% and a peak desorber temperature of 125oC, the CO2 absorber column requires 20m of structured packing and the intercooling of the solvent, compared to an estimated 14m of structured packing and no intercooling for 5% residual emission hydrogen (95.2% capture fraction). For a 1 GW hydrogen production facility, we use public domain cost studies to estimate that this translates to an increase in total capital requirements of 6.5%, from £987M to £1051M, and a marginal increase in specific CO2 capture energy requirements of 1.6%, from 3.62 GJ/tCO2 to 3.67 GJ/tCO2 of low grade thermal energy, provided by low pressure steam extracted from the process. The resulting net operating costs, including CO2 transport and storage, natural gas fuel and steam for solvent regeneration but excluding any CO2 emission costs associated with the cases with residual emissions, increase by 3.7% from £468M to £485M p/a. The additional CO2 captured reduces hydrogen production efficiency by 1.9 percentage points on an HHV basis (from 68.7% HHV to 66.8% HHV). For 2020 UK capital costs, an assumed natural gas price of 28 £/MWhth HHV (82 p/therm) and average electricity selling price of 90 £/MWhe, hydrogen can be produced with zero residual emissions at a Levelised Cost of Hydrogen (LCOH) of the order of 62 £/MWhth HHV (2.4 £/kg H2) with an associated levelised cost of capture (LCOC), excluding transport and storage, of 54.1 £/tCO2. This translates to a marginal increase of 0.34 £/tCO2 per percentage point increase in net capture fraction when compared to operating with 5% residual emissions (52.4 £/tCO2). Hydrogen production with residual CO2 emissions of 5% results in the same LCOH of 62 £/MWhth HHV with a carbon price of 172 £/tCO2.