By Professor Jon Gibbins, UKCCSRC Director
The key message from a recent paper on blue hydrogen production from natural gas, which has attracted some media attention, should be that it is a good description of how NOT to do it. The authors present a great number of calculations for the performance of their concept of what a blue hydrogen system would be, but this does not justify a general assertion that blue hydrogen would not work as part of a net zero energy system. The real issue is that, if we want to produce net zero blue hydrogen, then the industry needs to use appropriate technologies to do it – and regulators need to set standards that make sure that the good players are not disadvantaged by organisations, or countries, that try to take short cuts.
A properly designed net zero hydrogen system based on natural gas would reduce upstream methane leakage emissions as much as possible, and take note of the residual emissions and offset them using biomass energy with CCS (BECCS) or direct air carbon capture and storage (DACCS, which might also be driven by natural gas with net zero emissions to the atmosphere – for example as in the Carbon Engineering system). Even at the more realistic 100 year Global Warming Potential just one percent of methane leakage from a natural gas supply system will equal the emissions of 28% of the CO2 formed when the natural gas is burnt or converted to hydrogen – and these methane emissions cannot be addressed by adding CCS at the point of use. The media did not pick up that it was a combination of assumed multi-percent methane leakage rates and focusing on the relatively-much-higher (vs. CO2) 20 year impact of methane that delivered the most extreme calculated numbers for the GHG impact of hydrogen made from natural gas. But a number of oil and gas companies are targeting a major reduction in methane emissions from current levels (e.g. OGCI’s methane intensity target), down to fractions of a percent – and the technology is there to sniff out accidental and systematic offenders; see the figure above.
Then the natural gas would be reformed, either using a steam methane reformer with external heating, from which 95% or more of all of the CO2 can be captured if required (not the lower levels for the few current CO2 capture projects on hydrogen plants cited in the paper, which were not designed for net zero blue hydrogen production), or from an oxygen-based reforming process that generates its heat internally and can, if designed to, achieve similarly high CO2 capture levels. The latter approach uses electricity to generate the oxygen, but of course a properly designed hydrogen supply system would use a net zero electricity generation mix. Again DACCS or other permanent carbon dioxide removal (CDR) would be used to indirectly capture any residual CO2 emissions.
Of course, net zero blue hydrogen is not the only option for achieving net zero energy systems while still retaining some gaseous fuel use. A combination of direct CO2 capture at source, including on as much biomass use as reasonably possible, plus large-scale Direct Air CO2 Capture and Storage will also allow some natural gas use to continue, for example in power plants with CCS and in hybrid heat pump/boiler systems, where the small amounts of CO2 are captured indirectly via the air. The choice between these different fossil-based routes, and also achieving net zero by using other non-fossil energy sources, is a matter of cost and convenience.
But what is not optional, based on the latest IPCC assessment report, is achieving net zero GHG emissions by about mid-century and net-negative emissions in the latter half of the century, if we want to keep peak global temperature increase in the 1.5-2 degree range. The climate does not care at all what colour hydrogen we use – it just cares about CO2 emissions and these will need to be net zero for all hydrogen sources.