Study explores most promising low carbon hydrogen Well-to-Tank pathways


Renewables-based electrolysis is set to represent one of the lowest emissions Well-to-Tank (WTT) pathways in the medium-term, according to research.

On 9 August, the Zemo Partnership published a study, prepared by Element Energy, exploring a range of pathways for the production, distribution and dispensing of low carbon hydrogen to transport end-users. It sought to identify the greenhouse gas emissions associated with each hydrogen supply chain pathway, based on technologies that are available today, while also those that are expected to be commercialised in the medium-term. These include offshore electrolysis, gas reformation with carbon capture and storage (CCS) and waste gasification with CCS.

Alongside renewables-based electrolysis as one of the lowest emissions pathways in the medium-term, the study found natural gas reformation, using emerging autothermal (ATR) technology with CCS has the potential to significantly reduce emissions when compared with the current industrial steam methane reforming (SMR) process for grey hydrogen. There are also potential pathways where carbon-negative hydrogen can be created, through using biomethane or gasification of waste, paired with CCS. There are potential limitations, however, when it comes to the future availability and supply of biomethane.

WTT greenhouse gas emission values for pathways in 2030 and 2035 ranged from -108.2gCO2e/MJ in 100% biogenic biomass gasification with CCS and gas grid distribution, to 54.3gCO2e/MJ in SMR with retrofit CCS and liquified tanker distribution. Improvements to electrolyser efficiency in the next 15 years, as the UK’s electricity grid becomes less carbon intensive, will result in greenhouse gas emissions for the on-site electrolyser pathway dropping by around 50%.

Figure 1: WTT GHG emissions (gCO2e/MJ) for different low carbon hydrogen production and distribution pathways, based on compressed HRS at 350bar dispensing.

Overall, the method of producing hydrogen was found to be the dominant factor impacting the WTT greenhouse gas emissions and energy consumption, accounting for around 90% of the overall pathway. If hydrogen production plants are completely decarbonised, the contribution of hydrogen distribution was found to become the main factor in the WTT pathway in terms of greenhouse gas emission impacts.

It identified hydrogen liquefaction as the most energy intensive step in the distribution value chain, whereas hydrogen at 100% blend transported by the gas network pipeline from 2035 was found to be the most energy efficiency distribution pathway, as well as the one with the lowest greenhouse gas emission impact. It noted that blending of hydrogen at 20% is regarded as a stepping stone to enable full grid conversion but does involve significant energy use for deblending and purification.

Looking ahead, it called for future policy for all fuel and energy options in transport to fully consider both greenhouse gas and energy consumption aspects if an efficient net zero energy and transport system is to be delivered. Resource and other environmental considerations should also come into play over the longer term.