The world is changing rapidly, and the pandemic of 2020 has accelerated plans to reduce greenhouse gas (GHG) emissions, particularly in Europe. A growing number of governments are putting “net zero” targets into law . Environmental, social and corporate governance (ESG) metrics are motivating investment decisions globally.
Whilst the electrification of transport, increased renewables generation and efficiency measures help reach these targets, emissions from heavy industries are much more challenging to abate. “Heavy industry” includes steel, cement, glass and chemicals manufacture, together with bulk transport by ship and heavy goods vehicles . A “hydrogen economy” has long been suggested to meet these challenges and provides one of the few realistic pathways to achieve “net zero” targets.
The term “hydrogen economy” was first proposed by Lawrence Jones at the University of Michigan in 1970 . His paper outlined a solution to link the growth of nuclear power to the transport sector in order to address air pollution and peak oil supply. Bulk manufacture and cryogenic storage of hydrogen had recently been mastered at the time to supply rocket fuel for space exploration, thereby providing his inspiration.
Today the interest in hydrogen is motivated more by climate change rather than peak oil supply. The principles however are the same as outlined in 1970 and include at their heart the concept of producing hydrogen by the electrolysis of water.
The production of hydrogen however is currently dominated by steam methane reforming (SMR). This is one of the most economic ways to produce the 80 million tons of hydrogen required globally each year, largely for ammonia plants and petroleum refineries . Unfortunately, SMR is a high temperature process and produces CO2 as a by-product. Hydrogen production today is responsible for over 1% of global GHG emissions .
To categorize the carbon footprint of hydrogen (or other chemicals) a color system has become popular. Hydrogen produced from electrolysis of water is referred to as “green hydrogen” whereas fossil fuel sourced SMR produces “grey hydrogen”. The gas itself has no color but the terms, rightly or wrongly, attempt to distinguish the environmental credentials.
The true carbon footprint of any product over its life cycle must be quantified in a detailed “life cycle assessment” and is dependent on many factors including the specific application, geographical location and end-of-life waste management . Schlumberger is implementing its own “science based” targets to reduce emissions following similar principals .
The carbon footprint of “grey hydrogen” can be improved by capturing the CO2 from the SMR process and sequestering it underground. SMRs including a “water-gas shift reaction” produce by-product gasses of water and CO2, from which pure CO2 can be easily extracted. Placing this CO2 safely in geological storage greatly reduces the carbon footprint and the resulting product is referred to as “blue hydrogen”. With its ‘Carbon Services for C02 Storage’ Schlumberger has led the industry in CO2 sequestering technology for many years . In a vision to sequester vast quantities of CO2 the “Northern Lights” project in Norway is aiming to provide CO2 shipping and sequestering networks to service Europe .
Producing low-carbon hydrogen is one technological problem, however the storage of hydrogen is also a challenge. Being the lightest element, hydrogen requires significant energy to liquify at atmospheric pressure (-253 °C). Alternately, cylinders can be used to store hydrogen at ambient temperatures and high pressures (up to 10,000 psi). The compression process is less energy intensive and costly than liquification, although the volumetric density of the hydrogen is lower. Hydrogen has a density of 71 kg/m3 as a liquid versus 42 kg/m3 as a gas at 10,152 psi .
Salt caverns have been used for decades to store natural gas and some facilities are currently used for hydrogen storage. Two hydrogen storage salt caverns have operated in Texas since the 1980s with three smaller caverns in Teeside, UK . Due to the vast size of these caverns (10^5 – 10^6 m3) they represent the least expensive option for large scale hydrogen storage . Salt caverns could feasibly enable seasonal storage of hydrogen from summer to winter months, greatly enhancing the value of solar and wind power generation. Schlumberger has a history of expertise in salt cavern construction  and previously owned a specialist consultancy company in the field .
Ultimately achieving “net zero” targets will demand the mass production of “green hydrogen” by electrolysis with the lowest carbon footprint. This trend is further motivated by the increasing capacity of wind and solar generation and the need to store and transport this energy. Energy storage is critical for providing grid flexibility, limiting the need for expensive transmission line upgrades and wasteful curtailment of intermittent renewables. Electrolysis provides a key “electron-to-molecule bridge” and is a focus of Schlumberger New Energy’s Genvia joint venture with the CEA . Genvia aims to create a Giga-factory manufacturing a gigawatt of high efficiency solid oxide electrolysers and will establish future business at the heart of the energy transition.
The hydrogen economy is diverse and complex covering low carbon alternatives for transport, heat, energy storage and chemical feedstocks. One of the key chemicals requiring a hydrogen feedstock currently is ammonia. Around 160 million metric tons of ammonia are produced every year by the Haber Bosch process, primarily for agricultural fertilizers. Curiously the Haber Bosch process operates at similar temperatures to solid oxide electrolysers and has been identified for tight integration to efficiently produce low carbon footprint “green ammonia” .
Hydrogen can also be used with captured CO2 to produce “carbon neutral” products. Using the Fischer Tropsch process, methanol, diesel and an array of polymers can be synthesized . This provides the pathway to a “circular economy” where waste products are fully recycled.
Hydrogen is versatile and can enable a range of “Power to X” processes that unlock a growing low-carbon future. It can also solve the energy storage challenges holding back the full-scale deployment of wind and solar power generation. As the world changes, hydrogen is set to take a key role in our sustainable future.
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Author information: David Snoswell is a principal scientist based at Schlumberger Cambridge Research in the UK, where he works in the downhole tools group on the fundamental science of cutter-rock interactions. Since joining Schlumberger in 2012 he has championed energy transition initiatives and regularly contributes to technical evaluations for investment decisions. In April 2017 he presented energy transition business opportunities to the Schlumberger CEO and CTO, these included ground source heat and lithium extraction concepts that are now pursued through Schlumberger New Energy (SNE) programs. Since the formation of the hydrogen group in SNE David has provided weekly scientific advice on applications and continues to work closely with the team. With a chemical engineering background, a PhD in colloid science and nine years’ experience in academic research in physics and chemistry, David brings a broad range of applied scientific knowledge to our vision for a sustainable future.