The dream of a global economy powered by renewable hydrogen is coming into sharper focus, except for one key sticking point. Getting hydrogen from one place to another adds costs. Energy loss is also an issue. An inexpensive, efficient, and sustainable transportation medium would fill the gap, and apparently green ammonia is first in line.
Getting Hydrogen From Here To There
The US Department of Energy is among those eyeing ammonia for improving the cost-efficiency of hydrogen storage and transportation. The chemical formula for ammonia is NH3. The challenge is how to crack the hydrogen off when it’s needed, economically and efficiently.
In 2006, the Energy Department published a white paper in which it explained why ammonia is worth pursuing, rather than transporting hydrogen alone.
The Energy Department surmised that new purpose-built pipelines for hydrogen transportation would not be in the cards, at least not during the early years of the expanding hydrogen market. That was a prescient observation considering the opposition to the Keystone XL oil pipeline and other fossil energy pipelines in recent years.
The agency also noted that truck and rail alternatives were available, but were relatively expensive. They reached the same conclusion for liquefied hydrogen.
“Liquid hydrogen tankers are cheaper, but there is a considerable energy and cost penalty associated with liquefaction (currently >30% of hydrogen’s energy content is required to liquefy it),” the Energy Department observed.
The Ammonia Connection
To overcome these obstacles, the Energy Department favored the carrier approach, in which hydrogen is transported as an element in another medium, then extracted at its use point.
“For carriers to be effective, they need to satisfy several criteria. They should have high effective energy (hydrogen) densities (liquids or solids). The associated hydrogenation-dehydrogenation processes should be simple and energy efficient,” the Energy Department explained.
While acknowledging ammonia as a hazardous substance, the agency advocated for its use as a hydrogen carrier.
“Ammonia is one of the only materials that can be produced cheaply, transported efficiently and transformed directly to yield hydrogen and a non-polluting byproduct,” they concluded.
From Green Hydrogen To Green Ammonia
There is nothing particularly green about the ammonia-as-a-carrier approach when the vast majority of the global hydrogen supply comes from natural gas and other fossil resources. However, the script has flipped in recent years. More sustainable sources of hydrogen are surging into the global economy, primarily from electrolysis systems that push green hydrogen from water with renewable energy. Add ambient nitrogen from the air, and the result is a more sustainable means of producing ammonia.
In an interesting twist, the falling cost of electrolysis has opened up a new opportunity to develop networks of small scale hydrogen facilities, aimed at production for on-site use. The Energy Department looked at that pathway in 2006 and discarded it as cost-prohibitive under a fossil-sourced hydrogen scenario. Now the agency is advocating for the distributed production model to aid farmers. The idea is to deploy wind turbines on farms to run electrolysis systems, providing farmers with the ability to produce their own hydrogen fuel and ammonia fertilizer on site.
Green Ammonia As A Hydrogen Carrier
Regardless of the availability of low-cost, decentralized renewable energy resources, centralized electrolysis facilities will most likely continue to play a leading role in the emerging hydrogen economy, and Siemens is among the private sector stakeholders betting that it will.
The firm’s Siemens Energy branch is spearheading a consortium to build a £3.5m ammonia cracker in the UK, in Newcastle. The aim is to produce green hydrogen from ammonia at an industrial scale, at its point of use.
Siemens cites the high energy density and transport-ability of ammonia, along with the advantage of an existing supply chain infrastructure and the sustainable production of green ammonia from green hydrogen.
“The system will be designed to deliver high-purity hydrogen, suitable for PEM fuel cell use, using FFI’s Metal Membrane Technology (MMT) purification process,” Siemens Explains.
“The MMT process developed by FFI and Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) is key to producing high-purity hydrogen from the ammonia cracking process,” Siemens adds. “It selectively filters the hydrogen whilst blocking other gases, allowing it to be used as a fuel and converted as needed, at the time of re-fuelling.
The Return Of The Hydrogen Car
In terms of providing sustainable hydrogen for off-grid use, the green ammonia project is off to a head start. GeoPura is already deploying its transportable green hydrogen fuel cell “Hydrogen Power Units” for use at off-grid locations including the site of the Netflix/BBC Winterwatch series and the ambitious HS2 zero carbon railway project.
If all goes according to plan, the new green ammonia cracker will be scaled up and put to use decarbonizing industrial facilities as well as grid-scale power generation and thermal energy.
In the meantime, Siemens also envisions some mobility applications for hydrogen from the green ammonia project.
The mobility angle circles back around to that Energy Department white paper from 16 years ago (here’s that link again). The paper was subtitled, “A Study of Issues Related to the Use Ammonia for On-Board Vehicular Hydrogen Storage.” DaimlerChrysler Corporation, Ford Motor Company, and General Motors were the automotive fuel cell stakeholders teaming up with the Energy Department to produce the paper.
BP America, Chevron Corporation, ConocoPhillips, Exxon Mobil Corporation, and Shell Hydrogen were also on board, having spotted the potential for hydrogen fuel cell vehicles to provide them with a new market for hydrogen sourced from natural gas.
Things certainly have changed in the past 16 years. Hydrogen fuel cell vehicles have been slow to catch on here in the US, dispelling any thoughts of easy pickings in the mobility market for fossil energy stakeholders. If and when fuel cell vehicles go mainstream, fleet owners will most likely prefer to fuel up with green hydrogen, not fossil-sourced hydrogen.
As for green ammonia as an onboard hydrogen carrier for fuel cell vehicles, that appears to have fallen by the wayside. As of last year, the Energy Department’s US DRIVE partners seem to be focusing more attention on improving hydrogen storage tank technology.
At some point in the sparkling green future, green ammonia may also have to compete with liquid organic hydrogen carriers, carbon-based hydrogen “sponges” and other high tech storage materials for onboard energy storage in vehicles.
The shipping industry is a whole different story, as Maersk and other leading fleet owners begin to zero in on green ammonia fuel to decarbonize maritime emissions.
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Image: Off-grid use of sustainable hydrogen for film production, courtesy of GeoPura.
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Source: Clean Technica