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…
Read More: Green Ammonia To Solve Green Hydrogen Transport Conundrum