Carbon Neutral Liquid Fuels

The U.S. Department of Energy’s ARPA-E recently announced funding for a new program to support technology development proposals that use renewable energy to convert air and water into “carbon neutral liquid fuels (CNLF)”.  These cost-competitive, energy dense fuels must be storable, transportable and convertible to hydrogen or electricity.

Examples of CNFLs include: ammonia, hydrazine hydrate, carbohydrazide, and synthetic hydrocarbons that extract carbon from air or water thus meeting the carbon neutral criteria.  The overarching goal is to find suitable substitutes for carbon dioxide emitting transportation fuels like gasoline and diesel while retaining their advantageous energy density, storability and compatibility with the existing distribution infrastructure.

Perhaps paradoxically, “carbon zero” liquid hydrogen is specifically excluded from consideration.  No doubt, there are programmatic reasons for this exclusion based on other efforts in the DOE portfolio and investments previously made in hydrogen technologies and systems development.  But there are also technical reasons to look beyond liquid hydrogen.

The Challenges with Liquid Hydrogen

Hydrogen’s low volumetric density and cryogenic normal boiling point of -253 C poses unique challenges.  ARPA-E’s funding announcement document  succinctly describes how this impacts storage and distribution:

 
Hydrogen compression and, especially, liquefaction incur additional energy losses (up to 10 and 35%, respectively). In contrast to liquid H2, which boils-off with a rate of 1 – 4% per day depending on the tank, hydrogen storage and transportation as a compressed gas has very low losses. Therefore, the latter is a more attractive option for long-term storage (from days to seasonal).
— Source: “Renewable Energy To Fuels Through Utilization Of Energy-Dense Liquids (REFUEL)”, Funding Opportunity No. DE-FOA-0001563, April 26, 2016.

While the above may be true for currently available commercial systems, liquefaction energy and boil-off losses can be significantly reduced with proven technologies developed in the aerospace industry.  In fact, zero boil-off liquid hydrogen systems have been developed by NASA and other aerospace organizations with combinations of advanced insulation, optimized structural/penetration design, Joule–Thomson cooling, para-to-ortho conversion cooling, crycoolers, and other technologies and innovative design features.  An example test article is shown below .

 

Source: Hastings, et al., “Large-Scale Demonstration of Liquid Hydrogen Storage With Zero Boiloff for In-Space Applications”, NASA TP-2010-216453.

 

Keep It Local?

The table below shows parameters for evaluating the full costs of delivery transportation power using carbon-free energy sources from the subject ARPA-E funding announcement .  Note that there’s an inherent assumption in this table that’s an artifact of our current transportation fuels paradigm that’s not in the footnotes.

 

 Source: REFUEL announcement, April 26, 2016.

 

By necessity, the evolution of our fossil fuel industries and infrastructure has been largely predicated on geographic separation of extraction, refining/processing and point of use.  Oil or coal or natural gas doesn’t exist in every location where their derivative products are used.  In addition to the far reaching geopolitical ramifications, this reality has resulted in the need for a vast distribution system to service every link in the fossil fuel supply chain.

But is this a mandatory constraint in a carbon-less energy ecosystem based on renewable energy sources and hydrogen?  Renewable energy sources can be found anywhere, along with local sources for hydrogen production.  It’s interesting to consider the case where transportation costs of hydrogen are not applicable due to production and point of use occurring in the same location.  In that scenario, the total source-to-energy cost for hydrogen in the previous table becomes lower than the other carbon-free energy sources shown.

Many Paths Forward

Some combination of CNLFs, along with carbon-free hydrogen, will provide a transition path away from fossil fuels in transportation and stationary energy systems.  Isotherm Energy is positioned for whatever that combination may turn out to be with our hydrogen energy architecture.  Any of the CNLF options are compatible since they can be readily integrated into our architecture and processed into hydrogen at the point of use for the target application.  The destination of a more sustainable energy future is worth the journey.


Matt Moran is a Managing Partner at Isotherm Energy and has been developing power, thermal, and fluid systems since 1982.  He has a passion for the business and engineering of technology development and its integration into commercial products. Matt was the Sector Manager for Energy and Materials at NASA Glenn Research Center where he worked for over 30 years.  He has also co-founded or been a key contributor to five technology based start-ups; and provided R&D and engineering consulting to many industrial, government and research organizations.  More about Matt here