Renewable Hydrogen: Biomass for Sustainable Hydrogen Transportation Fuel
Practically speaking, since we will not run out of oil in the next 20 to 30 years, the replacement of significant quantities of fossil-derived fuels and the replacement of traditional automobile propulsion systems will be slow. An important word is transition, defined here as a period of change in fuel types and production, fuel distribution and vehicle types. We have been using gasoline and diesel fuel in engines that were designed and built 100 years ago, with few fundamental changes since.
Hydrogen as an alternative fuel can and will become a reality, but we appear to be going through a transition phase of first using ethanol and biodiesel in vehicles, requiring few changes. The introduction of alternative fuel vehicles such as hydrogen cars will be slow, unless market drivers force a more rapid transition. There is an ever-increasing possibility of politically-driven global disruption of oil supply, which could push hydrogen technologies into the forefront within five years.
Demand for hydrogen in the oil, food, aeronautics and utility industries is met by reforming natural gas. During a time of transition toward hydrogen-powered vehicles, it is obvious that we will need to lean on conventional fossil technologies for hydrogen production, but eventually more sustainable renewable options will be desired to lower greenhouse gas emissions and increase energy security.
This is where we enter the dawn of a new era. Renewable hydrogen options currently include using wind, solar and hydroelectric energies, and biomass feedstocks. Wind, solar and hydroelectric systems produce renewable electricity, which can be used to power an electrolyzer to produce hydrogen. Biomass or biobased resources can be converted through current thermochemical or biological processes to produce hydrogen. Biomass is probably the best resource in the next several decades for producing reliable, sustainable, large-scale quantities of renewable hydrogen.
Current electrolyzers are inefficient, and solar and wind-based systems simply do not have the capacity for producing sustainable, large quantities of hydrogen. Biomass can be collected in quantities ranging in the thousands of tons. Gasification, anaerobic digestion and conventional corn or next-generation cellulosic ethanol technologies can produce renewable hydrogen. A biomass gasifier produces primarily carbon monoxide, carbon dioxide, methane and hydrogen. Gasifiers can be operated to optimize that hydrogen component. Anaerobic digesters will convert biomass to methane, which can be reformed like fossil-based natural gas to hydrogen. The ethanol production process can be interrupted in the wet mixed-alcohol stage with thermochemical processing to produce hydrogen. These are all fairly conventional technologies that can be improved, optimized and made cost-effective through economies of scale.
Strains of bacterial microbes are being discovered that maximize hydrogen production yield and rates. Microbial systems are being integrated within fuel cells to deliver their hydrogen directly across a membrane for fuel cell electricity generation. A similar concept was developed and tested at the laboratory scale at the Energy & Environmental Research Center using thermochemistry instead of biology. A biomass gasifier was thermally integrated with a solid oxide fuel cell so that hydrogen and other syngas products would fuel electricity production. The distributed energy system could conceptually generate between 100 kilowatts and one megawatt of electrical power.
We have entered an exciting age of hydrogen potential, and research is advancing the use of biomass as a resource for the production of biomass-based hydrogen.
Chris J. Zygarlicke, is a deputy associate director for research at the EERC and is vice chairman of the National Hydrogen Association Renewable Hydrogen Working Group. Reach him at firstname.lastname@example.org or (701) 777-5123.