On The Brink

Reliable and affordable storage equipment for refueling facilities is readily available and can be leased and maintained through a number of vendors or purchased outright and managed on site. Gas handling and storage is not a new industry, although methods are always evolving. Refueling can be accomplished using free-flow or pressurized delivery systems. Free flow systems are simpler, but do not ensure complete refueling of the on-board vehicle tank. Pressurized systems are more complex and costly, but more efficient.

Hydrogen production (extraction) methods include thermal (most common), such as natural gas reforming and coal gasification, electrolytic, which splits water molecules by passing current through water, and photolytic, which relies on sunlight to split water via biological or electrochemical materials. The production options which currently produce commercially viable quantities of hydrogen are natural gas reforming, cryogenic gas separation and electrolysis.

Environmental Considerations for Extraction Options
The use of hydrogen power yields both risks and benefits. The obvious benefit is derived from end use applications; hydrogen-powered fuel cells generate zero emissions. Generating hydrogen for fueling those cells, however, has unique risks depending on the method used.

There are multiple possible methods for hydrogen generation. All methods require some source of energy, some more than others. Options range from powering the process using the common electrical grid to using purely renewable energy sources. Some methods use fossil fuel feedstocks, such as coal, while others use renewable feedstocks like water.

The most obvious environmental concern with electrolysis is it requires the use of electricity. If a common, commercial fossil-fueled electrical grid is used as the source of electrical power, the amount of fossil-fuel energy used to generate hydrogen and the corresponding atmospheric emissions may negate the environmental benefits. Fossil-fueled electricity produces greenhouse gases and other pollutants. If the system is powered by the Pacific Gas and Electric power grid in California, for example, energy sources used to power the grid range from wind power to imported electricity from out-of-state coal power plants. The average percentage of power derived from renewable sources is 25 percent across the U.S., but up to 40-45 percent in California. There is, however, the option of powering the electrolysis system using a separate, dedicated grid powered purely by renewable sources, such as wind or solar energy. This may achieve hydrogen generation with zero emissions.

The reforming method most commonly uses fossil fuels as a feedstock; however, reforming methods using renewable liquid fuels, such as ethanol or methanol, are also under development. Reforming using fossil fuels does generate CO2 emissions, but there is still a 40 to 50 percent reduction in these emissions when compared to gasoline-powered cars. Greenhouse gas emissions from reforming renewable liquid fuels are predicted to be 60 to 85 percent lower. When methanol is used as a feedstock, despite its benefits as a renewable energy source, there is an environmental downside that should be addressed. It is a known neurotoxin, even when ingested in small amounts and it can be absorbed through skin. Special handling procedures are required to mitigate this risk, but methanol is not expected to put the general population at risk.

The concern with cryogenic separation is again emissions resulting from fuel consumption for an energy-intensive hydrogen generation process and greenhouse gases emitted by processing coal as a feedstock. Cryogenic separation methods that sequester greenhouse emissions and are powered by renewable sources are currently under development, but are not technologically mature and are costly.

Other options for advanced gasification are being developed with the intention of reducing the need for fossil fuel-based energy inputs.

There are several other technologies under development that will reduce or eliminate emissions from hydrogen generation, although they are mostly in research and development. These include photobiological, photochemical, biomass gasification, coal gasification with sequestration of CO2 emissions and high temperature thermo-chemical hydrogen production.