Technology – Hydrogen production

7 05 2009

Production

Hydrogen may also be extracted from water via biological production in an algae bioreactor, or using electricity (by electrolysis), chemicals (by chemical reduction) or heat (by thermolysis); these methods are less developed for bulk generation in comparison to chemical paths derived from hydrocarbons.

The pathway to cleaner Hydrogen production

Water Electrolysis – Hydrogen can also be produced through a direct chemical path using electrolysis. With a renewable electrical energy supply, such as hydropower, wind turbines, or photovoltaic cells, electrolysis of water allows hydrogen to be made from water without pollution. Usually, the electricity consumed is more valuable than the hydrogen produced so this method has not been widely used in the past, but the importance of high pressure electrolysis is increasing as human population and pollution increase, and electrolysis will become more economically competitive as non-renewable resources (carbon compounds) dwindle and as governments remove subsidies on carbon-based fuels. Hydrogen can also be used to store renewable electricity when it’s not needed (like the wind blowing at night) and then the hydrogen can be used to meet power needs during the day or fuel vehicles. This helps make hydrogen an enabler of the wider use of renewables.

Nuclear – One side benefit of a nuclear reactor that produces both electricity and hydrogen is that it can shift production between the two. For instance, the plant might produce electricity during the day and hydrogen at night, matching its electrical generation profile to the daily variation in demand. If the hydrogen can be produced economically, this scheme would compete favorably with existing grid energy storage schemes. What is more, there is sufficient hydrogen demand in the United States that all daily peak generation could be handled by such plants. However, Generation IV reactors are not expected until 2030 and it is uncertain if they can compete by then in safety and supply with the distributed generation concept.

Other types of production

The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained through many thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermolysis, or as a microbial waste product called biohydrogen or Biological hydrogen production. Most of today’s hydrogen is produced using fossil energy resources, and 85% of hydrogen produced is used to remove sulfur from gasoline. Hydrogen can also be produced from water by electrolysis or by chemical reduction using chemical hydrides or aluminum.Current technologies for manufacturing hydrogen use energy in various forms, totaling between 25 and 50 percent of the higher heating value of the hydrogen fuel, used to produce, compress or liquefy, and transmit the hydrogen by pipeline or truck. Electrolysis, currently the most inefficient method of producing hydrogen, uses 65 to 112 percent of the higher heating value on a well-to-tank basis.

Environmental consequences of the production of hydrogen from fossil energy resources include the emission of greenhouse gases. Studies comparing the environmental consequences of hydrogen production and use in fuel-cell vehicles to the refining of petroleum and combustion in conventional automobile engines find a net reduction of ozone and greenhouse gases in favor of hydrogen.

Hydrogen production using renewable energy resources would not create such emissions or, in the case of biomass, would create near-zero net emissions assuming new biomass is grown in place of that converted to hydrogen. The scale of renewable energy production today is small and would need to be greatly expanded to be used in producing hydrogen for a significant part of transportation needs.

While methods of hydrogen production that do not use fossil fuel would be more sustainable,currently such production is not economically feasible, and diversion of renewable energy (which represents only 2% of energy generated) to the production of “Green” hydrogen for transportation applications is inadvisable.

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