Hydrogen from Biomass

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Biomass could potentially become an important source of hydrogen [94]. Biomass includes a large variety of materials such as agricultural residues from farming and wood processing, dedicated bioenergy crops such as switchgrass, and even algae in the sea. As mentioned in Chapter 6, biomass can be used for the production of such liquid fuels as ethanol, biodiesel and methanol. Like fossil hydrocarbons, biomass can also be converted into hydrogen by gasification or pyrolysis coupled with steam reforming. This approach can greatly benefit from the extensive knowledge accumulated over the years in the field of fossil fuel transformation and refining. Gasification plants designed for biomass are generally limited to midsize-scale operations, due to the high cost of gathering and transporting the usually dispersed and relatively limited amounts of available biomass. Currently, such plants operate only at some 26% efficiency with estimated hydrogen production costs over $7 kg-1 H2 [91]. Although with technology improvements and in creased efficiencies, lower hydrogen prices can be expected, the cost is expected to remain at or above $3 kg-1. An interesting alternative, which has been demonstrated commercially [95], is to gasify biomass together with coal, with mixtures containing up to 25% biomass. The construction of biomass-specific gasification units would be unnecessary, and in case the biomass feedstock is seasonal, the plant could operate on coal only.

With regard to greenhouse gas emissions, biomass combustion releases CO2 that was previously captured from the atmosphere, so that in this recycling the net CO2 emission is near zero. However, the cultivation of crops requires fertilizers (that need hydrogen in the form of ammonia) and water, as well as energy for the production, harvesting and transportation. All of these factors, together with their environmental impacts on soil, water supply and biodiversity, must be taken into account and the possible consequences of a large-scale intensive energy-related crop farming carefully assessed. Dedicated high-yield energy crops such as switchgrass, which can be grown with minimal energy input, would be preferable, although biomass for energy would still have to compete for huge areas of land with other agricultural products. Algae grown in the vast expanses of the sea could, however, change this picture in the future. In any case, biomass could only be expected to supply a part of the large quantities of hydrogen required.

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Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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