Biomass Energy Summary

From Thermal-FluidsPedia

Biomass is a result of photosynthetic activities where carbon dioxide and water, in the presence of sunlight, combine to form carbohydrates. The conversion efficiency is rather low, however; only 0.3% of the incoming solar energy is converted to the chemical energy stored in plants. In contrast, as we will see in later chapters, solar cells can convert up to 40% of the solar energy directly into electricity.

Biomass is considered by many as a renewable source of energy. Others point out that in order for biomass to be truly renewable, the rate of cultivation of new trees must be equal to that of biomass consumption. That is to say, for every tree that is cut down and burned, another tree must be replanted.

Even if biomass were entirely renewable, it is not a clean source of energy. As is the case with fossil fuels, burning biomass creates major air pollutants such as carbon monoxide and particulates. In addition to these pollutants, biomass produces aldehydes which, although not carcinogenic, produce an unpleasant odor at high concentrations. Since there are low levels of sulfur and nitrogen in biomass, fewer products that cause acid rain are formed. Biomass, however, does not contribute to global warming and is relatively low in sulfur; it therefore contributes little to the acidity of the environment.

Besides pollution, biomass as a source of energy has been controversial for other reasons. Harvesting forests for fuel wood and lumber will ultimately lead to deforestation. Crop farms will not be able to produce such crops for a very long time, as soil erosion and massive use of herbicides and fertilizers will reduce their productivity. Furthermore, these farms are built on lands which could otherwise produce the food-crops necessary to feed many parts of the world. Burning trees, dung, and other animal wastes deprives the soil of its essential nutrients, reduces the yields, and makes the land less capable of supporting natural vegetation. It is therefore, important to use plants that are not suitable for food consumption, and are planted in marginal land unsuitable for food crops.

Trash and municipal solid wastes have become a major problem for many countries. Trash must be stored in landfills, shipped away to areas with lower population densities, or simply burned. Landfills are filling up fast, especially near towns. They are polluting, may leak hazardous chemicals into the ground and water, and are breeding grounds for rats, flies, and microbes that cause diseases, rot foods, and may react to produce other unwanted products. Hauling trash is not popular with its potential recipients. Incinerators are appealing to many because they reduce trash volume by 60-80% and produce energy at the same time. Incinerators, however, produce deadly smoke and ash, which require expensive scrubbers, filters, and other control equipment. Furthermore, many toxic metals such as mercury, lead, and cadmium cannot be effectively removed and will eventually find their way into the ground or be released into the atmosphere.

Recycling seems to be a sensitive solution to the problems of waste disposal. The problem with this approach is that it encourages waste, which ultimately increases energy use and generates a considerable amount of air pollutants. In addition, recycling demands consuming additional energy-- as much as 25% of the energy used in manufacturing the original material.

The only solution to our trash problem is to create less trash. This means we must produce only goods that are essential, made of materials that are harmless to the environment, last longer, and have been designed to be disposed with minimal waste when they are no longer needed.

References

(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Sims, R., Bioenergy Options for a Cleaner Environment in Developed and Developing Countries, Elsevier, 2003.

Tillman, D., Combustion of Solid Fuels & Wastes, Academic Press, 1991.

Biofuels for Transport: Global Potential and Implications for Energy and Agriculture, The Worldwatch Institute, 2007.

Biomass and Bioenergy, Science Direct Elsevier Science Publishing Company.

External Links

National Renewable Energy Laboratory: Biomass Research (http://www.nrel.gov/biomass).

US Department of Energy (http://www1.eere.energy.gov/biomass).

Biomass Energy Research Association (http://www.bera1.org).

American Bioenergy Association (http://www.biomass.org).