Other Pellets and Biomass
The organic materials produced by plants, such as leaves, roots, seeds, and stalks are biomass. In some cases, microbial and animal metabolic wastes are also considered biomass. The term “biomass” is intended to refer to materials that do not directly go into foods or consumer products but may have alternative industrial uses. Common sources of biomass are agricultural wastes, such as corn stalks, straw, seed hulls, sugarcane leavings, nutshells, and manure from cattle, poultry, and hogs; wood materials, such as wood or bark, sawdust, timber slash, and mill scrap; municipal waste, such as waste paper and yard clippings; and energy crops, such as poplars, willows, alfalfa, corn (starch), and soybean (oil).
Biomass is a complex mixture of organic materials, such as carbohydrates, fats, and proteins, along with small amounts of minerals, such as sodium, phosphorus, calcium, and iron. The main components of plant biomass are carbohydrates (approximately 75%, dry weight) and lignin (approximately 25%), which can vary with plant type. The carbohydrates are mainly cellulose or hemicellulose fibers, which impart strength to the plant structure, and lignin, which holds the fibers together. Some plants also store starch and fats as sources of energy, mainly in seeds and roots (such as corn, soybeans, and potatoes).
There are two principal advantages of using biomass as a source of fuels or chemicals. One major advantage is its renewability. Utilizing sunlight energy in photosynthesis, plants metabolize atmospheric carbon dioxide to synthesize biomass. An estimated 140 billion metric tons of biomass are produced annually. The second is that as biomass, it has no direct affect on food and consumer stocks and does not directly affect prices or availability.
Major limitations of solid biomass fuels include the difficulty of handling and lack of portability for mobile engines. To address these issues, research is being conducted to convert solid biomass into liquid and gaseous fuels.
Ethanol for automotive fuels is currently produced from starch biomass in a two-step process. About 1.5 billion of ethanol are produced from starch each year in the United States.