Additional Energy Sources

In addition to the gaseous and liquid fuels discussed in this chapter, there are a host of other energy sources that may be productively used in providing for heating, cooling, process use, and power generation at commercial, industrial, and institutional (CI&I) facilities. These range from fossil fuel sources, such as coal, shale, and tar sands, to renewable sources, such as solar, geothermal, wind, water, and biomass. Other diverse sources range from hydrogen gas to a wide variety of energy sources congealed in common trash. Below is a brief review of several of these alternative sources.


While mentioned earlier only as a feedstock for various coal-derived fuel gases, coal itself is the world's second leading energy source, providing nearly one-third of the world's energy. It is also still the most commonly used fuel for large-scale utility electric power generation plants, which consume about one third of the energy used in the United States. While far less costly on a heat content basis, relative to gas and oil, its use is still limited at most CI&I facilities in the United States due to increased costs for transportation, handling, combustion equipment, and environmental compliance. Except in very large applications, these facilities typically do not enjoy the economies of scale achieved in central utility applications, where the many peripheral cost obstacles can be overcome. Still, coal is found in use in some industrial facilities and in numerous homes throughout the country.

Coal is formed from plants by chemical and geological processes that occur over millions of years. Layers of plant debris are deposited in wet or swampy regions under conditions that prevent exposure to air and complete decay as the debris accumulates. Bacterial action, pressure, and temperature act on the organic matter over time to form coal. This geochemical process is called coalification. In the early stages, peat is formed. It is progressively transformed into lignite, which eventually can become anthracite, given the proper progression of geological changes.

The four basic types of coal are as follows:

• Lignite is the lowest rank coal. Lignite coals are soft and brownish and have heating values of less than 8,300 Btu/lbm (6,980 kJ/kg), with a moisture content of about 30%. Lignite coals dry out when exposed to air, so spontaneous combustion during storage is a concern. Long distance shipment is often not economical due to their high moisture content and low energy density.

• Subbituminous coals have a reasonably high heating value of 8,300 to 11,500 Btu/lbm (19,300 to 26,750 kJ/kg), with moisture content ranging from 15 to 30%. They have become increasing attractive as fuel sources due to their relatively low ash and sulfur content. With a sulfur content of 1% or less, switching to subbituminous coals has become an attractive option for many power plants to limit SO2 emissions. Like lignite coals, they are high in volatile matter content and can easily ignite.

• Bituminous coals are the most commonly used coals in electric utility boilers. They have heating values of 10,500 to 14,000 Btu/lbm (24,420 to 36,050 kJ/kg) and lower moisture content and higher fixed carbon content (69 to 86%) than subbituminous coals. With a higher energy density, lower moisture content, and lower volatility, these coals are easier to transport and store than lignite and subbituminous coals. They are still fairly volatile, which, combined with their high energy density, enables bituminous coals to burn easily when pulverized to a fine powder. Some types of bituminous coal, when heated in the absence of air, soften and release volatiles to form the porous, hard, black product known as coke. Coke, referred to earlier in the chapter, is used as fuel in blast furnaces to make iron and can also serve as a feedstock for various types of fuel gases.

• Anthracite is the highest rank of coal. It is shinny, hard, and brittle and has the highest fixed content of carbon (86 to 98%) and the lowest moisture content (about 3%) of all coals. Heating values are about 15,000 Btu/lbm (34,900 kJ/kg), which is similar or sometimes a bit lower than the best quality bituminous coals. Anthracite is low in sulfur and volatiles and burns with a hot, clean flame, making it a premium coal for domestic heating.

There are a variety of criteria for ranking coal, given its wide characteristic variability. Some of the various ASTM analyses include determination of moisture, volatile matter, fixed carbon, and ash. ASTM D 3176 analysis includes measurements of carbon, hydrogen, nitrogen, and sulfur content and the calculation of oxygen content. ASTM D 2015 analysis is used to determine the gross calorific value of coal on various bases (i.e., dry, moisture and ash free, etc.). These constituents vary tremendously amongst different types of coal and even different variations of the same classes of coals. Carbon content may vary anywhere from less than 20% to more than 95% and sulfur content may vary from less than 0.5% to more than 8%. HHV is defined as the heat released from combustion of a unit mass of fuel, with the products in the form of ash, gaseous CO2, SO2, nitrogen and liquid water, exclusive of any water added as vapor. LHV is calculated from HHV (ASTM Standard D 407) by deducting 1,030 Btu/lbm (2,396 kJ/kg) of water derived from the fuel, including the water originally present as moisture and that formed by combustion.

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.

Get My Free Ebook

Post a comment