Energy content, coal

The chemical characteristics of biomass vary over a broad range because of the many different types of species. Table 8 compares the typical analyses and energy contents of land- and water-based biomass, ie, wood, grass, kelp, and water hyacinth, and waste biomass, ie, manure, urban refuse, and primary sewage sludge, with those of cellulose, peat, and bituminous coal. Pure cellulose, a representative primary photosynthetic product, has a carbon content of... 

Coal competes primarily in the market for low-cost boiler fuels. Coal is also characterized by a relatively low energy content per unit of weight (at best two-thirds chat of residual oil). Consequently, low-cost... 

NOTE Prices hove been converted into Btus assuming 5,800,000 Btus per barrel of oil, 3,412,000 Btus per 1000 kWh, 1,000,000 Btus per 1000 mcf of natural gas, and 22,500,000 Btus per short ton of coal. A Btu is about of a food calorie or a kilocalorie, 1,000 Btus contain the energy content of a candy bar. 

As a fuel, municipal solid waste (MSW) does not compare too favorably with more traditional solid fuels, such as coal. M.SW averages somewhere around 4500 Btu/lb, versus coal at 10,500-13,000 Btu/lb. Flowever, given the current U.S. population of 250 million and the annual generation of waste per person of fifteen hundred pounds, the potential energy content in the annual waste generated in the U.S. alone is comparable to nearly seventy million tons of coal and has the potential to generate over 13,000 MW of electrical power. As of a published report in 1993, 128 facilities were actually in operation, with an additional... 

Lignite. Lignite is geologically very young (upward of around 40,000 years). It is brown and can be soft and fibrous, containing discernible plant material. It also contains large amounts of moisture (typically around 70%) and hence, it has a low energy content (around 8 to 10 MJ/kg). As the coal develops it loses its fibrous character and darkens in color. 

Black coal. Black coal ranges from Cretaceous age (65 to 105 million years ago) to mid-Permian age (up to 260 million years ago). They are all black some are sooty and still quite high in moisture (sub-bituminous coal). A common name for this coal in many parts of the world is "black lignite. Coals that get more deeply buried by other rocks lose more moisture and start to lose their oxygen and hydrogen they are harder and shinier (e.g., bituminous coal). Typical energy contents are around 24 to 28 MJ/kg. These coals generally have less than 3% moisture, but some power stations burn coal at up to 30% ash. 

Anthracite. Anthracite is a hard, black, shiny form of coal that contains virtually no moisture and very low volatile content. Because of this, it bums with little or no smoke and is sold as a "smokeless fuel. In general, coals only approach anthracite composition where bituminous coal seams have been compressed further by local crustal movements. Anthracites can have energy contents up to about 32 MJ/kg, depending on the ash content. 

It is important to note that coal rank has little to do with quality. As a coal matures its ash content actually increases as a proportion because of the loss of moisture and volatiles. Lower rank coals may have lower energy contents, but they... 

Developing new approaches to preparing and feeding low-rank coals and alternative feeds such as biomass. This includes addressing the removal of moisture from certain alternative fuels like biomass in order to increase energy content. 

Because of its high calorific energy content, hard coal is internationally traded (unlike lignite). Total trade in 2005 amounted to 790 Mt (16% of production), of which around 90% was traded by sea transport from the harbours, the coal is further distributed either by inland waterways or rail. The most important exporters of hard coal are Australia, South Africa and Indonesia. 

Long-distance transport has a large impact on the total costs. Compared with other fuels, the volumetric energy content of hydrogen is comparatively low, which makes long-distance transportation less efficient. Therefore, if natural gas or hard coal are the considered feedstock for hydrogen production, it would be better to import the feedstock and produce hydrogen at (or near to) the place of use. 

Hydrogen corridors based on hard coal or natural gas are not suitable. It is better to transport these feedstocks directly instead of hydrogen, because of their much higher energy content and consequently lower transport cost and because the infrastructure for it is already in place. 

The chemical energy content of fossil fuels generally parallels the H/C ratio as shown in Table 1. Methane has the highest heating value of the hydrocarbon series, corresponding to its high H/C ratio while coal has the lowest heating value. The normal physical state of fossil fuels also parallels the H/C ratio. Methane is a gas at ambient temperature and pressure conditions. Petroleum fractions are mobile liquids except for the heaviest fraction which can be solid at ambient temperature. Coal is a solid material. 

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