Kalyan Annamalai, Siva Sankar Thanapal, Ben Lawrence, Wei Chen, Aubrey Spear & John Sweeten

3.1 INTRODUCTION

Coal in the power generation industry is the norm since it represents a steady supply in lieu of the vast reserves in the USA and it is the cheapest available fossil fuel. According to the US Energy Information Administration (EIA), coal accounts for 43.1% of the total energy consumed for power generation. In the year 2010 coal consumption in the power sector was to the tune of

1085.3 million short tons, which is around 92% of the total coal consumption in the USA (Watson et al., 2011).

The combustion of fossil fuels particularly coal, a solid fuel, poses many challenges due to the pollution it creates. Coal combustion releases carbon dioxide (CO2) of about 90 kg/GJ, which aids in the phenomena of global warming. The US Environmental Protection Agency (EPA) reports that nitrogen oxides are one of the major pollutants generated in the USA and a large fraction of it comes from coal-fired power plants. As opposed to fossil fuels, the biomass fuels are CO2 neutral. Thus, extensive research is being conducted to reduce CO2 emission by using renewable fuels such as wind, solar, agricultural biomass fuels (AgB) and hydrogen generated from fossil fuels and splitting water into hydrogen (H2) and oxygen (O2).

Figure 3.1 shows a comparison between AgB energy and hydrogen energy cycles. In the biomass cycle, photosynthesis is used by autotrophs (photosynthesizing organisms, Fig. 3.2) to split CO2 into carbon (C), O2, and water (H2O) into H2, O2, produce hydrocarbon (HC) fuel (e. g. leaf) and release O2. The O2 released is used back to combust HC and produce the CO2 and H2O, which are returned to produce wood and AgB and release O2. On the other hand, in the hydrogen cycle

H2O is dissociated using the photo-splitting process to produce H2 and O2, and then use H2 and O2 for the combustion process. Photosynthesis is water intensive; most of the water supplied to plants evaporates through leaves and is highly inefficient for conversion to electrical power.

The AgB is consumed by herbivores and processed into solid waste called manure or animal waste based biomass (AnB) as a byproduct of digestion and this biomass is almost a chemical replica of foods they consumed. As a matter of fact, Sweeten et al. (2003) had shown that the dry ash-free (DAF) gross or higher heat value (HHV) of cattle manure or cattle biomass (CB) is almost the same as the DAF HHV of agricultural ration fed to the cattle. The heat values of CB are comparable to low quality TX lignite coal.

This chapter gives an overview on energy conversion from animal wastes, fuel properties and TGA analyses, and various thermal energy conversion processes including co-firing, rebum and gasification.