The results of the proximate, ultimate (or elemental), and heat value analyses of the fossil and various animal waste based biomass fuels and coals are presented in Table 3.3. In general, the cattle biomass fuels are higher in ash, lower in heat content, higher in moisture, and higher in nitrogen and sulfur (which can cause air pollution) compared to the Texas and Wyoming coals. The HV of a fuel is the amount of heat released when a unit (mass or volume) of the fuel is burned. Typically, bomb calorimeters are used to determine the HV. Table 3.3 tabulates the higher or gross heat values of animal-waste-biomass (AWB) (Table 3.3). Generally, the HHV of CB on a dry, ash-free basis (DAF) tends to be between 18,000 and 22,000 kJ/kg (average about 20,000 kJ/kg) depending on the animal’s feed ration (Sweeten et al., 2003) while coals on DAF basis yield about

30,0 kJ/kg. Since DAF HHV is almost constant, it is the moisture and ash, which reduce the heat value and affect the flame temperatures as shown in Figure 3.5.

Using ultimate analyses, one can determine the empirical chemical formula. If the overall carbon content of gasoline is 82.6% (by mass) and hydrogen is 17.4%, then the empirical formula is given as C = (82.6/12.01) = 6.88, H = 17.23 or the empirical formula is C6.88H17.23 or after normalization with C atoms, CH2.5. Since AnB and AgB contain C, H, O, N and S, the empirical formulae contain all these 5 atoms. Table 3.3 lists the empirical chemical formula for AgB and AnB fuels. The feedlot manure is collected from pens using wheel loaders, and is composted in windrows with composting unit. Manure is termed as raw if samples were collected from each windrow on day 1 (raw FB or unprocessed manure), partially composted, (or PC) if collected on day 31 and finished-composted, or FiC if collected on day 125. The composting helps in improving the homogeneity of the biomass.

Cattle biomass typically contains 1-3% nitrogen depending on the type of biomass, while coals generally contain up to 1% nitrogen, which is called fuel nitrogen depending on the rank of coal (Annamalai et al., 2003a). The N content in fuels is of extreme importance since typically higher fuel N results in higher NOX. Fuel nitrogen is released as a mixture of HCN, NH3 and N2 from coal and biomass. The NOX generated from fuel N compounds is termed as fuel NOX while the NOX from atmospheric N2 is referred to as thermal NOX. For most coal-fired units, thermal NOX contributes about 25% of the total NOX emission, and fuel NOX contributes the other 75% of the total (Annamalai et al., 2003b). The AgB fuels contain a lower amount of N compared to coals. The reduction in NOX when agricultural biomass (typically lower N content) is blended with coal occurs due to the following reasons: (i) lowerN inAgB, (ii) reduced local O2% due to higher VM,

(iii) more N in the form of NH3 than HCN since reduction via NH3 + NOX is more rapid compared to HCN + NOX but it is noted that the lower N content in biomass will produce a lower amount of NH3. Thus Tillman et al. (2000) examined co-fired coal with low nitrogen AgB and showed that NOX can be reduced by co-firing due to reduced N in blend; thus, NOX was reduced simply by reducing the nitrogen loading to the furnace. However the reported amount of NOX reduction (measured trend line) was greater than expected based on theoretical data (Fig. 3.6) since higher volatile matter in AgB (almost 80%) depletes the local O2 rapidly resulting in lesser availability of O2 for fuel N oxidation to NO. Thus Figure 3.6 shows that lower N in blend, the greater the NOX reduction in kg/GJ of heat released. However, since AnB contains more N compared to coal, there is a concern for increased NOx emission during direct combustion. As seen later the N in AnB is mostly of urea type, which may help in better reduction of NOx under appropriate temperature and oxygen %.

In Figure 3.7 it may be seen that raw FB, partially composted (PC) FB, fully/finished composted (FiC) FB, and cattle ration (cattle feed) all fall under this DAF HHV range. Similar results are also found when blending 5% crop residues with each FB fuel (Sweeten et al, 2006).