## 2 Fuel Properties of Rice Husk and Rice Straw  
The organic matter of RH and RS consists predominantly of cellulose, hemicellulose, and lignin [91]. Table 1 lists organic contents, proximate and ultimate analysis as well as the ash compositions of RH and RS. Wood is included as a reference material for comparison. Fuel properties of high quality wood pellets fulfilling requirements of class A1 of the ENplus certification scheme were obtained from [PERSON] et al. [92]. According to Table 1, the ash obtained from wood uncontaminated by soil impurities is mainly composed of alkaline earth metals followed by silicon and potassium [93; 94; 95; 96; 97]. According to Table 1, since RH and RS have different ash forming elements than wood, they show completely different ash melting behavior. The ash content of RH and RS is one order of magnitude higher than the ash content of clean wood. Silicon is by far the most abundant element among the inorganic matter both in RH and RS [58; 59; 72; 98; 99; 100; 101]. Ca, Mg, K, Na, P, S, Cl, and Al are also included but to a far lesser extent [99; 73; 98; 102; 103; 104; 105]. Association of these ash forming elements as well as their distribution in the biomasses have a major impact on ash melting behavior [106] and consequently determine the remaining silica purity and quality [107; 108; 109; 105]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Characteristic**} & \multicolumn{3}{c}{**Rice Husk (RIB)**} & \multicolumn{3}{c}{**Rice Staav (BS)**} & \multicolumn{3}{c}{**Clean Wood Pellet 1 (W)**} \\ \hline \multicolumn{1}{c}{**Organic Type**} & \multicolumn{3}{c}{**CHL and HLC**} & \multicolumn{3}{c}{**CHL**} & \multicolumn{3}{c}{**CHL**} \\ \hline \multicolumn{1}{c}{**Inorganic Type**} & \multicolumn{3}{c}{**5 Type**} & \multicolumn{3}{c}{**5 Type**} & \multicolumn{3}{c}{**C Type**} \\ \hline \multicolumn{1}{c}{**Inorganic Sub-Type**} & \multicolumn{3}{c}{**HA**} & \multicolumn{3}{c}{**HA**} & \multicolumn{3}{c}{**LA**} \\ \hline \multicolumn{1}{c}{**Inorganic Type**} & \multicolumn{3}{c}{**Mean**} & \multicolumn{1}{c}{**Minimum**} & \multicolumn{1}{c}{**Maximum**} & \multicolumn{1}{c}{**n**} & \multicolumn{1}{c}{**Mean**} & \multicolumn{1}{c}{**Minimum**} & \multicolumn{1}{c}{**Maximum**} & \multicolumn{1}{c}{**n**} & \multicolumn{1}{c}{**Mean**} & \multicolumn{1}{c}{**Minimum**} & \multicolumn{1}{c}{**Maximum**} & \multicolumn{1}{c}{**n**} \\ \hline \multicolumn{1}{c}{Moisture content (MC), wt \% db} & 8.79 & 4.64 & 12.08 & 21 & 87.4 & 5.58 & 13.06 & 12 & 6.90 & 3.30 & 10.80 & 209 \\ \multicolumn{1}{c}{**Ash content (AC), wt \% db} & 16.30 & 7.68 & 24.60 & 48  
Origin of the raw materials can have a significant impact on the inorganic composition of fuel ashes of RH and RS. For instance, as shown in Table 2, RH from Egypt, Cambodia, and Italy was evaluated in the same laboratory with the same measurement techniques [72; 98]. Results highlight that Si, K and P contents of the fuel ash can vary significantly. Differences in compositions are due to a variety of factors, such as climate, soil types, harvesting season, the amount of fertilizers used during the rice cultivation, geographical and environmental aspects [179; 180; 53; 178; 181]. In Table 1, organic and inorganic types of biomass samples are defined according to [PERSON] et al. [182; 183; 184; 110]. Accordingly, Figure 2 illustrates a possible biomass classification based on the organic and inorganic composition. In Figure 2a, biomasses are arranged according to their relative share of cellulose, hemicellulose and lignin. For the majority of biomasses, cellulose is the predominant macromolecule based on the weight portion [110] followed by hemicellulose and lignin (Cellulose > Hemicellulose > Lignin, i.e., CHL). Marine organisms are usually characterized by hemicellulose as the predominant macromolecule and particularly low contents of lignin (Hemicellulose > Cellulose > Lignin, i.e., HCL). Nut shells and pits are often located in the LCH region based on their high lignin contents.