# The Influence of Co-Firing Coal with Biomass Syngas on the Thermodynamic Parameters of a Boiler
## 4 Results and Discussion  
### Effect of Co-Firing on Radiant Heat Transfer  
The primary thermodynamic parameters of the boiler under BMCR are shown in Figure 3. The heating value of the fuel, the quantity, and the specific heat of the combustion products determine the theoretical combustion temperature, which represents the highest temperature that the combustion products can achieve [28]. The available heat of fuels is correlated to the volume, specific heat, and theoretical combustion temperature if the fuel is burnt completely and adiabatically. It can be seen from Figure 3a that the available heat would rise monotonically, as the consumption rates and heating value of biomass syngas increase. The result is the same as that in our previous study [23]. Compared with \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Value**} \\ \cline{2-6}  & **BMCR** & **75\% THA** & **50\% THA** & **30\% THA** \\ \hline Power generation (MW) & 330 & 225 & 150 & 113 \\ Main steam output (t h\({}^{-1}\)) & 1025 & 662 & 441 & 335 \\ Main steam pressure (MPa) & 17.47 & 14.45 & 9.79 & 6.23 \\ Outlet temperature of superheated steam (\({}^{\circ}\)C) & 540 & 540 & 540 & 540 \\ Reheated steam output (t h\({}^{-1}\)) & 880.0 & 582.4 & 395.6 & 313.7 \\ Outlet temperature of reheated steam (\({}^{\circ}\)C) & 540 & 540 & 540 & 535 \\ Outlet pressure of reheated steam (MPa) & 3.68 & 2.44 & 1.63 & 1.25 \\ Desuperheating water output (t h\({}^{-1}\)) & 0 & 0 & 0 & 0 \\ Desuperheating water temperature (\({}^{\circ}\)C) & 193 & 176 & 160 & 140 \\ Excess air coefficient of furnace exit & 1.25 & 1.25 & 1.25 & 1.35 \\ Exhaust gas temperature (\({}^{\circ}\)C) & 114 & 108 & 108 & 106 \\ Thermal efficiency (\%) & 93.88 & 94.13 & 92.61 & 92.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main design parameters of the boiler. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Ultimate Analysis, wt.\%**} & \multicolumn{4}{c}{**Proximate Analysis, wt.\%**} & **LHV** \\ \cline{2-10}
**Fuel** & **C\({}_{\text{ar}}\)** & **H\({}_{\text{ar}}\)** & **O\({}_{\text{ar}}\)** & **N\({}_{\text{ar}}\)** & **S\({}_{\text{ar}}\)** & **\(A_{\text{ar}}\)** & **\(M_{\text{ar}}\)** & **FC\({}_{\text{ar}}\)** & **\(V_{\text{ar}}\)** & \\ \hline Coal & 47.49 & 3.25 & 4.97 & 0.80 & 0.98 & 36.21 & 6.30 & 36.95 & 20.54 the other two types of biomass syngases, the increment of available heat can reach 10.8% after introducing wood syngas with \(5\times 10^{4}\) m\({}^{3}\) h\({}^{-1}\). It can be noted from Figure 3b that the theoretical combustion temperature increases with ascending heating values, while the trend reverses with increasing consumption rates. The result is similar to that in the study of [PERSON] et al. [2]. The reason for the variations in volume and specific heat might be different compositions and quantities of combustion products. The variation in the straw syngas consumption rate has the most pronounced influence on the theoretical combustion temperature, the highest decrement of which is 3.8%. Figure 3: Furnace thermodynamic parameters for various biomass syngas consumption rates (BMCR). (**a**) Available heat of fuel; (**b**) theoretical combustion temperature; (**c**) water vapor volume fraction in flue gas; (**d**) radiant attenuation factor of flue gas; (**e**) heat absorption of flue gas; (**f**) furnace exit flue-gas temperature. It is believed that the radiant attenuation factor of flue gas (\(k\), m\({}^{-1}\) MPa\({}^{-1}\)) can be applied to represent the radiative characteristics of flame [28]. The water vapor volume fraction rises with increasing biomass syngas consumption rates after the introductions of straw and wood syngases, while that decreases after the introduction of palm syngas (see Figure 3c). The radiant attenuation factor is related to that of triatomic gases (\(k_{\mathrm{q}}\)), soot (\(k_{\mathrm{C,q}}\)), fly ash (\(k_{\mathrm{h}}\mu_{\mathrm{h}}\)), and char (\(k_{\mathrm{K}}\mu_{\mathrm{K}}\)) according to Equation (14).