## 4 Waste Conversion for Fuel Gas Production
### Pyrolysis and Gasification of Coal-Water Slurries with Industrial Waste Additives
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fuel** & **Process** & \begin{tabular}{c} **Characteristics of the** \\ **Plant** \\ \end{tabular} & **Temperature** & **Key Result** & **Ref.** \\ \hline \hline \multirow{7}{*}{\
\begin{tabular}{c} Corn starch, clover \\ grass, and corn slage \\ in supercritical water \\ \end{tabular} } & Gasification & & & Gasification of biomass in supercritical water is & \\  & & & highly temperature-dependent. Almost & \\  & & & complete conversion of the feed can be achieved & \\  & & & at 700 \({}^{\circ}\)C. As the temperature rises, the H\({}_{2}\) yield & \\  & & & increases, but the CO concentration decreases. & \\  & & & & Syngas composition: & \\  & & & H\({}_{2}\): 29.7-34.4 vol\%; CO: 0.62–2.8 vol\%; CO\({}_{2}\): & \\  & & & & 39.7–43.9 vol\%; CH\({}_{4}\): 15–20.5 vol\%; C\({}_{2}\)H\({}_{2}\): & \\  & & & 2.6–48 vol\%. & & \\ \hline \hline \multirow{7}{*}{
\begin{tabular}{c} Water–semicoke \\ slurry \\ 10–30 wt%. \\ \end{tabular} } & Gasification & & & & \\  & & & fluidized bed & & The temperature of 600 \({}^{\circ}\)C is the most preferred \\  & & & reactor system. & & to provide full gasification of the fixed carbon is \\  & & & Pressure 23 MPa. & & realized. The use of K\({}_{2}\)CO\({}_{3}\) as a catalyst made it \\  & & & & & possible to increase the hydrogen yield by 92\%. \\ \cline{1-1}  & & & & Syngas composition: & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._and synthesize ammonia. [PERSON] et al. [38] found that the use of CWWS instead of CWS did not lead to disruptions in the operating modes of the gasifier. The total gas yield was 515,116.8 m\({}^{3}\)/day. This made it possible to conclude that the gasification proceeded stably regardless of the fuel type (CWS or CWWS). The comparison of the syngas composition showed that the average share of the effective gas component (CO + H\({}_{2}\)) during CWWS gasification was higher and amounted to 78.3%, while, for CWS, this parameter was 77.2%. In addition, [PERSON] et al. [38] calculated that the carbon conversion rate and cold gas efficiency during gasification of CMWS are 0.45% and 1.57% higher than that of CWS, respectively. This result [38] is because CWWS contains more organic matter, the decomposition of which produces gas of better quality. Alkali and alkaline earth metals, as well as organic alkalis in wastewater, influenced the char structure in the direction of increasing the reactivity and decreasing the activation energy during coal gasification [38]. [PERSON] et al. [39] studied the synergistic effects arising from the co-pyrolysis of coal and waste mineral oil (MWO). Sub-bituminous coal with high volatile content and MWO obtained from a local company were used in the experiments. The components were mixed in a 50/50 ratio. The pyrolysis of the mixture was carried out in a laboratory fluidized bed reactor with the fuel feed rate of 550 g/h. The gas was analyzed using gas chromatography, the liquids were analyzed by GC/MS. [PERSON] et al. [39] defined that the pyrolysis of the mixture increased the yield of gas (2.2 times) and liquid (1.7 times) pyrolysis products, while the amount of char decreased (1.7 times) in comparison with coal. At the same time, the quality of the products of coal and oil co-pyrolysis increased. [PERSON] et al. [39] recorded a significant increase in the concentrations of methane, ethylene, and propylene. For MWO/coal slurry, the concentrations of CH\({}_{4}\), C\({}_{2}\)H\({}_{6}\), and C\({}_{2}\)H\({}_{4}\) were 4.9 wt%, 3 wt% and 6.4 wt%, respectively. For coal, the concentrations of these gases were 1.2 wt%, 0.3 wt% and 0.2 wt%. The obtained result was explained by gas-phase reactions between volatile substances of coal and vapors of MWO. In addition, [PERSON] et al. [39] estimated the distribution of heavy metals in liquid and solid pyrolysis products and found that the concentrations of Pb and Ni in the pyrolysis liquid were lower than in the original waste oil.