Agricultural waste + heat + inert → Bio-oil + Biochar + pyrolytic gas (2)

Another vital thermochemical process is the gasification of the agro-waste that works on the principle of a partial oxidative atmosphere at some specific high temperature between 800–1000 ◦C. It employs a similar feedstock (e.g., agricultural waste) to that which is used in pyrolysis but produces an important end-product, i.e., syngas, made up of 85% of carbon monoxide (CO)and hydrogen gas (H2), with some proportion of tar (5%) and biochar (10%) [38,39]. The gases produced can also be used in a turbine or engines as fuel as they contain a high calorific value. Studies have shown that, for the gasification to work, it depends on two different modes of processing, i.e., fixed-or fluidized-bed processing. Gases with a lower calorific value of 4–6 MJ/NM<sup>3</sup> are seen in the fixed-bed processes. In contrast, fluidized-bed gasification is mostly seen in the provision of uniform temperature distribution, usually in the gasification zone [40]. For combustion, a standardized oxidativehigh temperature process is used for the feedstock. As such, it is said to be a heat-based degradation process involving the conversion of chemical energy of biomass to yield heat and power in addition to carbon dioxide and water [41]. The generated energy from combustion can be used in turbines and boilers, among other processes, albeit the moisture content of the waste to be combusted should be below 50%.
