**3.5 Gasification**

Gasification is the process through which combustible gas is produced through partially oxidising waste at high temperatures of 800–900°C [24]. Gasification could be considered in-between pyrolysis and combustion because oxygen added neither

**Figure 10.** *Illustration of the pyrolysis process [38].*

*Evaluating Waste-to-Energy Technologies as a Waste Management Solution for Uganda DOI: http://dx.doi.org/10.5772/intechopen.101904*

**Figure 11.** *Huayin plastic to diesel oil plant, Bulgaria [42].*

allows full oxidation nor allow full combustion. The gasification process mainly produces its heat however part of the heat is needed to start and continue the process [6]. The gas produced is known as syngas which can be burned to generate heat or in gas engines and gas turbines as a fuel to produce electricity [24]. **Figure 12** illustrates the process of MSW gasification to generate power [43].

The gas generated from gasification is reported to have Net CV varying between 4 and 10 MJ/Nm3 . Another product is a solid residue of ash which is non-combustible and has relatively low levels of carbon [6]. The produced gas can be utilised to generate power using IC engines [19].

The gasification process has advantages of reasonable costs, and flexibility of integrating the working conditions of temperature and equality ratio, and the reactor

**Figure 12.** *Schematic of MSW gasification to produce power [43].*

**Figure 13.** *Waste gasification plant in Lebanon, Tennessee [44].*

arrangement to obtain syngas [24]. The process is reported to improve the heating value of gas produced and has lesser quantities of residues compared to incineration and pyrolysis [19].

A report [24] indicates it is associated with the complexity to adapt to various characteristics of different waste and these usually prevent it from commercial applications. The issue is that the source of fuel for gasification will change over time due to variations in waste. Also, MSW in its raw form is usually not suitable for gasification and normally would need pre-treatment through mechanical preparation and separation to remove inert materials as well as glass, and metals [6]. The process suffers disposition of tars that causes blockages leading to operational challenges. This problem has been linked to plants failing and inefficiencies in some pilot and commercial-scale plants. However, it has been observed that when higher temperatures are applied, the tars 'cracks' and generate a relatively clean syngas. The plasma gasification technology is a high-temperature process that is potentially used at different stages in different configurations in the gasification process and the ash generated can be transformed into an inert residue under extremely high-temperature thermal methods. Also, other initiatives are set to ensure that the efficiencies of energy recovery from Gasifiers are maximised by using hydrogen fuel cells and gas engines [6]. **Figure 13** shows a waste gasification plant in Lebanon which has a capacity of 64 tonnes/day to generate 420 kW. The waste (wood and tires) is collected and shredded into 1–3 inches and the sludge is blended on the site as well. The target moisture for post-treated waste is 30% for this specific site [45].
