**4. Conclusion**

The organic content and minerals of the biomass feedstock have different level of persistency in leaving the matrix of the composite pellets at different temperatures. Organic content of biomass has fairly lower resistance against high temperature gasification and is fully consumed in the combustion region of the reactor where highest temperature takes place. At higher temperature, the mineral content of the biomass transforms into ash and prepares the ash sintering process at which liquid and viscous slag is generated. The formation of slag is due to the interactive reaction between the melted ash and the mineral matter content of the ash matrix. This process continues until the generated molten ash accumulates and makes the chunk of clinkers which deposits in the bottom part of the reactor. It is also reported that liquid slag flows under the force of gravity and out of the bottom of the gasifier into a water quenching system which is not the case for the

The inductively coupled plasma (ICP) mass spectrometry analysis of individual and composite paper and plastic waste indicates presence of six major elements in the matrix of the composite pellet including sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), calcium (Ca) and silicon (Si). The majority of the contaminants (i.e. Na, Mg, Al, K and Ca) originates from paper fiber existed in the municipal waste stream, and silicon is derived from plastic wastes. It is reported that these elements could be detected in typical paper waste such as brown toilet paper, cardboard, industrial paper towel, magazine paper and printer papers. The use of these elements is for the purpose of grading and sizing of the papers [25, 27]. Characteristics of the clinker are also a function of degradation mechanism depending on the composition of volatiles and consequently the gaseous phased products are affected. The thermal degradation of polymers and plastics typically begins with random scission followed

**Figure 7.** Clinkering during gasification of composite pellet of fiber and plastic (unit: cm) [25].

current system [25].

90 Gasification for Low-grade Feedstock

In this chapter, the potential of bioenergy production from each of which was investigated. The failure scenario of "bridging" was observed in this stage. Next, multiple feedstocks were examined for seeking the possible improvement in the quantity and quality of the produced gas. This chapter also aimed to find how the increase in plastic specifically in the recycled fiber stream would affect the performance of a downdraft gasifier. The failure scenario of "clinkering" was observed in this stage which could be considered as an individual project to work on. The chapter also showed that a mixture of silicon with aluminum, calcium and sodium under high temperatures would result in the generation of a solid clinker that ultimately moves through the reactor and is deposited at the bottom of the reactor. It may be concluded that due to the presence of plastic, the generated ash is superheated and melts into glass-like materials causing formation of metallic chunk. The chunk is cooled down through partially endothermic nature of the gasification and results in generation of clinker. This chapter presented informative tools for improving advanced biofuel production through gasification technology and using different types of biomass feedstock which can be continued in further researches.

This study also focused on the development of gasification technology to enhance the efficiency of biomass conversion within the process. In a nutshell, the following recommendations are offered for future research:

