Plasma gasification thesis

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On comparing the local priority vectors obtained from software and the manual method, similar results were obtained. Therefore, the local priority vectors resulting from both manual calculations and expert choice software application can be given as: 0. Therefore, by using equation 2 , the consistency index CI is calculated as:. The RI value of 1. The manually calculated CR is compared with the CR obtained from the expert choice Table 5 , both show the same value. As the value of CR 0. If the CR was more than 0.


The next evaluation involves the comparison to derive the effects of sub-factor on the prime factor. In Table 7 , the sub-factor of operational and maintenance cost and capital cost are compared with respect to main criterion economic. The judgements in Table 7 , indicated that the influence of the operational and maintenance cost is perceived higher than the capital cost in selecting a treatment technology.

Therefore, judgement 4 is entered in the second row of first column and its reciprocal is added in the transpose position. Consequently, the operational and maintenance cost is ranked highest as shown in the priority vector column.


However, the sub-criteria under the main criteria of environment are perceived to be equally important for decision making, as illustrated in Table 7. Meanwhile, the comparison matrix depicts the higher influence of energy production in decision making than the energy consumption of the technology. The judgements in the comparison matrices are consistent, as the CR of all three matrices is zero. Table 7. Pairwise comparison of sub-criteria with respect to relative criteria. The final stage involves the assessment of the comparison between WTE technology options based on the individual sub-criteria and criteria.

The judgements given by the experts on pairwise comparisons between WTE option with respect to each criterion and sub-criterion formed eight matrices that were assessed method used in Table 6 matrix to obtain priority vectors; these priorities of WTE option with respect to criteria and sub-criteria are presented in Table 8. Figure 2 presents the ranking of WTE technology options based on the influence of all sub-criteria and criteria.

Anaerobic digestion is perceived to produce lower amounts of GHG emission, hazardous residue, operation and maintenance cost, and is preferred more socially. Furthermore, considering the influence of capital cost, anaerobic digestion is perceived to be the second most suitable option. Similarly, socially fermentation is widely accepted; it generates less hazardous residue, GHG emissions, operation and maintenance cost, and capital cost.

In Table 8 , summary of weights of WTE technology options for each factor are shown. The interpretation of priorities in Table 8 are as follows: To set up a treatment technology that perfectly matches the waste composition and characteristics of Oman, with lowest capital cost and energy consumption; incineration will be preferred. Plasma arc gasification is perceived to produce a high amount of energy, lower GHG emissions and hazardous residue. Whereas, it is the least suitable option while considering economic criterion owing to its very high cost.

Gasification appears to consume less and produce more energy, and to be accepted socially. Meanwhile gasification becomes less favourable owing to its environmental impacts and higher capital cost.

However, respondents believe incineration contributes most in terms of air emissions. This perception is contrary to the fact of how the popularity of incineration is growing in Europe for instance. Palvas et al. Thus, a change in the approach of managing solid waste is required as the research and recent advances reveal a lot of benefits, particularly of incineration Abba et al. Table 8. Summary of priorities for weights of factors on WTE options.

Figure 2. Ranking of WTE options based on each sub-criteria and criteria. The local priorities of all sub-criteria, criteria and alternatives are obtained from the pairwise comparisons Table 5 , 7 and 8. Then throughout the hierarchy, weights are aggregated to determine the composite priorities.

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Consequently, the composite or final priorities of alternatives are determined by synthesising all the matrices. Synthesis is the process in which the local priority vector of alternatives is multiplied by the local priority vector of each criterion and aggregated to get the final priority vector global weight for each alternative Daniel et al. However, when a criterion consists of sub-criteria, first the rating of each alternative is multiplied with the weights of the sub-criteria, which are then aggregated to obtain local priority vector of alternatives with respect to each criterion.

Afterwards, the obtained local priority vector of alternatives is multiplied by the local priority vector of each criterion and then aggregated to get the global weight for each alternative Babalola, ; Daniel et al. Accordingly, the local priority vectors of alternatives are determined for all other criteria that contains sub-criteria.

Afterwards, these local priorities vectors of alternatives are multiplied with the weights of each criterion to determine the overall priorities of alternatives, which is given below in equation 5 :. Figure 3. Overall priority of all alternatives obtained from expert choice software. Table 9 demonstrates results in the ideal form, and this is obtained by dividing each priority by the largest value among all, which is 0. This method makes the largest value ideal and for others to obtain their proportionate values.

Table 9.

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Final results in form of normalised and idealised priorities. Based on the analysis this study presented, the most suitable WTE technology for a waste management system in Oman appears to be anaerobic digestion followed by fermentation and incineration. Results also show that environmental and economic criteria are found to be the most important factors informing the selection of WTE technology in Oman.

These results are consistent with those obtained by Abba et al. Anaerobic digestion not only proved to be the most suitable in the overall goal, but also in the criteria of environmental, economic and social acceptance. The results show that anaerobic digestion and fermentation are perceived to be the cheapest WTE option and create the least negative environmental impacts for treating solid waste. As anaerobic digestion and fermentation secured the top priority in the top ranked criteria environmental and economic for Oman, they have been ranked above all the alternative options in overall ranking.

However, in technical and WQQ criteria, anaerobic digestion and fermentation are not ranked first because their energy production potential is lower than thermal technologies and they can only process food, park and bio wastes. This perspective makes not only anaerobic digestion an attractive option but also incineration technology, despite the economic and environmental concerns.

Meanwhile, the current waste managing practices of landfilling and dumping waste in Oman without energy recovery possess the highest environmental impacts in contrast to any WTE technology; which includes GHG emission, and groundwater and soil contamination. Therefore, in terms of environmental impact, setting up either anaerobic digestion or incineration in Oman would dramatically decrease these environmental issues; though biochemical technologies would perform much better than incineration.

Moreover, the capital and operational cost of incineration, pretreatment of feedstock and flue gas cleaning system impose higher expenses in contrast to anaerobic digestion. The reason behind proposing these two scenarios is that replacing landfilling or incineration of organic waste food, park and bio waste with anaerobic digestion is a way of increasing sustainability; incineration can also treat food, park and bio waste, but these types of waste are more suitable to be treated by anaerobic digestion than incineration Davidsson et al.

These parameters ensure economic feasibility and auxiliary fuel to make the incineration process self-sustaining World Energy Council, However, Oman should make greater efforts to reduce toxicity-related emissions from incineration processes to comply with environmental concerns. Moreover, dry fermentation has several benefits over wet fermentation in terms of cost, groundwater contamination, energy consumption, pre-treatment or sorting and limitation to input material Al Harrasi H, Personal Communication, 7 December ; Viessman Group, However, efficient operation of biochemical technologies anaerobic digestion and fermentation requires effective source separation, which is not implemented in Oman Lou et al.

Therefore, Oman should also focus on implementing a door-to-door collection system as it gives best quality characteristics in terms of inert material content and meets the quality requested for the anaerobic digestion process Cecchi and Cavinato, ; Palanivel, Furthermore, mild mechanical separation of organic fraction of MSW is also recommended, even if a high quality of biodegradable matter is obtained from the door-to-door collection system Cecchi and Cavinato, The AHP model is a flexible and robust framework that can fit a variety of criteria or more levels of sub-criteria and options.

The AHP method was adopted in two ways in this study, that is the manual method and expert choice software, and the results from both were compared consistent, which proves the accuracy of final results. As it can be seen in this research, the AHP model proved to be a guiding framework for decision making by involving a panel of experts for the selection of WTE technology options for sustainable MSW management in Oman. This research considered thermochemical and biochemical WTE technologies for review and evaluation.

However, with the assistance of waste management experts in Oman, the criteria and sub-criteria are determined. Further the preference for criteria and sub-criteria are obtained from the results of AHP analysis, which shows that the most important factors of decision making for waste management system in Oman are environmental and economic criteria with a local PVE of 0.

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Based on these criteria preferences for a MSW management system in Oman, the results obtained from AHP analysis show that anaerobic digestion is the best performing option followed by fermentation and incineration. In conclusion, Oman should set up an anaerobic digestion dry fermentation facility to process organic fraction of MSW food, park and bio waste as it is the best option in terms of environmental, economic and social aspect.


But first Oman needs to invest in a door-to-door collection system and mild mechanical separation to obtain high quality of biodegradable waste. Furthermore, considering the fact that Oman is struggling to handle the growing amounts of waste and requires effective waste reduction, feedstock limitations of anaerobic digestion would not thoroughly solve the problem; therefore, setting up an incineration technology along with anaerobic digestion would be a better choice. However, Oman should make great efforts to reduce toxicity-related emissions from the incineration process to comply with environmental concerns and prepare itself for bigger investment.

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  • Furthermore, investment in these waste management facilities will produce energy that can be used to run seawater desalination plants, which are also of prime importance for water management of Oman.

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