Methodology for Selecting an Ideal Thermal Gasification Technique for Municipal Solid Waste Using Multi-Criteria Decision Analysis

Abstract

Awareness of the consequences of waste mismanagement has resulted in urban planners looking for effective disposal techniques with the added benefit of energy generation. The decision regarding an energy conversion technique to adopt on a community level is based on different technology assessment factors with maximum weightage on environmental effects. Gasification techniques in general and thermal gasification strategies in particular are appropriate methods when environmental impacts are to be minimized. Thermal gasification techniques have evolved with different configurations, syngas generation rates, and other advantages and disadvantages; hence, the selection of the right technique is essential, and establishing guidelines for decision-makers is necessary. The six different gasifiers considered in the present study were updraft gasifiers, downdraft gasifiers, cross-draft gasifiers, bubbling fluidized bed gasifiers, circulating fluidized bed gasifiers, and dual-bed fluidized bed gasifiers. The assessments performed in the present study are based on the attributes of the different techniques using the multi-criteria decision method. Multi-criteria decision analysis is an appropriate method proven to be an ideal procedure in these situations. Attribute values for gasifier performance, environmental effects, economic performance indices, and fuel requirements were determined from collected waste assessment data and published information. Analysis was performed for both recycling and non-recycling scenarios of waste utilization by applying different weight scenarios for the attributes. Results of the study indicate that downdraft gasifiers showed the best performance in terms of environmental effects under the recycling scenario, with 0.1% and 0.0125% by volume of carbon dioxide and methane emissions, and under the non-recycling scenario, with 0.125% and 0.02% by volume of carbon dioxide and methane emissions. Downdraft gasifiers had high overall rankings in performance when evaluated against different entropy weights for both scenarios. The results of the study can be applied to urban communities in different climatic regions as well as for different scales of operation.

Keywords

• municipal solid waste
• gasification
• fixed-bed gasifier
• fluidized bed gasifier
• multi-criteria decision making