Biomass pre-treatment for bioenergy – Case study 3: Pretreatment of municipal solid waste (MSW) for gasification
Gasification is a flexible technology for converting solid fuels into heat, power, chemicals or fuels. When applied to biomass-based materials, carbon-neutral energy production is possible. Biomass gasification is a well-established technology, but typical biomass feedstock materials tend to be relatively expensive and the process is generally not cost-competitive. Waste materials such as municipal solid waste (MSW) include high fractions of non-recyclable but combustible biomass/ organic components such as paper, cardboard, wood and textiles that make MSW an interesting opportunity fuel for gasification systems. In addition, a gate or tipping fee is usually paid to the receiving facility by the waste disposer and that fee can favourably alter the economics of an energy production plant.
By its nature, MSW is very heterogeneous both physically and chemically, which creates operational challenges for energy conversion systems. In addition, the physical nature of waste complicates mechanical feeding into such systems. In order for MSW to be used in systems such as gasifiers, it should be pre-treated to remove non-combustible materials, homogenized to minimize operational variations, and ideally transformed to a physical nature compatible with mechanical feeding systems.
This report, prepared through collaboration between IEA Bioenergy Task 33 (Gasification of Biomass and Waste) and Task 36 (Integrating Energy Recovery into Solid Waste Management Systems), examines technical and economic aspects of MSW pretreatment, focusing on two established technologies, mechanical pretreatment and mechanical-biological pretreatment. Case studies in Germany and Italy, considered representative of many countries within IEA Bioenergy, are presented.
The evaluation highlights that mechanical and mechanical-biological pretreatment of MSW can allow waste to meet the physical and chemical specifications required of gasification facilities. The pretreatment processes are relatively straightforward and involve several stages of sorting, separating, size reduction, and in some cases, biological treatment. Capital costs for the pretreatment systems are moderate and generally worth the benefit of making a low-cost, readily available feedstock stream available. Overall economic analysis is favourable, but viability depends strongly on the gate/tipping fees associated with collecting the municipal waste.