Environmental and exergetic life cycle assessment of incineration- and gasification-based waste to energy systems in China

Abstract

The clean and efficient energy production from municipal solid waste (MSW) is highly desirable due to increasing energy demand and environmental concerns. In this study, four incineration-(S1) and gasification-based (S2 with combustion boiler, S3 with gas turbine/combined cycle and S4 with internal combustion engine) MSW treatments were compared using methods of environmental life cycle assessment (LCA) and exergetic life cycle assessment (ELCA). LCA was applied to measure the environmental performances and ELCA was supplemented to reflect the thermodynamics efficiencies. Afterwards, cumulative degree of perfection (CDP) and abatement exergy (AbatCExC) efficiency of the considered systems were also calculated to determine the imperfection and environmental sustainability of the processes. Results showed that gasification-based systems were effective to mitigate the environmental impacts of acidification, nutrient enrichment, and photochemical ozone formation potential, but caused higher global warming impacts. The S3 system exhibited the best performance from both environmental and exergetic perspective, due to its high net efficiency of electricity generation and low exhaust emission into air. Results from ELCA indicated that the rest two gasification-based systems (S2 and S4) were inefficient as compared to MSW direct incineration, mainly due to auxiliary energy consumption for MSW pretreatment and more conversion steps. The CDP and AbatCExC of the systems in descending order was expressed as S3 system > S1 system > S2 system > S4 system.

Life Cycle Assessment of Advanced Circulating Fluidized Bed Municipal Solid Waste Incineration System from an Environmental and Exergetic Perspective

“…As the CDP indicates the thermodynamics perfection and the degree of the renewability of a system or a process, as well as quantifying the energy utilization efficiency at a life cycle level [ 21 ], the advanced CFB system (S1) showed a higher thermodynamics perfection and degree of renewability. S2 showed the lowest thermodynamics perfection and degree of renewability because of the large amounts of coal and diesel that were used.…”

“…ELCA was proposed and developed by combining the concept of exergy analysis and environmental LCA. Consequently, the general framework of ELCA was recognized as identical compared to LCA [ 21 ]. The life cycle-based exergy analysis quantified the cumulative exergy consumption of a system from cradle to grave.…”

“…The LCA is able to identify and quantify energy, material and waste emissions; however, as it is based on the first law of thermodynamics, it encounters many difficulties in application, especially when comparing different energy forms because it considers only quantity but not quality [ 21 , 22 ]. Exergy not only reflects both the quantity and quality of energy carriers by the first and second law of thermodynamics, but represents the value of natural resources too, by means of the unified evaluation standard.…”

“…The studies on cumulative exergy consumption indicators applied to the Ecoinvent database were conducted with the aim of convenient calculations [ 26 ]. Based on the concept of CExC, ELCA was applied to assess “CO 2 zero-emission” energy systems [ 22 ], different sludge treatment techniques [ 27 ], and MSW gasification-based thermal treatments [ 21 ]. However, the advanced CFB incineration system equipped with MBT and EHE has not been assessed yet.…”

“…Therefore, the ELCA should also be conducted. Recent studies recognized ELCA as a part of LCA representing the impact category of resources depletion and took environmental burdens into account via the abatement exergy of released pollutants [ 19 , 21 ], while the land resources were not considered.…”