A techno-economic assessment of the reutilisation of municipal solid waste incineration ash for CO₂ capture from incineration flue gases by calcium looping

Abstract

Waste-to-Energy (WtE) through municipal solid waste (MSW) incineration is a key waste management strategy to reduce the mass and volume of landfilled wastes, especially for land-constrained areas such as urban centres. However, this process releases large amounts of CO2 into the atmosphere and the ash that remains after burning, which contains a variety of metals and minerals, is often sent to the landfill after some metal recovery. In this study, the CaO containing ash is used to derive sorbents for the calcium looping (CaL) process for post-combustion CO2 capture and storage (CCS), and a techno-economic assessment was performed to preliminarily probe the feasibility of retrofitting a CaL plant using ash-derived sorbents to capture CO2 from a 200MWth WtE plant, as a possible means to decarbonise WtE plants. The analysis was performed through process modelling of the CaL plant using 4 different supplementary fuels in the calciner, namely, biomass charcoal (BC), solid recovered fuel (SRF), coal, and natural gas (NG). At the base purge ratio of 5%, all the cases show increases in the levelised cost of electricity (LCOE) over the base WtE, ranging from 184 (NG) to 246 (BC) USD/MWhe. The sale of additional electricity generated from the heat recovery steam cycle could slightly mitigates the capital intensiveness of the process, resulting in a levelised cost of carbon abatement (LCCA) range of USD 89 (SRF) to 184 (coal)/tCO2, which is competitive with other bioenergy with CO2 capture and storage (BECCS) technologies. The biogenic fuels also result in lower specific primary energy consumption per CO2 avoided (SPECCA) of 5.6 (BC) and 6.8 (SRF) MJLHV/tCO2, which are comparable to values from other CCS technologies and CaL implementation studies. Sensitivity analysis of 14 economic and process parameters reveals that further improvements can be achieved through optimisation of the energy intensive sub-processes, such as cryogenic air separation and CO2 compression and purification. Tighter solid heat integration (SHI) concepts were also modelled and are shown to effectively reduce fuel and O2 requirements by up to 22.2%, thereby lowering annualised costs by up to 11.9%. In addition, this paper highlights the importance of regulatory support through favourable policies such as higher carbon pricing and CO2 credit trading to push the development and adoption of negative emission technologies to meet global decarbonisation targets.