Time-integrated GHG emissions in advanced waste-to-energy plants producing fuels, chemicals and electricity from MSW refuse

Resumo

The evaluation of the climate benefit in the production of fuels from conventional biomass has recently evolved by incorporating a dynamic approach, a comparison with the reference system and other recommendations from the IPCC. Important drawbacks have been identified in the comparison of conventional (static) and dynamic (time-integrated) assessments for the production of biofuels. This thesis contributes to a better understanding of the real climate benefit in the production of products and services using a specific and plentiful waste in Europe, i.e., MSW refuse (the unsorted stream of MSW usually disposed of). Lately, some dynamic assessments have been made for the production of fuels and electricity using forest and agricultural residues. In this thesis, the existing work is expanded by considering a residue (MSW refuse) which is already in-use within the different regional waste management schemes in Europe (incineration and landfilling) and the production of a material that stores biogenic carbon, i.e., renewable-derived plastic materials. The climate benefit of the proposed advanced waste-to-energy (WtE) plant is evaluated by defining two systems (the one proposed in the thesis and the reference system) using system expansion and substitution. The dynamic modeling of the waste management scheme in Europe (current and future) as well as the temporary storage of the biogenic carbon fraction in the renewable-derived plastics (intimately related to the management scheme) are the main contributions to the field. The proposed methodology is based on two climate benefit indicators: the climate mitigation index (CMI) and the differential climate impact (DCI). The indicators analyze the impact of the replacement of the current waste management system for one based on advanced WtE plants. In Paper I, a preliminary work applying the static methodology (GHG balance) is carried out for the analysis of the results in advanced WtE plants producing biofuels, drop-in chemicals and electricity and with the possibility of carbon capture and storage in bioenergy (Bio-CCS). In Paper II, the dynamic GHG emission assessment is applied to the advanced WtE plant analyzed in Paper I. In Paper III and IV, two countries are selected for the comparison of the systems: Spain, where landfilling is dominant; and Sweden, where incineration is dominant. Moreover, two different scenarios are taken into account: Scenario 1, in which the reference system remains unaltered, and Scenario 2, in which there is an evolution towards landfill banning and decarbonization of the energy mix. The results reveal that the landfilling replacement in dominant-landfill European countries has a positive climate impact in the short term, although the long-term impact depends on the evolution of the reference system (waste management and electric mix). Renewable-derived plastics are proposed (Paper IV) as an alternative greenhouse gas removal (GGR) technology and compared with Bio-CCS as the common GGR technology in most Integrated Assessment Models (IAMs). The production of plastics compares favorably in terms of climate benefit in the short and medium term and would even provide a larger climate benefit in incineration-dominant regions in the long term. In Paper V and VI, the static and dynamic assessment for the production of electricity is analyzed.