Valorisation des déchets en matière plastique

vignette|Déchets banals industriels triés : sacs plastiques en attente d'être transportés pour retraitement. La valorisation des déchets en matière plastique est l’ensemble des opérations dont le but consiste à donner à ces déchets une nouvelle valeur d’usage. Valorisation énergétique La valorisation énergétique consiste à transformer un déchet en énergie thermique et ceci grâce à son potentiel calorifique. Cette énergie est utilisée pour la production de chaleur et/ou d'électricité. La valorisation énergétique s'applique à tous les types de plastiques et surtout à ceux qui n'ont pas été triés ou qui ont été contaminés par d’autres déchets ou qui sont composés d'un mélange de polymères. L’incinération des ordures ménagères est parfois aidée par la présence des déchets plastiques, sans lesquels il faudrait injecter dans l’incinérateur du fioul pour permettre une bonne combustion. L'injection de résidus de matière plastique a été testée à l'échelle industrielle sur des h

Network design optimization of waste management systems: the case of plastics

François Maréchal

Failure in appropriately managing complex municipal solid waste systems in general and waste plastics in particular negatively affects public health and environment. A decision-making tool incorporating concepts of logistics and supply chain, considering different types of waste was developed. A multi-objective, multi-period mixed-integer linear programming (MILP) formulation, focusing on the plastic recycling network, incorporating features of multimodal transportation was implemented. The model aims at minimizing net present cost (NPC) and environmental impacts, illustrated by a case study of a Swiss waste treatment cluster. A reference situation was used for benchmarking and 7 new scenarios considered - corresponding to different plastics collection configurations. From the solutions space, designs arise that lead to a 2-fold decrease of NPC at the expense of increasing by 20 % current emissions, as well as solutions that provide small net gains in environmental aspects - close to 3 %, albeit a 4-fold increase in NPC due to large investments in recycling facilities and increased transportation costs. This work sheds light on the impact of supply chain and logistics aspects on the separate collection and treatment of waste plastics, in the context of a real municipal waste treatment policy, where a thermodynamic model to deal with the conversion processes is integrated into the general supply chain decision. As a result, important insights to guide decision-makers were obtained.

Elsevier2021

Flexibilisation of Biogas-Based Power-to-Gas Processes: A Techno-Economic and Experimental Assessment

Andreas Gantenbein

Biogas-based power-to-X technology allows storing renewable electricity, while producing CO2-neutral products.This work investigates the conversion and upgrading of digestion-derived gas mixtures with focus on increasing the operational flexibility of the overall process. Compensation of fluctuations in the feed gases enable a better economic predictability of the processes and increase the product gas output.A techno-economic evaluation was performed on bubbling fluidised bed (BFB) methanation and biological methanation for CO2 conversion in all-year operation. Each considered process was modelled and optimised to obtain grid-ready biomethane. Rate-based models were used for the main units (BFB reactor, H2-separation membrane). For the biological methanation, simulated performance data from literature were included. The analysis revealed a 17 - 19% lower production cost for BFB methanation, mainly due to lower investment cost for the main reactor vessel. Instead of using PEM electrolysis, high temperature electrolysis (SOE) would allow for heat integration with the BFB reactor, which increases the plant efficiency from 54% to 73% (LHV). A further production cost reduction can be achieved by direct methanation of biogas, omitting prior separation of CO2.Based on gas separation experiments with a commercial biogas upgrading module (Evonik Sepuran) performed in a TRL 5 plant, a flexible upgrading concept using a permeation model was developed. It allows to swiftly switch between conventional membrane-based CO2 separation by a 2-stage membrane unit and direct methanation of biogas and subsequent H2 recycling.A techno-economic analysis was performed on the flexible upgrading concept. The operation hours of the electrolyser were determined by applying a threshold to the electricity price distribution of the past years. The sensitivity on electricity cost (i.e. PtG operation hours) is clearly reduced with the flexible processes, resulting in a better economic predictability of the overall process, compared to a pure PtG installation. System analysis shows the need to allow part load operation of the methanation.Symmetric part load operation (reduced availability of CO2 and H2) was tested in a field experiment by direct methanation of biogas with subsequent H2 recycling in the TRL 5 methanation pilot plant. Stable operation of the methanation plant could be achieved at part load levels from 45% to 100% with closed recycle loop. The BFB reactor alone was tested in a load range of 20 to 100%. A dynamic experiment demonstrated fast, successive load changes while still producing grid-ready biomethane.Asymmetric part load (only H2 limiting) operation was investigated by process simulations and field experiments. Since CO2 is present in the system in an over-stoichiometric amount, H2 recycle and CO2 separation have to be performed simultaneously. Process simulations showed that selecting a most ideal PtG configuration based on technical feasibility is difficult, as further constraints, such as overall economics and operation scheduling have to be considered in process design and evaluation. In all cases, the CO2 separation from the integrated processes leads to a loss of H2 and CH4 from the process. The introduction of an additional membrane stage with a sweep stream is proposed to reduce the loss of reactive gases via the off gas stream.

EPFL2022

Flexibilisation of Biogas-Based Power-to-Gas Processes: A Techno-Economic and Experimental Assessment

Andreas Gantenbein

EPFL2022