P. Sessiecq

Solid Particles Concentration Profiles in an Agitated Vessel

Local solid concentration profiles were investigated in a contoured bottom cylindrical reactor, mechanically stirred by a 45° pitched blade turbine and equipped with four baffles. The solid-liquid system consisted of a suspension of spherical glass beads or alumina grains in water. The effects of the stirring rate and of the size and density of the solid particles were examined. To interpret the solid distribution profiles in the vessel, a one-dimensional sedimentation dispersion model was employed. The description was based on the continuity equation and made use of the experimental knowledge of the flow velocity distribution of the liquid phase and of the calculated terminal velocity in a still medium of the solid particles.

Development of the regionalised municipal solid waste incineration (RMWI) model and its application to France

PurposeIncineration is mainly studied when municipal solid waste (MSW) treatment options are assessed in life cycle assessment case studies. A variety of incineration models have been used to create life cycle inventories (LCIs), but they often do not represent the technology and input waste composition of a given incineration situation. This article describes development of the regionalised municipal solid waste incineration (RMWI) model designed at the city-to-country level and its application to French MSW incineration.MethodsRMWI is based on previously published incineration models from the ecoinvent database and Koehler et al. (Environ Sci Technol 45:3487–3495, 2011). Its system boundaries include furnace, gas-treatment steps, transport and management of by-products (e.g. clinkers, residues from cleaning flue gas, scrap). Its first strong point is the ability to adapt input waste composition. Its second strong point is that MSW collection and energy, scrap and clinker recovery options are modelled as stocks. Thus, users may adapt RMWI for the types of waste input and regional outlets for energy and matter recovery. French data were used in the model for MSW input composition, emission limits of some exhaust gases and transport distances of by-products. The method used to the collect these data is described so it can be reproduced for another region.Results and discussionThe RMWI model is designed in GaBi 6. Environmental impacts predicted by RMWI for France are assessed to identify hot spots and input parameters with high influence. Chemical production for gas treatments was identified as a major contributor to abiotic depletion, whilst NH3 and NOx emissions were mainly responsible for acidification and eutrophication. In a second approach, the consideration of the recovery of by-products as heat, electricity, clinker, iron and aluminium scraps aims at understanding their contributions to environmental impacts. Sensitivity analyses were performed to determine to what extent RMWI predictions are sensitive to French incineration conditions. Comparison to generic LCI approaches highlighted merits of a regionalised model, especially concerning the type of gas treatment. The RMWI model effectively links input waste composition and environmental impacts.ConclusionsRMW-predicted impacts, representation of stocks, sensitivity analyses and comparison to generic approaches were assessed to examine the model’s relevance, robustness and limits. The model is now available for French incineration but also can be used to assess environmental impacts of an incineration plant or another regional (city-to-country) incineration situation by adapting and calibrating it.