Etude cinétique de la formation et réduction du monoxyde d'azote lors de la combustion du charbon à haute température

Afin de permettre l’optimisation des brûleurs et chambres de combustion, il est nécessaire de déterminer les mécanismes réactionnels de la formation et réduction de NO dans les conditions du charbon pulvérisé (1000-1300 C). Pour ce faire, des expériences ont été effectuées dans un four à chute à différentes températures, concentrations de NO, CO, O2 et résidu carboné et temps de séjour. Les ordres apparents de réaction sont égaux à 0,9 par rapport à NO dans le cas de la réduction de NO et à 0,8 par rapport à O2 dans le cas de la formation de NO. Par ailleurs, une influence de CO sur la réduction de NO a été observée, ce qui confirme une libération de sites pour la réaction C/NO plutôt qu’une réaction catalytique CO/NO. La simulation de la combustion des particules à l'aide d'un modèle bidimensionnel établi à partir de FLUENT a permis la détermination des paramètres cinétiques pour la réduction de NO (59*exp[14400/T] m/s) et pour la formation de NO 100*exp[9600/T] m/s).The aim of this study is to determine the kinetics of the heterogeneous NO formation and reduction at pulverized coal combustion conditions (1000-1300 C) to allow the simulation and optimisation of the burner and combustion-chamber geometry for low NOx emissions. Experiments were performed in a drop tube furnace for various temperatures, NO, CO, O2 and char concentration and reaction times. The apparent reaction orders for NO reduction are 0.9 towards NO and 1 towards char. CO concentration showed a small effect on NO reduction. Hence this effect is not linear to CO concentration. In consequence it seems that CO interacts by freeing active sites for NO-C reaction rather than by surface catalysed reaction with NO. Kinetic parameters of NO-reduction (59*exp[14400/T] m/s) and NO-formation (100*exp[9600/T] m/s) were determined by simulation, using a complete 2-D simulation developed with FLUENT. Particle combustion using a reduced kinetic model was implemented with user defined functions.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Recovery of an Agro-industrial Vinasse by Adsorption on Different Wood Materials: Parametric Study at Laboratory Scale

Three types of biomasses (miscanthus, spruce, and a mixture of different woodchips species) were tested as low-cost adsorption media for an industrial agro-industrial effluent, typically a vinasse. Influences of effluent dilution, working temperature, and time duration were studied. Kinetic modelling studies of adsorption were proposed. Ratios of adsorption at ambient temperature and without dilution expressed in g of dry vinasse per g of dry biomass were 1.0, 0.85, and 0.65 for miscanthus, woodchips mixture, and spruce, respectively. An increase of the temperature from 10 °C to 50 °C led to a decrease of the vinasse viscosity and favored its penetration in the biomasses. Maximal adsorbance of dry matter of vinasse was obtained at 50 °C for a vinasse viscosity of 20 mPas. Whatever the experimental conditions required during adsorption processes, miscanthus showed the best affinity for the vinasse. Pseudo-second order and intra-particle diffusion model well described the adsorption process. This study indicates that conventional biomasses could be used as natural low-cost adsorbent for by-products such as vinasse

Parametric investigations on the formation and concentration of fine particles in a small scale biomass combustion unit

International audienc

Parametric investigations on the formation and concentration of fine particles in a small scale biomass combustion unit

International audienc

Fluorescence Microscopy Analysis of Particulate Matter from Biomass Burning: Polyaromatic Hydrocarbons as Main Contributors

International audienceNew efficient approaches to the characterization of fly ash and particulate matter (PM) have to be developed in order to better understand their impacts on environment and health. Polycyclic aromatic hydrocarbons (PAH) contained in PM from biomass burning have been identified as genotoxic and cytotoxic, and some tools already exist to quantify their contribution to PM. Optical fluorescence microscopy is proposed as a rapid and relatively economical method to allow the quantification of PAH in different particles emitted from biomass combustion. In this study samples were collected in the flue gas of biomass-combustion facilities with nominal output ranging from 40 kW to 17.3 MW. The fly ash samples were collected with various flue gas treatment devices (multicyclone, baghouse filter, electrostatic precipitator); PM samples were fractionated from the flue gas with a DEKATI® DGI impactor. A method using fluorescence observations (at 470 nm), white-light observations and image processing has been developed with the aim of quantifying fluorescence per sample. Organic components of PM and fly ash, such as PAH, humic-like substances (HULIS) and water-soluble organic carbon (WSOC) were also quantified. Fluorescence microscopy analysis method assessment was first realized with fly ash that was artificially coated with PAH and HULIS. Total amounts of PAH in the three size fractions of actual PM from biomass burning strongly correlated with the intensities of fluorescence. These encouraging results contribute to the development of a faster and cheaper method of quantifying particle-bound PAH

Thermochemical recovery of waste wood in a domestic wood stove: influence of the geometry of wood batch in the fireplace on pollutant emissions

In the current energy context, pallet boards represent a wood of opportunity strongly used on an individual scale as a means of heating at a low cost. However, French stoves are certified to burn only hardwood species. The main objective of this work is to study the combustion behavior of pallet boards in a commercial stove designed to burn hardwood. The novelty of this work lies in the study of the influence of the wood surface exposed to fire and the identification of the conditions that promote the production of ultrafine particles. The results of the combustion tests show that the surface exposed to the fire influences the combustion. Of the six wood dispositions tested, two stand out with gaseous and particulate emissions at similar levels of a conventional hornbeam log and a densified log. Low temperature conditions and high levels of unburned gaseous products were identified as promoters of ultrafine particles. Overall conclusion of the study is that it is possible to use pallets in a non-designed stove, provided that the user carefully manages the combustion. This opens the way to the clean and rational use of a new type of fuel in a low carbon circular economy.</p

Wood washing: influence on gaseous and particulate emissions during wood combustion in a domestic pellet stove

International audienceNowadays, the use of biomass increasingly replaces the fossil fuels for the domestic heating production. In order to reduce pollutant emissions from biomass combustion, wood was washed at room temperature in order to represent natural rain leaching before burning in a recent pellet stove (2010s) of nominal output of 6.3 kW. Raw and washed woods were combusted for three different types of wood (oak, beech and fir) and the study focused on their particulate and gaseous emissions (Total Suspended Particles (TSP), Particulate Matter with diameter below 2.5 μm (PM2.5), carbon monoxide (CO), nitrogen oxides (NOx) and Total Volatile Organic Compounds (TVOC)). Polycyclic Aromatic Hydrocarbons (PAH), aldehydes and wood tracers as phenols compounds were also measured. In addition, considering the toxic equivalent factor, the human health impact of adsorbed and gaseous PAH is considerably reduced (96%) in the case of washed fir combustion. Emission factors of CO and TSP for washed wood combustion also show a decrease up to 50% depending on the type of wood used. Furthermore, phenolic compounds, Benzene, Toluene, Ethylbenzene, Xylenes and Trimethylbenzene (BTEXT) emissions can also be reduced by the washing of biomass. Washed oak combustion leads to a clear decrease by 60% of the total of BTEXT. In the case of phenols emissions, phenol shows a significant decrease by 91% during the combustion of washed fir wood

Fluorescence Microscopy Analysis of Particulate Matter from Biomass Burning: Polyaromatic Hydrocarbons as Main Contributors

<div><p>New efficient approaches to the characterization of fly ash and particulate matter (PM) have to be developed in order to better understand their impacts on environment and health. Polycyclic aromatic hydrocarbons (PAH) contained in PM from biomass burning have been identified as genotoxic and cytotoxic, and some tools already exist to quantify their contribution to PM. Optical fluorescence microscopy is proposed as a rapid and relatively economical method to allow the quantification of PAH in different particles emitted from biomass combustion. In this study samples were collected in the flue gas of biomass-combustion facilities with nominal output ranging from 40 kW to 17.3 MW. The fly ash samples were collected with various flue gas treatment devices (multicyclone, baghouse filter, electrostatic precipitator); PM samples were fractionated from the flue gas with a DEKATI® DGI impactor. A method using fluorescence observations (at 470 nm), white-light observations and image processing has been developed with the aim of quantifying fluorescence per sample. Organic components of PM and fly ash, such as PAH, humic-like substances (HULIS) and water-soluble organic carbon (WSOC) were also quantified. Fluorescence microscopy analysis method assessment was first realized with fly ash that was artificially coated with PAH and HULIS. Total amounts of PAH in the three size fractions of actual PM from biomass burning strongly correlated with the intensities of fluorescence. These encouraging results contribute to the development of a faster and cheaper method of quantifying particle-bound PAH.</p><p>Copyright 2015 American Association for Aerosol Research</p></div