Particle emissions from biomass pyrolysis in a flat flame

1. Particle emissions from biomass pyrolysis in a flat flame Jiaxi Fang, Anna Leavey, and Pratim Biswas* Aerosol & Air Quality Research Laboratory (AAQRL), Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA AAAR2012 2CO.3 Adam Ferguson for The New York Times Reduce Environmental Impacts Laboratory Studies Current Uses Motivation: 1) improve cookstove efficiency 2) reduce pollutant emissions Drop Tube Furnace Mechanisms of Biomass Combustion: Aerosol Formation TGA Lignin(~20%) Cellulose(~20%) Hemicellulose(~30%) Thermal Degradation (Pyrolysis) Light Gases (20-70%) Gases, Organic Aerosols VOC, HC. CO2 , CO , H2O, NO x, SOx, O2 Objective: Characterize factors affecting particle formation during the initial stages of combustion for use with a comprehensive cookstove model to predict aerosol formation Oxidation CO2 energyalmanac.ca.gov Ktar, Kgas Kchar CO HC Wheelabrator Shasta Company Forest Residue Energy Power Plant Drying Dry Biomass H2 PAH Tar (10-40%) H2 O H2O Kdry Char Oxidation2: 2C+O 2C(O) C(O)CO C(O)+C(O)CO2 +C Methane-Air Flat Flame Biomass Tainstruments.com Char(~10-50%) Ash(<20%) Fixed Carbon(<20%) Light Gases3: ~10% H2 ~40% CO ~21% CO2 ~25% H2O ~13% HC Tar: Heavy Organics Char: Remaining carbonaceous species after pyrolysis H2O 5-30% moisture Wood Fired cookstoves used in rural India Introduction Particle Number Size Distributions Kinetics of Pyrolysis (TGA) SEM Imaging • Over half of the world’s population cannot access electricity and burn biomass in cook stoves. • 1.5 million deaths per year due to chronic exposure. • Cookstove startup exhibit significant increases in PM2.5 emissions1. • Initial stages of combustion are critical in particle formation • Both the weight percentage and DTG curves demonstrate that higher levels of moisture cause a delay in devolatilization. Char Particle High Moisture Biomass Experimental Methods Delay in Devolatilization Methane- Air Flat Flame Reactor 10μm • Methane Air Flat Flame(1000K/s) • Biomass particles(1g/hr) • Particle number size distributions (PNSD) using SMPS(Online) • Five types of biomass , three levels of moisture • Thermogravimetric Analysis(TGA)(Offline) Char Particle, Oven Dry Biomass Particulates Char/Tar particles Volatiles gases Quartz Tube CH4 +Air(Φ=1)_ T(K) 5μm Burner Head Fine particulates from pyrolysis • Modulated TGA revealed similar kinetic parameters for different types of biomass. Biomass Particles, N2 PNSD Statistics 2 μm α=mass loss fraction β=heating rate(400K/min) A=pre-exponential factor E=activation energy R= ideal gas constant T=temperature • Higher aspect ratio char particles demonstrate lower conversion efficiencies. • Higher moisture content results in suppressed particle formation during the initial stages. Conclusions • Different types of biomass has similar kinetics for pyrolysis and generate similar PNSD during flash pyrolysis • Increased moisture content results in suppressed devolatilization and particle formation during flash pyrolysis which will lead to more inefficient combustion References • Sahu, M. et al.Evaluation of Mass and Surface Area Concentration of Particle Emissions and Development of Emissions Indices for Cookstoves in Rural India. Environ. Sci. Technol. 45:2428–2434. • Janse et al. Combustion Kinetics of Char Obtained by Flash Pyrolysis of Pine Wood, Ind. Eng. Chem. Res. 1998, 37, 3909-3918 • Lu et al. Comprehensive Study of Biomass Particle Combustion, Energy & Fuels 2008, 22, 2826–2839 Acknowledgements Partial funding from MAGEEP is gratefully acknowledged http://www.aerosols.wustl.edu/aaqrl/ *E-mail: pratim.biswas@wustl.edu