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ECI Digital Archives BioEnergy IV: Innovations in Biomass Conversion for Heat, Power, Fuels and Chemicals

Proceedings

Spring 6-10-2013

Experimental and modeling study of the gasification of char from millimetric wood chips pyrolysis Santiago Septien CNRS

Follow this and additional works at: http://dc.engconfintl.org/bioenergy_iv Part of the Chemical Engineering Commons Recommended Citation Santiago Septien, "Experimental and modeling study of the gasification of char from millimetric wood chips pyrolysis" in "BioEnergy IV: Innovations in Biomass Conversion for Heat, Power, Fuels and Chemicals", Manuel Garcia-Perez,Washington State University, USA Dietrich Meier, Thünen Institute of Wood Research, Germany Raffaella Ocone, Heriot-Watt University, United Kingdom Paul de Wild, Biomass & Energy Efficiency, ECN, The Netherlands Eds, ECI Symposium Series, (2013). http://dc.engconfintl.org/ bioenergy_iv/5

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EXPERIMENTAL AND MODELING STUDY OF THE GASIFICATION OF CHAR FROM MILLIMETRIC WOOD CHIPS PYROLYSIS S. Septien, F.J. Escudero – Sanz, S. Salvador RAPSODEE, CNRS UMR 5302, Mines – Albi, 81013 Albi, France

10/06/2013

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Context of the study GAYA project (supported by the ADEME)

Demonstration of the techno-economic feasibility of biomethane production through biomass gasification in France

Wood Agriculture residues Sewage sludge

Biomass gasification occurs in a Fast Internally Circulating Fluidized Bed (FICFB) = Gasifier (Fluidized bed) coupled to a combuster (transported bed)

CH4

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Objectives of the study Important to optimize char residence time in the gasifier

Char gasification modeling

 Maximize syngas production in the gasifier  Dispose of enough of char for the combuster to keep autothermicity

Experimental study - Effect of gasification conditions - Effect of particle size - Effect of conditions during char formation (heating rate)

Fundamentals understanding

Better understanding

Development of a particle simple model to be introduced into a reactor model

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Experimental setup Sample preparation Pyrolysis under high heating rates (HHR) in the macro TGA Pyrolysis under relative low heating rates (LHR) in a screw reactor

Wood chips

Gasification experiments Char characterization (SEM, BET, porosity…)

~ 100°C/s

~ 10°C/s

Sieve classification by particle thickness REF

0.3

1.2

0.6

0.9

2.4

1.8

1.5

2.1

3.0

2.7

mm

3.3 mm

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Experimental setup Gasification experiments Macro TGA

Determination of gasification kinetics through the measured mass loss

Measurement of apparent kinetics T=750°C – 800°C – 850°C – 900°C – 950°C PH2O= 0.35 bar Raw char samples Measurement of intrinsic kinetics T=750°C – 780°C – 800°C PH2O= 0.15 – 0.25 – 0.35 bar Grinded char samples (< 250 µm)

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Modeling approach Assumptions

Gasification controlled by chemical kinetics and internal transfers

Cchar + H2O  CO + H2

𝑟𝑎𝑝𝑝 = η × 𝑟𝑖𝑛𝑡 𝑇, 𝑃𝐻2𝑂 , 𝑋 𝑛

𝑟𝑖𝑛𝑡 𝑇, 𝑃𝐻2𝑂 , 𝑋 = 𝑘 𝑇 × 𝑃𝐻2𝑂 × 𝑓 𝑋 𝑟𝑎𝑝𝑝 η= 𝑟𝑖𝑛𝑡

η=

with

No limitation of external transfers (verified through experiments and calculations)

with

−𝐸𝑎 𝑘 𝑇 = 𝑘0 × exp 𝑅×𝑇

3 1 1 × − ∅ 𝑡𝑎𝑛ℎ∅ ∅

For spheres and first reaction orders

𝑖𝑛𝑡𝑟𝑖𝑛𝑠𝑖𝑐 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 ∅= = 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑟𝑎𝑡𝑒

𝑘(𝑇) × 𝐿𝑐 𝐷

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Modeling approach 𝑟𝑖𝑛𝑡 𝑇, 𝑃𝐻2𝑂 , 𝑋 = 𝑘 𝑇 × 𝑃𝐻2𝑂 𝑛 × 𝑓 𝑋

with

−𝐸𝑎 𝑅×𝑇

𝑘 𝑇 = 𝑘0 × exp

Parameters determined from experiments on intrinsic conditions for HHR char: Ea = 280 kJ/mol

k0 = 1.9x1011 s-1.bar-1

n=1

First order

f(X) = 26,92X6 − 48,32X5 + 26,06X4 + 4,15X3 − 5,67X2 + 1,96X + 0,35 3 1 1 η= × − ∅ 𝑡𝑎𝑛ℎ∅ ∅

with

∅=

𝑘(𝑇) × 𝐿𝑐 𝐷

For spheres and first reaction orders

Char particles assimilated to spheres through an equivalent diameter Lc = Vp / Sp = f(thickness) = 2.46 x thickness0,77 D = f(T) fitted from apparent kinetics = 2.7x1012xT-5

BLACK BOX

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Results and discussion HHR char – Thickness = 1,8 mm – PH2O = 0.35 bar

Temperature Temperature

Thickness

Model validated but very low values for D

Dash line: exp Smooth Line : model

HHR char – T = 850°C – PH2O = 0.35 bar Thickness

Dash line: exp Smooth Line : model

Reaction rate

Dmodel ~ 10-10 m2/s

1mm) , specially at high temperatures (around 950°C)



The use of Thiele effectiveness to describe large particles gasification is a simple and efficient modeling approach



Char prepared under HHR has faster kinetics and better enhance internal transfers than char from LHR

Perspectives: To better understand the results obtained in this study and to include the effect of heating rate during char formation in the model; to extend the model for char from different biomass

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ACKNOWLEDGMENTS

THANK YOU FOR YOUR LISTENING, NOW I WILL ANSWER YOUR QUESTIONS WITH PLEASURE. I wait for your visit to discuss about this study during the poster session!

Contact: [email protected]