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Research Article

2D Modeling and Simulation of Pyrolysis of a Thermally Thick Biomass Particle

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Received 25 Mar 2024, Accepted 12 Jun 2024, Published online: 19 Jun 2024
 

ABSTRACT

A transient 2D kinetic-heat transfer model incorporating primary and secondary reactions is proposed to investigate the effect of reactor temperature and particle length/diameter (L/D) ratio on the pyrolysis behavior and validate it with the experimental results. The RMS error between the experimental and the model predictions are found to be 0.36–1.89% for 2D model and 13.00–13.11% for 1D model at reactor temperatures 723–798 K and L/D of 1.0. This uncderscores the necessity for the use of the 2D model in place of the 1D model, particularly at the lower L/D ratio. Temporal propagation of temperature and mass fractional residue profiles at different locations of the pyrolyzing casuarina (Casuarina equisetifolia) biomass particle is analyzed. At a high L/D (~6), two symmetric hot spots are found to appear at two axial end faces, which gradually merge to form a dumbbell-shaped hot spot near the central core. For a low L/D (~1), a symmetrical, concentric, elliptical, shell-shaped hot spot appears at a short distance from the outer surface, which quickly propagates toward the center, eventually merging into a sphere at the particle center. It is estimated that for a 0.0254 m diameter particle at the reactor temperature of 673 K, the optimal residence time is 10 min for L/D = 1, while it is 17 min for L/D = 2.

Nomenclature

B=

mass fraction of virgin biomass

C1, C2=

mass fraction of char

Cps=

heat capacity of solid (J kg−1 K−1)

Ei=

activation energy (J mol−1)

G1, G2=

mass fraction of volatiles

hc=

convective heat transfer coefficient (J m−2 s−1 K−1)

kci=

reaction rate constant (s−1) for char formation

kvi=

reaction rate constant (s−1) for volatile formation

kci0=

pre-exponential factor (s−1) for char formation

kvi0=

pre-exponential factor (s−1) for volatile formation

n1, n2=

reaction order

Pr=

Prandtl number

r=

radial coordinate (m)

Re=

Reynolds number

Rg=

universal gas constant (J mol−1 K−1)

t=

time (s)

T=

temperature

T0=

initial temperature

Tf=

bulk temperature

W=

residual mass fraction

X=

Moisture mass fraction in biomass

Z=

axial coordinate (m)

Greek letters=
ΔH=

heat of reaction (J kg−1)

δ=

deposition coefficient

ρs=

solid density (kg m−3)

ρs0=

initial solid density (kg m−3)

λe=

thermal conductivity (J m−1 s−1 K−1)

ε=

emissivity coefficient

σ=

Stefan – Boltzmann constant (J m−2 s−1 K−4)

Subscripts=
i=

reaction index

1=

primary pyrolysis products

2=

secondary pyrolysis products

LIST OF ABBREVIATIONS=
1D=

One-dimensional

2D=

Two-dimensional

CFD=

Computational Fluid Dynamics

GBEP Global bioenergy partnership=
GHG=

Greenhouse gases

H/C=

Hydrogen to carbon

L/D=

Length diameter ratio

O/C=

Oxygen to carbon

RMS=

Root mean square

TGA=

Thermogravimetric analysis

Acknowledgements

The authors acknowledge the infrastructural and financial support of the National Institute of Technology, Durgapur and the FIST program of DST, Government of India and the National Institute of Technology Durgapur for this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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