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Research Article

Adaptation of the Chemical Percolation Devolatilization Model for Low Temperature Pyrolysis in a Fluidized Bed Reactor

, , , , , & show all
Pages 417-434 | Received 18 Jan 2019, Accepted 16 Sep 2019, Published online: 01 Nov 2019
 

ABSTRACT

In the present study, the CPD model originally developed based on predictions from heated grid (HGR) and entrained flow (EFR) experiments, has been adapted to analyze pyrolysis kinetics in a small-scale fluidized bed reactor. Impacts of particle feed, particle heat up as well as tar cracking reactions in the gas phase are considered. Furthermore, an optimized solver structure allows a time step independent solution and enables the use of implicit methods. A comparison with experimental results is undertaken for pulverized Rhenish lignite fuel particles in the temperature range from 673 to 973 K in N2 atmosphere. The comparison between simulated and experimentally derived volatile release rates reveals a good agreement, indicating that the high temperature derived kinetic parameters from HRG and EFR experiments can be extrapolated to lower temperatures. Nevertheless, discrepancies in the tar to light gas ratio occur with the proposed model implementation.

Nomenclature

A=

pre-exponential factor

A=

cross-sectional area

B=

Boolean function

a=

acceleration

Cd=

drag coefficient

c=

heat capacity

D=

damping constant

d=

diameter

Ea=

activation energy

Fij=

view factor from surface i to j

g=

gravity

H=

height

M=

molar mass

m=

mass

m˙=

mass flow

N=

number

P=

probability of occurrence

Pr=

Prandtl number

Q˙=

heat flux

R=

universal gas constant

Re=

Reynolds number

r=

reaction rate

S=

surface area

T=

temperature

t=

time

V=

volume

V˙=

volume flow

v=

velocity

X=

bridge population parameter

x=

position

y=

mass fraction/yield

α=

heat transfer coefficient

Δhreac=

reaction enthalpie

ε=

emissivity

ε=

porosity

λ=

thermal conductivity

μ=

mean value

ξ=

reaction progress

ρ=

density

σ=

coordination number

σ=

standard deviation

σ=

Stefan-Boltzmann constant

m=

molecular weight

Subscripts

0=

initial

a=

ash

ar=

aromatic

act=

activated

bot=

bottom

bro=

broken

cl=

cluster

cross=

cross-linking

exp=

experimental

ext=

external

FB=

fluidized bed

FP=

feed pipe

flush=

gas flush for injection

frag=

fragment

fuel=

fuel

GPR=

gas phase reaction

g=

gas

int=

intact

lab=

labile

LG=

light gas

liq=

liquid

N2=

nitrogen

p=

particle

PT=

percolation theory

rad=

radiation

reac=

reaction

rel=

relative

SC=

side chain

stab=

stable

tar=

tar

top=

top

tot=

total

vol=

volatiles

Additional information

Funding

This work has been funded by the German Research Foundation (DFG) – project number [215035359] – within the SFB/TRR 129 ‘Oxyflame’.

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