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Fire Technology

, Volume 54, Issue 5, pp 1219–1247 | Cite as

Natural Downward Smouldering of Peat: Effects of Inorganic Content and Piled Bed Height

  • Jiuling Yang
  • Haixiang Chen
Article

Abstract

The ash thickness formed above the combustion front of peat, which is affected by the inorganic content and the piled bed height of peat column, plays both positive and negative effects on peat smouldering fires. This work investigated the effects of the inorganic content and the piled bed height (5, 10 and 20 cm) on the natural downward smouldering mechanism of peat, both experimentally and numerically. It was observed that the char formation and char oxidation processes are stable and dominant during the downward smouldering. The spread rate of the pyrolysis front was found to decrease almost linearly with the inorganic content, while the spread rate of the char oxidation front was less dependent on the inorganic content and the piled bed height at higher inorganic content. The spread rate of the char oxidation front levelled off when the ash layer above the char layer was thick enough, which was also well-predicted by a 1-D numerical model. The model also predicted the nonlinearly increasing peak temperature and decreasing downward spread rate with depths in experiments. This work provides a better understanding of the multiple role of inorganic content in peat smouldering fires, especially for the fires in the in-depth peat layer with abundant inorganics in natural peatlands.

Keywords

Peatlands Downward smouldering Inorganic content Numerical model Surface regression 

List of symbols

Letters

A

Pre-exponential factor (1/s)

c

Specific heat capacity (J/kg K)

d

Characteristic pore size (m)

D

Diffusivity (m2/s)

E

Activation energy (kJ/mol)

g

Gravity (m/s2)

hc

Convective heat transfer coefficient (W/m2 K)

hcv

volumetric heat transfer coefficient (W/m3 K)

hm

Mass transfer coefficient (kg/m2 s)

ΔH

Heat of reaction (J/g)

IC

inorganic content

k

Thermal conductivity (W/m K)

K

Permeability (m2)

m

Mass (kg)

M

Molecular mass (g/mol)

MC

Moisture content (dry base)

n

Reaction order

N

Total node number

P

Pressure (Pa)

q

Heat flux (W/m2)

R

Universal gas constant (J/mol K)

T

Temperature (°C)

v

Flow velocity (m/s)

X

Volume fraction

y

Mass fraction (mi/m0)

z

z Coordinate (m)

z0

Initial height (m)

Δz

Cell size (m)

Greek symbols

ε

Emissivity

\( \dot{\omega }^{\prime \prime \prime } \)

Non-dimensional reaction rate (1/s)

ν

Mass fraction coefficient

φ

Porosity

μ

Dynamic viscosity (kg/m s)

ρ

Density (kg/m3)

σ

Stefan–Boltzmann constant (W/m2 K4)

Subscripts

0, ∞

Initial, ambient

α/αo

α-char/α-char oxidation

β/βo

β-char/β-char oxidation

a

Ash/added

b

Bulk/bottom layer

eff

Effective coefficient

fg

Gas formation

g/gp

Gas phase/gas products

i

Condensed-phase species i

j

Gaseous species j

k

Heterogeneous reaction k

mix

Gas mixture

p/po/pp

Peat/peat oxidation/peat pyrolysis

s

Solid phase

sh

Shrinkage

t

Top layer

w/wv

Water/water vapor

Superscripts

(−)

Weighted or averaged

(′)

Transient status

Notes

Acknowledgements

This work was sponsored by National Key R&D Program of China (No. 2016YFC0800100) and National Natural Science Foundation of China (No. 51576184). HC was supported by Science and Technological Fund of Anhui Province for Outstanding Youth (No 1808085J21) and Fundamental Research Funds for the Central University (WK2320000036).

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.State Key Laboratory of Fire ScienceUniversity of Science and Technology of ChinaHefeiPeople’s Republic of China

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