STUDIES ON THE MEAT OF COMBUSTION OF WOOD: PHYSICAL PROPERTIES AND THERMAL ANALYSIS
STUDIES ON THE MEAT OF COMBUSTION OF WOOD: PHYSICAL PROPERTIES AND THERMAL ANALYSIS
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Date
2014-02-10
Authors
MUSA, MOMOH
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Abstract
In this work, the studies are concerned with: -
(i) The burning parameters of wood and the influence of physical
properties
(ii) Thermoanalytical analysis and (LOI) of combustion of wood,
(iii) The kinetics of the thermal degradation,
(iv) The mechanism of complex formation between wood and
selected flame-retardants on the burning behavior of the wood.
In case (i), four parameters namely ignition, burning rate, afterglow,
char yield and degradation pattern were examined for fourteen tropical wood.
It was found that the timbers may be ranked differently depending on which
of the parameters is considered and no simple correlation of the four
parameters exists. These observations were explained in terms
of the variation in the composition of the wood and the effect of these on the
phenomena of heat and mass transfer. Experiments were conducted to find
the influence of physical properties on the burning characteristics. It was
found that for the fourteen wood studied there is a highly significant
correlation between both time of ignition and flame spread rate and timber
oven-diy density. It was also found that the rate of flame spread depends on
the orientation of the samples; for each wood, vertical orientation gives a
higher flame spread value than horizontal orientation; Moisture content, as
expected reduces ease of ignition and flame spread, and the afterglow time is
dependent on char yield and ash residue. The latter observation was
interpreted to have arisen from the probable presence of metallic salts known
to increase afterglow. Scanning electron micrographs of the wood show that
the wood samples have different surface topographies. The wood specimens
are seen as having striations, voids and lacunae, which in some samples
coalesce to form network structures. .
Thermal analysis was studied. All measurements were made in a static
atmosphere of air. By reference to the TG/DTG traces, two-step significant
*
decomposition profile with the first step comprising two adjacent mass loss
transitions separated by about 30°C were assigned to all the timbers. It was
further found that the start, peak, and end temperatures of degradative
transitions are similar for both steps for all wood samples and do not depend
on timber density. These observations are interpreted in terms of the
mechanisms of the wood pyrolysis/combustion. Differential Thermal
Analysis methods (DTA and DSC) were also employed for comparison.
Furthermore, experiments were conducted to determine the limiting oxygen
index (LOI) of the wood. It was found that these LOI values are between
22% to 32%, and indeed, indicating that wood has some inherent flame
tolerant or resistant properties.
The kinetics of the thermal degradation of the timbers were obtained
using Broido's analytical procedure. The kinetic behaviour of pyrolysis of all
wood in air is very similar and fairly high activation energies are required for
the first step involving dehydration and chain scission reactions. The second
step which is predominantly secondary product and char oxidations have
significantly lower activation energies. The calculated kinetic parameters
were also discussed within the context of other published values for
wood/cellulose.
The influence that a range of selected inorganic flame-retardants have
on the burning parameters, burning behaviour and pyrolysis of the wood
were investigated. It was found that the flame retardancy related directly to
char-forming tendency for all retardants and their ability to reduce the
dominance of flammable volatile formed during the active first stage of wood
pyrolysis. Among the flame retardants tested, diammonium phosphate
(DAP),diammonium phosphate-borax (DAP:B) and boric acid-borax (B:B)
are highly effective for reducing wood flammability as indicated by
increased LOI and char yield values and reduced intensity of DTA peaks.
Local alum and fertilizer are moderately effective. The possible retandancy
mechanisms of these systems are discussed in detail.
Description
Dissertation submitted to the postgraduate school, Ahmadu Bello University,
Zaria, in partial fulfillment of the requirement for the degree of
Ph.D. (Physics).
Department of Physics
Faculty of Science
Ahmadu Bello University,
Zaria, Nigeria.
Keywords
MEAT,, COMBUSTION,, WOOD,, PHYSICAL,, PROPERTIES,, THERMAL ANALYSIS