Thermogravimetric Kinetic Behavior of Malaysian Poultry Processing Dewatered Sludge (PPDS) During Combustion
N. Aniza1, a*, S. Hassan1, b, M.F.M. Nor1, c and M. Fadhil1,d 1Universiti Teknologi Petronas, Bandar Seri Iskandar, Tronoh, Perak, Malaysia
[email protected], [email protected], [email protected], [email protected]
Keywords: Combustion, Biomass, TGA, Reaction kinetics, FWO model free method.
Abstract. The combustion characteristic and kinetic analysis of Malaysian poultry processing
dewatered sludge (PPDS) from two different origins, namely as PPDS 1 and PPDS 2 using
Thermogravimetric analysis (TGA) were examined. The non-isothermal step was practiced under
oxidative atmosphere during the investigation. The temperature was ramped from 30ºC to 1000ºC at
four different heating rates to allow the calculation of kinetic analysis parameter i.e. activation
energy. Derivative thermogravimetric (DTG) curves for both samples resulted from TGA shows 3
different peaks. Calculation of apparent activation energy was adopted using iso-conventional
model free method. The different of activation energy value embedded in each samples was due to
the non-similarity of its fuel characteristic and combustion behavior.
Introduction
Poultry processing industry is one of the major contributors in food processing sector in
Malaysia. The waste generated by poultry processing industries contains blood, offal, bone meal,
feather and so on [1]. The solid by-product which has been going through wastewater treatment in
poultry processing industry is known as poultry processing dewatered sludge (PPDS). Due to its
source availability, fuel potential and solves the problem related to the waste disposal issues,
researchers have started paying attention to propose PPDS as a potential fuel candidate for biomass
feedstock in thermal conversion technologies [2,3,4]. In those previous studies, determination of
fuel characterization and energy prediction of Malaysian PPDS have been successfully carried out.
There is a gap in available reaction kinetics information of the combustion and gasification of
newly discovered biomass waste material such as PPDS. A comprehensive understanding of
reaction kinetics and a well-defined of the minimum energy required during the combustion process
of PPDS will contribute towards an efficient design and an effective operation of the thermo
chemical conversion process. A proper study on a reaction model for poultry processing waste will
support further research work in converting this waste material into a viable fuel source.
Material and Methodology
The PPDS samples were taken from the plants located at North (PPDS 1) and South (PPDS 2)
region of Peninsular Malaysia which ranged approximately 357 km. Moisture content of sample
was first removed by oven drying at temperature 105°C for 24 hours. The fuel characterizations of
PPDS sample involve the proximate analysis which has been done using the thermogravimetric
analyzer (TGA model Labsys Evo Setaram) to allow the determination of moisture content, volatile
matter, fixed carbon and ash. The content of Carbon (C), Hydrogen (H), Nitrogen (H), and Sulphur
(S) of the sample were measured through the ultimate analysis using the CHNS analyzer. The
higher heating value (HHV) of PPDS sample was carried out using the bomb calorimeter. In order
to conduct the TGA test, 10 mg measured sample was filled in an alumina crucible. The
temperature from 30°C to 1000°C was raised at heating rate, β equal to 5, 10, 15 and 20 K/min in
oxidizing atmosphere. The system of TGA will continuously recording the thermogravimetric (TG)
and derivative thermogravimetric (DTG) curves during the process of combustion.
Results and Discussion
A. Fuel Characterization
Table 1 shows the fuel characteristic of both PPDS 1 and PPDS 2 for proximate analysis,
ultimate analysis and higher heating value (HHV) test.
Table 1 Proximate Analysis, Ultimate Analysis and Higher Heating Value
PPDS Sample
Proximate analysis (wt %) Ultimate Analysis (wt %) HHV (MJ/kg) Moisture
content Volatile Matter
Fixed Carbon
Ash C H N S
PPDS 1 8.66 57.28 22.46 11.6 69.95 10.66 3.29 0.96 22.90
PPDS 2 2.02 85.81 8.51 3.66 52.85 8.87 5.66 0.80 23.43
It can be seen that PPDS 1 has higher moisture content, fixed carbon and ash content compare to
PPDS 2. However, PPDS 2 contains higher volatile matter than PPDS 1. The ultimate analysis
findings depicted that C, H and S content of PPDS 1 are higher than PPDS 2. On the contrary, the N
content is low. Caloric value for both samples indicates 2.26% different.
B. Thermogravimetric Analysis (TGA)
Fig.1. TG-DTG curves for PPDS 1 at different Fig.2. TG-DTG curves for PPDS 2 at different
heating rates. heating rates.
Fig.1 and Fig. 2 show the TG and DTG curves of PPDS 1 and PPDS 2 at heating rates 5, 10, 15
and 20 K/min respectively. As can be observed from Fig.1 and Fig. 2, three regimes of the
approximately starting and ending from the peak of DTG curves can be pointed out. These regimes
can be described as evaporation of moisture, devolatilisation process and char oxidation [5]. The
first region for PPDS 1 shows higher peaks for every heating rate when compared to the result of
PPDS 2 as shown in Fig.2. The percentage of weight loss at this stage is approximately 30%-35%
while for PPDS 2 is just around 10%.
At the next region for devolatilisation process, the DTG curves behave differently for both
samples, where PPDS 1 shows less mass loss (approximately 15%) than the PPDS 2 (approximately
25%). DTG curves at the second region are shorter and wider depicted that the devolatilisation
process of PPDS 1 was very slow. For oxidation of char regime in the third stage again shows
opposite behavior where mass loss for PPDS 1 is higher than PPDS 2. The mass correspoding to the
ashes become constant at temperature approximately 500ºC for both sample, once the fuel content
exhausted [6]. The different behavior of each sample showed in the results was assigned by the
different of fuel characteristic embedded in the sample as shown in table 1. PPDS 2 with higher
volatile matter react actively in devolatilisation stage where the reaction is faster, thus has higher
value of peak height of DTG compare to PPDS 1. Oppositely, higher moisture and fixed carbon
content in PPDS 1 resulted higher value of mass loss and peak height of DTG curves in the first and
third region than that in PPDS 2.
C. Kinetic Analysis
For the calculation of activation energy, data from TG curves have been used. By changing
several heating rates in a same condition of a series of TGA experiments, the frequently used iso-
conversional method, the Flynn-Wall-Ozawa (FWO) model was applied to find out the activation
energy [7]. In this calculation, determination of temperature corresponding to the fixed value of
conversion degrees, α from the experiment at different heating rates was pointed out. This was
conducted by adopting the Doyle's approximation of p(χ) [8]. The degree of conversion rate for
PPDS sample, α can be obtained by the following equation:
(1)
where , and , refer to sample‘s initial, instantaneous and final masses respectively. Fig. 3
and Fig. 4 present the conversion vs. temperature curves for PPDS 1 and PPDS 2 at heating rates of
5, 10, 15 and 20 K/min respectively. Conversion degrees, α from 0.05 to 0.6 have been ascertained
and the corresponding temperature have been found.
Fig. 3 Conversion vs. temperature curves for Fig. 4 Conversion vs. temperature curves for
PPDS 1 at four different heating rates PPDS 2 at four different heating rates
Fig. 5 Flynn-Wall Ozawa (FWO) linear fitting Fig. 6 Flunn-Wall-Ozawa (FWO) linear fitting
plot at different conversion for PPDS 1 plot at different conversion for PPDS 2
The following equation (2) is applied for FWO method. According to T.Ozawa [9], a straight lines
will resulted, obtained from a repetition of experiment at four different heating rates through the
1n(β) vs. 1000/T plotted graph. In Fig. 5 and Fig. 6, a straight lines resulted by plotting the 1n(β) vs.
1000/T when applying the FWO method in equation (2) can be observed. The at the
right side of this equation is equal to the slope value, m of the regression line. The activation
energy, can be subsequently calculated.
[
]
(2)
Table 2 Activation Energy for PPDS 1 and PPDS 2 at conversion, α using FWO model
Sample/
α Activation Energy, (kJ/mol)
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.5 0.6
PPDS 1 38.22 44.98 46.42 44.64 39.56 27.18 13.86 21.13 70.34 78.9
PPDS 2 14.58 25.22 69.57 93.08 100.4 102.5 102.3 100.5 91.36 68.58
The activation energy result of PPDS 1 and PPDS 2 are summarized in Table 2. For PPDS 1,
activation energy is range between 13.86-78.9 kJ/mol, while for PPDS 2 range between 14.58-102.5
kJ/mol. It was observed that for all conversion degrees, α the apparent activation energy for both
samples were different. The main reason is due to the fact that during the combustion, a complex
multi-step mechanism takes place in solid state. Apparent activation energy depends on the
conversion which reveals the phenomenon that the mechanisms of reaction are different at every
steps of the decomposition process [10].
The apparent activation energy shows the minimum energy required during the degradation
process of the sample with the increment of temperature. High temperature and longer time are
required for the reaction with high activation energy [11]. It can be noticed that from the point of
conversion 0.15, the apparent activation energy for PPDS 2 was started to increase until it reach a
stable value. On the contrary, activation energy of PPDS 1 drops drastically. To relate with the
TGA results earlier, this region occurs at the interval temperature of 77ºC-277ºC for PPDS 1, the
mass of sample is almost constant and achieving stability. The moisture evaporation process was
about to finish, thus apparent activation energy shows a sudden fall. As for PPDS 2, this point of
conversion represents interval temperature of 227ºC-277ºC as showed earlier in Fig. 4. According
to the TGA results in Fig. 2, it appears that the mass is decreasing. The decomposition process was
attributed as release of volatile matter. In the middle of this process, it requires maximum activation
energy to complete the thermal breakdown of the combustion stage.
Conclusion
Thermogravimetric kinetic analysis of PPDS sample from two different origins has been
successfully carried out. Despite the same material, the fuel characterization and combustion
behavior of both samples were not same. The data in this experiment shows that the process and
method in extracting PPDS does effects the outcome of the sample. The process in the water
treatment system and sample storage management in each plant plays an important role that affects
the characteristic embedded in the sample. In the future study, these conditions have to be
highlighted to ensure the standard condition and behavior of sample.
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