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

anoor.aniza87@gmail.com, bsuhaimiha@petronas.com.my, cmfaizairi_mnor@petronas.com.my, dfarfiez@yahoo.com

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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