Co-pyrolysis kinetics of sewage sludge and oil shale thermal decomposition using TGA–FTIR analysis

Energy Conversion and Management 118 (2016) 345–352

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Co-pyrolysis kinetics of sewage sludge and oil shale thermal decomposition using TGA–FTIR analysis Yan Lin, Yanfen Liao ⇑, Zhaosheng Yu, Shiwen Fang, Yousheng Lin, Yunlong Fan, Xiaowei Peng, Xiaoqian Ma School of Electric Power, South China University of Technology, 510640 Guangzhou, China Guangdong Province Key Laboratory of Efficient and Clean Energy Utilization, 510640 Guangzhou, China

a r t i c l e

i n f o

Article history: Received 1 March 2016 Received in revised form 31 March 2016 Accepted 1 April 2016

Keywords: Co-pyrolysis Sewage sludge Oil shale TGA–FTIR analysis Kinetics

a b s t r a c t TGA–FTIR system was equipped under N2 for the kinetics behavior characteristics of sewage sludge (SS) and oil shale (OS) blends during co-pyrolysis. The SS was blended with OS in the range of 10–90 wt.%, and then heated from 105 °C to 1000 °C at 10, 20 and 30 °C/min under N2 atmosphere with a flow rate of 80 ml/min. Two model-free methods, Kissinger–Akhira–Sunose (KAS) method and Starink method, were used to study their co-pyrolysis kinetics. There existed promoting effects on the degradation of oil shale during co-pyrolysis. The absorption of hydrocarbon became stronger with adding 10% SS. The best proportion of SS was selected as 10% due to better pyrolysis performance of OS and lower apparent activation energy (253.6 kJ/mol obtained by Starink, 253.3 kJ/mol obtained by KAS). The results afford a theoretical groundwork for the co-pyrolysis technology of SS and OS and the development of their thermochemical conversion systems. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Sewage sludge is the major by-product of municipal sewage treatment. With the high-speed growth of population and rapid urbanization, numerous sewage sludge is generated increasingly. By the end of 2013, it was reported that about 35 million tons of sewage sludge was generated annually in China, and this number would reach 50–60 million per year for 2020 [1,2]. In Europe, the annual production of sewage sludge accounted for more than 10 million tons in 2010 and is expected to increase up to 13 million tons for 2020 [3]. Sewage sludge has many toxic substancs such as pathogens, heavy metals and some organic contaminants (such as dead bacteria and microbe), which will cause serious environment pollution without proper treatment [4]. Up to the present, most of sewage sludge has been used widely in agriculture as valuable fertilizer, disposed of in landfills or combustion and incineration. However, there are many environmental limitations in these options [5]. With the echo of environment protection, these traditional technologies for sewage sludge disposal were held back and their gate costs were increased due to increasingly strict legislation and law. Thus, it is important to

⇑ Corresponding author at: School of Electric Power, South China University of Technology, 510640 Guangzhou, China. E-mail address: [email protected] (Y. Liao). http://dx.doi.org/10.1016/j.enconman.2016.04.004 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved.

develop a more clean and effective technology for sludge handling and disposal. The co-utilization technology is such an environmental friendly and highly-efficient technology for solid waste management, in particular co-combustion and co-pyrolysis [6–10]. Parshetti et al. observed that an appreciable reduction of pollutant emissions was found during the co-combustion of biomass and coal [11]. Peng et al. studied the kinetics and products during co-pyrolysis process of microalgae and textile dyeing sludge, the results indicated that there existed positive interaction in co-pyrolysis process [7]. Moreover, some researchers found that co-pyrolysis has successfully improved the quantity and quality of liquid products and gaseous products [12,13]. Compared to the pyrolysis of individual materials, the apparent activation energy of co-pyrolysis significantly declined, which suggested that it was feasible to cut down the energy consumption of solid wastes resourceful utilization with the proper blending proportion [14]. As the above findings showed, co-utilization technology is a promising, economic and environmental friendly technology for both waste management and energy production. Therefore, Co-pyrolysis has great potential for sewage sludge treatment and recycling. Presently, this new technology is still in development. More investigations should be launched for enriching the theoretical groundwork of the application of co-pyrolysis. According to

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previous researches, people seemed to be concentrated on studying co-pyrolysis process between biomass and sewage sludge [6,15]. Apparently, there were still many possible materials for co-pyrolysis with sewage sludge. For the several decades, people have made a great effort on searching potential crude oil substitute resources. Shale oil (calculated based on the in situ oil shale) accounts for about 400 billion tons of oil, all over the world, which is higher than the total for traditional crude oil (which is more than 300 billion tons) [16]. But, the traditional oil-extraction of oil shale is usually criticized for the environment pollution [17,18]. A more cleaning and effective technology is in urgent need. So it may not be a bad choice to apply co-pyrolysis technology for the energy conversion of oil shale. More importantly, the metal-salts of sewage sludge have promoting effect on the cracking of Hydrocarbon (contained in oil shale) [19,20]. And the organic matter, such as cellulose, lipids and protein, decomposes into high-calorific-value by-products (like H2, CO, CxHy and bio-oil), which are beneficial to improve the quantity and quality of oil and gas from degradation of oil shale. Thereby, it has a good prospect on the industrial application of co-pyrolysis between oil shale and sewage sludge. The development of co-pyrolysis for oil shale and sewage sludge and proper equipment design requires the knowledge of several process features involving understanding of the dominating reaction mechanisms, determination of significant reaction parameters as well as cognition of reaction kinetics [21]. A careful conception of solid-state kinetics for co-pyrolysis process is practically crucial. However, few literatures mentioned this subject for co-pyrolysis between oil shale and sewage sludge. In this paper, TGA–FTIR systems were employed to investigate to co-pyrlysis behavior between sewage sludge and oil shale. Two of the model-free methods, Kissinger–Akhira–Sunose (KAS) and Starink methods were adopted for apparent activation energy acquisition. The potential global optimum for co-pyrolysis would be figured out overall consideration. 2. Material and methods

microbalance sensitivity was less than ±0.1 lg. Blank experiments were carried out without samples to obtain the baselines, which were used to calibrate the experiments with samples, at different heating rate (10, 20 and 30 °C/min). Under a inert atmosphere of high purity nitrogen (a flow rate of 80 ml/min), the samples for co-pyrolysis investigations were heated from 50 °C to 105 °C, keeping at 105 °C for 10 min to remove the moisture content, and then heated from 105 °C to 1000 °C. Besides, all samples were kept at 10 ± 1 mg for avoiding heat transfer limitations. To enhance the repeatable performance for these TG data, all the experiments were carried out at least twice to decrease the test error. The gaseous products from co-pyrolysis of SS and OS were determined by coupled with Fourier transform infrared measurements (NicoletTM iSTM 10 FT-IR spectrometer). Before the sample inserted, passing nitrogen for 5 min and then corrected the background baseline. The gaseous products from co-pyrolysis travel through the heated transfer line, which was heated at a constant temperature of 215 °C for preventing the condensation of gases, and then systems began to collect FTIR spectra of it. FTIR gas analysis was carried out using a resolution of 4 cm
1, and 8 scan per sampling. FTIR spectra was recorded from 4000 to 500 cm
1 2.3. Kinetics theory The kinetics of heterogeneous solid-state thermal degradation is dominated by the fundamental equation [22].


 da
Ea f ðaÞ ¼ kðTÞf ðaÞ ¼ A exp dt RT

where t is time, T is the reaction temperature, A is the preexponential factor, k(T) is the rate constant which is temperature dependent, f(a) is the dependence of extent of conversion (a) in relation to reaction model, Ea is the apparent activation energy at the conversion a, R is the universal gas constant (8.314 kJ/mol K). The conversion degree a typically reflects the progress of the transformation of a reactant to products described by:

a¼

2.1. Materials and preparation The sewage sludge (SS) is from Liede Wastewater Treatment Plant of Guangzhou city, Guangdong province of China. Oil shale (OS) is from Maoming, Guangdong province of China. SS and OS were dried at 105 °C for 24 h in a drying oven to remove the moisture content. After drying, the SS and OS were all crushed and sieve to <178 um particle size. The ultimate analyses, proximate analyses of the dried SS and OS were shown in Table 1. The blending ratio of SS was defined as SP, and the SS was blended with OS at the weight ratios of 90%, 70%, 50%, 30%, 10% (named as SP90, SP70, SP50, SP30, SP10, respectively) for analysis and further experiment. 2.2. Apparatus and methods TG analysis of co-pyrolysis between SS and OS was investigated on TGA (thermogravimetric analyzer) apparatus (METTLER TOLEDO TGA/DSC1). Its temperature precision was ±0.5 °C and

ð1Þ

m0
mt m0
m1

ð2Þ

where m0 and m1 is the initial weight and the final weight of the sample, respectively. mt is the weight of the sample at temperature T. When heating rate b = dT/dt is introduced, Eq. (1) can be transformed to:

b


 da
Ea ¼ A exp f ðaÞ dT RT

ð3Þ

Thermal decomposition is a particularly complicated process which is considered the presence of hundreds of complex components and their parallel and/or consecutive reactions. As a consequence, the iso-conversional method is highly recommended to evaluate apparent activation energy for the reliability and objectiveness by International Confederation for Thermal Analysis and Calorimetry (ICTAC). In this paper, Starink and Kissinger–Akahira–Sunose (KAS) methods are employed in this work to evaluate apparent activation energy of the feedstock at conversions because of their good

Table 1 The ultimate analyses and proximate analyses of SS and OS on dry basis. Samples

SS OS

Ultimate analyses (wt.%)

Proximate analyses (wt.%)

Qnet,d

C

H

O

N

S

Volatile

Fixed carbon

Ash

kJ/kg

21.61 12.08

4.037 2.383

19.423 14.396

3.53 0.57

0.55 1.741

42.54 22.78

6.61 8.39

50.85 68.83

9875 5543

Y. Lin et al. / Energy Conversion and Management 118 (2016) 345–352

adaptability and validity for model-free approaches. By taking logarithm, the KAS method gives:

b

ln

!


¼ ln

T 2a

 AR Ea
Ea gðaÞ RT a

ð4Þ

where g(a) is the integral expression of kinetics model function, Ta is the temperature at conversion a. Starink (1996) examined two iso-conversional techniques (Flynn–Wall–Ozawa (FWO) and Kissinger–Akhira–Sunose (KAS)) and found out that both conform to the expression in gives [23]:




ln

b T sa



¼ Cs


BEa RT a

ð5Þ

where for FWO s = 0, B = 0.457 and for KAS s = 2, B = 1. Starink optimized the values for constants s and B and proposed that s = 1.8, B = 1.0037. Thus, the Starink method can be expressed as:

ln

b 1:8

Ta

!

¼ C s
1:0037

Ea RT a

ð6Þ

At a constant value of conversion rate a, the plots of ln(b/Ta2) vs. 1/Ta (KAS method) or ln(b/Ta1.8) vs. 1/Ta (Starink method) obtained from thermograms recorded at several heating rates help in yielding a straight line whose slope allows evaluation of the apparent activation energy. 3. Results and discussion 3.1. Themogravimetric analysis of SS and OS The thermogravimetric data (TG) curves and first derivative data curves (DTG) of SS and OS at 10 °C/min were shown in Fig. 1(a). As is presented in Fig. 1(a), the pyrolysis process of SS could be distinguished into four individual stages: pre-heating phase (mass lost 0.87% below 150 °C), the main degradation of organic contents phase (mass lost 36.49% at 150–584 °C), stable phase (mass lost 2.50% at 584–800 °C) and the degradation of inorganic contents phase (mass lost 5.07% over 800 °C). Firstly, the preheating phase corresponded with the release of a very low quantity of volatiles and dehydration of organic contents by loss of both free water and chemically bonded water. The main devolatilisation took place in the second phase and it could be divided into three parts due to the organic contents of sewage sludge mentioned above [24]. Lipids were highly reactive in temperature range of 150–240 °C, so the first stage of the SS mass loss peak

corresponded to the degradation of lipids and mass lost 6.28% during this stage. And then, from 240 to 400 °C, a remarkable peak was observed in the main loss peak of SS DTG curve and mass loss, reached 21.35%, was the maximum among the triplet. This phenomenon suggested that the degradation of cellulose accounted for most of mass loss during pyrolysis process. Finally, another shoulder was shown at 400–584 °C, which indicated that there were actively-decomposing reactions of proteins [6,25,26]. The mass loss of proteins was slightly higher than lipids, reached 8.85%. After the triplets, the degradation process came into next phase, which was the decomposition of residual organic matter. The mass loss rate became slow and kept stable until 800 °C. During this phase, there was only 2.50% lost in total mass. When the temperature reached 800 °C, the inorganic contents, such as quartz, calcite or microline [27], began to decompose, but this phase was not the focus in our works. In case of OS, there were also four stages involved in the degradation of OS [28]: pre-heating phase (mass lost 2.35% below 299 °C), the main degradation of organic contents (mass lost 17.25% at 299–600 °C), stable phase (mass lost 2.00% at 600– 800 °C)) and the degradation of inorganic contents phase (mass lost 3.18% over 800 °C). The first phase was similar to SS, which was caused by dehydration and water evaporation. The main degradation of organic matter happened in the second phase. A sharp mass loss peak was observed from 299 °C to 600 °C. This phenomenon related to the cracking of long carbon chains in kerogen, a kind of hydrocarbons consisted of aliphatic and aromatic groups.etc. Actually, it was the most important stage for the generation of shale oil and gas during pyrolysis process. After 600 °C, organic matter was almost decomposed completely in previous phase. And the mass loss rate became slow and kept into stability, waiting for the pyrolysis process accomplished. When the temperature reached 800 °C, the inorganic contents began to decompose, but it could hardly provide any potential bio-oil or bio-gas. So this phase was not the focus in our works. The total mass loss of SS and OS were 44.92% and 24.78%, respectively. As for SS, there were still 39.85% for SS without counting inorganic matter. And it was a considerable figure for volume reduction and resourceful utilization of SS by pyrolysis technology.

3.2. The synergistic interaction between SS and OS As given in Fig. 2(a) and (b), all TG and DTG curves of the blends, at 10 °C/min, laid between the individual materials. With increasing OS content in blends, the pyrolysis evolution profiles of the blends changed with a tendency from that of SS to OS gradually. And the contributions of SS and OS to these profiles were obvious. Significantly, the pyrolysis processes of the blends could be distinguished into two steps. The first stage, from about 150 °C to 380 °C, was attributed to decomposition of organic matter contained in SS. And then the second stage took place in the temperature range of 380–600 °C, which was mainly caused by the decomposition of kerogen. A comprehensive index D is used as a criterion for pyrolysis release characteristics depiction [14], and improvements were adopted in DT1/2 (°C) for this work:

D¼

Fig. 1. The TG and DTG curves of OS and SS.

347

ðdw=dtÞmax ðdw=dtÞmean M 1 T i T max DT 1=2

ð7Þ

where (dw/dtmax) and (dw/dtmean) represents the maximum an the average mass loss rate (%/min), respectively. M1 is the pyrolysis mass loss (%), Ti is the initial temperature (°C); Tmax (°C) and DT1/2 (°C) represents the temperature related to the temperature range of pyrolysis process.

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than OS. These findings above suggested that the co-pyrolysis process was beneficial for OS decomposition, while negative for SS decomposition. To evaluate the pyrolysis characteristics of SS and OS, the calculated curves of the blends are weighted average of the individuals [30].

W ¼ ass W SS þ aos W OS

ð9Þ

where WSS, WOS are the experimental value of a TG curve of the individual materials and ass, aos are the blending ratio of the each individual in the blends, respectively. To further investigate the synergistic interaction between OS and SS, DW was defined as:

DW ¼ W experimental
W caclculated

Fig. 2. (a) The TG curves of OS, SS and their blends. (b) The DTG curves of OS, SS and their blends.

As the pyrolysis composed of series of stage, the characteristic index D can be rewrote in to Eq. (8):

D¼

X

gi Di

ð8Þ

i

where gi is the mass loss percentage of each step in the total mass loss (%); Di is the index D of each stage. the bigger the index D is, the more vigorously the material decomposed. The greater (dw/dtmax), (dw/dtmean) and the lower Ti represent easier and stronger release of volatiles; the lower Tmax and DT1/2 suggest that the mass loss peak appears earlier and more concentrated. As Table 2 and Fig. 3(a) given, the initial temperature of the first step increased gradually with the weight ratio of OS enhanced. And the index D1 was also declined. It suggested that the pyrolysis process of SS would be delayed with the addition of OS. A similar phenomenon was observed by Eglinton et al. [29], they found that some minerals hindered the pyrolysis of organic matter. So the degradation of SS might be inhibited by the minerals contained in OS. However, it was worthy to note that there were totally different results for OS pyrolysis with the addition of SS. With the proportion of SS increased, the index D2 became higher and reached maximum at SP10. As Table 2 shown, the index D2 of SP10 was three times as OS, which indicated that the decomposition of OS was promoted vigorously. The initial temperature of second step was delayed into 308 °C, which was just slightly higher

ð10Þ

As shown in Fig. 3(b), it was obvious that the DW of all samples were positive at below 450 °C, suggesting that the decomposition of SS was inhibited with the addition of OS. The kerogen, the main organic matter of OS, converted into bitumen and oil at the initial stage of OS degradation [16]. Therefore, the possible reason to explain the inhibition is that the SS powder would be coated by these flowing and sticky liquid products, consequently the volatile matter from SS was difficult to release. Similar results were found in other researches [7,31]. Peng et al. found that the bio-oil derived from pyrolysis of microalgae would coat the textile dyeing sludge powder so that the volatile matter from sludge was difficult to release [7]. When the temperature reached 400 °C, the bitumen started converting to oil, gas and residue. As a result, the diffusion resistance of volatile matter of the blends declined and made it easy for the diffusion of volatile matter. Moreover, the DW of all samples decreased after 400 °C. Especially, the DW of the blends of SP50, SP30 and SP10 turned into negative but not observed in other blends after 450 °C. This phenomenon indicated that the promoting effect might exist in the pyrolysis of OS with the blends of SP50, SP30 and SP10. P. Manara et al. found that SS was consisted of silicates, aluminates and metal salts (such as Zn, Pb, Cu, Cr, Ni, and Cd) [5]. The inorganic matter, especially the metal salts, might play catalytic roles in promoting the degradation of OS [32]. As for SP90 and SP70, the curves still exhibited a similar tendency to SP50, SP30 and SP10, but they did not turn into negative after 450 °C as these triplet. It might be the reason that the proportion of OS was too low to dominate the second stage during the co-pyrolysis process. Thereby, the second stage of co-pyrolysis of SP90 and SP70 were determined by the degradation of sludge, specifically related to protein decomposing, and it was inhibited by adding OS. Care must be taken when determining the blending ratio to ensure the best promoting effect for OS decomposition and more reduction of SS. 3.3. TG–FTIR for the gaseous products Fig. 4 showed the FTIR detection of gaseous products from OS, SS and SP10 under heating by 10 °C/min. The absorptions of carboxyl, carbonyl, carbon dioxide, methane and ammonia were observed during the SS pyrolysis. All products appeared in the time range of 0–45 min, and quite coincided with the TG results. As Fig. 4(b) and (e) depicted, the carbonyl (1159 cm
1) and carboxyl (1764 cm
1) groups appeared after 5 min and reached the maximum at about 20 min (300 °C) [32]. Fig. 4(d) showed that the absorption peak of carbon dioxide (2360 cm
1) reached maximum about 7 min earlier than carbonyl and carboxyl. This phenomenon might correspond with the decomposition of protein and celluloses. Fig. 4(c) showed that CH4 (2935 cm
1) appeared at 10–45 min [33]. The maximum reached at 35 min (450 °C), which is corresponded the pyrolysis of slight hydrocarbon contents. Fig. 4 (f) showed that there were three obvious peaks appeared in

3.55 9.22 8.05 5.30 3.11 1.62 / 0.572 0.766 0.814 0.757 0.661 0.556 / 453.2 452.7 451.8 451.7 451.7 444.7 /

349

12 min, 22 min and 34 min respectively. The emission of NH3 (964 and 930 cm
1) at 12 min could be ascribed to the thermal instability of small molecular nitrogen carriers, such as carbamide and amino acid [34]. The other two peaks were related to the decomposition of protein and its secondary reactions. The gaseous products from OS and SP10 mainly contained methane (2935 cm
1). As Fig. 4(a) presented, the emission of methane from OS and SP10 was in agreement with TG results. The emission appeared in the time range of 30–45 min, which also was the primary mass loss stage. The maximum absorption of methane with 10% SS was twice as much as individual OS. The addition of SS had a promoting effect on methane productions. 3.4. Kinetics analysis

1.72 2.19 1.92 1.56 1.22 0.92 /

DTGmean
2g %/min

299 308 350 374 381 395 /

600 568 570 573 574 573 /

301 260 220 199 193 178 /

14.71 19.92 17.92 15.08 12.79 9.92 /

According to Eqs. (5) and (6), the apparent activation energy of OS, SS and their blends at a 0.2–0.8 obtained by the KAS and Starink methods were shown in Table 3. Most of the correlation coefficients (R2) of Ea were greater than 0.95, declaring the acceptable accuracy of the results. And the solutions of Ea were almost equal, so it was acceptable to discuss the solution from Starink method merely. As Fig. 5(a) shown, the apparent activation energy of the blends were increased with the a increased. There were two minimal peaks of the Ea average in Fig. 5(b), according to SP = 30% and 70% respectively (SP was defined in Section 2.1). And the Ea average of SP = 30% and 70% obtained by Starink was 239.0 kJ/mol,

h

f

g

e

d

c

a

b

Ti
1, Ti
2, the initial temperature according to the first step and the second step. Tf
1, Tf
2, the terminal temperature according to the first step and the second step. DT1/2
1, DT1/2
2, the temperature range (DTG P 0.15%/min) according to the first step and the second step. M1
1, M1
2, the pyrolysis mass loss according to the first step and the second step. DTGmax
1, DTGmax
1, the mass loss rate according to the first peak, the second peak and the third peak. DTGmean
1, DTGmean
2, the average mass loss rate according to the first step and the second step. Tmax
1, Tmax
2, the temperature according to the first peak, the second peak and the third peak. D1, D2, the comprehensive pyrolysis characteristic index according to the first stage and the second stage.

/ / 1.64 6.69 16.70 33.86 48.78 / / 0.405 0.599 0.811 0.997 1.105 / / 291.7 281.7 280.5 280.8 280.5 / / 0.54 0.85 1.13 1.49 1.68 / / 6.68 12.72 18.04 23.86 27.64 / / 165 212 222 239 250 / / 185 162 159 156 150 OS 90%OS10%SS 70%OS30%SS 50%OS50%SS 30%OS70%SS 10%OS90%SS SS

/ / 350 374 381 395 584

DTGmax
1e %/min M1
1d %

DT1/2
1c °C Tf
1b °C Ti
1a °C Samples

Table 2 The pyrolysis characteristic parameters for samples at heating rate 10 °C/min.

Tmax
1 °C

f

DTGmean
1g %/min

D1h 10
7

Ti
2a °C

Tf
2b °C

DT1/2
2c °C

M1
2d %

DTGmax
2e %/min

Tmax
2f °C

D2h 10
7

Y. Lin et al. / Energy Conversion and Management 118 (2016) 345–352

Fig. 3. (a) The comprehensive pyrolysis index D1 and D2 at different ratios. (b) Variation of DW versus temperature at different ratios.

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Y. Lin et al. / Energy Conversion and Management 118 (2016) 345–352

Fig. 4. (a) CH4 absorption from SP10 and OS. (b) Carbonyl absorption from SS. (c) CH4 absorption from SS. (d) CO2 absorption from SS. (e) Carboxyl absorption from SS. (f) NH3 absorption from SS.

239.6 kJ/mol. When the a reached 0.6, the Ea of OS was increased sharply. It might attribute to the decomposition of inorganic matter, which required higher energy to start and generated undesirable products. Actually, most of organic matter had finished their decomposition process below 800 °C, so the pyrolysis process should be controlled for energy-saving consideration. Besides, it was worthy to mention that the apparent activation energy of OS was decreased due to addition of SS, which meant the less energy would be inputted to the pyrolysis process. Although the minimum

of the apparent activation energy did not occur at SP = 30%, there was still acceptable for the energy saving at SP = 10%. Overall consideration, the best SS proportion in the blend could be selected as 10%. 4. Conclusions Blending with SS, the pyrolysis performance of OS was evidently improved. When the proportion of SS reached 10%, the

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Y. Lin et al. / Energy Conversion and Management 118 (2016) 345–352 Table 3 Results of E (kJ/mol) from KAS and Starink (St) method.

a

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Average

Method

KAS

St

KAS

St

KAS

St

KAS

St

KAS

St

KAS

St

KAS

St

KAS

St

OS 90%OS10%SS 70%OS30%SS 50%OS50%SS 30%OS70%SS 10%OS90%SS SS

237.7 185.5 168.6 184.7 183.3 203.1 185.9

238.0 185.9 169.0 185.0 183.5 203.3 186.0

258.4 224.8 181.4 197.3 203.5 215.9 199.9

258.6 225.2 181.8 197.6 203.7 216.1 200.1

266.3 241.2 221.6 200.4 214.9 236.1 223.4

266.5 241.5 222.0 200.8 215.1 236.2 223.5

272.9 251.8 247.4 236.5 231.9 254.4 241.3

273.1 252.1 247.6 236.7 232.1 254.4 241.4

282.7 263.2 261.8 275.0 261.0 280.7 265.6

282.9 263.4 262.0 275.2 261.2 280.8 265.4

310.6 282.0 274.4 288.0 277.7 310.5 322.0

310.7 282.2 274.7 288.2 277.9 310.5 322.0

367.4 324.9 316.1 318.9 303.5 336.4 361.1

367.4 325.0 316.2 319.0 303.6 336.4 361.0

285.1 253.3 238.8 243.0 239.4 262.4 257.0

285.3 253.6 239.0 243.2 239.6 262.5 257.1

Acknowledgements This work was supported by the National Basic Research Program of China (973 Program) (2013CB228100); National Natural Science Foundation of China (51406058); the Guangdong Natural Science Foundation (2015A030313227); the Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes, South China University of Technology (KLB10004); the Fundamental Research Funds for the Central Universities (2015ZZ015).

References

Fig. 5. (a) The relation between E and a for OS, SS by Starink method. (b) The relation between E and SP obtained by KAS and Starink method.

Ea average was declined about 11.11% from 285.3 kJ/mol to 253.6 kJ/mol (Starink), compared to the individual OS. And according to the tendency of pyrolysis comprehensive index D, the OS pyrolysis was processed more completely under this condition. Besides, the weight loss peak became stronger and Stronger emission of methane was observed in the SP10 pyrolysis process. It might suggest that more hydrocarbons were released during the co-pyrolysis process. So the best SS proportion in the blend could be selected as 10%. The results afford a theoretical groundwork for the co-pyrolysis technology of SS and OS and the development of their thermochemical conversion systems.

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