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The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas
Journal of the Energy Institute xxx (2015) 1e9
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The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas Zhifeng Hu a, b, Xiaoqian Ma a, b, *, Longjun Li a, c a
School of Electric Power, South China University of Technology, Guangzhou 510640, China Guangdong Province Key Laboratory of Efficient and Clean Energy Utilization, South China University of Technology, Guangzhou 510640, China c WTO/TBT Notification, Consultation & Research Center of Guangdong Province, Guangzhou 510000, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 December 2014 Received in revised form 2 February 2015 Accepted 2 February 2015 Available online xxx
The co-pyrolysis of oil shale (a fine-grained and kerogen-rich sedimentary rock) and Chlorella vulgaris (one of microalgae) was carried out in a quartz tube reactor under different temperatures and blending ratios. The product fractional yields, gaseous products and different blending ratios were analyzed in order to obtain the optimal pyrolysis conditions for producing syngas (CO þ H2) from oil shale and the synergistic effect of co-pyrolysis. The results indicated that temperature obviously affected the product fractional yields and syngas production from oil shale. High temperature was beneficial to the CO and H2 emission. And 800 C was the optimal temperature for oil shale to produce syngas. Under co-pyrolysis, the liquid and gas production from oil shale was promoted by C. vulgaris, but the liquid and gas production from C. vulgaris was inhibited by oil shale. Furthermore, the inhibition of oil shale was stronger than the promotion of C. vulgaris. Meanwhile, blending with oil shale could reduce the total HVe,s and postpone the pyrolysis. © 2015 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Microalgae Oil shale Co-pyrolysis Synergistic effect Syngas
1. Introduction The conventional fossil fuels are still the most widely used energy sources in recent decades. The consumption of fossil fuel is very large. However, they are non-renewable resources. Moreover, the usages of conventional fossil fuels remarkably cause serious environmental problems [1,2]. Therefore, in order to solve the energy crisis and environmental problems [3], it is necessary and stringent to develop a renewable energy to replace the conventional fossil fuels [4]. Microalgae, as an environmental-friendly and renewable energy source, has been widely considered to be the most potential biomass to replace the conventional fossil fuels [5] for many advantages, such as: (1) they have a high biological CO2 fixation so they can absorb a large amount of CO2 during its growth [6]; (2) they can provide a stable energy supply because they have a high photosynthesis efficiency and biomass production [1,7]; (3) they have a high growth rate because they can increase doubly within 24 h [5,8]; (4) they can be cultivated on waste water, aquatic medium and non-arable land without threatening traditional agricultural resources [9]. Thanks to the energy production and the biological CO2 fixation, more and more economic and environmental benefits can be gained through the utilization and development of microalgae. Therefore, it is very valuable and important to study the energy utilization of microalgae. Oil shale, which can be converted into energy by thermal processes [10,11], is a fine-grained sedimentary rock and contains a large amount of kerogen (10e65 wt. %) and mineral porous matrix (consists of carbonates, clay and quartz) [12]. It has been estimated that more than 2.7 104 billion tons of oil may exist in the known worldwide oil shale resources [10,13]. And the oil shale resource is around 30 times as much as the crude oil reserve [14]. So oil shale has been considered to be a valuable potential source of energy [15]. There are more and more researchers focusing on the effective and economic utilization of oil shale [11,16,17]. Therefore, it is significant to study the energy utilization and development of oil shale. Among many conversion processes, pyrolysis is an efficient energy conversion technology, converts biomass and oil shale resources into solid, liquid and gaseous products [15,18,19]. Presently, many researchers have focused on pyrolysis technology for energy conversion. Rice
* Corresponding author. School of Electric Power, South China University of Technology, Guangzhou 510640, China. Tel.: þ86 20 87110232; fax: þ86 20 87110613. E-mail addresses: [email protected] (Z. Hu), [email protected] (X. Ma). http://dx.doi.org/10.1016/j.joei.2015.02.009 1743-9671/© 2015 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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husk [20] and marine macroalgae [21] were pyrolyzed to study the effects of temperature on the production yields and the characteristics of the bio-oil products. And the studies of lignocellulosic biomass [22] and Chlorella [23] focused on the catalysts effects on the production yields. Furthermore, there are some studies discussed the effects of co-pyrolysis on oil shale and forest biomass residues [18], microalgae and coal [24]. Besides, oil shale represents mineral porous matrix while microalgae, which is different from oil shale, represents organic matter. Furthermore, coal is different from biomass, just like the relationship between oil shale and microalgae. And synergistic behaviors were reported in the co-pyrolysis between coal and biomass [25,26]. Similarly, we consider that there may be synergistic behaviors in the co-pyrolysis of microalgae and oil shale. However, there are few discussions on the syngas (CO þ H2) production and synergistic effect on copyrolysis of microalgae and oil shale. Therefore, the study on the optimal condition for syngas production and the synergistic effect of copyrolysis could make a significant contribution to the co-pyrolysis of microalgae and oil shale. This paper investigated the pyrolysis of oil shale and co-pyrolysis of Chlorella vulgaris and oil shale under different temperature and blending ratios. The product fractional yields, the CO and H2 trends and syngas production were analyzed in order to obtain the optimal conditions and the synergistic effect of co-pyrolysis using and evaluation method based on the higher heating value and energy consumption. 2. Materials and methods 2.1. Materials C. vulgaris was provided by Jiangmen Yuejian Biotechnologies Co., Ltd.. The C. vulgaris was cultivated in fresh water. Oil shale was obtained from Guangdong Maoming oil shale mining area in China. Pretreatments of samples were carried out before the experiments. Firstly, the samples were dried in an oven at 105 C for 24 h, and then finely pulverized by a pulverizer. Finally, they were sieved with a mesh size of less than 200 mm and stored in a desiccator. The proximate and elemental analysis of C. vulgaris and oil shale were carried out using GB212-91 standard and ASTM D5373 standard methods which were shown in Table 1. According to different experimental conditions, the blending ratios (weight basis) of C. vulgaris and oil shale were 10:0, 9:1, 7:3, 5:5 and 0:10, respectively. For consistent comparison, the amount of sample used for each experiment was 0.200 g. 2.2. Experimental procedure and methods The schematic diagram of pyrolysis experimental system is displayed in Fig. 1. In this study, the co-pyrolysis of C. vulgaris and oil shale was carried out in the quartz tube reactor with an internal diameter of 0.06 m and the length of 1.30 m. The quartz tube reactor was controlled by the tube furnace with a temperature controller. The tube furnace was heated from the room temperature to a desired temperature (500 C, 600 C, 700 C, 800 C and 900 C). In order to maintain anoxic atmosphere in the reaction zone, nitrogen was ventilated as inert carrier gas at a flow rate of 0.08 m3/h for 20 min before and during the experiment. The crucible with sample was placed into the quartz tube reactor for 900 s after the tube furnace was heated to the desired temperature. At the same time, a flue gas analyzer (Testo 350-S) was operated to analyze and record the gaseous products in each experiment. The gaseous product emissions were reported as ppmv (part-per million by volume). The Testo 350-S flue gas analyzer, which has an accuracy of 10 ppmv and a resolution of 1 ppmv, was tested regularly by Testo AG (the manufacturer of Testo 350-S). The evaluation method based on higher heating value and energy consumption was proposed in the previous paper [27]. In order to obtain the optimal conditions and co-pyrolysis characteristic of C. vulgaris and oil shale, this paper will continue studying the co-pyrolysis of C. vulgaris and oil shale based on the evaluation method. 3. Results and discussion 3.1. The effect of temperature on the product fractional yields of oil shale The effect of different pyrolysis temperatures on the product fractional yields of oil shale is shown in Fig. 2. Fig. 2 reveals that the yield of solid residue decreased gradually from 92.00% to 69.15% as temperature increased from 500 C to 900 C. When the pyrolysis temperature increased from 500 C to 800 C, there was a significant increase on the liquid and gas production. However, when the pyrolysis temperature increased from 800 C to 900 C, the increasing amplitude (only 3%) of liquid and gas production was not obvious. Overall, higher temperature usually enhanced the production of liquid and gas because of the gasification reactions and the secondary tar reactions [8]. This is because when the pyrolysis temperature increases, the sample gained more energy, and then the Table 1 The proximate analysis and elemental analysis of Chlorella vulgaris and oil shale. Proximate analysisa (wt, %)
Moisture Volatile Ash Fixed Carbon a b c
Elemental analysisb (wt, %) Chlorella vulgaris
oil shale
6.54 51.75 9.61 32.10
3.63 38.52 52.47 5.38
C H O4c N S
Chlorella vulgaris
oil shale
53.32 7.14 27.87 10.04 1.63
37.34 4.90 51.99 1.47 4.30
On wet basis. On dry ash free basis. Calculated by difference, O (%) ¼ 100 C H N S.
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Fig. 1. The schematic diagram of pyrolysis experimental system: (1) nitrogen bottle; (2) pressure reducing valve; (3) float flowmeter; (4) quartz tube reactor; (5) tube furnace; (6) thermocouple; (7) crucible and samples; (8) the first condenser; (9) the second condenser; (10) acquisition sensor; (11) the flue gas analyzer; (12) the data acquisition system; (13) gas collecting bottle; (14) the second liquid collecting bottle; (15) the first liquid collecting bottle; (16) the temperature controller.
pyrolysis reactions carry out more easily and intensely. Then more kerogen organic matters are converted into small molecules, producing more liquid and gas. Moreover, the gasification and secondary tar reactions of solid residue become significant at a higher temperature, forming more liquid and gas but decreasing solid residue [21,28]. Therefore, there is an increase on the yields of liquid and gas with increasing temperature, which is similar to those reported in the literature [21,28,29]. This study has shown that temperature has a significant impact on the yields of the pyrolysis products. In the previous paper [27], the effect of temperature on the product fractional yields of C. vulgaris was studied. Although C. vulgaris was different from oil shale, the effect of temperature was similar to a certain extent. The previous paper indicated that the higher the pyrolysis temperature was, the higher the liquid and gas yield was. Among the several temperatures, 900 C was the best temperature to obtain the minimum solid residue yield. 3.2. The effect of temperature on the syngas production from oil shale Under different pyrolysis temperatures, the CO emissions, H2 emissions and HVe,s are shown in Fig. 3(a)e(c) respectively. The total CO, H2 emissions and HVe,s of oil shale under different temperatures are shown in Table 2. As shown in Fig. 3(a), the emission of CO increased rapidly at first and then decreased as the temperature increased from 500 C to 900 C. As shown in Table 2, since the temperature increased from 500 C to 600 C, 600 C to 700 C and 700 C to 800 C, the total CO emissions of oil shale increased by 52.20%, 134.75% and 226.30%, respectively. However, when the temperature increased from 800 C to 900 C, the total CO emissions of oil shale decreased by 28.85%, which was lower than that of 700 C. Thus it can be concluded that temperature has a significant impact on the CO emission. Moreover, high temperature is beneficial to the CO emission and the CO emission of 800 C is the best, followed by 700 C. As shown in Fig. 3(b), the emission of H2 increased rapidly since the temperature increased from 500 C to 900 C. As shown in Table 2, when the temperature increased, the total H2 emissions of 600 C, 700 C, 800 Cand 900 C was 20.01 times, 24.86 times, 30.07 times and 35.61 times as much as that of 500 C, respectively. Therefore, temperature has a transcendent effect on the H2 emission. Moreover, high temperature is beneficial to the H2 emission and the H2 emission of 900 C is the best, followed by 800 C. As mentioned above, the trend of CO emission was different from that of H2. This result can be explained by the following reasons. Firstly, primary energy conversion factor is different, which will express different effect on the emission of CO and H2. Secondly, this is may be because when the temperature increases from 500 C to 800 C, kerogen organic matters in the oil shale decompose into bio-oil and small molecules such as CO2, CO, CH4 and H2. Moreover, the following endothermic reactions [1,27,30] play a major role: CH4 þ CO2 42CO þ 2H2 ; DH298K ¼ 247:9 kJ=mol
(1)
Fig. 2. Product fractional yields of oil shale under different pyrolysis temperatures.
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Fig. 3. The effect of temperature (a) the CO emission (b) the H2 emission and (c) HVe,s.
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Table 2 The total CO, H2 emissions and HVe,s of oil shale under different temperatures. Temperature 500 600 700 800 900
C C C C C
CO (ppmv)
H2 (ppmv)
HVe,s (ppmv kJ)/(L W h)
43,406 66,064 101,896 141,634 100,768
2898 58,016 72,050 87,130 103,187
45.5466 85.8560 97.1347 97.4206 70.1186
CðsÞ þ CO2 42CO; DH298K ¼ 173 kJ=mol
(2)
CðsÞ þ H2 O4CO þ H2 ; DH298K ¼ 173 kJ=mol
(3)
CH4 þ H2 O4CO þ 3H2 ; DH298 K ¼ 206:1 kJ=mol
(4)
So at this stage the CO and H2 emission increase rapidly with increasing temperature. When the temperature continues to increase to 900 C, the energy is so high that the pyrolysis reactions develop strongly. Meanwhile, some CO2 release rapidly, so there is no enough residence time for the reactions of Eqs. (1) and (2), resulting in the decrease of CO emission at 900 C. However, in this situation some H2 are formed by deep cracking reactions and direct dehydrogenation of char [31,32]. Hence, there is more H2 emission at 900 C, which is different from that of CO. Fig. 3(c) reveals that HVe,s increased rapidly since the pyrolysis temperature increased from 500 C to 800 C, and then decreased to lower than that of 600 C when the pyrolysis temperature continued to increase to 900 C. As shown in Table 2, compared with 500 C, the total HVe,s at 600 C, 700 C, 800 C and 900 C had increased by 88.50%, 113.26%, 113.89% and 53.95%, respectively. This phenomenon can be explained by three reasons. The first one is the difference between the CO and H2 emission trend. The second one is the difference of the higher heating value between CO and H2. The third one is that the energy consumption is greater at a higher pyrolysis temperature. Therefore, a conclusion can be indicated that the total HVe,s increased firstly and then decreased sharply as the pyrolysis temperature increased from 500 C to 900 C. From this analysis, there is a significant impact on the syngas production under different pyrolysis temperatures. Moreover, 800 C is the best pyrolysis temperature for oil shale to produce syngas. In the previous paper [27], the effect of temperature on the syngas production from C. vulgaris was studied. The previous paper indicated that the highest emission of CO and H2 were achieved under the pyrolysis temperature of 800 C and 900 C, respectively. Furthermore, there was a significant impact on the syngas production under different pyrolysis temperatures. In addition, 800 C was the optimal pyrolysis temperature for C. vulgaris to produce syngas, which, to a certain extent, was similar to oil shale. 3.3. The effect of different blending ratios on the product fractional yields and syngas production The effect of different blending ratios on the product fractional yields of C. vulgaris and oil shale is shown in Fig. 4. Under different blending ratios of C. vulgaris and oil shale, the CO emissions, H2 emissions and HVe,s is shown in Fig. 5(a), (b) and (c), respectively. The total CO, H2 emissions and HVe,s of C. vulgaris and oil shale under different blending ratios are shown in Table 3. As shown in Fig. 4, the solid residue yield of 10:0, 9:1, 7:3, 5:5 and 0:10 was 10.84%, 22.55%, 32.85%, 41.50% and 70.10%, respectively. This is mainly because the volatile and fixed carbon of C. vulgaris is high (51.75% and 32.10%, wt, respectively), but the ash is quite low (9.61%, wt), resulting in a low solid residue yield of C. vulgaris. However, the volatile and fixed carbon of oil shale is only 38.52% and 5.38% (wt), respectively, and the ash is very high (52.47%, wt), resulting in a very high solid residue yield. Therefore, the solid residue yield will increase obviously with increasing the percentages of oil shale. As shown in Fig. 5(a), after blending with oil shale, the time of the max CO emission was postponed. As shown in Table 3, compared with the pure C. vulgaris, the total CO emissions of 9:1, 7:3, 5:5 and 0:10 had decreased by 60.20%, 74.78%, 75.05% and 75.33%, respectively. So it can be concluded that blending with oil shale will markedly reduce the CO emission and postpone the pyrolysis. Moreover, blending with higher percentage of oil shale will produce less CO emission.
Fig. 4. Product fractional yields of C. vulgaris and oil shale under different blending ratios at 800 C.
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Fig. 5. The effect of blending ratio at 800 C (a) the CO emission (b) the H2 emission and (c) HVe,s.
As shown in Fig. 5(b), after blending with oil shale, the time of the max H2 emission was postponed too. As shown in Table 3, compared with the pure C. vulgaris, the total H2 emissions of 9:1, 7:3, 5:5 and 0:10 had decreased by 61.86%, 66.18%, 69.71% and 75.00%, respectively. Therefore, blending with oil shale will markedly reduce the H2 emission and postpone the pyrolysis. And less H2 emission will be produced as blended with higher percentage of oil shale. Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Table 3 The total CO, H2 emissions and HVe,s of C. vulgaris and oil shale under different blending ratios at 800 C. Blending ratios
CO (ppmv)
H2 (ppmv)
HVe,s (ppmv kJ)/(L W h)
10:0 9:1 7:3 5:5 0:10
574,209 228,551 144,795 143278 141634
348,560 132,928 117,874 105,580 87130
398.6850 156.4338 112.1848 105.8949 97.4206
As shown in Fig. 5(c), after blending with oil shale, the time of the max HVe,s was postponed. This was similar to that of CO and H2. As shown in Table 3, compared with the pure C. vulgaris, the total HVe,s of 9:1, 7:3, 5:5 and 0:10 had decreased by 60.76%, 71.86%, 73.44% and 75.56%, respectively. So it can be concluded that blending with oil shale will markedly reduce HVe,s and postpone the pyrolysis. Moreover, blending with higher percentage of oil shale will produce less HVe,s. When the percentage of oil shale was increased from 0% to 10%, 10% to 30%, 30% to 50% and 50% to 100%, the total HVe,s had decreased by 60.76%, 28.29%, 5.61% and 8.00%, respectively. Thus, it can be seen that there were three stages in the decreasing process. At first, the total HVe,s decreased rapidly, and then decreased gradually, at last decreased slowly. From this section, there is a significant impact on the syngas production after blending with oil shale. 3.4. The synergistic effect of co-pyrolysis of Chlorella vulgaris and oil shale As explained in the Section 3.3, after blending with different percentages of oil shale, the changes of the product fractional yield and syngas production did not present a linear change. Therefore, a synergistic effect was shown in the co-pyrolysis of C. vulgaris and oil shale. The synergistic effect of co-pyrolysis on the liquid and gas yield at 800 C is shown in Table 4. The synergistic effect of co-pyrolysis on the total HVe,s at 800 C is shown in Table 5. Liquid and gas yield by calculation means the liquid and gas yield of the percentage of C. vulgaris plus the liquid and gas yield of the percentage of oil shale. Liquid and gas yield of C. vulgaris means the liquid and gas yield of the percentage of C. vulgaris. And the meanings of HVe,s by calculation and HVe,s of C. vulgaris are the same as that of Liquid and gas yield by calculation and Liquid and gas yield of C. vulgaris, respectively. As shown in Table 4, the liquid and gas yield of C. vulgaris of 9:1 was 80.25%, which was higher than the liquid and gas yield of 9:1 (77.45%). Compared with the pure C. vulgaris, the liquid and gas yield of 9:1 had decreased by 13.14%, but in the meantime, the C. vulgaris had only decreased by 10%. Therefore, after blending with oil shale, the liquid and gas production from C. vulgaris was inhibited by oil shale. Moreover, the liquid and gas yield of 9:1, 7:3 and 5:5 was 77.45%, 67.15% and 58.50%, but the liquid and gas yield of C. vulgaris of 9:1, 7:3 and 5:5 was 80.25%, 62.41% and 44.58%, respectively. With decreasing the C. vulgaris (less than 70%), the liquid and gas yield of 7:3 and 5:5 was higher than the liquid and gas yield of C. vulgaris of 7:3 and 5:5, respectively. Therefore, the liquid and gas decreasing production from C. vulgaris caused by the inhibition of oil shale was weakening because of the decrease of C. vulgaris. Furthermore, compared with the pure C. vulgaris, the liquid and gas yield of 9:1, 7:3 and 5:5 had decreased by 13.14%, 24.69% and 34.39%, respectively. However, the decrease of C. vulgaris was 10%, 30% and 50%, respectively. With increasing the percentage of oil shale, the decrease of liquid and gas production was quite lower than the decrease of C. vulgaris. Hence, it can be deduced that the liquid and gas production from oil shale was promoted by C. vulgaris. Moreover, the promotion of C. vulgaris on the liquid and gas production from oil shale was enhanced because of the increase of oil shale. The synergistic effect between C. vulgaris and oil shale can be explained that the solid residue of pyrolysis C. vulgaris is a quite good catalyst [8], resulting in the promotion on the liquid and gas production from oil shale. On the other side, the ash of oil shale is very high (52.47%, wt). So the ash particles of oil shale block out the apertures of C. vulgaris, resulting in the inhibition on the liquid and gas production from C. vulgaris. Compared with the liquid and gas yield by calculation, the liquid and gas yield of 9:1, 7:3 and 5:5 had decreased by 6.95%, 5.93% and 1.73%, respectively. So it can be seen that the differences between experiments and calculations became smaller since increased the percentage of oil shale, and the liquid and gas yields by experiments were lower than that of calculations. Hence, a conclusion can be made that the inhibition of oil shale is stronger than the promotion of C. vulgaris. As shown in Table 5, compared with the total HVe,s by calculation, the total HVe,s of 9:1, 7:3 and 5:5 had decreased by 57.56%, 63.61% and 57.31%, respectively. And the total HVe,s of C. vulgaris of 9:1 was 358.8165 (ppmv.kJ)/(L.W.h), which was much higher than the total HVe,s of 9:1 (156.4338 (ppmv.kJ)/(L.W.h)). Compared with the pure C. vulgaris, the total HVe,s of 9:1 had decreased by 60.76%, but in the meantime, the C. vulgaris had only decreased by 10%. Therefore, after blending with oil shale, the total HVe,s of C. vulgaris was obviously inhibited by oil shale. Furthermore, compared with the pure C. vulgaris, the total HVe,s of 9:1, 7:3 and 5:5 had decreased by 60.76%, 71.86% and 73.44%, respectively. However, the decrease of C. vulgaris was 10%, 30% and 50%, respectively. With increasing the percentage of oil shale from 10% to 50%, the decrease of total HVe,s was much higher than the decrease of C. vulgaris. This phenomenon can be explained that the HVe,s of oil
Table 4 The synergistic effect of co-pyrolysis on the bio-fuel yield at 800 C. Blending ratios
Bio-fuel yield (%)
Bio-fuel yield by calculation (%)
Bio-fuel yield of C. vulgaris (%)
10:0 9:1 7:3 5:5 0:10
89.16 77.45 67.15 58.50 29.90
89.16 83.24 71.38 59.53 29.90
89.16 80.25 62.41 44.58 0
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Table 5 The synergistic effect of co-pyrolysis on the total HVe,s at 800 C. Blending ratios
HVe,s (ppmv kJ)/(L W h)
HVe,s by calculation (ppmv kJ)/(L W h)
HVe,s of C. vulgaris (ppmv kJ)/(L W h)
10:0 9:1 7:3 5:5 0:10
398.6850 156.4338 112.1848 105.8949 97.4206
398.6850 368.5586 308.3057 248.0528 97.4206
398.6850 358.8165 279.0795 199.3425 0
shale was so low that it could not offset the decrease of HVe,s caused by C. vulgaris reduction. And the inhibition of oil shale on the HVe,s of C. vulgaris was strong. However, with increasing the percentage of oil shale from 10% to 50%, the decreasing extent of total HVe,s was quite lower than the decreasing extent of C. vulgaris. This is because the decreasing HVe,s of C. vulgaris caused by the inhibition of oil shale was weakening because of the decrease of C. vulgaris. From this analysis, a conclusion can be made that the total HVe,s of C. vulgaris was inhibited by oil shale. 4. Conclusions These results show that pyrolysis temperature significantly affected the product fractional yields of oil shale. Higher pyrolysis temperature usually enhanced the production of liquid and gas. Moreover, higher temperature also enhanced the gasification and secondary tar reactions of solid residue. Temperature also had a significant impact on the CO, H2 emission and syngas production. High temperature was beneficial to the CO and H2 emission. 800 C and 900 C was the best pyrolysis temperature for CO and H2 emission, respectively. Moreover, after considered the evaluation method, 800 C was the best pyrolysis temperature for oil shale to produce syngas. Under co-pyrolysis, the liquid and gas production from oil shale was promoted by C. vulgaris, but the liquid and gas production from C. vulgaris was inhibited by oil shale. Moreover, the inhibition of oil shale was stronger than the promotion of C. vulgaris. Meanwhile, after blended C. vulgaris with oil shale, the decrease of total HVe,s was much higher than the decrease of C. vulgaris. Moreover, blending with oil shale markedly reduced the total HVe,s of C. vulgaris and postpone the pyrolysis. Furthermore, the inhibition of oil shale on the HVe,s of C. vulgaris was strong. Acknowledgments The authors are grateful to National Natural Science Foundation of China (51476060), National Basic Research Program of China (973 Program) (2011CB201500, 2013CB228101) and Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes (KLB10004) for the financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
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The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas Zhifeng Hu a, b, Xiaoqian Ma a, b, *, Longjun Li a, c a
School of Electric Power, South China University of Technology, Guangzhou 510640, China Guangdong Province Key Laboratory of Efficient and Clean Energy Utilization, South China University of Technology, Guangzhou 510640, China c WTO/TBT Notification, Consultation & Research Center of Guangdong Province, Guangzhou 510000, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 December 2014 Received in revised form 2 February 2015 Accepted 2 February 2015 Available online xxx
The co-pyrolysis of oil shale (a fine-grained and kerogen-rich sedimentary rock) and Chlorella vulgaris (one of microalgae) was carried out in a quartz tube reactor under different temperatures and blending ratios. The product fractional yields, gaseous products and different blending ratios were analyzed in order to obtain the optimal pyrolysis conditions for producing syngas (CO þ H2) from oil shale and the synergistic effect of co-pyrolysis. The results indicated that temperature obviously affected the product fractional yields and syngas production from oil shale. High temperature was beneficial to the CO and H2 emission. And 800 C was the optimal temperature for oil shale to produce syngas. Under co-pyrolysis, the liquid and gas production from oil shale was promoted by C. vulgaris, but the liquid and gas production from C. vulgaris was inhibited by oil shale. Furthermore, the inhibition of oil shale was stronger than the promotion of C. vulgaris. Meanwhile, blending with oil shale could reduce the total HVe,s and postpone the pyrolysis. © 2015 Energy Institute. Published by Elsevier Ltd. All rights reserved.
Keywords: Microalgae Oil shale Co-pyrolysis Synergistic effect Syngas
1. Introduction The conventional fossil fuels are still the most widely used energy sources in recent decades. The consumption of fossil fuel is very large. However, they are non-renewable resources. Moreover, the usages of conventional fossil fuels remarkably cause serious environmental problems [1,2]. Therefore, in order to solve the energy crisis and environmental problems [3], it is necessary and stringent to develop a renewable energy to replace the conventional fossil fuels [4]. Microalgae, as an environmental-friendly and renewable energy source, has been widely considered to be the most potential biomass to replace the conventional fossil fuels [5] for many advantages, such as: (1) they have a high biological CO2 fixation so they can absorb a large amount of CO2 during its growth [6]; (2) they can provide a stable energy supply because they have a high photosynthesis efficiency and biomass production [1,7]; (3) they have a high growth rate because they can increase doubly within 24 h [5,8]; (4) they can be cultivated on waste water, aquatic medium and non-arable land without threatening traditional agricultural resources [9]. Thanks to the energy production and the biological CO2 fixation, more and more economic and environmental benefits can be gained through the utilization and development of microalgae. Therefore, it is very valuable and important to study the energy utilization of microalgae. Oil shale, which can be converted into energy by thermal processes [10,11], is a fine-grained sedimentary rock and contains a large amount of kerogen (10e65 wt. %) and mineral porous matrix (consists of carbonates, clay and quartz) [12]. It has been estimated that more than 2.7 104 billion tons of oil may exist in the known worldwide oil shale resources [10,13]. And the oil shale resource is around 30 times as much as the crude oil reserve [14]. So oil shale has been considered to be a valuable potential source of energy [15]. There are more and more researchers focusing on the effective and economic utilization of oil shale [11,16,17]. Therefore, it is significant to study the energy utilization and development of oil shale. Among many conversion processes, pyrolysis is an efficient energy conversion technology, converts biomass and oil shale resources into solid, liquid and gaseous products [15,18,19]. Presently, many researchers have focused on pyrolysis technology for energy conversion. Rice
* Corresponding author. School of Electric Power, South China University of Technology, Guangzhou 510640, China. Tel.: þ86 20 87110232; fax: þ86 20 87110613. E-mail addresses: [email protected] (Z. Hu), [email protected] (X. Ma). http://dx.doi.org/10.1016/j.joei.2015.02.009 1743-9671/© 2015 Energy Institute. Published by Elsevier Ltd. All rights reserved.
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husk [20] and marine macroalgae [21] were pyrolyzed to study the effects of temperature on the production yields and the characteristics of the bio-oil products. And the studies of lignocellulosic biomass [22] and Chlorella [23] focused on the catalysts effects on the production yields. Furthermore, there are some studies discussed the effects of co-pyrolysis on oil shale and forest biomass residues [18], microalgae and coal [24]. Besides, oil shale represents mineral porous matrix while microalgae, which is different from oil shale, represents organic matter. Furthermore, coal is different from biomass, just like the relationship between oil shale and microalgae. And synergistic behaviors were reported in the co-pyrolysis between coal and biomass [25,26]. Similarly, we consider that there may be synergistic behaviors in the co-pyrolysis of microalgae and oil shale. However, there are few discussions on the syngas (CO þ H2) production and synergistic effect on copyrolysis of microalgae and oil shale. Therefore, the study on the optimal condition for syngas production and the synergistic effect of copyrolysis could make a significant contribution to the co-pyrolysis of microalgae and oil shale. This paper investigated the pyrolysis of oil shale and co-pyrolysis of Chlorella vulgaris and oil shale under different temperature and blending ratios. The product fractional yields, the CO and H2 trends and syngas production were analyzed in order to obtain the optimal conditions and the synergistic effect of co-pyrolysis using and evaluation method based on the higher heating value and energy consumption. 2. Materials and methods 2.1. Materials C. vulgaris was provided by Jiangmen Yuejian Biotechnologies Co., Ltd.. The C. vulgaris was cultivated in fresh water. Oil shale was obtained from Guangdong Maoming oil shale mining area in China. Pretreatments of samples were carried out before the experiments. Firstly, the samples were dried in an oven at 105 C for 24 h, and then finely pulverized by a pulverizer. Finally, they were sieved with a mesh size of less than 200 mm and stored in a desiccator. The proximate and elemental analysis of C. vulgaris and oil shale were carried out using GB212-91 standard and ASTM D5373 standard methods which were shown in Table 1. According to different experimental conditions, the blending ratios (weight basis) of C. vulgaris and oil shale were 10:0, 9:1, 7:3, 5:5 and 0:10, respectively. For consistent comparison, the amount of sample used for each experiment was 0.200 g. 2.2. Experimental procedure and methods The schematic diagram of pyrolysis experimental system is displayed in Fig. 1. In this study, the co-pyrolysis of C. vulgaris and oil shale was carried out in the quartz tube reactor with an internal diameter of 0.06 m and the length of 1.30 m. The quartz tube reactor was controlled by the tube furnace with a temperature controller. The tube furnace was heated from the room temperature to a desired temperature (500 C, 600 C, 700 C, 800 C and 900 C). In order to maintain anoxic atmosphere in the reaction zone, nitrogen was ventilated as inert carrier gas at a flow rate of 0.08 m3/h for 20 min before and during the experiment. The crucible with sample was placed into the quartz tube reactor for 900 s after the tube furnace was heated to the desired temperature. At the same time, a flue gas analyzer (Testo 350-S) was operated to analyze and record the gaseous products in each experiment. The gaseous product emissions were reported as ppmv (part-per million by volume). The Testo 350-S flue gas analyzer, which has an accuracy of 10 ppmv and a resolution of 1 ppmv, was tested regularly by Testo AG (the manufacturer of Testo 350-S). The evaluation method based on higher heating value and energy consumption was proposed in the previous paper [27]. In order to obtain the optimal conditions and co-pyrolysis characteristic of C. vulgaris and oil shale, this paper will continue studying the co-pyrolysis of C. vulgaris and oil shale based on the evaluation method. 3. Results and discussion 3.1. The effect of temperature on the product fractional yields of oil shale The effect of different pyrolysis temperatures on the product fractional yields of oil shale is shown in Fig. 2. Fig. 2 reveals that the yield of solid residue decreased gradually from 92.00% to 69.15% as temperature increased from 500 C to 900 C. When the pyrolysis temperature increased from 500 C to 800 C, there was a significant increase on the liquid and gas production. However, when the pyrolysis temperature increased from 800 C to 900 C, the increasing amplitude (only 3%) of liquid and gas production was not obvious. Overall, higher temperature usually enhanced the production of liquid and gas because of the gasification reactions and the secondary tar reactions [8]. This is because when the pyrolysis temperature increases, the sample gained more energy, and then the Table 1 The proximate analysis and elemental analysis of Chlorella vulgaris and oil shale. Proximate analysisa (wt, %)
Moisture Volatile Ash Fixed Carbon a b c
Elemental analysisb (wt, %) Chlorella vulgaris
oil shale
6.54 51.75 9.61 32.10
3.63 38.52 52.47 5.38
C H O4c N S
Chlorella vulgaris
oil shale
53.32 7.14 27.87 10.04 1.63
37.34 4.90 51.99 1.47 4.30
On wet basis. On dry ash free basis. Calculated by difference, O (%) ¼ 100 C H N S.
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Fig. 1. The schematic diagram of pyrolysis experimental system: (1) nitrogen bottle; (2) pressure reducing valve; (3) float flowmeter; (4) quartz tube reactor; (5) tube furnace; (6) thermocouple; (7) crucible and samples; (8) the first condenser; (9) the second condenser; (10) acquisition sensor; (11) the flue gas analyzer; (12) the data acquisition system; (13) gas collecting bottle; (14) the second liquid collecting bottle; (15) the first liquid collecting bottle; (16) the temperature controller.
pyrolysis reactions carry out more easily and intensely. Then more kerogen organic matters are converted into small molecules, producing more liquid and gas. Moreover, the gasification and secondary tar reactions of solid residue become significant at a higher temperature, forming more liquid and gas but decreasing solid residue [21,28]. Therefore, there is an increase on the yields of liquid and gas with increasing temperature, which is similar to those reported in the literature [21,28,29]. This study has shown that temperature has a significant impact on the yields of the pyrolysis products. In the previous paper [27], the effect of temperature on the product fractional yields of C. vulgaris was studied. Although C. vulgaris was different from oil shale, the effect of temperature was similar to a certain extent. The previous paper indicated that the higher the pyrolysis temperature was, the higher the liquid and gas yield was. Among the several temperatures, 900 C was the best temperature to obtain the minimum solid residue yield. 3.2. The effect of temperature on the syngas production from oil shale Under different pyrolysis temperatures, the CO emissions, H2 emissions and HVe,s are shown in Fig. 3(a)e(c) respectively. The total CO, H2 emissions and HVe,s of oil shale under different temperatures are shown in Table 2. As shown in Fig. 3(a), the emission of CO increased rapidly at first and then decreased as the temperature increased from 500 C to 900 C. As shown in Table 2, since the temperature increased from 500 C to 600 C, 600 C to 700 C and 700 C to 800 C, the total CO emissions of oil shale increased by 52.20%, 134.75% and 226.30%, respectively. However, when the temperature increased from 800 C to 900 C, the total CO emissions of oil shale decreased by 28.85%, which was lower than that of 700 C. Thus it can be concluded that temperature has a significant impact on the CO emission. Moreover, high temperature is beneficial to the CO emission and the CO emission of 800 C is the best, followed by 700 C. As shown in Fig. 3(b), the emission of H2 increased rapidly since the temperature increased from 500 C to 900 C. As shown in Table 2, when the temperature increased, the total H2 emissions of 600 C, 700 C, 800 Cand 900 C was 20.01 times, 24.86 times, 30.07 times and 35.61 times as much as that of 500 C, respectively. Therefore, temperature has a transcendent effect on the H2 emission. Moreover, high temperature is beneficial to the H2 emission and the H2 emission of 900 C is the best, followed by 800 C. As mentioned above, the trend of CO emission was different from that of H2. This result can be explained by the following reasons. Firstly, primary energy conversion factor is different, which will express different effect on the emission of CO and H2. Secondly, this is may be because when the temperature increases from 500 C to 800 C, kerogen organic matters in the oil shale decompose into bio-oil and small molecules such as CO2, CO, CH4 and H2. Moreover, the following endothermic reactions [1,27,30] play a major role: CH4 þ CO2 42CO þ 2H2 ; DH298K ¼ 247:9 kJ=mol
(1)
Fig. 2. Product fractional yields of oil shale under different pyrolysis temperatures.
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Fig. 3. The effect of temperature (a) the CO emission (b) the H2 emission and (c) HVe,s.
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Table 2 The total CO, H2 emissions and HVe,s of oil shale under different temperatures. Temperature 500 600 700 800 900
C C C C C
CO (ppmv)
H2 (ppmv)
HVe,s (ppmv kJ)/(L W h)
43,406 66,064 101,896 141,634 100,768
2898 58,016 72,050 87,130 103,187
45.5466 85.8560 97.1347 97.4206 70.1186
CðsÞ þ CO2 42CO; DH298K ¼ 173 kJ=mol
(2)
CðsÞ þ H2 O4CO þ H2 ; DH298K ¼ 173 kJ=mol
(3)
CH4 þ H2 O4CO þ 3H2 ; DH298 K ¼ 206:1 kJ=mol
(4)
So at this stage the CO and H2 emission increase rapidly with increasing temperature. When the temperature continues to increase to 900 C, the energy is so high that the pyrolysis reactions develop strongly. Meanwhile, some CO2 release rapidly, so there is no enough residence time for the reactions of Eqs. (1) and (2), resulting in the decrease of CO emission at 900 C. However, in this situation some H2 are formed by deep cracking reactions and direct dehydrogenation of char [31,32]. Hence, there is more H2 emission at 900 C, which is different from that of CO. Fig. 3(c) reveals that HVe,s increased rapidly since the pyrolysis temperature increased from 500 C to 800 C, and then decreased to lower than that of 600 C when the pyrolysis temperature continued to increase to 900 C. As shown in Table 2, compared with 500 C, the total HVe,s at 600 C, 700 C, 800 C and 900 C had increased by 88.50%, 113.26%, 113.89% and 53.95%, respectively. This phenomenon can be explained by three reasons. The first one is the difference between the CO and H2 emission trend. The second one is the difference of the higher heating value between CO and H2. The third one is that the energy consumption is greater at a higher pyrolysis temperature. Therefore, a conclusion can be indicated that the total HVe,s increased firstly and then decreased sharply as the pyrolysis temperature increased from 500 C to 900 C. From this analysis, there is a significant impact on the syngas production under different pyrolysis temperatures. Moreover, 800 C is the best pyrolysis temperature for oil shale to produce syngas. In the previous paper [27], the effect of temperature on the syngas production from C. vulgaris was studied. The previous paper indicated that the highest emission of CO and H2 were achieved under the pyrolysis temperature of 800 C and 900 C, respectively. Furthermore, there was a significant impact on the syngas production under different pyrolysis temperatures. In addition, 800 C was the optimal pyrolysis temperature for C. vulgaris to produce syngas, which, to a certain extent, was similar to oil shale. 3.3. The effect of different blending ratios on the product fractional yields and syngas production The effect of different blending ratios on the product fractional yields of C. vulgaris and oil shale is shown in Fig. 4. Under different blending ratios of C. vulgaris and oil shale, the CO emissions, H2 emissions and HVe,s is shown in Fig. 5(a), (b) and (c), respectively. The total CO, H2 emissions and HVe,s of C. vulgaris and oil shale under different blending ratios are shown in Table 3. As shown in Fig. 4, the solid residue yield of 10:0, 9:1, 7:3, 5:5 and 0:10 was 10.84%, 22.55%, 32.85%, 41.50% and 70.10%, respectively. This is mainly because the volatile and fixed carbon of C. vulgaris is high (51.75% and 32.10%, wt, respectively), but the ash is quite low (9.61%, wt), resulting in a low solid residue yield of C. vulgaris. However, the volatile and fixed carbon of oil shale is only 38.52% and 5.38% (wt), respectively, and the ash is very high (52.47%, wt), resulting in a very high solid residue yield. Therefore, the solid residue yield will increase obviously with increasing the percentages of oil shale. As shown in Fig. 5(a), after blending with oil shale, the time of the max CO emission was postponed. As shown in Table 3, compared with the pure C. vulgaris, the total CO emissions of 9:1, 7:3, 5:5 and 0:10 had decreased by 60.20%, 74.78%, 75.05% and 75.33%, respectively. So it can be concluded that blending with oil shale will markedly reduce the CO emission and postpone the pyrolysis. Moreover, blending with higher percentage of oil shale will produce less CO emission.
Fig. 4. Product fractional yields of C. vulgaris and oil shale under different blending ratios at 800 C.
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Fig. 5. The effect of blending ratio at 800 C (a) the CO emission (b) the H2 emission and (c) HVe,s.
As shown in Fig. 5(b), after blending with oil shale, the time of the max H2 emission was postponed too. As shown in Table 3, compared with the pure C. vulgaris, the total H2 emissions of 9:1, 7:3, 5:5 and 0:10 had decreased by 61.86%, 66.18%, 69.71% and 75.00%, respectively. Therefore, blending with oil shale will markedly reduce the H2 emission and postpone the pyrolysis. And less H2 emission will be produced as blended with higher percentage of oil shale. Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Table 3 The total CO, H2 emissions and HVe,s of C. vulgaris and oil shale under different blending ratios at 800 C. Blending ratios
CO (ppmv)
H2 (ppmv)
HVe,s (ppmv kJ)/(L W h)
10:0 9:1 7:3 5:5 0:10
574,209 228,551 144,795 143278 141634
348,560 132,928 117,874 105,580 87130
398.6850 156.4338 112.1848 105.8949 97.4206
As shown in Fig. 5(c), after blending with oil shale, the time of the max HVe,s was postponed. This was similar to that of CO and H2. As shown in Table 3, compared with the pure C. vulgaris, the total HVe,s of 9:1, 7:3, 5:5 and 0:10 had decreased by 60.76%, 71.86%, 73.44% and 75.56%, respectively. So it can be concluded that blending with oil shale will markedly reduce HVe,s and postpone the pyrolysis. Moreover, blending with higher percentage of oil shale will produce less HVe,s. When the percentage of oil shale was increased from 0% to 10%, 10% to 30%, 30% to 50% and 50% to 100%, the total HVe,s had decreased by 60.76%, 28.29%, 5.61% and 8.00%, respectively. Thus, it can be seen that there were three stages in the decreasing process. At first, the total HVe,s decreased rapidly, and then decreased gradually, at last decreased slowly. From this section, there is a significant impact on the syngas production after blending with oil shale. 3.4. The synergistic effect of co-pyrolysis of Chlorella vulgaris and oil shale As explained in the Section 3.3, after blending with different percentages of oil shale, the changes of the product fractional yield and syngas production did not present a linear change. Therefore, a synergistic effect was shown in the co-pyrolysis of C. vulgaris and oil shale. The synergistic effect of co-pyrolysis on the liquid and gas yield at 800 C is shown in Table 4. The synergistic effect of co-pyrolysis on the total HVe,s at 800 C is shown in Table 5. Liquid and gas yield by calculation means the liquid and gas yield of the percentage of C. vulgaris plus the liquid and gas yield of the percentage of oil shale. Liquid and gas yield of C. vulgaris means the liquid and gas yield of the percentage of C. vulgaris. And the meanings of HVe,s by calculation and HVe,s of C. vulgaris are the same as that of Liquid and gas yield by calculation and Liquid and gas yield of C. vulgaris, respectively. As shown in Table 4, the liquid and gas yield of C. vulgaris of 9:1 was 80.25%, which was higher than the liquid and gas yield of 9:1 (77.45%). Compared with the pure C. vulgaris, the liquid and gas yield of 9:1 had decreased by 13.14%, but in the meantime, the C. vulgaris had only decreased by 10%. Therefore, after blending with oil shale, the liquid and gas production from C. vulgaris was inhibited by oil shale. Moreover, the liquid and gas yield of 9:1, 7:3 and 5:5 was 77.45%, 67.15% and 58.50%, but the liquid and gas yield of C. vulgaris of 9:1, 7:3 and 5:5 was 80.25%, 62.41% and 44.58%, respectively. With decreasing the C. vulgaris (less than 70%), the liquid and gas yield of 7:3 and 5:5 was higher than the liquid and gas yield of C. vulgaris of 7:3 and 5:5, respectively. Therefore, the liquid and gas decreasing production from C. vulgaris caused by the inhibition of oil shale was weakening because of the decrease of C. vulgaris. Furthermore, compared with the pure C. vulgaris, the liquid and gas yield of 9:1, 7:3 and 5:5 had decreased by 13.14%, 24.69% and 34.39%, respectively. However, the decrease of C. vulgaris was 10%, 30% and 50%, respectively. With increasing the percentage of oil shale, the decrease of liquid and gas production was quite lower than the decrease of C. vulgaris. Hence, it can be deduced that the liquid and gas production from oil shale was promoted by C. vulgaris. Moreover, the promotion of C. vulgaris on the liquid and gas production from oil shale was enhanced because of the increase of oil shale. The synergistic effect between C. vulgaris and oil shale can be explained that the solid residue of pyrolysis C. vulgaris is a quite good catalyst [8], resulting in the promotion on the liquid and gas production from oil shale. On the other side, the ash of oil shale is very high (52.47%, wt). So the ash particles of oil shale block out the apertures of C. vulgaris, resulting in the inhibition on the liquid and gas production from C. vulgaris. Compared with the liquid and gas yield by calculation, the liquid and gas yield of 9:1, 7:3 and 5:5 had decreased by 6.95%, 5.93% and 1.73%, respectively. So it can be seen that the differences between experiments and calculations became smaller since increased the percentage of oil shale, and the liquid and gas yields by experiments were lower than that of calculations. Hence, a conclusion can be made that the inhibition of oil shale is stronger than the promotion of C. vulgaris. As shown in Table 5, compared with the total HVe,s by calculation, the total HVe,s of 9:1, 7:3 and 5:5 had decreased by 57.56%, 63.61% and 57.31%, respectively. And the total HVe,s of C. vulgaris of 9:1 was 358.8165 (ppmv.kJ)/(L.W.h), which was much higher than the total HVe,s of 9:1 (156.4338 (ppmv.kJ)/(L.W.h)). Compared with the pure C. vulgaris, the total HVe,s of 9:1 had decreased by 60.76%, but in the meantime, the C. vulgaris had only decreased by 10%. Therefore, after blending with oil shale, the total HVe,s of C. vulgaris was obviously inhibited by oil shale. Furthermore, compared with the pure C. vulgaris, the total HVe,s of 9:1, 7:3 and 5:5 had decreased by 60.76%, 71.86% and 73.44%, respectively. However, the decrease of C. vulgaris was 10%, 30% and 50%, respectively. With increasing the percentage of oil shale from 10% to 50%, the decrease of total HVe,s was much higher than the decrease of C. vulgaris. This phenomenon can be explained that the HVe,s of oil
Table 4 The synergistic effect of co-pyrolysis on the bio-fuel yield at 800 C. Blending ratios
Bio-fuel yield (%)
Bio-fuel yield by calculation (%)
Bio-fuel yield of C. vulgaris (%)
10:0 9:1 7:3 5:5 0:10
89.16 77.45 67.15 58.50 29.90
89.16 83.24 71.38 59.53 29.90
89.16 80.25 62.41 44.58 0
Please cite this article in press as: Z. Hu, et al., The synergistic effect of co-pyrolysis of oil shale and microalgae to produce syngas, Journal of the Energy Institute (2015), http://dx.doi.org/10.1016/j.joei.2015.02.009
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Z. Hu et al. / Journal of the Energy Institute xxx (2015) 1e9
Table 5 The synergistic effect of co-pyrolysis on the total HVe,s at 800 C. Blending ratios
HVe,s (ppmv kJ)/(L W h)
HVe,s by calculation (ppmv kJ)/(L W h)
HVe,s of C. vulgaris (ppmv kJ)/(L W h)
10:0 9:1 7:3 5:5 0:10
398.6850 156.4338 112.1848 105.8949 97.4206
398.6850 368.5586 308.3057 248.0528 97.4206
398.6850 358.8165 279.0795 199.3425 0
shale was so low that it could not offset the decrease of HVe,s caused by C. vulgaris reduction. And the inhibition of oil shale on the HVe,s of C. vulgaris was strong. However, with increasing the percentage of oil shale from 10% to 50%, the decreasing extent of total HVe,s was quite lower than the decreasing extent of C. vulgaris. This is because the decreasing HVe,s of C. vulgaris caused by the inhibition of oil shale was weakening because of the decrease of C. vulgaris. From this analysis, a conclusion can be made that the total HVe,s of C. vulgaris was inhibited by oil shale. 4. Conclusions These results show that pyrolysis temperature significantly affected the product fractional yields of oil shale. Higher pyrolysis temperature usually enhanced the production of liquid and gas. Moreover, higher temperature also enhanced the gasification and secondary tar reactions of solid residue. Temperature also had a significant impact on the CO, H2 emission and syngas production. High temperature was beneficial to the CO and H2 emission. 800 C and 900 C was the best pyrolysis temperature for CO and H2 emission, respectively. Moreover, after considered the evaluation method, 800 C was the best pyrolysis temperature for oil shale to produce syngas. Under co-pyrolysis, the liquid and gas production from oil shale was promoted by C. vulgaris, but the liquid and gas production from C. vulgaris was inhibited by oil shale. Moreover, the inhibition of oil shale was stronger than the promotion of C. vulgaris. Meanwhile, after blended C. vulgaris with oil shale, the decrease of total HVe,s was much higher than the decrease of C. vulgaris. Moreover, blending with oil shale markedly reduced the total HVe,s of C. vulgaris and postpone the pyrolysis. Furthermore, the inhibition of oil shale on the HVe,s of C. vulgaris was strong. Acknowledgments The authors are grateful to National Natural Science Foundation of China (51476060), National Basic Research Program of China (973 Program) (2011CB201500, 2013CB228101) and Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes (KLB10004) for the financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
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