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Pyrolysis of oil shale by solid heat carrier in an innovative moving bed with internals
Fuel 159 (2015) 943–951
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Pyrolysis of oil shale by solid heat carrier in an innovative moving bed with internals Dengguo Lai a,b, Zhaohui Chen a,b, Yong Shi c, Lanxin Lin a,b, Jinhui Zhan a, Shiqiu Gao a, Guangwen Xu a,⇑ a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China University of Chinese Academy of Sciences, Beijing 100049, China c Anhui University of Technology, Anhui 243032, China b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A moving bed with internals was
devised for small-size oil shale pyrolysis using solid heat carrier. The new reactor obviously improved the pyrolysis performance. The shale oil yield in the new reactor could be close to 90% of the Fischer Assay yield. The gasoline and diesel content was over 70 wt.% and dust content was about 0.1 wt.%. Optimized operating parameters were obtained to support scale-up design.
a r t i c l e
i n f o
Article history: Received 20 May 2015 Received in revised form 13 July 2015 Accepted 20 July 2015 Available online 28 July 2015 Keywords: Pyrolysis Oil shale Internals Solid heat carrier Moving bed Secondary reactions
a b s t r a c t This article reports a new moving bed with particularly designed side and central channels as its internals for small-size oil shale pyrolysis by solid heat carrier. The bed is called moving bed with internals (MBI), and the solid heat carrier is shale ash from industrial Fushun retorting furnace. The pyrolysis was tested by varying the temperature of solid heat carrier, thickness of particle bed between the side and central channels, and ash-to-shale mass blending ratio in terms of the oil and gas product distribution and qualities. The shale oil yield is close to 90% of the Fischer Assay yield, and of the produced oil over 70 wt.% is gasoline and diesel and its dust content is only about 0.1 wt.%. The highest shale oil yield occurs at the pyrolysis temperature of 495 °C. The shale oil yield decreases with increasing particle bed thickness due to the increased shale oil cracking over shale ash in the prolonged residence time of volatile products inside the particle bed. Mechanism analysis shows that the central channel in the MBI directs the pyrolysis products to flow from the annulus to center of the particle bed, and this makes the moving bed as a filtration layer that considerably reduces the dust content in the produced oil. Meanwhile, this lateral flow greatly shortens the time of secondary reactions occurring to the pyrolysis products so that MBI could be applied to small-size oil shale to produce shale oil with high yield and high quality. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction ⇑ Corresponding author. Tel.: +86 10 82544886; fax: +86 10 82629912. E-mail address: [email protected] (G. Xu). http://dx.doi.org/10.1016/j.fuel.2015.07.068 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved.
Vast oil shale resource around the world can be used to produce shale oil in a big amount by pyrolysis or retorting as an alternative
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liquid fuel [1,2]. Heating oil shale particles is the key of all pyrolysis processes, and there are indirect heating and direct heating methods. The commercially available oil shale pyrolysis technologies are mainly based on direct heating by introducing a gas or solid heat carrier into the reactor [3,4]. As the typical structure of the retorts based on gas heat carrier, the Fushun and Kiviter processes impel hot gas generated from gasifying oil shale char or burning the pyrolysis gas to pass through the oil shale bed to provide the required endothermic heat for heating and pyrolyzing oil shale [5]. Although the technical process itself is relatively simple, it has a big gas volume to treat for recovering shale oil. The large volume of carrier gas greatly dilutes the produced oil and gas products to increase their recovery difficulty and cost, and also makes the pyrolysis gas have low heating value [3,6,7]. What is more, only large oil shale particles such as above 15 mm can be treated so that small-size oil shale cannot be effectively used by this kind of technologies. Consequently, it has long been challenging to pyrolyze small-size oil shale particles, which are nearly 20–40 wt.% of the total oil shale production, by gas heat carrier pyrolysis technologies. Comparing with the preceding gas heat carrier pyrolysis technologies, the solid heat carrier pyrolysis processes have usually higher shale oil yield, better adaptability for small-size oil shale, and smaller effluent gas volume that simplifies the shale oil recovery system [4,8,9]. Of this kind of technologies, we envisage that the ones using hot shale ash as the solid heat carrier is more promising than using external heat carrier particles (e.g., ceramic balls) [10,11]. It offers the advantage of co-production of shale oil and pyrolysis gas with high heating value through in-system high-efficiency combustion of oil shale char to provide the endothermic heat. Nonetheless, the literature reported processes of this kind such as the Galoter [12], L-R [7,13], DG [14] and Chevron STB processes [15,16] still suffer from technological problems of high intake of dust into shale oil product by poor separation of oil and dust. With more than 10 wt.% dust in shale oil, it actually seriously lowers the oil quality and causes difficulty in downstream processing of the oil [17]. Adherence of heavy oil mixed with fine particles tends to block pipeline and preclude continuous operation. The LLNL-HRS process [18–21] was developed to reduce fine particle generation by using a fluidized bed classifier before moving bed pyrolyzer, and the Kentort II process [22,23] adopted a multi-stage fluidized bed to integrate pyrolysis, gasification and char cooling by steam. Not mention the complexity of these processes, these processes cannot realize production of low-dust and high-yield oil for raw oil shale starting from zero millimeter. The so-called ATP process [24,25] is not only too complicated for commercial operation but is also unable to fully solve the ash-intake problem. Hot-gas filtering and heavy oil recycling are tested to reduce dust content in shale oil but the blockage of the filter is definitely a hard problem for treating pyrolysis product [18,26]. For almost all existing technologies, the high shale oil yield is accompanied with high heavy oil content in shale oil, giving the necessity to compromise yield and quality of shale oil in technology development [6,7]. With the intention of developing a new pyrolysis technology for small-size oil shale (<13 mm) but producing shale oil in high yield and high quality, the present study proposed and further tested a newly designed moving bed pyrolysis reactor with internals by using spent shale ash (after combustion) as heat carrier to realize the expected in-bed reduction of dust-intake and in-bed oil upgrading. The performance of pyrolysis in terms of yield and quality of shale oil was investigated to demonstrate the technical feasibility and superiority of oil shale pyrolysis using the new reactor. This study also clarified the influence of major operating parameters including temperature of solid heat carrier, thickness of
particle bed and mass blending ratio of shale ash to oil shale to optimize the pyrolysis performance and meanwhile to obtain the necessary data supporting scale-up of the new pyrolysis reactor.
2. Materials and methods 2.1. Facility and operation Fig. 1 presents a schematic diagram of the experimental facility. It is a continuous operation system in about 6.0 m high and consists of five major parts: heating the heat carrier particles (shale ash), controlled feeding of heat carrier particles and oil shale, mixing of heat carrier particles and oil shale, oil shale pyrolysis in the new moving bed, and finally recovery of pyrolysis products. The entire facility is made with iron steel or stainless steel. A shale ash bin of 0.2 m in inner diameter and 1.2 m high equipped with an electric furnace is used to store and preheat the shale ash of about 30 kg for each test. Two screw feeders are used to quantitatively feed the preheated shale ash and raw oil shale into the mixing section, respectively. The particle mixing is implemented in a few seconds (<2 s) inside a rectangular vertical column of 1.2 m high and mounted with cascaded baffles to enhance the mixing of particles. Particular designs are made for the baffles by considering their shapes, sizes and installations in the column. The mixed particles fall into the moving bed reactor to occur pyrolysis and generate volatile products. The pyrolysis reactor was 0.4 m long, 0.1 m wide and 0.5 m high. As illustrated in Fig. 1, three channels are created using metal-made internals, a central channel connecting the front and rear sidewalls of the length direction and two side channels in the width direction. Both walls of the central channel and the inner sidewalls of the two side channels allow the volatile products to pass but prevent particles from dropping into the channels from the particle bed. The outside walls of the side channels are the reactor walls in
Fig. 1. A process diagram of experimental facility for solid heat carrier pyrolysis of oil shale in a moving bed with internals (MBI).
D. Lai et al. / Fuel 159 (2015) 943–951
the width direction. As shown in the inset plot of the reactor configuration, the side channels serve to pass volatile products coming from the oil shale whose pyrolysis volatile cannot directly enter the central channel. The central channel provides the only pass for the volatile products to flow out of the reactor. Overall, from Fig. 1 we can see that the volatile products from pyrolysis, including shale oil vapor, water vapor and non-condensable gas, pass laterally through the shale char and heat carrier bed and finally enter the central channel to flow out of the reactor. The exit of the reactor is connected to the water cooler/condenser of the facility. Most shale oil and water vapor are stripped from the gaseous product stream through cooling and condensation by water and glycol. The residual oil in the non-condensable gas is further recovered via acetone adsorption in bottles immersed in an ice-water bath. The oil is fully recovered if the last acetone bottle does not change its color during a test. The cleaned non-condensable gas finally flows through a volumetric meter to determine its gas volume and then sampled using gas bags for GC analysis. For each test, 25–30 kg shale ash was loaded into the ash bin, while a given amount of shale ash was meanwhile loaded into the reactor to maintain an expected bed level there. The shale ash in the ash bin was in turn preheated to 650–900 °C for 5 h to ensure the uniform temperature of ash, and that in the reactor was also preheated to a preset temperature. Then, both hot ash and oil shale were simultaneously fed according to a preset ratio into the reactor to start the pyrolysis reactions. During pyrolysis, the particle bed height in the reactor was maintained at about 0.45 m through balancing the continuous supply of hot ash and fresh oil shale with the continuous discharge of spent ash and oil shale char into a storage bin under the control of a star valve. This particle bed height in the reactor was slightly above the top end of the central channel to prevent the possible upward flow of volatile products. In each pyrolysis test, 4.0–6.0 kg of oil shale was treated via a feeding rate of about 6.0 kg/h. While a high-temperature screw feeder was used for the heated shale ash from the ash bin, a normal screw feeder supplied the oil shale. Six K-type thermocouples online measured the temperatures of mixed particles and generated volatile products. The pyrolysis temperature referred to herein was the one for the mixed particles in the reactor under steady pyrolysis state. An induction pump maintained the central channel for slightly negative pressure to ensure the flow of pyrolysis volatile into this channel. The mean residence time of oil shale particles inside the reactor was about 25 min, for ensuring the complete reaction or possibly highest yield at all tested temperatures. 2.2. Material and analysis The tested oil shale in this study was from Huadian oil shale mine and had sizes below 13 mm. This kind of small-size material cannot be treated using the industrial Fushun retorting furnace. Table 1 shows the general characteristics of the tested oil shale. The oil yield determined by Fischer Assay analysis was 10.15 wt.% on dry mass base. The mean diameter of the used oil shale was about 6.9 mm and the percent of fine particle below 3 mm was about 20 wt.%. The used shale ash was from industrial Fushun retorting furnace and was also sieved into sizes below 13 mm. Table 1 also characterizes the tested shale ash via X-ray fluorescence (XRF), showing that its main components were SiO2, Al2O3, CaO, Fe2O3 and sulfates. After each test, the entire pipeline and water cooler/condenser were washed using acetone. The obtained washing liquid was mixed with the absorption acetone and in turn treated in vacuum rotary evaporator to remove the acetone solvent. The recovered oil from evaporating acetone was further mixed with the shale oil
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received from the condenser after separating its containing water to the highest possible degree. The obtained shale oil was weighted and determined for its moisture content through the toluene azeotropic method. In turn, the shale oil yield was calculated and further centrifuged to remove its water for composition analysis. The distillate fraction distribution of the shale oil was obtained in a simulated distillation GC (Agilent 7890B) according to the ASTM D2887 method. On the basis of the distillate fraction distribution, the shale oil was grouped into gasoline at temperatures of IBP-180 °C, diesel at 180–350 °C, vacuum gas oil (VGO) at 350– 500 °C and heavy oil over 500 °C. Here, IBP means the initial boiling point. In this study, the so-called light oil includes gasoline and diesel factions, while the heavy oil fraction contains both VGO and heavy oil components. The non-condensable gas product from oil shale pyrolysis was analyzed using a micro GC (Agilent 3000A) to get its molar composition of major gas species including H2, CH4, CO, CO2, C2H4, C2H6, C3H6 and C3H8. In the context, the hydrocarbons C2H4 and C2H6 were defined as C2 species and the hydrocarbons C3H6 and C3H8 were denoted as C3 species. The gas yield in this article was calculated from the measured total volume in a gas meter and molar composition by the micro GC. All yields referred to in this article were on the dry mass basis of oil shale. The dust mass content in shale oil was determined to be the content of toluene-insoluble matters. It was performed by adding 20 ml toluene into 20 g shale oil and then filtered to get the insoluble matters. Nonetheless, detailed characterization and its results of spent shale ash and also pyrolysis char will be presented in a separate article of this study.
3. Results and discussion 3.1. Demonstration of effects from internals Pyrolysis of oil shale by solid heat carrier in the moving bed reactors with and without the particularly designed gas flow channels as internals was conducted to demonstrate the effects of the internals on oil shale pyrolysis in terms of yield and quality of shale oil and pyrolysis gas. The tests were all at a mass blending ratio of 5:1 between shale ash to oil shale and a particle bed thickness of 150 mm between the side and central channels. Fig. 2 compares the yields of shale oil and pyrolysis gas at three pyrolysis temperatures that are varied by changing the temperatures of the heat carrier (shale ash) displayed in the upper abscissa. The shale ash temperatures of 700, 750 and 800 °C ensured the pyrolysis temperatures of 465, 495 and 525 °C, respectively. The reactor with the designed internals enabled obviously the higher shale oil yield and pyrolysis gas production in comparison with the case without internals. Corresponding to the pyrolysis temperatures of 465, 495 and 525 °C, the oil yield was 8.75 wt.%, 8.97 wt.% and 8.34 wt.% for the former but about 8.04 wt.%, 8.05 wt.% and 7.73 wt.% for the latter, respectively. The pyrolysis temperature for the highest shale oil yield was 495 °C or 750 °C of the shale ash temperature. The realized highest shale oil yield was reasonably high as 88% of the Fischer Assay yield. The pyrolysis gas yield similarly increased with raising the pyrolysis temperature but at each temperature the ratio of gas production rate was 1.15–1.22 between the cases with and without internals. Analyzing the composition of produced shale oil in terms of distillate fraction, as shown in Fig. 3(a), clarified that the oil from the tests without internals had slightly higher gasoline and diesel contents but lower VGO and heavy oil contents. With increasing the pyrolysis temperature the gasoline and diesel contents slightly increased for both types of the reactor. Fig. 3(b) shows further the actual yields of all distillates including gasoline, diesel, VGO
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Table 1 Properties of Huadian oil shale and shale ash. Proximate analysis (wt.%, db)
Ultimate analysis (wt.%, db) a
Ash
Volatile
Fixed carbon
C
H
O
73.07
25.84
1.09
12.15
1.58
11.97
N
S
0.38
0.85
HHV (kJ/kg)
Fischer Assay oil yield (wt.% db)
6744.4
10.15
XRF analysis of tested shale ash (wt.%) SiO2
Al2O3
Fe2O3
CaO
Na2O
MgO
K2O
SO3
Others
56.10
14.39
6.50
10.08
1.15
1.88
1.62
4.91
3.37
Sieve analysis of tested oil shale Particle size (mm) Weight percent (wt.%) a
<1 8.5
1–3 11.7
3–5 13.3
5–8 21.6
8–10 21.2
10–13 23.7
By difference.
Consequently, for the tested conditions the oil shale was not fully pyrolyzed. Table 3 presents the result of ultimate analysis for shale oil obtained at the pyrolysis temperatures varying from 465 °C to 525 °C in the reactor with internals. The mass contents of carbon and nitrogen increased, whereas those of hydrogen and oxygen decreased with increasing the pyrolysis temperature. Thus, the oil atomic ratio (molar) of H to C decreased from 1.63 to 1.56. The sulfur mass content was not significantly affected by pyrolysis temperature. In comparison with crude oil, the produced shale oil has the similar atomic H/C ratios but obviously higher nitrogen and oxygen contents. This is why additional upgrading is required for using shale oil as gasoline and diesel. After the tests using the reactor without internals we found plenty of dust, mixed with some oily heavy matters, were attached on the inner wall of outlet pipes in which gaseous pyrolysis products flow from the reactor exit. This sometimes caused the
Fig. 2. Comparison of shale oil and pyrolysis gas yields at different pyrolysis temperatures in reactors with and without internals.
and heavy oil. It obviously demonstrated that the lowered VGO yield was the major reason for the lowered shale oil yield in the case without internals. The heavy oil yield was very small but one can still see that it is higher for the reactor with internals. All these thus demonstrated that in the reactor without internals the relatively heavy oil species did not come out from the reactor or they were retained inside the pyrolysis reactor. It also explains why in Fig. 3(a) the reactor without internals has slightly higher gasoline and diesel contents in composition. Table 2 presents the results of proximate analysis and heating value for oil shale char obtained from all tests shown in Figs. 2 and 3. The volatile content and also heating value of oil shale char commonly decreased with increasing the pyrolysis temperature, but at every tested pyrolysis temperature the char from the reactor without internals had the higher volatile content and heating value due to the less extent of pyrolysis of oil shale in this case. Thus, the oil shale char production rate in the reactor without internals was higher than that in the reactor with internals. The fixed carbon content was basically very low of about 1.5 wt.% for all cases, which was much lower than the volatile content of 7.0–9.0 wt.%.
Fig. 3. Comparison of shale oil yield and quality at three pyrolysis temperatures in reactors with and without internals (corresponding to Fig. 2).
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D. Lai et al. / Fuel 159 (2015) 943–951 Table 2 Proximate analysis and heating values of oil shale char from tests with and without internals. Reactor type
Temperature (°C)
Proximate analysis (wt.%, db) Ash
Volatile
Fixed carbon
With internals
465 495 525
90.55 91.24 91.34
8.28 7.71 7.53
1.17 1.05 1.13
1750.5 1564.3 1507.4
Without internals
465 495 525
89.58 89.72 89.86
9.30 8.78 8.56
1.12 1.50 1.58
2060.8 1910.6 1836.7
blockage of gas flow and thus the instability of operation. In the worst case it even led to the termination of experiment. The outlet for volatile products in the reactor without internals was above the particle bed and close to the mixing section of the facility. The volatile products flowed upward by passing through the solid particles, which fall in the gravitational direction. Thus, fine dust or powder much be entrained into the stream of volatile products so that its produced shale oil has high dust content. In fact, it reached 5.0 wt.% in our tests, comparing to about 0.2 wt.% for the pyrolysis in MBI. The low dust content in the produced shale oil provided an essential advantage for MBI to be an advanced pyrolysis reactor. In this case, as schematically illustrated in Fig. 1, all volatile products enter the central channel by passing through the stationary particle bed to filter the possibly entrained dust, and the flow of pyrolysis products is also isolated from the particle dropping stream from the mixing section. The well-organized lateral flow of gaseous pyrolysis products in the reactor with internals, especially the central channel, shortens the flow path of gaseous pyrolysis products. This thus makes the moving bed reactor applicable to small-size feedstock, such as below 13 mm in this study, which is impossible for the traditional moving bed pyrolyzer without any internals. The short flow path causes the short residence time for pyrolysis products in the particle bed to reduce the secondary reactions occurring to them, which are mainly the cracking of relatively heavy species adsorbed on the particles (mainly hot ash). This thus explains the slightly higher light oil content in the shale oil from the bed without internals (Fig. 3(a)). The short residence time of gaseous products in the particle bed also makes the volatile products to quicker leave the reactor, which can facilitate the volatile release reactions occurring to oil shale particles. Consequently, in Fig. 2 the bed with internals has the higher yields of shale oil and pyrolysis gas at each temperature. It is reasonable that the more volatile released in this case should be heavier because the light species should be similarly easier to be released in both of the reactors. On the other hand, for heavy matters there are suppressed secondary reactions in the bed with internals. Thus, Fig. 3(b) clarifies that the higher shale oil yield for this case is mainly due to its more VGO as well as heavy oil fractions.
High heating value (kJ/kg)
should be about 4.7 for ensuring the pyrolysis temperature of about 520 °C. Thus, the effect of solid heat carrier (SHC) temperature, equivalently the pyrolysis temperature was conducted at the ash-to-shale mass ratio of 5:1 and the particle bed thickness was set to be 150 mm. Fig. 4 shows the result obtained in the reactor with internals. The shale oil yield first increased and then decreased with increasing the SHC temperature from 650 to 900 °C or pyrolysis temperature from 435 to 585 °C, resulting in a peak shale oil yield of about 88.4% against the Fischer Assay at the pyrolysis temperature of 495 °C. At low pyrolysis temperatures (i.e., 435 °C), the oil shale pyrolysis was not carried out completed and had thus the low oil and gas yield. The low oil yield at high temperatures such as 555 °C and 585 °C was due to the excessive cracking of oil vapor into light hydrocarbon gases and also light oil species [27]. Only the intermediate pyrolysis temperature such as about 495 °C in our reactor guaranteed both the deep pyrolysis of oil shale to release volatile as much as possible and the moderate cracking of the formed volatile matters into gases [28]. The oil yield was close to 90% of the Fischer Assay yield at 495 °C and exceeded 80% at 460–530 °C (pyrolysis temperature). Fig. 4 also showed that the pyrolysis gas yield and gas/oil mass ratio gradually increased with increasing the SHC or pyrolysis temperatures. We found that the variations in shale oil and pyrolysis gas yields well balanced to maintain the nearly constant total pyrolysis product yield. Thus, the reduced oil fraction was actually converted into gas product by cracking. Fig. 5 shows the composition of shale oil as well as the yields of individual distillates for the same tests shown in Fig. 4. In Fig. 5(a), the contents of gasoline and diesel relatively increased by 60.9% and 32.0% respectively for the pyrolysis temperature variation from 435 to 585 °C. The total light oil fraction (gasoline + diesel) was over 70 wt.% at the pyrolysis temperature above 495 °C and it ultimately reached 82.62 wt.% at 585 °C. In Fig. 5(b), the yield
3.2. Variation with pyrolysis temperature The temperature of shale ash from oil shale char combustor is usually about 800 °C. The blending ratio of such hot ash to oil shale Table 3 Ultimate analysis of shale oil at pyrolysis temperature from 465 to 525 °C in the reactor with internals.
a
Pyrolysis temperature (°C)
Ultimate analysis (wt.%) C
H
Oa
N
S
465 495 525
83.88 84.60 84.87
11.36 11.16 11.05
3.32 2.73 2.52
1.01 1.14 1.16
0.43 0.37 0.40
By difference.
Atomic H/C ratio
1.63 1.58 1.56
Fig. 4. Shale oil and pyrolysis gas yields varying with solid heat carrier temperature (upper X) or pyrolysis temperature (lower X) in reactor with internals.
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Fig. 5. Shale oil quality varying with pyrolysis temperature in reactor with internals.
of gasoline initially increased and then constantly remained from 495 °C. For diesel yield it first increased and then decreased to form a peak yield at about 495 °C. Overall, raising the pyrolysis temperature obviously reduced the yield of VGO, say, its content varied from 39.23 wt.% to 17.38 wt.% in Fig. 5(a) and its yield from 2.74 wt.% to 1.14 wt.% in Fig. 5 (b) when the pyrolysis temperature increased from 435 to 585 °C. All of these show that the particle bed plays a kind of upgrading effect for the produced shale oil in the MBI pyrolyzer based on solid heat carrier [27,28], but the suitable temperature should be around 495 °C for ensuring the high oil yield and quality simultaneously. At very high pyrolysis temperatures there should be significant loss of shale oil [28,29]. Fig. 6 shows the corresponding composition of pyrolysis gas. In Fig. 6(a), the yields of all individual components except for CO2 increased with raising the pyrolysis temperature, although by different levels or degrees. The obvious increase occurred for the yields of H2, CH4 and C2 hydrocarbons, while slight rise was shown by CO and C3 hydrocarbons. Thus, with raising the pyrolysis temperature more volatile was released and more high-carbon aliphatic species in the formed shale oil were cracked to form more H2 and also some CH4 and C2 hydrocarbons [30]. The yield of CO2 was almost constant at the tested pyrolysis temperatures of 435 to 585 °C. It consisted with the results of many literature studies [30,31] and was because that CO2 was formed mainly from decomposition of carboxyl groups and inorganic minerals so that the temperature above 465 °C little affected the evolution of CO2. The molar ratio of alkene to alkane in the non-condensable pyrolysis gas can be used to understand the reaction mechanism [31–33]. Campbell et al. [31] reported an increase in the ethene/ethane and propene/propane molar ratios to indicate essentially the facilitated vapor phase cracking reactions. Fig. 6(b) shows that in our tests all the calculated ratios as well as the gas production rate of alkane and alkene increased with raising the pyrolysis temperature. Nonetheless, the production rate of alkene (ethene and propene) increased more rapidly than that of alkane (ethane and propane). For the propene/propane molar ratio, it first
Fig. 6. Production rates of major gas species and molar ratios of ethene/ethane, propene/propane and alkene/alkane in pyrolysis gas product varying with pyrolysis temperature in reactor with internals.
increased slightly and then significantly above 495 °C. All of these demonstrate essentially that the cracking of oil vapor in the pyrolyzer become substantial since 495 °C through its interactions with both char and shale ash particles. The oil cracking forms more alkene than alkane, being the case especially for propene and propane. This makes the propene/propane ratio highest at all the tested temperatures and also the quickest increase in Fig. 6(b). Consequently, the alkene/alkane ratio is in-between the ratios of propene/propane and ethene/ethane. 3.3. Variation with particle bed thickness As illustrated in Fig. 1, we define the distance between the side channel and central channel as the particle bed thickness. In this article, we chose the particle bed thickness of 120, 150 and 180 mm to investigate the influence of particle bed thickness at the ash-to-shale blending ratio of 5:1 and pyrolysis temperature of about 490 °C. Fig. 7(a) shows the oil and gas yields varying with the bed thickness. Increasing the thickness from 120 mm to 180 mm decreased the oil yield from 9.22 wt.% to 8.66 wt.% and also increased the gas yield and gas/oil mass ratio. Nonetheless, the influences from varying the particle bed thickness were not as significant as varying the pyrolysis temperature clarified above. At thin particle bed (i.e., 120 mm), the pyrolysis volatile flowed out quickly after its generation, thus suffering less secondary cracking to allow the higher shale oil yield. Increasing the bed thickness caused the longer residence time of primary volatile product inside the particle bed and thus the higher extent of secondary cracking and the lower oil yield. Fig. 7(a) also shows that the increase in the gas yield well matched the reduction in the oil yield, meaning that the reduced oil production is mainly converted into gas product by oil vapor cracking in the particle bed. Increasing the particle bed thickness caused the higher light oil content (gasoline and diesel) but the lower VGO and heavy oil fractions, as is shown in Fig. 7(b). This was also a result from enhancing
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explained why all alkene/alkane ratios elevated with raising the bed thickness. In Fig. 7(c) the ratio of propene/propane was the highest, while the ethene/ethane ratio was the lowest. These demonstrated further that the increased shale oil cracking in thicker bed formed more alkene in comparison with the formation of alkane. The volatile product through the particle bed can get also a dust filtration effect. This is another technology advantage of the tested moving bed with internals. Our experimental results shows that the produced shale oil at a bed thickness of 180 mm contained only 0.04 wt.% dust, whereas this dust content was 0.22 wt.% and 0.16 wt.% at the thickness of 120 mm and 150 mm. Thus, the thicker the particle bed, the better the dust filtration effect was. Overall, a thick particle bed led to the expected oil upgrading effects including both cracking of heavy oil fraction and filtration of dust containing in the produced shale oil. However, increasing the particle bed thickness had to reduce the shale oil yield, although it increased the gas yield. Practically, there should be a tradeoff condition that balances both such beneficial and reverse effects. This optimal bed thickness should be related to practical conditions, and in all tests of this article we chose 150 mm to be the ‘‘standard’’ bed thickness for the reactor with internals. 3.4. Variation with ash-to-shale ratio The pyrolysis temperature is determined by the temperature of shale ash and its mass ratio to oil shale. For testing the influence of ash-to-shale mass blending ratio, we varied the temperature of shale ash according to the calculation that keeps the same
Fig. 7. Influence of particle bed thickness on (a) shale oil and pyrolysis gas yields, (b) shale oil composition and distillate yields, (c) molar ratio and production rates of alkene and alkane gases for pyrolysis in reactor with internals.
the secondary cracking of formed shale oil in the thicker particle bed. Concretely, varying the particle bed thickness from 120 mm to 180 mm increased the light oil content to 73.21 wt.% or relatively by 16.2% and meanwhile relatively reduced the content of heavy oil fractions (VGO + heavy oil) by 27.6%. Correspondingly, the yield of light oil fraction had a slight increase from 5.81 wt.% to 6.34 wt.%, whereas that of ‘‘VGO + heavy oil’’ decreased from 3.41 wt.% to 2.32 wt.%. The result showed further that the raised light oil yield (gasoline and diesel) was firmly from the conversion (i.e., cracking) of the reduced ‘‘VGO and heavy oil’’ productions. This conversion formed also gaseous product and carbon to increase the gas yield and the gas/oil ratio (see Fig. 7(a)). Fig. 7(c) shows the gas production rate of alkenes and alkanes in liter per kilogram oil shale and their molar ratios varying with the particle bed thickness. Increasing the bed thickness led to the higher ratios of ethene/ethane, propene/propane and alkene/alkane and also the higher production rate of alkenes and alkanes. At the bed thickness of 120 mm, the yield of gaseous alkene product was lower than that of alkane product. Increasing the bed thickness caused the quicker rise in the alkene production rate than in the alkane so that the alkene gas production rate became higher at the bed thickness of 150 mm and 180 mm. This also
Fig. 8. Influence of ash-to-shale blending ratio on (a) shale oil and pyrolysis gas yields and (b) shale oil composition and distillate yields for pyrolysis in reactor with internals.
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pyrolysis temperature. Fig. 8(a) shows the shale oil and pyrolysis gas yields at a pyrolysis temperature of about 490 °C and a bed thickness of 150 mm but different blending ratios of shale ash to oil shale. A low blending ratio of 3:1 with a high ash temperature of about 900 °C caused the high extent of oil vapor thermal cracking. The high blending ratio of 7:1 provided the high probability for the interaction between shale ash and oil vapor. Thus, obtaining the possibly highest oil yield required well-matched blending ratio and shale ash temperature. This seems to be about 5:1 at ash temperatures of about 750 °C. Under this condition the shale oil yield was the highest and gas yield was the lowest, verifying that there was the higher degree of secondary cracking to shale oil vapor at the ratios 3:1 and 7:1 due to the high ash temperature and high load of ash particles, respectively. Fig. 8(b) shows the corresponding variation in shale oil composition and the yields of distillates. It was obvious that the produced shale oil at the ratio of 5:1 had relatively lower fractions of gasoline and diesel, while the fraction of VGO was lower for the ratios of 3:1 and 7:1. At the ratio of 7:1 the VGO fraction was the lowest, while its total content of light oil fraction (gasoline + diesel) also reached 81 wt.%. This content was about 69 wt.% at 5:1 and 76 wt.% at 3:1. The yields of distillates exhibited difference mainly in the heavy oil fraction of ‘‘VGO + heavy oil’’, which was about 2.0 wt.%, 2.8 wt.% and 1.5 wt.% at the blending ratios of 3:1, 5:1 and 7:1, respectively. The yield of light oil fraction was not much different among the three blending ratios. Consequently, we can believe that the higher extent of secondary cracking at the ratios of 3:1 (due to high ash temperature) and 7:1 (due to much more ash) mainly converted the heavy oil fraction into light oils and also pyrolysis gas. Its formed light oils then compensated for the cracked gasoline and diesel oils (into gas particularly) under such conditions so that the content of light oil fraction remained to vary little with the blending ratio of shale ash to oil shale.
4. Conclusions A laboratory facility was developed to pyrolyze small-size oil shale (below 13 mm) by solid heat carrier in an innovative moving bed with particularly designed gas channel as internals (MBI). The yields and qualities of shale oil were studied with respect to the major influential parameters such as solid heat carrier temperature or pyrolysis temperature, particle bed thickness between the side and central channels and ash-to-shale mass blending ratio. For the tested Huadian oil shale, good performance was achieved. The use of the internals increased the shale oil yield, while it also made the particle layer as a filtration bed between the side and central channels to reduce the dust content in the produced oil to about 0.1 wt.%. The highest shale oil yield appeared at the pyrolysis temperature of about 495 °C or shale ash temperature of about 750 °C. The shale ash bed facilitated the secondary cracking of shale oil, especially at temperatures above 525 °C. The secondary cracking converted VGO and heavy oil into light oil fractions and gas products, and it was affected by both the temperature of ash particles or bed and the blending ratio of ash to shale. The higher temperature and blending ratio, the more intensive the secondary reaction was. Consequently, there should be an optimal matching between the ash temperature and ash-to-shale ratio. Overall, the use of MBI for pyrolyzing small-size oil shale by hot shale ash as the heat carrier has achieved oil yield close to 90% of the Fischer Assay yield, referring to an advanced level that is obviously higher than 65–70% of the Fischer Assay yield enabled by the Fushun retort widely applied in China. The produced shale oil had gasoline and diesel content over 70 wt.% which is much higher than 50 wt.% from Fischer Assay retorting test. In addition, the shale oil recovered from the pyrolysis in MBI presents a good
oil–water separation property and its density is around 0.85 g/ml, about 50 kg/m3 lower than that of the oil produced by Fushun retort. The generated pyrolysis gas has also high quality by containing about 15 vol.% C2–C3 hydrocarbons and its higher heating value reaches 20 MJ/N m3. All of these show that the use of MBI is potential to solve the bottleneck problems for pyrolysis of small-size feedstock based on solid heat carrier, which include high dust content in produced oil and high content of heavy oil fraction. Thus, a prospective technology is actually presented for the pyrolysis or retorting of small-size oil shale. Acknowledgments The study was financed by the National Basic Research Program of China (Grant 2014CB744303) and the National Natural Science Foundation of China (Grant 21306210). References [1] Jiang XM, Han XX, Cui ZG. New technology for the comprehensive utilization of Chinese oil shale resources. Energy 2007;32(5):772–7. [2] Dyni JR. Geology and resources of some world oil-shale deposits. Oil shale 2003;20(3):193–252. [3] Cook EW. Oil-shale technology in the USA. Fuel 1974;53(3):146–51. [4] Golubev N. Solid oil shale heat carrier technology for oil shale retorting. Oil shale 2003;20(3SI):324–32. [5] Qian JL, Wang JQ, Li SY. World oil shale utilization and its future. J Jilin University (Earth Science Edition) 2006;36(6):877–87 [in Chinese]. [6] Dung NV, Yip V. Basis of reactor design for retorting Australian oil shales. Fuel 1991;70(11):1336–41. [7] Dung NV. A new concept for retorting oil shale. Fuel 1987;66:377–83. [8] Na JG, Im CH, Chung SH, Lee KB. Effect of oil shale retorting temperature on shale oil yield and properties. Fuel 2012;95(1):131–5. [9] Liang P, Wang ZF, Bi JC. Process characteristics investigation of simulated circulating fluidized bed combustion combined with coal pyrolysis. Fuel Process Technol 2007;88(1):23–8. [10] Trikkel A, Kuusik R, Maljukova N. Distribution of organic and inorganic ingredients in Estonian oil shale semicoke. Oil shale 2004;21(3):227–35. [11] Wong CM, Crawford RW, Burnham AK. Source and kinetics of sulfur species in oil shale pyrolysis gas by triple quadrupole mass spectrometry. ACS Petrol Div 1984;29(2):317–21. [12] Opik I, Golubev N, Kaidalov A, Kann J, Elenurm A. Current status of oil shale processing in solid heat carrier UTT (Galoter) retort in Estonia. Oil shale 2001;18(2):99–107. [13] Rammler RW. The production of synthetic crude oil from oil sand by application of the Lurgi-Ruhrgas Process. Can J Chem Eng 1970;48:552–60. [14] Guo SC, Luo CQ, You LB, Han W, Han Z. Experimental research on Huadian oil shale retorting using solid heat carrier. J Dalian Inst Technol 1986;25(4):25–30 (In Chinese). [15] Tamm PW, Langlois GE. Staged turbulent bed retorting process. USA. 4199432. 1980-04-22. [16] Tamm PW, Bertelsen CA, Handel GM, Spars BG, Wallman PH. The Chevron STB oil shale retort. Energy Prog 1982;2(1):37. [17] Li WY, Deng Y, Yu CL. Development of lignite pyrolysis with solid heat carrier. Coal Chem Ind 2012;158(1):1–5 (In Chinese). [18] Burnham AK, McConaghy JR. Comparison of the acceptability of various oil shale processes. In: Golden: 26th Oil shale symposium; 1991. UCRL-CONF226717. [19] Cena RJ, Thorsness CB. LLNL oil shale pilot plant status report. In: Eastern oil shale symposium; 1990. UCRL-JC-105170. [20] Camp DW, Braun RL, Diaz JC. Results of mathematical modeling of an oil shale retort having a fluidized-bed pyrolyzer and a lift-pipe combustor. Fuel Process Technol 1989;21(2):135–63. [21] Aldis DF. Attrition and abrasion models for oil shale process modeling. Fuel 1992;71:1447–53. [22] Carter SD, Robl TL, Taulbee DN, Rubel AM. Testing of an Irati oil shale in a multi-stage fluidized bed retorting process. Fuel 1991;70(11):1347–51. [23] Carter SD, Robl TL, Rubel AM, Taulbee DN. Processing of eastern US oil shale in a multistaged fluidized bed system. Fuel 1990;69(9):1124–8. [24] Schmidt SJ. New directions for shale oil: path to a secure new oil supply well into this century: on the example of Australia. Oil shale 2003;20(3S):333–46. [25] Brandt AR. Converting oil shale to liquid fuels with the Alberta Taciuk Processor: energy inputs and greenhouse gas emissions. Energy Fuels 2009;23:6253–8. [26] Coburn HT, Duewer TI, King KJ. Shale oil form the LLNL pilot retort: metal irons as markers for water and dust. In: Eastern oil shale symposium; 1993. UCRLJC-115740. [27] Rubel AM, Rimmer SM, Keogh R, Thomas LR, Scott DC, Frank JD. Effect of process solids on secondary reactions during oil shale retorting. Fuel 1991;70(11):1352–6.
D. Lai et al. / Fuel 159 (2015) 943–951 [28] Lai DG, Chen ZH, Lin LX, Zhang YM, Gao SQ, Xu GW. Secondary cracking and upgrading of shale oil from pyrolyzing oil shale over shale ash. Energy Fuel 2015;29:2219–26. [29] Dung NV. Pyrolysis of Stuart oil shale in the presence of recycled shale. Fuel 1990;69(4):497–501. [30] Niu MT, Wang S, Han XX, Jiang XM. Yield and characteristics of shale oil from the retorting of oil shale and fine oil-shale ash mixtures. Appl Energy 2013;111:234–9.
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Fuel journal homepage: www.elsevier.com/locate/fuel
Pyrolysis of oil shale by solid heat carrier in an innovative moving bed with internals Dengguo Lai a,b, Zhaohui Chen a,b, Yong Shi c, Lanxin Lin a,b, Jinhui Zhan a, Shiqiu Gao a, Guangwen Xu a,⇑ a
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China University of Chinese Academy of Sciences, Beijing 100049, China c Anhui University of Technology, Anhui 243032, China b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A moving bed with internals was
devised for small-size oil shale pyrolysis using solid heat carrier. The new reactor obviously improved the pyrolysis performance. The shale oil yield in the new reactor could be close to 90% of the Fischer Assay yield. The gasoline and diesel content was over 70 wt.% and dust content was about 0.1 wt.%. Optimized operating parameters were obtained to support scale-up design.
a r t i c l e
i n f o
Article history: Received 20 May 2015 Received in revised form 13 July 2015 Accepted 20 July 2015 Available online 28 July 2015 Keywords: Pyrolysis Oil shale Internals Solid heat carrier Moving bed Secondary reactions
a b s t r a c t This article reports a new moving bed with particularly designed side and central channels as its internals for small-size oil shale pyrolysis by solid heat carrier. The bed is called moving bed with internals (MBI), and the solid heat carrier is shale ash from industrial Fushun retorting furnace. The pyrolysis was tested by varying the temperature of solid heat carrier, thickness of particle bed between the side and central channels, and ash-to-shale mass blending ratio in terms of the oil and gas product distribution and qualities. The shale oil yield is close to 90% of the Fischer Assay yield, and of the produced oil over 70 wt.% is gasoline and diesel and its dust content is only about 0.1 wt.%. The highest shale oil yield occurs at the pyrolysis temperature of 495 °C. The shale oil yield decreases with increasing particle bed thickness due to the increased shale oil cracking over shale ash in the prolonged residence time of volatile products inside the particle bed. Mechanism analysis shows that the central channel in the MBI directs the pyrolysis products to flow from the annulus to center of the particle bed, and this makes the moving bed as a filtration layer that considerably reduces the dust content in the produced oil. Meanwhile, this lateral flow greatly shortens the time of secondary reactions occurring to the pyrolysis products so that MBI could be applied to small-size oil shale to produce shale oil with high yield and high quality. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction ⇑ Corresponding author. Tel.: +86 10 82544886; fax: +86 10 82629912. E-mail address: [email protected] (G. Xu). http://dx.doi.org/10.1016/j.fuel.2015.07.068 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved.
Vast oil shale resource around the world can be used to produce shale oil in a big amount by pyrolysis or retorting as an alternative
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liquid fuel [1,2]. Heating oil shale particles is the key of all pyrolysis processes, and there are indirect heating and direct heating methods. The commercially available oil shale pyrolysis technologies are mainly based on direct heating by introducing a gas or solid heat carrier into the reactor [3,4]. As the typical structure of the retorts based on gas heat carrier, the Fushun and Kiviter processes impel hot gas generated from gasifying oil shale char or burning the pyrolysis gas to pass through the oil shale bed to provide the required endothermic heat for heating and pyrolyzing oil shale [5]. Although the technical process itself is relatively simple, it has a big gas volume to treat for recovering shale oil. The large volume of carrier gas greatly dilutes the produced oil and gas products to increase their recovery difficulty and cost, and also makes the pyrolysis gas have low heating value [3,6,7]. What is more, only large oil shale particles such as above 15 mm can be treated so that small-size oil shale cannot be effectively used by this kind of technologies. Consequently, it has long been challenging to pyrolyze small-size oil shale particles, which are nearly 20–40 wt.% of the total oil shale production, by gas heat carrier pyrolysis technologies. Comparing with the preceding gas heat carrier pyrolysis technologies, the solid heat carrier pyrolysis processes have usually higher shale oil yield, better adaptability for small-size oil shale, and smaller effluent gas volume that simplifies the shale oil recovery system [4,8,9]. Of this kind of technologies, we envisage that the ones using hot shale ash as the solid heat carrier is more promising than using external heat carrier particles (e.g., ceramic balls) [10,11]. It offers the advantage of co-production of shale oil and pyrolysis gas with high heating value through in-system high-efficiency combustion of oil shale char to provide the endothermic heat. Nonetheless, the literature reported processes of this kind such as the Galoter [12], L-R [7,13], DG [14] and Chevron STB processes [15,16] still suffer from technological problems of high intake of dust into shale oil product by poor separation of oil and dust. With more than 10 wt.% dust in shale oil, it actually seriously lowers the oil quality and causes difficulty in downstream processing of the oil [17]. Adherence of heavy oil mixed with fine particles tends to block pipeline and preclude continuous operation. The LLNL-HRS process [18–21] was developed to reduce fine particle generation by using a fluidized bed classifier before moving bed pyrolyzer, and the Kentort II process [22,23] adopted a multi-stage fluidized bed to integrate pyrolysis, gasification and char cooling by steam. Not mention the complexity of these processes, these processes cannot realize production of low-dust and high-yield oil for raw oil shale starting from zero millimeter. The so-called ATP process [24,25] is not only too complicated for commercial operation but is also unable to fully solve the ash-intake problem. Hot-gas filtering and heavy oil recycling are tested to reduce dust content in shale oil but the blockage of the filter is definitely a hard problem for treating pyrolysis product [18,26]. For almost all existing technologies, the high shale oil yield is accompanied with high heavy oil content in shale oil, giving the necessity to compromise yield and quality of shale oil in technology development [6,7]. With the intention of developing a new pyrolysis technology for small-size oil shale (<13 mm) but producing shale oil in high yield and high quality, the present study proposed and further tested a newly designed moving bed pyrolysis reactor with internals by using spent shale ash (after combustion) as heat carrier to realize the expected in-bed reduction of dust-intake and in-bed oil upgrading. The performance of pyrolysis in terms of yield and quality of shale oil was investigated to demonstrate the technical feasibility and superiority of oil shale pyrolysis using the new reactor. This study also clarified the influence of major operating parameters including temperature of solid heat carrier, thickness of
particle bed and mass blending ratio of shale ash to oil shale to optimize the pyrolysis performance and meanwhile to obtain the necessary data supporting scale-up of the new pyrolysis reactor.
2. Materials and methods 2.1. Facility and operation Fig. 1 presents a schematic diagram of the experimental facility. It is a continuous operation system in about 6.0 m high and consists of five major parts: heating the heat carrier particles (shale ash), controlled feeding of heat carrier particles and oil shale, mixing of heat carrier particles and oil shale, oil shale pyrolysis in the new moving bed, and finally recovery of pyrolysis products. The entire facility is made with iron steel or stainless steel. A shale ash bin of 0.2 m in inner diameter and 1.2 m high equipped with an electric furnace is used to store and preheat the shale ash of about 30 kg for each test. Two screw feeders are used to quantitatively feed the preheated shale ash and raw oil shale into the mixing section, respectively. The particle mixing is implemented in a few seconds (<2 s) inside a rectangular vertical column of 1.2 m high and mounted with cascaded baffles to enhance the mixing of particles. Particular designs are made for the baffles by considering their shapes, sizes and installations in the column. The mixed particles fall into the moving bed reactor to occur pyrolysis and generate volatile products. The pyrolysis reactor was 0.4 m long, 0.1 m wide and 0.5 m high. As illustrated in Fig. 1, three channels are created using metal-made internals, a central channel connecting the front and rear sidewalls of the length direction and two side channels in the width direction. Both walls of the central channel and the inner sidewalls of the two side channels allow the volatile products to pass but prevent particles from dropping into the channels from the particle bed. The outside walls of the side channels are the reactor walls in
Fig. 1. A process diagram of experimental facility for solid heat carrier pyrolysis of oil shale in a moving bed with internals (MBI).
D. Lai et al. / Fuel 159 (2015) 943–951
the width direction. As shown in the inset plot of the reactor configuration, the side channels serve to pass volatile products coming from the oil shale whose pyrolysis volatile cannot directly enter the central channel. The central channel provides the only pass for the volatile products to flow out of the reactor. Overall, from Fig. 1 we can see that the volatile products from pyrolysis, including shale oil vapor, water vapor and non-condensable gas, pass laterally through the shale char and heat carrier bed and finally enter the central channel to flow out of the reactor. The exit of the reactor is connected to the water cooler/condenser of the facility. Most shale oil and water vapor are stripped from the gaseous product stream through cooling and condensation by water and glycol. The residual oil in the non-condensable gas is further recovered via acetone adsorption in bottles immersed in an ice-water bath. The oil is fully recovered if the last acetone bottle does not change its color during a test. The cleaned non-condensable gas finally flows through a volumetric meter to determine its gas volume and then sampled using gas bags for GC analysis. For each test, 25–30 kg shale ash was loaded into the ash bin, while a given amount of shale ash was meanwhile loaded into the reactor to maintain an expected bed level there. The shale ash in the ash bin was in turn preheated to 650–900 °C for 5 h to ensure the uniform temperature of ash, and that in the reactor was also preheated to a preset temperature. Then, both hot ash and oil shale were simultaneously fed according to a preset ratio into the reactor to start the pyrolysis reactions. During pyrolysis, the particle bed height in the reactor was maintained at about 0.45 m through balancing the continuous supply of hot ash and fresh oil shale with the continuous discharge of spent ash and oil shale char into a storage bin under the control of a star valve. This particle bed height in the reactor was slightly above the top end of the central channel to prevent the possible upward flow of volatile products. In each pyrolysis test, 4.0–6.0 kg of oil shale was treated via a feeding rate of about 6.0 kg/h. While a high-temperature screw feeder was used for the heated shale ash from the ash bin, a normal screw feeder supplied the oil shale. Six K-type thermocouples online measured the temperatures of mixed particles and generated volatile products. The pyrolysis temperature referred to herein was the one for the mixed particles in the reactor under steady pyrolysis state. An induction pump maintained the central channel for slightly negative pressure to ensure the flow of pyrolysis volatile into this channel. The mean residence time of oil shale particles inside the reactor was about 25 min, for ensuring the complete reaction or possibly highest yield at all tested temperatures. 2.2. Material and analysis The tested oil shale in this study was from Huadian oil shale mine and had sizes below 13 mm. This kind of small-size material cannot be treated using the industrial Fushun retorting furnace. Table 1 shows the general characteristics of the tested oil shale. The oil yield determined by Fischer Assay analysis was 10.15 wt.% on dry mass base. The mean diameter of the used oil shale was about 6.9 mm and the percent of fine particle below 3 mm was about 20 wt.%. The used shale ash was from industrial Fushun retorting furnace and was also sieved into sizes below 13 mm. Table 1 also characterizes the tested shale ash via X-ray fluorescence (XRF), showing that its main components were SiO2, Al2O3, CaO, Fe2O3 and sulfates. After each test, the entire pipeline and water cooler/condenser were washed using acetone. The obtained washing liquid was mixed with the absorption acetone and in turn treated in vacuum rotary evaporator to remove the acetone solvent. The recovered oil from evaporating acetone was further mixed with the shale oil
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received from the condenser after separating its containing water to the highest possible degree. The obtained shale oil was weighted and determined for its moisture content through the toluene azeotropic method. In turn, the shale oil yield was calculated and further centrifuged to remove its water for composition analysis. The distillate fraction distribution of the shale oil was obtained in a simulated distillation GC (Agilent 7890B) according to the ASTM D2887 method. On the basis of the distillate fraction distribution, the shale oil was grouped into gasoline at temperatures of IBP-180 °C, diesel at 180–350 °C, vacuum gas oil (VGO) at 350– 500 °C and heavy oil over 500 °C. Here, IBP means the initial boiling point. In this study, the so-called light oil includes gasoline and diesel factions, while the heavy oil fraction contains both VGO and heavy oil components. The non-condensable gas product from oil shale pyrolysis was analyzed using a micro GC (Agilent 3000A) to get its molar composition of major gas species including H2, CH4, CO, CO2, C2H4, C2H6, C3H6 and C3H8. In the context, the hydrocarbons C2H4 and C2H6 were defined as C2 species and the hydrocarbons C3H6 and C3H8 were denoted as C3 species. The gas yield in this article was calculated from the measured total volume in a gas meter and molar composition by the micro GC. All yields referred to in this article were on the dry mass basis of oil shale. The dust mass content in shale oil was determined to be the content of toluene-insoluble matters. It was performed by adding 20 ml toluene into 20 g shale oil and then filtered to get the insoluble matters. Nonetheless, detailed characterization and its results of spent shale ash and also pyrolysis char will be presented in a separate article of this study.
3. Results and discussion 3.1. Demonstration of effects from internals Pyrolysis of oil shale by solid heat carrier in the moving bed reactors with and without the particularly designed gas flow channels as internals was conducted to demonstrate the effects of the internals on oil shale pyrolysis in terms of yield and quality of shale oil and pyrolysis gas. The tests were all at a mass blending ratio of 5:1 between shale ash to oil shale and a particle bed thickness of 150 mm between the side and central channels. Fig. 2 compares the yields of shale oil and pyrolysis gas at three pyrolysis temperatures that are varied by changing the temperatures of the heat carrier (shale ash) displayed in the upper abscissa. The shale ash temperatures of 700, 750 and 800 °C ensured the pyrolysis temperatures of 465, 495 and 525 °C, respectively. The reactor with the designed internals enabled obviously the higher shale oil yield and pyrolysis gas production in comparison with the case without internals. Corresponding to the pyrolysis temperatures of 465, 495 and 525 °C, the oil yield was 8.75 wt.%, 8.97 wt.% and 8.34 wt.% for the former but about 8.04 wt.%, 8.05 wt.% and 7.73 wt.% for the latter, respectively. The pyrolysis temperature for the highest shale oil yield was 495 °C or 750 °C of the shale ash temperature. The realized highest shale oil yield was reasonably high as 88% of the Fischer Assay yield. The pyrolysis gas yield similarly increased with raising the pyrolysis temperature but at each temperature the ratio of gas production rate was 1.15–1.22 between the cases with and without internals. Analyzing the composition of produced shale oil in terms of distillate fraction, as shown in Fig. 3(a), clarified that the oil from the tests without internals had slightly higher gasoline and diesel contents but lower VGO and heavy oil contents. With increasing the pyrolysis temperature the gasoline and diesel contents slightly increased for both types of the reactor. Fig. 3(b) shows further the actual yields of all distillates including gasoline, diesel, VGO
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Table 1 Properties of Huadian oil shale and shale ash. Proximate analysis (wt.%, db)
Ultimate analysis (wt.%, db) a
Ash
Volatile
Fixed carbon
C
H
O
73.07
25.84
1.09
12.15
1.58
11.97
N
S
0.38
0.85
HHV (kJ/kg)
Fischer Assay oil yield (wt.% db)
6744.4
10.15
XRF analysis of tested shale ash (wt.%) SiO2
Al2O3
Fe2O3
CaO
Na2O
MgO
K2O
SO3
Others
56.10
14.39
6.50
10.08
1.15
1.88
1.62
4.91
3.37
Sieve analysis of tested oil shale Particle size (mm) Weight percent (wt.%) a
<1 8.5
1–3 11.7
3–5 13.3
5–8 21.6
8–10 21.2
10–13 23.7
By difference.
Consequently, for the tested conditions the oil shale was not fully pyrolyzed. Table 3 presents the result of ultimate analysis for shale oil obtained at the pyrolysis temperatures varying from 465 °C to 525 °C in the reactor with internals. The mass contents of carbon and nitrogen increased, whereas those of hydrogen and oxygen decreased with increasing the pyrolysis temperature. Thus, the oil atomic ratio (molar) of H to C decreased from 1.63 to 1.56. The sulfur mass content was not significantly affected by pyrolysis temperature. In comparison with crude oil, the produced shale oil has the similar atomic H/C ratios but obviously higher nitrogen and oxygen contents. This is why additional upgrading is required for using shale oil as gasoline and diesel. After the tests using the reactor without internals we found plenty of dust, mixed with some oily heavy matters, were attached on the inner wall of outlet pipes in which gaseous pyrolysis products flow from the reactor exit. This sometimes caused the
Fig. 2. Comparison of shale oil and pyrolysis gas yields at different pyrolysis temperatures in reactors with and without internals.
and heavy oil. It obviously demonstrated that the lowered VGO yield was the major reason for the lowered shale oil yield in the case without internals. The heavy oil yield was very small but one can still see that it is higher for the reactor with internals. All these thus demonstrated that in the reactor without internals the relatively heavy oil species did not come out from the reactor or they were retained inside the pyrolysis reactor. It also explains why in Fig. 3(a) the reactor without internals has slightly higher gasoline and diesel contents in composition. Table 2 presents the results of proximate analysis and heating value for oil shale char obtained from all tests shown in Figs. 2 and 3. The volatile content and also heating value of oil shale char commonly decreased with increasing the pyrolysis temperature, but at every tested pyrolysis temperature the char from the reactor without internals had the higher volatile content and heating value due to the less extent of pyrolysis of oil shale in this case. Thus, the oil shale char production rate in the reactor without internals was higher than that in the reactor with internals. The fixed carbon content was basically very low of about 1.5 wt.% for all cases, which was much lower than the volatile content of 7.0–9.0 wt.%.
Fig. 3. Comparison of shale oil yield and quality at three pyrolysis temperatures in reactors with and without internals (corresponding to Fig. 2).
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D. Lai et al. / Fuel 159 (2015) 943–951 Table 2 Proximate analysis and heating values of oil shale char from tests with and without internals. Reactor type
Temperature (°C)
Proximate analysis (wt.%, db) Ash
Volatile
Fixed carbon
With internals
465 495 525
90.55 91.24 91.34
8.28 7.71 7.53
1.17 1.05 1.13
1750.5 1564.3 1507.4
Without internals
465 495 525
89.58 89.72 89.86
9.30 8.78 8.56
1.12 1.50 1.58
2060.8 1910.6 1836.7
blockage of gas flow and thus the instability of operation. In the worst case it even led to the termination of experiment. The outlet for volatile products in the reactor without internals was above the particle bed and close to the mixing section of the facility. The volatile products flowed upward by passing through the solid particles, which fall in the gravitational direction. Thus, fine dust or powder much be entrained into the stream of volatile products so that its produced shale oil has high dust content. In fact, it reached 5.0 wt.% in our tests, comparing to about 0.2 wt.% for the pyrolysis in MBI. The low dust content in the produced shale oil provided an essential advantage for MBI to be an advanced pyrolysis reactor. In this case, as schematically illustrated in Fig. 1, all volatile products enter the central channel by passing through the stationary particle bed to filter the possibly entrained dust, and the flow of pyrolysis products is also isolated from the particle dropping stream from the mixing section. The well-organized lateral flow of gaseous pyrolysis products in the reactor with internals, especially the central channel, shortens the flow path of gaseous pyrolysis products. This thus makes the moving bed reactor applicable to small-size feedstock, such as below 13 mm in this study, which is impossible for the traditional moving bed pyrolyzer without any internals. The short flow path causes the short residence time for pyrolysis products in the particle bed to reduce the secondary reactions occurring to them, which are mainly the cracking of relatively heavy species adsorbed on the particles (mainly hot ash). This thus explains the slightly higher light oil content in the shale oil from the bed without internals (Fig. 3(a)). The short residence time of gaseous products in the particle bed also makes the volatile products to quicker leave the reactor, which can facilitate the volatile release reactions occurring to oil shale particles. Consequently, in Fig. 2 the bed with internals has the higher yields of shale oil and pyrolysis gas at each temperature. It is reasonable that the more volatile released in this case should be heavier because the light species should be similarly easier to be released in both of the reactors. On the other hand, for heavy matters there are suppressed secondary reactions in the bed with internals. Thus, Fig. 3(b) clarifies that the higher shale oil yield for this case is mainly due to its more VGO as well as heavy oil fractions.
High heating value (kJ/kg)
should be about 4.7 for ensuring the pyrolysis temperature of about 520 °C. Thus, the effect of solid heat carrier (SHC) temperature, equivalently the pyrolysis temperature was conducted at the ash-to-shale mass ratio of 5:1 and the particle bed thickness was set to be 150 mm. Fig. 4 shows the result obtained in the reactor with internals. The shale oil yield first increased and then decreased with increasing the SHC temperature from 650 to 900 °C or pyrolysis temperature from 435 to 585 °C, resulting in a peak shale oil yield of about 88.4% against the Fischer Assay at the pyrolysis temperature of 495 °C. At low pyrolysis temperatures (i.e., 435 °C), the oil shale pyrolysis was not carried out completed and had thus the low oil and gas yield. The low oil yield at high temperatures such as 555 °C and 585 °C was due to the excessive cracking of oil vapor into light hydrocarbon gases and also light oil species [27]. Only the intermediate pyrolysis temperature such as about 495 °C in our reactor guaranteed both the deep pyrolysis of oil shale to release volatile as much as possible and the moderate cracking of the formed volatile matters into gases [28]. The oil yield was close to 90% of the Fischer Assay yield at 495 °C and exceeded 80% at 460–530 °C (pyrolysis temperature). Fig. 4 also showed that the pyrolysis gas yield and gas/oil mass ratio gradually increased with increasing the SHC or pyrolysis temperatures. We found that the variations in shale oil and pyrolysis gas yields well balanced to maintain the nearly constant total pyrolysis product yield. Thus, the reduced oil fraction was actually converted into gas product by cracking. Fig. 5 shows the composition of shale oil as well as the yields of individual distillates for the same tests shown in Fig. 4. In Fig. 5(a), the contents of gasoline and diesel relatively increased by 60.9% and 32.0% respectively for the pyrolysis temperature variation from 435 to 585 °C. The total light oil fraction (gasoline + diesel) was over 70 wt.% at the pyrolysis temperature above 495 °C and it ultimately reached 82.62 wt.% at 585 °C. In Fig. 5(b), the yield
3.2. Variation with pyrolysis temperature The temperature of shale ash from oil shale char combustor is usually about 800 °C. The blending ratio of such hot ash to oil shale Table 3 Ultimate analysis of shale oil at pyrolysis temperature from 465 to 525 °C in the reactor with internals.
a
Pyrolysis temperature (°C)
Ultimate analysis (wt.%) C
H
Oa
N
S
465 495 525
83.88 84.60 84.87
11.36 11.16 11.05
3.32 2.73 2.52
1.01 1.14 1.16
0.43 0.37 0.40
By difference.
Atomic H/C ratio
1.63 1.58 1.56
Fig. 4. Shale oil and pyrolysis gas yields varying with solid heat carrier temperature (upper X) or pyrolysis temperature (lower X) in reactor with internals.
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Fig. 5. Shale oil quality varying with pyrolysis temperature in reactor with internals.
of gasoline initially increased and then constantly remained from 495 °C. For diesel yield it first increased and then decreased to form a peak yield at about 495 °C. Overall, raising the pyrolysis temperature obviously reduced the yield of VGO, say, its content varied from 39.23 wt.% to 17.38 wt.% in Fig. 5(a) and its yield from 2.74 wt.% to 1.14 wt.% in Fig. 5 (b) when the pyrolysis temperature increased from 435 to 585 °C. All of these show that the particle bed plays a kind of upgrading effect for the produced shale oil in the MBI pyrolyzer based on solid heat carrier [27,28], but the suitable temperature should be around 495 °C for ensuring the high oil yield and quality simultaneously. At very high pyrolysis temperatures there should be significant loss of shale oil [28,29]. Fig. 6 shows the corresponding composition of pyrolysis gas. In Fig. 6(a), the yields of all individual components except for CO2 increased with raising the pyrolysis temperature, although by different levels or degrees. The obvious increase occurred for the yields of H2, CH4 and C2 hydrocarbons, while slight rise was shown by CO and C3 hydrocarbons. Thus, with raising the pyrolysis temperature more volatile was released and more high-carbon aliphatic species in the formed shale oil were cracked to form more H2 and also some CH4 and C2 hydrocarbons [30]. The yield of CO2 was almost constant at the tested pyrolysis temperatures of 435 to 585 °C. It consisted with the results of many literature studies [30,31] and was because that CO2 was formed mainly from decomposition of carboxyl groups and inorganic minerals so that the temperature above 465 °C little affected the evolution of CO2. The molar ratio of alkene to alkane in the non-condensable pyrolysis gas can be used to understand the reaction mechanism [31–33]. Campbell et al. [31] reported an increase in the ethene/ethane and propene/propane molar ratios to indicate essentially the facilitated vapor phase cracking reactions. Fig. 6(b) shows that in our tests all the calculated ratios as well as the gas production rate of alkane and alkene increased with raising the pyrolysis temperature. Nonetheless, the production rate of alkene (ethene and propene) increased more rapidly than that of alkane (ethane and propane). For the propene/propane molar ratio, it first
Fig. 6. Production rates of major gas species and molar ratios of ethene/ethane, propene/propane and alkene/alkane in pyrolysis gas product varying with pyrolysis temperature in reactor with internals.
increased slightly and then significantly above 495 °C. All of these demonstrate essentially that the cracking of oil vapor in the pyrolyzer become substantial since 495 °C through its interactions with both char and shale ash particles. The oil cracking forms more alkene than alkane, being the case especially for propene and propane. This makes the propene/propane ratio highest at all the tested temperatures and also the quickest increase in Fig. 6(b). Consequently, the alkene/alkane ratio is in-between the ratios of propene/propane and ethene/ethane. 3.3. Variation with particle bed thickness As illustrated in Fig. 1, we define the distance between the side channel and central channel as the particle bed thickness. In this article, we chose the particle bed thickness of 120, 150 and 180 mm to investigate the influence of particle bed thickness at the ash-to-shale blending ratio of 5:1 and pyrolysis temperature of about 490 °C. Fig. 7(a) shows the oil and gas yields varying with the bed thickness. Increasing the thickness from 120 mm to 180 mm decreased the oil yield from 9.22 wt.% to 8.66 wt.% and also increased the gas yield and gas/oil mass ratio. Nonetheless, the influences from varying the particle bed thickness were not as significant as varying the pyrolysis temperature clarified above. At thin particle bed (i.e., 120 mm), the pyrolysis volatile flowed out quickly after its generation, thus suffering less secondary cracking to allow the higher shale oil yield. Increasing the bed thickness caused the longer residence time of primary volatile product inside the particle bed and thus the higher extent of secondary cracking and the lower oil yield. Fig. 7(a) also shows that the increase in the gas yield well matched the reduction in the oil yield, meaning that the reduced oil production is mainly converted into gas product by oil vapor cracking in the particle bed. Increasing the particle bed thickness caused the higher light oil content (gasoline and diesel) but the lower VGO and heavy oil fractions, as is shown in Fig. 7(b). This was also a result from enhancing
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explained why all alkene/alkane ratios elevated with raising the bed thickness. In Fig. 7(c) the ratio of propene/propane was the highest, while the ethene/ethane ratio was the lowest. These demonstrated further that the increased shale oil cracking in thicker bed formed more alkene in comparison with the formation of alkane. The volatile product through the particle bed can get also a dust filtration effect. This is another technology advantage of the tested moving bed with internals. Our experimental results shows that the produced shale oil at a bed thickness of 180 mm contained only 0.04 wt.% dust, whereas this dust content was 0.22 wt.% and 0.16 wt.% at the thickness of 120 mm and 150 mm. Thus, the thicker the particle bed, the better the dust filtration effect was. Overall, a thick particle bed led to the expected oil upgrading effects including both cracking of heavy oil fraction and filtration of dust containing in the produced shale oil. However, increasing the particle bed thickness had to reduce the shale oil yield, although it increased the gas yield. Practically, there should be a tradeoff condition that balances both such beneficial and reverse effects. This optimal bed thickness should be related to practical conditions, and in all tests of this article we chose 150 mm to be the ‘‘standard’’ bed thickness for the reactor with internals. 3.4. Variation with ash-to-shale ratio The pyrolysis temperature is determined by the temperature of shale ash and its mass ratio to oil shale. For testing the influence of ash-to-shale mass blending ratio, we varied the temperature of shale ash according to the calculation that keeps the same
Fig. 7. Influence of particle bed thickness on (a) shale oil and pyrolysis gas yields, (b) shale oil composition and distillate yields, (c) molar ratio and production rates of alkene and alkane gases for pyrolysis in reactor with internals.
the secondary cracking of formed shale oil in the thicker particle bed. Concretely, varying the particle bed thickness from 120 mm to 180 mm increased the light oil content to 73.21 wt.% or relatively by 16.2% and meanwhile relatively reduced the content of heavy oil fractions (VGO + heavy oil) by 27.6%. Correspondingly, the yield of light oil fraction had a slight increase from 5.81 wt.% to 6.34 wt.%, whereas that of ‘‘VGO + heavy oil’’ decreased from 3.41 wt.% to 2.32 wt.%. The result showed further that the raised light oil yield (gasoline and diesel) was firmly from the conversion (i.e., cracking) of the reduced ‘‘VGO and heavy oil’’ productions. This conversion formed also gaseous product and carbon to increase the gas yield and the gas/oil ratio (see Fig. 7(a)). Fig. 7(c) shows the gas production rate of alkenes and alkanes in liter per kilogram oil shale and their molar ratios varying with the particle bed thickness. Increasing the bed thickness led to the higher ratios of ethene/ethane, propene/propane and alkene/alkane and also the higher production rate of alkenes and alkanes. At the bed thickness of 120 mm, the yield of gaseous alkene product was lower than that of alkane product. Increasing the bed thickness caused the quicker rise in the alkene production rate than in the alkane so that the alkene gas production rate became higher at the bed thickness of 150 mm and 180 mm. This also
Fig. 8. Influence of ash-to-shale blending ratio on (a) shale oil and pyrolysis gas yields and (b) shale oil composition and distillate yields for pyrolysis in reactor with internals.
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pyrolysis temperature. Fig. 8(a) shows the shale oil and pyrolysis gas yields at a pyrolysis temperature of about 490 °C and a bed thickness of 150 mm but different blending ratios of shale ash to oil shale. A low blending ratio of 3:1 with a high ash temperature of about 900 °C caused the high extent of oil vapor thermal cracking. The high blending ratio of 7:1 provided the high probability for the interaction between shale ash and oil vapor. Thus, obtaining the possibly highest oil yield required well-matched blending ratio and shale ash temperature. This seems to be about 5:1 at ash temperatures of about 750 °C. Under this condition the shale oil yield was the highest and gas yield was the lowest, verifying that there was the higher degree of secondary cracking to shale oil vapor at the ratios 3:1 and 7:1 due to the high ash temperature and high load of ash particles, respectively. Fig. 8(b) shows the corresponding variation in shale oil composition and the yields of distillates. It was obvious that the produced shale oil at the ratio of 5:1 had relatively lower fractions of gasoline and diesel, while the fraction of VGO was lower for the ratios of 3:1 and 7:1. At the ratio of 7:1 the VGO fraction was the lowest, while its total content of light oil fraction (gasoline + diesel) also reached 81 wt.%. This content was about 69 wt.% at 5:1 and 76 wt.% at 3:1. The yields of distillates exhibited difference mainly in the heavy oil fraction of ‘‘VGO + heavy oil’’, which was about 2.0 wt.%, 2.8 wt.% and 1.5 wt.% at the blending ratios of 3:1, 5:1 and 7:1, respectively. The yield of light oil fraction was not much different among the three blending ratios. Consequently, we can believe that the higher extent of secondary cracking at the ratios of 3:1 (due to high ash temperature) and 7:1 (due to much more ash) mainly converted the heavy oil fraction into light oils and also pyrolysis gas. Its formed light oils then compensated for the cracked gasoline and diesel oils (into gas particularly) under such conditions so that the content of light oil fraction remained to vary little with the blending ratio of shale ash to oil shale.
4. Conclusions A laboratory facility was developed to pyrolyze small-size oil shale (below 13 mm) by solid heat carrier in an innovative moving bed with particularly designed gas channel as internals (MBI). The yields and qualities of shale oil were studied with respect to the major influential parameters such as solid heat carrier temperature or pyrolysis temperature, particle bed thickness between the side and central channels and ash-to-shale mass blending ratio. For the tested Huadian oil shale, good performance was achieved. The use of the internals increased the shale oil yield, while it also made the particle layer as a filtration bed between the side and central channels to reduce the dust content in the produced oil to about 0.1 wt.%. The highest shale oil yield appeared at the pyrolysis temperature of about 495 °C or shale ash temperature of about 750 °C. The shale ash bed facilitated the secondary cracking of shale oil, especially at temperatures above 525 °C. The secondary cracking converted VGO and heavy oil into light oil fractions and gas products, and it was affected by both the temperature of ash particles or bed and the blending ratio of ash to shale. The higher temperature and blending ratio, the more intensive the secondary reaction was. Consequently, there should be an optimal matching between the ash temperature and ash-to-shale ratio. Overall, the use of MBI for pyrolyzing small-size oil shale by hot shale ash as the heat carrier has achieved oil yield close to 90% of the Fischer Assay yield, referring to an advanced level that is obviously higher than 65–70% of the Fischer Assay yield enabled by the Fushun retort widely applied in China. The produced shale oil had gasoline and diesel content over 70 wt.% which is much higher than 50 wt.% from Fischer Assay retorting test. In addition, the shale oil recovered from the pyrolysis in MBI presents a good
oil–water separation property and its density is around 0.85 g/ml, about 50 kg/m3 lower than that of the oil produced by Fushun retort. The generated pyrolysis gas has also high quality by containing about 15 vol.% C2–C3 hydrocarbons and its higher heating value reaches 20 MJ/N m3. All of these show that the use of MBI is potential to solve the bottleneck problems for pyrolysis of small-size feedstock based on solid heat carrier, which include high dust content in produced oil and high content of heavy oil fraction. Thus, a prospective technology is actually presented for the pyrolysis or retorting of small-size oil shale. Acknowledgments The study was financed by the National Basic Research Program of China (Grant 2014CB744303) and the National Natural Science Foundation of China (Grant 21306210). References [1] Jiang XM, Han XX, Cui ZG. New technology for the comprehensive utilization of Chinese oil shale resources. Energy 2007;32(5):772–7. [2] Dyni JR. Geology and resources of some world oil-shale deposits. Oil shale 2003;20(3):193–252. [3] Cook EW. Oil-shale technology in the USA. Fuel 1974;53(3):146–51. [4] Golubev N. Solid oil shale heat carrier technology for oil shale retorting. Oil shale 2003;20(3SI):324–32. [5] Qian JL, Wang JQ, Li SY. World oil shale utilization and its future. J Jilin University (Earth Science Edition) 2006;36(6):877–87 [in Chinese]. [6] Dung NV, Yip V. Basis of reactor design for retorting Australian oil shales. Fuel 1991;70(11):1336–41. [7] Dung NV. A new concept for retorting oil shale. Fuel 1987;66:377–83. [8] Na JG, Im CH, Chung SH, Lee KB. Effect of oil shale retorting temperature on shale oil yield and properties. Fuel 2012;95(1):131–5. [9] Liang P, Wang ZF, Bi JC. Process characteristics investigation of simulated circulating fluidized bed combustion combined with coal pyrolysis. Fuel Process Technol 2007;88(1):23–8. [10] Trikkel A, Kuusik R, Maljukova N. Distribution of organic and inorganic ingredients in Estonian oil shale semicoke. Oil shale 2004;21(3):227–35. [11] Wong CM, Crawford RW, Burnham AK. Source and kinetics of sulfur species in oil shale pyrolysis gas by triple quadrupole mass spectrometry. ACS Petrol Div 1984;29(2):317–21. [12] Opik I, Golubev N, Kaidalov A, Kann J, Elenurm A. Current status of oil shale processing in solid heat carrier UTT (Galoter) retort in Estonia. Oil shale 2001;18(2):99–107. [13] Rammler RW. The production of synthetic crude oil from oil sand by application of the Lurgi-Ruhrgas Process. Can J Chem Eng 1970;48:552–60. [14] Guo SC, Luo CQ, You LB, Han W, Han Z. Experimental research on Huadian oil shale retorting using solid heat carrier. J Dalian Inst Technol 1986;25(4):25–30 (In Chinese). [15] Tamm PW, Langlois GE. Staged turbulent bed retorting process. USA. 4199432. 1980-04-22. [16] Tamm PW, Bertelsen CA, Handel GM, Spars BG, Wallman PH. The Chevron STB oil shale retort. Energy Prog 1982;2(1):37. [17] Li WY, Deng Y, Yu CL. Development of lignite pyrolysis with solid heat carrier. Coal Chem Ind 2012;158(1):1–5 (In Chinese). [18] Burnham AK, McConaghy JR. Comparison of the acceptability of various oil shale processes. In: Golden: 26th Oil shale symposium; 1991. UCRL-CONF226717. [19] Cena RJ, Thorsness CB. LLNL oil shale pilot plant status report. In: Eastern oil shale symposium; 1990. UCRL-JC-105170. [20] Camp DW, Braun RL, Diaz JC. Results of mathematical modeling of an oil shale retort having a fluidized-bed pyrolyzer and a lift-pipe combustor. Fuel Process Technol 1989;21(2):135–63. [21] Aldis DF. Attrition and abrasion models for oil shale process modeling. Fuel 1992;71:1447–53. [22] Carter SD, Robl TL, Taulbee DN, Rubel AM. Testing of an Irati oil shale in a multi-stage fluidized bed retorting process. Fuel 1991;70(11):1347–51. [23] Carter SD, Robl TL, Rubel AM, Taulbee DN. Processing of eastern US oil shale in a multistaged fluidized bed system. Fuel 1990;69(9):1124–8. [24] Schmidt SJ. New directions for shale oil: path to a secure new oil supply well into this century: on the example of Australia. Oil shale 2003;20(3S):333–46. [25] Brandt AR. Converting oil shale to liquid fuels with the Alberta Taciuk Processor: energy inputs and greenhouse gas emissions. Energy Fuels 2009;23:6253–8. [26] Coburn HT, Duewer TI, King KJ. Shale oil form the LLNL pilot retort: metal irons as markers for water and dust. In: Eastern oil shale symposium; 1993. UCRLJC-115740. [27] Rubel AM, Rimmer SM, Keogh R, Thomas LR, Scott DC, Frank JD. Effect of process solids on secondary reactions during oil shale retorting. Fuel 1991;70(11):1352–6.
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