Flash Pyrolysis of Jatropha Oil Cake in Gas Heated Fluidized Bed Research Reactor

Transcription

1 International Journal of Chemical Engineering Research ISSN Volume 2, Number 1 (2010), pp Research India Publications Flash Pyrolysis of Jatropha Oil Cake in Gas Heated Fluidized Bed Research Reactor S. Antony Raja 1, Z. Robert Kennedy 2 and B.C. Pillai 3 1 Research scholar, School of Mechanical Sciences, Karunya University, Coimbatore. 2 Associate professor, School of Mechanical Sciences, Karunya University, Coimbatore. 3 Dean, Research, Karunya University, Coimbatore. santonyraja@yahoo.co.in; santonyraja@karunya.edu Abstract Fluidized bed flash pyrolysis experiments have been conducted on a sample of jatropha oil cake to determine particularly the effects of particle size, pyrolysis temperature and nitrogen gas flow rate on the pyrolysis yields. The particle size of jatropha oil cake was varied in the range of mm. Reaction temperatures were varied from 350ºC to 500ºC.The nitrogen gas flow rate were varied from 1LPM to 4 LPM. The maximum oil yield of 47.9 was obtained at a nitrogen gas flow rate of at 3 LPM, particle size of mm and at a pyrolysis temperature of 450ºC. The calorific value of pyrolysis oil is MJ/kg. The pyrolysis gas can be used as fuel gas. Key words: Flash pyrolysis, fluidized bed, jatropha oil cake, and pyrolysis oil Introduction The diminishing reserves and apparent negative effects such as green house gases and acid rain of fossil fuel has lead the world community to recognize the importance of renewable and cleaner energy in recent years [1]. The recovery of energy from a renewable source like biomass involves chemical, biochemical and thermo chemical processes, depending on the nature of the source. The main advantages of using biomass are its negligible sulfur, nitrogen and metal content. Reduced carbon dioxide and sulfur dioxide emissions as a result of utilization of biomass for energy generation are important for preventing the green house effect and acid rain. The net flow of carbon dioxide to the atmosphere, and thereby the global potential, is reduced when fossil fuels are replaced with sustainable produced biomass. Consumption of

2 2 S. Antony Raja et al agricultural residues for energy production would also reduce the environmental damage [2]. Among the thermo chemical processes, pyrolysis has become an attractive alternative because of the ease of operation. Its suitability as fuel for energy production and as feed stock for chemical industries, relatively few polluting emissions, carbon dioxide neutral cycle and ease of reproduction; make pyrolytic oil a favorable option. The proportion of gas, liquid and solid products depend very much on the pyrolysis technique used and on the reaction parameters. Depending on the operating conditions, the pyrolysis process can be divided into three sub classes: conventional pyrolysis (carbonization), fast pyrolysis and flash pyrolysis. Slow pyrolysis processes are performed at a low-heating rate and a long residence time. The longer residence times can cause secondary cracking of the primary products reducing yield and adversely affecting bio oil properties. In additions, a low heating rate and long residence time may increase energy input. All of these are not attractive for commercial application of liquid fuel production. At present, the preferred technology for production of oily products is fast or flash pyrolysis at high temperatures with very short residence times [3]. The pyrolysis oil from biomass waste was found to be highly oxygenated and complex, and chemically unstable. Thus, the liquid products still need to be upgraded by lowering the oxygen content and removing residues [4]. The range of the main operating parameters for pyrolysis processes is given in Table 1. Table 1: The range of the main operating parameters for pyrolysis processes. Parameters Conventional pyrolysis Fast pyrolysis Flash pyrolysis Pyrolysis temperature (k) Heating rate (k/s) >1000 Particle size (mm) 5-50 <1 <0.2 Heating time (sec) <0.5 In this study, the flash pyrolysis of jatropha oil cake was investigated in a fluidized bed reactor. Particularly, the influences of pyrolysis temperature, particle size range and Nitrogen gas flow rate on the product yields were studied. In addition to this the properties of pyrolysis oil was determined. Methods Materials The pressed oil cake from jatropha was taken in this study. Jatropha press cake is the biomass remaining as a by-product of industrial processes after removal of the oil by

3 Flash Pyrolysis of Jatropha Oil Cake in Gas 3 pressing. Prior to use, the sample was air dried, ground in a ball mill, and then screened to give fractions 0.3<Dp< 0.6, 0.6 <Dp <1.0, 1.0< Dp <1.18 mm and 1.18< Dp <1.4 mm in size [5, 6]. The values for volatiles, fixed carbon, ash, moisture (wt. % as-received), elemental composition (dry, ash-free basis) and calorific value (MJ/kg) were determined for jatropha oil cake and are reported in table 2.The main characteristics of the jatropha oil cake are given in Table 2. Table 2: Main characteristics of the jatropha oil cake. Proximate analysis Moisture Ash Volatile matter Fixed carbon Sulfur Ultimate analysis Carbon Hydrogen Oxygen Nitrogen Gross calorific value 08.71% 04.30% 70.92% 16.06% 00.01% 59.17% 06.52% 33.93% 00.38% MJ/kg Pyrolysis reactor Figure 1 shows the gas heated fluidized bed research reactor. The crushed jatropha oil cake was fed into the fluidized bed reactor by means of hopper and screw rod. The liquefied petroleum gas was used as heat source. The nitrogen gas was used as fluidizing gas. The velocity of fluidizing gas was kept above the minimum fluidization velocity. The rate of flow of nitrogen gas was measured by a rotometer.the feeder was switched on when the reactor reaches the desired temperature. In the reactor, the temperature was measured with thermocouples at five different points. The experiments were carried out in three series. The first was to determine the effect of the pyrolysis temperature on pyrolysis yields. When the reactor reached the selected pyrolysis temperature under a sweeping gas (nitrogen) rate of 3 LPM, a screw feeder at a rate of 30g/min fed the sample. In order to avoid pyrolysis of the sample prior to the reactor, the feeding system was cooled by water. The other two groups of experiments were performed to establish the effect of particle size and the effect of sweep gas velocity on the pyrolysis yields. These experiments were conducted using four different particle size ranges of 0.3<Dp< 0.6, 0.6 <Dp <1.0, 1.0< Dp <1.18 mm and 1.18< Dp <1.4 mm, and sweep gas flow rate of 1, 2, 3 and 4 liter per minute (LPM). Based on the results of the first group of experiments, the

4 4 S. Antony Raja et al pyrolysis temperature of the second series was kept at 450 o C. The solids were collected on the cyclone separator, which was placed next to the reactor. The liquid phase, consisting have aqueous and oil phases, was separated and weighted. Then the gas yield was calculated from the material balance. Figure 1: Schematic diagram of gas heated fluidized bed research reactor. Results and Discussion Effect of Nitrogen gas flow rate on Product yields To determine the effect of nitrogen gas flow rate on yield of pyrolysis products the experiments were performed at four different nitrogen gas flow rate of 1, 2, 3 and 4 liter per minute (LPM). For this group of experiments the particle size ranges were mm, mm, mm and mm.the oil yield increases slightly as the nitrogen gas flow rate increases from 1 to 3 LPM and then decreases at 4 LPM.The char yield decreases slightly as the nitrogen gas flow rate increases. The gas yield decreases slightly as the nitrogen gas flow rate increases from 1 to 3 LPM and then increases at 4 LPM. The highest oil yield of 47.9 was obtained at a nitrogen gas flow rate of 3 LPM and a particle size of mm.it was observed that oil yield increased by only 3.7 upon increasing the nitrogen gas flow rate from 1 to 3 LPM. The char yield of 13.4 was obtained at a nitrogen gas flow rate of 1 LPM. The gas yield of 34.8 was obtained at a nitrogen gas flow rate of 4 LPM. Our experimental results show that the yields of oil and non-condensable gases were affected slightly by the nitrogen gas flow rate. The nitrogen gas flow rate had no significant effect on the char and water yields, remaining constant at and respectively. As reported in the literature, the sweep gas (nitrogen gas) removed the volatiles from the pyrolysis environment.

5 Flash Pyrolysis of Jatropha Oil Cake in Gas 5 Therefore, secondary reactions such as thermal cracking, re-polymerization and re-condensation were kept to a minimum for maximum liquid yield [7, 8, and 9]. The short residence time of the volatiles in the reactor as the nitrogen gas velocity increased causes relatively minor secondary decomposition of higher molecular weight products [10, 11]. Figure2 and table3 shows the effect of nitrogen gas flow rate on product yield at Particle size of mm and at a pyrolysis temperature of 450 C. Figure 2: Nitrogen gas flow rate vs. product yield. (Particle size: mm and Pyrolysis temperature: 450 C) Table 3: Effect of nitrogen gas flow rate on product yield (Particle size: mm and pyrolysis temperature: 450 C). Nitrogen gas flow rate, LPM Oil Gas Char Water

6 6 S. Antony Raja et al Effect of particle size on Product yields To determine the effect of particle size on product yields, experiments were conducted in a gas heated fluidized bed reactor at different particle sizes and at different nitrogen gas flow rates. For this group of experiments the particle size range were mm, mm, mm and mm.the-nitrogen gas flow rate were 1,2,3 and 4 LPM. The oil and char yield slightly increases as the particle size increases and then decreases for larger particle sizes. The gas yield decreases as the particle size increases and then increases for larger particle sizes. The yield of pyrolysis oil is 47.9 for the particles of mm with a char yield of 10.8 at nitrogen gas flow rate of 3 lpm.the smallest ( mm) particle sizes produced an oil yield of 46.5 with a char yield of 8.7.Larger ( mm) particle sizes produced an oil yield of 42.3 with a char yield of 9.4. This result suggested that mass and heat transfer restrictions had a profound influence at a larger particle size, resulting in minimum oil yield [12]. The gas yield obtained was found at the level of 27.2 to 35.1 for all the particle sizes investigated. Particle size is known to influence pyrolysis product yield [13, 14]. Our experimental results show that particle size had significant effect on product yields. If the particle size is sufficiently small it can be heated uniformly results in high oil yield. The oil yield had an increasing trend as the particle size increased from mm to mm. working at a particle size range of mm seems suitable for obtaining a high yield of oil (47.9 wt %) at nitrogen gas flow rate of 3 LPM. Reaction Completion time increases with increasing size of particle due to the heat transfer from outer of a small particle into inner is carried out lower time than that of a big particle [15]. The water contents in the pyrolysis oil resulting from the original moisture in the feedstock and as a product of the dehydration reactions occurring during pyrolysis could be up to 14.1 at nitrogen gas flow rate of 3 LPM and particle sizes of mm. Figure 3 and table 4 shows the effect of particle size on product yield at nitrogen gas flow rate of 3 LPM and at a pyrolysis temperature of 450 C. Table 4: Particle size vs. product yield. (Nitrogen gas flow rate: 3 LPM and pyrolysis temperature: 450 C). Particle size, mm Oil Gas Char Water

7 Flash Pyrolysis of Jatropha Oil Cake in Gas 7 Figure 3: Particle size vs. product yield (Nitrogen gas flow rate: 3 LPM and Pyrolysis temperature: 450 C) Effect of temperature on Product yields To determine the effect of yields of pyrolysis products, experiments were conducted at a particle size of 1 mm, nitrogen gas velocity of 3lpm and at final temperatures of either 350,400,450 or 500ºC.The oil, gas and water yield increases as the pyrolysis temperature increases. The char yield decreases as the pyrolysis temperature increases. It is known that increasing the final pyrolysis temperature increases carbon conversion to gas [16]. The oil yield was at the pyrolysis temperature of 350ºC, it appeared to go through a maximum of at the final temperature of 500 ºC and at a nitrogen gas flow rate of 3 lpm. The char yield decreased roughly by as the temperature was raised from 350ºC to 500ºC.The gas yield was at the pyrolysis temperature of 350ºC, it appeared to go through a maximum of at the final temperature of 500 ºC and at a nitrogen gas flow rate of 3 LPM. The water yield increases as the pyrolysis temperature increases. The water yield increased roughly by 3.41 as the temperature was raised from 350ºC to 500ºC. Figure 4 and table 5 shows the effect of temperature on product yield at nitrogen gas flow rate of 3LPM and at particle size of 1.00 mm.

8 8 S. Antony Raja et al Figure 4: Temperature vs. product yield. (Particle size: 1.0 mm and nitrogen gas flow rate: 3 LPM Table 5: Temperature vs. product yield. (Particle size: 1.0 mm and nitrogen gas flow rate: 3 LPM) Temperature, C Oil Water Char Gas Figure 5 shows the effect of nitrogen gas flow rate on oil yield at different particle sizes. The highest oil yield of 47.9 was obtained at a nitrogen gas flow rate of 3 LPM and a particle size of mm.

9 Flash Pyrolysis of Jatropha Oil Cake in Gas 9 Figure 5: Nitrogen gas flow rate vs. oil yield. Analysis of pyrolysis oil The properties of pyrolysis oil obtained from flash pyrolysis of Jatropha oil cake are given in Table 6.The oil analyzed in this study have been obtained under experimental conditions that gives maximum oil yield. Prior to study, the pyrolysis liquids were first decanted and then centrifuged for 15 minutes at about 2000 rpm, inorder to separate an organic phase from aqueous phase and char traces [16]. The properties of pyrolysis oil are compared with diesel. Table 6: Comparison of Properties of pyrolysis oil with diesel. Properties Diesel Pyrolysis oil EFFECTS Calorific value MJ/kg MJ/kg Effects in engine performance Conradson carbon % Affect the engine, deposited in residue injector Kinematic viscosity at 40ºC 2.0 to 4.5 cst 7.4 cst Effects in pumping, fuel injection Flash point 80ºC 140ºC Safety storage. High fire point leads to starting problem. Pour point 2ºC 4ºC Effects in cold conditions Ash content 0.01 to 0.1% 0.1% Erosion and corrosion Acidity as mg of KOH/gm Damage to injector, deposits in fuel systems like pump filters etc. The calorific value of diesel is MJ/kg. The high flash point suggested that the oil could be safely stored at room temperature. Calorific value of oil indicates that the energy contents of the oil are nearly half that of diesel. Literature survey shows

10 10 S. Antony Raja et al that in their pure form, vegetable oils are not suitable for use in modern diesel engines. The high viscosity of the vegetable oil may be a major factor in carbon deposits in the combustion chamber and exhaust ports. A reduction in viscosity greatly reduces engine operation problems. Dilution and transesterification are the techniques used to solve the problem related to high viscosity [17]. The presence of ash in the oil can cause erosion and corrosion problems [18]. The main source of ash in pyrolysis oil is the solid char particles carried over by pyrolysis vapors. The calorific values of the jatropha oil cake and pyrolysis oil are listed in Table 10. Table 7: Calorific values of the sample of jatropha oil cake and pyrolysis oil. Material Calorific value (MJ/kg) Jatropha oil cake Pyrolysis oil Conclusion The highest oil yield of 47.9 was obtained at a nitrogen gas flow rate of 3 LPM and a particle size of mm. The gas yield was at the pyrolysis temperature of 350ºC, it appeared to go through a maximum of at the final temperature of 500 ºC and at a nitrogen gas flow rate of 3 LPM. The nitrogen gas flow rate had no significant effect on the char and water yields, remaining constant at and respectively. The oil and char yield slightly increases as the particle size increases and then decreases for larger particle sizes. The gas yield decreases as the particle size increases and then increases for larger particle sizes. This result suggested that mass and heat transfer restrictions had a profound influence at a larger particle size, resulting in minimum oil yield. Particle size is known to influence pyrolysis product yield. Our experimental results show that particle size had significant effect on product yields. The pyrolitic oil was identified as a bio fuel candidate. The liquid may be used as a source of low-grade fuel directly or it may be upgraded to higher quality liquid fuels. The pyrolysis gas can be used as fuel gas. The calorific value of pyrolysis oil is MJ/kg. Calorific value of oil indicates that the energy contents of the oil are nearly half that of diesel. In their pure form, pyrolysis oils are not suitable for use in modern diesel engines. The high viscosity of the oil may be a major factor in carbon deposits in the combustion chamber and exhaust ports. A reduction in viscosity greatly reduces engine operation problems. Dilution and transesterification are the techniques used to solve the problem related to high viscosity [19, 20].By the application of various processes (cracking, hydrogenation, etc.) fuel characteristics may be improved and under this circumstance the oil may either be used directly or its fractions may be evaluated as an alternative to gasoline, diesel fuel and fuel oil [21].

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12 12 S. Antony Raja et al [18] Experiments on the pyrolysis of large beech wood particles in fixed beds. Elisabeth schroder, J. Anal. Appl. pyrolysis 71 (2004) [19] Fluidized bed pyrolysis of Moroccan oil shale using the Hamburg pyrolysis process A.Sadiki, et.al J. Anal. Appl. pyrolysis 70 (2003) [20] Bio oil production from pyrolysis and steam pyrolysis of soybean cake: product yields and composition. Ayse E.Putun, Esin A paydin and Ersan putun. Energy volume 27, issue7, July 2002, pages [21] Bio oil production from soybean; fuel properties of bio oil. Sevgi sensoz and iike kaynar. Industrial crops and products Volume 23, issue 1, January 2006, pages