Parametric Study for Production of Dimethyl Ether (DME) As a Fuel from Palm Wastes

Parametric Study for Production of Dimethyl Ether (DME) As a Fuel from Palm Wastes

Available online at www.sciencedirect.com ScienceDirect Energy Procedia 105 (2017) 1242 – 1249 The 8th International Conference on Applied Energy – ...

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Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 105 (2017) 1242 – 1249

The 8th International Conference on Applied Energy – ICAE2016

Parametric Study for Production of Dimethyl Ether (DME) As a Fuel from Palm Wastes Abrar Inayata,*, Chaouki Ghenaia, Muhammad Naqvib, Muhammad Ammarc, Muhammad Ayoubc, M N B Hussinc a

Department of Sustainable and Renewable Energy Engineering, University of Sharjah, 27272 Sharjah, UAE Future Energy Center, School of Business, Society and Engineering, Mälardalens University, Västerås, Sweden c Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar 32610, Perak, Malaysia b

Abstract Dimethyl Ether (DME) has been getting numerous attention as it’s potential as the second generation bio-fuel. Traditionally DME is produced from the petroleum based stock which involves two steps of synthesis (methanol synthesis from the syngas and DME synthesis from methanol). DME synthesis via single step is one of the promising methods that has been developed. In Malaysia, due to the abundance of oil palm waste, it is a good candidate to be used as a feedstock for DME production. In this paper, single step process of DME synthesis was simulated and investigated using the Aspen HYSYS. Empty Fruit Bunch (EFB) from palm wastes has been taken as the main feed stock for DME synthesis. Four parameters (temperature, pressure, steam/biomass ratio and oxygen/biomass ratio) have been studied on the H2/CO ratio and DME yield. The results showed that optimum H2/CO ratio of 1.0 has been obtained when having an oxygen to biomass ratio (O/B) of 0.37 and steam to biomass ratio (S/B) of 0.23. The increment in the steam to biomass ratio increased the production of DME while the increment in oxygen to biomass ratio will cause reduction in DME production. ©©2017 Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.

Keywords: Biomass Gasification; DME synthesis; Process simulation; Aspen Hysys

1. Introduction With regards to energy shortage and global warming crisis, the possibility of producing fuel from biomass and wastes has been even more promising as it involves the renewable sources. The second generation of biofuels such as methanol, bioethanol, dimethyl ether (DME), synthetic natural gas and hydrogen are more promising [1]. The usage of biomass for DME production is an attractive approach to be explored in Malaysia due to its abundance. Being the world largest producer of palm oil [2], the availability of empty fruit bunch (EFB) provides excellent feedstock for DME production. Dimethyl Ether (DME) as one of the second generation of biofuels can be produced traditionally from the * Corresponding author. Tel.: +971-65053972; fax: +971-65585191. E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.431

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petroleum based feed which involves two steps of production (methanol synthesis from the syngas and DME synthesis from methanol) [3]. A Recent study showed that DME production process is now possible to be done with biomass as the raw material and a single step for DME production process has been developed [4]. Single step of DME synthesis is more economical and has overcome the equilibrium limitation poses by methanol synthesis [5]. Lee et al. [6] performed experimentally single step synthesis of dimethyl ether (DME) from syngas using bio-functional catalysts. On the other hand, Zhu et al. [7] developed a new technical route to improve two step synthesis for DME production, which was composed of methanol synthesis and methanol dehydration in a fixed-bed reactor. Furthermore, they investigated the operating conditions including reaction pressure, temperature, H 2/CO on the yield of DME. Chang et al. [8] proposed a novel route for DME production from biomass and tested in a bench scale experimental system as well. There are very limited studies that have been carried out on the modelling and simulation of DME synthesis. Xiang et al. [9] simulated DME production process and investigated integrated energy-exergy based evaluation using Aspen PLUS. Their system contained a combination of biomass torrefaction unit (BTU) and entrained-flow gasification (EFG) followed by single-step DME synthesis. Moreover, Fudong et al.[4] simulated the single-step process of dimethyl ether (DME) synthesis via gasification using wood as biomass in ASPEN Plus. They have divided the whole process into four parts: gasification, water gas shift reaction, gas purification, and single-step DME synthesis. In addition, the influence of the oxygen/biomass and steam/biomass ratios on biomass gasification and DME synthesis performance has been investigated. In view of the recent development on gasification process and current scenario in Malaysia, this work is focusing on the simulation of the DME production process from Empty Fruit Bunch (EFB) by using Aspen HYSYS software. Furthermore, a parametric study was performed on the process to explore the operation limits for DME production from EFB using a single step process. The effects of four variables i.e. temperature, pressure, steam/biomass ratio and oxygen/biomass ratio, are studied to identify their impacts on the H2/CO ratio and DME yield. 2. Technical Approach The overall process route for DME production from palm wastes involved series of processes namely Gasification, Water Gas Shift, CO2 Removal and single step DME Synthesis as illustrated in Figure 1.

Figure 1: DME Production process Block Diagram

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There are five major reactions happening in the gasification stage as listed in Table 1 (Partial Oxidation, Gasification, Boudouard, Methanation, and Methane Reforming). The C, H and O component of the EFB reacted and transformed to produce H2, CO, CO2 and CH4. Later the gas produced is channeled into water gas shift (WGS) reactor to adjust the H2/CO ratio to the desired value. The modulated gas is then being transferred to CO2 Removal stage to purify the stream from CO2 gases. Next the purified gas is transferred into DME Synthesis reactor where two main reactions are involved; Methanol synthesis and methanol dehydrationIn the parametric study of DME production process, there are a few assumptions considered in the process development and modelling. x x x x

Ideal reaction condition The reaction occurs isothermally and at constant volume. Tar formation in the process is negligible in the calculation. Perfect mixing and uniform temperature and pressure distribution in the gasifier .

Table 1: DME production process reaction scheme Reaction

Gasification

Water gas shift CO2 removal DME synthesis

Partial Oxidation

Reaction scheme C3.4H4.1O3.3+2.775O2→3.4CO2+2.05H2O

Gasification

C3.4H4.1O3.3+0.1H2O↔2.15H2+3.4CO

Boudouard

C3.4H4.1O3.3+CO2↔4.4CO+0.9H2O+1.15H2

Methanation Methane Reforming

C3.4H4.1O3.3+8.05H2↔3.4CH4+3.3H2O CH4+H2O↔CO+3H2 CO+H2O↔H2+CO2 CaO+CO2↔CaCO3 3CO+3H2↔CH3OCH3+CO2

3. Process simulation The developed simulation model, as shown in Figure 2, derived from the reactions that are listed in Table 2. The configuration consists of four major sections; gasification (partial oxidation, gasification, boudouard, methanation, and methane reforming), water gas shift, CO 2 removal and DME synthesis. Peng- Robinson property package was used as thermodynamic property package. The stoichiometric reactor, Rstoic, was introduced to simulate the partial oxidation reaction, CO 2 removal and DME synthesis, while RGibbs reactor that is based on the Gibbs free energy minimization approach was used to simulate the gasification, methanation and methane reforming reactions. Pre-treated EFB of 100 kg/h was fed together with the oxygen and steam at 514˚C into conversion reactor where partial oxidation reaction occurred to transform EFB into CO2 gas and H2O. Next, the product and unreacted EFB continued the journey into gasification reactor where three reactions occurred simultaneously (gasification, methanation and methane reforming). The gaseous product from gasification reactor mainly composed of H2 and CO was sent into the water gas shift (WGS) reactor to modulate the H2/CO molar ratio to the required value. This work adapted the JFE technology which adopted a H 2/CO ratio of 1. WGS reaction was used and 70% of CO conversion was set. The product stream then entered the purifications section where CO2 removal reaction took place. CO2 removal reaction was simulated using Rstoic Module in the conversion reactor. The top product of the reactor which was CO 2 free stream next transported into DME synthesis reactor which was modulated by conversion reactor. The 90% conversion on H2 basis was set for the reaction to occurs. DME synthesis reactor was modulated by Rstoic Module.

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Figure 2: DME Production Process Simulation

4. Results and Discussion 4.1 Effect of H2/CO ratio H2/CO ratio of feed gas is an important factor in DME production processes. It can be varied by either changing the molar flow of steam or oxygen stream into the process. As this work adopted the JFE Technology in developing the DME synthesis reaction equation, a H 2/CO ratio of 1 is needed. Based on the simulated work the desired ratio was achieved when having a 370 kg/hr of Oxygen stream with the stream of 23 kg/hr steam in a basis of 1000 kg/hr of EFB fed as shown in Table 2. Table 2: Comparison of O/B and S/B ratio for H2/CO ratio of 1 .

Feed This work (EFB) (Dried Wood) [4]

100 kg/h 75.6 t/h

(O/B) 0.37 0.370

(S/B) 0.23 0.143

H2/CO ratio 1 1

This deviation in getting a H2/CO ratio of 1 can be explained by the difference in the feed used. Fudong et al. [4] was using dried woody biomass as the feedstock while this work is based on EFB as the feed. Difference in the properties of the feed might give different result as dried woody is having a higher content of oxygen compared to EFB. Dried woody contains 41.90% of oxygen while EFB have only 36.3% of oxygen. Other than that, Fudong et al. [4] have included an integration system to produce steam in the WGS stage and DME synthesis stage which could give effect on the hydrogen amount in the process as well. 4.2 Effect of oxygen to biomass ratio (O/B) Oxygen to biomass ratio (O/B) also have a significant effect in the production of DME. Oxygen is needed in the gasification section which will react with the EFB in partial oxidation reaction to produce CO2 and H2O. The oxygen is supplied at 170 kpa and 25˚C which was in the same condition with the supplied feed, EFB. The effect of O/B on H2 produced and DME produced is shown in the Figure 3. The rise in O/B ratio causes the decrease in production of H2 and DME. The reduction trend is due to the increase of CO2 gas that was produced in the stream line. As, 3.4 moles of CO2 gas will be produced for every single mole of EFB and 2.77 moles of oxygen.

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Figure 3: Effect of Oxygen to Biomass (O/B) ratio on DME production

4.3 Effect of steam to biomass ratio (S/B) The change in steam flow in the DME production process also affects the production. The optimum S/B ratio for the process is below 2. It is observed that the DME produced will be decreased when the S/B is more than 2 as shown in Figure 4.

Figure 4: Effect of Steam to Biomass ratio on hydrogen and DME production

In contrast the hydrogen produced after WGS reactor is keep increasing when S/B increasing. Steam was consumed highly in the methane reforming reaction and water gas shift reaction which apparently produced high hydrogen gas and in the same time reduced the carbon monoxide.

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Although hydrogen gas is now available for DME production process when S/B is increase, but limiting reactant now changed to CO as the supply of hydrogen is in excess. The results showed that the DME produced in not linearly with the hydrogen produced while both hydrogen and carbon dioxide are necessary for the production of DME. 4.4 Effect of pressure The effect of pressure towards the process is also being studied by correlating it with the amount of DME produce. Different set of pressure were used to show the significant effect on DME production as shown in Figure 5.

Figure 5: Effect of pressure towards DME production

Starting with the lowest possible pressure for reaction to occur which is at 170 kpa, the pressure of the feed is increase gradually until 3000 kpa. In order to have a better result, pressure of the steam and oxygen feed is maintained at 10 Mpa. Operating temperature of the DME synthesis section also was maintained at 140˚C which found to be the optimum temperature for DME production. From the run, we could see a trend of the DME production responding towards the various operating pressure. The DME production started to increase while we increase the pressure. This trend is maintain up till pressure 100 kpa where it started to show a decreasing trend. The DME produced keeps decreasing when the pressure increased. The optimum production happens at 100 kpa as shown in Figure 5. 4.5 Effect of temperature Temperature also is giving a significant effect towards DME production. Studies has been done to investigate the behavior and trend of DME production in a specific temperature range. The results of the simulation study for effect of temperature shown in Figure 6. It has been observed that the trend of DME produced is in a decreasing trend as the temperature increases. When the temperature reached at 300˚C, the production is at the minimum and approaching zero. This situation might happen as the reaction of DME synthesis is highly exothermic which mostly favored low temperature condition.

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Figure 6: Effect of temperature towards DME production

5. Conclusion Single step of DME production process is simulated by using HYSYS simulation software and the parametric study was performed on it to identify the optimum condition. Operating parameter is giving a significant effect towards the DME production process especially H 2/CO ratio as the DME synthesis reaction is highly dependent on the hydrogen and carbon monoxide as the reactant. Pressure and temperature are also giving direct effect towards the process. In getting H 2/CO feed ratio of 1 for DME production, the 0.37 of O/B and 0.27 S/B is needed. The optimum pressure and temperature for DME production process are 1000 kpa and 140˚C respectively for H2/CO feed ratio of 1. 6. Copyright Authors keep full copyright over papers published in Energy Procedia Acknowledgement Authors wish to thank Universiti Teknologi PETRONAS for the facilities for the completion of this project. References [1] Lide Oar-Arteta, Florence Epron, Nicolas Bion, Andrés T. Aguayo, Ana G. Gayubo, Comparison in Dimethyl Ether Steam Reforming of Conventional Cu-ZnO-Al2O3 and Supported Pt Metal Catalysts. Chemical Engineering Transactions. 37: p. 487492. [2] S. Sumathi, S. P. Chai, A. R. Mohamed, Utilization of oil palm as a source of renewable energy in Malaysia. Renewable and Sustainable Energy Reviews, 2008. 12(9): p. 2404-2421. [3] Anita Kovac Kralj, Jernej Hosnar, Replacing the Existing Methanol Production With in DME Production by Using Biogas Chemical Engineering Transactions, 2012. 27: p. 25-30.

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[4] Fudong Ju, Hanping Chen, Xuejun Ding, Haiping Yang, Xianhua Wang, Shihong Zhang, Zhenghua Dai, Process simulation of single-step dimethyl ether production via biomass gasification. Biotechnology Advances, 2009. 27(5): p. 599-605. [5] Mario Marchionna, Renata Patrini, Domenico Sanfilippo, Gabriele Migliavacca, Fundamental investigations on di-methyl ether (DME) as LPG substitute or make-up for domestic uses. Fuel Processing Technology, 2008. 89(12): p. 1255-1261. [6] Yeong Jun Lee, Min Hye Jung, Jong-Bae Lee, Kwang-Eun Jeong, Hyun-Seog Roh, Young-Woong Suh, Jong Wook Bae, Single-step synthesis of dimethyl ether from syngas on Al2O3-modified CuO–ZnO–Al2O3/ferrierite catalysts: Effects of Al2O3 content. Catalysis Today, 2014. 228: p. 175-182. [7] Yingying Zhu, Shurong Wang, Xiaolan Ge, Qian Liu, Zhongyang Luo, Kefa Cen, Experimental study of improved two step synthesis for DME production. Fuel Processing Technology, 2010. 91(4): p. 424-429. [8] Jie Chang, Yan Fu, Zhongyang Luo, Experimental study for dimethyl ether production from biomass gasification and simulation on dimethyl ether production. Biomass and Bioenergy, 2012. 39: p. 67-72. [9] Yangyang Xiang, Jingsong Zhou, Chao Chen, Zhongyang Luo, Integrated energy-exergy-based evaluation and optimization of a bio-dimethyl ether production system via entrained flow gasification. Journal of Renewable and Sustainable Energy, 2014. 6(5): p. 053133.

Biography Dr Abrar Inayat has graduated Master in Sustainable Energy Systems from Mälardalen University, Sweden. He has completed his PhD from Universiti Teknologi PETRONAS, Malaysia. He has more than 50 publications including journals and conferences. His research areas are biomass and bioenergy, process system engineering, production of biofuels, hydrogen production from biomass, modelling, simulation and optimization of biomass processing technologies. He has also obtained several international awards.

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