Hydrogen and Syngas Generation from Gasification of Coal in an Integrated Fuel Processor

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vol. 625, pp doi:1.28/ 214 Trans Tech Publications, Switzerland Hydrogen and Syngas Generation from Gasification of Coal in an Integrated Fuel Processor Sujan Chowdhury a*, Abrar Inayat b, Bawadi Abdullah c, Abdul Aziz Omar d, and Saibal Ganguly e Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 3175 Tronoh, Perak, Malaysia a sujan.chowdhury@gmail.com.my, b abrar.inayat@petronas.com.my, c bawadi_abdullah@petronas.com.my, c aaziz_omar@petronas.com.my, d saibal_ganguly@petronas.com.my Keywords: Coal, Gasification, Syngas, Hydrogen generation, Electricity. Abstract. Hydrogen is a clean and new energy carrier to generate power and effectively turned out through the gasification of organic material such as coal. The main objective of this manuscript is to present an analysis of the coal gasification for the generation of high-purity hydrogen in a lab-scale fixed-bed downdraft gasifier. Better understanding of the rank, formation, structure, composition and calorific value, and method of analysis of the material is crucial for the proper utilization of these resources requirements. Traditionally the quality of the coal samples has been determined by their physical and proximate analysis such as bulk density, free swelling index, gross calorific value, sulfur content, moisture content, fixed carbon, volatile matter, and ash content. In this study, coal is partially oxidized and ultimately converts into hydrogen rich syngas (CO and H 2 ). As well, approximately 22 kg h 1 of coal would be gasified at K and 46.2 atm with the reactor volume of.27 m 3 to obtain approximately kcal h 1 of thermal energy during over 67% syngas generation with the generation of 11 kw electrical powers. Introduction Coal is the most abundant fossil fuel for power generation through gasification process and has been applied for a long time. Coal can be found in all over the countries and its price has remained relatively constant in the recent years. The maximum electric energy is generated by fossil fuel, gas, and coal causes the air and water pollution which is considered to be one of the main contributors to the greenhouse effect [1]. Coal is characterized as having the highest concentration of carbon element compared to its caloric value. Properties of coal constitute an inherent part of technology to process and optimize the carbon emission. In the coal-mining process, replacing the inefficient power units with more efficient ones are the largest contributing factors to reduce carbon emission in coal-to-energy chain. In 21, Malaysia generated 18,175 GWh of electricity where 39.51% was sourced from coal. Within the next two decades, coal power generation is also planned to overtake natural gas as the main fuel for electricity generation [2 4]. In addition, coal gasification technology for power generation is related to the combined system involving steam and gas turbine implementation. Solid fuel coal gasification process is not completely converted to CO 2 and H 2 O, but mainly to CO and H 2. Indeed, hydrogen production processes and utilization as a fuel would produce almost negligible amount of pollutants to open up the window for enormous environmental impact with energy generation issues. The high purity of hydrogen fed to a proton exchange membrane fuel cell (PEMFC) stack for power generation makes solid fuel coal utilization system economically and environmentally attractive. Therefore, the main objective of the present work is to assess the feasibility of five different types of available solid fuel coals (from Barapukuria and Khalaspir, Indian 1, Indian 2, and Australian) gasification with syngas recycling for the potential application on an integrated fuel processor (e.g. PEMFC) system. Lab scale coal gasification experiments are conducted in the All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-11/5/16,:5:57)

2 Applied Mechanics and Materials Vol present study to ensure an operationally simple and economically attractive process development. The physicochemical properties of different types of coals are also measured. Experimental In this typical study, coal samples were collected from Barapukuria and Khalaspir, which denoted as BP and BK respectively. In addition, Indian (IJ 1 and IJ 2) and Australian (IA) coal samples were collected from Birampur Hard Coke Limited and Geological Survey of Bangladesh, Dhaka. The coal sample operation could be divided into two main steps involving first, the collection of a gross sample followed by the reduction to a size convenient for laboratory work and finally, the preparation of laboratory sample for analysis [2]. The various contents of coal vary slightly from depth to depth. The maximum analysis followed by ASTM standard. The calorific values of the all the coal samples were calculated using ASTM D method with a bomb calorimeter (C, Germany) in pure oxygen of 3 kp/cm 2. In addition, experimental data obtained from a lab scale coal gasification system could be used as the basis for the scale up of this technology. In that follows, some simulation calculations and parameter evaluations were given for this system with the reaction or equilibrium equations using Microsoft Excel software. Results and Discussions Coal is an extremely complex heterogeneous organic rock as it formed from compaction and indurations of variously altered natural processes. The proximate analysis of the as obtained coal revealed that the indication of coal ranking for endeavor utilization. The results of proximate analysis for five different coal samples were shown in Fig. 1 and Table 1. Systematic proximate analysis on the coal under investigation included the moisture content, ash content, fixed carbon content, and etc. were shown Fig. 1 (a). Indeed, moisture content of coal could range from 2% to 15% in bituminous coal to nearly 45% in lignite. The higher the moisture content, the lower the energy values and bulk density of coal [2, 4]. Maximum moisture content of BP and BK were observed as 3.% and 3.45% and the minimum were 2.71% and 2.5% respectively. On the other hand, among the three other imported coal samples, the maximum moisture content was observed at 3.% and minimum was at 2.% with average moisture was 2.63%. This observation confirmed that the moisture content of BP and BK coal was nearly about Indian 1, Indian 2, and Australian coal. Table 1: Results of bulk density, free swelling index, calorific value, and sulphur of coal. Parameters Sample name Sample Bulk density (gm.cc -1 ) Free swelling index Calorific value (Btu/lb) Sulphur (%) Barapukuria Coal BP Khalaspir Coal BK India, S. Jaria IJ India, Tirap IJ Australia IA The coal rank decreased with decreasing of bulk density mainly due to increase of moisture fraction. Higher rank coal may have density more than 1.5 gm.cc -1 and lower one was lower than 1.3 gm/cc -1 [2]. The determined bulk density for BP, BK, IJ 1, IJ 2 and IA were around 1.45±.5 gm.cc -1 as shown in Fig. 1(b) and Table 1. It was observed from the analytical data that BP and IJ 2 coal exceeded the higher rank limit of bulk density. The ultimate analysis determined the amount of carbon (C), hydrogen (H), oxygen (O), sulphur (S), and other elements within the coal samples.

3 Weight percent [%] Weight percent [%] Weight percent [%] 646 Process and Advanced Materials Engineering These variables were also measured in weight percent (wt%) and calculated. Dry ash free (DAF) basis neglected all moisture and ash constituents in coal. The DAF basis of ultimate analysis of coal was chosen for this work. The major oxides of ash consisted of silicon dioxide (SiO 2 ), aluminium oxide (Al 2 O 3 ), ferric oxide (Fe 2 O 3 ), phosphorus penta-oxide (P 2 O 5 ), calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na 2 O), and sulphur trioxide (SO 3 ) were observed as shown in the Fig. 2(a). In where, BP had higher SiO 2, while Al 2 O 3 content was lower than that of IJ 1, IJ 2, and IA coals. Indeed traces amount of Fe 2 O 3, P 2 O 5, CaO, MgO, Na 2 O, and SO 3 were observed. The calorific value was the most important value to determine for coal that was used for heating purpose. The calorific value (CV) for bituminous coal ranged from 1,5 Btu/lb to 14, Btu/lb. The gross CV among these five different types of solid coals varied from 1,7 Btu/lb to 12,931 Btu/lb. As per free swelling index and calorific value of BK and followed by BP coals were highly volatile and IJ 1, IJ 2, and IA coals were sub-volatile bituminous type respectively. The sulphur content was found less than 1% in both BP and BK coals, where IJ 1, IJ 2, and IA had consisted with higher sulphur content of less than 1%. (a) 1 8 (b) 2 2 Moisture Ash Fixed carbon Mineral Mater S N H O C Proximate analysis of coal Ultimate analysis of coal Fig. 1: (a) Proximate analysis and (b) ultimate analysis of coal. The principal operational units in the united gasification of simulated coal (BK) include a gasifier section (including a CO shift section), H 2 purification section (pressure swing adsorption (PSA) and Pd membrane purifier), and a final PEMFC were represented in Fig. 2 (b). Particulate free syngas was obtained from the gasification unit to convert CO and steam into CO 2 and H 2. 8 (a) (b) 2 Na 2 OP 2 O 5 SO 3 MgO K 2 O CaO TiO 2 Fe 2 O 3 Al 2 O 3 Major oxides of ash SiO 2 Fig. 2: (a) Major oxides of ash of coal and (b) material and energy balances of a pilot scale. The gaseous mixtures produced from gasification process also contained other gases in considerable amount like CH 4, CO and H 2 O vapors. The water gas shift reaction could be simply expressed by the following Eq. 1:

4 Applied Mechanics and Materials Vol Since the reaction was highly exothermic, a conventional heat recovery exchanger could be used to generate medium pressure steam for export or captive consumption [2, 4]. The effluent gas from the CO shift unit was then fed into a PSA unit with Pd membranes to obtain a high purity (> 99.99%) of H 2 stream as shown in Fig. 2 (b). The material and energy balances of a gasification process may provide the essential information about the feed system, a downdraft type gasifier, an ash discharge system, a coke/tar/slag or water adsorber, an internal combustion engine for power generation, CO/H 2 separator, hydrogen purifier, and an integrated fuel processor. Simulated data indicate that in order to generate a 11 kw of electric power, approximately 22 kg h -1 of coal would be gasified at 1173 K and 46.2 atm with the reactor volume.27 m 3. In the simulated pilot scale continuous operation of downdraf type gasification system included with individual units to be as stand aloned as possible in moderate to high level of automation was carried out with temperatures were much higher than K and the main product gases were CO and H 2 as were calculated in Fig 2(b). The global material balance for this gasification process was more than 67% (dry basis) of H 2 and CO were generated. In addition, the pressure of the gasifier was usually based on the pressure required for the delivery of the ultimate product (CO or H 2 ) to the end use (for instance, an integrated fuel processor or the refinery hydrogen header pressure) and purification was carried out through a PSA to separate CO 2. Indeed, approximately kcal h -1 of thermal energy may be recovered with and intregrated PEMFC for power generation owed to the consisting high purity H 2. Generally, operating pressures in the commercial biowaste or coal noncatalytic gasification processes were ranged from 5 to 8 bar. It was noteworthy that a commercial gasifier often operated at mid term temperatures or pressures and a well mixed gaseous environment in which the partial oxidation reactions take place. Conclusions Analytical results and subsequent rank classifications of Khalaspir coals are highly volatile to medium volatile bituminous type and Indian and Australian coals are sub bituminous type. BK and BP coals are better for power generation owing to their higher calorific value and lower sulphur content asses to suitable for environmental concern. Based on the gasification data analysis, approximtely 22 kg h -1 of BK coal would be gasified to generate 11 kw electric power with more than 67% (dry basis) of H 2 and CO are generated at 9 K and 46.2 atm, and in addition to the hydrogen generation, approximately kcal h -1 of thermal energy may be recovered. Futhermore, the catalytic gasification of coal to syngas, production of high purity hydrogen, and final processing make it suitable for the integrated fuel cell power generation system. References [1] A. H. Mondal, M. Denich, Hybrid systems for decentralized power generation in Bangladesh, Energy for Sustainable Development, 14 (21) [2] A. A. Rahman, A. H. Shamsuddin, Cofiring biomass with coal: Opportunities for Malaysia, IOP Conference Series: Earth and Environmental Science, 16 (213) [3] E. N. Grigorieva, T. L. Fedorova, D. N. Kagan, V. Y. Korobkov, S. S. Panchenko, I. V. Kalechitz, Thermal craking of coal strong bonds on diaryl ethers' and diarylmethanes' models, Coal Science and Technology, (1995) [4] K. Sakanishi, H. Hasuo, H. Taniguchi, I. Mochida, O. Okuma, Effects of coal pre-treatment and catalyst recovery on the liquefaction, Coal Science and Technology, (1995) (1)

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