Characterization of South Asian Agricultural Residues for Potential Utilization in Future ‘energy mix’ 1876-6102 © 2015 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 Applied Energy Innovation Institute doi: 10.1016/j.egypro.2015.07.604 Energy Procedia 75 ( 2015 ) 2974 – 2980 ScienceDirect The 7th International Conference on Applied Energy – ICAE2015 Characterization of South Asian agricultural residues for potential utilization in future ‘energy mix’ Muhammad Danishac*, Muhammad Naqvib, Usman Farooqc, Salman Naqvid aSchool of Resource and Environmental Engineering East China University of Science and Technology,200237 Shanghai, China bDepartment of Energy, Building and Environment, Mälardalen University, 72123 Västerås, Sweden cDepartment of Chemical Engineering, Faculty of Engineering, University of Gujrat, Pakistan d Centre For Biofuel and Biochemical Research, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Malaysia Abstract This paper characterizes various locally available agricultural residues in South Asian region to evaluate their potential as feedstock for renewable energy production and contributing toward solving energy crisis and environmental issues. The thermo-chemical characterization has been performed in order to determine if the residues have potential to be used in biomass conversion technologies producing combined heat and power. The characterization methods for comparing different agricultural residues include proximate and ultimate analysis, heating value, ash content, thermo gravimetric analysis (TGA) and structural composition analysis (SCA). Widely available agricultural wastes in South Asian region were selected for the characterization i.e. bagasse, almond shell, corn cob, cotton stalks, wheat straw, sawdust, corn leaf, rice husk, rice straw, and corn straw. The analysis showed that the corn cob had the highest moisture content that will result in low energy efficiency of the thermal conversion technology due to energy requirement for drying. Whereas almond shell had the lowest moisture content. Ash and volatile contents were found to be highest in rice straw and almond shell respectively. The thermo gravimetric analysis showed that most of the agricultural residues can be easily decomposed and represent potential feedstock for biomass flexible combined heat and power systems through pyrolysis or gasification. © 2015 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICAE Keywords: agriculture residue, future energy, characterization, pyrolysis, gasification 1. Introduction 1.1. Background South Asian region (Pakistan, India, Bangladesh, and Sri Lanka) has one of the largest agriculture sector that plays a vital role in the region’s economy. [1, 2] According to United Nations Environment Programme (UNEP), a single district in South Asia produces about 2.5 million tonnes of agriculture residues as wheat straw, rice straw, rice husk, bagasse, corn leaf, saw dust, cotton stalks etc. [3-5]. Currently, the agriculture residues are utilized for domestic heating and as food for domestic cattle [6, 7]. However, the energy content from the substantial amount of agriculture waste represents potential for bio-fuel or combined heat and power production [8, 9]. In Pakistan, about 30 million people lives in remote areas/villages and around 30,000 villages are not provided with natural gas and electricity that are major energy requirements [10]. Since the agriculture waste is widely distributed and locally available, each district or village can produce its own electricity together with heat. In addition, the distributed electricity production can contribute towards reducing severe energy crisis in the country [11]. Most of the developed countries are utilizing all waste streams in the energy system as feedstock for renewable energy production [12, 13]. However, South Asian countries still lagging behind the right methodology and execution of biomass and agricultural residues as alternative renewable energy resource [14, 15]. Efficient utilization of biomass Available online at www.sciencedirect.com © 2015 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 Applied Energy Innovation Institute http://crossmark.crossref.org/dialog/?doi=10.1016/j.egypro.2015.07.604&domain=pdf http://crossmark.crossref.org/dialog/?doi=10.1016/j.egypro.2015.07.604&domain=pdf Muhammad Danish et al. / Energy Procedia 75 ( 2015 ) 2974 – 2980 2975 and agricultural wastes to bio-energy can also contribute towards solving energy crisis and reducing complete dependency on fossil based resources [16, 17]. 1.2. Objective of the study A number of thermo-chemical technologies, e.g. pyrolysis, gasification etc., are available to convert various agriculture residues to produce energy products [18, 19]. For efficient utilization of the feedstock as renewable energy resource through thermal conversion methods requires detailed understanding of different properties of the locally available feedstock. This study characterizes widely available and distributed agriculture residues such as bagasse, cotton stalks, rice husk, corn cob, corn leaf, fruit shells, rice straw and corn straw that can be introduced in pyrolysis or gasification to produce flexible fuels like char, pyrolysis vapors, bio-oil or synthesis gas. The flexible fuels may then be utilized for combined heat and power production. The thermo-chemical characterization was performed and feedstocks are compared using proximate and ultimate analysis, heating values and thermo gravimetric analysis (TGA). Based on available residue properties, the efficient thermo-chemical conversion technology is identified for each resource. This research work will provide base for future studies on estimating potential biofuel or combined heat and power production at small scale that may be sufficient to meet local energy requirement of a single district or village. 2. Methodology Following sub-sections describes the characterization methods used to compare biomass properties of various available agriculture residues in South Asia. 2.1. Agriculture residues Agricultural residues such as bagasse, corn cob, corn leave, saw dust, almond shell, rice husk, cotton stalks, cotton straw, rice straw and wheat straw were used in the present study. It was estimated that production of these residues in south Asia is 898864388 metric tons [35]. The residues are the left over products obtained after harvesting. Most of the residue such as corn cob, corn leaves, saw dust, cotton straw and wheat straw were obtained from Kabirwala District in Pakistan. While almond shells and bagasse were collected from Faisalabad and Jhang districts. Rice husk and rice straw were collected from Gujranwala district. Each residue was analyzed in triplicate for characterization and average results are reported. 2.2. Methods used for biomass analysis Proximate analysis was performed to determine fixed carbon, ash content, volatile content, and moisture content present in the desired amount of agriculture residue sample [20]. The standard test method for proximate analysis used i.e. D-3172 ASTM [21]. The moisture content was estimated by the weight loss of the biomass sample as a result of heating the sample at 115 oC in a drying oven. To estimate the volatile contents, the weight loss was recorded after placing the sample in muffle furnace at 800 oC for 10 minutes. Ash contents were calculated by the residue left after heating the sample at 650 oC until the constant weight was achieved [22]. The elemental composition of the agriculture residues were determined through ultimate analysis of samples [23]. Leco CHN-600 analyzer was used to estimate the carbon, hydrogen and nitrogen contents of the dried agriculture residue samples. To estimate the sulfur content, Leco Sulfur Analyzer SC32 was used as per ASTM standards. It is significantly important to estimate the lignin, cellulose, and hemi-cellulose contents together with extractives for reliable characterization of biomass. Different techniques can be used for structural analysis based on qualitative and quantitative methods [24]. The structural analysis is done by using magnetic resonance techniques, as this technique has been proved to be most efficient analytical tool. More extraction was also done by using an acid detergent solution, containing 60% sulfuric acid solution. A large number of extraction processes are recommended for the hemicellulose, cellulose and lignin content [25]. The calorific values of the agriculture residue samples were determined by bomb calorimeters and also using empirical relationship obtained from the literature [26]. ASTM D2015 was used as standard analytical method to determine calorific values of biomass samples [27]. The empirical relation used for the determination of high heating values are extracted from basic analysis data, i.e. Ultimate analysis, proximate analysis and structural analysis for the specific sample of the biomass. The formula according to the composition of elements is as follow: 2976 Muhammad Danish et al. / Energy Procedia 75 ( 2015 ) 2974 – 2980 Higher heating value Dry (MJ/kg) = 0.3491C + 1.1783H + 0.1005S − 0.1034O − 0.0151N − 0.0211 ash [26]. Where C, N, S, H and O are the weight percentages of carbon, nitrogen, sulphur, hydrogen and oxygen on dry basis respectively. 2.3. Thermo-gravimetric Analysis (TGA) LECO TGA-701 thermo-gravimetric analyzer was used in selectable atmosphere of N2. The analyzer determine the weight loss as function of varying temperature in selectable atmosphere. The temperature used for the TGA start slowly from 80 oC at an incremental rate of 20 oC/min till the final temperature of 660 oC. 3. Results and Discussion The proximate and ultimate analysis of the agriculture residue samples are reported in Table 1 and Table 2. Each estimated property is discussed in following sub-sections. 3.1. Moisture content The moisture content plays a vital role in the selection of efficient thermal conversion technology. The biomass containing high moisture content represents significantly low new energy density by mass due to the mass of water. This results in utilization of energy-intensive drying operation to reduce the moisture content and to be able to operate conversion technology [28]. For efficient performance of the thermal conversion technology, gasification or pyrolysis, the biomass shall not represent more than 10-14% of moisture content. Biomass resources with higher moisture contents can be converted through bio-chemical processes such as anaerobic digestion for biogas production. The estimated moisture content in the obtained agriculture residue samples ranges between about 4.8 %wt. (almond shell) and about 11.8 %wt. (corn cob). It is important to note that the estimated moisture contents of available agriculture residues showed slightly different results for most of the agriculture residues when compared to values reported in the literature data previously published [29-31]. The marginal differences in reported values are mainly due to agriculture residues obtained from different locations, climate differences. In addition, the handling and storage also contributes towards moisture content. Table 1 Proximate analysis of selected agricultural residues (% wt. as dry) Samples Moisture Contents Volatile Matter Ash Contents Fix Carbon Wheat straw 8.45 65.59 4.99 20.97 Rice Husk 7.88 54.39 14.02 23.71 Corn Cob 11.74 72.33 10.67 4.97 Corn Leaf 7.44 79.08 7.82 5.66 Saw Dust 8.52 73.68 2.91 14.89 Bagasse 8.77 79.39 8.02 3.82 Cotton Stalks 6.85 81.08 7.12 4.95 Corn straw 8.78 73.25 5.95 12.02 Rice straw 6.96 58.25 20.02 14.77 Almond shell 4.75 84.79 4.78 5.68 Muhammad Danish et al. / Energy Procedia 75 ( 2015 ) 2974 – 2980 2977 Table 2 Ultimate analysis of selected agricultural residues (% wt. as dry) Sr. No Samples Carbon Hydrogen Nitrogen Sulphur Oxygen HHV(MJ/Kg) 1 Saw Dust 47.14 5.59 0.37 0.06 46.03 19.22 2 Bagasse 46.96 5.81 0.28 0.23 46.72 17.54 3 Corn Cob 46.20 5.42 0.92 0.24 47.22 18.36 4 Rice Husk 44.13 5.01 0.39 0.07 50.40 15.45 5 Wheat Straw 47.25 5.28 0.61 0.18 46.68 17.25 6 Cotton Stalks 46.81 5.67 0.67 0.04 46.81 19.01 7 Corn Leaf 47.04 5.41 0.68 0.05 46.82 17.37 8 Corn straw 41.85 5.38 1.36 0.07 51.34 17.08 9 Rice straw 28.55 3.98 1.15 0.61 65.71 13.48 10 Almond shell 50.12 5.47 0.29 0.17 43.95 18.05 3.2. Volatile and ash contents The volatile contents of the agriculture waste samples were determined on dry basis. The lowest volatile content was found in the rice husk i.e. 54 %wt. and the highest volatile content in the almond shell i.e. 84.79 %wt. The results regarding the ash contents determined in the study are considerably different from the data of literature due to the agriculture residues available in different regions and climate conditions. The samples of wheat straw, corn leaf, saw dust, almond shell, cotton stalks and corn straws had low ash contents that were less than 8 % wt. The sugarcane bagasse and corn cob had medium ash contents that were less than 10 % wt. Among the selected biomass samples, rice straw and rice husk had substantially higher ash content i.e. greater than 15 % wt. Soil pollution (decay) is different for every biomass sample taken due to the difference origin of sources of samples. It is beneficial from another perspective that the inorganic compounds present in the agriculture waste resources with higher ash contents have potential to be used as catalysts in the thermal conversion technologies e.g. gasification and pyrolysis [32]. 3.3. Elemental composition and Heating values The calorific values of the samples are reported in the ultimate analysis (see Table 2). The heating/calorific values of the agriculture waste samples determined by Bomb Calorimeter showed nearly identical values as reported in the literature. Cotton stalks and saw dust showed the highest higher heating values (HHV) i.e. about 19 MJ/kg. Whereas, rice straw showed the lowest HHV among the available sample i.e. about 13 MJ/kg. The considerable heating values of the agriculture waste samples showed that these locally available renewable resources can potentially be converted to substantial amount of bio-energy products from effective conversion technologies. From the elemental composition perspective, Sulfur and nitrogen were found to be in small amounts in all samples except corn straw that has highest nitrogen and rice straw that has highest sulfur content. 3.4. Chemical characterization Chemical characterization of the agriculture residues will provide useful information for modeling of thermal conversion processes. Hemicellulose and cellulose contents present in agro-waste samples were found to be less than 50 %wt. Almond shell samples has highest cellulose content and corn leaf with the lowest cellulose content. The highest hemi-cellulose content was found in the corn cob samples. Corn cob and cotton stalk samples represented lower lignin content, i.e. about 7 %wt. and 8 % wt. respectively. Since the biomass with low lignin contents are suitable for bio-oil production from pyrolysis, Corn cob and cotton stalk will be interesting option to be utilized in pyrolysis as compared to other selected samples. Whereas, rice husk and wheat straw samples could be gasified due to higher lignin content, i.e. about 40% wt. lignin content. 2978 Muhammad Danish et al. / Energy Procedia 75 ( 2015 ) 2974 – 2980 Table3: Structural analysis of agriculture waste samples (dry and free ash basis) Sr. No Samples Cellulose Hemicellulose Lignin Extractives 1 Saw Dust 42.58 18.54 11.21 27.67 2 Bagasse 43.87 21.49 17.02 17.62 3 Corn Cob 37.52 47.47 6.85 25.78 4 Rice Husk 38.35 11.14 40.16 10.35 5 Wheat Straw 45.12 9.16 37.41 8.31 6 Cotton Stalks 44.75 25.19 7.89 22.17 7 Corn Leaf 29.74 30.14 9.25 30.87 8 Corn straw 44.01 25.12 8.98 21.98 9 Rice straw 32.03 8.42 30.34 29.21 10 Almond shell 46.25 7.56 29.85 16.47 3.5. Thermal gravimetric analysis (TGA) The thermal gravimetric analysis was used to study and analyze the degradation of selected samples. The TGA curves are shown in Figure 1. TGA combustion and pyrolysis techniques were adopted to found the molecular deterioration characteristics. TGA curves from 1-3 show that almost 60-75% of the weight of samples has been decomposed before 590°C. Major portion of the weight of the sample was decomposed in between 200-400 oC. The TGA curves are the best option to determine the optimum temperature for the gasification or pyrolysis reactions [33]. Easy decomposition of all the waste samples during thermal decomposition shows that these samples would be ideal feedstocks in combustion Processes [34]. The TGA curves indicates the optimum temperatures of the each of the biomass samples corresponding to their loss in weight .Sawdust, cotton stalks, Sugarcane bagasse, corn cobs and corn leaf have temperature range, ranging from 190 oC to 560 oC. The least value of the weight loss of the biomass samples is for corn leaf, i.e. 45%, while bagasse and almond shell indicate highest weight loss, i.e. 70%, at pyrolysis temperatures. Figure 1 Thermo-gravimetric analysis curves of selected agriculture wastes Muhammad Danish et al. / Energy Procedia 75 ( 2015 ) 2974 – 2980 2979 4. Conclusions The study were conducted to determine the thermochemical properties of available agriculture residues in South Asian region to identify their potential to be used in thermal conversion processes for biofuel, heat or power production. The agriculture residues included bagasse, almond shell, corn cob, cotton stalks, wheat straw, sawdust, corn leaf, rice husk, rice straw, and corn straw. The estimated moisture contents of available agriculture residues showed slightly different results for most of the agriculture residues when compared to values reported in the literature. The marginal difference in reported values is mainly due to agriculture residues obtained from different locations, climate differences, handling and storage. The lowest volatile content was found in the rice husk i.e. 54 %wt. and the highest volatile content in the almond shell i.e. 84.79 %wt. Rice straw and rice husk had substantially higher ash content i.e. greater than 15 % wt. Cotton stalks and saw dust showed the highest higher heating values (HHV) i.e. about 19 MJ/kg. Based on available biomass in south Asia region, calculated amount of energy is 152, 806, 9459, 6MJ annually which can at least contribute to the basic needs of the countries. Hemicellulose and cellulose contents present in agro-waste samples were found to be less than 50 %wt. From the elemental composition perspective, Sulfur and nitrogen were in small amounts in all samples except corn straw that has highest nitrogen and rice straw that has highest sulfur content. TGA curves show that almost 60-75% of the weight of samples has been decomposed before 590°C. 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"Fundamentals, kinetics and endothermicity of the biomass pyrolysis reaction." Renewable energy 35.1 (2010): 232-242. [34] Skodras, George, et al. "Pyrolysis and combustion characteristics of biomass and waste-derived feedstock." Industrial & engineering chemistry research 45.11 (2006): 3791-3799. [35] Electricity Generation from Agricultural Residues in Five South Asian Countries: Prospects and Potential Md. Mizanur Rahman and Jukka V. Paatero Department of Energy Technology, School of Engineering, Aalto University, Finland. 4th International Conference on Sustainable Energy and Environment (SEE 2011): A Paradigm Shift to Low Carbon Society 27-29 February 2012, Bangkok, Thailand. Biography I did my B.Sc Chemical Engg. From University of the Punjab, Lahore in 2006 & M.Sc chemical Engg. from U.E.T Lahore,Pakistan in 2011.Then I joined as a Lecturer in Department of Chemical Engg.University of Gujrat.Currently I am PhD Scholar in East China University of Science and Technology, Shanghai, China