Energy Sources, Part A: Recovery, Utilization, and

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The Physicochemical Characterization of a Newly Explored Thar Coal Resource a

b

A. Sarwar , M. N. Khan & K. F. Azhar

c

a

Fuel Research Centre, Pakistan Council of Scientific & Industrial Research , Karachi , Pakistan b

Department of Chemistry , University of Karachi , Karachi , Pakistan c

Scientific Information Centre, Pakistan Council of Scientific & Industrial Research , Karachi , Pakistan Published online: 06 Feb 2014.

To cite this article: A. Sarwar , M. N. Khan & K. F. Azhar (2014) The Physicochemical Characterization of a Newly Explored Thar Coal Resource, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 36:5, 525-536, DOI: 10.1080/15567036.2010.542447 To link to this article: http://dx.doi.org/10.1080/15567036.2010.542447

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Energy Sources, Part A, 36:525–536, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1556-7036 print/1556-7230 online DOI: 10.1080/15567036.2010.542447

The Physicochemical Characterization of a Newly Explored Thar Coal Resource A. Sarwar,1 M. N. Khan,2 and K. F. Azhar3 Downloaded by [INASP - Pakistan (PERI)] at 04:19 07 February 2014

1

Fuel Research Centre, Pakistan Council of Scientific & Industrial Research, Karachi, Pakistan 2 Department of Chemistry, University of Karachi, Karachi, Pakistan 3 Scientific Information Centre, Pakistan Council of Scientific & Industrial Research, Karachi, Pakistan

The samples of Thar coalfield were characterized using a thermogravimetric analyzer, atomic absorption spectrophotometer, X-ray diffractometer, Fourier transform infrared spectra, and scanning electron microscopy-energy dispersive x-ray spectroscopy analysis. The samples were ranked as lignite and subbituminous according to American Society for Testing and Materials standard classification. Differential thermogravimetric analysis results specified chemical reactivity of coal at the primary devolatilization region (257–412ıC) and secondary devolatilization region (741–900ıC). The minerals identified were quartz, kaolinite, dikite, halloysite, gold copper indium, graphite hydrogen nitrate, and magnesium vanadium molybdenum oxide. X-ray diffraction study confirmed the presence of mineral constituents as indicated by microscopic investigation. Fourier transform infrared spectra identified CDC aromatic groups at 1,500–1,700 cm 1 as maturity indicator and 2,800–3,000 cm 1 and 2,300 cm 1 as aliphatic stretching regions. The peaks of quartz and kaolinite were observed at 900–1,100 cm 1 . Strong correlations between mineral matter-SiO2 .r 2 D 0:808/ and Al2 O3 -SiO2 .r 2 D 0:957/ indicates Al and Si as the dominant inorganic components. Cluster analysis appeared as an additional tool for coal ranking based on their physicochemical properties. Keywords: atomic absorption spectrophotometer, coal characterization, proximate analysis, thermogravimetric analyzer, X-ray diffractometer

1. INTRODUCTION The world energy consumption of coal is increasing day by day and it has acquired an indispensable position in the electricity generation of the world. The use of coal in cement industries, brick industries, and steel mills is well understood. A small amount is also used as home heating fuel. Some other potential uses are generation of synthetic natural gas, liquid fuels, and fertilizer products. Volatile matter, ash content, fixed carbon, sulfur, and mineral matters in coal require special consideration as they tell about the reactivity and ignitibility of coal along with erosion, slugging, and fouling problems (Demirbas, 2005). Hence, characterization of the explored coal resource is the fundamental requirement for the assessment of its efficient utilization as a fuel Address correspondence to M. N. Khan, Department of Chemistry, University of Karachi, Karachi 75270, Pakistan. E-mail: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ueso.

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A. SARWAR ET AL.

(Bjorkman, 2001). The common instrumental techniques used for the characterization of coal are nuclear magnetic resonance spectroscopy, scanning electron microscopy, liquid chromatography, gas chromatography, thermogravimetry, X-ray diffractometry, and Fourier transform infrared spectrometry (Tonbul and Erdogan, 2007; Yongkang et al., 2001; Bjorkman, 2001; Gupta, 2007). At present, Pakistan is facing an acute shortage of electricity and natural gas, which is damaging the national economy. The government had only been depending on hydropower, furnace oil, and very limited nuclear energy to generate electricity. Surprisingly, the share of coal in the energy sector of Pakistan is limited to brick kilns, processing industries (cement, sugar, fertilizer, etc.), and as household fuel. Pakistan has 1 million tonnes of anthracite to bituminous and 2,075 million tonnes of subbituminous to lignite coal as a proven reserve (BP, 2009). Pakistan has come into view in the leading countries of the world after the discovery of huge coal reserves in Tharparker district of Sindh province in 1992. So far the coalfield has not been developed, but the efforts are underway for its proper utilization. Based on the available infrastructure and favorable geology, Thar coalfield has been divided into eight blocks (I–VIII). In the present work, seven samples of block VI in replicates for characterization have been randomly selected. The extensive research on the newly explored resource is a subject of interest to provide the solution of electricity shortage by effective and efficient utilization of Thar resource. The study is mainly focused on the physical, chemical, mineralogical, and surface characterization of the samples of Thar using a thermogravimetric analyzer (TGA), atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), and X-ray diffractometer (XRD). 2. MATERIALS AND METHODS Air dry loss (ADL) was determined by partially drying a sample in an air-drying oven (ASTM D-3302). The lumps of samples were crushed, grinded, and pulverized to 60 mesh (ASTM D2013). Proximate analyses were made sequentially by a thermogravimetric analyzer (TGA-2000A, Navas Instruments, Spain) following ASTM D-5142. Total sulfur content and gross calorific value were measured using a sulfur determinator (SC-32, LECO) and adiabatic bomb calorimeter (Parr 6300, USA) in accordance with ASTM D-4239 and D-5865, respectively. The percentages of carbon, hydrogen, and nitrogen were calculated using an empirical formula derived by Carpenter and Diederichs (Nino et al., 1997). The percentage of oxygen was calculated by difference. The experimental data of as-determined (ad) basis was converted into as-received (ar) basis, dry, ash-free (daf) basis (ASTM D-3180-89), and moist, mineral-matter-free (m,mmf) basis (ASTM D-388-99). Fourier transform infrared (FT-IR) spectra of the samples were recorded using a NicoletTM 380, Fourier transform infrared spectrophotometer (Thermo Electron Corporation, USA), consuming KBr pellets with spectral resolution of 4 cm 1 interfaced with a computer operated under Windows-based software. Major and minor constituents of combustion residue of coal were analyzed by atomic absorption spectrophotometer (Perkin Elmer, 2380) using ASTM D-3286 standard method. National Bureau Standards 1633a and 1635 (Washington D.C.) were used as the standard reference materials. Parr formula .Mm D 1:08A C 0:55S / was used to estimate the total mineral matter in coal samples, where A and S represent ash yield and sulfur content, respectively (Speight, 2005). The mineralogical characterization was performed by X-ray diffraction using monochromatic Cu K/ radiation at 40 kV and 30 mA . D 1:5406 Å). Scans were conducted at a scanning range from 5ı –80ı at 2 with a scanning step size of 0.02ı and a counting time up to 1s/step. Scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) (JEOL-5300) was used to examine the morphology of the coal. The samples were coated with gold and the images were taken at the magnification of 3700.

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3. RESULTS AND DISCUSSION


3.1. Proximate Analysis Proximate and ultimate composition of the samples is shown in Table 1. Air dry loss and inherent moisture ranged from 8.61–27.41% and 18.78–41.08%, respectively. High moisture content is attributed to the water aquifers, which are present at Thar at an average depth of 50, 120, and more than 200 m (Government of Sindh, Pakistan). Samples 1–7 are classified as lignite except sample 6, which is ranked as subbituminous B. The classification was made on the basis of gross calorific value (GCV) on moist, mineral-matter-free basis (ASTM D388-99). The quality of coal was assessed on as-received basis (Coal Services International, 1990). All samples contain high volatile matter (29%) except sample 4, which has a moderate value. Sulfur content of samples 1–4 is high, 5 is medium, and 6 and 7 is low. Ultimate analysis shows total carbon 58.00–73.37%, hydrogen 7.00–11.18%, nitrogen 1.96–3.88%, and oxygen 13.53–25.16% on dry-ash-free (daf) basis. 3.2. Thermogravimetric Studies Approximately 3% of the physically bounded inherent moisture was evaporated at 68ıC. The water chemically bound in the coal was removed at 105ıC except the mineral hydrates that decomposed at above 110ı C. Coal samples undergo appreciable physico-chemical changes when heated from 250–900ıC in an inert atmosphere. Figure 1 shows the loss of volatile organics with thermal decomposition at low temperature range (257–412ıC), due to the breakdown of weak bonds of low volatile compounds. As a result, free radicals were formed that recombine with other radicals

TABLE 1 Classification of Thar Coal Samples Sample No. Parameters Proximate composition (ar basisa ), % Total moisture Air dry loss Inherent moisture Volatile matter Ash yield Fixed carbon Ultimate composition (daf basisa ), % Carbon Hydrogen Nitrogen Sulfur Oxygen Others GCV (m,mmf basisa ), Btu/lb ASTM rank a ar

1

2

3

4

5

6

7

40.15 20.55 36.12 32.50 13.38 18.00

42.34 27.41 38.25 28.82 17.56 15.38

19.74 8.61 18.78 32.12 24.81 24.28

22.73 15.64 21.62 23.96 40.14 14.28

31.53 18.95 29.15 35.68 8.16 27.01

20.58 3.39 20.00 46.88 5.23 27.89

46.43 25.31 41.08 35.26 2.65 21.01

68.08 8.46 2.53 5.52 15.41

66.89 8.80 2.67 2.63 19.02

68.06 8.53 2.72 7.16 13.53

58.00 11.18 3.88 1.79 25.16

73.37 7.00 2.03 1.49 16.11

72.80 7.06 1.96 1.18 17.01

72.24 7.24 2.04 0.60 17.89

6,779.78

6,013.88

4,512.91

6,930.34

8,118.77

10,344.90

8,061.18

Lignite B

Lignite A

Lignite A

Lignite B

Lignite B

Subbituminous B

Lignite B

basis: as-received basis; daf basis: dry, ash-free basis; m,mmf basis: moist, mineral-matter-free basis.

A. SARWAR ET AL.


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FIGURE 1

Thermograms of samples 1–7 showing volatile profile.

or molecules to form some new volatile compounds with the release of CO2 , CO, and CH4 (Saika et al., 2009). Maximum rate of emission of volatile organics occurs at 684ıC for sample 1 and 528–550ıC for samples 2–7. The samples show less chemical activity than Indonesian brown coal (384–451ıC) as reported by Umar et al. (2006). The reactivity of Thar coal is comparable with Nigerian coal, which releases maximum volatile at 470–580ıC (Sonibare et al., 2005). The peaks at high temperatures (741–900ıC) are responsible for the release of H2 , CH2 , and other inorganic

THAR COAL

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TABLE 2 Volatile and Combustion Profiles of Thar Coal Sample No.


Profiles Volatile Primary volatile temperature, ı C Maximum rate temperature, ı C Secondary volatile temperature, ı C Combustion Ignition temperature Ti , ı C Ignition time ti , min Peak temperature Tp , ı C Peak time tp , min Burnout temperature Tb , ı C Burnout time tb , min

1

2

3

4

5

6

7

285.00 550.00 814.00

287.00 546.00 788.00

277.00 528.00 774.00

412.00 684.00 900.00

284.00 533.00 781.00

279.00 546.00 741.00

257.00 530.00 804.00

370.00 33.00 460.00 42.00 735.00 70.50

360.00 32.00 462.00 43.00 960.00 92.00

395.00 36.00 465.00 43.00 800.00 77.00

470.00 44.00 576.00 54.00 688.00 66.00

358.00 34.00 430.00 43.00 795.00 65.00

380.00 31.68 473.00 38.53 690.00 74.95

355.00 31.56 434.00 38.53 730.00 68.28

compounds containing H as the secondary volatile products (Saika et al., 2009). It is a well known fact that the coals that contain a minimum of 32% volatiles and 8% oxygen (dry basis) give a good yield of gas when converting from coal to gas. The synthetic raw gas may further be converted to substitute of natural gas (SNG) after purification or as a feed to synthesis of chemicals or liquid fuel (Tsai, 1982; Karaca and Koyunoglu, 2010). All samples of Thar coal have more than the required amount of both entities showing its suitability for gasification process. On the basis of volatile profile, it is concluded that pyrolysis at about 900ı C is essential to convert entire primary and secondary volatiles of Thar coal into gaseous products during coal gasification. The burning profile of the samples is shown in Table 2. The main combustion peak is preceded by smaller peaks or shoulders that are partly attributed to the release of moisture and volatile matter. Ignition temperature .Ti /, peak temperature .Tp /, and burnout temperature .Tb / and their corresponding times (ti , tp , and tb ) were measured using thermogravimetric data as described by Ma et al. (2006). On the basis of ignition, peak, and burnout temperatures and their corresponding times, sample 7 is identified as the more reactive and sample 4 as the least reactive coal. The characteristic combustion temperatures are in good agreement with the data reported by Umar et al. (2006) and Ma et al. (2006). They reported 232–458.5ıC as Ti , 384–587ıC as Tp , and 715.7–757ıC as Tb for Indonesian and Chinese coals. The Tp and Tb for Nigerian coal were observed as 445–500ıC and 560–620ıC, respectively (Sonibare et al., 2005). 3.3. Mineral Matter in Coal The mineral matter of the coal was evaluated as 25.02, 31.74, 35.73, 55.78, 13.16, 7.66, and 5.17% for samples 1–7, respectively. Percent mineral matter was found to be higher than the corresponding percent ash. It is due to the weight changes that take place during incineration of mineral matter to ash, such as loss of water of hydration from silicate minerals, loss of carbon oxide from carbonate minerals, oxide of pyrite to iron oxides, and fixation of sulfur oxides by bases, such as calcium and magnesium oxides (Tsai, 1982). 3.4. X-ray Diffraction Analysis X-ray diffraction data of samples 1–7 show that the samples are crystalline in nature. A typical X-ray diffraction pattern of sample 4 is shown in Figure 2. Sample 1 is mainly made up of

530 FIGURE 2

XRD of sample 4.



THAR COAL

531

hexagonal-shaped quartz low, dauphine-twinned SiO2 at 4.28, 3.35, 2.45, 2.10, and 1.82 Å. The sample is also comprised of monoclinic carbon oxide hydrate (COOH)2 .2H2 O at 3.06 and 2.87 Å, rhombo H. axes carbon oxide sulfides (COS) at 3.06 Å, and orthorhombic barium carbon oxide BaCO3 at 3.79 Å. Sample 2 consists of hexagonal shaped Halloysite-7A (Al2 Si2 O5 .OH/4 at 7.20, 4.48, 3.58, and 2.58 Å. The sample also contains lignite (NR) C-SiO2 at 3.50 and 2.34 Å. Sample 3 comprises of Kaolinite 1A Al2 .Si2 O5 /.OH/4 , triclinic in shape at d D 10:27, 7.60, 4.45, 4.27, 3.57, and 1.60 Å. Sample 4 shows monoclinic Dikite 2M1 .Al2 Si2 O5 .OH/4 as the most dominant phase, which occurs at d D 7:16, 4.46, 4.35, 4.15, 3.57, 2.55, 2.49, 2.34, and 1.49 Å. The sample also contains hexagonal crystals of quartz alpha (SiO2 ) at 3.34 Å. Sample 5 consists of Boron nitride (BN) having a hexagonal shape at 3.34 Å and hexagonal orlymanite Ca4 Mn3 C 2 Si8 O20 .OH/6 :2H2 O at 7.64, 4.29, and 3.58 Å. Sample 6 contains hexagonal gold copper indiumzeta .Au6:8 Cu1:2In2 / at 2.21 Å and graphite hydrogen nitrate C16 HNO3 at 3.34 Å. Sample 7 is made up of orthorhombic magnesium vanadium molybdenum oxide .Mg15 V6 Mo6 O48 / at 3.37 and 1.25 Å. 3.5. SEM-EDX Analysis The SEM images of the samples showed micropores of less than 4–12 Å, mesopores of 12–300 Å, and macropores of >300 Å. Irregular shaped aggregates of minerals were also observed in the samples. SEM micrograph of samples 2 and 4 are shown as the representatives in Figure 3. The mineral rich coal surface was further quantified by EDX analysis. C, O, Si, Al, Fe, S, Ca, P, Na, and Mg were found as the major constituents and Ti, Cu, and Mn as the trace elements. The results are similar to Pittsburgh No. 8 coal (Abreu et al., 2007). High peaks of sulfur identified in samples 1, 2, and 3 are in good agreement with the results summarized in Table 1. The peaks of S with Fe, and Ca in EDX spectral profile show the possibility of the existence of pyrite (FeS2 ) or gypsum .CaSO4 :2H2 O/ in the samples. Al was primarily associated with Si in all samples and the results of EDX studies were in good agreement with XRD findings. Si was found to be present either in the form of quartz SiO2 (as shown by XRD pattern of sample 4 in Figure 2) or combined with Al to form aluminosilicates like hallosite 7A .Al2 Si2 O5 .OH/4 /, kaolonite 1A .Al2 .Si2 O5 /.OH/4 /, and dickite 2M1 .Al2 Si2 O5 .OH/4 (confirmed by XRD pattern of samples 2, 3, and 4, respectively). A lesser amount of K in all EDX micrograph is agreed with the AAS observations. The peaks of P were also identified in all samples. 3.6. Major and Minor Elements The oxides of major and minor elements found in the combustion residue of coal are shown in Table 3. A high amount of Si was found in all samples except sample 6. Samples 2 and 4 are Al rich. The highest amount of Fe was found in sample 3. Traces of Mn were observed in all samples. Sample 6 is rich with Fe, Ca, Na, and Mg. Sample 7 has significant amounts of K, Ca, and Mg. The presence of exchangeable metal cations in coal is thought to enhance the reactivity of coal in a gasification process. In an oxidizing atmosphere, sodium, potassium, and calcium look up the reactivity of char. In a reducing atmosphere, sodium acts as the most effective hydrogenation catalyst below 45% carbon combustion, while iron acts as an efficient catalyst at higher combustion. In hydrogen-steam atmosphere, iron was found to be the best catalyst (Tsai, 1982). Correlation analysis was applied on mineral content and ash analysis data. Strong positive correlations were observed between Al2 O3 -SiO2 (r 2 D 0:957, p D 0:001), CaO-MgO (r 2 D 0:934, p D 0:001), mineral matter-SiO2 (r 2 D 0:808, p D 0:028), Na2 O-SiO2 (r 2 D 0:795, p D 0:033), and mineral matter-Al2 O3 (r 2 D 0:746, p D 0:054). Significant correlations were also observed between Fe2 O3 -Al2 O3 (r 2 D 0:643, p D 0:119) and K2 O-SiO2 (r 2 D 0:626, p D 0:132).

A. SARWAR ET AL.


532

FIGURE 3

(a) SEM of sample 2, (b) SEM of sample 4, (1)–(7) EDX of samples 1–7.

THAR COAL

533

TABLE 3 Major and Minor Elements in Thar Coal Sample No.


Oxides, % Major SiO2 Al2 O3 Minor Fe2 O3 Na2 O K2 O MgO CaO MnO2

1

2

3

4

5

6

7

17.59 6.34

47.19 20.01

32.77 8.02

56.75 24.48

27.92 12.21

1.97 1.50

24.44 8.20

35.43 16.99 0.08 4.05 12.53 0.10

7.94 6.38 0.33 4.15 10.9 0.10

42.27 7.13 0.25 1.4 4.14 0.10

5.72 3.6 0.27 1.1 3.11 0.10

16.5 7.17 0.25 6.69 23.82 0.20

30.34 29.05 0.119 5.49 30.18 0.05

2.58 3.02 0.36 13.5 41.8 0.10

Inverse strong correlations were found between mineral matter-CaO (r 2 D 0:906, p D 0:005), mineral matter-MgO (r 2 D 0:801, p D 0:030), K2 O-Na2 O (r 2 D 0:831, p D 0:030), and K2 O-Fe2 O3 (r 2 D 0:728, p D 0:035). 3.7. FT-IR Analysis FT-IR study of the samples was performed to investigate the aromatic and aliphatic character as the quantitative evidence for the maturation of coal (Figure 4). The aliphatic stretching region (2,300–2,400 cm 1 and 2,800–3,000 cm 1 ) is well developed in samples 4–7. All samples exhibit bands in the region of 910–913 cm 1 indicating the presence of quartz and kaolinite, respectively (Abreu et al., 2007) except samples 6 and 7. A noticeable change is the decrease in the absorption intensity of the peaks in 1,000–1,200 cm 1 (Si–O bending vibration) and 3,600–3,727 cm 1 region (aliphatic CH, CH2 , CH3 stretching modes) from samples 1–5. The prominent peaks at 1,500– 1,700 cm 1 (CDC aromatic group) and 3,030 cm 1 (aromatic C–H stretching) were observed in samples 4–7 showing the greater maturity of these samples compared with samples 1–3 (Stephens et al., 1985). The absorbance band at 1,450–1,460 cm 1 region represents CH2 and CH3 bending modes in samples 4–7. The spectra of samples 4–7 are distinguished with others as they have distinct peaks at 2,850–2,920 cm 1 (aliphatic –CH stretching vibration) along with some additional peaks in the region 1,500–1,700 cm 1 (CDC aromatic group). Since the intensities of bands at 1,620 cm 1 is higher than the bands at 2,960 cm 1 (stretching vibration of methyl’s group), it is concluded that the aromatic character of coal due to CDC stretching vibration is more pronounced than the aliphatic character as observed by Abreu et al. (2007) for Pittsburgh No. 8 coal. 3.8. Cluster Analysis Standard classification of coals (ASTM D 388–99) classifies low-rank coals according to gross calorific value (m,mmf basis) only. Cluster analysis (CA) was used as a statistical tool to discriminate the coal samples on the basis of their overall physicochemical properties (proximate analysis, ultimate analysis, gross calorific value, and major and minor elements). CA was performed using the Ward linkage method and squared Euclidean distance measurements. The dendrogram classified the samples into lignite and subbituminous groups (Figure 5). The highest levels of similarity (99.98 and 99.92%) were observed between samples 5–7 and 1–4, respectively. Other


534

A. SARWAR ET AL.

FIGURE 4 FT-IR spectrum of Thar coal samples.

lignite samples were joined with 65.11% similarity level. Sample 6, ranked as subbituminous B, was joined with the lignite samples with 34.35% similarity level. The dendrogram shows good agreement with ASTM standard classification of coals.

4. CONCLUSIONS Thar coal is characterized as lignite to subbituminous with high moisture and high volatile matter. The extraction of coal via classical mining is not economical as its moisture content is extremely high. Kaolinite and quartz are the main minerals of coal. FT-IR analysis is evidence of the immature nature of coal. CA, as a conventional tool, provides aid to the standard classification with the visualization of the level of similarity between samples. On the basis of the authors’ findings, it is suggested that Thar coal can be utilized more effectively either by underground gasification or by converting into liquid products (diesel, naphtha, kerosene, etc.).


THAR COAL

FIGURE 5

535

Dendrograph showing the similarity index between the properties of coals.

REFERENCES Abreu, Y. D., Patil, P., Marquez, A. I., and Botte, G. G. 2007. Characterization of electroxidized Pittsburgh No. 8 coal. Fuel 86:573–584. Bjorkman, A. 2001. Projects on coal characterization. Fuel 80:155–166. BP. 2009. BP Statistical Review of World Energy. Available at: http://bp.com/statisticalreview. Coal Services International. 1990. The International Coal Encyclopedia. Time Off Set Pte Ltd., 1st Ed. of the International Encyclopedia (ICE), vol. 1. Kildare, Ireland: Coal Services International. Demirbas, A. 2005. Biomass co-firing for boilers associated with environmental impacts. Energy Sources, Part A 27:1385– 1396. Government of Sindh, Pakistan, Mines and Mineral Development Department. Thar Coal Resources in Sindh-Pakistan. Available at: http://www.sindhmines.gov.pk/pdf/Thar Coal Resources-brochure.pdf. Gupta, R. 2007. Advanced coal characterization: A review. Energy Fuels 21:451–460. Karaca, H., and Koyunoglu, C. 2010. The co-liquefaction of Elbistan lignite and biomass. Part II: The characterization of liquefaction products. Energy Sources, Part A 32:1167–1175. Ma, B. G., Li, X. G., Xu, L., Wang K., and Wang, X. G. 2006. Investigation on catalyzed combustion of high ash coal by thermogravimetric analysis. Thermochim Acta 445:19–22. Nino, E. F., Nino, T. G., and Man, E. M. S. 1997. Fuels and Combustion, Revised Ed. Manila: Rex Book Store, Inc. Saika, B. K., Boruah, R. K., Gogoi, P. K., and Baruah, B. P. 2009. A thermal investigation on coals from Assam (India). Fuel Process. Technol. 90:196–203. Sonibare, O. O., Ehinola, O. A., Egashira, E., and KeanGiap, L. 2005. An investigation into the thermal decomposition of Nigerian coal. J. Appl. Sci. 5:104–107. Speight, J. G. 2005. Handbook of Coal Analysis. Hoboken, NJ: John Wiley & Sons, Inc., p. 100. Stephens, J. F., Leow, H. M., Gilbert, T. D., and Philip, R. P. 1985. Investigation of the relationship between coal maturity and aromaticity: Characteristics of sodium dichromate oxidation products of Australian vitrinite concentrates. Fuel 64:1537–1541. Tonbul, Y., and Erdogan, S. 2007. Investigation of pyrolysis kinetics of humic acids from low rank Anatolian coal by thermal analysis. Energy Sources, Part A 29:931–938. Tsai, S. C. 1982. Coal Science and Technology, Series 2: Fundamentals of Coal Beneficiation and Utilization. The Netherlands: Elsevier Scientific Publishing Company. Umar, D. F., Usui, H., and Daulay, B. 2006. Change of combustion characteristics of Indonesian low rank coal due to upgraded brown coal process. Fuel Process. Technol. 87:1007–1011. Yongkang, L., Liping, C., and Kechang, X. 2001. Effects of coal structure on its pyrolysis characteristics under N2 and Ar Atmosphere. Energy Sources, Part A 23:717–725.

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NOMENCLATURE TGA AAS SEM XRD ad ar daf m,mmf FT-IR GCV SNG Ti Tp Tb CA

thermogravimetric analyzer atomic absorption spectrophotometer scanning electron microscope X-ray diffractometer as-determined as-received basis dry, ash-free basis moist, mineral-matter-free basis Fourier transform infrared gross calorific value substitute of natural gas ignition temperature peak temperature burnout temperature cluster analysis

Energy Sources, Part A: Recovery, Utilization, and

Energy Sources, Part A: Recovery, Utilization, and

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