steel belt fitted with medium wave infrared radiators (IR) in a negative pressure ... horizontal belt filters, or plate-and-frame filter presses; however, removal of ...
FINE COAL DRYING AND PLANT PROFITABILITY M. K. Mohanty1 and H. Akbari2 1 Professor; 2PhD Student Department of Mining and Mineral Resources Engineering Southern Illinois University Carbondale Carbondale, IL 62901. G.H. Luttrell, Professor, Mining and Mineral Engineering, Virginia Tech, Blacksburg, VA. Abstract This paper describes the increased plant revenue that can be achieved by coal preparation plants by using a suitable drying technology to significantly (by ~50%) lower the product moisture content of the fine clean coal fraction. The equalization of incremental inert (i.e., combined ash and moisture) content approach and real plant feed washability data for an Illinois basin coal have been utilized to estimate the potential increase in plant yield that can be achieved for a simple two circuit plant by the above mentioned reduction in moisture content of the fine clean coal product. Computer simulation results indicate that the overall plant yield of a typical coal preparation plant can be potentially increased by 5.74% if the moisture content of the clean coal product can be further reduced by 50%, i.e., from the ~18% level commonly achieved by the best available mechanical dewatering processes, such as screen-bowl centrifuges, vacuum disc filters or plate-and-frame filter presses to ~9% with the use of a suitable fine coal drying technology. With the substantial reduction in the moisture content and thus the inert content of the fine clean coal product, the specific gravity-cut of the coarse coal circuit can be increased from 1.47 to 1.69, resulting in the majority of the above mentioned yield improvement for the overall plant while still maintaining the desired heat content specification of the total clean coal product. The Parsepco Drying Technology (PDT) and Nano Technology Dryer (NTD), two recently developed drying technologies, have shown the feasibility of providing the above mentioned moisture reduction of the fine clean coal product. The PDT dewaters the moist coal on a woven steel belt fitted with medium wave infrared radiators (IR) in a negative pressure environment, whereas the NDT utilizes molecular sieves to absorb the excess moisture from fine coal. These two emerging drying technologies along with several other commercially available coal drying technologies, more commonly used for low-rank coal, have been reviewed in this publication for their potential integration into higher rank coal preparation plant circuits. COAL DRYING PRINCIPLE Coal drying generally refers to evaporating the water trapped in coal particles and thereby lowering the moisture content of coal. Commonly, moisture content in coal is categorized as surface moisture and inherent moisture. However, a comprehensive list of five of these categories, as reported by Osman et al. (2011), includes interior adsorption water, located in the micro pores and micro capillaries within each coal particle; surface adsorption water, located on individual particle surface; capillary water, located in the capillaries of coal particles; interparticle water, located in small crevices found within particle aggregates; and adhesive water 1
contained in the film around the surface of particle aggregates. The first three categories constitute what is commonly referred as inherent moisture, whereas the last two are included in the surface moisture category. Most of the surface water can be removed using some type of mechanical dewatering systems, whereas removal of the inherent moisture requires some type of drying method. The majority of the surface moisture content of fine coal is usually removed in coal preparation plants by mechanical dewatering systems, such as screen-bowl centrifuges, vacuum disc filters, horizontal belt filters, or plate-and-frame filter presses; however, removal of inherent moisture from fine coal is not a usual practice. In very specific cases needed to satisfy the overall moisture specification, convective thermal drying is the only method commonly utilized to remove residual surface moisture and at times a part of the inherent moisture content of fine coal. The mostly used thermal drying system is the fluidized bed dryer, which uses coal, oil or natural gas as the fuel source to heat the intake air stream (Pratton et al. 2012). The amount of fuel required depends on the amount of water content of the fine coal fed to the dryer and the desired moisture content of the product. However, thermal dryers require a substantially large capital and installation cost and also a large operating and maintenance cost. That is why they are rarely used in the coal preparation plants. Irrespsective of the drying method used, each fine coal type will have a drying charateristic curve as a function of drying temperature, hot air (gas) velocity and pressure envirment. A typical drying curve (shown in Figure 1), as described by De Korte and Mangena (2004) indicates three distinctly different time periods: the initial increasing drying rate period followed by a constant drying rate period and a falling drying rate period. As shown, the moisture reduction rate reduces significantly after the removal of all surface moistures in the constant drying rate period.
Figure 1. Typical drying curve for fine coal During the initial period the wet coal is heated from the ambient temperature to the process temperature maintained inside the dryer. Heat energy is transferred to the coal particles resulting in the evaporation of the contained moisture. The rate of evaporation and thus the drying rate increases rapidly with the removal of most of the surface moisture during this initial period. This causes the exponential decay in the moisture content during this period. At the end of this initial 2
period, when the heat transferred from the source (hot air, gas etc.) becomes equal to the the cooling caused by evaporation of surface water from coal particles, the drying rate stops increasing and cotinues at a constant rate through out this second period. This is shown as the constant dry rate period with a horizontal line for the drying rate and and a straight inclined line with the same slope over this entire second period for the moisture content change. Once all the the surface moisture from coal particles is evaporated, drying of the ineherent moisture begins and that is marked by a substantially reduced drying rate in the falling rate period, shown in Figure 1. The cost of drying of the inherent moisture becomes prohibitively expensive due to the exteremly slow drying rate observed while removing moisture from the micro pores and micro capillaries of individual coal particles. The authors believe that a suitable drying technology can be used to remove almost all the surface moisture content of the mechanically dewatered fine coal product in a coal preparation plant at a relatively low cost. This is how the moisture content of the fine clean coal can be brought down to almost the same range of values as that of mechanically dewatered coarse coal. It is true that such change in commercial practice will require significant capital investment and increase operating costs for coal preparation plants. However the resulting reduction in the moisture content of the fine clean coal product would allow suitable increase in the specific gravity-cut achieved in both coarse and fine coal cleaning circuits and thus significantly increase the plant clean coal yield while maintaining the heat content of the plant product at the original level. It is believed that the resulting increase in plant revenue will far offset the additional cost of integrating the suitable drying technologies to a conventional coal preparation plant and thus, increase plant profitability. POTENTIAL BENEFITS OF DRYING TECHNOLOGY INTEGRATION TO A COAL PREPARATION PLANT Coal mining companies are usually paid on the basis of the heat content of coal they deliver. Therefore, most of the mining companies utilize coal preparation plants to remove both in-seam and out-of-seam dilution from the run-of-mine coal to produce clean coal having a low ash value. Since most of the coal preparation plants today operate with wet separation processes, the addition of water to the run-of-mine coal is a common practice followed in these plants. Today's coal preparation plants attempt to dewater the clean coal product using the best available mechanical dewatering processes based on the particle size distribution of the fine coal and the desired ultimate moisture content. However, due to the inherent difficulty of removing water from fine coal, the final moisture content of the fine clean coal product is usually 2 to 3 times higher than that of the coarse clean coal product generating from the same plant, although the product ash values are in a similar range. This is why, although the fine coal proportion of the total clean coal tonnage produced from a plant is in 10 to 15% range, as much as 1/3rd of the total moisture content in the clean coal product is contributed by the fine coal fraction. Through this publication, the authors attempt to show the potential plant profitability that can be achieved by using some of the emerging fine coal drying technologies to further lower the moisture content of the mechanically dewatered fine coal product of a coal preparation plant to nearly the same level as that of the mechanically dewatered coarse coal product. To explain the potential benefits that could be realized in a realistic plant environment, a computer simulation exercise has been conducted using the real feed washability data obtained from a coal preparation plant operating in the Illinois basin. To keep the calculations relatively 3
simple, only two cleaning circuits, i.e., coarse and fine coal circuits of the plant, have been considered for this analysis. The plant cleans the +2 mm size coarse coal and 2 mm x 75 m size fine coal using dense-medium cyclones and coal spirals, respectively. The two circuit plant cleans 900 tons per hour (tph) of raw coal having an overall ash value and moisture content of 21.85% and 5.65%, respectively. The feed washability data for both coarse and fine coal are listed in Table 1. The as-received heat content of the feed coal has been calculated based on the strong correlation between the heat content (Btu/lb) and the combined ash and moisture content of a variety of Illinois basin coals, shown in Figure 2. The product moisture contents of coarse and fine clean coal for the simulation exercise have been assumed to be 6% and 18%, which is quite comparable to the moisture content that is commercially achieved in the coal preparation plants in the Illinois basin. The computer simulation exercise targeted to maximize the plant yield while producing an overall product heat content of 11900 Btu/lb (on as-received basis). The equalization of incremental inert content (combined ash and moisture) approach of plant optimization was pursued for two different cases: the first case being the conventional plant without using any drying technology, whereas the second case made use of a suitable drying technology to lower the moisture content of mechanically dewatered fine coal by 50%, i.e., from 18% to 9%. For both cases, the coarse clean coal moisture content was set at 6%, which is quite comparable to the moisture content that is commercially achieved in the coal preparation plants in the Illinois basin. Table 1. Washability data for the coarse and fine coal obtained from a coal preparation plant operating in the Illinois basin Coarse Coal (86.96% of the total feed; ash: 22.57% ; moisture: 5.02% ) Individual Sink Float % Wt dry % Ash dry Btu/lb (ar) 1.30 44.12 6.35 12609 1.30 1.40 26.81 10.84 11910 1.40 1.50 5.68 19.58 10552 1.50 1.60 1.74 26.25 9516 1.60 1.70 0.83 32.21 8590 1.70 1.80 0.69 34.67 8208 1.80 1.90 0.58 41.13 7204 1.90 2.00 0.89 48.13 6116 2.00 2.10 1.31 61.23 4080 2.10 17.33 76.80 1660 Fine Coal (13.04% of the total feed; ash: 17.01% ; moisture: 9.97% ) Individual Sink Float % Wt dry % Ash dry Btu/lb (ar) 1.30 62.00 4.54 12120 1.30 1.40 13.90 12.17 10935 1.40 1.50 5.90 17.48 10110 1.50 1.60 2.50 25.75 8824 1.60 1.70 0.50 30.73 8051 1.70 1.80 0.90 35.32 7337 1.80 1.90 0.80 41.29 6410 1.90 2.00 0.40 46.68 5572 2.00 2.10 0.60 49.40 5149 2.10 12.50 76.34 963
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% Wt 44.12 70.93 76.62 78.36 79.19 79.88 80.46 81.35 82.67 100.00
Cumulative % Ash dry 6.35 8.06 8.92 9.26 9.57 9.76 9.97 10.61 11.98 22.57
Btu/lb (ar) 12609 12345 12212 12152 12114 12080 12045 11980 11855 10088
% Wt dry 62 75.9 81.8 84.3 84.8 85.7 86.5 86.9 87.5 100
Cumulative % Ash dry 4.54 5.94 6.77 7.33 7.47 7.76 8.07 8.25 8.53 17.01
Btu/lb (ar) 12120 11903 11774 11686 11665 11619 11571 11544 11500 10183
Figure 2. Strong correlation of the heat content of a variety of coal samples collected from the Illinois coal basin with the combined ash and moisture content of the coal samples Figures 3 and 4 illustrate the clean coal yield versus the overall inert content and incremental inert content relationships obtained for both case 1 and 2, respectively. For case 1, the incremental inert content for both coarse and fine coal circuit was equalized at 25.5% to achieve the desired heat content >11900 Btu/lb for the overall plant product. As indicated in Table 2, the heat content of the individual products from the coarse coal and fine coal circuits were 12081 and 10799 Btu/lb, respectively, and the total clean tonnage produced was 673 tph. The significantly lower heat content of the fine coal product was the result of the high moisture content of 18% of this product. Case 2 simulations show the increase in clean coal production that can be achieved by lowering the fine coal moisture content by 50%, i.e., from 18% to about 9% level by using a suitable fine coal drying technology. As shown in Table 2, using the plant optimization approach, clean coal tonnage can be increased to nearly 725 tph, while still maintaining the heat content of the overall clean coal product at the original level of 11937 Btu/lb. Thus, the additional 52 tph of clean coal can be produced by suitably increasing the specific gravity-cuts of both coarse and fine coal circuits to 1.69 and 1.74, respectively. In spite of the significant increase in the incremental inert content of both circuits to 39.1% level, the overall inert content of both products and thus, the overall heat content could be maintained at the original level. At a rate of $50/ton of Illinois basin clean coal and 6000 working hours per year, the additional clean coal production would result in an increase in annual revenue by $15.6 million. This will require capital investment in a suitable technology to dry nearly 100 tph mechanically dewatered fine clean coal from 18% moisture to 9% level. This can be achieved by three full-scale Parsepco Dryers having a capital cost of $1 million each (Buisman 2012). Clearly, the above mentioned increase in annual revenue would pay off the additional capital investment for the coal dryers in a few months time.
5
(a)
(b)
Figure 3. The clean coal yield versus incremental inert (moisture+ash) and overall inert content relationships for the coarse and fine coal circuit of a coal preparation plant not using any coal drying technology
6
(a)
(b)
Figure 4. The modified clean coal yield versus incremental inert (moisture+ash) and overall inert content relationships for the coarse and fine coal circuit of a coal preparation plant simulated with the use of drying technology to further lower the moisture content of the fine clean coal product from 18% to 9%.
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Table 2. Potential increase in clean coal tonnage that can be achieved by integrating a drying technology into the fine coal circuit of a simple two-circuit plant preparing Illinois basin coal Without Drying Technology Coarse Fine Total Clean Coal With Drying Technology Coarse Fine Total Clean Coal
Tph (dry)
Tph (ar)
Moisture% (ar)
Ash% (dry)
Btu/lb (ar)
Inert% (ar)
Increm. Inert% (ar)
561.4 62.2 623.6
597.2 75.9 673.1
6 18 7.4
8.76 5.01 8.39
12081 10799 11937
14.8 23.0 15.7
25.5
588.6 89.7 678.3
626.19 98.6 724.8
6 9 6.4
9.53 7.68 9.29
11961 11783 11937
15.5 16.7 15.7
39.1
COMMERCIALLY AVAILABLE DRYING TECHNOLOGIES Most of the commercially used coal drying technologies are of convective thermal drying type, in which drying occurs when a hot gas (air) is allowed to be in contact with moist coal. The circulating hot gas (air) also acts as a carrier for the removal of evaporated moisture from the dryer (De Korte and Mangena 2004). Drying of coal is more widely practiced commercially for low rank coals, having very high inherent and surface moisture contents. Pikon and Mujumdar (2006) provide a detailed discussion on various commercially used coal dryers in the Handbook of Industrial Drying. Jangam et al. (2011) provides a comparative analysis (Table 3) of the advantages and disadvantages of the state-of-the art coal drying technologies. Various past studies (Pikon and Mujumdar 2006; Bongers et al. 1998; Wilson et al. 1997; Suwono and Hamdani 1991; Mujumdar 1990) indicate the significant advantages associated with superheated steam drying. These include reduced risk of fire hazard/spontaneous combustion due to the absence of oxygen, increased drying rate and energy efficiency and reduction in dust emission. These types of superheated steam dryers could be very suitable for large-scale fine coal drying applications at coal preparation plants. EMERGING FINE COAL DRYING TECHNOLOGIES/METHODS Extensive studies conducted in the food processing industry in the past indicate the superiority of radiation-based drying methods (Chou and Chua 2001; Das et al. 2004; Wang and Sheng 2006). One of these studies indicates that drying time can be reduced by 50 to 60% by the use of infrared radiation based drying system in comparison to that of the convective air-based system. It is known that some of the Infrared Radiation (IR) systems can evaporate more than 3 liter of water in a vacuum environment while consuming only 1 kWh of energy in comparison to only 0.5 liter of water that is evaporated using the thermal dryers utilizing convective heating mechanism (Fisher 2012). IR drying systems transfer thermal energy to the materials to be dried in the form of electromagnetic waves. Past studies indicate medium wave infrared radiation (MIR) to be more effective than short wave or long wave IR in removing water from a substrate (Buisman 2010). A new highly efficient drying system has recently emerged in the form of the Parsepco Dryer with the combination of MIR, a steel belt dryer and a pin mixer.
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Table 3. Comparative analysis of the conventional drying technologies available for coal drying Coal Dryer Type (listed in alphabetical order) Belt dryer (Pikon and Mujumdar 2006; Li 2004) Fluid bed dryer (Karthikeyan et al. 2009; Li 2004) Horizontal agitated bed dryer using jacket or screw heating (Mujumdar 2006) Pneumatic dryer (Li 2004) Pulsed combustion dryer (Ellman et al. 1966) Rotary dryer (Clayton et al. 2007; Li 2004; Hatziylberis 2000) Rotary tube dryer (Pikon and Mujumdar 2006; Li 2004) Spouted bed dryer (Karthikeyan et al. 2009) Superheated steam using various types (Bongers at al. 1998; Wilson et al. 1997; Suwono and Hamdani 1991; Mujumdar 1990) Vibrated bed dryer
Key Advantages
Key Disadvantages
compact construction; simple design; lower temperature drying intensive drying due to good mixing indirect heating through shaft and jacket; very low drying medium flow rate needed simple construction short drying time; high drying efficiency; environmentally friendly operation drying along with disintegration; internal heating with coils; no fire hazard indirect heating; no fire hazard; high efficiency very good heat and mass transfer rate high thermal efficiency; no danger of fire or explosion; energy efficient; suitable for high capacity continuous operation low gas velocity required for fluidization
limited capacity; large foot print high pressure drop; attrition high power requirement; high maintenance attrition noise problem; scale-up issues; fire hazard high maintenance
capital intensive scale-up issues; limited particle size only suited for high capacity applications; lot of heat loss in the exhaust
more moving parts
Source: Jangam et al. 2011 This Parsepco Drying Technology (PDT) dries fine coal/mineral feed from ~25% moisture to below 10% level utilizing ceramic MIR emitter boards on a negative pressure environment of a steel belt. Parsepco Drying Technology As shown in the schematic diagram in Figure 5, the PDT consists of a woven steel belt on which the moist fine coal is dried using MIR emitter boards from the top and a vacuum system from the bottom of the belt. Steel belts are unaffected by variances in temperatures and can easily accept high temperatures. Where normal plastic or material belts would stretch or deform at elevated temperatures, steel belts can easily withstand high temperatures. While polyesters and polyamides are hydrophilic, the steel is neutral; thus the steel belts provide a better drainage of water than the plastic belts. In addition, because of the non-hydrophilic property of steel, cake 9
does not tend to adhere to the steel belts at the discharge end unlike the plastic belts. The negative pressure environment on the belt created by vacuum greatly assists the transfer of the IR energy into the substrate removing all vapor downward and away from the MIR emitters. In cases of extremely fine clean coal below 75 m, a pin mixer (shown in Figure 6) is utilized to prepare the feed for the dryer in the form of 3 to 6 mm size micro-granules. More details about the PDT is available elsewhere (Buisman 2010), which reports some of best drying results achieved from the Parsepco Dryer for extremely fine (-45 m) coal tailings. Product moisture contents of 9.51% and 13.73% were achieved by drying the dewatered tailings product obtained from a plate-and-frame filter press. Pin Mixer Product or plant dewatered fine coal with up to 30% Moisture
Dry Coal
Figure 5. Parsepco Dryer schematic (Fisher 2012)
Feed
Product
Figure 6. Schematic of a pin mixer (Buisman 2010) 10
Nano Drying Technology The Nano Drying Technology (NDT™) drying system, a patent pending process (Bland et al. 2011), uses molecular sieves to extract the majority of the reminaing moisture from a mechanciallly dewatered fine clean coal product from about 25% in the feed to less than 10% in the product. The molecular sieves are mixed with fine coal paticles at a desired sieve-to-coal ratio for a suitable retention time to absorb almost all the surface moisture from the fine coal aggregates. After this step, as shown in the schematics of batch and pilot-scale process steps in Figures 7 and 8, the soaked molecular sieves are screened off leaving behind the nearly dry fine coal product. The pores of the molecular sieves are sufficiently large to draw in and absorb water molecules, but too small to allow any of the fine coal particles from entering the sieves. Some molecular sieves can absorb up to 42% of their weight in water (Bland et al. 2011). In the subsequent step, the water absorbed in the molecular sieves are evaporated using a heating system to regenerate those for their reuse in the next cycle. Greater details of the the NDT™ drying system is available elsewhere (Bratton et al. 2012). The same study reported product moisture contents in the range of 5 to 10% for both -0.6 mm and -0.15 mm coal having feed moisture contents in the range of 22 to 28%. Dry Dry high-moisture high-moisture coal coal fines fines by by combining combining with with molecular molecular sieves. sieves.
Separate Separate dewatered dewatered coal coal fines fines from from molecular molecular sieves. sieves.
Reuse Reuse molecular molecular sieves sieves after after thermal thermal regeneration. regeneration.
Rotary Mixer
Laboratory Sieve
Microwave Dryer
Figure 7. Schematic of the batch-scale NDT process steps (Bratton et al. 2012) Feed Coal
Coal/Sieve Contactor
Coal/Sieve Screen
Make-Up Sieves Water Vapor
Dry Coal
Sieve Regenerator
Figure 8. Schematic of the pilot-scale NDT process steps (Bratton et al. 2012)
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Dielectric Heating and Drying Dielectric heating refers to heating by high frequency electromagnetic radiation, i.e., microwave frequency and radiofrequency waves (Menendez et al. 2010). In order to avoid the interference with microwave bands used for telecommunications, the wavelengths for industrial heating and other applications are regulated by national and international authorities. Thus, the main operating microwave frequency for industrial/domestic applications in the majority of the countries is 2.45 (±0.05) GHz (Meredith 1998). Microwave drying is well known for its advantages, such as volumetric heating and faster drying rates. The Drycol Process, developed by DBAGlobal- Australia is based on the use of microwave drying for coal. A 15 tph plant operates to dry low rank coal from 28% to 12% moisture content product (Graham 2008). The presence of microwave (MW) absorbing impurities in coal can result in hot spots and can also result in fire hazards during drying. Intermittent MW drying is a possible option to remove moisture efficiently during the final stages of coal drying (Jangam et al. 2011). CONCLUDING REMARKS The wide-scale practice of drying of coal to lower its moisture content has been so far restricted mostly to low rank coal having significantly higher proportion of inherent moisture, which cannot be removed by mechanical means. However, results reported in this publication based on a detailed plant optimization analysis conducted using the approach of equalization of incremental inert content of each cleaning/dewatering circuit of a two-circuit plant, indicates that suitable coal drying technologies should also be integrated to the bituminous coal and anthracite preparation plants of the future. Some of the emerging drying technologies, based on superheated steam, infrared heating, microwave heating and/or molecular-sieve based nano-technology drying may be quite useful in lowering the moisture content of the mechanically dewatered fine clean coal product by removing only its residual surface moisture content. Attempting to lower inherent moisture content of fine coal may not be quite viable in most cases, due to the extremely slow drying rate achieved during the last stage of drying period, i.e., the falling rate period. However, the residual surface moisture content of fine clean coal could be nearly eliminated by the use of high efficiency emerging drying technologies while adding to the profitability of the coal preparation plant and thus, the mining operations.
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Buisman, R. 2010. Agglomeration and drying of mineral fines, Fines Beneficiation, Dewatering and Agglomeration Conference, The South African Institute of Mining and Metallurgy. Misty Hills, South Africa, November 16-17; pp:1-7. Chou, S.K., and Chua, K.J. 2001. New hybrid drying technologies for heat sensitive foodstuffs. Trends in Food Science & Technology. 12:359-369. Clayton, S.A., Desai, D., and Hadley, A.F.A. 2007. Drying of brown coal using a superheated steam rotary dryer. Proceedings of the 5th Asia-Pacific Drying Conference. Hong Kong, August. 179-184. Das, I., Das, S.K., and Bal S. 2004. Drying performance of a batch-type vibration aided infrared dryer. Journal of Food Engineering. 64:129-133. De Korte, G.J., and Mangena, S.J. 2004. Thermal drying of fine and ultra-fine coal, Coal Tech 2020, Report No: 2004-0255, Division of Mining Technology, CSIR, South Africa. Ellman, R.C., Belter, J.W., and Dockter, L. 1966. Adapting a pulse-jet combustion system to entrained drying of lignite. Fifth International Coal Preparation Congress, Pittsburgh. October 3-7. 463-476. Fisher, B. 2012. Fine coal drying - a presentation at the Illinois Clean Coal Institute, March. Graham, J. 2008. Microwave for coal quality improvement: The Drycol Project; DBAGlobal, Milton, Queensland, Australia. Hatzilyberis, K.S., Androutsopoulos, G.P., and Salmas, C.E. 2000. Indirect thermal drying of lignite: Design aspects of a rotary dryer. Drying Technology. 18(9):2009-2049. Karthikeyan, M., Zhonghua, W., and Mujumdar, A.S. 2009. Low-rank coal drying technologiesCurrent status and new developments. Drying Technology. 27(3):403-405. Li, C.Z. 2004. Advances in the Science of Victorian Brown Coal; Elsevier: Oxford. Li, C.Z., Su, W., Wu, Z., Wang, R., and Mujumdar, A.S. 2010. Investigation of flow behaviors and bubble characteristics of a pulse fluidized bed via CFD modeling. Drying Technology. 28(1-3):2071-2087. Luttrell, G.H. 2012. Nano Drying Technology: A New Approach for Fine Coal Dewatering- a presentation at Coal Prep 2012, April 30-May 3, 2012. Meredith, R. 1998. Engineers’ Handbook of Industrial Microwave Heating. The Institution of Electrical Engineers. London. Mohanty, M.K. 2003. Evaluation of a High-Efficiency Fine Coal Dewatering Technology, Final Technical Report: ICCI Project Number: 02-1/4.1A-3; Illinois Department of Commerce and Economic Opportunity / Illinois Clean Coal Institute. Mujumdar, A.S. 2006. Handbook of Industrial Drying, 3rd Ed; CRC Press: Boca Raton, Florida. Mujumdar, A.S. 1990. Superheated Steam Drying: Principles, Practice and Potential for use of Electricity; Canadian Electrical Association: Montreal, Quebec, Canada, 1990. Report No. 817, U 671.
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Mujumdar A.S., and Jangam S.V. 2011. Drying of low rank coal: Minerals, Metals and Materials Technology Center (M3TC) Report-M3TC/2011/01, National University of Singapore. Osman, H., Jangam, S.V., Lease J.D., and Mujumdar, A.S. 2011. Drying of low-rank coal-A review of recent patents and innovations: Minerals, Metals and Materials Technology Center (M3TC) Report-M3TC/TIPR/2011/02, National University of Singapore. Pikon, J., and Maujumdar, A.S. 2006. Drying of Coal. Handbook of Industrial Drying, 3rd Ed; Edited by A.S. Mujumdar. CRC Press: Boca Raton, Florida. 993-1016. Suwono, A., and Hamidani, U. 1991. Upgrading the Indonesia's low rank coal by superheated steam drying with tar coating process and its application for preparation of CWM. Coal Preparation. 21:41-54. Wang J., and Sheng, K. 2006. Far-infrared and microwave drying of peach, LWT-Food Science and Technology, 39:247-255. Wilson, W.J., Walsh, D., and Irvin, W. 1997. Overview of low rank coal drying. Coal Preparation. 18:1-15.
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