Moisture readsorption and low temperature oxidation characteristics of upgraded low rank coal

Choi, Hokyung; Chinnasamy, Thiruppathiraja; Kim, Sang-Do; Rhim, Youngjoon; Lim, Jeong-Hoon; Lee, Sihyun

doi:10.1016/j.fuproc.2011.05.025

Cited by 109 publications

(37 citation statements)

References 10 publications

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“…The dewatered lignite readily re-adsorbs water, which is affected by many factors, including the coal particle size, pore structure, and oxygen and moisture content in both coal and ambient atmosphere. [5,6] The literature shows that the water in large pores is first removed by evaporation, followed by those in the larger capillaries, the shrinkage forces caused by emptying small capillaries because of their complete collapse. [7] Pore shrinkage and pore emptying occurs due to the counteraction of particle contraction and moisture removal.…”

Section: Effect Of Drying Conditions On Moisture Re-adsorption Performentioning

confidence: 99%

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

Yang

Jing

et al. 2013

Drying Technology

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In order to improve the drying efficiency of lignite and restrain the moisture re-adsorption of dewatered coal, the drying characteristics of typical Chinese lignite, the re-adsorption performances of dewatered samples and the change in pore structure throughout the entire processes were investigated in this study. Lignite samples with four different particle size fractions were dried in a fixed-bed reactor in the temperature range 60-160 C. The re-adsorbing moisture behaviors of dewatered coal samples containing different water contents were investigated at temperatures of 20-40 C and humidities of 55-95%. The changes in the pore structure of raw coal and different dried samples were measured by mercury intrusion porosimetry (MIP) and the relations between their re-adsorption performance and change in pore structure were explored. The moisture removal yields of lignite increased with an increase in drying time and temperature and was close to 100% above 120 C and over 100% after holding 40 and 15 min at temperatures of 140 and 160 C due to the release of CO 2 from the decomposing carboxyl group in the coal matrix. The re-adsorbed moisture content in dewatered coal was influenced by drying temperature and coal particle size through varying pore structure. The temperature and relative humidity in the re-adsorbing process were the main factors that influenced the moisture re-adsorption capacity of dewatered lignite, in which the re-adsorbing temperature mainly operated by varying the bonding ability of water on the surface of dewatered coal, and the relative humidity was connected with the pore structure as well. The mesopore was the main factor that influenced the re-adsorption of dewatered coal and the re-adsorption of moisture in dewatered coal at 100 C was highest due to the narrow range of the pore radius and because the relative volume ratio of 5 to 50 nm mesopore (above 91%) was high. The water loss yield of lignite with smaller particle size was higher due to its larger pore volume and surface area, but its re-adsorption capacity was lower because of lower volume ratio of 5 to 50 nm mesopore volume in dewatered coal obtained from the smaller size lignite. INTRODUCTIONCoal will continue to play an important role in China to maintain the steady development of China's economic society and improve the people's living standards. Inferior coals with relatively abundant in resource reserves, especially lignite, have attracted increasing attention in supplying primary energy with the rapid consumption of high-quality coal. However, the high moisture content of lignite and re-adsorption properties of dewatered coal, which result in a lower calorific value, higher power consumption, lower efficiency, greater spontaneous combustion risk, and higher storage and transportation cost, critically restrict the exploitation and utilization range of lignite. [1,2] Therefore, it is important to efficiently reduce its moisture content and restrain the re-adsorption capacity of dewatered coal.Removing moisture by drying enables ...

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Section: Effect Of Drying Conditions On Moisture Re-adsorption Performentioning

confidence: 99%

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

Yang

Jing

et al. 2013

Drying Technology

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“…This point is regarded as the initial point of coal self-heating. The other is the crossing point temperature (CPT), at which the air temperature curve crosses the oven temperature curve [22,23]. This point is usually regarded as the ignition temperature, which provides information about the susceptibility of the coal to spontaneous combustion [24,25].…”

Section: Low Temperature Oxidationmentioning

confidence: 99%

Experimental study on the self-heating characteristics of Indonesian lignite during low temperature oxidation

Zhao

Liu

et al. 2015

Fuel

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“…There are various upgrading processes proposed to prevent or minimize the re-adsorption of moisture such as (1) heat treatment at high temperature, (2) coating of dried coal samples using bitumen, (3) coating of dried coal samples using bitumen along with a solvent, and (4) blending of hot dried coal samples with raw coal samples [15] . Choi and his coworkers investigated moisture re-adsorption behavior of upgraded low rank coal produced by a coal-oil slurry dewatering process [19] . The moisture re-adsorption behavior of coal samples dried at different temperatures was studied, and Jing found that the equilibrium moisture content decreased with increasing of drying temperature [20] .…”

Section: Introductionmentioning

confidence: 99%

Removal behaviors of moisture in raw lignite and moisturized coal and their dewatering kinetics analysis

et al. 2016

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In order to investigate the dewatering kinetics and mechanism of low rank coal, the dewatering behaviors of a Chinese lignite and its moisturized sample (prepared from dewatered coal moisturized under relative humidity of 75% at 303 K for 48 h) in nitrogen and the temperature range of 333-433 K were tested. Physical structure changes of raw coal, moisturized coal before and after drying were determined. The results indicate that drying process of lignite could be divided into four stages, which are increasing rate stage, constant rate stage, relatively fast decreasing rate stage and relatively slow decreasing rate stage. Jander model and First order kinetics model are favorite to describe the relatively fast decreasing rate stage and relatively slow decreasing rate stage, respectively, and the corresponding dewatering mechanism equations are y= 1/3 2 [1-(1-α)] and y= -ln(1-α) . The effective diffusion coefficients and diffusion activation energy were calculated by Fick's second law. The diffusion activation energy of the dewatering stages, related to the relatively fast and slow decreasing rate stages, were 35.80 kJ/mol, 40.75 kJ/mol for raw coal and 27.80 kJ/mol, 37.34 kJ/mol for moisturized coal, respectively. The effective Downloaded by [University of Cambridge] at 17:16 04 June 20162 diffusion coefficient was significantly affected by drying temperature through the pore structure change of coal when other drying operation parameters were fixed. These prove that the forms of re-adsorbed water are not entirely the same as that in raw lignite, in which the former is relatively simple and the latter is more complex.

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Moisture readsorption and low temperature oxidation characteristics of upgraded low rank coal

Cited by 109 publications

References 10 publications

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

Experimental study on the self-heating characteristics of Indonesian lignite during low temperature oxidation

Removal behaviors of moisture in raw lignite and moisturized coal and their dewatering kinetics analysis

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