Zhenyong Miao

Energy consumption during dewatering process affected by carboxyl on coal surface

ABSTRACT The energy consumption during dewatering and carboxyl concentrations on the surfaces of six different coals were examined. Three stages of dewatering were investigated based on the energy consumption. The water in the spaces between coal particles and large pores, water in progressively smaller capillaries and pores, water clusters around the functional groups, and water directly absorbed by oxygen functional groups were subsequently removed with increasing energy consumption. The moisture present in three forms was significantly affected by carboxyl concentrations. In the first and second stages, the energy consumption at the same residual moisture content was closely related to the carboxyl concentrations. Even at the same ratio of moisture content to carboxyl concentration, energy consumption increased with an increase in carboxyl concentration on coal surface in the second stage.

Binderless briquetting of lignite by the mechanical thermal expression process

ABSTRACT The mechanical thermal expression (MTE) process, which has been widely studied as a dewatering technology, could also be used for the briquetting of lignite. In this study, the effect of operating conditions on the compressive strength and shatter index of briquette produced by the MTE process was investigated. The compressive strength of briquette increased with the increase of pressure and temperature. The increase in pressure and temperature also resulted in a decrease of residual moisture content in briquettes, which had a positive effect on the compressive strength and shatter index. It was demonstrated that the briquettes produced by the MTE process could survive handling and transportation. The dewatering of lignite during the MTE process strengthened the bond between particles, which enhanced the compressive strength of briquette. The presence of humic acid and functional groups, such as carboxyl and hydroxyl, enhanced the compressive strength of briquette by promoting the formation of hydrogen bonds between the surfaces of lignite particles. The combustion efficiencies and particle emission of lignite could be improved by the MTE briquetting process.

A comparison of desorption process of Chinese and Australian lignites by dynamic vapour sorption

ABSTRACT Modified BET model and Do and Do (D.D.) model were chosen to interpret the desorption process of water on hard and soft lignites. The organic and inorganic hydrophilic sites were determined by X-ray photoelectron spectroscopy and X-Ray fluorescence spectroscopy. From the modified BET model, only a small part of hydrophilic sites (HSs) acted as effective primary sites due to space restraint, intramolecular hydrogen bond and maybe more than one hydrophilic site connecting with one water molecule. From the D.D. model, the total adsorption sites (St) of Loy Yang lignite (LY) is 18.7 mmol/g, which is higher than that of Shengli (SL) 17.0 mmol/g in spite of lower primary sites, and the saturation concentration of water (qus) in the micropore of LY is 33.7 mmol/g, which is much higher than that of SL (12.5 mmol/g). So the high moisture-holding capacity of LY is mainly determined by the high St and qus, and not the primary sites. The size of water clusters entering the micropores is 7 for SL and 6 for LY, which is related to relative location of HS. When dewatered, the higher total sites density and smaller water cluster size of LY both implied higher dewatering energy.

Multiphysics modeling of water transport in high-intensity lignite drying process on pore scale

ABSTRACT The understanding of the moisture transfer process in the pore network is quite important to improve the lignite drying efficiency. Scanning electronic microscopy image was used for construction of pore topology closely approximating the true topology of the real lignite for the heat and mass transfer processes on pore scale by COMSOL simulation. Considering the gas‒liquid phase coexistence of water, “Laminar Two-Phase Flow, Phase Field” module and “Liquid Heat Transfer” module were used. The pore size had significant effects on the flow velocity and the larger pores acted as the main pathway for the moisture transport, therefore affected the maximum drying rate. On the other hand, the connection of pores and the throats distribution in the pathway also had a significant effect on the flow velocity, and the moisture between the throats was hard to transfer as a flow, maybe by vapor diffusion. In high-intensity lignite drying process, the moisture vaporization quickly when heated up and vapor pressure was beneficial to keep the pore size and ensure the smooth of moisture flow pathway, thus improving the efficiency of the drying process.

Thermal fragmentation and pulverization properties of lignite in drying process and its mechanism

ABSTRACT The fragmentation and pulverization properties of lignite in the different drying processes were investigated in this study. Lignite particles were dried at different temperatures (100, 140, and 180°C), particle sizes (6–25 mm) and drying time (0–60 min), and the parameters of fragmentation index (Sf) and pulverization ratio (β) were used to describe the fragmentation and pulverization properties of lignite. The results indicated the fragmentation index increased from 3.10 to 30.41 with the increase in temperature and particle size. Pulverization ratio increased slightly from 0.39 to 0.63% with temperature, and it decreased from 0.58 to 0.36% with particle size. Fragmentation index and pulverization ratio increased rapidly from 1.20 to 5.50 and 0.05 to 0.47%, respectively, and then tended to grow slowly with drying time. Fragmentation index was linearly related to the loss of moisture content. Different kinds of fragmentation and pulverization occurred at the same time: fine particles exfoliated from the surface, and there were also fragmentation at the outer zone or the core of the particles to produce the smaller particles. The evolutions of macropores might be the main reason of thermal fragmentation.

Effect of moisture distribution in pore structure on fragmentation characteristics of lignite

ABSTRACT The experiments were performed to explore the effect of moisture on fragmentation properties of Mengdong (MD) lignite, Xiao Longtan (XLT) lignite, and Zhaotong (ZT) lignite with temperature of 200°C and particle size of 13–10 mm using the fixed bed reactor. It showed fragmentation ratio and pulverization ratio increased, and particle size variation ratio decreased with an increase in initial moisture of lignite. The distribution of moisture in pores under different initial moisture contents was analyzed by nuclear magnetic resonance. The distribution of moisture in pores between raw and dried lignite was different. The water content in macropores rapidly decreased, but water content in mesopores remained constant in prior period and then slightly decreased with the residence time increasing. There was a good connectivity between macropores and mesopores. The water in micropores, which hardly influenced fragmentation, was generally closed and not favored for the mobility of water. The water in macropores had a significant effect on fragmentation of lignite. However, when the moisture content in macropores was less than 0.10 g/g coal, the degree of fragmentation became little.