Xuliang Yang

Brown coal drying processes-a review

Brown coals become increasingly important in energy consumption with the deposits of other energy resources decreasing every year. The direct utilization of moist brown coals without drying brings many problems such as low combustion efficiency, high greenhouse gas emissions, and it is not acceptable for coal gasification or liquefaction. Pre-drying brown coal is necessary and meaningful. Various drying processes, mainly classified into evaporative and non-evaporative drying, are summarized in this paper, introducing the principles and analyzing the advantages and disadvantages.

Separation of <6 mm oil shale using a compound dry separator

ABSTRACT A large amount of fine granular materials (<6 mm) are produced during the mining of oil shale. The combustion characteristics of oil shale improve with decreasing size of these materials, for which reason fine-grain oil shale has a high utility value. However, fine oil shale also contains a significant amount of inorganic mineral impurities which can be reduced by physical separation to improve the oil quality. Based on an analysis of the physical properties of oil shale, this paper proposes a compound dry separation process for the cleaning of <6 mm oil shale grains. The effects of the vibration intensity, air velocity, and back angle of the employed separator on the separation results and oil content of the cleaned oil shale were systematically analyzed. Under the optimal vibrational conditions defined by a vibration intensity of 25.76 (amplitude = 4.0 mm, frequency = 40 Hz), air velocity of 0.66 m/s, and back angle of 45°, the yield comprised 35.8% concentrate and 64.2% tailings, with corresponding oil contents of 10.02% and 0.85%, respectively. The probable error of the highest intensity of segregation achieved was 0.155. The proposed compound dry separation of oil shale particles of up to 6 mm was found to be more efficient compared with conventional methods, and the separated fine grade material can be comprehensively utilized by further pyrolysis treatment.

Effect of vibration energy on fluidization and 1–6 mm coal separation in a vibrated dense medium fluidized bed

ABSTRACT In this study, a uniform and stable vibrated dense medium fluidized bed (VDMFB) with Geldart B magnetite powder was formed, where it was considered suitable for 1–6 mm coal separation. The formation mechanisms of the best separation environment including the fluidization phenomena under different vibration parameters, the transfer process of the vibration energy, the pressure drop fluctuation and particle oscillation velocity distribution at different bed heights, as well as the corresponding effect on the uniformity and stability of the bed density were investigated. Furthermore, the separation experiment was carried out, and the results exhibited an efficient dry separation performance in the VDMFB.

Spontaneous segregation behavior in a vibrated gas-fluidized bed for fine lignite dry cleaning

ABSTRACT Fine lignite dry cleaning, which has the significant advantage of without process water, is becoming increasingly important due to global water shortage. Lignite particles of various compositions were experimentally studied in a vibrated gas-fluidized bed. This is the first report of the size-based segregation of fine particles in the vibrated gas-fluidized bed. Experimental results demonstrate that the –2 +0.5 mm lignite particles play an irreplaceable role in particle fluidization and segregation. To ensure good separation performance, the minimum content of –2 +0.5 mm lignite particles should be 13%. Separation results show that for –6 +0.5 mm lignite particles, the ash contents of clean coal and tailings are 23% and 45%, with the corresponding yields of 82% and 18%, respectively, which shows good separation performance.

Fine Coal Beneficiation via Air-Dense Medium Fluidized Beds with Improved Magnetite Powders

Dry beneficiation technology of an air-dense medium fluidized bed offers a number of advantages and expands the choices of efficient dry coal cleaning. Recently, the applications of coal beneficiation by the air-dense medium fluidized bed mainly focus on the size fraction of −50 + 6 mm, but it is difficult to separate −6 mm fine coal using the conventional deployment of dense medium. The objective of this study is to expand the lower separation limit of an air-dense medium fluidized bed by using improved magnetite medium. The smaller magnetite powders of narrow size range having lower minimum fluidization velocity could produce a homogeneous gas-solid fluidized bed, which will be in favor of fine coal separation. The experimental results demonstrate that, for −6 + 3 mm fine coal, the tailing product, having the yield, high-ash content, and total sulfur of 34.39%, 70.27%, and 3.42%, respectively, is efficiently removed. Consequently, the clean coal with a yield of 27.33% has a significant reduction of ash content and total sulfur from 45.92% to 31.29% and from 3.02% to 2.57%, respectively, as well as a considerable calorific increment from 3284 Kcal/kg to 4637 Kcal/kg, and the middling product accounted for 38.27% of the feed has a lower ash content of 35.57%. The ash rejection and the combustible recovery are 52.16% and 89.26%, respectively, indicating that −6 + 3 mm fine coal can be effectively separated in an air-dense medium fluidized bed with improved magnetite powders.