Experimental Observation and Image Analysis for Evaluation of Swelling and Fluidity of Single Coal Particles Heated with CO₂ Laser

Abstract

Swelling characteristics of three kinds of single coal particles heated with a well-characterized CO2 laser were directly observed and quantitatively evaluated by combined application of a high-speed video camera with an image analysis system. The results are as follows: (1) The interval time between swelling and shrinking of bubbles of coking coal particles (Blue Creek, Goonyella) could be used to express the ease of reforming bubbles after bursting and the growth of the bubbles before bursting. The distribution of the interval time of coking coals depends on laser intensity, particle size, and coal properties. (2) For the high-volatile weak coking coal (Witbank), there is no formation of bubbles during heating and the maximum swelling ratio is much smaller than that of coking coals. (3) The maximum swelling ratio and final swelling ratio evaluated with the relative projection area decrease with the increasing of laser intensity (or temperature and heating rate) and particle size. (4) There is a monotonously increasing relationship between the maximum relative projection area and the maximum Gieseler fluidity for all three kinds of coal, although the maximum relative projection area increases with increasing laser intensity. This result suggests that the relative projection area of coal particles on heating can be used for evaluating both the swelling and fluidity properties of coals. (5) The present results suggest a possibility that the “surface tension” of bubble film of the coking coal on heating seems to be attainable from the calculation of the rupture pressure of bubbles.

Effect of Temperature, Pressure, Feed Particle Size, and Feed Particle Density on Structural Characteristics and Reactivity of Chars Generated during Gasification of Pittsburgh No.8 Coal in a High-Pressure, High-Temperature Flow Reactor

“…Interestingly, the particle size marginally affected the char swelling ratio as it increased from 1.58 for the char from −425 + 212 µm fraction to 1.65 for the char from −150 + 106 µm fraction. Earlier studies under pyrolysis observed that swelling (or porosity) decreased with an increase in coal particle size [17,44,45]. It is important to recognize that chars from the coarser size fractions are in early stages of conversion (<50%), while the chars from the fine-sized fractions (i.e., −106 + 75 and −150 + 106 µm) are in middle stages of conversion (50%-70%).…”

Sulfur and Nitrogen Distributions during Coal Carbonization and the Influences of These Elements on Coal Fluidity and Coke Strength

“…The thermoplastic behavior of coal particles during carbonization has thus been studied extensively with several types of analysis techniques and different kinds of coals. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Some researchers exhibit that coal thermoplasticity depends strongly on the amounts of chloroform solubles naturally-present in coal, 1,4,6) low-molecular-weight compounds (metaplasts) 2,3) and/or transferable hydrogen 7,10) formed upon carbonization. It has also been reported that the sulfur and nitrogen present in coal, denoted as coal-S and coal-N, respectively, affect coal fluidity, [17][18][19][20] and that the addition of denzo-[c]-acridine (C17H11N) to a coal blend, even at a small amount of 3 mass%, enhances the tensile strength of the coke after carbonization by a factor of about 1.2.…”

Simulation of the Swelling of High-Volatile Bituminous Coal during Pyrolysis

“…The growth, coalescence, and rupture of the bubbles lead to the swelling and shrinking of the coal particle during pyrolysis. A dynamic variation of the particle size because of multiple ruptures during coal pyrolysis has been observed, 9,10 and, overall, the change of particle size is an increasing then decreasing trend. Studies at low heating rates in thermogravimetric analysis (TGA) devices and wire mesh reactors indicate that the final swelling ratio of coal particle increases as the heating rate increases; 11 however, studies with drop-tube furnaces and flat-flame burners show that the swelling ratios decrease at rapid heating rates.…”