Influence of Coal Particle Size on Coal Adsorption and Desorption Characteristics

Abstract

Accurate testing coal isotherm can play a significant role in the areas of coal seam gas drainage, outburst control, CO 2 geo-sequestration, coalbed methane (CBM) and enhanced coalbed methane recovery (ECBM) etc. The effect of particle size on the CO 2 and CH 4 sorption capacity of bituminous coal from Illawarra, Australia was investigated at 35°C and at pressure up to 4 MPa. A unique indirect gravimetric apparatus was used to measure the gas adsorption and desorption isotherms of coal of different particle sizes ranging from around 150 μm to 16 mm. Langmuir model was used to analysis the experimental results of all gases. Coal particle size was found to have an apparent effect on the coal ash content and helium density results. Coal with larger particle size had higher ash content and higher helium density. The sorption isotherm was found to be highly sensitive with helium density of coal which was determined in the procedure of testing the void volume of sample cell. Hence, coal particle size had a significant influence on the coal sorption characteristics including sorption capacity and desorption hysteresis for CO 2 and CH 4 , especially calculated with dry basis of coal. In this study, the 150-212 μm (150 μm) coal samples achieved higher sorption capacity and followed by 2.36-3.35 mm (2.4 mm), 8-9.5 mm (8 mm) and 16-19 mm (16 mm) particle size samples. However, the differences between different coal particles were getting smaller when the sorption isotherms are calculated with dry ash free basis. Test with 150 μm coal samples were also found to have relatively smaller desorption hysteresis compared with the other larger particle size samples. The different results including adsorption/desorption isotherm, Langmuir parameters and coal hysteresis were all analysed with the CO 2 and CH 4 gases.Keywords: coal adsorption, desorption, coal particle size, isotherm, Langmuir volume Dokładne zbadanie izoterm sorpcji na węglu odgrywa kluczową rolę w takich dziedzinach jak odgazowanie pokładów węgla, zapobieganie wybuchom, sekwestracja geologiczna CO 2 , odzysk metanu ze złoża. Wpływ wielkości ziaren na pojemność sorpcyjną bitumicznego węgla z Illawara (Australia) względem CO 2 i CH 4 zbadano w temperaturze 35°C przy ciśnieniu do 4 MPa. Wykorzystano oryginalną aparaturę do badań grawimetrycznych do zmierzenia izoterm adsorpcji i desorpcji na węglu w którym rozmiar ziaren wahał się od 150 μm do 16 mm. Analizę wyników doświadczalnych dla wszystkich gazów przeprowadzono w oparciu o model Langmuira. Stwierdzono, że rozmiary ziaren węglowych w znacznym stopniu warunkują zawartość popiołu i gęstość helową. Węgiel grubiej uziarniony charakteryzował się wyższą zawartością popiołu i większą gęstością helową. Wykazano, że izoterma sorpcji wykazuje wysoką wrażliwość na zmiany gęstości helowej, co stwierdzono na podstawie badania martwej przestrzeni ampułki w której umieszczono próbkę. Wnioskować stąd można, że rozmiar ziaren węgla w dużym stopniu wpływa na charakterystyki sorpcyjne węgla, w tym także na chłonność sorpcyjną i hi...

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