Abstract
Transient sorption and desorption of helium and carbon dioxide in Upper Freeport coal powder and lumps were analyzed. Differences in texture and porosity between the powder and lumps may affect the transport and interaction of the penetrant and coal. In this work, we address macroscopic and mesoscopic structural differences between powdered and non-powdered coals that influence the rates of the gas transport kinetics and changes in coal texture (swelling, shrinkage, and changes in the pore structure and interconnectivity) and the reciprocal free-phase pressure decay (relaxation). Comparison of the multi-exponential relaxation time constants as a function of pressure, for CO2 and inert gas (helium), allows us to postulate several mechanisms responsible for observed pressure decay patterns.
Highlights
Coal is an abundant sedimentary rock commonly associated with energy, primarily used as a solid fuel to produce electricity and heat
We address macroscopic and mesoscopic structural differences between powdered and non-powdered coals that influence the rates of the gas transport kinetics and changes in coal texture and the reciprocal free-phase pressure decay
The average pore size in Upper Freeport coal is (0.63 ± 0.07) nm (Hayashi et al 2001), which is slightly larger than the typical size (\0.58 nm) corresponding to onset of activated diffusion in coal (Walker 1981)
Summary
Coal is an abundant sedimentary rock commonly associated with energy, primarily used as a solid fuel to produce electricity and heat. Significant research efforts were directed toward development of coal liquefaction, especially, in Germany, South Africa, and China (Wasaka et al 2002). The state-of-the-art in coal-based energy conversion technologies is not adequate in the current regulatory environment concerned with potential environmental crisis. If the known methods were adopted industrywide to reduce oil consumption, carbon dioxide emission could increase on a global scale (Romanov et al 2009). Deep unmineable coal seams may find use as the reservoirs for sequestration of ‘green house’ gases. Interaction of CO2 with coal, which is occasionally referred to as heterogeneous geo-polymer in nature (Marzec 2002) is governed by the aggregate properties of the two
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