Applied Geology by Unknown
Author:Unknown
Language: eng
Format: epub
ISBN: 9783030439538
Publisher: Springer International Publishing
In this chapter, a summary of India’s dependence on coal for the energy production, importance of CCUS worldwide and in India, and the status of ECBM from an Indian point of view have been presented.
10.2 Background Knowledge
10.2.1 Mechanism of CO2 Sequestration and ECBM Recovery
Primarily, CBM extraction from coalbeds can be achieved in two different ways; the dewatering process and the process involved with the injection of CO2 into the coalbeds. The dewatering process reduces the hydrostatic pressure of the coalbed, allowing the entrapped gases to move from the coal surface. In contrast, the second method is involved with the CO2 injection into coalbeds, thereby enhancing the desorption of methane gas from the porous coal surface.
In case of CBM and ECBM recovery, parameters such as temperature, pressure along with the rank of coal, moisture content, and maceral composition of coal become significant (Azmi et al. 2006; Kedzior 2009). Some coals may have a higher amount of sorption capacity despite being rich in inorganic content (mineral matters). This is due to the presence of certain maceral types and clay minerals that also have a larger surface area compared to other minerals that facilitate adsorption. The adsorption capacity of coal is predominantly dependent on the coal rank or its maturity, along with its type and maceral composition (Hildenbrand et al. 2006; Butland and Moore 2008). The process of CO2 adsorption and CH4 desorption are the foremost mechanism of CO2 sequestration and ECBM recovery (Wang et al. 2016b). During the process of interaction of CH4 and CO2 with the coal surface molecules, changes in adsorption energy, equilibrium distance, and molecular bond occur. Chemical reactions leading to the generation of new substance does not occur, which indicates the adsorption between these gases and coal surfaces to be physical (Baisheng et al. 2013). Primarily, coal is composed of carbon atoms that are of organic origin. Inside the coal structure, an equilibrium force is maintained between these carbon atoms. However, on the surface of the coal, without the attractive effect from one side, a force imbalance results. As a result of which the surficial coal atoms lack to maintain the balanced attractive force as compared to the internal carbon atoms. Hence, with strong free energy, these surficial coal atoms act as potential adsorption sites for gases like CO2 and CH4, depending upon their adsorption affinity. (Stevens et al. 1998; Wang et al. 2014, 2016a; Vishal et al. 2018). The injection of CO2 gas into the cleats of the coal results in a reduction in the CH4 partial pressure in the free gas phase without affecting the reservoir pressure and thereby promoting the desorption of CH4 from the coal matrix (Mazumder et al. 2006).
On these sites, adsorption affinity varies from gas to gas. In a comparison of CO2 and CH4, the earlier has an advantage of preferential adsorption on the coal surfaces. Being nonpolar, the weak van der Waals force or the London dispersion forces is the only intermolecular force that acts in the molecules of CH4 and CO2.
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