Determination of gas content of coal

Abstract

Introduction Coalbed gas content measurements are normally carried to estimate methane emission rates into mine workings and for coalbed methane gas recovery applications. Techniques of gas content determination are broadly divided into two categories, viz. direct methods which actually measure the volume of gasreleased from a coal sample sealed into a desorption canister and indirect methods based onempirical correlations, or laboratory derived sorption isotherm gas storage capacity data. Direct gas content determination techniques are sub-categorised into quick-crushing and extendeddesorption methods. In quick-crushingmethods the coal sample is crushed soon after collection to release all the desorbablegas. Extended desorptiontechniques are most commonly used for recovery applications and resource assessment whereinformation on desorption rates is usefulfor fundamental coalbedmethane research, andfor reservoir modelling. CBM in India
India, having the fourth largest proven coal reserves in the world, holds significant prospects for exploration and exploitation of CBM.India has one of the most investor friendly CBM policies in the world. In our country a totally transparent and fair bid evaluation criteriahas been evolved and is in place. There is, therefore, a huge opportunity for potential CBM investors in India.Commercial production of CBM has already commenced in Raniganj (South) CBM block in West Bengal. Efforts are also being made in Shoagpur blocks in Madhya Pradesh and Jharia block in Jharkhand for commencement of commercial production at the earliest.It is expected that CBM production in India will go up to 7.4 MMSCMD by the year 2013 - 14. Experimental Investigation The freshly blasted coal samples were immediately sealed in a container then brought to the laboratory for experimentation. The samples were crushed and put into the desorption canister. The sample was heated at a very low heating rate to allow desorption of gas. The pressure developed inside the canister was noted down and then the valve of the canister was opened and gas was collected by downward displacement of water. The sample was allowed to desorb until a low desorption rate cut-off point was reached.Results As a part of the project work, extended desorption method was followed to find out the gas content of block samples brought from 10 different mines of MCL. The results are shown below in table 1.
Table 1: Gas Content of Coal Samples

Sample no. Colliery/Mine Gas content(in m3/tonne)
1 Lakhanpur 0.050
2 Basundhara 0.248
3 Kulda 0.206
4 Nadira colliery 0.325
5 Lingaraj 0.130
6 Bhubaneshwari 0.104
7 Dera colliery 0.352
8 Jagannath 0.204
9 Ananta 0.101
10 Bharatpur 0.152

Discussions and Conclusion
It could be observed from the experimental investigation that the gas content of coal samples varied from 0.05 m3/tonne to 0.352 m3/tonne. Coal samples collected from underground mines had greater amount of residual gas content as compared to the rest this corroborates the fact that gas content of coal increases with depth. If the gas content is found to be very high then vertical bore holes may be put up to extract methane for a variety of commercial applications, starting from domestic heating to generation of electricity
References
1. Diamond W.P. and Schatzel S.J., (1998), “Measuring the Gas Content of Coal: A Review”, International Journal of Coal Geology, Vol.35 (1), pp.311-331
2. http://www.dghindia.org/CBMRounds.aspx