Page 233 - Advanced Mine Ventilation

13
Origin of Gases in Coal Mines

Chapter Outline

13.1 Introduction 213
13.2 Properties of Gases in the Mine Atmosphere 214
13.2.1 Methane 214
13.2.2 Ethane 214
13.2.3 Propane and Butane 214
13.2.4 Carbon Monoxide 214
13.2.5 Carbon Dioxide (Oxygen Depletion) 217
13.2.6 Hydrogen 217
13.2.7 Hydrogen Sulphide 217
13.2.8 Oxides of Nitrogen 217
13.2.9 Sulfur Dioxide 218
13.2.10 Variations in TLV 218
13.3 Characteristics of Coal 218
13.3.1 Proximate Analysis 219
13.3.2 Ultimate Analysis 219
13.3.3 Rank of Coal Versus Vitrinite Reflectance, R o 219
13.4 Characterization of Methane from Coal 219
13.4.1 Hydrocarbon Index 219
13.4.2 CO 2 Percent 221
13.4.3 Gas Wetness Index 222
13.4.4 The d 13 C and dD Isotropic Ratios 222
13.4.5 Differentiating Between Thermogenic Coalbed Methane and Natural Gas 222
13.5 Coalbed MethanedAn Energy Source 223
13.5.1 Global Reserve of Coalbed Methane 224
13.5.2 The United States Reserves of Coalbed Methane 224
References 226

13.1 Introduction

Coal seams were formed over millions of years by the biochemical decay and meta-
morphic transformation of the original plant material. This process, known as coalifi-
cation, produces large quantities of by-product gases increasing with the rank of coal
3
and is the highest for anthracite at about 27,000 ft /t [1] for methane alone. Most of
these gases escape to the atmosphere during the coalification process but a small frac-
tion is retained in coal. The amount of gas retained in coal depends on a number of

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