Natural Gas: A Basic Handbook

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2 Natural Gas: A Basic Handbook Copyright 2007 by Gulf Publishing Company, Houston, Texas. All rights reserved. No part of this publication may be reproduced or transmitted in any form without the prior written permission of the publisher. HOUSTON, TX: Gulf Publishing Company 2 Greenway Plaza, Suite Houston, TX AUSTIN, TX: 427 Sterzing St., Suite 101 Austin, TX Library of Congress Cataloging-in-Publication Data Speight, J. G. Natural gas : a basic handbook / James G. Speight. p. cm. Includes bibliographical references and index. ISBN ( : alk. paper) 1. Natural gas. I. Title. TP350.S dc Printed in the United States of America Printed on acid-free paper. Text design and composition by TIPS Technical Publishing, Inc.

3 Contents List of Figures List of Tables Preface xiii ix xi Part I Origin and Properties 1 History and Uses Introduction History Composition and Properties Reservoirs Conventional Gas Associated Gas Non-Associated Gas Unconventional Gas Coal-Bed Methane (CBM) Shale Gas Gas Hydrates Reserves Uses Natural Gas Regulation Historical Aspects Federal Regulation of the Industry Natural Gas and the Environment References 33 v

4 vi Contents 2 Origin and Production Origin Exploration Geological Survey Seismic Survey Magnetometers Logging Reservoirs and Production Natural Gas Reservoirs Petroleum Reservoirs Production Well Completion The Wellhead Natural Gas Production Well Treatment References 59 3 Composition and Properties Composition Properties Density Heat of Combustion (Energy Content) Measurement Volatility, Flammability, and Explosive Properties Behavior Compression and Expansion Liquefied Natural Gas Environmental Properties References 82 Part II Gas Processing 4 Recovery, Storage, and Transportation Recovery 87

5 Contents vii 4.2 Storage Depleted Gas Reservoirs Aquifers Salt Caverns Transportation Pipelines Liquefied Natural Gas Liquefied Petroleum Gas Compressed Natural Gas Gas-to-Solid Gas-to-Power Gas-to-Liquids Gas-to-Commodity References History of Gas Processing Coal Gas Natural Gas References Process Classification Water Removal Liquids Removal Absorption Cryogenic Expander Process Membrane Processes Nitrogen Removal Acid Gas Removal Olamine Processes Carbonate and Water Washing Processes Metal Oxide Processes Catalytic Oxidation Processes Molecular Sieve Processes Fractionation Hydrogen Sulfide Conversion References 158

6 viii Contents 7 Processes Olamine Processes Girdler Process Flexsorb Process Physical Solvent Processes Rectisol Process Sulfinol Process Metal Oxide Processes Iron Sponge Process Other Processes Methanol-Based Processes Carbonate Washing and Water-Washing Processes Sulfur Recovery Processes Claus Process Redox Process Wet Oxidation Processes Tail-Gas Treating Processes Hydrogenation and Hydrolysis Processes Process Selection References Emissions Control and Environmental Aspects Greenhouse Gas Emissions Air Pollutants and Greenhouse Gases Emissions During Production and Delivery Gas Processing Combustion Industrial Emissions Smog and Acid Rain References 207 Conversion Factors 209 Glossary 211 Index 233

7 Preface Gas processing, although generally understandable using chemical and/or physical principles, is often confusing because of the frequent changes in terminology and the myriad mathematical equations and symbols used to describe a process. This renders gas processing a subject that is, at best, difficult for the layman to understand and appreciate. This book represents an attempt to alleviate the confusion that arises from mathematical relationships and the uncertainties in the terminology. Thus, the book falls into two convenient subdivisions: Part One deals with the origin and occurrence of natural gas and describes recovery, properties, and composition. Part Two deals with processing methods and explains the principles by which natural gas can be prepared for consumer use by removal of unwanted or noxious constituents. Although gas processing employs different process types, there is always an overlap between the various concepts. In an introductory text such as this, repetition is helpful to the reader, and this is achieved by subdividing the subject categories and using cross-referencing so that the reader will not miss any particular aspect of the processing operations. While every effort is made to ensure adequate cross-referencing, each chapter is a stand-alone segment of the book and has sufficient information to give the reader the necessary background. In summary, the book describes gas processing for the non-technical reader and serves as a handy, easy-to-use source to compare the scientific and technological aspects of gas-processing operations and the means by which the environment might be protected. In addition, the book is suitable for use in courtrooms and boardrooms as well as for junior scientists and first-year engineering students. James G. Speight, Ph.D., D.Sc. The University of Trinidad and Tobago xiii

8 CHAPTER 1 History and Uses 1.1 Introduction Natural gas (also called marsh gas and swamp gas in older texts and more recently landfill gas) is a gaseous fossil fuel found in oil fields, natural gas fields, and coal beds. As one of the cleanest, safest, and most useful of all energy sources, it is a vital component of the world s supply of energy. While it is commonly grouped in with other fossil fuels and sources of energy, there are many characteristics of natural gas that make it unique. Natural gas is the result of the decay of animal remains and plant remains (organic debris) that has occurred over millions of years. Over time, the mud and soil that covered the organic debris changed to rock and trapped the debris beneath the newly-formed rock sediments. Pressure and, to some extent, heat (as yet undefined) changed some of the organic material into coal, some into oil (petroleum), and some into natural gas. Whether or not the debris formed coal, petroleum, or gas depended upon the nature of the debris and the localized conditions under which the changes occurred. Natural gas is found in reservoirs beneath the surface of the earth (see Composition and Properties ) and is often associated with petroleum, although gas that is not associated with petroleum is also known. Production companies use sophisticated, expensive technology to find and drill into these reservoirs. Once brought from underground, the natural gas is refined to remove impurities such as water, other gases, sand, and other compounds. Some hydrocarbons, such as propane and butane, are removed and sold separately. Other 3

9 4 Chapter 1 History and Uses impurities are also removed, such as hydrogen sulfide (the refining of which can produce sulfur, which is then also sold separately). After refining (Chapter 7), the clean natural gas is transmitted through a network of pipelines that deliver natural gas to its point of use. Two new and possibly large sources of methane that may extend the availability of natural gas are methane hydrates (also called gas hydrates) and coal-bed methane (Berecz and Balla-Achs, 1983; Sloan, 1997; Gudmundsson et al., 1998; Max, 2000; Sloan, 2000). Their production technologies have only recently been developed, and these sources are now becoming economically competitive. Methane-rich gases are also produced by the anaerobic decay of nonfossil organic material and are referred to as biogas. Sources of biogas include swamps, which produce swamp gas; marshes, which produce marsh gas; landfills, which produce landfill gas, as well as sewage sludge and manure, by way of anaerobic digesters, in addition to enteric fermentation, particularly in cattle. Although natural gas is a vital component of the world s supply of energy and one of the most useful of all energy sources, it must be understood that the word gas has a variety of different uses, and meanings. Fuel for automobiles is also called gas (being a shortened version of gasoline), but that is a totally different fuel. The gas used in a barbecue grill is actually propane (C 3 H 8 ), which, while closely associated with and commonly found in natural gas and petroleum, is not really natural gas. Natural gas is the flammable gaseous mixture that occurs alone or with petroleum in reservoirs and is predominantly methane (CH 4 ) and some of the higher molecular weight paraffins (C n H 2n+2 ) generally containing up to five carbon atoms (Table 1 1). Briefly, methane is the simplest member of the hydrocarbon series and has one carbon atom and four hydrogen atoms (Figure 1 1). In its purest form, the natural gas delivered to the consumer is almost pure methane, and the remaining hydrocarbons and non-hydrocarbons have been removed though refining. The non-hydrocarbon constituents include, but are not limited to, carbon dioxide (CO 2 ), hydrogen sulfide (H 2 S), nitrogen (N 2 ), and helium (He). All of the hydrocarbon constituents of natural gas are combustible, but non-flammable non-hydrocarbon components (carbon dioxide,

10 1.1 Introduction 5 (a) (b) Figure 1 1 Simplified representation of methane as (a) a two-dimensional formula and (b) a three-dimensional formula. Table 1 1 Range of Composition of Natural Gas Gas Composition Range Methane CH % Ethane C 2 H 6 Propane C 3 H % Butane C 4 H 10 Pentane and higher hydrocarbons C 5 H % Carbon dioxide CO 2 0 8% Oxygen O % Nitrogen N 2 0 5% Hydrogen sulfide, carbonyl sulfide H 2 S, COS 0 5% Rare gases: Argon, Helium, Neon, Xenon A, He, Ne, Xe trace hydrogen sulfide, nitrogen, and helium) detract slightly from the heating value of natural gas. However, they are valuable, and in certain natural gases where their concentrations are relatively high, they may be extracted commercially.