Table Of Content

EmilSupp How to Produce Methanol from Coal With 83 Figures Springer-Verlag Berlin Heidelberg GmbH DipJ.-Ing. Emil Supp Lurgi GmbH Gerviniusstral3e 17119 D-6000 FranHurt/Main II Germany ISBN 978-3-662-00897-3 ISBN 978-3-662-00895-9 (eBook) DOI 10.1007/978-3-662-00895-9 Library of Congress Cataloging·in·Publication Data Supp.Emil How to produce methanol from coal/Emil Supp. I. Methanol. 2. Synthesis gas. 3. Coal gasilication. I. Title. TP358.S83 1990 662'.669--dc20 90-38554 This work is subject to copyright. All rights are reserved, whetherthe whole or part of the material is concerned, specilically the rights of translation, reprinting, re-use of illustrations, recitation, broad casting, reproduction on microlilms or in other ways, and stor'dge in data banks. Duplication of this publication or parts thereof is only permitted under the provisions ofthe German Copyright Law of September9,1965, in its current version and a copyright fee must always be paid. Violations lall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1990 Urspriinglich erschienen bei Springer-Verlag Berlin Heidelberg New York 1990 Softcover reprint ofthe hardcover I st edition 1990 The use of registered names,trademarks,etc. in this publication does not imply,even in the absence ofa specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. 216113020-543210 -Printed on acid-free paper Preface Owing to efforts and legislative action - initiated above all by the government of the United States - to use cleaner fuels and thus make a contribution towards a better environment, public attention is back again on using methanol in carbu rettor and diesel engines. Most prominent among the raw materials from which methanol can be produced is coal, whose deposits and resources are many times larger than those of liquid and gaseous hydrocarbons. This book deals with the production of methanol from coal. It describes both the individual steps that are required for this process and the essential ancillary units and offsites associated with the process itself. . It is not meant to inform the reader about the intricate details of the processes, which can much better be taken from the specialized literature that deals exclusively and in detail with them or from the well-known standard engineering books. Rather, this book is to give the reader an impression how manifold a field this is, how many process variations and combinations the designer of such plants has to consider in order to arrive at an optimum design in each particular case. Apart from the production of chemical-grade methanol, the book deals briefly also with fuel methanol production, i.e. with the production of alcohol mixes. One of the many possible routes from coal to methanol is illustrated by a process flow diagram, and a material and energy balance is compiled for this typical example. No one can trace precisely all the influences which affect a work of this kind. My sincere thanks go to numerous colleagues who have unselfishly assisted me with a number of process steps and with the preparation of this book. I am also indebted to all whose publications I have used to gain information from, and whom I have hopefully all quoted without fail. This book would probably not have been conceived without the support of Dr. Jens Peter Schaefer, Chairman of the Board of Lurgi GmbH, Frankfurt, and it would not have come to an end without a few benevolent pushes from my wife. October 1989 Emil Supp Contents 1. How to Produce Gas from Coal? . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 What and Where Is Coal? ............................. 1 1.1.1 Reserves and Resources? ....................... 1 1.1.2 Properties of Different Types of Coal ............. 2 1.1.3 Exploration, Mining and Coal Preparation ......... 3 1.2 Coal Gasification .................................... 6 1.2.1 History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2.2 Methods of Coal Gasification ................... 7 1.2.3 Selection of Suitable Processes .................. 7 1.2.4 Fundamentals of Coal Gasification ............... 9 1.3 Technology of Gasification Processes .................... 15 1.3.1 Moving Bed Gasification ....................... 16 1.3.2 Fluidized Bed Gasification ...................... 27 1.3.3 Entrained Flow Gasification ..................... 32 1.3.4 Slurry Gasification ............................ 37 1.4 Interim Summary .................................... 41 2. How to Purify and to Condition Methanol Synthesis Gas? 44 2.1 Why and to What Extent Is Gas Purification Required? 44 2.2 Principles of Gas Purification .......................... 45 2.2.1 Adsorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.2 Absorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 2.2.3 Mechanical/Physical Gas Purification ............. 55 2.3 Different Types of Gas Purification Processes ............. 58 2.3.1 Physical Purification Processes .................. 58 2.3.2 Chemical Purification Processes . . . . . . . . . . . . . . . . . 71 2.3.3 Processes Using Mixed Solvents ................. 77 2.3.4 COS-Shift to Assist Gas Purification ............. 84 2.4 Conditioning of Methanol Synthesis Gas ................. 87 2.4.1 Conditioning to Improve the Stoichiometric Number. 87 2.4.2 Conditioning to Improve the Syngas Yield ......... 93 3. How to Synthezise Methanol and Alcohol Mixtures? . . . . . . . . . 102 3.1 Methanol-Its History, Its Properties and What Becomes of It 102 3.1.1 History of Methanol ........................... 102 3.1.2 The Use of Methanol .......................... 104 3.1.3 Physical Properties ............................ 104 3.1.4 Chemical Properties ........................... 106 3.1.5 Toxicity. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 107 3.2 Fundamentals of Methanol Synthesis .................... 107 3.2.1 Physical Basis ................................ 107 3.2.2 Methanol Yield from Syngas .................... 110 3.2.3 Catalysts for Methanol Synthesis ................. 112 3.2.4 Selection of Reaction Conditions ................. 115 3.3 Synthesis Loop and Its Various Appearances .............. 119 3.3.1 The Loop .................................... 119 3.3.2 Methanol Syntheses Using Fixed Bed Catalysts ..... 121 3.3.3 Other Methanol Syntheses ...................... 128 3.4 Production of Mixed Alcohols ......................... 130 3.4.1 Why Mixed Alcohols and Which Ones? ........... 130 3.4.2 Different Types of Mixed Alcohols Processes ...... 130 4. How to Obtain Pure Methanol? . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 4.1 Why Refining Methanol? .............................. 133 4.2 Basic Methanol Distillation Systems .... . . . . . . . . . . . . . . . . 135 4.3 Production of Grade AA Methanol ...................... 138 4.4 Purification of Mixed Alcohols ......................... 144 5. How to Process By-Products and Wastes? . . . . . . . . . . . . . . . . . . 146 5.1 Water and Aqueous Condensates ....................... 146 5.1.1 Treatment of Aqueous Condensates .............. 147 5.1.2 Removal and Recovery of Sulfur and Ammonia .... 152 5.1.3 Biological Treatment .......................... 155 5.2 Hydrocarbon Condensates ............................. 157 5.3 Waste Gases ........................................ 158 5.3.1 Recovery of Elemental Sulfur ................... 159 5.3.2 Design Variations of the CLAUS Process .......... 161 5.3.3 Production of Sulfuric Acid ..................... 162 5.3.4 Tailgas Clean-up .............................. 164 6. How to Supply Utilities to a Coal-to-Methanol Plant? . . . . . . . . 170 6.1 Air Separation Units ................................. 170 6.2 Steam and Electric Power ............................. 173 6.3 Water and Boiler Feed Water .......................... 176 6.4 Cooling Systems .................................... 180 6.5 Inert Gas ........................................... 181 6.6 Instrument and Operating Air .......................... 182 VII 6.7 Other Off-Sites ...................................... 182 7. What Could a Methanol Plant Look Like? .................. 183 7.1 Methanol from Lignite - Application of the LURGI Pressure Gasification Process .................................. 183 7.2 Description of the Process Concept ..................... 185 8. Future Outlook 197 VIII 1. How to Produce Gas From Coal 1.1 What and Where Is Coal? Coal owes its origin almost exclusively to plants that grew on our earth many millions of years ago from the Carboniferous to the Tertiary Period. Vast expanses of forest land slowly subsided so that the forests were covered with water and largely shut off from the oxygen of the air. Various microbiological processes occurring at normal pressures and temperatures turned the dead organic material at first into peat, and later on, as it went further down, into brown coal. After this first coalification stage termed the biochemical phase had been completed, the morphologically and chemically inhomogeneous brown coals were converted to bituminous coals in a second, geochemical stage. This second stage, which took place under the long-term effect of an elevated temperature reaching about 150°C at a depth around 5000 m, is also called metamorphosis. The end product of this development is believed to be graphite. The great variety of decomposition processes taking place during the coal ification phase produced very different types of coal with different chemical, physical and technological properties even if their degree of coalification is the same. Each type of coal contains not only major quantities of intergrown min erals which are mostly removed during coal preparation - e.g. clay, dolomite, pyrite and quartz, to name only a few of them - but also numerous trace ele ments which range, in alphabetical order, from gold (Au) to zirconium (Zr) and normally account for 0.001 to about 3 wt. % of the coal ashes [1.1]. Not least of all these trace elements - as it will be demonstrated later - are responsible for the difficulties in producing pure synthesis gases. 1.1.1 Reserves and Resources Bituminous coals and brown coals are abundant almost everywhere on earth. Total reserves are estimated at some 13OOO0t of bituminous coals and 26000t of brown coals, of which more than 90 % are anticipated to lie in the northern hemisphere. In spite of the sizable new oil and gas deposits found in recent years, the total coal reserves are still four times as large as the estimated reserves of liquid and gaseous energy sources. They alone would be sufficient to meet the energy demand of a steadily growing world population until long after the tum of the millenium, even though this demand grows beyond proportion. However, only about 400 Ot of brown coals and some 12oo0t of bituminous coals are proven. America USSR 4284 4677 Australia Fig. I.!. Distribution of the world's coal resources 784 and reserves (figures in Gt) The current state of mining technology probably does not allow more than 7 to 10 % of the proven and anticipated 15 600Gt to be produced under econom ically justifiable conditions. The geographic distribution of the anticipated and proven coal reserves is shown in Fig. 1.1. Coal deposits throughout the world, their thicknesses and mining depths, as well as their current and future mining potentials are dealt with in many detailed reports [1.2,3]. 1.1.2 Properties of Different Types of Coal Coals are products of nature with very different compositions and properties. Most countries with rich coal deposits have developed their own classification systems for bituminous coals, the better known ones among them being the 1956 ECE classification according to DIN 23003 and the classification described in ASTM 0 388-66 used in the USA. The latter classifies bituminous coals into four coalification ranges tenned Bituminous I, Bituminous II, Sub-bituminous II and Lignite IV. Each of these ranges is then further broken down into groups according to volatile contents or calorific value. A uniform classification exists for brown coals. It is described in ISO 2950-1974-(E) and distinguishes between six classes defined according to the water content of the raw coals, which are in turn subdivided into five groups on the basis of tar contents. Coals can be quickly characterized with respect to their technological properties by looking at their moisture, ash and volatile contents. The latter also indicates the degree of coalification; it defines the weight of the gas, tar and water that is lost if the coal is heated to 900 C. 0 2 The main chemical components of all coals are carbon, hydrogen and oxy gen, but they also contain nitrogen and sulfur. As the degree of coalification increases, the carbon content will increase and the hydrogen and oxygen con tents decrease. Brown coals are characterized by particularly high contents of oxygen - as much as 30 % of the moisture- and ash-free carbon substance (maf) in the case of soft brown coals -, whereas anthracite contains 92 wt. % or more of carbon. The C/H ratio also increases from 1 to more than 2 as the degree of coalification increases. In addition to the volatile, ash and moisture contents, and to the ultimate analysis, an assessment of the gasification behaviour of the coal and its effect on the product gas properties also requires a knowledge of several other factors such as the swelling index, which describes the extent to which the coal softens as it is heated and defines its caking properties the composition of the ash and its softening and melting behaviour the calorific value. Compositions of some of the world's commonest coals have been compiled in Table 1.1. 1.1.3 Exploration, Mining and Coal Preparation A considerable effort is required to locate and mine the coals and to make them "digestible", so to speak, for the different gasification processes. Without going into greater detail about the numerous operations involved - they are described in the relevant literature [1.1] - the list below will give the reader an idea about the number of individual steps to be taken before the coal eventually reaches the gasifier. Essentially, these steps include establishing whether a coal seam is worth mining in view of its structure and thickness, and deciding on the most suitable mining method (shaft or strip mining) preparing the deposits for mining; this may take decades and include sink ing shafts, developing working levels, and then subdividing the developed deposit into workable sections by opening suitable galleries mining the coal from open pits (lignite, young bituminous coal) or slopes (steeply inclined bituminous coal seams), or by room-and-pillar methods (flat seams), including the required lifting and hauling operations ventilating the working areas to ensure a largely dustfree supply of well tempered breathing air for the miners and to extract harmful gases, above all the mine gas (methane) that, when left to accumulate, may lead to the much-dreaded firedamp explosions preparing the lifted coal for subsequent upgrading. As a first step, this nor mally involves pre screening the coal to obtain a certain desirable minimum lump size (usually about 150 mm) for the crusher, removing the unwanted material, crushing the coarse lumps, and producing a steady flow of mate- 3