The circulating load : practical mineral processing plant design by an old-time ore dresser PDF
Preview The circulating load : practical mineral processing plant design by an old-time ore dresser
CirLoadv4.qxd 4/9/02 10:40 PM Page 1 The Circulating Load Practical Mineral Processing Plant Design by an Old-Time Ore Dresser Robert S. Shoemaker Published by the Society for Mining, Metallurgy, and Exploration, Inc. © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. Society for Mining, Metallurgy, and Exploration, Inc. (SME) 8307 Shaffer Parkway Littleton, Colorado, USA 80127 (303) 948-4200 / (800) 763-3132 www.smenet.org SME advances the worldwide mining and minerals community through information exchange and professional development. Copyright© 2002 Society for Mining, Metallurgy, and Exploration, Inc. Electronic edition published 2009. All Rights Reserved. Printed in the United States of America No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Disclaimer Any statement or views presented here are those of the author and are not necessarily those of the Society for Mining, Metallurgy, and Exploration, Inc. The mention of trade names for commercial products does not imply the approval or endorsement of SME. ISBN 978-087335-308-3 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 3 C ONTENTS Preface v 1 Primary Crushers 1 2 How to Clean Up a Dirty Dump Pocket 3 3 Sampling a Ball Mill 5 4 Vibrating Feeders 7 5 Notes on Conveyors 9 6 Storage Bins 16 7 The Design and Operation of Floors 20 (From the Mill Operator’s Standpoint) 8 Determining Velocities in Pipelines the 26 Easy Way 9 Notes on Fines 27 10 Overengineering 32 11 Cage Mills, Impactors, and Hammer 35 Mills 12 Environment Controls for Grinding Mills 38 13 That Odious Pump 40 14 Never Hire a Plumber Who Claims to 43 Be a Pipefitter 15 Pilot Plants 45 16 Precious Metals Column and Heap 49 Leaching Pilot Plants 17 Sumps, Pumps, Etc. 51 18 Foolproof Plug Valves 55 19 Design for Maintenance 57 20 Mexican Feeders 61 21 Supervising the Engineer–Constructor 63 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 4 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 5 P REFACE In 1964 when I became chief metallurgist of Bechtel’s Mining and Metals Division in San Francisco, I was fortunate to be able to see not only the minerals processing plants that Bechtel was designing and building but many others designed and built by other engineering firms. When I was in an area that had such plants other than the one I was visiting, I found that the managers and mill superintendents of these plants were most hospitable in showing me their operations and freely answered any questions I asked. During those visits I observed many clever ideas in plant design developed by the plant operators and other engineering firms and also many mistakes that resulted in higher capital and operating costs. The mistakes, by the way, were not limited to other engineering firms as we were not by any means omniscient and bloodied our noses as often as did others. As a result of these observations and in order to improve our engineering capabilities, I started writing down what I (and some of my metallurgists) had seen and distributing the ideas not only to my people but also to the chief engineers in our other disciplines. These publications were called The Circulating Load and, very often, clients who had seen them would ask for back copies and to be put on the mailing list. These people would often copy them and send to their friends in the industry. v © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 6 THE CIRCULATING LOAD On the cover sheet of each issue were the words “Published frequently in the interest of fewer spills in the mill.” In this rewrite I have recaptured the best incidents from the past and added some observations and recollections from the last twenty years as a consultant. It is hoped that these practical methods will be of help to all the mill men who have made the mineral processing industry what it is today. vi © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 7 THE CIRCULATING LOAD 1 PRIMARY CRUSHERS We got one of our best ideas concerning primary crushers from a 54- × 74-inch gyratory crusher installed at the Ray Mines division of Kennecott Copper. This crusher had a rubber belt feeder under its surge pocket— one that we believe to be the first ever installed. It was 6 feet wide and about 80 feet long and was also used as a picking belt to remove timbers that came from the old underground mine. The total height of the installation from the belt feeder floor to the top of the dump pocket was 63 feet. The belt, which also handled old drill steel and miscellaneous scrap iron, had a life of about 14 months and handled 10 million tons in that time. When we were designing the Similkameen copper plant in British Columbia for Newmont, Frank McQuiston and I spent many hours discussing the possibility of using an 8-foot- wide belt under the 54- × 74-inch gyratory crusher we planned to install there. There were several advantages that finally tipped the scales to the belt feeder rather than an apron feeder. The belt feeder was 40 feet long so that it permitted the downward-sloping takeaway conveyor to be straight instead of having a reverse vertical curve. The belt feeder required less height than an apron feeder, did not require the height for a takeaway conveyor under an apron feeder, and lastly, because of its width, permitted more live storage and less 1 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 8 THE CIRCULATING LOAD height in the surge pocket under the crusher. The capital cost savings was very substantial, and the total height from the feeder floor to the edge of the dump pocket was only 59 feet. When we last heard, the belt feeder had handled 120 million tons of the hard, jagged Similkameen ore without an hour of unscheduled downtime. The few gouges it had sustained were repaired with liquid rubber during regularly scheduled downtime. Newmont had purchased a spare belt, and Rolly Nice, the plant manager, told us that if the belt should ever need replacing they could probably never unroll the spare belt as it was so old. A few months after this crusher was completed, Gibraltar also installed an 8-foot belt feeder under their new crusher, and we used a belt feeder under the third gyratory at Palabora. Many other belt feeders have been used by others since then. Unfortunately, a few apron feeders are still being installed under primary crushers. This (the Similkameen) was the first gyratory crusher we ever installed without using an overhead crane. Newmont had purchased an 80-ton mobile crane to lift the bodies on their 100-ton trucks, and this crane was capable of handling the 45-ton crusher mantle. After a year’s operation we talked to Similkameen’s manager and mill superintendent and asked their opinions on the crusher installation. They told us that when they arrived on the site before operations had begun they had been very apprehensive about maintaining the crusher, and visitors from other British 2 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. CirLoadv4.qxd 4/9/02 10:40 PM Page 9 THE CIRCULATING LOAD Columbia copper plants had predicted doom and destruction when they had seen this “cheap” installation. Actual operation had, however, proved all their prognostications wrong. The first relining job using the mobile crane had taken 48 hours—no record of course, but very creditable, considering it was the first crusher relining job for the maintenance crew. They were certain the second relining could be done much faster. (A similar first relining job we know of using an overhead traveling crane at another plant required 87 hours.) To say the least, the manager and superintendent were very pleased. 2 HOW TO CLEAN UP A DIRTY DUMP POCKET Dust collection or suppression at primary crusher dump pockets has always been such a problem that many people have simply ignored it with the idea that dump pockets have always been dusty and always will be. (At the time of this re-editing, in 2002, the rules have been radically changed and such dusty conditions are rarely tolerated. However, the ideas presented here are the best we have ever seen and could be of use at a number of mines I have seen recently.) The problem here is the enormous, but momentary, need for dust collection volume during and shortly after a 3 © 2002 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009.
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