CHAIRMAN'S ADDRESS - Coke Oven Managers Association

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A REVIEW OF C.O.M.A. ACTIVITIES, 1939-1945 - CLARKE 209.was necessary to enable British coals to be assessed with some measure ofconfidence in respect of their coking pressure characteristics.In May 1940 Dr. R.A. Mott's paper “Coals Dangerous to Coke Ovens”,based on the work of the Midland Coke Research Committee waspresented for discussion before a joint meeting of the Northern Section ofthe Association and the Institute of Fuel at Newcastle-upon-Tyne. Acomprehensive report of the Committee’s researches on this subject, underthe title “The Assessment of Coals Liable to Damage Oven Walls” hadbeen published a few months earlier by Dr. R.A. Mott andMr. C.E. Spooner in Fuel, Volume 18, 329-344 & 371-379, 1939. TheCommittee’s investigations had started at the request of a coke ovenconstruction company, which was experiencing some difficulty inevaluating the results of tests on a Durham coal, using the large-scaleversion of Koppers swelling apparatus. Through the co-operation of theKoppers Coke Oven Company, Sheffield, the Committee was providedwith a laboratory-scale Koppers apparatus and also the loan of a large-scaleswelling test apparatus, located at the Orgreave coking plant, with facilitiesprovided by the United Steel Companies. (It may be of interest to recallthat some fifty years ago, in the days of shoe-string budgets for U.K. coaland coke research, donations “in kind” were appreciated as much asfinancial contributions by local coke-makers to the work of the Committee.See R.A. Mott, 1963 C.O.M.A. Year-Book, p.200.)The difficulties of interpretation of the results obtained with the largescaleswelling test apparatus on the Durham coal were traced to blockageof the gas outlets with plastic coal, which caused abnormal internalpressure and resultant swelling. When the coal charge in the crucible wassurrounded by thick asbestos paper the blockages did not occur, and theresults then obtained showed that although the coal developed excessiveplasticity and swelling on carbonisation, a dangerous pressure was notproduced, and it was unnecessary, therefore, to reduce the bulk density andrate of carbonisation in the full-scale plant. It appeared from theCommittee’s enquiries that several Durham coals were being labelled asunsuitable for carbonisation, and foreign buyers of Durham coking and gascoals regarded some of these as dangerous, based on results obtained insmall-scale swelling tests. Similar indications had been shown when coalsfrom Somersetshire, Kent and Monmouthshire were examined. In view ofthe experiences with the Koppers large-scale swelling test. Dr. Mottconsidered that many of the “dangerous” labels acquired from small-scale
210. THE COKE OVEN MANAGERS’ YEAR-BOOKtest results were probably erroneous, and accordingly a critical examinationof the apparatus and technique was undertaken. For the preliminaryinvestigations into the small-scale Koppers test, the Durham coal whichhad given spurious results in the large-scale Koppers test were used, inconjunction with a South Wales coal which was known to be dangerous.Both coals, when tested in the small-scale Koppers apparatus, using thestandard method, were classified in the “dangerous” category, as theyswelled above the datum line and gave only a small final contraction. Aninvestigation into the heat distribution in the coal charge, when using thestandard method for the small-scale Koppers test, showed that a maximumtemperature of only 600 0 C was reached, and as the temperature at the topof the crucible did not exceed 400 0 C after four hours heating, the coal wasnot passing completely through the plastic range. It was considereddesirable for the charge to reach a temperature of 900 o C in order that thefull effect of the contraction occurring in the later stages of carbonisationcould be revealed. Changes were, therefore, made to the lower portion ofthe furnace by replacing the firebrick construction with high temperatureinsulating brick (Gibbons H.T.I.). The combustion space and number ofwaste gas offtakes were increased, allowing higher temperatures to bereached with the 1 / 2 ” Teclu gas burner. In a further modification, the upperportion of the firebrick furnace surrounding the test crucible was alsoreplaced by insulating brick, enabling a maximum temperature ofapproximately 940 0 C to be reached and the top of the charge to rise to750 0 C. These changes reduced the time taken for a test from four to twohours. The next stage was to devise procedures which would result in theDurham coal producing a “safe” curve, but permit the South Wales coal toretain its “dangerous” label. This objective was achieved by the simpleprocedure of removing the dust less than 20 mesh I.M.M. (1/40”) from thesample prepared for testing, thus ensuring that abnormal pressures were notgenerated owing to fine coal blocking the interstices and restricting gasescape.Enquiries made by the Committee to coke oven construction firmsresulted in the supply of further U.K. coals which were being classed asdangerous, together with American and German coals, some of which wereknown to have damaged oven walls. Forty coals were assembled, and inaddition to the usual proximate analysis and calorific value were alsoexamined by the Sheffield laboratory coking test (slow rate of heating) andthe B.S. crucible swelling test (fast rate of heating). The majority of thesamples were subjected to examination by the small-scale Koppers test in
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CHAIRMAN'S ADDRESS - Coke Oven Managers Association

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