CHAIRMAN'S ADDRESS - Coke Oven Managers Association

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A REVIEW OF C.O.M.A. ACTIVITIES, 1939-1945 - CLARKE 199.also, in another important aspect, differed from full-scale operation, wheremovement of the walls of one oven is affected by any forces beinggenerated in an adjacent chamber. Incorporating a small additional safetymeasure, Dr. Koppers therefore concluded that coals generating pressuresof more than 1.1 lb./sq.in. (at the bulk density obtaining) should not becarbonised in 4.5 metre coke ovens.Reference was then made by the author to the studies of Koppers andJenkner of the pressures developed by coals during carbonisation. For thispurpose these workers designed a small coking chamber heated from bothsides and having walls which could move independently of each other,being carried separately on frames supported by rollers (Publication of theKoppers Company, Essen, 1937). On the outside of one wall a hydraulicmeasuring device was fitted, and a record could be made either of thepressure generated or wall movement during carbonisation. With this unit itwas also possible to demonstrate the increase in coking pressure with anincrease in both bulk density and rate of heating, and also illustrate thepressure developed as the plastic layers coalesce in the final stages ofcarbonisation. Coals tested in the oven gave pressures generally between0.1 kg./sq.cm. (1.4 lb./sq.in.) and 1.0 kg./sq.cm. (14.0 lb./sq.in.), but somepoorly-coking coals exhibited much lower pressures.The movable-wall oven was constructed for research purposes, andowing to the cost of operation was not considered suitable for routine use,for which purpose simpler equipment was required. Dr. Foxwell thendevoted attention to some of the laboratory-scale tests which had beendevised to distinguish between coals safe to carbonise and those having apotential for causing damage to oven walls. He noted that no small-scaleequipment had then been devised to register the maximum pressureoccurring when the plastic layers meet, and that the best guide which couldbe expected from laboratory testing was to carbonise the coal under strictlydefined conditions, giving an empirical indication which would then enablethe safety or otherwise of a coal to be deduced.In the Koppers laboratory-scale apparatus (Koppers Mitteilung, 1930,Volume 12, p.1) an 80 gram sample of the coal to be tested (air-dried, andcrushed to below 1 mm) is contained in an asbestos-lined heat-resistingsteel crucible, 60 mm internal diameter, heated from below with astandardised gas flame. A standard bulk density of 740/760 kg./cu.m. (dry)
200. THE COKE OVEN MANAGERS’ YEAR-BOOKis employed for each test. A steel piston is placed on top of the coal, whichis subjected to a pressure of 1 kg./sq.cm. by a 10 kg. weight and leversystem. Any movement of the piston by the expansive force within the coalduring carbonisation is measured on a recording chart, which also denotesthe contraction occurring in the course of the 4-hour test period. From theoutline of the chart, Koppers gave a guide, based on experience, concerningthe swelling characteristics of the coal and its potential for causing damageto oven walls.The Nedelmann apparatus for the determination of coking pressure(Brennstoff-Chemie, 1931, Volume 12, p.42), although derived from theKoppers laboratory-scale equipment, differs from it in using 120 grams ofcoal contained in a steel crucible of 80 mm internal diameter, andmeasuring on a gauge the pressure set up by the coal on carbonisation. Thecoal sample at standard bulk density is loaded into the crucible, which has alining of asbestos paper, and heat is applied unidirectionally by a Mekerburner under closely-defined conditions over a period of three hours, to afinishing temperature of 900 0 C at the bottom and 700 0 C at the top of thecharge. The pressure developed within the coal is transmitted through apiston covering the whole area of the test crucible, to a lever arm pivotedbetween the plunger and a pressure recorder, reading directly in kg./sq.cm.Based on the maximum pressure recorded in the Nedelmann apparatus,tentative safety limits were proposed; beyond these levels the coal wasconsidered dangerous. Nedelmann also proposed that coals showing lessthan 3% of shrinkage should be regarded as dangerous, or likely to giveproblems in pushing the coke.The importance of bulk density of the charge in relation to developmentof coking pressure was recognised at an early stage, and Koppers designeda large-scale swelling apparatus (H. Koppers, publication of KoppersGmbH, Essen, 1937) in which the behaviour of coals at various densitiescould be assessed. This equipment was designed to record only pressuresgenerated in the coal charge which are in excess of the safety limit of0.08 kg./sq.cm. for coke oven walls, set previously by Koppers andJenkner. The apparatus differed from the earlier laboratory-scale equipmentmainly in respect of size of the components. A crucible of 200 mmdiameter with perforated base was used, and coal of the required bulkdensity charged to a height of 200 mm (i.e. half-oven width,approximately). On top of the coal charge was placed a plunger connected
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CHAIRMAN'S ADDRESS - Coke Oven Managers Association

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