NEW ZEALAND COAL.

Auckland Star, Volume LX, Issue 52, 2 March 1929, Page 21

NEW ZEALAND COAL.

CARBONISATION METHODS. NEW TEMPER ATTIRES. INVESTIGATION INTO BEHAVIOUR. Conclusions arrived at as the result ot investigations conducted on behalf of the New Zealand Institute and the Department of Scientific and Industrial Research, into the behaviour of New Zealand coals when subjected to lowtam.asj*fture carbon ieation, are summarised in a statement issued under the suspires of the Fuel Research Committee. "In 1927," runs the statement, "the Fuel Research Board of Great Britain issued a paper setting out staaidard methods for coal analysis. By a universal acceptance of these methods it was hoped to avoid overlapping and enable co-ordination of results from different localities. Since no direct information regarding gaseous and liquid products of carbonisation was obtainable from laboratory methods of proximate and ultimate analyses, the Fuel Research Board adopted the "Gray-King assay" as a standard laboratory method of estimating the value of coals by their earbonraation at low temperatures. The Gray-King assay re-sults <shed light on the general properties of a coal, and afford data for predicting its behaviour on carbonisation on a large seale at the same temperature. The yields of coke, ga>s, tar, lkjuor, and ammonia are readily and accurately measured, and largescale. yields may be predicted from them M follows: - - "'(I) Coke: The yield and the volatile matter remaining are approximately the same as in large-scale pra<*tTce. The appearance of the coke cylinder formed is similar to that obtainable by carbonisation on a large scale provided that powdered coal is used and that the working temperature is the same. "(2) Gae: The yield from t>n« assay is usually slightly greater than that obtained a. large scale, owing to the necessity of limiting the time of carbonisation in industrial working. "(3) Tar: The large-scale yield is in most oases approximately 60 per cent of tihe assay yield. There is, however, no reason to suppose that this may not be improved by future developments so that the ultimate large-scale yield may approach much more nearly the assumed 100 per cent of the assay method. "(4) The yields of ammonia are usually comparable. "The ratio of the results of horizontal letorts to Gray-King assay result» is as follows: Coke, 1.02; oils, 0.00; ammonia, 1.00; gas, 0.96; liquor, 1.18. "In the present investigation the Gray-King assay has been used to determine the behaviour of New Zealand eoals when subjected to low-temperature carbonisation. "The bituminous coals of New Zealand swell excessively when carbonised at 600 deg. C. Taey contain more binding material than is required to form a coherent coke. The brown coals and lignites are devoid of coking powers, and on carbonisation yield non-coherent residues. Where a solid residual fuel is the object of carbonisation two method* have proved successful in overcoming tihe difficulties presented by the uneven distribution of binding material: (1) Bituminous coal when subjected to 0, preliminary process of partial oxidation loses its excess swelling properties and yields on carbonisation a non-swol-len coherent cokes; (2) by blending bituminous and brown coals iu suitable proportions the excess binding material of the former is utilised in binding the inert brown coal substance into a strong coherent coke."

The summarised conclusions are au follow; — Low-temperature carbonisation of a number of New Zealand brown coal's gives an average yield per ton jl 10.59 owt carbonised residue, 27.58 gallons of oils, 51 A3 gallons of liquor, 3.301b ammonium sulphate, and 3841 cubic feet •f gas. The average 'bituminous coal yield !er ton is 14."23cwt carbonised residue, 7.42 gallons of oils, 9.35 gallons of liquor, 1.241b ammonium sulphate, and 3530 cubic feet of gas. Low -temperature carbonisation of unblended New Zealand coals leaves either • non-coherent, non-coking residue, or a much-swollen mass of friable coke, according as the coal is brown or bituminous. Semi-cokes of a very satisfactory texture and hardness are obtained by carbonising suitable blends of brown and 'bituminous coals at 600 deg. C. The work was carried out at CanterXnyy College under the direction of Dr. XL O. Dennam.