SLACK COAL.

Hawera Star, Volume XLV, 26 October 1925, Page 4

SLACK COAL.

CONVERTING WASTE INTO PROFIT. POSSIBILITIES OF BRIQUETTS. If the vast quantities of slack coal of th© Dominion cannot ultimately be turned to profitable use it will not be because the wide field of experiment has not been fully availed of. On the contrary, tests that have been going on for some time at the Dominion Laboratory at the expense of the Mines Department are reported to he extremely encouraging, and the experiments are being conducted on a large scale (says the Dominion). The principal methods suggested were (1) dust firing, (2) low temperature carbonisation, and (3) briquetting. As the latter appeared to be the most promising of th© three methods, it was decided to investigate the conditions necessary for its successful application to New Zealand waste coals. The Mines Department secured an experimental hydraulic press giving pressures up to 30 tons to the square inch. One of the first series of tests was on Waikato brown or sub-bituminous coal, about 40 per cent of which, as mined, was rejected as slack and was practically unsaleable. This was found to be friable and of a soft nature without hinder. On th© other hand no difficulty was, experienced in briquetting lignite from Alexandra, Otago. However, in all qases the experiments made with mixtures of other coals showed definite results.

One conclusion which the experimenters have come to is that it did not seem possible to briquett the Waikato coals successfully without using a binder, and coal tar pitch was th© most suitable of the binders examined. The blending of 50 per cent of Waikato coal with 50 per cent bituminous coal produced briquetts free from the tendency to spark, so characteristic of the Waikato coal. f Experiments were, made with bituminous coal alone, and the briquetts were found to be hard, compact, and brittle, whereas the briquetts made by blending brown coals with the bituminous coals were more friable.

The experiments carried out are of a particularly interesting nature. The waste coal is put through a sieve before being put into the hydraulic press which consolidates the coal. “The small tablet produced is then submitted to all sorts of tests. It is put into a tank with other tablets and briskly rotated. The manner jn which it weathers this pummelling is a pretty good indication as to how it would stand transport. Just how brittle or how friable it is is noted, and further experiments are made with the addition of a hinder, and all grades of coal are tried with all different kinds of hinder, .such as coal tar, pitch, etc. Then the tablet is placed under a . miniature pile driver, which falls dead on to the block. The manner in which it stands up to these hard knocks is also of interest to the experimenter. But there are dozens of other intersting processes used to determine*what shall he absolutely the best method of dealing with the waste coals of the Dominion. Mr W. ‘H. Penseler, B.Sc., 8.E., A.0.5.M., who is carrying out the experiments under the direction of the Dominion Analyst, has hundreds of samples representing every conceivable “blend” test, and the calorific value of the coal is also made a feature of by the experimenter. A comprehensive report is to be made to the Minister shortly.