WASTE COAL.

Hokitika Guardian, 30 October 1925, Page 4

WASTE COAL.

.MEANS OF UTILISATION. INTERESTING EXPERIMENTS. WELLINGTON', Oct. 23. It tin' vast- quantities of slack coal of tiie Dominion cannot ultimately be turned into profitable use it will not l.c because a 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 I lie expense of the .MinesDepartment, tire extremely encouraging and the experiments are being eon ducted on a large scale. Ihe princi pal methods that had been suggested were: tl) Dust firing. (2) low temperature carbonisation, and (3) briquetting. As the last mentioned appeared to be the most promising of the three methods, it was decided to investigate the conditions necessary for its successful application to New Zealand waste coal. The Mines Doartment seemed an experimental livitra illic press, ixiviilj? pressures up to thirty tons to the square inch. One of the first series of tests was on Waikato brown or sub-bituminous coal, about -fit per cent of which as mined was rejected as slack and wa< practically unsaleable. This was found to lie friable and ot a soli nature without a binder. On the othei hand, no difiicultv was experienced in hriquothting lignite front Alexandra. Otago. However, in all cases experiments made with mixtures of other coals had shown definite results. One of the conclusions which the experimenters have come to is that it did not. seem possible to briquet the Waikato coals successfully without using a binder, and coal tar pitch was the most suitable of hinders examined. The blending of 30 per cent ot AAaihato coal with 30 per cent bituminous coal would produce briquets which would he free from the tendency tn spark so characteristic of the Waikato coal. In regard to the experiments made with bituminous coal alone, the briquets were hard, compart and brittle, whereas briquets made by blending brown coals with bituminous coals were more friable. The experiments carried out are of a particularly interesting nature. The waste coal is first 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 corrugated tank with other tablets and briskly rotated. The manner in which it weathers ibis pummelling is a pretty good indication as to how it would stand transport. dust how brittle it is or iust bow friable is noted, and further experiments are made with the addition ot ‘'binder,' and all grades of cal are tried with different kinds of binder, such a- coal tar. pitch, etc-. Then the tablet is placed undet" a miniature pile-driver, which, being of even weight., tails dead on to the block. The manner in which it stands these hard knocks is also of interest to the expelimeuter.

But there are dozens of other interesting processes used to determine uhnt shall he absolutely the best method of dealing with the waste coals of the Dominion! Mr AY. TL Penseler. B.Sc., 8.E., who is carrying out the

experiments under the direction of ibe Dominion Analyst, has hundreds ot samples reoreso’iting every corn t-ivahle “blend" and test, and l.e is still working away. Every single detail is taken down carefully and the calorific value of the- coal is also made a feature of bv the experimenter. A comprehensive report is to be made to the Ministei shortly.