WAIKATO COAL.

Waikato Times, Volume 107, Issue 18024, 20 May 1930, Page 10

WAIKATO COAL.

CARBONISATION OF SLACK

SUCCESS OF SCHEME ASSURED. AUCKLAND, Tuesday. “ I am confident that we shall make a success of the carbonisation of Waikato coal slack and that there will be a very great market for it,” said Mr W. D. Holgate, president of the New Zealand Coal Mine Owners’ Association, in an address to the Auckland Rotary Club yesterday. He had no doubt as to the success of the process on lignite slack, but how far it would be extended in New Zealand he could not say. it depended upon the price at which the coal was put into the carboniser.

Mr Holgate, in leading up to an interesting description of the carbonising plant that-was now being Rotowaro, reviewed the progress that has been made during the last 130 years in the investigation of more economic methods in the use of coal. Germany had specialised, mainly since the war, in the treatment of coal by low-temperature distillation, and had made a claim that was supported by statistics, that their processes were a commercial success.

New Zealand possessed large deposits of lignite coals of much better quality than those in Germany, the United States and Canada. Unfortunately the lignite mines in New Zealand averaged 42 per cent, of slack which would pass through an inch screen, and, although it was of the same calorific value as the other grades of coal, it was more difficult to sell. Thus other grades had to bear the loss sustained by selling the slack at 4s to 6s below the cost of production.

Affected by hydro-Electrlc Power. The introduction of hydro-electric power had seriously affected the coal industry in the South Island, and in the North Island the use of Arapuni power had thrown 80,000 tons of slack that was formerly taken by the Auckland Power Board back on to the hands of the mine owners. Unless some other use was found for that slack it would become not only a loss to the Waikato companies, but a national loss. The carbonisation company was trying to convert that loss into a national gain. By carbonisation the by-products were extracted and a firecoke or briquette of high calorific value was obtained.

To bring that about the Waikato coal companies had formed a subsidiary company known as the Waikato Carbonisation Company, and purchased a Lurgi plant capable of treating 80,000 tons of slack a year. The German plant Was purchased because there was no process in England for treating lignite coal. The Lurgi plant in particular was chosen because there were more of this type in operation than any other, and the manufacturers gave a guarantee as to certain performances which no other process owner would give or was in a position to give. O'he two-unit plant now being erected at Rotowaro was guaranteed to treat 250 tons of slack a day. It was also guaranteed to produce a hard fuel residue of over 50 per cent, of the original amount treated, with a calorific value of over 12,500 British thermal units, and to yield a certain percentage of tar oils which, however, was only a secondary consideration in the present case.

Plant to Cost £150,000. “ The plant, which is the first in the southern hemisphere, will cost £150,000," Mr Holgate said. The carboniser was 80ft. high and was made of steel and brick. The slack passed from the Rotowaro mine on a belt conveyor to the storage bunkers, and from the Pukemiro mine by aerial tramway. After being taken to the top of the carboniser it gravitated through three different zones, firstly for drying, secondly for carbonisation, and lastly for cooling. The tar oils were extracted in the process and conveyed to a distillation plant, where the pitch was' isolated for subsequent use in making the briquettes. The carbonised char dropped on a conveyor and was taken to the coolers, mixing vats, crushing plant and briquetting plant. In regard to the market for the residues, the company had already received inquiries from overseas as to the possibilities of obtaining supplies of pulverised char for steamers. The briquettes should be ideal for railway locomotives, as they could be easily handled, and should have a calorific value of 13,000 British thermal units. In addition, they were practically smokeless and sparkless, which removed the nuisance of sulphurous smoke in tunnels and the danger of countryside fires, which was one of the chief objections to the use of Waikato coal on the railways.