MAKING BRIQUETTES

Evening Post, Volume CXXIII, Issue 142, 17 June 1937, Page 23

MAKING BRIQUETTES

PLANT IN WAIKATO

A YOUNG INDUSTRY

UTILISING SLACK COAL

factors governing the successful manufacture of briquettes from coal, the difficulties that ruined early attempts, and the operation of a large carbonising and briquetting plant at Rotowaro, near Huntly, were discussed last evening by Mr. 'W. G. Hughson, of the Dominion Laboratory, in an address to the technological section of the Philosophical Society. The industries, he said, were comparatively unknown in New Zealand, plants having been established only in the Jast few years. Mr. Hughson illustrated his .Jecture with lantern-slides of the Rotowaro plant. In Great Britain, said Mr. Hughson, manufactured fuels were rare because of the superabundance of superior coal. In Germany, on the other hand, large deposits of lignite had for many years led to the development of machinery specially suited for the drying, carbonisation, and briquetting of low-grade deposits into higher-grade manufactured fuel. Consequently, Germany was recognised as the home of briquetting. Of the world annual total of 50,000,000 tons Germany produced 34,930,000 tons, France 7,530,000 tons, Belgium 1,384,000 tons, the Netherlands 1,138,000 tons, and England only 941,000 tons. New Zealand and Australia each produced 20,000 tons, and Canada 15,000. The six factors governing the successful operation of briquetting plants might be summarised thus: Economic conditions; nature of the coal; necessary pre-treatment (drying or carbonising); type of binder; mechanical considerations; and use of by-products. ECONOMIC FACTOES. Different factors had to be considered in different countries, continued Mr. Hughson. In Germany, for instance, a market had been built up over a long period; briquettes were familiar fuel, and were preferred to the poor-class raw, lignite. In America briquettes were comparatively new, and a popular market could not be assumed immediately in competition with highgrade anthracites and bituminous | coals. Block briquettes were not popular, and presses had to be evolved to make them other shapes and sizes. As with other industries during the experimental stage, many failures had occurred through lack of knowledge and insufficient finance. Fire toll on briquetting plants had been heavy, and the record in many cases was "Burned down—never rebuilt." In America, in the period 1907-1932, fiftyfour plants, about 68 per cent, of those established, were abandoned. Intimate knowledge of the > composition and physical and chemical characteristics of the fuel under consideration, as well as the knowledge of the heating and firing propensities of the manufactured briquette; were essential. Dealing with tfre various types of coal, and the binders that had been experimented with, Mr. Hughson said a tremendous number of binders had been tried, but their chief failings were that very few of them gave the briquette the required strength, and that only a limited number of them were waterproof. The necessity for the binders being waterproof was obvious, and had led to the almost exclusive use of bitumen or pitch, or mixtures containing a percentage of those materials. Different types of coal required peculiar treatment at each stage, drying, carbonising, and briquetting; and that had meant the elaboration of a great variety of mechanical equipment. Prospectuses frequently over-esti-mated-the value of by-products for which there was no market. As a rule, a plant must stand or fall by the sale of its briquettes. Gas and 'oil byproducts, although important, were only subsidiary. DOMINION INVESTIGATIONS. The Dominion Laboratory conducted an investigation into the possibilities of briquetting in New Zealand in 1924, and in 1931 an experimental roll press designed to produce from four to five tons of one-ounce ovoid briquettes daily was set up at the State Coal Depot. After ijreliminary tests it was able to produce quantities of briquettes sufficient for firing and locomotive tests. In 1927 some preliminary work on low-temperature carbonisation was done at Canterbury College with blended New Zealand coals. More than twenty years ago briqueU ting works were set up at Westport, but through inadequate knowledge were soon abandoned. The Waikato Carbonisation Company started the erection of its plant at Rotowaro in 1930. For some years the Smokeless Fuel Company, of Sockburn, Christchurch, had been running a briquette plant in conjunction with its carbonisation works, using untreated West Coast coals, alone or blended to give a non-swelling, strongly-cooking product, and a briquette with about 6 per cent, of bitumen binder. About three years ago a plant was erected at Onehunga for the briquetting of untreated Waikato slack coal from the Wilton mine. It was found necessary to add a good percentage of West Coast cooking coal, in order to obtain a product which would hold together in the fire. HYDRO-ELECTRIC AID. With the advent of an extensive Government hydro-electric programme, and more particularly with the opening of Arapuni and the consequent curtailment of the quantity of slack coal for the King's Wharf Power Station, 'Auckland, the Waikato collieries found .themselves in search of an outlet for their surplus slack. The slack had to be removed from the mine, and special equipment was required to transfer the unwanted portion to huge dumps, which had to be watered to prevent spontaneous firing. Many dumps in that area were burning continuously, and constituted both a menace and a nuisance. The Director of the Dominion Laboratory investigated several plants in Canada and the United States, and on his recommendation a plant was ordered from Germany for the drying, carbonisation, and briquetting of Waikato slack coaL Describing the process, Mr. Hughson said the slack was accepted direct from the screens of the Rotowaro mine. It was subjected to a pre-drying and low-temperature carbonisation process, and the resulting char was briquetted with bitumen or pitch to give a two and a half to three-ounce briquette suitable for domestic and commercial j use.

Mr. Hughson described in detail the working and construction of the plant, saying that the products were subjected to the strictest analysis. .

Mr. M. G. Templeton, "Wellington, has secured a contract for the erection of the new railway bridge at Waipawa.It will be a single-track bridge, 1400 ft long, in thirty-five 40ft spans,. Mr. Templeton's contract consists of the driving of 234 piles In 35 groups. Work has been started.