Early technology

Once charged with coal the open end of the retort was closed by an iron cover and the join was sealed, or luted, with clay or ensure no air was admitted. Self-sealing doors, which required no luting, gradually replaced the older method. The clay retort and the 'through' retort were important early developments in the practice of gas making. The clay retort gave a longer life and could be operated at higher temperatures than cast iron. Iron and clay retorts evolved through various cross sections and dimensions to settle, though not universally, on a D section, flat side down and between three and six metres long. Later, the open ended or 'through' retort was introduced which allowed the hot coke to be withdrawn from the end opposite to that where the coal was charged, or loaded.

In Australia, gasmaking was a fully imported technology and for its introduction all plant, most gas engineers and some tradesmen were brought from England. In these early British-designed gasworks the tarry smoke which was driven off in the retorts was condensed to remove tar and ammonia and bubbled through limewater to remove hydrogen sulphide. The coal gas was then stored in a holder which exerted pressure which forced the gas through the distribution system and ensured that the gaslights would burn with an even and steady flame.

Gas reticulation design was difficult because delivery of sufficient pressure depended on the maintenance of a precise mathematical relationship in the diameters of all the mains. Most gas distribution systems took advantage of the density of gas being lower than that of air by locating the gasworks at the lowest possible available location. Natural buoyancy then aided the passage of the gas through mains which were laid in upwardly inclined sections. The penalty for utilising this natural advantage was the frequency with which many of the gasworks suffered from floods.

By the time that most Australian gasworks were built advances in technology had eliminated many of the problems that confronted the initial Sydney Company. The Gas Works built in Adelaide for instance, used the newer clay retorts rather than cast iron and also employed a more efficient system of gas purification.

As the quality of light depended on the properties of the gas flame, good gas-making coal was needed which contained a high proportion of volatile hydrocarbons and it was found that Newcastle and Maitland coals were very suitable. They were therefore used by nearly all Australian gas companies throughout the gaslight era. Even when gas was required for its calorific or heating value, however, rather than its luminosity, gas companies still depended almost exclusively on coal from the same sources.

Except for those few supplying capital cities, Australian country and suburban gasworks remained small. Typically, they occupied less than two hectares, functioned with small hand operated, horizontal retorts, stored moderate amounts of gas in relatively small holders and depended on few employees. The other work required for gas making on the other hand continued to be labour intensive. Coal was manhandled from collier or railway siding to a stockpile within shovel reach of the retorts, where it was charged and heated for about five hours. The red hot coke which resulted was then raked out into a barrow where it was quenched and taken to be stored. Byproducts like tar and ammonia were often difficult to sell and the gas industry constantly endeavoured to create additional markets for these materials.

Australian Academy of Technological Sciences and Engineering