Interlude
Before discussing the final flowering of pulverised fuel firing, it is of some interest to look back at three other parallel innovations affecting the fuel efficiency of locomotive design, namely the Brotan boiler and two ‘flash’ steam generators. By the start of the twentieth century, steam boilers for many power plants and marine installations were of the high-pressure water-tube type. They avoided the problems of clogging up with scale by using pure water, recirculated exhaust steam that had been passed through cooling towers and condensers. And they were very fuel efficient, but also very large. Locomotive engineers looked with envy at this way of producing safe, high-pressure steam with the added promise of low maintenance costs, but were defeated by the problems of fitting everything on to a drive chassis within the restrictions of the loading gauge.
The Brotan boiler – and its later Brotan/ Deffner derivative – was an attempt at a ‘hybrid’ solution. Invented originally in 1902, it was essentially a flue-tube boiler and steam reservoir with a water-tube firebox constructed from a closely packed nest of steel tubes. It was claimed that this offered many potential benefits, particularly at high rates of steam generation.
