An Article published in New Scientist magazine, vol 158 issue 2130,
18/4/1998, page 6.

Cutting edge

A humble lab tool could burn holes in gas firms' profits

A Blowtorch that can melt steel has been developed by researchers in Britain who simply remodelled that tireless workhorse of the chemistry lab - the Bunsen burner. The blowtorch uses ordinary gas or propane rather than expensive acetylene and oxygen.

The British inventors of the device say the torch is ideal for a blacksmith's forge, or for cutting up scrap metals on farms and car dumps. They expect it to be especially
valuable in developing countries where acetylene is scarce and expensive. In the developed world, acetylene is 20 times more expensive than propane, the torch's principal fuel; in the developing world, it is up to 50 times more expensive.

Neil Downie, who founded DRAX Torches two years ago to market the invention, says that this is the first big redesign of the Bunsen burner since it was invented.  "Robert Bunsen's design has been little improved since 1860, but we've taken a more sophisticated approach," he says.

As in the Bunsen, a mixture of hydrocarbon fuel and air is burnt, forming a flame at the end of the barrel. The big difference is that the DRAX torch burns the fuel in two
stages. The first plume is inside the "gun" and preheats the mixture that feeds the second flame to around 500 °C.

Over the past two years, Downie and Graham Ball of the Department of Aeronautics at the University of Southampton established that a more powerful, intense flame can be created if the gases are preheated. The same ploy has long been used to improve fuel efficiency in furnaces, but it had never been tried before in blowtorches.

Preheating has two effects which create a more powerful flame. First, the gas mixture travels faster, which concentrates the flame into a smaller cone. "You get a
more intense flame, which means you're getting more combustion per cubic centimetre of flame," says Downie.

Second, the preheated propane is broken down into hydrogen and other hydrocarbons such as acetylene. These burn at higher temperatures than propane, which helps to concentrate the heat in the torch flame.

The net result is that the flame is much smaller-as little as a tenth of that found in a Bunsen-but is much more intense. Once concentrated, the heat can be transferred
far more efficiently to the material you are working on, even though the temperature of the flame barely exceeds 2000 °C, which is roughly the temperature of a Bunsen burner's flame.

But a Bunsen burner cannot even melt copper, which has a melting point of 1087 °C, let alone melt mild steel or iron at 1540 °C. The DRAX torch can melt both. "If you put any glass test tube in our flame, it melts," says Downie, who is looking for partners to develop the torch. He says that DRAX, which is based in Guildford, Surrey, has found that industrial gas manufacturers are worried about losing sales of acetylene if the invention makes oxyacetylene torches obsolete.

Andy Coghlan