Furnace sensor irons out waste energy

A new type of high-temperature sensor could help increase the efficiency of steelmaking furnaces and reduce greenhouse gas emissions, according to its developers at the

. The sensor, which monitors the concentration of oxides of carbon inside the furnace, could also improve the quality of steel.

Steelmaking furnaces operate at about 1600

C — too hot for most sensors. This means there is no way to monitor in detail what is happening inside the furnace, which can le

ad to inefficiency. Blast furnaces work by using oxygen to remove carbon from pig iron; the gas is injected into the furnace, where it oxidises the carbon in the metal. This produces carbon monoxide and carbon dioxide. But once the carbon is exhausted, the iron itself starts to burn.

Research leader Murray Thomson said about half of the energy used in the process is wasted and generates unnecessary carbon dioxide emissions. 'If they knew what the CO

and CO levels were, they could stop the oxygen injection as soon as the carbon oxide levels disappear,' he said.

Thomson and his combustion group at

have applied the principles of infrared spectroscopy to devise an optical sensor that monitors the oxides of carbon. Looking through a heat-shielded 20cm x 20cm window in the furnace, the sensor collects the wavelengths of light produced inside the furnace and separates them to analyse the various wavelengths of light emitted by the hot gases. The bond between oxygen and carbon is a strong emitter of infrared at a characteristic wavelength, so it is easy to spot.

The sensor allows the researchers to detect a change in CO

or CO levels within five seconds, which would allow furnace operators to switch off oxygen injection before the iron started to burn.