Mitigating the risk of explosions in metallurgical furnaces

The Siemens LDS6 laser gas analyser is helping to improve safety and save millions of dollars in damage repairs for the Tasmanian Electro Metallurgical company (TEMCO), a subsidiary of BHP Billiton that is located in Tasmania. It does this by alerting workers at the manganese ferro-alloy plant of an imminent furnace explosion and giving them sufficient time to prevent it.

Paul Dennis, Process Technology Supervisor at the TEMCO plant, explained the common cause of explosions in the submerged arc furnaces, which have been classified as some of the most dangerous furnaces in the world: “Sudden explosions are known to arise in these furnaces due to the temperature control mechanism, which pumps water through a series of tubes inside the furnace to maintain the internal temperature. Over time, the water eventually erodes these steel tubes and this allows some water to leak into the furnace.

“The extremely high furnace temperatures and increasing water leakage are the main causes of the sudden explosions. At 400 to 600 °C, the water that enters the furnace through the eroded steel tubes is immediately converted into steam. As this erosion continues and causes more steam to accumulate inside the furnace, the internal pressure builds up until it eventually explodes.”

Brendan Welsh, Siemens Product Manager, outlined the technology behind the LDS6 laser gas analyser and the challenges that Siemens had to overcome for this application to be successful: “As this was a first-time application for the LDS6 in submerged arc furnaces on a global scale, great caution had to be taken in order to guarantee its accuracy, sensitivity, reproducibility, reliability and maintainability.

“One of the major challenges we experienced was to counteract the extremely high levels of dust that were present at the facility. Around 100 g of dust per cubic metre was recorded, which ordinarily was much too high for the laser analyser to work accurately.

“Siemens modified the analyser specifically to address this challenge. Extensive consultation occurred between our Siemens manufacturing facility in Germany, the local Siemens-authorised reseller and the client, BHP Billiton, to develop an analyser which was suitable. We built an air chamber that is used to blow the dust off the laser every few minutes, which allows the laser to gain an accurate scan of the water levels and, consequently, deliver consistent and reliable readings.

“Trials that were undertaken by Paul Dennis enabled a set of control limits to be established, with the analyser actually detecting water leaks several hours before any other traditional methods had been able to detect them. These limits are used to forewarn of any imminent future explosions, so that plant workers can take the appropriate safety measures, including shutting down the facility if needed.”

TEMCO’s Dennis said the safety procedure developed around the analyser was a significant step towards achieving zero fatalities in the highly volatile and unpredictable environment around plant furnaces: ”I’m hopeful that with the new analyser, submerged arc furnaces will not be the cause of any safety issues for BHP Billiton. Safety issues are of critical concern for TEMCO and BHP Billiton, and we are considering other applications of the LDS6 within our operations and the operations of other industries, such as mining, around the world.”

The only plant of its kind in Australia, TEMCO supplies the critical steel additive manganese ferro-alloy to more than 50 companies around the world. With their four electric arc furnaces, TEMCO can produce more than 250,000 tonnes of manganese alloys per year, 80% of which is exported. This can now be achieved more safely than ever with the aid of the LDS6 gas analyser.

Dennis has made a significant contribution towards safety in the minerals process industry. In formally recognising this invaluable contribution, BHP Billiton recently awarded Dennis with the Excellence in Safety Award. His extensive research into understanding the sporadic nature of submerged arc furnaces, accurately measuring water levels, predicting explosions and establishing safety standards has already enabled critical decisions to be made that have prevented imminent furnace explosions.