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| CSIRO | SOLVE | Issue 2 Feb 05 | |
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ENVIRONMENT
Change in the Wind
By Graeme O'Neill
When the breeze has passed over the industrial suburbs of most Australian cities, it bears the noisome whiff of industry: an odour redolent of sewage farms, tanneries, rendering plants, paint and agrochemical factories, pulp and paper mills and oil refineries. CSIRO chemical engineer Dr Manh Hoang says the problem is largely one of perception, not hazard: the human nose just happens to be particularly sensitive to the sulfur-rich organic compounds that dominate the mix, most notably hydrogen sulfide, or ‘rotten-egg gas’. The gaseous cocktail poses no dire threat to human health at the very low concentrations found in air – typically in the parts per billion range. But it is offensive to the nose, and prolonged exposure may cause headaches, nausea and respiratory ailments. But change is in the wind. Dr Hoang’s team at CSIRO Manufacturing and Infrastructure Technology in Clayton, Melbourne, has developed a low-temperature technology that can ping the pong at source, by trapping and catalytically destroying the offending gases. The heart of the catalytic converter is a lightweight, highly porous ceramic, available off the shelf, wash-coated with the CSIRO catalyst. It provides a very large surface area for catalysis within a relatively compact volume. Inside the converter, foul-smelling sulfur-containing organic compounds are burnt at temperatures between 80°C and 300°C in the presence of the catalyst, and are oxidised into odourless, non-toxic compounds. The low-temperature process consumes minimal amounts of fossil fuel. Dr Hoang says the technology can be used to treat exhaust gases from industrial processes, or to strip gaseous pollutants from liquid industrial effluents or sewage after solids have been removed. Factories can recycle their own treated water, or it can be reticulated to irrigate parks and gardens. The catalyst is long-lived and not expensive. CSIRO has tested it in a pilot plant for more than 1000 hours – six weeks – of continuous operation, with no significant decline in its efficiency. Dr Hoang said the catalytic equipment can be scaled to an individual company’s requirements, and can accommodate low or high gas flow rates. A typical industrial vent gas flow of 100 cubic metres per hour would require a catalytic unit of about two cubic metre capacity. Current deodorising technologies for industry include dilution, masking or neutralising agents, high-temperature (>800°C) oxidation, wet scrubbing, adsorption and biofiltration. Such technologies come with their own problems. High-temperature oxidation is energy-intensive, and can give rise to various sulfur and nitrogen oxide compounds, which are air pollutants. Chemical masking and neutralisation consume large quantities of expensive chemicals, and may even worsen the problem when the chemical agents combine with the odorants to create even more offensive odours. Wet scrubbing merely transfers odour compounds from air to water, leaving another waste disposal problem. Surface adsorption is inexpensive, but the adsorption media must be replaced or regenerated with steam to maintain efficiency – which may create similar disposal problems to wet scrubbing. Biofiltration plants, which employ microbes to break down the offensive compounds, are suitable for large gas flow rates and cheap to operate, but the treatment plant has a very large 'footprint'. A major advantage of the CSIRO technology is that its compactness means that factories do not have to install expensive ducting to collect contaminated air and pipe it to a central disposal plant – small plants can be installed at the source of the odours. Dr Hoang believes CSIRO’s new low-temperature catalysis technology has considerable export potential, because of its relatively low cost and low energy consumption. CSIRO is negotiating with an Australian company interested in commercialising it.
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Science treats the whiff of industry.
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