ABB SCC-K Operator's Manual

ABB SCC-K Operator's Manual Manual pdf 19 page image

42/23-52 EN Rev. 2 SCC-K NO 2 / NO Converter Operator’s Manual 19Conversion PrincipleReaction Equation The conversion of nitrogen dioxide NO 2 into nitrogen monoxide NO occursaccording to the following gross reaction equation:2 NO 2 <–> 2 NO + O 2Reaction Equilibrium The reaction equilibrium is shifted entirely onto the side of the original materialNO 2 . A shift of the equilibrium towards the products and the resultant high productyield can only be achieved subject to a high expenditure of energy, i.e. temperature(100% conversion at temperatures over 600 °C).Using a Catalyst By using a catalyst the activation energy of the above reaction is reducedconsiderably so that conversion rates of 99% are possible at temperatures below400 °C.Catalyst A carbon-molybdenum mixture is used as catalyst. The carbon supportingmaterial guarantees optimal contact between the gas to be converted and thesurface of the catalyst combined with a simultaneously low flow resistance.CatalystTemperaturesThe catalyst temperature can be adjusted continuously using the temperaturecontroller on the front of the converter.The recommended settings for catalyst temperatures depending on the gas flow-rate for a conversion rate above 95% are:30 l/h: 320 °C – 60 l/h: 320 °C – 90 l/h: 340 °C – 150 l/h: 360 °CGas Conditioning For reasons associated with the filter effect of the catalyst filling an appropriategas conditioning system is to be mounted upstream of the converter in order toseparate out suspended particles and to dry the sample gas!Cross-Sensitivities Ammonia NH3 in the sample gas converts a part of the NO 2 into dinitrogen oxideN 2 O and elementary N 2 . Depending on the ammonia concentration, this can causea substantial reduction in the conversion rate.