Both the SCR systems operated by the German cement industry employ catalysts with vanadium pentoxide (V2O5) as active component to reduce NOx emissions. These are also known to have a certain reducing effect on organic compounds in the exhaust gas.
As part of the IGF research project 17364 N funded by the AiF, studies were performed in conjunction with the research institute of the cement industry (FIZ) and the Institute of Chemical and Electrochemical Process Engineering at Clausthal University (ICVT) on the catalytic reduction of CO and organic components in the rotary kiln exhaust gas of cement plants. In addition to two standard SCR catalysts, two commercially available noble metal-based oxidation catalysts were also investigated. Both on a laboratory scale and in a trial plant attached to an industrial kiln plant, systematic tests were performed to establish which exhaust gas conditions and compositions have an influence on the oxidation action of the catalysts. In the laboratory set-up, the influences of various exhaust gas components on oxidation activity were observed in the temperature range between 250 and 400 °C. In six plant trials, the catalysts were used at a normal tail-end SCR operating temperature of 260 °C in the industrial exhaust gas.
Important findings were obtained with regard to the efficacy of oxidation catalysts converters used under the specific exhaust gas conditions of a rotary cement kiln. For example, it became apparent that the regeneration of already deactivated catalyst elements is possible at temperatures above 310 °C. Whether or not an increase in temperature alone is sufficient to achieve a longterm oxidation however remains to be clarified. Further investigations are required, as here again NH3, dust and other exhaust gas components may have an influence on catalysts activity.