In recent years the reduction of nitrogen oxide (NOx) emissions in kiln lines has been an important topic which is expected to further gain prominence as central European emission limits are set to reduce to 200mg/Nm³ at the start of 2019. NH3 slip emission will also be limited to 30mg/Nm³. To meet these new limits, current SNCR technology will need to be reconsidered as a realistic NOx reduction degree is between 50-75 per cent depending on the kiln line design. By C Helmreich, MAL Umwelttechnik GmbH, Austria.
To produce a high-quality clinker, the burning process in the kiln takes place under oxidising conditions, under which the partial oxidation of the molecular nitrogen in the combustion air results in the formation of nitrogen monoxide (NO) – a reaction called thermal NOx formation.
At the lower temperatures that prevail in the kiln inlet or calciner firing, however, thermal NOx formation is negligible. Here fuel-bound nitrogen can result in the formation of what is known as fuel-related NOx.
