The paper provides an overall assessment of the environmental effects of co-incineration of cutting oil emulsions in cement plants through the quantification of emissions of key pollutants, namely NOx, CO and VOC. Two realistic scenarios are considered. In the first, the cutting oil emulsion is injected directly into the rotary kiln while the second scenario involves injection of the cutting oil emulsion in the tertiary air stream and thus directly into the precalciner. A detailed kinetic PSR modelling study is performed for combustion conditions relevant both to cement kiln and precalciner operating conditions. It is demonstrated that, although NOx emissions from the precalciner are generally substantially lower than those from the cement kiln, emulsion injection in the latter appears to be favourable and can lead up to 50% reductions in NO levels. However, injection of cutting oil emulsion with relatively high nitrogen content in the precalciner may lead, under lean conditions, to increases in the emitted NO levels. The effect of cutting oil emulsion on CO and VOC emissions both under cement kiln and precalciner conditions is also quantified. (c) 2006 Elsevier Ltd. All rights reserved.