The excess quantity of alkali compounds present in the raw material adversely affects
the quality of the cement. Most of this alkali is evaporated inside the kiln and gets recycled
due to condensation of alkali vapour at the cold raw meal feed or the top cyclones. In order
to reduce this recycling a certain quantity of gas is bled off from the back end of the kiln.
This gas contains around 80% alkali. As can be seen from the Table 4: (a) the temperature
of by-pass gas can go up to 1050C and the dew point is very low in the range of 35–45C,
(b) the resistivity of dust is not very high due to the presence of alkalis but a large fraction,
around 90%, of particles lies below 10 m.