12 PROjECT PRIDE
up to the core of the material which reduces thermal
loading in the kiln.
Bigger size pre-calciner with retention time in the range
of 12–17 sec in PC and goose neck benefits us in slow and
uniform heating of material and better heat transfer, which
eventually results in better quality of clinker, reduction
in CO% and lower NOX generation in entire pre-heater
system, and therefore no coating formation and lower fuel
and power consumption.
Because of bigger size pre-calciner, higher raw mill
residue can be maintained, which leads to slow and
uniform heating of material. Hence, raw mill output shall
be increased, resulting in lesser power consumption while
maintaining higher residue on 90 and 212 microns.
Downcomer Duct
For downcomer duct the specific requirement was given
to all suppliers to design for velocity less than 10 m/sec, so
that pressure drop across downcomer duct could be in the
range of 20–25 mmwg only, resulting in a further reduction
in PH fan power. Suppliers have offered the downcomer
duct diameter accordingly, i.e. in the range of 5.6–6.6 m
against standard from 4.25–5.0 m for a similar capacity
plant. But Waste Heat Recovery System (WHRS) has also
been taken in concept since the beginning and so finally,
we have retained the diameter of direct line as 4.75 m;
however, before PH boiler entry it was 6 m diameter.