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World Cement
Five-stage preheater
The preheater is a Holcim-patented two-string, ‘hybrid’
in-line calciner, designed for low NO
X
and low CO. Each
string has five cyclone stages, with twin low-pressure
cyclones for the top four stages and a single
low-pressure cyclone at the bottom stage.
Fuel is burned in a single 10 m dia. calciner to
achieve approximately 92 − 95% of the total material
calcination. The calciner is designed to burn a variety of
fuels, including coal, petcoke, oil, and various types of
non-hazardous alternative fuels. Approximately 7 sec.
of total retention time is available within the calciner,
including the time in the exit-loop duct, to combust the
fuel and give low CO emission.
A ‘notch’ in the calciner vessel enhances the mixture
of hot gas, fuel, and meal for optimal heat transfer
and burn-out. A splitter gate for the material of one of
the Stage IV cyclones in each preheater string diverts a
portion of the meal directly into the upper section of
the calciner. This creates a high-temperature oxidation
zone in the lower section of the calciner to burn
petcoke and other non-hazardous AFs.
Three-support rotary kiln
The plant’s kiln has a rated production capacity of
12 000 tpd of clinker, making it the largest single
clinker production line in the US. Measuring
93 m x 6.6 m dia., the three-support rotary kiln has a
nominal speed of 3.6 rpm and maximum speed of
5.0 rpm. The kiln has an installed power of 2 x 1250 kW
and tangential tyre suspension that reduces the kiln
ovality compared to a traditional floating tyre design
and semi-rigid roller supports. The kiln operates with a
Holcim-designed crank-absorbing system where trusion
rolls at pier 2 hydraulically adjust to maintain constant
contact and support for the tyre.
Clinker cooler
The latest-generation IKN clinker cooler (7.8 m x 119 rows)
provides a material loading of 45 t/d/m
2
and is designed
for a clinker discharge temperature of 84 °C plus ambient
at a clinker production of 13 000 tpd. A roll breaker at the
end of the cooler crushes the clinker.
Coal/petcoke grinding mill
The coal/petcoke grinding system consists of two
identical VRMs with 740 kW gear reducers. Each mill
is designed to produce around 37 tph of petcoke with
a Hardgrove Index (HGI) greater than 45. Alternately,
each mill may produce up to approximately 70 tph of
coal with the same HGI, depending upon the moisture
in the raw coal. After milling, the product is extracted
from the dust collector and pumped to one of the
pulverised fuel bins. There are two bins for the calciner
and one bin for the kiln with rotor feeders to deliver
the fuel to the burners.