1. Fine dusty clinker
2.Segregtion in kiln due to
wide range in particle size.
Material characteristics ,
and rotation of kiln
3. Cooler design,
air flow distribution
Non-uniform clinker bed
4.Operation and maintenance
Hot fine dust , wide granulometry in size and the consequent segregation
are the key reasons for the red river formation in cooler
When the cooling air tries to penetrate the closely packed fine clinker dust
layer the air gets heated and expands manifold in volume , fluidizes
dust and it stars flowing like water much faster than the grate speed and
stops when it becomes black with bubbles. The shear stress exerted by the
air results in kinetic energy of the mass, like thixotrpic in non newtonian
fluids. Higher the shear force ( here air flow velocity ) higher the fluidity
over a period of time.
Finer and hotter the dust the more it shoots like flooded wild river.
Some designers tried to put some dam ring in conventional grate coolers
or flow arrestors on its way to reduce its velocity but it did not help
as it jumps over the hurdles.
This hot clinker dust erode and burn the plates .
These are the reasons that make the cooler designers to invent
new generation coolers .The stationary inclined grates with control flow
aeration and controlled flow air regulators reduced red river problems
considerably .In some new generation also coolers the problems still exists.
Reason for red river
1.Dusty clinker and improvements
To day it is common problem that clinker is dusty. In 1 mm sieve, if pass- through is
15-20 % it is a normal clinker. In classic wet process the clinker nodules are
very good like pebbles. In this dry process with precalciner and higher production ,the
fines generation is on the higher Side. Volatiles like sulfur ,alkalies and alternate fuels
further aggravate this . Forced kilns and reduced conditions are also key reasons for
dusty Clinker. Ring formation in the outlet or in the burning zone deteriorates
nodulisation and force the kiln to operate on higher rpm which shifts clnker discharge
away from center of the cooler
• The nodulisation can be improved by modifying Alumina and silica
ratio, to great extent. Optimise the liquid with right viscosity yield good nodules
• Grinding the raw meal finer helps too especially when quartz and calcite are present .
• Good homogenised raw meal having standard deviation in CaO <0.2 and
SiO2 < 0.02 will reduce dust fraction in clinker.
• Addition of mineralisers like MgO , if limit allows, improve the nodularity.
• Intense convergent flame without impinging the charge also helps to reduce
the fines in the clinker.
• Higher rpm aids good nodulisation but not more than requirement and with
There are many more reasons for poor nodulisation.
In 1 mm sieve if the pass through is around 15 % is
Normally considered to be good clinker.
Of cooling air
Of air, only
This segregated fine
Dust causes red river
To air flow
To air flow
100 75 50 25 20 15 10 5 2 1 0.1 0.5 0 mm
and big balls)
Best recuperation area
Red river area
Cooling efficiency curve
Segregation inside the kiln at the discharge end
The hotter fine dust, it gets lifted farther up inside the kiln and good nodules cascade
farther down which results in segregation. If the kiln has shark teeth at the kiln tip
it becomes worse which results in more intense red river or even snowman formation.
Higher rpm also aids segregation .Higher secondary air velocity causes circulation of
fine dust between cooler and kiln which makes dust more sticky. Secondary and
Tertiary air take off velocity in the hood is to be less than 5 m/s.The fine dust falls
on towards the rotation side of the kiln. Though theCooler center point is offset
by 0.2 D of kiln , expecting center of clinker Discharge and center of cooler falls on
the same line but it never happens .Technology has not been fully developed to
have uniform clinker distribution on cooler grate But the cooling air distribution has
been achieved by mechanical air flow Controllers which regulates air flow depending
upon the resistance created by Clinker bed and its packing density. Latest generation
coolers like SF cooler, IKN pendulum , Eta cooler and pyro floor are already in use.
This helps in reducing the red river problem or at least reduction In cooler grate
Plate damage considerably.
bad distributionbetter distributionBest distribution worst distribution
Required rpm High rpm Very high rpmHigher rpm
Normal segregation High segregation Higher segregation Very high segregation
Influence of Kiln rpm on particle segregation and distribution of clinker bed in cooler
Mechanical flow regulators in the new generation coolers optimise the cooler
Air flow avoiding starvation or excess flow. This can be rearranged in either case
altering the orifice size.
Mechanical air flow regulators
Automatic air flow regulator installed underneath the grates
The ultimate solution is to produce good nodules. Coolers are designed for good
Nodules and 25 mm is the reference .Modify the chemistry with good
homogenisation to get good uniform nodules .
Good convergent flame in center of the kiln , without impinging on charge reduces
dust fraction .Oxidised conditons in burning zone will have control over volatiles
Which improves nodulisation.
Distribution of coolng air helps to reduce the red river . Combination of stationary
Inclined KIDs and controlled air flow regulators in the rest of the grate reduce the
Narrow down the stationary KIDS with thicker clinker bed , atleast 600-700mm
thick bed helps further.
Thank you for your kind attention
- K.P.PRADEEP KUMAR