3. Cooler design, air flow distribution Non-uniform clinker bed
2.Segregtion in kiln due to wide range in particle size. Material characteristics , and rotation of kiln
4.Operation and maintenance of cooler
Reason for red river 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.
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 11-12% filling. 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.
This segregated fine Dust causes red river
0.2* D
More escape good nodules Of cooling air Best Less recuperation recuperation
Less passage Of air, only fluidisation occurs Bad recuperation
Q Q1> Least Resistance To air flow
Q2
More resistance To air flow
Cooling efficiency curve
Un cooled area(lumps and big balls) Reddsh core When broken
100
75
50
Best recuperation area
Red river area
25
20 15 10 5 2 1
0.1 0.5
0 mm
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.
Influence of Kiln rpm on particle segregation and distribution of clinker bed in cooler
Best distribution
better distribution
Required rpm
High rpm
Normal segregation
High segregation
bad distribution Higher rpm
worst distribution Very high rpm
Higher segregation Very high segregation
New generation cooler
Mechanical air flow regulators
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.
Automatic air flow regulator installed underneath the grates
Solution 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 Redriver. 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
