Unit II Process 2012 13

Residue Control In Raw Mill & Its Impact In Kiln Operation 14th Aug2013Presented by : Roopesh Agrawal

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Contents What is Residue ?How it is measured?Residue control in raw mill operation?What is the significance of the raw meal residue measurement on 90 micron and 212 micron sieves, respectively.?What are the impact/ role of raw meal residue in Kiln Operation?Conclusion

What is Residue ?

It is the measurement of fineness where the retained is estimated in percentage by sieve analysis or by mixing in chemical solution.

quantity of retained (over size or insoluble) on selective sieve or in base of pot is calculated in percentage w.r.t. total sample quantity is known as %residue

Residue Measurement

In case of Raw meal It is measured by sieving methods :

1) Dry sieving 2) Wet sieving dry sieving - the certain amount of grounded material passed through desired sieve size ,after sufficient shaking % age retained calculated

wet sieving - the certain amount of grounded material passed through desired sieve size through water shower with sufficient shaking % age retained calculated wet sieving method is well established for raw meal residue measurements

This is to analyze that the >90u fraction of the raw meal done by XRF , dry sieving and wet sieving then compare with the SiO2 content. The dry sieving such as by an Alpine air jet system does not remove all of the ultra-fine clay particles which stick to the larger particles by static attraction and bias the chemical analysis.

Residue Control!

Residue control in raw mill operation It is a main control parameter of raw mill operation hourly the sample collected from circuit sampler and residue measured on 90 and 212 , results variation controlled by regulating the separator speed and mill fan flow

Variation in Residue controlled by regulating the separator speed and mill fan flow

Raw meal residue on 90 and 212 the values are in range between:

R(90) = 17 19 % R(212) = 1- 2 %

It is normal to see ratio between R90 : R212 =10:1 in VRM. For better burnability in kiln

Significance of Raw Meal Residue Measurements on 90 & 212

Measurements of residues on 90 and 212 allows the Rosin Rambler distribution line to be calculated. The residues of quartz at the coarse size fraction and calcite at the fine fraction are also used for kiln feed burnability assessments.

The critical size for calcite is thought to be around 90um, while the critical size for quartz is about 32um. Significant amounts of calcite or quartz above these levels are generally agreed toworsen raw meal burnability test

After analyzing the chemistry, we can conclude- Quartz(>32u) and Calcite (>90u) It is possible to determine the best way for proper control / improving the burnability of your raw mix.

17Impact of Raw Meal Residue in Kiln Operation

Raw meal fineness directlyinfluences the relative quantities of clinker minerals produced i.e. finer particles will react faster and therefore reaction more completely in the given time

Along withLSF and SR, the amount of oversize calcite and quartz particles have a strong impact on the raw meal burnability, CaO(free) = 0.6 * Quartz(>32u) + 0.2 * Calcite(>90u) + 0.3 * LSF + 1.6 * SR 34 where the coefficients would be slightly different for each plant.

Conversion of C2S into C3S by reaction with CaO occurs by diffusion of CaO through the liquid phase The rate of reaction is dependent on the diffusion rate of CaO through the liquid. this diffusion rate and the burning zone residence time together determine the critical distance..

21 That dissolved CaO has to travel through the liquid for complete reaction. therefore particles have to besmaller than this critical distance to allow CaO diffusion and complete reaction in the time available in the kiln.

Coarser particles will not react timely and resulting in unreacted free lime in clinker If the quartz particles are too coarse (>~40um) ,frequent large C2S clusterswill be produced at the expense of C3S... leaving a proportionateamount of unreacted free lime.

If the calcite particles are too coarse (>~100um), localized CaO over-saturation producesa "wall"of C3S crystals around the particle and the remaining CaO cannot readily diffuse out through this barrierand react with nearbysilica... againresulting in unreacted free lime.

Conclusion

Raw meal residue directly effects the kiln feed burnability Along withLSF and SR, the amount of oversize calcite and quartz particles have a strong impact on the raw meal burnability, and hence theresultant clinker free lime.

Thank You27