Raw meal residue and clinker litre weight

Measuring two residues allows the Rosin Rammler distribution line to be calculated. The residues of quartz at the coarse size fraction and calcite at the fine fraction are also used for burnability assessments.
 
Litre weight is not really comparable between plants. It is used as a qualitative indicator of the degree of burning comparing one time to another on a particular kiln.

Reply to point no.2

There exists a corelationship (Y=mX + C) between litre weight and free lime for different clinker size fractions.The corelationship (-ve) will be either week or strong for different clinker size fractions.

Based on this suitable clinker size fraction can be evolved after carrying out proper study for each Kiln to decide which clinker size sieve should be used.

In this context a paper has been published by me at NCBM New Delhi international Seminar which you may refer and get back to me on bhaskar.agate@gmail.com for any clarifications on the study.

Regards

Bhaskar Agate

I

R B GARG:

1) What is the significance of the raw meal residue measurement on 90 micron and 212 micron sieves, respectively.?

 Along with LSF and SR, the amount of oversize calcite and quartz particles have a strong impact on the raw meal burnability, and hence the resultant clinker free lime.

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 or quartz above these levels are generally agreed to worsen raw meal burnability (as measured by the freelime content of raw meal nodules burned at 1400 deg C for 30-40 minutes)

By carrying out a multiple regression on the results of many such burnability tests, using a wide range of raw material samples, a burnability model can be obtained for a given plant. The resultant formula would look something like this;-

 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.

This relationship shows several important points;-

1. The major influences on raw meal burnability are SR and coarse quartz.

2. There is the possibility of differentiating between the influence of chemical composition (LSF and SR) and that of raw meal particle size.

3. By analysing the chemistry,  Quartz(>32u) and Calcite (>90u) it is possible to determine the best method for improving the burnmability of your rawmix.

The burnability test requires special equipment and procedures, not to mention experience. But there is a quick comparative method that most laboratories can use to estimate and compare the potential burnability of their raw meal on a routine basis.

This is to analyse the >90u fraction of the raw meal by XRF and compare the SiO2 content. It is important to prepare the >90u fraction by wet sieving because, in our experience, dry sieving such as by an Alpine airjet 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.

If measures are taken to minimise the +90u SiO2 content of raw meals analysed in this way, the raw meal burnability will improve and can be controlled, without the need for expensive, time consuming burnability tests.

 

R B GARG:

2) In some plants, we use to determine the clinker litre weight of clinker size between-10mm +6 mm sieves, while in some plant determine the clinker litre weight of clinker size between -10mm & +5mm sives. Please clarify, what is the significance of this clinker size for measuring clinker litre weight.

 

Since the object of the litre-weight test is to estimate free lime based on clinker density, it is essential that any particles which are not normally-formed nodules are excluded from the litre-weight test. This includes large lumps or nodules which may have a different origin (such as rings,coating material of buildups) as well as very small particles and dust which have not had a chance to nodulise properly.

Also, the bulk density of  clinker nodules is related to their particle size. A mixture of both small and large particles will have the highest density because the smaller particles will fill the voids between the larger particles. Small changes in the particle size distribution will therefoer have a marked effect on the overall bulk density and potentially overshadow the effect of density changes due to softer or harder burning.

For all these reasons it is common practice to select a narrow range of nodule sizes, usually between 5mm and 10mm, however the selection of these sieves depends on the average nodule size of your clinker and  by 'trial and error' to find the size range that gives the most consistent relationship between litre-weight and free lime determined by chemical analysis.

The danger with relying on litre-weight for kiln burning, particularly in large diameter kilns, is the intermittent effect of dusty conditions on the density of the clinker nodules.

 Excessive dust in the burning zone can create an outer spongy layer that reduces the overall density of the nodule and may severly lower the litre-weight result, even though the dusty clinker has a very low free lime.

I don't recommend using litre-weight tests in kilns which exhibit frequent dusty conditions because the litre-weight / free lime relationship may fluctuate suddenly and become dangerously misleading.

Regards,

 Ted.