Raw Mill response time test

The most common way to determine the retention time in the mill is to use a fluorescent dye as a tracer. Suitable dyes include fluorescein, rhodamine, pyranine  and sulfhordamine.

10-20kg of dye is added to the mill feed (noting the time) and samples of raw meal are taken every 5 -10 minutes at the location where you wish to determine retention time.

Small portions of these samples are then mixed with water, shaken well and then allowed to stand until a clear water layer is observed above the settled solids. The retention time (at the point of sampling) is the difference between the time that the dye was added and the time of the sample which exhibits the highest dye intensity. If a UV fluorescent dye is used a UV light source can be used to increase visibility.

More accurate tests can be carried out by filtering off the water layer and using a UV/VIS spectrophotometer (if one is available) to analyse the intensity of the dye in each sample. In most instances visual inspection is all that is required, if enough dye is used.

Appropriate dyes for this purpose can be found by searching on line.

Hope this helps,

Ted.

Hi Ted

Thanks so much for your kind reply 

I just want to have your opinion for what I did:

1-  I increased Lime stone ( soft to grind material ) from 88 % to 95 % and take a sample every 2 min .

2- let the mill to stabilize again 

3- I increased Kaolin ( hard to grind material due to high scillicious content  ) from 3 % to 10 % and sample every 2 min.

 then detect the mill response for the 2 materials and then take the sum product of both results regarding to the tonnage of each during the test

 what is your opinion in that  

Yes, over-dosing the raw mix with a corrective and tracing the increase in the corresponding element oxide is a very simple and easy method of finding the mill retention time.

Of course the big drawback with this method is that for the length of the trial you are producing off-specification raw meal. However, if you are willing to tolerate some out of spec. raw meal, this method has the advantage of including comminution time in the retention time.

With a powdered tracer dye you are effectively only measuring the retention time of fine dust particles, whereas with the 'corrective tracing' method you are measuring the time it takes to pulverize the raw mix into fine dust particles plus the time it takes for those particles to exit the milling system and reach the raw meal sample point you have chosen downstream.

You will find that the softer corrective will exit the mill faster than the harder corrective, so you will have to average the retention times of the two trials you described above.

Regards,

Ted.