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Technical Cement Forum / how to increase C3S & reduce freelime in clinker

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xxxx 12/04/2013 09:28:51

how to increase C3S & reduce freelime in clinker

dear all,

my raw mix lsf is 93.5 to 94% , SM 2.25-2.26%

Coal fired is mix (80% Petcoke & 20% Imported coal)

coal Mix cv=7400-7500 kcal/kg

Coal Mix ash=4-5%

No CO formation in the system even at 2% O2 at preheater exit.

System is ILC with grate cooler.

We get 1.5-2% free lime in clinker with 47-48% C3S.

Raw Meal fineness is 14% on 90 mic. & 1.6% on 212 mic.

Coal Mix fineness is 3.5% on 90 mic.

Without reducing the clinker & Raw Meal production how can I increase C3S% in clinker.?

Please do suggest.

Arthur Harrisson 12/04/2013 13:44:11

To increase C3S the options are increase LSF, decrease free lime, increase silica ratio.

With 14% residue on 90 microns you probably don't wish to increase the silica ratio so increasing the LSF seems a good idea, but if you can't reduce free lime below 1.5% with less than 93% LSF (after ash is added from fuel) then this may just make things more difficult. To tackle high free lime you either may need to mill finer if the silica residue is high (check this by measuring acid insoluble residue) or look at the temperature profile (early formation of belite can make free lime very difficult) or see if anything is present which may stabilise free lime (phosphate, high clinker SO3, high alkali can all do this under some circumstances).

Microscopy will let you know which of these might be an issue and avoid rying the wrong solution which may not help.

Arthur

xxxx 13/04/2013 08:38:09

Dear All

I am thinking to increase the % of Petcoke to 90% instead of 80% in the fuel mix. It will reduce the silica content by from fuel ash & will automatically result in more lime for combination & will result in more C3S & less C2S.I think it will also give reduction in free lime.

Please comment on this point.

Is it useful or not

Arthur Harrisson 15/04/2013 11:36:00

There are a lot of variables here to consider. It looks as though your coal must be about 20% ash. Is this ground together with the pet coke or separately? Is the same mix put to the calciner and the front end?

If the fuels are milled together then the petcoke will mill finer than the coal and it may be that coarse pieces of ash are contributing to the difficulty in reducing free lime. In this case reducing the ash content may help.

On the other hand by reducing the coal the fuel mix will be less volatile and the burning zone in the kiln may be extended. To make good C3S the ideal is to have a short, hot burning zone. You need some clue as to why the free lime is high. Is the clinker lumpy?, brown centred? dusty? fine? coarse?

The differences we are looking at here are pretty small in terms of ash and probably of volatiles as well. If the alumina modulus is in a sensitive area and you reduce the ash you may need to adjust oxide addition if you are using any to manage the potential to form liquid too early and make rings.

Regards

Arthur

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