Troubles in using 100% petcoke

Dear Experts

I am using 100 % petcoke in ILC polysius Kiln [ 7500 tpd].

We have 6% S in petcoke .[ 1.6-1.8% retention on 90 mic.]

LSF in kiln feed 93.6-94%

SM 2

AM 1.2

KF residue 15-17% on 90 mic & 1.7-2% on 212 mic

Kiln filling 12.8-13%

Kiln inlet oxygen 4 to 5%, nil CO

TAD damper full open

Molar ratio  2.6

clinker litre weight 1250-1270

Free lime 0.5 to 0.8%

Flame Momentum 1800-1900 % m/s

Liquid % 28.5-28.9%

Fuel CV 7850-7900

Ash 2-4%

Heat Consumption 720 kcal/kg

We have problems with kiln dusty conditions , ring formation towards kiln inlet ?

How to eleminate such problems permanently?

Any suggestions for change in chemistry or kiln operation parameters and or burner settings etc.

Please do suggest.

 

thanks

 

Sidhant

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re Troubles in using 100% petcoke

Hello Sidhant,

I suspect your dusty conditions and kiln inlet ring are the result of very high sulphur recirculation as a consequence of using petcoke. Even though you may have no CO in the kiln inlet, the large amount of SO3 introduced by the petcoke may not be properly balanced by alkalis in the kiln feed. This will result in a high SO3 recirculation and a reduction of the the liquid phase surface tension and viscosity. This will cause poor clinker nodulisation and a corresponding increase in the dust load in the kiln and the likelihood of kiln rings near the kiln inlet.

The solutions are;-

1. Ensure that the high SO3 input is balanced with the appropriate amount of alkalis.
2. Optimise the burnability of the raw meal in order to reduce the burning zone temperature.
3. Optimise the flame shape to reduce the length of the burning zone.
4. You may even have to increase the O2 at the kiln inlet even more to ensure enough oxygen is present to remove the increased amount of alkali sulphates from the kiln.
5. If chloride levels are high in the raw materials this can react preferentially with the alkalis in the bottom cyclones, reducing the amount of alkalis available to remove SO3 from the kiln. In this case the only practical solution is to try and reduce the chloride input.

Could you please send me the SO3, K2O and Na2O content of both your raw meal and clinker, as well as the SO3, K2O, Na2O and Cl- content of your hot meal.

Regards,
Ted.

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re Troubles in using 100% petcoke

Dear Ted

Thanks a lot for the reply.

But under the same conditions & without having additional alkalies what to do to avoid ring formation & dusty kiln?

Well as far as oxygen at kiln inlet is concerned as you can see it is more than 4% which is I think quit enough that too with nil CO. But sometimes we get CO along with reduced oxygen at kiln inlet , in this condition kiln becomes dusty & gives low litre weight.

Can I go for reducing the litre weight from 1250 to 1150 & accept free lime upto 1 to 1.2% instead of 0.8% ? I think it will reduce the fuel consumption & inturn the SO3 input.

Well I am trying to make a log sheet of samples of alkalies & SO3 for hot meal,clinker to find out the evaporation factor of SO3 .

As fas as chloride is concerned it is 0.01% in Raw Material.

Please suggest.

Thanks once again 

Sidhant

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re Troubles in using 100% petcoke

Hello Sidhant,

Petcoke sometimes needs more O2 at the kiln inlet than you would expect.  It is common in some plants to have to run with 6-8% O2 at the kiln inlet to keep SO3 recirculation down to an acceptable level. You have to remember that just having a small excess of O2 in the kiln inlet (sufficient to ensure zero CO) may not be enough to control the high sulphur input from petcoke;-

2K2O + 2SO2 + O2 = 2K2SO4

2CaO  + 2SO2 +O2 = 2CaSO4

2SO2 = 128
O2     =  32

Therefore every 4t of SO2 needs at least 1t of O2 to be converted to SO4-2, no matter if there are sufficient alkalis or not.

You should be able to calculate the % O2 required at the kiln inlet from the total input of SO2 from petcoke and the gas flow rate at the kiln inlet.

I would agree that burning softer (ie lower litre weight) is a good idea since. In addition to using less fuel and lowering the sulphur input , softer burning will reduce the sulphur volatilisation in the burning zone. And, since CaSO4 is one way that sulphur can leave the kiln, ensuring oxidising conditions in the burning zone is critical since CaSO4 is more susceptable to thermal decomposition under slightly reducing conditions than alkali sulphates.

Chloride does not appear to be a problem for you.

In summary, I would suggest that you try to run the kiln with as high a free lime as you can tolerate.

Regards,
Ted.

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