Quality control Question 45

Our ball mill is closed circuit. Its design capacity is 70tph, but we can run 85tph. However, we run it now 80tph, ie total feed is 80tph. We add limestone feed with clinker & gypsum. The limestone percantage is increasing & deceasing based on LOI. The Blaine is: 3300 to 34700 cm²/g Residue (return): 12-13 per cent SO3: 2.6-3.0. LOI: 0 to 2.5. When mill is in steady condition our seperator speed is 76 and sepex damper position within 59 to 61. But now my new terget is that Blaine is same i.e. within 3300 to 3400 cm²/g but residue to be within 8-9 per cent. Is it possible to control the blaine with respect to the requisite residue levels?

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Re: Quality control

To control the residue separately to the Blaine you need to vary the recirculating load of the cement mill. To maintain the same Blaine and reduce the residue you will need to operate with a higher recirculating load.

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Quality control Question 46

We are having Polysius design ILC six-stage kiln have dimension of 3.8m ID and 64m length. We are firing 100 petcoke in both main firing and calciner firing. We are facing problem of reduction in output and percentage of fines generation in clinker increased.The kiln feed and petcoke chemical analysis are as under: SiO₂ 13.80 - 14.10 Al2O₃ 3.6 - 3.75 Fe₂O₃ 3.4 -3.6 CaO 42.7 - 42.9 MgO 0.7 - 0.9 SO₃ 0.1 -0.16 K₂0 0.28 - 0.35 Na₂O 0.10 - 0.12 Cl 0.06- 0.09 Petcoke Analysis C 88.5 - 89.5 H₂ 3.8 - 4.2 S 6.0 - 6.5 Violatile Content 9.8 -10.4 Calorific Value 7960 - 8020 Kcal/Kg Coal Ash Content 0.30 - 0.70 Please suggest suitable counter measures to increase throughput rate and stable running of kiln.

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Re: Quality control

Unfortunately these problems are regularly reported on kilns burning petroleum coke. The problem is caused by the sulphur content in the petroleum coke. This has the effect of reducing the viscosity of the flux and this leads to the increased fines generation in the clinker. You must ensure that you have good oxidising conditions in the burning zone to minimise the recirculation of sulphates. After that you need to change the chemistry to adjust the viscosity of the flux. Increasing the Al₂O₃ content may help, but perhaps the best solution would be to add some calcium fluoride to the kiln feed.

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