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Technical Cement Forum / RAW MIX, BURNING, RING FORMATION AND PREHEATER JAMMING PROBLEM.

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uksengupta 27/11/2012 08:59:48

RAW MIX, BURNING, RING FORMATION AND PREHEATER JAMMING PROBLEM.

M MATERIAL IS HAVING HIGH SULPHUR AND COAL USED AS FUEL ALSO HAVING HIGH SULPHUR.

Raw components	Chemical
Raw components	LOI	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	SO₃	Total
Limestone	38.66	6.90	0.75	1.49	49.20	0.89	1.11	99.00
Shale	7.78	60.99	20.56	7.55	0.19	0.67	1.26	99.00
Laterite	8.88	39.70	4.51	44.57	1.13	0.22		99.00

.COAL:- 25% ASH, MOISTURE:- 12% INHEARENT MOISTURE:- 3%, VM 34%, SULPHUR:-4%

ASH ANALYSIS:- SiO2 50%, Al2O3:- 25%, Fe2O3:- 14%, CaO:- 2%, MgO:- 0.5% CV:- 5660 kcal/kg

What should I do to handle this problem?

UKS

Raj Sahu 28/11/2012 11:51:37

Sulphur –Induced rings are formed when molar sulfur-to- alkali ratio in the system is more than 1.2.In such cases, there is a considerable amount of free SO3 circulating in the kiln. At a certain concentration level in the kiln gas, sulfation of free lime occurs with anhydride (CaSO4).If the kiln is burning under slightly reducing conditions, more volatile and lower melting sulfur salts may form, therefore increasing the severity of the problem. The salts in the molten state, coat the travelling clinker dust, forcing it to stick to the kiln wall in the form of rings. Sometimes the chemical analysis of such rings does not indicate high sulfur concentrations, proving that even a small amount of free sulfur is sufficient to cause ring. The severity of the problem increases with the dust concentration in the kiln gas. Dustier kilns have a tendency to form more rings than cleaner kilns.

Kiln Buildup and Rings: Kiln rings can be minimized by:

Stable kiln operation

Lower kiln system velocities and dust loads

Control internal sulphur cycle

Maintain an oxidizing environment in the burning zone

Maintain short and strong flame (Optimum flame momentum as per the type of fuel used)

Optimize chemistry and mineralogy of raw mix to give easier burning kiln feed.

Ted Krapkat 29/11/2012 04:04:19

Hello Uksengupta,

In addition to the operational controls given by Raj, I would also suggest the following;-

1. If possible try, to source a lower sulphur coal.

2. Depending on what is available in your deposit, try to blend limestone and shale with a lower SO3 content.

3. Increase the alkali input to the raw meal to bring your molar SO3/(K2O+Na2O) ratio closer to 1.0

4. Maintain the kiln inlet temperature as low as practically possible.

5. Increase the oxygen content of the kiln inlet gases to >3%, to reduce the sulphur volatility.

6. In the worst case scenario, where the above controls are not possible or ineffective, a kiln gas bypass might be the only alternative.

In addition, Raj's point about optimum burner performance is very important, especially if performance is so bad that free carbon enters the hot meal stream. This is because at 900-1000oC the following reaction can occur;- CaSO4 + 2C --> 4CaO + 2SO2 + 4CO2, which increases the sulphur recirculation load dramatically. This is another reason why keeping the O2 content at the kiln inlet >3% is essential under high SO3 input conditions.

Regards,

Ted.

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