Fly Ash Mix with Raw Meal

Dear experts,

Recently we are planning to use fly Ash in Raw Mill Product at Product Airslide before going to CF Silo. Our fly ash having rich in carbon, allumina and silica. If we use this fly ash what problems will occured in kiln operation as well as quality of the Clinker(OPC & SRC). Pl. give me your valuable suggestions.

with regards

BK 

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Re: Fly Ash Mix with Raw Meal

Hello Bandari,

Adding flyash to the raw meal is reasonably common. Using flyash is usually a way of overcoming a raw meal production bottle-neck. By adding a percentage of flyash into the raw mill product increases the kiln throughput for the same raw mill output.

Sometimes the quarry has a very low clay component available and must be suplimented with flyash or bottom ash.

The things to watch for when adding flyash are;-

1. The raw meal chemistry (ex mill) must be adjusted carefully to suit the quantity of flyash being added, so that the required clinker chemistry remains unchanged.

2. Because of this there is a danger that if the flyash feed rate varies widely or stops suddenly, the clinker quality will suffer badly.eg very high LSF and free lime. A solution to this is to have a reserve supply of flyash available to feed into the raw meal in the event of a stoppage of the main supply. Flyash feed mechanisms must also be very accurate and reliable,

3. There will be an upper limit to the amount of flyash you can add. This limit will be reached when the amount of fly ash being added equals the clay (or argillaceous) component of your raw mix. ie. when are just milling pure limestone, silica corrective, iron corrective and then adding flyash. Usually this limit is between 10-20% depending on the quality of the limestone and corrective materials.

4. If you have limits on stack emissions for VOCs (volatile organic carbon compounds) the organic carbon content of the flyash might give you problems. This can be solved by insufflating the flyash directly into the burning zone, but care has to be taken to ensure the flyash is properly absorbed into the raw mix without causing problems with clinker mineralogy.

Hope this helps,

Regards,

Ted.

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