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Residence Time in Relation to the Angle, Speed etc. of Kiln

I own a pilot sized rotary kiln which operates about 2000ºF in order to activate carbon obtained from coconut shell. I'm having problems in taking results from the lab to the pilot equipment, so I'm looking for technical papers to help me to find out my residence time and it's relation with the angle of the kiln, speed, particle size, gas flow, etc. Could you give me advice as to where can I go to find this information? Thank you for any help.

To calculate the retention time use the commonly accepted formula published by the US Bureau of Mines and used by most rotary equipment manufacturers. T = (1.77x L x (A)^0.5)/(P x D x N) Where A = the natural angle of repose of the material in degrees P = slope of the kiln in degrees D = the inside diameter of the kiln in feet L = length of the kiln shell in feet N = rotation speed in revolutions per minute T = retention time in minutes Calculate twice; once with the feed material characteristics and again with product characteristics and average the two. When internal lifters are present, as is typical with dryers, the time is usually increased 50%.

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