Has anyone had experience with calcining material in a rotary tube kiln/furnace? A process of mine went swimmingly in the experimental runs on production scale. We began our first full scale run this week, and, as expected, the unexpected has happened
The process ran for about 36hrs without problem and then we noted the material began to build up a coating around the inside of the tube (it's a quartz tube). The coating is inhibiting heat transfer. After stopping/cleaning/restarting we had observed the coating problem in about 6 hrs. We did not observe this coating during the experimental runs, though to be fair the experiments never went this long.
I should note that the the kiln is not one of the giant ones like you'd see for portland cement but rather an 8-10 foot quartz tube that passes through a hot zone and then into a collection container. Moisture does come off of the product during calcining, and in fact I want that to happen. Actually, it's the combo of the high heat and the water vapor that gives the desired characteristics of the final product.
My question is, what could be causing the coating to build up? Has anyone observed coating formation in a calcining process? Any ideas on how to prevent it? I unfortunately cannot reveal specifics other than the material being calcined is an inorganic salt.