Separation of alkali-rich dust from cement kilns

Claim 2

The method according to claim 1 which includes recovering the solids formed in the second zone, separating from at least a part of said solids a fraction having a particle size of less than from about 5 to about 15 microns, and recycling at least a portion of the remainder fraction to said first zone.

Claim 3

A plant for making cement clinker comprising a rotary kiln for burning cement raw materials thereby producing an exhaust gas containing alkalies vaporized from the raw materials, gas discharge means for discharging gas into the atmosphere means for contacting said exhaust gas with raw materials being fed to said kiln to heat said materials and to cool the exhaust gas to a temperature sufficiently low to cause solidification of the vaporized alkalies therein, two groups of means for separating solidified alkalies from said gas interposed between said contacting means and said gas discharge means, means for conveying said gas successively through said separating means, means for fractionating the solids separated from said gas in the first group of separating means into two fractions one of which has a particle size less than from about 5 to about 15 microns, means for recycling at least a portion of the other fraction to the kiln, and said gas discharge means being operatively constructed and arranged fro discharging said gas into the atmosphere from said second group of separating means, and said two groups of means for separating solidified alkalies from said gas being operatively constructed and arranged for effecting the separation of solidified alkalies and entrained solids from said gas in said two groups of means without passing the cooled gas through a layer of the raw materials being fed to said rotary kiln.