Manufacture of cement by intergrinding carbonaceous fuel

DETAILED DESCRIPTION We claim: 1.
A continuous method of manufacturing Portland cement clinker comprising: (1) forming an intimate mixture by intergrinding (a) unsintered Portland cement raw materials and (b) a low volatile carbonaceous fuel having a high ignition temperature, (2) passing said intimate mixture through a set of preheating cyclones wherein said intimate mixture is preheated prior to passing into a calcining zone, and (3) passing said preheated intimate mixture into said calcining zone wherein said intimate mixture (a) is maintained in a substantial fluidized condition, and (b) is heated rapidly up to a calcination temperature of from about 1000.
degree.
to about 2000.
degree.
F.
to accomplish calcination of said Portland cement raw material in said calcining zone and to accomplish the ignition of said carbonaceous fuel such that the heating in said calcining zone is effected at least in part by combustion of said carbonaceous fuel within said calcining zone, said calcination temperature being below the temperature of insipient fusion of said Portland cement raw materials to effect thermal decomposition of calcium carbonate with evolution of carbon dioxide.
2.
Method as in claim 1 wherein the calcined Portland cement raw materials are introduced from said calcining zone into an inclined rotary vessel comprising a clinkering zone wherein said Portland cement raw materials are heated at sintering temperatures generally ranging from about 2300.
degree.
to about 2900.
degree.
F.
, said sintering temperature being at or above the insipient fusion temperature of said Portland cement raw materials to effect clinkering.
3.
Method as in claim 2 wherein said set of preheating cyclones are in the form of a four-stage cyclonic preheater, and wherein said intimate mixture from said intergrinding step is passed countercurrently into a stream of hot gases emanating from said rotary kiln to the first stage, then on through the other stages of said calcining zone, and finally to said rotary kiln