Method for Producing Cement

#The present invention relates to a method for producing cement, in particular a method of producing calcium sulfoaluminate cement.

#The compound 4CaO.3Al2O3.SO3, also known as Kline's compound and Ye'elemite, and abbreviated “C4A3$”, is well known and has been used as the basis for forming expansive cements for a number of years.

#C4A3$ is readily formed by calcination (heating) of appropriate amounts of CaO, (or equivalent CaCO3) , Al2O3 (or hydrates of alumina) and calcium sulphate (or its dihydrate, gypsum, or hemihydrate), typically at temperatures in the range 1000° C.-1200° C. With careful attention to the granulometry and mixing of the reactants, high yields, >90% of theoretical of C4A3$, can be obtained by heating in 0.5-2 hours at 1300° C.

#The present invention will now be described in detail with reference to the accompanying drawing, in which:

#FIG. 1 is a flow-diagram illustrating the method of the present invention.

#Thus, as illustrated by FIG. 1, in the present invention, thermal energy is provided by combustion of sulphur, preferably elemental sulphur. In preferred embodiments, the sulphur oxides produced by combustion of the sulphur are reacted in a suspension or cyclone pre-heater with a mixture of calcium oxide and/or carbonate, and alumina and/or its hydrates, to provide a source of sulphur for the calcium sulfoaluminate cement. This may occur, for example, at a temperature from 750-900° C. This enriches the reactants with sulphur, so that the resulting clinker preferably contains 8-10 wt % sulphur (as SO3 in calcium sulfoaluminate/Kline's compound).

#In addition to the sulphur oxides generated by combustion of sulphur as described above, sulphur may optionally be added directly to the other reagents, for example by injection into the rotary kiln during calcination (see below), or injection through multiple entry points.

#The enriched solid feed is then calcined, for example in a rotary kiln or other suitable calcination apparatus, such as a fluid bed, to form clinker. Calcination may occur at a temperature of 1000-1200° C. or higher, for example 1300° C., and may take place over a period of for example 30 minutes to 2 hours. Alternatively, flash calcination may be used, in which the solid feed is calcined at a higher temperature, for example, of 1250 to 1350° C., for a period of tens of seconds, for example 30 seconds to a minute.