Granulation of urea phosphate from urea and merchant-grade phosphoric

Abstract

A process for direct granulation of unpurified urea phosphate from urea and merchant- or filter-grade wet-process phosphoric acid to produce a product with exceptional satisfactory physical and chemical properties for direct application to the soil or for use in production of fluid fertilizers. The process involves the utilization of sweep air in both the reactor and the granulator to remove water from the heat-sensitive urea phosphate mixture to enhance the granulation characteristics of the product. Product drying with applied heat after granulation is essentially eliminated. Moisture content of the urea phosphate is reduced to an acceptable level (about 1.0 percent) in the granulator; however, the granules are somewhat sticky. It has been found, however, that the resulting urea phosphate with about 1.0 percent moisture is less sensitive to heat than high (4 to 6 percent) moisture product. Consequently, heated air (up to about 200.degree. F.) may be applied downstream from the granulator and into the dryer chiefly for control of relative humidity of ambient air introduced therein to less than 40 percent, thereby resulting in still further water removal and curing to effect a very dry and free-flowing product. This alternative is a viable expedient in geographic areas wherein the relative humidity of ambient air is normally in the range of about 50 percent and 80 percent.