EFFECT OF HUMIDITY ON NPK FERTILIZER DRYING

The drying process within rotary coolers during the manufacture of gra nular NPK fertilizer plays an important role in the production of fert ilizer granules possessing both a low moisture content and low caking propensity. A theory for fertilizer drying has been developed which ta kes into account the low critical relative humidity of complex fertili zer found at high temperature. The theory proposes that the gradient b etween the partial vapour pressure of moisture in the air and the vapo ur pressure moisture adjacent to the surface of the fertilizer granule , is the rate controlling stage in the drying of hot granular fertiliz er rather than the internal diffusion of moisture within the particle.