The importance of critical relative humidity—temperature relationship on design of rotary dryers for fertilizers

Fertilizer salts are sensitive to the humidity of the surrounding air; above certain relative humidities, they will absorb water. The humidity above which they absorb water is defined as critical relative humidity (CRH). The CRH decreases with increasing temperature.Fertilizer drying usually takes place at relatively high temperatures to facilitate heat exchange. The optimum drying effect is obtained only when the CRH of the product is sufficiently greater than the actual relative humidity (RH) of the air. A method that takes into account both the heat exchange and the CRH of the material has been developed for designing rotary dryers for fertilizers. A computer program is available that supports this design procedure.