Granulation of fertilizers

Granulation in Coalescence Mode 1. Solution-Phase Theory 

Therefore, the weight of liquid per unit weight of solids is 

Actual measurements of the liquid content have shown that the larger granules have more liquid associated with them than the average and the smaller granules have less, in agreement with Eq. (98). Assuming that S and g are independent of pellet size, the liquid content may be related to the pellet size distribution in the following manner (B9)  

A comparison of the measured mean relative size with the model in Eq. (101) is shown in Fig. 28. The material was monosize glass beads. The data fit the model quite well, with the exception of fine 0.038-mm powder. It is evident that the steady-state size distribution is a function of the liquid content, and consequently, as shown by Sherrington (S9), there is an optimal granulating liquid for maximum granulation efficiency, that is, percentage of the product-grade material. 

The liquid-phase requirement for the snowballing mechanism may be computed in the following manner (S10). It is assumed that the liquid withdrawal is negligible (i.e., g = 0) and the fractional saturation in the deposited 

Shortly after postulating the need for fertilization of plants with the basic nutrients nitrogen (N), phosphorus (P), and potassium (K) by Justus von Liebig, it was determined that, if solid fertilizer materials are applied, the availability of these elements depends to a large extent on solubility. In most cases a high solubility is desired requiring large surface area which is synonymous with small particle size. It was also found that, additionally, micronutrients are necessary and, because of the small amount of these trace elements in a fertilizer formulation, they had to be added as fine powders. 

Such powder systems exhibit a number of problems, i.e.  

Uniform mixing of the components is difficult and time consuming. 

Segregation of components occurs due to differences in particle size and/or density. 

Danger of caking exists during storage and transportation. 

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Reduced caldng and lump formation, as in granulation of fertilizer. 

Tai Van Ha of the Nebraska State Agriculture Laboratory inspects a sample of fertilizer that is obviously not homogeneous. There are various light- and dark-colored granules of fertilizer in the bag. 

Figure 12.12. Paddle blending granulator and typical performance, (a) Sketch of a double paddle trough granulator (Sherrington and Oliver, 1984). (b) Performance in granulation of fertilizers (Feeco International).

Factors affecting granulation of fertilizer mixtures. Ind. Eng. Chem., 30 668-672. 

Prevention of caking and lump briquets granulation of fertilizers... 

Space and energy requirements as well as investment costs are frequently factors that render an otherwise perfectly feasible and desirable process uneconomical and kill a project. Sometimes they also incorrectly direct the interest toward methods which, after superficial investigation, seem to offer cheaper alternatives. In this context it should be stressed that the entire process must always be considered. For example, for the granulation of fertilizers a granulation drum may seem to be the cheaper solution in comparison with a roller compactor if only investment costs are considered this may even be true if the entire system is investigated. However, if space requirements and energy (operating) costs are compared, a different conclusion may be obtained (see Section 5.4.4). 

Large scale applications were developed in the fertilizer industry during the first half of this century, While early research of the US Department of Agriculture (USDA) on the granulation of fertilizers, which started in 1922, aroused some interest among fertilizer manufacturers, little commercial adoption took place until the 1950s. 

The fust documented development of fertilizer granulation in suspended solids agglomerators was in the early 1960s using the spouted bed technique, and in 1970 Fisons Fertilizer Ltd, UK, introduced prilling , the granulation of fertilizers from a melt by solidification of droplets in a vertical cooling chamber. 

The selection criteria for the roller presses and peripheral equipment were discussed in Section 4.2.2.4.7. Some specific remarks relating to granulation of fertilizers will be made in the following. 

A number of important reasons exist for the decision to adopt compaction with roller presses for the granulation of fertilizers. 

J. J. Schultz and T. P. Hignett, Granulation of fertilizers History, current practices, and future trends , in Agglomeration 85 (ed. C. E. Capes), Proceedings of Fourth International Symposium on Agglomeration, Toronto, Canada. The Iron and Steel Society, Inc., Warrendale, Pa., USA, 1985, pp. 339-55. 

W. Pietsch and C. Rodriguez, Granulation of fertilizers by compaction , in Proceedings of Twentieth Biennial Conference, IBA, 1987, pp. 113-26. 

R. Zisselmar, Compaction/granulation of fertilizers , in Proceedings of International Workshop, IFDC Special Publication SP-9, Madras, India, 1988, pp.46-56. 

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