Fertilizer granulation

Essentially all the ammonium sulfate fertilizer used in the United States is by-product material. By-product from the acid scmbbing of coke oven gas is one source. A larger source is as by-product ammonium sulfate solution from the production of caprolactam (qv) and acrylonitrile, (qv) which are synthetic fiber intermediates. A third but lesser source is from the ammoniation of spent sulfuric acid from other processes. In the recovery of by-product crystals from each of these sources, the crystallization usually is carried out in steam-heated sa turator—crystallizers. Characteristically, crystallizer product is of a particle size about 90% finer than 16 mesh (ca 1 mm dia), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable, however, as a feed material to mixed fertilizer granulation plants, and this is the main fertilizer outlet for by-product ammonium sulfate. 

Fig. 5. Double-shaft mixer used in fertilizer granulation. Courtesy of Reimeburg Division of Heyl Patterson.

Significant changes in the moisture content in the drum due to recycle fluctuations (recycle of diy granules in fertilizer granulation) [Zhang et al., Control of Pai ticulate Processes TV (1995)]. 

Han (H3) and Han and Wilenitz (H4) have also presented steady-state models of fertilizer granulators based on population balance on the granules in the process loop operating in the snowballing mode. From the viewpoint of process control some interesting interrelationships between various recycle ratios, crusher speed, crusher product size, and the granule growth rate have been established. 

Sherrington P. J. The Chemical Engineer No. 220 (1968) CE201. The granulation of sand as an aid to understanding fertilizer granulation. 

Usually crystallizer product has a particle size that is about 90% finer than 16 mesh (about 1 mm in diameter), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable for use as a feed material to mixed fertilizer granulation plants, which is the main outlet for by-product ammonium sulfate244. 

Hardesty and Ross made careful studies of the pressure to which fertilizer granules could be subjected without degradation. They described a simple device for determining the force necessary to crush individual particles consisting of a rack and pinion similar to that used in adjusting the elevation of a microscope. Below the rack, and resting on a sensitive scale or balance, is a small anvil. The particle is placed on a container in the anvil directly below the rack, the latter being turned down so as to rest on the particle. The pinion is turned until the particle breaks, at which time the maximum deflection of the scale pointer is observed. In this type of experiment it is important that the particles... 

Up to 100 tons/hr for iron ore balls 200 tons/hr or more for sinter preparation 50 tons/hr for fertilizer granulation. 

Equation (20) and the deviation of the index n from the uniform-bonding value of 2 have been used to interpret compressive strength data for wet and dry iron ore balls [55] and for fertilizer granules [56]. 

These machines are widely used in fertilizer granulation and iron ore balling and consist of an inclined rotary cylinder powered by a fixed- or variable-speed drive. Agglomeration occurs when the feed contains an optimal amount of liquid phase and is subjected to the rolling, tumbling action of the... 

Feed material, consisting of fresh and recycled particles, may be introduced by a belt conveyor, a chute, pipe or similar devices. Liquid phase may be introduced either before or immediately after the solids enter the cylinder. In iron ore balling, premoistened wet filter cake usually constitutes the feed but water sprays may also be located inside the drum for moisture addition to aid balling control. Although water is the usual wetting agent, various solutions and slurries may be used in mixed fertilizer granulation. These may... 

Characteristics of some fertilizer granulation drums. (Courtesy The A.J. Sackett and Sons Co.)... 

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