Fertilizers bulk blends

Fig. 24.19. Typical batch-type NPK fertilizer bulk-blending plant. (Source Fertilizer Manual.)...

To minimize the cost of the product, raw materials can be purchased on the world markets without specific requirements on particle size, shape and mass. Fines which are off-specification for, for example, fertilizer bulk blending can be used and are often even preferred. 

Fig. 6.6-25 Flow diagram of a plant combining fertilizer bulk blending (2-7) and compaction/ granulation (8-27). 1, front-end loader input of components 2, 8, 18, bucket elevators 3, distributor 4, silos for components 5, compounding scale 6, blender 7, bulk blend receiving hopper (courtesy Sackett, Baltimore, USA). 9, mill for feed homogenization 10, feed bin 11, 27, screw conveyors 12, belt mixer 13, metal separators 14, 25,...

Based on the IFDC surveys, it is estimated that dry mixed compound fertilizers (bulk blends) account for an additional 40-50 million tonnes of product annually to bring the total production of all types of compound fertilizers to about 100 million tonnes annually (Figure 16.1). 

Figure 16.8. Typical Batch-Type NPK Fertilizer Bulk-Blending Plant. 

Hoffmeister, G. 1973. Quality Control in a Bulk-Blending Plant, IN TVA Fertilizer Bulk-Blending Conference, pp. 59-70, Bull. Y-62, TVA, Muscle Shoals, AL, U.S.A. 

Granular TSP (—6 + 16 mesh (1.19 to 3.35 mm dia)) is preferred for direct appHcation and is used in bulk blend fertilizers. A widely used slurry granulation process, the Dorr-OHver process, is illustrated in Figure 11. The ground rock is mixed with 38—49% P2 5 series of reaction vessels. 

Since about 1968, triple superphosphate has been far outdistanced by diammonium phosphate as the principal phosphate fertilizer, both in the United States and worldwide. However, production of triple superphosphate is expected to persist at a moderate level for two reasons (/) at the location of a phosphoric acid—diammonium phosphate complex, production of triple superphosphate is a convenient way of using sludge acid that is too impure for diammonium phosphate production and (2) the absence of nitrogen in triple superphosphate makes it the preferred source of phosphoms for the no-nitrogen bulk-blend fertilizers that frequendy are prescribed for leguminous crops such as soy beans, alfalfa, and clover. 

When 20% of the phosphoms was polyphosphate, the compounds ia the product were ia the ratio of 3.5 mole MAP per mole of the pyrophosphate. The principal use of the material was ia the production of suspension fertilizers. In this appHcation the polyphosphate content imparted improved storage properties to the suspensions. The granular soHd APP, however, also had excellent storage properties and was a good material for use ia bulk blends and for direct appHcation. 

Fig. 20. U.S. market share for several types of mixed fertilizer, where (—) represents bulk blends (-) ammoniation—granulation and ( ) fluids.

Table 12. Fertilizer Materials Used in Bulk Blends...

O. Miserque and E. Pirard. Segregation of the bulk blend fertilizers. Chemom. Intell. Lab. Syst., 74, 215-224 (2004). 

Mixed solid fertilizers can be made by either direct granulation methods (40%) or bulk blending (40%). Bulk blending is made by mechanical mixing of the separate granular intermediate materials. It is usually done in small plants near the point of use. This technique is employed because the fertilizer can be tailor-made to fit the exact requirements of the user. Fluid or liquid fertilizers (clear, suspension, and slurry) account for 20% of all NPK mixed fertilizers. 

In 2002/03 about 57 million mt of bulk-blended fertilizers was produced. This corresponded to about 16 percent of the global fertilizer production. 

The simplicity of the bulk-blending procedure is illustrated in Fig. 24.19. The operations consist of (1) in-shipment of granular fertilizer materials, (2) temporary storage, (3) proportioning, (4) blending, and (5) movement of the finished blend to the field for spreading. 

Mention was made earlier of the significant quantity of nitrogen applied to farmlands in the form of urea-ammonium nitrate solution and aqua ammonia. Since the late 1950s, there has also been a growing practice of applying mixed fertilizers (NP and NPK) in fluid form. In fact, the growth of the fluids market paralleled bulk-blended products. In 2002/03 about 25 million mt of fluids was produced and corresponded to 7 percent of the world production. North America, and Europe are major markets for fluids. Fluids are also used in high-value crops in some countries of the Middle East and Latin America. 

Young, R. D., Providing Micronutrients in Bulk-Blended, Granular, Liquid and Suspension Fertilizer, Comm. Fert., 118(1), 21-24 (Jan. 1969). 

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