Sulfur coated urea

Sulfur-Coated Fertilizers. Sulfur-coated urea technology (SCU) was developed in the 1960s and 1970s by the Tennessee Valley Authority, now called the National Fertilizer and Environmental Research Center. A commercial-scale demonstration plant (9.1 t/h) was put in operation by TVA in late 1978. Sulfur was chosen as the principle coating material because of its low cost and its value as a secondary nutrient. 

Fig. 5. Response of Kentucky bluegrass to sulfur-coated urea. Apphcation of 2 lbs N/1000 ft (9.76 g/m ). Quahty ratings of 1—3 are good, 4—6 fak.

Sulfur-coated urea is produced ki North America by a number of suppHers including ICl Canada (Courtright, Ontario), Lesco, Inc. (Martins Ferry, Ohio), PurseU Industries (Sylacauga, Alabama), and The O.M. Scott Sons Co. (Marysville, Ohio). All produce a number of fertilizer grades and particle sizes. Sulfur-coated ureas and compound (N—P—K) fertilizers also are produced by Mitsui Toatsu (Japan). 

Sulfur-coated urea (SCU) is a controlled-release material developed by TVA during the 1960s and 1970s.53 Sulfur was selected as the coating material on the basis of economy and efficiency after many coating materials were tried. Urea was selected as the material to be coated because of its high nitrogen content, low cost, and commercial availability. 

Young, R. D., TVA S Development of Sulfur-Coated Urea, TVA Bull. Y-79, Tennessee Valley Authority, Muscle Shoals, AL (1974). 

Figure 1. Flow diagram for sulfur-coated urea pilot plant...

The textural and solid-state characteristics of sulfur coatings on urea were investigated in the laboratory to identify the controlling factors. The objective was to determine how the interrelated properties of sulfur coatings affect the dissolution mechanism of sulfur-coated urea (SCU) as a controlled-release nitrogen fertilizer. The fine textural details of the sulfur coatings required that the primary investigation be done by scan-... 

Sulfur-Coated Urea from a 1-Ton-Per-Hour Pilot Plant... 

Cost estimates have indicated that sulfur-coated urea can be produced for about one-third more per unit of nitrogen than straight urea. This would be much cheaper than other controlled-release products now marketed such as urea formaldehyde or isobutylene diurea (IBDU). 

Urea. The physical characteristics of the substrate material are very important in producing any coated material, and this is especially true of sulfur-coated urea. The urea should be spherical and have a smooth surface. If the granules or prills have sharp corners, surface blips, cracks, dimples, or holes or if they are agglomerated so that the granules have a very irregular joint, they are much more difficult to coat completely and effectively with sulfur. 

The process and the related variables depend on whether the plant is producing sulfur-coated urea with or without a sealant and whether the sulfur is being applied with the pneumatic or hydraulic sulfur-spraying system. 

Pneumatic Sulfur-Spraying System. Sulfur-Coated Urea with Sealant. Figure 3 is a flow diagram of the pneumatic sulfur-spraying system. This system provides better atomization than the hydraulic system, which is discussed later. With the pneumatic system less sulfur is required, producing a higher analysis sulfur-coated urea fertilizer. 

SULFUR COATED UREA MADE USING A SEAL COATING... 

EARTH. SULFUR COATED UREA WITHOUT A SEAL COATING. 

Figure 5. Sulfur-coated urea quality using optimum production rates and operating conditions for pneumatic and hydraulic spraying systems...

Figure 6. Effect of eight vs. four spray nozzles on the total coating requirement for sulfur-coated urea at the production rate of 1 ton/hr...

Liquid wax temperature. When using the wax referred to above, the preheat temperature is 220°F. The wax tempreature does not appear critical. When applied, the wax quickly adjusts to the temperature of the sulfur-coated urea granules because their mass is 50 times greater. 

Figure 8. Effects of urea temperature in sulfur-coating drum on dissolution of sulfur-coated urea with no seal coating using the pneumatic sulfur-spraying process...

Sulfur-coating drum temperature. The sulfur-coating drum temperature should not exceed about 200°F. Best results were obtained when the exit temperature of the sulfur-coated urea was maintained at 160-185 °F. 

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