1971 Blouin Sulfurcoated fertilizers for controlled release – pilot plant production
The continuous sulfur coating of urea to produce controlled-release fertilizer was studied by TVA in a 300-lb-per-hr pilot plant. Molten sulfur and a molten wax sealant (containing coal tar microbicide to prevent degradation in soil) were sprayed in successive layers on to a rolling bed of heated fertilizer. The waxed material was cooled and dusted with conditioner to obtain a free-flowing product. A typical coated product contained 17% sulfur, 3% wax, 0.2% coal tar, and 1.8% conditioner. The substrate dissolution rate in water at 100°F was 15% in 1 week and 0.5% per day during the second week. The operating conditions that represent departures from previously reported batch laboratory work were: continuous operation; use of several spray nozzles rather than one; and higher atomizing air pressure in the sulfur spray nozzles. Estimated costs should permit use on long-term crops in some areas.