Prilling products

Evaporation. The evaporator is normally needed to remove water from the AN solution. It must produce a solution with the required concentration at a temperature that avoids crystallization. The acceptable water content is normally below l percent for a prilled product and up to 8 percent for the feed to some granulation processes. Evaporators in commercial use include circulatory systems, shell and tube heat exchangers, and falling film-type evaporators.103... 

Urea may be supplied as a solid or in a solution, and solid urea is classified as granular or prilled products. Prilled products have less desirable qualities than granules and are usually marginally cheaper than granulated product.109... 

A large share of ammonium nitrate is supplied to the domestic and international markets as prilled product although granulated material is preferred in many industrialized countries. The main difference is in the size and strength of the particles. The granules are usually coarser and harder than prills and are more suitable for bulk blending. For industrial use some quantities of crystalline product are produced. 

Appearance Prilled product without foreign admixtures ... 

Sodium nitrate produced by the Guggenheim method from caliche is usually a crystalline product about 48 mesh in size the product contains approximately 3.5% of free moisture. Prilled product contains about 98% sodium nitrate and 0,2%-0.3% free moisture, and the size of the product is in the range of 10-20 mesh. 

Crystallization of urea from the urea-water solution produces a relatively pure product. The biuret content is lower than that in the standard prilled product because the biuret in the urea-water solution is removed with the mother liquor in the crystallization step. Prills with low biuret content can be produced by starting with crystallized urea. 

The urea solution is evaporated in a two-stage system (99.8%) if the final product is prills, and a single-stage system (+95%) if granules are to be provided. 

The urea solution stream is then fed to the vacuum concentrator unit which operates at 17.3 kPa (130 mm Hg abs) and produces 88.7 wt % urea. It then goes to either two-stage evaporators if prills are made, or a single-stage unit for granule production. 

Urea processes provide an aqueous solution containing 70—87% urea. This solution can be used directiy for nitrogen-fertilizer suspensions or solutions such as urea—ammonium nitrate solution, which has grown ia popularity recentiy (18). Urea solution can be concentrated by evaporation or crystallization for the preparation of granular compound fertilizers and other products. Concentrated urea is sohdified ia essentially pure form as prills, granules, flakes, or crystals. SoHd urea can be shipped, stored, distributed, and used mote economically than ia solution. Furthermore, ia the soHd form, urea is more stable and biuret formation less likely. 

Prilling. The manufacture of ptiUs is rapidly decreasiag owiag to both environmental problems and product quaUty as compared to granules. 

The crystallized iodine is decanted and transferred into a fusion kettie. The melted product is contacted with strong sulfuric acid to remove organic impurities and humidity. Finally the iodine is flaked or prilled and packed. 

Three steps are essential to ammonium nitrate manufacture neutralization of nitric acid with ammonia to produce a concentrated solution evaporation to give a melt and processing by prilling or granulation to give the commercial soHd product. 

Concentration. Evaporation procedures depend on the concentration of the solution produced during neutralization and the water content required for the subsequent production of soHd product. Neutralizer solutions can contain as Httle as 2% and as much as 25% water feeds to drum granulators can contain 5% water, prill towers 0.3 to 0.5% water. 

The Osmocote product line is based on coating prilled N—P—K fertilizers. Product longevities range from 5 to 16 months, depending on the temperature. The Osmocote line also kicludes a coated N—P—K miniprill which lasts 2—3 months. 

Product diameter is small and bulk density is low in most cases, except prilling. Feed hquids must be pumpable and capable of atomization or dispersion. Attrition is usually high, requiring fines recycle or recoveiy. Given the importance of the droplet-size distribution, nozzle design and an understanding of the fluid mechanics of drop formation are critical. In addition, heat and mass-transfer rates during... 

Urea Plants - In urea plants, wet scrubbers or fabrie filters are used to control fugitive emissions from prilling towers fabric filters are used to eontrol dust emissions from bagging operations. These equipment are an integral part of the operations, to retain product. New urea plants should achieve levels of particulate matter in air emissions of less than 0.5 kg/t of product for both urea and ammonia. 

Ammonium Nitrate Plants - In ammonium nitrate plants, wet scrubbers can be considered for prill towers and the granulation plant. Particulate emissions of 0.5 kg/t of product for the prill tower and 0.25 kg/t of product for granulation should be the target. Similar loads for ammonia are appropriate. Other effluents that originate in a nitrogenous fertilizer complex include boiler blowdown, water treatment plant backwash, and cooling tower blowdown from the ammonia and nitric acid plants. 

The sulfiu can be piped long distances in liquid form or transported molten in ships, barges or rail cars. Alternatively it can be prilled or bandied as nuggets or chunks. Despite the vast bulk of liquid sulfur mined by the Frasch process it is obtained in very pure form. There is virtually no selenium, tellurium or arsenic impurity, and the product is usually 99.5-99.9% pure. ... 

The second reaction represents the decomposition of the carbamate. The reaction conditions are 200°C and 30 atmospheres. Decomposition in presence of excess ammonia limits corrosion problems and inhibits the decomposition of the carbamate to ammonia and carbon dioxide. The urea solution leaving the carbamate decomposer is expanded by heating at low pressures and ammonia recycled. The resultant solution is further concentrated to a melt, which is then prilled by passing it through special sprays in an air stream. Figure 5-3 shows the Snamprogetti process for urea production. ... 

Uses. Since 1947, 70 to 85% of the annual USA production of nitric acid has gone into the production of NH4 nitrate fertilizer, initially in the form of solid prills currently, increasing amounts have been supplied mixed with excess ammonia and/or urea as aqueous nitrogen solution for direct application to the soil. Some 15% is used in explsj (nitrates nitro compds), and about 10% is consumed by the chemical industry. As the red fuming acid or as nitrogen tetroxide, nitric acid is used extensively as the oxidizer in proplnts for rocketry. It is estimated that current USA capacity for nitric acid is in excess of 10 million tons (Refs 30, 34, 36 37)... 

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