Ammonium nitrate production granulation

In pressure-neutralized processes, the neutralizer usually operates at 4-5 atm and 175°-180°C. Nitric acid is fed to the neutralizer at a usual concentration range of 50%-60%. In some cases it may be preheated with byproduct steam. Ammonia is fed to the neutralizer in gaseous form. If it is available in liquid form, it is vaporized in a heat exchanger by steam or air. If. air is used the cooled air may be used to cool the prilled or granulated ammonium nitrate product. The neutralizer may be operated at a low pH (3-4) to avoid ammonia loss, and more ammonia may be added later to adjust the pH to 7. The concentration of the solution from the neutralizer is usuaDy in the range of 80%-87% ammonium nitrate. It is evaporated further by using steam from the neutralizer to a concentration of 94%-98%. In many plants, a final evaporator-concentrator is used to increase the solution concentration to 99.5%-99.8%. 

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. 

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

Pan granulation of ammonium nitrate also has been developed commercially (16,17). Essentially water-free melt (<0.5%moisture) is sprayed onto a cascading bed of fines (usually cmshed recycle) ia a tilted, rotatiag pan. Production of 18—20 t/h is common. Product made ia this manner is said to require ao conditioning. The pan is an excellent size classifier, making it easy to produce granules of any desired size from 1 to 11 mm diameter. 

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. 

Many plants outside of North America pfill or granulate a mixture of ammonium nitrate and calcium carbonate. Production of this mixture, often called calcium ammonium nitrate, essentially removes any explosion hazard. In many cases calcium nitrate recovered from acidulation of phosphate rock (see Phosphoric acid and the phosphates) is reacted with ammonia and carbon dioxide to give a calcium carbonate—ammonium nitrate mixture containing 21 to 26% nitrogen (23). 

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 reaction is carried out in aqueous phase using a slight excess of nitric acid. The heat of reaction is utilized to evaporate the water. Also, evaporation may be carried out under vacuum. Alternatively, solid ammonium nitrate is obtained by crystallization from a concentrated solution. The particle size of the dry product may be controlled by vacuum crystallization, granulation or... 

The resulting AN solution may be handled in various ways103. It can be stored as a solution, used in down-stream plants or sold as a solution it can be formed into solid AN by prilling or granulation, or it can be mixed with a solid filler. The most common filler is calcium carbonate in the form of ground limestone, dolomite or by-product calcium carbonate. This product is known as Calcium Ammonium Nitrate (CAN) and can be prilled or granulated. Granular products that contain AN and either ammonium or calcium sulphate are also manufactured. 

One process modification that overcomes these difficulties uses only nitric acid for acidulation the extraction slurry is cooled to crystallize calcium nitrate, which then is removed by centrifugation. This process is referred to as the Odda process. The calcium nitrate byproduct is either sold as a fertilizer or converted to co-product ammonium nitrate. The extraction slurry, with its lowered calcium content, then is ammoniated and granulated. 

The manufacture of ammonium phosphates can be combined with the production of mixed fertilizers e.g. ammonium phosphate with ammonium sulfate (partial substitution of sulfuric acid with phosphoric acid) or ammonium nitrate. The ammonium phosphates can also be converted into mixed fertilizers during granulation by adding potassium salts, urea etc. 

FIGURE 11.9 Ammonium nitrate by the Stengel process. Intermediate evaporation before prilling or granulation would be employed for the production of a high-density product. 

In 1926 a branch of IG Farbenindustrie, the predecessor company of BASF in Germany, introduced Nitrophoska , which, according to aUSDA circular, differed from ordinary salt mixtures in that it had been subjected to a graining treatment in the process of mixing .Production started in 1927 and from 1927 to 1933 the process involved granulating a slurry of diammonium phosphate and ammonium nitrate in pug mills with additional potash salts. 

N. A. Shakova et al., Production of granulated complex fertilizers from ammonium nitrate , Soviet Ghent. Ind., 5 (9), 586-9 (1973) Investigation of the granulation of ammonium nitrate in a fluidized bed under industrial conditions , Int. Ghent. Engng., 13 (10), 658-61 (1973). 

Fig. 6.6-36 Flow diagram of a plant for the production of fertilizer grade granulated ammonium nitrate (courtesy Kaltenbach-Thuring, Beauvais, France)...

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