Method for Preparation of Ammonium Nitrate Fertilizer



Method for Preparation of Ammonium Nitrate Fertilizer

Ammonium Nitrate contains about 35% nitrogen content. Production of ammonium nitrate involves the following three steps:

PRODUCTION OF AMMONIA

Ammonia is obtained from natural gas after being purified and compressed, is subjected to combustion in the presence of nickel pallets as catalyst. The gaseous mixture contains CO2, H2 and N2 of the air. The CO2 gas is absorbed in NH4OH solution to form ammonium bicarbonate.

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The remaining gases are H2 and N2. The ratio of H2 and N2 in this mixture is adjusted to 3 volumes of H2 and one volume of N2. This.mixture is compressed and sent to converter containing Fe203 as a catalyst. The catalyst is blended with chromium and cerium which act as promoters.

N2+ 3H2   →     2NH3

The reaction is carried out at a temperature of 450 C° to get maximum yield of ammonia. The gases coming out of the converter are cooled when ammonia is converted to liquid state at 33.3 C° . This liquid NH3 is separated and unreacted gases are sent back to converter.

PRODUCTION OF NITRIC ACID

Nitric acid is obtained by Oswald’s process in which oxidation of ammonia is carried out in presence of a catalyst. The most commonly used catalyst is platinum (Pt) metal blended with Rhodium (Rh) to act as promoter. Various reactions taking place in the Oswald’s process are represented as follows:

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Aqueous nitric acid and gaseous ammonia are introduced into a “Reactor” which is a cylindrical vessel made of stainless steel, with a second cylinder inside it. The annular space between the inner and the outer cylinders serves as an evaporator. The reaction is represented as:

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The heat of a reaction is used for concentrating the solution. The solution containing ammonium nitrate flows over the upper rim of the cylinder into the evaporator part. Steam is used to raise the concentration to about 98 percent, in the tank called separator. This concentrated solution is then sent to the granulator, where the molten mass forms granules, which are cooled by the air forced up through the tower by fans. The granules drop onto a conveyer belt, which takes the product to the drying and packing sections. As ammonium nitrate is hygroscopic moisture proof bags with clay coating are used for packing.

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