Nitric acid majorly produced in the countries of USA, USSR, West Germany, France, and Italy. Due to its use in manufacturing of nitrogen fertilizer like ammonium nitrate, potassium nitrate and nitro phosphate its demand increased year to year and so 55 to 65 % is consumed by fertilizer industries from its overall annual production.
Nitric acid process facilities are modified from time to time to produce it in larger capacity and less cost. There are about 15 chemical processes that can be used for producing nitric acid which are chosen from many based on optimization. Based on Le Chatelier’s Principle a reaction can be governed and controlled by temperature, pressure and flow rates to shift the equilibrium conversion in forward direction. Each method obtained from the research done on chemical kinetics and types of catalyst used. Ammonia is used has raw material for many processes.
A typical process can be briefed in three steps:
- Ammonia is converted into nitric oxide in the presence of platinum alloy by oxidation. 4NH3 +5O2 → 4NO + 6H20 +216.7 Kcal/mole
- Nitric oxide is oxidized to dinitrogen tertroxide. 2NO + O2→ N2O4
- Finally nitric acid is formed by absorption process where dinitogen tertroxide absorption takes place by water. 3N2O4 + 2H2O → 4HNO3 + 2NO2
Types of commercial process are described with their distinct features for conducting the above process steps:
Bamag (monopressure) Method: Approximate operating pressure for the above three steps are maintained at any 1,4or 8 atmosphere absolute. This process produce nitric acid with the concentration between 55 to 70, it has a feature of using a plate tower constructed with water coils with the plates for cooling.
Bamag (combustion) process: It is same as above process but it required platinum as catalyst about 45 mg per ton of nitric acid, this is an upgrade to mono pressure process.
Chemico Method: This process operates at pressure about 8 to 9 atmospheres absolute, producing with concentration 55 to 65 percent of nitric acid. It is designed to use steam turbine at 510 degree centigrade and a plus expander which is a unique feature of this process.
C and I Method: It is designed with operating pressure of 8 atm, and produces about 55 to 67 concentration HNO3; it has developed a cascade cooling system for the process of oxidation, absorption.
Grand Paroisse Method: The section of combustion, oxidation and absorption operate at pressures 3 to 4, 7 to 8 and the same respectively. HNO3 is produced with concentration ranging from 56 to 70 percent. It unique feature lies in the cooling system that is an external cooling system is applied for oxidation tower and internal cooling for absorption tower along with turbo compressor facility.