Question

Why there are two compressors in Ostwald process of preparation of HNO_​​​3 ? State the use of each.

Answer 1

Air Compressor and Turbine:
Air from atmosphere is suck at ambient temperature (room temperature) into the compressor. The compression is done in three stage driven by electric motor and turbine which is in turn run by tail gases .The air first passes through 1st stage at room temperature and leaves at temperature of 130°C and pressure of 2.02kg/cm2.This is then cooled in the inter cooler to 55°C by using raw water as cooling medium. Then air enter the second stage where it is compressed to 3.5kg/cm2 and temperature of 118°C and after the second stage is cooled to 70°C in the inter cooler then it enters the third stage where it is compressed to 4.5kg/cm2 abs and outlet temperature of 143°C. 40% of the energy required for carrying out compression operation is supplied by tail gas turbine. These tail gases are generally taken from absorption tower which leave at 19°C.it is heated up to 260°C by the series of heat exchangers. Major amount of air which is called as a primary air is sent to Air-heater.
Secondary Air Compressor-1, 2:
The secondary air which is supplied by secondary air compressor-1, 2 used is in the bleaching tower