Mono Pressure Process
Simplified process description:
In the single pressure plants, the oxidation and absorption steps take place at essentially the same pressure. The oxidation and absorption steps can be classified as:
- Low pressure (pressure below 0,1 MPa)
- Medium pressure (pressure between 0,1 and 0,6 MPa)
- High pressure (pressure between 0,6 and 1,3 MPa)
The raw material for production of nitric acid air and liquid ammonia. Filtered atmospheric air is compressed to one of above mentioned pressure levels. Liquid ammonia fed to the Nitric acid plant is vaporized and mixed with compressed air. The mixed air/ammonia gas is directed to the catalytic oxidizing reactor, which is connected with boiler for waste heat . Nitrous gases from the burner are cooled down and the energy is recovered with steam production, tail gas and process air heating.
During final cooling down weak acid is condensed, nitrous gases are recycled to the absorption tower at 0,7 MPa where they react with water to form nitric acid. The product is bleached with secondary air and cooled down before sending to battery limit. The tail gas (reduced nitrous gas) leaves to the absorption tower in temperature from 25 to 35°C with concentration NOx approximately 1000 ppmv. Tail gas is heated by hot nitrous gas on the output from the boiler. Residual content of NOx in tail gas is dissolved by selective catalytic reduction. The energy of hot tail gas is recovered by passing the expander, where it expands from operation pressure to pressure close atmospheric pressure and is then passed by the stack to the atmosphere.
Advantages:
- Proven reliability
- Low investment costs
- Low NOx tail gas content (up to 100 ppm after SCR)
