Dual Pressure Process

Simplified process description:

Ammonia oxidation occurs at low pressure while high pressure improve absorption of the nitrous gases and process of an acid formation. Liquid ammonia imported to the Nitric acid plant is evaporated and mixed with air before oxidation in the burner at low pressure about 0,4 MPa. Maximum energy is recovered by steam generation and cooling of nitrous gases via cross exchange with tail gas. After further cooling of the low pressure nitrous gases with simultaneous weak acid condensation gases are compressed to above 1,1 MPa in the NOx compressor. The high pressure nitrous gases are then cooled by cross exchange with tail gas and further weak acid condensation before entering the absorption tower where they react with water to form nitric acid. The product acid is bleached with secondary air and cooled down before sending to battery limit. The tail gas from the absorption tower is heated in the tail gas heater and than mixed with ammonia and introduced to the selective catalytic reactor (SCR) for reduction of  N20 content. Nitric acid from absorber is stripped by hot air and cooled before dispatch to the store.

Advantages: 

• Proven reliability
• Low investment costs
• High ammonia conversion efficiency
• High heat recovery
• Low NOx tail gas content (up to 50 ppm after SCR)