In the dual-pressure process, nitric acid is produced through high-temperature oxidation of ammonia in a platinum catalyst chamber at approx. 600 °C under low-pressure. The oxidized product then passes through the heat exchanger to recover the majority of the heat and reduce the temperature of the nitric oxide to around 150 °C. After cooling, a secondary oxidation of the process gas is carried out in a low-pressure condenser that combines NO, NO2 and O2 with water to create a dilute form of HNO3.
A proportion of the energy created in the course of the process is recovered and used to heat the tail gas. In a next step, low-pressure process gas enters a NOx gas compressor, then fed into a high pressure cooler-condenser and absorption tower for recycling to produce HNO3 of almost 68wt%. In the final step, HNO3 steam is passed over concentrated H2SO4 to produce concentrated HNO3.