2.B.2 - Nitric Acid Production

During the production of nitric acid (HNO₃), nitrogen oxide is produced unintentionally in a secondary reaction during the catalytic oxidation of ammonia (NH₃). HNO₃ production occurs in two process stages:

• Oxidation of NH₃ to NO and
• Conversion of NO to NO₂ and absorption in H₂O.

Details of the process are outlined below:

Catalytic oxidation of ammonia

A mixture of ammonia and air at a ratio of 1:9 is oxidised, in the presence of a platinum catalyst alloyed with rhodium and/or palladium, at a temperature of between 800 and 950 °C. The reaction according to the Oswald process is as follows:

4 NH₃ + 5 O₂ –> 4 NO + 6 H₂O

Simultaneously, nitrogen, nitrous oxide and water are formed by the following undesired secondary reactions:

4 NH₃ + 3 O₂ –> 2 N₂ + 6 H₂O

4 NH₃ + 4 O₂ –> 2 N₂O + 6 H₂O

All three oxidation reactions are exothermic. Heat may be recovered to produce steam for the process and for export to other plants and/or to preheat the residual gas. The reaction water is condensed in a cooling condenser, during the cooling of the reaction gases, and is then conveyed into the absorption column.

In Germany, there are currently nine nitric acid plants.

As this source category is a key category for N₂O, plant specific activity data is collected here according to the IPCC guidelines.

This data is made available basically via a co-operation agreement with the nitric acid producers and the IVA (Industrieverband Agrar). As the data provided by the producers has to be treated as confidential, it is anonymised by the IVA before submitting it to the UBA. However, one producer is delivering its data directly to the UBA. After checking this specific data, it is merged with that provided by the IVA.

According to the IVA, catalytic reduction is used as an abatement method in some of the plants.

Different T2 default NO_x emission factors based on different technology types and abatement systems are used from the EEA Emission Inventory Guidebook 2019 (EF for medium and high pressure processes and for catalytic reduction of low, medium and high pressure process)¹⁾. The applied emissions factors are listed in Table 1.

Table 1: Tier 2 emission factor of NOx for source category 2.B.2 Nitric acid production

With emission factors revised for each plant, recalculations of NOx have been carried out compared to last year's submission. So far a T1 method with a T1 Default EF was used. With the sabmissionsubmission 2022 a T2 method is applied with T2 EFs. The total emissions from 1990 to 2019 for the latest two submissions and their difference are listed in Table 2.

Table 2: NOx emissions from nitric acid production

No category-specific improvements are planned.