Catalytic Emission Control for Nitric Acid Plants

The chemical industry needs nitric acid (HNO3) as a base material for fertilisers, medicines, colorants, special fuels and many other products.

The process of manufacturing nitric acid involves the oxidisation of ammonia (NH3), the problem being that the undesirable substances nitrogen oxide (NOX) and laughing gas (N2O) are emitted into the atmosphere.

Due to its high reactivity, nitrogen oxides are considered one of the main causes of acid rain. In view of the strict limits prevailing in many countries, catalytic reduction is now a standard process.

Some countries do not recognise laughing gas (N20) as an air pollution problem. However, many scientists worldwide consider it an absolute killer”, its negative impact on the greenhouse effect being about 300 times stronger than that of carbon dioxide.

In the wake of the Kyoto Protocol, which identifies laughing gas as a greenhouse gas, emission limits for laughing gas were first introduced in Germany followed by many other countries. For manufacturers of nitric acid, who have since been under great pressure, Süd-Chemie has developed special catalysts that are used by its partners to reduce laughing gas and nitrogen oxide in their plants.

Problem solver No. 1 – EnviCat® HNO3
Non-Selective Catalytic Reduction (NSCR)

At tail-gas temperatures of more than 400º C, direct disintegration offers a most effective method of reducing both NOX and laughing gas, whereby the catalysts must normally be positioned extremely close to the reactor.

The NSCR method functions in a similar way to a threeway catalytic converter in that reduction takes place while other undesirable emission content is being oxidised.

NOX and N2O react with residual hydrocarbons which must still be present in the tail gas. The level of hydrocarbons must therefore be constantly checked to ensure efficient functioning of the reduction process – if it is too low, methane or hydrogen must be added.

EnviCat® HNO3

Problem solver No. 2 – EnviCat® N2O and EnviCat® NOX
Selective Catalytic Reduction (SCR)

In the case of nitric acid plants with tail-gas temperatures below 400º C, selective reduction is efficient and cost-effective. It can however also be used for emission exceeding 400º C if hydrocarbons are added.

The innovative EnviNOx® technology developed by Süd-Chemie in co-operation with the plant engineering company UHDE, a Thyssen-Krupp subsidiary, is based on a vanadium-free catalyst containing special iron zeolites.

EnviCat® N2O

Using ammonia as a reducing agent, this process converts laughing gas and NOX into the atmospheric elements of nitrogen and oxygen, as well as water.

At the same time, the catalyst removes the ammonia originally added, achieving conversion rates of >98% over a wide temperature range. In this way, ammonia leakage is effectively prevented.

Brochure: Catalytic Emission Control for Nitric Acid Plants (pdf)

Questions? Please contact us!