Nitric Acid

Nitric acid is a major basic chemical widely produced throughout the world. It is the basis of ammonium nitrate fertilizer production, nitrate explosive production and various other complex acid products.

Catalytic Gauzes and Systems

For almost 100 years Heraeus has been manufacturing gauzes made from platinum group metal alloys. The main use of these gauzes has been to oxidise ammonia in the nitric acid process. The gauzes are made up of fine wires which are woven or knitted together to form a metal fabric. For oxidation of ammonia, alloys containing large proportions of platinum have proven to be most useful to withstand the conditions and high temperatures (830°C +) found in nitric acid plants.

Heraeus developed catalytic systems based on varying the physical parameters and metal alloys in the various gauze layers to achieve higher performance and economy. These solutions are referred to as catalytic systems.

FTC Systems

FTC, Functional Total Control, is a concept for the catalytic oxidation of ammonia. Using computer models, a fully integrated catalytic package is designed to reduce total production costs: The cost savings are primarily achieved by reducing precious metal losses and reducing the precious metal weight of installed catalysts. FTC does away with the requirement of catchment systems to be installed in the reactor.

To accomplish this, FTC systems utilise specially developed, complex alloys which enable the total weight of precious metals required to be substantially reduced. When compared to conventional catalyst systems, cost reductions of up to 35 % per tonne of nitric acid have been achieved in numerous industrial applications. This result has been achieved without sacrificing ammonia conversion efficiency or campaign length. On the contrary, ammonia conversion efficiencies are bench marked over even extended campaigns.

The catalyst system, FTCplus, reduces the nitrous oxide emissions at source. After installation of the system, the emissions of nitrous oxide have been reduced by more than 30 % over extended campaign lengths in many industrial applications.

FTC and FTCplus consist of a number of metallic gauze layers and can be installed in virtually any reactor. No changes to the reactor itself and no additional catalyst is required in order to operate FTCplus.

Heraeus offers a number of innovative solutions based on the corrugated technology. Corrugation was originally developed for use in high pressure nitric acid plants in order to allow the installation of catchment or getter gauze technology while avoiding the problems of massive pressure drop occurring in the reactor. Heraeus has further developed this basis technology to extend its utilization into the field of catalysis as well as modifying it for application to packaged catalyst solutions.

A major leap forward is the Heraeus development of corrugated and profiling technology for medium pressure applications.

By utilizing the Heraeus MP profiling techniques, Heraeus can achieve the following advantages for operators of reactors with diameter of 2 to 7 meters:

  • 20 – 30 % reduction in specific load of nitrogen per unit area
  • Reduced volatilization of PGMs during the production cylcle
  • Considerably extended campaign durations
  • Higher ammonia conversion efficiency
  • Easy installation and removal

Each system is individually designed by Heraeus for the reactor, the production parameters and the specific campaign.

At the high temperatures present in the oxidation reactors, a significant proportion of precious metal (platinum/rhodium) is volatilised in the catalyst system and is carried off by the process gases into downstream areas of the plant. This results in a significant metal and financial loss to the plant operator. In order to reduce these gas-phase losses, systems have been developed which are referred to as catchment or getter systems. These systems are manufactured in the form of gauzes which are made up of mainly palladium metal and are installed in the reactor directly below the platinum based catalyst gauzes. These systems can typically achieve a catchment rate of over 80 percent of the volatilised platinum being lost from the catalyst gauzes. Although these catchment or getter gauzes lose palladium during operation, this occurs at a lower rate than platinum is being accumulated at, and palladium is usually significantly less expensive than platinum.

Heraeus has developed primary, secondary and tertiary catalytic solutions to reduce N2O emissions significantly. The main application field is in nitric acid plants, where large amounts of N2O, commonly referred to as laughing gas, are set free.

The greenhouse gas N20 is known to have a global warming potential 310 times higher than CO2. Annually, about 1.2 mio. tonnes of this gas are emitted by the nitric acid industry, which is equivalent to the CO2 emissions of 80 mio. passenger cars