Combined HF / NOx
Abatement Systems in the stainless steel industry

Steuler Anlagenbau GmbH & Co. KG has successfully designed, manufactured, erected and commissioned over 20 combined NOx/HF abatement systems worldwide in the stainless steel industry.

The exhaust air containing NOx and HF is generated during the treatment of stainless steel surfaces by using a mixed acid solution (composed of hydrofluoric acid and nitric acid) in order to remove the scale and any impurities such as grease/ lubricants from the steel surface.

The exhaust air from the pickling process is sucked off and purified in the exhaust air treatment system before being discharged into the atmosphere.

At first the acidic droplets contained in the exhaust air are removed via demister.
Then the cold raw gas is heated in counter flow to the hot pure gas via heat exchanger. In order to avoid incrustations and to eliminate the risk of corrosion the raw gas is being preheated to over 70°C before entering the heat exchanger.
After passing the heat exchanger the raw gas is supplied to the HF dry sorption system. This HF reactor is equipped with several layers of honeycomb lime modules featuring a low pressure loss. The Ca(OH)2 modules react with the hydrofluoric acid contained in the exhaust air and calcium fluoride (CaF2) is produced as end product.
The partly purified exhaust air is heated to the operating temperature required for the SCR process by means of burner. Directly after the burner a 40% aqueous urea solution (or 25% ammonia solution) is injected into the exhaust air flow via nozzles. To achieve a finest spraying compressed air is mixed thus ensuring a homogenous distribution of the reducing agent in the exhaust air.

The exhaust air mixed with the reducing agent is supplied to the downstream SCR reactor filled with the SCR catalyst modules where the NOx and the injected ammonia react on the catalyst surface thus reducing the NOx to harmless nitrogen and water.

These generated reaction products can be discharged into the atmosphere via stack.

NOx Sampling and Monitoring System

After passing the SCR catalyst an exhaust air sample is taken and supplied to the NOx analyzer which determines the residual content of NOx.

The fully automated process uses the analyzer output to adjust the rate of ammonia/urea injected into the exhaust air flow to an optimum level thus controlling the NOx in order to meet the requirements of the regulatory authority.

Steuler is recognized as one of the world's leading supplier of combined SCR/HF abatement systems being used in the stainless steel industry. Steuler is specialized in the field of catalyst technology for removal of other pollutants such as dioxins, furans, CHx, CO, volatile organic compounds (VOC) and solids as well as acid scrubbing systems for removal of SOx, HF and HCl.