Catalyst Technology

 

Catalyst System for HF/NOx / Combined HF/NOx Abatement Systems

 

We are one of the world’s leading suppliers of combined NOx/HF abatement systems for the stainless steel industry; worldwide there are over 20 of our reduction plants in operation right now.

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 steel surface. Before being discharged into

the atmosphere this exhaust air has to be sucked off from the pickling process and purified in the ex- haust air treatment system.

Process description:
At first the acidic droplets contained in the exhaust air are removed via a demister.  Then the cold raw

gas is heated in counter flow to the hot pure gas by a heat exchanger. In order to avoid incrustations

and to eliminate the risk of corrosion the raw gas is preheated to over 70°C before entering the heat exchanger.  After passing heat exchanger the raw gas is supplied to 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 a burner. Directly after burner a 40% aqueous urea solution (or 25% ammonia solution) is injected into exhaust air flow via nozzles.  To achieve a finest spraying compressed air

is mixed.  Thus a homogenous distribution of the reducing agent in the exhaust air is ensured.  The exhaust air mixed with the reducing agent is supplied to the downstream SCR reactor filled with the SCR catalyst modules where NOx and the injected ammonia react  on the catalyst surface 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 a 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 exhaust air flow to an optimum level.   Hence

it is guaranteed that our plants meet the requirements of the regulatory authority at any time.

 

The main benefits are:
— High degrees of decomposition
— The produced reaction products (water and nitrogen) are natural constituents of the atmosphere and therefore they are harmless to the

    environment
— No waste material, because the SCR-catalysts are recyclable
— PIC-controlled; simple and user-friendly user interface because of a SCADA (Supervisory Control and Data Acquisition) system
— In order to reduce the NOx emission values even further our plants can be easily retrofitted and upgraded