Selective catalytic reduction (SCR) is the most effective DeNOx process. Nitrous oxides (NOx) are converted into nitrogen and water vapour at a catalytic surface, with ammonia water or urea used as a reducing agent.
Using a catalytic converter allows the reduction of nitrous oxides at significantly lower temperatures and is considerably faster than the SNCR process. DeNOx rates of more than 90% can be achieved. Other advantages of the process are low consumption of ammonia water (almost stoichiometric) and low ammonia slip. If the catalytic surface is sufficiently large, part of the dioxins and furans are destroyed at the same time.
The SCR process is flexible in terms of operating temperature and can be deployed at various points along the flue gas treatment process chain. On this basis, a distinction is made between the following approaches:
Raw gas catalytic converter:
At the boiler outlet, with upstream electrostatic precipitator
Operating temperature approx. 260-300°C
Clean gas catalytic converter:
After prior dust and SO2-separation
Operating temperature approx. 240-250°C
Low temperature catalytic converter:
After prior dust and SO2-separation
Operating temperature approx. 180-190 °C
Periodic regeneration at approx. 320°C required
The main advantages of the SCR process:
Achieves very high removal of nitrous oxides
Low consumption of ammonia water (almost stoichiometric) and low ammonia slip
Simultaneous removal of nitrous oxides (NOx) and dioxins/furans
Optimum integration in the overall flue gas treatment system thanks to availability of different approaches (raw gas, clean gas and low temperature catalytic converter)
Reliably achieves the low BREF emission levels for nitrogen oxides (NOx)
:quality(80))
:quality(80))