Environmental technologies are the basis for ecological and economic pollution control in many different industrial sectors. As environmental protection is getting more and more important, emission values will be tightened. Dürr Environmental and Energy Systems has responded to this: The specialist for environmental equipment now offers selective catalytic systems for the reduction of NOx.
For Dürr, these new emission limits are relevant mainly for the design of Ecopure VAR thermal oxidizers. Especially for high-combustion temperatures of more than 1,100°C in the combustion chamber (thermal NOx), and if nitrogen is contained in the fuel (fuel NOx), selective catalytic reduction (SCR) is the only efficient method, according to the company. In both cases, NOx concentrations are high after the combustion process, and these can be reduced with SCR.
In the SCR systems used by Dürr, a reducing agent is first of all injected into the flue gas at temperatures of 260° to 390°C. Suitable substances are, depending on customers’ requirements, gaseous ammonia, ammonia water or urea. The subsequent process is the selective conversion of NOx and NH3 and/or NH2 (as the case may be) to N2 and H2O. Selective means that the nitrous oxides are reduced with first preference, whereas unintentional side reactions of other substances are largely suppressed. In case the flue gas does not have the temperature necessary for catalyst operation, it is heated up to the required temperature. A recuperator (heat exchanger) and burner are installed upstream for this purpose. The heat contained in the purified flue gas is utilized and fed back to the unpurified flue gas via the recuperator.
As NOx emissions are produced by all combustion processes, Dürr offers SCR technology for more than just its own air pollution control systems. Other combustion processes used in steam and power generation systems, or in chemical production processes, can also be equipped with Dürr's SCR technology, which is installed as a stand-alone flue gas purification stage.
Customers have the option of buying this equipment with or without controls. Especially for gas turbines with a capacity of approximately 30 MW, Dürr offers a special system that also operates efficiently at temperatures of 500° to 520°C.
For more information, please visit www.durr.com.