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Show stringent, and a number of approaches have been applied to reducing this emission. However, in some circumstances this can compromise performance. ppcr\/*ec 500 400 300 200 100 1700 1800 1900 2000 2100 2200 °C Figure 6 : Effect of Temperature on NOx Formation Low NOx Burner- Work has continued on the development of improved recuperators and recuperative burners, aimed at achieving even higher levels of heat recovery. For example, B G Technology was involved in an E U project concerned in the development of a new recuperator which was linked to a high temperature radiant burner. The new recuperators was designed and tested at the Gas Research and Technology Centre and utilised proprietary silicon carbide (SiC) elements to produce a counterflow heat exchanger. Using the new system resulted in radiant burner efficiencies of the order of 3 5 % with N O x levels of less than lOppm. The new heat exchanger has an effectiveness of 7 0 % (70% of the available heat in the flue gas was transferred to the air). In Germany a number of burner manufacturers are now incorporating ceramic sections of this type into recuperative burners. These new burner often include low-NOx technology based around either air or fuel staging. Air and fuel staging is an increasingly common approach used to reduce NOx emissions. The approach results in a lower peak flame temperature and hence a reduction in thermal NOx. by delaying the combustion. However, this can lengthen the flame, and at extreme staging ratios can compromise the burners stability envelope. Again with regenerative burners the high air preheat achieved (>1000°C) can give rise to high NOx levels. L o w - N O x versions of the BG/Dyson-Hotwork regenerative burners have been developed in which the N O x emissions have been reduced by 50%. The N O x can be reduced still further by utilising Flue Gas Recycle (FGR) to give levels of around 250ppm. Other manufactures offer their |