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Compact Fired Heating Units

Deliverables

This extensive two-year research program, which was originally planned for three years, has provided the partnership with a huge amount of new experimental data as well as a variety of state-of-the-art mathematical modelling approaches. New techniques have been researched, and the applications of these new techniques have been extended. The main conclusions are: 1) For "cold-wall appliances" such as small to large steam boilers, hot water boilers, thermal oil heaters and process fluid heaters in general like those used in the chemical process industries, swirl burners are superior to the conventional and widely-used nozzle-mixing burners with regard to NOx emissions. In particular: -Swirl burners are more robust with respect to the increase of NOx in combination with combustion air preheat up to 300 °C and possible up to 400 degrees Celsius. -The use of swirl burners does allow for an increase in the firing intensity of the heating units by at least a factor of 2. -With a proper design of the gas gun, i.e. with an optimal degree of non-premixedness of the gas mixture that is jetted out of the burner, a turn-down ratio of 1 : 5 of the burner is possible. 2) For "hot-wall appliances" such as the vast number of heating and reheating furnaces and melting furnaces, staging to variable degrees is recognised as the better technique to combat NOx formation. In particular: -Staging burners are very robust with respect to the increase of NOx in combination with combustion air preheat up to 600 °C and even up to 900 degrees Celsius. -The degree of staging should be optimised with respect to the application, i.e. the combustion air preheat and the furnace temperature. In general, the higher temperatures allow for an extended delay of mixing up to the point of flameless oxidation. -In this project, modified designs for the staged and FLOXTM burners have been proposed for the first time that have reduced the NOx emission noticeably. The overall main conclusion is that an optimisation of the system: burner -furnace -furnace load has to be done to reach satisfying results with regard to combustion air preheat and compactness of the furnace volume.

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