• Research Report on NOx formation and primary reduction techniques in heavy oil fired bulk glass melters

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Today we publish Research Report F45/y/2, Experimental investigations in NOx reduction techniques in oil fired glass melting furnaces by M. Tamura,  J. Haas,  R. Weber.

This report was originally prepared by the IFRF Research Station BV in 1999 as part of the EC co-funded CLEAN GLASS projects.  The report has been reviewed by the IFRF for publication to IFRF members. Today it is republished and is now available to IFRF Members as a PDF download on http://www.research.ifrf.net/research/new.html

Bulk glass melters use large reversing regenerators to preheat the combustion air in order to enhance thermal efficiency of the melting process. One of the downsides of this is a high level of NOx in the flue gases, with values exceeding 3000 ppm not uncommon in the past. NOx formation in glass melting furnaces is mostly due to thermal NOx, and should be amenable to primary reduction measures by altering the fuel air mixing arrangement to reduce peak flame temperatures while maintaining heat transfer to the glass and avoiding excessive refractory temperatures. The Clean Glass program attempted to better understand the formation of NOx in glass melting furnaces. The IFRF program consisted of an experimental part and a modelling part, which are combined to validate the improvements of the mathematical modelling. Specific objectives of this study were as follows:

1.  To reduce the NOx emission to less than 500mg/Nm3 @8 percent O2 with complete combustion by primary means

Several oil atomiser conditions, burner configurations and atomisation media were tested to better understand the NOx and CO emission behaviour.

2.  To maintain optimum heat flux and distribution while reducing NOx

The heat release profile in the glass tank condition should be maintained similar while arranging the burner gun configurations to get the target NOx level. Detailed in-flame measurements were undertaken to distinguish the flame properties of low NOx and high NOx performance.

Experimental work

Experiments were executed in February 1999. Heavy fuel oil was fired in the glass melting furnace simulator (~1MWt) at the IFRF Research Station. Air preheats of  over 1000C were achieved by means of a direct fired air preheater with oxygen addition to return to oxygen levels to  21 percent. Air assisted oil atomisers were prepared by Hotwork-Köster. The following parameters were evaluated to investigate the NOx and CO emission behaviour.

  • Atomisation medium (air, nitrogen, natural gas, steam)
  • Atomisation air flow and pressure
  • Combustion air velocity (14m/s, 24m/s)
  • Firing modes (6 different burner gun arrangements)
  • Atomiser angle (5o – 18o)

At the same time in-flame measurements were carried out in three different flames to assess the flame properties of high NOx and low NOx flames.

A monochromatic infrared camera for tomographic flame reconstruction was applied in the glass melting furnace simulator in co-operation with IST (Instituto Superior Técnico).


Research Report F45/y/2 contains a detailed description of the way in which the IFRF furnace was used to simulate a full scale glass melter. It also gives complete data on the experimental conditions, fuels, parametric studies of the effect of the experimental parameters on flue NOx levels, and the detailed in-flame data collected.

It was shown that the primary measures listed above can achieve reductions in NOx emissions of 30 percent to 50 percent. The specific conditions giving rise to the best NOx/CO/Heat transfer  combinations are identified in the body of the report. It was also recognised that application of different firing modes also offer further potential, but that additional studies will be needed to explore and exploit this potential.