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Heymann, Claas

Name:Heymann, Claas
Thema:NOx-Fomation and Reduction in Regemerative End-Port Glass Melting Funaces


Glass and its products play an important role in our daily life. But the melting of glass requires high temperatures and thus a large energy consumption and produce hazardous emissions. Since many glass products cannot be replaced by other materials, solutions are needed to reduce the energy consumption and the emission of pollutants. Only then the advantages of the material glass can flower out. This thesis is intended to improve the understanding of NO formation and destruction in regenerative end-port furnaces and presents a novel technology to reduce the NO emissions. Therefore measurements in an operating furnace are taken and experiments with the injection of oxygen were made. The oxygen was injected through the sidewalls at approximately 1/3 of the furnace length. Three pairs of lances of different diameter were compared to identify the impact of injection velocity and volume flow. The furnace had a melting area of 78m², a pull rate of 185 to 221tpd at specific energy consumption of around 1160 kcal/kg. The batch was charged by one doghouse at the left side of the furnace. Beside measurements of the refractory temperatures in the regenerators, the crown temperatures and the glass throat temperature, the flue gas components CO, NO, O2 and CO2 were continuously measured in the top of the regenerator. CFD simulations of the furnace without (baseline case) and with oxygen injection were made. Four distributions of the batch gas release and five doghouse intrusion air volume flows were calculated to derive boundary conditions for the calculation of the baseline case. The analysis of the baseline case showed that both intrusion air and batch gases are impacting flue gas NO formation. Batch gases were found to decrease NO formation by 66% mainly by cooling the flame. Doghouse intrusion air was found to further reduce flue gas NO concentration during right firing by up to 56% and to increase flue gas NO during left firing by 2%. The intrusion air stages the oxygen supply and consequently only during right firing the distance between preheated air and intrusion air is sufficient long. Considering batch gas release, doghouse intrusion air and metal line intrusion air, the flame shape of the left firing change from a smooth lower shaper into a lifted flame shape of high turbulence. Video sequences confirm the calculations. The injection of oxygen was found to stabilise the combustion and to reduce fluctuations in flue gas concentrations. The excess oxygen was reduced until CO was formed, which results further flue gas NO concentration reductions. Thus the staging of the oxidizer is increased and less NO is formed. Exceeding a critical injection volume flow and velocity, the recirculation of flue gas is enhanced and further flue gas NO concentration reductions were measured and calculated. During left firing the flue gas NO concentration was reduced from 969 ppm to 477 ppm (injecting 100 Nm³/hr oxygen at 98 m/s). The excess oxygen was decreased from 3.1 to 1.7 % dry. During right firing the flue gas NO concentration was reduced from 526 ppm to 295 ppm (80 Nm³/hr oxygen at 78m/s). The flue gas oxygen was reduced from 3.0 to 2.6 % dry. The corresponding average mass concentration was 546 mg NOx/ Nm³ related to 8% oxygen dry. The influence of flue gas recirculation and oxidizer staging was more or less the same. An increase in energy consumption was not measured. 


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