| 1. |
- Gimenez-López, Jorge, et al.
(författare)
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NO2 Emissions in Oxy-Fuel Combustion
- 2011
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Ingår i: Proceedings of the 5th International Conference on Clean Coal Technologies.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Few studies are available about the chemistry of NO2 in oxy-fuel combustion, despite the thought that the formation of NO2 in oxy-fuel plants is higher than in air combustion. A kinetic modeling study of the NO2 formation and reduction process in oxy-fuel combustion is performed. Calculations are based on experiments carried out in a 100 kW test unit fired with pulverized coal. The modeling approach is performed in order to assimilate the process as a gas-phase flow reactor system. NO2 is mainly formed through the HO2 mechanism. In the high temperature region, all NO2 is reduced, but the low temperatures favor the formation of NO2 in the final section of the boiler. SO2 has an important effect on the in-furnace NO2 formation, while the influence of O2 is minor. According to the model, a much higher formation of NO2 is attained in oxy-fuel compared to air combustion, while similar NOx reduction efficiencies are found with recycled-NO2 than with recycled-NO.
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| 2. |
- Kuehnemuth, Daniel, 1979
(författare)
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Combustion and Nitrogen Chemistry in Oxy-Fuel Flames
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oxy-fuel combustion is a Carbon Capture and Storage (CCS) technology that recently has shown afast progress towards the industrial scale application. In oxy-fuel combustion, oxygen instead of air isused as oxidizer to burn the fuel. The oxygen is mixed with recycled flue-gas in order to control theoverall combustion and heat transfer conditions. The resulting combustion atmosphere has asignificant impact on the combustion chemistry and its interaction with the nitrogen chemistry. Thiswork investigates the influence of oxy-fuel operation on the formation and oxidation of CO and thenitrogen chemistry with special attention on the reburning conditions. An indication of the effects ofthe CO2-rich atmosphere on the combustion chemistry in oxy-fuel flames is the elevated CO-peakconcentration compared to air fired flames. This work characterizes the reactions with CO2 whichform CO in oxy-fuel flame by modeling. The reduction of nitrogen oxides are investigated bycombining a similar modeling approach with experimental work at the Chalmers 100 kWth oxy-fuelunit.The model results show that CO formation in gaseous fired oxy-fuel flames is dominated by thereaction between CO2 and H-radicals. In oxy-fuel combustion of pulverized lignite, char gasificationby CO2 can be the dominating reason for an increased CO formation. However, the importance ofgasification is dependent on char particle temperature (which is related to char properties such asreactivity and particle size), as well as on the mixing conditions between fuel and oxidizer.The results from the propane fired reburning experiments show that the combustion chemistry of anoxy-fuel flame is disadvantageous for NO reburning compared to an air flame. The reduction of finalNO emissions [mg/MJ] to about 30% of those observed in air firing is caused by the recycle. Theeffect of the recycle ratio is particularly significant for cases with low reduction efficiencies in theflame.
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| 3. |
- Kuehnemuth, Daniel, 1979, et al.
(författare)
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Reburning of Nitric Oxide in Oxy-Fuel Firing-The Influence of Combustion Conditions
- 2011
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 25:2, s. 624-631
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were carried out to obtain data on the efficiency of nitric oxide (NO) reduction by reburning under oxy-fuel conditions. The work was carried out in a 100 kW test facility fired with propane. The data were analyzed by means of a combustion model, which included a detailed description of the reburning chemistry. The importance of several combustion parameters on the reburning efficiency was studied: inlet oxygen concentration, flue gas recycle ratio, temperature, and stoichiometric ratio. The inlet oxygen concentration was kept between 25 and 37 vol % and the burner stoichiometric ratio between 0.7 and 1.15. NO was injected in the oxidizer. As expected, similar to air-firing, reburning in oxy-fuel is favored by substoichiometric conditions. A decrease in combustion temperature, caused by a lowered stoichiometric ratio, is shown to be advantageous for reduction of NO under oxy-fuel conditions. The effect of inlet oxygen concentration on reburning is not significant as long as the combustion conditions are fuel-lean. However, the amount of recycled flue gas, which increases with decreasing oxygen content, significantly improves the total reduction. Instead, when the stoichiometric ratio is decreased, the recycle flow of the flue gas is reduced, which, to some extent, counteracts the otherwise positive effect of fuel-rich conditions in the flame zone in oxy-fuel conditions. Thus, during oxygen-rich combustion, the total reburning efficiency in oxy-fuel combustion is superior to once-through reburning in air-firing, but during substoichiometric conditions, the reduction in air and oxy-fuel combustion is comparable.
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