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- Acke, Filip, et al.
(författare)
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Study of the reduction and reoxidation of a CaO surface
- 1997
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Ingår i: J Phys Chem B. - 1520-5207 .- 1520-6106. ; 101:33, s. 6484-
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Tidskriftsartikel (refereegranskat)abstract
- The reduction of NO with CO and H2 is shown to comprise two basic reactions: a surface oxygen abstraction by the reducing agent and a reoxidation of the surface by NO. The former reaction step has been demonstrated by transient CO2 formation during CO exposure of oxidized CaO surfaces, while the latter was demonstrated by N2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 °C) both N2 and N2O were formed, but at temperatures above 500 °C only N2 was observed. The activation energies of the respective steps have been determined using temperature-programmed reaction experiments. The activation energy of the surface oxygen abstraction was determined to be 25 kcal/mol and is similar to the apparent activation energy of the overall reaction. The activation energy of the NO bond breakage was determined to be maximum 10 kcal/mol as measured by N2O formation. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N2 at temperatures above 500 °C will be compared with a N surface diffusion mechanism.
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| 2. |
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| 3. |
- Feng, Xinbin, et al.
(författare)
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On-line speciation of mercury in flue gas
- 1999
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Ingår i: Book of Abstract. 5th International Conference on Mercury as a Global Pollutant, Rio de Janeiro, Brazil, 1999.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Feng, Xinbin, et al.
(författare)
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On-line Speciation of Mercury in the Flue Gases
- 1999
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Ingår i: Proceedings of A&WM Mercury in the Environment Specialty Conference, Air & Waste Management Association, Minneapolis, MN. USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
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| 6. |
- miettinen, heije, et al.
(författare)
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Laboratory study of N2O formation from burning char particles at FBC conditions
- 1995
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Ingår i: Energy and Fuels. - 1520-5029. ; 9:1, s. 10-19
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Tidskriftsartikel (refereegranskat)abstract
- Coal combustion in fluidized bed combuster is a cause of nitrous oxide emissions to the atmosphere. The formation of NzO seems to be related both to homogeneous and heterogeneous reactions taking place in the combustion process. The purpose of this investigation was to study the formation of NzO from burning char particles under different combustion conditions. The experiments were carried out in a fmed bed reactor containing quartz sand (SiOz) to support the coal particles. A monolayer of bituminous coal particles between two layers of quartz sand was devolatilized prior to the actual combustion in an argon flow. The coal particle sizes were varied between 0.090 and 2.80 mm. The inlet gas mixture contained NO, 0 2 , and Ar or just 0 2 and Ar. The oxygen concentration was varied between 0.5 and 20% 0 2 and the NO concentration was varied between 0 and 1000 ppm NO. The inlet gas flow was varied between 590 and 1581 mL/ min NTP (273 K, 1 atm) and the bed temperature was varied between 1023 and 1123 K. The off-gases were analyzed for NzO, NO, CO, and COZ. Addition of NO to the flue gas increased the NzO yield. A low combustion temperature also favors high yields of N20. A great influence of the oxygen concentration was found (high oxygen concentrations give low Nz0 yields), which indicates that the combustion conditions are very important for the NzO yield. A particle size of 1 mm gives the highest NzO yields.
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| 7. |
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| 8. |
- Olanders, Birgitta, et al.
(författare)
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Reduction of nitric oxide over magnesium oxide and dolomite at fludised bed conditions
- 1995
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Ingår i: Energy and Fuels. - 1520-5029. ; 9:4, s. 680-684
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Tidskriftsartikel (refereegranskat)abstract
- The reduction of nitric oxide over lime and char at fluidized bed conditions has been studied by many authors, but less attention has been paid to other surfaces existing in the boiler. This investigation concerns the reduction of nitric oxide by carbon monoxide, with or without oxygen present, and also the effect of small amounts of water, The reactions were studied in a fixed-bed quartz reactor with quartz, magnesium oxide, magnesium hydroxide, and dolomite as bed materials in the temperature interval 600-950 “C. The residence time and the concentrations of nitric oxide, carbon monoxide, and oxygen were varied. Magnesium oxide formed from heated magnesium hydroxide and calcined dolomite were more active than magnesium oxide of analytical grade, which indicates that the origin of the surface is important for the reaction. The reaction between nitric oxide and carbon monoxide is very sensitive to the presence of oxygen. When oxygen was present the reduction of NO almost ceased. However, if the gases were thoroughly dried, the effect of oxygen addition was not that severe.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Xiao, Zifan, et al.
(författare)
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Influence of humic substances on photolysis of divalent mercury in aqeous solution
- 1995
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Ingår i: Water Air and Soil Poll. - 0049-6979 .- 1573-2932. ; 80:1-4, s. 789-
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (II) solutions were irradiated by a simulated sunlight in the presence of humic acid (HA) or fulvic acid (FA). Results show that, under the experimental conditions and the FA and HA chosen, less than 20% of the Hg in solution was photolysed with a rate of (1.63±0.29)×10–2 s–1 (n=23) and the rest of (2.38±0.40)×10–4 s–1 (n=23) depending on the substitutes of humic substances to which Hg were bond. The sunlight photolysis lifetimes were estimated to be 4 and 250 sunlight hours respectively under summer conditions at Stockholm latitude.
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