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- Andersson, Klas, 1977, et al.
(författare)
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Experiments and modeling on oxy-fuel combustion chemistry during lignite-firing
- 2007
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Ingår i: The Proceedings of the 32nd International Technical Conference on Coal Utilization & Fuel Systems, Clearwater, USA, 2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents experimental and modeling work on the combustion chemistry of the oxy-fuel(O2/CO2 recycle) process with focus on the difference in NO formation between oxy-fuel and air-firedconditions. Measurements have been carried out in a 100 kW test unit, which facilitates oxy-fuelcombustion with real flue gas recycle. These measurements include in-furnace gas concentrations andtemperature profiles from lignite-fired tests. The tests comprise a reference test in air and three oxy-fuel test cases with different oxygen fractions in the recycled feed gas. Additional oxy-fuelexperiments were performed in order to study the sensitivity of the NO formation to bothstoichiometry and air ingress.The results show that for the burner settings used in this work, lignite oxy-combustion with a globaloxygen fraction of 25 vol % in the feed gas results in flame temperature levels close to those duringair-firing. Similar to previous work, it is seen that the NO emission levels in [mg/MJ] during oxy-fueloperation are reduced to less than 30 % of the emission level during air-fired conditions. The resultsfrom the modeling shows that the reduction of NO emissions during oxy-fuel combustion is caused byan increased destruction of formed and recycled NO. Further experimental tests on the OF 27condition show that an increased stoichiometric ratio (from l = 1.18 to 1.41) as well as an increasedN2 content in the feed gas (from about 1% to 15%) only has a small effect on the NO formation duringoxy-combustion.
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- Andersson, Klas, 1977, et al.
(författare)
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Flame and radiation characteristics of gas-fired O2/CO2 combustion
- 2007
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 86:5-6, s. 656-668
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental study on the flame properties of O2/CO2 combustion (oxy-fuel combustion) with focus on the radiation characteristics and the burn-out behaviour. The experiments were carried out in a 100 kWth test unit which facilitates O2/CO2 combustion with real flue gas recycle. The tests comprise a reference test in air and two O2/CO2 test cases with different recycled feed gas mixture concentrations of O2 (OF 21 @ 21 vol.% O2, 79 vol.% CO2 and OF 27 @ 27 vol.% O2, 73 vol.% CO2). In-furnace gas concentration, temperature and total radiation (uni-directional) profiles are presented and discussed. The results show that the fuel burn-out is delayed for the OF 21 case compared to air-fired conditions as a consequence of reduced temperature levels. Instead, the OF 27 case results in more similar combustion behaviour compared to the reference conditions in terms of in-flame temperature and gas concentration levels, but with significantly increased flame radiation intensity. The information obtained from the radiation and temperature profiles show that the flame emissivity for the OF 21 and OF 27 cases both differ from air-fired conditions. The total emissivity and the gas emissivity of the OF 27 and the air-fired environment are discussed by means of an available model. The gas emissivity model shows that the increase in radiation intensity (up to 30%) of the OF 27 flame compared to the air flame can partly, but not solely, be explained by an increased gas emissivity. Hence, the results show that the OF 27 flame yields a higher radiative contribution from in-flame soot compared to the air-fired flame in addition to the known contribution from the elevated CO2 partial pressure.
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- Andersson, Klas, 1977, et al.
(författare)
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Process evaluation of an 865 MWe lignite fired O2/CO2 power plant
- 2006
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 47:18-19, s. 3487-3498
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Tidskriftsartikel (refereegranskat)abstract
- In order to reduce emissions of carbon dioxide from large point sources, new technologies can be used in capture plants for combustion of fossil fuel for subsequent capture and storage of CO2. One such technology is the O2/CO2 combustion process (also termed oxy-fuel combustion) that combines a conventional combustion process with a cryogenic air separation process so that the fuel is burned in oxygen and recycled flue gas, yielding a high concentration of CO2 in the flue gas, which reduces the cost for its capture. In this work, the O2/CO2 process is applied using commercial data from an 865 MWe lignite fired reference power plant and large air separation units (ASU). A detailed design of the flue gas treatment pass, integrated in the overall process layout, is proposed. The essential components and energy streams of the two processes have been investigated in order to evaluate the possibilities for process integration and to determine the net efficiency of the capture plant. The electricity generation cost and the associated avoidance cost for the capture plant have been determined and compared to the reference plant with investment costs obtained directly from industry. Although an existing reference power plant forms the basis of the work, the study is directed towards a new state of the art lignite fired O2/CO2 power plant. The boiler power of the O2/CO2 plant has been increased to keep the net output of the capture and the reference plant similar. With the integration possibilities identified, the net efficiency becomes 33.5%, which should be compared to 42.6% in the reference plant. With a lignite price of 5.2 $/MWh and an interest rate of 10%, the electricity generation cost increases from 42.1 to 64.3 $/MWh, which corresponds to a CO2 avoidance cost of 26 $/ton CO2.
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- Andersson, Klas, 1977, et al.
(författare)
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Radiation intensity of lignite-fired oxy-fuel flames
- 2008
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777. ; 33:1, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- The radiative heat transfer in oxy-fuel flames is compared to corresponding conditions in air-fuel flames during combustion of lignite in the Chalmers 100 kW oxy-fuel test facility. In the oxy-fuel cases the flue-gas recycle rate was varied, so that, in principle, the same stoichiometry was kept in all cases, whereas the oxygen fraction in the recycled flue-gas mixture ranged from 25 to 29 vol.%. Radial profiles of gas concentration, temperature and total radiation intensity were measured in the furnace. The temperature, and thereby the total radiation intensity of the oxy-fuel flames, increases with decreasing flue-gas recycle rate. The ratio of gas and total radiation intensities increases under oxy-fuel conditions compared to air-firing. However, when radiation overlap between gas and particles is considered the ratios for air-firing and oxy-fuel conditions become more similar, since the gas-particle overlap is increased in the CO2-rich atmosphere. A large fraction of the radiation in these lignite flames is emitted by particles whose radiation was not significantly influenced by oxy-fuel operation. Therefore, an increment of gas radiation due to higher CO2 concentration is not evident because of the background of particle radiation, and, the total radiation intensities are similar during oxy-fuel and air-fuel operation as long as the temperature distributions are similar.
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- Andersson, Klas, 1977, et al.
(författare)
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Radiation Intensity of Propane-Fired Oxy-Fuel Flames: Implications for Soot Formation
- 2008
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Ingår i: Energy & Fuels. ; 22:3, s. 1535-1541
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Tidskriftsartikel (refereegranskat)abstract
- The changes in the soot-related radiation intensity between two different oxy-fuel flames and an air-fired flame were investigated in a 100 kW oxy-fuel test unit firing propane. The oxy-fuel test cases with 21 and 27 vol % O2 in the recycled flue gas (RFG) were run with different amounts of dry RFG, which in principle only consisted of CO2 from combustion and some excess O2. The stoichiometric oxygen-to-fuel ratio was kept at 1.15 in all cases. Total radiation intensity was measured with a narrow angle radiometer. Temperature and gas composition measurements served as inputs to computations of gas radiation. A comparison of the computed gas radiation with the measured total radiation intensity enabled estimation of the radiation related to soot. Clear differences were observed in the amount of soot formed in the two oxy-fuel flames (also compared to the air flame). In the oxy-fuel flame with 21 vol % O2 in the RFG, soot formation is almost completely suppressed, but when the total flow through the burner is reduced by about 20% (by volume) (i.e., from 21 to 27 vol % O2 in the RFG), the amount of soot present in the flame becomes significant. This change in soot volume fraction affects the radiation emitted from the flames; images of the flames qualitatively confirm these differences in the flame luminosity. Thus, carbon dioxide not only increases the gas radiation, but it can also drastically influence soot formation and the radiation originating from soot during oxy-fuel combustion.
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