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- Ajdari, Sima, 1985, et al.
(författare)
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NOx AND SOx CHEMISTRY IN PRESSURIZED FLUE GAS SYSTEMS: IMPORTANCE FOR CHEMICAL LOOPING COMBUSTION
- 2014
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Ingår i: 3rd International Conference on Chemical Looping, 9-11 September 2014, Gothenburg, Sweden.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The control of NOx and SOx in chemical-looping combustion systems is discussed with the focus on the importance of the pressurized flue-gas train. The chemistry of nitrogen and sulfur under pressurized conditions and the experiences gained from operating oxy-fuel combustion pilot plants that pertain to chemical looping are reviewed. In the flue gases from the combustion process, SO2 and NO are the principle NOx and SOx species. The oxidation of NO to NO2 is favored by low temperature and high pressure and is enhanced during the compression of flue gases. The oxidation of NO to NO2 in the flue-gas train is significant at pressures >15 bar. The solubilities of NO2 and SO2 in water are high and results in the formation of acids. Once NOx and SOx are absorbed, the liquid-phase N-S interactions lead to the formation of sulfuric and nitric acids. Thus, the chemistry of NOx and SOx is of importance for flue-gas conditioning of chemical-looping combustion systems. Similar to oxy-fuel combustion, the conditions in the chemical-looping flue-gas train offer new opportunities for the design of NOx and SOx removal processes.
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- Andersson, Viktor, 1983, et al.
(författare)
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Efficient Utilization of Industrial Excess Heat for Post-combustion CO2 Capture: An Oil Refinery Sector Case Study
- 2014
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 63, s. 6548-6556
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Konferensbidrag (refereegranskat)abstract
- A key issue in post-combustion carbon capture is the choice of absorbent. In this paper two different absorbents, monoethanolamine (MEA) and ammonia (NH3), have been modeled in Aspen Plus at different temperatures for possible implementation at an oil refinery. The focus of investigation is the possibilities of heat integration between the oil refinery and the carbon capture process and how these possibilities could change in a future situation where energy efficiency measures have been implemented.The results show that if only using excess heat from the refinery for heating of the carbon capture process, the MEA process can capture more CO2 than the NH3 process. It is shown that the configuration requiring least supplementary heat when applying carbon capture to all flue gases is MEA at 120 °C.The temperature profile of the excess heat from the refinery suits the MEA and NH3 processes differently. The NH3 process would benefit from a flat section above 100 °C to better integrate the heat needed to reduce slip, while the MEA process only needs heat at stripper temperature.
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- Ekvall, Thomas, 1986, et al.
(författare)
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Modeling the Alkali Sulfation Chemistry of Biomass and Coal Co-firing in Oxy-fuel Atmospheres
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:5, s. 3486-3494
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Tidskriftsartikel (refereegranskat)abstract
- In the present modeling work, the gas-phase alkali sulfation process is investigated. The combined effects of oxyfuel combustion and co-combustion on the sulfation of alkali metals are examined and compared to the corresponding process under air-fired conditions. According to the modeling results, the degree of sulfation of gas-phase alkali metals is generally higher for oxy-fuel combustion than for air fuel combustion. The recirculation strategy, in terms of the flue gas composition in oxy-fuel combustion, is important for the sulfation of alkali metals. The increased contents of sulfur and water contribute significantly to the degree of sulfation of the alkali species. The modeling also reveals that an increased content of HCl, which is present during wet recirculation, has a negative effect on the sulfation. Thus, the degree of sulfation is lower in wet recirculation than in dry recirculation. The effects of other important parameters, such as the sulfur/potassium ratio, oxygen concentration, and temperature, are discussed.
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| 7. |
- Ekvall, Thomas, 1986, et al.
(författare)
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Sulphation of potassium chloride in air and oxy-fuel combustion
- 2013
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Ingår i: The Proceedings of the 38th International Technical Conference on Clean Coal & Fuel Systems, June 2-6 2013, Clearwater, Florida, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During combustion of biomass, alkali and chlorine species are released to the gas phase, species which can react to form corrosive salts that potentially may cause severe corrosion problems on heat transfer surfaces upon condensation. This corrosion process is referred to as high-temperature corrosion (HTC) and it limits steam data in biomass combustion, with corresponding limitation in thermal efficiency. The flue gas composition and also the HTC conditions can be altered by introducing a second fuel, e.g. coal for co-combustion. The flue gas composition can be altered even more drastically when applying oxy-fuel combustion where the concentration of combustion products are higher than in air firing due to the use of pure oxygen and flue gas recycling. In this work, the alkali sulphation process in different oxy-fuel and air-fuel atmospheres has been investigated by modelling the gas phase chemistry. The overall purpose is to examine the combined effects of oxy-combustion and co-combustion on the HTC process and to make a comparison with air-fired conditions. The flue gas composition in oxy-fuel combustion depends on the recirculation strategy used which in turn also influences the sulphation. According to the modelling results the degree of sulphation of gas-phase alkali metals is in general higher for oxy-fuel combustion compared to air-fuel combustion. It is concluded from the modelling results that an increased amount of sulphur and water contribute to a substantial effect on the degree of sulphation of alkali species. On the other hand, the modelling also shows that an increased content of HCl, which is present during wet recirculation, has a negative effect on the sulphation; the degree of sulphation is therefore lower in wet compared to dry recirculation. The effects of other important parameters such as sulphur-to-potassium and air-to-fuel ratios, temperature and residence time are also discussed further in the paper.
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- Fleig, Daniel, 1980, et al.
(författare)
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SO3 Formation under Oxyfuel Combustion Conditions
- 2011
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 50:14, s. 8505-8514
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Tidskriftsartikel (refereegranskat)abstract
- The sulfur chemistry in oxyfuel combustion systems has received growing attention lately. The formation of SO(3) is of special concern, because of the elevated SO(2) concentrations found in oxyfuel, compared to air-fuel conditions. The present study focuses on the gas-phase chemistry and examines the impact of different combustion parameters and atmospheres on the formation of SO(3) in oxyfuel and air-fuel flames, using a detailed gas-phase model. The work also includes a summary of the presently available SO(x) data from experiments in laboratory and pilot-scale combustors. The reviewed experimental data, as well as the modeling results, show significantly increased SO(3) concentrations in oxyfuel, compared to air-fuel conditions. The modeling results reveal a complex behavior of the SO(3) formation, which is influenced by direct and indirect effects of the SO(2), O(2), NO(x), and CO content in the flue gas. One of the main contributors to the increased SO(3) concentration in oxyfuel, compared to air-fuel conditions, is the high concentration of SO(2) in oxyfuel combustion. The modeling also shows that the stoichiometry, residence time, and flue-gas cooling rate are critical to the SO(3) formation. Thus, in addition to the stoichiometry of the flame, the flue-gas recycling conditions are likely to influence the formation of SO(3) in oxyfuel combustion.
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- 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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