| 1. |
- Ajdari, Sima, 1985, et al.
(författare)
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Reduced Mechanism for Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
- 2016
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 55:19, s. 5514-5525
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Tidskriftsartikel (refereegranskat)abstract
- The gas- and liquid-phase chemistry of nitrogen and sulfur species under pressurized conditions is of high importance to the design and performance of the pressurized flue gas systems in carbon capture and storage (CCS) schemes. Yet, the available description of this chemistry is complex and difficult to apply in design studies for removal of NOx and SOx during the compression. This work proposes a reduced mechanism for engineering calculations of pressurized flue gas systems, a mechanism that is able to describe the relevant gas and liquid-phase chemistry as well as the S/N-product distribution. The reduced mechanism is derived by identifying the rate-limiting reactions using sensitivity analysis. The performance of the mechanism subsets are compared with results of a detailed mechanism. The identified rate-limiting reactions for the formation of key products form the basis for two different types of reduced mechanisms. The sets include one general reduced mechanism (valid for all pH conditions) and sets of pH-specific mechanisms. The general reduced mechanism and the pH-specific mechanisms perform satisfactorily compared to the detailed mechanism under different pH conditions. The results show that depending on the purpose of the modeling, whether it is to predict the pollutant removal (where sulfurous acid and nitrogen acids are mainly important) or capture the liquid composition, for which the N-S chemistry products are also important, different levels of simplification can be made. The number of reactions is reduced from 34 reactions (39 species) in the detailed mechanism to 12 reactions (20 species) in the general reduced mechanism and 7-8 (14-17 species) in the pH-specific mechanisms.
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| 2. |
- Normann, Fredrik, 1982, et al.
(författare)
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Oxidation of ammonia over a copper oxide-containing solid oxygen carrier with oxygen uncoupling capability
- 2016
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 165, s. 445-452
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Tidskriftsartikel (refereegranskat)abstract
- Measurements and modelling of the oxidation of ammonia over copper oxide (CuO) under conditions relevant to chemical-looping combustion with oxygen uncoupling show that CuO fully converts NH3 into NO or N-2 under most of these conditions. Our experiments demonstrate that considerable amounts of NO are formed when the oxygen carrier is fully oxidised. Decreasing the degree of oxidation of the oxygen carrier affected the selectivity of the NH3 oxidation towards NO. Ageing of the oxygen carrier had a similar effect. Modelling suggests that these results reflect a change in the rate of oxygen release from the CuO particles.
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| 3. |
- Òsk Gardarsdòttir, Stefanìa, 1987, et al.
(författare)
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Challenges for coal based electricity generation in energy systems with high capacity of variable renewable energy sources
- 2016
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Ingår i: Proceedings of the 41st International Technical Conference on Clean Coal & Fuel Systems.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The market conditions for thermal power plants in Europe are changing rapidly with ever increasing share of the supply provided by variable renewable energy sources. Operators are struggling to keep up with the new conditions in a system where power plant flexibility has historically been of less importance. This is however starting to change and in line with this development, the power industry is increasingly interested in R&D work on improving plant flexibility. Based on interviews with several experts within the power industry, a literature review and dynamic power plant modelling this work highlight and discusses important areas of development for flexible coal-based power generation. Four flexibility aspects were specifically emphasized by the experts interviewed; turn-down, part-load efficiency, start-up times and ramp rates. All experts interviewed regarded retrofits of existing plants to be a more likely development than building of new flexible plants and at present, it seems as the focus is mainly to use all low-cost options for increasing plant flexibility. The extent of beneficial effects from increased plant flexibility for both the plant operator, and the electricity system is still unclear. A techno-economic modeling study of power systems combined with dynamic power plant modeling, taking into account the possible development in plant flexibility as highlighted in this work, could further provide valuable insight and underline which flexibility aspects are of most importance to develop.
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| 4. |
- Zhao, Dongmei, 1963, et al.
(författare)
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The faith of fuel bound nitrogen in a solid fuel chemical looping combustion process over oxygen carriers of ilmenite and Fe2O3 supported on Mg-ZrO2
- 2016
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Ingår i: Proceedings of the 41st International Technical Conference on Clean Coal & Fuel Systems.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The formation of NOx from fuel bound nitrogen is of importance to the design of chemical looping combustion (CLC) power plants. This work studies to what extent different nitrogen containing species are formed in solid fuel CLC. The influence of combustion environment (steam level and temperature) and type of oxygen carrier on the formations of nitrogen containing species is mapped. It is also desired to achieve data that can be used to assist partly the selection and the evaluation of CO2 storage sites. The study has been carried out in a lab scale fluidized bed reactor using iron oxide and ilmenite as bed materials. The solid fuel is a wood char containing 1.9 wt.% of nitrogen on dry and ash free basis. Steam is used to gasify the solid fuel in the fuel reactor. The measurements show presence of both nitric oxide (NO) and ammonia (NH3) in the outlet gas stream from the fuel reactor. The inlet concentration of steam and the reactor temperature are both important to formation of NO and NH3. As expected, high inlet steam fractions increases fuel conversion at all temperatures for both oxygen carriers tested. Interestingly, high inlet steam fractions leads to increased NO formation in presence of iron oxide, but to decreased NO formation with ilmenite. This might be explained by the competing reactions between the oxygen carrier and CO and NO and CO in the gas phase. It is concluded that both NO and NH3 are formed however substantial amount of N2 are coming along in the process. In conclusion, the choice of oxygen carrier and operating conditions of chemical looping combustion is crucial to the faith of the fuel bound nitrogen introduced to the process.
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