| 11. |
- Edland, Rikard, 1990, et al.
(författare)
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Evaluation of NOx-Reduction Measures for Iron-Ore Rotary Kilns
- 2020
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:4, s. 4934-4948
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Tidskriftsartikel (refereegranskat)abstract
- The grate-kiln process is employed for sintering and oxidation of iron-ore pellets. In this process, a fuel (typically coal) is combusted with a large amount of excess air in a rotary kiln, and the high air-to-fuel ratio leads to significant NOx formation. The current Article is an assessment of NOx reduction measures that have been tested in pilot-scale and in full-scale by the Swedish iron-ore company Luossavaara-Kiirunavaara Aktiebolag (LKAB). The results show that the scaling between the full-scale kiln and the pilot-scale kiln is crucial, and several primary measures that reduce NOx significantly in pilot-scale achieve negligible reduction in full-scale. In the investigated full-scale kiln, thermal NOx formation is efficiently suppressed and low compared with the NO formation from the fuel-bound nitrogen (especially char-bound nitrogen). Suppressing the NO formation from the char-bound nitrogen is difficult due to the high amounts of excess air, and all measures tested to alter mixing patterns have shown limited effect. Switching to a fuel with a lower nitrogen content is efficient and probably necessary to achieve low NOx emissions without secondary measures. Simulations show that replacing the reference coal with a biomass that contains 0.1% nitrogen can reduce NOx emissions by 90%.
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| 12. |
- Edland, Rikard, 1990, et al.
(författare)
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Formation of Soot in Oxygen-Enriched Turbulent Propane Flames at the Technical Scale
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Soot is an important component for heat transfer in combustion processes. However, it is also a harmful pollutant for humans, and strict emissions legislation motivates research on how to control soot formation and release. The formation of soot is known to be triggered by high temperature and high pressure during combustion, and it is also strongly influenced by the local stoichiometry. The current study investigates how the formation of soot is affected by increasing the oxygen concentration in the oxidizer, since this affects both the temperature profile and partial pressures of reactants. The oxygen-to-fuel ratio is kept constant, i.e., the total flow rate of the oxidizer decreases with increasing oxygen concentration. Propane is combusted (80 kWth) while applying oxygen-enriched air, and in-flame measurements of the temperature and gas concentrations are performed and combined with available soot measurements. The results show that increasing the oxygen concentration in the oxidizer from 21% to 27% slightly increases soot formation, due to higher temperatures or the lower momentum of the oxidizer. At 30% oxygen, however, soot formation increases by orders of magnitude. Detailed reaction modeling is performed and the increase in soot formation is captured by the model. Both the soot inception rates and surface growth rates are significantly increased by the changes in combustion conditions, with the increase in soot inception being the most important. Under atmospheric conditions, there is a distinct threshold for soot formation at around 1200 °C for equivalence ratios >3. The increase in temperature, and the slower mixing that results from the lower momentum of the oxidizer, have the potential to push the combustion conditions over this threshold when the oxygen concentration is increased
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| 13. |
- Ehlmé, Elias, 1998, et al.
(författare)
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Heat Transfer Conditions in Hydrogen-Fired Rotary Kilns for Iron Ore Processing
- 2023
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Ingår i: Industrial & Engineering Chemistry Research. - 1520-5045 .- 0888-5885. ; 62:37, s. 15098-15108
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Tidskriftsartikel (refereegranskat)abstract
- This work analyzes the heat transfer conditions in a rotary kiln used for the heat treatment of iron ore pellets in the grate-kiln process. The analysis concerns conditions relevant to fuel switching from coal to hydrogen gas. A modeling assessment of the radiative heat transfer in the kiln is conducted including the pellet bed and inner kiln wall temperature conditions. The results show that the heat transfer rate to the iron ore pellets under conditions of a pure hydrogen flame is comparable to the conditions relevant to coal firing. However, it is higher at the kiln wall surfaces near the burner region and lower in the remaining parts of the kiln. Increasing the particle concentration in the hydrogen flame represents a practical implication of co-firing coal with hydrogen. By adding particles, the emittance of radiation from the flame is significantly influenced, leading to further increased kiln surface temperatures closer to the burner position. Increased flame length also showed enhanced heat transfer rates to the kiln wall, although further away from the burner region.
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| 14. |
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| 15. |
- Gall, Dan, et al.
(författare)
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A new technique for real-time measurements of potassium and sodium aerosols based on field-reversal surface ionization
- 2021
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Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 32:7
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Tidskriftsartikel (refereegranskat)abstract
- A new method for real-time measurements of potassium and sodium containing aerosol particles is described and verified. The method is based on surface ionization technique and may be used to explore the alkali chemistry related to high temperature chemistry processes. The measurement device is a further development of the simple and cost-effective surface ionization detector previously used for online alkali measurements in combustion and gasification research. The discrimination between sodium and potassium is possible due to differences in their surface desorption kinetics and facilitated by rapidly reversing the field potential between the ion source and the nearby collector. The instrument is evaluated in a series of laboratory experiments using size-selected alkali salt particles containing KCl, NaCl, K2SO4, Na2SO4, KNO3 and NaNO3. The filament temperature was found to be a key influencing factor in order to optimize the strength and Na-K deviation of the observed ion current. The ability to simultaneously report absolute concentrations of Na and K makes the instrument attractive for solid fuel conversion of alkali-rich fuels such as low-grade biomass and to explore behavior deviations of Na and K in high temperature processes. © 2021 The Author(s). Published by IOP Publishing Ltd.
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| 16. |
- Gall, Dan, 1981, et al.
(författare)
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Alkali Monitoring of Industrial Process Gas by Surface Ionization─Calibration, Assessment, and Comparison to in Situ Laser Diagnostics
- 2021
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 35:24, s. 20160-20171
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present rigorous calibration and assessment of a surface ionization detector (SID) for alkali monitoring in industrial process gases and compare it to an in situ laser diagnostic method called collinear photofragmentation and atomic absorption spectroscopy (CPFAAS). The side-by-side comparison of the time-resolved alkali concentration was performed in a technical-scale gas burner seeded with selected alkali salts, corresponding to alkali molar fractions of 10-100 ppm in the flue gas. The SID operates at room temperature and relies on extraction, dilution, and conditioning of the sample gas, whereas CPFAAS provides in situ molecular data. During KCl addition, the instruments were in good agreement: 80.1 ppm (SID) and 88.5 ppm (CPFAAS). In addition to the field measurements, internal validation of SID performance parameters (flow, electric field strength, and filament temperature) and external parameters (particle size and salt composition) was performed. The difference in sensitivity toward different alkali salts was found to be considerable, which limits the quantitative assessment for a sample gas of unknown composition. The results demonstrate the capability and limitations of the SID and show that a SID can satisfactory monitor KCl levels in a process gas over several days of continuous measurements. However, for heterogeneous fuels with deficient characterization of the gas composition, the obtained SID signal is difficult to interpret without supportive diagnostics. The generic ability of the SID to detect Na and K in both gas and particle phases makes it a valuable complement to alkali diagnostics, such as spectroscopic techniques.
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| 17. |
- Gall, Dan, 1981, et al.
(författare)
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Recirculation of NO x and SO x Scrubber Effluent to an Industrial Grate Fired MSW Boiler-Influence on Combustion Performance, Deposition Behavior, and Flue Gas Composition
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 36:11, s. 5868-5877
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Tidskriftsartikel (refereegranskat)abstract
- The concept of scrubber effluent recirculation has recently received attention in connection to NOxemission control. Here, we present data from an industrial-scale MSW-fired plant, where effluent from a combined NOxand SOxscrubber was recirculated and injected into a grate-fired boiler. The combustion characteristics were carefully studied during the injections to observe the potential effects on burnout and flue gas composition. In addition, deposition measurements were performed to observe effects on growth rate and chemical composition of deposits, which are critical factors for any solid fuel-fired heat and power plant. The recirculation of the nitrogen-rich waste streams was performed via pre-existing liquid injection equipment, and the results show that the N-containing compounds in the scrubber effluent were efficaciously reduced to inert nitrogen gas. Furthermore, the recirculation of the scrubber effluent may reduce ammonia demand for selective non-catalytic reduction systems by inhibiting the formation of ammonium chloride. Sulfur and alkali components in the effluent increased the deposition growth rate and also changed the chemical composition of the deposits. Understanding how the local conditions at the injection point influence the distribution and speciation of the injected compounds is essential for a successful recirculation strategy.
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| 18. |
- Gunnarsson, Adrian, 1990, et al.
(författare)
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Discrete-Ordinates Modelling of the Radiative Heat Transfer in a Pilot-Scale Rotary Kiln
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:9
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents work focused on the development, evaluation and use of a 3D model for investigation of the radiative heat transfer in rotary kilns. The model applies a discrete-ordinates method to solve the radiative transfer equation considering emission, absorption and scattering of radiation by gas species and particles for cylindrical and semi-cylindrical enclosures. Modelling input data on temperature, particle distribution and gas composition in the radial, axial and angular directions are experimentally gathered in a down-scaled version of a rotary kiln. The model is tested in its capability to predict the radiative intensity and heat flux to the inner wall of the furnace and good agreement was found when compared to measurements. Including the conductive heat transfer through the furnace wall, the model also satisfactorily predicts the intermediate wall temperature. The work also includes a first study on the effect of the incident radiative heat flux to the different surfaces while adding a cold bed material. With further development of the model, it can be used to study the heat transfer in full-scale rotary kilns.
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| 19. |
- Gunnarsson, Adrian, 1990, et al.
(författare)
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Full-scale 3D-modelling of the radiative heat transfer in rotary kilns with a present bed material
- 2020
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 147
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Tidskriftsartikel (refereegranskat)abstract
- This work discusses the development and use of a detailed 3D radiative heat transfer model of a rotary kiln with a present bed material, used for iron ore pelletizing. A discrete ordinates method is used to solve the radiative heat transfer equation with radiative properties calculated using a weighted-sum-of-grey-gases (WSGG) model for gases and Mie and Rayleigh theory for particles including fuel, ash and soot. Measurement data gathered from a pilot-scale test furnace, comprising temperature, gas composition and particle concentration, is used in combination with temperature data and operation parameters gathered from a conventional rotary kiln to model a full-scale rotary kiln with a present bed material. The modelled cases have a thermal input of about 37 MWth and in addition to radiative heat transfer, conductive heat transfer within, as well as between, the bed and wall material are included in the model along with convective heat transfer from the gas and heat release from exothermic reactions in the bed. The model also considers the rotational wall and includes a simplified mixing model of the bed material as well as heat losses from the outside wall of the rotary kiln due to radiation and convection. For two different flames, one coal and one oil flame, surface temperatures are calculated on the inside and outside of the rotary kiln and compared to measurements. The model appears to predict the inner wall and bed surface temperatures well with errors less than 11%. The total heat transfer to the present bed material was also studied revealing that more than 80% originated from the radiative heat transfer within the furnace.
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| 20. |
- Johansson, Jakob, 1990, et al.
(författare)
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Influence of Nitrogen Dioxide Absorption on the Sulfite Oxidation Rate in the Presence of Oxygen: Online Raman Measurements
- 2023
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Ingår i: Industrial & Engineering Chemistry Research. - 1520-5045 .- 0888-5885. ; 62:49, s. 21048-21056
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of sulfite(aq) is investigated by passing O2, N2, and NO2 over a sulfite solution in a bubbling flask. The influence on sulfite oxidation of NO2 absorption and the presence of thiosulfate (an oxidation inhibitor) is investigated. The experiment is focused on conditions relevant to a combined SO2 and NO2 industrial flue gas cleaning system. Liquid composition is measured in situ using Raman spectroscopy equipped with immersion probes. Regression models are developed to quantify SO32-, HSO3-, S2O32-, SO42-, NO2-, NO3-, and CO32- also in mixtures of the mentioned chemicals. The results show that Raman spectroscopy is a possible method for liquid analysis of a NOx/SOx removal system. Speciation is successful within the limits of the experiment for most molecules. SO42-, CO32-, and S2O32- are quantified with high certainty; SO32- and HSO3- are quantified with some uncertainty and should be above 10 mM for quantitative measurements. NO3- concentration is below the limit of detection in the continuous experiments. The measured reaction rates of sulfite (SO32-) and bisulfite (HSO3-) oxidation with O2 are in agreement with the reviewed literature. Absorption of NO2(g) and the consequent formation of nitrite enhance sulfite oxidation. The addition of thiosulfate to the liquid reduces the rate of SO32- oxidation by ∼90% while maintaining NO2 absorption. The influence of NO2(g) and thiosulfate supports a previously proposed mechanism for sulfite oxidation via a radical chain mechanism.
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