| 1. |
- Bäckström, Daniel, 1985, et al.
(author)
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On the use of alternative fuels in rotary kiln burners - An experimental and modelling study of the effect on the radiative heat transfer conditions
- 2015
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In: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 138, s. 210-220
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Journal article (peer-reviewed)abstract
- Abstract In this work, the radiative heat transfer conditions in a 400 kWfuel test furnace were studied. The test furnace is a scaled pilot of a rotary kiln furnace used in iron ore pellet production. In particular, the study focuses on the choice of fuel and the subsequent effect on temperature and radiative conditions in the flame. Several co-firing flames of coal and biomass were investigated and also other fuels such as heavy fuel oil and natural gas. The test furnace was used in the experiments, and radiative intensity was measured with a narrow angle radiometer. Detailed radiation modelling was performed using spectral models for gas and particle properties. The results show that all co-firing flames give a shorter radiating flame length. Based on the radiation modelling, it was also shown that the particle radiation dominates the heat transfer from the flames. Due to the high pre-heating temperature of the combustion air (1100°C), the flame temperatures were generally very high. The flame temperature in the natural gas flame was likely around 2000°C while the coal flame temperatures were estimated to 1500-1600°C. The two coals tested, having almost identical fuel specifications, resulted in a substantial difference in the radiation intensity emitted by the flame. This emphasizes the need of direct radiation measurements to evaluate fuel changes in industrial processes that are highly dependent on the heat transfer conditions.
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| 2. |
- Edland, Rikard, 1990, et al.
(author)
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Scaling of Pulverized-Fuel Jet Flames That Apply Large Amounts of Excess Air - Implications for NOx Formation
- 2019
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In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 12:14
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Journal article (peer-reviewed)abstract
- Measures to reduce nitrogen oxides (NOx) formation in industrial combustion processes often require up-scaling through pilot-scale facilities prior to being implemented in commercial scale, and scaling is therefore an important aspect of achieving lower NOx emissions. The current paper is a combined experimental and modelling study that aims to expand the understanding of constant velocity scaling for industrial jet flames applying high amounts of excess air. These types of flames are found in e.g., rotary kilns for production of iron ore pellets. The results show that, even if the combustion settings, velocity, and temperature profiles are correctly scaled, the concentration of oxygen experienced by the fuel during char combustion will scale differently. As the NO formation from the char combustion is important in these flames, the differences induced by the scaling has important impacts on the efficiencies of the applied primary measures. Increasing the rate of char combustion (to increase the Damköhler number), by using, for example, smaller-sized particles, in the pilot-scale is recommended to improve scaling.
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| 3. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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3D-modelling of the radiative heat transfer in a rotary kiln for iron ore pellets production
- 2015
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In: Nordic Flame Days, 2015.10.06-2015.10.07, Helsingör.
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Conference paper (other academic/artistic)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 the discrete-ordinates method to solve the radiative transfer equation considering emission, absorption and scattering of radiation by gas species and particles. The model uses input of temperature, particle distribution and gas composition in the radial, axial and angular directions. The model is compared with literature data and a 1D-model for validation. The model is tested in its capability to model radiative intensity using experimental data from a 400 kW rotary kiln test furnace and used to calculate the radiative heat flux to the wall using different temperature and particle loads as well as different fuels and fuel combinations. The results show that the 3D-model can be used to predict trends when operating conditions are changed.
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| 4. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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Heat Transfer Conditions in a Rotary Kiln Test Furnace Using Coal, Biomass and co-firing Burners
- 2016
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In: Clearwater Clean Coal Conference, 2016.06.05-2016.06.09, Clearwater, Florida, USA.
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Conference paper (other academic/artistic)abstract
- In this work the radiative heat transfer in a 580 kWth pilot scale test furnace resembling a full scale rotary kiln used for production of iron ore pellets has been studied. The aim has been to quantify the radiative heat transfer in coal and co-firing flames in a project which examines the use of biomass in the grate-kiln process. Three cases of coal and co-firing are in this work studied and evaluated using a detailed radiation model. The model treats the furnace as an axisymmetric and infinitely long cylinder. Overall, the differences in radiative intensities and heat fluxes between the three studied fuel combinations are minor which implies that introduction of renewable fuels by co-firing in a full scale rotary kiln should be feasible with respect to heat transfer conditions. The modeling results show reasonable to good predictivity compared to the measured intensity data, which implies a satisfactory quality of the collected experimental data.
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| 5. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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Modelling and measurements of radiation in a 400kWth rotary kiln test furnace
- 2015
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In: Industrial Furnaces and Boilers, 2015.04.07-2015.04.10, Porto Gaia, Portugal.
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Conference paper (other academic/artistic)abstract
- This work is focused on the radiative heat transfer in rotary kilns used for iron ore production with the aim to obtain a better understanding of the radiation and peak flame temperatures. This was done by performing measurements in a cylindrical, refractory lined, 400 kWth down scaled model of a rotary kiln and evaluating the results with a detailed radiation model. A mixture of coal and torrefied biomass was used as fuel in the experiments. Radiative intensity, gas composition, temperature and particle concentration were measured along the diameter in the flame. The radiation model treats the furnace as an axisymmetric and infinitely long cylinder. The gas properties are calculated with a statistical narrow-band model while the particle properties are calculated with Mie theory. The radiative heat transfer, peak flame temperatures and the influence from different parameters using sensitivity analyses are studied. It is shown that the total radiation is dominated by the contribution of particles, hence the total radiation is sensitive to changes in the particle concentration and size distribution. It was also possible to estimate the peak flame temperatures, and conclude that more accurate temperature and particle measurements are needed in future work.
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| 6. |
- Gunnarsson, Adrian, 1990, et al.
(author)
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Radiative Heat Transfer Conditions in a Rotary Kiln Test Furnace Using Coal, Biomass, and Cofiring Burners
- 2017
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 31:7, s. 7482-7492
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Journal article (peer-reviewed)abstract
- This work studies the radiative heat transfer in a 580 kW(th) pilot scale test furnace that resembles a full-scale rotary kiln for iron ore pellet production. The aim is to quantify the radiative heat transfer in coal and cofiring flames and also to study the possibility to model the radiative heat transfer for such combustion conditions. Three combustion cases of coal and cofiring are studied, and an evaluation is made using a detailed radiation model. The test furnace is cylindrical and refractory lined but does not rotate and no iron ore pellet bed material is included. In-flame measurements of temperature, gas composition, particle concentration, radiative intensity, and radiative heat flux are conducted for the different fuels and fuel combinations. Overall, the differences in measured radiative intensities and heat fluxes among the three studied fuel cases are minor, which implies that introduction of renewable fuels by cofiring in a full-scale rotary kiln should be feasible with respect to heat transfer conditions. In the model, the furnace is treated as an axisymmetric and infinitely long cylinder, and gas properties are calculated with a statistical narrow-band model, while particle properties are calculated using Mie theory. The modeling results show reasonable to good predictivity compared to the measured intensity data. This indicates that the experimental data is of good quality but also indicates the potential use of the model in full-scale rotary kiln calculations in future work.
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| 7. |
- Colin, Samuel, et al.
(author)
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Flame Characterization of Cofiring Gaseous and Solid Fuels in Suspensions
- 2024
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In: ACS Omega. - 2470-1343. ; 9:26, s. 28268 -28282
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Journal article (peer-reviewed)abstract
- This work characterizes technical scale flames of suspension firing of gaseous and solid fuel mixtures through in-flame measurements with focus on nitrogen oxide (NOx) formation. The aims are to investigate the impacts of substituting a solid fuel with a gaseous fuel on the important mechanisms for NOx formation and to highlight important considerations for burner design. The investigation was performed in a 100 kW test unit that fires mixtures of propane and lignite. The global emissions levels and in-flame compositions were measured. A detailed reaction model was used to interpret the experimental results. The study highlights the importance of the early release of volatile nitrogen to reduce the levels of NOx. The findings indicate that substituting lignite by propane is advantageous in terms of reducing NO emissions, primarily due to the diminished input of fuel-bound nitrogen to the flame. However, this holds true only if the flame temperature of the gaseous fuel does not increase excessively. Finally, introducing a relatively small quantity of solid fuel to a propane flame appears to alter the flame behavior to resembles that of the “solid fuel,” with a longer and wider flame. Despite this, carbon monoxide and nitrogen oxide concentrations remain like gas combustion but more dispersed.
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| 8. |
- Edland, Rikard, 1990, et al.
(author)
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Evaluation of NOx-Reduction Measures for Iron-Ore Rotary Kilns
- 2020
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:4, s. 4934-4948
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Journal article (peer-reviewed)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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| 9. |
- Edland, Rikard, 1990, et al.
(author)
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Formation of nitrogen oxides in rotary kiln burners: an assessment of pilot scale experiments using gaseous, liquid and solid fuels
- 2015
-
In: INFUB 2015.
-
Conference paper (other academic/artistic)abstract
- The combustion process in rotary kilns for iron ore production is associated with high temperatures and large amounts of highly preheated air (λ=5-6). These conditions are favourable for NOx formation. Further, coal is typically the main fuel in the process and the CO2 emissions need to be reduced. Thus, emission control strategies are becoming of increasing importance for this type of industrial processes. The present work studies the formation of NOx during combustion of oil, gas, two coals and different blends of coal and biomass. The paper includes both experimental and modelling work. The experiments were performed in co-operation with LKAB using their pilot scale burner test facility (400 kWfuel), which is able to simulate the conditions of the full-scale process. The model, which is used to interpret the experimental results, is based on detailed reaction kinetics with simplified descriptions of temperature and mixing profiles. The results show that oil and gas flames lead to significantly higher NOx formation than solid fuel flames. In general, the thermal formation route is shown to be an important contributor to NOx formation, i.e. also for the solid fuels.
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| 10. |
- Edland, Rikard, 1990, et al.
(author)
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Implications of Fuel Choice and Burner Settings for Combustion Efficiency and NOx Formation in PF-Fired Iron Ore Rotary Kilns
- 2017
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In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 31:3, s. 3253-3261
-
Journal article (peer-reviewed)abstract
- The combustion process applied in the grate-kiln process for iron ore pellet production employs air-to-fuel equivalence ratios in the range of 4-6, typically with coal as fuel and high-temperature air (>1000 degrees C) as oxidant. The NOx emissions from these units are in general significantly higher than those in other combustion systems, and the large flows of flue gases make the implementation of secondary measures for NOx control costly. Therefore, it is of importance to investigate NOx. formation under combustion conditions relevant for iron ore production, in order to control the emissions from these units. The present work examines NO formation during the combustion of four pulverized coals, as well as during cofiring with biomass in a pilot-scale kiln (580 kWfuel) based on a two-week experimental campaign. The influence of burner settings was also included in the investigation. Based on the presented experimental results and the results of previous modeling and experimental studies, we suggest that the NOx emissions are mainly the result of a high conversion of fuel-bound nitrogen (fuel-N) to NO. In particular, char-bound nitrogen (char-N) conversion appears to be higher than in conventional pulverized fuel flames, presumably due to the high levels of oxygen present in the char-burnout region. The temperatures in the kiln varied between the test cases, but thermal NO formation is estimated to be of low importance.
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