| 1. |
- Svensson, Elin, 1980, et al.
(författare)
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Assessing the value of a diversified by-product portfolio to allow for increased production flexibility in pulp mills
- 2020
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 35:4, s. 533-558
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a model for design optimization of pulp mill steam utility systems subject to variations in energy prices and steam demands. A Scandinavian Kraft pulp mill is used as case study to investigate investment opportunities in lignin extraction and new turbines. The model enables solutions to be identified that are more flexible than the solutions that would have been identified with a corresponding model using, for example, annual average values for key input data. The results from the case study show that lignin extraction has a potential to contribute to flexibility in pulp mill electric power production under certain conditions provided that the mill invests in both lignin extraction and condensing turbine capacity. However, the potential electric power production flexibility will vary over time. In the studied mill, with a capacity increased to around 1.3 million tonnes/a of pulp, it is estimated to vary between 15 and 30 MW. Furthermore, investment in new condensing turbine capacity only seems to be attractive if electricity prices that are considerably higher than the spot prices of recent years are assumed. Such prices may occur if there is a clear value of tradable electricity certificates or if future electricity prices rise significantly.
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| 2. |
- Allgurén, Thomas, 1986, et al.
(författare)
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NO formation during co-combustion of coal with two thermally treated biomasses
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The behavior of biomass as a fuel varies a lot. Not only between different sources of raw material, but also depending on if they have been pre-treated, and if so, also depending on the type of treatment. Two types of thermal pre-treatments of woody biomass used for combustion in suspension systems are torrefaction and steam explosion. These two types of pre-treated biomass were investigated in this work with focus on the nitrogen chemistry, and were investigated both experimentally in a 1.5MWth combustion unit and by performing detailed reaction simulations. Three different cases have been investigated. One case with 100% Utah Sufco coal and two cases where 15% of the coal (on a mass basis) has been replaced with either torrefied or steam exploded biomass. Even though only 15% of the coal has been substituted there is a clear difference in the amount of NO formed between the cases. The pure coal had the highest amount of NO formed which was expected due to the higher amount of fuel-bound nitrogen in the coal compared to the biomasses. The fuel analyses indicate that the nitrogen content is the same in the two investigated bio fuels. Despite this fact, the amount of NO formed was when coal was co-fired with torrefied biomass than with steam exploded biomass. The gas composition data from the in-flame measurements show that the concentration of volatile nitrogen species (HCN and NH3) varies between the cases, which is suggested as the reason for the difference in the NO formation. The importance of when and where the nitrogen species are released is also shown in the modelling work, supporting what was observed experimentally.
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| 3. |
- 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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| 4. |
- Edland, Rikard, 1990, et al.
(författare)
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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
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Ingår i: INFUB 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 5. |
- 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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| 6. |
- Edland, Rikard, 1990, et al.
(författare)
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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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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 31:3, s. 3253-3261
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Edland, Rikard, 1990, et al.
(författare)
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Modeling the Contributions of Volatile and Char-Bound Nitrogen to the Formation of NOx Species in Iron Ore Rotary Kilns
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:2, s. 2321-2331
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Tidskriftsartikel (refereegranskat)abstract
- Given that more stringent NO x emission limits are expected in the near future, several industrial processes are in need of NO x mitigation measures. The Grate-Kiln process, applied in the iron ore industry, is one such process. NO x formation is inherently high in the process, and due to the combustion conditions, several standard mitigation strategies are impractical. Alternative solutions are thus needed. The current paper aims at developing a model capable of describing the NO formation under conditions relevant in iron ore rotary kilns and to identify governing parameters that may be modified for mitigation purposes. The developed model uses detailed reaction modeling for the homogeneous combustion chemistry combined with simpler modeling with apparent kinetics for the heterogeneous chemistry. The main findings are that thermal NO is of low significance and that the NO formation during char combustion is the main contributor to the high NO x emissions. Attempting to control the partitioning between the volatile nitrogen and the char-bound nitrogen is suggested as a mitigation strategy, since the combustion of char is challenging to control compared to the combustion of volatiles.
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| 8. |
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| 9. |
- Edland, Rikard, 1990
(författare)
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NOx formation in iron ore rotary kilns
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron ore pellets are often produced using the so-called Grate-Kiln process, which is designed to oxidize the magnetite (Fe3O4) to hematite (Fe2O3) and to sinter the pellets so they can be used in steel manufacturing. The heat required for this process comes from the combustion of a pulverized fuel in a rotary kiln, involving the formation of a jet flame. To oxidize the pellets, large amounts of air are introduced into the kiln, and an air-to-fuel equivalence ratio of 4–6 is obtained. Furthermore, the air is pre-heated to >1000°C. High temperatures and large amounts of excess air are known to promote NOx formation and NOx emissions from iron ore processing plants are in general high. This thesis describes the NOx formation in the rotary kiln and identifies the governing parameters, with the aim of reducing the emissions. The work involves experiments in a pilot-scale kiln, as well as modeling work based on the same experiments. Data from a full-scale iron ore pelletization plant are also provided. From the experiments and the modeling work in this thesis, thermal NO is deemed to be of low importance in iron ore rotary kilns when solid fuels are combusted. Instead, the conditions during char combustion contribute significantly to the overall NOx formation. These results explain why many of the primary measures used to date have failed to achieve reductions in NOx emissions. Suggested additional primary measures include: raising the pyrolysis temperature (e.g., through oxygen addition) to deplete the char of nitrogen; or switching to a fuel with a lower nitrogen content (e.g., wood pellets). These are interesting alternatives for the future, and the latter may be tested in the coming years.
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| 10. |
- Edland, Rikard, 1990
(författare)
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NOx Formation in Rotary Kilns for Iron Ore Pelletization
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of iron ore pellets is often performed in the so-called Grate-Kiln process. The aim of the process is to oxidize the magnetite (Fe3O4) to hematite (Fe2O3) and to sinter the pellets so they can be used in steel manufacturing. The heat required for this is produced by combusting a pulverized fuel in a rotary kiln, forming a suspension flame. Due to the need to oxidize the pellets, large amounts of air are introduced to the kiln. Relating the amount of air to the fuel, an air-to-fuel equivalence ratio of 4-6 is obtained. Furthermore, the air is pre-heated to above 1000°C. High temperatures and large amounts of excess air are known to promote NOx formation and NOx emissions from iron ore processing plants are in general high.The aim of this work is to describe the NO formation in the rotary kiln and to identify governing parameters that may be altered to reduce the emissions. The thesis contains results from experiments in a pilot-scale kiln and from modeling work based on the same experiments. In the experiments, four coals were tested as well as co-firing coal with biomass. In-flame measurements of temperature and gas concentrations were performed with the use of a suction pyrometer and FTIR spectroscopy (+paramagnetism). Different primary measures for NOx reduction were also tested. Overall, reducing the primary air flow in the burner and co-firing coal with biomass were the most effective measures for reducing NOx emissions, compared to the reference case. Using natural gas and oil resulted in three times the amount of NOx. Reducing the total amount of excess air only resulted in a small NOx reduction, and increasing the secondary air temperature resulted in slightly decreased NOx formation.The general assumption in rotary kilns is that NOx is mostly formed by the thermal NO mechanism due to the high temperatures involved. Although this is certainly true for the cases with gas and oil, the experimental results indicate that NOx formed from the fuel-bound nitrogen is dominating the total NOx formation when solid fuels are used. The results from the detailed reaction modeling show that the thermal NO formation is of minor importance. Instead, the reduction of NO by char appears to be remarkably low in the kiln and responsible for the high net conversion of fuel-bound nitrogen to NO.
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