| 1. |
- Allgurén, Thomas, 1986, et al.
(författare)
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Alkali sulfation during combustion of coal in a pilot scale facility using additives to alter the global sulfur to potassium and chlorine to potassium ratios
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:3, s. 4171-4178
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Tidskriftsartikel (refereegranskat)abstract
- Due to the urgent needs to reduce anthropogenic carbon dioxide emissions there is an increasing interest in the use of alternative fuels. For this reason, there is a need for new knowledge on how to design and adapt existing heat and power plants to biogenic and waste-derived fuels. This work relates to co-firing of biomass and coal and the sulfation of alkali chlorides in coal-fired flames doped with chemical additives. We aim to examine the global time scales of alkali sulfation and chlorination based on combustion experiments that were conducted in a 30-kW coal flame. Temperature, gas and particle composition measurements were conducted. Both experiments and modelling support that the apparent alkali sulfation kinetics are fast in a coal-fired flame and that it is dominated entirely by the presence of SO 2. The availability of oxygen and carbon monoxide, or hydrocarbons, is also critical to sustain the sulfation reaction cycle; low concentrations are sufficient. For industrial boilers this implies that sulfur addition, in combination with reburning, should constitute an efficient strategy to mitigate alkali-chlorination and the related high temperature corrosion.
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| 2. |
- Allgurén, Thomas, 1986
(författare)
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Chemical Interactions between Potassium, Nitrogen, Sulfur and Carbon Monoxide in Suspension-Fired Systems
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Drastic cuts in global CO2 emissions are needed to mitigate global warming and limit the average temperature increase to well below 2ºC. The power generation sector is largely based on fossil fuels and generates a significant share of the global CO2 emissions. Thus, new power generation processes with substantially reduced CO2 emissions need to be employed to mitigate global warming. Two alternatives that may be part of the solution is the replacement of coal with biomass or to apply the concept of carbon capture and storage (CCS). In CCS processes the CO2 is captured and processed on the plant site and thereafter transported to a storage location. Oxy-fuel combustion, which has been studied in this thesis, has been demonstrated in large-scale pilot plants (30-60 MW). This work investigates the possibilities to co-combust biomass and coal in oxy-fuel combustion with CO2 capture. Biomass combined with CO2 capture has the potential to contribute to negative CO2 emissions. However, the high temperature corrosion (HTC) and the related K-Cl-S chemistry need to be studied in detail to determine the potential consequences for corrosion on heat transfer surfaces. This, since the use of biomass in power generation is problematic due to the relative high content of alkali (mainly potassium) and chlorine. Together these compounds form KCl, a salt that causes corrosive deposits and subsequent issues with so called high temperature corrosion (HTC). When sulfur is present, alkali sulfates may form instead of alkali chlorides. Sulfates have a higher melting point and causes less problems with corrosion and sulfates are therefore preferred instead of chlorides. The work in this thesis is based on experiments performed in a 100 kW combustion unit and modelling of chemical kinetics. Both the experimental and modelling results show that a high SOX concentration is preferable to achieve a high degree of sulfation of the alkali chlorides. In oxy-fuel combustion, the SOX concentration is typically high due to flue gas recycling that enables almost complete potassium sulfation in some of the studied oxycombustion atmospheres. This makes oxy-fuel combustion an attractive process for cocombustion of coal and biomass, since alkali chloride formation can be suppressed. In addition, the effect of KCl and SO2 on the CO oxidation and NO formation has been studied in both experimental and modelling work. The results show that KCl can promote COoxidation in a CO2 rich environment. However, no change was observed for the total burnout time even though the CO concentration was decreased locally. Regarding the nitrogen chemistry, KCl was found to inhibit the formation of NO whereas SO2 promotes the oxidation of already formed NO to NO2.
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| 3. |
- Allgurén, Thomas, 1986, et al.
(författare)
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Chemical Interactions between Potassium, Sulfur, Chlorine, and Carbon Monoxide in Air and Oxy-fuel Atmospheres
- 2020
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:1, s. 900-906
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental and modeling work on the interaction between the K, Cl, and S components, and these chemical interactions are studied in both air-fuel and oxy-fuel atmospheres. Detailed kinetic modeling is conducted to examine the potassium chloride sulfation and its interaction with CO oxidation in both nitrogen- and carbon-dioxide-based atmospheres. The oxidation of CO enhances the kinetics of alkali sulfation for typical post-flame conditions, below 1000 °C, in both atmospheres. For higher temperatures, sulfation kinetics are promoted even further in CO2-rich atmospheres. Oxy-fuel atmospheres, i.e., CO2-rich atmospheres, also promote increased levels of CO in technical-scale flames. Therefore, in practical systems, enhanced sulfation kinetics will automatically be promoted by flue gas recirculation. Also, the availability of sulfur, in the form of an increased SO2 concentration, often enables complete sulfation of alkali in oxy-fuel atmospheres as a result of the flue gas recirculation. The availability of SO3 may increase in oxy-fuel compared to air-fuel atmospheres as a result of either elevated SO2 levels or different sulfation reaction patterns, as discussed in the modeling of this work. However, SO3 has no significant impact on the overall sulfation rates in oxy- compared to air-fired systems.
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| 4. |
- Allgurén, Thomas, 1986, et al.
(författare)
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Influence of KCI and SO2 on NO Formation in C3H8 Flames
- 2017
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 31:10, s. 11413-11423
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Tidskriftsartikel (refereegranskat)abstract
- The use of low-quality fuels in power generation plants is typically motivated by the potential for reducing fuel costs or CO2 emissions, the latter in the case of a fuel based on biomass. These features make low-quality fuels attractive, although their use for power generation is usually problematic due to their composition. One of the main issues is high-temperature corrosion (HTC), which is caused by alkali-containing chlorides. The alkali chlorides, which are formed from alkali metals and chlorine released from the fuel during the combustion process, are a particular problem. HTC is often related to the combustion of fuels with a low sulfur-to-potassium ratio, such as biomass, and it has a significant effect on the thermal efficiency and/or the maintenance cost of the power plant. Sulfuric and alkali species not only influence the formation of highly corrosive salts but also affect other aspects of combustion chemistry. While the present work relates to HTC chemistry, it focuses on how potassium chloride and sulfur dioxide influence the formation of NO. The experiments were carried out in a 100 kW test facility using C3H8 as the fuel. In order to examine the influence of SO2 and KCI on combustion, these two components were injected into the combustion reactor. In the experiments, pure gaseous SO2 was injected upstream of the burner. KCI was fed as an aqueous solution (3.34%, of KCI) that was sprayed directly into the flame. Pure water was also injected, to distinguish any possible interaction between KCI and water. Kinetic modeling was conducted to examine the reaction routes and activities. The results show that both KCI and SO2 suppress the formation of NO. KCI appears to inhibit the formation of NO, whereas SO2 decreases the concentration of NO by enhancing its oxidation to NO2.
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| 5. |
- Allgurén, Thomas, 1986, et al.
(författare)
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Investigation of the Behavior of Alkali Chlorides during Sulfur Recirculation in a Waste-to-Energy Facility
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High temperature corrosion related issues are known problems for Waste-to-Energy facilities where the formation of alkali chlorides is among the most problematic species formed during the combustion. Sulfur Recirculation is a novel technology developed to reduce the chlorine content in the ash and in that way also the corrosivity of the ash. This concept has been installed at the Maabjerg Energy Center (MEC) in Denmark. This work aims to take a first step towards a reaction kinetics based model that can describe systems like the MEC boiler and to evaluate the impact of Sulfur Recirculation. This is done by implementing a plug flow reactor model in the software Chemkin. Previously obtained data from on-site experiments and CFD simulations is used as input to the model. The model is focused on describing the sulfation of alkali chlorides and the result from the model is compared to experiments. The model is able to predict the degree of sulfation with less than 10% deviation from the experimental results. Both the experiment and the model show a clear benefit from implementing sulfur recirculation which lowers the chlorine content in the up to as much as 70%. It is, however, also shown that the results are sensitive towards several of the assumptions made. Even though there is a relatively good agreement in final sulfation between model and experiments the model is not able to represent the detailed chemistry in a realistic way in its current state; further development is required.
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| 6. |
- 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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| 7. |
- Allgurén, Thomas, 1986, et al.
(författare)
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NO formation during co-combustion of coal with two thermally treated biomasses
- 2022
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- The combustion behavior of biomass as a fuel varies dependent on source of the raw material, but also on the type of pre-treatment. In this work steam exploded and torrefied woody biomass were studied with respect to NOx formation in co-firing experiments. Most of the reported data is based on small scale experiments and simulations. In this work, however, have three different cases been investigated experimentally in a 1.5MW(th) combustor supported by reaction simulations. One case corresponds to firing 100% Utah bituminous coal and two cases where 15% of the coal (on a mass basis) has been replaced with either torrefied or steam exploded biomass. Two of the cases was also studied in a utility scale 1.3 GW(th) industrial boiler. In both units did the case with pure coal result in the highest amount of NO formed, which was expected due to the higher amount of fuel-bound nitrogen in the coal, as compared to the biomass fuels. The fuel analyses indicate that the nitrogen content is the same in the two investigated biofuels. However, the amount of NO formed differed. Gas composition measurements reveal that the partitioning of volatile nitrogen species (HCN and NH3) varies between the biomass co-firing cases. This was investigated further using detailed reaction simulations and is suggested as the main reason for the observed difference in NO formation.
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| 8. |
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| 9. |
- Allgurén, Thomas, 1986, et al.
(författare)
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The Influence of Alkali, Chlorine and Sulfur on Aerosol Formation
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of low-quality fuels in power generation is typically motivated by a potential reduction in fuel costs or CO2 emissions, the latter in case the fuel is based on biomass. These features make low quality fuels attractive at the same time as such fuels are usually problematic to use in power generation due to fuel composition. One of the main issues is deposition of aerosols upon heating surfaces reducing heat transfer and causing high-temperature corrosion (HTC). The later most often related to alkali chlorides, and these are formed from alkali species and chlorine when released during the combustion process. The present work aims to investigate how the gas phase chemistry are connected to the formation aerosols and their characteristics. This is an ongoing work why only part of the preliminary results is presented focusing on the interaction between alkali, sulfur and chlorine in the gas phase. The results presented here indicate a clear correlation between the S/Cl ratio and the formation of alkali sulfates over chlorides. It is also indicated that the local conditions at which the species are released and available in the gas phase is important for the resulting formation of alkali sulfates.
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| 10. |
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