International Journal of Greenhouse Gas Control, Oct 1, 2017
Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example ... more Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example power plants and cement factories. Chemical-looping combustion (CLC) is one of the most promising capture technologies with potentially very low cost of CO 2 capture. In this study we present findings from a solid-fuel 100 kW chemical-looping combustor. A new oxygen carriera sintered manganese ore called Sinaushas been studied in the Chalmers 100 kW unit. The material has been investigated for an operational time of 51.5 h using five fuels: two bituminous coals, two types of wood char, and petcoke. The operational results clearly demonstrate the viability of the CLC process. In comparison to previously used iron-based oxygen carriers, the Sinaus material showed higher gas conversionup to 88%and lower loss of char to the air reactor, with carbon capture reaching as high as 100%. Furthermore, the solid-fuel conversion was higher, which is mainly an effect of the choice of fuel size. It was found that the choice of fuel has a crucial impact on performance. Previous experience has shown that the use of large fuel particles gives low carbon capture, whereas pulverized fuel leads to low solid-fuel conversion. By choosing the appropriateintermediatesize of fuel, it is possible to combine high carbon capture with high solid-fuel conversion. Previous studies indicate that the drawback of many manganese ores is the mechanical stability. Hence, a lot of emphasis was put on an in-depth study of the lifetime of the Sinaus material. Analyzing the production rate of fines, it was found the expected lifetime of the Sinaus particles was 100-400 h. This is lower than what has been found for iron-based material, but most likely sufficient for operation in full-scale chemical-looping applications. Whilst the production of fines was highest during operation with fuel, a lot of fines were produced also during operation without fuel. Seven experiments without fuel, i.e when the observed mechanical degradation was only due to high-velocity impacts and not chemical stress caused by phase transformations, gave a lifetime in the interval 220-1230 h. In conclusion, this first-of-its-kind investigation shows that the lifetime of the oxygen carrier is related to both the change in oxygen-carrier conversion and high-velocity impacts.
The global emissions of greenhouse gases are increasing and the development of mitigation measure... more The global emissions of greenhouse gases are increasing and the development of mitigation measures is becoming more important. One of the alternatives proposed is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground storage sites. Many of the largest point sources of carbon dioxide are power plants fuelled by fossil fuels. There are several technologies for adapting the combustion process to capture carbon dioxide. Chemical-looping combustion is one such option and has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming carbon dioxide-nitrogen separation. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrying material needs to meet a number of requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining the manganese with for example iron, silica and calcium. Chemicallooping combustion is mainly developed as a technology for fluidised-bed combustion with the oxygen carrier present as the bed material in the form of small particles. To perform well in a circulating fluidised bed the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. During the development of manganese combined oxides, materials with such properties have been identified.
International Journal of Greenhouse Gas Control, Oct 1, 2016
Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxi... more Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxide separation. A solid oxygen carrier circulates between the fuel reactor, where it provides oxygen for fuel oxidation, and the air reactor, where it is reoxidized. In this study a 10 kW th pilot reactor was used to examine a calcium manganite based oxygen carrier in continuous operation with natural gas as fuel during 99 h. The composition of the oxygen carrier can be described by the formula CaMn 0.775 Ti 0.125 Mg 0.1 O 3-␦. The main part of the material forms a perovskite crystal structure which has oxygen releasing properties. The fuel conversion was generally above 95% and full conversion was reached for certain operating conditions. The elutriation of fines, defined as particles smaller than 45 m, decreased over time to eventually be below detection limit. That suggested a loss of fines of less than 0.011 wt%/h, indicating a lifetime of over 9000 h. A high fuel conversion with no thermodynamic limitation, good mechanical strength, low cost and very low toxicity shows that this calcium manganite material qualifies as a very promising oxygen carrier.
Chemical engineering research & design, Sep 1, 2019
Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of... more Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese combined oxides, (Mn3O4)3.8-SiO2, (Mn3O4)5.8-(SiO2)1.5-TiO2, (Mn3O4)2-Fe2O3and Mn3O4-(Fe2O3)2.2-(Al3O4)1.1 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900℃ for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-loop... more Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-looping combustion. Three materials with varying composition of iron, manganese and silica have been evaluated in oxygen release experiments and during continuous operation with syngas and natural gas as fuel. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900°C. The other two materials showed similar performance, albeit with higher syngas conversion for the material with the lowest manganese fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10-14 h of operation with fuel addition before circulation disruption occurred, which was likely caused by particle attrition in all three cases. A phase diagram of the iron-manganese-silica system was constructed and the possible relevant phase transitions were identified. This analysis showed that more phase transitions could be expected for the materials with higher manganese content which could explain the superior performance of the material with the highest manganese content. This could possibly also explain the much higher oxygen release of this material. It should however be noted that this material was operated with the highest fuel reactor inventory per thermal power which could also be a contributing factor to the better performance of this material. The study shows that it is possible to achieve very high fuel conversion with combined oxides of iron, manganese and silica as oxygen carrier. The mechanical stability of the particles was rather poor though and would need to be improved. On the other hand the findings relating to material stability is not necessary valid for natural materials containing a number of additional elements. The results are also of interest as an indication of how natural materials with similar composition, i.e. manganese ores, would perform as oxygen carriers.
Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt... more Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt hydrocarbons in the flue gases. In order to minimize these emissions commercial combustion plants are operated with an excess of air added to the furnace. This increases the heat loss associated with the flue gas and thus decreases the overall efficiency of the plant. If combustion is carried out in a fluidised bed, the mixing between fuel and oxygen could be facilitated by using an active bed material with the ability to absorb and release chemically bonded oxygen, depending on the local oxygen concentration. Such active oxygen carriers would also facilitate conversion of relatively stable fuel components such as methane inside the bed, where ignition may be hampered by thermal inertia. This technology, Oxygen Carrier Aided Combustion (OCAC), which is a spin-off technology from Chemical-Looping Combustion (CLC), has recently been proposed. In this study, the potential of using manganese ores as active bed material has been investigated. Combustion of methane in a fluidised bed was carried out with two mixtures of manganese ore and silica sand (50/50 wt.%) in a laboratory circulating fluidised bed combustor. The performance of the manganese ores as active bed materials was compared with the performance of only silica sand in the same experimental unit. The main conclusion drawn from these experiments is that it was possible to significantly reduce the exhaust concentration of carbon monoxide by replacing 50 wt.% of the bed inventory of silica sand with manganese ore. Both ores released gaseous oxygen in inert atmosphere and oxygen was present in the exhaust gas at all times during combustion. The use of the active bed materials thus increased the fuel conversion for a given air-to-fuel ratio.
One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where ... more One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground geological formations. Many of the largest point sources of carbon dioxide are power plants and industries fuelled by fossil fuels or biomass. There are several technologies for adapting the combustion process to capture carbon dioxide and chemical-looping combustion is one such option. It has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming and costly separation of carbon dioxide and nitrogen. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrier material needs to meet several requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining manganese with for example iron, silica and calcium. Chemical-looping combustion is mainly developed as a technology for fluidised-bed combustion, with the oxygen carrier present as bed material in the form of small particles. To perform well in a circulating fluidised bed, the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. The work presented in this thesis examines the performance of manganese combined oxides as oxygen carriers in chemical-looping combustion units and in a conventional circulating fluidised bed. The operation has been carried out in two reactor systems with gaseous fuels and in a large-scale biomass boiler, in which the properties of the materials have been evaluated. It has been shown that full conversion of the fuel can be achieved in chemical-looping combustion with calcium manganites as oxygen carrier. Furthermore, combined oxides of ironmanganese-silica and manganese-silica have been examined. High fuel conversion was achieved with both combined oxide systems, but the mechanical stability of these materials was poor. It was found that the mechanical stability of combined oxides of manganese-silica could be improved by adding titania to the material. Interactions between a manganese ore and biomass ash were studied and it was found that ash components accumulated in the particles during operation in the biomass boiler. The reactivity of the ore decreased during operation which could be an effect of deactivation by the ash elements.
Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers f... more Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers for chemical-looping combustion. In this study, one pure manganese–silicon oxide and one similar material with titanium included in the formulation were examined as oxygen carriers. Experiments studying the oxygen release and the reactivity with syngas, methane, and wood char were carried out in a bench-scale circulating chemical-looping combustor and in a batch fluidized-bed reactor in the temperature range of 800–1050 °C. Both oxygen carriers released oxygen in inert atmosphere, and the concentration of oxygen released increased with temperature. The conversion of syngas and methane also increased with temperature for both materials and in both experimental setups. The reactivity with devolatilized wood char showed that the rate of oxygen uncoupling increased with temperature. However, it was concluded that the main fuel conversion mechanism was CLC and not CLOU for these materials. The inclusion of titanium ...
Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-loop... more Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-looping combustion. Three materials with varying composition of iron, manganese and silica have been evaluated in oxygen release experiments and during continuous operation with syngas and natural gas as fuel. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900°C. The other two materials showed similar performance, albeit with higher syngas conversion for the material with the lowest manganese fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10-14 h of operation with fuel addition before circulation disruption occurred, which was likel...
One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where ... more One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground geological formations. Many of the largest point sources of carbon dioxide are power plants and industries fuelled by fossil fuels or biomass. There are several technologies for adapting the combustion process to capture carbon dioxide and chemical-looping combustion is one such option. It has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming and costly separation of carbon dioxide and nitrogen. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrier material needs to meet several requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combin...
Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt... more Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt hydrocarbons in the flue gases. In order to minimize these emissions commercial combustion plants are operated with an excess of air added to the furnace. This increases the heat loss associated with the flue gas and thus decreases the overall efficiency of the plant. If combustion is carried out in a fluidised bed, the mixing between fuel and oxygen could be facilitated by using an active bed material with the ability to absorb and release chemically bonded oxygen, depending on the local oxygen concentration. Such active oxygen carriers would also facilitate conversion of relatively stable fuel components such as methane inside the bed, where ignition may be hampered by thermal inertia. This technology, Oxygen Carrier Aided Combustion (OCAC), which is a spin-off technology from Chemical-Looping Combustion (CLC), has recently been proposed. In this study, the potential of using manganes...
Carbon capture and storage (CCS) has been proposed as a bridging technology between the current e... more Carbon capture and storage (CCS) has been proposed as a bridging technology between the current energy production and a future renewable energy system. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. The interaction between oxygen carriers and biomass ashes is a poorly explored field. To make CLC a viable process, and thereby creating carbon emission reductions, more knowledge about the interactions between biomass ashes and oxygen carriers is needed. This study investigated solid-state reactions of three promising oxygen carriers, hematite, hausmannite and synthesised ilmenite with different biomass ash components. Oxygen carriers were exposed with the ash components: calcium carbonate, silica and potassium carbonate at 900℃ and at different reducing potentials. Crystalline phases of the exposed samples were determined using powder x-ray diffraction (XRD). Results showed that the oxygen carriers hausmannite and hematite interact to a higher extent compared to synthesised ilmenite regarding both physical characteristics and detectable phases. Synthesised ilmenite formed new phases only in systems including potassium. Thermodynamic calculations were performed on the multicomponent system and compared with experimental results. The results suggest that optimisation of systems involving manganese and potassium should be performed.
Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of... more Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese combined oxides, (Mn3O4)3.8-SiO2, (Mn3O4)5.8-(SiO2)1.5-TiO2, (Mn3O4)2-Fe2O3and Mn3O4-(Fe2O3)2.2-(Al3O4)1.1 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900℃ for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
Oxygen carrier aided combustion (OCAC) is a combustion concept which utilises oxygen carriers as ... more Oxygen carrier aided combustion (OCAC) is a combustion concept which utilises oxygen carriers as bed material in existing fluidised bed boilers. In this study, a manganese ore was used in a 12 MW th CFB boiler. During the experimental session with the manganese ore, the boiler was operated with wood chips as fuel for more than a week without replacement of the bed material. Bed samples were extracted each day in order to investigate interactions between the manganese ore and the wood ash components. The samples were examined with SEM/ EDX to follow the chemical distribution of ash elements in the bed particles. Physical properties such as density, size distribution and attrition resistance were followed as well. The impact on the reactivity of the oxygen-carrier bed particles was examined in a batch fluidised bed reactor at laboratory scale with gaseous fuels. Elemental composition analysis of the samples showed that common ash elements such as silicon, calcium, potassium, magnesium and sulphur had been accumulated in the manganese ore. Silicon, calcium and potassium were found throughout the particles as well as in formed surface layers. Sulphur was only found at the surface of the particles. The reactivity of the oxygen-carrying particles was affected during operation and showed a continuous decrease with increasing residence time in the boiler. The decrease in reactivity could be coupled to the layers of ash formed. Thus, this is an important issue when developing novel combustion concepts, such as OCAC and chemical-looping combustion (CLC), for biomass fuels.
International Journal of Greenhouse Gas Control, 2017
Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example ... more Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example power plants and cement factories. Chemical-looping combustion (CLC) is one of the most promising capture technologies with potentially very low cost of CO 2 capture. In this study we present findings from a solid-fuel 100 kW chemical-looping combustor. A new oxygen carriera sintered manganese ore called Sinaushas been studied in the Chalmers 100 kW unit. The material has been investigated for an operational time of 51.5 h using five fuels: two bituminous coals, two types of wood char, and petcoke. The operational results clearly demonstrate the viability of the CLC process. In comparison to previously used iron-based oxygen carriers, the Sinaus material showed higher gas conversionup to 88%and lower loss of char to the air reactor, with carbon capture reaching as high as 100%. Furthermore, the solid-fuel conversion was higher, which is mainly an effect of the choice of fuel size. It was found that the choice of fuel has a crucial impact on performance. Previous experience has shown that the use of large fuel particles gives low carbon capture, whereas pulverized fuel leads to low solid-fuel conversion. By choosing the appropriateintermediatesize of fuel, it is possible to combine high carbon capture with high solid-fuel conversion. Previous studies indicate that the drawback of many manganese ores is the mechanical stability. Hence, a lot of emphasis was put on an in-depth study of the lifetime of the Sinaus material. Analyzing the production rate of fines, it was found the expected lifetime of the Sinaus particles was 100-400 h. This is lower than what has been found for iron-based material, but most likely sufficient for operation in full-scale chemical-looping applications. Whilst the production of fines was highest during operation with fuel, a lot of fines were produced also during operation without fuel. Seven experiments without fuel, i.e when the observed mechanical degradation was only due to high-velocity impacts and not chemical stress caused by phase transformations, gave a lifetime in the interval 220-1230 h. In conclusion, this first-of-its-kind investigation shows that the lifetime of the oxygen carrier is related to both the change in oxygen-carrier conversion and high-velocity impacts.
Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed materia... more Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed material in fluidized bed boilers. The active material is reduced in fuel rich parts of the boiler and oxidized in air rich parts. Advantages could be achieved such as new mechanisms for oxygen transport in space and time. Here calcined manganese ore has been used as active bed material in a 12 MW th circulating fluidized bed boiler. The fuel was wood chips and the campaign lasted more than two weeks. From an operational point of view, manganese ore worked excellently. From the temperature profile of the boiler it can be concluded that fuel conversion was facilitated, especially in the dense bottom bed. The effect did not always translate to reduced emissions, which suggests that final combustion in the cyclone outlet was also influenced. Substituting 10% of the sand bed with manganese ore made it possible to reduce the air to fuel ratio without generating large amounts of CO. The use of 100% manganese ore resulted in higher emissions of CO than the sand reference, but, when combined sulphur feeding, dramatic reductions in CO emissions, up to 90% compared to sand reference, was achieved.
International Journal of Greenhouse Gas Control, 2016
Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxi... more Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxide separation. A solid oxygen carrier circulates between the fuel reactor, where it provides oxygen for fuel oxidation, and the air reactor, where it is reoxidized. In this study a 10 kW th pilot reactor was used to examine a calcium manganite based oxygen carrier in continuous operation with natural gas as fuel during 99 h. The composition of the oxygen carrier can be described by the formula CaMn 0.775 Ti 0.125 Mg 0.1 O 3-␦. The main part of the material forms a perovskite crystal structure which has oxygen releasing properties. The fuel conversion was generally above 95% and full conversion was reached for certain operating conditions. The elutriation of fines, defined as particles smaller than 45 m, decreased over time to eventually be below detection limit. That suggested a loss of fines of less than 0.011 wt%/h, indicating a lifetime of over 9000 h. A high fuel conversion with no thermodynamic limitation, good mechanical strength, low cost and very low toxicity shows that this calcium manganite material qualifies as a very promising oxygen carrier.
The global emissions of greenhouse gases are increasing and the development of mitigation measure... more The global emissions of greenhouse gases are increasing and the development of mitigation measures is becoming more important. One of the alternatives proposed is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground storage sites. Many of the largest point sources of carbon dioxide are power plants fuelled by fossil fuels. There are several technologies for adapting the combustion process to capture carbon dioxide. Chemical-looping combustion is one such option and has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming carbon dioxide-nitrogen separation. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrying material needs to meet a number of requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining the manganese with for example iron, silica and calcium. Chemicallooping combustion is mainly developed as a technology for fluidised-bed combustion with the oxygen carrier present as the bed material in the form of small particles. To perform well in a circulating fluidised bed the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. During the development of manganese combined oxides, materials with such properties have been identified.
Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers f... more Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers for chemical-looping combustion. In this study, one pure manganese–silicon oxide and one similar material with titanium included in the formulation were examined as oxygen carriers. Experiments studying the oxygen release and the reactivity with syngas, methane, and wood char were carried out in a bench-scale circulating chemical-looping combustor and in a batch fluidized-bed reactor in the temperature range of 800–1050 °C. Both oxygen carriers released oxygen in inert atmosphere, and the concentration of oxygen released increased with temperature. The conversion of syngas and methane also increased with temperature for both materials and in both experimental setups. The reactivity with devolatilized wood char showed that the rate of oxygen uncoupling increased with temperature. However, it was concluded that the main fuel conversion mechanism was CLC and not CLOU for these materials. The inclusion of titanium ...
International Journal of Greenhouse Gas Control, Oct 1, 2017
Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example ... more Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example power plants and cement factories. Chemical-looping combustion (CLC) is one of the most promising capture technologies with potentially very low cost of CO 2 capture. In this study we present findings from a solid-fuel 100 kW chemical-looping combustor. A new oxygen carriera sintered manganese ore called Sinaushas been studied in the Chalmers 100 kW unit. The material has been investigated for an operational time of 51.5 h using five fuels: two bituminous coals, two types of wood char, and petcoke. The operational results clearly demonstrate the viability of the CLC process. In comparison to previously used iron-based oxygen carriers, the Sinaus material showed higher gas conversionup to 88%and lower loss of char to the air reactor, with carbon capture reaching as high as 100%. Furthermore, the solid-fuel conversion was higher, which is mainly an effect of the choice of fuel size. It was found that the choice of fuel has a crucial impact on performance. Previous experience has shown that the use of large fuel particles gives low carbon capture, whereas pulverized fuel leads to low solid-fuel conversion. By choosing the appropriateintermediatesize of fuel, it is possible to combine high carbon capture with high solid-fuel conversion. Previous studies indicate that the drawback of many manganese ores is the mechanical stability. Hence, a lot of emphasis was put on an in-depth study of the lifetime of the Sinaus material. Analyzing the production rate of fines, it was found the expected lifetime of the Sinaus particles was 100-400 h. This is lower than what has been found for iron-based material, but most likely sufficient for operation in full-scale chemical-looping applications. Whilst the production of fines was highest during operation with fuel, a lot of fines were produced also during operation without fuel. Seven experiments without fuel, i.e when the observed mechanical degradation was only due to high-velocity impacts and not chemical stress caused by phase transformations, gave a lifetime in the interval 220-1230 h. In conclusion, this first-of-its-kind investigation shows that the lifetime of the oxygen carrier is related to both the change in oxygen-carrier conversion and high-velocity impacts.
The global emissions of greenhouse gases are increasing and the development of mitigation measure... more The global emissions of greenhouse gases are increasing and the development of mitigation measures is becoming more important. One of the alternatives proposed is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground storage sites. Many of the largest point sources of carbon dioxide are power plants fuelled by fossil fuels. There are several technologies for adapting the combustion process to capture carbon dioxide. Chemical-looping combustion is one such option and has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming carbon dioxide-nitrogen separation. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrying material needs to meet a number of requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining the manganese with for example iron, silica and calcium. Chemicallooping combustion is mainly developed as a technology for fluidised-bed combustion with the oxygen carrier present as the bed material in the form of small particles. To perform well in a circulating fluidised bed the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. During the development of manganese combined oxides, materials with such properties have been identified.
International Journal of Greenhouse Gas Control, Oct 1, 2016
Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxi... more Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxide separation. A solid oxygen carrier circulates between the fuel reactor, where it provides oxygen for fuel oxidation, and the air reactor, where it is reoxidized. In this study a 10 kW th pilot reactor was used to examine a calcium manganite based oxygen carrier in continuous operation with natural gas as fuel during 99 h. The composition of the oxygen carrier can be described by the formula CaMn 0.775 Ti 0.125 Mg 0.1 O 3-␦. The main part of the material forms a perovskite crystal structure which has oxygen releasing properties. The fuel conversion was generally above 95% and full conversion was reached for certain operating conditions. The elutriation of fines, defined as particles smaller than 45 m, decreased over time to eventually be below detection limit. That suggested a loss of fines of less than 0.011 wt%/h, indicating a lifetime of over 9000 h. A high fuel conversion with no thermodynamic limitation, good mechanical strength, low cost and very low toxicity shows that this calcium manganite material qualifies as a very promising oxygen carrier.
Chemical engineering research & design, Sep 1, 2019
Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of... more Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese combined oxides, (Mn3O4)3.8-SiO2, (Mn3O4)5.8-(SiO2)1.5-TiO2, (Mn3O4)2-Fe2O3and Mn3O4-(Fe2O3)2.2-(Al3O4)1.1 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900℃ for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-loop... more Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-looping combustion. Three materials with varying composition of iron, manganese and silica have been evaluated in oxygen release experiments and during continuous operation with syngas and natural gas as fuel. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900°C. The other two materials showed similar performance, albeit with higher syngas conversion for the material with the lowest manganese fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10-14 h of operation with fuel addition before circulation disruption occurred, which was likely caused by particle attrition in all three cases. A phase diagram of the iron-manganese-silica system was constructed and the possible relevant phase transitions were identified. This analysis showed that more phase transitions could be expected for the materials with higher manganese content which could explain the superior performance of the material with the highest manganese content. This could possibly also explain the much higher oxygen release of this material. It should however be noted that this material was operated with the highest fuel reactor inventory per thermal power which could also be a contributing factor to the better performance of this material. The study shows that it is possible to achieve very high fuel conversion with combined oxides of iron, manganese and silica as oxygen carrier. The mechanical stability of the particles was rather poor though and would need to be improved. On the other hand the findings relating to material stability is not necessary valid for natural materials containing a number of additional elements. The results are also of interest as an indication of how natural materials with similar composition, i.e. manganese ores, would perform as oxygen carriers.
Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt... more Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt hydrocarbons in the flue gases. In order to minimize these emissions commercial combustion plants are operated with an excess of air added to the furnace. This increases the heat loss associated with the flue gas and thus decreases the overall efficiency of the plant. If combustion is carried out in a fluidised bed, the mixing between fuel and oxygen could be facilitated by using an active bed material with the ability to absorb and release chemically bonded oxygen, depending on the local oxygen concentration. Such active oxygen carriers would also facilitate conversion of relatively stable fuel components such as methane inside the bed, where ignition may be hampered by thermal inertia. This technology, Oxygen Carrier Aided Combustion (OCAC), which is a spin-off technology from Chemical-Looping Combustion (CLC), has recently been proposed. In this study, the potential of using manganese ores as active bed material has been investigated. Combustion of methane in a fluidised bed was carried out with two mixtures of manganese ore and silica sand (50/50 wt.%) in a laboratory circulating fluidised bed combustor. The performance of the manganese ores as active bed materials was compared with the performance of only silica sand in the same experimental unit. The main conclusion drawn from these experiments is that it was possible to significantly reduce the exhaust concentration of carbon monoxide by replacing 50 wt.% of the bed inventory of silica sand with manganese ore. Both ores released gaseous oxygen in inert atmosphere and oxygen was present in the exhaust gas at all times during combustion. The use of the active bed materials thus increased the fuel conversion for a given air-to-fuel ratio.
One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where ... more One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground geological formations. Many of the largest point sources of carbon dioxide are power plants and industries fuelled by fossil fuels or biomass. There are several technologies for adapting the combustion process to capture carbon dioxide and chemical-looping combustion is one such option. It has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming and costly separation of carbon dioxide and nitrogen. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrier material needs to meet several requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining manganese with for example iron, silica and calcium. Chemical-looping combustion is mainly developed as a technology for fluidised-bed combustion, with the oxygen carrier present as bed material in the form of small particles. To perform well in a circulating fluidised bed, the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. The work presented in this thesis examines the performance of manganese combined oxides as oxygen carriers in chemical-looping combustion units and in a conventional circulating fluidised bed. The operation has been carried out in two reactor systems with gaseous fuels and in a large-scale biomass boiler, in which the properties of the materials have been evaluated. It has been shown that full conversion of the fuel can be achieved in chemical-looping combustion with calcium manganites as oxygen carrier. Furthermore, combined oxides of ironmanganese-silica and manganese-silica have been examined. High fuel conversion was achieved with both combined oxide systems, but the mechanical stability of these materials was poor. It was found that the mechanical stability of combined oxides of manganese-silica could be improved by adding titania to the material. Interactions between a manganese ore and biomass ash were studied and it was found that ash components accumulated in the particles during operation in the biomass boiler. The reactivity of the ore decreased during operation which could be an effect of deactivation by the ash elements.
Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers f... more Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers for chemical-looping combustion. In this study, one pure manganese–silicon oxide and one similar material with titanium included in the formulation were examined as oxygen carriers. Experiments studying the oxygen release and the reactivity with syngas, methane, and wood char were carried out in a bench-scale circulating chemical-looping combustor and in a batch fluidized-bed reactor in the temperature range of 800–1050 °C. Both oxygen carriers released oxygen in inert atmosphere, and the concentration of oxygen released increased with temperature. The conversion of syngas and methane also increased with temperature for both materials and in both experimental setups. The reactivity with devolatilized wood char showed that the rate of oxygen uncoupling increased with temperature. However, it was concluded that the main fuel conversion mechanism was CLC and not CLOU for these materials. The inclusion of titanium ...
Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-loop... more Combined oxides of iron, manganese and silica have been used as oxygen carriers for chemical-looping combustion. Three materials with varying composition of iron, manganese and silica have been evaluated in oxygen release experiments and during continuous operation with syngas and natural gas as fuel. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900°C. The other two materials showed similar performance, albeit with higher syngas conversion for the material with the lowest manganese fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10-14 h of operation with fuel addition before circulation disruption occurred, which was likel...
One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where ... more One alternative proposed to reduce greenhouse gas emissions is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground geological formations. Many of the largest point sources of carbon dioxide are power plants and industries fuelled by fossil fuels or biomass. There are several technologies for adapting the combustion process to capture carbon dioxide and chemical-looping combustion is one such option. It has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming and costly separation of carbon dioxide and nitrogen. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrier material needs to meet several requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combin...
Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt... more Insufficient mixing between fuel and air during combustion results in carbon monoxide and unburnt hydrocarbons in the flue gases. In order to minimize these emissions commercial combustion plants are operated with an excess of air added to the furnace. This increases the heat loss associated with the flue gas and thus decreases the overall efficiency of the plant. If combustion is carried out in a fluidised bed, the mixing between fuel and oxygen could be facilitated by using an active bed material with the ability to absorb and release chemically bonded oxygen, depending on the local oxygen concentration. Such active oxygen carriers would also facilitate conversion of relatively stable fuel components such as methane inside the bed, where ignition may be hampered by thermal inertia. This technology, Oxygen Carrier Aided Combustion (OCAC), which is a spin-off technology from Chemical-Looping Combustion (CLC), has recently been proposed. In this study, the potential of using manganes...
Carbon capture and storage (CCS) has been proposed as a bridging technology between the current e... more Carbon capture and storage (CCS) has been proposed as a bridging technology between the current energy production and a future renewable energy system. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. The interaction between oxygen carriers and biomass ashes is a poorly explored field. To make CLC a viable process, and thereby creating carbon emission reductions, more knowledge about the interactions between biomass ashes and oxygen carriers is needed. This study investigated solid-state reactions of three promising oxygen carriers, hematite, hausmannite and synthesised ilmenite with different biomass ash components. Oxygen carriers were exposed with the ash components: calcium carbonate, silica and potassium carbonate at 900℃ and at different reducing potentials. Crystalline phases of the exposed samples were determined using powder x-ray diffraction (XRD). Results showed that the oxygen carriers hausmannite and hematite interact to a higher extent compared to synthesised ilmenite regarding both physical characteristics and detectable phases. Synthesised ilmenite formed new phases only in systems including potassium. Thermodynamic calculations were performed on the multicomponent system and compared with experimental results. The results suggest that optimisation of systems involving manganese and potassium should be performed.
Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of... more Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese combined oxides, (Mn3O4)3.8-SiO2, (Mn3O4)5.8-(SiO2)1.5-TiO2, (Mn3O4)2-Fe2O3and Mn3O4-(Fe2O3)2.2-(Al3O4)1.1 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900℃ for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
Oxygen carrier aided combustion (OCAC) is a combustion concept which utilises oxygen carriers as ... more Oxygen carrier aided combustion (OCAC) is a combustion concept which utilises oxygen carriers as bed material in existing fluidised bed boilers. In this study, a manganese ore was used in a 12 MW th CFB boiler. During the experimental session with the manganese ore, the boiler was operated with wood chips as fuel for more than a week without replacement of the bed material. Bed samples were extracted each day in order to investigate interactions between the manganese ore and the wood ash components. The samples were examined with SEM/ EDX to follow the chemical distribution of ash elements in the bed particles. Physical properties such as density, size distribution and attrition resistance were followed as well. The impact on the reactivity of the oxygen-carrier bed particles was examined in a batch fluidised bed reactor at laboratory scale with gaseous fuels. Elemental composition analysis of the samples showed that common ash elements such as silicon, calcium, potassium, magnesium and sulphur had been accumulated in the manganese ore. Silicon, calcium and potassium were found throughout the particles as well as in formed surface layers. Sulphur was only found at the surface of the particles. The reactivity of the oxygen-carrying particles was affected during operation and showed a continuous decrease with increasing residence time in the boiler. The decrease in reactivity could be coupled to the layers of ash formed. Thus, this is an important issue when developing novel combustion concepts, such as OCAC and chemical-looping combustion (CLC), for biomass fuels.
International Journal of Greenhouse Gas Control, 2017
Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example ... more Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example power plants and cement factories. Chemical-looping combustion (CLC) is one of the most promising capture technologies with potentially very low cost of CO 2 capture. In this study we present findings from a solid-fuel 100 kW chemical-looping combustor. A new oxygen carriera sintered manganese ore called Sinaushas been studied in the Chalmers 100 kW unit. The material has been investigated for an operational time of 51.5 h using five fuels: two bituminous coals, two types of wood char, and petcoke. The operational results clearly demonstrate the viability of the CLC process. In comparison to previously used iron-based oxygen carriers, the Sinaus material showed higher gas conversionup to 88%and lower loss of char to the air reactor, with carbon capture reaching as high as 100%. Furthermore, the solid-fuel conversion was higher, which is mainly an effect of the choice of fuel size. It was found that the choice of fuel has a crucial impact on performance. Previous experience has shown that the use of large fuel particles gives low carbon capture, whereas pulverized fuel leads to low solid-fuel conversion. By choosing the appropriateintermediatesize of fuel, it is possible to combine high carbon capture with high solid-fuel conversion. Previous studies indicate that the drawback of many manganese ores is the mechanical stability. Hence, a lot of emphasis was put on an in-depth study of the lifetime of the Sinaus material. Analyzing the production rate of fines, it was found the expected lifetime of the Sinaus particles was 100-400 h. This is lower than what has been found for iron-based material, but most likely sufficient for operation in full-scale chemical-looping applications. Whilst the production of fines was highest during operation with fuel, a lot of fines were produced also during operation without fuel. Seven experiments without fuel, i.e when the observed mechanical degradation was only due to high-velocity impacts and not chemical stress caused by phase transformations, gave a lifetime in the interval 220-1230 h. In conclusion, this first-of-its-kind investigation shows that the lifetime of the oxygen carrier is related to both the change in oxygen-carrier conversion and high-velocity impacts.
Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed materia... more Oxygen Carrier Aided Combustion (OCAC) is realized by using an active oxygen-carrying bed material in fluidized bed boilers. The active material is reduced in fuel rich parts of the boiler and oxidized in air rich parts. Advantages could be achieved such as new mechanisms for oxygen transport in space and time. Here calcined manganese ore has been used as active bed material in a 12 MW th circulating fluidized bed boiler. The fuel was wood chips and the campaign lasted more than two weeks. From an operational point of view, manganese ore worked excellently. From the temperature profile of the boiler it can be concluded that fuel conversion was facilitated, especially in the dense bottom bed. The effect did not always translate to reduced emissions, which suggests that final combustion in the cyclone outlet was also influenced. Substituting 10% of the sand bed with manganese ore made it possible to reduce the air to fuel ratio without generating large amounts of CO. The use of 100% manganese ore resulted in higher emissions of CO than the sand reference, but, when combined sulphur feeding, dramatic reductions in CO emissions, up to 90% compared to sand reference, was achieved.
International Journal of Greenhouse Gas Control, 2016
Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxi... more Chemical-looping with oxygen uncoupling is a technology for combustion with inherent carbon dioxide separation. A solid oxygen carrier circulates between the fuel reactor, where it provides oxygen for fuel oxidation, and the air reactor, where it is reoxidized. In this study a 10 kW th pilot reactor was used to examine a calcium manganite based oxygen carrier in continuous operation with natural gas as fuel during 99 h. The composition of the oxygen carrier can be described by the formula CaMn 0.775 Ti 0.125 Mg 0.1 O 3-␦. The main part of the material forms a perovskite crystal structure which has oxygen releasing properties. The fuel conversion was generally above 95% and full conversion was reached for certain operating conditions. The elutriation of fines, defined as particles smaller than 45 m, decreased over time to eventually be below detection limit. That suggested a loss of fines of less than 0.011 wt%/h, indicating a lifetime of over 9000 h. A high fuel conversion with no thermodynamic limitation, good mechanical strength, low cost and very low toxicity shows that this calcium manganite material qualifies as a very promising oxygen carrier.
The global emissions of greenhouse gases are increasing and the development of mitigation measure... more The global emissions of greenhouse gases are increasing and the development of mitigation measures is becoming more important. One of the alternatives proposed is carbon capture and storage, where the carbon dioxide emitted from large point sources is captured, compressed and stored in underground storage sites. Many of the largest point sources of carbon dioxide are power plants fuelled by fossil fuels. There are several technologies for adapting the combustion process to capture carbon dioxide. Chemical-looping combustion is one such option and has the advantage of keeping the fuel and the combustion air apart, thus avoiding energy consuming carbon dioxide-nitrogen separation. This is achieved by transferring oxygen from the air to the fuel by a cyclic oxidation and reduction of a solid metal oxide. The oxygen-carrying material needs to meet a number of requirements in order to achieve an efficient combustion process. Manganese oxides have promising properties as oxygen-carrier material and these can be further improved by combining the manganese with for example iron, silica and calcium. Chemicallooping combustion is mainly developed as a technology for fluidised-bed combustion with the oxygen carrier present as the bed material in the form of small particles. To perform well in a circulating fluidised bed the oxygen carrier needs to be mechanically stable as well as have good reactivity with the fuel. During the development of manganese combined oxides, materials with such properties have been identified.
Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers f... more Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers for chemical-looping combustion. In this study, one pure manganese–silicon oxide and one similar material with titanium included in the formulation were examined as oxygen carriers. Experiments studying the oxygen release and the reactivity with syngas, methane, and wood char were carried out in a bench-scale circulating chemical-looping combustor and in a batch fluidized-bed reactor in the temperature range of 800–1050 °C. Both oxygen carriers released oxygen in inert atmosphere, and the concentration of oxygen released increased with temperature. The conversion of syngas and methane also increased with temperature for both materials and in both experimental setups. The reactivity with devolatilized wood char showed that the rate of oxygen uncoupling increased with temperature. However, it was concluded that the main fuel conversion mechanism was CLC and not CLOU for these materials. The inclusion of titanium ...
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Papers by Malin Hanning