Oxy-fuel Combustion Conditions Research Articles

Combustion Characteristics of a Non-Premixed Oxy-Flame Applying a Hybrid Filtered Eulerian Stochastic Field/Flamelet Progress Variable Approach

The oxidation of methane under oxy-fuel combustion conditions with carbon capture is attractive and deserves huge interest towards reducing CO2 and NOx emissions. The current paper reports on the predictions and analysis of combustion characteristics of a turbulent oxy-methane non-premixed flame operating under highly diluted conditions of CO2 and H2 in oxidizer and fuel streams, respectively. These are achieved by applying a novel, well-designed numerical combustion model. The latter consists of a large eddy simulation (LES) extension of a recently suggested hybrid model in Reynolds averaging-based numerical simulation (RANS) context by the authors. It combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) on the one hand, and a flamelet progress variable (FPV) turbulent combustion model under consideration of detailed chemical reaction mechanism on the other hand. This novel hybrid ESF/FPV approach removes the weaknesses of the presumed-probability density function (P-PDF)-based FPV modeling, along with the solving of associated additional modeled transport equations while rendering the T-PDF computationally less affordable. First, the prediction capability of the LES hybrid ESF/FPV was appraised on the well-known air-piloted methane jet flame (Sandia Flame D). Then, it was assessed in analyzing the combustion properties of a non-premixed oxy-flame and in capturing the CO2 dilution effect on the oxy-fuel flame behavior. To this end, the so-called oxy-flame B3, already numerically investigated in a RANS context, was analyzed. Comparisons with experimental data in terms of temperature, scalar distributions, and scatter plots agree satisfactorily. Finally, the impact of generating the FPV chemistry table under condition of unity Lewis number, even with CO2 dilution, was investigated on the general prediction of the oxy-fuel flame structure, stability and emissions. In particular, it turns out that 68% molar percentage of CO2 leads to 0.39% of CO formation near the burner fuel nozzle and 0.62% at 10 dfuel above the nozzle.

Experimental and numerical study of laminar flame speeds of CH4/NH3 mixtures under oxy-fuel combustion

Abstract The laminar flame speeds of CH4/NH3 mixtures during oxy-fuel combustion conditions were measured under variable NH3/CH4 ratios (0.1–0.2), O2 mole fractions (35%–40%), and CO2 mole fractions (45%–65%) in a counterflow flame configuration (set at atmospheric pressure and unburnt mixture temperature (Tu = 300 K)). These experimental results were compared to the numerical results obtained through three detailed chemical kinetic mechanisms: the Okafor, Mendiara and HUST (Huazhong University of Science and Technology) mechanisms. The comparisons showed that the results obtained through the HUST Mechanism were in good agreement with the experimental results. The experimental results showed that the laminar flame speeds increased linearly with decreasing CO2 or increasing O2 concentrations under the conditions considered, while the slopes were irrelevant for the equivalence ratio. Nevertheless, the effects of NH3 concentration depended on the equivalence ratio: the sensitivity and pathway analyses of NH3 oxidation revealed that, among the N-containing reactions in the fuel-lean region, NO oxidation and reduction (NO + HO2 = NO2+OH, NH2+NO = NNH + OH, NO2+H = NO + OH, and CH3+NO2 = CH3O + NO) had the largest impact on the laminar flame speeds. In stoichiometric region, the NO reduction pathway (NH2+NO = N2+H2O, NH2+NO = NNH + OH, NH + NO = N2O + H, and NH + NO = N2+OH) greatly contributed to flame propagation. In fuel-rich region, N + NO = N2+O and N + OH = NO + H had the biggest impact over laminar flame speeds.

Fuel processing in a swirl flow: numerical modelling of combustion and gasification

This study presents the concept of a cyclone furnace for coal dust combustion and gasification under conditions of oxy-fuel combustion. A two-chamber design of the cyclone furnace allows for the separation of the process of heating, drying and devolatilization of fuel from processes of its combustion and gasification of carbon residue. The choice of process parameters helps control fuel gasification. Supplying the driving gas with a specific composition (O2, CO2) to the chamber PC1 ensures the control of temperature and composition of combustible gases obtained through gasification. These gases can be used as a fuel for power boilers and, consequently, allow for utilization of the oxy-fuel combustion technology in new or existing power boilers.

Reactivities of American, Chinese and Estonian oil shale semi-cokes and Argonne premium coal chars under oxy-fuel combustion conditions

Reactivities of American, Chinese and Estonian oil shale semi-cokes and Argonne premium coal chars under oxy-fuel combustion conditions

Examinations of the sulfur emission from pulverized lignite fuel, under pyrolysis and oxy-fuel combustion condition

Problem of gas emission as NOX, SOX, heavy metals from fossil fuel combustion process is still under study. Especially the oxy-condition effect on gas emissions from oxy-fuel requires more analysis and research. This paper focuses on SO2 and SO3 behaviour investigation during air and oxy-fuel combustion processes, and formation of H2S and SO2 from N2 and CO2 atmosphere. The research focuses especially on Polish medium sulphur coals. In the paper selected brown coals were examined on the content of total sulphur. During the tests campaign one type of lignite, predried to Mraw = 15% was a subject of pyrolysis at 800 and 1000 °C under N2 and CO2 atmosphere, and further combusted in three different atmospheres: air atmosphere, and two different oxy atmospheres with O2/CO2 ratios, equal 25/75% and 30/70% (vol.). Tests were carried out on an isothermal flow reactors (IFR) in a large laboratory scale. The influence of the CO2 atmosphere in oxy-condition in comparison with to the air atmosphere on SO2, SO3 emission intensity was determined. The results showed that the change of atmosphere from the air atmosphere to oxy atmosphere and increase of oxygen concentration in O2/CO2 combustion atmosphere results in the increase of the conversion ratio ofsulphur from solid phase to a the gas phase for the lignite. During the pyrolysis process it is mainly the H2S that is released in the gaseous form.

Insights into the Effects of Atmosphere and Chlorine on Potassium Release during Biomass Combustion: Temporal Measurement and Kinetic Studies

The effect of atmosphere and chlorine on potassium release under air and oxy-fuel combustion conditions of biomass in a fluidized bed was investigated using a temporal measurement system. The results showed that the release proportion of potassium in air atmosphere was bigger than oxy-fuel environment at the temperatures below 900 °C. The overall activation energy for potassium release under air atmosphere is less than that under oxy-fuel atmosphere. The influence of chlorine on potassium release behavior also revealed an obvious difference in the two kinds of combustion environments. In general, the enhancement degree of chlorine to potassium release under air atmosphere was higher than the case under oxy-fuel atmosphere, probably caused by variations produced in chlorine species by massive CO2 under oxy-fuel atmosphere. Thermodynamic analysis was performed to determine final potassium species in air and oxy-fuel environment. The impact of mass CO2 under oxy-fuel condition on release mechanism of potassi...

Homogeneous and heterogeneous formation of SO3 in flue gases burning high sulfur coal under oxy-fuel combustion conditions

The formation of SO3 when burning high-sulfur coal under oxy-fuel combustion conditions was investigated by performing experiments in which homogeneous and heterogeneous formation processes occurred using ash from five types of coal with high sulfur contents. Increasing the temperature favored homogeneous SO3 formation processes (600 °C–1000 °C). The heterogeneous formation processes to SO3 formation was related to the ash composition. Heterogeneous formation processes contributed 20.0%–57.9% of the SO3 produced. Fe2O3 catalyzes SO3 formation, but a simple positive correlation was not found between the amount of SO3 formed and the Fe2O3 content. More SO3 was formed when the ash had high sodium and potassium contents than when the ash had low sodium and potassium contents. This may have been because ash produced by high-sulfur coal has high alkali metal sulfate contents because of the abilities of sodium and potassium to capture sulfur. SO3 is released during the processes through which sulfates are transformed into aluminosilicates. Increasing the O2 concentration promoted homogeneous and heterogeneous formation of SO3, while increasing the SO2 concentration increased the SO3 concentration but decreased the SO3 formation ratio. Heterogeneous formation of SO3 catalyzed by ash during coal combustion cannot be ignored.

Combustion characteristics of Turkish lignites at oxygen-enriched and oxy-fuel combustion conditions

Combustion and oxy-fuel combustion characteristics of two Turkish lignites (Orhaneli and Soma) were investigated by Thermogravimetric Analysis (TGA) method. Experiments were carried out under oxygen-enriched air and oxy-fuel combustion conditions with 21, 30, 40% oxygen concentrations. Three heating rates of 5, 10, and 20 °C/min were considered and the isoconversional kinetic methods of FWO, KAS, and Friedman were employed to estimate activation energies. The uncertainty assessment in obtaining the activation energy values was also considered. The obtained results indicated that the combustion of volatiles at both air and oxy-fuel conditions were approximately identical. However, at air combustion conditions, the decomposition of CaCO3 took place at temperatures above 700 °C. This decomposition process was independent of the oxygen concentration and took place when the temperature reached to a certain threshold. The decomposition of CaCO3 did not accomplish in oxy-fuel conditions as far as the temperature was higher than 900 °C. Combustion in oxy-fuel conditions had higher activation energy values comparing to conventional combustion atmosphere. The activation energy values were approximately unchanged at the start of combustion regardless of oxygen concentration or combustion atmosphere at about 165 kJ/mol and 150 kJ/mol for Orhaneli and Soma lignites, respectively. The apparent activation energies were higher at elevated oxygen concentrations. The uncertainties values related to FWO method were lower than KAS and Friedman methods. The calculated average uncertainty values were found to be at the range of 5–15% for most of the cases.

Direct observations of single particle fragmentation in the early stages of combustion under dry and wet conventional and oxy-fuel conditions

This article investigates the single particle fragmentation of three solid fuels in the early stages of combustion under dry and wet conventional and oxy-fuel conditions. The three solid fuels studied were a low rank sub-bituminous Colombian coal, a low-rank/high-ash sub-bituminous Brazilian coal, and a charcoal residue from black acacia. Particles, with size in the range 125–150 µm, were burned in a drop tube furnace with a constant wall temperature of 1475 K, under six different mixtures of O2/N2/CO2/H2O, which allowed simulating dry and wet conventional and oxy-fuel combustion conditions. A high-speed camera was used to record the fragmentation process during the early stages of combustion and the collected images were treated to characterize the fragmentation mode, probability and time. The observed fragmentation modes are characterized by the occurrence of exfoliation, radial fragmentation or a combination of both. The results disclose that the fragmentation mode is strongly affected by the fuel type, but less affected by the atmosphere; the fragmentation probability is strongly affected by both the fuel type and the atmosphere; and, finally, fragmentation in air occurs significantly dispersed after ignition, but it tends to cluster closer to the ignition under simulated oxy-fuel conditions.

Effect of steam on the single particle ignition of solid fuels in a drop tube furnace under air and simulated oxy-fuel conditions

This article investigates the effect of steam on the ignition of single particles of solid fuels in a drop tube furnace under air and simulated oxy-fuel conditions. Three solid fuels, all in the size range 125–150 µm, were used in this study; specifically, a low rank sub-bituminous Colombian coal, a low-rank/high-ash sub-bituminous Brazilian coal and a charcoal residue from black acacia. For each solid fuel, particles were burned at a constant drop tube furnace wall temperature of 1475 K, in six different mixtures of O2/N2/CO2/H2O, which allowed simulating dry and wet conventional and oxy-fuel combustion conditions. A high-speed camera was used to record the ignition process and the collected images were treated to characterize the ignition mode (either gas-phase or surface mode) and to calculate the ignition delay times. The Colombian coal particles ignite predominately in the gas-phase for all test conditions, but under simulated oxy-fuel conditions there is a decrease in the occurrence of this ignition mode; the charcoal particles experience surface ignition regardless of the test condition; and the Brazilian coal particles ignite predominately in the gas-phase when combustion occurs in mixtures of O2/N2/H2O, but under simulated oxy-fuel conditions the ignition occurs predominantly on the surface. The ignition delay times for particles that ignited in the gas-phase are smaller than those that ignited on the surface, and generally the simulated oxy-fuel conditions retard the onset of both gas-phase and surface ignition. The addition of steam decreases the gas-phase and surface ignition delay times of the particles of both coals under simulated oxy-fuel conditions, but has a small impact on the gas-phase ignition delay times when the combustion occurs in mixtures of O2/N2/H2O. The steam gasification reaction is likely to be responsible for the steam effect on the ignition delay times through the production of highly flammable species that promote the onset of ignition.

NOx Emissions from Regenerator of Calcium Looping Process

The calcium looping (CaL) process usually employs a dual-fluidized bed (DFB) solid circulating unit. In the regenerator (calcinator or calciner), decomposition of CaCO3 proceeds. To supply the heat of decomposition, oxyfuel combustion of coal is conducted. However, since coal contains nitrogen, the NOx formation occurs during oxyfuel combustion. Because of the fact that NOx formation and destruction during combustion of solid fuels in a fluidized bed is a complex process, a predictive approach of NOx emissions has not yet been sufficiently recognized, especially during oxyfuel combustion conditions in the CaL systems. The paper introduces a regression-based method for the prediction of NOx emissions from a CaL DFB experimental unit. Effects of fuel type, excess oxygen feed, and NO addition to primary or secondary feed gas on NOx emissions in the regenerator were evaluated. The presented way constitutes a straightforward method to run a complementary technique in relation to other methods of data handling,...

Experimental study and chemical reactor network modeling of the high heating rate devolatilization and oxidation of pulverized bituminous coals under air, oxygen-enriched combustion (OEC) and oxy-fuel combustion (OFC)

Experimental and numerical investigations of the combustion of 2 bituminous coals under air, oxygen-enriched and oxy-fuel combustion conditions have been performed. 7 pulverized coal jet flames have been stabilized using a specifically designed flat flame reactor (FFR) allowing industrial heating rates to be reproduced. The investigated reacting media have been fully characterized in terms of temperature fields, fuel residence time, devolatilization rates and concentration profiles of O2, CO2, CO, NO and SO2. Obtained data have then been compared with predictions derived from a chemical reactor network (CRN) modeling approach. This latter incorporates a detailed reaction mechanism the formulation of which has been defined by comparing the results obtained through the implementation of 3 different detailed gas-phase combustion reaction schemes. On the whole, obtained numerical results show a good agreement with experimental data. By analyzing the reaction paths relying on the CRN predictions, the present study allowed highlighting and further exploring the influence played by the combustion atmosphere on the chemical pathways leading to species like CO, NO, SO2 or soot precursors. The main findings drawn through this work especially led to trace the increased CO concentrations measured under oxy-fuel combustion (OFC) to heightened HCO production and tar oxidation. Alternative NO formation pathways arising under OFC conditions (like the HCN → HNCO → NH → NO and HCN → NCO → HNCO → HNO → NO routes) have, moreover, been highlighted. While the SO2 production has been found to mainly depend on the quantity of fuel-S emitted during the devolatilization and on the local oxygen partial pressure (the main SO2 formation pathway being indeed not truly affected by the nature of the combustion atmosphere), the analysis of the main routes involved in the oxidation of aromatics such as benzene, naphthalene and phenanthrene has been found well insightful in order to explain some reduced soot productions recently reported in the literature under OFC.

Effect of oxy-fuel combustion on flame characteristics of low calorific value coal gases in a small burner and combustor

Currently, using oxygen instead of air in a combustion process is being widely discussed as an option to reduce fuel consumption and utilization of oxygen is expected to improve the thermal efficiency and combustion performances. The main goal of this study is to determine the combustion behaviors of low calorific value coal gases under oxy-fuel combustion conditions and to compare with the results of air-fuel combustion conditions in the existing burner and the combustor. The coal-derived low calorific value coal gases (syngases) have been properly oxy-combusted using the existing burner within the present study. Temperature and emission values have been experimentally measured and investigated on different axial and radial positions by using thermocouples and a flue gas analyzer throughout the combustion chamber. All experiments have been performed under a thermal power of 10 kW and an excess oxygen coefficient of λ = 1.2 combustion conditions for both turbulator distances of 7 cm and 2 cm. The burner walls were overheated due to using of pure oxygen instead of air during combustion when the turbulator position of the burner was further to the burner exit (7 cm). Because of that, the turbulator position of the burner has also been changed as a small modification to alleviate overheating of the burner walls and hence, it was drawn near to the burner exit (2 cm). Therefore, it can be said that the burner either can be used with modification or the burner material should be changed to be withstood higher temperature levels. It is consequently concluded that the flame that has emerged under combustion condition with 2 cm of the turbulator distance is wider and smoother than that of the flame showing up under combustion condition with 7 cm of the turbulator distance. CO, CO2 and NOX emissions have also been determined on different axial and radial positions. According to the measurements, it has been demonstrated that CO2 and NOX decrease while CO increase on the axial measurements as the turbulator distance is draw near to the burner exit. When the oxy-fuel combustion results are compared with the air-fuel combustion results, it can be concluded that the oxy-fuel combustion performances of the coal-derived syngases are better than that of the air-fuel combustion, which corresponds to an increment of about 22% in their flame temperatures. However, it has been obtained that oxy-fuel NOX values are not lower than that of the air-fuel values due to the higher flame temperatures. It has been revealed that oxy-fuel CO emission values are lower and oxy-fuel CO2 emission values are higher (approximately 30%) than values of the air-fuel combustion due to the absence of nitrogen in the oxidizer.

A compatible configuration strategy for burner streams in a 200 MWe tangentially fired oxy-fuel combustion boiler

The configurations of burner streams under oxy-fuel combustion are highly affected by its increased initial oxygen level. In this study, an air combustion and oxy-fuel combustion compatible configuration strategy for burner streams is proposed for a 200 MWe tangentially fired boiler, by aid of numerical simulation. Firstly, to achieve a momentum of primary and secondary streams that is similar to that of air combustion, the tertiary stream is switched-off in oxy-fuel combustion. In addition, the opposing tangential primary stream technology is suggested to reduce the gas temperature deviation in the upper furnace, which affects the quality of the steam and the safe operation of the boiler. For the present study, the appropriate opposing tangential angle is 5°–7° relative to the original primary stream design, and the ratio of opposing tangential momentum flow moment should be controlled at the low limit of 0.8 to decrease gas temperature deviation. To achieve a supported flame by the secondary stream, the momentum of the bottom secondary stream in oxy-fuel combustion should not be less than that in air combustion. The study illustrates for the first time that, the key design features of tangentially fired burners under oxy-fuel combustion. Although there are significant changes in the oxidant volume, oxidant composition, and chemical reaction under oxy-fuel combustion conditions, the design criteria of oxy-fuel tangentially fired boiler, in terms of momentum of the primary stream, momentum of the bottom secondary stream, and momentum ratio and momentum flow moment ratio of the secondary stream to primary stream, are consistent with those under air combustion.

Calcium looping performance under extreme oxy-fuel combustion conditions in the calciner

Calcium looping (CaL) for post-combustion CO2 capture is an emerging technology that has developed rapidly due to its similarities with existing circulating fluidized bed combustion boilers. This work presents an alternative calciner configuration as it is applied in La Pereda CaL pilot plant, the aim of which is to minimize or altogether eliminate the need to recycle CO2 during the oxy-fuel combustion of coal in the calciner. The strategy underlying this configuration is to reduce the heat demand in the calciner, and hence the energy penalty of the whole CaL system. After undergoing several modifications, the pilot was able to operate under O2-rich conditions in a series of experiments with a coal thermal input of up to 2.0 MWth in the calciner and 75 O2%v in the oxidant. No hot spots were detected in the calciner reactor in these conditions due to the thermal ballast effect produced by the circulating solids from the carbonator. This new operation mode in the calciner in no way undermined the performance of the carbonator and CO2 capture efficiencies close to the maximum limit permitted by the equilibrium were achieved during the experimental campaigns. In short, the results of this work indicate that it may well be possible to operate the calciner of a CaL system using pure oxygen.

Mercury Interaction on Modified Activated Carbons under Oxyfuel Combustion Conditions

Mercury pollution is a cause for concern that requires global action. The most demonstrated and commercially available technology for mercury control is pulverized activated carbon injection. During oxy-coal combustion, the elevated concentrations of SOx, the moisture level in the flue gas, and the recirculation streams may affect the performance of activated carbons as mercury sorbents. This works evaluates mercury oxidation and capture using impregnated-activated carbons. In this study a novel aspect is considered by the application of a novel thermal desorption procedure for mercury species identification and the elucidation of the interaction mechanism. The results show oxidation efficiencies ranging from 85% to 96%. The mercury is partially retained in the solid by chemical adsorption. The formation of new mercury species HgS, HgI2, and HgO by the interaction was established.

Global reaction mechanisms for MILD oxy-combustion of methane

This paper optimizes global reaction mechanisms under the MILD (Moderate and Intensive Low-oxygen Dilution) oxy-combustion combustion. Seven global mechanisms are compared and validated with two detailed mechanisms under the oxy-fuel combustion, MILD air-combustion, and MILD oxy-combustion conditions. The ability of these global models to capture the combustion process under different conditions is compared first using computational fluid dynamics (CFD) simulations of both the MILD oxy-combustion in a laboratory-scale furnace and non-premixed turbulent jet open flames, and later using a plug flow reactor (PFR) approach. Experiments of the MILD oxy-combustion are also carried out for the mechanism validation. The detailed comparison shows that the present optimized global mechanism significantly improves the prediction of temperatures, equilibrium concentrations of major species, and the peak CO concentration, relative to other global mechanisms, for the MILD oxy-combustion. The present refined mechanism is an appropriate global reaction mechanism for methane MILD oxy-combustion, if the computational cost of detailed reaction mechanism is unaffordable.

Oxy-fuel combustion study of biomass fuels in a 20 kWth fluidized bed combustor

Oxy-fuel combustion is one of the promising carbon capture technologies considered to be suitable for future commercial applications with stationary combustion plants. Although more and more biomass and waste are now being burned in stationary combustion plants, research on oxy-fuel combustion of biomass has received much less attention in comparison to oxy-fuel combustion of coal. In this work, a series of tests was carried out in a 20 kWth fluidized bed combustor under oxy-fuel conditions firing two non-woody fuels (miscanthus and straw pellets) and one woody fuel (domestic wood pellet). The effects of the combustion atmosphere (air and oxy-fuel) and oxygen concentration in the oxidant of the oxy-fuel combustion on gas emissions and temperature profiles were systematically studied with the overall excess oxygen coefficient in the combustor being maintained roughly constant throughout the tests. The experimental results showed that replacing the air with an oxy-fuel oxidant of 21 vol% O2 and 79 vol% CO2 resulted in a significant decrease in combustion temperature and ultimately led to the extinction of the biomass flame due to the larger specific heat of CO2 compared to N2. To keep a similar temperature profile to that achieved under the air combustion conditions, the oxygen concentration in the oxidant of O2/CO2 mixture had to be increased to 30 vol%. A drastic decrease in CO emissions was observed for all three biomass fuels (up to 80% reduction when firing straw) under oxy-fuel combustion conditions providing that the oxygen concentration in the oxidant of O2/CO2 mixture was above 25 vol%. NOx emissions were found to decrease with the oxygen concentration in the oxy-fuel oxidant, due to i) the increase of bed temperature, which implies more volatile-N released and converted in the dense bed zone and ii) the less dilution of the gases inside the dense bed zone, which leads to a higher CO concentration in this region enhancing the reduction of NOx. Similar NOx emissions to those obtained with air combustion were found when the oxygen concentration in the oxy-fuel oxidant was kept at 30 vol%. Further analysis of the experimental results showed that the gas emissions when firing the non-woody fuels were controlled mainly by the freeboard temperature instead of the dense bed region temperature due to the characteristically high volatile matter content and fines of this kind of biomass fuels.

Thermogravimetric and mass spectrometric (TG-MS) analysis of sub-bituminous coal-energy crops blends in N2, air and CO2/O2 atmospheres

During oxy-fuel combustion, the gas composition inside the boiler differs from that of conventional combustion in air, which affects to different aspects in combustion processes. Besides, the need to increase the efficiency in energy production in a sustainable way leads to increasingly extreme conditions imposing more demanding performances on materials such as higher temperatures and pressures in more corrosive environments.The scope of this work is to understand the thermal behaviour and the kinetic of an energetic crop with high chlorine content blended with a Spanish coal at different atmospheres with special attention to oxyfuel combustion conditions and to determine the formation of those compounds which may induce corrosion, by means of mass spectrometry analysis.The addition of biomass to the fuel mixture seems to increase the reactivity of the samples. The rate maximum of mass change increases with the oxygen content reaching values from 13.6, 16 and 17.7%/min with N2, air and oxyfuel atmosphere respectively using 100% of cynara as fuel. The greater reactivity of the oxygen decreases the peak temperature being about 325 °C with N2, 309 °C with air and 304 °C at oxyfuel conditions.The activation energy increased when the biomass share in the blend independently of the atmosphere and the heating rate. The activation energy is similar to combustion and oxyfuel combustion conditions but about 5–7 kJ/mol higher than pyrolysis atmosphere for all biomass mixture studied. The optimal blend based on the lowest activation energy is 20:80% of cynara/coal.HCl presence is higher when the percentage of biomass increased. However, SO2 presence is more related with coal presence. It is important to stand out that any percentage of cynara in the mixture shift to lower temperatures the SO2 emission profile, from 500 °C to 300 °C. This fact is also observed in the curves of the weight loss derivative.

SO3 formation and the effect of fly ash in a bubbling fluidised bed under oxy-fuel combustion conditions

This study investigates SO3 formation under air-fired and oxy-fuel combustion environments in a bench-scale bubbling fluidised bed. Flue gas compositions typical of air-fired and oxy-fuel environments were simulated with synthetic gas mixtures. Parameters such as bed temperature and SO2 and H2O concentrations were varied to determine their effect on the formation of SO3. Tests were also performed using three fly ashes produced from three different coals and combustion systems. Oxy-fuel combustion led to increased SO3 concentration as compared to typical air-fired environments. SO3 concentrations increased with combustion temperature and O2 concentrations. SO3 formation also depends on the chemical composition of the fly ash.