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Christopher R. Shaddix - One of the best experts on this subject based on the ideXlab platform.
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the effect of bulk gas diffusivity on apparent pulverized coal Char combustion kinetics
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher R. Shaddix, Cristina Gonzalotirado, Ethan S Hecht, Brian S HaynesAbstract:Abstract Apparent Char kinetic rates are commonly used to predict pulverized coal Char burning rates. These kinetic rates quantify the Char burning rate based on the temperature of the particle and the oxygen concentration at the external particle surface, inherently neglecting the impact of variations in the internal diffusion rate and penetration of oxygen. To investigate the impact of bulk gas diffusivity on these phenomena during Zone II burning conditions, experimental measurements were performed of Char particle combustion temperature and Burnout for a subbituminous coal burning in an optical entrained flow reactor with helium and nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in cooler Char combustion temperatures than in equivalent N2 environments. Measured Char Burnout was similar in the two environments for a given bulk oxygen concentration but was approximately 60% higher in helium environments for a given Char combustion temperature. To augment the experimental measurements, detailed particle simulations of the experimental conditions were conducted with the SKIPPY code. These simulations also showed a 60% higher burning rate in the helium environments for a given Char particle combustion temperature. To differentiate the effect of enhanced diffusion through the external boundary layer from the effect of enhanced diffusion through the particle, additional SKIPPY simulations were conducted under selected conditions in N2 and He environments for which the temperature and concentrations of reactants (oxygen and steam) were identical on the external Char surface. Under these conditions, which yield matching apparent Char burning rates, the computed Char burning rate for He was 50% larger, demonstrating the potential for significant errors with the apparent kinetics approach. However, for specific application to oxy-fuel combustion in CO2 environments, these results suggest the error to be as low as 3% when applying apparent Char burning rates from nitrogen environments.
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an intrinsic kinetics model to predict complex ash effects ash film dilution and vaporization on pulverized coal Char Burnout in air o2 n2 and oxy fuel o2 co2 atmospheres
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher R. ShaddixAbstract:Abstract During coal combustion, Char chemical reaction is the slowest step, particularly in the last Burnout stage, where the Char consists of small amounts of carbon in a predominant ash framework. Existing kinetics models tend to deviate from experimental measurements of late Char Burnout due to the incomplete treatment of ash effects. Ash can improve pore evolution through vaporization, hinder oxygen transport by forming an ash film, and reduce active carbon sites and available surface per unit volume by penetrating into the Char matrix. In this work, a sophisticated kinetics model, focusing on these three ash evolution mechanisms (ash vaporization, ash film, and ash dilution) during pulverized coal (PC) Char combustion, is developed by integrating them into a thorough mechanistic picture. Further, a detailed comparison of the three distinct ash effects on PC Char conversion during air (O2/N2) and oxy-fuel (O2/CO2) combustion is performed. For the modeled coal, the mass of ash vaporization is approximate 3 orders less than the mass of ash remaining, which participates in ash dilution and ash film formation, both in O2/N2 and O2/CO2 atmospheres. The influence of these phenomena on Burnout time follows the order: ash dilution > ash film > ash vaporization. The influence of ash vaporization on Burnout time is minor, but through interactions with the ash dilution and ash film forming processes it can have an impact at high extents of Burnout, particularly in O2/CO2 atmospheres. In O2/N2 atmospheres the residual ash predominately exists as an ash film, whereas it mainly exists as diluted ash in the Char matrix in O2/CO2 atmospheres. The residual ash particle is encased by a thick film when the ash film forming fraction is high (low ash dilution fraction). These results provide in-depth insights into the conversion of PC Char and further utilization of the residual ash.
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a sophisticated model to predict ash inhibition during combustion of pulverized Char particles
Proceedings of the Combustion Institute, 2015Co-Authors: Yanqing Niu, Christopher R. ShaddixAbstract:Final Burnout of Char particles from practical fuels such as coal and biomass occurs in the presence of a large ash component. Also, newly utilized coal resources, such as those from India, often contain much larger ash fractions than have traditionally been utilized. In the past, the inhibitory influence of ash on pulverized coal particle combustion has been most frequently modeled using an ash film model, though such films are rarely found when examining partially combusted particles. Conversely, some measurements have suggested that mineral components exposed on the surface of burning pulverized coal (pc) particles may diffuse back into the Char matrix, the effect of which can be modeled as an ash dilution effect. To explore the implications of these different ash inhibition models on the temporal evolution of Char combustion during Burnout, we have developed a new computational model that considers the possibility of an ash film effect, an ash dilution effect, or some arbitrary combination of the two effects acting in tandem, which is the most realistic scenario. This new model predicts that restricted diffusion through the ash film has a significant impact on the Char Burnout rate throughout its lifetime, whereas Char dilution only inhibits combustion significantly when most of the Char has been consumed and the combustion mode shifts from predominantly external diffusion control to mixed diffusion control, with sensitivity to both external and internal diffusion resistance. The comparison of the model predictions with experimental results also confirms the previously suggested need to include gasification reaction steps when modeling coal Char combustion.
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determination of Char combustion kinetics parameters comparison of point detector and imaging based particle sizing pyrometry
Review of Scientific Instruments, 2014Co-Authors: Martin Schiemann, Manfred Geier, Nikita Vorobiev, Christopher R. Shaddix, Viktor SchererAbstract:In this study, the Char Burnout Characteristics of two German coals (a lignite and a high-volatile bituminous coal) were investigated using two different experimental configurations and optical techniques in two distinct laboratories for measurement of temperature and size of burning particles. The optical diagnostic hardware is quite different in the two systems, but both perform two-color pyrometry and optical sizing measurements on individual particles burning in isolation from each other in high-temperature laminar flows to Characterize the Char consumption kinetics. The performance of the specialized systems is compared for two different combustion atmospheres (with 6.6 and 12 vol.% O2) and gas temperatures between 1700 and 1800 K. The measured particle temperatures and diameters are converted to Char burning rate parameters for several residence times during the course of the particles’ Burnout. The results confirm that comparable results are obtained with the two configurations, although higher lev...
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effect of co2 gasification reaction on Char particle combustion in oxy fuel conditions
Fuel, 2014Co-Authors: Sangmin Choi, Christopher R. Shaddix, Manfred GeierAbstract:CO2 gasification of coal Char may play an important role in oxy-combustion environments with flue gas recirculation (FGR), but its effect on the overall reaction rate has not been clearly understood. To give clarity to the likely impact of CO2 gasification on the oxy-combustion of pulverized coal Chars, Burnout simulations of coal Char particles were carried out, adopting apparent Char reactivity and a single-film model that includes the Stefan flow effect on mass and energy transfer. Three oxygen concentrations (21%, 30%, and 5% O2), representing air, oxy-fuel, and oxygen-deficient combustion environments were simulated. A new experimental approach was used to directly measure the CO2 gasification rate of a subbituminous coal Char at high temperatures and atmospheric pressure. The measured gasification rate is somewhat higher than previous measurements. The simulation results show that the endothermic gasification reaction reduces the Char particle temperature and thereby reduces the oxidation rates. However, due to the contribution of the direct gasification reaction on carbon consumption, the Char Burnout time and the carbon consumption were improved. The gasification reaction has a greater influence on the Char Burnout time and the relative carbon consumption in an oxygen-deficient environment and on the drop of particle temperature in an oxygen-enriched environment (for a given gas temperature). In addition, the influence of the gasification reaction on Char combustion increases as the gas temperature increases and as the particle size increases. Further, it was observed that the impact of the gasification reaction is dependent on the presumed kinetic rate, which highlights the importance of using reliable kinetic parameters in simulations. Based on the present results, it is important to include the gasification reaction by CO2 when simulating Char combustion in oxy-fuel combustion environments.
Kefa Cen - One of the best experts on this subject based on the ideXlab platform.
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experimental study of potassium release during biomass pellet combustion and its interaction with inhibitive additives
Fuel, 2020Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Kaidi Wan, Kefa CenAbstract:Abstract In the present study, two types of biomass were investigated as typical agricultural and woody biomass fuel, i.e., corn straw and poplar. Firstly, laser induced breakdown spectroscopy (LIBS) was employed to investigate the release Characteristics of potassium (K) from a burning biomass pellet. In order to further investigate the correlation between K release and the combustion process, combustion parameters including pellet surface temperature and pellet diameter were simultaneously measured with LIBS. A dual-peak trend is observed in the K release history of poplar, but only a single peak is found in that of corn straw. Both biomass samples show the strongest K release during the devolatilization stage in comparison with the subsequent Char Burnout and ash cooking stages. Similar tendencies are observed between K release and pellet temperature, which suggests that K release is closely related to the combustion process. The K release mechanism can be attributed to temperature rise and therefore breakdown of chemical bonds during combustion. Then the release of different chemical forms of K was investigated by chemical fractionation treatment of the biomass samples. The released amount of H2O-soluble, NH4Ac-soluble and HCl-soluble potassium compounds were obtained. The H2O-soluble potassium is found to be the major released potassium compound. Finally, four kinds of additives (two pure additives, i.e., silica and alumina, and two typical natural mineral additives, i.e., kaolin and mica) were added to the biomass samples to investigate their inhibition effects on K release. The natural sorbent additives show better inhibition effects than the pure ones.
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Measurement and kinetics of elemental and atomic potassium release from a burning biomass pellet
Proceedings of the Combustion Institute, 2019Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Luc Vervisch, Kaidi Wan, Ronald Whiddon, Hamid Bahai, Kefa CenAbstract:Combining polarizing-filtered planar laser-induced fluorescence (PLIF) with simultaneous laser absorption, quantitative laser-induced breakdown spectroscopy (LIBS) and two-color pyrometry, the potassium release during the combustion of biomass fuels (corn straw and poplar) has been investigated. The temporal release profiles of volatile atomic potassium and potassium compounds from a corn straw show a single peak. The woody biomass, poplar, produces a dual-maxima distribution for potassium and potassium compounds. For both biomass samples, the highest concentrations of released atomic potassium and potassium compounds occur in the devolatilization stage. The mass ratios between volatile atomic potassium and potassium compounds in the corn straw and poplar cases are 0.77% and 0.79%, respectively. These values agree well with chemical equilibrium predictions that 0.68% of total potassium will be in atomic form. A two-step kinetic model of potassium release has been developed, which gives better predictions during the devolatilization stage than the existing single-step model. Finally, a map of potassium transformation processes during combustion is developed. Starting with inorganic and organic potassium, there are eight proposed transformation pathways including five proposed release pathways that occur during the combustion. The pathways describe the transformation of potassium between the fuel volatile matter, Char, and ash. Potassium release during the devolatilization stage is due to pyrolysis and evaporation; during the Char Burnout stage, potassium release is due to Char oxidation and decomposition; and during the ash cooking stage, potassium release is caused by reactions between the ash and H2O in the co-flow.
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multi point libs measurement and kinetics modeling of sodium release from a burning zhundong coal particle
Combustion and Flame, 2018Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Kaidi Wan, Jianzhong Liu, Kefa CenAbstract:Abstract A multi-point Laser-Induced Breakdown Spectroscopy (LIBS) method for quantitative measurement of sodium concentrations in the gas phase, the surface temperature and the particle diameter during the combustion of a Zhundong coal particle is presented. To obtain multi-point LIBS data, the laser focusing and signal collection optics are mounted on a translational platform which is able to traverse cyclically. With this setup multi-point LIBS measurements above a burning particle can be performed and the time-resolved sodium release process can be obtained. The results show that 42.2% of the total sodium mass is released during the burning of the Zhundong coal sample. For a 4 mm particle, in the Char Burnout stage sodium is released most strongly, i.e., 87% of the total released sodium mass, while in the de-volatilization and ash reaction stages the percentages are 5% and 8%, respectively. The atomic sodium and NaOH are the most favored species at chemical equilibrium in the plume according to CHEMKIN. The sodium release is found to be closely related to the particle burning stages by analyzing the sodium release, particle surface temperature and its diameter. A linear relationship is found between the residual sodium mass in the particle and the volume of the particle. The volatile sodium release rate obeys a two-step Arrhenius expression. Predictions by the developed two-step kinetics model agree well with the measured sodium release profiles in all the three coal-burning stages.
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computational modeling of oxy coal combustion with intrinsic heterogeneous Char reaction models
Fuel Processing Technology, 2017Co-Authors: Zhijun Zhou, Zhihua Wang, Liping Chen, Longzhen Guo, Bin Qian, Kefa CenAbstract:Abstract This paper simulated single Char particle conversion and oxy-coal combustion in furnaces using modified intrinsic Char reaction models that accounted for CO 2 gasification. Firstly, modified Char reaction models were exhibited, which encompassed intrinsic reaction mechanism, optimized ratio of primary Char oxidation products, specific surface area and Char density submodel, and effectiveness factor for reactants' diffusion. Then, simulations for single Char particle conversion were conducted to explore the sensitivities of model parameters, and also to analyze the effects of conversion fraction on reaction rate and reactants' diffusion; the results showed that the pre-exponential factor, tortuosity factor, and roughness factor had the largest effect on reaction rate, meanwhile, oxidation rate and O 2 diffusion were not greatly affected by conversion fraction until a high value (above 0.9), whereas gasification rate and CO 2 diffusion were hardly influenced. Finally, the availability of the modified model was validated by several CFD calculations (maximal deviation of Burnout 2 gasification on overall temperature and Char Burnout revealed that the reaction temperature was crucial.
Chunlong Liu - One of the best experts on this subject based on the ideXlab platform.
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study of the influence of vane angle on flow gas species temperature and Char Burnout in a 200 mwe lignite fired boiler
Fuel, 2010Co-Authors: Jianping Jing, Zhichao Chen, Guangkui Liu, Chunlong LiuAbstract:Abstract We measured various operational parameters of a 200-MW e , wall-fired, lignite utility boiler under various outer secondary air vane angles. The parameters measured were gas temperature, gas species concentrations, Char Burnout, and component release rates (C, H and N). Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has a single ring recirculation zone that forms in the secondary air region in the burner. By decreasing vane angles, maximum values of radial velocity, tangential velocity and turbulence intensity all increase. Moreover, swirl intensity of air flow and recirculation zone size increase. Concomitantly, in the central region of the burner, decreasing the vane angles of outer secondary air increases gas temperatures, CO concentrations, Char Burnout and component release rates of C, H, and N, while O 2 and NO x concentrations decrease, and an early ignition of pulverized-coal occurs. Meanwhile, in the secondary air region of the burner, conditions are similar except that NO x mean concentrations are reversed showing instead an increase. In the side wall region, gas temperatures increase, O 2 and NO x concentrations decrease, but CO concentrations vary only slightly.
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measurement of gas species temperatures Char Burnout and wall heat fluxes in a 200 mwe lignite fired boiler at different loads
Applied Energy, 2010Co-Authors: Jianping Jing, Zhichao Chen, Guangkui Liu, Chunlong LiuAbstract:Abstract We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, Char Burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O2 concentration, NOx concentration, Char Burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O2 concentration, NOx concentration, Char Burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O2 concentration, and NOx concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the Burnout region. Compared with a 120-MWe load, the mean NOx emission at the air preheater exits for 190-MWe load increases from 589.5 mg/m3 (O2 = 6%) to 794.6 mg/m3 (O2 = 6%), and the boiler efficiency increases from 90.73% to 92.45%.
Zhichao Chen - One of the best experts on this subject based on the ideXlab platform.
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effect of the air temperature on combustion Characteristics and nox emissions from a 0 5 mw pulverized coal fired furnace with deep air staging
Energy & Fuels, 2012Co-Authors: Yong Liu, Zhichao Chen, Qunyi Zhu, Jinzhao Jia, Zhenwang Wang, Yukun QinAbstract:This paper evaluates the effect of the air temperature on the combustion Characteristics and NOx formation in a 0.5 MW laboratory furnace fired by a pulverized coal swirl burner with deep air staging. The temperature and compositions of flue gas and fly ash in the primary zone and the second Burnout zone were sampled and measured. The results show that air temperature in the deep air staging has a significant effect on the flame stability, emissions of NOx, and unburnt carbon content in fly ash. When the air temperature is increased from 200 to 400 °C, in the primary zone (the stoichiometric ratio is 0.85), the ignition of flame is advanced, the flame stability improved significantly, the overall temperature level and combustion rate increased significantly, the CO concentration increased, the NOx concentration decreased significantly, and the carbon, hydrogen, and nitrogen release rates and the Char Burnout increased significantly. After the overfire air injection, in the second Burnout zone, as the air ...
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study of the influence of vane angle on flow gas species temperature and Char Burnout in a 200 mwe lignite fired boiler
Fuel, 2010Co-Authors: Jianping Jing, Zhichao Chen, Guangkui Liu, Chunlong LiuAbstract:Abstract We measured various operational parameters of a 200-MW e , wall-fired, lignite utility boiler under various outer secondary air vane angles. The parameters measured were gas temperature, gas species concentrations, Char Burnout, and component release rates (C, H and N). Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has a single ring recirculation zone that forms in the secondary air region in the burner. By decreasing vane angles, maximum values of radial velocity, tangential velocity and turbulence intensity all increase. Moreover, swirl intensity of air flow and recirculation zone size increase. Concomitantly, in the central region of the burner, decreasing the vane angles of outer secondary air increases gas temperatures, CO concentrations, Char Burnout and component release rates of C, H, and N, while O 2 and NO x concentrations decrease, and an early ignition of pulverized-coal occurs. Meanwhile, in the secondary air region of the burner, conditions are similar except that NO x mean concentrations are reversed showing instead an increase. In the side wall region, gas temperatures increase, O 2 and NO x concentrations decrease, but CO concentrations vary only slightly.
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Influence of coal-feed rates on bituminous coal ignition in a full-scale tiny-oil ignition burner
Fuel, 2010Co-Authors: Zhengqi Li, Yang Zhao, Zhichao ChenAbstract:Abstract A tiny-oil ignition burner has been proposed to reduce oil consumption during the firing-up process and partial-load operations. To investigate the influence of different feed rates on bituminous coal ignition in the tiny-oil ignition burner, full-scale reacting-flow experiments were performed on an experimental set-up. The ignition burner was identical to that normally used in an 800-MWe utility boiler. Gas temperature distributions in the burner were obtained at coal-feed rates of 2, 3, 4, and 5 tonnes/h. Char Burnout and release of C and H were observed at the exit of the burner nozzle. Gas compositions such as O2 and CO were measured in the center of the burner. A change in resistance was obtained within the burner. A saving of 90% over previous oil consumption was gained in the firing-up process by using the new oil-gun technology.
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measurement of gas species temperatures Char Burnout and wall heat fluxes in a 200 mwe lignite fired boiler at different loads
Applied Energy, 2010Co-Authors: Jianping Jing, Zhichao Chen, Guangkui Liu, Chunlong LiuAbstract:Abstract We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, Char Burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O2 concentration, NOx concentration, Char Burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O2 concentration, NOx concentration, Char Burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O2 concentration, and NOx concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the Burnout region. Compared with a 120-MWe load, the mean NOx emission at the air preheater exits for 190-MWe load increases from 589.5 mg/m3 (O2 = 6%) to 794.6 mg/m3 (O2 = 6%), and the boiler efficiency increases from 90.73% to 92.45%.
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combustion Characteristics and nox emissions of two kinds of swirl burners in a 300 mwe wall fired pulverized coal utility boiler
Combustion Science and Technology, 2008Co-Authors: Zhengqi Li, Zhichao Chen, Jianping Jing, Bin Xu, Zhihong GeAbstract:Measurements were performed in a 300-MWe wall-fired pulverized-coal utility boiler. Enhanced ignition-dual register (EI-DR) burners and centrally fuel rich (CFR) swirl coal combustion burners were installed in the bottom row of the furnace during experiments. Local mean concentrations of O2, CO, CO2 and NO x gas species, gas temperatures, and Char Burnout were determined in the region of the two types of burners. For centrally fuel rich swirl coal combustion burners, local mean CO concentrations, gas temperatures and the temperature gradient are higher and mean concentrations of O2 and NO x along the jet flow direction in the burner region are lower than for the enhanced ignition-dual register burners. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. For centrally fuel rich swirl coal combustion burners in the bottom row, the combustion efficiency of the boiler increases from 96.73% to 97.09%, and NO x emission decreases fro...
Yingzu Liu - One of the best experts on this subject based on the ideXlab platform.
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experimental study of potassium release during biomass pellet combustion and its interaction with inhibitive additives
Fuel, 2020Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Kaidi Wan, Kefa CenAbstract:Abstract In the present study, two types of biomass were investigated as typical agricultural and woody biomass fuel, i.e., corn straw and poplar. Firstly, laser induced breakdown spectroscopy (LIBS) was employed to investigate the release Characteristics of potassium (K) from a burning biomass pellet. In order to further investigate the correlation between K release and the combustion process, combustion parameters including pellet surface temperature and pellet diameter were simultaneously measured with LIBS. A dual-peak trend is observed in the K release history of poplar, but only a single peak is found in that of corn straw. Both biomass samples show the strongest K release during the devolatilization stage in comparison with the subsequent Char Burnout and ash cooking stages. Similar tendencies are observed between K release and pellet temperature, which suggests that K release is closely related to the combustion process. The K release mechanism can be attributed to temperature rise and therefore breakdown of chemical bonds during combustion. Then the release of different chemical forms of K was investigated by chemical fractionation treatment of the biomass samples. The released amount of H2O-soluble, NH4Ac-soluble and HCl-soluble potassium compounds were obtained. The H2O-soluble potassium is found to be the major released potassium compound. Finally, four kinds of additives (two pure additives, i.e., silica and alumina, and two typical natural mineral additives, i.e., kaolin and mica) were added to the biomass samples to investigate their inhibition effects on K release. The natural sorbent additives show better inhibition effects than the pure ones.
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Measurement and kinetics of elemental and atomic potassium release from a burning biomass pellet
Proceedings of the Combustion Institute, 2019Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Luc Vervisch, Kaidi Wan, Ronald Whiddon, Hamid Bahai, Kefa CenAbstract:Combining polarizing-filtered planar laser-induced fluorescence (PLIF) with simultaneous laser absorption, quantitative laser-induced breakdown spectroscopy (LIBS) and two-color pyrometry, the potassium release during the combustion of biomass fuels (corn straw and poplar) has been investigated. The temporal release profiles of volatile atomic potassium and potassium compounds from a corn straw show a single peak. The woody biomass, poplar, produces a dual-maxima distribution for potassium and potassium compounds. For both biomass samples, the highest concentrations of released atomic potassium and potassium compounds occur in the devolatilization stage. The mass ratios between volatile atomic potassium and potassium compounds in the corn straw and poplar cases are 0.77% and 0.79%, respectively. These values agree well with chemical equilibrium predictions that 0.68% of total potassium will be in atomic form. A two-step kinetic model of potassium release has been developed, which gives better predictions during the devolatilization stage than the existing single-step model. Finally, a map of potassium transformation processes during combustion is developed. Starting with inorganic and organic potassium, there are eight proposed transformation pathways including five proposed release pathways that occur during the combustion. The pathways describe the transformation of potassium between the fuel volatile matter, Char, and ash. Potassium release during the devolatilization stage is due to pyrolysis and evaporation; during the Char Burnout stage, potassium release is due to Char oxidation and decomposition; and during the ash cooking stage, potassium release is caused by reactions between the ash and H2O in the co-flow.
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multi point libs measurement and kinetics modeling of sodium release from a burning zhundong coal particle
Combustion and Flame, 2018Co-Authors: Yingzu Liu, Zhihua Wang, Jun Xia, Kaidi Wan, Jianzhong Liu, Kefa CenAbstract:Abstract A multi-point Laser-Induced Breakdown Spectroscopy (LIBS) method for quantitative measurement of sodium concentrations in the gas phase, the surface temperature and the particle diameter during the combustion of a Zhundong coal particle is presented. To obtain multi-point LIBS data, the laser focusing and signal collection optics are mounted on a translational platform which is able to traverse cyclically. With this setup multi-point LIBS measurements above a burning particle can be performed and the time-resolved sodium release process can be obtained. The results show that 42.2% of the total sodium mass is released during the burning of the Zhundong coal sample. For a 4 mm particle, in the Char Burnout stage sodium is released most strongly, i.e., 87% of the total released sodium mass, while in the de-volatilization and ash reaction stages the percentages are 5% and 8%, respectively. The atomic sodium and NaOH are the most favored species at chemical equilibrium in the plume according to CHEMKIN. The sodium release is found to be closely related to the particle burning stages by analyzing the sodium release, particle surface temperature and its diameter. A linear relationship is found between the residual sodium mass in the particle and the volume of the particle. The volatile sodium release rate obeys a two-step Arrhenius expression. Predictions by the developed two-step kinetics model agree well with the measured sodium release profiles in all the three coal-burning stages.