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Soonjai Khang - One of the best experts on this subject based on the ideXlab platform.
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the effect of coal volatility on mercury removal from bituminous coal during Mild Pyrolysis
Fuel Processing Technology, 2000Co-Authors: Min Wang, Tim C Keener, Soonjai KhangAbstract:Abstract Two high volatile and one low volatile bituminous coals (Lower Freeport #6A, Pittsburgh #8 and Lower Kittanning, respectively) used primarily for electricity production were tested to determine the percentage of mercury content removed during Mild Pyrolysis. Size-segregated samples of the well-characterized coals were tested in a tube furnace with a nitrogen blanket at different residence times for different processing temperatures through the range 275–600°C. The resulting char was analyzed for mercury and compared to the original parent coal concentration to determine the percentage of removal. Experiments have shown that as much as 80% of the original mercury is removed from these coals at these conditions. The percentage mercury removal was found to be a function of residence time and temperature. The high volatile bituminous coals show a near-constant mercury removal rate as the temperature increases until the temperature reaches a level where mercury removal is inhibited and the rate decreases with increasing temperature. For the low volatile coal, the rate of mercury does not show a change in mechanism as temperature increases and follows the Arrhenius form throughout the temperature range studied. The results were modeled as a homogeneous reaction with distinct maximum percent mercury available for conversion ( X max ) for a specified temperature. Data analysis indicates the following: at 500°C, Mild Pyrolysis of the Lower Kittanning low volatile sample resulted in 75% maximum mercury removal and the corresponding reaction rate coefficient is 1.56 min −1 ; Mild Pyrolysis of Lower Freeport #6A coal sample at 500°C resulted in 74% maximum mercury removal and the corresponding reaction rate coefficient is 0.42 min −1 ; the Pittsburgh #8 coal sample had a maximum mercury removal amount of 80% at a furnace temperature of 400°C and a reaction rate coefficient of 0.44 min −1 .
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investigation into the fate of mercury in bituminous coal during Mild Pyrolysis
Fuel, 1998Co-Authors: Amy C Merdes, Tim C Keener, Soonjai Khang, Robert G JenkinsAbstract:Abstract Two high-volatile bituminous coal (Lower Freeport #6A and Pittsburgh #8), used primarily for electricity production, were tested to determine the fate of their mercury content during Mild Pyrolysis. Mono-sized samples of the well characterized coals were tested under nitrogen in a horizontal tube furnace at different residence times at different temperatures throughout the range 275–600°C. The resulting char was analyzed for mercury, and compared to the original parent coal concentration. The percent Hg removal was found to be a function of both residence time and temperature. The data for both coals have shown two distinct regimes; a low temperature chemical evolution mechanism which follows an Arrhenius form (apparent activation energies for the Lower Freeport #6A and the Pittsburgh #8 coals are 25.6±1.5 and 21.7±1.9 kcal/mol respectively), and a higher temperature regime where the Hg evolution dramatically decreases. This can be attributed to the changing structure of the coal at these higher temperatures. The results of bomb calorimetry analysis performed on the Lower Freeport #6A coal samples verify that the overall heating value of the coal is essentially unaffected by Mild Pyrolysis at temperatures lower than 400°C.
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coal desulfurization by Mild Pyrolysis in a dual auger coal feeder
Fuel Processing Technology, 1997Co-Authors: L Lin, Soonjai Khang, Tim C KeenerAbstract:Abstract A dual-screw coal feeder reactor was constructed and tested for desulfurization of coal. The reactor consists of two concentric screw tubes, the inner tube acting as a coal pyrolyzer and the outer tube acting as a desulfurizer with hot calcined lime (CaO) pellets or other renewable sorbent pellets. The experimental results showed that under Mild Pyrolysis conditions, the devolatilization and the desulfurization processes of Ohio #8 coal could be represented by a pseudo first-order reaction model. Up to 33.2% of the total sulfur, which includes almost all the organic sulfur, was removed at a temperature of 475°C and a residence time of 6 min using a coal particle size of 4–35 mesh. The activation energies for the devolatilization and the desulfurization processes were estimated to be 170,021 kJ/kg mol and 78,732 kJ/kg mol, respectively. The H2S concentration in the pyrolyzed gas was reduced from 4% to an undetectable level in the outer tube desulfurizer indicating a high sulfur removal efficiency of CaO pellets in the dual-screw feeder reactor.
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precombustion removal of mercury from coal by Mild Pyrolysis
Preprints of Papers American Chemical Society Division of Fuel Chemistry, 1996Co-Authors: Amy C Merdes, Tim C Keener, Soonjai KhangAbstract:Mercury is present in coal at varying ppm ({mu}g/g) levels and is considered to pose a significant environmental health risk from coal combustion. Reviews on mercury in the ambient air have suggested that the average concentration of mercury in the gaseous form in regionally polluted areas, such as the east coast, are in the range between 3 to 4 ng Hg/m{sup 3}. And in urban air the average concentrations may be as high as 10 ng Hg/m{sup 3}. Coal combustion has been estimated to account for over 8 % of the mercury emissions to the atmosphere. Lindber reported that in the plume of a coal-fired power plant, gaseous mercury is present in excess of 1000 ng Hg/m{sup 3} within a few kilometers of the source. Material balances on mercury in power plants have shown that only approximately 10% of the total mercury from the coal is found in the fly ash, and the remainder exits the stack in vapor form. Other studies investigating the effects of existing flue gas clean-up (FGC) technologies on mercury concentration in flue gases report that varying levels of removal can be achieved, ranging from 10% to 90% removal. This large variation is most likely duemore » to differences in combustion reactors as well as differences in the chemical form of mercury and variations in chlorine levels in the feed coal. This study investigates the influences of temperature and time on the evolution of mercury from coal during Mild Pyrolysis.« less
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precombustion removal of mercury from coal by Mild Pyrolysis
Coal science and technology, 1995Co-Authors: Tim C Keener, A C Gieske, Soonjai KhangAbstract:Abstract The fate of mercury during Mild Pyrolysis of a high volatile bituminous coal at two temperatures was investigated as a part of an ongoing study. The determination method for mercury content in the original coal sample and the pyrolyzed coal is described. During Mild Pyrolysis, more than 50% of the parent coal mercury is released at temperatures as low as 300°C with a residence time of 10 minutes. The heating value of the coal is not significantly affected by Mild Pyrolysis at such low temperatures. A relationship between the residence time, the temperature, and the maximum achievable removal is applied.
Tim C Keener - One of the best experts on this subject based on the ideXlab platform.
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the effect of coal volatility on mercury removal from bituminous coal during Mild Pyrolysis
Fuel Processing Technology, 2000Co-Authors: Min Wang, Tim C Keener, Soonjai KhangAbstract:Abstract Two high volatile and one low volatile bituminous coals (Lower Freeport #6A, Pittsburgh #8 and Lower Kittanning, respectively) used primarily for electricity production were tested to determine the percentage of mercury content removed during Mild Pyrolysis. Size-segregated samples of the well-characterized coals were tested in a tube furnace with a nitrogen blanket at different residence times for different processing temperatures through the range 275–600°C. The resulting char was analyzed for mercury and compared to the original parent coal concentration to determine the percentage of removal. Experiments have shown that as much as 80% of the original mercury is removed from these coals at these conditions. The percentage mercury removal was found to be a function of residence time and temperature. The high volatile bituminous coals show a near-constant mercury removal rate as the temperature increases until the temperature reaches a level where mercury removal is inhibited and the rate decreases with increasing temperature. For the low volatile coal, the rate of mercury does not show a change in mechanism as temperature increases and follows the Arrhenius form throughout the temperature range studied. The results were modeled as a homogeneous reaction with distinct maximum percent mercury available for conversion ( X max ) for a specified temperature. Data analysis indicates the following: at 500°C, Mild Pyrolysis of the Lower Kittanning low volatile sample resulted in 75% maximum mercury removal and the corresponding reaction rate coefficient is 1.56 min −1 ; Mild Pyrolysis of Lower Freeport #6A coal sample at 500°C resulted in 74% maximum mercury removal and the corresponding reaction rate coefficient is 0.42 min −1 ; the Pittsburgh #8 coal sample had a maximum mercury removal amount of 80% at a furnace temperature of 400°C and a reaction rate coefficient of 0.44 min −1 .
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investigation into the fate of mercury in bituminous coal during Mild Pyrolysis
Fuel, 1998Co-Authors: Amy C Merdes, Tim C Keener, Soonjai Khang, Robert G JenkinsAbstract:Abstract Two high-volatile bituminous coal (Lower Freeport #6A and Pittsburgh #8), used primarily for electricity production, were tested to determine the fate of their mercury content during Mild Pyrolysis. Mono-sized samples of the well characterized coals were tested under nitrogen in a horizontal tube furnace at different residence times at different temperatures throughout the range 275–600°C. The resulting char was analyzed for mercury, and compared to the original parent coal concentration. The percent Hg removal was found to be a function of both residence time and temperature. The data for both coals have shown two distinct regimes; a low temperature chemical evolution mechanism which follows an Arrhenius form (apparent activation energies for the Lower Freeport #6A and the Pittsburgh #8 coals are 25.6±1.5 and 21.7±1.9 kcal/mol respectively), and a higher temperature regime where the Hg evolution dramatically decreases. This can be attributed to the changing structure of the coal at these higher temperatures. The results of bomb calorimetry analysis performed on the Lower Freeport #6A coal samples verify that the overall heating value of the coal is essentially unaffected by Mild Pyrolysis at temperatures lower than 400°C.
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coal desulfurization by Mild Pyrolysis in a dual auger coal feeder
Fuel Processing Technology, 1997Co-Authors: L Lin, Soonjai Khang, Tim C KeenerAbstract:Abstract A dual-screw coal feeder reactor was constructed and tested for desulfurization of coal. The reactor consists of two concentric screw tubes, the inner tube acting as a coal pyrolyzer and the outer tube acting as a desulfurizer with hot calcined lime (CaO) pellets or other renewable sorbent pellets. The experimental results showed that under Mild Pyrolysis conditions, the devolatilization and the desulfurization processes of Ohio #8 coal could be represented by a pseudo first-order reaction model. Up to 33.2% of the total sulfur, which includes almost all the organic sulfur, was removed at a temperature of 475°C and a residence time of 6 min using a coal particle size of 4–35 mesh. The activation energies for the devolatilization and the desulfurization processes were estimated to be 170,021 kJ/kg mol and 78,732 kJ/kg mol, respectively. The H2S concentration in the pyrolyzed gas was reduced from 4% to an undetectable level in the outer tube desulfurizer indicating a high sulfur removal efficiency of CaO pellets in the dual-screw feeder reactor.
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precombustion removal of mercury from coal by Mild Pyrolysis
Preprints of Papers American Chemical Society Division of Fuel Chemistry, 1996Co-Authors: Amy C Merdes, Tim C Keener, Soonjai KhangAbstract:Mercury is present in coal at varying ppm ({mu}g/g) levels and is considered to pose a significant environmental health risk from coal combustion. Reviews on mercury in the ambient air have suggested that the average concentration of mercury in the gaseous form in regionally polluted areas, such as the east coast, are in the range between 3 to 4 ng Hg/m{sup 3}. And in urban air the average concentrations may be as high as 10 ng Hg/m{sup 3}. Coal combustion has been estimated to account for over 8 % of the mercury emissions to the atmosphere. Lindber reported that in the plume of a coal-fired power plant, gaseous mercury is present in excess of 1000 ng Hg/m{sup 3} within a few kilometers of the source. Material balances on mercury in power plants have shown that only approximately 10% of the total mercury from the coal is found in the fly ash, and the remainder exits the stack in vapor form. Other studies investigating the effects of existing flue gas clean-up (FGC) technologies on mercury concentration in flue gases report that varying levels of removal can be achieved, ranging from 10% to 90% removal. This large variation is most likely duemore » to differences in combustion reactors as well as differences in the chemical form of mercury and variations in chlorine levels in the feed coal. This study investigates the influences of temperature and time on the evolution of mercury from coal during Mild Pyrolysis.« less
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precombustion removal of mercury from coal by Mild Pyrolysis
Coal science and technology, 1995Co-Authors: Tim C Keener, A C Gieske, Soonjai KhangAbstract:Abstract The fate of mercury during Mild Pyrolysis of a high volatile bituminous coal at two temperatures was investigated as a part of an ongoing study. The determination method for mercury content in the original coal sample and the pyrolyzed coal is described. During Mild Pyrolysis, more than 50% of the parent coal mercury is released at temperatures as low as 300°C with a residence time of 10 minutes. The heating value of the coal is not significantly affected by Mild Pyrolysis at such low temperatures. A relationship between the residence time, the temperature, and the maximum achievable removal is applied.
Bo-jhih Lin - One of the best experts on this subject based on the ideXlab platform.
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modeling and prediction of devolatilization and elemental composition of wood during Mild Pyrolysis in a pilot scale reactor
Industrial Crops and Products, 2019Co-Authors: Bo-jhih Lin, Edgar A Silveira, Baptiste Colin, Wei Hsin Chen, Yu Ying Lin, Francois Leconte, Anelie PetrissansAbstract:Abstract Mild Pyrolysis, operated at 200–300 °C in an inert atmosphere, is a promising technology to produce sustainable materials (i.e., heat treated woods for construction and building) and solid fuels (i.e., torrefied woods or biochars for combustion and gasification). To aid in process and reactor design, the aim of this work is to conduct thermal degradation kinetics of wood. A two-step kinetics model is developed to predict the elemental composition (C, H, and O) and devolatilization dynamics of wood materials during heat treatment in a pilot-scale reactor by kinetic analysis. A hardwood poplar (Populus nigra) and a softwood fir (Abies pectinata) sever as feedstock, and the experiments are carried out at 200–230 °C with a heating rate of 0.2 °C min−1 in a low-pressure environment (200 hPa). The predictions in the weight losses of the woods are in a good agreement with the experimental data. The evolutions of solids, volatiles, elements (C, H, and O), and the heating values of treated woods are further analyzed. The predictions suggest that the intermediate solid is the main product, and almost all the woods are converted when the treatment temperature is as high as 230 °C. The devolatilization process, which is responsible for the mass loss of wood, can be clearly identified, and the volatile liberation amounts from poplar and fir at 230 °C are 17.05 and 12.44 wt%, respectively. The predicted HHVs of treated woods from the empirical formula are between 19.62 and 20.55 MJ kg−1, and the enhancement factors at the end of treatment are between 1.01 and 1.07 which is close to torrefied wood after light torrefaction. During the treatment, the extents of decarbonization, dehydrogenation, and deoxygenation in fir are all smaller than those in poplar, resulting from the lower intensity of devolatilization in the former.
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Investigations of wood treated by Mild Pyrolysis in a semi-industrial reactor for sustainable material production: thermal behavior, property changes and kinetic modeling
2019Co-Authors: Bo-jhih LinAbstract:Mild Pyrolysis is a promising and widely applied process conducted at 200-300 °C in an inert condition to produce sustainable materials (i.e. heat treated wood) or solid fuel (i.e. torrefied wood). The aim of this study is to investigate the woods heat treated in a semi-industrial scale reactor for sustainable material production. Two different European wood species, a hardwood species (poplar, Populus nigra) and a softwood species (fir, Abies pectinata), are used to perform the experiments. The present research is divided into three parts. In the first part, the thermal behavior of wood boards is studied in a semi-industrial scale reactor. The experiments are carried out at 200-230 °C with a heating rate of 0.2 °C min-1 in a vacuum condition (200 hPa) to intensify the thermal degradation. Four different stages of thermal degradation during wood heat treatment are defined based on the intensity of differential mass loss (DML). The devolatilization characteristics of treated woods are evaluated by the devolatilization index (DI) based on the results of proximate analysis. The correlation of DI with respect to mass loss of the two wood species is strongly characterized by linear distribution, which is able to provide a simple tool to predict the mass loss of wood. In the second part of the study, a number of analyses, such as Fourier-transform infrared spectroscopy, X-ray diffraction, measurement of color change, equilibrium moisture content, and contact angle) are performed to evaluate the property changes of treated woods. The obtained results clearly demonstrate the thermal degradation through dehydration, deacetylation, depolymerization, and condensation reactions during the heat treatment. The observed phenomena of color change and hygroscopic transformation are illustrated and discussed in detail. The decarbonization, dehydrogenation, and deoxygenation of the treated woods are also evaluated. It is found that the three indexes can be well correlated to the total color difference and hygroscopicity reduction extent (HRE). In the last part of the study, the kinetic modeling of wood heat treatment is developed based on a two-step kinetic scheme. The obtained kinetics successfully predict dynamic solid yield of wood boards during the treatment in the semi-industrial reactor. Meanwhile, the prediction of elemental composition is also performed by a direct method based on the elemental analyses of untreated and treated woods at the end of the treatment, as well as the instantaneous solid yield. The results point out that the prediction of C, H, and O profiles are in good agreement with expected composition changes in the wood materials during treatment. In summary, the obtained results and established kinetics are conducive to recognizing the mechanisms of wood thermal degradation and can be used for heat treatment process and reactor design in industry to produce wood materials for various applications.
Robert G Jenkins - One of the best experts on this subject based on the ideXlab platform.
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investigation into the fate of mercury in bituminous coal during Mild Pyrolysis
Fuel, 1998Co-Authors: Amy C Merdes, Tim C Keener, Soonjai Khang, Robert G JenkinsAbstract:Abstract Two high-volatile bituminous coal (Lower Freeport #6A and Pittsburgh #8), used primarily for electricity production, were tested to determine the fate of their mercury content during Mild Pyrolysis. Mono-sized samples of the well characterized coals were tested under nitrogen in a horizontal tube furnace at different residence times at different temperatures throughout the range 275–600°C. The resulting char was analyzed for mercury, and compared to the original parent coal concentration. The percent Hg removal was found to be a function of both residence time and temperature. The data for both coals have shown two distinct regimes; a low temperature chemical evolution mechanism which follows an Arrhenius form (apparent activation energies for the Lower Freeport #6A and the Pittsburgh #8 coals are 25.6±1.5 and 21.7±1.9 kcal/mol respectively), and a higher temperature regime where the Hg evolution dramatically decreases. This can be attributed to the changing structure of the coal at these higher temperatures. The results of bomb calorimetry analysis performed on the Lower Freeport #6A coal samples verify that the overall heating value of the coal is essentially unaffected by Mild Pyrolysis at temperatures lower than 400°C.
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dentrification of coal by Mild Pyrolysis in a novel coal feeder
Fuel Processing Technology, 1993Co-Authors: T L Yeh, Tim C Keener, Soonjai Khang, Robert G JenkinsAbstract:A series of experiments have been performed with Ohio No. 8 coal in a novel coal feeder device to investigate the fate of coal nitrogen during processing. The feeder has been primarily designed to remove organic sulfur from coal prior to combustion, but tests have shown that a significant portion of the fuel nitrogen may also be removed under Mild Pyrolysis conditions of temperatures from 350-550 °C. The degree of devolatilization and denitrification has been found to depend on the coal particles residence time in the feeder and the feeder temperature. A linear relationship was found between the percentage of devolitilization and denitrification indicating that denitrification of the volatile fraction of the coal nitrogen occurs in conjunction with the other non-nitrogen containing volatile species. The activation energies for both denitrification and devolatilization indicate the loss of volatiles and coal nitrogen are limited by heat transfer in the device, as the addition of stainless steel balls to the coal during feeding substantially increases the loss rates of both. The results indicate that it may be possible to reduce the formation of NOx from coal combustion by the use of Mild Pyrolysis prior to combustion of the char.
Akira Ohki - One of the best experts on this subject based on the ideXlab platform.
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determination of mercury in ash and soil samples by oxygen flask combustion method cold vapor atomic fluorescence spectrometry cvafs
Journal of Hazardous Materials, 2008Co-Authors: Wenhua Geng, Tsunenori Nakajima, Hirokazu Takanashi, Akira OhkiAbstract:Abstract A simple method was developed for the determination of mercury (Hg) in coal fly ash (CFA), waste incineration ash (WIA), and soil by use of oxygen flask combustion (OFC) followed by cold vapor atomic fluorescence spectrometry (CVAFS). A KMnO 4 solution was used as an absorbent in the OFC method, and the sample containing a combustion agent and an ash or soil sample was combusted by the OFC method. By use of Hg-free graphite as the combustion agent, the determination of Hg in ash and soil was successfully carried out; the Hg-free graphite was prepared by use of a Mild Pyrolysis procedure at 500 °C. For six certified reference materials (three CFA samples and three soil samples), the values of Hg obtained by this method were in good agreement with the certified or reference values. In addition, real samples including nine CFAs collected from some coal-fired power plants, five WIAs collected from waste incineration plants, and two soils were analyzed by the present method, and the data were compared to those from microwave-acid digestion (MW-AD) method.
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release behavior of mercury during Mild Pyrolysis of coals and nitric acid treated coals
Powder Technology, 2008Co-Authors: Akira Ohki, Akira Iwashita, Shomei Tanamachi, Tsunenori Nakajima, Kota Sagayama, Hirokazu TakanashiAbstract:Abstract Seven powdery coals (four SS coals and three Argonne premium coals) were subjected to Pyrolysis at 300 °C under a flow of nitrogen, and the release of Hg from coal was examined. The % release of Hg greatly varied from 24 to 83% depending upon the type of coals. In order to remove pyrite from coal, powdery coal was treated with 0.5 M HNO3 at 80 °C. The HNO3-treated coals were also subjected to the 300 °C-Pyrolysis, and the release of Hg was evaluated. Even for coals, which gave low %Hg release when the raw coal was pyrolyzed, nearly complete release of Hg was attained when the treated coal was pyrolyzed. The release behavior of Hg was discussed on the basis of the mode of occurrence of Hg in coal.
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removal of mercury from coal by Mild Pyrolysis and leaching behavior of mercury
Fuel, 2004Co-Authors: Akira Iwashita, Shomei Tanamachi, Tsunenori Nakajima, Hirokazu Takanashi, Akira OhkiAbstract:Various types of coals were subjected to the Pyrolysis at 300 and 400 °C (Mild Pyrolysis), and the removal of Hg from coal was determined. The removal efficiency of Hg greatly varied with coal type from 20 to 80%. The removal efficiency was dependent neither on the specific surface area of coal nor on the particle size of coal. The leaching of Hg from coal was tested using sulfur-containing chelating agents such as 3-mercaptopropionic acid (MPA). The Hg leaching efficiency also varied greatly with coal type. There was a good correlation between the degree of %Hg leaching in the MPA leaching and that of %Hg removal in the Mild Pyrolysis.