- Email: [email protected]
02201 A numerical study on smoke movement in longitudinal ventilation tunnel fires for different aspect ratio
08 Combustion (fire safety) however, superior to that of Pd, due to the changing nature of the active site in CH 4 oxidation (PdO/Pd), as is consistent with the literature based on other type of reactor studies. Methane combustion was enhanced by both HzS and SO2 on the Pt catalysts as opposed to the Pd and Rh catalysts, which saw a decrease in the methane conversion.
06•02195 Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers. Part I: Fundamental study Hua, J. et al. Chemical Engineering Science, 2005, 60, (13), 3497 3506. Understanding of micro-scale combustion mechanism is very essential to the development of combustion-based micro-power devices, which may supply much higher energy density than the batteries used nowadays. In part I of this paper, computational fluid dynamics-based numerical simulations have been performed to study the combustion of premixed hydrogen-air mixture in a series of chambers with same shape aspect ratio but various dimensions from millimetre to micron level. The transition of the combustion phenomena in the chambers from relatively large scale to micro-scale has been studied numerically to investigate the micro-combustion mechanism. The combustion model of premixed hydrogen-air mixture represents the detailed reaction mechanism with 19 reversible elementary reactions and nine species. The effect of various heat transfer conditions at chamber wall, e.g. adiabatic wall, with heat loss and heat conduction within the wall, on the combustion is analysed. These thermal conditions have strong effects on the combustion especially when the chamber dimension goes smaller and the ratio of surface area to volume becomes larger. Both factors, such as larger heat loss through the chamber wall and smaller chamber dimension size, may lead to the thermal quenching of microscale combustion. The simulation results also indicate that the stable combustion in a micro-scaled chamber may be sustained through increasing the ratio of flow residence time in chamber to chemical reaction time, and maintaining proper thermal condition. In part II of this paper, the numerical modelling method developed here is applied to analyse the micro-combustion characteristics in a three-dimensional micro-combustor based on the prototype developed by the MIT group for a micro gas turbine engine.
06•02196 Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers. Part Ih CFD analysis for a micro-combustor Hua, J. et al. Chemical Engineering Science, 2005, 60, (13), 3507-3515. Understanding of the flow dynamics, chemical kinetics and heat transfer mechanism within micro-combustors is essential for the development of combustion-based power MEMS devices. In Part I, computational fluid dynamics (CFD)-based numerical simulation has been proven to be an effective approach to analyse the performance of the micro-combustor under various conditions. In this paper, numerical simulations are performed to analyse the combustion behaviour in a three-dimensional micro-combustor based on the prototype used in the MIT micro-gas turbine engine. The CFD model of the microcombustor includes fuel/air flow path, combustion chamber as well as solid walls used to construct the combustor. The simulation analysis includes not only the detailed chemical reactions occurred in the combustion chamber, but also the fluid flow dynamics, heat transfer within the combustor and heat loss to the ambient. The performance of the combustor is evaluated under various fuel/air ratio, flow rate and heat loss conditions. Through such systematic numerical analysis, a proper operation space for the micro-combustor is suggested, which may be used as the guideline for micro-combustor design. In addition, the results reported in this paper illustrate that the numerical simulation can be one of the most powerful and beneficial tools for the micro-combustor design, optimization and performance analysis.
06102197 The flammability limits of H2-CO-CH4 mixtures in air at elevated temperatures Wierzba, I. and Wang, Q. hlternational Journal of Hydrogen Energy, 2006, 31, (4), 485-489. The present contribution reports experimentally obtained values of the flammability limits of some fuel mixtures made up of H2, CO, and CH4 in air at different initial mixture temperatures of up to 300°C. The potential catalytic effects of the surface of the test apparatus when the fuel-air mixtures were allowed to reside within the test apparatus at elevated temperatures for different time periods prior to ignition were also considered. Both stainless steel and quartz flame tubes of identical design and size were employed in the investigation. It was found that at relatively low initial temperatures the experimentally obtained limit values of fuel mixtures containing relatively low concentration of hydrogen, followed closely the corresponding values calculated according to Le Chatelier's rule. However, for higher concentrations of hydrogen in the fuel mixtures and/or for temperatures higher than 200°C, significant deviations could be observed for values of the rich limits, even for short residence times prior to ignition.
06•02198 The influence of the space between the billets on the productivity of a continuous walking-beam furnace Jaklic, A. et al. Applied Thermal Engineering, 2005, 25, (5-6), 783-795. This paper presents a study of the influence of the space between billets on the productivity of a continuous walking-beam furnace. The study was performed using a simulation model of a billet-reheating process for three different billet dimensions. The simulation model considered the exact geometry of the furnace enclosure, including the geometry of the billets inside the furnace. A view-factor matrix of the furnace enclosure was determined using the Monte Carlo method. The heat exchange between the furnace gas, the furnace wall and the billet's surface was calculated using a three-temperature model. The temperature of the furnace floor was determined using a heat-balance equation, and the heat conduction in the billets was calculated using the 3D finite-difference method. The model was validated using measurements from trailing thermocouples positioned in the test billet during the reheating process in the furnace.
06102199 Thermal characteristics of a premixed impinging circular laminar-flame jet with induced swirl Huang, X. Q. et al. Applied Energy, 2006, 83, (4), 401 411. A swirling flow has been induced in a premixed gas-fired impinging circular flame jet by adding two tangential air flows to the main axial air/fuel flow. The flame jet system was considered to be small-scale and operated under low-pressure, laminar flow conditions. The effects of Reynolds number of the air/butane mixture and nozzle-to-plate distance on the heating performance of the flame were studied and compared with the heat-flux distributions on an impingement plate under different operating conditions. The whole investigation was conducted under the stoichiometric air/fuel condition (i.e. equivalence ratio, q, = 1) with the Reynolds number being varied from 800 to 1700, and nozzle-to-plate distance being selected between 1.5 and 4.0. The introduction of swirl to small-scale, low-pressure, laminar premixed gas-fired impinging circular flame jets is the method for enhancing their thermal performances. The heat-flux distribution on the impingement plate was more uniform and the flame temperatures essentially higher when compared with a similar flame jet system without induced swirl.
06•02200 Use of artificial intelligence techniques for optimisation of co-combustion of coal with biomass Tan, C. K. et al. Journal of the Energy Institute, 2006, 79, (l), 19 25. This paper describes a strategic framework in which artificial intelligence (A1) techniques can be applied to solve the problem of the optimization of burner operation in conventional pulverized-coalfired boilers for co-combustion applications. The effectiveness of the proposed system is demonstrated by a case study that simulates the cocombustion of coal with sewage sludge in a 500-kW pilot-scale combustion rig equipped with a swirl stabild low-NOx burner. A series computational fluid dynamics (CFD) simulations were performed to generate data for different operating conditions, which were then used to train several artificial neural network (ANNs) to predict the cocombustion performance Once trained, the ANNs were able to make estimations of unseen situations in a fraction of the time taken by the CFD simulation. Consequently, the networks were capable of representing the underlying physics of the CFD models and could be executed efficiently for a large number of iterations as required by optimization techniques based on evolutionary algorithms (EAs). Four operating parameters of the burner, namely the swirl angles and flow rates of the secondary and tertiary combustion air were optimized with the objective of minimizing the nitrogen oxides and carbon monoxide emissions as well as the unburned carbon at the furnace exit. The results suggest that ANNs combined with EAs provide a useful tool for optimizing co-combustion processes.
Fire safety 06•02201 A numerical study on smoke movement in longitudinal ventilation tunnel fires for different aspect ratio Lee, S. R. and Hong, S. R. Building and Enviromnent, 2006, 41, (6), 719 725. In this study, numerical simulation was carried out to analyse the effect of the aspect ratio on smoke movement in tunnel fires using FDS 3.0. Temperature distribution under the ceiling showed a relatively good agreement with experimental results within 10"C. It confirmed the possibility of application of FDS code to tunnel fires. Results from varying of the aspect ratio showed good agreement with experimental data. Temperature near the fire sourcedecreased with the increase of the aspect ratio. But, the rate of the temperature decrease was reduced by the decrease of the heat loss in the spanwise direction. Clear height
Fuel and Energy Abstracts
September 2006
337
09 Process heating, power and incineration (energy applications in industry) of the simulation by the analysis of the velocity distribution was about 3% higher than that of the experimental result. Numerical results predicted the back-layering distance and the critical velocity reasonably.
compared to conventional hot air-based dryer. Benefits will be more while drying temperature sensitive herbal, agricultural and pharmaceutical products.
06•02202
06102205 reheater
Flammability of gas mixtures. Part 1: fire potential
Experimental thermal behavior of a power plant
Schr6der, V. and Molnarne, M. Journal of Hazardous Materials, 2005, 121, (1-3), 37 44. International and European dangerous substances and dangerous goods regulations refer to the standard ISO 10156 (1996). This standard includes a test method and a calculation procedure for the determination of the flammability of gases and gas mixtures in air. The substance indices for the calculation, the so called 'Tci values', which characterize the fire potential, are provided as well. These ISO Tci values are derived from explosion diagrams of older literature sources which do not take into account the test method and the test apparatus. However, since the explosion limits are influenced by apparatus parameters, the Tci values and lower explosion limits, given by the ISO tables, are inconsistent with those measured according to the test method of the same standard. In consequence, applying the ISO Tci values can result in wrong classifications. In this paper internationally accepted explosion limit test methods were evaluated and Tci values were derived from explosion diagrams. Therefore, an 'open vessel' method with flame propagation criterion was favoured. These values were compared with the Tci values listed in ISO 10156. In most cases, significant deviations were found. A detailed study about the influence of inert gases on flammability is the objective of Part 2.
Gonzfilez, M. M. P. et al. Energy, 2006, 31, (5), 665-676. The process conditions of power plant components subjected to high pressures and temperatures are essential to determine their remaining life, availability and efficiency. It is, therefore, expedient to pay special attention to critical components, such as superheater and reheater heat exchangers, headers, and main and reheated steam lines. In this paper, on-line and off-line variables of a power plant reheater that has presented problems of thickness losses and repetitive tube fissures are studied. The fissures are associated with the effect of a thermalmechanical mechanism. Off-line measurements were taken of the following variables: pressure, temperature, velocity and composition of the gases. On-line instrumentation was completed by the installation of specific thermocouples to ascertain the temperatures in the tubes outlet. Various angles for the fuel inlet of the burners and variations in the number and location of the working burners were also assayed. As a consequence of this analysis, it can be deduced that there are important differences in the outlet temperature of the reheater tubes that decrease for lower powers. Finally, it is pointed that a non-uniform distribution of the steam flow in the reheater might be the cause of the problem.
06•02203 Flammability of gas mixtures. Part 2: influence of inert gases
06102206 Liquid-phase mixing time in boiling stirred tank reactors with large cross-section impellers
Molnarne, M. et al. Journal of Hazardous Materials, 2005, 121, (1-3), 45-49. Ternary systems, which contain flammable gas, inert gas and air, were studied in order to give the user an evaluation of the ISO 10156 calculation method for the flammability of gas mixtures. While in Part 1 of this article the fire potential of flammable gases was the focal point, the influence of inert gases on the flammability of gas mixtures was studied in Part 2. The inerting capacity of an inert gas is expressed by the dimensionless K value, the so-called "coefficient of nitrogen equivalency'. The experimental determination of K values is demonstrated by using explosion diagrams. The objective of this study was to compare the estimated results, given by ISO 10156, with measurements of explosion ranges based on the German standard DIN 51649-1, given by CERN and CHEMSAFE. The comparison shows that ISO 10156, Table 1, supplies conservative K values, which can be regarded as safe in all cases. Nevertheless. in a number of cases ISO underestimates the inerting capacity, so that non-flammable gas mixtures are considered flammable.
09
PROCESS HEATING, POWER AND INCINERATION Energy applications in industry
06102204
Energy efficient liquid desiccant-based dryer
Rane, M. V. et al. Applied Thermal Engineering, 2005. 25, (5 6), 769 781. A liquid desiccant-based dryer is developed that has higher energy efficiency compared to conventional hot air based drying systems used in industrial and agricultural sectors. Two-stage regeneration of the liquid desiccant, an aqueous solution of calcium chloride, is used to improve the energy efficiency. It is demonstrated that the liquid desiccant-based dryer is techno-economically superior. Contacting device is an important component in the absorber and regenerator of a liquid desiccant system. Carryover of liquid desiccant into the process and/or regenerated air streams is eliminated with the novel contacting device, which has 120-185% greater surface density compared to conventional packing. The air-side pressure drop through the contacting device is very low. This paper presents the experimental results of a liquid desiccant-based dryer, designed for a paper tray drying application. It also includes the effect of variation of operating parameters and that of solution heat exchanger on specific moisture extraction rate (SMER). The average SMER of the liquid desiccantbased dryer is experimentally found to be 1.5 kg/kW h of heat. Energy savings and resultant reduction in CO2 emissions is about 56%
338
Fuel and Energy Abstracts September 2006
Takahashi, T. et al. Chemical Engineering and Processing, 2006, 45, (4), 303 311. Liquid-phase mixing times in boiling systems were measured in a 0.2 m i.d. stirred tank reactors with large cross-section impellers, i.e. Maxblend and Fullzone impellers. For reference, a triple-impeller system consisting of three six-flat blade disk turbines was also used. The impeller speed and vapour generation rate were varied from 0.83 to 7.5 s 1 and 0.011 to 0.045 m/s, respectively. Nucleation occurred at the impeller instead of the heater at higher impeller speeds, whereas vapour was mainly generated from the heater at lower impeller speeds. The mechanical power consumption decreased due to vapour generation. Although the gas hold-ups increased with increasing vapour generation rate, for the large cross-section impellers the gas hold-ups in the boiling systems at higher gas flow rates and lower impeller speeds changed only slightly with increasing impeller speeds and were rather larger than those in the cold systems. This finding for the large cross-section impellers was quite different from the result for the triple-impeller system. The mixing times for larger-scale impellers decreased with increasing vapour generation rate and were almost independent on the impeller speed at low rotational speeds of impeller. At higher impeller speeds, the mixing time decreased with impeller speed. The experimental results for dimensionless mixing times were reasonably correlated with the inverse of the power number.
06•02207 Mass transfer study on counter current multistage fluidized bed ion exchanger Kishore, K. and Verma, N. Chemical Engineering and Processing, 2006, 45, (1), 31 45. A counter current multi-stage fluidized bed ion exchanger is developed to study mass transfer during the continuous removal of dissolved anions from wastewater using commercially available resin. OH ion is used as an example in the study. A higher removal efficiency in the multi-stage fluidized bed than in a single-stage fixed and fluidized bed is demonstrated. The experiment shows progressive fluidization on a stage, smooth flow of resin across the stage and transfer of resin from one stage to the other. In each stage of the fabricated four-stage Perspex-made column, a downspout has been provided to facilitate the downward flow of resin on to the next stage, while water flows counter currently upward through the mesh of the stage. In addition, provision has been made to adjust the downcomer height on the stage without disturbing the operation with the aid of the rack and pinion arrangement. The experimental variables in the multi-stage column operated under steady state includes the flow rates of water and resin, feed concentration, stage height and the number of stages. A mathematical model is also developed for determining the key parameters that affect the overall mass transfer in the multi-stage continuous counter current column. In general, number of stages and diffusional resistance on the resin side control the extent of separation in the column.
06/02208 Shrinkage characteristics of Casuarina wood during devolatilization in a fiuidized bed combustor Kumar, R. R. et al. Biomass and Bioenergy, 2006, 30, (2), 153 165. The shrinkage characteristics of Casuarina wood in terms of the effect of fuel particle shape and size on the longitudinal, transverse, and volumetric shrinkage during devolatilization in a laboratory scale
06•02195 Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers. Part I: Fundamental study Hua, J. et al. Chemical Engineering Science, 2005, 60, (13), 3497 3506. Understanding of micro-scale combustion mechanism is very essential to the development of combustion-based micro-power devices, which may supply much higher energy density than the batteries used nowadays. In part I of this paper, computational fluid dynamics-based numerical simulations have been performed to study the combustion of premixed hydrogen-air mixture in a series of chambers with same shape aspect ratio but various dimensions from millimetre to micron level. The transition of the combustion phenomena in the chambers from relatively large scale to micro-scale has been studied numerically to investigate the micro-combustion mechanism. The combustion model of premixed hydrogen-air mixture represents the detailed reaction mechanism with 19 reversible elementary reactions and nine species. The effect of various heat transfer conditions at chamber wall, e.g. adiabatic wall, with heat loss and heat conduction within the wall, on the combustion is analysed. These thermal conditions have strong effects on the combustion especially when the chamber dimension goes smaller and the ratio of surface area to volume becomes larger. Both factors, such as larger heat loss through the chamber wall and smaller chamber dimension size, may lead to the thermal quenching of microscale combustion. The simulation results also indicate that the stable combustion in a micro-scaled chamber may be sustained through increasing the ratio of flow residence time in chamber to chemical reaction time, and maintaining proper thermal condition. In part II of this paper, the numerical modelling method developed here is applied to analyse the micro-combustion characteristics in a three-dimensional micro-combustor based on the prototype developed by the MIT group for a micro gas turbine engine.
06•02196 Numerical simulation of the combustion of hydrogen-air mixture in micro-scaled chambers. Part Ih CFD analysis for a micro-combustor Hua, J. et al. Chemical Engineering Science, 2005, 60, (13), 3507-3515. Understanding of the flow dynamics, chemical kinetics and heat transfer mechanism within micro-combustors is essential for the development of combustion-based power MEMS devices. In Part I, computational fluid dynamics (CFD)-based numerical simulation has been proven to be an effective approach to analyse the performance of the micro-combustor under various conditions. In this paper, numerical simulations are performed to analyse the combustion behaviour in a three-dimensional micro-combustor based on the prototype used in the MIT micro-gas turbine engine. The CFD model of the microcombustor includes fuel/air flow path, combustion chamber as well as solid walls used to construct the combustor. The simulation analysis includes not only the detailed chemical reactions occurred in the combustion chamber, but also the fluid flow dynamics, heat transfer within the combustor and heat loss to the ambient. The performance of the combustor is evaluated under various fuel/air ratio, flow rate and heat loss conditions. Through such systematic numerical analysis, a proper operation space for the micro-combustor is suggested, which may be used as the guideline for micro-combustor design. In addition, the results reported in this paper illustrate that the numerical simulation can be one of the most powerful and beneficial tools for the micro-combustor design, optimization and performance analysis.
06102197 The flammability limits of H2-CO-CH4 mixtures in air at elevated temperatures Wierzba, I. and Wang, Q. hlternational Journal of Hydrogen Energy, 2006, 31, (4), 485-489. The present contribution reports experimentally obtained values of the flammability limits of some fuel mixtures made up of H2, CO, and CH4 in air at different initial mixture temperatures of up to 300°C. The potential catalytic effects of the surface of the test apparatus when the fuel-air mixtures were allowed to reside within the test apparatus at elevated temperatures for different time periods prior to ignition were also considered. Both stainless steel and quartz flame tubes of identical design and size were employed in the investigation. It was found that at relatively low initial temperatures the experimentally obtained limit values of fuel mixtures containing relatively low concentration of hydrogen, followed closely the corresponding values calculated according to Le Chatelier's rule. However, for higher concentrations of hydrogen in the fuel mixtures and/or for temperatures higher than 200°C, significant deviations could be observed for values of the rich limits, even for short residence times prior to ignition.
06•02198 The influence of the space between the billets on the productivity of a continuous walking-beam furnace Jaklic, A. et al. Applied Thermal Engineering, 2005, 25, (5-6), 783-795. This paper presents a study of the influence of the space between billets on the productivity of a continuous walking-beam furnace. The study was performed using a simulation model of a billet-reheating process for three different billet dimensions. The simulation model considered the exact geometry of the furnace enclosure, including the geometry of the billets inside the furnace. A view-factor matrix of the furnace enclosure was determined using the Monte Carlo method. The heat exchange between the furnace gas, the furnace wall and the billet's surface was calculated using a three-temperature model. The temperature of the furnace floor was determined using a heat-balance equation, and the heat conduction in the billets was calculated using the 3D finite-difference method. The model was validated using measurements from trailing thermocouples positioned in the test billet during the reheating process in the furnace.
06102199 Thermal characteristics of a premixed impinging circular laminar-flame jet with induced swirl Huang, X. Q. et al. Applied Energy, 2006, 83, (4), 401 411. A swirling flow has been induced in a premixed gas-fired impinging circular flame jet by adding two tangential air flows to the main axial air/fuel flow. The flame jet system was considered to be small-scale and operated under low-pressure, laminar flow conditions. The effects of Reynolds number of the air/butane mixture and nozzle-to-plate distance on the heating performance of the flame were studied and compared with the heat-flux distributions on an impingement plate under different operating conditions. The whole investigation was conducted under the stoichiometric air/fuel condition (i.e. equivalence ratio, q, = 1) with the Reynolds number being varied from 800 to 1700, and nozzle-to-plate distance being selected between 1.5 and 4.0. The introduction of swirl to small-scale, low-pressure, laminar premixed gas-fired impinging circular flame jets is the method for enhancing their thermal performances. The heat-flux distribution on the impingement plate was more uniform and the flame temperatures essentially higher when compared with a similar flame jet system without induced swirl.
06•02200 Use of artificial intelligence techniques for optimisation of co-combustion of coal with biomass Tan, C. K. et al. Journal of the Energy Institute, 2006, 79, (l), 19 25. This paper describes a strategic framework in which artificial intelligence (A1) techniques can be applied to solve the problem of the optimization of burner operation in conventional pulverized-coalfired boilers for co-combustion applications. The effectiveness of the proposed system is demonstrated by a case study that simulates the cocombustion of coal with sewage sludge in a 500-kW pilot-scale combustion rig equipped with a swirl stabild low-NOx burner. A series computational fluid dynamics (CFD) simulations were performed to generate data for different operating conditions, which were then used to train several artificial neural network (ANNs) to predict the cocombustion performance Once trained, the ANNs were able to make estimations of unseen situations in a fraction of the time taken by the CFD simulation. Consequently, the networks were capable of representing the underlying physics of the CFD models and could be executed efficiently for a large number of iterations as required by optimization techniques based on evolutionary algorithms (EAs). Four operating parameters of the burner, namely the swirl angles and flow rates of the secondary and tertiary combustion air were optimized with the objective of minimizing the nitrogen oxides and carbon monoxide emissions as well as the unburned carbon at the furnace exit. The results suggest that ANNs combined with EAs provide a useful tool for optimizing co-combustion processes.
Fire safety 06•02201 A numerical study on smoke movement in longitudinal ventilation tunnel fires for different aspect ratio Lee, S. R. and Hong, S. R. Building and Enviromnent, 2006, 41, (6), 719 725. In this study, numerical simulation was carried out to analyse the effect of the aspect ratio on smoke movement in tunnel fires using FDS 3.0. Temperature distribution under the ceiling showed a relatively good agreement with experimental results within 10"C. It confirmed the possibility of application of FDS code to tunnel fires. Results from varying of the aspect ratio showed good agreement with experimental data. Temperature near the fire sourcedecreased with the increase of the aspect ratio. But, the rate of the temperature decrease was reduced by the decrease of the heat loss in the spanwise direction. Clear height
Fuel and Energy Abstracts
September 2006
337
09 Process heating, power and incineration (energy applications in industry) of the simulation by the analysis of the velocity distribution was about 3% higher than that of the experimental result. Numerical results predicted the back-layering distance and the critical velocity reasonably.
compared to conventional hot air-based dryer. Benefits will be more while drying temperature sensitive herbal, agricultural and pharmaceutical products.
06•02202
06102205 reheater
Flammability of gas mixtures. Part 1: fire potential
Experimental thermal behavior of a power plant
Schr6der, V. and Molnarne, M. Journal of Hazardous Materials, 2005, 121, (1-3), 37 44. International and European dangerous substances and dangerous goods regulations refer to the standard ISO 10156 (1996). This standard includes a test method and a calculation procedure for the determination of the flammability of gases and gas mixtures in air. The substance indices for the calculation, the so called 'Tci values', which characterize the fire potential, are provided as well. These ISO Tci values are derived from explosion diagrams of older literature sources which do not take into account the test method and the test apparatus. However, since the explosion limits are influenced by apparatus parameters, the Tci values and lower explosion limits, given by the ISO tables, are inconsistent with those measured according to the test method of the same standard. In consequence, applying the ISO Tci values can result in wrong classifications. In this paper internationally accepted explosion limit test methods were evaluated and Tci values were derived from explosion diagrams. Therefore, an 'open vessel' method with flame propagation criterion was favoured. These values were compared with the Tci values listed in ISO 10156. In most cases, significant deviations were found. A detailed study about the influence of inert gases on flammability is the objective of Part 2.
Gonzfilez, M. M. P. et al. Energy, 2006, 31, (5), 665-676. The process conditions of power plant components subjected to high pressures and temperatures are essential to determine their remaining life, availability and efficiency. It is, therefore, expedient to pay special attention to critical components, such as superheater and reheater heat exchangers, headers, and main and reheated steam lines. In this paper, on-line and off-line variables of a power plant reheater that has presented problems of thickness losses and repetitive tube fissures are studied. The fissures are associated with the effect of a thermalmechanical mechanism. Off-line measurements were taken of the following variables: pressure, temperature, velocity and composition of the gases. On-line instrumentation was completed by the installation of specific thermocouples to ascertain the temperatures in the tubes outlet. Various angles for the fuel inlet of the burners and variations in the number and location of the working burners were also assayed. As a consequence of this analysis, it can be deduced that there are important differences in the outlet temperature of the reheater tubes that decrease for lower powers. Finally, it is pointed that a non-uniform distribution of the steam flow in the reheater might be the cause of the problem.
06•02203 Flammability of gas mixtures. Part 2: influence of inert gases
06102206 Liquid-phase mixing time in boiling stirred tank reactors with large cross-section impellers
Molnarne, M. et al. Journal of Hazardous Materials, 2005, 121, (1-3), 45-49. Ternary systems, which contain flammable gas, inert gas and air, were studied in order to give the user an evaluation of the ISO 10156 calculation method for the flammability of gas mixtures. While in Part 1 of this article the fire potential of flammable gases was the focal point, the influence of inert gases on the flammability of gas mixtures was studied in Part 2. The inerting capacity of an inert gas is expressed by the dimensionless K value, the so-called "coefficient of nitrogen equivalency'. The experimental determination of K values is demonstrated by using explosion diagrams. The objective of this study was to compare the estimated results, given by ISO 10156, with measurements of explosion ranges based on the German standard DIN 51649-1, given by CERN and CHEMSAFE. The comparison shows that ISO 10156, Table 1, supplies conservative K values, which can be regarded as safe in all cases. Nevertheless. in a number of cases ISO underestimates the inerting capacity, so that non-flammable gas mixtures are considered flammable.
09
PROCESS HEATING, POWER AND INCINERATION Energy applications in industry
06102204
Energy efficient liquid desiccant-based dryer
Rane, M. V. et al. Applied Thermal Engineering, 2005. 25, (5 6), 769 781. A liquid desiccant-based dryer is developed that has higher energy efficiency compared to conventional hot air based drying systems used in industrial and agricultural sectors. Two-stage regeneration of the liquid desiccant, an aqueous solution of calcium chloride, is used to improve the energy efficiency. It is demonstrated that the liquid desiccant-based dryer is techno-economically superior. Contacting device is an important component in the absorber and regenerator of a liquid desiccant system. Carryover of liquid desiccant into the process and/or regenerated air streams is eliminated with the novel contacting device, which has 120-185% greater surface density compared to conventional packing. The air-side pressure drop through the contacting device is very low. This paper presents the experimental results of a liquid desiccant-based dryer, designed for a paper tray drying application. It also includes the effect of variation of operating parameters and that of solution heat exchanger on specific moisture extraction rate (SMER). The average SMER of the liquid desiccantbased dryer is experimentally found to be 1.5 kg/kW h of heat. Energy savings and resultant reduction in CO2 emissions is about 56%
338
Fuel and Energy Abstracts September 2006
Takahashi, T. et al. Chemical Engineering and Processing, 2006, 45, (4), 303 311. Liquid-phase mixing times in boiling systems were measured in a 0.2 m i.d. stirred tank reactors with large cross-section impellers, i.e. Maxblend and Fullzone impellers. For reference, a triple-impeller system consisting of three six-flat blade disk turbines was also used. The impeller speed and vapour generation rate were varied from 0.83 to 7.5 s 1 and 0.011 to 0.045 m/s, respectively. Nucleation occurred at the impeller instead of the heater at higher impeller speeds, whereas vapour was mainly generated from the heater at lower impeller speeds. The mechanical power consumption decreased due to vapour generation. Although the gas hold-ups increased with increasing vapour generation rate, for the large cross-section impellers the gas hold-ups in the boiling systems at higher gas flow rates and lower impeller speeds changed only slightly with increasing impeller speeds and were rather larger than those in the cold systems. This finding for the large cross-section impellers was quite different from the result for the triple-impeller system. The mixing times for larger-scale impellers decreased with increasing vapour generation rate and were almost independent on the impeller speed at low rotational speeds of impeller. At higher impeller speeds, the mixing time decreased with impeller speed. The experimental results for dimensionless mixing times were reasonably correlated with the inverse of the power number.
06•02207 Mass transfer study on counter current multistage fluidized bed ion exchanger Kishore, K. and Verma, N. Chemical Engineering and Processing, 2006, 45, (1), 31 45. A counter current multi-stage fluidized bed ion exchanger is developed to study mass transfer during the continuous removal of dissolved anions from wastewater using commercially available resin. OH ion is used as an example in the study. A higher removal efficiency in the multi-stage fluidized bed than in a single-stage fixed and fluidized bed is demonstrated. The experiment shows progressive fluidization on a stage, smooth flow of resin across the stage and transfer of resin from one stage to the other. In each stage of the fabricated four-stage Perspex-made column, a downspout has been provided to facilitate the downward flow of resin on to the next stage, while water flows counter currently upward through the mesh of the stage. In addition, provision has been made to adjust the downcomer height on the stage without disturbing the operation with the aid of the rack and pinion arrangement. The experimental variables in the multi-stage column operated under steady state includes the flow rates of water and resin, feed concentration, stage height and the number of stages. A mathematical model is also developed for determining the key parameters that affect the overall mass transfer in the multi-stage continuous counter current column. In general, number of stages and diffusional resistance on the resin side control the extent of separation in the column.
06/02208 Shrinkage characteristics of Casuarina wood during devolatilization in a fiuidized bed combustor Kumar, R. R. et al. Biomass and Bioenergy, 2006, 30, (2), 153 165. The shrinkage characteristics of Casuarina wood in terms of the effect of fuel particle shape and size on the longitudinal, transverse, and volumetric shrinkage during devolatilization in a laboratory scale