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Theoretical analysis of the propagation of a reaction front in a packed bed
10 Engines (power generation comprehensive code: the results of the prediction provide a reactivity distribution expressed in the form of a pre-exponential factor as a function of particle size.
02/01071 The structure of coal-air-CH4 laminar flames in a low-pressure burner: CARS measurements and modeling studies Bradley, D. er crl. Comhusrion and Flcrme, 2001, 124, (l/2), 82-105. An experimental study is described of the structure of a flat, premixed, laminar, coal-air flame, with some methane added for flame stability. A low-pressure burner, at a combustion pressure of 30.4 kPa, was employed, in order to extend the reaction zone. Gas temperatures were measured by the CARS technique and the Cz emissions observed with the laser diagnostics were found to depend upon the laser power. Concentration profiles of permanent species also were measured over a range of equivalence ratios. Measured values are compared with those predicted by a mathematical model, which assumes that CHI and HCN devolatilize from the coal and react in the gas phase. Allowance also is made for reactions of char and radiative heat transfer. The model gives good predictions of the temperature and oxygen concentration profiles, while predictions of NO are somewhat higher than those measured. Formation of NO is favoured by OH and removal of it by NHz and NH. The sensitivity of the modelled results to various activation energies and pre-Arrhenius constants is examined and optimal values of these are in line with other values in the literature. The principal limitation in the model is the overprediction of CO concentration. An explanation of this lies in the formation, neglected in the model, of tarry structures of high molecular mass, followed by the generation of soot. This interpretation is supported by the measured profiles of Cz emission intensity and their dependence upon the laser power, in contrast to the weaker emissions from rich CH,-air flames, which show no such dependence and are less persistent.
02/01072 Theoretical analysis of the propagation of a reaction front in a packed bed Gort, R. and Brouwers, J.J.H. Comhus/mn clnd Flame, 2001, 124, (l/2). l-13. The propagation of a reaction front through a packed bed is analysed theoretically. The chemical reaction rate is represented by Arrhenius temperature kinetics with external transfer limitation and general power law dependency on both gaseous and solid reactant concentrations. Analogous to so-called ‘Activation Energy Asymptotics’ developed for premixed laminar flames, the largeness of the activation energy of the chemical reaction is exploited to derive asymptotic solutions from the three governing differential equations pertaining to transport of heat, of solid reactant, and of gaseous reactant, making use of the method of matched asymptotic expansions. Two regions are distinguished, i.e. an outer region or preheat zone and an inner region or reaction zone. In the preheat zone, the reaction terms can be neglected as compared to the convective and diffusive terms. In the reaction zone, the diffusion of heat is dominating over the convective heat transport mechanism and balances the heat of reaction. In accordance with the magnitudes taken for the Lewis numbers, for solid and gaseous reactants convective transports are dominating and submitting diffusive transports in the reaction zone, respectively. Solutions in closed form are presented for governing variables including reaction front velocity whereby previously published results appear as special cases. The solutions provide direct insight into underlying physical processes and enable the effects of important parameters to be quantified analytically.
02lO1073 Two-dimensional analysis of the combustion of a low temperature-carbonized semicoke particle Mori, T. cl al. Kquku Koguku Ronhrmshu, 2000, 26, (2), 157-164. (In Japanese) A two-dimensional combustion model was developed to predict the transport phenomena in semicoke burning at the surface in a CDQ (Coke Dry Quencher) pre-chamber and blast furnace. Experiments and numerical simulation were carried out to analyse the transport phenomena in a spherical semicoke particle burning in a laminar gas stream. The model assumes that the semicoke particle is a packed bed of micro semicoke particles, and the combustion of fixed carbon is calculated as the char. Coke pyrolysis is also estimated involving the deposition and decomposition of tar and the combustion of VM (volatile matter). Gas flow in the packed bed and gas phase around the particle are calculated by Darcy’s equation and Navier-Stokes equation, respectively. The effect of heterogeneous and homogeneous reactions of the single semicoke particle on its property is calculated by the control volume method (CVM). The analysis shows that the combustion of the semicoke particle is governed by boundary layer diffusion and the homogeneous reactions prevent the semicoke particle from consumption by heterogeneous reactions.
10
and propulsion,
electrical vehicles)
ENGINES Power generation electrical vehicles
and propulsion,
02/01074 Ammonia-water bottoming cycles: a comparison between gas engines and gas diesel engines as prime movers Jonsson, M. and Yan, J. Energy, 2001, 26, (1) 314. Ammonia-water cycles can produce more power than steam Rankine cycles in severall applications. One of these applications is as a bottoming cycle to internal combustion engines. In the present study, ammonia-water bottoming cycle configurations for spark-ignition gas engines and compression-ignition gas diesel engines have been compared. Single-pressure Rankine cycles have been used as a basis for the comparison. Low heat source temperatures should increase the difference in power output between the ammonia-water cycle and the Rankine cycle. However, in this study, the results of the simulations show different trends. In most cases, the ammonia-water bottoming cycles with gas engines as prime movers generate more power compared to a Rankine cycle than when gas diesel engines are the prime movers. The temperature of the most important waste heat source, the exhaust gas, is approximately 100°C higher for the gas engines than for the gas diesel engines. Therefore, for the gas engines, most of the waste heat available to a bottoming cycle is in the form of relatively high-temperature exhaust gas, while for the gas diesel engines more of the waste heat is in the form of relatively lowtemperature heat sources. 02/01075 Control of high performance induction motors: theory and practice Lyshevski, S.E. Energ_r Conversion und Manugemenf, 2001,42, (7), 877898. In this paper, new trends in nonlinear analysis and control of induction motors are analysed. In particular, non-linear mathematical models in muclrine variables as well as in an urhirrury reference frame are found in Cauchy’s form, and the motion control problem is studied for induction motors from closed--loop perspectives. Voltage-frequency and vector control concepts are examined, novel bounded controllers are designed, and advantages and drawbacks are discussed. The conventional constant volts per hertz principle, known as V//control, is widely used, and torque-speed characteristics can be shaped by controlling the magnitude of phase voltages and the frequency. However, voltage-frequency control has been mainly studied from open-loop perspectives. In this paper, an innovative control law is synthesized to attain the constant and variable voltage-frequency operations from closed-loop perspectives, and beneficial advantages of the control algorithm designed have been utilized and thoroughly examined. An innovative procedure is reported to design controllers to attain the ifrc~or control of induction motors. To validate the results, controllers are designed and tested. Numerical and experimental studies have been performed and documented. 02/01076 Economic feasibility of combined heat and power and absorption refrigeration with commercially available gas turbines Monk, CD. Ed ~1. Energy Conversion and Management, 2001, 42, (l3), 1559-1573. Combined heat and power (CHP) systems often use absorption technology to supply heating and cooling to a facility. With the availability of gas turbines spanning an increasingly wide range of capacities, it is becoming more and more attractive to utilize CHP via a combination of gas turbines and absorption chillers. The present study investigates the economic feasibility of implementing such CHP systems with existing, commercially available gas turbines and single, double, and triple effect absorption chillers. The maximum amount of thermal energy available for the chiller is calculated based on the size of turbine, exhaust flow rate and exhaust temperature, yielding approximately 300 000 kW of cooling (85 379 tons) for a large power turbine. The annual demand and usage avoided costs for varying turbine and absorption system sizes are discussed as well, showing that a CHP system is capable of saving millions of dollars annually on electricity. 02lO1077 Engine performance using vaporizing carburetor Ahu-Qudais, M. er rrl. Emvgy Conversion and Mnnagemenr, 2001, 42, (6) 755-761. Fuel and Energy Abstracts
March 2002
131
02/01071 The structure of coal-air-CH4 laminar flames in a low-pressure burner: CARS measurements and modeling studies Bradley, D. er crl. Comhusrion and Flcrme, 2001, 124, (l/2), 82-105. An experimental study is described of the structure of a flat, premixed, laminar, coal-air flame, with some methane added for flame stability. A low-pressure burner, at a combustion pressure of 30.4 kPa, was employed, in order to extend the reaction zone. Gas temperatures were measured by the CARS technique and the Cz emissions observed with the laser diagnostics were found to depend upon the laser power. Concentration profiles of permanent species also were measured over a range of equivalence ratios. Measured values are compared with those predicted by a mathematical model, which assumes that CHI and HCN devolatilize from the coal and react in the gas phase. Allowance also is made for reactions of char and radiative heat transfer. The model gives good predictions of the temperature and oxygen concentration profiles, while predictions of NO are somewhat higher than those measured. Formation of NO is favoured by OH and removal of it by NHz and NH. The sensitivity of the modelled results to various activation energies and pre-Arrhenius constants is examined and optimal values of these are in line with other values in the literature. The principal limitation in the model is the overprediction of CO concentration. An explanation of this lies in the formation, neglected in the model, of tarry structures of high molecular mass, followed by the generation of soot. This interpretation is supported by the measured profiles of Cz emission intensity and their dependence upon the laser power, in contrast to the weaker emissions from rich CH,-air flames, which show no such dependence and are less persistent.
02/01072 Theoretical analysis of the propagation of a reaction front in a packed bed Gort, R. and Brouwers, J.J.H. Comhus/mn clnd Flame, 2001, 124, (l/2). l-13. The propagation of a reaction front through a packed bed is analysed theoretically. The chemical reaction rate is represented by Arrhenius temperature kinetics with external transfer limitation and general power law dependency on both gaseous and solid reactant concentrations. Analogous to so-called ‘Activation Energy Asymptotics’ developed for premixed laminar flames, the largeness of the activation energy of the chemical reaction is exploited to derive asymptotic solutions from the three governing differential equations pertaining to transport of heat, of solid reactant, and of gaseous reactant, making use of the method of matched asymptotic expansions. Two regions are distinguished, i.e. an outer region or preheat zone and an inner region or reaction zone. In the preheat zone, the reaction terms can be neglected as compared to the convective and diffusive terms. In the reaction zone, the diffusion of heat is dominating over the convective heat transport mechanism and balances the heat of reaction. In accordance with the magnitudes taken for the Lewis numbers, for solid and gaseous reactants convective transports are dominating and submitting diffusive transports in the reaction zone, respectively. Solutions in closed form are presented for governing variables including reaction front velocity whereby previously published results appear as special cases. The solutions provide direct insight into underlying physical processes and enable the effects of important parameters to be quantified analytically.
02lO1073 Two-dimensional analysis of the combustion of a low temperature-carbonized semicoke particle Mori, T. cl al. Kquku Koguku Ronhrmshu, 2000, 26, (2), 157-164. (In Japanese) A two-dimensional combustion model was developed to predict the transport phenomena in semicoke burning at the surface in a CDQ (Coke Dry Quencher) pre-chamber and blast furnace. Experiments and numerical simulation were carried out to analyse the transport phenomena in a spherical semicoke particle burning in a laminar gas stream. The model assumes that the semicoke particle is a packed bed of micro semicoke particles, and the combustion of fixed carbon is calculated as the char. Coke pyrolysis is also estimated involving the deposition and decomposition of tar and the combustion of VM (volatile matter). Gas flow in the packed bed and gas phase around the particle are calculated by Darcy’s equation and Navier-Stokes equation, respectively. The effect of heterogeneous and homogeneous reactions of the single semicoke particle on its property is calculated by the control volume method (CVM). The analysis shows that the combustion of the semicoke particle is governed by boundary layer diffusion and the homogeneous reactions prevent the semicoke particle from consumption by heterogeneous reactions.
10
and propulsion,
electrical vehicles)
ENGINES Power generation electrical vehicles
and propulsion,
02/01074 Ammonia-water bottoming cycles: a comparison between gas engines and gas diesel engines as prime movers Jonsson, M. and Yan, J. Energy, 2001, 26, (1) 314. Ammonia-water cycles can produce more power than steam Rankine cycles in severall applications. One of these applications is as a bottoming cycle to internal combustion engines. In the present study, ammonia-water bottoming cycle configurations for spark-ignition gas engines and compression-ignition gas diesel engines have been compared. Single-pressure Rankine cycles have been used as a basis for the comparison. Low heat source temperatures should increase the difference in power output between the ammonia-water cycle and the Rankine cycle. However, in this study, the results of the simulations show different trends. In most cases, the ammonia-water bottoming cycles with gas engines as prime movers generate more power compared to a Rankine cycle than when gas diesel engines are the prime movers. The temperature of the most important waste heat source, the exhaust gas, is approximately 100°C higher for the gas engines than for the gas diesel engines. Therefore, for the gas engines, most of the waste heat available to a bottoming cycle is in the form of relatively high-temperature exhaust gas, while for the gas diesel engines more of the waste heat is in the form of relatively lowtemperature heat sources. 02/01075 Control of high performance induction motors: theory and practice Lyshevski, S.E. Energ_r Conversion und Manugemenf, 2001,42, (7), 877898. In this paper, new trends in nonlinear analysis and control of induction motors are analysed. In particular, non-linear mathematical models in muclrine variables as well as in an urhirrury reference frame are found in Cauchy’s form, and the motion control problem is studied for induction motors from closed--loop perspectives. Voltage-frequency and vector control concepts are examined, novel bounded controllers are designed, and advantages and drawbacks are discussed. The conventional constant volts per hertz principle, known as V//control, is widely used, and torque-speed characteristics can be shaped by controlling the magnitude of phase voltages and the frequency. However, voltage-frequency control has been mainly studied from open-loop perspectives. In this paper, an innovative control law is synthesized to attain the constant and variable voltage-frequency operations from closed-loop perspectives, and beneficial advantages of the control algorithm designed have been utilized and thoroughly examined. An innovative procedure is reported to design controllers to attain the ifrc~or control of induction motors. To validate the results, controllers are designed and tested. Numerical and experimental studies have been performed and documented. 02/01076 Economic feasibility of combined heat and power and absorption refrigeration with commercially available gas turbines Monk, CD. Ed ~1. Energy Conversion and Management, 2001, 42, (l3), 1559-1573. Combined heat and power (CHP) systems often use absorption technology to supply heating and cooling to a facility. With the availability of gas turbines spanning an increasingly wide range of capacities, it is becoming more and more attractive to utilize CHP via a combination of gas turbines and absorption chillers. The present study investigates the economic feasibility of implementing such CHP systems with existing, commercially available gas turbines and single, double, and triple effect absorption chillers. The maximum amount of thermal energy available for the chiller is calculated based on the size of turbine, exhaust flow rate and exhaust temperature, yielding approximately 300 000 kW of cooling (85 379 tons) for a large power turbine. The annual demand and usage avoided costs for varying turbine and absorption system sizes are discussed as well, showing that a CHP system is capable of saving millions of dollars annually on electricity. 02lO1077 Engine performance using vaporizing carburetor Ahu-Qudais, M. er rrl. Emvgy Conversion and Mnnagemenr, 2001, 42, (6) 755-761. Fuel and Energy Abstracts
March 2002
131