- Email: [email protected]
02703 Simulation of chemical reaction kinetics in turbulent flames with detailed and global mechanisms
09
and combustion frequencies are presented and discussed. For example, by increasing the combustion frequency from 30 to 59 Hz (at 25 kW input firing rate, stoichiometric air-fuel ratio and 0.12 bar pressure amplitude), the NO emissions reduced monotonically from 61 ppm to 29 ppm (dry ppm, corrected to 3% 02). The general conclusion from this study was that the lowest NO emissions occurred under conditions of high combustion frequency and high maximum pressure amplitude. Possible mechanisms for this are discussed.
Fire extinguishment of dust-collecting hoppers in combustion facilities uslng fossil fuels
99102696
Kuroda, T. er al. Jpn. Kokai Tokkyo Koho JP 10 300,056 [98 300,056], (Cl. F23Jl/OO), 13 Nov 1998, Appl. 97/108,403,25 Apr 1997,4 pp. (In Japanese) Fire extinguishing methods of dust-collecting hoppers are reviewed. Granular dry ice and inert gases are sprayed without water into the hoppers through nozzles. Unfortunately, dust- and ash-discharging feeders may become clogged.
Introduction to combustion technology 99102697 Mandai, S. Yosha, 1998, 35, (2) 139-145. (In Japanese) The fundamental issues of combustion and thermodynamics in relation to a spray coating are reviewed. Firstly, combustion phenomena are classified on fuels, boundary conditions and flame types. Secondly, theoretical combustion gas temperature, oxygen and carbon monoxide partial pressure are shown as a function of equivalence ratio. Under high temperature conditions, the disassociation phenomenon is noticeable. Thirdly, it is shown that high pressure combustion makes higher heat release rate possible. Low volatile fine coal boiler using new pollutionminimum burner and circular ultra firing
99102696
Kaneko, S. et al. Kogyo Kanetsu, 1998, 35, (4), 21-27. (In Japanese) A 145-MW power plant fired with low-volatile coal is described in this paper. By using circular ultra firing (CUF) mode, combustion stability and good in-furnace luminance are obtained whilst enabling low NO, and low air ratio condition. Furthermore, the boiler uses an advanced-pollutionminimum (A-PM) burner which has even lower NO, emissions compared to conventional PM burners.
Measurement of radial gas flow in upper shaft and its influence on blast furnace performance
99102699
Bachhofen, H.-J. et al. Comm. Eur. Communities, [Rep.] EUR, 1998, (EUR 18360) 61-70. In this paper, the performance of a blast furnace is aimed to be improved by measuring gas flow. The development of an inclined probe with nine measuring points just above the stock line is discussed. When simultaneous measurements are taken from this inclined probe and the horizontal probe in the burden it is shown that the gas flow can vary considerably. Additionally, at times the ETA CO values and H2 contents can vary between the horizontal probe or the tuyere gas, respectively, and the centre of the blast furnace. Thus indicating that the injected coal has, in part, not even lost its volatile components when leaving the raceway zone before being torn by the kinetic energy of the blast into the centre of the furnace. Many relationships are shown between rates of gas flows. Charging centre coke enable a matching gas composition to be set in both probes thus stabilizing the central flow of gas. However, this stability can be lost again depending on the absolute flow of gas in the centre of the furnace.
Noise in non-premixed turbulent coal gas flames 99lO2700 Klein, S. A. and Kok, J. B. W. Turbul., Heat Mass Transfer 2, Proc. Int. Symp., 2nd, 1997, 675-684. Edited by Hanjalic, K. and Peeters, T. W. J., Delft University Press, Delft, The Netherlands A wave equation for pressure fluctuations is derived from a flame acting as a fluctuating monopole volume source. It is suggested that the acoustic intensity generated in a turbulent non-premixed tlame can be factorized as a function of the flame chemical and the fluctuation of the mixed fraction. The theory was tested experimentally. Both flame chemical and turbulence were found to have the expected effect on the generated acoustic intensity. A reduced kinetic model for NO. reduction by advanced reburning
99io2701
Xu, H. et al. Energy Fuels, 1998, 12, (6). 1278-1289. Up to 85-95% of the NO in pulverized coal-fired furnaces can be removed by an advanced reburning technology which utilizes natural gas injection followed by ammonia injection. The development of a seven-step, llspecies reduced mechanism for the prediction of nitric oxide concentrations using advanced reburning from a 312~step, 50-species full mechanism is described. The predictions of this seven-step reduced mechanism have been found to be in good agreement with those of the full mechanism over a wide range of parameters applicable to coal-, gas- and oil-based combustion cases. Predictions were compared with three independent sets of experimental laminar data. The comparisons indicate that the reduced mechanism correctly predicts the observed trends. Included in the trends analysed were; the effects of temperature, the ratio of (NHsiNO)i., concentrations of CO, CO*, Oz and Hz0 on NO reduction and the effects of CO on NHz slip. Parametric studies of the effects of COz and Hz0 have been performed with the reduced mechanism.
Combustion
(burners, combustion
systems)
Reduction of N20 emissions from a coal-fired circulating fluidized bed combustor by afterburning
99lQ2702
Liu, H. and Gibbs, B. M. Fuel, 1998, 77, (14) 1579-1587. Afterburning is a method of reducing NzO emissions from coal combustion. Experimental results of afterburning from a pilot-scale, coal-fired, circulating fluidized bed combustion (CFBC) system with a riser of diameter 161 mm and length 6.2 m are presented in this paper. The main part of the afterburning zone was situated in the primary and secondary cyclones and propane was used as the afterburning fuel. Two afterburning configurations were investigated, one a commercial gas-fired burner and the other a direct tool injection via a simple fuel injector. Up to 80% NzO reduction could be achieved experimentally. Experimental results further showed that propane afterburning by direct fuel injection is more effective in reducing NzO emission than afterburning with the burner. It was also shown that when afterburning is conducted through the burner, a higher NzO reduction can be achieved with a lower air flow rate to the burner, especially if the thermal input to the burner is limited. Few adverse effects of afterburning were observed. Analysis of the experimental results and simple kinetic estimates indicate that radical reactions probably contribute more than NzO thermal decomposition in reducing NzO emissions in the afterburning zone.
Simulation of chemical reaction kinetics in turbulent flames with detailed and global mechanisms
99lQ2703
Magel, H.-C. Fortschr.-Ber. VDI, Reihe 6, 1997, 377, i-viii, 1-129. (In German) A mathematical model, valid under practical combustion chamber configurations, was developed to describe chemical reaction kinetics in turbulent flames. The flow aspects were modelled as a finite-volume formulation, while the interactions between turbulence and the reaction chemical were modelled using eddy dissipation theory. A detailed and global reaction mechanism was used to model the flame chemical. The results of the model were used to accurately describe a pulverized coal flame.
Soifos multi-fuel burners with single or twin airflow and radiant type burners
99lO2704
Usai, A. and Sivestrini, S. Rev. Metall.lCah. Inf. Technical, 1998, 95, (6). 785-788. (In French) The Sollac Fos hot strip mill is discussed in this paper. It is equipped with three walking beam furnaces, each with a heating capacity of 350 tons/h, which are fired with a fuel mix of blast furnace and coke oven gas with heating capacity of initially 10 to now 16 MJ/m3. Natural gas is also used. Temperature heterogeneity problems along the length of the slabs were apparent due to the dimensions of the furnaces, their relatively low maximum working conditions (70%) and the variable size of the slabs. Any increase of the calorific value of the gas contributed to a degradation and reduction of the flow rate of the gas, causing hot centres or cold ends. Better temperature homogeneity was sought by modifying the burners operating conditions. A specification for the length and temperature characteristics of the flame was established before a series of tests was performed. The discussion includes details of the lateral Solfos DF burner, the Solfos SF front burner and the Solfos radius roof burner.
Some simple considerations on the turbulent mixing process in relation to flame-scaling
99102796
Smart, J. P. .I. Inst. Energy, 1998, 71, (488) 152-155. An analysis of turbulent flow in relation to burner- and flame-scaling. The results suggest that it is effectively impossible to scale a burner to achieve even the most basic flame thermo-chemical structural features using constant-velocity (n = 2) or constant-residence-time scaling (n = 3) criterion. With the constant-velocity scaling criterion, flame chemical becomes dominant over mixing as the scale is reduced. With the constant-residence-time scaling criterion, mixing becomes dominant over chemical as scale is reduced. Actual data obtained in a scaling programme on pulverized coal flames are used to support the conclusions.
99lQ2799 Soot deep oxidation cataiysed by molybdena and molybdates. A thermogravimetric investigation Hasan, M. A. et al. Thermochim. Acta, 1998, 320, (l-2), 23-32. X-ray powder difractometry and IR spectroscopy were used to synthesize and then characterize molybdena (Mo03) and molybdates of bismuth (BizMosOiz), chromium (CrzMo30iz), barium (BaMoO& manganese (MnMo04) and copper (CU3M0r09). They were subsequently assessed as ‘loose contact’ catalysts for soot deep oxidation in air by thermogravimetry. Commercial chromia (CrzOs) and tungsta (WO3) were assessed in a similar way, and the high oxidation activity of Mo03, as compared to both CrzOs and WOs was observed, which was attributed to the higher volatility of MOO, species. The high activity of Moos and Cu3M0z09, as compared to the other test molybdates, can also be explained in this way. However, a relatively higher activity was observed for Cu~Moz09 compared to Mo03, as soot ignition temperature decreased from 571°C (uncatalysed oxidation) to 43o”C, occurring within the temperature range of diesel exhaust (200450°C). This observation is attributed to the copper-promoted redox conduct of Mo(VI) in the oxidation reaction of soot. The kinetics of the reaction were studied non-isothermally, and the kinetic parameters calculated.
Fuel and Energy Abstracts
July 1999 261
and combustion frequencies are presented and discussed. For example, by increasing the combustion frequency from 30 to 59 Hz (at 25 kW input firing rate, stoichiometric air-fuel ratio and 0.12 bar pressure amplitude), the NO emissions reduced monotonically from 61 ppm to 29 ppm (dry ppm, corrected to 3% 02). The general conclusion from this study was that the lowest NO emissions occurred under conditions of high combustion frequency and high maximum pressure amplitude. Possible mechanisms for this are discussed.
Fire extinguishment of dust-collecting hoppers in combustion facilities uslng fossil fuels
99102696
Kuroda, T. er al. Jpn. Kokai Tokkyo Koho JP 10 300,056 [98 300,056], (Cl. F23Jl/OO), 13 Nov 1998, Appl. 97/108,403,25 Apr 1997,4 pp. (In Japanese) Fire extinguishing methods of dust-collecting hoppers are reviewed. Granular dry ice and inert gases are sprayed without water into the hoppers through nozzles. Unfortunately, dust- and ash-discharging feeders may become clogged.
Introduction to combustion technology 99102697 Mandai, S. Yosha, 1998, 35, (2) 139-145. (In Japanese) The fundamental issues of combustion and thermodynamics in relation to a spray coating are reviewed. Firstly, combustion phenomena are classified on fuels, boundary conditions and flame types. Secondly, theoretical combustion gas temperature, oxygen and carbon monoxide partial pressure are shown as a function of equivalence ratio. Under high temperature conditions, the disassociation phenomenon is noticeable. Thirdly, it is shown that high pressure combustion makes higher heat release rate possible. Low volatile fine coal boiler using new pollutionminimum burner and circular ultra firing
99102696
Kaneko, S. et al. Kogyo Kanetsu, 1998, 35, (4), 21-27. (In Japanese) A 145-MW power plant fired with low-volatile coal is described in this paper. By using circular ultra firing (CUF) mode, combustion stability and good in-furnace luminance are obtained whilst enabling low NO, and low air ratio condition. Furthermore, the boiler uses an advanced-pollutionminimum (A-PM) burner which has even lower NO, emissions compared to conventional PM burners.
Measurement of radial gas flow in upper shaft and its influence on blast furnace performance
99102699
Bachhofen, H.-J. et al. Comm. Eur. Communities, [Rep.] EUR, 1998, (EUR 18360) 61-70. In this paper, the performance of a blast furnace is aimed to be improved by measuring gas flow. The development of an inclined probe with nine measuring points just above the stock line is discussed. When simultaneous measurements are taken from this inclined probe and the horizontal probe in the burden it is shown that the gas flow can vary considerably. Additionally, at times the ETA CO values and H2 contents can vary between the horizontal probe or the tuyere gas, respectively, and the centre of the blast furnace. Thus indicating that the injected coal has, in part, not even lost its volatile components when leaving the raceway zone before being torn by the kinetic energy of the blast into the centre of the furnace. Many relationships are shown between rates of gas flows. Charging centre coke enable a matching gas composition to be set in both probes thus stabilizing the central flow of gas. However, this stability can be lost again depending on the absolute flow of gas in the centre of the furnace.
Noise in non-premixed turbulent coal gas flames 99lO2700 Klein, S. A. and Kok, J. B. W. Turbul., Heat Mass Transfer 2, Proc. Int. Symp., 2nd, 1997, 675-684. Edited by Hanjalic, K. and Peeters, T. W. J., Delft University Press, Delft, The Netherlands A wave equation for pressure fluctuations is derived from a flame acting as a fluctuating monopole volume source. It is suggested that the acoustic intensity generated in a turbulent non-premixed tlame can be factorized as a function of the flame chemical and the fluctuation of the mixed fraction. The theory was tested experimentally. Both flame chemical and turbulence were found to have the expected effect on the generated acoustic intensity. A reduced kinetic model for NO. reduction by advanced reburning
99io2701
Xu, H. et al. Energy Fuels, 1998, 12, (6). 1278-1289. Up to 85-95% of the NO in pulverized coal-fired furnaces can be removed by an advanced reburning technology which utilizes natural gas injection followed by ammonia injection. The development of a seven-step, llspecies reduced mechanism for the prediction of nitric oxide concentrations using advanced reburning from a 312~step, 50-species full mechanism is described. The predictions of this seven-step reduced mechanism have been found to be in good agreement with those of the full mechanism over a wide range of parameters applicable to coal-, gas- and oil-based combustion cases. Predictions were compared with three independent sets of experimental laminar data. The comparisons indicate that the reduced mechanism correctly predicts the observed trends. Included in the trends analysed were; the effects of temperature, the ratio of (NHsiNO)i., concentrations of CO, CO*, Oz and Hz0 on NO reduction and the effects of CO on NHz slip. Parametric studies of the effects of COz and Hz0 have been performed with the reduced mechanism.
Combustion
(burners, combustion
systems)
Reduction of N20 emissions from a coal-fired circulating fluidized bed combustor by afterburning
99lQ2702
Liu, H. and Gibbs, B. M. Fuel, 1998, 77, (14) 1579-1587. Afterburning is a method of reducing NzO emissions from coal combustion. Experimental results of afterburning from a pilot-scale, coal-fired, circulating fluidized bed combustion (CFBC) system with a riser of diameter 161 mm and length 6.2 m are presented in this paper. The main part of the afterburning zone was situated in the primary and secondary cyclones and propane was used as the afterburning fuel. Two afterburning configurations were investigated, one a commercial gas-fired burner and the other a direct tool injection via a simple fuel injector. Up to 80% NzO reduction could be achieved experimentally. Experimental results further showed that propane afterburning by direct fuel injection is more effective in reducing NzO emission than afterburning with the burner. It was also shown that when afterburning is conducted through the burner, a higher NzO reduction can be achieved with a lower air flow rate to the burner, especially if the thermal input to the burner is limited. Few adverse effects of afterburning were observed. Analysis of the experimental results and simple kinetic estimates indicate that radical reactions probably contribute more than NzO thermal decomposition in reducing NzO emissions in the afterburning zone.
Simulation of chemical reaction kinetics in turbulent flames with detailed and global mechanisms
99lQ2703
Magel, H.-C. Fortschr.-Ber. VDI, Reihe 6, 1997, 377, i-viii, 1-129. (In German) A mathematical model, valid under practical combustion chamber configurations, was developed to describe chemical reaction kinetics in turbulent flames. The flow aspects were modelled as a finite-volume formulation, while the interactions between turbulence and the reaction chemical were modelled using eddy dissipation theory. A detailed and global reaction mechanism was used to model the flame chemical. The results of the model were used to accurately describe a pulverized coal flame.
Soifos multi-fuel burners with single or twin airflow and radiant type burners
99lO2704
Usai, A. and Sivestrini, S. Rev. Metall.lCah. Inf. Technical, 1998, 95, (6). 785-788. (In French) The Sollac Fos hot strip mill is discussed in this paper. It is equipped with three walking beam furnaces, each with a heating capacity of 350 tons/h, which are fired with a fuel mix of blast furnace and coke oven gas with heating capacity of initially 10 to now 16 MJ/m3. Natural gas is also used. Temperature heterogeneity problems along the length of the slabs were apparent due to the dimensions of the furnaces, their relatively low maximum working conditions (70%) and the variable size of the slabs. Any increase of the calorific value of the gas contributed to a degradation and reduction of the flow rate of the gas, causing hot centres or cold ends. Better temperature homogeneity was sought by modifying the burners operating conditions. A specification for the length and temperature characteristics of the flame was established before a series of tests was performed. The discussion includes details of the lateral Solfos DF burner, the Solfos SF front burner and the Solfos radius roof burner.
Some simple considerations on the turbulent mixing process in relation to flame-scaling
99102796
Smart, J. P. .I. Inst. Energy, 1998, 71, (488) 152-155. An analysis of turbulent flow in relation to burner- and flame-scaling. The results suggest that it is effectively impossible to scale a burner to achieve even the most basic flame thermo-chemical structural features using constant-velocity (n = 2) or constant-residence-time scaling (n = 3) criterion. With the constant-velocity scaling criterion, flame chemical becomes dominant over mixing as the scale is reduced. With the constant-residence-time scaling criterion, mixing becomes dominant over chemical as scale is reduced. Actual data obtained in a scaling programme on pulverized coal flames are used to support the conclusions.
99lQ2799 Soot deep oxidation cataiysed by molybdena and molybdates. A thermogravimetric investigation Hasan, M. A. et al. Thermochim. Acta, 1998, 320, (l-2), 23-32. X-ray powder difractometry and IR spectroscopy were used to synthesize and then characterize molybdena (Mo03) and molybdates of bismuth (BizMosOiz), chromium (CrzMo30iz), barium (BaMoO& manganese (MnMo04) and copper (CU3M0r09). They were subsequently assessed as ‘loose contact’ catalysts for soot deep oxidation in air by thermogravimetry. Commercial chromia (CrzOs) and tungsta (WO3) were assessed in a similar way, and the high oxidation activity of Mo03, as compared to both CrzOs and WOs was observed, which was attributed to the higher volatility of MOO, species. The high activity of Moos and Cu3M0z09, as compared to the other test molybdates, can also be explained in this way. However, a relatively higher activity was observed for Cu~Moz09 compared to Mo03, as soot ignition temperature decreased from 571°C (uncatalysed oxidation) to 43o”C, occurring within the temperature range of diesel exhaust (200450°C). This observation is attributed to the copper-promoted redox conduct of Mo(VI) in the oxidation reaction of soot. The kinetics of the reaction were studied non-isothermally, and the kinetic parameters calculated.
Fuel and Energy Abstracts
July 1999 261