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air mixtures induced by radiation-heated large inert particles
08 Combustion (bumers, combustion systems) 06•01236 Use of almond residues for domestic heating. Study of the combustion parameters in a mural boiler Gonzgdez, J. F. et al. Fuel Processing Technology, 2005, 86, (12 13), 1351 1368. The combustion process of a l m o n d residues in a 12 k W mural boiler for domestic heating was studied. The fuels used were three residues of a l m o n d (almond tree pruning, a l m o n d shell, and a l m o n d peel) and one forest p e l l e t r e c o m m e n d e d by the boiler manufacturer. Previously, the fuels were characterized by means of the higher heating value and, proximate and ultimate analyses. The influence of the residue type, fuel mass flow, d r a u g h t and residue mixture on the combustion p a r a m e t e r s was studied. A T E S T O 300 M-I analyser was employed to d e t e r m i n e the principal p a r a m e t e r s of the combustion process (CO2, CO, and O2 contents, fumes t e m p e r a t u r e , not-burnt gaseous and sensitive heat losses in the fumes, air excess coefficient and efficiency). The behaviour shown by a l m o n d tree p r u n i n g and a l m o n d shell was similar to that of the forest pellet, but a l m o n d peel d i d n ' t burn well in this boiler, and moreover the ashes accumulated in the fireplace i m p e d i n g the combustion process. The boiler efficiencies obtained with the m a x i m u m fuel mass flow (100%) and m i n i m u m draught (0%) were 88.3%, 85%, 78.5% for a l m o n d tree pruning, a l m o n d shell, and a l m o n d peel, respectively. The obtained efficiency with the forest p e l l e t was 90.5%. The o p t i m u m residue mixture was a l m o n d tree p r u n i n g (75%) and forest p e l l e t (25%), with a boiler efficiency of 87.9% for a mass flow and d r a u g h t of 100% and 0%, respectively.
08
COMBUSTION Burners, combustion systems
06•01237 Calculations of bluff-body stabilized flames using a joint probability density function model with detailed chemistry Liu, K. et al. Combustion and Flame, 2005, 141, (1 2), 89 117. Joint probability density function (PDF) calculations are reported of the bluff-body stabilized flames (HM1, HM2, and HM3) and the results are c o m p a r e d with the available experimental data. The calculations are based on the m o d e l l e d t r a n s p o r t equation for the j o i n t P D F of velocity, turbulence frequency, and composition (species mass fractions and enthalpy) using the interaction by exchange with the mean and E u c l i d e a n m i n i m u m spanning tree mixing models. The m e t h a n e chemistry is described by a 19-species a u g m e n t e d reduced mechanism, and is i m p l e m e n t e d using in situ adaptive tabulation. The n u m e r i c a l accuracy of the calculations is carefully studied, and the associated errors are quantified. For flame HM1 (which has the least local extinction), there is generally good a g r e e m e n t between calculations and m e a s u r e m e n t s , although (for all flames) the quality of the a g r e e m e n t deteriorates at d o w n s t r e a m locations. The calculations correctly show essentially inert mixing in the shear layer between the recirculation zone and the coflow in flame HM1, but not in flames H M 2 and HM3. In general, the calculations of flames H M 2 and HM3 are not in good a g r e e m e n t with the e x p e r i m e n t a l data and do not exhibit the observed local extinction. This deficiency is attributed to the inaccurate calculations of the m e a n mixture fraction in the recirculation zone (for flames H M 2 and HM3). The sensitivity of the calculation to the mixing m o d e l constant is investigated, and the m e a n scalar dissipation is reported.
06•01238 Characteristics of premixed flame in microcombustors with different diameters Li, Z. W. et al. Applied Thermal Engineering, 2005, 25, (2 3), 271 281. Microcombustors with d i a m e t e r s of 2 and 6 m m are studied. The effect of the d i a m e t e r on the transverse profiles of velocity, t e m p e r a t u r e and species mass fraction, as well as the axial volumetric heat loss and the wall shear stress were simulated and analysed. The results show that there is a flat region on the transverse profiles for the 6 m m microcombustor. However, there is no flat region on the profiles for the 2 m m microcombustor. The non-flat structure reflects the wall effects. In addition, both the volumetric heat loss and the wall shear stress increase with decreasing the diameter.
06•01239
Co-combustion of coal and meat and bone meal
Gulyurtlu, I. et al. Fuel, 2005, 84, (17), 2137 2148. F e e d i n g m e a t and bone meal (MBM) to cattle, sheep or other animals has been b a n n e d within the E U since 1 of July 1994. The quantities to be eliminated are m e a s u r e d in millions of tons. Disposal to landfill is not an option, as simply burying the m a t e r i a l cannot destroy any
186
Fuel and Energy Abstracts
May 2006
p o t e n t i a l bovine spongiform e n c e p h a l o p a t h y (BSE) pathogens. One disposal option is the co-combustion of coal and MBM, to ensure that any living organism is totally thermally destroyed and at the same time valorizing its energetic potential. Fluidized bed co-combustion of M B M is considered a viable technological option as it has the flexibility to burn coal with different materials in an efficient way, at relatively low t e m p e r a t u r e s (750 850°C) with lower e n v i r o n m e n t a l impact. For this purpose, co-combustion tests of coal and M B M were carried out on a pilot scale FBC, to investigate the implications of the results. This involved the d e t e r m i n a t i o n of the emissions of p o l l u t a n t s like NOx, N20, VOC, CO2, as well as the composition and the valorization of the ashes produced. The ashes from the bed, the cyclones and the stack were collected and analysed for biological activity, ecotoxicity, heavy m e t a l concentration and leachability. The results obtained suggest that the ashes were suitable to be deposited in m u n i c i p a l landfills.
06•01240 Detailed soot field in a turbulent non-premixed ethylene/air flame from laser scattering and extinction experiments Yang, B. and Koylu, U. O. Combustion andFlame, 2005, 141, (1 2), 55 65. A soot-containing t u r b u l e n t non-premixed flame burning ethylene in atmospheric-pressure air was investigated by conducting non-intrusive laser scattering and extinction experiments at various axial and radial flame locations. Mean soot p r o p e r t i e s of principal interest-soot volume fraction, spherule (primary particle) diameter, and aggregate size and fractal dimension-were characterized based on the Rayleigh Debye Gans scattering theory, which can properly account for the actual particulate size and morphology. In situ evidence for the formation of precursor particles and their carbonization to m a t u r e soot, as well as the onset of the aggregation process, was observed low in the flame. M a x i m u m m e a n soot volume fraction and spherule d i a m e t e r were about 1 p p m and 28 rim, respectively, both p e a k i n g at similar axial locations. The m e a n n u m b e r of spherules per aggregate continuously increased along the flame centreline with the cluster cluster aggregation m e c h a n i s m leading to a fractal dimension of 1.8. R a d i a l variations of m e a n soot field were also observed with the possible exception of the aggregate radius of gyration. D e c o u p l i n g of spherule and aggregate sizes during the present analysis of optical m e a s u r e m e n t s allowed the separation of soot surface growth, oxidation, and aggregation processes. Such accurate descriptions of soot dynamics in a lightly sooting t u r b u l e n t flame are valuable in assessing c o m p u t a t i o n a l soot models and other particulate diagnostics.
06•01241 Experimental study of the resulting flow of plume-thermosiphon interaction: application to chimney problems Zinoubi, J. et al. Applied Thermal Engineering, 2005, 25, (4), 533 544. The quality of the s u r r o u n d i n g air depends on the various dismissals of the combustion gases (exhaust cars, smokes of chimneys, etc.), their scattering in the environment. U r b a n d e v e l o p m e n t around industrial zones and overexploitation of lands near factories triggered responsible interest in the p r o b l e m of pollution. In order to decrease the i m p a c t of air pollution, several chimneys have been constructed in the different industrial facilities. So the i m p r o v e m e n t of the industrial chimney range b e c a m e one of the current research problems. In order to improve the industrial chimney efficiency and to increase the vertical scattering of combustion products, the authors studied a system that could be integrated to the industrial chimney exit. This system is essentially constituted of an o p e n - e n d e d vertical cylinder of larger diameter. T h e r m a l radiance emitted by smoke heats the internal cylinder wall. The heating of the fluid at the cylinder-inlet is the cause of the t h e r m o s i p h o n effect a r o u n d the t h e r m a l plume. To study the p r o b l e m in the laboratory the authors simulated the p l u m e exiting of a chimney by a disk h e a t e d uniformly by the Joule effect at constant temperature. Different configurations were studied, while acting, on the source cylinder spacing and the cylinder height. The study of the average fields permits, in a first stage, to get better information about the m e c h a n i s m of the resulting flow development, and in a second stage, to d e t e r m i n e the spacing of the source cylinder and cylinder height optima, for which a clean increase of fluid flow rate is obtained.
06•01242 Explosions of methane/air mixtures induced by radiation-heated large inert particles Stamatov, V. A. et al. Fuel, 2005, 84, (16), 2086 2092. This work presents the results of an e x p e r i m e n t a l and m o d e l l i n g investigation of the ignition of quiescent m e t h a n e / a i r mixtures caused by r a d i a t i o n - h e a t e d large inert particles. The e x p e r i m e n t a l data indicate that the explosion-delay time is inversely p r o p o r t i o n a l to the radiative power flux. The delay time exhibits a m i n i m u m at a m e t h a n e / air ratio near to stoichiometric. The m a t h e m a t i c a l m o d e l incorporates the basic principles of the t h e r m a l initiation mode of d e t o n a t i o n p h e n o m e n a . The e x p e r i m e n t a l values of the explosion-delay time correlate with the predictions, hence lending w e i g h t to the p r o p o s e d model.
08
COMBUSTION Burners, combustion systems
06•01237 Calculations of bluff-body stabilized flames using a joint probability density function model with detailed chemistry Liu, K. et al. Combustion and Flame, 2005, 141, (1 2), 89 117. Joint probability density function (PDF) calculations are reported of the bluff-body stabilized flames (HM1, HM2, and HM3) and the results are c o m p a r e d with the available experimental data. The calculations are based on the m o d e l l e d t r a n s p o r t equation for the j o i n t P D F of velocity, turbulence frequency, and composition (species mass fractions and enthalpy) using the interaction by exchange with the mean and E u c l i d e a n m i n i m u m spanning tree mixing models. The m e t h a n e chemistry is described by a 19-species a u g m e n t e d reduced mechanism, and is i m p l e m e n t e d using in situ adaptive tabulation. The n u m e r i c a l accuracy of the calculations is carefully studied, and the associated errors are quantified. For flame HM1 (which has the least local extinction), there is generally good a g r e e m e n t between calculations and m e a s u r e m e n t s , although (for all flames) the quality of the a g r e e m e n t deteriorates at d o w n s t r e a m locations. The calculations correctly show essentially inert mixing in the shear layer between the recirculation zone and the coflow in flame HM1, but not in flames H M 2 and HM3. In general, the calculations of flames H M 2 and HM3 are not in good a g r e e m e n t with the e x p e r i m e n t a l data and do not exhibit the observed local extinction. This deficiency is attributed to the inaccurate calculations of the m e a n mixture fraction in the recirculation zone (for flames H M 2 and HM3). The sensitivity of the calculation to the mixing m o d e l constant is investigated, and the m e a n scalar dissipation is reported.
06•01238 Characteristics of premixed flame in microcombustors with different diameters Li, Z. W. et al. Applied Thermal Engineering, 2005, 25, (2 3), 271 281. Microcombustors with d i a m e t e r s of 2 and 6 m m are studied. The effect of the d i a m e t e r on the transverse profiles of velocity, t e m p e r a t u r e and species mass fraction, as well as the axial volumetric heat loss and the wall shear stress were simulated and analysed. The results show that there is a flat region on the transverse profiles for the 6 m m microcombustor. However, there is no flat region on the profiles for the 2 m m microcombustor. The non-flat structure reflects the wall effects. In addition, both the volumetric heat loss and the wall shear stress increase with decreasing the diameter.
06•01239
Co-combustion of coal and meat and bone meal
Gulyurtlu, I. et al. Fuel, 2005, 84, (17), 2137 2148. F e e d i n g m e a t and bone meal (MBM) to cattle, sheep or other animals has been b a n n e d within the E U since 1 of July 1994. The quantities to be eliminated are m e a s u r e d in millions of tons. Disposal to landfill is not an option, as simply burying the m a t e r i a l cannot destroy any
186
Fuel and Energy Abstracts
May 2006
p o t e n t i a l bovine spongiform e n c e p h a l o p a t h y (BSE) pathogens. One disposal option is the co-combustion of coal and MBM, to ensure that any living organism is totally thermally destroyed and at the same time valorizing its energetic potential. Fluidized bed co-combustion of M B M is considered a viable technological option as it has the flexibility to burn coal with different materials in an efficient way, at relatively low t e m p e r a t u r e s (750 850°C) with lower e n v i r o n m e n t a l impact. For this purpose, co-combustion tests of coal and M B M were carried out on a pilot scale FBC, to investigate the implications of the results. This involved the d e t e r m i n a t i o n of the emissions of p o l l u t a n t s like NOx, N20, VOC, CO2, as well as the composition and the valorization of the ashes produced. The ashes from the bed, the cyclones and the stack were collected and analysed for biological activity, ecotoxicity, heavy m e t a l concentration and leachability. The results obtained suggest that the ashes were suitable to be deposited in m u n i c i p a l landfills.
06•01240 Detailed soot field in a turbulent non-premixed ethylene/air flame from laser scattering and extinction experiments Yang, B. and Koylu, U. O. Combustion andFlame, 2005, 141, (1 2), 55 65. A soot-containing t u r b u l e n t non-premixed flame burning ethylene in atmospheric-pressure air was investigated by conducting non-intrusive laser scattering and extinction experiments at various axial and radial flame locations. Mean soot p r o p e r t i e s of principal interest-soot volume fraction, spherule (primary particle) diameter, and aggregate size and fractal dimension-were characterized based on the Rayleigh Debye Gans scattering theory, which can properly account for the actual particulate size and morphology. In situ evidence for the formation of precursor particles and their carbonization to m a t u r e soot, as well as the onset of the aggregation process, was observed low in the flame. M a x i m u m m e a n soot volume fraction and spherule d i a m e t e r were about 1 p p m and 28 rim, respectively, both p e a k i n g at similar axial locations. The m e a n n u m b e r of spherules per aggregate continuously increased along the flame centreline with the cluster cluster aggregation m e c h a n i s m leading to a fractal dimension of 1.8. R a d i a l variations of m e a n soot field were also observed with the possible exception of the aggregate radius of gyration. D e c o u p l i n g of spherule and aggregate sizes during the present analysis of optical m e a s u r e m e n t s allowed the separation of soot surface growth, oxidation, and aggregation processes. Such accurate descriptions of soot dynamics in a lightly sooting t u r b u l e n t flame are valuable in assessing c o m p u t a t i o n a l soot models and other particulate diagnostics.
06•01241 Experimental study of the resulting flow of plume-thermosiphon interaction: application to chimney problems Zinoubi, J. et al. Applied Thermal Engineering, 2005, 25, (4), 533 544. The quality of the s u r r o u n d i n g air depends on the various dismissals of the combustion gases (exhaust cars, smokes of chimneys, etc.), their scattering in the environment. U r b a n d e v e l o p m e n t around industrial zones and overexploitation of lands near factories triggered responsible interest in the p r o b l e m of pollution. In order to decrease the i m p a c t of air pollution, several chimneys have been constructed in the different industrial facilities. So the i m p r o v e m e n t of the industrial chimney range b e c a m e one of the current research problems. In order to improve the industrial chimney efficiency and to increase the vertical scattering of combustion products, the authors studied a system that could be integrated to the industrial chimney exit. This system is essentially constituted of an o p e n - e n d e d vertical cylinder of larger diameter. T h e r m a l radiance emitted by smoke heats the internal cylinder wall. The heating of the fluid at the cylinder-inlet is the cause of the t h e r m o s i p h o n effect a r o u n d the t h e r m a l plume. To study the p r o b l e m in the laboratory the authors simulated the p l u m e exiting of a chimney by a disk h e a t e d uniformly by the Joule effect at constant temperature. Different configurations were studied, while acting, on the source cylinder spacing and the cylinder height. The study of the average fields permits, in a first stage, to get better information about the m e c h a n i s m of the resulting flow development, and in a second stage, to d e t e r m i n e the spacing of the source cylinder and cylinder height optima, for which a clean increase of fluid flow rate is obtained.
06•01242 Explosions of methane/air mixtures induced by radiation-heated large inert particles Stamatov, V. A. et al. Fuel, 2005, 84, (16), 2086 2092. This work presents the results of an e x p e r i m e n t a l and m o d e l l i n g investigation of the ignition of quiescent m e t h a n e / a i r mixtures caused by r a d i a t i o n - h e a t e d large inert particles. The e x p e r i m e n t a l data indicate that the explosion-delay time is inversely p r o p o r t i o n a l to the radiative power flux. The delay time exhibits a m i n i m u m at a m e t h a n e / air ratio near to stoichiometric. The m a t h e m a t i c a l m o d e l incorporates the basic principles of the t h e r m a l initiation mode of d e t o n a t i o n p h e n o m e n a . The e x p e r i m e n t a l values of the explosion-delay time correlate with the predictions, hence lending w e i g h t to the p r o p o s e d model.