- Email: [email protected]
02191 Co-pyrolysis of polymethyl methacrylate with brown coal and effect on monomer production
08 Combustion (burners, combustion systems) variation in the fraction of mercury that is emitted in the gaseous phase, as elemental and oxidized mercury vapour, and as particulatebound mercury. Oxidized mercury is a preferable species because is less volatile at stack temperatures, water-soluble, and tends to interact with mineral matter and char, and cold-end air pollution control devices. There is also evidence that boiler-operating conditions could be used to influence mercury behaviour in the boiler, since they affect the thermo-chemical conditions for mercury formation and reduction. However, operation of boiler control settings, which result in mercury removal benefits, should also consider the tradeoff between mercury reduction and other emissions (for example, NO,. and CO), the level of unburned carbon in the fly ash, unit efficiency and the performance of particulate control equipment. This paper reports fieldwork performed to investigate the feasibility of affecting mercury emissions from coalfired plants by manipulating boiler control settings. Full-scale testing was performed at two units. One of the units is equipped with a backend train that includes a rotary air preheater followed by two electrostatic precipitators in series. The other unit is equipped with hot and cold precipitators and a tubular air preheater. A strategy for mercury control by selectively manipulating boiler control settings, if used in combination with other control measures such as sorbent injection, should provide a cost-effective option for mercury control.
08
COMBUSTION Burners, combustion systems
06102189 Application of neural dynamic optimization to combustion-instability control Fichera, A. and Pagano, A. Applied Energy, 2006, 83, (3), 253 264. The suppression of thermo-acoustic combustion instabilities represents one of the main goals in the design of reliable high-performances combustion chambers. Unstable dynamics arise when a non-linear coupling is established between the acoustic field and the flame front generating high-amplitude and low-frequency pressure and heat release oscillations, associated with the excitation of the combustor's natural modes. Temperature and pressure peaks due to these phenomena are particularly harmful for the structural damage they can cause as well as for performance degradations and increase of pollutant emissions. Due to the non-linear nature of the phenomenon, relevant problems arise when it is necessary to define model-based control-systems. The aim of this study is to define a control strategy, based on the application of recent results in the field of neural control of non-linear systems. The proposed strategy is an application of an innovative neural-network-based technique, namely neural dynamic optimization, which is able to exploit the potential of optimal control strategies in dealing with complex non-linear systems and the flexibility and the generalization properties of neural networks. Reported simulations show the satisfactory performance of the proposed controller in suppressing undesired thermo-acoustic combustion instabilities.
06/02190 Boron nitride: a high potential support for combustion catalysts Postole, G. et al. Thermochimica Acta, 2005. 434, (1-2), 150-157. High surface area BN powders have been prepared from different precursors to be used as supports for noble metal catalysts. The more suitable boron nitride powders were obtained using polytrichoroborazine, pTCB, as precursor, leading to a surface area higher than 150 m2/g. The BN powders were characterized by XRD, XPS, TG, SEM and adsorption microcalorimetry measurements (aniline and ammonia). The preliminary results showed a remarkable stability of the BN supports, even in the presence of moisture. Palladium impregnation of the BN powders was performed using a classical method and the obtained catalysts exhibited a high dispersion with Pd particles of about 4 nm.
06/02191 Co-pyrolysis of polymethyl methacrylate with brown coal and effect on monomer production Orinfik, A. et al. Fuel, 2006, 85, (1), 1~18. Pyrolysis capillary gas chromatography has been applied to the study of the co-pyrolysis of polymethyl methacrylate (PMMA) with Slovakian brown coal with the aim of finding pyrolysis conditions yielding a maximum amount of methyl methacrylate (MMA). Effects of pyrolysis temperature and PMMA-coal weight ratios were investigated. Capillary gas chromatography coupled with mass spectrometric detector (cGC-MS) was used for MMA identification. The highest yield of
336
Fuel and Energy Abstracts September 2006
MMA in the pyrolysate was obtained at 750°C. The optimal PMMAcoal weight ratio for maximum MMA production lies in the interval 0.5 mg PMMA and 0.6-0.8 mg brown coal with an MMA yield of 64%. Coal addition to the sample affects species recombination in gaseous phase, augments MMA production at higher temperatures and eliminates degradation products of PMMA and coal pyrolysis. Different conversion diagrams are characteristic for thermal degradation of single PMMA and in the mixture with coal. Detailed mechanism of synergetic effects arisen during co-pyrolysis are not yet known. It was also found that lower pyrolysis temperatures are more suitable to study degradation mechanism and kinetics while higher temperatures are more applicable for identification purposes. MMA decomposes completely at 900°C.
06/02192 Compositions and leaching behaviours of combustion residues Saikia, N. et al. Fuel, 2006, 85, (2), 264-271. Combustion residues generated from different incineration processes create major environmental problems because these materials contain high amounts of toxic substances. This paper reports the leaching behaviours of three residues along with their mineralogical compositions. Column leaching experiments at two different pH values were conducted to study the leaching behaviours. Leachants were analysed to determine the pH, the concentrations of some toxic elements like Pb, Cr. As, Cd, Se, B, Mo and the volume of leachants passing through the columns. Raw and some treated residues were also characterized by XRD and SEM-EPMA techniques. It was found that the concentrations of some toxic elements present in the residues as well as in the leachant fractions collected at different time intervals after leaching were very high. The amounts of soluble salts and toxic elements in the municipal solid waste incinerator (MSWI) ash were higher than those in the other two residues. The order of alkalinities of the three residues was: fly ash > MSWI ash > sewage sludge ash. The final pH of the leachant was related to the volume of leachant passing through the column. Some leachant properties were related to the mineralogical compositions of the residues and to the secondary minerals formed during the leaching period.
06102193 Estimation of LOC (limiting oxygen concentration) of fuel-air-inert mixtures at elevated temperatures by means of adiabatic flame temperatures Razus, D. et al. Chemical Engineering and Processing, 2006, 45, (3), 193-197. The limiting values of fuel concentration in a flammable fuel-air mixture are the lower explosion limit (LEL) and upper explosion limit (UEL). The addition of an inert component to fuel/air mixtures determines the increase of LEL and decrease of UEL, until these values finally merge at the inerting point. The maximum oxygen amount of a non-flammable fuel-air-inert mixture is the limiting oxygen concentration (LOC), an important safety characteristics. The investigation of a comprehensive set of flammability data at elevated temperatures and ambient pressure taken from literature sources was made for systems containing nitrogen, carbon dioxide and water (vapour) as inert components, at 100 °, 200 ° and 250°C. The adiabatic flame temperatures at LEL (CAFT LEL) and LOC (CAFT 5°c) were calculated by taking into account the dissociation of gases within the flame. A linear correlation of CAFT L°c versus CAFT LEL was empirically derived for the examined systems. The slope and intercept of the correlation are dependent on temperature and on nature of the inert gas. The correlation allows the development of a simple procedure for estimating LOC, when the LEL of fuel-air and the equivalence ratio of the fuel-air-inert mixture at the inerting point are known. Knowing the scarce information concerning the flammability of fuel-air-inert mixtures at temperatures higher than ambient, the proposed procedure brings about an useful tool for estimation of LOC.
06•02194 Kinetics of CH4, H2S and SO2 oxidation on precious metal catalysts under stagnation point flow conditions Rickett, G. et al. Journal of the Energy Institute, 2006, 79, (1), 12-18. A new methodology combining reactor experiments and numerical modelling to derive kinetic rates of solid-gas heterogeneous reactions in a stagnation point flow reactor (SPFR) is developed and used to investigate the effects of small concentrations of H2S and SO2 on the lean catalytic combustion of methane on precious metal catalysts. The activity of polycrystalline Pt foil, then Pt-, Rh- and Pd-containing washcoats supported on stainless-steel foils are investigated in the SPFR, where the washcoat consisted of a thin layer of 7-alumina or ceria/7-alumina. The porous washcoats supported on steel foil were more active than the equivalent flat surface of pure precious metal (Pt) • • ~ with pre-exponentlal factors of 7.4 x 105 cm s 1 and 4.9 x 104 cm" s ~1 respectively. Repeated use of the washcoated catalyst and the effect of pore opening gives rise to a change in the pre-exponential factor from 7.4 x 105 cm s -1 to 1.1 x 109 cm s 1 for Pt. The high-temperature activity behaviour of Pt in presence of sulphur species in the feed was,
08
COMBUSTION Burners, combustion systems
06102189 Application of neural dynamic optimization to combustion-instability control Fichera, A. and Pagano, A. Applied Energy, 2006, 83, (3), 253 264. The suppression of thermo-acoustic combustion instabilities represents one of the main goals in the design of reliable high-performances combustion chambers. Unstable dynamics arise when a non-linear coupling is established between the acoustic field and the flame front generating high-amplitude and low-frequency pressure and heat release oscillations, associated with the excitation of the combustor's natural modes. Temperature and pressure peaks due to these phenomena are particularly harmful for the structural damage they can cause as well as for performance degradations and increase of pollutant emissions. Due to the non-linear nature of the phenomenon, relevant problems arise when it is necessary to define model-based control-systems. The aim of this study is to define a control strategy, based on the application of recent results in the field of neural control of non-linear systems. The proposed strategy is an application of an innovative neural-network-based technique, namely neural dynamic optimization, which is able to exploit the potential of optimal control strategies in dealing with complex non-linear systems and the flexibility and the generalization properties of neural networks. Reported simulations show the satisfactory performance of the proposed controller in suppressing undesired thermo-acoustic combustion instabilities.
06/02190 Boron nitride: a high potential support for combustion catalysts Postole, G. et al. Thermochimica Acta, 2005. 434, (1-2), 150-157. High surface area BN powders have been prepared from different precursors to be used as supports for noble metal catalysts. The more suitable boron nitride powders were obtained using polytrichoroborazine, pTCB, as precursor, leading to a surface area higher than 150 m2/g. The BN powders were characterized by XRD, XPS, TG, SEM and adsorption microcalorimetry measurements (aniline and ammonia). The preliminary results showed a remarkable stability of the BN supports, even in the presence of moisture. Palladium impregnation of the BN powders was performed using a classical method and the obtained catalysts exhibited a high dispersion with Pd particles of about 4 nm.
06/02191 Co-pyrolysis of polymethyl methacrylate with brown coal and effect on monomer production Orinfik, A. et al. Fuel, 2006, 85, (1), 1~18. Pyrolysis capillary gas chromatography has been applied to the study of the co-pyrolysis of polymethyl methacrylate (PMMA) with Slovakian brown coal with the aim of finding pyrolysis conditions yielding a maximum amount of methyl methacrylate (MMA). Effects of pyrolysis temperature and PMMA-coal weight ratios were investigated. Capillary gas chromatography coupled with mass spectrometric detector (cGC-MS) was used for MMA identification. The highest yield of
336
Fuel and Energy Abstracts September 2006
MMA in the pyrolysate was obtained at 750°C. The optimal PMMAcoal weight ratio for maximum MMA production lies in the interval 0.5 mg PMMA and 0.6-0.8 mg brown coal with an MMA yield of 64%. Coal addition to the sample affects species recombination in gaseous phase, augments MMA production at higher temperatures and eliminates degradation products of PMMA and coal pyrolysis. Different conversion diagrams are characteristic for thermal degradation of single PMMA and in the mixture with coal. Detailed mechanism of synergetic effects arisen during co-pyrolysis are not yet known. It was also found that lower pyrolysis temperatures are more suitable to study degradation mechanism and kinetics while higher temperatures are more applicable for identification purposes. MMA decomposes completely at 900°C.
06/02192 Compositions and leaching behaviours of combustion residues Saikia, N. et al. Fuel, 2006, 85, (2), 264-271. Combustion residues generated from different incineration processes create major environmental problems because these materials contain high amounts of toxic substances. This paper reports the leaching behaviours of three residues along with their mineralogical compositions. Column leaching experiments at two different pH values were conducted to study the leaching behaviours. Leachants were analysed to determine the pH, the concentrations of some toxic elements like Pb, Cr. As, Cd, Se, B, Mo and the volume of leachants passing through the columns. Raw and some treated residues were also characterized by XRD and SEM-EPMA techniques. It was found that the concentrations of some toxic elements present in the residues as well as in the leachant fractions collected at different time intervals after leaching were very high. The amounts of soluble salts and toxic elements in the municipal solid waste incinerator (MSWI) ash were higher than those in the other two residues. The order of alkalinities of the three residues was: fly ash > MSWI ash > sewage sludge ash. The final pH of the leachant was related to the volume of leachant passing through the column. Some leachant properties were related to the mineralogical compositions of the residues and to the secondary minerals formed during the leaching period.
06102193 Estimation of LOC (limiting oxygen concentration) of fuel-air-inert mixtures at elevated temperatures by means of adiabatic flame temperatures Razus, D. et al. Chemical Engineering and Processing, 2006, 45, (3), 193-197. The limiting values of fuel concentration in a flammable fuel-air mixture are the lower explosion limit (LEL) and upper explosion limit (UEL). The addition of an inert component to fuel/air mixtures determines the increase of LEL and decrease of UEL, until these values finally merge at the inerting point. The maximum oxygen amount of a non-flammable fuel-air-inert mixture is the limiting oxygen concentration (LOC), an important safety characteristics. The investigation of a comprehensive set of flammability data at elevated temperatures and ambient pressure taken from literature sources was made for systems containing nitrogen, carbon dioxide and water (vapour) as inert components, at 100 °, 200 ° and 250°C. The adiabatic flame temperatures at LEL (CAFT LEL) and LOC (CAFT 5°c) were calculated by taking into account the dissociation of gases within the flame. A linear correlation of CAFT L°c versus CAFT LEL was empirically derived for the examined systems. The slope and intercept of the correlation are dependent on temperature and on nature of the inert gas. The correlation allows the development of a simple procedure for estimating LOC, when the LEL of fuel-air and the equivalence ratio of the fuel-air-inert mixture at the inerting point are known. Knowing the scarce information concerning the flammability of fuel-air-inert mixtures at temperatures higher than ambient, the proposed procedure brings about an useful tool for estimation of LOC.
06•02194 Kinetics of CH4, H2S and SO2 oxidation on precious metal catalysts under stagnation point flow conditions Rickett, G. et al. Journal of the Energy Institute, 2006, 79, (1), 12-18. A new methodology combining reactor experiments and numerical modelling to derive kinetic rates of solid-gas heterogeneous reactions in a stagnation point flow reactor (SPFR) is developed and used to investigate the effects of small concentrations of H2S and SO2 on the lean catalytic combustion of methane on precious metal catalysts. The activity of polycrystalline Pt foil, then Pt-, Rh- and Pd-containing washcoats supported on stainless-steel foils are investigated in the SPFR, where the washcoat consisted of a thin layer of 7-alumina or ceria/7-alumina. The porous washcoats supported on steel foil were more active than the equivalent flat surface of pure precious metal (Pt) • • ~ with pre-exponentlal factors of 7.4 x 105 cm s 1 and 4.9 x 104 cm" s ~1 respectively. Repeated use of the washcoated catalyst and the effect of pore opening gives rise to a change in the pre-exponential factor from 7.4 x 105 cm s -1 to 1.1 x 109 cm s 1 for Pt. The high-temperature activity behaviour of Pt in presence of sulphur species in the feed was,