Polymer combustion

Experimental conditions have been defined for the steady-state combustion of vertically positioned polymer rods burning at the top surface. Temperature and composition profiles through solid and gas phases of the system, polymer consumption rate, and flame height were measured, and the response of these parameters to changes of the oxygen concentration in the environment were determined. Measurements showed that unreacted oxygen diffused from the environment to the burning surface and was absorbed into the polymer, forming a well defined oxygen-rich layer. Concentration of chemically bound oxygen at the surface of this layer were high, e.g., with polypropylene ca. 26 wt-%, and identical with the stoichiometry of the gases leaving the surface and serving as fuel for the flame. The composition of the gas phase at the surface indicated the conversion of 11.4% of the hydrocarbon fuel to CO, CO₂, and H₂O. An energy balance for the system confirmed that fuel production in this surface layer takes place via simultaneous oxidative and pyrolytic degradation of the polymer, with exothermic processes supplying the energy for endothermic processes. Conductive and radiative contributions from the gas phase were found to play a minor role in maintaining fuel formation. The rate of degradation of a polymer to fuel, normalized to the area of the burning surface, was found to be independent of polymer supply rate and to increase with the oxygen concentration in the environment. The degradation process was successfully modeled in TGA experiments at temperatures and oxygen concentrations representative of the burning surface. The existence of an oxidative surface layer was confirmed and the TGA degradation rate related to the surface-to-volume ratio of the polymer sample. Compositional analysis of a methane diffusion flame of a geometry identical to that of the polymer flame, revealed the presence of unreacted oxygen throughout the preheating zone and at the surface of the burner. Conversion of fuel to final combustion products at the surface was 6.3%. Temperature and composition changes as a function of oxygen concentration in the environment were determined and compared with the polymer diffusion flame. It was concluded that a polymer flame, because of its autogenerative fuel production, possesses only one degree of freedom, viz., the oxygen concentration in the environment, in contrast to the conventionally fueled diffusion flame for which fuel supply rate is an additional independent parameter. Due to this single degree of freedom, the sensitivity of the polymer flame to environmental influences is increased. Effects caused by these extrinsic factors will be the subject of a separate report.     

Kinetic models of natural gas combustion in an internal combustion engine

In this study, combustion of methane was simulated using four kinetic models of methane in CHEMKIN 4.1.1 for 0-D closed internal combustion (IC) engine reactor. Two detailed (GRIMECH3.0 & UBC MECH2.0) and two reduced (One step & Four steps) models were examined for various IC engine designs. The detailed models (GRIMECH3.0, & UBC MECH2.0) and 4-step models successfully predicted the combustion while global model was unable to predict any combustion reaction. This study illustrated that the detailed model sh...     

Catalytic combustion of soot

The OCM reaction in the presence of HCl over NaCl−MnO/H−ZSM catalyst at 750°C has been studied. Effect of HCl partial pressure on the CH₄ conversion and selectivities to principal products, also on the time-on-stream of catalyst has been examined. Addition of HCl into initial methane-oxygen mixture can increase selectivity to C₂₊ formation and ethene selectivity, in particular. It seems that the time-on-stream of this catalyst is nearly 35–40 h in the presence of HCl.     

Mechanism of methane combustion

Conclusions Calculations have been carried out on a cold-flame oxidation mechanism in which it is assumed that the reaction is at first accelerated, and then retarded, as the result of thermal decomposition of the peroxide radicals and formation of formaldehyde followed by reaction of the latter with the active centers. The results were in satisfactory agreement with the observed kinetics.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2658–2663, December, 1982.The authors would like to thank M. G. Neigauz who supplied the standard kinetic program and was continually helpful in carrying out the calculations.     

Environmental effects of coal combustion

First an introduction is given about the environmental effects of coal combustion. Then the thermoanalytical research in this field is reviewed. Modern topics are the catalytic reduction of NO_x in exhaust-gases and the development of regenerative sulfur capture sorbents for use in fluidized-bed coal combustion.

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Zusammenfassung Es wird zuerst eine Einführung über die Umwelteinflüsse auf die Kohleverbrennung gegeben. Dann folgt ein überblick über die thermoanalytische Forschung auf diesem Gebiet. Moderne Themen sind dabei die katalytische Reduktion von NO_x in Auspuffgasen und die Entwicklung von Schwefel-Sorptionsmitteln zur Verwendung bei der Flie\bett-Kohleverbrennung.

     

Kinetics of crude oil combustion

In this research, thermal characterization and kinetics of Karakus crude oil in the presence of limestone matrix is investigated. Thermogravimetry (TG/DTG) is used to characterize the crude oil in the temperature range of 20-900°C, at 10°C min ^-1 heating rate using air flow rate of 20 mL min ^-1. In combustion with air, three distinct reaction regions were identified known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). Five different kinetic methods used to analyze the TG/DTG data to identify reaction parameters as activation energy and Arrhenius constant. On the other hand different f(α) models from literature were also applied to make comparison. It was observed that high temperature oxidation temperature (HTO) activation energy of Karakus crude oil is varied between 54.1 and 86.1 kJ mol ^-1, while low temperature oxidation temperature (LTO) is varied between 6.9 and 8.9 kJ mol ^-1.     

Polymer degradation during combustion

A novel driven-rod, radiant pyrolysis technique has been used to study the steady-state linear regression of vertically mounted poly(methyl methacrylate) and polypropylene rods degrading from the top under high-flux, nonflaming conditions that simulate those of combustion. With this technique reliable temperature-depth and oxygen-depth profiles have been obtained and used to calculate the observed mass loss rates and to elucidate the mode of polymer degradation during combustion, respectively. For poly(methyl methacrylate) burning in this rod configuration, condensed phase oxidation is unimportant and the degradation mechanism is similar to that under more conventional slow-heating conditions in the absence of air. In contrast, for burning polypropylene condensed phase oxidation occurs; the lack of oxygen incorporation suggests that the polymer degrades by oxygen-promoted pyrolysis.     

Polystyrene degradation during combustion

A novel driven-rod, radiant pyrolysis technique has been used to study steady-state linear regression of vertically mounted polystyrene rods degrading under high-flux, nonflaming conditions that simulate those of combustion. With this technique a reliable, reproducible temperature-depth profile (identical for combustion and radiant pyrolysis) for polystyrene has been obtained and used to successfully calculate the observed mass loss rate. Residues and volatiles have been analyzed. Mechanistic treatment of these results indicates that degradation of polystyrene under these rapid-heating conditions is similar to that under more conventional slow-heating conditions in the absence of oxygen. Oxidation is unimportant in the condensed-phase degradation of polystyrene in this configuration. This radiant pyrolysis technique has also been used to obtain the heat of gasification of polystyrene.     

Synergism in combustion processes

The effect of CF₃H, CF₄, and N₂ on the ignition of methane–air mixtures has been investigated. The effect of trifluoromethane is due to its being involved in reaction chain termination. A nonadditive effect of trifluoromethane and nitrogen on the concentration limits of ignition and flame propagation in methane–air mixtures has been predicted and revealed. The synergistic effect arises from the exponential dependence of the rate of the chain process on the concentrations of the initial components.     

不同煤燃烧方式降低NOx排放比较及解耦燃烧应用

采用两段反应器研究了三种煤在不同燃烧方式下抑制NO_x生成的效果。结果表明,煤的热解气和部分气化生成气再燃均能较好的抑制NO_x生成,抑制效果优于空气分级燃烧,解耦燃烧方式抑制NO_x生成的效果最显著,相对于传统燃烧其NO_x排放降低了32%以上。煤种对各种燃烧方式降低NO_x的程度有明显影响,煤中单位氮含量的燃料比(固定碳/挥发分)越小,煤的热解气和部分气化生成气再燃以及解耦燃烧方式下NO_x的排放量越低。在煤部分气化生成气再燃烧方式中,部分氧化气化段通氧量不同,降低NO_x排放的效果也不同,在氧气体积分数为8%~10%时的NO_x生成量最低。基于解耦燃烧技术原理,研制了1.4 MW解耦燃烧工业锅炉,在燃烧同一煤种时,解耦燃烧锅炉和传统立式锅炉相比,烟气中NO_x排放量降低了32.9%。     

Determination of the energies of combustion and enthalpies of formation of nitrobenzenesulfonamides by rotating-bomb combustion calorimetry

The energies of combustion for 2-nitrobenzenesulfonamide (cr), 3-nitrobenzenesulfonamide (cr), and 4-nitrobenzenesulfonamide (cr) were determined using a recently described rotating-bomb combustion calorimeter. The condensed phase molar energies of combustion obtained were ?(3479.2 ± 1.0) kJ · mol^?1 for 2-nitrobenzenesulfonamide (cr), ?(3454.2 ± 1.1) kJ · mol^-1 for 3-nitrobenzenesulfonamide (cr), and ?(3450.1 ± 1.9) kJ · mol^-1 for 4-nitrobenzenesulfonamide (cr). From these combustion energy values, the standard molar enthalpies of formation in the condensed phase were obtained as: ?(341.3 ± 1.3) kJ · mol^?1, ?(366.3 ± 1.3) kJ · mol^?1, and ?(370.4 ± 2.1) kJ · mol^?1, respectively. Polyethene bags were used as an auxiliary material in the combustion experiments. The heat capacities and purities of the compounds were determined using a differential scanning calorimeter.