Geoffrey D. Sergeant

Combustion rate of bituminous coal char in the temperature range 800 to 1700 K

Abstract The combustion rates of three different sized fractions of char from a swelling bituminous coal have been measured in the temperature range 800 to 1700 K. The mass-median sizes of the fractions were 70, 35 and 18 μm. For each fraction the combustion rate was less than the limiting rate set by diffusion of oxygen to the particle. The chemical reaction rate coefficient (g/g s atm O 2 ), calculated from the measured rates and corrected for the external diffusion resistance, varied with temperature in a manner appropriate to an apparent activation energy of approximately 27 kcal/mol for the three fractions. The chemical reaction rate coefficient when expressed on the basis of unit external area of particle (g/cm 2 s atm O 2 ) increased with increasing particle size at 800 K: at 1250 K the coefficients for the 35 and 18 μm fractions were equal, and lower than those of the 70 μm fraction by a factor of 4. The densities of the particles did not vary appreciably with burn-off, except the density of the 70 μm fraction which increased sharply for values of burn-off between 0 and 0.01. It is probable that combustion occurred in a rate-control regime which was intermediate between that caused by chemical reaction alone and that caused by the combined effects of pore diffusion and chemical reaction.

The effects of design factors on emissions from natural gas cooktop burners

The effects of the following burner design factors on the emissions of NO2, NOX, CO, and hydrocarbon were investigated: cap material, cap size, port shape, port size, port spacing, central secondary aeration, and flame insert. The approach used in this study was designed to overcome the possibility of ambiguous or contradictory conclusions encountered in earlier studies. The factorial experimental design method was used to arrange the experiments, and the results were statistically analysed using the analysis of variance. Flame stability was found to be crucial; a slight instability promoted a large increase in emissions of CO, hydrocarbon, and NO2. Port shape was found to be the most significant burner design factor affecting the emissions, and hence it is a potential factor to be studied further for lower emissions.

Reactivity of Australian coal-derived chars to carbon dioxide

Abstract The reactivities to CO 2 of four chars derived from Australian coals at 610 °C, were measured thermogravimetrically. Reaction rates in 100% CO 2 (total pressure, 101 kPa) varied from 0.026 mg h −1 mg −1 at 803 °C for char derived from a Lithgow coal to 6.3 mg h −1 mg −1 at 968 °C for a Millmerran coal char. Activation energies for the four chars were in the range 219–233 kJ mol −1 . The results show that for Lithgow (Hartley Vale) coal char, reactivity increases with CO 2 concentration and decreasing particle size. The apparent reaction order for this char with respect to CO 2 concentration was found to be 0.7. For different chars, reactivity is inversely proportional to the rank of the parent coal. No general correlation has been established between total mineral content (ash) and char reactivity.

A comparative study of products derived from Rundle and Stuart shale oils and petroleum lubricating oil base stocks (based on n.m.r., molecular weight and elemental analysis)

Abstract As part of a study to evaluate the potential of shale oils for lubricating oil production, samples from the Rundle and Stuart oil shale deposits in Australia have been processed to produce a range of products which were then characterized by 1 H and 13 C high resolution nuclear magnetic resonance (n.m.r.) techniques, molecular weight determination and elemental analysis. The data have been compared with that obtained for two petroleum derived lubricating oil base stock samples. The comparison shows that the products derived from Rundle and Stuart shale oils in the lubricating oil boiling range have lower molecular weight and a lower hydrogen content. The lubricating oil samples are shown to contain monoaromatic rings, with one or more branched, long, alkyl side chains per ring, some naphthenic but no olefinic structure. The shale oil samples show distinct differences, with the distillate being monoaromatic with some polyaromatic and naphthenic structures, but with less alkyl substitution. The alkyl side chains are unbranched and contain some olefinic bonds. The maltenes are in turn less substituted and have less naphthenic structure. The alkylation and dewaxing processing steps did not significantly modify the structures of the shale oil products, while in the hydrogenation process some of the olefinic material was modified to paraffinic. Further reduction of the aromatic content of the shale oil is required to improve the prospects of producing a lubricating oil base stock.

Properties of vacuum residual fractions from Australian shale oils compared with a petroleum bitumen

Abstract Crude shale oils derived from oil shale deposits at Julia Creek, Stuart and Rundle in Australia were processed to produce vacuum residual bitumens. The properties of these bitumens were compared with those of a petroleum bitumen. All were subjected to solvent extraction to produce asphaltene, maltene, and polar and naphthenic aromatic fractions. Elemental analysis and molecular weight distributions were determined for all samples. Julia Creek bitumen was found to have a lower hydrogen to carbon ratio and higher aromaticity than the others. Rundle and Stuart samples had many properties similar to those of the petroleum bitumen, including those based on the standard bitumen tests for penetration and Ring and Ball temperature. Further research is justified to establish the potential of shale oil as a source of road making bitumen.

The onset of luminosity in propane/air flames

Abstract The onset of luminosity in propane/air flames, enclosed in a furnace operated at two temperature levels, has been examined at four stoichiometric values by determining carbon dioxide, carbon monoxide, oxygen and hydrocarbon concentrations together with temperature, total radiation, and radiation in the 4.3 to 4.5 μm wavelength region at distances along the flames. The data obtained have been processed to give values of total and spectral flame emissivity. The results show that luminous radiation is spectral in nature; the intermediate carbon-forming compounds emit more radiation than the products that are formed. A significant proportion, 10 to 40%, of the radiation is emitted in the 4.3 to 4.5 μm waveband. The concentrations of carbon monoxide, carbon dioxide and oxygen remain essentially constant, and there appears to be no set temperature for the onset of luminosity.

Relative roles of chemical and mass transfer rate control in fluidized-bed combustion of coal chars

Abstract The relative roles of mass transfer and chemical reaction in controlling combustion rates in fluidized beds are examined in the light of measurements of char-particle combustion kinetics and correlated data on gas—particle mass transfer in fluidized beds. It is concluded that at 1200 K mass transfer is the main rate-control influence for materials having reactivities the same as, or higher than, a char from a swelling bituminous coal. Mass transfer has little effect on the combustion rate of materials whose reactivity to oxygen is one-tenth that of the bituminous coal char. At 800 K, chemical reaction control is dominant for all reactivities considered. The main uncertainty in the present calculations arises from the lack of a suitable analysis of mass-transfer rates in conditions appropriate to fluidized-bed combustion.

Methodology for the simultaneous measurement of emissions and efficiency for natural gas‐fired cooktop burners

A methodology has been developed to investigate the factors affecting both gaseous emissions (particularly NO2) and thermal efficiency of natural gas‐fired burners for domestic cooking appliances. Many factors are reported, in the literature, to affect the NO2 emission rate and the reported effects are sometimes contradictory, suggesting that these studies may not be definitive. The methodology reported here is designed to produce a definitive study or, at least, to allow the identification of results that are not definitive and therefore require further investigation. An experimental rig has been developed and its performance has been well‐characterized to select operating conditions that minimize the experimental error. The gas sampling and analysis train tested favourably in an international inter‐laboratory comparison. In developing the methodology, hydrocarbon leakage into the air surrounding the burner and flame impingement on the load were found to affect the results, so these factors were studied ...

Molecular weight determination in the study of the lubricating oil potential of shale oils

Abstract Molecular weight determination is necessary for the structural analysis of potential lubricating oil products derived from oil shale. Three methods — vapour pressure osmometry, gel permeation chromatography and viscosity correlation — for determining the number-average molecular weight of samples derived from the processing of Rundle and Stuart shale oils were studied. Three petroleum-derived lubricating oil base stocks were also analysed for comparison. Results from the three methods for petroleum-derived base stocks were in reasonable agreement. However, for the shale oil-derived samples, the molecular weights from vapour pressure osmometry were lower than those from both gel permeation chromatography and viscosity correlation, and results from viscosity correlation were lower than those from gel permeation chromatography for molecular weights >500. The viscosity correlation method developed for petroleum-derived lubricating oils could not be used to predict the number-average molecular weight for shale oil products as determined by gel permeation chromatography or vapour pressure osmometry.

Processing of shale oil for potential lubricating oil base stocks

Abstract Much of the emphasis on shale oil processing research has been towards the production of the transport fuels, diesel oil and gasoline, as an alternative to petroleum crude oil products. This research project was aimed at a broader product range and specifically directed to evaluate the potential for the production of lubricating oil base stocks from the high boiling distillate fraction and residual maltenes of shale oil. The processing steps included vacuum distillation, solvent extraction, alkylation, de-waxing, and hydrogenation of the shale oil from Rundle and Stuart oil shale deposits in Queensland, Australia. Yields of the products were measured at each stage of the process and the elemental compositions determined. The analyses were compared with those of the petroleum-derived lubricating oil base stocks. Significant yields were obtained in the lubricating oil boiling range, but the elemental analysis showed that the products were still lower in hydrogen, compared to the petroleum products. Further investigation of the Rundle distillate is warranted, using more rigorous extraction and hydrogenation conditions.