• Energy Research

Abstract The composition of a multicomponent pool fire will vary over the course of burning due to preferential distillation of more volatile compounds. As a result, key fire properties like the burning rate, flame temperature, flame height, and soot emissions will change as the properties of the fuel change. This adds uncertainty about the combustion properties of the fire, especially for fuel blends with widely varying boiling points (e.g., gasoline-ethanol). The heat release rate, which is proportional to the burning rate, is essential for estimating the radiative flux to nearby structures or personnel, so understanding how fire dynamics are impacted by the composition of a fuel mixture is a pre-requisite for dealing with hazard assessments of fire scenarios involving multicomponent fuels. Continuously fed pool fire experiments were conducted in a 0.30 m diameter pan with binary mixtures of ethanol-water, ethanol-isopropanol, and ethanol-hexane. The relationship between burning rate and fuel composition was strongly dependent on vapour-liquid equilibria and relative volatility of the mixture. It was found that burning rate models dependent on fuel properties gave better predictions of the relationship between burning rate and fuel composition. Heskestad’s flame height and flame temperature correlations were found to be suitable for use in multicomponent pool fire scenarios.

Abstract The combustion of methanol was studied in an open system. Quantitative measurement of the unburnt carbon formed during the combustion process was continuously followed by applying a semi-analytical technique based on the composition of the flue gas. The combustion of the alcohol was determined to be zero order under the experimental conditions. The change in the rate of burning, K, was found to correspond in magnitude to the change in the ratio of actual air volume flow-rate, Qa, to the stoichiometric air volume flow-rate, Qs.

Abstract In this work, we have theoretically studied the imbibition process related to a block in a fractured carbonate reservoir under an assumed constant, vertical temperature gradient, GT. An analytical solution to an ordinary differential equation we developed has been obtained using a computer program, and the original Washburn law normally valid for isothermal conditions of spontaneous imbibition has been found to hold true for GT equal to zero. The theoretical results of our study show that the space and time evolution of the imbibition front is strongly dependent on surface tension and dynamic viscosity of the imbibing fluid under a given temperature gradient. We have also validated our model against experimental data from a literature source based on spontaneous imbibition into a Hele Shaw Cell under longitudinal temperature gradient. The general conclusion of our study is that spontaneous imbibition in fractured carbonate reservoirs will be accelerated the higher the temperature of the injected water. This corresponds to a negative temperature gradient where the temperature of the injected water exceeds the ambient temperature of the reservoir.

Abstract Recycling and upgrading of low-grade materials plays a pivotal role in building a sustainable circular bioeconomy. The present study explored the potential of energy recovery from biorefinery landfills by means of in-situ thermal processing of municipal solid waste (MSW) with a techno-economic analysis and using RETScreen clean energy project analysis software. An environmental assessment was performed to validate the sustainability of the proposed process. The biorefinery landfill uses existing MSW landfill infrastructure to move from a disposal-only paradigm to a product-creation paradigm. This innovative concept can reduce the extra costs of ex-situ conventional power plants by avoiding waste transportation to a secondary site. A case study in Atlantic Canada was employed to optimize energy reclamation from MSW via two principal pathways: (1) Rankine cycle steam power plant and (2) gas turbine. A plant with a 30 t h−1 capacity and 2 MW power production was proposed as a base case. The results indicated that the gross reduction in annual greenhouse gas emissions was 1115 t CO2 greater for a gas turbine than a steam cycle. Further, for a steam power plant, the capital cost was approximately three-fold higher, and the operating and maintenance costs were nearly eight-fold higher than a gas turbine plant. Study results will encourage progress towards a sustainable biopower system and lay the foundation for comprehensive analysis of renewable resources like MSW. The key outcomes of this study target growth of the circular bioeconomy. Moreover, they can serve as the basis to draw recommendations on the techno-economic feasibility of implementing such biorefineries, specifically at high latitudes where energy costs are relatively high.

Abstract Mixtures of combustible dust and flammable gas pose an increased explosion risk in processing equipment due to reduced flammability limits over the dust and gas alone. Although correlations have been proposed based on experimental testing for predicting the flammability limits of hybrid mixtures from those of the dust and gas, none appear to be applicable across a range of fuel mixtures. The objective of this work is to use computational fluid dynamics to explore the lower flammability limits of 10 μm coal dust particles and methane gas under laminar, free-flame conditions, and to compare the limits to the experimentally determined mixing rules. This comparison gives an understanding of the baseline behaviour upon which different fuel mixtures, equipment geometry, and various operational conditions can be added in the future. The results from the computational model suggest that Le Chatelier's Law, which proposes linear mixing between the dust and gas limits, is applicable for the small particles studied. Bartknecht's curve, which proposes wider flammability limits than linear, appeared to be overly conservative, while new relations that predict narrowing of the limits did not appear to delineate flammable mixtures under the conditions investigated.

Abstract An experimental investigation of coal dust explosions was conducted in a 26 1 spherical chamber. Channel (mine-face) samples of coal from the Prince and Phalen mines of the Cape Breton Development Corporation were used. The objective of the work was to investigate the ignitability characteristics of the coals, alone and with admixed methane. The apparent lean flammability limit of the coal dust-air mixtures was observed to decrease with increasing ignition energy. The decrease was rapid at low energies, with an approach to an asymptotic value of the lean limit at high energies. A stored ignition energy of 5 kJ was required to measure these asymptotic values which represent the true lean flammability limit. The apparent lean limit at a given ignition energy was found to decrease in the presence of methane, with a reduction in mass mean diameter of the parent coal, and with an increase in coal volatile matter. These three conditions also enhanced the ignitability of the coal dust-air mixtures, meaning that ignition of a given coal dust concentration was possible with lower energies. The lowering of the lean limit with methane admixture, particle size reduction and increase in volatiles was more pronounced at lower ignition energies.

Abstract Inherent safety is a proactive approach to process safety in which hazards are removed or minimized so as to reduce risk without engineered (add-on) or procedural intervention. Four basic principles are available to attain an inherently safer design—minimization, substitution, moderation, and simplification. The subject of the current paper is the principle of moderation as it applies to the prevention and mitigation of dust explosions. Moderation can be achieved by processing a material under less severe operating conditions or by processing the material in a less hazardous form. With respect to the latter approach, it may be possible to alter the composition of a dust by admixture of solid inertants, or to increase the dust particle size so as to decrease its reactivity. Additionally, avoidance of the formation of hybrid mixtures of explosible dusts and flammable gases is an application of moderation of the material hazard. Several examples are given for each of the above three forms of moderation. The discussion on admixture of solid inertants includes examples from the following industrial applications: (i) refractory materials manufacturing, (ii) food processing, (iii) power generation, (iv) industrial recycling, and (v) foundry shell mold fabrication. The importance of particle size consideration is explained first from the perspective of engineering tools such as the Dow Fire & Explosion Index, and professional guidance on the definition of a dust and suitable particle sizes for explosibility testing. Industrial examples are then drawn from the following areas: (i) rubber recycling and textile manufacturing, (ii) industrial recycling, (iii) wood processing, (iv) dry additive handling (polyethylene facility), (v) polyethylene production, (vi) carbon block recycling, and (vii) coal mining. The concluding discussion on hybrid mixtures includes brief cases from the process safety literature.

Abstract A non-intrusive measurement technique has been developed for accurate determination of gas and particle velocities in a turbulent two-phase flow field. The principle of the technique is based on the discrimination between the scattered light from particles and the fluorescence emission from particles coated with a fluorescent dye. A high-powered, argon-ion based, single-channel, on-axis backscatter laser-Doppler velocimetry system was used. The fluorescent dye was Rhodamine 6G. A study of the gas-solid two-phase flow behaviour in the freeboard of a cold gas-fluidized bed was undertaken. The solid phase contained two particle groups: bed material (sand) and fuel particles (wood). Measurements of the axial velocity and turbulence intensity distributions of the gas phase and both particle groups within the solid phase were made along the column centre and across the freeboard. Excellent discrimination of velocities from the two phases and from the two particle groups within the solid phase was achieved.

An experimental study into the hot surface ignition of coal dust layers has been conducted. Two coals were examined: Prince coal from the Cape Breton Development Corporation and Pittsburgh coal from the United States Bureau of Mines. The effect of admixed inerts (dolomite and limestone) on the dust layer ignition temperature has been analyzed using a steady-state thermal explosion model. The analytical procedure used for evaluating the ignition temperature of a dust layer, heated from below and losing heat from its upper surface by convection, is an extension of the thermal explosion model of Thomas (Ref. [8]); namely, that of Thomas and Bowes (Ref. [15]). To commission the hot plate apparatus and validate the model predictions, a series of experiments were undertaken using sodium dithionite. This material is known to exhibit self-heating and there have been previous layer ignition temperature studies with which to compare results. It was demonstrated that an adequate estimate of the critical ignition temperature may be readily obtained by this analytical method. Furthermore, computed values of the critical ignition parameters for layers of coal dust admixed with inerts, accounting for changes in thermal conductivity, were in reasonable agreement with experimentally determined values.