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This paper presents the numerical research findings for the conditions and characteristics of methane-propane hydrate particle ignition. The curves of the ignition delay times of a hydrate particle versus its size and ambient temperature were obtained. The effect of the rates of phase transformations (evaporation and dissociation) on the hydrate particle ignition behavior was analyzed. Following the mathematical modeling of the processes under study using different heating schemes of gas hydrates, the patterns of processes developing in a particle during the induction period were identified. It was established that the ignition behavior of methane, propane, and other gases was significantly different from that of other gases produced from hydrate decomposition. The established differences form the basis for predicting the characteristics of gas hydrate ignition at different power plants. [ABSTRACT FROM AUTHOR]

Cylinder-shaped fuel pellets that were 3 mm in diameter and 3 mm in height, with a mass of 20 mg, were produced by compressing dry coal processing waste under the pressure of 5 MPa. The first group of pellets from coal dust with a particle size less than 140 µm did not contain any additives. The pellets of the second group of fuel compositions contained an oil-impregnated porous polymer material particle with a size of 0.5 mm in the central part of the experimental sample. The particle was surrounded by coal dust from all sides. The ratio of components was 90:10% for coal dust: polymer particle. The latter value almost completely corresponds to the fraction of oil in the fuel composition, since the mass of a porous polymer material particle is negligible. The third group of compositions was a 70:30% mixture of coal dust with wood sawdust with a particle size less than 45 µm, or 45–100, 100–200 and 200–500 µm. The ignition and combustion of single fuel pellets were studied under radiant heating in an air medium while varying the temperature from 800 to 1000 °C. The processes during the fuel combustion were recorded by a high-speed video camera, and the concentrations of the main anthropogenic emissions in flue gases were measured by a gas analyzer. The main characteristics were established—ignition delay times (2–8 s) and duration of burnout (40–90 s)—at different heating temperatures. A difference was established in the combustion mechanisms of the pellets, when adding various components to the fuel mixture composition. This has a direct influence on the induction period duration and combustion time, other conditions being equal, as well as on the concentration of nitrogen and sulfur oxides in the flue gases. Adding an oil-impregnated porous polymer particle to the fuel composition intensifies ignition and combustion, since the times of ignition delay and complete burnout of fuel pellets under threshold conditions decrease by 70%, whereas adding wood sawdust reduces the content of nitrogen and sulfur oxides in the flue gases by 30% and 25%, respectively. [ABSTRACT FROM AUTHOR]

A wide range of wastes can potentially be used to generate thermal and electrical energy. The co-combustion of several types of waste as part of water-containing waste-derived fuels is a promising method for their recovery. In this research, we use thermogravimetric analysis and differential scanning calorimetry to study the thermal behavior and kinetics of coal slime, biomass, waste oils, and blends on their basis. We also analyze the concentrations of gaseous emissions. The results show that biomass, oils, and coal slime significantly affect each other in the course of their co-combustion when added to slurry fuels. The preparation of coal-water slurry based on slime and water reduced the ignition and burnout temperature by up to 16%. Adding biomass and waste oils additionally stimulated the slurry ignition and burnout, which occurred at lower temperatures. Relative to dry coal slime, threshold ignition temperatures and burnout temperatures decreased by 6%–9% and 17%–25%, respectively. Also, the use of biomass and waste oils as part of slurries inhibited NO х and SO 2 emission by 2.75 times. According to the kinetic analysis, added biomass and waste turbine oil provide a 28%–51% reduction in the activation energy as compared to a coal-water slurry without additives. [Display omitted] [ABSTRACT FROM AUTHOR]

To expand the database of kinetic parameters used for modeling the ignition of coals and their processing waste, promising coal-water slurry and coal-water slurry containing petrochemicals, studies have been performed on an experimental set-up using thermal gravimetric analysis. The research into coals of various ranks (flame, gas, coking, low-caking, and non-baking) and their processing waste (filter cakes) has yielded the decomposition parameters of the organic matter of coal and the formation of volatile substances as well as the oxidation parameters of the coke residue of all the coals and filter cakes under study. The studies cover the temperature range of the burning processes: 450-1300 K (for low-, medium-, and high-temperature burning modes). We have ascertained the dependence of kinetic parameters (pre-exponential factor and activation energy) describing the thermal decomposition of the organic matter of coal on the rank of coals and filter cakes. The findings show that the kinetic parameters describing the thermal decomposition of the organic matter of coal and its processing waste are practically the same. The thermokinetic parameters of coke residue oxidation are close for all the coals under study but they differ significantly for coke residue of filter cakes. The values of thermokinetic parameters obtained in the research are necessary to devise adequate physical and mathematical models and perform numerical studies (for mathematical modeling) of fuel slurry combustion processes in the combustion chambers of power plants. [ABSTRACT FROM AUTHOR]

To expand the resource base of fuels and methods of hydrocarbon waste recovery, this paper presents the study of the ignition features and conditions of composite fuel slurries based on wastes from coal, chemical, petrochemical, energy, and transport industries. Composite liquid fuels have been prepared using basic components: filter cakes of low-caking, nonbaking, and bituminous coal; engine, turbine, and transformer oil waste; plasticizer. According to a well-known experimental approach, the investigations of the ignition processes have been performed for single fuel droplets (with a radius ranging from 0.5 mm to 1.5 mm) covering a fast-response thermocouple junction. A heated air flow – the ignition source of a droplet – was formed by a specialized blower and a heater. The air temperature varied within the range of 600–900 K. The oxidizer flow velocity was about 3 m/s. With the help of particle image velocimetry hardware and Actual Flow software, we determined the conditions and characteristics of the oxidizer flow transformation around droplets of various shapes. The typical stages of fuel droplet ignition were identified using high-speed video cameras and Tema Automotive software: heating; the evaporation of water and flammable liquid; the thermal decomposition of coal; the formation and ignition of a gas-vapor mixture; the heating of coke residue; the heterogeneous ignition and combustion of carbon. Further, ignition delay times were determined under the conditions of low temperature (600–900 K) heating, as well as the combustion times of fuel droplets with different compositions. Finally, the minimum temperatures were specified sufficient for the sustainable ignition of composite liquid fuel. The established ranges of minimum temperatures show the possibility of burning fuel slurries based on coal and oil processing wastes in heat and power boilers of different capacity. The temperature modes can be adjusted to the required environmental, economic and energy performance indicators. The maximum temperature of a droplet during the combustion process is more than 1100 K. This result confirms the high combustion heat of fuel slurries, even those based on typical industrial wastes, and shows great prospects of their application in the thermal power engineering. The wide use of abundant industrial wastes as the main fuel components of coal water slurries containing petrochemicals is a high-potential solution to the global problem of their recovery and the reduction of the environmental load of coal-based thermal power engineering on the nature and humankind. [ABSTRACT FROM AUTHOR]

The paper examines the integral characteristics (minimum temperature, ignition delay times) of stable combustion initiation of organic coal-water fuel droplets (initial radius is 0.3-1.5 mm) in the oxidizer flow (the temperature and velocity varied in ranges 500-900 K, 0.5-3 m/s). The main components of organic coal- -water fuel were: brown coal particles, filter-cakes obtained in coal processing, waste engine, and turbine oils. The different modes of soaring and ignition of organic coal-water fuel have been established. The conditions have been set under which it is possible to implement the sustainable soaring and ignition of organic coal-water fuel droplets. We have compared the ignition characteristics with those defined in the traditional approach (based on placing the droplets on a low-inertia thermocouple junction into the combustion chamber). The paper shows the scale of the influence of heat sink over the thermocouple junction on ignition inertia. An original technique for releasing organic coal-water fuel droplets to the combustion chamber was proposed and tested. The limitations of this technique and the prospects of experimental results for the optimization of energy equipment operation were also formulated. [ABSTRACT FROM AUTHOR]

Numerical researches have been carried out to study the influence of air flow temperature and a fossil fuel particle rate on sufficient conditions of ignition in a "coal particle - air" system. Developed mathematical model takes into account interconnected processes of heat transfer in a coal particle and gas area, thermal decomposition of organic material, diffusion and gas-phase oxidation of volatiles, heating of a coke (carbon) and its heterogeneous ignition. The effect of low-temperature (about 600 K) ignition for a single coal particle is impossible even at variation of its rate (radius) from 0.05 mm to 0.5 mm. Nevertheless this process is possible for group of particles (two, three, et al.) situated at close-range from each other. The physical aspects of the problem are discussed. [ABSTRACT FROM AUTHOR]

Gas hydrates are widespread all over the world. They feature high energy density and are a clean energy source of great potential. The paper considers experimental and theoretical studies on gas hydrates in the following key areas: formation and dissociation, extraction and transportation technologies of natural methane hydrates, and ignition, and combustion. We identified a lack of research in more areas and defined prospects of further development of gas hydrates as a promising strategic resource. One of the immediate problems is that there are no research findings for the effect of sediments and their matrices on hydrate saturation, as well as on gas hydrate formation and dissociation rates. No mathematical models describe the dissociation of gas hydrates under various conditions. There is a lack of research into the renewal and improvement of existing technologies for the easier and cheaper production of gas hydrates and the extraction of natural gas from them. There are no models of gas hydrate ignition taking into account dissociation processes and the self-preservation effect. [ABSTRACT FROM AUTHOR]

A model was developed to research the critical conditions and time characteristics of the ignition of gel fuels in the course of conductive, convective, radiant and mixed heat transfer. MATLAB was used for numerical modeling. Original MATLAB code was established pursuant to the developed mathematical model. For gel fuel ignition at initial temperatures corresponding to cryogenic storage conditions with different heating schemes, a numerical analysis of interconnected processes of heat and mass transfer in the chemical reaction conditions and exothermic and endothermic phase transitions was conducted. The model was tested by comparing the theoretical results with the experimental data. Dependencies were established between the key process characteristic (i.e., the ignition delay time) and the ambient temperature when the following parameters were varied: emissivity, heat emission coefficient, activation energy and pre-exponential factor of the fuel vapor oxidation reaction. The critical values of the main parameters of the energy source were determined. For these values, gel fuel ignition conditions were consistently realized for each heating scheme. The critical heat fluxes necessary and sufficient for the ignition of typical gel fuels were determined. [ABSTRACT FROM AUTHOR]

This paper describes modern research methods of the ignition and combustion processes of slurry fuel droplets. The experiments were carried out using a muffle furnace to ensure the conditions of radiation heating, the hot surface to reproduce the conditions of conductive heating, the high-temperature channel with convective heating, the chamber with the processes of soaring, i.e., a significant increase in the time of fuel residence in the combustion chamber. We identified the differences in combustion modes, threshold ignition temperatures, delay times and durations of combustion processes. We obtained the quantitative differences in the characteristics of the ignition and combustion processes for typical registration methods. It was found that for all heating schemes, the minimum ignition temperatures have comparable values. Minimum ignition delay times were recorded during convective heating. The maximum combustion temperatures were achieved with radiation heating. We determined the values of limiting heat fluxes, sufficient to initiate the combustion of slurries fuels during conductive, convective and radiative heating. [ABSTRACT FROM AUTHOR]

• Small child droplets can be obtained by reducing the viscosity and surface tension. • The higher the viscosity and surface tension, the higher the breakup delay time. • The lower the interfacial tension, the higher number of heterogenic child droplets. • Micro-explosion delay time is minimum with the minimum emulsifier content. • The boundaries between breakup regimes depend of liquid and gas temperatures. Micro-explosion and puffing of multi-component slurry and emulsified fuel droplets can provide a several-fold increase in the evaporation and chemical reaction surface area. As a result, micro-explosion and puffing shorten the heating, evaporation, and ignition time of fuel compositions, improve the efficiency of their combustion, reduce fuel consumption, and provide its smooth spraying in combustion chambers. There are still no thorough studies on how the viscosity as well as surface and interfacial tension of emulsified fuels affect the integral characteristics of micro-explosive breakup of droplets under intense heating. In certain ranges of temperatures and component concentrations, there may be synergistic effects of these fuel characteristics on the threshold conditions and outcomes of micro-explosive droplet atomization. Such synergistic effects can make the secondary atomization of fuel droplets much more effective. In this research, we experimentally determine the heating times until breakup of relatively large emulsion droplets, the size and velocity distributions of newly formed child droplets with varying heating temperature, initial size of parent droplets, as well as component type and concentration. The results of this research are important for developing the current micro-explosion models and creating new, accounting for the breakup mechanisms and outcomes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneous ignition occurred at a distance between the droplet centers of 3–5 mm. • At low temperatures, increasing the distance between droplets eliminates synergism. • The use of an oil additive (5%) reduced the ignition delay time of droplets by 15–20%. • The increase in air flow velocity contributed to the formation of a common flame zone. • The ignition delay in the droplet group increased with an increase in air flow velocity. Waste-derived slurries can be burned both in a fluidized bed and when injected into a boiler furnace. This paper is the first to analyze the dynamic characteristics of ignition and combustion of a group of three slurry droplets based on coal slime, water, and waste industrial oil in a low-temperature air flow with a temperature of 500–600 °C and velocity of 0.1–1.2 m/s. The distance between the droplet centers varied from 3 to 15 mm. The results of the study can develop innovative technologies for flare and fluidized bed combustion of fuel slurries at the boiler start-up stage. It was found that a distance of 3–5 mm between droplet centers provides almost simultaneous gas-phase ignition of all droplets. A further increase in the distance critically worsened the ignition and combustion and eliminated the synergy. An increase in the air flow velocity contributed to the appearance of a common flame zone but at the same time increased the ignition delay of droplets by a factor of 1.2–1.6. The negative effects of cooling and entrainment of combustion products by a low-temperature flow can be effectively reduced by adding 5 wt% of industrial oil to the slurry. Also, the use of oil reduced the droplet ignition delay time by 15–20%. At the stages of flame and heterogeneous combustion, the differences for droplets in a group increased (the stage durations differed by 1.5–3 times). For the low-temperature start-up of a boiler, it was found advisable to provide a droplet flow with a sufficient density to stabilize their ignition without significant flow deviations (dimensionless distance 1.5–2.5). [ABSTRACT FROM AUTHOR]

Slurry fuels based on coal and waste oil can be a viable alternative to coal in terms of environmental, cost, and energy performance. This paper presents a database of promising components for such fuels based on the experimental characteristics of their ignition and combustion. When analyzing the properties of high-potential components, we classified those components into four groups in terms of normalized ash and sulfur content. The components within each group have comparable ignition characteristics: ignition delay time, duration of complete combustion, maximum combustion temperature, and ignition temperature. Using the newly created database and results of experiments on highly heterogeneous fuels, one can predict the conditions and special aspects of their combustion in power plants of various capacities. The key outcome of the research is the procedural database and algorithm for selecting combustible components of slurry fuels with high relative efficiency for the heat and electricity generation in typical coal-fired power stations and boiler plants. Image 1 • Database was compiled with environmental and energy parameters of slurry combustion. • Coal and oil wastes can be combined to produce economically competitive fuel slurries. • Slurries are effective fuels based on a wide range of components. • Slurry performance can significantly vary with changing ratio and type of components. [ABSTRACT FROM AUTHOR]

One of the known and still unsolved problems of internal combustion engines and liquid fuel power plants is the complexity of efficient (i.e. with minimal cost of basic resources: time, energy and raw materials) ignition of fuels issued from valorization of waste. A promising way to improve the efficiency of ignition of liquid fuels is a secondary atomization using the micro-explosion of water-fuel droplets. This phenomenon is called micro-explosion when concerning an individual water-in-oil emulsion drop among the combusting spray. This process dramatically accelerates fuel heating and ignition, since fuel droplets issued from the secondary atomization are smaller and faster, increasing interfacial area. To investigate the atomization efficiency and its causes, the present work quantifies the occurrence of successful micro-explosion under large samples of experimental data. The behavior of water-fuel drops in the form of fine, middle-size emulsions or two immiscible liquids is observed using schemes with conductive, convective or radiative heat transfer provided at the same range of temperature. [ABSTRACT FROM AUTHOR]