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The synthesis and dissociation of methane hydrate and carbon dioxide hydrate were studied. Nonflammable gas hydrates can be used to extinguish flames in confined spaces. To increase the extinguishing efficiency, it is necessary to increase the dissociation rate (gas release rate) by using surfactant. The work investigates gas hydrates synthesized using sodium dodecyl sulfate (SDS). Experimental studies were carried out in wide ranges of surfactant concentration, the number of the stirrer revolutions and the initial water volume. To achieve the maximum rate of synthesis and dissociation, optimization of the specified parameters was performed. The influence of the key parameters on the dissociation rate was investigated experimentally and theoretically. The novelty of the work lies in solving a complex of interrelated tasks on the synthesis and dissociation of gas hydrate. It is shown that in order to achieve the maximum dissociation rate of carbon dioxide hydrate, it is necessary to optimize the following parameters: the diameter of the particles and their porosity, the porosity of the layer and the external heat flux. [ABSTRACT FROM AUTHOR]

Hydrogen plays a key role in the transition to a carbon-free economy. Substitution of hydrocarbon fuel with hydrogen in gas turbine engines and power plants is an area of growing interest. This review discusses the combustion features of adding hydrogen as well as its influence on the characteristics of gas turbine combustion chambers as compared with methane. The paper presents the studies into pure hydrogen or methane and methane–hydrogen mixtures with various hydrogen contents. Hydrogen combustion shows a smaller ignition delay time and higher laminar flame speed with a shift in its maximum value to a rich mixture, which has a significant effect on the flashback inside the burner premixer, especially at elevated air temperatures. Another feature is an increased temperature of the flame, which can lead to an increased rate of nitrogen oxide formation. However, wider combustion concentration ranges contribute to the stable combustion of hydrogen at temperatures lower than those of methane. Along with this, it has been shown that even at the same adiabatic temperature, more nitrogen oxides are formed in a hydrogen flame than in a methane flame, which indicates another mechanism for NOx formation in addition to the Zeldovich mechanism. The article also summarizes some of the results of the studies into the effects of hydrogen on thermoacoustic instability, which depends on the inherent nature of pulsations during methane combustion. The presented data will be useful both to engineers who are engaged in solving the problems of designing hydrogen combustion devices and to scientists in this field of study. [ABSTRACT FROM AUTHOR]

This article investigates the recovery of typical wastes (coal slime, sawdust, cardboard and tire pyrolysis residue) as part of high-moisture slurry fuels. Using a laboratory furnace, the ignition and combustion characteristics of fuels as well as NO x and SO x emissions were determined. Using multiple-criteria decision-making (MCDM) methods and experimental results, we access the performance of four different slurry fuels in comparison with bituminous coal. The novelty of the study is based on the following features: we consider a unique set of parameters of the fuels (economic, environmental, safety and energy indicators), as well as three countries for their potential use (the USA, India and Russia); three different methods for calculating the efficiency indicator of each fuel were used. Despite rather low energy performance, the summarizing efficiency indicator of waste-based slurries was 53–93% higher than that of coal. The use of cardboard in the composition of a fuel blend showed the best complex result (the increase in the efficiency indicator was 80–93% relative to coal). The least promising additive was the pyrolysis residue of automobile tires. Its addition resulted in a 10–15% decrease in overall efficiency relative to a slurry without additives. The research results are useful for optimizing the component composition of waste-based slurries, technical and economic development of projects for the incineration of various wastes in the form of high-moisture fuel slurries. [ABSTRACT FROM AUTHOR]

This paper shows the analysis of burnout characteristics of droplets of the following slurry fuels: (i) based on coal slime with or without the addition of waste turbine oil; (ii) based on coal dust with or without the addition of waste turbine oil. The oil share in the mixtures varied from 0% to 15%. The solid component share varied in the range of 40–60%. Single droplets with an initial size of 1–5 mm were burned in a tubular muffle furnace at temperatures of 700–900 °C. The inertia of gas-phase and heterogeneous ignition and the combustion time of mixtures were estimated. Based on experimental data, the values of the linear and mass burnout rates of fuel droplets were calculated. At a furnace temperature of less than 800 °C, the characteristics of ignition and burnout of droplets of water-containing fuel mixtures and solid particles deteriorated significantly. The most preferred is the combustion of coal slime in the composition of aqueous slurry with the addition of high-reactive components (for example, waste oil of petroleum origin or vegetable oils). To intensify ignition and combustion, it is recommended to use no more than 50% of the solid component in the mixture. The maximum linear burnout rate was typical for droplets about 3 mm in size and reached values of 0.5–0.6 mm2/s. The mass burnout rates of droplets of the investigated fuels with a size of 5 mm varied in the range of 0.0005–0.0018 g/s. [Display omitted] • Waste oil is particularly useful in combination with coal slime to intensify combustion. • To stabilize ignition and combustion, it is enough to use no more than 5% of oil. • With a solid content above 50%, incomplete combustion of slurry may increase. • To burn coal slime slurries effectively, the temperature of not lower than 800 °C is required. • Coal slime mixed with water burns 2–3 times faster than a dry particle. [ABSTRACT FROM AUTHOR]

The comparison of the ignition delay times and emission concentration ranges from the combustion of a filter cake and composite fuels revealed that the latter are characterized by lower ignition times and the emission of harmful substances. When conducting research into the integral characteristics of composite fuel spraying, it is especially important to study the collisions of droplets with particles making up these fuels. Water in the composition of composite fuels has a significant effect on the integral characteristics of their ignition and combustion. Three regimes of coal slime particle ignition and combustion were identified: flame combustion, smoldering, and micro-explosion. [Extracted from the article]

This paper presents experimental research findings for those involved in the early phase of fire in office buildings. Class A model fires with a reaction area from 5 cm2 to 300 cm2 were chosen for investigation. To mock up a fire, the following combustible materials typical of offices were used: wood pieces, heat-insulated linoleum, paper and cardboard. The main characteristics of a model fire were recorded: temperature in the combustion zone, heat release, time of complete burnout and concentration of flue gas components. Typical trends and histograms of changes of these characteristics over time were presented; stages of ignition, flame combustion and smoldering were illustrated. The key characteristics of fire detector activation at different stages of model fire combustion were analyzed. Dead bands and operation conditions of a group of detectors (smoke, heat, optical, flame), their response time and errors were identified. It has been established that the most effective detectors are flame and smoke detectors. Specific operational aspects of detectors were established when recording the ignition of different types of model fires. The viability of combining at least two detectors to record fire behavior was established. Recommendations were made on using the obtained findings when optimizing the systems for detecting and recording the start of a compartment fire. [ABSTRACT FROM AUTHOR]

The article discusses the modern achievements in the field of thermal recovery of industrial and municipal waste. The average accumulation rate and calorific value of typical wastes were analyzed. The focus is on the opportunities to exploit the energy potential of high-moisture waste, low-grade liquid components, and fuel slurries. We consider the relevant results in the field of combustion, pyrolysis, and gasification of such fuels. The main attention is paid to synergistic effects, the influence of additives, and external conditions on the process performance. Vortex combustion chambers, boilers with burners, and nozzles for fuel injection, grate, and fluidized bed boilers can be used for the combustion of waste-derived liquid, high-moisture, and slurry fuels. The following difficulties are possible: long ignition delay, incomplete combustion, low combustion temperature and specific calorific value, high emissions (including particulate matter, polycyclic aromatic hydrocarbons), fast slagging, and difficult spraying. A successful solution to these problems is possible due to the use of auxiliary fuel; boiler modifications; oxy-fuel combustion; and the preparation of multi-component fuels, including the use of additives. An analysis of methods of waste recovery in the composition of slurries for fuel gas production showed that there are several main areas of research: pyrolysis and gasification of coal–water slurry with additives of oil waste; study of the influence of external conditions on the characteristics of final products; and the use of specialized additives and catalysts to improve the efficiency of the pyrolysis and gasification. The prospects for improving the characteristics of thermochemical conversion of such fuels are highlighted. [ABSTRACT FROM AUTHOR]

Coal processing waste is generated annually in large volumes by the coal exporting countries. More than 70% of run-of-mine coal is enriched. At the same time, typical coal processing waste (slime, flotation waste, mid-coal and tailings) make up at least 10–15% of the raw coal mass. Approximately 220–300 million tons of coal processing waste is generated annually at coal-preparation plants in Russia and China. The results of experimental researches in recent years illustrate the growing interest in such wastes as promising energy components. In this paper, we performed a comparative analysis of the main physical properties, ignition and combustion characteristics of several types of coal processing waste. The comparison is made for typical flotation waste (filter cakes or coal slime) generated in Russia and China. It is shown that for wastes from different countries the ignition delay times differ by no more than 50% and the heat of combustion by 9–15%. Concentrations of main anthropogenic emissions were determined. Generalization is made using criterion expressions to illustrate the advantages and disadvantages of coal processing waste incineration in comparison with pulverized coal combustion. [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]

The laser processing becomes more and more popular for different objects and purposes including different fuels and combustibles. We have investigated experimentally some details of the light-induced conversion of the waste-derived coal-water slurry into the syngas. The process was “cold” enough (the temperature of the fuel was less than 350 K). The specific gasification energy strongly depends on the chosen content of the raw fuel and does not exceed the 6 MJ/kg. It was shown that there are two possible alternative processes with dominant production of the hydrogen or methane. The production of the combustible gases is accompanied with generation of certain amounts of SO 2 and much less amount of CO . [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]

High concentrations of hazardous anthropogenic emissions (sulfur, nitrogen and carbon oxides) from solid fuel combustion in coal burning plants cause environmental problems that have been especially pressing over the last 20–30 years. A promising solution to these problems is a switch from conventional pulverized coal combustion to coal-water slurry fuel. In this paper, we pay special attention to the environmental indicators characterizing the combustion of different coal ranks (gas, flame, coking, low-caking, and nonbaking coals) and coal-water slurry fuels based on the coal processing waste – filter cakes. There have been no consistent data so far on the acceptable intervals for the anthropogenic emissions of sulfur (SO x ), nitrogen (NO x ) and carbon (CO, CO 2 ) oxides. Using a specialized combustion chamber and gas analyzing system, we have measured the concentrations of typical coal and filter-cake-based CWS combustion products. We have also calculated the typical combustion heat of the fuels under study and measured the ratio between environmental and energy attributes. The research findings show that the use of filter cakes in the form of CWS is even better than coals in terms of environment and economy. Wide utilization of filter cakes solves many environmental problems: the areas of contaminated sites shrink, anthropogenic emissions decrease, and there is no need to develop new coal mines anymore. [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]

This study examines the temperature change of droplets of coal-water slurry containing petrochemicals (CWSP). The slurry consists of coal and oil processing waste. The temperature of oxidant in a modelled combustion chamber is varied between 600 and 1200 K. The initial size (radius) of CWSP droplets varied in the range of 0.5–3 mm. The study identifies typical temperature trends at the center and on the surface of the CWSP droplet. The temperature trends represent the following stages: (i) heating of fuel, (ii) evaporation of water and a liquid combustible component, (iii) thermal decomposition of coal and yield of volatiles, (iv) gas phase ignition of volatiles together with vapor of the combustible liquid, and (v) heterogeneous ignition of carbon and its burnout. Moreover, these trends indicate the maximum combustion temperatures of CWSP that reflect corresponding heat release. The study specifies the parameters which influence the maximum combustion temperature: fuel component composition, properties of components, droplet size, and the oxidant temperature. Finally, the study defines the minimum ignition temperatures and delay times of sustainable combustion initiation that characterize the ignition inertia. The knowledge of influence of these factors will allow one to predict the optimal conditions for the combustion of the CWSP. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations on the deceleration and entrainment of water droplets during their motion in the counter flow of high-temperature combustion products (up to 1900 K). High-speed video cameras (10 5 frames per second), specialized software applications (with continuous tracking functions), as well as panoramic optical methods (Particle Image Velocimetry, Stereoscopic Particle Image Velocimetry, Particle Tracking Velocimetry, Shadow Photography) registered the processes under study. We used several typical oils, gasoline, kerosene, acetone, and industrial alcohol to generate combustion products with a controlled high temperature. The initial sizes (radius) of droplets and their velocities were varied from 0.05 mm to 0.35 mm and from 0.5 m/s to 5 m/s. The velocities of counter motion of combustion products were varied from 0.1 m/s to 2.5 m/s. In this paper we have also determined the characteristic trajectory length of the droplets of different sizes until their complete stop (and subsequent entrainment) in the counter flow of high-temperature gases. As a result of studies, we summarized the research results through the establishment of Weber and Reynolds numbers ranges for droplets and gases, when the full stop and entrainment of droplets may occur. This paper also covers a comparison of the characteristics of water droplet deceleration under the conditions of non-stationary (when the temperature of combustion products varies from 1900 K to 400 K in channel) and nearly stationary (when the temperature is 1100 ± 30 K) heat transfer. Thus, it has been found out that the values of these parameters correlate well (deviation did not exceed 7%) under such conditions (stationary and nearly stationary) during short heating (less than 0.5 s). [ABSTRACT FROM AUTHOR]

The paper discusses the results of lab-scale combustion of complex waste-derived fuel mixtures in different forms. Composite fuels based on a combination of widespread industrial and municipal waste were considered. The scientific and practical novelty of this study comes from the fact that for the first time, a group of integral parameters was researched. They describe the ignition and combustion of mixtures in different forms: pressed dry fuel (pellets), a wet slurry, and granules of different moisture content. The most efficient method in terms of increasing the rate and reducing the temperature threshold of the oxidation reaction is firing a low-moisture mixture based on municipal solid waste (with a predominance of wood components). Pelleted coal sludge combustion was characterized by a rather long delay in heterogeneous ignition and underburning. It was shown that in order to reduce emissions and increase the degree of burnout, coal processing waste should be burned as wet granules or slurry droplets. [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]

Anthropogenic emissions from coal combustion pose a serious threat to human wellbeing. One prospective way to solve this problem is by using slurry fuels instead of coal. The problem is especially pressing in China and Russia, so these countries need reliable experimental data on the SOx and NOx emissions reduction range more than others do. The experiments in this research are based on the components that are typical of Russia. Experimental research was conducted on the way typical forest fuels (ground pine needles, leaves and their mixtures, bark, sawdust, and charcoal) affect the gas emissions from the combustion of slurry fuels based on the wastes. It was established that using forest fuels as additives to coal-water slurries reduces SOx and NOx emissions by 5–91% as compared to coal or to slurries based on used turbine oil. It was revealed that even small concentrations of such additives (7–15%) could result in a several-fold reduction in SOx and NOx. The higher the temperature, the more prominent the role of forest biomass. The calculated complex criterion illustrates that forest fuels increase the performance indicator of fuel suspensions by 1.2–10 times. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental research, determining the conditions for suppressing the combustion front of forest fuels (FF) with the use of a protective water line. Integral parameters, velocities and other characteristics of the main interrelated heat and mass transfer processes, phase transformations and chemical reactions are studied. The conditions for suppressing the combustion front of typical forest fuels (needles; leaves; a mixture of needles, leaves and branches) are established. The experimental conditions are designed to be the utmost close to those of ground forest fires and parameters of fire lines: in terms of temperature, wind velocity, the forest fuel layer thickness, the size of water droplets, etc. The rational dimensions (width, length, depth) of the protective water lines, the density of water irrigation of the material surface, the volume of liquid, the time of spraying are determined. It is shown that effective conditions for forest burning localization can be achieved at almost complete thermal decomposition of a small layer of FF near the barrier line. It is established that necessary and sufficient conditions of FF combustion localization can be reliably predicted using the obtained dependences of specific water flow rate on FF volume. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • To obtain 30 MJ of heat we need 1–1.2 kg of coal, 1.8–3.6 kg CWS and 1.5–1.7 kg of CWSP. • Concentrations of sulfur and nitrogen oxides for some suspensions are 6–190 ppm lower than for coal. • Mass of ash residue may vary 0.7–5.5 times for coal versus waste slurries. • If coal and oil processing wastes are used, slurry fuel cost may be 2–5 times lower. • Relative efficiency factor of waste-derived fuels may reach 165. Abstract The replacement of coals by less environmentally hazardous coal-water slurries with and without petrochemicals is often discussed with an emphasis on quite a long list of advantages of composite fuels. In this research, we perform a compound analysis of the main prospects of switching from coal to slurries containing coal and oil processing waste. The main focus is on comparing a group of parameters to produce the same amount of heat from the combustion of coals and high-potential fuels. The compound analysis includes fuel consumption, the most hazardous anthropogenic emissions (sulfur and nitrogen oxides), the mass of the ash residue, the cost of components as well as their properties and concentrations. The numerical values of the relative efficiency factor of fuels based on municipal and industrial wastes vary in a wide range from 2 to 165. The best results are shown by the slurries based on flotation wastes (filter cakes) of coking and nonbaking coals (ranks C and N). For them, the aggregated criterion indicators are 70–90% higher than for the respective coals. A forecast has been made on the amount of energy that can be generated using fuels from wastes. According to our forecast, the waste-based fuels under study may be used to generate 773 TWh of energy annually. [ABSTRACT FROM AUTHOR]

The synthesis of an effective composite fuel from industrial wastes almost always requires mixing several components with different properties. Features of certain components can effectively compensate for the limitations of others, eventually improving the fuel as whole. We propose the optimization of the waste-derived coal-water slurry (CWS) by doping it with a small amount (2–5 wt%) of non-hydrocarbon dopants (metal-bearing powders with aluminium, iron, copper and chalk). It allows the stabilization of the combustion temperature (or even its increase), while keeping the ignition delays at the reasonable level ( ∼ 2 s at 1000 K). Doping the CWS by 2–5 wt% of chalk powder allows a radical decrease in the production of harmful exhausts (up to an order of magnitude regarding the SO 2 and 2–5 times regarding NO x ). A strong ecological effect was observed when the fuel is doped by iron powder, too. Therefore, the usage of non-organic dopants is a very promising way to prepare environmentally friendly fuel compositions with high power efficiency. [ABSTRACT FROM AUTHOR]

The combustion predictive model was developed based on the results of experiments with coal water slurry and coal water slurry containing petrochemicals. Unlike other known models, it takes into account the effect of liquid flammable component (in particular, engine oil waste) on the main mass and heat transfer as well as other physical and chemical processes in the combustion chamber. The main differences, conditions and characteristics of the combustion of coal water slurries containing petrochemicals and without additives have been studied theoretically with different defining parameters: fuel composition, component properties, and furnace chamber temperature. Temperature fields and volumetric concentration distribution of combustion products in the furnace chamber are established for fuel compositions based on water, coal, and industrial oil waste. Temperatures and concentrations for both the initial fuel components and their combustion products are established at different points of the furnace chamber for various component concentrations, properties, and furnace air temperatures. The main research findings are the quantitative differences between the characteristics of ignition and combustion of slurries with and without a liquid fuel component. These differences are critical to illustrate the benefits of using coal water slurries containing petrochemicals in heat and power plants. Adding as little as 10% (relative mass fraction) of waste industrial oils was shown to significantly reduce the ignition delay times and improve the combustion efficiency of fuel compositions. Possible ranges, in which the ignition delay of slurry fuels can be reduced, and the displacement of their ignition zones in the combustion chamber were determined when changing the temperature and the main fuel component – coal (as illustrated by brown and bituminous coals, as well as anthracite). [ABSTRACT FROM AUTHOR]

This research experimentally determines the major gas emissions from the industrial combustion of coal, coal processing waste, and coal derivatives in the form of traditional coal dust as well as slurry fuels with water and flammable additives. Several types of coal are considered: gas coal, flame coal, bituminous, non-coking and low-caking coal, as well as coal processing waste (filter cakes), coal derivatives (coke, semi-coke), and flammable liquids (industrial oil waste, fuel oil). Experimental data for charcoal and carbon dust from recycled car tires are presented as well. The concentration is evaluated for the most hazardous gas emissions: sulfur and nitrogen oxides. A number of factors defining the said concentrations are established: the quality of components, their elemental composition and concentration (40–60% coal, 30–50% water, 5–15% flammable liquid); slurry preparation method (homogenizer or cavitator); coal grind (8–250 μm); and the mass of the batch (0.5–1.5 g). In particular, changing coal concentration in a slurry from 40 to 60% increases the emission of nitrogen oxide by 35% and sulfur oxide by 67%. Varying water concentration from 30 to 50% decreases the emission of nitrogen oxide by 17% and sulfur oxide by 62%. Increasing the flammable liquid concentration from 5 to 15% slightly lowers the emission of nitrogen oxide (by 5%), while the sulfur oxide emission grows by 28%. The advantages of coal-water slurry containing petrochemicals combustion are identified over coal. Moreover, the main limitations are determined for large-scale usage of slurry fuels instead of traditional heat and power industry fuels. [ABSTRACT FROM AUTHOR]

The paper presents the results of the experimental research into maximum concentrations of anthropogenic emissions from typical brown low-rank coal combustion in the traditional pulverized state as well as from the combustion of coal-water slurries with or without petrochemicals. The temperature of fuel heating in the model combustion chamber varied in the range from 500 °C to 1000 °C. The relative values of concentrations of anthropogenic emissions are calculated with due consideration of key energy characteristics of the fuel: combustion heat, specific mass of the fuel component in a mixture, specific energy obtained per fuel cost. The findings illustrate considerable differences not only between the concentrations of the analyzed anthropogenic emissions, but also between the times, during which these concentrations remained high. In addition, we compare the boundary conditions (i.e. borderline or minimum sustainable ignition temperatures) necessary and sufficient for the combustion of the fuel compositions under study and analyze fuel heating and ignition delay times. Special aspects are determined of the environmentally friendly combustion of coals as part of coal-water slurries with or without petrochemicals at different temperatures: from minimum temperatures usually observed at the beginning of sustainable ignition to those typical of small- or medium-sized power plants. Concentrations of the most hazardous oxides of sulfur and nitrogen produced during coal combustion are 3–5 times higher than during coal-water slurry combustion. The differences between these parameters for coals and coal-water slurries containing petrochemicals are less noticeable. Nevertheless, the emissions of nitrogen and sulfur oxides from the combustion of coal-water slurries containing petrochemicals are at least 30–60% lower than from the combustion of coals. Taking into account the cost of the components of coal-water slurries containing petrochemicals, as well as the combustion heat and the concentrations of anthropogenic emissions, specific indicators show that coal-water slurries containing petrochemicals are more efficient than coals or the coal-water slurries without petrochemicals. If filter cakes are used as the main component of coal-water slurries containing petrochemicals, the specific indicators of such fuels grow 5–6 times higher (or even 10 times higher in special cases) versus pure coals. The research findings show that the temperature monitoring in the combustion chamber is obligatory to provide high ecological indicators. At temperatures below 1000 °C, it is possible to provide stable combustion of fuels and significantly reduce emissions as compared to the traditional high-temperature regimes (above 1000 °C). Thus, temperatures lower than 1000 °C are more rational. Finally, the conditions for the optimal coal fuel combustion are presented in terms of the environmental friendliness, energy and cost efficiency, as well as fire and explosion safety. [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]

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950 K). The temperature of a gas-vapor mixture in the area of droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The paper considers aerosol flows with droplet size of 0.04–0.4 mm and concentration of 3.8·10 −5 –10.3·10 −5 m 3 of droplets/m 3 of gas, as well as individual droplets (sized 1.5–2.5 mm), and relatively large water massifs (sized 22–30 mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15 K to 140 K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3 s to 30 s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the ignition conditions and characteristics of the single droplets of organic coal-water fuels. The study examines suspension compositions based on low-grade coals, typical (with various characteristics of combustion) coal processing wastes (filter cakes obtained after the filtration of crushed coal), waste oils, water–oil emulsions. In the experiments, the mass fraction of the main components of organic coal-water fuel varies within the following ranges: 40–60% coal dust or filter cakes, 0–20% flammable liquid, 40–60% water. For recording the main parameters of ignition, we use high-speed video cameras, cross-correlation complexes, and a quartz cylindrical channel. To process the experimental results, specialized software systems Tema Automotive and Actual Flow are applied. We find the times of the ignition delay and complete combustion of organic coal-water fuel droplets with the sizes (radius) of 0.5–1.5 mm. The temperature and rate of air flow vary between 500 and 900 K and 0.5–5 m/s (to enable the use of research results in different fuel technologies). Further, we identify the boundary conditions of the sustainable ignition of organic coal-water fuel droplets with various compositions (by component concentrations). Also, the study establishes the scale of the effect of organic coal-water fuel component composition on these conditions. [ABSTRACT FROM AUTHOR]

Experimental investigation of integral characteristics of typical extinguishing liquid (water) droplet evaporation in flaming combustion zone was carried out with varying of their basic initial parameters (sizes, relative concentration in a flow or current, temperature, screenings content, structure homogeneity, motion velocities into a flow). Optical methods of two-phase and heterogeneous gas–vapor–droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging”) were employed. The significant influence of temperature, sizes, structure and droplet concentration in the atomized water flow on evaporation characteristics was determined. The sufficiently moderate influence of salt admixtures on water evaporation conditions at its finely divided injection in the flame was established. Some modes of water droplet motion in the flame area were indicated according to their moving velocity and sizes, and combustion product velocities too. Values of water droplet basic parameters were calculated. These parameters provide the maximum evaporation in the flame zone with intended sizes. [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]

Various fuel composites became popular for a last decade because smart mixture of different combustibles allows effective minimization of the negative features of components. In this paper we have observed the influence of water evaporation on the different stages of ignition of the waste derived coal-water slurry with addition of the waste petrochemicals. It was shown that the gas-phase ignition stage and heterogeneous ignition stage of the slurry have the increasing time-separation (from 4 to 50 ms) with a growth of the furnace temperature after 1000 K. It happens because the peak of water vaporization in the volume of fuel shifts closer to the moment of ignition with furnace temperature increase. As result, an additional fuel heating is required before the heterogeneous ignition. The volume power density of volatiles combustion around the fuel droplet grows for 30–40 times with furnace temperature changes from 870 K to 1070 K. However, combustion of the volatiles does not produce heat enough for the immediate beginning of the stable heterogeneous ignition when the water content is about 30–40%. The obtained results can be used in future for an effective optimization of the ignition of the water-filled fuels as well as for a choice of the most effective and ecological combustion regime. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fuel component mixing procedure affects the fuel combustion characteristics. • Slurry becomes 25–30% more effective when coal dust is replaced by coal slime. • Auxiliary components should be mixed with water first, and then with coal or coal slime. • Iterative component mixing improves slurry homogenization. • The most stable slurry fuel can be obtained using a colloid mill. This paper presents the results obtained from a comprehensive study of how the conditions and methods of preparing three-component fuel slurries affect their ignition, combustion, emissions, as well as viscosity and static stability. The data obtained for slurry fuels based on bituminous coal and water with added waste hydrocarbon oil and wood biomass as well as a slurry based on coal slime. A tubular muffle furnace was used for combustion at 700–900 °C. The influence of the mixing conditions of the components on the ignition and combustion behavior was moderate. It was established that surfactants should not be added to composite slurry fuels at the final stage of component mixing. To provide more uniform burnout of a blend with wood biomass, the latter should first be mixed with water and then the coal component should be added. Iterative mixing can provide a 10–15% improvement of ignition and burnout characteristics. To obtain a more homogeneous and stable blend, it is advisable to use a cavitator (colloid mill) rather than a homogenizer or a magnetic stirrer. Based on a set of parameters (viscosity, stability, cost, ignition and combustion characteristics), a dimensionless efficiency indicator was calculated using Weighted Sum Method. The calculated values of the relative efficiency indicator of the fuel blends based on coal dust ranged from 0.67 to 0.73. The relative efficiency of a slurry was found to increase by 25–30% when coal dust is replaced by coal slime due to the economic parameter. [ABSTRACT FROM AUTHOR]

This paper describes the results of an experimental investigation on the stages of thermochemical transformation of fuels prepared from waste. We studied the combustion of coal slime and its co-combustion with additives (waste turbine oil, sawdust, and rapeseed oil). The mass fraction of the additive was 5%. Fuels in the forms of a pellet, dry loose layer, and slurry were heated in a tubular muffle furnace. The reactivity of the fuels was evaluated, and the duration of the main process stages was recorded. Experiments have shown that it is more expedient to burn coal slime in combination with other components, which improved the ignition and burnout performance of the blends. The addition of turbine oil accelerated the flame combustion by 3–6 times. Rapeseed oil reduced the duration of the endothermic stage by 50–60%. The slurry droplets had the longest pre-flame stage. Their burnout was more intense than that of pellets or a layer and was less dependent on the temperature in the furnace. The longest burnout was typical of pellets. The data obtained are essential in planning and conducting industrial tests on the energy recovery of coal slime, biomass, and refined products. [Display omitted] • Combustion of coal slime is advisable in combination with other components. • The burnout of slurry droplets is the best in comparison with pellets and layers. • The addition of turbine oil (5 wt%) reduced the endothermic period by 3–6 times. • Minimal ignition temperature of waste-derived blends varied from 450 °C to 500 °C. • Coal slime pellets tend to low reactivity and incomplete burnout. [ABSTRACT FROM AUTHOR]

This study is based on the analysis of a set of industrial sectors (coal processing, wood processing, transport, oil, and water treatment) in order to identify the amount and type of combustible waste suitable for incineration. The main ignition and combustion parameters of these wastes have been experimentally obtained from their direct individual incineration in the original form and as part of a slurry based on wastewater. It has been established that a set of parameters allow waste-derived fuel mixtures to compete with coal dust and fuel oil with an environmental advantage. In particular, the concentration of sulfur and nitrogen oxides in the combustion products of all the tested slurries is 1.5–3 times as low as that of coal dust. Most of the wastes in question do not provide such advantages when burnt individually. We have assessed the fire safety of fuel mixtures and analyzed the prospects of mass waste incineration technologies. The calculations show that about 14–20% of coal and oil can be saved annually by extensively involving industrial waste in the energy sector. The experimental results obtained are the basis for the development of useful technologies for the safe and efficient combustion of waste from different industries. Image 1 • The combustion heat of the studied slurries was 12.8–17.5 MJ/kg. • SO x and NO x emissions did not exceed 250 ppm and 390 ppm. • The efficiency of slurries compared to coal and fuel oil was within a range of 0.098–23.1. • More than 1500 million tons of different waste can be utilized in fuel slurries. • By burning waste-derived slurries, about 14–20% of coal and fuel oil may be saved. [ABSTRACT FROM AUTHOR]