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The results of experimental studies of the cocombustion of coal–water fuel with fuel oil are presented. According to the results of experimental studies, the efficiency of joint ignition of stationary single droplets of coal–water fuel and fuel oil was substantiated. A decrease in the ignition delay times of fuel droplets was found in comparison with the ignition of only coal–water fuel droplets under identical conditions. A significant decrease in the ignition delay times of coal–water fuel droplets is typical for droplets with sizes of 2 and 3 mm in the entire studied temperature range of the oxidizer (from 873 to 1,273 K) and distances (from 2 to 4 mm) between drops of coal–water fuel and fuel oil. It has been experimentally established that the reduction of ignition delay times is 58 and 70%. For droplets of coal–water fuel with a characteristic size of 1 mm, the changes in ignition delay times are ambiguous. The joint combustion of coal–water fuel and fuel oil affects the ignition of droplets of coal–water fuel, and the characteristic size of which is more than 1 mm. With this method of burning coal–water fuel and fuel oil, the latter acts as a catalyst when igniting coal–water fuel, thereby ensuring a stable combustion of such fuel. The combustion of two-component coal–water fuel together with fuel oil can avoid the problems typical of such fuels: reduce the requirements for spraying devices, solve the problem of low reactivity, increase the completeness of combustion of this fuel, and fully use it in the production of thermal and electrical energy. [ABSTRACT FROM AUTHOR]

Relevance. An analysis of the current state of the global energy agenda shows that the problem of anthropogenic impact on the planet’s atmosphere by thermal energy facilities is one of the most important for humanity. At the same time, the growth in electricity consumption stimulates the introduction of ever new power generating capacities. For a long time, it was believed that the solution to this problem was the large-scale introduction of non-traditional renewable energy sources (wind generators and solar panels) into the overall balance of electricity generation. However, it is now becoming obvious that renewable energy sources cannot fully cover all electricity needs. The latter creates incentives for the commissioning of new thermal power plants, usually operating on coal fuel. But the main problem of coal energy – its anthropogenic impact – still remains unresolved. This situation creates the prerequisites for the development of new “clean” coal technologies with a full cycle of sequestration of combustion products. One of the most promising technologies for burning coal with low emissions is the combustion of coal in the composition of coal-water fuel. However, coal-water fuel technology has a number of disadvantages. One of the most significant is the high ignition delays of typical (with a characteristic size of 3–5 mm) droplets of coal-water fuel. One of the most promising methods for solving this problem is spraying coal-water fuel in an ultra-fine state (with a characteristic droplet size of 0.1–1 mm). Aim. Experimental study of the conditions and characteristics of crushing droplets of coal-water fuel in a high-speed air flow. Object. Coal-water fuel prepared on the basis of lean coal. Method. Special experimental stand to establish the main characteristics and conditions of dispersion of coal-water fuel droplets. Results. The results of experimental studies show that for stable fragmentation of typical droplets of coal-water fuel, the speed of the latter (during the spraying process) must be at least 40 m/s.

This work presents a review of modern devices for spraying coal–water fuels. The efficiency of their operation was analyzed according to several criteria: the simplicity of their design (A), the fuel channel's predisposition to clogging (B), durability in terms of the erosive wear of the nozzle channel (C), and dispersion of the jet—the average size of droplets in the jet (D). It was established that, from the point of view of operational efficiency, the most preferred devices for spraying coal–water fuels are those with a quasi-internal mixing of fuel and spraying agents. In combination with refractory or ceramic materials and the large diameter of the fuel channel, its rapid erosion wear and the likelihood of clogging with large particles of coal or agglomerates of viscous coal–water fuel are excluded. At the same time, the possibility of forming a fine-dispersed jet remains. The cooling of the nozzle with an external mixing of fuel and spraying agents during its operation also reduces the rate of erosion wear. Narrowing the fuel channel was proven to be an undesirable solution when creating a coal–water fuel nozzle. This review will be useful for both researchers studying the processes of spraying coal–water fuels and designers involved in the creation of coal–water fuel injectors or the transfer of existing boilers to coal–water fuel. [ABSTRACT FROM AUTHOR]

Background. The increase in the number of publications on the production and use of coal-water suspensions is due to the global increase in energy consumption, rising energy prices, as well as the needs to expand the fuel base in modern energy. On the other hand, interest in this area is associated with the issues of disposal of accumulated coal waste. In this regard, the task of systematizing and classifying the approaches proposed by various authors in the field of effective use of coal-water suspensions and coal-water fuel becomes urgent. Materials and methods. This paper presents an analysis of publications using modern methods of statistical and semantic analysis of big data. Results and conclusions. In particular, based on frequency analysis data, latent trends in the field of research related to coal-water fuel have been identified, methods for recycling water-coal fuel, and factors that determine the rheological properties of water-coal fuel have been identified. In addition, a classification of studies by type of coal was made.

The usage of coal-water fuel instead of dry coal for heat and power generation is a promising way to decrease harmful emissions during power generation. Improvement of the coal-water fuel ignition and combustion parameters is important due to the specifics of the fuel. The use of glycerol as a flammable additive to the coal-water fuel is environmentally friendly and leads to reducing the ignition time and threshold temperature of that composition fuel. Generally accepted approximation of the dependence of the main combustion parameters includes the ignition temperature and the time delay before ignition on the glycerol content of the fuel composition does not correspond to the physical nature of the process and does not reflect the real nature of the change. To approximate the experimental data in the case of complex two-component fuel based on the coal-water slurry and glycerol, a more suitable and physically correct inverse sigmoid function is proposed. The applicability of the proposed function has been confirmed by experimental studies. [ABSTRACT FROM AUTHOR]

Utilization of phenol-containing pyrolysis water (PW) formed as the by-product of biomass pyrolysis is challenging issue due to large number of various organic substances in its composition. Combustion of PW as part of coal-water fuel (CWF) is effective, but poorly studied solution, which allows to neutralize all contaminants. Current study is devoted to the ignition and combustion characteristics of CWF droplets with PW and 3 fractions obtained in different temperature ranges—<100, 100–150 and 150–200 °C. The PW was obtained by separation and sedimentation from industrial biochar-producing facility. The waste of coal facility was used as a solid component of CWF. The ignition and combustion of CWF was studied via the combustion chamber in the temperature range 500–800 °C as well as a CWF with distilled water as a reference sample. The use of PW resulted into an increase in CWF reactivity, which was reflected in a reduction in the ignition delay time (up to 50% at 500 °C and up to 90% at 800 °C) and the minimum ignition temperature (by 6.9% on average). The most prominent effect was observed for CWF with PW fraction obtained in temperature range 150–200 °C, the least—for fraction < 100 °C. The heating value of CWF due to substitution of distilled water on different PW fractions was increased by 0.1–1.4 MJ/kg. According to material and energy balances, the 16.2 wt% of PW should be used for CWF to ensure energy-sufficiency of the pyrolysis facility. Obtained results provide technical background for integration of such technology into pyrolysis technological cycle. [ABSTRACT FROM AUTHOR]

This work presents a review of modern devices for spraying coal–water fuels. The efficiency of their operation was analyzed according to several criteria: the simplicity of their design (A), the fuel channel’s predisposition to clogging (B), durability in terms of the erosive wear of the nozzle channel (C), and dispersion of the jet—the average size of droplets in the jet (D). It was established that, from the point of view of operational efficiency, the most preferred devices for spraying coal–water fuels are those with a quasi-internal mixing of fuel and spraying agents. In combination with refractory or ceramic materials and the large diameter of the fuel channel, its rapid erosion wear and the likelihood of clogging with large particles of coal or agglomerates of viscous coal–water fuel are excluded. At the same time, the possibility of forming a fine-dispersed jet remains. The cooling of the nozzle with an external mixing of fuel and spraying agents during its operation also reduces the rate of erosion wear. Narrowing the fuel channel was proven to be an undesirable solution when creating a coal–water fuel nozzle. This review will be useful for both researchers studying the processes of spraying coal–water fuels and designers involved in the creation of coal–water fuel injectors or the transfer of existing boilers to coal–water fuel.

The relevance of the work is explained by the absence of the results of the heating effect of multicomponent coal-water slurries on rheological properties and characteristics of spraying in the literature.PURPOSE. Efficiency substantiation of thermal preparation of coal-water slurries based on pyrogenetic liquid by the results of experimental studies.METHODS. When solving this problem, the Brookfield RVDV-II+Pro rotary viscometer, general-purpose hydrometers, and the Interferometric Particle Imaging method were used.RESULTS. It was found that when water in coal-water fuel is replaced by a similar amount of pyrogenetic liquid (no more than 25%), the density of the slurry increases by 14% at a temperature of 293 K. Preheating of coal-water slurries to 363 K reduces the increase in the density value to 7%. The experimental results showed that the greatest influence of the thermal preparation of the studied slurries on their dynamic viscosity is characteristic of the temperature range from 293 to 333 K. At such temperatures, a decrease in the viscosity of the fuel is possible by 17-20%. Preheating of slurries before spraying in the temperature range from 293 to 333 K makes it possible to increase jet spraying angle by 21-29% in comparison with two-component coal-water fuel at a temperature of 293 K. Substitution of more than 25% by weight of water with pyrogenetic liquid in coal-water fuel is impractical for the studied grade of coal from the point of view of a significant increase in viscosity. Preheating coal-water fuel before spraying reduces the average droplet size by 5-9%.CONCLUSION. The efficiency of thermal preparation of coal-water slurries based on pyrogenetic liquid by the results of experimental studies of rheological properties and spraying characteristics was substantiated.

Experimental results of the influence of thermal preparation of coal-water slurries on their rheological properties and spraying characteristics are presented. The slurry density was found to increase by 14% at a temperature of 293 K with the substitution of water in coal-water fuel with a similar by weight amount of pyrogenetic water (no more than 25%). Preliminary thermal preparation of coal-water slurries up to 333 K reduces its density by 7%. The experimental results showed that the greatest influence of thermal preparation of the studied slurries on their dynamic viscosity is characteristic of the temperature range from 293 to 323 K. At such temperature values, a decrease in the slurry viscosity is by 17–20% in comparison with two-component coal-water fuel. Preheating of slurries before spraying, in the temperature range from 293 to 333 K, makes it possible to increase the jet spraying angle by 21–29% compared to conventional two-component coal-water fuel at a temperature of 293 K. The velocity of droplets of the investigated coal-water fuels in the range of changes in their initial temperature from 293 to 333 K varies slightly. The difference is no more than 5%. Increase in the pyrogenetic water concentration in coal-water fuel of more than 25% by weight is impractical for lignite due to the dramatic increase in its viscosity. In the studied range of the third component concentration of the slurry, increase in the average size of fuel droplets is about 8%. Preheating of CWF before spraying can significantly reduce the average size of the droplets. The changes are 5–9% in comparison with coal-water slurry at a temperature of 293 K. Thermal preparation of slurries, according to the results of thermal imaging studies of coal-water fuel jet, affects the thermal contour of the jet and the geometry of its temperature zones. [Display omitted] • slurry viscosity was found to increase with PW addition (no more than 25%). • heating such CWS to 323 K reduces the viscosity by 17–20%. • increase in PW concentration more than 25% is impractical for such coal grade. • CWF preheating before spraying can significantly reduce the average size droplets. [ABSTRACT FROM AUTHOR]

This article proposes a method for grinding coal based on the use of the energy of a pulsed shock wave resulting from a spark electric discharge in a liquid. The main purpose of the scientific work is the development of an electric pulse device for producing coal powder, the main component of coal-water fuel. The diameter of the initial coal fraction averaged 3 mm, and the size of the resulting product was 250 μm. To achieve this goal, the dependence of the length of a metal rod electrode (positive electrode) on the length and diameter of its insulation is investigated. Various variants of the shape of the base (bottom) of the device acting as a negative electrode are considered, and an effective variant based on the results of coal grinding is proposed. An experimental electric pulse installation is described, the degree of coal grinding is determined depending on the geometric parameters. The optimal characteristics of the obtained coal powder have been established. [ABSTRACT FROM AUTHOR]

The results have been presented of the theoretical and experimental research of the ignition processes of single drops of coal–water fuel (CWF). Their surface is covered by a water film. The temperature of the environment Tehas also been recorded and the main characteristics of the process — the times of complete evaporation of the water film (tewf)) and the ignition delays (tign). The errors in determining Tehave not exceeded 5%.According to the results of the detailed analysis of the video recordings of the investigated process of ignition, the mathematical models have been developed. They describe the interrelated complex of the thermophysical and thermochemical processes. The approximate analytical solutions of the multistage nonlinear problem of ignition of a coal–water particle have been obtained using the asymptotic procedures.According to the results of the experimental and theoretical studies, it has been established that the thickness of an aqueous film is one of the parameters determining the conditions and characteristics of the CWF ignition. Moreover, under the conditions of the experiments it has been established that the characteristic evaporation time of the near-surface layer can be from 45 to 60% of the total induction period. They depend on the thickness of the film.

The process and equipment have been developed for preparation and burning (at small and medium capacity boiler plants) of slurry coal-water fuel, produced from finely dispersed coal preparation waste (filter cakes) from coal preparation plants of Komsomolets Mine and Named after S. M. Kirov Mine. It was shown that, based on these wastes, it is possible to produce slurry coal-water fuel with solids content of 56-60 %, the required structural and rheological characteristics, and lower heating value of up to 13 MJ/kg. Based on the research findings, detail design was developed for creation of the pilot process complex for processing of waste coal to produce slurry coal-water fuel for burning at boiler plant. Assessment of using the whole volume of the SUEK Kuzbass coal preparation plants waste coal at the nearby Belovskaya SDPP was performed, which showed high economic and environmental efficiency of the proposed project.

Results of experimental studies of pneumomechanical atomization process of slurry fuel with a plasticizer in an aerodynamic simulator of power boiler furnace are presented. Analysis of the current state in the field of research of slurry fuel atomization processes has been conducted. Influence of pressure of slurry fuel and air on the structure of the emerging spray cone have been analyzed. The values of characteristic dimensions of three zones of spray cone have been determined: core, middle and outer zones. Effect of pressure of the sprayed slurry fuel and air on the period of stable spray cone formation and geometric characteristics of the zones has been experimentally confirmed. Ranges of velocities and sizes of droplets in the flow at various pressures have been distinguished. The quantitative values of slurry fuel droplets with different velocities in the process of its pneumatic spraying have been obtained. It has been established that the largest number of particles in the study area have velocities up to 8 m/s; a significant number of droplets (up to 20%) have velocities from 8 to 32 m/s; velocities of 32 m/s and more are typical for 1% of droplets. During the results processing, aerosol particles with a size of 1 micron or less have not been taken into account. The values of We criterion for the respective sizes and velocities of the sprayed fuel droplets have been determined. It has been established that significant part of the droplets undergoes catastrophic crushing, which is characteristic for the values of We numbers from 7800 and higher. The obtained results can be used for mathematical and physical modeling of the process of slurry fuels atomization in the furnaces of power boilers in order to predict the aerodynamic characteristics of the designed and existing units.

Summary Under research, there is a combustion process of multicomponent coal‐water fuel (CWF) that was conducted with mixing ratio of coal, pyrolysis, and technical water. The pyrolysis water was extracted through pyrolysis oil settling, where the oil was obtained from pyrolysis of wood waste. Ignition and combustion of CWF samples were carried out in a combustion chamber at heating medium temperatures (Tg = 600‐1000°C, with an interim step of 50°C). Gas‐phase combustion products were analyzed with a flow‐line gas analyzer. Technical water in CWF composition was replaced with pyrolysis one that was acted to raise the reactive capacity. It resulted in reducing the ignition delay time τi (by an average of 25%) and the minimum ignition temperature Timin (from 440°С to 393°С, reliance on a CWF composition). In addition, increase in flame combustion time was recorded by an average of 20%, as well as dependence on a heating medium temperature and a CWF composition. In the case when a CWF liquid‐phase component was completely replaced with the pyrolysis water, the significant increase in heat value by 2.14 MJ/kg was observed. According to the data of the flow‐line gas analyzer, we concluded that the CWF combustion based on the pyrolysis water was accompanied by less NOx emission (by an average of 22%) but more CO and CO2 amount (by an average of 1.4 and 1.2, respectively). It was found according to the results of the energy balance assessment that application of pyrolysis water in CWF composition leads to a decrease in fuel consumption for heat production by 16.7%. [ABSTRACT FROM AUTHOR]

Summary: For the fuel ignition, the thermal conductivity and heat capacity are the key properties that determine the pre‐ignition behavior of the drop of the fuel. The classic monophase fuels, such as natural gas, liquid propellants, or solid one‐component fuels, have been investigated for a long time; and their thermophysical properties are well known in most of the cases. Composite fuels, which have recently attracted the attention of the researchers, have complex contents. In many cases, composite fuel is a mixture of solid and liquid components in the form of a slurry. Coal‐water fuel and its derivatives with different additives are examples of such type fuels. For those fuels, the thermophysical properties are usually unknown. Nowadays, researchers use simple additivity theory for the calculation of the thermophysical properties of complex fuels for the first approach. Authors of this research believe that the simple additivity approach is not correct and can lead to the wrong results in the case of the numerical research of the ignition and burning processes of such a fuel. In the present research, the thermophysical properties of coal‐water fuel with glycerol additives were experimentally obtained. It was found that the coefficient of thermal conductivity increases with temperature and varies in the range of 0.45 to 0.53 W/(m·K). The heat capacity of the fuel also increases with the temperature and varies from 4.7 to 5.5 kJ/kg·K. The higher the glycerol content, the lower the thermal conductivity and heat capacity of the composite fuel in the investigated temperature range. The results confirm the failure of the approach of the additivity law usage. Neither, thermal conductivity coefficient or heat capacity of the coal‐water fuel with the addition of up to 20% glycerol complies with the additivity law. Differences between real values of the thermophysical properties and calculated ones are more than 30% to 50%. Empirical expressions for calculation of the thermophysical properties of coal‐water fuel with the addition of up to 20% glycerol are presented. [ABSTRACT FROM AUTHOR]

In the article there is considered one of directions of increase of efficiency of use of coal — burning coal-water fuel (CWF). There is developed a physical and mathematical models of the combustion of droplets of CWF with division of the process into a sequence of repetitive stages of evaporation and burning out of the solid phase. The formula for calculating the time of burnout of a single drop of CWF on the basis of the Sreznevsky equation is obtained. The results of calculation of time of burning of a drop depending on a radius of a drop and a moisture content are presented.

Research on the combustion of coal-water fuel has grown significantly in recent years. Many experimental and numerical calculated data are available in the scientific literature. Nowadays, a large number of different models of the combustion of coal-water fuel have been developed for numerical research. However, there is no systematic generalization of all these data in the published results. This article is an attempt to fill the gap in the field of such a generalization. Simple equations are obtained based on a generalization of experimental data on the combustion of coal-water fuel for engineering applications, as well as to verify already existing and new mathematical models being developed. Those equations are basic for calculation of each stage duration of "pure" coal-water fuel (without any additions) combustion parameters in still air; they take into account all metamorphic stages of source coal, the different water content in the range of 25–50% and mineral impurities content (ash) 0.5–60% in the temperature range of the oven medium 550–1000 °C. • Main physics of combustion is described with exponent (power) functions. • Burning time depends on droplet size in exponent with constant degree 1.6 • Usage of fuel ignition temperature allows simplifying empirical equations. • The effect of water, ash, and coal metamorphic stage are multiplicative. [ABSTRACT FROM AUTHOR]

This paper presents the results of the comparative research of combustion specifics of coal-water fuel produced from low-ash and high-ash Ukrainian flame coal. The analysis shows that the effect of the ash content in the coal-water fuel on the duration of the burning of a fuel drop depends on the drop size. The full combustion time of CWF drop based on the low-ash coal can be both less and longer than that of high-ash coal under the identical conditions for different equivalent diameters of the fuel drop. This specific is explained with the domination of different physical factors during the fuel combustion process. The results of this research extend significantly our knowledge of coal-water fuel, allow understanding some issues of its combustion and are important for the design of the specialized energy facility which is used coal-water fuel as an energy source. • Ash content in the coal-water fuel has an ambiguous effect on fuel combustion. • Burning time is the same for different ash content for a critical drop size. • Critical drop size depends on medium temperature of fire box. [ABSTRACT FROM AUTHOR]

The paper describes a theoretical study on the influence of filtration of a mixture of gaseous products of pyrolysis and water vapor on the dynamic of ignition of coal-water fuel particles under conditions of high temperature heating. The developed mathematical model offers simulation of the process of ignition of coal-water fuel droplets under conditions close to the furnace space (characterized by intense radiation-convective heating) in typical boilers. Comparisons of experimental data (found previously) and simulation data on the ignition delay time (tign) demonstrate good compliance. Simulation results show that filtration of water vapor and volatiles is a significant factor (influence up to 40 %) affecting the characteristics and conditions of ignition of coal-water fuel droplets. The higher velocity of the vapor-gas mixture flow through the porous structure of the fuel particle results in a longer ignition delay. The effect of using the "simplified" model of filtration heat transfer on the prognostic estimates of coal-water fuel ignition is analyzed. It is demonstrated that using of rather simple models for filtration heat transfer does not bring any significant errors in calculating the ignition delay time. [ABSTRACT FROM AUTHOR]

Despite all efforts, alternative energy sources cannot meet the growing energy demand of humanity at the moment; and coal keeps its position as an energy source. One the main problem of the coal-water fuel utilizing is to find the balance between its rheological properties, mainly its viscosity, which defines the efficient feeding and atomization of fuel, and combustion efficiency. Fuel viscosity is determined by the fraction of the water phase in fuel. On the other hand, water can influence negatively the combustion process. This paper describes the results of the experimental investigations on the influence of the water phase contents in the coal-water fuel on its combustion efficiency. It was found, that there is an optimal value of the water phase in the coal-water fuel. This optimal value is independent on general combustion parameters like the temperature of the oven medium and source coal metamorphic stage. It characterizes the rational combination of chemical and thermal processes involved in the fuel combustion. The results obtained are new and made a significant contribution to knowledge. They allow changing the viewpoint on the development of the methods for improvement of the utilizing of such type of fuel. • Water phase in the coal-water fuel effects on fuel combustion in controversial manner. • Optimal water share was found in the range of traditional CWF formulations. • Optimal value is independent on coal grade and medium temperature of fire box. • The optimal water share allows getting the best CWF combustion parameters. • Using the optimal water share allows easy improving CWF combustion. [ABSTRACT FROM AUTHOR]

Findings of more efficient energy recovery methods are focused on composite fuels consisting of coal, water, and waste materials. The use of such slurry fuels has enormous environmental benefits due to the potential for waste utilization and low emissions of harmful oxides to the atmosphere during the combustion process. In this study, we report the effect of waste glycerol on the rheological properties of coal-water fuel (CWS). The addition of glycerol to CWS increases the viscosity (from 45.5 to 184.2 mPa·s at a shear rate of 100 rpm) and density (from 1.08 to 1.11 g/cm3) of these suspensions. The utility of choice of the most favorable parameters is equal to 0.85 for both CWS and CWS with added glycerol. Due to the fact that CWS is dosed to heated chamber, its modification with glycerol results in easier nebulization into the combustion chamber, lowering of the solidification temperature and increasing the calorific value of the resulting fuel. During combustion of CWS with glycerol, the amount of SO2 and NOx emitted is reduced by half as compared to the emission of these gases during hard coal combustion. [ABSTRACT FROM AUTHOR]

Abstract The results of the numerical simulation of heat transfer from the combustion products of coal and coal-water fuels (CWF) to the internal environment. The mathematical simulation has been carried out on the sample of the pipe surfaces of the combustion chamber of the boiler unit. The change in the characteristics of heat transfer (change of thermochemical characteristics) in the conditions of formation of the ash deposits have been taken into account. According to the results of the numerical simulation, the comparative analysis of the efficiency of heat transfer has been carried out from the furnace environment to the inside pipe coolant (water, air, or water vapor) from the combustion of coal and coal-water fuels. It has been established that, in the initial period of the boiler unit operation during coal fuel combustion the efficiency of heat transfer from the combustion products of the internal environment is higher than when using CWF. The efficiency of heat transfer in CWF combustion conditions is more at large times (t ≥ 1.5 h) of the boiler unit. According to the results the numerical simulation of the temperature distributions in the system "pipeline environment — pipe wall — a layer of ash — the products of combustion" have been obtained. A significant decrease in heat flux from the combustion products to the inside pipe coolant in the case of coal combustion compared to CWF has been found. It has been proved that this is due primarily to the fact that massive and strong ash deposits are formed during coal combustion. Highlights • A comparative analysis of the efficiency of heat transfer through the deposition of ash from coal combustion and coal-water fuel. • Displaying advantages of coal-water fuel compared to coal. • It was found that the burning of coal as coal-water fuel more efficiently than in the pulverized state. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of the thermal preparation and ignition of a coal-water fuel droplet under intense radiative-convective heating with diffusion of gaseous pyrolysis products of the solid fuel into the ambient gaseous medium. It has been found that gaseous pyrolysis products are ignited at a distance from the heating surface approximately equal to the radius of the droplet, after which the coke of the main fuel layer is ignited. The time between the ignition of volatiles and the coke residue is less than 0.5 s. Comparison of the ignition delays obtained by mathematical modeling and experimentally has shown satisfactory agreement between theoretical and experimental values. [ABSTRACT FROM AUTHOR]

The present study describes the rheological behavior of three types of coal-water slurry in the presence of a dispersant saponin isolated from the fruit of Sapindous Mukorossi. The critical micelle concentrations of the saponin wereas 0.016 and 0.007 g/cc through aqueous extraction and chemical extraction processes, respectively. The rheological characteristics of slurry were measured in the function of coal loadings, pH, saponin concentration, and temperature. The zeta potential of the slurry without additive was found to be 120 mV which exhibited a decreasing trend with the adoption of additives. The static stability of the slurry could be maintained up to a maximum period of 30 days. [ABSTRACT FROM AUTHOR]

The creation of general-purpose combustion chambers and drafting of regulations (unified technologies) which would secure efficient combustion of complex fuel compositions necessitates reliable experimental data concerning the main ignition and combustion characteristics of high-potential oil-water emulsions, coal-water slurries and coal-water slurries containing petrochemicals. In the conducted experiments, we varied the main factors of heating, ignition and combustion processes: properties and concentrations of solid and liquid fuels, the temperature in the model combustion chamber, and initial sizes of fuel droplets. It was established that ignition delay times of oil-water emulsions and coal-water slurries containing petrochemicals based on typical industrial waste can differ 3–4 times. The combustion heat of typical waste industrial oil (collected from power plants after use) makes up 50–90% of the total combustion heat of oil-water emulsions and coal-water slurries containing petrochemicals. The main anthropogenic emission concentrations (sulfur and nitrogen oxides) are 5–6 times higher from burning oil-water emulsions than from burning coal-water slurries containing petrochemicals. We have defined thermal conditions providing close values of the main combustion parameters for oil-water emulsions and fuel slurries. Using two approaches, we have calculated relative efficiency indicators (criteria) of burning high-potential oil-water emulsions, coal-water slurries, and coal-water slurries containing petrochemicals versus coal. These criteria take into account environmental, economic and energy performance. Environmental and energy performance indicators of coal-water slurries containing petrochemicals are 35–90 times higher than those of oil-water emulsions, and 6–16 times higher than those of coal dust fuel. [ABSTRACT FROM AUTHOR]

The results of theoretical studies of the processes of ignition of water-coal fuel droplets based on brown coal, semi-anthracite, anthracite, long-flame and fat coal under the conditions corresponding to the combustion spaces of typical modern boilers are presented. The influence of the degree of metamorphism (structural-molecular transformation of organic matter of coal) and concentration of the organic component of the base fuel (coal) on the conditions of ignition of water-coal fuel particles is analyzed. It is determined that the type and grade of coal have a significant impact on the dynamics of fuel ignition. It was shown that in the case of ignition of coal-water fuel made of mineral coal, the ignition of particles based on semi-anthracite and anthracite is the fastest (by 20%), and ignition of coal-water fuels of fat coal is the slowest. The latter is explained by the lower heat capacity and thermal effect of pyrolysis of this fuel, as well as the relatively high heat conductivity of anthracite coal as compared to fat coal. It has been determined that drops of coal-water fuel made of brown coal ignite substantially (2 times) faster than drops prepared from coal of coal-water particles. This is due to the high content of volatiles in the composition of brown coal.Comparative analysis of the main characteristics of the process: ignition delay times (tign) obtained by mathematical modeling and experiments showed a satisfactory agreement between the theoretical and experimental values of tign. [ABSTRACT FROM AUTHOR]

Summary: Based on the Wender coal model, the processes of brown coal pyrolysis and coal‐water slurry (CWS) gasification were studied by molecular dynamics simulations with the ReaxFF reactive force field. To examine the pyrolysis/gasification process and the initiation mechanism of brown coal and its CWS, some large‐scale reactive systems containing different numbers of brown coal and water were built in this work. A relatively high simulation temperature, which was proven reasonable in other studies, was used to control the simulation within an acceptable period of time. The products and the change of potential energy of the systems were analyzed. The related initial reaction mechanisms and factors were discussed. It was found that the pyrolysis of brown coal began with the rupture of bridge bonds, closely followed by the separation of some functional groups such as carboxyl, methoxyl, and methyl. Then, gas products were generated from the reactions between small intermediate structures. Some mechanisms of CO and H2 generation were discussed in the article. It was observed that temperature significantly enhanced the reactions in the brown coal pyrolysis process and the yields of gas products. For the gasification of CWS, it was observed that the reaction started from the pyrolysis of coal, and then water reacted with the fragments. The effects of temperature and mass fraction were taken into consideration. It was found that gas products were hardly generated and the consumption of water was relatively less at low temperatures and that rising temperature could significantly enhance gas yield and water consumption. There was an inflection point in the curve of water consumption when the temperature is greater than 3000 K. The mass fraction could not affect the gasification process as great as temperature. However, an appropriate amount of water could enhance the yield of gas products and the CWS with 70% mass fraction could provide enough water for H2 and CO generation. Some of the important reactions and intermediate structures agreed with other experimental data from the literature. [ABSTRACT FROM AUTHOR]

Wettability of nonylphenol ethoxylate with four ethylene oxide groups (NP-4) on a subbituminous coal was carried out. As the concentration of NP-4 gradually increases, the contact angle firstly increases and then decreases with maximum contact angle at about critical micelle concentration (CMC) of NP-4. The monolayer adsorption behaviour of NP-4 on the model surface of Hatcher subbituminous coal was investigated by means of molecular dynamics simulations. The surfactant molecules could be detected at the water-coal interface. The water molecules are repelled and stronger hydrophobicity of the coal is obtained in the presence of NP-4, which are consistent with contact angle results at low concentration. The aggregated structure of the surfactant molecules on the coal surface in terms of head group and tail group density profiles along the perpendicular direction shows that the ethoxylate groups of the surfactant are attached at the solid surfaces. The negative interaction energy between NP-4 and the subbituminous coal surface calculated suggests that adsorption process is spontaneous. The self-diffusion coefficients results indicate that the presence of NP-4 causes higher water mobility meaning improving the hydrophobicity of low-rank coal, which is consistent with the experimental results of contact angle. [ABSTRACT FROM AUTHOR]

Promising solutions have been identified that allow to significantly reduce hazardous emissions from combustion by substituting coal with coal-water slurries (CWS) and coal-water slurries containing petrochemicals (CWSP) as combustion fuels. Experiments show that satisfactory environmental indicators can be achieved even using coal and oil processing wastes as main components of CWSP. [ABSTRACT FROM AUTHOR]

Simulation results are presented for thermal treatment and ignition of coal-water fuel drops under conditions of radiative-convective heating. The data demonstrate reasonbble compliance between theory and experiment for the integral parameter of ignition process — the delay time of ignition. The radiative component of heat transfer is significant for parameters and conditions of ignition. The increase in the fuel particle size makes this influence bigger. Prognostic potential was evaluated for differnet models of radiative heat tarnsfer. The delay time of ignition obtained from radiative heat transfer model “grey wall” is in good agreement with experimental data. Meanwhile, the method based on radiation diffusion approximation gives the simulation data for delay time much higher than experimental data. It is confirmed that while the process of inflammation of a coal-water particle, the key impotance belongs not to fuel-oxidizer reactions, but rather to a chain of heat treatment events, such as radiative-convective heating, water evaporation, and thermal decomposition of fuel. [ABSTRACT FROM AUTHOR]

This introductory study presents the analysis of the environmental, economic and energy performance indicators of burning high-potential coal water slurries containing petrochemicals (CWSP) instead of coal, fuel oil, and natural gas at typical thermal power stations (TPS) and a boiler plant. We focus on the most hazardous anthropogenic emissions of coal power industry: sulfur and nitrogen oxides. The research findings show that these emissions may be several times lower if coal and oil processing wastes are mixed with water as compared to the combustion of traditional pulverized coal, even of high grades. The study focuses on wastes, such as filter cakes, oil sludge, waste industrial oils, heavy coal-tar products, resins, etc., that are produced and stored in abundance. Their deep conversion is very rare due to low economic benefit. Effective ways are necessary to recover such industrial wastes. We present the cost assessment of the changes to the heat and power generation technologies that are required from typical power plants for switching from coal, fuel oil and natural gas to CWSPs based on coal and oil processing wastes. The corresponding technological changes pay off after a short time, ranging from several months to several years. The most promising components for CWSP production have been identified, which provide payback within a year. Among these are filter cakes (coal processing wastes), which are produced as a ready-made coal-water slurry fuel (a mixture of flocculants, water, and fine coal dust). These fuels have the least impact on the environment in terms of the emissions of sulfur and nitrogen oxides as well as fly ash. An important conclusion of the study is that using CWSPs based on filter cakes is worthwhile both as the main fuel for thermal power stations and boiler plants and as starting fuel. [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]

Using of coal-water slurries as fuel for heat and power generation is interesting for researchers for a long time. Coal-water fuel (CWF) application has two major aspects of investigation: rheological properties to provide its transportation and atomization; and improvement of fuel combustion parameters. CWF combustion characteristics improvement can be achieved with the help of different physical and chemical methods. Influence of electromagnetic field on the structure and properties of hydrocarbon fuels is known. However, influence of electromagnetic treatment on the combustion parameters of coal-water fuel produced from coal of different metamorphic stages was not investigated before. Experimental investigations of coal-water fuel combustion parameters: ignition time, time-temperature correlations, ignition temperature, maximal temperature of flame and others were performed. Fuels produced from coal of 6 basic metamorphic stages, which cover a wide range from Brown coal to Anthracite, were used for research. Investigations were carried out in two cases: without fuel pre-treatment with an electromagnetic field, and with it. It is shown in the article that electromagnetic pre-treatment of coal-water fuel improves fuel ignition and combustion stability, increases combustion process efficiency and reduces the total time of fuel burning. [ABSTRACT FROM AUTHOR]

Coke-water slurries can be used as biogenic intermediates in conversion of residual biomass into high value fuels such as liquefied petroleum gas or synthetic natural gas. The effect of particle size and shape on the flow behavior of slurries including coke particles obtained from fast pyrolysis was investigated. Particles were shaped in a planetary ball mill and equivalent sphere diameter and circularity were used to characterize size and shape. An increased circularity resulted in a strong decrease in slurry viscosity. Accordingly, a higher mass fraction of particles can be mixed into the slurry, thus, increasing the higher heating value while still preserving good processing properties. [ABSTRACT FROM AUTHOR]

To improve cold gas efficiency of entrained-flow gasification, coal water slurry (CWS) as a fuel must have high heating value at low viscosity. Especially, considering unstable supply of bituminous coal, the preparation of CWS with high coal content from low-rank coal remains a challenging topic. In this study, we report a remarkable improvement in coal content of CWS at low viscosity (1000 cP) through torrefaction of low-rank coal. Compared to dried coal (moisture-free coal), the torrefaction of low-rank coal leads to an improvement in hydrophobic nature of coal surface and a decrease in coal porosity. The moisture readsorption ratio of the torrefied low-rank coal significantly decreases due to its high hydrophobic nature and low porosity. As a result, Kideco coal showed a 6% and 58.7% increase in the coal content and heating value of CWS after torrefaction at 300 °C in comparison to those of CWS made with dried coal. Ultimately, the torrefied coal-based CWS with enhanced coal content and heating value at low viscosity is expected to contribute to an increase in the efficiency of a gasifier and IGCC process. [ABSTRACT FROM AUTHOR]

A technoeconomic analysis of transition from coal to water-coal-organic chemical slurry fuels (WCOSF) prepared from wastes of coal, petroleum, and used oil treatment was made with reference to a typical heat and electric power generating plant. The economic cost associated with transition to WCOSF and possible effects therefrom are evaluated. The studied fuel compositions are classified in terms of ignition and combustion properties, combustion heat, and cost. The specific parameters illustrating the expedience of WCOSF combustion in spite of the required structural and operational variations of heat and power generating blocks are determined. [ABSTRACT FROM AUTHOR]

Usage of the waste-derived fuels is a very promising way for different industrial processes. It can yield both environmental and economic benefits, but for the heat production to be effective, fuel compositions must be prepared in an intelligent way. The combustion heat of such fuels is lower than that of conventional ones, so their improvement and successful application is in our best interests. Our goal was to investigate experimentally the effect of adding a small amount of aluminium powder (particle size ∼ 10 µm) to optimize waste-derived coal-water slurry with waste petrochemicals. We show the optimal metal concentration rate (3 wt%) that provides a significant increase in the maximum combustion temperature (by more than 100°), while keeping the ignition delay time at the appropriate level. Moreover, another mode is possible, when the combustion temperature is almost independent of the temperature inside the combustion chamber. The combustion duration and underburning levels were observed, too. [ABSTRACT FROM AUTHOR]

TAA, a new dispersant for making coal–water slurry (CWS), has been synthesized by grafting copolymerization of oxidized tannic acid (TA) and acrylic acid (AA). 1 H NMR and FTIR tests revealed that TAA has a unique jellyfish-like 3D molecular structure, in agreement with experimental evidences from contact angle and zeta potential measurements. The surfactivity of TAA in aqueous solution was characterized using a surface-tension meter. The rheological properties and static stability of CWS containing 66 wt.% coal with 0.3 wt.% TAA dosage were examined and compared with slurries prepared with two commercial dispersants, i.e. sodium dodecyl sulfate (SDS) and sodium polystyrene sulfonate (PSS). TAA showed excellent slurry-making performance due to its special 3D structure, with polar and non-polar sites in the bottom plane exhibiting affinity to those on the coal particle surfaces to build strong interactions. CWS prepared with TAA showed good stability and favorable rheological properties compared with slurries prepared with SDS and PSS. The present work provides a new approach to the development of high-performance and environmentally friendly S/N-free dispersants from renewable resources. [ABSTRACT FROM AUTHOR]

A technoeconomic analysis of the suitability of using suspended organic coal-water fuels (OCWF) of various component compositions was performed to determine the parameters that illustrate the priority of individual components and of the suspensions as a whole from the point of cost, ignition delay time, minimally adequate oxidizer temperature, combustion duration, and combustion heat of OCWF. The obtained data can be used to optimize the choice of the type and concentration of OCWF components that ensure efficient utilization of this type of fuel. An analysis was made of the feasibility of expanding the raw materials base for development of OCWF combustion technology. [ABSTRACT FROM AUTHOR]

It is extremely important to reveal the adsorption behavior of polycarboxylate (PC) on coal to improve the performance of PC and even enhance its fabrication and preparation. In this work, three kinds of low rank coal with different ratios of oxygen to carbon (O/C) were employed to prepare coal-water slurries and analyze performances. Apparent viscosities of the slurries were tested. The contact angle and adsorption of PC dispersant on coal were measured. It is observed that the viscosity reduction of CWS is dependent on the saturated adsorption of PC on coal. The order of viscosity reduction is same with the hydrophilicity/hydrophobicity of the PC on the coal surfaces, which corresponds well with the ratio of O/C in coal. So the future dispersant should be designed to improve its adsorption on coal according to the ratio of O/C in coal. Moreover, using a Scanning Electron Microscopy-Energy Dispersive Spectrometer, and zeta potential analysis, we demonstrate the morphology of PC dispersant on coal and clarify further the mechanism of the efficient PC dispersant. Extra dosage of the PC will prevent relative movement between coal particles thus increasing the viscosity of CWSs. So, it is quite necessary to control the proper dosage of the PC dispersant on the basis of the adsorption values in the slurry processing. [ABSTRACT FROM AUTHOR]

The results of the experimental and numerical study of the coal–water fuel particles ignition (CWF) have been given, where the thermal properties (thermal conductivity ( λ ), heat capacity ( C ), density ( ρ )) have been calculated using the different mathematical models. The heterogeneity and porosity of the structure of CWF have been taken into account in calculating λ, C and ρ . The influence of the shape, configuration and size of the pores on the thermal characteristics of coal–water fuel has been analyzed. It has been established that the effective thermal conductivity ( λ eff ) is changed when there are the different ways of describing the thermophysical properties. It has been shown that increasing porosity ( m p ) of fuel during thermal decomposition affects λ eff (or leads to the higher values of the effective coefficient of thermal conductivity, or to its decrease). The set of the core processes of heat and mass transfer (thermal conductivity, filtration of water vapor, ignition) has been taken into account when conducting mathematical modeling. It has been carried out with taking into account the intense physicochemical (thermal decomposition of the organic part of the fuel, thermochemical interaction of water vapor and carbon coke) and phase (evaporation of water) transformations together in the WCF particle in the conditions of high temperature heating. According to the results of the mathematical modeling the delay time of ignition of the coal–water fuel particles has been calculated. The “influence” of the ways of describing the thermal characteristics of CWF has been shown, which can be changed in the process of temperature increase on the delay time of ignition. It has been established that even if the maximum possible change of the coefficient of thermal conductivity (depending on the model λ eff ) deviation of the ignition delay time from the average values does not exceed 13%. [ABSTRACT FROM AUTHOR]