Coal-water Mixture Research Articles

Coupled CFD-FEM analysis of the damage causes of the retention bunker: a case study at hard coal mine

Underground coal storage bunkers serve as crucial infrastructural components in the coal mining industry, providing secure and accessible locations for the storage of mined coal. The interaction between stored coal and underground water in coal storage bunkers indeed poses significant challenges due to the unpredictable nature of the resulting coal-water mixture. This phenomenon is particularly prevalent in coal mines operating under water hazards, where groundwater infiltration into storage areas can lead to the formation of coal-water mixtures, altering the physical properties of the stored coal. The interaction between coal and water can result in the formation of coal-water mixtures (hydromixture), which exhibit complex rheological properties. These mixtures may vary in viscosity, density, and particle size distribution, making their behavior difficult to predict. Underground water may exert hydrostatic pressure on the stored coal, influencing its mechanical behavior and compaction properties. Changes in pressure can result in coal compaction or expansion, affecting bunker stability and the integrity of surrounding rock strata. The main goal of the paper was to determine the values of pressure field variations exerted by the flowing hydromixture within underground coal storage bunkers. This objective reflects a critical aspect of understanding the dynamic behavior of coal-water mixtures (hydromixture) under varying conditions, particularly in environments where water hazards pose significant challenges to storage and operational stability. The paper utilized computational fluid dynamics (CFD) methods to examine the changes in pressure within underground coal storage bunkers induced by the flow of coal-water mixtures. The examination of damage to an underground coal storage bunker due to stress distribution was conducted using the finite element method (FEM). This computational technique is widely utilized in engineering and structural analysis to model complex systems and predict the behavior of materials under various loading conditions The results of the CFD numerical simulation were compared with the mathematical models.

Mixture composition and coal size effect on coal water mixture quality

Coal usage as a primary energy source is targeted to continue to increase and replace petroleum as the main energy source. Further processing is required to achieve the standard fuel characteristics, one of which is through a process called Coal Water Mixture (CWM) by adding water and additives to coal to produce fuel with characteristics like heavy oil. This research was conducted to analyze the best composition and size of the coal for CWM processing using variations in coal composition (20 %; 30 %; 40 %; 50 %; and 60 %) and coal particle size (40, 80, and 120 mesh). The parameters studied for each CWM product are product quantity, inherent moisture, density, pH, and calorific value. The results of the initial analysis show that the CWM product with a coal composition of 50 % has characteristics that most closely resemble Heavy Fuel Oil (HFO). CWM product with a coal composition of 50 % with all three variations of coal size was then tested for its calorific value and the respective values ​​were 3476.3153 cal/g; 4025.5551 cal/g; and 4488.4248 cal/g. The resulting product meets the physical characteristics qualifications, but to substitute HFO as fuel, it is necessary to use high quality coal, namely anthracite with a higher calorific value or upgrade the coal raw materials that will be used for the CWM processing.

Experimental and Mathematical Investigation of the Thermophysical Properties of Coal–Water Slurries Based on Lignite

The burning of organic fuel is one of the main factors influencing the greenhouse effect on the climate of the planet. The article examines the influence of the properties of lignite and coal–water slurries on the amount of carbon dioxide molecules formed as a result of chemical reactions. The authors give an overview of the results of other researchers in recent years and give the results of their research and development in the field of burning lignite and coal–water slurries in industrial recycling plants. The authors present the results of experimental studies of the thermophysical properties of coal and a coal–water mixture. The results obtained were compared with the results of calculations using a mathematical model and the results of numerical modeling in Ansys. New methods of approximation of step functions were used for the mathematical model. These methods make it possible to reduce errors in the approximation of the functions of the thermal properties of coal. The proposed methods do not have the disadvantages of traditional decompositions of step functions into Fourier series and can be used in problems of mathematical modeling of a wide class of processes and systems. In particular, when determining the coefficient of kinematic viscosity, ash content, and humidity by the method of approximation of the obtained data, the use of new mathematical methods makes it possible to reduce the error in calculations. In addition, data on numerical modeling of hydraulic transport and combustion processes are provided, and a data validation procedure is carried out. The data convergence shown and their location in the selected band of uncertainties satisfy the requirements for verification of experimental data adopted in the European Union and in the Eurasian Union.

Potential of Coal–Water Slurries as an Alternative Fuel Source during the Transition Period for the Decarbonization of Energy Production: A Review

Coal–water slurry or coal–water mixture (CWS or CWM) is a complex solid–liquid dispersion. Several research works have been done concerning the production and use of CWSs being developed worldwide in several different governmental, industrial and academic facilities. In the present paper, studies on the developments achieved in the past three decades with regard to the field mentioned above are systematically reviewed, with particular regard to several different aspects during the combustion process. The structure and properties of the coal are highlighted, as are the different additives used and their adaptability with different types of coal, where the particle size distributions are of great importance in determining both the slurryability of coal and the rheological behavior of a produced CWS for its intended characteristics. At a time when there is much debate about the end of the age of coal as a primary source of thermal and electrical energy, alternative forms of use that can contribute to the reduction of pollutant emissions, as well as particles, in the atmosphere offer alternatives that may allow us to continue using coal, at least during this transition period until a viable alternative is found. In-depth knowledge of these coal slurries may allow, in the future, the development of similar products produced from fuels derived from biomass, such as charcoal or torrefied biomass.

Prediction Method on the Static Stability of a Coal Water Mixture

To shorten the testing duration on the static stability of a coal water mixture (CWM), the temperature was selected as an acceleration factor and its influence on the static stability of the CWM wa...

Gasification of Coal–Water Compositions by Laser Pulses of Various Intensity

The paper analyzes the processes occurring on the interaction of high-power nanosecond laser pulses with a coal–water mixture prepared from gas-coal waste. It was found that the rate of production of a mixture of CO and H2 sharply increased at a laser radiation intensity higher than 8 J/cm2. This was expressed in a sharp increase in the concentration of the combustible components of synthesis gas (CO, up to 0.57 vol %) and in a noticeable acceleration of the growth of the mass of a gas–aerosol fuel mixture upon the absorption of laser pulses (by 40%). At low pulse energy densities, the generation of a finely dispersed (particle size, 30–70 μm) fuel aerosol was a predominant process. Gasification came into play above the effective ablation threshold when the weight ratio between synthesis gas and the sprayed aerosol reached 1 : 3. Thus, the action of laser pulses makes it possible to convert coal preparation wastes into a highly flammable gas–aerosol fuel mixture.

Influence of surfactants and experimental variables on the viscosity characteristics of coal water mixtures

To improve the fluidity of a coal water mixture (CWM) having lower viscosity and higher solid concentration, the effects of surfactants (five kinds) and experimental variables such as temperature (5-65 °C), pH (1-11), particle size distribution (PSD) on the viscosity characteristics of two different coals (Shenhua and Kideco Coal) were investigated. Relatively economical surfactants were chosen in this study: sulfonated melamine formaldehyde polymer (SMF-30), naphthalene formaldehyde sulfonate (Sikament-NN), naphthalene sulfonate water reducer (NSWR), naphthalene formaldehyde sulfonate (PC-1000) and poly-carboxylate (PC). The SMF-30, an anionic surfactant, revealed the most significant reduction in viscosity of CWM among the five surfactants since the SMF-30 forms electric double layer on the surface of coal, and the repulsive force of this layer surpasses the aggregation of coal particles. In addition, the viscosity of CWM decreased with increasing pH and temperature, in particular, the increase in OH- on the surface of coals by the addition of NaOH caused the increase in the repulsive force between the negatively charged coal particles. Furthermore, the very fine particles (less than 45 μm) of coals should be removed before making CWMs since it revealed the increase in viscosity of CWMs.

Syngas production through gasification of coal water mixture and power generation on dual-fuel diesel engine

In the present study, a syngas was produced by preparing coal water mixtures of two different concentrations and gasifying the coal water mixtures. An entrained-flow gasifier of 1 ton/day scale was used and, after undergoing a purification process, the produced syngas was applied to a modified diesel engine for power generation. As the gasification temperature increased, the carbon conversion and the cold gas efficiency were found to increase. In the composition of the produced syngas, the content of H2 remained constant, that of CO increased, and those of CO2 and CH4 decreased. The carbon conversion increased with equivalence ratio. A maximum cold gas efficiency of 66.1% was found at the equivalence ratio of 0.43. N2 was additionally supplied to verify the gasification characteristics depending on the gas feed flow rate. The optimum feed flow rate was verified at different slurry concentrations and equivalence ratio. The produced syngas was supplied to a modified diesel engine and operated depending on the syngas feed flow rate and the engine operation conditions. The brake thermal efficiency of the engine was constant regardless of the syngas feed flow rate. The diesel engine showed high efficiency despite the mixing of the syngas.

Strategy for technology energy selection to achieve coal value added in PT. Bukit Asam (Persero), Tbk.,

The role of coal in providing national energy has already increased nowadays, and still taking an important subject. Government obligation to support added value is not really encourage industry player to applied technology energy that has been developed widenly in South Africa, China and others developing country. The scope of this research is technology energy for coal diversification, such as Coal Upgrading, Coal Gasification, Coal Liquefaction, Coal Water Mixture, and applied Coal Bed Methane Technology that extract gas methane from the pore of coal. The purpose of this research is to estimate coal resources, quality range and to select technology energy that can be potentially develop in PT. Bukit Asam (Persero), Tbk. Coal Resources and coal quality in each mining licences area becomes the basic strength for developing technology energy as part of SWOT Analysis. Based on the SWOT Analysis from 5 technology energy then the scope limited into 3 highest technology energy that is Coal Gasification, Coal Liquefaction and Coal Bed Methane as the most potential technology energy to develop in PT. Bukit Asam (Persero), Tbk.

Gasification of coal water mixture in an entrained-flow gasifier: Effect of air and oxygen mixing ratio

Entrained-flow gasifiers used in commercial integrated gasification combined cycles are usually oxygen-blown. However, oxygen-blown gasification system is expensive to install and operate due to the equipment involved in oxygen purification and supply. To resolve this issue, this study mixed air and oxygen to perform coal gasification. An entrained-flow gasifier of 1 T/D scale was used with the coal water mixture as feedstock. Gasification was carried out at a temperature range of 970–1220 °C, an equivalence ratio of 0.25–0.62, and an air/O2 ratio of 2.17–9.0. With an increasing gasification temperature, the amount of CO in the syngas increased while CO2 and CH4 decreased. Carbon conversion and cold gas efficiency continued to increase with the gasification temperature. In the equivalence ratio test, cold gas efficiency reached 52.1% at around 0.53 before decreasing under a fixed air flow rate of 90 N m3/h. By performing gasification with a varying air/O2 ratio after fixing the flow rate, the influence of the equivalence ratio was examined. In addition, the influence of the flow rate was observed through changes in the air/O2 ratio of the gasification agent with fixing the equivalence ratio. The maximum carbon conversion and cold gas efficiency were 90.7 and 57.7%, respectively, and the optimal air/O2 ratio fell in the range of 2.86–3.1.

12.石炭-水スラリー(CWM)における石炭風化の影響

12.石炭-水スラリー(CWM)における石炭風化の影響

Flash spray characteristics of a coal-liquid carbon dioxide slurry

Liquid carbon dioxide (LCO2) could potentially be utilized in coal gasification plants for effectively transporting coal particles, replacing conventional carriers such as water (H2O), particularly in wet-fed gasifiers. However, it is essential to understand the atomization behavior of LCO2 leaving an injector nozzle under both coal-free and coalfed conditions. We examined the atomization behavior of a coal-LCO2 slurry during the throttling process. The injector nozzle was mounted downstream of a high-pressure spray system. The effect of upstream pressure on flash atomization and devolatilization behavior was presented. Compared with the coal-LCO2 mixture, the spray pattern of the coal-water mixture was significantly different, since it evidenced a Rayleigh-type breakup mode. This difference indicates that the coal-water slurry did not transport the coal as effectively as the coal-LCO2 slurry.

Combustion process of direct injected water-coal mixture in diesel engine

The paper describes the problem of coal-water mixture combustion process in heavy duty diesel engines in the energetic sector application. In the future due to depletion of crude oil resources we have to foreseen another fuel for application in power plants. Large deposits of coal and lignite in the world enable to utilize these fuels in different thermal machines, especially in internal combustion engines. A carbon powder containing small molecules about 10–20 micrometers dissolved in water is good fuel for applying in large capacity engines in electrical plants. Aqueous emulsion of coal has possibility of good cooling of injectors cooling and has also good lubricity. Initial experimental tests done in the world indicate a higher thermal efficiency of engine fuelled by water coal emulsion than engine fuelled by diesel oil and also gas turbine driven by gas from coal gasification technology. The increased emission of CO2 can be reduced in the plants simply by chemical reduction. The paper explains thermochemical processes taking place in the engines during combustion process. The work parameters results obtained from calculations were compared with those obtained from CI engine fuelled by diesel oil. The paper is a certain challenge for finding a new fuel sources as a competition for crude oil and allows to get acquainted with new engine fuelling technology.

Influence of Particle-Size Distribution and Temperature on Rheological Behavior of Coal Slurry

The rheological behavior of coal-water slurry of Indian coal is studied using rheometer. The effect of particle size, solid concentration, and temperature on the rheology of the coal-water slurry has been investigated. The settlement analysis of various size ranges of coal particles has been carried out. A particle size less than 75 µm is used for analysis of rheological behavior of coal slurry and it is found that the increase in solid concentration caused the increase in apparent viscosity of the coal-water mixture. Also, it is observed that as the solid concentration increases the coal-water mixture converts to a non-Newtonian fluid. The rheological behavior of the slurry is also analyzed by blending the coal samples with mixture of coarse and fine particles, hence making a bimodal particle-size distribution. The slurry having the bimodal particle-size distribution is prepared by blending the fine particles of 53–75 µm with the coarse particles of 106–150 µm or 150–250 µm with various proportions. The optimum fraction obtained in bimodal slurry sample is 30% at which point the apparent viscosity is minimum. The change in the flow behavior of coal slurries are fitted to rheological models and the model parameters are calculated.

Effect of hydrophobicity on viscosity of carbonaceous solid–water slurry

Carbonaceous solid–water slurry rheology is greatly affected by the surface properties of the carbonaceous solids used. Slurriability studies showed that, for the same solids loading, viscosities of highly hydrophobic petcoke and bitumen–water slurries were approximately one order of magnitude higher than the viscosity of non-hydrophobic Illinois #6 (bituminous) coal–water slurry. Apart from slurriability, the hydrophobicity of the carbonaceous solids was found to influence the type of additives used to reduce the viscosity. Selected to reduce viscosity, the addition of non-ionic additive Triton X-405 caused a drastic reduction in petcoke and bitumen–water slurry viscosities, whereas anionic additive ammonium lignosulfonate reduced Illinois #6 coal–water mixture viscosity more effectively. Optimum particle-size distribution was also found to be dependent on the surface properties of the solids. Experimentally determined optimum particle-size distributions were observed to deviate from the theoretical predictions. A deviation of 8% was noted in the case of Illinois #6 coal–water slurry, whereas deviations of 30% were observed in the case of hydrophobic bitumen and petcoke–water slurries. Viscosity predictions of semi-empirical models were compared to experimentally measured viscosities. The predicted viscosities did not match the experimental results, especially at higher solids loading. A thixotropic model taking into account particle aggregation was found to predict viscosity more accurately in the case of these hydrophobic carbonaceous solid–water slurries.

Application of the fractal theory for evaluating effects of coal comminution by waterjet

Comminution of coal to ultrafine sizes by high-pressure waterjet provides a novel method for preparation of coal-water fuels for next generation, near-zero emission electric power generation. The particle size distribution (PSD) of ground coal is a key parameter in the preparation of slurries as it determines the settling behavior of the particles and viscosity of the coal-water mixture. There are several methods available for representation and evaluation of particle size analysis data. However, fractal theory provides a means by which the entire PSD of comminuted materials can be quantified by using of a specific and exact value. In this paper, a volume-based fractal model was deduced to characterize the PSD of the coal which is ground in a specially designed comminution cell. During the size reduction process, the inlet pressures up to 276 MPa were used.

Combustion of black coal in the form of coal-water slurry in low-capacity boilers

The present paper describes the examples of experimental and industrial implementation of technologies of flame-droplet combustion of the coal-water mixture in furnaces above a bed consisting of burning coal and in a swirling-type furnace chamber. For preparing coal-water fuel (CWF), Kuznetsk coals of G and D ranks, as well as tailings of coking coals, were used. The future prospect of both technologies of coal combustion has been shown from both economic and environmental standpoints.

The Preparation of Coal Pitch Slurry with Coking Wastewater

This study explored the feasibility of using coking wastewater and coal pitch powder to make coal pitch wastewater slurry. The medium temperature coal tar pitch powder was prepared by freezing and pulverizing coal tar pitch. The dispersant, JL-C01 medium-breaking emulsifier, had a large adsorption value on the coal pitch surface. At the same time, the Zeta potential on the coal pitch having added dispersant had a big increase. On the basics of that, putting some dispersants and wastewater into the powder under high speed stirring, the coal pitch wastewater slurry was obtained. The slurryability, rheological behavior, and static stability of coal pitch wastewater slurry were investigated at different dispersant dosages and slurry concentrations. The results showed that the apparent viscosity decreased with increasing the shearing rate. The rheological behavior of the slurry exhibited pseudo-plasticity. The biggest slurryability could be up to 70%. When the slurry concentration was 70%, the slurry could be kept for 28 d. At last, considering the test methods for quality of coal water mixture, the combustion analysis of the slurry was carried out and many indexes accorded with the national standard. The low heat value, the ash content, and the volatile matter met the coal water slurry first grade standard, and the sulfur content met the second grade standard.

Investigation on Interaction of Combustion Parameters of Coal-Water Mixtures Used in Fluidized Bed Combustor

Three different Turkish Lignites (İstanbul-Yeniköy, Manisa-Soma, and Muğla-Milas) were prepared in accordance with coal-water mixtures technology to determine the combustion parameters of a laboratory-scale fluidized bed combustor. In this context, the effects of parameters such as Ca/S, mean bed temperature, preheat, air emission, and feed rate were investigated on SO2, NOx, and CO emissions, while the combustion efficiency and the amount of unburned C were also calculated. In the combustion tests, it was observed that the quantity of SO2 in the flue gas is reduced when there is an increase in the Ca/S ratio in the mixtures. A maximum 95% of sulfur can be removed with Ca/S:4. It was observed that when the temperature in the fluidized bed unit increases, NOx emission increases and CO emission decreases. The optimum bed temperature was found to be approximately 900°C. The preheat temperature of the mixture significantly affects combustion and the efficiency is advanced by increasing preheat temperature. It was also determined that the amount of air added to the combustor affects the efficiency of combustion, with larger quantities of air resulting in lower amounts of unburned C in fly ash; however, increases in air quantities result in higher emissions of NOx.

Properties and Developments of Combustion and Gasification of Coal and Char in a CO2-Rich and Recycled Flue Gases Atmosphere by Rapid Heating

Combustion and gasification properties of pulverized coal and char have been investigated experimentally under the conditions of high temperature gradient of order 200°C·s−1by a CO2gas laser beam and CO2-rich atmospheres with 5% and 10% O2. The laser heating makes a more ideal experimental condition compared with previous studies with a TG-DTA, because it is able to minimize effects of coal oxidation and combustion by rapid heating process like radiative heat transfer condition. The experimental results indicated that coal weight reduction ratio to gases followed the Arrhenius equation with increasing coal temperature; further which were increased around 5% with adding H2O in CO2-rich atmosphere. In addition, coal-water mixtures with different water/coal mass ratio were used in order to investigate roles of water vapor in the process of coal gasification and combustion. Furthermore, char-water mixtures with different water/char mass ratio were also measured in order to discuss the generation ratio of CO/CO2, and specified that the source of Hydrocarbons is volatile matter from coal. Moreover, it was confirmed that generations of CO and Hydrocarbons gases are mainly dependent on coal temperature and O2concentration, and they are stimulated at temperature over 1000°C in the CO2-rich atmosphere.