Coal-water Slurry Combustion Research Articles

The composition of an atomized slurry fuel jet

Slurry fuels have become increasingly popular over the last decades. The combustion of coal-water slurries does not only help with waste recovery but also produces heat and electricity. Studying the process of slurry atomization for further combustion is high on the research agenda. It is still disputable whether a homogeneous slurry jet can be produced by a twin-fuel atomizer. With split component feeding, fuel premixing will become unnecessary; component storage and transportation is simplified as well. In this research, the composition of an atomized slurry fuel jet is reliably determined using shadowgraphy and laser-induced fluorescence. The results show that an internal-mixing twin-fluid atomizer produces a homogeneous atomized flow. Conditions have been determined in which a fuel slurry jet is formed with an optimal composition of solid particles and droplets with and without particles. It is established that split component feeding leads to a 13–23 % increase in jet angle, a 1–4° reduction in the jet deviation angle from its original path, as well as a considerable reduction (up to twofold) in the droplet velocity in a jet. The results obtained here can be used to optimize the storage and transportation of fuel components.

Combustion Characteristics of Coal-Water Slurry Droplets in High-Temperature Air with the Addition of Syngas

An experimental study of the ignition and combustion processes of coal-water slurry (CWS) droplets based on coal enrichment waste in a high-temperature oxidizer at 650–850 °C with a syngas addition was carried out. The fuel slurry was a mixture of finely dispersed solid combustible particles (coal sludge, 10–100 µm in size) and water. The syngas was a product of biomass pyrolysis and two waste-derived fuels in a laboratory gasifier. Composition of the syngas was controlled by a precision analytical gas analyzer. The feasibility of co-firing CWS with syngas was experimentally established. Under such conditions, the CWS droplets ignition process was intensified by 15–40%, compared to fuel combustion without the addition of syngas to the combustion chamber. The greatest positive effect was achieved by adding the gas obtained during the biomass pyrolysis. The ignition delay times of CWS droplets are 5.2–12.5 s versus 6.1–20.4 s (lower by 15–39%) when ignited in a high-temperature medium without adding syngas to the combustion chamber. Based on the results obtained, a concept for the practical implementation of the CWS combustion technology in a syngas-modified oxidizer medium is proposed.

Anthropogenic emissions from coal-water slurry combustion: Influence of component composition and registration methods

The flue gas composition is often measured using a combination of techniques that differ in terms of both physical operation principle and type of output. Gas analyzers, FTIR spectrometers, and mass spectrometers are the most popular tools used for this purpose. In this research, we study the composition of the flue gas from the combustion of fuel slurries and dry composite fuels based on industrial and agricultural waste. It has been established that the use of slurry fuels makes the anthropogenic emissions 2–4 times lower than from the combustion of coal slime. For example, the CO2 emissions from the combustion of dry coal slime were 2.5–3.7 times higher than from the combustion of slurry fuels. In addition, the combustion of slurry fuels made it possible to cut down the nitrogen oxide emissions by 1.3–1.5 times and sulfur oxide emissions by 1.3–2.7 times. A comparison of the results obtained using different measurement techniques has shown that differences between the CO and CO2 content in the combustion products measured by a gas analyzer and an FTIR spectrometer did not exceed 20%. The use of FTIR spectroscopy provided new knowledge on the concentrations of hydrocarbons from the combustion of fuels based on promising industrial wastes.

Slagging Characteristics of a Steam Boiler Furnace with Flare Combustion of Solid Fuel When Switching to Composite Slurry Fuel

Two interconnected mathematical models have been developed to describe slagging of a steam boiler furnace at the macro and micro levels. The macro-level model is implemented in Ansys Fluent. Using the fuel characteristics and temperature in the furnace, this model can predict the characteristics of ash formation on heat exchanger tubes when the melting temperature of the mineral part of solid fossil fuel is exceeded. The obtained values of slagging rates are used as initial data in the software implementation of the original Matlab microlevel model. Under conditions of dynamic change in the thickness of the slag layer, this model can evaluate the heat transfer characteristics in the hot gas/slag layer/tube wall/water coolant system. The results showed that switching a coal-fired boiler from a solid fossil fuel to a fuel slurry will improve stability and uninterrupted boiler operation due to a lower slagging rate. The combustion of coal water slurries with petrochemicals compared with coal–water fuel is characterized by higher maximum temperatures in the furnace (13–38% higher) and a lower average growth rate of slag deposits (5% lower), which reduces losses during heat transfer from flue gases to water coolant by 2%.

Composition of a gas and ash mixture formed during the pyrolysis and combustion of coal-water slurries containing petrochemicals

This paper presents the results of experimental research into the component composition of gases and ash residue from the combustion of a set of high-potential coal-water slurries containing petrochemicals. We have established that the use of slurry fuels provides a decrease in the CO2, CH4, SO2, and NOx concentrations as compared to those from coal combustion. The content of carbon monoxide and hydrogen in the gas environment from the combustion of slurries is higher due to the intense water evaporation. It is shown that adding biomass allows a further 5–33% reduction in the emissions of nitrogen and sulfur oxides as compared to the coal-water slurry and the composition with added waste turbine oil and a 23–68% decrease as compared to coal (per unit mass of the fuel burnt). The mechanisms and stages of CO2, SO2, and NOx formation are explained with a view to controlling gaseous anthropogenic emissions and ash buildup. The values of the relative environmental performance indicator are calculated for slurry fuels. It is shown to exceed the same indicator of bituminous coal by 28–56%.

Disposal of fly ash in the production of ash-concrete within the coal-watercoal cluster

Technologies for the disposal of industrial waste in the production of building materials are becoming particularly relevant in connection with the global trend of systematic reduction of the negative anthropogenic impact on the environment. Therefore, one of the goals of the pilot project of the innovative coal-watercoal cluster of housing and communal services is the utilization of ash waste from the combustion of coal-water fuel suspension in the production of building materials. The methodology of ash waste disposal consists in the modification of Portland cement with fine fly ash additives in the production of heavy concrete. As a result of the experiments, the authors proposed a recipe for a concrete mixture with ash waste additives. Tests of control samples of concrete and proposed samples of ash concrete with the addition of ash from the combustion of coal-water slurry were carried out. The brand of the proposed ash concrete in terms of compressive strength, corresponding to the design brand, is determined. Thus, we save the consumption of Portland cement as a binder, which is the most expensive component of concrete. At the same time, we dispose of man-made waste as a safe additive in the production of concrete with specified performance characteristics. The result obtained with the utilization of ash waste as an effective and safe aggregate for heavy concrete can be used in the implementation of a pilot project of an innovative coal-watercoal cluster of housing and communal services. Ash concrete with the addition of ash from the combustion of coal-water slurry can be recommended for use in industrial and civil construction.

Application Research on deep recovery and utilization technology of flue gas waste heat of coal water slurry boiler

Coal water slurry boiler has attracted great attention in the field of urban heat system because of its efficient and clean coal combustion. The coal water slurry contains 35% moisture, which makes the waste heat recovery potential of flue gas greater. After the combustion of coal water slurry, the 100°Cunsaturated flue gas becomes 50°C saturated wet flue gas after Wet Desulfurization Process. The Direct Contact Thermal Storage System and Heat Pump technology are used to realize the deep recovery of low-temperature flue gas. The technology has been successfully applied in the 6×70MW coal water slurry boiler of La Shan Heat Source Company. After 120 days of operation, 393000 GJ of flue gas waste heat is recovered, about 23000 tons of coal water slurry is replaced, and 84000 tons of flue gas condensate is recovered. It has good economic and social utility. It is an effective way to recover and utilize waste heat from flue gas of coal-fired boiler, and has a broad application prospect.

Ignition of coal‐water fuel droplets with addition of isopropyl alcohol

Coal-water fuels have been actively studied in the last decade due to the fact that when they are burned in the furnaces of steam and hot-water boilers, much less anthropogenic oxides of sulfur, nitrogen, and carbon are formed in comparison with coal. The main problem that hinders the widespread introduction of such fuels in the energy sector is long (up to 30 seconds) ignition delay times. Significant (10%-50%) reduction in the ignition delay time is possible when a small (up to 10%) amount of available and inexpensive liquid combustible organic compounds are added to the suspension. The purpose of the work is to substantiate (from the results of experimental studies) the possibility of significant reduction of the ignition delay times of coal-water fuels by introducing a third component into the suspension—isopropyl alcohol in relatively small (from 3% to 8%) concentrations. According to the results of experimental studies on the ignition process of multicomponent coal-water fuel droplets, based on long-flame coal, with addition of isopropyl alcohol in oxidizer (still air) heated to high temperatures (from 873 to 1273 K), with recording the processes of heating, ignition, and combustion by a high-speed video camera (speed of shooting up to 105 frames per second), the mechanism, characteristics, and conditions of ignition of the researched compositions of quite promising fuels were established. Experiments have shown that the delay time of stable ignition of the studied suspensions based on long-flame coal decreases by 12% to 47% with the increase (from 3% to 8%) of the mass concentration of isopropyl alcohol in the composition of coal-water fuel at the initial characteristic size of droplets from 1.5 to 3.5 mm. Each studied composition was compared with conventional coal-water fuel burned under similar conditions. The influence of mass concentration of isopropyl alcohol in the composition of the coal-water fuel on the characteristics of the initiation of ignition and combustion processes, established in the experiments, proves the possibility of effective an application of such three-component suspensions in thermal power engineering. The possibility of formation of a significantly larger quantity (about 80%) of small droplets (250-400 μm) in the flow during atomization of coal-water fuel with addition of isopropyl alcohol in comparison with the usual coal-water suspension was experimentally proved. The results are of significant practical importance because they illustrate the possibility of achieving optimum conditions for ignition and combustion of promising multi-component coal-water slurries with the addition of alcohol in the furnaces of boiler plants of large- and small-scale power engineering.

Micro-explosive droplet fragmentation of environmentally promising coal-water slurries containing petrochemicals

The findings of experimental research into the environmental and energy performance indicators characterizing the combustion of promising coal-water slurries based on the coal processing waste (filter cake), rapeseed oil, and water are presented. The relative environmental, economic, and energy characteristics of their combustion are compared with those of coal. The most promising composition in terms of environmental characteristics and relative indicators is based on 90% of filter cake N (wet) and 10% of rapeseed oil. A composition is also identified that sustainably undergoes the intense micro-explosive fragmentation: it is based on 9% of filter cake N (dry), 10% of water, and 81% of rapeseed oil. The micro-explosive fragmentation of the parent drop provides a significant increase in the slurry surface area. This increases the heat release per unit time due to fuel burnout. We establish the regimes, threshold conditions, and outcomes of droplet micro-dispersion with varying temperature in a wide range (200–1100 °C) typical of the so-called low-temperature fuel combustion. This regime is generally considered the most environmentally friendly, i.e., producing the least anthropogenic emissions. Using the research findings, we calculate the size distributions of child droplets, the ratios of their average size to the original size of the parent droplet, the evaporation surface areas, and the external surface area of the resulting aerosol cloud. The combustion of coal-water slurries containing petrochemicals can produce less anthropogenic emissions due to the presence of water in the component composition and through the micro-explosive fragmentation of droplets.

Experimental investigation and demonstration of pilot-scale combustion of oil-water emulsions and coal-water slurry with pronounced water contents at elevated temperatures with the use of pure oxygen

In this study, a high-temperature combustion chamber was fueled with oil-water-emulsions (OWE) and coal-water-slurry (CWS) from pyrolytic carbon black in order to experimentally examine the feasibility of co-processing low-calorific value fuels in industrial high-temperature applications by using pure oxygen as oxidizer. The present paper is the first report on the oxy-fuel combustion characteristics of liquid fuels with a pronounced water content including flame characteristics, temperature distribution, thermal output and emission measurements in a semi-industrial combustion chamber at a thermal input of 300 kW and ambient pressure. The obtained results demonstrated the beneficial character of oxy-fuel combustion and showed that co-processing of OWE and CWS from pCB with pronounced water contents is technically feasible. A stable oxy-fuel combustion of OWE was achieved with water contents of up to 75 wt%. In addition, a successful combustion of CWS with a water content of 65 wt% and oxygen concentrations above 50 vol.% was observed. The obtained results further demonstrated the beneficial character of oxy-fuel combustion of OWE and CWS especially with regard to reduced NOx emissions. The combustion of OWE with a water content of 75 wt% resulted in a significant reduction of the NOx concentration compared to pure heating oil, namely from 760 to 110 ppm, whereas the maximum temperature of the combustion chamber decreased only slightly, while in the case of CWS combustion, the concentration of CO emitted decreased significantly from 34 to 9 ppm by increasing the oxygen concentration in the oxidizer from 50 to 100 vol.%.

Experimental studies on coal-water slurry fuel prepared from pretreated low-grade coal

ABSTRACT Low-grade coal is characterized by high ash content and low calorific value. However, gaseous emissions from coal power plants are a serious environmental issue. In this regard, coal-water slurry fuel is a potential substitute for solid fuels used in power plants, which can reduce harmful gaseous emission. In this work, coal-water slurry fuel is prepared from precleaned coal. Prior to its use in the preparation of coal-water slurry, coal was subjected to float and sink followed by froth flotation (pretreatment) to reduce its ash content (from 33.5% to 17.4%). The rheological properties of coal-water slurry were examined and effects of stabilizing agents, dispersion agent, and temperature on viscosity were studied. According to analysis results, increasing concentration of coal increases its viscosity. The viscosity also increases if the particle size of coal decreases. Furthermore, the concentration of stabilizing agent and viscosity of coal-water slurry are directly proportional to each other. Combustion of coal-water slurry was performed under controlled conditions, which showed that the burning efficiency of CWS is fairly larger (around 21% more than that of dry coal), with hydrogen (6% by volume) generated as a by-product.

Experimental researches of the effect of vegetable oil addition on the emissions during combustion of coal liquid fuels

This paper presents the findings of research into combustion of vegetable oils in the composition of coal liquid fuel. The aim of the research was to study the influence of additives of typical vegetable oils (rapeseed, olive, coconut oil, etc.) on concentrations of anthropogenic emissions during combustion of coal water slurries based on coal processing waste. In order to study the effect of different parameters on the emissions efficiency, the tests were done in different operating conditions: muffle furnace temperature, share of oil (up to 15%) in the mixtures, and oil type. The differences between the concentrations of SOx and NOx in the combustion of typical filter cakes (waste coal), as well as those of suspensions with the addition of vegetable impurities have been investigated. It is shown that the concentrations of SOx can be reduced by 5-63% and those of NOx – by 5-62% in comparison with coal liquid fuels based on oil refinery waste. Using the generalizing criterion, the paper illustrates the advantages of adding vegetable oils to enhance the prospects of slurry fuels (even based on coal processing waste) in comparison with coal that is the most dangerous in terms of environmental pollution.

К вопросу о переходе тепловых электрических станций с традиционных топлив на органоводоугольные топливные композиции

Актуальность исследования обусловлена необходимостью эффективной утилизации многочисленных аккумулированных отходов углеобогащения и нефтепереработки в составе водоугольных и органоводоугольных топлив, существенного снижения потребления полезных ископаемых для получения тепловой и электрической энергии, минимизации влияния теплоэнергетики на здоровье населения и состояние природы. Цель исследования: оценка преобразования систем топливоподачи при переходе тепловых электрических станций с твердого, жидкого и газового топлива на органоводоугольные топлива; проведение технико-экономического анализа применения органоводоугольных топлив на ТЭС с учетом основных статей затрат. Объект: тепловая электрическая станция тепловой мощностью 800 Гкал/ч и электрической мощностью 300 МВт, расположенная в Сибирском регионе Российской Федерации. В качестве основных видов топлива используется каменный уголь марки «Д» и природный газ, в качестве растопочного топлива используется мазут. Методы: проведение технико-экономического анализа эффективности перехода тепловой электрической станции с традиционного топлива на органоводоугольные топлива путем расчета следующих затрат: топливные, эксплуатационные, хранение топлива, хранение и утилизация золошлаковых отходов, уплата штрафов и экологические мероприятия, переоборудование системы топливного хозяйства. Результаты. Переход с традиционного твердого топлива (угля) на органоводоугольные суспензии существенно упрощает системы топливных хозяйств ТЭС и котельных, так как для создания таких систем требуется значительно меньшее количество оборудования. При выработке общей установленной мощности всеми угольными электростанциями мира за счет сжигания органоводоугольных топлив экономия одних только топливных затрат может составить от сотен млн р до десятков млрд р в год.

The influence of liquid plant additives on the anthropogenic gas emissions from the combustion of coal-water slurries

At present, coal is considered one of the main components for the production of cheap, high-energy and environmentally attractive slurry fuels. The latter can be produced on the basis of low-grade coal dust or coal processing wastes. Thus, coal-water slurries and coal-water slurries containing petrochemicals are produced. The involvement of coal and oil processing wastes expands the scope of raw materials, reduces the fuel costs from traditional energy sources and modifies the main economic characteristics of power plant performance. However, it also increases the impact of coal-fired thermal power stations on the environment. In the last 30–50 years, many efforts have been made to decrease the negative impact of human industrial activity on climate. Involving plant-based components in the process of energy generation to save energy and material resources looks very promising nowadays. This research studies the influence of adding typical bioliquids (bioethanol, turpentine, glycerol) on the concentration of anthropogenic emissions from coal-water slurry combustion. Relative mass concentrations of bioliquids varied in a small range below 20%. We focused on the concentration of the most hazardous sulfur and nitrogen oxides from the combustion of typical filter cakes, as well as plant-containing slurries. It was established that the concentration of sulfur oxides can be decreased (as compared to coal) by 75%, whereas that of nitrogen oxides by almost 30%. Using a generalizing criteria expression, we illustrated the main benefits of adding bioliquids to slurry fuels in comparison with coal. Adding 20% of glycerol was found to provide maximum advantages.

Anthropogenic Emissions from Combustion of Coal-Water Slurries Containing Petrochemicals Based on Coal and Oil Processing Wastes

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.

Computational modeling of the combustion of coal water slurries containing petrochemicals

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).

Energy efficiency and environmental aspects of the combustion of coal-water slurries with and without petrochemicals

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.

Development of 3D transient wall filming mechanism during combustion by coupling Eulerian-Lagrangian approach and particle-wall interaction model

In the present study, the developments of 3D wall filming mechanism for coal combustion in a small scale furnace under air and oxy-fuel combustion conditions are presented. The principle objective of this study is to develop the film flow behavior and particle deposition characteristics on the furnace refractory wall using a commercial CFD code coupled with some user-defined sub-routines. Eulerian-Lagrangian approach of the gas-particle flow is coupled with the particle-wall interaction mechanisms including particle capturing, entrainment and wall burning sub-models. A case study has been presented to validate the model in a small scale furnace by comparing the available temperature, species data for coal-water slurry combustion and reasonable agreement has been observed. Visualization of the transient film formation and flow characteristics under air and oxy-firing cases are presented. The film thickness deposited on the refractory wall was found to be reasonably in good range with the available data. The deposited film thicknesses for both the conditions are found in the range of 0–1.0mm. The average molten film velocity was 0.0001m/s due to higher viscosity and greater surface tension properties. Slightly higher amount of films are formed in oxy-firing condition due to slower char oxidation rate.

Modelling of CWS combustion process

The paper considers the combustion process of coal water slurry (CWS) drops. The physico-chemical process scheme consisting of several independent parallel-sequential stages is offered. This scheme of drops combustion process is proved by the particle size distribution test and research stereomicroscopic analysis of combustion products. The results of mathematical modelling and optimization of stationary regimes of CWS combustion are provided. During modeling the problem of defining possible equilibrium composition of products, which can be obtained as a result of CWS combustion processes at different temperatures, is solved.

Modelling of slag deposition and flow characteristics of coal combustion under oxy-firing condition in a 550 MW tangentially fired furnace

In this paper, the development of three dimensional slagging combustion model for coal-firing in a 500MW tangentially fired industrial furnace under oxy-fuel condition is presented. The model incorporates the Eulerian-Lagrangian model for the gas-particles flow and the particles-wall interaction sub-model for predicting the deposition and conversion characteristics of char/ash particles. A commercial CFD package coupled with some user-defined functions were used for consideration of char particle combustion and tracking, particle capturing and deposition and other related phenomenons. Validation of the model was achieved by comparing the available slag thickness data for coal-water slurry combustion under oxy-fuel condition in a 5MW small scale furnace. The slag thickness deposited on the furnace wall was found to be in good agreement with the available data. Species distributions such as O2, CO2, H2O, flame temperature distribution and flow dynamics were presented at different heights. Coal particles appeared to be combusted at a relatively higher rate in the near burner region and burn in situ because of enriched O2 concentration. The deposited slag thicknesses on the vertical wall of reaction zone were found in the range of 0–1.0mm. Due to the effect of gravitational force, the molten slag flows downward and velocity was slow (maximum 0.05mm/s) because of higher viscosity and greater surface tension properties. Overall, this study provides an understanding of how the ash/char particles are deposited on the refractory wall and its dynamics in an industrial furnace.