Combustion Of Coal Particles Research Articles

Morphology and elemental composition of individual solid dust particles: From different sources to the atmosphere

This study investigates the morphology and elemental composition of individual solid dust particles from various sources (e.g., thermal power plant, domestic coal combustion, building construction dust, wind-blown dust, Asian dust storm, and road related dust) to the atmosphere under high and low relative humidity (RH) conditions in a coastal city of north China by using high-resolution electron microscopes. The results showed that distinct variations between dust particles from thermal power plant and domestic coal combustion, despite both using coal as fuel. Specifically, 88.6% (by number) of thermal power plant particles were spherical, whereas only 2 out of 347 particles from domestic coal combustion exhibited a spherical shape. Furthermore, domestic coal combustion particles showed a higher proportion of Ca-rich particles compared to those from thermal power plant. The wind-blown dust and Asian dust storm particles were mainly “Si + Al” subtype (52.0% v.s. 75.3%) and Si-dominant subtype (16.4% v.s. 11.7%) particles, which were mainly from crustal sources. However, wind-blown dust contained a higher fraction of Ca-rich (11.6%) and Fe-rich (5.3%) particles than Asian dust. The building construction dust particles primarily consisted of irregular Ca-dominant (39.4%) and “Ca + Si” subtype (29.8%) particles. Road related dust were also mainly Si-rich particles (52.9%), likely from re-suspended soil, along with a notable presence of spherical (8.0%) and Fe-rich particles (19.3%), possibly linked to vehicle emissions and brake wear. Additionally, relative number percentage of Na-rich particles and the average weigh ratios of Na in the atmospheric particles were higher than those from all above-mentioned source samples, suggesting that sea-salt related particles might be an important source of the atmospheric dust at the coastal city. The results indicated that Ca-rich particles were significantly modified by S and NaCl particles might lose Cl through heterogeneous reactions under higher RH.

Combustion in a chamber furnace with a tangentially swirling vortex

Relevance. The need to analyze the furnace processes in boiler units with vertical vortex when arranging pulverized coal combustion with the enhancement of environmental parameters through the installation of tertiary blast nozzles. Despite the carbon-free policy in modern power engineering coal remains one of the main sources of energy, so the reconstruction of boiler units in order to reduce harmful emissions is very relevant. Aim. To study aerodynamics and combustion processes of pulverized coal fuel in the furnace chamber of a boiler unit with a tangential arrangement of burner devices using a combustion scheme with tertiary air blowing. Methods. The Eulerian–Lagrangian approach was applied to numerical study of flow characteristics, heat transfer and combustion in a furnace with a tangential burner arrangement. Also, k-ε model of gas turbulence, particle-turbulence interaction, diffusion model of particle dispersion, P-1 radiation modeling method and pulverized coal particle combustion model based on global particle kinetics and experimental data were used for numerical calculations. Results. Based on numerical calculations and analysis, the dependences of combustion product concentrations, temperature, hydrodynamics at combustion of Kuznetsky coal grade D in the furnace chamber with tangential arrangement of burners for brown coal, as well as at installation of tertiary blast nozzles have been obtained. Insufficient redistribution of air between burners and tertiary nozzles is revealed, as for maintenance of stable twist of vertical vortex and accordingly presence of high values of velocities at the outlet of burner devices it is not possible to increase the portion of tertiary air without reconstruction of burners. It is also established that the volume of the furnace chamber below the burners is poorly involved in heat exchange.

Physicochemical Characterization and Oxidative Potential of Iron-Containing Particles Emitted from Xuanwei Coal Combustion.

Respiratory diseases have been proven to be directly related to air pollutants. Xuanwei, located in South China, has been known to have the highest mortality rate for lung cancer in China because of the air pollutants emitted through local coal combustion. However, the mechanism of lung cancer induced by air pollutants is not clear. Based on the fact that a large number of iron-bearing mineral particles was found in Xuanwei coal combustion particles, the iron-containing particles were hypothesized to play important roles in the pathogenesis of the high incidence rate of lung cancer in this area. In this study, raw coal samples were collected from a coal mine in the Xuanwei area. Size-resolved particles emitted from the raw coal samples were collected using an Anderson high-volume sampler. Mineralogical characterization and an assessment of the oxidative potential of the iron-containing particles were conducted using cutting-edge technologies, and the biological activity of the particles were evaluated via DTT assay. Our data showed that the iron-containing minerals accounted for more than 10% of the measured particles emitted from Xuanwei coal combustion samples. The content analysis of ·OH generated from Xuanwei coal combustion particles showed that ·OH content was dependent on the size of particles in the surrogated lung fluid. The concentration of ·OH increased as the particle size decreased. The DTT assay data further demonstrated that when the mass concentration of dissolved irons increased, the oxidation potential of the particles increased. The highest proportion of divalent iron in the total dissolved iron was found in the submicron particles in low pH solution(pH = 1), which indicated that the oxidative potential induced by submicron particles was stronger than that induced by coarse particles and fine particles. Armed with the above data, the toxicological mechanism of the iron-containing mineral particles can be investigated further.

Investigation of non-uniform characteristics in a 300 MWth circulating fluidized bed with different coal feeding modes

Circulating fluidized bed (CFB) has been practised in many engineering fields, but the non-uniform characteristics deteriorate combustion performance and system control. In this study, the improvement of external-loop and in-furnace non-uniformity of a 300 MWth industrial-scale CFB with multiple cyclones by a dual-side coal feeding mode was numerically quantified. The results show that the pressure is non-uniformly distributed among three external loops, where the pressure in the middle loop seal is lower than that in the corner loop seals by 4.5 %. The pressure gradient positively correlates with the solid holdup. As compared with the traditional single-side coal feeding mode, the dual-side coal feeding mode: (i) promotes the final mixing degree by 11.15 %; (ii) extends the residence time of coal particles by 10.3 %; (iii) reduces the magnitude and fluctuation of the horizontal solid flux by 28.5 % and 77%, respectively; (iv) narrows the temperature range and reduces the mean temperature by 7 °C; (v) enhances the combustion of coal particles by consuming more O2; (vi) decreases the concentrations of SO2 and NO by 3 % and 5 %, respectively. The present study shows the superiority of the dual-side coal feeding mode to the traditional single-side coal feeding mode in the optimization of CFBs in practical industrial processes.

Unsteady Concentration Field of a Reacting Gas in the Vicinity of a Burning Coal Particle

Unsteady Concentration Field of a Reacting Gas in the Vicinity of a Burning Coal Particle

Unsteady concentration field of reacting gas in the vicinity of a burning coal particle

Unsteady concentration field of reacting gas in the vicinity of a burning coal particle

Combustion of Coal and Coal Slime in Steam-Air Environment and in Slurry Form

One of the ways to minimize anthropogenic emissions from coal combustion is to replace conventional schemes used for the introduction of coal dust into the furnaces of power plants through the injection of water-containing fuels. In this research, the three most promising schemes for fuel combustion were implemented: (i) the simultaneous introduction of coal particles and water droplets into the combustion chamber; (ii) steam injection into the fuel particle combustion zone; and (iii) the introduction of coal–water slurries into the furnace. Three methods of supplying water to the combustion zone were evaluated using the multi-criteria decision-making technique. Experimental research was conducted to record a range of process characteristics: the time of the gas-phase and heterogeneous ignition, the time of complete combustion, minimum ignition temperatures, maximum combustion temperatures, the completeness of the fuel burnout and the concentrations of the main gaseous emissions. It has been found that the most favorable scheme for coal particle combustion in water-steam environments is to produce fuel slurries. The cumulative indicator integrating the energy and environmental characteristics is 7–47% higher for slurries than for the other examined schemes for burning coal particles and slime.

Effects of oxygen concentration on devolatilization and combustion behavior of coal particles: A multi-parameter study

The devolatilization and volatile combustion of lignite coal (LC), sub-bituminous coal (SBC) and bituminous coal (BC) with different O2 concentrations (21%-50%) were investigated on a concentrating photothermal experiment platform. The characteristics and mechanism of different coal particle combustion were analyzed by using multiple diagnostics, including Planar Laser Induced Fluorescence (PLIF) of OH radicals and polycyclic aromatic hydrocarbons (PAHs), high-speed cinematography and FT-IR. The results showed that, with increasing O2 concentration, the ignition delay time (tign) of different ranks of coal decreased, which was associated with the increase of OH concentrations during the ignition stage. The good correlation between tign and OH concentration was observed. For the volatile combustion, the OH concentration, volatile release amount and volatile flame duration time (tvol) significantly increased with the increasing of O2 concentration at low O2 concentrations. In the higher O2 concentrations, coals with different PAHs generation amount responded differently on the increasing of O2 concentration. On one hand, for the coals with lower PAHs generation amount, the OH concentration increased with the increasing of O2 concentration, while the tvol was not sensitive to changes of the O2 concentration. On the other hand, for the coals with higher PAHs generation amount, the OH concentration decreased with the increasing of O2 concentration while the tvol increased with the increasing of O2 concentration. It can be concluded that PAHs inhibited the OH generation, and the generation characteristics of OH and PAHs affected the sustained state of volatile combustion. The higher PAHs concentration consumed higher amount of OH during the volatile combustion. Meanwhile, with the increasing of PAHs concentration, the reaction rate of H + O2+M→HO2+M in which PAHs participate was increased, inhibiting the reaction H + O2→OH+O, and the increasing of polymer soot of PAHs will reduce the flame temperature through thermal radiation, which further inhibited the OH formation.

Fully-resolved simulations of volatile combustion and NO[formula omitted] formation from single coal particles in recycled flue gas environments

The interaction of coal particles and recycled/recirculated flue gas (RFG) with elevated temperatures and low levels of oxygen occurs in various pulverised coal combustion scenarios. In this work, the effect of oxygen level and temperature on single coal particle combustion characteristics and NOx formation in N2 diluent is studied by means of fully-resolved particle simulations. Comprehensive gas-phase kinetics are utilised to consider the critical pathways of NOx formation including tar-N. Results show that higher RFG temperatures decrease the time to reach the peaks of temperature and species profiles and increase the corresponding peak values. When decreasing O2, irrespective of the RFG temperature, the fuel release period is prolonged, the volatile combustion time increases and the combustion process becomes overall less intense. The reduction of O2 in RFG results in a significant decrease of NO production, while the reduction of the RFG temperature has a smaller effect. The analysis of the key reactions that contribute to NO production in the region around stoichiometry shows that fuel-NOx is the major contributor. Both NH3 and HCN in fuel-N play a major role, while tar-N only contributes in the case with the lowest temperature and O2 concentration. The classical NOx formation pathways are negligible and the initiation reaction of the Zeldovich mechanism is even reversed, i.e. NO⟶+NN2 is dominant and contributes to NO destruction. The destruction of NO mainly occurs in a rich region close to the particle surface where abundant tar species and their derivatives play a major role for NO destruction via the re-burn mechanism. The prompt mechanism is also active in this region and eventually contributes to NO reduction via production of HCN which is the feed to the re-burn mechanism.

Iron from coal combustion particles dissolves much faster than mineral dust under simulated atmospheric acidic conditions

Abstract. Mineral dust is the largest source of aerosol iron (Fe) to the offshore global ocean, but acidic processing of coal fly ash (CFA) in the atmosphere could be an important source of soluble aerosol Fe. Here, we determined the Fe speciation and dissolution kinetics of CFA from Aberthaw (United Kingdom), Krakow (Poland), and Shandong (China) in solutions which simulate atmospheric acidic processing. In CFA PM10 fractions, 8 %–21.5 % of the total Fe was found to be hematite and goethite (dithionite-extracted Fe), and 2 %–6.5 % was found to be amorphous Fe (ascorbate-extracted Fe), while magnetite (oxalate-extracted Fe) varied from 3 %–22 %. The remaining 50 %–87 % of Fe was associated with other Fe-bearing phases, possibly aluminosilicates. High concentrations of ammonium sulfate ((NH4)2SO4), often found in wet aerosols, increased Fe solubility of CFA up to 7 times at low pH (2–3). The oxalate effect on the Fe dissolution rates at pH 2 varied considerably, depending on the samples, from no impact for Shandong ash to doubled dissolution for Krakow ash. However, this enhancement was suppressed in the presence of high concentrations of (NH4)2SO4. Dissolution of highly reactive (amorphous) Fe was insufficient to explain the high Fe solubility at low pH in CFA, and the modelled dissolution kinetics suggest that other Fe-bearing phases such as magnetite may also dissolve relatively rapidly under acidic conditions. Overall, Fe in CFA dissolved up to 7 times faster than in a Saharan dust precursor sample at pH 2. Based on these laboratory data, we developed a new scheme for the proton- and oxalate-promoted Fe dissolution of CFA, which was implemented into the global atmospheric chemical transport model IMPACT (Integrated Massively Parallel Atmospheric Chemical Transport). The revised model showed a better agreement with observations of Fe solubility in aerosol particles over the Bay of Bengal, due to the initial rapid release of Fe and the suppression of the oxalate-promoted dissolution at low pH. The improved model enabled us to predict sensitivity to a more dynamic range of pH changes, particularly between anthropogenic combustion and biomass burning aerosols.

Experimental Study on Spontaneous Combustion Characteristics of Large Coal Particles after Soaking.

The spontaneous combustion of coal is affected by many factors, among which the influence of water is significant and complicated. To explore the influence of water on the spontaneous combustion characteristics of goaf residual coal, coal samples with similar particle size distributions to those of goaf residual coal were prepared. After the coal samples were immersed in water for 7–21 days and the external flowing water was drained, spontaneous combustion experiments were carried out using a temperature-programmed method. The results showed that soaking in water could promote and inhibit the spontaneous oxidative combustion of large coal particles in different temperature ranges. When the coal temperature was below 50 °C, water immersion had a significant inhibition effect on coal oxidation and spontaneous combustion. When the temperature of coal was 50–110 °C, soaking in water for 7 days could promote the oxidation and spontaneous combustion of coal. However, soaking for 14 and 21 days had a significant inhibition effect in this temperature range. When the coal temperature was higher than 110 °C, water immersion had a significant inhibition effect on the coal. Moreover, a prolonged immersion time significantly enhanced the inhibition effect. When the immersion time was less than 21 days, the spontaneous combustion of large coal particles by short-term soaking was mainly inhibited.

Квазистационарная задача о концентрационном поле реагирующего газа в окрестности горящей угольной частицы

When developing coal deposit, the coal dust is formed. Mixing with the atmosphere of the mine workings, it forms the dust-gas-air mixtures that are prone to chemical reactions in various forms. As a rule, such mixtures are neutralized in the dust source area. However, in the coal mines the danger remains related to the normal combustion turning into the detonation of the coal dust. It can be both in the composition of the dust-gas-air mixture, and in the form of the settled layers suspended in the atmosphere of the workings by a methane explosion. In this case there is a risk of a multiple increase in the explosion power due to the ignition of the coal particles as and when the burning spreads through the working. Coal particles burning is considered as a stationary process. However, under certain conditions it becomes necessary to consider accounting the non-stationarity of its flow. This circumstance significantly complicates the consideration of the burning process. Quasi-stationary problem that considers the change in the concentration fields of the reacting gas around a coal particle at different time intervals is studied in the article. The formulas are obtained for determining the concentrations of the reacting gas in the vicinity of the burning coal particle and on its surface. Based on the law of mass conservation of the substances involved in the burning reaction, the formula was found for calculating the radius of the burning coal particle over time. The formula is also derived for determining the complete burning time of the coal particle. The graphs are constructed concerning the dependences of the coal particle burnout time on the number of its parameters. The concentration fields of the reacting gas around the coal particle at various stages of its burning are revealed.

Effects of Cofiring Coal and Biomass Fuel on the Pulverized Coal Injection Combustion Zone in Blast Furnaces

CO2 emissions are a major contributor to global warming. Biomass combustion is one approach to tackling this issue. Biomass is used with coal combustion in thermal power plants or with blast furnaces (BFs) because it is a carbon-neutral fuel; therefore, biomass provides the advantage of reduced CO2 emissions. To examine the effect of co-firing on pulverized coal injection (PCI) in BFs, two coals of different ranks were blended with the biomass in different proportions, and then their combustion behaviors were examined using a laminar flow reactor (LFR). The PCI combustion primarily functions as a source of heat and CO to supply the upper part of the BF. To create a similar PCI combustion environment, the LFR burner forms a diffusion flat flame with an oxygen concentration of 26% with a flame temperature of ~2000–2250 K at a heating rate of 105 K/s. The combustion characteristics, such as the flame structure, burning coal particle temperature, unburned carbon (UBC), and CO and CO2 emissions were measured to evaluate their effect on PCI combustion. With the increase in the biomass blending ratio, the brightness of the volatile cloud significantly increased, and the particle temperature tended to decrease. The fragmentation phenomenon, which was observed for certain coal samples, decreased with the increase in the biomass blending ratio. In particular, with an increase in the biomass blending ratio, the optimum combustion point occurred, caused by the fragmentation of coal and volatile gas combustion of biomass.

Analysis of the Single Coal Particle Combustion Process under O2/CO2 Atmosphere Based on Spectral Diagnostics Technology: Combination of Spectroscopic Characteristics and Flame Temperature

This work studies the single coal particle combustion process in an O2/CO2 atmosphere based on spectral diagnostics technology in a visual drop tube furnace (VDTF). The chemiluminescence characteristics of OH*, CH*, Na*, and K* in single coal particles at two reaction stages and different oxygen fractions (Xi,O2) are investigated. The results show that both flame temperature and alkali metal spectral intensity increase first and then decrease, and the trend of temperature variation is consistent with that of alkali metal spectral intensity. Meanwhile, with Xi,O2 increases, Na* and K* peak intensities are enhanced because of the improvement in the oxygen flow rate. In the volatile reaction stage, the coal particle shows a typical envelope flame with high soot generation and luminosity. As the reaction time increases from 10 to 30 ms, the flame size increases and the flame temperature increases from 1550 to 1950 K. The spectroscopic results corresponding to the volatile reaction stage show that, as Xi,O2 increases from 30 to 50, the OH* and CH* intensity peaks increase linearly. Moreover, the intensities of the Na* and K* peaks increase by approximately 50.2 and 89.2%, respectively. During the volatile–char reaction stage, the coal particle exhibits a brighter luminous characteristic. As the reaction time increases from 40 to 70 ms, the flame size reduces and the flame temperature decreases from 1900 to 1700 K. The spectroscopic results corresponding to the volatile–char reaction stage indicate that, with the increase in Xi,O2, the positions of the OH* and CH* peaks change little and the intensities of the Na* and K* peaks increase by 21.3 and 75.1%, respectively. Our results prove that the flame temperature and alkali metal atomic emission spectroscopy exhibit the same trends as a function of the reaction time, and the alkali metal atomic emission spectroscopy can be used to characterize the flame temperature.

Temperature and NOx distribution characteristics of coal particles under high-temperature and low-oxygen environments simulating MILD oxy-coal combustion conditions

A diffusion-flamelet-based Hencken burner was used to produce moderate and intense low-oxygen dilution oxy-coal combustion (MILD-OCC) of coal particles under O2/CO2 environments with the coflow temperatures of 1000–1400 K and oxygen concentrations of 2.86–8.75%. The flame temperature distributions were measured by a R-type thermocouple coupled with temperature continuous recorder. The NOx was captured by a self-made air extraction sampling device and measured by UV spectrophotometer. Three influencing factors including fuel-air ratio of methane, secondary air and particle size of pulverized coal on temperature and NOx distributions were experimentally researched. It is found that increasing the fuel-air ratio and the volume of secondary air leads to lower peak temperature, more uniform temperature distribution, lower NOx and stronger NO-reburning effect in flame. To a certain extent, decreasing the particle size of pulverized coal causes lower ignition delay, higher release rate of volatiles and little change in NOx emissions, further reducing the particle size of pulverized coal results in higher NOx in flame. Moreover, the mathematical criterion of MILD-OCC state is deduced based on criterion of MILD coal combustion. The research has important reference value for in-depth understanding of MILD-OCC regime and the generation mechanism of fuel NOx.

Analysis and ways for advancing of mathematical model of pulverized coal ignition and combustion

An analysis of mathematical models of ignition and burning of a single particle and a coal cloud is given. Models which take into account the presence of ash in particles, the influence of the ratio of the amount of coal and primary air (excess coefficient) and the size of coal particles on the ignition process are presented and analyzed. It is shown that simplifications in mathematical models in most cases lead to a loss of accuracy and therefore the results cannot be used for practical purposes. Simulation of complex air supply processes by approximation of uniformity also leads to questionable results. A significant influence on the ignition and combustion of coal particles affects the content and intensity of the release of volatile substances and the chemical reactions that occur in this case. The rate of volatiles yield is proposed to be calculated according to the Arrhenius law, and the activation energy and frequency factor are considered to be those that do not depend on the type of coal, but are determined only by the temperature of the particle. Taking into account heat transfer by radiation and a decrease in the particle diameter during combustion has a positive effect on the results obtained. According to the results, the reactivity and losses with underburning significantly depend on the initial diameter of coal particles. Most models do not take into account the change in temperature inside the particles during heating, ignition and combustion in the apparatus, but there are works that are specifically devoted to the study of temperature fields inside the particles and the influence of the particle shape on the combustion rate. Modeling showed that motion relative to the gas leads to an intensification of heat transfer between the particles and the environment, while the volatile matter yield time decreases at a high ambient gas temperature. A decrease in the rate of combustion chemical reactions is noted with an increase in the concentration of water vapor in the gaseous medium around the particle, i.e. oxygen diffusion is the limiting factor in particle combustion. The most complete and physically correct gas dynamics during combustion is calculated in models where known turbulence models are used, such as the standard k-e model, RNG k-e model, BSL model and SST model. At the end of the article, the concepts for improving the model of ignition and combustion of coal particles are outlined.

Mathematical modeling of the thermochemical processes of sequestration of SOx when burning the particles of the coal and wood mixture

The article presents the results of mathematical modeling of the initial stage of the combustion of wood and coal particles in conditions corresponding to the combustion chambers of boiler units of thermal power plants. A hypothesis is formulated that describes the sequestration of anthropogenic sulfur oxides (SOx) under the conditions of combustion of mixed fuels based on coal and wood as a result of the interaction of water vapors (formed during the evaporation of interporeal and adsorbed biomass moisture) with SOx with the formation of sulfuric (H2SO4) acid vapors. When these vapors of sulfuric acid H2SO4 interact with iron oxides of the mineral part of the coal. To test the formulated hypothesis, a new mathematical model has been developed for the processes of co-ignition and combustion of wood and coal particles under high-temperature heating conditions. The mathematical model of the ignition process developed by the authors differs from the known ones (published in leading international scientific periodicals on the combustion of solid fuels) by a detailed description of a complex of gas-phase and heterogeneous thermochemical reactions occurring both in the boundary layer of fuel particles and in their porous structure. The mathematical model of the combustion process of wood-coal fuel particles developed by the authors is currently the most detailed in describing the thermophysical, thermochemical and aeromechanical processes occurring both in the fuel particles and in their small vicinity. Multistage kinetic schemes for the oxidation of the main volatile components (methane ‒ CH4, carbon monoxide ‒ CO, hydrogen ‒ H2), as well as the formation of sulfur oxides by means of oxidation of hydrogen sulphide (H2S), released as a result of pyrolysis of the organic part of coal, have been adopted. Based on the results of numerical modeling, the possibility of intensifying the processes of sequestration of sulfur oxides by moistening the wood component of the fuel mixture has been established. It is shown that water vapor can act as an agent adsorbing anthropogenic sulfur oxides, transforming the latter into sulfuric acid vapor, respectively. In turn, the vapors H2SO4 and HNO- 3 can be relatively easily captured by means of condensation. It has been established that for effective SOx capture during co-combustion of coal and biomass, the moisture content of the latter must be at least 5% by weight. The research provides grounds for the conclusion about the possibility of environmentally efficient combustion of coal in the composition of wood-coal fuel composites.

Investigation on the OH*and CH* chemiluminescence characteristics of single coal particle flames under O2/CO2 atmosphere

Here, the OH* and CH* chemiluminescence characteristics of a single coal particle flame combustion in a visual drop-tube furnace (VDTF) for different oxygen fraction, Xi,O2, in O2/CO2 atmosphere were investigated using an optical diagnostic technique. The results indicate that the combustion of single coal particles is composed of a volatile reaction stage followed by a volatile-char reaction stage. During volatile reaction stage, the single coal particle burns in an enveloped flame. The flame becomes brighter and the flame length increases gradually. In addition, the OH* and CH* intensity shows peak values with axial distance along the furnace, with that of OH* appearing earlier as the oxygen fraction increases. In the volatile-char reaction stage, the flame length fluctuates slightly, and OH* and CH* peak position are spread over a smaller range of distance. The value of Xi,O2 affects the reaction rate as it promotes the diffusion of oxygen to the interior of coal particle, as the intensity of OH* and CH* increasing rapidly for Xi,O2 > 0.4. This indicates that the rate of reaction is controlled by Xi,O2. Furthermore, the peak intensity ratio of OH* and CH* increases linearly with Xi,O2.

ON SOME ASPECTS OF THE STUDY OF PULVERIZED COAL AND FUEL MIXTURES COMBUSTION IN A DROP TUBE FURNACE

The article considers some aspects of the pulverized fuel combustion modelling in the laboratory on installations called vertical tube furnaces (referred to as drop tube furnaces in scientific periodicals). We have considered the scheme of the installation to study the process of pulverized coal (PС) combustion in conditions similar to the conditions of heating and ignition of coal particles in the blast flow of the blast furnace and their subsequent gasification in the raceway. We have formulated the basic requirements for ensuring the reliability of modelling results. We have examined the methods of combustion completeness (burnout) estimation used in similar studies. We have proposed a convenient method for the estimation of the burnout of two-component fuel mixtures. According to this method, the estimation can be performed for any ratio of components in a two-component fuel mixture with the use of data on the initial ash content in each of them and the relevant burnout. We have obtained the estimated data on the dependence of the burnout of PC (anthracite, lean coal) with fuel additives. It has been shown that the proposed approach can be used to evaluate experimental data regarding the study of the combustion completeness of fuel mixtures. It has been established that for the initial stages of PC combustion (heating, emission and ignition of volatile matters), which occur before the fuel particles enter the blast furnace raceway, the fuel mixtures burnout values recorded in the experiments do not differ significantly from the estimated ones. For the final stages of PC combustion (heating and burnout of char), which occur mainly in the raceway and outside, the combustion completeness determined in laboratory studies was significantly higher than the estimated one. The obtained results confirmed the efficiency in the use of drop tube furnace to model the PC combustion process during the fuel injection with the heated blast flow in the blast furnace raceways and study of the influence of various factors on the combustion process. The results of such studies can be used to improve the design of PC injection units in the blast furnace and to study the possibilities for improving the coal particles combustion completeness and the specific consumption of PC.

Ignition and Combustion of Large Coal Particles in Cold Nitrogen–Oxygen Mixtures

Ignition and Combustion of Large Coal Particles in Cold Nitrogen–Oxygen Mixtures