Combustion Of Suspensions Research Articles

Distinguishing the vertical air-staging low-NOx function of secondary air for suspension combustion within an industrial-scale coal-fired reversal grate furnace

The numerous coal-fired grate furnaces in China, which were designed to partition primary air on the grate and arrange secondary air in the freeboard for air-staging combustion, suffered from poor burnout and high NOx. However, secondary air was conventionally closed or set at marginal openings in real operations and no investigation was reported to explain why. Upon these off-design secondary-air circumstances, industrial-scale tests and modeling investigations were performed for a 75 t/h coal-fired reversal grate furnace at secondary-air ratios of 0 %, 3 %, 6 %, 10 %, and 16 %, respectively. The primary aims were to (i) uncover its combustion and NOx formation characteristics with varying secondary air and (ii) confirm whether secondary air acted on a real air-staging function in reducing NOx. Flow-field deflection and asymmetric combustion were found in the furnace, with the upward gas entirely deflecting towards the rear side. The front-half furnace was filled with a large but weak recirculation zone without effective combustion, acting on a huge dead zone to waste the furnace-space utilization. With increasing the secondary-air ratio, the upward gas deflection deteriorated continuously. Layer combustion worsened while suspension combustion first strengthened and then weakened. NOx emissions displayed an ascent-to-descent trend. Carbon in slag raised while carbon in fly ash decreased. Among the five case setups, the 0 % setting (i.e., fully closing secondary air) exhibited the lowest NOx emissions and burnout loss. Compared with the habitual 6 % setup, fully closing secondary air not only reduced NOx emissions by 22 % but also improved a little burnout. These trends meant that opening secondary air only strengthened suspension combustion for burning well fly ash while raised both NOx and total burnout loss. Secondary air thus failed to role as an air-staging function in reducing NOx.

Effect of the coal-spreading air on airflow and low-NOx combustion within a 75 t/h coal-fired grate furnace

Coal-fired grate furnaces equipped with coal throwers, which conventionally own a low-NOx combustion framework consisting of (i) the partitioned primary air for the horizontal air staging on the grate and (ii) the coal-spreading air and secondary air for the vertical air staging in the freeboard, actually suffer from poor burnout and apparently high NOx emissions at habitual operations. While comprehensive investigations on the in-furnace airflow, coal combustion, and NOx formation, which are devoted to first explaining and then improving these problems, are absent up to now. In order to unveil the airflow, combustion, and NOx emission characteristics within a 75 t/h coal-fired reverse grate furnace, evaluate its coal-spreading air impact on the low-NOx combustion performance, and determine an appropriate coal-spreading air ratio for improving the furnace performance, both industrial-scale tests and numerical simulations were performed at the coal-spreading air ratios of 2 %, 4 %, 6 %, and 8 %, respectively. The flow-field deflection and asymmetric combustion appeared in the upper furnace, with the upward gas deflecting towards the rear-wall side and the front-half furnace part dominated by a weak recirculation zone without effective combustion. With increasing the coal-spreading air, problems of the flow-field deflection and asymmetric combustion aggravated. The combustion intensity weakened in the layer combustion zone while displayed an increase-to-decrease trend in the suspension combustion zone. In terms of indexes related to the furnace performance, burnout rate decreased continuously, and NOx emissions initially raised but then decreased. A comprehensive consideration of the coal-spreading requirement via air, flow-field symmetry, low-NOx combustion, and burnout suggests that a 2 % coal-spreading air ratio should be preferred, where NOx emissions and burnout loss were gained at 249 mg/m3 (6 % O2) and 5.75 %, respectively. It reduced NOx emissions by 49 % while raised slightly burnout loss, as compared with the corresponding levels of 486 mg/m3 and 5.4 % at the habitual case. These results not only negate the air-staging function of the coal-spreading air but also highlight the novelty of this work.

Potassium release and mitigation by additives in different biomass combustion systems

Deposition formation on heat-exchanging surfaces and corrosion limit the use and efficiency of solid biomass combustion systems. The main influencing factors on these ash-related problems are the potassium content, the form in which the potassium is bound to the fuel matrix, and the temperature in the combustion system. To avoid these deposition problems, choosing the right fuel for a particular combustion system and vice versa is important.In this work, the temperature in fluidized bed, grate firing, and suspension combustion systems is analyzed by using the example of the power plants Altenstadt and Avedøre, as well as a European municipal solid waste incineration plant. Additionally, the temperature-resolved potassium release of ten different biofuels is analyzed in an electrothermal vaporization unit (ETV) connected to an inductively coupled plasma optical emission spectrometer (ICP-OES). The potential of additives to mitigate the potassium release is analyzed by adding kaolin and coal fly ash to miscanthus, torrefied wood, and beechwood.The results show that hardly any potassium is released into the gas phase at the typical temperatures of fluidized bed systems. Most of the potassium release occurs between 1000 °C and 1400 °C, the typical temperature range of grate combustion systems. This shows that reducing the temperature of the fuel on the grate could drastically reduce the potassium release. However, due to the negative effect on the efficiency, other measures, such as using additives for capturing potassium species, are favored. At the temperatures in suspension-fired combustion systems, almost all potassium is released into the gas phase, and additives cannot mitigate the release at these temperatures. Additives can shift the potassium release of miscanthus and torrefied wood while showing no positive effect when mixed with beechwood.All in all, this work enables a quantitative comparison of various biofuels and a rough evaluation of the suitability of a fuel regarding the deposition formation for different combustion systems.

Study of the influence of external heat and mass exchange on the features of combustion and extinction of gas suspensions of carbon particles

In the work, the regularities of the influence of heat and mass exchange of gas suspensions of carbon particles with the external gas environment on the processes of ignition, burning and quenching at different mass concentrations of carbon fuel are studied. A monodisperse gas suspension of carbon particles located in a gas heated to a high temperature, which contains an oxidant, is considered. As a result of the conducted physical and mathematical modeling, the following characteristics of high-temperature processes were determined: induction period, burning time and time of complete transformation of particles, critical parameters of ignition and extinction of particles. The influence on these characteristics of the initial particle diameter, mass concentration and temperature of the surrounding gas was analyzed. It was found that the external heat and mass exchange has a slight effect on the induction period and critical parameters of the ignition of gas suspensions, but it has a sufficiently strong effect on the characteristics of the combustion and extinguishing processes. The existence of an upper limit for fuel concentrations and particle diameters at which complete combustion of gas suspensions is not observed in the absence of external mass transfer is proved. Ranges of mass concentrations were found for which complete conversion of carbon fuel burning in the form of gas suspensions is carried out. It is shown that for open gas suspensions, the range of mass concentrations, where complete transformation of particles is observed, expands to the side of large values. The diameters of the particles characterizing the quenching of gas suspensions, taking into account the external mass transfer, are smaller, as a result of a greater supply of oxygen to the volume of the gas suspension.

Combustion of suspensions of mixed aluminum and silicon carbide in the products of hydrocarbon flames

A stabilized methane/air Bunsen flame is seeded with powder fuel mixtures containing various combinations of spherical, micron-sized aluminum (Valimet H-2 with nominal d50 = 3.5 µm and H-15 with nominal d50 = 20 µm) and silicon carbide (SiC) at different mass ratios over a ∼0-400 g/m3 concentration range. It is observed that in dispersions of only H-2 aluminum, a bright white aluminum flame front forms and couples to the methane-air flame, resulting in a sustained flame speed even at concentrations beyond 400 g/m3. In contrast, dispersions of only H-15 powder decrease flame speed rapidly and cause an open-tipped methane-air flame at concentrations beyond 200 g/m3, similar to inert SiC powder. When blended together into H-2:H-15 1:1 (mass ratio) mixture dispersions, an aluminum flame front forms and couples to the methane-air flame, with a flame speed comparable to unitary H-2 aluminum in contrast to mixtures of H-2:SiC 3:1 which produce no noticeable difference in flame speed from purely inert mixtures of SiC at nearly 200 g/m3. Mixtures of H-2:SiC 3:1 demonstrate an aluminum flame coupling to the methane flame, but with an increased separation between the fronts that was not observed in previous hybrid flames studies. The flame temperatures, flame coupling, and aluminum combustion efficiency behaviors are attributed to the effective amount of slowly reacting or inert solid material in the mixed powder fuels. The behaviors are consistent with a simple hybrid flames model, developed in previous work, where the effectively reduced heat of reaction of the powder fuel is unable to support sufficient heat feedback to the methane-air flame permitting effective secondary flame front formation and flame-coupling. From this understanding, a method for determining the relative energy contribution of a lower reactivity component in a fuel mixture when it is thermally driven by a higher reactivity fuel is demonstrated using the secondary front formation and flame coupling as a benchmark for reaching a certain heat of reaction of the fuel solid mixture. It is estimated that the H-15 component of a H-2:H-15 1:2 mixture contributes to approximately 55% of the thermal energy required to achieve the same behavior as a H-2:SiC 3:1 fuel mixture.

Single-Particle Analysis of Atmospheric Aerosols: Applications of Raman Spectroscopy

Atmospheric aerosols, produced as a consequence of different anthropogenic and natural processes, impart significant control over the global energy budget, climate, and human–environmental health. Their size varies across the nano–micrometer scale. Based on their origin, they may be classified into primary or secondary aerosols. Biomass burning, incomplete combustion of fossil fuels, volcanic eruptions, and traffic-related and wind-driven suspensions contribute to primary aerosol emissions. In contrast, gas-to-particle conversion within the atmosphere leads to secondary particle production. The study of atmospheric aerosols is vital to the field of atmospheric research. The dynamic nature (highly variable concentration composition and size with space and time) of aerosols makes them difficult to investigate. Today, aerosol research involves the application of various spectrometric and spectroscopic techniques. The single-particle analysis of aerosols is yet a challenge. In this review, the merits and demerits of various offline and online techniques used for aerosol research are discussed in a nutshell. Mass spectrometric techniques fail in distinguishing certain species. However, Raman spectroscopy’s emergence for the compositional analysis of aerosols resolves most of the present characterization challenges. This review focuses on Raman spectroscopy applications, the merits of this technique, and its immense scope for the measurement of various types of aerosols and their properties. Surface-enhanced Raman spectroscopy (SERS) has an advantage over conventional micro-Raman spectroscopy (MRS). The review depicts the dominance of SERS, specifically in the context of the measurement of ambient atmospheric aerosols. This review discusses two important components, namely laboratory simulation and ambient aerosol studies.

A Review of Methods, and Analytical and Experimental Studies on the Use of Coal–Water Suspensions

Research in the field of building mathematical models for combustion processes has been ongoing ever since the chemical reactions of combustion were first discovered. The authors of this review have systematized mathematical models of coal–water suspension (CWS) combustion processes, the sequence of analytical and experimental studies, and have also shown the global genesis of the CWS use. In addition, this review touches upon a topic that is inextricably linked with the combustion of CWS, namely their transportation from the place of coal mining to their place of thermal utilization. For developing countries, their own energy independence is in the foreground, as it is the basis for their economic independence and also a means for other sectors of their economy to be protected from the impact of market changes in fuel prices in the future spot world market. The authors of this review explored the possibility of using Kyrgyz brown coal and transporting it through a coal pipeline from a mountainous area to an industrial site for thermal utilization in specialized steam boiler units. As the economic analysis showed, for the conditions of the Republic of Kyrgyzstan, the use of CWS and coal pipelines with rising prices for natural gas is economically justified. The recommendations of the authors are used in scientific reports and methodological recommendations for the energy and mining sectors of the Republic of Kyrgyzstan, how the recommendations can also be applied to similar conditions in the highlands of Russia, China, and India.

Ignition of water-coal fuel droplets during radiative-convective- conductive heating in relation to boilers operating on the technology of circulating fluidized bed

• Inert material significantly accelerates the ignition of a drop of coal-water fuel. • The effect of an inert material is most pronounced at moderate temperatures (Tg = 873 K). • At high oxidizer temperatures, the inert material does not affect the ignition process. • Inert material leads to dispersion of the near-surface layer of the fuel. One of the most promising options for reducing anthropogenic heating of coal-fired power plants on the environment is the use of not homogeneous coal as the main fuel, but coal-water suspensions. But the combustion of coal-water fuels is associated with the solution of the problem of large values of the ignition delay times for such fuels. Therefore, an important task of great practical importance is the selection (or development) of technologies for combustion of coal-water suspensions in the furnaces of steam and coal-water boilers. The article presents the results of experimental studies of the coal-water fuel drops ignition processes. They were carried out in order to establish the temporal characteristics and conditions of ignition under conditions of a flare mode and combustion in a circulating fluidized bed of an inert material. According to the results of experiments, it was found that at moderate temperatures of the environment (T g ≤ 873 K), particles of inert material (sand) accelerate the ignition of coal-water fuel drops. With high-temperature heating, the ignition delay times for these two fuel combustion technologies are identical in relation to the combustion of coal-water fuels prepared from typical (for energy purposes) semi-anthracite and high-volatile A bituminous coal. Colloquium. The energy crisis in autumn 2021 showed the problem of the rapid transition of the world community from traditional thermal energy to the energy of non-traditional renewable energy generators (wind, sun, biomass). It became obvious that in the next few decades, developed countries will be forced to use coal as their main energy source. Therefore, at present, an urgent task is to reduce the concentration of anthropogenic oxides in the flue gases of coal-fired power plants. One of the most promising technological solutions to this problem is the combustion of coal in the composition of coal-water fuel (CWF). But the technologies of combustion of coal-water fuels in the furnaces of steam and hot water boilers have not yet been developed, mainly due to the problem of large values of the ignition delay times for droplets of such fuels. Therefore, furnace devices of the traditional design of the chamber type with flare combustion of CWF have not yet been developed. One of the promising technologies for the combustion of coal-water fuel can be the technology of a circulating fluidized bed of inert material. But the results of studies of the coal-water fuels drops ignition processes under conditions corresponding to combustion devices operating on the technology of a circulating fluidized bed have not yet been published.

Combustion characteristics of aromatic-enriched oil droplets produced by pyrolyzing unrecyclable waste tire rubber

The purpose of this work is to study the combustion characteristics of aromatic-enriched tire pyrolysis oil (TPO) produced from typical small vehicles and truck tires. Pyrolysis oils (NRTO: natural rubber tire oil and SRTO: synthetic rubber tire oil) from two raw radial tire materials were produced and condensed at 25 °C and 130 °C in a three-stage auger pyrolysis reactor under negative pressure. Combustion particularities were acquired using a single-droplet suspension combustion device and evaluated by five different indicators: kinetics, flame shape, burning rates, flame stand-off ratio (FSR) and mass transfer parameters. It was found that TPO was a potential fuel with higher calorific value (40–44 MJ/kg) and lower combustion apparent activation energy (10–40 MJ/mol) than that of bio-oil and solid fuels. Oil produced from synthetic rubber and condensed at 25 °C exhibited higher stable burning rate (1.93 ± 0.03 mm2/s) than that of nature rubber pyrolysis oil. Comparing with traditional fuels, tire oil droplets displayed higher surface local heat transfer coefficient, but the mass transfer number (B ≈ 2.5) and FSR (<3.1) under stable combustion conditions were much lower. The combustion behavior of TPO has partial similarity with unsaturated hydrocarbons and ester biofuels. The reported results support the well-characterized TPO condensates for subsequent atomized combustion in realistic industrial burners.

Detailed measurements of in-furnace gas temperature and species concentration distribution regarding the primary-air distribution mode in a spreader and reversal chain-grate furnace

In order to uncover the coal combustion and NOx formation characteristics of chain-grate furnaces and evaluate the effect of the primary-air distribution mode, industrial-size tests with measurements taken of the overall gas temperature distribution in the furnace height direction and gas components (O2, CO, and NO) in the grate zone in a 35 t/h reversal chain-grate furnace were performed at four primary-air distribution modes of the uniform air mode, front-lean air mode, middle-concentrated air mode, and rear-enhanced air mode. Gas temperature decreased continuously in the furnace height direction while showed an increase-to-decrease trend as the grate proceeded. The high-temperature zones with levels below 1350 °C and a small suspension combustion share in the furnace height direction not only confirmed that the primary NOx formation relied on fuel-NO but also ruled against the availability of air staging along the furnace height for NOx reduction. The uniform air mode achieved the highest levels in both burnout and NOx emissions. The other three setups with a sharp air flux reduction in the former air box, decreased apparently NOx emissions while affected burnout to some extent. The rear-enhanced air mode delayed coal combustion with the largest extent and achieved the lowest NOx emissions but highest carbon in slag. In contrast, the middle-concentrated air mode relying on the highest air flux at the central air boxes for strengthening the primary combustion stage, resulted in both NOx emissions and carbon in slag showing acceptable levels of 493 mg/m3 (at 6% O2) and 9.27%, respectively. NOx emissions were reduced by about 18% and meanwhile carbon in slag raised only a limited extent in comparison to the conventional uniform air mode. Therefore, the middle-concentrated air mode was recommended as the optimal primary-air distribution pattern among the four setups.

Particle formation during suspension combustion of different biomass powders and their fast pyrolysis bio-oils and biochars

The fly ash formation during suspension combustion of five different biomass powders (stem wood, bark, forest residue, willow, and reed canary grass) and the corresponding products from fast pyrolysis (bio-oil and biochar) of the powders was investigated. The fifteen fuels were burned in a drop tube furnace under normal (20 vol-% O2) and oxygen-enriched combustion conditions (40 vol-% and 60 vol-% O2). The trends in the data were used to discuss differences in combustion behavior and devise recommendations for the use of the fuels. There was a general difference in fly ash formation mechanism between the solid fuels (biomass and biochar) and the bio-oil fuels, which was attributed to parts of the ash-forming elements in bio-oil being dissolved in the oil. Oxygen-enrichment did not affect the release of inorganic elements to the gas phase for bio-oil combustion. Since the bio-oils generate lower fly ash during combustion, ~100 times compared to the original biomasses, they should be reserved for combustion technologies demanding fuels with very low ash content, whereas the biochar should be used in large scale combustion facilities with advanced gas cleaning technology operated by teams with experience of handling ash related operational problems.

Comparison of emission concentrations during the combustion of a double hydrate propane-methane at different temperatures in a muffle furnace

In recent years, more and more attention in the world has been paid to the development of environmentally friendly technology for combustion gas hydrates. In this work, experimental studies of the combustion of a propane-methane double gas hydrate at different temperatures in a muffle furnace of 650 °C and 950 °C were performed. The increase in temperature in the muffle furnace allowed to reduce harmful emissions and reduce fuel loss. With increasing temperature, the CO concentration decreases by 2.2-2.5 times, CO2 from 7-8% to 3-4% and NOX changes by 1.2–1.5 times, which is associated with an increase in the reaction rate. Emissions of NOX gases during combustion of coal-water suspensions are many times higher than the obtained values of NOX concentrations of methane-propane gas hydrates.

Spark ignition of a mixture of aluminum and boron powders

The paper presents the results of the numerical solutions of the problem of spark ignition aero suspension mixture of powders of aluminum and boron. The physical and mathematical model of gas suspension combustion is based on the approaches of the mechanics of two-phase reacting media. The solution to the problem is based on the decay algorithm of an arbitrary discontinuity S. K. Godunov. From the solution of the problem, the dependence of the minimum energy of spark ignition on the radius, mass concentration and the fraction of aluminum and boron particles in the gas suspension were determined.

Ash Composition in the Combustion of Promising Slurry Fuels

Abstract—Of all the traditional energy sources (coal, natural gas, fuel oil, and petroleum), coal has the greatest environmental impact. Coal combustion at thermal power plants produces copious atmospheric emissions, as well as ash and slag. The discovery of new fuels is a high priority at present. One possibility is the use of industrial wastes. Composite liquid fuels could permit the use of coal-mining, oil-processing, and other wastes, as well as biomass, in the energy cycle. However, too little is known about the ash produced in the combustion of such fuels. In the present work, the ash residue from the combustion of coal suspensions and water-based slurry fuel is analyzed. The ash mass from the combustion of a fixed mass of fuel is calculated, as well as the ash mass produced in the generation of a fixed quantity of energy.

A numerical investigation of NOx concentration at the outlet of a coal-fired chain grate boiler

ABSTRACTA 3D computational fluid dynamic (CFD) simulation is performed on a 35t/h grate boiler to investigate the compound combustion, consisting of grate firing of lump coal on the fire grate and suspension combustion of pulverized coal sprayed in the middle of the stoker. A grate boiler-based low-nitrogen combustion method is proposed in the present study. The influences of this technology on the boiler temperature field and flue gas components as well as NOxare studied by comparing two different combustion modes before and after the transformation. Results show that the compound combustion technology can significantly improve the boiler efficiency and reduce the NOx concentration at the outlet. Therefore, the proposed method may have favorable applications in different industries. It is found that the boiler NOx emission can reach an optimal status, when the pulverized coal feed rate of the burner and the proportion of pulverized coal are set to 20m/s and 20%, respectively. It is observed that when the forward spinning arrangement form is adopted, the emission can be reduced up to 58.08%. The NOx at the outlet of a 35t/h boiler was reduced by 35.71% after retrofitting, which is in consistency with the obtained results.

Analysis of coal suspensions evolution during combustion process

PurposeThe paper aims to undertake coal–water suspension combustion, in air and in fluidised bed conditions. Fluidised bed conditions are the best to efficiently and ecologically use fuel. Combustion technologies using coal–water fuels create a number of new possibilities for organising combustion processes so that they fulfil contemporary requirements. The aim of the process was to show how the specificity of combustion of coal–water suspensions in the fluidised bed changes the kinetics of the process, compared to combustion in the air stream. Changes of the surface and the centre temperature and mass of the coal suspension during combustion, and evolution of fuels during process are presented in the paper.Design/methodology/approachExperimental character of the research required the research stand preparation, as well as working out of the measurements methodology (Kijo-Kleczkowska, 2010). The research stand (Figure 1a) was made of ceramic blocks in which the quartz pipes were put. The heating element of the stand comprised three heating coils of 2.0 kW. Each heater was placed in small quartz tubes. These tubes were built into the quartz tube which was thermally insulated by fibre material Al2O3 and which was covered with steel sheet. Combustion chamber constituted the quartz pipe, which was additionally insulated thermally, to keep the necessary temperature of the entering gas and to reduce the heat loss. The compressed air was transported to the quartz tube through the electro-valve, the control valve and the rotameter. This study stand allowed for the comparison of the combustion process of coal–water suspensions, in air and in fluidised bed conditions. To study in the fluidised bed, quartz sand was used. Depending on the velocity of air inflowing from the bottom of the bed, different bed characteristics were obtained – from bubble – to circulating-beds. The fumes were removed outside by means of a fan fume cupboard. To regulate the temperature inside the combustion chamber, the Lumel microprocessor thermoregulator was applied. The regulator controlled the work of tri-phase Lumel power controller supplying the main heating elements (gas heater) allowing to measure the actual temperature with accuracy of measurements to 20°C. The temperature measurements in the combustion chamber were carried out by means of the thermocouple NiCr-NiAl. To establish the centre and surface temperature and mass of the fuel, a special instrument stalk was constructed (Figure 1b). It had two thermocouples PtRh10-Pt, placed in two thin quartz tubes connected to the scale. One of the thermocouples was located inside the fuel, while the other served as a basket which was to support the fuel. It also touched the surface of the fuel. The thermocouples were connected to the computer to record the experimental results. The essential stage of the preliminary work was to make out a suspension, which was a mixture of fuel dust (hard coal dust or dried coal-sludge dust) and water. To produce the suspension it was necessary to prepare fuel dust after grinding and sifting it, and then adding water, to obtain a suspension moisture of 20, 35 or 50 per cent. The hard coal was applied in the research. The analysis of fuel dust (in air-dry state) is shown in Table I. The testing of the porosity of fuel was made with mercury porosimetry, carried out in the Pascal 440 apparatus, applying pressure from 0.1 to 200 MPa. This method involves the injection of mercury into the pores of the fuel, using high pressures (Kijo-Kleczkowska, 2010).Findings1. Under experimental conditions, during combustion in the fluidised bed, intensive heating of the suspension is observed in the initial stage of the process, followed by the removal of heat from the suspension by the contacting quartz material, leading to lowering of the average fuel temperature and extension of the combustion time, compared to the process carried out in air. 2. Measurements using mercury porosimetry enable the identification of the change of suspension porosity. 3. Devolatilisation and combustion of volatiles lead to an increase in the pores’ size in the fuel and their coalescence. 4. Combustion of fuel leads to the development of cracks in the suspension, and its structure changes under the influence of temperature. Cracks are caused by the formation of thermal stresses inside the fuel. 5. Under experimental conditions, suspension combustion in the fluidised bed causes an increase in volume participation of pores, with larger sizes of pores (3,500-5,000 nm), compared to combustion in the air.Originality/valueThe paper undertakes the evolution of suspension fuel, made of a hard coal and a coal-sludge, during combustion in air and in the fluidised bed.

Morphologic, chemical, and spectral analyses of combustion products of micro- and nano-dispersed particles of aluminium borides

This study presents the findings of an investigation of flame propagation in air suspension of nanodispersed polyboride particles, and provides spectral, morphological, and mass-spectrometric analyses of condensed combustion products generated during an air suspension combustion.

Publisher's Note: “Experimental and numerical study of the characteristics of biomass suspension combustion in a hot-water boiler” [J. Renewable Sustainable Energy 10, 033103 (2017)

Publisher's Note: “Experimental and numerical study of the characteristics of biomass suspension combustion in a hot-water boiler” [J. Renewable Sustainable Energy <b>10</b>, 033103 (2017)

An influence of expressions for thermophysical parameters on calculation results of melting and detonation combustion of aluminum suspensions

The influence of the method for determining the specific heat coefficient on the processes of aluminium melting and propagation of heterogeneous detonation in a mixture of gas and ultrafine aluminum particles is analyzed. Melting process is described within the phenomenological approach for particles with a radius of 6 and 15 nm. An insignificant effect of the relation between the heat capacity and the particle temperature and radius on melting time and temperature distribution inside the particle has been established. The detonation process is studied for stoichiometric suspensions of 50-nm and 1-µm aluminum particles, taking into account the transition from diffusion to kinetic regime of combustion with decreasing particle size. An insignificant influence of the specific heat coefficient representations on the results of detonation structure calculations is established for nanoparticles. For micron aluminum particle suspensions, the 20% difference in the Chapman-Jouguet pressure has been obtained.

Experimental and numerical study of the characteristics of biomass suspension combustion in a hot-water boiler

Biomass powder fuel is an abundant and widely available biomass resource with potential advantages including simple manufacturing process, low energy consumption during processing, high bulk density, convenient storage and transport and high combustion efficiency over other forms of biomass fuels such as bulk, compact block and grain fuels. However, the nature of biomass powder produces a series of issues during combustion including inferior combustion stability, which demands a deep investigation to enhance the energy production and utilization from powder biomass. In this paper, a combined experimental and theoretical study on combustion characteristics is carried out based on a recently developed biomass suspension hot-water boiler with a new design. When the fuel powder concentration is 450 g/m3 and the primary/secondary air ratio is 0.8, the biomass suspension combustion hot-water boiler reaches its optimal condition and the combustion chamber temperature and the thermal efficiency are at their highest levels. The thermal performance of the designed biomass suspension hot-water boiler is tested for the rated condition. Data show that the combustion efficiency and the thermal efficiency reach 97% and 83%, respectively, whereas the harmful gas (CO, SO2, NOx) content in the fumes meet the requirements of the national industrial boiler atmospheric pollutant emission standard in China. The computational fluid dynamics simulation of the temperature field in the furnace shows that combustion of a biomass powder fuel in a pre-combustion chamber and a furnace is not only closely related to the oxygen supply but also related to the airflow ratio and the furnace temperature. The simulated results show that the furnace temperature field, the primary and secondary airflow streamlines, the biomass powder grain movement trajectory and the component field distribution are in agreement with the experimental results. Our findings may help to design an efficient biomass suspension hot-water boiler.