Ash Size Distribution Research Articles

Ash deposition behavior in co-combusting high-alkali coal and bituminous coal in a circulating fluidized bed

High contents of alkali and alkali earth metals (AAEMs) induce severe ash slagging and fouling during coal combustion. In this regard, co-combustion is an effective method to mitigate ash deposition. The ash deposition behavior in co-combusting high-alkali Zhundong (ZD) coal and a bituminous coal, i.e. Shenhua (SH) coal was tested in a 30 kW circulating fluidized bed test system. The results revealed that the condensation of Na2SO4 triggered the slag formation of ZD coal in the furnace. The Na-Ca-Fe eutectics were responsible for the melting or partial melting of slags at high temperatures. After blending SH coal with ZD coal, the volatilization of Na was effectively suppressed, and compacted slags practically disappeared at 20% blending ratio of SH coal. In the convective backpass, fine particles (<10 µm) tended to be deposited on the leeward side of the heating surface because of the eddy impaction. As the blending ratio of SH coal increased, the size distribution of fly ash shifted to a large size range, because of the dilution effect and capture of AAEMs by silicates or aluminosilicates. The minimum blending ratio of SH coal was recommended as 20% to mitigate the ash deposition tendency of ZD coal.

An experimental study on the jet breakup of Bingham plastic slurries in air

The aim of this experimental study is to determine the jet breakup of non-Newtonian, Bingham plastic slurries in air, notably to obtain an experimentally verified formula for the breakup length. The ash-to-water concentration varies between appr. 9% and 57% resulting in Ohnesorge-numbers between 0.0215 and 0.0476. The Bingham plastic fluid discharge from a circular orifice and the jet exit Weber-numbers were varied between 983 and 46866. The Hedström-numbers are between 172 and 235, the Reynolds-numbers were in the range of 906–7169 and the tested Froude-numbers are between 7.06 and 42.13 at standard temperature and ambient pressure. Most of our experiments fall into the second wind-induced regime. A linearly increasing correlation was found for the dimensionless breakup length as a function of We, the Reynolds-, and the Froude-number. The rheology and the particle size distribution of the (fly and bottom) ash were measured and are reported, respectively.

Optimization of fly ash particle size distribution for cementitious systems with high compactness

Compactness is of special importance for aggregates in concrete; however, the particle-size distribution (gradation) of powdery ingredients is commonly disregarded especially for pozzolanic materials such as fly ash. Without good gradation, powdery materials will result in higher void ratios, as in the case of aggregates, and the products obtained after hydration will still have some voids. Using a vacuum sieve, this study found the particle-size distribution of fly ash in accordance with the Dinger–Funk particle-size-distribution modulus, q, and explored the effects of various fly ash particle-size distributions on the compressive and flexural strengths of 7-, 28- and 90-day-old fly ash-blended cement mortars. After defining the optimal size distribution, the mechanical properties of cement mortars were assessed for several fly ash replacement levels. Results reveal that q of 0.4 yields the best mechanical property results. Further, the cement mortar with a 20% fly ash replacement level and a previously optimized particle-size distribution offered improved mechanical properties and high-compactness results over the control cement mortar after 90 days. Experimental results clearly indicate that only by properly adjusting the particle size distribution of fly ash used in the mixtures, better mechanical properties than the control mixtures without any fly ash addition can be achieved at a fly ash replacement ratio of 20%. The findings of current study are believed to greatly contribute to new lines of research on more effective replacement techniques for different pozzolanic materials without risking basic properties expected from cement-based materials.

Influence of Particle Size Distribution of High Calcium Fly Ash on HVFA Mortar Properties

This study evaluates the effect of particle size distribution (PSD) of high calcium fly ash on high volume fly ash (HVFA) mortar characteristics. Four PSD variations of high calcium fly ash used were: unclassified fly ash and fly ash passing sieve No. 200, No. 325 and No. 400, respectively. The fly ash replacement ratio of the cementitious material ranged between 50-70%. The results show that with smaller fly ash particles size and higher levels of fly ash replacement, the workability of the mixture was increased with longer setting time. There was an increase in mortar compressive strength with finer fly ash particle size, compared to those with unclassified ones, with the highest strength was found at those with fly ash passing mesh No. 325. The increase was found due to better compactability of the mixture. Higher fly ash replacement reduced the mortar’s compressive strength, however, the rate was reduced when finer fly ash particles was used.

Effect of chemical additives on hard deposit formation and ash composition in a commercial circulating fluidized bed boiler firing Korean solid recycled fuel

Combustion of SRF (solid recycled fuel) and biomass with potassium (K), sodium (Na), and chlorine (Cl) contents can result in operational problems such as hard deposit formation and convection pass tube corrosion. Two types of commercially available chemical additives, ammonium sulfate [(NH4)2SO4] and borax solution, were examined to elucidate their effect on hard deposit formation and the particle composition of fly ash on the convection pass of a commercial CFBC (circulating fluidized bed combustion) boiler. The addition of ammonium sulfate/borax solution hindered metal chloride formation and reduced the amount of hard deposit formation on the convection pass tubes. Both the alkali and potassium chloride content and the point load hardness of the hard deposit were reduced, while the melting temperature increased according to the borax solution use. When chemical additives were employed, the particle size distribution of the fly ash shifted to coarse particles. In particular, SEM (scanning electron microscopy) images of the fly ash particles revealed the attachments of fine particles to the ash particles. These were assumed to be mineral salts attached to the coarse particles, which increased the overall particle size distribution.

Ash cenosphere fragmentation during pulverised pyrite combustion: Importance of cooling

This paper as the first time in the field reports the direct experimental evidence for demonstrating the important role of cooling in ash cenosphere fragmentation using a simple but unique combustion system. The combustion system used pulverised pyrite (38–45 µm) for combustion in drop-tube furnace under designed conditions (gas temperature: 1000 °C; residence time: 1.2 s), which produced dominantly ash cenosphere particles or fragments. The combustion products were quenched under various cooling conditions (represented by nominal cooling rates of 6400–11,800 °C/s) for sampling. The results show that increasing cooling rate from 6400 to 11,800 °C/s substantially intensifies ash cenosphere fragmentation. Such enhanced ash cenosphere fragmentation leads to a significant shift in the particle size distribution of ash collected in the cyclone (>10 µm) to much smaller sizes. It also produces considerably more particulate matter (PM) with aerodynamic sizes less than 10 µm (i.e., PM10) that consists of dominantly PM with aerodynamic sizes between 1 and 10 µm (i.e., PM1–10) and some PM with aerodynamic sizes less than 1 µm (i.e., PM1). It is further noted that the PM1 is mainly PM with aerodynamic sizes between 0.1 and 1 µm (i.e., PM0.1–1) and to a considerably lesser extent PM with aerodynamic sizes less than 0.1 µm (i.e., PM0.1). Chemical analyses further show that both ash and PM samples contain only Fe2O3, indicating that complete consumption of sulphur and full oxidation of iron have been achieved during pulverised pyrite combustion under the conditions.

Application of digital holographic microscopy and microfluidic chips to the measurement of particle size distribution of fly ash after a wet electrostatic precipitator

In-line digital holographic microscopy is used to obtain a particle size distribution of fly ash after wet electrostatic precipitators. A polydimethylsiloxane microfluidic chip with a cross section of 50 × 200 µm2 is fabricated to offer a suitable experimental environment and constant background. Equivalent Charge Coupled Device pixels are calibrated to be 0.1016 µm, leading a 35.4-times magnification. A sample containing standard particles of 2 µm is first analyzed to confirm the validity and stability of the digital holographic microscopy under flowing condition. The average diameter is reconstructed to be 2.03 µm, leading to a relative standard deviation of 1.5%. Then samples acquired after the wet electrostatic precipitator of a coal power plant is analyzed. Large amounts of holographic pictures are taken and reconstructed to obtain a particle size distribution from 0.5 µm to 3.52 µm. Finally the obtained results are compared with that from a laser particle size analyzer. The acceptable deviation indicates that the method is feasible and accurate to measure fly ash after wet electrostatic precipitators as well as other microparticles.

Particle size distribution of fly ash from co-incineration of bituminous coal with municipal solid waste

One of the source of air pollutants is emission from local coal-fired boiler-houses and domestic heating boilers. The consequence of incineration of municipal waste is the introduction of additional pollutants into the atmosphere, including fly ash. The aim of this work was to evaluate the particle size distribution of fly ash emitted by coal combustion and co-incineration of coal with municipal waste in a domestic 18 kW central heating boiler equipped with an automatic fuel feeder. Mixtures of bituminous coal with different types of solid waste (5, 10 and 15% of mass fraction) were used. Solid waste types consisted of: printed, colored PE caps, fragmented cable trunking, fragmented car gaskets and shredded tires from trucks. During the incineration of a given mixture of municipal waste with bituminous coal, the velocity of exhaust gas was specified, the concentration and mass flow of fly ash were determined together with the physico-chemical parameters of the exhaust gas, the samples of emitted fly ash were taken as the test material. Particle size analysis of fly ash was performed using laser particle sizer Fritch Analysette 22. The PM10 share from all fly ashes from incineration of mixtures was about 100%. Differences were noted between PM2.5 and PM1.

The operational eEMEP model version 10.4 for volcanic SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and ash forecasting

Abstract. This paper presents a new version of the EMEP MSC-W model called eEMEP developed for transportation and dispersion of volcanic emissions, both gases and ash. EMEP MSC-W is usually applied to study problems with air pollution and aerosol transport and requires some adaptation to treat volcanic eruption sources and effluent dispersion. The operational set-up of model simulations in case of a volcanic eruption is described. Important choices have to be made to achieve CPU efficiency so that emergency situations can be tackled in time, answering relevant questions of ash advisory authorities. An efficient model needs to balance the complexity of the model and resolution. We have investigated here a meteorological uncertainty component of the volcanic cloud forecast by using a consistent ensemble meteorological dataset (GLAMEPS forecast) at three resolutions for the case of SO2 emissions from the 2014 Barðarbunga eruption. The low resolution (40 × 40 km) ensemble members show larger agreement in plume position and intensity, suggesting that the ensemble here does not give much added value. To compare the dispersion at different resolutions, we compute the area where the column load of the volcanic tracer, here SO2, is above a certain threshold, varied for testing purposes between 0.25 and 50 Dobson units. The increased numerical diffusion causes a larger area (+34 %) to be covered by the volcanic tracer in the low resolution simulations than in the high resolution ones. The higher resolution (10 × 10 km) ensemble members show higher column loads farther away from the volcanic eruption site in narrower clouds. Cloud positions are more varied between the high resolution members, and the cloud forms resemble the observed clouds more than the low resolution ones. For a volcanic emergency case this means that to obtain quickly results of the transport of volcanic emissions, an individual simulation with our low resolution is sufficient; however, to forecast peak concentrations with more certainty for forecast or scientific analysis purposes, a finer resolution is needed. The model is further developed to simulate ash from highly explosive eruptions. A possibility of increasing the number of vertical layers, achieving finer vertical resolution, as well as a higher model top, is included in the eEMEP version. Ash size distributions may be altered for different volcanic eruptions and assumptions. Since ash particles are larger than typical particles in the standard model, gravitational settling across all vertical layers is included. We attempt finally a specific validation of the simulation of ash and its vertical distribution. Model simulations with and without gravitational settling for the 2010 Eyjafjallajökull eruption are compared to lidar observations over central Europe. The results show that with gravitation the centre of the ash mass can be 1 km lower over central Europe than without gravitation. However, the height variations in the ash layer caused by real weather situations are not captured perfectly well by either of the two simulations, playing down the role of gravitation parameterization imperfections. Both model simulations have on average an ash centre of mass below the observed values. Correlations between the observed and corresponding model centres of mass are higher for the model simulation with gravitational settling for four of the six stations studied here. The inclusion of gravitational settling is suggested to be required for a volcanic ash model.

The relationship between mineral contents, particle matter and bottom ash distribution during pellet combustion: molar balance and chemometric analysis.

This paper aims to identify the correlation between the mineral contents in agropellets and particle matter and bottom ash characteristics during combustion in domestic boilers. Four agrifood residues with higher mineral contents, namely grape marc (GM), tomato waste (TW), exhausted olive mill solid waste (EOMSW) and olive mill wastewater (OMWW), were selected. Then, seven different pellets were produced from pure residues or their mixture and blending with sawdust. The physico-chemical properties of the produced pellets were analysed using different analytical techniques, and a particular attention was paid to their mineral contents. Combustion tests were performed in 12-kW domestic boiler. The particle matter (PM) emission was characterised through the particle number and mass quantification for different particle size. The bottom ash composition and size distribution were also characterised. Molar balance and chemometric analyses were performed to identify the correlation between the mineral contents and PM and bottom ash characteristics. The performed analyses indicate that K, Na, S and Cl are released partially or completely during combustion tests. In contrast, Ca, Mg, Si, P, Al, Fe and Mn are retained in the bottom ash. The chemometric analyses indicate that, in addition to the operating conditions and the pellet ash contents, K and Si concentrations have a significant effect on the PM emissions as well as on the agglomeration of bottom ash.

粒度分布と凝集構造から見た有珠山2000年3月噴火の火山灰(＜特集＞2000年有珠山噴火 (3))

粒度分布と凝集構造から見た有珠山2000年3月噴火の火山灰(＜特集＞2000年有珠山噴火 (3))

C1-06 パーシベルを用いた火山灰の粒度分布測定に関する実験的研究(噴火のダイナミクス,口頭発表)

C1-06 パーシベルを用いた火山灰の粒度分布測定に関する実験的研究(噴火のダイナミクス,口頭発表)

Distribution Characteristics of Heavy Metals in Different Size Fly Ash from a Sewage Sludge Circulating Fluidized Bed Incinerator

Fly ash samples were collected from a sewage sludge incineration power plant in Zhejiang Province, China, where household sludge was mixed with industrial sludge in a ratio of 1:1. A dry-type centrifugal air classifier was used to separate and obtain particles with different sizes. According to the different air flow rates, five size fractions were obtained. The total size distribution of fly ash is described in this paper, and the chemical composition, mineralogical phase, and microstructure of the five fractions of fly ash were detected using X-ray fluorescence spectrometry, X-ray diffractometry, and scanning electron microscopy with energy-dispersive X-ray spectrometry, respectively. The heavy metal content and speciation with various particle sizes were analyzed using a sequential chemical extraction procedure. An integrated evaluation method that considers the type, content, toxicity, and stability of heavy metals was used to evaluate pollutants of the different particle size segments. An attempt was...

Upgraded Mineral Sand Fraction from MSWI Bottom Ash: An Alternative Solution for the Substitution of Natural Aggregates in Concrete Applications

This paper presents the results of an experimental investigation on the substitution of natural sand by municipal solid waste incineration (MSWI) bottom ash in concrete applications in order to preserve non-renewable natural resources and then, reduce the carbon footprint of buildings sector. First of all, physical, chemical and leaching test have been performed on upgraded MSWI bottom ash and the obtained results were compared to natural sand usually used in France in concrete applications. In the second time, a preliminary campaign carried out by utilizing 100% MSWI bottom ash 0-2 mm for the substitution of natural sand in the mortar applications. Physical characterization revealed that grain size distribution and specific gravity of MSWI bottom ash are similar to natural sand identified. However, water absorption content (WAb equal to 7.50%) of bottom ash is higher than natural sand. In order to improve the workability of mixing, a superplasticizer has been used at 0%, 1.5%, 2% and 3% by weight of cement. After 14 days of curing, compressive and flexural strengths were performed on hardened samples. Results showed compressive strength of bottom ash samples ranging from 19.4 MPa (without superplasticizer) to 33.3 MPa (3% of superplasticizer), following a linear trend while flexural strength ranging 4.7 MPa to 5.4 MPa. No health threat has been detected for the MSWI bottom ash 0-2 mm fraction and it was categorized as non-hazardous waste according to European legislation of waste. Study developments are currently oriented towards the analysis of physical, mechanical and thermal properties of concrete containing bottom ash and durability assessment.

Impact of Selected Properties of Raw Material on Quality Features of Granular Fertilizers Obtained from Digestates and ASH Mixtures

Abstract The paper presents the results of research, the objective of which was to determine the impact of particle size distribution and density of digestates and ash on density and tensile strength of granular fertilizer obtained from mixtures of these substrates. Particle size distribution, absolute density, envelope density and porosity of substrates were determined. Granular fertilizers were made of clean substrates and their mixtures. Envelope density of the obtained granulates was within 0.81 - 1.88 g⋅cm-3. The determined compaction degree was within 3.65 - 10.12. While, the compaction index IS of granulates made of mixtures was within 0.5 - 0.55 and was lower in comparison to IS of granulates from digestates (0.6) and ash (0.76).

Relation between leaching characteristics of heavy metals and physical properties of fly ashes from typical municipal solid waste incinerators

ABSTRACTDue to the alkalinity and high concentration of potentially hazardous heavy metals, fly ash from a municipal solid waste (MSW) incinerator is classified as hazardous waste, which should be of particular concern. Physical and chemical characterizations of the contrasted fly ashes were investigated to explore the relation between leaching characteristics of heavy metals and physical properties of fly ashes. The results showed that CaClOH, NaCl, Ca(OH)2, KCl and SiO2 were primary mineral compositions in the MSWI fly ashes, and the particle size distribution of fly ash ranged between 10 μm and 300 μm. The smaller the particle size distribution of fly ash, the larger the BET-specific surface area, which was beneficial to the leaching of heavy metals. As a result of various pores, it easily accumulated heavy metals as well. The leaching tests exhibited a high leachability of heavy metals and the leaching concentration of Pb in almost all of the fly ash samples went far beyond the Standard for Pollution Control on the Landfill Site of Municipal Solid Waste. Thereupon, it is necessary to establish proper disposal systems and management strategies for environmental protection based on the characteristics of MSW incineration (MSWI) fly ash in China.

Initializing HYSPLIT with satellite observations of volcanic ash: A case study of the 2008 Kasatochi eruption

AbstractThe current work focuses on improving volcanic ash forecasts by integrating satellite observations of ash into the Lagrangian transport and dispersion model, HYSPLIT. The accuracy of HYSPLIT output is dependent on the accuracy of the initialization: the initial position, size distribution, and amount of ash as a function of time. Satellite observations from passive infrared, IR, sensors are used both to construct the initialization term and for verification. Space‐based lidar observations are used for further verification. We compare model output produced using different initializations for the 2008 eruption of Kasatochi in the Aleutian Islands. Simple source terms, such as a uniform vertical line or cylindrical source above the vent, are compared to initializations derived from satellite measurements of position, mass loading, effective radius, and height of the downwind ash cloud. Using satellite measurements of column mass loading of ash to constrain the source term produces better long‐term predictions than using an empirical equation relating mass eruption rate and plume height above the vent. Even though some quantities, such as the cloud thickness, must be estimated, initializations which release particles at the position of the observed ash cloud produce model output which is comparable to or better than the model output produced with source terms located above and around the vent. Space‐based lidar data, passive IR retrievals of ash cloud top height, and model output agree well with each other, and all suggest that the Kasatochi ash cloud evolved into a complex three‐dimensional structure.

Effect of particle size of fly ash on the properties of lightweight insulation materials

The paper reports the effects of fly ash particle size on the properties of the lightweight insulation materials. The microstructure and mechanical properties of lightweight insulation materials are separately investigated by SEM (scanning electron micrograph) and tabulate thermal conductivity apparatus methods. In addition, the effects of particle size distribution of fly ash on the properties of lightweight insulation materials is studied by grey incidence analysis. The results show that when the ball milling time increases, the particle size of fly ash decreases and the distribution becomes narrow. At the same time, the polymerization state of fly ash would be depolymerize from high poly structure to low polymeric structure. Moreover, the linear shrinkage, bulk density, compressive strength, acid resistance and thermal conductivity of lightweight insulation materials have also increased, but the apparent porosity decreases. And the studies highlight that when the content of fine fly ash particles increases, the nucleation and growth of mullite is accelerated and the sintering driving force is improved at high temperature, which have a positive effect on improving the physicochemical properties of materials. The particles ranging from 20 to 30μm has a great influence on the linear shrinkage, bulk density, compressive strength, acid resistance rate and thermal conductivity of lightweight insulation materials.

EFFECT OF BALL MILLING OF FLY ASH PARTICLE SIZE ON FOAM STABILIZATION FOR EOR APPLICATIONS

In enhanced oil recovery (EOR), nanoparticles have gained the potential to improve foam stability. In this study, the potential of fly ash to produce stable foam by using shaker was studied. Fly ash nanoparticles were developed by the mechanical treatment using ball mill. Sample to ball ratio of 1 to 10 was applied to investigate the effect of ball milling on particle size distribution of fly ash. The mechanically activated fly ash was mixed at various concentrations (ppm) with the anionic foaming surfactants AOS14-16. Foam stability tests were performed at ambient conditions by making solution through shaker. Stable foams were generated using varies types of fly ash particles. It was observed that the small sized fly ash has more potential towards foam forming ability and foam stability. Therefore, the mechanically activated fly ash resulted in a considerably increased EOR.

Fluidized bed co-combustion of hydrothermally treated paper sludge with two coals of different rank

Fluidized bed co-combustion of raw paper sludge (Raw-PS) and hydrothermally treated paper sludge (HTT-PS) with either low (Lo-Coal) or high reactivity coal (Hi-Coal) was investigated. The paper sludge was treated in a pilot-scale hydrothermal reactor at 197°C and 1.9MPa for 30min. South African bituminous and Thai subbituminous coals were selected as representative of Lo-Coal and Hi-Coal, respectively. A 110-mm bubbling fluidized bed combustor was used in this study. During the steady combustion tests the nominal temperature was 858°C, the fluidization velocity was 0.5m/s, and the excess air was varied as 20%, 40%, and 60%. Both single fuel combustion and co-combustion were tested. Co-combustion tests were conducted by feeding the sludge at mixing ratios of 30% and 50% (mass basis) with coal. The main focus of this study was on NOx emissions and unburned carbon performance. Results showed that at 30% mixing ratio using HTT-PS instead of Raw-PS could reduce NOx emission by 3–6% and 9–17% in the case of Lo-Coal and Hi-Coal, respectively, and the loss of unburned carbon could be decreased by 15–18% and 36–53% for Lo-Coal and Hi-Coal, respectively. The particle size distribution of fly ash of all samples was similar regardless of the excess air variation. On the whole, the hydrothermally treated paper sludge showed better performance for co-combustion with coal and would be a better choice compared to the original raw paper sludge.