Compacted Ash Research Articles

Long-term evaluation of palm oil mill effluent (POME) steam reforming over lanthanum-based perovskite oxides

To replace the obsolete ponding system, palm oil mill effluent (POME) steam reforming (SR) over net-acidic LaNiO3 and net-basic LaCoO3 were proposed as the POME primary treatments, with promising H2-rich syngas production. Herein, the long-term evaluation of POME SR was scrutinized with both catalysts under the optimal conditions (600 °C, 0.09 mL POME/min, 0.3 g catalyst, & 74–105 μm catalyst particle size) to examine the catalyst microstructure changes, transient process stability, and final effluent evaluation. Extensive characterization proved the (i) adsorption of POME vapour on catalysts before SR, (ii) deposition of carbon and minerals on spent SR catalysts, and (iii) dominance of coking deactivation over sintering deactivation at 600 °C. Despite its longer run, spent LaCoO3 (50.54 wt%) had similar carbon deposition with spent LaNiO3 (50.44 wt%), concurring with its excellent coke resistance. Spent LaCoO3 (6.12 wt%; large protruding crystals) suffered a harsher mineral deposition than spent LaNiO3 (3.71 wt%; thin film coating), confirming that lower reactivity increased residence time of reactants. Transient syngas evolution of both SR catalysts was relatively steady up to 4 h but perturbed by coking deactivation thereafter. La2O2CO3 acted as an intermediate species that hastened the coke removal via reverse Boudouard reaction upon its decarbonation. La2O2CO3 decarbonation occurred continuously in LaCoO3 system but intermittently in LaNiO3 system. LaNiO3 system only lasted for 13 h as its compact ash blocked the gas flow. LaCoO3 system lasted longer (17 h) with its porous ash, but it eventually failed because KCl crystallites blocked its active sites. Relatively, LaCoO3 system offered greater net H2 production (72.78%) and POME treatment volume (30.77%) than LaNiO3 system. SR could attain appreciable POME degradation (>97% COD, BOD5, TSS, & colour intensity). Withal, SR-treated POME should be polished to further reduce its incompliant COD and BOD5.

Physicochemical characteristics of ash-bridges in diesel particulate filter

The diesel particulate filter (DPF) is one of the most effective devices for reducing particulate emissions from diesel engines so as to satisfy emission regulations, and it has been widely utilized worldwide. After prolonged operation of the DPF, the accumulated non-combustible ash particulates can be sintered with filter walls and form ash-bridges, which will deteriorate DPF performance and increase emissions. Understanding physicochemical characteristics of ash-bridges is essential for elucidating the generation and evolution mechanisms of ash-bridges. Since lubricant additives are the main source of ash particulates, this study prepared four DPFs containing ash-bridges through accelerate ash loading experiments based on Zn-based, Ca-based, Mg-based, and composite lubricant additives. Subsequently, X-ray computed tomography (X-CT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were employed to analyze the structural characteristics, micro-morphology, and chemical composition of ash-bridges inside each DPF. The results indicate that Zn-based and composite ashes formed numerous fine ash-bridges in the middle of the DPF, whereas Ca-based and Mg-based ashes resulted in fully shaped and highly blocked ash-bridges. These ash-bridges aggregated into compact ash plugs downstream in all DPFs. The micro-morphology of Zn-based ash-bridges appeared as ball-and-stick, Ca-based ash-bridges aggregated into large ash aggregates in DPF downstream, Mg-based ash-bridges exhibited characteristics of high porosity, and the micro-morphology of composite ash-bridges is spherical in DPF downstream. The primary components of ash-bridges in Zn-based, Ca-based, and Mg-based DPFs are Zn2P2O7, CaSO4, and MgO, respectively. The main components of ash-bridges in composite DPF include Ca7Mg2P6O24, Zn3(PO4)2(H2O)4, and CaSO4. These findings provide valuable insights into the understanding of ash-bridges, contributing to the enhancement of DPF performance and durability.

Performance Evaluation of Abandoned Fly Ash Deposit Improved by Dynamic Compaction for Construction of Highway Embankment

Abstract In developing countries such as India and China, large amounts of unused fly ash were landfilled into ash deposit on uncultivated land. With an increase in traffic engineering, these ash ponds could probably be reclaimed to construct heavyweight engineering. This requires sufficient strength of foundation to ensure the safety of engineering located on the fly ash deposit. In this paper, a successful utilization of dynamic compaction on a fly ash pond is reported based on embankment engineering of a national highway. Field and lab tests of the ponded ash before and after the compaction are carried out, showing calibration of construction parameters and increased strength of the compacted ash. It has been found that the drop numbers should be determined mainly by the calculated total of penetrated settlement, though the increase in the penetrated settlement is less than 5 cm. The limited value of the bearing capacity of the post-compacted ash can be increased by about 300 %, which meets the design requirement of strength. Results also show that the improved thickness and bearing capacity at the side compaction locations are lower than those of the central position because of the boundary effect. Considering the slope stability of embankment under traffic loading, at least two main compaction locations should be set outside the boundary of the slope toe in the design process.

Blending organic material with municipal solid waste incinerator bottom ash to promote in-situ carbonation in road base.

The use of municipal solid waste incinerator bottom ash for road-base construction is an accepted practice in Europe and Asia, and of growing interest in the US. It is common practice to cure bottom ash by stockpiling it for several weeks before using it in this application. The curing process exposes the bottom ash to atmospheric carbon dioxide, which promotes carbonation, lowering its pH (making it less alkaline), and making many heavy metals less soluble. While this process makes bottom ash a more environmentally acceptable material, it takes time and requires additional handling. This article investigates a concept to facilitate carbonation of bottom ash in its compacted state, potentially eliminating the stockpile curing process. It is demonstrated here that blending a small amount of organic material with bottom ash will accelerate carbonation and lower pH in compacted samples by providing a carbon source for bacteria to produce carbon dioxide. Different quantities of biosolids (1%, 2%, 3%, and 5% by mass) were added to compacted bottom ash samples to examine the effect of organic materials on carbonation, and results were compared with a compacted control bottom ash sample. The pH of the control bottom ash sample decreased from 12.07 to 9.78 after 63 days, while the pH of the sample containing 5% biosolids decreased from 11.70 to 9.74 in only 7 days and to 8.18 after 63 days. Physical testing was conducted to examine suitability for beneficial use. The results indicate that bottom ash containing less than 3% biosolids met minimum bearing strength requirements for road base.

Detailed characterization of particulate matter emitted by lean-burn gasoline direct injection engine

This study presents detailed characterization of the chemical and physical properties of particulate matter emitted by a 2.0-L BMW lean-burn turbocharged gasoline direct injection engine operated under a number of combustion strategies that include lean homogeneous, lean stratified, stoichiometric, and fuel-rich conditions. We characterized particulate matter number concentrations, size distributions, and the size, mass, compositions, and effective density of fractal and compact individual exhaust particles. For the fractal particles, these measurements yielded fractal dimension, average diameter of primary spherules, and number of spherules, void fraction, and dynamic shape factors as function of particle size. Overall, the particulate matter properties were shown to vary significantly with engine operation condition. Lean stratified operation yielded the most diesel-like size distribution and the largest particulate matter number and mass concentrations, with nearly all particles being fractal agglomerates composed of elemental carbon with small amounts of ash and organics. In contrast, stoichiometric operation yielded a larger fraction of ash particles, especially at low speed and low load. Three distinct forms of ash particles were observed, with their fractions strongly dependent on engine operating conditions: sub-50 nm ash particles, abundant at low speed and low load, ash-containing fractal particles, and large compact ash particles that significantly contribute to particulate matter mass loadings.

Effectiveness of a Trench Filled with Waste Material in Reducing the Propagation of Ground Vibration Induced by Soil Roller Compaction

The vibration generated by construction activities is transferred through soil media to the surroundings and has influence on the surrounding structures. However, the response of the structures may depend on the amount of energy received by them. The objective of this study is to investigate the characteristics of ground vibration induced by soil roller compaction and the effectiveness of waste material in reducing the propagation of the ground vibration. Several construction sites where soil compaction has been done by rollers were selected for this study. A site with a stone crushing machine which induces ground vibration similar to roller compaction (i.e., frequency and magnitude) was selected for the investigation of the effectiveness of waste material in reducing the propagation of ground vibration. A trench was introduced in the path of vibration wave propagation. The ground vibration was measured by using a four channel seismograph in the open trench and for the trench filled with locally available waste material such as rice husk and bottom ash. When operating a soil roller compactor, ground vibration in the horizontal directions (i.e., transverse and longitudinal directions)are greater than those in the vertical direction. Rice husk, compacted rice husk and bottom ash contributed to the reduction of ground vibration by 38%, 42% and 49% respectively in the transverse direction and by 14 %, 22 %, and 47 %, respectively in the longitudinal direction indicating that rice husk and bottom ash can be effectively used as in-filled damping layers.

Attenuative Capacity of Compacted Bagasse Ash Treated Foundry Sand

Attenuative Capacity of Compacted Bagasse Ash Treated Foundry Sand

Volume change behavior of clayey soil–fly ash mixtures

At present, more than 150 million tonnes of fly ash is generated annually in India, posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent in combination with soils. For the bulk utilization of fly ashes in geotechnical applications such as embankments/dykes, as back fill material, as base material and in water retaining structures either alone or with soil, the volume change behavior of soil–fly ash mixture forms an important consideration. Only few data are available concerning the volume change behavior of clayey soil–fly ash mixtures and require further investigations. In the present study, high-calcium (ASTM Class C-Neyveli fly ash (NFA)) and low-calcium (ASTM Class F-Badarpur fly ash (BFA)) fly ashes in different proportions by weight (10, 20, 40, 60, and 80%) were added to a highly expansive soil [known as Black Cotton (BC) soil from India] to evaluate the effect of fly ashes on the volume change behavior of clayey soils–fly ash mixtures. Compacted clay-fly ash samples were cured for 7 and 28 days and subjected to consolidation test under different pressures ranging from 50 kPa to 800 kPa. In this study, the void ratio, the compression index, swelling potential, coefficient of consolidation, permeability, and preconsolidation pressure of clayey soil–fly ash specimens were investigated. The test results indicate a significant decrease in compressibility characteristics and swell potential of the treated soils. It was seen that 20% high-calcium fly ash content is the optimum quantity to improve the compressibility characteristics of clayey (BC) soil cured for 7 days against 60% for immediate tests. It is also observed that 10% of NFA is the optimum amount required to minimize the swell potential compared to 40% of BFA. Thus, the main objective of the study was to study the effect of fly ashes on the volume change behavior of fly ash treated clayey soil and bulk utilization of industrial waste by-product without adversely affecting the environment.

Strength characteristics of compacted pond ash

Strength properties of compacted ash layers depend to a great extent on the moulding conditions. This paper focuses on the effects of compaction energy and degree of saturation on strength characteristics of compacted pond ash. The pond ash sample, collected from the ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 kJ/m3 to 3488 kJ/m3. The optimum moisture content and maximum dry densities corresponding to different compactive energies were determined by conventional compaction tests. The shear strength parameters, unconfined compressive strengths (UCS) and California bearing ratio (CBR) values of specimens compacted to different dry densities and moisture content were assessed and reported. The effects of compaction energy and degree of saturation on shear strength parameters i.e. unit cohesion (cu) and angle of internal friction (Ф) values and also the UCS values are evaluated and presented herein. The results indicate that the dry density and strength of the compacted pond ash can be suitably modified by controlling the compactive energy and moulding moisture content. The strength achieved in the present study is comparable to the good quality, similar graded conventional earth materials. Hence, it may be safely concluded that pond ash can replace the natural earth materials in geotechnical constructions.

Optical modeling of vesicular volcanic ash particles

We present a realistic shape model for nonspherical, vesicular particles and use the model to derive single-scattering properties of volcanic fine-ash particles. Light-scattering computations with discrete-dipole approximation reveal that, qualitatively, scattering by the model particles resembles that of the measured, real volcanic ash particles. Comparison of compact and vesicular ash shows that porosity promotes positive degree of linear polarization and decreases the depolarization ratio for both large and small vesicles. Yet, the single-scattering properties of ash particles with large vesicles are found to be surprisingly similar to those of compact ash particles. A comparison with Mie computations of equal-volume spheres indicates that for small size parameters, the spherical shape underestimates the asymmetry parameter of volcanic ash particles; whereas, for larger size parameters, it is overestimated.

Settlement of Footing on Compacted Ash Bed

Compacted coal ash fills exhibit capillary stress due to contact moisture and preconsolidation stress due to the compaction process. As such, the conventional methods of estimating settlement of footing on cohesionless soils based on penetration tests become inapplicable in the case of footings on coal ash fills, although coal ash is also a cohesionless material. Therefore, a method of estimating load-settlement behavior of footings resting on coal ash fills accounting for the effect of capillary and preconsolidation stresses is presented here. The proposed method has been validated by conducting plate load tests on laboratory prepared compacted ash beds and comparing the observed and predicted load-settlement behavior. Overestimation of settlement greater than 100% occurs when capillary and preconsolidation stresses are not accounted for, as is the case in conventional methods.

Settlement of compacted ash fills

The coal ash is a by-product of coal-fired thermal power station. It is extensively used as a geo-material for landfill. The compacted ash is used as a structural fill if it is properly characterized for load-bearing capacity and settlement. The main objective of the present work is to characterize ash material and to evaluate its settlement characteristics. The ash is normally compacted by vibration at or near optimum moisture for its performance as structural fill. The overt characteristics of ashes are viewed similar to cohesionless soils. However, the mass behavior may have differences due to the subtle influence of chemical and physical processes involved in its formation. The empirical and analytical methods predicting settlement of footing under static loading require direct or indirect measurement of density and stress state in the deposit. In the present work, experimental investigations for settlement prediction were carried out on compacted coal ash produced at Ropar thermal power station in India, which was conveniently classified as ASTM class F ash. The settlement was experimentally obtained for the rigid plates having least dimension more than 0.3 m on ashes compacted at varying degree of compaction. The predicted settlement based on the observed data of coal ash using conventional techniques for soils was found to be conservative. A relationship between settlement and foundation size is proposed at varying compaction to obtain the settlement of compacted ash. At a higher degree of compaction, the settlement of a foundation may not exceed the allowable settlements in the working stress range.

Collapse Behavior of Compacted Coal Ash Fills

Abstract Coal ash is widely used in construction of embankments and fills. Compacted coal ash fills are likely to undergo collapse on inundation due to rise of water table or infiltration of rainwater. This paper brings out various factors influencing collapse potential of coal ash. Single oedometer and double oedometer collapse tests and plate load collapse tests were carried out on compacted fly ash (FA), bottom ash (BA), and mixture of fly ash and bottom ash in equal proportion (FA50 + BA50). The results reveal that fly ash is susceptible to collapse, while bottom ash and FA50 + BA50 show negligible collapse. However, a plate load collapse test conducted on compacted ash bed of FA50 + BA50 shows large settlement of plate on inundation. This suggests that the use of the results of single oedometer collapse tests can help estimate only that component of settlement of footing or test plate that is due to compression of the test bed on inundation, and not the total settlement that is due to both collapse compression and shear deformation of the loaded bed.

Cone Resistance of Compacted Ash Fill

Abstract Coal ash is a granular byproduct of the combustion of coal in coal-fired thermal power plants. The compacted ash is frequently used as a structural fill material. Standard geotechnical investigation methods used for natural soils have revealed inconsistencies when extended to ash fills. The characterization of ash shows morphological dissimilarity with natural soils. It is observed that several groupings of in situ density and stress level lead to similar penetration resistance in coal ash. Thus, the correlations reliable for soils may have questionable interpretations of blow count or measured cone resistance in coal ash. The static cone penetration test results analyzed at various combinations of stress level and relative density indicated the need for a new scheme for interpretation of behavior of ash fills on the basis of relative dilatancy of the ash. The resistance to penetration of the standard cone was interpreted at varying depths on ash fill compacted at varying relative densities. Correlations are suggested to estimate bearing capacity and settlement characteristics of coal ash on the basis of cone penetration test results for direct geotechnical design.

Shear and Deformation Characteristics of Municipal Waste Combustor Bottom Ash for Highway Applications

Municipal waste combustor (MWC) bottom ash from mass-burn (MB) and refuse-derived-fuel (RDF) facilities was evaluated for potential use as highway fill material. MWC bottom ash exhibits acceptable shear and deformation characteristics for many highway applications. RDF ash contains a lower metals percentage than MB ash. The specific gravity of both ashes was found to be a function of metals content. Moisturedensity relationships and unconfined compressive strengths were found to be a function of compaction energy and moisture content. Allowing compacted ash to age increased its unconfined compressive strength. Stress-strain characteristics of both ashes are similar to those of sands. Cohesion exists possibly because of pozzolonic reactions in the bottom ash. The angle of internal friction increased with compacted density. Elastic moduli are a function of density and confining pressure. RDF ash was found to be twice as stiff as MB ash. California bearing ratio results greater than 100 indicated that MB ash could be utilized as road base, and values between 25 and 95 indicated that RDF would be acceptable for use in subgrade and subbase. Bearing ratio results were highly dependent on moisture conditions. Both ashes exhibit little to no swell and should not cause field problems during saturation.

Prospects of using dynamic compaction when placing ASH materials and preparing bases for ASH dumps

1. There are considerable prospects of the practical use of dynamic methods of compaction with the use of heavy tampers, vibrating rollers, and explosives for compacting the body of an ash dump in the “dry” method of storing soils of the enclosing embankments and soils in the base of an ash dump with the “dry” and hydraulicking method of storing, in road construction, and when constructing earth structures with the use of ash materials. 2. In the case of dynamic compaction of ash materials and soils in the base of ash dumps, the useful volume should be increased by 20–40% compared with placement of ash materials by the hydraulicking method and by 10–30% compared with compaction by static action, including mechanical. 3. The shear strength increases considerably as a result of dynamic compaction. In particular, the angle of internal friction of loose ash deposits increases 8–12%, and the cohesion coefficient of compacted ash can be increased to 0.04–0.06 MPa. It is possible to reduce the permeability coefficient of ash and soils of the base by a half-order to one or two orders. 4. The use of dynamic compaction promises considerable economic advantages. In particular, prolonging the service life of an ash dump by 1/3 makes it possible to reduce (owing to the absence of the need to construct a new ash dump) capital expenditures for constructing ash dumps by 20–40% with assurance of a high service reliability. 5. This work should be done both for the purpose of further in-depth scientific and practical studies and, mainly, for the purpose of developing and introducing the necessary equipment and highly efficient technologies for dynamic compaction of ash materials of the enclosing embankments and preparation of the bases for ash dumps, compaction of road beds, etc., on various objects. For this there are domestic specialists able to competently solve this problem with the necessary organizational support and financing of the appropriate departments and organizations of the object of use.

Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: Geochemical evidence of ensialic marginal basin volcanism

AbstractMetabentonites occur extensively in the Moffat Shale Group of the Southern Uplands of Scotland. At Dob's Linn 135 metabentonite beds, 1–50 cm thick, occur in Ashgill to Llandovery strata, representing an aggregate thickness of 6 m of compacted ash accumulated over approximately 25 Ma. The metabentonites are characterized by relatively high concentrations of trace elements, including Ba, Cs, Hf, Nb, Rb, Ta, Th, U, Y, Zr and REEs, which were inherited from evolved vitric ash. Immobile trace element data indicate that a spectrum of silicic ash compositions accumulated, ranging from subalkaline to mildly peralkaline. In the late Ordovician N. gracilis to G. persculptus biozones, subalkaline ash falls predominated, whereas peralkaline ash falls predominated in the Llandovery (Silurian) P. acuminatus to M. convolutes biozones, giving way to predominantly subalkaline ash falls during accumulation of the M. sedgwickii to R. maximus biozones. Changeovers in the dominant ash types are marked by increased proportions of ash. The magmas from which the ash types evolved were generated in an ensialic arc transitional to a back-arc setting, and involved attenuated sialic crust and mantle characterized by variable depletion in HFS elements. Lithological, petrological and REE characteristics suggest that the Moffat Shale Group is not exclusively pelagic in origin and probably accumulated in a back-arc basin bordering an ensialic arc terrane.

Down-core distribution of live and dead deep-water benthic foraminifera in box cores from the Weddell Sea and the California continental borderland

Five short cores sub-sampled from box cores from three sites in the eastern Weddell Sea off Antarctica and in the eastern Pacific off southern California, covering a range in water depth from 500 to 2000 m, were analysed for the down-core distribution of live (stained with Rose Bengal) and dead benthic foraminifera. In the California continental borderland, Planulina ariminensis, Rosalina columbiensis and Trochammina spp. live attached to agglutinated polychaetes tubes that rise above the sediment-water interface. Bolivina spissa lives exclusively in or on the uppermost sediment. Stained specimens of Chilostomella ovoidea are found down to 6 cm within the sediment and specimens of Globobulimina pacifica down to a maximum of 8 cm. δ 13C values of live G. pacifica decrease with increasing depth from the sediment surface down to 7 cm core depth, indicating that this infaunal species utilizes 13C-depleted carbon from pore waters. In the dead, predominantly calcareous benthic forminiferal assemblage, selective dissolution of small delicate tests in the upper sediment column causes a continuous variation in species proportions. In the eastern Weddell Sea, the calcareous Bulimina aculeata lives in a carbonate corrosive environment exclusively in or on the uppermost sediment. The arenaceous Cribrostomoides subglobosum, Recurvoides contorus and some Reophax species are frequently found within the top 4 cm of the sediment, whereas stained specimens of Haplophragmoides bradyi, Glomospira charoides and Cribrostomoides wiesneri occur in maximum abundance below the uppermost 1.5 cm. Species proportions in the dead, predominantly arenaceous, benthic foraminiferal assemblage change in three distinct steps. The first change is caused by calcite dissolution at the sediment-water interface, the second coincides with the lower boundary of intense bioturbation, and the third results from the geochemical shift from oxidizing to reducing conditions below a compacted ash layer.

Microincineration and elemental X-ray microanalysis of single Bacillus cereus T spores.

Single whole spores of bacillus cereus T were analyzed by scanning electron microscopy and electron microprobe X-ray microanalysis before and after high-temperature (600 degrees C) ashing in air. High-temperature ashing consisted of a centripetal oxidation of the spore surface combined with pyrolysis of the spore's interior. Ashing of single spores produced a compact central ash particle, mimicking the much larger unashed spore body in outline but containing craterlike microregions, and a peripheral thin ash film. Ashing mostly eliminated the spore's organic matrix; however, ash residues still gave residual carbon-characteristic X-ray counts. Ashing of single spores produced a two-, five-, and six-fold increase of potassium, magnesium, and calcium X-ray intensities, respectively. Iron, although low in actual counts, became detectable after ashing. Phosphorus characteristic X-rays were decreased by 41% after ashing, while volatilization lowered sodium and manganese X-ray intensities by over 80%. High-temperature ashing enhanced element-characteristic X-ray intensities of the non-volatilizable mineral(ized) elements of spores by compacting them into ash residues, more so than by simply abolishing their organic matrix. Microincineration appears a generally useful preconcentration technique for elemental detection and localization in X-ray microanalysis.

A proposed origin of the olympus Mons escarpment

Olympus Mons (Nix Olympica) is delimited by a step nearly circular scarp that is unique to this largest of Martian volcanic constructs. The origin of the scarp is most probably by erosion; such an origin is difficult to explain if the volcanic pile is assumed to be made up exclusively of basalt flows. Although interpretive evidence is accepted for basalt flows underlying the central slope areas, additional criteria are presented here to support the hypothesis that the outer reaches of the slopes comprise dominantly ash-flow tuffs which presumambly were deposited by nuées ardentes. Because of cooling during emplacement, the average degree of compaction of each ash sheet would normally decrease with radial distance from its source vent. It is suggested that the tuffs originally extended greater distances from the central caldera complex and merged the slopes with the surrounding substrate. At the distal edges eolian erosion worked on the relatively noncompacted tuffs and was a major factor in the development of the scarp. The height of the scarp increased as it retreated toward the central caldera complex and eolian undercutting caused slump which in turn furthered the migration of the scarp. The rate of scarp migration would have decreased as the scarp increased in height and as more densely compacted ash nearer to the center of the construct was encountered. By this model, then, the circularity of the scarp in plan reflects an approximately concentric distribution of the zones of average degree of compaction about the center of Olympus Mons.