Low Fines Content Research Articles

Preparation of MgCl2-Supported Ziegler-Natta Catalysts via New Surfactants Emulsion for Propylene Polymerization

This article describes a MgCl2-supported Ziegler-Natta catalyst for propylene polymerization prepared via an in situ emulsion technique with new surfactants. The effect of preparation conditions such as the TiCl4/toluene molar ratio, TiCl4-contacting temperature, amount of phthaloyl dichloride, stirring rate, mixing time of TiCl4/toluene with the Mg complex, and the n-butyl chloride loading was investigated in detail. Scanning electron microscopy and laser particle size analyzer measurements showed that the catalyst particles exhibit a perfectly spherical shape, narrow particle size distribution, and low fine powder content. Energy-dispersive X-ray spectrometry indicated that the Ti, Mg, and Cl elements were evenly distributed throughout the particles. Powder X-ray diffraction measurements indicated the presence of δ-MgCl2 in the catalyst, and FTIR and GC-MS studies confirmed the presence of in situ formed di(ethylhexyl)phthalate (DEHP). Bulk polymerization of propylene using the catalyst was studied, and it was found that the catalyst displayed high activity, high bulk density with high stereospecificity, and excellent hydrogen sensitivity. The polymer produced by the catalyst has a narrow particle size distribution with a low fine powder content.

Wet route pellets production using primary sludge from kraft pulp mill

Abstract The substantial expansion of the Brazilian pulp and paper industry in the last years resulted in a significant increase in the solid waste generation. This paper investigates the production of pellets using primary sludge from the effluent treatment plant of a kraft pulp mill, as a fuel for producing energy, using a novel wet route process. The pellet samples were produced in a laboratory pelletizing press, which has a horizontal circular matrix. The samples were characterized by moisture content, high heating value, ash content, dimensions (diameter and length), mechanical durability and fines content. The net heating value and energetic density were also measured. The pellets manufactured with primary sludge were compared to the European standard for non-woody pellets. Pelletization caused a reduction of the moisture content by 37.8 %, and increased the net heating value by 41 % and bulk density by approximately 39 %, which resulted in a 263 % increase in the material´s energetic density. Pellet production using a wet route process was appropriate for the primary sludge, and produced pellets with a high mechanical durability (99.3 %) and low fines content (0.062 %), indicating the potential of thermal valorization for incineration in the biomass boiler to produce high-quality steam.

Effect of fish pond drainage on turbidity, suspended solids, fine sediment deposition and nutrient concentration in receiving pearl mussel streams.

Extensive fish production in earthen ponds is a common aquaculture practice, which requires draining of the ponds for fish harvesting. Despite their value for biodiversity and water retention, the impact of fish ponds on the receiving streams as regards fine sediment and nutrient pollution remains controversial. This holds particularly true for streams with endangered freshwater pearl mussels, requiring a highly permeable streambed with low fine sediment content for successful juvenile development. This study quantified the amount of fine sediment, suspended solids and nutrients delivered to pearl mussel streams in relation to the pond characteristics, distance to the receiving stream and applications of measures to prevent the input of fines. Comparing fine sediment deposition above and downstream of the pond inlets after 21 pond drainage operations, as well as continuous measurements of the turbidity for 12 operations revealed varying effects of pond fishing on the receiving streams. Average fine sediment deposition was increased by nearly six-fold compared to upstream and maximum turbidity values for single drainage operations exceeded 460 NTU. Draining between 1% and 92% of the water volume of individual ponds resulted in additional loading of 0.07-4.6t suspended particles. Physical mitigation structures that prevent mobilized material from reaching the receiving stream significantly reduced the fine sediment input and deposition rates. Harvesting methods that do not require complete drainage of the pond reduced the turbidity by ten-fold. Without mitigation measures, the impact of pond drainage operations on the fine sediment deposition was comparable to high discharge events. No significant increase in nutrient concentration was observed during most drainage operations. These results reveal remarkable effects of pond drainage on the aquatic environment, as well as the possibility to minimize such impacts by switching to harvest methods that do not require complete pond drainage and installation of sedimentation structures.

An Improved Set of Design Criteria for Slotted Liners in Steam Assisted Gravity Drainage Operation

Slotted liners are widely used in steam-assisted gravity drainage (SAGD) wells to control sand production and sustain wellbore productivity. The slotted liner can provide desirable performance when appropriately designed. A literature review indicates a limited number of studies that offer design criteria specifically for SAGD wells. Moreover, past criteria seem to neglect some key factors, which may lead to inadequate slot design. This paper proposes a set of graphical design criteria for slotted liners in SAGD production wells, using prepacked sand retention testing (SRT) data. The SRT is designed to incorporate several essential factors that are not present in the past design criteria, such as slot density, steam breakthrough, and particle size distribution (PSD). The proposed design criteria are presented graphically for normal and aggressive conditions, where the aggressive condition accounts for the potential occurrence of the steam breakthrough. It is found that the upper bound of the design window is substantially lower for the aggressive condition due to the higher sand production after the steam breakthrough. The design criteria also indicate that the slotted liner is suitable only for the formations with low fines content.

Influences of low fines content and fines mixing ratio on the undrained static shear strength of sand–silt–clay mixtures

Clay and silt have complicated effects on the undrained behaviour of sands. To study the influences of low clay and silt contents on the undrained behaviour of sands in the clay–silt–sand mixtures, sands with three different fine contents (0%, 5% and 10%) and three different fines mixing ratios were investigated based on the consolidated-undrained test by a strain-controlled triaxial testing system. The test results show that the static liquefaction takes place in clean sands under static loading; the undrained behaviours of the specimens are found to differ for the same fine content and different fine mixing ratios. The fines can simultaneously influence filling, bonding and soil skeleton characteristics of sand particles, and the extent of the influence on each characteristic varies depending on the clay and silt contents.

Estimation of the shear strength of coarse-grained soils with fine particles

The determination of the shear strength of coarse-grained soils in standard shear devices is a challenging task due to the presence of large grains. Three approaches could be used to reduce the grain size of the tested specimen. This study aimed to determine whether the shear strength of a coarse-grained soil with fines (particles smaller than 0.08 mm) can be estimated by the parallel gradation approach. Direct shear tests were conducted on parallel graded specimens of two soil types with different low plastic fines content. Two criteria can be used to select the dry density of the reconstituted specimen: the same dry density or the same relative density as the initial soil. The results showed that when the specimens had a low fines content, both criteria resulted in a similar dry density of the reconstituted soil, and the shear strength of the initial soil was correctly estimated. However, for the specimens with a high fines content, the friction angle of the initial soil was correctly estimated, and its cohesion was overestimated when the reconstituted soil was tested at the same dry density as the initial soil. A cohesion-fines content relationship was proposed to predict the initial soil cohesion.

Analyzing filtration flow rate change of woven geotextiles for fine grained slurries

Many studies have been performed in recent years to investigate the dewatering phenomena of slurry using geotextile tubes. The laboratory test methods primarily used the pressure filtration test (PFT) and falling head test (FHT) to evaluate the dewatering nature of geotextiles using slurries with different fines contents. The objective of this paper is to examine and analyze the published test data obtained from various testing conditions, and to develop a general equation that can predict the change of flow rate over time. For the PFT, a power law showed a good fit with test data at different fines content ranges. Furthermore, the change of filtration rate with time decreased with the fines content, indicating that slurry with high fines content resulted in a faster drop in filtration rate than slurry with low fines content. For the FHT, a two-term power law was found to fit all of the test data, indicating a two-stage filtration behavior.

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

AbstractIt is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.

Performance and design of reinforced slopes considering regional hydrological conditions

This study presents a series of numerical analyses investigating the impact of rainfall on the performance and design of geosynthetic-reinforced soil slopes (RSSs). The importance of considering regional hydrological conditions for designs of RSSs, particularly when marginal soil is used as backfill, is demonstrated and highlighted. RSSs with backfills containing five different fines contents subjected to various combinations of initial hydraulic conditions and major rainfall events were modeled. The input rainfall was determined from the rainfall intensity–duration–frequency (I–D–F) curves to realistically account for the impact of regional hydrological conditions. The hydraulic responses and stability of the RSSs including their porewater pressure development and factor of safety were then evaluated and compared. The results revealed that the applied rainfall scenarios had little influence on the performance of RSSs with high-quality backfills (i.e. backfill with low fines content), whereas those with prolonged rainfall duration substantially affected the performance of RSSs with high fines content backfills. Rainfall thresholds were established for the RSSs with various backfills and initial conditions and compared with the regional I–D–F curves to provide a simplified and robust method for facilitating backfill selection and assessing the failure risk of RSSs.

Comparison of wood and non-wood market pulps for tissue paper application

A comparison among ten market pulps at a laboratory scale using uncreped tissue handsheets was performed to study the performance of wood and non-wood pulps for tissue manufacturing, evaluate what fiber features are desired for a specific tissue property, and determine how non-wood pulps can be used to replace or complement wood pulps in tissue products. A characterization of the fiber morphology and handsheet properties (softness, water absorbency, and strength) was performed at different mechanical refining levels. The results showed that the fiber morphology had a major impact on tissue properties. Market pulps with a combination of long fibers, high coarseness, and low fines content can provide superior bulk and water absorbency. Short fibers with thin cell walls and low fines content can impart superior softness. Bleached bamboo soda pulp can replace hardwood and softwood pulps to provide an excellent combination of water absorbency and strength. Bleached bamboo soda pulp can also replace Northern bleached softwood kraft (NBSK) pulp to impart strength without sacrificing softness. Bleached and semi-bleached wheat straw soda pulps presented a similar combination of softness and strength as Southern bleached hardwood kraft (SBHK) pulp. The wheat straw pulps can be used to replace deinked pulp (DIP) pulp to impart intermediate levels of water absorbency and strength.

Dynamic behaviour of Kutch soils under cyclic triaxial and cyclic simple shear testing conditions

ABSTRACT The dynamic behaviour of soils from Kutch (seismically active region of Gujarat, India) was explored under cyclic triaxial (CTX) and cyclic simple shear (CSS) testing conditions. Under both the CTX and CSS conditions, the soil specimens exhibited cyclic strength that decreased rapidly at lower plasticity index and lower fines content. The reduction in cyclic strength was evaluated to be higher and faster for the clayey-sand specimens as compared to clayey specimens. Specimens with low plasticity index and lower fines content showed higher pore pressure response in both CTX and CSS tests. Pore pressure ratio under CSS conditions was observed to be higher as compared to CTX conditions. Degradation in shear modulus was found to be higher and quicker for clayey-sand specimens as compared to clayey specimens. Degradation index increased with plasticity index and fines content at a given number of loading cycles under both CSS and CTX conditions.

The effect of using low fines content sand on the fresh and hardened properties of roller-compacted concrete pavement

Aggregate gradation is one of the most important property that influence the behaviour of roller-compacted concrete pavement (RCCP). There are some limitations for gradation of coarse and fine aggregates from the standards. Based on the ACI 211.3R, the content of sand size less than 75 μm should be between 2 to 8% of the total aggregates. To study the effectiveness of using a nonstandard sand (a sand with a gradation out of the specified restrictions) on the properties of RCCP, three types of sand with a difference in very fine particles content were used. The sands used are: 1) standard sand, 2) modified sands containing about 6% limestone powder, and 3) a low fines content sand containing <1% very fine particles. Two types of RCCP containing 12 and 15% cement were used as control mix. The results show that using low fines content sand or limestone modified sand instead of standard sand in RCCP increased Vebe time. The use of low fines content sand in RCCP did not have significant effect on the compressive, splitting tensile and flexural tensile strengths. However, the use of limestone modified sand in the RCCP significantly reduced the mechanical properties. RCCP was made of low fines content sand had more porosity than RCCP with standard sand. It can be concluded from test results that sand with lack in very fine particles can be used in RCCP.

Particle-scale insight into transitional behaviour of gap-graded materials – small-strain stiffness and frequency response

This study aims to develop a fundamental understanding of the role of fine particles on the small-strain stiffness of gap-graded granular soils. Stiffness was measured using cyclic triaxial probes, which give a measure of static stiffness, and dynamic wave propagation data, from which the dynamic stiffness can be measured. Assemblies of loosely packed spherical particles were considered. In the laboratory, local deformation transducers were used to measure the static stiffness, while the dynamic stiffness was calculated from stress wave velocities, measured using planar piezoelectric elements. To relate the particle-scale responses to the overall soil stiffness, complementary discrete element method (DEM) simulations were performed in which both static and dynamic stiffnesses were measured. Both the laboratory and the DEM data indicate that at low fines contents (&lt; 30%) the stiffness decreases with increasing fines content. When the fines content increases from 30% to 35% there is a sharp increase in stiffness with increasing fines content; this is understood to mark the transition point at which the fines start to contribute significantly to the overall behaviour. Analyses of the frequency domain response of shear wave signals revealed that the lowpass frequency increases significantly at this transition point. This observation can be used to develop experimental interpretation protocols to assess to what extent fines are contributing to the overall soil stiffness.

Influence of stress anisotropy on stress distributions in gap-graded soils

The behaviour of gap graded soils comprising non-plastic fines (sand or silt) mixed with a coarser sand or gravel fraction has received attention from researchers interested in internal instability under seepage loading (a form of internal erosion) as well as researchers interested in load:deformation responses. Skempton and Brogan [1] postulated that resistance to seepage induced instability depends upon the proportion of the overall applied stress that is transmitted by the finer fraction. Shire et al. [2] explored Skempton and Brogan’s hypothesis using DEM simulations to look at the proportion of the applied stress transmitted by the finer fractions (α) in ideal isotropic samples. They showed that at low fines contents (FC&lt; FC*) the average stress transmitted by the finer grains is less than the applied stress (α&lt;1), while for FC&gt;FC+ the fines play a key role in stress transmission (α&gt;1); for FC*&lt;FC&lt; FC+, α depends on the sample density. The current contribution describes a series of constant p’ DEM triaxial test simulations carried out to assess the evolution of stress heterogeneity with shearing. The simulation data generated indicate that a sample can transition from being fines dominated (with the fines transmitting a significant proportion of the applied stress and α ≥1) to coarse or sand- dominated (with α &lt;1) as the material dilates during shear deformation. While α reduces as the samples dilate, the relationship between the α and the sample void ratio is non-trivial. The anisotropy of the coarse-coarse contact network exceeds the overall contact force anisotropy; this indicates that the deviator stress is transmitted through a strong force network passing through the coarse-coarse contacts supported by the fine-coarse contacts.

3D synchrotron computed tomography study on the influence of fines on gas driven fractures in Sandy Sediments

Production of methane from hydrate-bearing sediments requires hydrate dissociation for releasing mobile methane gas in sediments prior to gas production operations. Fines may migrate through or clog the pore space of sandy sediments depending on the geometry and topology of the pore space. Multiphase flow experiments were conducted on brine saturated uniform silica sand mixed with different percentages of kaolinite. Fines concentrations were correlated to computed tomography (CT) numbers in their host brine phase. Representative element volume (REV) procedure was used to study local porosity and local fines concentration. A cubical REV with a side length of 850 μm was selected. For low fines content (less than 6%), gas percolated through the specimens with no major particle translation or porosity change. For 6% kaolinite specimen, fractures were initiated, and propagated by densifying surrounding sediments. Local fines concentration study showed that fines migrated through the pores for specimens with fines content less than 6%. For the 6% kaolinite specimen, fines concentrated near fractures due to clogging. Clogging induced an increase in the capillary pressure at the pore throats and caused the capillary pressure to overcome the effective stress between sand particle, and fractures to be initiated. Sand particles experienced up to 200 μm translation and 15° rotation due to gas driven fracture in the 6% kaolinite specimen.

The Characteristics and the Erodibility Potentials of Soils from Different Geologic Formations in Anambra State, Southeastern Nigeria

The characteristics and the erodibility potentials of soils from Benin, Ogwashi-Asaba, and Nanka formations in Anambra state, Nigeria were studied. The study involved an integration of field observations, geotechnical analyses, and topographical modelling. About ten gullies were identified in the field. However, six major gullies labeled BN1, BN2, OA1, OA2, NK1, and NK2 were chosen and studied extensively to represent the three geologic formations. The results showed that soil properties, anthropogenic activities, topography, fierce surface runoff, and sparse vegetation are the factors that commonly and systematically influence the characteristics and erodibility potentials of all these soils. However, anthropogenic activities and soil properties play the most, dominant roles in the erosional processes. The specific gravity of the soils are similar, with values ranging from 2.50 to 2.69. Compaction test revealed all the soils were loose and collapsible. Grain size analysis further revealed that they have low content of fines (<25%, except for OA1 with 58.87%). The plasticity index of the fines indicated that they are nonplastic to low plastic soils (values range from 0–12%). The soils are highly to moderately permeable, with values ranging from 4.22×10−6m/sec to 4.34×10−4m/sec. All have low cohesion ranging from 1–7kPa, except for the OA1 with 27kPa. Based on the study, the three geologic formations have similar characteristics and high erodibility potentials; though OA1 has varied characteristics and thus, lower erodibility potential.

Gasification of Agroresidues for Syngas Production

Biomass residues from agriculture and agroindustry are suitable sources for the production of energy because they don’t compete with the food chain and they are produced cheaply. Their transformation into heat and power or energy vectors depends on morphology and composition. Shells of almonds and hazelnuts can be easily gasified in fixed beds because of their low fines content and high gas permeation. In this work we investigated the overall process performances and syngas composition, especially the H2/CO ratio, by changing the air and steam supply. The tests were carried out in a pilot updraft gasifier having a capacity of treating up to 20–30 kg/h of biomass. Experimental data were worked out by surface response analysis as function of the equivalence ratios (ER) in relation to the complete combustion and water reaction. By using only air at ER(O2) 0.24 the ratio H2/CO in the syngas was 0.33 while adding steam at ER(H2O) 0.28 the ratio reached a value of 1.0. The energy conversion efficiency from solid to gas and oils reached maximum values of 76% and 28%, respectively. As anticipated by TGA, hazelnut shells produced less organic volatiles and gas efficiency was generally higher than for almond shells.

EFFECTS OF SOIL RECOMPACTION ON PERMEABILITY

Presence of water changes the properties of soil such as dry density, shear strength, swelling-shrinkage and permeability. In this research, the effects of recompaction on permeability of laterite soil extracted from the Faculty of Engineering in Universiti Teknologi Malaysia was investigated in the design of liners and covers used as hydraulic barriers in sanitary landfills. Landfill liner needs to have sufficiently low permeability value so that it impedes migration of leachate through the compacted soil which causes groundwater contamination. The falling head permeability method of testing was adopted in the experimentation. Laterite soil samples were first mixed with water and compacted using Standard Proctor compaction. The same samples were then remixed at higher water contents and recompacted. The compacted and recompacted soil samples were subjected to falling head permeability tests. Based on the tests results, the permeability value of 2.24 x 10 -8 m/s for recompacted laterite soil at 40% moulding water content was lower than the permeability value of 5.95 x 10 -8 m/s for compacted sample at the same moulding water content. The laterite soil was observed to contain low fines content and is susceptible to crushing. Keywords: Permeability, Compaction, Laterite soil

Sedimentological and Scanning Electron Miscroscopic Descriptions of Afowo Oil Sand Deposits, South Western Nigeria

AbstractSedimentological and scanning electron microscopic analyses of some shallow reservoir tar sand samples in parts of Southwestern Nigeria were carried out with the aim of characterizing the reservoir properties in relation to bitumen saturation and recovery efficiency. The production of impregnated tar from the sands requires the reservoir to be of good quality. A total of thirty samples were collected at different localities within the tar sand belt (ten out of these samples were selected for various reservoir quality analyses based on their textural homogeneity). The result of particle size distribution study showed that bulk of the sands is medium – coarse grained and moderately sorted. The grain morphologies are of low to high sphericity with shapes generally sub-angular to sub-rounded, implying that the sands have undergone a fairly long transportation history with depositional energy having a moderate to high velocity. The quartz content was made up of about 96% of the total mineralogical components; the sediments of the Afowo Formation can be described to be mineralogically and texturally stable. The result of the scanning electron microscopy (SEM) analysis revealed that the oil sands contained minerals which had been precipitated and occurred as pore filling cement; these minerals include sheet kaolinite, block kaolinite, vermiform kaolinite, pyrite crystals and quartz. The SEM images also showed micro-pores ranging from 0.057µm to 0.446µm and fractures. The study showed that the clay minerals contained in the Afowo reservoir rocks were mainly kaolinite. Kaoline unlike some other clays (e.g Montimorillonite) does not swell with water, hence it is not expected to have any negative effects on the reservoir quality, especially during enhanced oil recovery operations.From overall results of the reservoir quality assessment, Oso J4 and Gbegude sands should be expected to make better reservoirs with good oil recovery efficiency due to their low content of fines and better sorting characteristics when compared to sediments of other areas.

Soil desiccation cracks as a suction–contraction process

Recent macro- and particle-scale advances in unsaturated soil behaviour have led to an enhanced understanding of the effects of moisture changes on soil response. This research examines desiccation cracks as a suction–contraction-coupled process using sand–clay mixtures. Suction–moisture measurements highlight the role of fines on suction potential even at low fines content; on the other hand, oedometer tests exhibit a marked transition from sand-controlled to clay-controlled compressibility. Time-lapse photography of desiccation tests in flat trays show the onset of crack initiation and the subsequent evolution in horizontal strains; concurrent gravimetric water content measurements relate crack nucleation to suction at air entry. Suction and compressibility increase with the soil-specific surface and have a compounded effect on desiccation-driven lateral contraction. Both layer thickness and its lateral extent affect the development of desiccation cracks. The recently proposed revised soil classification system properly anticipates the transitions in compressibility and capillary phenomena observed in this study (between 15 and 35% fines content).