Collector Concentration Research Articles

Stirling Engines for Distributed Low-Cost Solar-Thermal-Electric Power Generation

Due to their high relative cost, solar-electric energy systems have yet to be exploited on a widespread basis. It is believed in the energy community that a technology similar to photovoltaics, but offered at about $1/W, would lead to widespread deployment at residential and commercial sites. This paper addresses the feasibility study of a low-cost solar-thermal electricity generation technology, suitable for distributed deployment. Specifically, we discuss a system based on nonimaging solar concentrators, integrated with free-piston Stirling engine devices incorporating integrated electric generation. We target concentrator collector operation at moderate temperatures, in the range of 120°C to 150°C. This temperature range is consistent with the use of optical concentrators with low-concentration ratios, wide angles of radiation acceptance which are compatible with no diurnal tracking and no or only a few seasonal adjustments. Therefore, costs and reliability hazards associated with tracking hardware systems are avoided. This paper further outlines the design, fabrication, and test results of a single-phase free-piston Stirling engine prototype. A very low loss resonant displacer piston is designed for the system using a very linear magnetic spring. The power piston, which is not mechanically linked to the displacer piston, forms a mass-spring resonating subsystem with the gas spring, and has a resonant frequency matched to that of the displacer. The design of heat exchangers is discussed, with an emphasis on their low fluid friction losses. Only standard low-cost materials and manufacturing methods are required to realize such a machine. The fabricated engine prototype is successfully tested as an engine, and the experimental results are presented and discussed. Extensive experimentation on individual component subsystems confirms the theoretical models and design considerations. Based on the experimental results and the verified component models, an appropriately dimensioned Stirling engine candidate is discussed.

A comparison of anionic and cationic flotation of a siliceous phosphate rock in a column flotation cell

Flotation performance of a de-slimed (−150 + 53 μm) Jordanian siliceous phosphate was evaluated in a batch laboratory flotation column 100 cm high and 5 cm inside diameter. The collector used during anionic flotation was sodium oleate while an amine acetate (AEROMINE 3100C) was used for cationic flotation. Flotation comparison at different collector dosage, superficial gas velocity, and frother concentration showed that the maximum difference in performance between cationic and anionic flotation was obtained with these flotation parameters: 30 × 10 −6 (mg/L) frother concentration, 250 g/t collector concentration, and 3.4 cm/s superficial gas velocity. At these operating conditions amine (cationic) flotation gave 7% higher flotation recovery, a 6% cleaner concentrate grade, and was 6% more efficient at removing silica.

ToF-SIMS-derived hydrophobicity in DTP flotation of chalcopyrite: Contact angle distributions in flotation streams

Particle hydrophobicity has been derived from Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements and its impact on the flotation behaviour of chalcopyrite investigated. Batch flotation tests were performed using a dithiophosphate-type of collector in different concentrations. Three flotation regimes were studied using particle size ranges of 20–38μm, 75–105μm and 150–210μm. The individual particle contact angle, and hence, the distribution of contact angles of chalcopyrite within feed, concentrate and tail flotation samples has been determined using ToF-SIMS secondary ions. The effects of particle size and hydrophobicity on the flotation behaviour have been investigated using this new approach. The hydrodynamic effects of the particle size were highlighted by the different distributions of contact angles obtained for each concentrate size fraction, with fine and coarse sizes requiring higher average contact angles to float. This effect was overtaken by hydrophobicity when a high collector concentration was used. The broad distribution of contact angles observed in all samples, i.e. heterogeneity in hydrophobicity, has significant consequences for interpreting flotation behaviour. The methodology of analysis conducted in this study was applied to real ore and can be used as a quantitative, diagnostic tool for examining surface chemical factors affecting hydrophobicity. This new technique has promise and may advance the understanding of mechanisms, which may lead to better control strategies for improving flotation performance. Furthermore, any mineral–collector system can be targeted, provided appropriate calibration is performed.

Adsorption and column flotation studies on talc using anionic and cationic collectors

Adsorption properties and column flotation were studied to investigate the interaction of the anionic and cationic collectors and flotation recoveries for talc mineral. Adsorption capacity is dependent on pH, adsorption time, temperature, collector concentration, and particle size. Langmuir adsorption model was suitable for describing isotherms. Analyses were carried out using UV spectrometry. In this study, we analyzed some parameters affecting column flotation performance. It was determined that adsorption capacity, especially, had an important role in column flotation enrichment.

Types of particles recovery—water recovery entrainment plots useful in flotation research

This review paper deals with graphical representation of entrainment experienced by fine particles during passing, either barren or mineralized, bubbles through flotation cells. Entrainment, also called mechanical carryover or mechanical flotation, is harmful because it reduces the quality of flotation concentrates. It was presented in the paper that it is convenient to show the results of entrainment as upgrading separation plots relating recovery of fines vs. water recovery. The shape of the entrainment separation curves significantly depends on the way flotation test is performed, type of flotation machine, kinetics of process, froth collecting time, concentration of frothers, collectors and modifiers, amount of air in flotation, density of pulp, amount of supplied water etc. Five types of entrainment separation plots were distinguished and presented in the paper. They were categorized as linear (type 1), linear shifted down (type 2), reaching plateau (type 3), increasing (type 4) and linear shifted up (type 5). The plots are useful for determination of appropriate entrainment coefficients characterizing the process.

Numerical simulation of a trapezoidal cavity receiver for a linear Fresnel solar collector concentrator

A new trapezoidal cavity receiver for a linear Fresnel solar collector is analysed and optimized via ray-trace and CFD simulations. The number of receiver absorber tubes and the inclination of lateral walls in the cavity are checked with simplified ray-trace simulation. The CFD simulation makes possible to optimize cavity depth and rock wool insulation thickness. The simulated global heat transfer coefficient, based on primary mirror area, is correlated with a power-law fit instead of a parabolic fit. The correlation results are compared with heat transfer coefficients available for linear Fresnel collector prototypes.

Evaluation of ion collection area in Faraday probes

A Faraday probe with three concentric rings was designed and fabricated to assess the effect of gap width and collector diameter in a systematic study of the diagnostic ion collection area. The nested Faraday probe consisted of two concentric collector rings and an outer guard ring, which enabled simultaneous current density measurements on the inner and outer collectors. Two versions of the outer collector were fabricated to create gaps of 0.5 and 1.5 mm between the rings. Distribution of current density in the plume of a low-power Hall thruster ion source was measured in azimuthal sweeps at constant radius from 8 to 20 thruster diameters downstream of the exit plane with variation in facility background pressure. A new analytical technique is proposed to account for ions collected in the gap between the Faraday probe collector and guard ring. This method is shown to exhibit excellent agreement between all nested Faraday probe configurations, and to reduce the magnitude of integrated ion beam current to levels consistent with Hall thruster performance analyses. The technique is further studied by varying the guard ring bias potential with a fixed collector bias potential, thereby controlling ion collection in the gap. Results are in agreement with predictions based on the proposed analytical technique. The method is applied to a past study comparing the measured ion current density profiles of two Faraday probe designs. These findings provide new insight into the nature of ion collection in Faraday probe diagnostics, and lead to improved accuracy with a significant reduction in measurement uncertainty.

Hydrogen bubble flotation of silica

In this study the flotation recovery of silica using air, and molecular and electrolytically-generated hydrogen was investigated. For comparison of air and molecular hydrogen recoveries, a laboratory Denver, type D12, flotation machine was used. For both gases, pH of the suspension, gas flow rate, concentration of collector and frother, solids concentration, particle size and speed of impeller were kept constant. Almost identical recoveries were obtained for both gases, suggesting that gas composition played no significant role in silica flotation. Electroflotation experiments were carried out using 12.6 μm mean diameter silica particles. While fine particles had very poor recovery in the Denver cell, greater than 70% recoveries were achieved in the electroflotation cell. This was thought to be the result of the very small (less than 40 μm) bubbles generated by the electroflotation process. A population-balance model, incorporating the hydrogen generation process, supported the conclusion that increased recovery for electroflotation, for very fine silica particles at least, was attributed to the reduced bubble size and not by the composition of the gas.

Cinética de separación de Cu (II) por técnicas de flotación iónica, en celdas con dispersores flexibles

This research studies and experimentally determines the kinetic parameters and effect of modifying the hydrodynamics and chemical conditions of the air-liquid dispersions during the Cu (II) extraction by ion flotation techniques in cells with porous spargers. Results show that the elimination of Cu (II) from solution can be carried out by ion flotation in one stage, obtaining efficiencies of 68% and 56% for the flat and cylindrical sparger respectively with a xanthate concentration of 0,02 g/l. In multistage systems five cells, recoveries over 92 % were achieved for both sparger geometries. The behavior of the flotation apparent kinetic constant is linear to the parameters that characterize dispersion (Jg, eg y Db), until a point is achieved where the process instability makes the system inoperable. The results show that removing base metal ions by ion flotation is strongly affected by the following factors: collector concentration [C], Jg, eg, Db, Jl and Sb.

Surface chemistry features in the flotation of KCl

Despite the successful industrial practice to recover KCl by flotation, the adsorption state of collectors at KCl salt surfaces is still not fully understood. In this paper, the flotation behavior of KCl and NaCl using different collectors and captive bubble contact angle measurements at KCl and NaCl crystal surfaces in their saturated solutions are reported. The influence of collector concentration and collector structure is considered. The results show that both cationic and anionic collectors produce a hydrophobic state at the structure breaking KCl salt surface, with finite contact angle values of between 30 degrees and 60 degrees. In contrast, the contact angle at the structure making NaCl salt surface is zero at all collector concentrations, suggesting that no collector adsorption occurs, a supposition that is supported by results from molecular dynamics simulation (MDS). Further, it appears that the presence of surface defects such as edges and corners promote the adsorption of collectors at the KCl surface, and that the flotation is achieved by bubble attachment at the edges/corners of KCl particles with the formation of aeroflocs. (C) 2009 Elsevier Ltd. All rights reserved.

A new collector used for flotation of oxide minerals

A surfactant containing a mixed aliphatic structure, with a hydrocarbon chain and a diamine group, has proven to be collector for the flotation of quartz, calamine and calcite. And research about its collecting capability was carried out in laboratory. The test results show that the flotation recovery ascends sharply with increasing the concentration of collector. When the concentration of collector reaches 1.83×10 −4 mol/L, the flotation recoveries of quartz, calamine and calcite get their maximum of 97.64%, 91.04% and 95.99%, respectively. The flotation recoveries of quartz, calamine and calcite rise sharply with the rise of pH. And in a wide range of pH, their flotation recoveries all exceed 90%. And in the whole flotation experiment, the flotation recovery of hematite rises with the increase of collector concentration and pH, while the maximal recovery is not more than 55%. Compared with dodecylamine, the N-dodecylethylenediamine has strong capability to quartz and calamine, while the flotation recoveries of calcite are closely. Hydrogen binding adsorption and electrostatic adsorption occur between the collector and the surface of quartz.

Characterization and recovery of copper values from discarded slag

In any copper smelter large quantities of copper slag are discarded as waste material causing space and environmental problems. This discarded slag contains important amounts of metallic values such as copper and iron. The recovery of copper values from an Indian smelter slag that contains 1.53% Cu, 39.8% Fe and 34.65% SiO(2) was the focus of the present study. A complete investigation of the different phases present in the slag has been carried out by means of optical microscopy, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. It is observed that iron and silica are mostly associated with the fayalite phase whereas copper is present in both oxide and sulfide phases. These oxide and sulfide phases of copper are mostly present within the slag phase and to some extent the slag is also embedded inside the oxide and sulfide phases. The recovery of copper values from the discarded slag has been explored by applying a flotation technique using conventional sodium isopropyl xanthate (SIX) as the collector. The effects of flotation parameters such as pH and collector concentration are investigated. Under optimum flotation conditions, it is possible to achieve 21% Cu with more than 80% recovery.

Recycling the slagheap of an old coal mine (Morocco)

A slagheap of the Jarada coal mine (Morocco) was recycled using the following ore processing operations: sifting, gravimetry and flotation. This abandoned coal mine has greatly evolved over the years. The oxidation of its pyrite content is the most remarkable change. The only remains are iron oxides which are concentrated within the fine particles of the slagheap. This study shows that the recovery efficiency of iron(III) oxide depends on the particle size, pH and the collector concentration. When recycled under optimum conditions, a commercial product containing 35% iron(III) oxide (Fe 2O 3) used in paint and enamelling was obtained.

Influence of chemical parameters on selectivity and recovery of fine coal through flotation

This paper summarizes how the chemical parameters (collector concentration, frother concentration and different mixed frothers) affect the selectivity, kinetics and size wise flotation performance. Three different mixed frothers have been taken for this study. Frother ‘x’ is composed of alcohol and ketone. Frother ‘y’ consists of alcohol and aldehyde group chemicals. Frother ‘z’ is a blended product of alcohol and polyglycol ether. Flotation performance of different mixed chemical systems is correlated with affinity of frothers with air–water interface. Blended frothing molecules of short chain alcohol and polyglycol ether have shown a dramatic impact on the surface activity and flotation performance in term of ash reduction and improvement in coal yield.

Dissolved air flotation (DAF) of fine quartz particles using an amine as collector

Experimental studies concerning the dissolved air flotation (DAF) of fine ( d p < 100 μm) quartz particles, using two different flotation cells (setups), are presented. Pure and well characterised quartz samples were treated with a commercial amine as collector prior to flotation and bubbles were characterised by the LTM-BSizer technique. Bubble size distribution showed 71% (by volume) and 94% (by number) of the bubbles having sizes ( d b) lower than 100 μm (i.e. microbubbles). The Sauter and arithmetic mean diameters were 79 μm and 56 μm, respectively, for the bubbles generated at 300 kPa (gauge) saturation pressure (after 30 minute saturation time). Quartz particle size distribution (obtained by laser diffraction) showed a volume-moment diameter of 13 μm. The Rosin–Rammler–Bennett, Gates–Gaudin–Schumann and log-normal distribution functions were well fitted ( R 2 > 0.96) to the bubble size distribution and quartz particle size distribution data. Values of total quartz recovery ranging from 6% to 53% (by mass) were obtained for the DAF experiments under different collector concentrations (up to 2 mg g − 1 ), with an optimal collector concentration found at 1 mg g − 1 . These results are significant considering that 27% (by volume) of the quartz particles are ultrafine ( d p < 5 μm), demonstrating the widely-known efficiency of DAF to remove small particles when applied in the field of water and wastewater treatment. The true flotation behaviour, as a function of particle diameter ( d p), exhibits a local minimum when particles are approximately 3–5 μm in size. The results contribute to the discussion in the literature about the existence of such a minimum, which is generally interpreted as a change in the mechanism of particle collection from convection (collision) to diffusion at lower particle sizes.

Long-term performance calculations based on steady-state efficiency test results: Analysis of optical effects affecting beam, diffuse and reflected radiation

There are a growing number of commercially available solar thermal collector types: flat plates, evacuated tubes with and without back reflectors and different tubular spacing or low concentration collectors, using different types of concentrating optics. These different concepts and designs all compete to be more efficient or simply cheaper, easier to operate, etc. at ever higher temperatures, and to extend the use of solar thermal energy in other applications beyond the most common water heating purposes. In view of the proper dimensioning of solar thermal systems and proper comparison of different collector technologies, for a given application, there is a growing need for existing and future simulation tools to be as accurate as possible in the treatment of these different collector types. Collector heat losses are usually considered to be well determined, under variable operating conditions, through the use of the heat loss coefficients provided by efficiency curve parameters. Yet, the traditional approach to the optical efficiency fails to describe accurately the optical effects affecting the amount of radiation which actually reaches the absorber. This paper develops a systematic approach to the proper handling of incident solar radiation, folding that with the information available from tests for determination of collector efficiency curve (steady-state) and the way the optics of different collector types uses incident solar radiation and transforms it into useful heat.

Study on flotation characteristics of oxidised Indian high ash sub-bituminous coal

It is well known that high rank coals are generally more hydrophobic than low rank coal or oxidised coal. Non-coking coal (sub-bituminous) of the Talcher coal field in India has very high ash content and is believed to have oxidised surface. This coal is very difficult to float even at higher concentration of collector due to its oxidised surface with reduced hydrophobicity. This investigation has been carried out to study the flotation characteristics of oxidised Indian high ash sub-bituminous coal having particle size below 1 mm. Initially the flotation study was carried out using conventional reagents only in a Denver D-12 sub-aeration flotation cell. Then it was pre-treated with aliphatic alcohols i.e., ethanol and butanol to de-oxidise the coal surface. The attempt was also made using a non-conventional reagent known as black oil as promoter for this type of coal to enhance the floatability. The combinations of the above reagents were also studied to improve the flotation performance. Flotation study was also carried out at optimum reagent conditions to evaluate the flotation performance using flotation column. To characterize the flotation performance with respect to maceral's response, the petrography study was carried out on bulk, concentrate, +500 µm and −500 µm size fractions of tailings of the flotation. Based on the test data, it may be concluded that this coal has potential to give a product of around 31% ash content with 80.4% yield from 41–42% ash content of feed coal. In case of column flotation, the product ash could be reduced further to 26.6% from the same feed coal with 66.5% yield.

Methods for calculating the concentration fields of mirror solar collectors

Two methods for calculating the solar collector concentration fields, i.e., the tomographic and vector methods, are considered. They make it possible to calculate the energy distribution over the surface of the receivers of arbitrary shape. Three calculation examples are presented. The methods are shown to be equivalent.

Removal of hematite from silica sand ore by reverse flotation technique

Reverse flotation of hematite from a local silica sand ore has been investigated using a batch, bench-scale mechanical flotation cell. The effects of various operating parameters such as type and concentration of collectors, type of acid, pH, conditioning time, solid-in-pulp concentration, particle size and temperature have been studied on the hematite removal efficiency by reverse flotation. The results showed that the separation of hematite from silica sand by reverse flotation is possible and good selectivity can be achieved. Experimental data indicate that a larger amount of hematite can be removed from quartz in the presence of hydrochloric acid at elevated temperatures. Also, there exists an optimum collector concentration (Aero 800-series) at which the hematite removal is maximum. A first-order kinetic rate was obtained for the hematite removal from the silica sand.

Analytic solutions for the geometric and optical properties of stationary compound parabolic concentrators with fully illuminated inverted V receiver

Stationary low concentrator collectors ( C < 2), of the CPC type, are of great interest to supply thermal energy for industrial processes, at temperatures below or around 90 °C. In particular, concentrators with fully illuminated inverted V absorbers have attractive properties for thermal energy production. Two classes of CPC’s with inverted V absorber are identified, according to the relationship between the vertex angle of the absorber ( γ) and the acceptance angle of the cavity ( θ a), ( γ ⩾ θ a) or ( γ < θ a). The first class of CPC’s ( γ ⩾ θ a) converge to the fully illuminated CPC with horizontal flat receiver when ( γ = 90°). The second class of CPC’s ( γ < θ a) converge to the fully illuminated CPC with vertical flat receiver when ( γ = 0°). Both limiting cases have been published in the technical literature. This paper analyzes the class of concentrators satisfying ( γ ⩾ θ a). The ideal concentrator corresponding to a fully illuminated wedge absorber and ( γ ⩾ θ a) is a circular involute plus three parabolic segments. Closed-form analytic solutions are derived for its geometric and optical properties: reflector geometry, aperture, height, reflector length, angular acceptance function and average number of reflections for any degree of truncation. The equations obtained can be used as important design tools, for simulation techniques and optimization purposes. The collectible energy for North–South and East–West oriented collectors, for various receiver vertex angle and acceptance angle, was calculated. A cost-benefit figure, given by the relationship between collectible energy and reflector surface, is also estimated. Numerical results for any degree of cavity truncation are presented. As the degree of truncation varies, a clear minimum of the length over aperture ratio ( L/A) occurs. The geometric and optical characteristics of different low concentration CPC’s ( C, between 1 and 2, range of interest of stationary concentrators) show that the cavities with the minimal relationship between the length or height of the reflector surface and the aperture, ( L/A) and ( H/A), and the lower average number of reflections 〈 n〉 correspond to the lowest angular acceptance concentrator (highest nominal concentration). If a concentration of 1.2 is desired, then the smallest ratios of ( L/A), ( H/A) and 〈 n〉, within the set of concentrators with maximal concentration ( C) between 1 and 2, occur for ( C = 2) (nominal acceptance half angle θ a = 30°). Collectible energy results together with a cost-benefit relationship enable to conclude that a good choice for a well-designed collector for the city of Recife-PE, Brazil is: (a) East–West orientation; (b) receiver vertex angles ( γ) of the order of (65°); (c) acceptance angle of the CPC ( θ a = 30°) and (d) concentration of the truncated cavity ( C t) in the interval (1.0–1.2).