Feridun Boylu

Effect of coal particle size distribution, volume fraction and rank on the rheology of coal–water slurries

AbstractThe aim of this study was to understanding of the effect of coal particle size distributions onrheology of coal–water slurries (CWS). Experiments have been carried out on the coal samples thatwere different in rank. Besides two different Turkish lignites (Soma and Istanbul–Agacli), abituminous coal from Siberia (Russia) has been used. In addition to the determination of thechemical and physical properties of the coal samples, their zeta potentials were also measured. Thepulps of different solids percentage composed of coal particles with d 50 sizes of 19, 35 and 50 Amwere used to determine the effect of volume fraction on the viscosity of the slurry.D 2003 Elsevier B.V. All rights reserved. Keywords: Coal; Coal–water slurries; Viscosity; Fuel; Solid waste; Energy 1. IntroductionCoal–water slurries (CWS) developed as a new alternative to fuel has opened newavenues in the utilisation of coal fines that can avoid prohibitive cost of dewatering.A typical CWS consists of 60–75% coal, 25–40% water and about 1% chemicaladditives. The effects of a number of variables, such as the properties of the coal, theparticle sizes and their distribution, the type and the amount of chemical additives, themethod of preparation of the slurry and the effect of its rheological properties on thebehaviour of CWS are very important [1,2].

The effect of chemicals on the viscosity and stability of coal water slurries

Abstract In this study, the effects of different chemicals that were used as dispersing agent and stabiliser on the stability and viscosity of coal–water slurries have been investigated. In the experiments, anionic type of chemicals—polyisoprene sulphonic acid soda (Dynaflow-K), a derivative of carboxylic acid (AC 1320) and naphthalenesulfonate–formaldehyde condensate (NSF)—were used as dispersing agents and the stabiliser was the sodium salt of carboxymethyl cellulose (CMC-Na). The coal sample used was a bituminous coal (thermal code no. 434) of Turkish origin, with medium volatile matter. The results of the experiments showed that polymeric anionic dispersing agents such as Dynaflow have much greater effect on the viscosity and the stability of coal water slurry.

Production of Ultrapure Bentonite Clays through Centrifugation Techniques

In this study, the production of ultrapure Na-bentonite by centrifuge based techniques for organo and nano composite bentonite industry was investigated. Various parameters including centrifuging time, solids content, and g force were studied to determine the set points (cut size) for theoretical CEC (cation exchange capacity) and recovery limits. The experimental results were modeled using Response Surface Method (RSM) with high responses (regression > 85% and correlation coefficients > 0.85). it is shown that the commercial centrifugation equipment operating with residence time of 10–15 seconds and g values lower than 300 g such as Multi Gravity separator (MGS), Hydrocyclones and Falcon/Knelson concentrators are not suitable for obtaining pure quality Na-bentonite, since the set point size (5-8 µm) is higher than 2 µm which is defined for bentonite of high smectite contents. The RSM models demonstrate that only the kind of separators such as decanter centrifuges with operational g forces higher than 600 may exhibit the closest set point to 2 µm and thus enable the achievement of an ultra pure quality bentonite product. These assumptions obtained from the developed model were confirmed by running tests on Falcon and Mozley hydrocyclone separators.

Modeling of Free and Hindered Settling Conditions for Fine Coal Beneficiation Through a Falcon Concentrator

In this study, the free and hindered settling conditions for coal-shale-clay separation through a Falcon concentrator were determined experimentally using response surface methodology. The model parameters consisted of the separation efficiency and ash content of the concentrate and tailings. Based on the model with the highest response, free settling conditions dominated at centrifugal forces below 100 g and at solid concentrations of up to 30%–35%, especially for coarser particle sizes of 300 µm. These results revealed that, for effective fine coal beneficiation through a Falcon concentrator, the solid concentration should be maintained higher than 30%–35% (with a maximum of 45%–50%) to create hindered settling conditions because separation under these conditions is achieved based on specific gravity. The best results were obtained at a solid concentration of 50%. This finding was interesting because separations through enhanced gravity separators were achieved under conditions similar to separations performed in autogenous media.

Effect of Coal Moisture on the Treatment of a Lignitic Coal through a Semi-Pilot-Scale Pneumatic Stratification Jig

Dry processing methods are well known to be sensitive to the moisture content of the processed material. It is well known that cohesive forces among the particles originating from the surface moisture hinder the individual movement or appropriate stratification of particles during separation. Furthermore, high surface moisture also hampers the flow of feed material. In this study, the effect of total/surface moisture on separation of lignitic coals was investigated by using Allair stratification jig with the aim of finding possible critical surface moisture content for optimum separation. Coal samples in the size of −13 + 4 and −4 mm were processed at different particle total/surface moisture levels to recover as clean coal concentrate as possible along with obtaining tailings with minimum levels of combustibles. It is envisaged that a critical surface moisture on both classification (effective screening) and separation is available around 5.5% surface moisture (corresponding to 15% total moisture) for −13 + 4 mm whereas effective separation is not possible for the −4 mm size range even at minor changes in surface moisture of particles.

Autogenous Medium Fine Coal Washing through Falcon Concentrator

In this study, fine coal from the Tunçbilek Region (Turkey) was subjected to autogenous medium washing tests. The autogenous medium was formed in the presence of clayey minerals with the increased solids concentration of the feed slurry. The clayey minerals also acted as tracer to investigate the conditions of free settling conditions where the particle size based separation was observed. The effect of feed slurry, solids concentration, and the presence of clayey minerals on the separation of coal fines were investigated for the sizes of −300, − 150, and −75 µm. The results reveal that the solids concentrations lower than 10% resulted in the particle size based separation (free settling conditions) and the solids concentrations higher than 10% required the density based separations (hindered settling conditions). Satisfactory separations were achieved at solids concentrations of 10–40%. In the case of higher solids concentrations, an additional increase on separation was ascribed to the development of autogenous medium separation. In addition, the increase in the solids concentration, the presence of clayey minerals on feed also created the autogenous medium separation conditions.

Ultrafine coal flotation and dewatering: Selecting the surfactants of proper hydrophilic–lipophilic balance (HLB)

ABSTRACT Fine and ultrafine coal (−200 µm) enrichment and its further dewatering processes are more difficult than that of coarser sizes. Utilization of this size fraction, however, is inevitable owing to economic and environmental enforcements. Chemical reagents are widely used in fine coal dewatering to achieve lower cake moistures. Surfactants of the same structures are also used effectively in coal flotation within preparation and coal washing processes. These surfactants contain hydrophilic and lipophilic groups, the ratio of which is known as hydrophilic–lipophilic balance (HLB). Flotation separation efficiency and dewatering performance of hard bituminous coal slimes as well as water recovery characteristics and related entrainment degree during the flotation were investigated using eight various nonionic surfactants of different HLB values. The main motivation of the study is to suggest proper reagent properties by which highest efficiency in both flotation and dewatering can be achieved. This can result in significant economic advantages for industrial processes and also reduce the environmental disadvantages of using chemicals. The flotation separation efficiency of the most lipophilic surfactants (lower HLB) and conventional oily collectors were found to be the highest, while the surfactants with moderate HLB (~10) showed the best filtration performance.

An application of the “Pressure drop controlled discharging system” on pneumatic jigs

ABSTRACT Airjigs employ air instead of water or heavy liquids as separating media, thus separation is achieved by stratification through the fluidizing and pulsing (and/or vibrating) effects. In practice, although stratification is achieved successfully, proper discharge of the float and sink (light and heavy minerals) materials can be accomplished. In addition, the feed quality from mine sites can vary and this may negatively affect the optimized operational conditions. In this case, the discharging system of separators should be controlled automatically. In the pneumatic separators, this is currently achieved through a nuclear detector that controls the discharging system. We developed an alternative discharge controlling system based on the pressure drop (Dp), since the nuclear detector is a risky radioactive source that requires careful control for avoiding the radioactive leakage. In addition, it experiences considerable failure on application. In this study, an easy, secure, and effective Dp controlled discharging system is proposed as a new technique to control the discharging system and sustain the product qualities.