1、Processing of coal fines in a water-only cycloneA.K.Majumdera,J.P.BarnwalbaDepartment of Mining Engineering,Indian Institute of Technology,Kharagpur 721302,IndiabAdvanced Materials and Processes Research Institute,Hoshangabad Road,Bhopal 462 026,Indiaa r t i c l ei n f oArticle history:Received 6 Ju
2、ly 2009Received in revised form 19 October 2010Accepted 19 October 2010Available online 31 October 2010Keywords:Water-only cycloneCoal finesStatistical designHydrodynamic analysisa b s t r a c tIt is reported in the literature that a water-only cyclone(WOC),a centrifugal gravity concentrator,is anal
3、ternative to froth flotation to treat coal fines(below 0.5 mm).This unit overcomes the inherent limita-tions of froth flotation and the densemedium cyclone techniques as it requires no chemicals or artificialmedium.The literature dealing with WOC performance to treat coal fines is also limited and a
4、s a result itis not well established how the design variables affect the performance of a WOC while treating coalfines.Therefore,an attempt has been made to develop regression models based on factorial design ofexperiments to quantify the effects of major design variables of a WOC on the beneficiati
5、on characteris-tics of a typical coal fine sample.Further attempts have been made to provide possible explanations onthe observed trends of the data based on simple hydrodynamic analyses.?2010 Elsevier Ltd.All rights reserved.1.IntroductionFroth flotation is commonly used to process coal fines below
6、0.5 mm.However,due to environmental hazards and the use ofcostly chemical reagents,it is imperative to identify an alternativetechnique to process coal fines.The water-only cyclone(WOC)is acentrifugal gravity concentrator that uses water as the medium ofseparation and is also termed as an autogenous
7、 cyclone or auto-medium cyclone.The principle of operation of a WOC differs froma normal conventional cyclone because of its geometry.It has awide angle conical bottom,a long cylindrical portion and a longvortex finder extending along the length of the cylindrical portion.As it does not involve a me
8、dium recovery circuit as needed with adense-medium cyclone(DMC),the process is simple and environ-mentally friendly.The wide cone angle is believed to build up an autogenous bedof particles along the conical section of the cyclone 13.This bedprevents particles from moving unimpeded,and hindered-set-
9、tling conditions prevail 4.The long cylindrical portion increasesthe average retention time of particles inside the cyclone to enablebetter separation.Kim and Klima 5 reported that the performance of a WOC isgreatly influenced by changes in both geometry and operatingconditions.However,literature de
10、aling with the quantitativeprediction on the performance of a WOC at various operating con-ditions to process various coal fines is limited.A research projectwas,therefore,undertaken to quantify the effects of various designand process variables of a WOC on the separation characteristics ofvarious c
11、oal fines.In this paper,an attempt has been made to studythe effects of various design variables of a laboratory model(76 mm diameter)WOC to process a typical coal fine sample col-lected from an Indian coal preparation plant.2.Feed sample preparation and characterizationAround one ton of coal fines(
12、below 0.5 mm)sample was col-lected from the fine coal circuit of Patherdih coal preparation plantof Jharia coalfields,India for the present test work.The entire sam-ple was first dried in an oven for 24 h to remove surface moisture.After proper sampling,using a rotating type sampling device,therepre
13、sentative samples were kept in 50 kg bags for further studies.After repeated sampling,around 500 g of representative sampleswere taken out from a 50 kg bag for the conventional floatsinkstudies.The floatsink data are presented in Table 1.It is evident from the table that the coal fines are liberated
14、 en-ough to make gravity separation effective.The feed ash content ofthe coal fines is 36.13%.Approximately 30%of the feed coal is hea-vier than 1.8 specific gravity having a high ash content of around80%.3.Selection of test variablesFrom the literature review on the WOC,it is observed thatvortex fi
15、nder diameter(VFD),vortex finder length(VFL),coneangle(CA),spigot diameter(SPD),pulp density(PD)and feed inlet0016-2361/$-see front matter?2010 Elsevier Ltd.All rights reserved.doi:10.1016/j.fuel.2010.10.038Corresponding author.Tel.:+91 3222 281838.E-mailaddresses:,(A.K.Majumder).Fuel 90(2011)834837
16、Contents lists available at ScienceDirectFueljournal homepage: important variables.To study the effects of allthe above-mentioned variables was beyond the scope of this work.However,as mentioned earlier,the use of a wide cone angle and along vortex finder make a WOC geometrically different from aDMC.It is also difficult to correctly evaluate the performance ofany cyclone-type device without studying the effects of eitherVFD or SPD.Therefore,for the present study only VFL,VFD andCA were chosen a
