1、英文原文Processing of coal fines in a water-only cycloneA.K. Majumder,J.Pa,*. Barnwalba Department of Mining Engineering, Indian Institute of Technology, Kharagpur 721302, Indiab Advanced Materials and Processes Research Institute, Hoshangabad Road, Bhopal 462 026, IndiaAbstract It is reported in the li
2、terature that a water-only cyclone (WOC), a centrifugal gravity concentrator, is an lternative to froth flotation to treat coal fines (below 0.5 mm). This unit overcomes the inherent limitations of froth flotation and the densemedium cyclone techniques as it requires no chemicals or artificial mediu
3、m. The literature dealing with WOC performance to treat coal fines is also limited and as a result it is not well established how the design variables affect the performance of a WOC while treating coal fines. Therefore, an attempt has been made to develop regression models based on factorial design
4、 of experiments to quantify the effects of major design variables of a WOC on the beneficiation characteristics of a typical coal fine sample. Further attempts have been made to provide possible explanations on the observed trends of the data based on simple hydrodynamic analyses.Keywords:Water-only
5、 cyclone Coal fines Statistical design Hydrodynamic analysis1 IntroductionFroth flotation is commonly used to process coal fines below0.5 mm. However, due to environmental hazards and the use ofcostly chemical reagents, it is imperative to identify an alternativetechnique to process coal fines. The
6、water-only cyclone (WOC) is acentrifugal gravity concentrator that uses water as the medium ofseparation and is also termed as an autogenous cyclone or automediumcyclone. The principle of operation of a WOC differs froma normal conventional cyclone because of its geometry. It has awide angle conical
7、 bottom, a long cylindrical portion and a longvortex finder extending along the length of the cylindrical portion.As it does not involve a medium recovery circuit as needed with adense-medium cyclone (DMC), the process is simple and environmentallyfriendly.The wide cone angle is believed to build up
8、 an autogenous bedof particles along the conical section of the cyclone 1-3. This bedprevents particles from moving unimpeded, and “hindered-settling” conditions prevail 4. The long cylindrical portion increasesthe average retention time of particles inside the cyclone to enablebetter separation.Kim
9、 and Klima 5 reported that the performance of a WOC isgreatly influenced by changes in both geometry and operatingconditions. However, literature dealing with the quantitativeprediction on the performance of a WOC at various operating conditionsto process various coal fines is limited. A research pr
10、oject was, therefore, undertaken to quantify the effects of various designand process variables of a WOC on the separation characteristics ofvarious coal 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 proces
11、s a typical coal fine sample collectedfrom an Indian coal preparation plant.2 Feed sample preparation and characterizationAround one ton of coal fines (below 0.5 mm) sample was collectedfrom the fine coal circuit of Patherdih coal preparation plantof Jharia coalfields, India for the present test wor
12、k. The entire samplewas first dried in an oven for 24 h to remove surface moisture.After proper sampling, using a rotating type sampling device, therepresentative samples were kept in 50 kg bags for further studies.After repeated sampling, around 500 g of representative sampleswere taken out from a
13、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 enoughto make gravity separation effective. The feed ash content ofthe coal fines is 36.13%. Approximately 30% of the feed coal is heavierthan 1
14、.8 specific gravity having a high ash content of around 80%.3 Selection of test variablesFrom the literature review on the WOC, it is observed thatvortex finder diameter (VFD), vortex finder length (VFL), coneangle (CA), spigot diameter (SPD), pulp density (PD) and feed inletpressure (FIP) are impor
15、tant 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 ofan
16、y cyclone-type device without studying the effects of eitherVFD or SPD. Therefore, for the present study only VFL, VFD andCA were chosen as variable parameters, whereas the PD, FIP andSPD were kept at constant levels of 10% by weight, 0.7 kgf/cm2and 20 mm, respectively.4 Experimental procedureA 76 mm cylindrical diameter WOC made of stainless steel wasused. A closed circuit test rig, consisting of a slurry pump and a bypassline was used for carrying
