Stripa ağır ortam aygıtı ile kömürün zenginleştirilmesi

Abstract

Bu çalışmada, stripa ağır artanı aygıtının kömür zenginleştirmesinde uygulanabilirliği araştırılmıştır. Deneysel çalışmalarda Keleş, Saray ve Sama bölgelerin den alınan linyit kömür numuneleri ile Zonguldak'tan alınan taşkömürü numunesi kullanılmıştır. Yapılan araştırmanın birinci bölümünde, numunelerin yapısal, fiziksel ve kimyasal özelliklerinin yanısıra yıkanabilme özellikleri saptanmıştır. 4 ayrı numune ile yapılan yüzdürme-batırma deneyleri sonucunda, kabul edilebilir içerikte düşük küllü temiz kömür ürünlerinin üretilebileceği belirlenmiştir, Araştırmanın ikinci bölümünde; stripa ağır ortam aygıtı ile zenginleştirme deneylerinde ortam yoğunluğunun, kaldırma suyu miktarının ve parça boyutunun ayırmaya etki si incelenmiştir. -50+1 Omm boyut grubunda, ortam yoğunluğunun ayırma üzerindeki etkisi incelenirken, 1.0,1.30 ve 1.45 gr/cm3 ortam yoğunluklarında yapılan deneylerde, optimum sonuçların 1.30 gr/cm3 'de elde edildiği görülmüştür. -50+1 Omm boyut grubunda kaldırma suyunun etkisinin incelendiği deneylerde 1.30 gr/cm3 ortam yoğunluğunda; 0,10, 20 ve 40 It/dk kaldırma suyu verilerek deneyler yapılmış ve en uygun sonuçların 20 lt/dk kaldırma suyu verildiğin de elde edildiği belirlenmiştir. Tane boyutu dağılımının ayırmaya etkisinin incelen diği deneylerde; -50+1 Omm boyut grubu değişik fraksiyon lara ayrılarak (-50+30, -30+10 ve -19+1 Omm) deneyler ya pılmıştır. Ayrıca, -50+1 Omm boyut grubu hiç bir boyut- landırmaya tabi tutulmadan direkt olarak da zenginleşti rilmiştir. Sonuçta numunenin homojen olarak beslenmesi durumunda daha iyi sonuçların alındığı tesbit edilmiştir. Ayrıca hazırlanan yapay karışımlarla; -50+30, -30+19 ve -İ 9+10 nm boyut gruplarında gerek linyit, gerekse bitümlü kömürler için zenginleştirme kademe sayıları saptanmıştır. Çalışmanın son bölümünde ise stripa ağır ortam aygı tının ayırma performansı incelenmiştir. Elde edilen so nuçlara göre, stripa ağır ortam aygıtının Ep değerleri, Keleş kömürü için 0.040-0.203, Saray kömürü için 0.055- 0.200, Soma kömürü için 0.025-0.150, Zonguldak kömürü içinse 0.04D-0.140 olarak bulunmuştur. Bu değerlere göre, stripa ağır ortam aygıtının iri kömürlerin zenginleştiril- mesinde jiglere alternatif olabileceği sonucuna varılmıştır,

In this study, the applicability of stripa heavy medium process is investigated for the beneficiation of coal. The stripa method for sink-float seperation, differs in two respects from now used methods, namely, as to the medium used and as to the type of the seperator. In other methods, the content of the solid renocked by volume can't be higher than about 40% because in thicker suspensions the viskosity is too high for a god seperation. According to the Stripa method the seperation takes place in a bed -that is, a layer of settled sand-sized particles filled with water- instead of in a suspension. Such a bed contains usually about 60% of solids renocked by volume. The medium forming the bed and the crude ore to be separated are continuously supplied at one end of the trough and the trough is shaken in such a way that a very mobile bed is formed which moves rapidly from the feed end to the discharge end of the trough. During the passage through the trough, the crude ore is separated so that particles having a higher density than the specific gravity prevailing in the bed collect at the bottom of the trough, whereas particles having a lower density float on the bed. At the discharge end of the trough there is a plate at a suitable level above the bottom of the trough which divides the bed in an upper and a lower layer. As the depth of the bed is kept low end the viscosity in the mobile bed also is low, due to the coarse- sized particles, the time necessary for carrying out the separation is short. Ample time is provided as the trough is rather long. In order to facilitate the separation, a small flow of water is usually pressed from the bottom of the trough through the bed. The flow of water can be, and kept so low that the solid fraction in the bed is not appreciably decreased. The water can then be looked upon as a lubricant for the particles and the bottom of the trough, so that the bed becomes more mobile. With the water, it is possible to control the mobility and also the height of the bed flows faster forward in the trough than a more immobile bed. As the height of the bed above separating plate to some small extent determine the specific gravity of the separation -a higher bed gives a Vll somewhat higher specific gravity- the flow of water is also a means of controlling that quality. The Stripa device used in the experimental studies consists of a cone thickener in which the bed medium is thickened and stored, a washing screen by which the medium is separated from the sink and float, and a pump which pumps the bed medium back to the cone thickener. The shaking trough consists of a rectangular box with a length of 200 cm, a width of 16 cm and a height of 20 cm. The box is supported by three flexible rods which are inclined backward from the vertical at an angle of about 3° or 4°. The trough is shaken with a eccentric head motion. The effect of this motion is to make the trough approach its reversing point and recede from it much greater speed at the forward end than at the backward end of the stroke.This motion is the best as it gives a very mobile bed and a quick forward movement of the load in the trough. The length of stroke is 15 mm and the speed is 370 stroke per minute. Inserted at the discharge end of the trough is the separating plate by which the stream of material in the trough is divided in an upper and a lower layer. The height of the separating plate above the bottom of the trough can be changed, but provided that the maximum particle size in the feed does not exceed 50 mm; the maximum height is 60 mm. The bottom of the trough is perforated so that water can be pressed trough the bed.The water is controlled so that the mobility in the bed slowly decreases from the feed to the discharge end. The bed medium is discharged from the apex of the cone thickener through a valve by which the flow is regulated. The water or air is used to stir the settled medium in the cone before starting to flow. There is also a control panel to start moving the stripa trough, medium pump and washing screen. In the experimental studies, three types of lignitic coals from Keles, Saray and Soma regions and one bituminous coal from Zonguldak are used. Vlll The mineralogical, physical, chemical and washability properties of coal samples have been determined with the aim of identifying the conditions for the stripa heavy-medium process. In the first part of this investigation a series of sink and float experiments has been performed in the size range of -50 +10 mm coal samples. A summary of the results is given below: * Keles coal; a clean coal with an ash content of 13.77% and 78.3% combustible recovery at a medium density of 1.30 g/cm3 was obtained, * Saray coal; a clean coal with an ash content of 13.61% and 83.5% combustible recovery at a medium density of 1.30 g/cm3 was obtained, * Soma coal; a clean coal with an ash content of 7.89% and 74.4% combustible recovery at a medium density of 1.30 g/cm3 was produced, * Zonguldak coal; a clean coal with an ash content of 9.58% and 71.2% combustible recovery at a medium density of 1.30 g/cm3 was produced, The second part of this investigation encompasses the effect of medium density, buoyancy force and particle size on the separation performance of stripa process. The investigation on the effect of medium density, the experiments were conducted at 1.0, 1.30, 1.45 specific gravities. It was shown that the optimum results are obtained at 1.30 g/cm3 while 1.0 g/cm3 density medium is not sufficient to float the coal particles. At specific gravities higher than 1.30 g/cm3, the pump pressure was not maintained at the same level; the latter caused medium to behave as if at a lower specific gravity. The effect of buoyancy force was investigated at four levels of flow rate; 0, 10, 20 and 40 1/min. at a medium density of 1.30 g/cm3. For example, cleaning of -50+10 mm Keles coal at 1.30 g/cm3 medium density in the absence of buoyancy force yielded a clean coal with 16.96% ash and 51.1% combustible recovery. At 20 1/min. flow rate the ash content decreased to 14.37% whereas the combustible recovery increased to 60.9% This is because the buoyancy force of the water raises the relative density of IX the medium throughout the suspension. But at excessive flow rates, the buoyancy force causes turbulence and hinders the uniformity of the medium density. The effect of particle size range was investigated in the -50 +10 mm size range with the individual size fractions, i.e. -50 +30, -30 +19, -19 +10 mm. The comparison of feeding the coal samples with the individual size fractions and the whole size range indicates that the narrower size fraction gives the better results. The number of concentration stages was also studied using a synthetic mixture composed of clean coal and quartz. The experiments performed in different size fractions reveal the following: * -50 +30 mm Keles and Saray coals required only two concentration stages to achive approximately 100% recovery, while the -30 +19 mm fraction attained 95% recovery. The -19 +10 mm Keles and Saray coals required three concentration stages to obtain 80-85% recovery. * -50 +30 mm Soma and Zonguldak coals required only two concentration stages to obtain approximately 100% recovery, whereas the - 30 +19 mm fraction attained 95-100% recovery. The -19 +10 mm required three concentration stages to obtain 85-90% recovery. The above results show that as the coal quality increases, the number of concentration stages generally decreases. The separation performance of stripa process has been determined under various conditions. The separation performance was evaluated by probable error factor (Eckart probable number, Ep). The Ep values were calculated for the tests using -50 +10 mm size fraction and under the optimum conditions. The following Ep values were found: For Keles coal; Ep- 0.040-0.203 For Saray coal; Ep= 0.055-0.200 - For Soma coal; Ep= 0.025-0.150 - For Zonguldak coal: Ep= 0.040-0. 140 The above results and the calculated Ep values show that the stnpa process can be an alternative to Baum jigs particularly in the size range of - 50 ^20 mm. The stripa device used in our experiments is not suitable for sizes larger than 50 mm due to the dimensions of the trough and the splitter height. It is believed that particle sizes larger than 50 mm can be easily treated by stnpa; because higher efficiencies were obtained in the size range of -50 +19 mm than -19 +10 mm. This demonstrates that processing of coal by stripa can be a good alternative to Baum jigs in the size range of -100 + 19 mm.