A Study to Recover Coal from Turkish Lignite Fine Coal Tailings: Comparison of Falcon Concentrator and Multi Gravity Separator (MGS) PDF

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A Study to Recover Coal from Turkish Lignite Fine Coal Tailings: Comparison of Falcon Concentrator and Multi Gravity Separator (MGS) M. Fatih CAN, Selçuk ÖZGEN, Eyüp SABAH*, Department of Mining Engineering, Afyon Kocatepe University, 03200 Afyonkarahisar, Turkey ABSTRACT Lignite coal is the primary...

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A Study to Recover Coal from Turkish Lignite Fine Coal Tailings: Comparison of Falcon Concentrator and Multi Gravity Separator (MGS)

M. Fatih CAN, Selçuk ÖZGEN, Eyüp SABAH*, Department of Mining Engineering, Afyon Kocatepe University, 03200 Afyonkarahisar, Turkey

ABSTRACT Lignite coal is the primary domestic source of energy in Turkey, for this reason effective exploitation of the reserves of Turkey is very crucial. In Turkey the fine tailings of lignite coal processing plants are sent in most cases to the tailing ponds without any treatment. However, recovery of fine coals from coal preparation tailings and recycle of processing water are of both economic and environmental incentives, not only preserving natural resources but also reducing environmental consequences of discharging large volume of tailings. Recent developments in the use of various gravity equipments in fine-coal beneficiation have been discussed and their relative merits have been compared. In this study, the possibility of beneficiation of lignite tailings included quartz, kaolinite, siderite, mica/illite, dolomite, feldspar compounds in the Tunçbilek/Kütahya region was investigated by Multi Gravity Separator (MGS) and Falcon Concentrator and these two methods compared. The entire exercise revealed that the MGS could produce a clean coal with an ash content of 22.83%, 5696 kCal/kg calorific value and a recovery of 49.32% and that the Falcon could produce a clean coal with an ash content of 40.26%, 4224 kCal/kg calorific value and a recovery of 64.53% from a feed coal having an ash content of 66.21% and 1835 kCal/kg calorific value.

Key words: Fine lignite coal tailings, Waste processing, Hydrocyclone, Falcon Concentrator, Multi Gravity Separator (MGS)

*

Corresponding author: Prof. Dr. Eyüp Sabah

Afyon Kocatepe University Department of Mining Engineering 03200 AFYONKARAHİSAR e-mail: [email protected] Phone: +90-272-228-1423 / 1320 Fax: +90-272-228-1422

1. INTRODUCTION Coal is a fossil fuel which is the most abundant and geographically scattered all around the world. In world general 826 billion tones apparent reserve of coal is estimated. In other words, this means the world has coal reserves those can sustain more than 119 years [BP Statistical Rewiev, 2009]. However coal has this much long consume period, apparent oil and natural gas reserves consumption period is estimated between 40 to 60 years according to current production rates [Dağdelen, 2006]. For this reason coal will be one of the most important energy resources of the future.

As the demand on clean coal increase with developing environmental standarts, an increase of modern coal preparation plant numbers is observed in latest years. Modern coal preparation plants are consisting of coarse, medium and fine coal cleaning circuits. Fine coal has size distribution below 28 meshes (0.589 mm) and designated as slime in coal cleaning circuits. Generally, this size fractioned material must be processed in all coal preparation plants. In past year’s coals of below 28 meshes (0.589 mm) size discharge was economic, but with swiftly developing technologies fine coals are also utilized. Also today’s mining processes produces more fine materials as the mechanization applications have more frequently applied. Therefore it is a must to recycle the coal in fines. In this manner recovered fine coals are prevented to deploy in waste and avoid a series of problem in waste disposals.

Today 5% flotation and 95% gravimetric processes are used to prepare the produced coal all around the world. Gravimetric processes applied for coarse coal preparation have low cost, high capacity and selectivity. Gravimetric processes are also utilized for cleaning fine coal. However, some other problems arouse within the used separators. Only with developing technologies, some advanced gravity separation equipments as hydrocylones, Multi Gravity Separator (MGS), Falcon and Knelson concentrator, Kelsey Jig are used for ultra fine coal enrichment. There are many conducted researches with successful results on enrichment of coals [Honaker, 1995; Honaker et al., 1996; Honaker, 1998; Honaker, 2000; Parekh and Khalek, 2002; Majumder et al., 2007a; Majumder and Barnwal, 2008; Malkoç, 2008]. Yıldırım et. al. [1995], revealed clean coal with 75.8% efficiency and 7.01% ash content from 36.6% ash bearing run of mine Zonguldak coal by applying MGS equipment. Aslan et. al. [1999] examined enrichment of Yeniçubuk-Gemerek lignite coal with MGS and gained clean coal with 79.82% efficiency and 19.23% ash content from lignite coal of 35.75% ash content. In another research with MGS equipment for Manisa-Soma hard lignite coal which has 35.9% ash content was enriched and clean coal with 79.5% recovery efficiency and 18% ash content was obtained [Çiçek et al., 2002]. Abd-Elrahiem, [2003] utilize carrier column flotation to enrich very fine coal of 10.13% ash content, and as result obtained clean coal with 79.94% efficiency and 5.15% ash content. Li et. al. [2003] used cyclo-micro bubble column to clean 47.11% ash containing coal slime and finally obtained clean coal with 79.26% combustible recovery and 10.55% ash content. Majumder et. al. [2007b] was made to study the effects of different process variables on the performance of an MGS for the beneficiation of coal fines. The MGS is capable of producing clean coal having an ash content of 14.67% with a 71.23% yield (the float-sink yield was 72% at the same ash level) from a feed coal ash of 24.61%.

In this study, the aim is to recover -0.5 mm coal from Tunçbilek/Kütahya coal plant tailings and investigate the effect of MGS and Falcon concentrator parameters on coal enrichment. Ash content and coal recovery rates are designated as performance criteria.

2. MATERIALS AND METHODS 2.1 Materials Lignite coal tailings obtained from Tunçbilek Coal Preparation Plant of G.L.I of Turkish Coal Enterprises (Kütahya-Turkey) were used in this study. The samples were taken from slurry waste with standard of TS ISO 5667-10.

2.2 Methods 2.2.1. Characterization Tests A number of qualitative and quantitative analysis techniques were used to characterize the coal tailings. The chemical composition of the tailings was defined by X-ray fluorescence (XRF). The mineral composition of the tailings was determined by X-ray diffraction (XRD) method using a Rigaku-Giger Flex analyzer. The particle size distribution of the tailings was obtained using a Retsch AS200 Sieve Shaker and Fritsch-Analysette 22 Particle Size Analyzer. The specific gravity of the tailings was determined by Quantachrome Ultrapycnometer 1000. The ash and sulfur contents of the tailings were determined according to ISO 1171 and ISO 351, respectively. In addition, the calorific value was determined based on ISO 1928. Following the characterization tests, the beneficiation studies were immediately initiated before any physical and chemical decomposition of tailings.

2.2.2. Test Procedure Before MGS and Falcon Concentrator experiments, classification tests were performed using a hydrocyclone. The aim of this test was to separate the clay and/or carbonate minerals from the coal. Since large amounts of fine and ultra fine particles in the tailings cause a low cut point, a small diameter hydrocyclone (44 mm) was selected for the experiments. Underflow products were concentrated using a Multi-Gravity separator (MGS) or Falcon Concentrator. For each MGS and Falcon Concentrator tests, 2000 g of the dry coal sample was used. The effects of varying operating parameters such as drum speed, tilt angle, shaking amplitude, wash water rate, pulp feed rate and pulp solid ratio was investigated for MGS. The shaking frequency of the MGS was fixed at 4.9 cps for all the experiments. To obtain required solids ratio in feed, measured quantities of solids and water were mixed in the slurry tank. The MGS variables were adjusted at necessary levels. The feed slurry was pumped into the MGS drum at the required flow rate using the peristaltic pump while the MGS was in operation. Samples from the clean coal and tailing streams were collected at steady-state condition. The samples were filtered, dried and analyzed for ash content and combustible recovery. When changing a parameter in each test, the other parameters were kept constant and the optimization results were used in the other tests. However, a laboratory-scale Falcon SB-40 concentrator was used for the tests. Once the optimum hydrocyclone conditions were identified and applied, the concentrate was further processed in the Falcon concentrator. Ash rejection was achieved by optimizing variables such as gravity force, water pressure, pulp solids ratio and feed rate. The classification and concentration test results were analyzed with Minitab for MGS and Falcon Concentrator. The model included a set of equations relating the variables, ash content and combustible recovery in the clean coal.

3. Result and Discussion 3.1 Characteristics of Tailings The results of chemical analysis for the samples were presented in Table 1. As seen in Table 1, LOI of the samples are about 37% of Tunçbilek which means that the amount of organic material (coal) in the tailings was significant when compared to the amount of inorganic impurities. When Figure 1 was examined, - 80% of the Tunçbilek coal tailing was -28μm.

Table 1. Chemical analysis of coal tailings. Composition Weight (%)

Cumulative Distrubition, %

SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O TiO2 P2O5 MnO LOI

35.53 13.34 5.89 3.68 1.53...