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International Journal of Coal Preparation and Utilization

ISSN: 1939-2699 (Print) 1939-2702 (Online) Journal homepage: https://www.tandfonline.com/loi/gcop20

Investigation of Using Table Type Air Separatorsfor Coal Cleaning

M. Kademli & O. Y. Gulsoy

To cite this article: M. Kademli & O. Y. Gulsoy (2013) Investigation of Using Table Type AirSeparators for Coal Cleaning, International Journal of Coal Preparation and Utilization, 33:1, 1-11,DOI: 10.1080/19392699.2012.717566

To link to this article: https://doi.org/10.1080/19392699.2012.717566

Published online: 18 Jan 2013.

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Investigation of Using Table Type AirSeparators for Coal Cleaning

M. KADEMLI1 AND O. Y. GULSOY2

1Hacettepe Vocational School of Higher Education, HacettepeUniversity, Ankara, Turkey2Department of Mining Engineering, Hacettepe University,Ankara, Turkey

In the present study, the application of table type air separators was investigated onthree lignite samples and a hard coal sample collected from several regions inTurkey. The Yenikoy lignite sample was used to determine optimum test conditions.These test conditions were used to study Soma, Corum lignite, and Zonguldak hardcoal samples with reference to feed rate, riffle height, table frequency, and tableslope. Results were analyzed to determine calorific values and ash contents of cleancoal and tailing samples. It is concluded from the study that the table-type airseparator can be used for the Turkish coal with high-separation efficiency.

Keywords Air separator; Coal; Dry concentration

Introduction

Coal cleaning is applied to remove ash-bearing material such as silicate minerals,carbonate minerals, pyrite, etc. from coal. Density differences between coal andimpurities is generally utilized in the separation process, using a heavy mediumcreated using finely ground magnetite (under 74 micrometer). Magnetite is mixedwith water to prepare a suitable medium density between coal and ash-bearingmaterial densities. Currently, water-based coal preparation technologies are heavilyused around the world. However, wet processing of coal requires a large amount ofwater. Also, the final coal product requires dewatering and that adds additional costto the process. Water-based coal preparation technologies are unsuitable, especiallyin arid areas [1–3]. The wet technologies also have some other disadvantages, such asdischarge and storage of tailings problems [4–7].

Dry cleaning of coal offers a new alternative approach in coal cleaning. Some ofthe dry coal-cleaning processes such as air dense-medium fluidized Bed (ADMFB),air jigs, and FGX Separators are being used on an industrial scales around theworld. The operational costs of the dry coal-cleaning techniques are generally lower

Received 12 December 2011; accepted 30 July 2012.The authors would like to acknowledge The Scientific and Technological Research

Council of Turkey for their financial support.Address correspondence to Murat Kademli, Hacettepe Vocational School of Higher

Education, Hacettepe University, Ankara, Turkey. E-mail: kademli@hacettepe.edu.tr

International Journal of Coal Preparation and Utilization, 33:1–11, 2013Copyright # Taylor & Francis Group, LLCISSN: 1939-2699 print=1939-2702 onlineDOI: 10.1080/19392699.2012.717566

1

than wet methods, and the investment costs are also generally lower. The results ofan economic evaluation for different dry cleaning processes are given in Table 1.

Air-based separation technologies, like water based, utilizes density differencesin coal and ash-bearing minerals to separate one from the other [8]. It has beenshown that a highly efficient separation can be achieved between coal andash-bearing material if the ratio of particle sizes being treated is 3:1 or lower [9].

The principle of the air-flow machine involves stratifying coal and, after thelower layer (reject) is formed, it travels towards the other end of the table where theyare discharged. The upper layer (clean coal) continues to travel on the top of thelayer and is discharged at the lower end of the table. The pulsating air inside thebed creates dust particles, which are sucked into an overhead hood and are recoveredby a dust collector cyclone followed by a cloth filter [7, 10].

In the ADMFB process, the machine utilizes fluid-like characteristics of agas-solid fluidized bed. In this process, fine media particles are transformed froma fixed state to a pseudo-fluid state by fluidizing air through an air distributor platelocated at the bottom of vessel. During fluidization as air velocity is increases, theparticle bed goes from a fixed bed to a fluidized bed and to a transported bed,respectively [11–16]. Zhenfu et al. [17] reported that by using the ADMFB a goodseparation performance was achieved for the 50� 6mm size fraction obtaining cleancoal and tailings containing 11.80% and 85.75% ash, respectively, with a ProbableError (Ep) value of 0.03. Currently, there is no commercial installation due to thedifficulties in operating the system.

In this study, a table type air separator was selected because of its easy-to-con-trol operational parameters. The main goal of the study was to study the effective-ness of the table type air separator in cleaning Turkish coal. Another goal was todetermine the best operating parameters of different coal samples.

Table Type Air Separator

The table type air separator is an innovative design similar to the FGX dry com-pound separator marketed by the Tangshan Shengzhou Machinery Co., Ltd. Separ-ation principles of both of these separators are similar as both units employ acombination of table vibration and air to develop a fluidized bed on the separatorsurface, labelled as a ‘‘compound separator.’’ The fluidized bed formation enhancesthe separation process and the size range that can be treated. As a result, a relativelycompact unit installation allows high capacity per floor space [18, 19]. Gongmin andYunsong reported that the relative separation densities of the dry separator werebetween 1.78 g=cm3 and 1.98 g=cm3; Ep values were between 0.15 and 0.25 [20].The efficiency of FGX machine is relatively high compared to air jigs.

Table 1. Cost comparison of various dry beneficiation processes

ProcessProduct quality

(kcal=kg)Yield(%)

Process operatingcost ($=t)

Conventional 5947.11 84.2 1.79(ADMFB) 6281.5 68.4 1.91Electrostatic Separator 6639.75 59.9 1.42Air Table 6281.5 71.4 1.78

2 M. Kademli & O. Y. Gulsoy

Materials and Method

The apparatus used in this study is shown in Figure 1. The coal to the unit was fedusing a vibrating feeder. Splitters were positioned at the discharge ends to collectclean coal and tailings. The position of splitters was determined in pre-experimentsand was kept constant. Air for the stratification was generated using an air blower.The table surface had openings of 3mm size with the distances between openingsalso 3mm, for accessing air for fluidization. Two frequency control devicescontrolled both air supply and vibration.

For the study, a synthetic feed sample was used. The sample composed of 50%coal and 50% of ash mineral particles for providing easier visual observation of theseparation performance. The separation efficiency was analyzed by weighing concen-trate and tailings materials. Several other parameters such as particle size of feed,table slopes (horizontal and diagonal), discharge splitter position, feed rate, riffleheight, and table frequency within a wide range of intervals and multiple steps werealso investigated. After testing all parameters, some of the parameters were fixed tothe optimum positions in accordance with observed separation efficiency. Forexample, the horizontal slopes of the table and splitter position were fixed.

Figure 1. General profile of apparatus. (Color figure available online.)

Table 2. Dry table parameters used for the study

Name ofparameter Step 1 Step 2 Step 3

TableFrequency

45Hz (2700rev=min)

42Hz (2520rev=min)

39Hz (2340rev=min)

Table slope (14.6�) 0.26 (11.8�) 0.21 (8.5�) 0.15Feed Rate 1.32 t=h=m2 1.68 t=h=m2 2 t=h=m2

Riffle height 1.5 cm 2 cm 2.5 cm

Table Type Air Separators 3

Figure 2. Particle size distributions of all feed samples. (Color figure available online.)

Figure 3. Washability curves of Yenikoy lignite samples. (Color figure available online.)

Figure 4. Washability curves of Soma lignite samples. (Color figure available online.)

4 M. Kademli & O. Y. Gulsoy

Parameters, like feed rate, riffle height, table frequency, and diagonal slope ofthe table were changed in three steps as shown in Table 2. All of these steps weredetermined according to observations of pre-experiments and previous investigationson dry coal cleaning.

Out of 81 test conditions, the optimum testing conditions were determined inorder to obtain products with high calorific value and low-ash content. Next, thesetest conditions were repeated for other coal samples like Soma, Corum lignite sam-ples, and Zonguldak hard coal samples. The particle size distributions of all samplesare shown in Figure 2, and the washability curves are shown in Figures 3, 4, 5, and 6.

All tests were conducted basically in a batch mode with fixed air flow for eachrun. For each test, the system was cleaned before using a new feed. Coal sampleswith a particle size of �38þ 6mm were fed to table surface with the help of vibrating

Figure 5. Washability curves of Corum lignite samples. (Color figure available online.)

Figure 6. Washability curves of Zonguldak hard coal samples. (Color figure available online.)

Table Type Air Separators 5

feeder, at the end of which two different products were produced from tabledischarge units: clean coal and tailings. The clean coal and tailings were analyzedfor their calorific values and ash content. The proximate analysis of feed samplesis given in Table 3.

Results and Discussion

The Tromp curve was plotted from the data acquired from the various tests andwashability curves. The following equation was used for Ep calculations:

Ep ¼ q25� q752

; ð1Þ

Where, q25 and q75 are densities of the particles with 25% and 75% of dispersionfactor, which is the probability of elutriation.

Tromp curve test conditions were conducted by keeping the frequency and slopeat 45Hz and 0.15 degrees, respectively. Figure 7 shows the test results obtained with

Figure 7. Yenikoy lignite test results. (Color figure available online.)

Table 3. Proximate analysis of the various coal feed samples

Samples

Originalcalorificvalues

(kcal=kg)

Drycalorificvalues

(kcal=kg)

Originalash

content(%)

Dryash

content(%)

Originalvolatilematerial

(%)

Dryvolatilematerial

(%)

Originalmoisture

(%)

Yenikoy 1474 1630 42.56 45 37.79 40.41 6.7Soma 2375 2881 31.57 36.94 34.45 41.04 14.53Corum 1264 1667 50.81 61.81 27.15 33.03 17.8Zonguldak 3737 3807 47.32 48.08 20.04 20.36 1.59

6 M. Kademli & O. Y. Gulsoy

Table

4.Listofoptimized

testsresults

Test

sample

Feed

rate

(t=h=m

2)

Net

concentration

calories

(kcal=kg)

Mass

of

concentration

(%)

Ash

of

concentration

(%)

Ash

of

tailing(%

)

Combustion

recovery

(%)

Rem

oval

ash

content

(%)

Net

tailing

calories

(kcal=kg)

Yenikoy

1.32

3391

55.4

38.04

51.40

61.30

52.10

786

1.68

3305

59.8

36.25

52.53

68.08

47.99

642

23196

62.5

36.31

53.82

71.08

45.87

606

Soma

1.32

3776

58.5

30.20

44.18

64.81

49.55

1241

1.68

3573

67.8

31.66

45.14

73.55

39.28

1156

23396

70.3

32.49

44.31

75.33

35.57

1258

Corum

1.32

2320

52.4

53.42

68.36

64.23

52.48

1140

1.68

2218

55.1

54.42

67.98

66.09

49.23

1170

22194

56.5

54.76

67.51

67.26

47.37

1195

Zonguldak

1.32

5032

54.2

33.27

71.92

69.55

68.62

1308

1.68

4886

61.1

33.70

74.32

77.90

60.23

1198

24602

64.3

35.12

74.73

80.23

55.58

1186

7

the Yenikoy lignite. Most favorable test results are given in Table 4. Ep and d50values were calculated from the Tromp curves shown in Figures 8, 9, and 10 andare also shown in Table 5.

The parameters effecting the separation process were also investigated duringthe course of tests and it was observed that increasing the feed rate and table sloperesulted in decreasing calorific values and tailing ash contents of clean coal, whileyield and combustion recovery increased. Conversely, increasing table frequencyand riffle height resulted in increasing calorific values and tailing ash contents of

Figure 9. Tromp curves of all coal samples in 1.68 t=h=m2 feeding rate. (Color figure availableonline.)

Figure 8. Tromp curves of all coal samples in 1.32 t=h=m2 feeding rate. (Color figure availableonline.)

8 M. Kademli & O. Y. Gulsoy

Figure 10. Tromp curves of all coal samples in 2 t=h=m2 feeding rate. (Color figure availableonline.)

Table 5. Ep and d50 values obtained at various feed rates

Yenikoy Soma Corum Zonguldak

Test conditions Ep d50 Ep d50 Ep d50 Ep d50

1.32 t=h=m2 0.165 1.67 0.19 1.67 0.18 1.69 0.13 1.661.68 t=h=m2 0.175 1.64 0.195 1.65 0.19 1.67 0.13 1.632 t=h=m2 0.185 1.64 0.23 1.69 0.21 1.79 0.17 1.67

Figure 11. Yenikoy lignite sample fractional Ep analysis. (Color figure available online.)

Table Type Air Separators 9

clean coal while yield and combustion recovery were decreased. It was alsoconcluded that the particle size distribution was the most important parameter thataffected the separation process. The maximum particle size of feed affected the sep-aration Ep values directly. The relationships of Ep values with maximum particlesize are shown in Figures 11 and 12.

With lignite samples, most favorable results were obtained from Yenikoy samplewith an Ep value of 0.16. Corum and Soma samples had 0.18 and 0.19 Ep values,respectively. Their calorific values were elevated from 1630 kcal=kg to 3391 kcal=kgwith the combustion recovery of 61.3% while the calorific value of tailing decreasedto 768Kcal=kg with a 52.1% ash content. Zonguldak hard coal sample had thelowest Ep value of 0.12. During the process, its calorific value elevated from3961 kcal=kg to 5032 kcal=kg with the combustion recovery of 69.50% while thecalorific value of tailing was 1308 kcal=kg with a 68.62% ash content.

Conclusion

Table type air separators can be used as a dry separator with high-separationefficiency and high-feeding capacity not only in lignite separation but also in hardcoal separation processes. Test parameters of the table had some effects on the sep-aration process, such as increasing feed rate and table slope had negative effects oncalorific values and ash content of clean coal. On the other hand, increasing tablefrequency and riffle height has positive effects on calorific values and tailing ash con-tent of clean coal. However, it was found that the most effective parameter is particlesize distribution. It has also been observed that Ep values had a poor effect due todecreasing maximum particle size of feed. The most favorable feed size for thisapparatus has been between 38mm and 6mm.

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Figure 12. Zonguldak hard coal sample fractional Ep analysis. (Color figure available online.)

10 M. Kademli & O. Y. Gulsoy

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Table Type Air Separators 11