Docstoc

DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH

Document Sample
DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH Powered By Docstoc
					Edy Nursanto, DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH Thiobacillus ferrooxidans ATCC 127811 BACTERIA

DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH Thiobacillus ferrooxidans ATCC 127811 BACTERIA
By : Edy Nursanto Department of Mining Engineering Universitas Pembangunan Nasional “Veteran” Yogyakarta Jl. SWK 104, Lingkar Utara, Condong Catur, Yogyakarta 55283 Email : edynursantoyyk@yahoo.com.au

ABSTRACT An experiment of desulphurization utilizing Thiobacillus ferrooxidans ATCC 127811 has been conducted in the laboratory in a series of percolators to study the effect of time and leaching temperature on the pyritic sulphur content in coal. The experiment has the condition as follows : initial acidity (pH) : 2.0, time change observed on the 5 th, 10 th, and 15 th day with the room temperature 0f 24o C, 30o C, and 35o C, and the air rate is 1, 500 ml/minute. The results of the experiments show that the reduction of the pyritic sulphur content in coal reaches optimum of 0.20 % (75.90 % reduction) from the initial value of 0.83 %. However, the total reduction of sulphur content is only achieved at 1.63 % (27.87 % reduction) from 2.25 % sulphur content of the raw coal. These are found with 15 th day of the process and temperature of 35o C observed. Key word : Coal, Desulphurization,Thiobacillus ferrooxidans

INTRODUCTION Coal is solid fuel which it price is cheaper than fuel oil. Currently, the demand of coal has been increase especially for industrial use and power plant. Similary with oil and natural gas, coal also contain amount of undersirable element which can cause air pollution when coal is burned.

SO2 emission due to coal combustion which cantain high sulphur will caused acid rain. This evidence has experienced in some countries and appeared serious problems such as corrosion, forest degradation, and damage for special microorganism. Conseguently, the effort to reduce SO2 emission in atmospher is considerably important.

85

JURNAL TEKNIK GELAGAR Vol. 19. No. 02 Oktober 2008 : 85 - 90

SULPHUR IN COAL Sulphur in coal occurs in the forms of inorganic and organic (Tsai, 1982). Inorganic. The organic sulphur is present in coal as dispersed and discreted minerals while organic sulphur is bound directly to organic coal matrix. The organic sulphur in coal is present mainly in two forms (Jorjani, 2004), as disulfides (pyrite and marcasite) and sulfates (mainly barium, calsium, and iron). Sulfate in coal usually has very low concentration (<0,1 wt %). The sulfate form is water soluble which originate from pyrite oxidation and if left as ash component after coal cobustion. Iron disulfides namely pyrite and marcasite have similar chemical formula (FeS2) but different in their crystal structure. Marcasite is rhombic with density of 4,87 and its commonly boud to coal matrix. In the other hand, pyrite is cubic with density of 0,5 and it appear as discreted grain between the coal matrix or as fracture filling. Pyrite is more stable and less reactive than marcasite. The occurence of organic sulphur in

coal has still not clearly understood but it was expected as unseparable part of the organic matrix. Based on its functionality, the organic sulphur in coal can be classified into five functional groups : sulfides or thioether (RSR’), disulfides (RSSR’), marchaptan or thiol (RSH), thiopyrone and thiophenes. THE CHARACTERIZATION TONDONGKURA COAL OF

In order to find out the characteristic of Tondongkura coal, Pankajene, South Sulawesi, then the first step of investigation was to carry out the raw material analysis. These analysis consist of proximate, ultimate (total sulphur, pyritic sulphur), and X-ray diffraction analysis. The raw coal sample was ground and reduced with using Coning and Quartering method. Coal preparation was conducted using screen of 65 mesh. The results of proximate analysis, sulphur, calorific value, and HGI (Hard grove Grindability Index) can be seen at Table 1 below

Table 1. The characteristic of Tondongkura coal, South Sulawesi Parameter Proximate Analysis (wt, % ADB) Inherent Moisture Ash Volatile Matter Fixed Carbon Others Analysis Calarific Valaue (cal/gr) HGI Total Sulphur (wt % ADB) Pyritic Sulphur (wt % ADB) Value (grade) 4.56 5.91 31.03 58.50 6,899.8 34 2.26 0.83

86

JURNAL TEKNIK GELAGAR Vol. 19. No. 02 Oktober 2008 : 85 - 90

X-ray diffraction analysis on coal was carried out in the initial step before doing pretreatment and bacterial leaching proses. This is aims to find out the minerals phase in coal, in particulary of sulfides minerals. The data diffractogram was used to identify minerals in coal sample. Figure 1 shows that the mineralspresent in coal sample are kaolinite, pyrite, and quartz.

THE MECHANISM OF BIODESULFURIZATION In the coal biodesulphurization process, Thiobacillus ferroxidans bacteria is a micro organism which populer and commonly use. Such bacteria was described and identified for the first time in 1947 by Colmer and Hinkle, (Soetjijo, 1998

Figure 1. Diffractogram of coal sample from Tondongkura showing the presence of kaolinite, pyrite and quartz Brierley (1978) suggested that, there are two mechanism of desulphurization process by Thiobacillus ferroxidans, the first they make contact directly and utilize pyritic sulphur in coal for their metabolism, the second is they make contact inderectly where the ferric ions produced from oxidation process will react chemically with ferro iron from pyritic

sulphur. In this case, bacteria have function to generate feric ion. Based on the previously report, the presence of such bacteria will accelerate reaction. The oxidation process of sulphur pyritic both directly and inderectly might be explained by the following reactions :
4FeS2 + 15 O2 +2H2O 2Fe2(SO4)3

+2H2SO4.. ....(1) The reaction (1) is the series from chemical reactions below :

86

Edy Nursanto, DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH Thiobacillus ferrooxidans ATCC 127811 BACTERIA

bacteria

2FeS2 + 7O2 +2H2O

2Fe(SO4) + 2H2SO4 .. ....(2)

bacteria 2FeS2 + 7O2 +2H2O 2Fe2(SO4)3 + 2H2SO4 .. ....(3) FeS2+ 2Fe2(SO4)3 + 3O2 +2H2O 3Fe2SO4

regenerated. The experiment use a medium that has been recommended by American Type Culture Collection (ATCC) for reproducing Thiobacillus ferroxidans. The medium composition of ATCC as follow : - (NH4)2SO4 = 0.8 g - KH2PO4 = 0.4 g - MgSO47H2O = 0.16 g and - Destillation water = 1 lt. Experimental condition : The desulphurization experiment was carried out with condition as below : a. Medium : ATCC b. Initial acidity (pH) : 2.0 c. Temperature : 24oC, 30oC, 35oC d. Inoculum : 2 % volume e. Water debit : 1,500 ml/minute f. Time : 15 days Samples were withdrawn on 5 day intervals. The recovered coal then were washed, dried, and analysed for its total and pyritic sulphur content. Coal was used in this experiment taken from Tondongkura area, South Sulawesi. The particles size of coal use is 200 mesh. The amountof 15 g of coal was fed to a 250 ml medium for each experiment

+ 2H2SO4 .. ....(4)

Reaction (4) is actually the series of reactions below :
FeS2 +2Fe2(SO4)3 3FeSO4 +2 S ......(5)

bacteria 2S + 3O2 +2H2O 2 H2SO4.................(6)

EXPERIMENT In this experiment, we used a series of percolator with the volume of 350 ml and equiped with air pump, size of percolator that is with high 60 cm and diameter 5 cm. Bacteria was used in the experiment is Thiobacillus ferroxidans ATCC 127811 which has been regenerated. The experiment use a medium that has been

87

JURNAL TEKNIK GELAGAR Vol. 19. No. 02 Oktober 2008 : 85 - 90

Air Out Air in

Coal and bacteria

Porcelin disk

Figure 2. Process of coal leaching with bacteria RESULT AND DISCUSSION In this section, it will be discussed the results of experiment which have been done. Bacterial leaching experiment was conducted for coal fractions of -200#. This was performed with using percolator put into the dark room and also using air for its percolation. The results of biodesulphurization experiments for Tondongkura coal can be seen on Table 2. On the Table shows that the amount of total and pyritic sulphur reduction occured for both increase of temperature and time process. The reduction of pyritic sulphur was also accompanied by total sulphur with the maximum reached at the temperature of 35oC during 15 days of leaching. Reduction of 75.90 % for pyritic sulphur and 27.87 % for total sulphur.

88

Edy Nursanto, DESULPHURIZATION OF TONDONGKURA COAL OF SOUTH SULAWESI WITH Thiobacillus ferrooxidans ATCC 127811 BACTERIA

Table 2. The Results of Analysis for Pyritic and Total Sulphur Content of Tondongkura Coal After Bioleaching at Various of Temperature and Time Variables Leaching Time T
( C)
24o 30o 35o
o

Removal

% Reduction

Removal

% Reduction

Removal

% Reduction

Sp
0.46 0.45 0.37

St
1.89 1.88 1.80

Sp
44.58 45.78 55.42

St
16.37 16.81 20.35

Sp
0.37 0.25 0.21

St
1.80 1.68 1.64

Sp
55.42 69.88 74.70

St
20.35 25.55 27.43

Sp
0.32 0.21 0.20

St
1.75 1.64 1.63

Sp
61.44 74.70 75.90

St
2.56 7.43 7.87

Note : Initial condition for total sulphur = 2.26 % and pyritic sulphur = 0.83 % Sp = Pyritic sulphur St = Total sulphur The reduction of total sulphur in this experiments seem to be relatively small, this is possibly caused by the sulphur content on coal sample much more attached with organic. Others factors inhibited the leaching process namely the presence of toxic metals like aluminium and silikon( Malik, et al, 2004). Such inorganic elements occur on coal mainly in mineral phases like quartz and clay. During the coal biodesulphurization process, it will take place total sulphur reduction. This is caused dissolved iron from pyrite (FeS2) and it follow the reaction below (Juszczak et al, 1995) :
Thiobacillusferroxidans bacteria

Go298 = - 67.028 KJ/mole CONCLUSION On the base of experiments and discussion above, so that the conclusion can be conducted as follow : 1. Optimum value of bacterial leaching was achieved at time variable during 15 days with the temperature of 35o C. 2. Total sulphur of initial condition of 2.26 %, the reductions ranged from 1.89-1.80 %; 1.80 – 1.64 %, and 1.751.63 % with temperature of 24oC, 30oC, and 35oC respectively, highest reduction was 27.87 %. 3. The initial condition of pyritic sulphur was 0.83 %, decreased up to 0.20 % or percent reduction of 75.90 %.

2FeS2 + 7O2 +2H2O FeS2 + 2 Fe 3+

2Fe2+ + 4H+ + 4SO42- ..........(7) 3Fe2+ + 2S o ....(8)

89

JURNAL TEKNIK GELAGAR Vol. 19. No. 02 Oktober 2008 : 85 - 90

REFERENCES Brierly, J.A Murr, L.E., & Torman, A.E., 1978, Metallurgical Application of Bacterial Leaching and Relatif Microbiological Phenomena, Academic Press, New York, 526. Chandra D., Roy, P., Mishra, A.K, Chakrabarti, J.N, Prasad N.K., and Chaudhuri, S.G., 1980, Removal of Sulphur from Coal by Thiobacillus Ferrooxidans and by Mixed Acidophilic Bacteria Present in Coal, Fuel, Vol.59. Gomez C., M.L, Blazquez and Ballester, 1998, Bioleaching of A Spanish Complex Sulphide Ore Bulk Concentrate, Universidad Complutense, 28040 Madrid, Spain. Jorjani, E., 2004, Desulphurization of Tabas Coal with Microwave Irradiation/Peroxyacetic Acid Washing at 25, 55, 85oC., Fuel, Vol. 83, pp.943-949. Juszczak, A., Domka, F., Kozlowski, M., and Wachowska, H., 1995, Microbial Desulphurization of Coal With Thiobacillus Ferrooxidans Bacteria, Fuel, Vol.74, Number 5. Kargi, F., 1982, Enhancement of Microbial Removal of Pyritic Sulphur from Coal Using Concentrated Cell Suspension of Thiobacillus Ferrooxidans and an External Carbondioxide Suppley, Biotechnologi and Bioengineering, 24, P.749-757. Malik, A., Dastidar, M.G., & Roychoudhury, P.K., 2004, Factors Limiting Bacterial Ioron Oxidation in Biodesulphurization System, International Journal of Mineral Processing,Vol.73,p.13-21. Soetjijo, H., 1998, Modifikasi Medium Proses Desulphurisasi Batubara Secara Biologis Untuk meningkatkan Efisiensi Pengurangan Sulfur, Prosiding Kolokium Pertambangan. Tsai, S.C., 1982., Fundamental of Coal Beneficiation and Utulization, Elsevier, Amsterdam.

90


				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:255
posted:12/31/2009
language:English
pages:8