FUEL PROCESSING TECHNOLOGY
Fuel Processing Technology 47 ( 19%) 11 1- 118
Briquetting of Istanbul-Kemerburgaz Turkey
0. Gibiiz Beker, S. Kii@ikbayrak
br />lignite of
Istanbul Technical University, Chemical and Metallurgical Engineering Faculty, Maslak, 80626 Istanbul, Turkey
Received 2 March 1995; accepted 2 February 1996
Abstract A lignite sample from the Kemerburgaz-Istanbul area was briquetted with or without binder material. Molassesand Simak (Turkey) asphaltite were used as binder materials at different ratios. The effects of the moisture content of the lignite and the concentration of the binder on briquette strength were examined at two different briquetting pressures, 150 and 200 MPa. Briquetting of lignite samples without binder material gave products with low strength and low water resistance. The maximum briquette strength was achieved with a lignite moisture content of 13% and an asphaltite concentration of 12% at a briquetting pressure of 200 MPa. The strongest briquettes obtained with lignite-molasses blends were achieved with a molasses concentration of 12% and a lignite moisture content of 8% at a briquetting pressure of 200 IvPa.
Lignite is the primary national energy source of Turkey. Turkey has approximately 8.4 billion tons of lignite reserves, which make up two thirds of the total coal sources [ 11.Because of their low calorific value (2200 kcal kg-’ ), high ash levels (lo-30%) and high moisture contents (lo-40%), the increased use of lignites presents potential environmental problems [2,3]. Because of their fragile nature, Turkish lignites can dust easily by up to 60% during mining, cleaning, transportation and utilization processes. In conventional combustion plants, large amounts of unburnt fine lignite particles are released to the atmosphere. This type of operation reduces combustion efficiency and causes air pollution. Some of the problems arising during the combustion of lignite can be prevented by briquetting the lignite . Preliminary removal of moisture from high moisture content lignites significantly increases the calorific value of the briquettes obtained. Also,
0378-3820/96/$15.00 Copyright 8 1996 Elsevier Science B.V. All rights reserved.
Fuel Processing Technology 47 (1996) 11 I-l 18
storage and transportation become easier, as briquetting reduces the volume occupied by the same amount of fine lignite particles. Air pollution due to uncontrolled combustion associated with the burning of small lignite particles can be avoided by using briquettes. The aim of this study was to determine the optimum conditions for briquetting Kemerburgaz lignite, a lignite widely used in Istanbul. The lignite sample from the Kemerburgaz-Istanbul area was briquetted with or without binder material. Molasses and asphaltite were used as binder materials at different ratios.
2. Experimental Results of the analysis of the Kemerburgaz lignite and Simak asphaltite samples used in this study are given in Table 1. The lignite sample was first air dried to 20% moisture content, and it was then crushed and sieved to O-6 mm particle size taking care to minimize oxidation. The sample was then dried at 378 K to different moisture contents. The moisture content values were chosen according to the optimum moisture range, known to be B-14%, for briquetting of Turkish lignites [3,4]. The asphaltite sample was crushed and sieved to O-3 mm particles. The molasses sample was obtained as a waste product from a sugar factory, and originally had a solids content of 20% in water. A series of experiments was carried out to determine the effects of different moisture contents (8, 10 and 13%) of the lignite samples and of the briquetting pressures (150 and 200 MPa) on the shatter index and compressive stress of the briquettes obtained without binder. Another series of experiments was conducted using asphaltite and molasses as binder materials. The blends of lignite and binder material were prepared to contain 3, 5, 7, 9 and 12 wt% asphaltite or 7, 9 and 12 wt% molasses as binder material. During these experiments, the effect of the percentage of binder material (in the sample blend) on the shatter index and compressive stress of briquettes obtained at different briquetting pressures and different moisture contents was observed. The lignite samples were briquetted at room temperature, with or without binder material, in a calibrated laboratory scale hydraulic press, using a punch and die set (50 mm ID X 100 mm height), for 10 s under pressures of 150 and 200 MPa. The briquettes obtained, each 50 g in weight, were cylindrical in shape with a cross sectional area of = 20 cm2 and a volume of about 40 cm3.
Table 1 Analyses of Simak asphaltite and the Kemerburgaz lignite sample (as received basis) Lignite Moisture/% Ash/% Volatile matter/% Calorific value/MJ kg- ’ , gross 34.5 9.8 30.4 15.2 Asphalt&e 0.6 42.2 33.3 20.6
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Fuel Processing Technology 47 (1996) II 1 -I 18
All briquette samples were stored under ambient conditions for seven days before testing. Five briquettes were prepared for each set of experimental conditions and the arithmetic averages of the measurements were calculated. Some standard tests were applied to determine the shatter index, compressive stress and water resistance of the briquettes formed. The shatter indices (ISO-R 616) were determined by dropping each briquette from a height of 180 cm onto a steel plate and measuring the percentage of the sample retained on the sieve; this was repeated until all the particles formed by shattering passed through a 20 mm sieve. Finally, the sum of all the percentages was added to find the index of shatter [5-71. The compressive stress of each briquette was measured in a standard manner using an Instron table model 1195 testing machine [6,8-151. The flat surface of the briquette sample was placed on the horizontal metal plate of the machine. A motorized screw slowly reduced the distance between this metal plate and a second one parallel to it. An increased load was applied at a constant rate until the test sample failed by cracking or breaking. The load at the fracture point, i.e. the maximum load, was converted to compressive stress [13-151 using the following equation Compressive stress = Load at fracture Cross sectional area of plane of fracture (1)
The water resistances of the briquettes were arbitrarily tested by immersing them in a container filled with cold tap water and measuring the time required for the onset of dispersion in water. 3. Results and discussion The effect of the moisture content on the shatter index and the compressive stress of the briquette samples obtained without binder is quite pronounced. This is graphically displayed in Figs. 1 and 2, respectively. The relationships are nearly linear. The correlations were examined by regression analysis and the related regression coefficients r were calculated.
10 12 Moisture (%)
Fig. 1.Effect of moisture content of lignite sample on the shatter index.
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Fuel Processing Technology 47 (1996) 1 I I-1 18
/‘ r: 8
Fig. 2. Effect of moisture content of lignite sample on the compressive stress.
The regression coefficients for the relationship shown in Fig. 1 are 0.9858 and 0.9701 for 150 and 200 MPa briquetting pressure, respectively. Thus, the correlation for the lower briquetting pressure is slightly better. The regression coefficients for the relationship shown in Fig. 2 were calculated as 0.9498 and 0.9944 for 150 and 200 MPa briquetting pressures, respectively. The results suggest that, as the moisture content of the lignite samples increased significantly, the shatter index and compressive stress of the briquettes also increased. Figs. 1 and 2 also illustrate the effect of the briquetting pressure on the shatter index and the compressive stress of the briquettes. Both briquette properties increased with an increase in the briquetting pressure. The moisture content of the lignite samples and the briquetting pressure did not appear to have a significant effect on the water resistance of the briquettes obtained without binder. None of them was water resistant, and each began to disperse in water in less than 5 minutes. Comparing all these results with the national standards [3,16] that limit the shatter index value to 1000 and the water resistance period to 1 h, it can be concluded that Kemerburgaz lignite should not be briquetted without binder material.
‘ 0oo +
lSOMPa,10Kmoismre 200MPa.10Kmoisbne 150 Wa, 8 K moisture
1200v ‘ p .E 8
2ooMF&8%moi.9lIue 200 Mpa, 13 Ye moistme
v 6 400/&!$
Fig. 3. Effect of asphaltite percentage on the shatter index of briquettes.
l?.G. Beker. S. Kii@kbayrak/ Fuel Processing Technology 47 (1996) I1 I -I 18
8 Asphaltite (%)
Fig. 4. Effect of asphaltite percentage on the compressive stress of briquettes.
Figs. 3 and 4 illustrate experimental data showing the effect of asphaltite as binder material. The effect of asphaltite binder depends considerably on the moisture content of the lignite-asphaltite blend. A shatter index of 1000 could be achieved only for briquettes containing 9-12% asphaltite with a moisture content of 13% at a briquetting pressure of 200 MPa. The regression coefficient of the relationships shown in Fig. 3 varies between 0.8541 and 0.9977. This means that there is a good correlation between the shatter index of the briquettes formed and the percentage of asphaltite in the blend. The relationship between the compressive stress of the briquettes and the amount of asphaltite used is shown in Fig. 4. It is clear that the stress increases as the binder content is increased. The maximum briquette stress (11.9 MPa) was achieved with an asphaltite concentration of 12% and a moisture content of 13% at a briquetting pressure of 200 MPa. For the same amount of asphaltite the compressive stress increased as the briquetting pressure was increased from 150 to 200 MPa. This is attributable to the high compressibility of the binder. The regression coefficient of the relationships shown in Fig. 4 ranges from 0.9441 to 0.9671. The water resistance of the briquettes containing asphaltite as binder material was poor. However, this property also depends on the concentration of the binder and on the pressure applied. Briquettes obtained under 200 MPa pressure with an asphaltite concentration of 12% and a moisture content of 13% started to disintegrate in water after 40 minutes. Figs. 5 and 6 illustrate experimental results showing the effect of molasses as binder material on the shatter index of the resulting briquettes. The maximum shatter index at both briquetting pressures was observed for briquettes containing 8% moisture and 12% molasses. At pressures of 150 and 200 MPa the shatter indices of the briquettes produced were measured as 1714 and 2572, respectively. Figs. 7 and 8 show the variation of the compressive stress with the percentage of molasses. Increasing the concentration of molasses in the briquettes produced decreases their compressive stress. This is due to the low compressibility of molasses. However,
.!?.G. Beker, S. Kii@kbayrak/ Fuel Processing Technology 47 (1996) 1 I1 -I 18 2500 2000a % moi&Jm
10 % moisture 13 % moisture
+ I3 *
Fig. 5. Effect of molasses percentage on the shatter index of briquettes formed at 150 MPa.
g 2000'0 .E $ S z IOOO-
Fig. 6. Effect of molasses percentage on the shatter in&x of briquettes formed at 200 MPa.
0%moistum 10 % moiabn 13 % moistur
c g a‘ ii !! i? a8
:& 6 8 10 Molasses(%) 12
Fig. 7. Change in compressive stress of briquette with concentration of molasses at 150 MPa briquetting pressure.
l?.G. Beker, S. Kii@kbayrak/Fuel 20 z?
z I 2 ;
Processing Technology 47 (1996) 111-118 + 0
12 of molasses at 200 MPa briquetting
Fig. 8. Change in compressive pressure.
stress of briquette
the compressive stress of all briquettes produced using lignite-molasses blends was greater than the target level of 4 MPa [6-B]. Fig. 9 shows the effect of the concentration of molasses on the water resistance of the briquettes produced. The water resistance of the briquettes increases with an increase in molasses concentration. The maximum water resistance was observed for briquettes pressed at 200 MPa from a lignite-molasses blend containing 8% moisture and 12% molasses. These briquettes began to disperse after 23 h of immersion in water.
The moisture content of the briquettes had a distinct effect on the briquette strength.
Briquettes produced from Kemerburgaz lignite without any binder were not water resistant and began to disperse in water in less than 5 minutes.
Fig. 9. Water resistivity of briquette samples.
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Fuel Processing Technology 47 (1996) 11 I-l 18
The strongest briquettes (shatter index 1325.83; compressive stress 11.9 MPa) produced using asphaltite-lignite blends were achieved with an asphaltite concentration of 12% and a moisture content of 13% at a briquetting pressure of 200 MPa. The water resistance of the briquettes containing asphaltite as binder material was poor. The strongest briquettes (shatter index 2572; compressive stress 12.2 MPa) formed using molasses-lignite blends were achieved with a molasses concentration of 12% and a moisture content 8% at a briquetting pressure of 200 MPa. These briquettes began to disperse after 23 h of immersion in water. Asphaltite as binder gave weaker briquettes than those made with molasses as binder under the same conditions. Molasses is a good binder for the briquetting of Kemerburgaz lignite, and can be used successfully in the production of briquettes with acceptable strength and water resistance.
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