Utilization of Lignite Reserves and Simultaneous Improvement of Dust

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Energy & Fuels 2002, 16, 1516-1522

Utilization of Lignite Reserves and Simultaneous Improvement of Dust Emissions and Operation Efficiency of a Power Plant by Controlling the Calcium (Total and Free) Content of the Fed Lignite. Application on the Agios Dimitrios Power Plant, Ptolemais, Greece Nestoras Kolovos,† Andreas Georgakopoulos,*,‡ Anestis Filippidis,‡ and Constantinos Kavouridis§,| Public Power Corporation of Greece, Western Macedonian Lignite Center, GR-50200 Ptolemais, Greece, Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, GR-54124, Greece, Public Power Corporation of Greece, General Direction of Development and Exploitation of Mines, GR-10443, Athens, Greece, and Technical University of Crete, Department of Mineral Resources Engineering, GR-73100, Hania, Greece Received April 10, 2002

The lignite thermal plant operation is affected by the fuel quality. In the lignite mines of Northern Greece, both inorganic impurities and thin intercalations, especially when they consist of carbonate minerals, co-excavated with lignite, reduce the run-of-mine lignite quality. Before any lignite exploitation or combustion process study, both the lignite and the lignite ash quality have to be thoroughly investigated in order for the recoverable blocks of lignite to be determined. Marly layers, characterized as marly limestones, containing up to 95% CaCO3, are thermally decomposed producing a high percent of CaO and CO2. The high CaO(total) and CaO(free) contents of the lignite ash cause fouling problems in the combustion systems of the power plants and increase the solid particle emissions to the atmosphere. To control the CaO(free) content of the ash below a critical limit of 11%, an index (∑) ) [CO2 in lignite/ash(d.b.)] × 100 may be used. For values of (∑) lower than 17, the CaO(free) of the lignite ash is controlled approximately lower than 11%. The use of the index (∑) in determining the CaO(free) content of the ash and controlling the blending process of lignite layers has improved the operation of the Agios Dimitrios Power Plant, leading to economic and environmental advantages, such as reduction of lignite specific consumption, increase of the calorific value, and reduction and stabilization of the solid particle emissions.

1. Introduction Greece is the fifth largest world producer of lignite and the second largest within the European Community. The proven geological lignite reserves in Florina-Ptolemais-Kozani tectonic basin are 4.3 billion tons, representing the 2/3 of the total lignite reserves of Greece. The Western Macedonian Lignite Center produces annually more than 50 million tons of lignite to feed five thermal power plants, with 17 lignite thermal units and with a total installed capacity of 4048 MW. This intensive exploitation of lignite requires the excavation of about 250 million cubic meters (cubic meters bank material) of overburden and interbedded sediments per year. * Corresponding author: Tel.: (++30)-310998514. Fax: (++30)310998463. E-mail: [email protected]. † Public Power Corporation of Greece, Western Macedonian Lignite Center. ‡ Aristotle University of Thessaloniki. § Public Power Corporation of Greece, General Direction of Development and Exploitation of Mines. | Technical University of Crete.

Lignite is produced in four big mines, the biggest one being the Southern Field Mine, with an annual production of 22 million tons of lignite (2001) and total excavations of 87.5 million cubic meters. The Southern Field Mine feeds the Agios Dimitrios Power Plant, the biggest in Greece, with installed capacity of 1585 MW in five lignite thermal units, producing 29% of the total electricity power. Units 1 and 2 (300 + 300 MW) were constructed in 1984, unit 3 (310 MW) in 1985, unit 4 (310 MW) in 1986 and unit 5 (365 MW) in 1997. The quality of the recoverable lignite, from an economical and environmental point of view, among others, is related to the quality of the organic matter, the quality of lignite inorganic impurities, and the nature of the thin intermediate sterile layers, which are coexcavated with lignite.1-12 (1) Swaine, J. D. Trace elements in coal; Butterworths: London 1990; 278 pp. (2) Unsworth, J. F.; Barratt, D. J.; Roberts, P. T. Coal Quality and Combustion Performance: An International Perspective. Coal Science and Technology 19; Elsevier: Amsterdam, 1991; p 638. (3) Clarke, L. B.; Sloss, L. L. Trace elementssEmissions from coal combustion and gasification; IEACR/49: London, 1992; p 111.

10.1021/ef020090o CCC: $22.00 © 2002 American Chemical Society Published on Web 09/11/2002

Controlling the Ca Content of the Fed Lignite

The Southern Field lignite deposit is characterized by multiple interchanges of lignite and intermediate sterile layers consisting of marly limestones, marly, clayey, and sand formations. This form of deposit imposes selective excavation, where unavoidably, lignite and thin intermediate sterile layers are co-excavated. The quality of the run-of-mine lignite and its ash significantly affects both the operation of the Agios Dimitrios Power Plant combustion systems and the solid particle emissions to the atmosphere.13-15 The high carbonate minerals content of the recoverable lignite and the high CaO(free) content of the fly ash may cause serious economic and environmental effects on the exploitation and utilization of lignite.16-25 The free CaO is formed during the combustion process by thermal decomposition of carbonate minerals included both in the lignite and intermediate sterile layers, which are co-excavated with the lignite.13,15,26-29 Fly ashes of the Western Macedonian Lignite Center (4) Valceva, S.; Georgakopoulos, A. Proceedings of the International Conference on Current Research in Geology Applied to Ore Deposits; Fenoll Hach-Ali, F., Torres-Ruiz, J., Gervilla, F., Eds.; La Guioconda: Granada, 1993; p 779. (5) Georgakopoulos, A.; Fernańdez-Turiel, J. L.; Filippidis, A.; Llorens, J. F.; Kassoli-Fournaraki, A.; Querol, X.; Lopez-Soler, A. Proc. 8th ICCS Coal Sci. Technol. 1995, 24, 163. (6) Valceva, S.; Georgakopoulos, A.; Markova, K. Proc. 8th ICCS Coal Sci. Technol. 1995, 24, 259. (7) Michailidis, K.; Sakorafa, V.; Foscolos, A. Mineral Wealth (Athens) 1997, 102, 43. (8) Scott, D. IEA 1999, CCC/24, p 38. (9) Georgakopoulos, A. Energy Sources 2001, 23, 143. (10) Iordanidis, A.; Georgakopoulos, A.; Filippidis, A.; KassoliFournaraki, A. Int. J. Environ. Anal. Chem. 2001a, 79 (2), 133. (11) Iordanidis, A.; Georgakopoulos, A.; Markova, K.; Filippidis, A.; Kassoli-Fournaraki, A. Thermochim. Acta 2001b, 371, 137. (12) Kapina, V.; Georgakopoulos, A.; Kassoli-Fournaraki, A.; Filippidis, A. Proc. 9th Int. Congr., Bull. Geol. Soc. Greece 2001, XXXIV/3, 1205 (in Greek with English abstract). (13) Filippidis, A.; Georgakopoulos, A.; Kassoli-Fournaraki, A. Int. J. Coal Geol. 1996, 30, 303. (14) Filippidis, A.; Georgakopoulos, A.; Kassoli-Fournaraki, A.; Blondin, J.; Fernańdez-Turiel, J. L. Proceedings of European Seminar on Coal Flyash: A Secondary Raw Material, A. R. ENE.-Marseilles 1997, 149. (15) Kolovos, N.; Georgakopoulos, A.; Filippidis,A.; Kavouridis, C. Energy Sources 2002, 24 (6), 561. (16) Georgakopoulos, A.; Filippidis, A.; Kassoli-Fournaraki, A. Trends Mineralogy 1992, 1, 301. (17) Georgakopoulos, A.; Filippidis, A.; Kassoli-Fournaraki, A.; Fernańdez-Turiel, J. L.; Llorens, J. F. Proceedings of the 3rd International Conference on Environmental Pollution; Anagnostopoulos, A., Ed.; University of Thessaloniki, 1996; p 114. (18) Georgakopoulos, A.; Filippidis, A.; Kassoli-Fournaraki, A.; Iordanidis, A.; Fernańdez-Turiel, J. L.; Llorens, J. F.; Gimeno, D. Energy Sources 2002a, 24 (1), 83. (19) Georgakopoulos, A.; Filippidis, A.; Kassoli-Fournaraki, A.; Fernańdez-Turiel, J. L.; Llorens, J. F.; Mousty, F. Energy Sources 2002b, 24 (2), 103. (20) Kassoli-Fournaraki, A.; Georgakopoulos, A.; Michailidis, K.; Filippidis, A. Proceedings of the International Conference on Current Research in Geology Applied to Ore Deposits; Fenoll Hach-Ali, F., Torres-Ruiz, J., Gervilla, F., Eds.; La Guioconda: Granada, 1993; p 727. (21) Gerouki, F.; Typou, I.; Tzoulis, C.; Foscolos, A. E. Proceedings of the 5th International Conference on Environmental Pollution; Anagnostopoulos, A., Ed.; University of Thessaloniki, 2000; p 570. (22) Sachanidis, Ch.; Georgakopoulos, A.; Filippidis, A.; KassoliFournaraki, A.; Iordanidis, A. Proceedings of the 5th International Conference on Environmental Pollution; Anagnostopoulos, A., Ed.; University of Thessaloniki, 2000; p 533. (23) Triantafyllou, A. G. J. Air Waste Manage. Assoc. 2000, 50, 1017. (24) Triantafyllou, A. G. Environ. Pollut. 2001, 112, 491. (25) Triantafyllou, A. G.; Filippidis, A.; Patra, A.; Pavlidis, A.; Kantiranis, N. Proc. 1st Congr. Comm. Econ. Geol., Geochem. of the Geol. Soc. Greece, Kozani 2000, 452 (in Greek with English abstract). (26) Filippidis, A.; Georgakopoulos, A.; Kassoli-Fournaraki, A. Trends Mineralogy 1992, 1, 295. (27) Kassoli-Fournaraki, A.; Georgakopoulos, A.; Filippidis, A. Neues Jb. Miner. Mh. 1992, 11, 487.

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are characterized as sulfocalcic but their mineral and chemical composition vary between the power stations and units.14,30,31 Since no on-line analyzers are used, the recoverable lignite quality management is based mainly on the inorganic impurity control. This study deals with a method used to control the recoverable and the run-of-mine lignite quality, produced in the Southern Field mine and mainly used in the Agios Dimitrios Power Plant. It is based on blending of poor-quality lignite layers with good quality ones controlling the CaO(free) content of the ash. This method of lignite quality management is now in use, giving excellent economic and environmental results. 2. Geological Setting The Ptolemais basin was formed by NW-SE and NE-SW tectonic forces by the end of the Mesozoic era. It belongs to a larger basin located at the northwestern part of Greece. The sediments of the Ptolemais basin overlay both Paleozoic metamorphic rocks and Mesozoic crystalline limestones (Figure 1). The Neogene-Quaternary sediments of the basin are divided into three lithostratigraphic formations. The lowest (Upper Miocene to Lower Pliocene) consists of basal conglomerates, passing upward to marly limestone, marly sand, clay, and lignite (partly xylitic) layers. The Pliocene middle formation contains intensively exploited lignite beds alternating with marly limestones, clays, marls, and sands. The Quaternary upper formation consists of terrestrial and fluvioterrestrial conglomerates, lateral fans, and alluvial deposits. In the opencast Southern Field Mine the mean thickness of the overburden is 80 m, while the thickness of the coal seam is 80 m.15,32,33 3. Materials and Methods To investigate the effects of CaO(total) and CaO(free) contents of lignite ash on the Power Plant operation, first the monthly lignite and ash quality parameters data of the lignite burnt in the Agios Dimitrios Power Plant during 1993-1997 were studied. Moisture content, ash (dry basis) content, CO2 (dry basis) content, gross calorific value, and net calorific value were determined according to ASTM D-3302,34 ASTM D-3174,35 ASTM D-1756,36 and ASTM D-3286,37 while the analysis of the ash was carried out by ASTM D-2795.38 The (28) Iordanidis, A.; Georgakopoulos, A.; Filippidis, A.; KassoliFournaraki, A. Proc. 1st Congr. Comm. Econ. Geol., Geochem. of the Geol. Soc. Greece, Kozani 2000, 124 (in Greek with English abstract). (29) Sachanidis, Ch.; Georgakopoulos, A.; Filippidis, A.; KassoliFournaraki, A. Proc. 9th Int. Congr., Bull. Geol. Soc. Greece 2001, XXXIV/3, 1115 (in Greek with English abstract). (30) Filippidis, A.; Georgakopoulos, A. Fuel 1992, 71 (4), 373. (31) Georgakopoulos, A.; Filippidis, A.; Kassoli-Fournaraki, A. Fuel 1994, 73 (11), 1802. (32) Pavlides, S. B.; Mountrakis, D. M. J. Struct. Geol. 1987, 9 (4), 385. (33) Antoniadis, P.; Rieber, E. Mitt. Bayer. Staatslg. Pala¨ ont. Hist. Geol. 1995, 35, 193. (34) ASTM Standards D 3302-00ae1. Standard Test Method for Total Moisture in Coal; American Society for Testing Materials: Philadelphia, PA. (35) ASTM Standards D 3174-00. Standard Test Method for Ash in the Analysis Sample of Coal and Coke from Coal; American Society for Testing Materials; Philadelphia, PA. (36) ASTM Standards D 1756-96. Standard Test Method for Determination as Carbon Dioxide of Carbonate Carbon in Coal; American Society for Testing Materials: Philadelphia, PA.

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Kolovos et al.

Figure 1. Geological map of the study area.

CaO(free) content of the fly ash was determined using the EN 451-1 standard,39 proposed by the European Committee for Standardization. The average values of these parameters are presented in Tables 1 and 2. Quality parameters data during 1998-2000 were also studied and are presented in Tables 1 and 2. A comparison between these two periods is advisable for any improvements on the Power Plant operation to be considered. (37) ASTM Standards D 3286-96. Standard Test Method for Gross Calorific Value of Coal and Coke by the Isoperibol Bomb calorimeter (Discontinued 2000, Replaced by D5865-01ae1); American Society for Testing Materials: Philadelphia, PA. (38) ASTM Standards D 2795-95. Standard Test Methods for Analysis of Coal and Coke Ash; American Society for Testing Materials; Philadelphia, PA.

Table 1. Agios Dimitrios Lignite Quality Characteristics parameter

average value (1993-1997)


moisture content (wt %) ash (db) (wt %) CO2 (db) (wt %) gross calorific value (kcal kg-1) net calorific value (kcal kg-1)

51.4 34.2 13.2 3504 1327

50.9 33.1 8.6 3536 1363

The lignite burnt in the Agios Dimitrios Power Plant is considered as the run-of-mine lignite produced in the Southern Field Mine. Run-of-mine lignite is considered as the excavated recoverable lignite or lignite block, (39) EUROPEAN STANDARD, EN 451-1. Method of testing fly ash. Part 1: Determination of free calcium oxide content; 1994.



Table 2. Agios Dimitrios Lignite Ash Quality Characteristics parameter



SiO2 (wt %) Al2O3 (wt %) Fe2O3 (wt %) CaO(total) (wt %) MgO (wt %) CaO(free) (wt %) SO3 (wt %)

34.3 10.9 6.2 36.0 4.4 8.6 5.7

28.8 13.2 7.3 38.1 4.6 6.5 5.8

including the dilution from both the upper and lower waste seams due to the bucket wheel excavation. Recoverable lignite layer or block of layers is considered as any lignite layer or block of layers (before the excavation) having both ash content (db) < 40% and thickness > 50 cm. Waste layer or block of layers is considered as any layer or block of layers having both ash content (db) > 40% and thickness > 30 cm. Solid particle emission measurements were taken by opacity meters, installed during 1997 and 1998, next to the electrostatic precipitators of the Agios Dimitrios Power Plant. Opacity is considered the degree to which emission of dust, smoke, or gas reduces the transfer of light. LAND model 4500 Dust Density Monitors were installed during 1997 in Power Units 1, 2, 3, and 4, while a DURAG D-R 280-10 Dust Concentration Meter was installed in Power Unit 5 in 1998. The measuring procedure was carried out according to VDI 2066 standards.40,41 Opacity meters are used for determining the dust concentration along an optical path. The optical measurement “extinction” (absorbency) expresses the energy loss of light. The quantity of dust contained in the irradiated gas is proportional to the extinction value. This relationship is measured by comparing the average output of the device to the actual dust concentration measured gravimetrically. The device operates according to the time-division-multiplex (TDM) technique, which allows the measuring and reference light paths to be clearly differentiated. Taking into account these measurements, progressive improvements by blending in the mined lignite quality were introduced during 1998. Apart from the proximate analysis determined parameters, the recoverable lignite layers were also selected according to their CaO(free) content of the ash. During blending, special attention was paid in keeping the CaO(free) content of the ash lower than 11%, which is a limit over which the solid particle emissions exceed an allowable limit of 150 mg m-3. The blending process was carried out using the conveyor belt system of the Southern Field Mine. The layers having high CaO(free) content, were excavated and transported by a conveyor belt to the bunker of the mine and retransported to the main lignite conveyor belt where layers of mined lignite with low CaO(free) content were transported. The lignite quality management was achieved by blending 30% (wt) lignite layers with high (40) VDI (Verein Deutscher Ingenieure) 2066 Blatt 1. Particulate matter measurement; measuring of particulate matter in flowing gases; gravimetric determination of dust load; fundamentals 1975-10. (41) VDI (Verein Deutscher Ingenieure) 2066 Blatt 2. Measurement of particulate matter; manual dust measurement in flowing gases; gravimetric determination of dust load; tubular filter devices (4 m〈(hoch)3〉/h, 12 m〈(hoch)3〉/h), 1993-08.

Table 3. Quality Results of Agios Dimitrios Power Plant (1993-2000) year lignite specific consumption (kg kW h-1) net calorific value (kcal kg-1) ash(db) (%)



1.80

1.73

1327 34.2

1363 33.1

CaO(free) content and 70% (wt) lignite layers with low CaO(free) content. 4. Results and Discussion In Table 1 the lignite and the ash quality parameters of the lignite burnt in the Agios Dimitrios Power Plant during 1993-1997 and 1998-2000 are presented. During 1993-1997 the average value of moisture content was of 51.4% (wt). The ash content was 34.2% (wt) and the CO2 content was 13.2% (wt). The high value of CO2 content indicates the presence of carbonate minerals. Since CO2 content is produced during the thermal decomposition of carbonates, it has to be taken into account in order to have a better approach of the inorganic impurities content. The gross calorific value was 3504 kcal kg-1 and the net calorific value 1327 kcal kg-1, respectively. According to these parameters special attention had to be paid to the inorganic impurities control and especially to the carbonates content elimination. Apart from the quality characteristics of lignite, the quality characteristics of the ash were of prime importance (Table 2). The CaO(total) and CaO(free) contents of the ash were high enough, 36% (wt) and 8.6% (wt), respectively, causing problems to the normal Power Plant operation. Fouling effects and solid particle emissions exceeding the allowable limits of 150 mg m-3 have been observed. Due to the low value of S, a natural desulfurization process could not hold high amounts of CaO to form CaSO4. So, a high amount of CaO remained free, causing problems to the electrostatic precipitators operation. To minimize the poor lignite quality effects, both the ash quality and the ash quantity had to be taken into account paying special attention to the reduction of CaO(free). The CaO(free) control was achieved by using the equation y ) 1.0489X - 6.9077, with R2 ) 0.93, where y is the CaO(free) of the ash, and X is the index (∑) ) [CO2 in lignite/ash(db)] × 100.15 Index (∑) is easily estimated since both CO2 and ash(db) are determined during the first steps of physical and chemical determinations. Using these parameters the CaO(free) content of the ash can be estimated. For values of index (∑) > 17 the CaO(free) of the ash exceeds 11%, over which solid particle emissions from the electrostatic precipitators are increased.15 Taking into account the above-mentioned lignite and lignite ash quality parameters, in combination with the index (∑), the recoverable lignite blocks were determined. The main target was to reduce both the ash content and the CaO(free) content in the ash lower than 11%. After the application of the quality management program, previously described, these parameters were being improved. The ash content was reduced to 33.1% (wt), while the CO2 content was reduced to 8.6% (wt).

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Figure 2. Solid particle emissions in Unit 1 of Agios Dimitrios Power Plant.


Both gross calorific value and net calorific value increased to 3536 kcal kg-1 and 1363 kcal kg-1, respectively (Tables 1 and 2). Using this procedure during 1998-2000 remarkable results in both the run-of-mine lignite quality and the quality of the ash were observed. Both run-of-mine lignite and lignite ash quality were improved, thus presenting a better stability and lower variations with excellent economic and environmental results for the Agios Dimitrios Power Plant (Table 3). The specific consumption of lignite (kg kW h-1) was improved from 1.80 kg kW h-1 to 1.73 kg kW h-1 offering an extra profit to the Power Plant economic results. This parameter is of premium importance since it depends mainly on the fuel quality, which affects the overall Power Plant performance. Apart from the Power Plant improvement in operation and economic results, a remarkable elimination in the solid particle emissions to the atmosphere was achieved in the Power Units 1 to 4 (Figures 2, 3, 4, and 5). The significantly lower values observed in Power Unit 5 (Figure 6), are due to the modern technology and specifications of the ESPs which have been in operation since 1998 and the solid particle emissions have been measured since February 1998. Using the technique mentioned above, by determining the lignite recoverable blocks and progressively improving the mixing of the lignites with different qualities, the solid particle emissions were generally stabilized and reduced (lower than 150 mg m-3), with the best improvement observed around April 1999 and afterward (Figures 2-5).

Trend lines for emissions over a three years period (Figures 2-4), show that the lignite quality management was able to continually reduce emissions indicated continuing ability to learn from previous experience. In this case it is evident that the ESP’s operation is dependent on the lignite quality. Statistical analysis for the above trend lines gives the results of Table 4. The trend lines for Power Units 1-4 show that the solid particle emissions are dependent by almost 50% on the lignite quality. The scatter of data points around the trend lines was due to technical problems on the operation of conveyor belts system and their inefficiency to accept the proper blended lignite quality. The trend line in Figure 6 is almost straight and represents very low particulate emissions due to the high ESP efficiency. The trend line in Figure 6 is not dependent on the lignite quality. 5. Conclusions The lignite quality in the Southern Field Mine, the biggest in Greece, is strongly affected by the inorganic impurities and the intercalations of marly limestones, clays, sands, and marly formations, which are coexcavated with the bucket wheel excavator. Apart from ash quantity, the ash quality plays a significant role in the combustion process and the overall Agios Dimitrios Power Plant performance. The control of CaO(free) of the lignite ash lower than 11% can be achieved by controlling an index (∑) of the mined lignite lower than 17, where (∑) ) [CO2 in lignite/ash(d.b)] × 100. The lignite





Figure 6. Solid particle emissions in Unit 5 of Agios Dimitrios Power Plant. Table 4. Statistical Analysis for Particulate Emissions (confidence interval 95%) regresion coefficient (AX + B)

intercept P-value

Units

A

B

R2

1 2 3 4 5

-0.10829 -0.11609 -0.063 -0.07683 -0.00697

4065.93 4360.95 2410.83 2960.19 278.9

0.512 0.485 0.413 0.446 0.161

t

multiple R

µ

variant

intercept

variant

F

0.716 0.696 0.643 0.668 0.401

4.19 × 10-9 1.57 × 10-8 3.56 × 10-7 1.02 × 10-7 0.011

1.06 × 10-8 3.84 × 10-8 1.09 × 10-6 3.88 × 10-7 0.02

7.22 6.84 5.96 6.35 2.68

-6.96 -6.58 -5.63 -5.96 -2.43

48.39 43.35 31.73 35.51 5.95

quality management based on the combination of the (∑) index quality parameters of lignite and its ash, as well as the mixing of lignite with different qualities [keeping (∑) < 17], can improve the lignite quality and the overall Power Plant performance. Taking into account the above-mentioned lignite and lignite ash qual-

ity parameters, in combination with the index (∑), the recoverable lignite blocks were determined. The main target was to reduce both the ash content, and the CaO(free) content in the ash lower than 11%. After the application of the quality management program, the following parameters were getting im-

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proved: the ash content was reduced to 33.1% (wt), while the CO2 content was reduced to 8.6% (wt). Both gross calorific value and net calorific value increased to 3536 kcal kg-1 and 1363 kcal kg-1, respectively. Using this procedure during 1998-2000 remarkable results in both the run-of-mine lignite quality and the quality of the ash were observed. Both run-of-mine lignite and lignite ash quality were improved, presenting a better stability and lower variations with excellent economic and environmental results for the Agios Dimitrios Power Plant. The specific consumption of lignite (kg kW h-1) was improved from 1.80 kg kW h-1 to 1.73 kg kW h-1, offering an extra profit to the Power Plant economic results. This parameter is of premium importance since it depends mainly on the fuel quality, which affects the overall Power Plant performance. Apart from the Power Plant improvement in operation and economic results, a remarkable elimination in the

Kolovos et al.

solid particle emissions to the atmosphere was achieved in Power Units 1 to 4. The significantly lower values observed in Power Unit 5, are due to the modern technology and specifications of the ESPs which have been in operation since 1998 and the solid particle emissions have been measured since February 1998. Using the technique mentioned above, by determining the lignite recoverable blocks and progressively improving the mixing of the lignites with different qualities, the solid particle emissions were generally stabilized and reduced (lower than 150 mg m-3), with the best improvement observed around April 1999 and afterward. Trend lines for emissions over a three years period, show that the lignite quality management was able to continually reduce emissions, indicated continuing ability to learn from previous experience. EF020090O

Utilization of Lignite Reserves and Simultaneous Improvement of Dust

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