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Grecian lignite.

The dominant power source of Greece, and expansion continues

Power to Greece means lignite. In 1990, 79% of the country's power requirements were provided by the Public Power Corp.'s (PPC) lignite burning thermal power stations. The remainder was provided by oil (14%) and hydro-electricity (7%). That year, PPC extracted a total of 50 Mt of lignite from two lignite mining centres, Megalopolis in the extreme south of the country and Ptolemais-Aminteon in the extreme north (MM, February 1980, pp.126-139). That total output makes PPC the seventh largest coal producing company (all ranks) in the Western World.

Currently, PPC's lignite mines supply 19 power plant units with a total installed capacity of 4,463 MW. During 1990 the contribution of lignite to the country's total electric power output was 23,130 GWh.

Megalopolis is located on the Peloponnese peninsula 165 km south-south-west of Athens. Mining there started in 1969, and at the time it was the lowest calorific value lignite (1,000 kcal/kg) to be mined for electricity generation. The main equipment comprises five bucket wheel excavators (BWEs), three stackers and some 35km of belt conveyor installations. The complex includes the mines of Horemi, Marathousa, Thoknia and Kyparissia. Lignite production in 1990 was 6.9 Mt and the total excavated volume was 18.4 million |m.sup.3~ of material. The average stripping ratio was 1.8|m.sup.3~ of waste to each tonne of lignite.

The Megalopolis complex supplies the Megalopolis A power station, which has an installed capacity of 500 MW, and Megalopolis B, commissioned in September 1991 with installed capacity of 300 MW. The latter consumes about 4.5 Mt/y of lignite and produces 1,600 GWh/y of electricity. In 1990, Megalopolis accounted for 8.4% of national power demand. Total known reserves here amount to 370 Mt.

Much the larger of PPC's two mining complexes is Ptolemais-Aminteon which covers 120k|m.sup.2~ in Western Macedonia towards the Yugoslav border, some 120 km west of Thessaloniki, the second city of Greece. Here is one of the world's largest surface mining complexes, extracting 152.4 million |m.sup.3~ of lignite and waste in 1990, to provide 43.1 Mt of lignite; an average stripping ratio of 2.7|m.sup.3~ of spoil per tonne of lignite. Target production for 1991 was 182.4 million |m.sup.3~ of material to provide 42.6 Mt of lignite.

Ptolemais-Aminteon supplies four major power stations, Ptolemais with installed capacity of 620 MW (70+2 x 125+300), the 1,200 MW Kardia and Agios Dimitrios facilities (4 x 300 each), the 600MW Aminteon plant (2 x 300) and the 43 MW Liptol power station (10 + 33). In addition it supplies a dry lignite and briquette factory and the AEBAL nitrate fertilizer plant.

Major expansion plans

Greece is almost, but not quite, self-sufficient in energy production. There has been some interchange of energy with Yugoslavia and Bulgaria, but 1991 saw major problems with both those energy sources; Yugoslavia with its civil war and Bulgaria with the doubts about the safety of its nuclear power reactors. To ensure Greek self-sufficiency, PPC plans to raise lignite output at Ptolemais-Aminteon by almost 20% to 50 Mt by 1996/97. Currently Greek energy consumption is growing at 4% per year.

Already new mines are being developed to replace exhausted reserves. At the end of 1991 the operating mines were South Field, Kardia, Sector 6, North Field, Komanos and Aminteon. Kardia was nearing exhaustion and its equipment was being moved to Sector 6. At the same time a central workshop facility was being built at Kardia to serve all the mines south of Ptolemais. South Field and Aminteon

are key to the planned increase in Ptolemais-Aminteon lignite use in power generation.

The total reserves of the area amount to about 3,000 Mt. Since production of the Ptolemais lignite started in 1955, 465 Mt have been extracted and the area has some 50 years' of recoverable reserves left. Production has built up steadily but it is only recently that lignite has so dominated Greek power use. Back in 1981 Greece was heavily dependent on oil imports, costing $2,800 million that year and satisfying some 70% of the country's primary energy requirements.

The historical figures show the steady advance of lignite with an output of 1.4 Mt in 1960, 6.1 Mt in 1970, 15.4 Mt in 1980 and 27.3 Mt in 1985. It is a low calorific value lignite, 1,370 kcal/kg and 1,250 kcal/kg for the Ptolemais and Aminteon lignites respectively.

Further into the future, the mining activities of PPC at the Ptolemais-Aminteon Lignite Centre are to extend over an even wider area than they do now. PPC is to develop three new mines to secure supplies for five 300 MW power plants, due to be connected to the grid system by the year 2000. The first of these is Komnina, north-east of Ptolemais and south-east of Aminteon. Development of this 80 Mt deposit is to commence in 1995.

Some 50 km north-west of Ptolemais is Florina where development of a 120 Mt deposit is to start in 1995. The third mine, a totally new mining centre, could be based on Drama, some 450 km north-east of Ptolemais and 240 km north-east of Thessaloniki. The final decision on Drama, where the lignite is of very low calorific value although it is a large resource of some 960 Mt, will be taken after the completion of feasibility and environmental impact studies. The first power station at Drama is scheduled to be operational by 2000.

The two new mines in the Ptolemais-Aminteon area will secure lignite supplies for the three new 300MW power plants planned for the region. The first is to be an extra unit at Agios Dimitrios by 1996, the second will be a third unit for Aminteon, by 1999, and the third will be a new power station at Florina, to be operational by 2000.

The Ptolemais-Aminteon lignite complex is a massive mining undertaking which currently employs 44 BWEs (large and small), 14 stackers, 180 km of belt conveyor installations (accounting for close to 400 km of conveyor belting) and 400 units of auxiliary diesel earth-moving equipment including wheel loaders, hydraulic excavators, trucks, graders and dozers. Land Rovers and a variety of other vehicles account for a further 600 units. The current ten-year plan also calls for over 50% of this 1,000-strong diesel machine fleet to be changed.

A recent major order has been won by Terex Equipment of Scotland to supply its largest, 85 t capacity, truck to Ptolemais-Aminteon. The order is for 14 of the 3311E trucks and spare parts, and is valued at over |pounds~5 million. The first five trucks were to be delivered in April with the balance shipped before the middle of the year. Major features of the 3311E in- clude a Hardox 400 body, massive box-section frame with castings in the critical stress areas, a 1,050 hp engine matched to an Allison ATEC transmission and a full hydraulic braking system.

Ptolemais-Aminteon has an annual operating budget of 50,000 million drachma ($280 million). This does not include deprecia- tion costs or investment capital.

All the Ptolemais-Aminteon mines operate what they describe as the German mining system - continuous mining, transportation and dumping. The average belt speed throughout the mines is 5.24 m/s and the belt life varies from one to ten years depending, primarily, on whether they are carrying lignite or waste, and the abrasiveness of the waste.

The mines operate 24 hours per day, 365 days per year. The power consumption of the complex is, as one would expect, huge. Ptolemais-Aminteon has its own dedicated 43 MW power station, although it consumes somewhat more than this.

The major difficulty of mining in the area is the climatic variation over the year. Temperatures range from -20|degrees~C in the depth of winter to +40|degrees~C in the height of summer. One of the prime tasks in accommodating these temperature variations is to alter the belt tensioning of the many hundreds of kilometres of conveyors accordingly.

Predominant South Field

There are no plans to increase the current Ptolemais- Aminteon BWE fleet of 44 units this decade. The increase in output to 50 Mt/y of lignite will be attained by ensuring that this fleet achieves full capacity. The first BWE was brought into operation in 1958 and PPC engineers expect that such machines should operate economically for 35 years or more.

Output during 1991 was around 14 Mt from South Field, 10 Mt from Kardia/Sector 6, 10 Mt from Main/Komanos/North fields, and 9-10 Mt from Aminteon. In two to three years, production from the 24 |km.sup.2~ South Field should have risen to 20Mt/y and it will be one of the very largest single lignite mines in Europe.

South Field contains reserves of over 1,000 Mt, sufficient for another 40 years' life. Its 6-8 m thick lignite seams lie 160 m below surface, and the final depth of the pit will be 200 m. Its stripping ratio is 5:1 (|m.sup.3~) and mining is proceeding in a southerly direction. Much of the overburden has to be blasted and the complete mining method therefore combines continuous extraction by BWEs with shovel/truck or shovel/crusher/truck overburden removal. Stability problems occur due to clay bands encountered at South Field. Therefore efficient dewatering is critical.

The South Field range of BWEs and stackers includes machines from Krupp, Takraf, M.A.N. and O&K. The average bucket wheel diameter is 12 m. The largest machine, made by Krupp, has a 17.5 m diameter bucket wheel, weighs 5,000 t and will cut to a depth of 2.5 m. It is one of two such machines, type Sch Rs 3700/2.5 x 30, built for PPC in 1982. Its nominal bucket capacity is 3.7 |m.sup.3~ and there are 16 buckets, giving a theoretical output for bulk material of 11,100 |m.sup.3~/h. Its cutting height is 30 m, it can undertake selective digging up to 18 m and the outreach of the bucket wheel is 36 m.

Altogether, Krupp has delivered 16 bucket wheel excavators to PPC. The most recent deliveries include the two large units described above, six type C700 units with theoretical outputs of around 2,000 |m.sup.3~/h, built in 1982 and 1984/85, one C700 with a 21.5 m long discharge boom (the others have 25 m discharge booms), built in 1982, and three compact C300 units, also built in 1982, with theoretical outputs of 1,306 |m.sup.3~/h.

PPC operates an important reclamation programme as a follow-up to mining. As land is gradually released from the mining areas, it is suitably landscaped and recultivated. Alternatively, certain areas are used for experimental farming, to find alternatives to the traditional agricultural products of the region. To date over 800,000 trees have been planted on reclaimed mining areas.

As well as ensuring that mined land is properly reclaimed, PPC has also invested large sums recently to ensure that the pollution from its power plants is kept to a minimum. The ash from these power plants is an economic by-product, used in the manufacture of cement (to a total content of about 11%).

Occasionally mine development also requires the relocation of rivers, roads, railways and even entire villages. When population resettlement is necessary, new residential areas are created with modern fully equipped houses. To date the populations of two villages on the Ptolemais-Aminteon field (Kardia and Haravgi) and one Megalopolis village (Psathi) have been resettled; a total population of 3,000.

MINE FACTS

Name: Ptolemais-Aminteon Lignite Center Ownership: Public Power Corporation (PPC) Location: northern Greece Reserves: 3,000 Mt Grade: Lignite, 1,300 kcal/kg Started up: 1955 Mine life: some 50 years more Mining method: continuous surface mining with bucket wheel excavators Lignite production: being increased to 50 Mt/y Stripping ratio: 2.7 |m.sup.3~ waste to 1t of lignite Special features: currently supplies some 70% of Greek power needs
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Author:Chadwick, John
Publication:Mining Magazine
Date:May 1, 1992
Words:2044
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