Davids & Goliaths
Friday, November 9th, 2007
In the giant world of lignite mining, where bucket wheel excavators are able to dig 4,000m3 an hour, a team of â€˜littleâ€™ articulated haulers is helping boost recovery rates and overall operations efficiency. Brian Oâ€™Sullivan reports from Leipzig, Germany.
Depending on your perspective, lignite is either very old peat or very young coal. In fact it is the lowest rank of coal and has a relatively low calorific value, taking five tonnes of lignite to produce the same energy as one tonne of black coal. Because it is both low-density and energy-intensive, it is not traded on the world market like black coal, and prices have remained reasonably stable. Instead, lignite is used almost exclusively as fuel for nearby steam-electric power generation. And the eastern parts of Germany have many millions of tonnes of these fossilized forests at their disposal to use as a vast, cheap energy source.
During the 41-year existence of the German Democratic Republic, East Germany, as it was commonly known, was widely regarded as the most economically advanced member of the Warsaw Pact group. A vital element of the Soviet blocâ€™s command economy, it was an industrial powerhouse, manufacturing iron, steel, light metals, chemicals and engineering. As energy consumption and prices of imported oil grew, East Germany increasingly relied on lignite as its most abundant form of energy â€“ providing over 60 percent of its energy supply. But with reunification with West Germany in 1990 most of the former GDR was de-industrialised, leading to the closure of 19 lignite mines.
One that remained open was the Profen mine, 30-minutes drive from Leipzig and 200 km south of the German capital Berlin. The mine has been open since the 1930s and been jointly operated since 1994 by MIBRAG, a state-owned mining and power company and a consortium headed by Washington Group International and NRG Energy.. The mine will produce close to 9 million tonnes of lignite this year â€“ involving the removal of an incredible 50 million cubic metres of overburden. Almost all of the lignite is sold as feedstock for Schokopauâ€™s two modern 900-MW power plants, with the remainder being made into briquettes for domestic heating.
With such large amounts of material to move, the machinery involved in its extraction is equally massive. Profen has six enormous bucket wheel excavators that can dig over 4,000 m3 per hour and four equally large chain excavators. The material is carried along 28 km of conveyor belts and overburden is distributed using two gigantic spreaders. While suitable for most of the production, these mega-machines are not effective in all circumstances. Four years ago the mine looked for a new technology that could help them recover the lignite that would otherwise be lost. The answer? A team of hydraulic excavators and a rental fleet of 12 Volvo A35D articulated haulers from local dealer Swecon.
The â€˜mobile coalâ€™ team is operated by MIBRAG, whose equipment is recovering up to 8,000 tonnes of lignite per day. The smaller equipment targets exposed coal that is going to be covered over by the advancing overburden spreading, or coal where it is too costly or difficult to get the bucket wheel excavators to the area. â€œThe bucket wheel excavators need an access road 16 metres wide, pushed open by a dozer,â€ says Marcel Schmidt, MIBRAG project manager. â€œIn the time it takes to create a haul road 100 m long we could have recovered over 10,000 tonnes of lignite!â€
The construction equipment may only be able to work on a face 3 m high â€“ whereas the bucket wheel excavators bite at a face 27 m high â€“ but working in two shifts, over 3.5 million tonnes has been hauled by the Volvos in the last five years â€“ representing some 10 percent of total production.
Being a light material, the haulers have been fitted with 800-mm extended sides and tailgates to increase the capacity of the haul body. These have proved to be the perfect tools for the job and have recently replaced a team of larger rigid haulers, as they can cope both with steeper haul roads and with haul roads of a lower quality. The articulated haulers also help with the creation of the haul roads themselves. The haul distances vary wildly, from as little as 100m to as much as 3 km long.
The mobile team doesnâ€™t work in complete isolation but rather integrates its production into the continuous mining system. The haulers either dump their loads on a flatback feeder whose small chain buckets load the lignite onto the conveyor belt, or they stockpile 100,000 tonne heaps in a convenient place for the bucket wheel excavators to process. â€œThe haulers are very complimentary to the big equipment,â€ believes JÃ¶rg Benndorf of Washington Group International.. â€œItâ€™s not only increased our coal recovery rates but also allowed us to use it as a buffer on our production. We are also more flexible with our equipment â€“ the big machines stay where they are most effective, and the smaller excavators and haulers recover the valuable coal on the periphery of the operation.â€
â€œThe availability of the haulers is very important to us,â€ believes Marcel Schmidt. â€œAll our operators have gained a nationally recognized degree and are expert at getting the best out of the machines. And renting the Volvos from Swecon, who is based nearby, means that if we have a problem we have to make only one call and a quick resolution is reached.â€
The Profen mine is taking a very modern approach to its entire operations. By its nature lignite mining is disruptive of the landscape, but the mine takes its environmental duties seriously and goes to great lengths to restore the worked-out areas sensitively. Archeologists are invited to inspect areas prior to mining â€“ and have unearthed curiosities such as mammoth teeth and a horse skeleton found standing upright. At the time of writing a small community that was being disturbed by the work of the mine was being rehoused in a new village created by the mine to the communityâ€™s design. This involved building the new houses, but also moving 20 km â€“ in one piece â€“ an 800-year-old church.
It is clear that the use of â€˜mobile coal’ has been a success at the Profen mine, making the overall mining process more flexible and efficient, as well as increasing recovery rates. The mine is currently working on a long term-plan for integrating the haulers into the continuous mining system and thereby minimizing haul distances.