Since it began longwall production in 1982, the Bogdanka mine in eastern Poland has increased its output steadily, reaching 5.8 Mt in 2009. During its first 28 years of operation, the mine relied on shearers that achieved a maximum output of up to 20,000 t/d from thicker seams, but were limited in operation to seam thicknesses of at least 1.6 m.
In 2009, the owning company made the decision to use plows for working seams that are thinner than this, with the first set of equipment being commissioned in the mine’s Nadrybie section in March 2010. After a seven-month campaign, the first panel was mined out, with the plow system having achieved an output of up to 17,000 t/d. The second face to be extracted, in the Stefanów section, came on stream in October 2011. Since then the equipment has not only averaged an output of 17,000-20,000 t/d, but in February 2012 broke the long-standing world record for daily output from a plow face.
The mine commissioned its second plow face later in 2012. This system is equipped with Cat Medium Voltage Current Source Inverter Variable Frequency Drives (VFDs) as well as with the new generation of CST gear boxes on the Cat GH1600 plow and PF4/1032 face conveyor.
In the second half of 2014 Bogdanka will commission its third and fourth GH1600 plow systems, which also will be equipped with Cat VFDs. The four plow faces with the new equipment will enable Bogdanka to achieve its output target of 11.5 Mt/y of high-quality thermal coal in the coming years.
A leading Polish coal producer
Located in eastern Poland, close to the country’s borders with Ukraine and Belarus, Bogdanka is owned and operated by Lubelski Węgiel Bogdanka S.A. The mine lies in the southeastern part of the Central Coal District (CCD), part of the Lubelskie (Lublin.) Coal Basin (LCB), which has been evaluated in great detail. Bogdanka is the only mine producing hard coal in the LCB.
Lubelski Węgiel Bogdanka is one of Poland’s leading producers of hard coal, with the company having achieved this position over the past 30 years through a combination of financial restructuring and continuously improving the efficiency of its mining operations. Its output of high-volatile bituminous coal is used mainly for power generation and thermal energy, as well as for cement production.
The geological structure of this part of the coal basin consists of nearly horizontal coal seams overlain by approximately 700 m (2,300 ft) of overburden. The Carboniferous-age rocks that host the seams are relatively weak, and there is little significant faulting in the deposit.
However, the overlying Jurassic rocks are water-bearing, with some beds subject to significant water pressure. The rock also contains a layer of unconsolidated sand.
Coal resources available to the company total some 600 Mt (660 million short tons – Mst), of which around 255 Mt (280 Mst) make up the current mining reserve. A total of 18 seams occur within its 77 km2 (29.7 square-mile) license area at depths of between 650 and 730 m (2,130 and 2,400 ft), of which eight contain economic reserves. Mining currently takes place in two, seams 382 and 385/2.
The operation itself is split into three sections – Bogdanka, Nadrybie and Stefanów – all of which lie within a distance of a few kilometers. In total, the mine has six shafts and one coal preparation plant.
Development at Bogdanka began in 1975, with the first longwall being commissioned in 1982. Since then, Bogdanka has produced some 100 Mt (110 Mst) of coal. Its annual output is now around 5.8 Mt (6.4 Mst), a figure that will rise to 11.5 Mt (12.7 Mst) within next few years.
Bogdanka’s mining systems
For almost 30 years, underground mining at Bogdanka centered on shearer technology, with the mine having optimized its shearer operations to achieve satisfactory efficiency and reasonable economic results in seams that are thicker than 1.6 m (63 in.). In seams between 2.0 and 2.5 m (79-98 in.) thick, shearer faces have been able to achieve run-of-mine outputs of up to 20,000 t/d, while the mine has recorded outputs of up to 15,000 t/d in seams that are 1.6-2.0 m (63-79 in.) thick.
Nonetheless, using shearers in longwalls places some important limits on the thickness of seams that can be extracted. Significant factors here are human – the need for operators to be working on the face all the time – and technological, in relation to the physical size of the shearer and the armored face conveyor (AFC). Taken together, these factors mean that shearer faces need to be installed in seams that are at least 1.6-1.8 m (63-70 in.) thick to be economic.
This in turn means that many millions of tonnes of in-situ coal cannot be mined economically, because seams are too thin to be worked economically using shearer technology. At Bogdanka, this applies particularly to seam 385/2, which has been worked since 1997, and also to the prospective 389 and 391 seams. Being able to mine effectively in seams as thin as 1.2 m (47 in.) would significantly increase the operation’s mining reserves and would extend its operational life.
To achieve this, the company decided to introduce plow technology at Bogdanka. Seen as being of strategic importance for the mine, the introduction program has been carried out consistently for several years now, with the aim of achieving a reliable mining system in seams 1.2-1.6 m (47 to 63 in.) thick. Using this technology should both improve the cost effectiveness of mining and reduce significantly the amount of waste rock produced in the run-of-mine coal.
First plow panel – 1/VI/385
The first plow longwall at Bogdanka was set up in the Nadrybie section of the mine, in panel VI of the 385/2 seam. The face length was 250 m (820 ft), while the panel was 1,750 m (5,470 ft) long. Within the first plow panel, the seam was between 1.4 and 1.7 m (55-67 in.) thick, and dipped at a maximum of 2.5 degrees. The coal had a compressive strength of 8-19 MPa (1,160-2,756 psi), and a Protodyakonov strength index of between 0.75 and 1.2.
The roof in this panel contained alternating layers of siltstone, mudstone and sandstone, with the first 3 m (118 in.) of roof having a compressive strength between 24.4 and 40.7 MPa (3,540-5,900 psi). The seam floor consisted of alternating siltstone and mudstone, with some local thin layers of sandstone, and it had a compressive strength over the first 3 m depth of 12.9-31.8 MPa (1,870-4,610 psi).
For the first plow installation, the roof support system consisted of 1.75 m-wide, two-leg face shields operating between 950 and 2,000 mm (37-79 in.), with face-end shields with a height range of 1,480-2,300 mm (58/91 in.) that were spaced at distances of between 1,700 and 2200 mm (67-89 in.). All the face supports were rated at 2×3,619 kN capacity.
Plow system Bogdanka 1
The GH 1600-1 plow had a body height of 980-2,100 mm (39-83 in.), with a 42×137 mm drive chain. Two 210/630-kW (282/845-hp) motors driving through 16:1-ratio P45-UEL gearboxes provided plowing speeds of between 0.98 and 2.94 m/s (193-579 ft/min.).
The overhead-discharge PF 4/1032 AFC was powered by two 800-kW (1,073-hp) motors through 33:1 P45-CST gearboxes, giving a chain speed of 1.52 m/s (299 ft/min.). The AFC pans were 1,750 mm (69 in.) long, with a two-strand 42×146 mm chain assembly.
Both the AFC and the beam stage loader had a capacity of 3,000 t/h (3,300 st/h) of run-of-mine coal. The PF 4/1132 stage loader was equipped with a SK 1111 crusher, with twin 34×126 mm chains being driven at a speed of 2.03 m/s (400 ft/min.) by a single 400 kW (536 hp) motor. Power to all the face equipment was supplied at 3,300 V.
Learning the system
Bogdanka’s first plow longwall entered production on 23 March 2010, with the first few weeks of operation being used by the staff to gain experience in operating the automated plow system properly. With operators continuing to fine-tune the system’s control and automation software, and optimise it to the existing mining conditions, it was not long before the face was producing 6,000 t/d (6,600 st/d) of run-of-mine coal.
After that, its performance increased steadily, and within three months of start-up it had reached the expected output of 10,000 t/d (11,000 st/d). On 25 August 2010, the system achieved its peak daily output of 16,894 t (18,583 st), and the first panel was completed on 20 October. In its seven-month life, the plow system advanced an average of 10.4 m/d (34 ft), and achieved an output of 8,200 t/d (9,020 st) run-of-mine. On a monthly basis, this equated to an average advance of 247.4 m ((812 ft) and an output of 195,400 t (215,000 st). The daily running time for the plow averaged 5 hours 23 minutes, with the panel producing 1.38 Mt (1.52 Mst) overall.
The second panel – 7/VII/385
Having completed the first panel, the plow system was moved to a new area in Bogdanka’s Stefanów section. This panel, 7/VII/385, was different from the first, experimental one in some important respects. The face was widened from 250 to 305 m (from 820 to 1,000 ft) and the panel length was increased by about three times – to 5.022 km (3.12 miles). The thickness of the seam in this area ranges from 1.2 to 1.6 m (47 to 63 in.) – on average 1.42 m (56 in.). The 7/VII/385 longwall started up at the beginning of October 2011.
In this panel, Bogdanka used a different return belt conveyor station, with a 12 m (39 ft) overly instead of the 3 m (10 ft) used in the first panel. This allowed the face equipment to run longer before the conveyor belt had to be shortened, which achieved greater utilization of the plow.
In addition, the mine installed a special ramp in the main gateroad that helped load any material that had been pushed out from the face by the plow body on to the AFC. This eliminated the need for a dinting machine that had been used to handle this material on the first panel.
Figure 4: Stefanów plant
Another important change was to relocate the plow control station from its original position in the energy train underground to a special control room in the Stefanów administration building. The surface control room was also equipped with a number of additional control systems for monitoring ventilation, energy supply, conveying, transport and other vital processes.
A control center plays an important role in achieving high production. Next to effectively controlling all of the plow system components, the dispatcher has to react as quickly as possible when there are unscheduled stoppages. To act effectively, the dispatcher has to have direct access to all of the relevant monitoring systems, including the power supply, the pump stations for the high-pressure hydraulic fluid, and cooling and spraying water, the conveyors, bunkers and shaft system, ventilation and methane control, and material transport, amongst others. Being able to see all this information at a glance makes it easier to respond quickly should the face equipment stop unexpectedly. For a high-performance plow face, a one-minute break means a loss of 15-30 t (16.5-33 st), which quantifies the importance of quick responses to unusual situations.
Plow control center on Stefanów
The plow system in the second panel reached a daily production level of 10,000-15,000 t (11,000-16,500 st) run-of-mine relatively quickly. The daily utilisation rate for the plow increased from the six hours achieved in the first panel to more than ten hours in the second. This resulted not only from the longer face, but also from experience gained on the first panel and from technical improvements.
On 16 February 2012, Bogdanka smashed the world record for daily production from a plow-equipped longwall, with an output of 24,900 t (27,390 st) of coal from the 7/VII/385 panel. During the day, the plow face advanced more than 27 m (89 ft) at a 1.63-m (64-in.) cutting height.
The second panel was finished in February 2013. The average performance reached during the 16 months of operation in this panel was 11,778 t/d (12,983 st/d).
Bogdanka attributes this achievement to a number of factors. First, it is now one of the most advanced mines in the world, and it is able to make use of high-capacity, high-efficiency mining equipment.
Second, the workforce at the mine is well motivated and has a high level of technical expertise. In these conditions, it is easy to see the advantages of using plow technology. The machine utilization is critical, and is maximized when plowing from face-end to face-end with a double web at the face ends – the system that is used at Bogdanka.
By using a system like this, a plow face can achieve at least 50 percent better performance than a shearer working under comparable conditions, both overall and as a proportion of the daily running time.
Bogdanka’s second plow set
During the second half of 2012 Bogdanka installed a second plow system, this time in its Nadrybie section. The new longwall was located close to the first panel that was mined in 2010, but had moved in the opposite direction. The run-of-mine coal had been transported underground to the No.2.1 shaft at Stefanów.
The new system is used on 250-m- (820-ft)-long faces and is based mainly on the technology used in the original face. There are, however, some important changes.
Instead of using 210/630-kW (282/845-hp) motors, the new system is equipped with asynchronous motors with 800 kW (1073 hp) of installed power. In addition, 3.3 kV variable-frequency drives (VFDs) are used for powering the plow and AFC motors, and the specially developed P45-CST is be used for driving the plow instead of the P45-UEL gearboxes.
The explosion-proof medium-voltage VFDs of this type were used in a longwall in underground mining for the first time anywhere in the world. They are housed in a flame-proof enclosure, and they use a Pulse Width Modulated (PWM) Current Source Inverter (CSI) for the machine-side converter. VFDs of this type have an effective power structure, with a current-limiting DC link inductor. All four VFDs together with a special liquid cooling station are positioned in the energy train on the tailgate side of the plow system. The cooling station is acting on all four VFDs, using a closed circuit for the coolant.
The application of CSI VFD brings a significant improvement for the plow and AFC operation. It implements several advantages:
- Application of standard asynchronous motors
- Distance between motors and powering VFDs under Polish mining law up to 4 kilometers (2.5 miles)
- Variable speed for AFC and plow in a wide range (0 to 120 percent of nominal speed)
- Precise torque control of the asynchronous motors
- Full utilization of installed power on both plow’s motors through load shearing
- Improvement of overload protection for motors and chains
- Braking possibilities and thus returning back power to the network
- Unlimited start-ups of the motors
- No significant voltage drop during start-ups
- The usage of “weaker” networks possible
The control system for the VFDs is located on the surface.
Flame proof 3.3 kV 50 Hz 800 kW (1,073 hp) Variable Frequency Drive for Bogdanka.
Another important technical innovation is the very first application of a new CST gearbox. This unit is designed for operation at any rotational speed, unlike any CST drive previously in operation. The application of CST drives delivers very sensitive overload protection for the chains.
The third and fourth plow set
In the second half of 2014 Bogdanka will implement its third, and a couple of months later its fourth plow system. Both systems are based upon GH1600 technology with Cat roof supports. Every system will be equipped with CSI VFDs on the plow and AFC and with the newest generation of CST – VM gearboxes. At the beginning of the year 2015 there will be four high performance plow systems operational at the Bogdanka mine.
Bogdanka has proved beyond any doubt that plow technology can provide world-leading performance—not just one time, but day after day, month after month, year after year. At a time when Europe’s hard-coal mining industry has to operate within an increasingly competitive world market, the mine is relying on its plow systems to keep its production costs under control, and to help it reach its new production targets. Given its success to date, that should not be difficult.