The last ten years has seen major rationalisation and restructuring in the once Communist country with annual output dropping from about 24 million tons to around 13 million tons per annum, providing 20% of the country’s domestic primary energy.
Coal is today supplied by four main underground operations owned by OKD, the largest Czech mineral exploitation company. OKD, which underwent reorganization in the 1990s, produces all the country’s coal from a small group of underground mines using longwall face technology with a shearer or plough. In 2002 OKD employed 18,700 employees.
The changes of the last ten years have had a major impact on mine planning, equipment sizes and designs.
During the 1980s average face production was between 350 tons to 1500 tons per day, the average face width was 100m-120m, and seam thickness 0.5m–5m. Post the velvet revolution, the average daily production (from one face) increased to between 2,500 tons – 7,000 tons per day, average face width has increased to 250m and at some operations extracted face thickness is up to 6m.
Mine Lazy is the most productive of OKD’s four operations with average raw coal production of three million tons per year from five longwall faces.
This mine was also the first to use a shearer to mine a seam thickness of up to 6m, supplied by Charbonnages de France – Ingénierie.
Equipment incorporates a Panda shearer, produced by French company Sagem. The shearer has a drum diameter of 2,500mm and installed power of 2x450kW. It incorporates two ranging arms for Uni-Di or Bi-Di cutting system in longwalls with high seam thickness. The shearer started extraction in 1993 with chainless haulage system Dynatrac. Between 1993 and 2002 this shearer has operated in six faces and extracted 5.4 million tons.
Roof supports are 2-leg shield WS 1.7 version, supplied by French company MFI. This type of support is designed for temporary roof supporting of extracted rooms in flat seams ranging in thickness from 2.8m to 6m.
The AFC is a 1000-HB 280 supplied by Gelrach – Halbach&Braun (now DBT). The conveyor has a pan width of 1000mm and is rated at 1,500 tons per hour. The conveyor has Dynatrac chain integrated to its pans.
The stage loader used two Gelrach supplied pan conveyors 4 E74 VS with shifting gear, coal drum impact crusher SK 1700 C from Kllõckner.
The size of the equipment posed a major problem during installation. The Lazy mine shafts are equipped with an old hoisting winch, with cage dimensions of 3200 x 1500 x 950mm.
Manufacturers were required to take this into consideration in the design of all equipment. Once delivered to the pit bottom, equipment was transported by monorail to a working chamber (30m x 6m x6m) near the face, 70m from the tail gate. Here equipment was finally assembled and transported to the face. Some 2000 units weighing over 5000 tons were transported like this.
Transporting assembled roof support weighing 26 tons posed the biggest challenge. At the time of installation no transportation methods for such big equipment were available at the mine. Finally, a special footwall rail made by Scharf was used, with a rail width of 800mm and load capacity up to 30 tons.
An incident that occurred at the Lazy mine in 1996 gives some indication of the geological challenges in the Czech Republic.
The mine had just relocated to an area with a seam thickness of 3.6m-6.3m, averaging 5.02m. By December 1995, four months after mining had begun in the panel, high volumes of carbon monoxide and methane forced the workings to be closed. By April the following year the mine was back in operation, but only for a few days at a time as samples showed 77 ppm of CO along with methane. Production finally restarted in June.
By September 1996 the mine had to contend with major geological problems. Tectonic conditions caused the roof to collapse over roof supports 65 to 118. Recovery of the face was undertaken and included removal of oversized rock blocks, secondary blasting, gradual supporting of the roof and pillar sticking. By October 1996 the shearer was able to traverse the whole face. An artificial roof was inserted and drilling to the roof from main and tail gates was undertaken along with floor rock blasting.
Roof falls continued until early 1997 but with the help of the artificial roof the situation was eventually stabilized and mining without any measures was possible.
A year ago the mine was mining with five shearers simultaneously. These included an SL 500 (Eickhoff), KGE 800 (Famur) and KGS 445 (Famur) with pan conveyors PF 4/932 (Eicotrack) and PF 4/1032 (Dynaride); roof supports MEOS 26/56 and Fazos.
Today the mine is producing coal from two faces with shearers KGS 445 and KSW 500 at a seam thickness under 5m and daily production averaging 4500 tons.
Two of the shearers are currently undergoing overhaul.
During the next few months the mine is driving a heading to contiguous seams with a coal seam thickness of up to 1.5m. The mine plans to use plow technology to extract this coal.
