Lignite from marsh forest

The lignite of Mátra and Bükkalja were generated some 5 to 8 million years ago in the so-called Pliocene in the end of the tertiary period of recent epoch in historic geology. It was at that time when the formations of the predominantly fine detritus attaining great thickness were developed in the Carpathian basin – in the northern sea-basin (Parathetys) separated from Thetys, the forebear of Mediterranean – in the Pannonian inland sea getting more and more sweeter.

The occurrence in Mátra-Bükkalja was emerged from the destruction of the subtropical marsh flora accompanying the disattaching bays getting sweeter in the Pannonian inland sea when marsh cypress (Taxodium), leafy trees (e.g. alder, willow) and huge volume of sedge and reeds were accumulated. The lignite of 5 to 8 million years represents the initial phase of turning into coal and the plant components in them are recognised well. Because of the repeated sinking of the basin of the Pannonian inland sea and the processes of filling up more or less coping with sinking, bigger and bigger volumes of plants went under water and mud. This is how the lignite field seams going down at an angle of 2 to 3° toward the Great Hungarian Plain in south–south-eastern direction were developed. Because of the characteristics of seam formation, the quality of lignite is characterised by a comparatively low calorific value and a high ash and moisture content. There are sandy, muddy and clayey sediments between and above lignite seams.

The lignite seams in Hungary are relatively well known on the basis of geological research made in the sixties and seventies. Hungary has a remarkable asset of lignite. The lignite-bearing area of Mátra and Bükkalja has an exploitable mineral asset of several million tons which is suitable for energetic use in the long run.

Mining technology

The lignite production in Visonta and Bükkábrány takes place through strip mining. According to strip-mining technology, the dirt beds (clay, mud, sand etc.) above lignite seams must be removed first then dead materials must be backfilled into the mine-openings. As soon as one of the trenches is exhausted mine goes further on and any exploited dead materials is to be put into the hollow of the previous area.

The preliminary drainage of area in the area to be mined started 3 years before coal production. During which the water from overburden and interstage water-bearing strata is introduced to the deeper water-bearing formations from where the subterranean waters are lifted to surface by plunger-pump wells installed on the edge of strip-mining area. Winning the dead-ground primarily occurs with help of bucket wheel dredgers. Periodically also crawler-bucket ladder excavators participate in producing barren rock. It is also necessary to continuously use one-dipper dredgers during specific technological processes.

Winning coal occurs with help of crawler-bucket ladder excavators and one-bucket dredgers. The crawler-bucket ladder excavators and bucket-wheel dredgers deliver any materials won to the conveyor belt. The frontal, moorband- and dump-side conveyor-belts make systems of belts consisting of elements with 1200, 1400, 1600 and 1800 mm belt-width. In the system of belts for coal transportation, the slope bridges of Hungarian development and production are for bridging over great depths of the system of slopes in mines and for crossing belts for barren rock that are capable of bridging over a level difference of 22 to 25 m.

Placing barren rock is accomplished by arranging equipment for dumps. The dredgers, conveyor-belts and dump-producing machines are connected together into chains of machines. The so-called direct reloading system operating without any conveyor-belts and only consisting of a dredger and a dump-generating machine deserves to be mentioned especially.

Lignite arrives at the breaker row then to the power plant on a conveyor-belt from the Visonta mines. The crushing plant operating in Bükkábrány is capable of separating big-size fraction so it is possible for the people to use lignite for their own purposes. After crushing plant, the crushed lignite is put to the coal storage area providing delivery for railway from where the delivery of coal to the power plant is to be accomplished by railway cars of 55 to 60 tons. The reception of lignite takes place in wagon-tipping devices. The output of the two operating tipping devices is as follows: twin-dumper 800 to 1200 kilotons/year, rotary dumper 2500 to 3000 kilotons/year.

The delivery of coal to the coal storage area in power plant or directly to the power plant blocks occurs on conveyor belts from dumpers.