New coal mining method

A NEW underground coal mining system could deliver double the productivity of existing bord and pillar sections at around 20% of the cost of a new longwall system.

Angie Tomlinson

With origins in the Canadian potash industry and the South African and Australian coal industries, the new linear mining system will cost about 20% more than a traditional bord and pillar section but could set new benchmarks in productivity.

The first flexible belt haulage system, one of the key components of the system, is going into operation in a sub 2m South African mine (this mine will not be utilising the complete linear mining system) in February 2007. The haulage system was redesigned and adapted for coal in order to conform to the various legal requirements imposed by coal mine legislation.

The second unit goes into Australia’s Cook operation in June 2007 as part of a complete Magatar high production section.

Developed over the last four years by South African company Magatar Mining, the high production system is being touted as bridging the production gap between bord and pillar and longwall mining. It involves a bolter miner coupled with continuous haulage, mobile tail-end and belt storage magazine and supported by totally integrated logistics that aims to radically improve equipment utilisation.

The linear mining system is also considered to be a safer system in almost all known aspects in a CM production section, mainly owing to the harmonious operation that it offers in terms of movement, but also the methodology offering mainly mining in retreat, thus away from the danger area.

Leading bord and pillar mines in South Africa currently achieve cutting machine utilisation of around 35% and produce in excess of 100,000 tonnes of coal per month, according to Magatar managing director Philip Venter.

Longwall sections, on the other hand, achieve production rates of over 500,000t per month and are running at system utilisation figures of around 70%.

Bord and pillar’s relatively poor total utilisation performance is a result of a multitude of physical limitations presented by the current methodology that results in excessive tramming, unproductive change out times for haulers, damage to floors and poor working conditions, especially in longwall development.

The haulage system, produced by Canadian company Praire Machine and Parts (PMP), has been extensively used in potash applications, but not in coal. The integrated mining system consists of around 90% proven, off-the-shelf equipment.

“The linear mining methodology allows continuous miner utilisation to be increased to over 60 percent, which means production figures of over 200,000t per month could become a reality,” Venter said.

The equipment and sequences developed supports maximum advance rate with minimum roadways, identical to longwall gate road development, with maximum safety factor during this phase. During the production cycle, a single roadway is advanced without interruption, up to 100m or more, with extraction of the pillar on the retreat as one of the possibilities.

One of the development roadways is used as ventilation intake while the belt road functions as the return airway. With 300m of available belt in the active belt storage magazine (identical to that used on longwall belt systems), combined with a mobile boot end, cartridge type belt support structure and a 100m haulages system, the system’s reach, without stopping, is conceptually around 40,000sq.m of coal, Venter said.

While the system is extremely flexible, Venter detailed one conceptual mine plan consisting of driving into a block roughly 86m wide from two roadways. Entry into the ribs is at 60 degrees to enable easier access, resulting in a plunge about 100m long.

Analysis of the best current practice on coal mines resulted in the development of the linear mining system, which offers among others the following results: up to 40% reduction in dead tramming of the CM, up to 100% improvement in output from a single production section, and up to 50% less manning required.

In designing the system Venter said primary and secondary logistics have been totally integrated to reduce manhandling tasks in the section to an absolute minimum. Not only have the primary tasks of cutting, bolting, loading and conveying been integrated, but so have all secondary services: belt extension/shortening, ventilation, rockdusting, replenishing of consumables and maintenance.

“We believe the linear mining system offers a possible bridge between bord and pillar mining and longwall mining,” Venter said.

Article courtesy specialist coal consultancy and information provider Barlow Jonker, Coalportal.com

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