South Wales revisited – the Aberpergwm mine

Materials World magazine
,
1 Apr 2009

Regeneration work is well underway in the Aberpergwm coal mine in South Wales, UK. Michael Forrest finds out more about the strategy for expansion.

The UK will soon become a net importer of energy. Dependence upon natural gas, coal and electricity supplies from overseas will result in a negative effect on the balance of payments and energy security.

At present, some 42% of the UK's electrical energy is generated from natural gas, mainly from the North Sea. Thirty-five per cent is from coal, 16% from nuclear and seven per cent from renewables including hydro and other sources (source: Department for Business, Enterprise and Regulatory Reform [BERR]). However, ageing coal-fired and nuclear generating plants will increase the demand for gas at a time of declining domestic reserves.

Not all coal-powered stations will be retired and some have been retrofitted to meet emission standards. One such retrofitted plant is Aberthaw, near Barry in South Wales benefitting from a £235m upgrade. Operated by RWE npower, the station is designed to burn low-volatile coal, consuming three million tonnes per annum. Around 40% of this coal is locally sourced, the remainder is imported.

Close at hand

One local source is the Aberpergwm coal mine, which is operated by UK company Energybuild Group plc, that supplied Aberthaw with 225,000t of anthracite in 2008. The mine, located in the Neath valley of South Wales, is being expanded to increase production, as coal is taking an increasing share of the energy mix as it has a cost advantage over volatile oil and linked gas prices. It also offers the security of domestic supply and ease of storage at power stations, allowing stockpiling to meet peak energy demands.

Records indicate that mining has occurred around Aberpergwm since 1811. Following nationalisation of the coal industry in 1947, Aberpergwm Mine was owned and operated by the National Coal Board and subsequently British Coal. In September 1985, British Coal shut the mine under their national closure programme, sealing the entries and demolishing the surface infrastructure. The underground workings were allowed to flood.

Aberpergwm was reopened in 1996, and dewatering and recovery of mine infrastructure began, a process continued by Energybuild. In 2007, 569m of intake and return drift were recovered and dewatered at a cost of £2.4m, with 5,000t of incidental coal produced. Thirty per cent of the cost of this activity will be recovered from the BERR under the Coal Investment Aid Scheme.

Coal complications

The coal at Aberpergwm lies within the Carboniferous coal measures in an area dominated by strong north-south and northeast-southwest faults that control the continuity and thickness of the seams. The majority of the mine's underground coal reserves are located to the west of a major geological fault known as the Pentreclwydau fault.

Prior to the abandonment of the mine, British Coal had driven two inclined roadways to access and extract coal from the 18- and nine-feet seams to the west of this fault. It has a down throw of approximately 110m to the west. Historic mine workings are located to the north and south, as well as in the west towards the Treforgan mine. Here, ideally spaced boreholes have defined resources in a faulted sequence that is likely to be more intense to the south and the Neath Disturbance. This faulting will dictate mine plan layout and coal recovery.

Coal seam thicknesses are used to produce estimates of in situ and recoverable coal tonnages, and have been obtained from abandoned mine plans, borehole logs and underground observations. The seams show marked changes in thickness over short distances and there are uncertainties regarding 'complete' thickness in respect to the abandonment plans. In general, conservative thickness values have been used for coal resource calculations.

These resources are found in five seams with the nine-feet seam containing the largest measured resource of 4.7Mt, while the six-feet seam has the largest inferred resource of 65.3Mt. The coal quality in the largest seam has 7.7-8.7% volatiles and 0.6-0.8% sulphur. Calorific value is 37,250-37,625kj/kg and therefore does not require upgrading for use.

The mining method was stall and pillar. Coal was extracted from 'rooms' leaving pillars to support the roof. British Coal had planned a shortwall (less than 100m) mining system using a coal shearer and an armoured face conveyor but never put it into operation.

Energybuild's investment has transformed the mining operation and greatly expanded production. Beginning in 2003, the company re-established the infrastructure at the mine including dewatering, ventilation, and roadway recovery and repairs. It improved access and refurbished the surface facilities at the railhead and installed an onsite coal washery.

Energybuild has acquired plant from the nearby Tower Colliery, which closed in January 2008, at a cost of £1.4m. Perhaps more importantly, it has employed many of the skilled miners.

Driving on

The company accessed the main coal seam through the Pertreclydau fault in September 2007, recovering the old British Coal intake and return drifts. By February 2008 an air circuit had been completed and mining began a month later. The cost of recovering the drifts and setting up the ventilation circuit in the 18ft seam was £3.8m before Coal Investment Aid of £1.272 million. This was on budget. The company is currently using a coal preparation plant (CPP) and railhead at Tower although future plans include an onsite CPP and railhead.

These efforts have resulted in a number of expansions. The workforce increased from 45 in 2007 to 200 by October 2008. Driving new drifts for access and production (including a new portal) requires four road heading machines and a further two are due for delivery by June. Rock bolting using specialist machines is undergoing trials as the main form of roof support. Mining is now totally mechanised.

The plan is to increase production to 265,000t of clean coal this year to June. This will build on a coal production system introduced January in the area of the six-feet seam. Energybuild also intends to grow production to 750,000t by June 2011, while linking the Aberpergwm mine to the Treforgan mine underground -_they are approximately six miles apart.

An important stage of development will be driving the new drift, which received full planning consent in July 2008. This will improve ventilation capacity and help reduce production costs due to the efficiencies it will bring in terms of coal clearance, material handling and speedier conveying of miners to production areas.