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Technical | Ventilation | Thermal   > furnace

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Prior to the introduction of centrifugal fans in the mid 19th century, the principle form of artificial ventilation used in coal mines employed a furnace to heat the air in one shaft (the upcast). As the heated air had a lower density than the colder air in a nearby non-heated shaft (the downcast) there was a relative difference in the air pressures between the two shafts and as a consequence air flowed between them. By carefully directing the air flow through the workings they could be kept free from build up of gas.

The first attempts used a furnace at the top of the upcast shaft but it was soon realised that placing it at the bottom of the shaft would improve the effectiveness considerably. Whilst this was not a problem in non-fiery (gas free) mines, the presence of gas in the air-stream feeding the furnace or in the return air joining the hot flue gases in the shaft was potentially catastrophic. 

furnace front elev
furnace plan elev

Legislation was passed requiring that the return air entered the upcast shaft at a level above the furnace where the temperature of the flue gases had been sufficiently cooled. This was achieved by means of an inclined tunnel known as a dumb drift.

dumb drift

Although furnace ventilation could produce surprisingly effective ventilation, there were other serious disadvantages. Furnaces constructed at seam level could sometimes ignite the adjacent coal which could burn undetected for a considerable time. Shafts used as upcasts could not be used for winding coal or men and the flue gases had a corrosive effect on the shaft timbers and lining. This was particularly true where cast iron tubbing was used since both  the metal itself and the wood sheathing between the segments were both eaten away. The variations in temperature when the furnaces were damped down and then stoked up could cause tubbing segments to contract and expand and this would eventually lead to the wood sheathing being dislodged.

Furnace ventilation was used until quite late in the 19th century, especially in the North of England, but as collieries were sunk deeper and the workings became more extensive the inadequacies became more and more apparent and they were phased out in favour of mechanical ventilation. The 1911 Coal Mines Act prohibited their installation in new collieries but existing ones continued in use for some time. The fires at the last remaining one at Walsall Wood colliery were finally extinguished in the early 1950s.

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