Panel G – Limekilns and Limeburning
Seen around 1910, smoke billows from the New Road kilns with lime burning in full production. Loaded wagons wait on the upper level ready to charge the next combustion chamber (otherwise known as a kiln pot). Middle right, the western battery of Gnat Hole kilns stand deserted with collapsed walls evident. The covered lime-loading pens of the Middle Basin are disused. Middle left, the crusher appears busy with loaded wagons standing on the wooden staging leading to the upper level of the building.
The east and west batteries of Gnat Hole kilns still stand but long-since disused. The bridge over Silk Hill has been demolished and the collapsed walls of the western bank of kilns can be clearly seen. In the foreground, the limeshed spanning the Middle Basin Arm still stands.
The western battery of Gnat Hole kilns in the foreground as viewed across the head of the Lower Basin. The collapse has slumped further exposing the brickwork of the kiln pots.
limestone + heat = burnt lime + carbon dioxide gas
CaCO3 = CaO + CO2
Limestone is a sedimentary rock composed principally of calcium carbonate and it can be calcined by heating it in a kiln. The heating process chemically converts the stone to burnt lime (quicklime, calcium oxide, CaO). To do this the stone must be heated to a temperature of between 900° and 1100°C. This causes the limestone to dissociate yielding burnt lime and carbon dioxide gas. Left is shown a partly loaded pot with limestone and coal in alternate layers. The ratio used was 3 to 5 parts limestone : 1 part coal. Pots were from 2.5 to 5m diameter at the widest part and from 6 to 10m deep. The profile varied in shape, but it usually curved in at the top. The lining was either hard stone or firebrick to allow the kiln to be continuously fired for several years. The Bugsworth kilns appear to have been lined with stone. The number of draw-holes was normally between one and four.