Design of the Hoffman Kiln

The main structure of the Hoffman Kiln forms an oblong shape 150' long by 50' wide overall with rounded ends. Built entirely from local Trefonen brick, it is a continuous down draft ring kiln for lime burning. The cloister like internal circuit is18' wide and has coal feeder holes in the roof. There is a curved vaulted section down the centre of the kiln for the flue.

Set into the outer walls of the kiln are 14 limestone loading doors known as wickets, 6 on each side of the kiln and one at each end. The internal rectangular ring was divided into 14 burning chambers. The rock was stacked from floor to ceiling inside these chambers in the form of a series of dry stone walls constructed between the coal feeder holes. A series of trace holes or gaps were left at the base of the limestone to allow the fire, smoke and gases to exhaust both through to the next chamber to pre heat it, and to the flue under the floor. Alongside each wicket there is a dual purpose air vent.

At ground level the vent allows air to pass through the wall to the floor of the kiln. Air can also pass through a 2' deep pit into a flat bottomed 18" high semi circular flue to the centre of the kiln under the floor. The vents would have been fitted with hinged plates and draw tins to control the draught. The under floor central flue measures 4' wide and 26" high and runs longitudinally down the centre of the kiln before passing underground to the chimney.

It is covered by a small grill by the entrance to the kiln. The fire progressed anti clockwise round the kiln. At any one time several wickets would have been open into chambers which were being loaded, unloaded or empty. Other chambers would have been pre heating with hot flue gases, while some would be cooling. Possibly only two or three chambers were burning stone at 1000ºC. The last chambers were easing back after the fire had gone past.

A 2' gauge tramway system surrounded the Hoffman and short extensions of jubilee track were clipped on to bring loaded trucks inside the kiln. The whole structure was weather protected under a curved corregated iron roof. Sealing bricks burnt at one end can be found stacked on both sides.

Alongside the Hoffman there are two draw kilns at the end of a long and impressive embankment. These were built in 1871. The large one is 9' in diameter and 25' high internally. It had a coal hoist on the left hand side. The site also contains a stable block. Horses were used for transportation of the trucks on and around the site. There is a tally house on the canal embankment, a weighbridge/tally house by the tunnels which enter the site under the A483, footings for a store shed/ office, and an engineering area with machinery plinths for crushers, compressors and general repairs. There are also some very impressive embankments and canal docks.