The Partial remains of the earliest known Hoffman type limekiln can be found here. The design, which was patented in Germany by Friedrich Hoffman, enabled the process of lime production to be continuous, with a burning zone progressing around a circular or oval tunnel to areas newly packed with stone. The kiln at Minera, which was built in 1868, is some 80m long with a continuous tunnel accessible through 24 entrance archways. A smoke chamber survives at the top level at the south end and stoke holes and flues are apparent throughout.
Infromation from RCAHMW website
A brief history from wiki is below-
The Minera Limeworks were once the largest lime workings in the north of Wales. Limeburning at Minera is recorded from as early as 1620 but the Minera Lime Company was established in 1852. The total output from the Minera area quarries was estimated, in 1859, to be around 300,000 tons, with 200,000 tons of this converted to lime.
The Minera Lime Company became a limited company in 1865, and this prompted some heavy cash injection into the works. Using this money, the company erected a "Hoffmann kiln". Originally destined for brickmaking, it was soon converted to limeburning. This kiln still exists and is one of three that were purpose-built for lime burning left in the UK: another is located at Langcliffe in Yorkshire, another is located at Llanymynech Limeworks.
The quarries had their own steam locomotive and hundred of open coal wagons and closed lime wagons at its peak. Hornby Railways and Dapol both have model wagons detailing the Minera Lime Co. It also had extensive kilns, still there to this day. The works closed in 1972 and the Wrexham and Minera Branch railway lines were pulled up at around the same time.