Hoffmann kiln
Encyclopedia
The Hoffmann kiln is a series of batch process kiln
s. Hoffmann kilns are the most common kiln used in production of brick
s and some other ceramic products. Patent
ed by German Friedrich Hoffmann for brickmaking in 1858, it was later used for lime-burning, and was known as the Hoffmann continuous kiln.
A Hoffmann kiln consists of a main fire passage surrounded on each side by several small rooms. Each room contains a pallet of bricks. In the main fire passage there is a fire wagon, that holds a fire that burns continuously. Each room is fired for a specific time, until the bricks are vitrified
properly, and thereafter the fire wagon is rolled to the next room to be fired.
Each room is connected to the next room by a passageway carrying hot gases from the fire. In this way, the hottest gases are directed into the room that is currently being fired. Then the gases pass into the adjacent room that is scheduled to be fired next. There the gases preheat the brick. As the gases pass through the kiln circuit, they gradually cool as they transfer heat to the brick as it is preheated and dried. This is essentially a counter-current heat exchanger, which makes for a very efficient use of heat and fuel. This efficiency is a principal advantage of the Hoffmann kiln, and is one of the reasons for its original development and continued use throughout history. In addition to the inner opening to the fire passage, each room also has an outside door, through which recently-fired brick is removed, and replaced with wet brick to be dried and then fired in the next firing cycle.
In a classic Hoffmann kiln, the fire may burn continuously for years, even decades; in Iran, there are kilns that are still active and have been working continuously for 35 years. Any fuel may be used in a Hoffmann kilns, including gasoline
, natural gas
, heavy petroleum and wood fuel
. The dimensions of a typical Hoffmann kiln are completely variable, but in average about 5 m (height) x 15 m (width) x 150 m (length).
The Hoffmann Kiln is used in non-developed countries, and in current and former developing countries. In the British Isles there are only five Hoffmann kilns remaining. The only ones with a chimney are at Armadale, West Lothian, Carluke, Lanarkshire and Llanymynech
, which was used for lime-burning. There is an intact but abandoned Hoffmann kiln without a chimney present at Minera Limeworks
; the site is abandoned but all entrances to the kiln have been grated-off, preventing access. The kiln is in a very poor state of repair, with trees growing out of the walls and the roof. Minera Quarry Trust hopes one day to develop the area into something of a tourist attraction. There is a partly preserved Hoffmann lime kiln that was operated by the Craven Lime Works company at Langcliffe in the Yorkshire Dales. The Grade II listed Hoffmann brick kiln in Ilkeston
, Derbyshire, is also badly neglected, although the recently-installed fencing offers some protection for the building and for visitors. At Prestongrange Museum, outside Prestonpans in East Lothian, the Hoffman kiln is still standing and visitors can listen to more about it via a mobile phone tour.
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
s. Hoffmann kilns are the most common kiln used in production of brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...
s and some other ceramic products. Patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
ed by German Friedrich Hoffmann for brickmaking in 1858, it was later used for lime-burning, and was known as the Hoffmann continuous kiln.
A Hoffmann kiln consists of a main fire passage surrounded on each side by several small rooms. Each room contains a pallet of bricks. In the main fire passage there is a fire wagon, that holds a fire that burns continuously. Each room is fired for a specific time, until the bricks are vitrified
Glass transition
The liquid-glass transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass...
properly, and thereafter the fire wagon is rolled to the next room to be fired.
Each room is connected to the next room by a passageway carrying hot gases from the fire. In this way, the hottest gases are directed into the room that is currently being fired. Then the gases pass into the adjacent room that is scheduled to be fired next. There the gases preheat the brick. As the gases pass through the kiln circuit, they gradually cool as they transfer heat to the brick as it is preheated and dried. This is essentially a counter-current heat exchanger, which makes for a very efficient use of heat and fuel. This efficiency is a principal advantage of the Hoffmann kiln, and is one of the reasons for its original development and continued use throughout history. In addition to the inner opening to the fire passage, each room also has an outside door, through which recently-fired brick is removed, and replaced with wet brick to be dried and then fired in the next firing cycle.
In a classic Hoffmann kiln, the fire may burn continuously for years, even decades; in Iran, there are kilns that are still active and have been working continuously for 35 years. Any fuel may be used in a Hoffmann kilns, including gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
, heavy petroleum and wood fuel
Wood fuel
Wood fuel is wood used as fuel. The burning of wood is currently the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating, and occasionally for fueling steam engines and steam turbines that generate electricity. Wood fuel may be available as...
. The dimensions of a typical Hoffmann kiln are completely variable, but in average about 5 m (height) x 15 m (width) x 150 m (length).
The Hoffmann Kiln is used in non-developed countries, and in current and former developing countries. In the British Isles there are only five Hoffmann kilns remaining. The only ones with a chimney are at Armadale, West Lothian, Carluke, Lanarkshire and Llanymynech
Llanymynech
Llanymynech is a village straddling the border between Montgomeryshire/Powys, Wales and Shropshire, England about 9 miles north of the Welsh town of Welshpool. The name is Welsh for "Church of the Monks"....
, which was used for lime-burning. There is an intact but abandoned Hoffmann kiln without a chimney present at Minera Limeworks
Minera Limeworks
The Minera Limeworks were extensive lime quarries and kilns at Minera in Wrexham, Wales. It was located at , near the villages of Gwynfryn, Minera, and Coedpoeth and was locally referred to as The Calch.-History:...
; the site is abandoned but all entrances to the kiln have been grated-off, preventing access. The kiln is in a very poor state of repair, with trees growing out of the walls and the roof. Minera Quarry Trust hopes one day to develop the area into something of a tourist attraction. There is a partly preserved Hoffmann lime kiln that was operated by the Craven Lime Works company at Langcliffe in the Yorkshire Dales. The Grade II listed Hoffmann brick kiln in Ilkeston
Ilkeston
Ilkeston is a town within the Borough of Erewash, in Derbyshire, England. It lies on the River Erewash, from which the local borough takes its name. Its population at the 2001 census was 37,550...
, Derbyshire, is also badly neglected, although the recently-installed fencing offers some protection for the building and for visitors. At Prestongrange Museum, outside Prestonpans in East Lothian, the Hoffman kiln is still standing and visitors can listen to more about it via a mobile phone tour.
External links
- http://www.llanymynech-hoffman.co.uk/DIR1/History.htm
- http://www.prestongrange.org/tour/3.html
- http://www.itcltd.com/wastedisposal/1.1.4.d.Evaluation%20of%20Hoffman%20Kiln%20Technology.pdf
- http://www.britishlistedbuildings.co.uk/en-352235-brick-kiln-ilkeston