Lime kiln

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Kalkofen on the coat of arms of Kalkofen in der Pfalz

A lime kiln is a kiln used to produce quicklime from limestone . The process itself is called Kalkbrennen , the family name resulting from the occupational title Kalkbrenner is derived from this. The importance of lime burning can be seen in numerous places called lime kilns and their coats of arms.

history

The targeted processing of limestone into a versatile building material is one of the oldest and still most important technical production processes. The oldest evidence of lime production for processing in screed-like floors in cult facilities comes from the mountain temple of Göbekli Tepe in Anatolia and is 11,000 years old. The art of lime burning was already widespread in ancient times. Wood , peat or coal were originally used as fuel . The first facilities for this were so-called kilns , while later simple field ovens without walling were used. Simple earth pits, in which lime was burned in the 20th century, can be found in large numbers in the densely wooded Bükk Mountains in north-east Hungary .

Chemical processes

How a lime funnel furnace works
Reaction zones and temperature distribution in a lime kiln

Calcium carbonate (CaCO 3 , limestone) gives off carbon dioxide (CO 2 ) at temperatures between 900 and 1,200 ° C and reacts to calcium oxide (CaO, quicklime), which is called deacidification of limestone. This step is known as calcination . The quicklime is then processed with water to make lime paint , lime mortar or hydraulic lime .

Technical implementation

From a technical point of view, the procedure has changed again and again over the course of history. As in many other chemical-technical processes that were previously, more or less inevitably, discontinuous, modern, industrial processes are based on continuous processes .

Historic lime kiln

The main work steps were:

  • Filling the lime kiln
  • Lighting
  • Expelling water
  • Cover with clay
  • Glow through

Industrial manufacture

Nowadays, lime is delivered in the form of limestones from a lime quarry and heated to around 900–1300 ° C in vertical ring or shaft furnaces or in rotary kilns or eddy current furnaces. The advantage of this process lies, in addition to the more economical continuous procedure, also in the improved material and energy exchange between the solid and gaseous phase.

The ovens are fed continuously from above with a mixture of 90% limestone and 10% coke . This mixture passes through the various temperature zones of the oven, slowly sliding downwards. In the lower and middle area of ​​the shaft furnace, the coke burns and generates the temperature required for chemical conversion. At the bottom, the quick lime is discharged via a rotating cone.

See also

Web links

Commons : Lime Kiln  - Collection of pictures, videos and audio files