Production of lime in LIMEX OY

Description of the production of lime in Estonian LIMEX OY lime burning facility

(source: http://www.limex.ee/):

1. RAW MATERIAL. The raw material is the so-called Paadla deposit with different limestone layers. It hails from the Silurian Period (some 460 million years ago).  For extraction of lime of particularly high quality, stromotopor limestone is also collected from fields in the surroundings.

2. EXTRACTION OF RAW MATERIAL. Limestone is usually extracted manually with the help of smaller explosions.  Explosions are only used to heave and loosen the limestone, not to blow up entire formations. Breaking of limestone is done by hand using special sickles,wedges and bars. Click on the photo to enlarge.

Broken blocks of limestone have a diameter of approximately 20-30 centimetres and come in different shapes. They are transported to the lime oven by a tractor. Since different lime layers are of different quality, visual selection of stones of different quality takes place parallel to the breaking. The visual selection is mainly based on the colour of the layer according to the following scheme: the darker (browner) the limestone, the higher the quality.

3. THE LIME OVEN. Limestone is burned in a lime oven which is approximately 3,80 metres tall and 1,5 metres across, tapering at the top and bottom (egg-shaped). In order to restore the lime ovens, locally preserved knowledge about the ’secrets’ of the 50 year old ovens was used. The oven's interior is covered with chamotte bricks, then a heating insulation layer and finally an outside layer measuring 80-100 centimetres. The bricks are joined using a mix of special heat-resistant mud from the nearby Kuusnõmme Bay and chamotte mud, a mix that when it melts creates a very heat-resistant glaze on the bricks. The oven is loaded with limestone, a 2 metres long, 1 metre wide and  1,2 metre high fire passage on top of which large lime stones are placed in vaults. Wood is burned in the fire passage.

4 BURNING.  The lime oven can accommodate 27-28 tonnes of limestone , which are piled up on the top and to the sides of the fire passage. The way the limestone is burned depends on the raw material, the heating material, weather, etc.. 50�5 h. The heating material (dry wood) is constantly added to the fire passage by hand, which uses about  1m3 an hour.

Both logs from old houses and well-dried wood from the forest are used for burning; if needed they are added alternately.  Most of the wood has a diameter of 10-30 cm and a length of up to 2 metres. Using wood with smaller diameters is complicated, since it creates a lot of ash and darkens the oven. If needed, coarser and finer materials are added alternately. The wood is mainly dried in the storage next to the oven. Wood from the forest takes at least 2 years to dry. The oven is heated in shifts, each of which last for 8 hours. Both the stoker and the foreman follow the technological procedures, regulating them to suit the weather and the developing process. When burning lime, the following chemical reaction takes place:

CaCO3==>CaO+CO2^
CaCO3 - limestone
CaO – unslaked lime

The burning temperature is approximately 1100-1300°C. Here, the limestone breaks and CO2 volatilises. The finished limestone has a greenish-yellow tinge. After burning, the stone needs 48-72 hours to cool down. During this process, it shouldn’t come into contact with water, since unslaked lime is very chemically active. In order to avoid this, the oven is covered with a special cover if there is a chance of rain. If the air moisture is high, the limestone absorbs moisture from the air, and a slow waning process which makes the clearing process difficult begins.

5. SLAKING. Once the limestone has cooled down, the unslaked bits of lime are loaded onto a transport device using a lifting mechanism, and then transported to the slaking area. Usually, 100-200 kilos of poorly burnt limestone remain at the top and bottom of the oven. These are sorted and loaded into the next oven. 50-60 kilos of limestone mixed with ash are also left and used as fertiliser by locals. Slaking of lime is the reaction of unslaked lime and water which results in calcium hydroxide and releases warmth.
CaO+H2O ==> Ca (OH)2

The slaking/preservation complex is located approximately 2 kilometres from the ovens. Slaking takes place in a tin bathtub with the measurements 2 m *3 m *0.5 m. It can hold ca 300 kilos of CaO and 10 times more water.  During slaking, water is always added in excess in order to guarantee a complete slaking process. For the reaction to process successfully, the mass is constantly stirred using special tools. When the CaO has  dissolved, the  milk of lime is led through a 3mm coarse sifter (which separates larger insoluble parts and other mechanical additions) into 1,5 metres deep preservation holes or graves in the sand made from concrete and wood. The sand area is an important agent in ensuring an exchange of moisture between the surface and the lime paste. After-slaking takes place in the lime graves, over a period of 1-2 years, after which the lime paste (H2O content ca 5 % ) is fit to be sold.

Lime paste is used in construction work, mainly in lime mortar and plaster, for making lime paint, for calcification of acidic soils, etc.

Traditionally manufactured lime from Saaremaa

 

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Contacts:

Limex Ltd - Lümanda 93301, Saaremaa, ESTONIA, phone: +372 51 56 165, fax: +372 45 76 380, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

See also: www.limex.ee

 

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