Construction

Lime Manufacturing and Lime Kiln Dust – The Basics

Limekiln dust or LKD is a material often used in the production of lime, it has the consistency of a powder and is extracted from production plants. It has a high Calcium count and is used to replace carbon-intensive binders such as the cement used on construction sites, Portland cement. This is because it could be a substitute for Silica.  Various studies, such as this one, have been done to find the stability of this popular manufacturing ingredient.

When limestone is put under high heating temperatures, it produces dust gas. This component has some beneficial uses such as try poor soil. It is a very versatile material and industries such as steel manufacturing use it to remove impurities as well.

There are two different categories of Lime Kiln Dust, we look at these below.

Two Categories of LKD

Limekilns fall under two broad categories, namely:

  • Flare kilns or Periodic kilns
  • Running or Perpetual kilns

Flare or Periodic

In the first one, the flare kiln, the bottom layer is filled and the top layer is filled with chalk. In the latter category, which is usually a stone structure. It is layered with chalk, wood or coke and then lit. lime is then extracted from it through a hole. Further information can be found online: https://en.wikipedia.org/wiki/Lime_kiln#Types_of_kiln

In many regions lime is still being scorched using conventional methods and kilns. Originally derived in the Roman and Hellenistic craftsmanship’s. These kilns are mainly those that involve the flare kiln variety. It is likely that this was the most used variety and was operated by the Romans in c. 160 B. C.

The layers include from the bottom to the topmost layer:

  • Stoke hole, fuel and furnace
  • Limestone vault
  • Lime lining Kiln
  • Limestone charge

Running or Perpetual

Similar in construction to the flare kilns, these are often built on the side of a hill or slope. It is fed from the top, through a broad chimney-like structure, and fired from the bottom, and the lime kiln dust is extracted from the bottom as well. The fire lit kept lit and stoked for a number of days and sent to the pits, the entire process is then repeated with the same amount of limestone.

As the fuel scorches the mineral it is turned into a calcinated material and the drops of lime go through the grate or tray and are collected, and this is where it is removed or extracted. It is continuously fed throughout the process. The obvious benefit of this is that large amounts of the lime can be produced in one seating as well as being fuel-efficient. The result is mixed with ash from wood that is also burned alongside the kiln.

The different layers from the bottom to top comprise of:

  • Stoke hole and Furnace
  • Grate
  • Lime lining kiln
  • Fuel
  • Limestone charge

 

The temperatures at which the fuel is burned for both of the above-mentioned is 1,000°C. under the influence of this intense heat, the calcium carbonate and has two non-metals namely oxygen and carbon which decomposes.

Some of the oxygen that is mixed with the carbon escapes from the furnace in the form of gas carbon dioxide and the end product left behind is calcium oxide or what’s known in most industries as “quicklime”.

The chemical equation is as below:

Calcium Oxide + Carbon Dioxide = Calcium Carbonate

Various Uses of Quicklime

Sometimes the result is hard lumps of white mineral and sold to many different sectors such as building and construction, and this is used to make mortar and industrial plaster used in building homes and structures. The lumps are crushed and mixed with water to create a paste. Sometimes sand is added to the mixture.

It is also used in the creation of cement, which is a popular ingredient in buildings and is mixed with other types of clays.

Sometimes it is also sold to agricultural sectors and used to correct excess acidity in the soil and also to improve fertilizers to give plants nutrients. These are also inside bags of fertilizers we buy from plant and garden stores.

The above is just a basic idea of this type of mineral, and the wide variety of uses one can achieve from its extraction.

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