page_title: Lime kiln
section_title: Counter-current shaft kilns
hierarchical_section_title: Lime kiln / Modern kilns / Shaft kilns / Counter-current shaft kilns
caption_attribution_description: English: Simplified diagram of regenerative shaft lime kiln.
context_page_description: A lime kiln is a kiln used for the calcination of limestone to produce the form of lime called quicklime. The chemical equation for this reaction is
  CaCO₃ + heat → CaO + CO₂
  This reaction takes place at 900 °C, but a temperature around 1000 °C is usually used to make the reaction proceed quickly. Excessive temperature is avoided because it produces unreactive, "dead-burned" lime.
  Slaked lime can be formed by mixing quicklime with water.
context_section_description: The fuel is injected part-way up the shaft, producing maximum temperature at this point. The fresh feed fed in at the top is first dried then heated to 800 °C, where de-carbonation begins, and proceeds progressively faster as the temperature rises. Below the burner, the hot lime transfers heat to, and is cooled by, the combustion air. A mechanical grate withdraws the lime at the bottom. A fan draws the gases through the kiln, and the level in the kiln is kept constant by adding feed through an airlock. As with batch kilns, only large, graded stone can be used, in order to ensure uniform gas-flows through the charge. The degree of burning can be adjusted by changing the rate of withdrawal of lime. Heat consumption as low as 4 MJ/kg is possible, but 4.5 to 5 MJ/kg is more typical. Due to temperature peak at the burners up to 1200 °C in a shaft kiln conditions are ideal to produce medium and hard burned lime.
caption: Gas flows in two cycles of operation of regenerative shaft kilns
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