Where is heat used in Lime Manufacturing?
In our last post, we discovered that cement manufacturing utilizes limestone. Therefore, we decided to focus on lime manufacturing this week! Originating with its earliest use as building mortar, lime has many end uses today: steel manufacturing, asphalt, plaster, sugar refining, waste water treatment, and many others!
The National Lime Association has provided detailed lime production diagrams on their website.
As you can see from the illustration above, lime processing happens in three stages.
First Stage of Production- The limestone is mined from the quarry. The limestone undergoes crushing, which breaks it into smaller particles. The feed is screened, and the broken stones are washed.
Second Stage- The clean stones are then sent through a lime kiln. It is at the kiln where the limestone is subjected to heat and “calcined” into quicklime. A process air heater, typically direct fired, is placed at the lower end of the horizontally inclined kiln. The feed enters the higher end of the kiln and travels against the flow of the heat. According to the National Lime Association, the limestone goes through 3 stages in the kiln:
“Preheating – limestone is heated by direct contact with kiln exhaust gases that enter the preheater kiln.
Calcining – the kiln fuel is burned in the preheated air from the cooling zone and, as the limestone moves down the kiln the heat turns the limestone into quicklime and carbon dioxide (CO2).
Cooling – quicklime leaving the calcining zone is cooled by direct contact with ‘cooling air.’”
Third Stage: Depending upon the end use, the quicklime is then either sold as “pebble lime” or further processed into “hydrated lime” by adding water, or into “milled lime” by crushing and milling the quicklime.
For any questions, feel free to reach out!