Process Heating in Lime Manufacturing Today, lime has many end uses, such as: steel manufacturing, plaster, mortar, and asphalt. We’re nottalking about the food, but instead the product that originally began as a sedimentary rock. The National Lime Association has posted a fantastic diagram (see below) on their website (http://www.lime.org) to illustrate how lime is produced.
BOX 1: The limestone is first mined from the quarry. It is then placed into a crusher, which breaks therocks into smaller particles. The feed is screened and separated into various sizes. The divided stonesare then washed.BOX 2: The washed stones are then transported to the lime kiln. At the kiln, the limestone is subjectedto heat in 3 different stages. According to the National Lime Association, the 3 stages are:“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 limestonemoves 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.’”The most common kiln used in United States lime manufacturing plants is the rotary kiln. In box two youcan see that the kiln is placed horizontally on an incline. A process air heater (either directly or indirectlyfired, depending on the lime’s end use) is placed at the bottom of the kiln and sends heat up the kiln,against the flow of the limestone. As the limestone travels down the heated kiln it is “calcined” intoquicklime, or burnt lime. From here, depending on the end use, the quicklime is sold as is or it is furtherprocessed.BOX 3: When the end use calls for further processing, the quicklime is made into hydrated lime. Bycrushing the quicklime and adding water, hydrated lime is produced. The hydrated lime is classified bysize and then transported to the customer.For more information on indirect fired or direct fired air heaters used in lime processing, please call 513-367-9300 or visit Stelter & Brinck at http://www.stelterbrinck.com/process-air-heaters.htmKeywords: lime, hydrated lime, calcined lime, quicklime, stelter and brinck, heat, process air heater,directly fired, indirectly fired.