Production of quicklime

The choice of lime kiln is of paramount importance to a lime producer. It must be suitable for burning the selected feedstone and for producing the required quality of quicklime. It must have sufficiently low capital and operating costs to produce quicklime at a competitive price. Its capacity must also be appropriate for the market requirements. 

The following sections outline the principles underlying the production of quicklime, and describe briefly the main types of kiln being operated and available from suppliers. They also consider how the choice of kiln, feedstone and fuel affects quicklime quality, as well as discussing a number of related subjects. A number of references for further reading is given for most sections. The closely related topics of processing and despatch of quicklime are addressed in chapter 17. 

It is frequently stated that every limeworks is unique. This is because of the many permutations of technical, commercial and economic factors. The technical factors include stone, fuel and lime quality (see chapter 14) as well as kiln design. 

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Some carbonates are important industrial chemicals. Calcium carbonate occurs naturally in several forms, including limestone, and is used in the production of quicklime, calcium oxide CaO, slaked (or hydrated) lime, calcium hydroxide Ca(OH)2 and cement. 

The reaction between sulfur dioxide and dry limestone is too slow to be of commercial interest. However, the reaction with quicklime is more rapid. Investigations have, therefore, been made into the in situ production of quicklime, by the injection of finely divided limestone powder into the boiler. 

When selecting a limestone for the production of quicklime, the necessary tests should be done to ensure that it is suitable in all respects. Indeed, in the context of present day requirements for quicklime, only a small proportion of limestone deposits are suitable for lime burning. 

Published estimates of the global production of quicklime [25.1,25.2] suggest that the total is approximately 120 million tonnes per year (tpa), of which just under half is produced by the former USSR, China, and the USA (Table 25.1). The published figures do not include the multitude of small producers in the developing countries, nor many of the captive producers, whose lime products are not sold in the open market. If their contribution were included, the total would probably approach 300 million tpa. In most industrialised countries, jthe annual consumption per head of population is in the range 20 to 80 kg per year. 

The production of quicklime (CaO) from limestone (CaC03) in a rotary kiln. The models show structures of CaC03 and CaO and carbon dioxide molecules. 

Figure 5.4 Heating caldum carbonate, CaC03, to a high temperature results in the production of quicklime, CaO, and the evolution of carbon dioxide. The reaction is a decomposition reaction, and the process is called calcination.

Black demonstrated that the production of quicklime by heating chalk was also accompanied by a weight loss, and that when quicklime was treated with a mild alkali the original chalk was formed along with a caustic alkali ... 

The decomposition (calcination) of limestone is carried out in a long rotary kiln, whether for the production of quicklime, CaO, or for the manufacture of Portland cement. 

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