Gas bypassing in short kilns with suspension preheaters

Gas bypassing is an important way to protect against scale buildup in cyclone preheaters of short dry process kilns. In recent years its use grew, with the increasing use of alternative fuels containing a large amount of chlorine. The content of the latter in gases significantly (40 times) increases due to circulation in the kiln and the cyclone preheater. Chlorine deposited on the grains of raw materials in the preheater causes the formation of a liquid phase, which leads to scale build-ups. Bypassing a small amount of gases (usually about 5 %) solves this problem, but causes other problems, of which the greatest is the dust brought with these gases. It is deposited in dust collection devices, but it must be recovered. To do this, dust is added in small quantities to the cement, kiln feed, or raw materials fed to the mill. At HeidelnergCement plants, the following technical solutions are used:
after the dusty gases are cleaned in the cyclone, they are returned to the cyclone preheater, which makes it possible to reduce the amount of dust in bypass gases by about 40 %;
the bypass gases are fed to the calciner; or
these gases are fed to the clinker cooler (however, it is necessary to clean the grate and the gaps from dust every few months).
Author: W. Kurdowski, E. Jelito

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