Assessment of waste preheater gas and dust bypass systems: Al-Muthanna cement plant case study

Preheaters are used industrial dry kiln cement production plants to heat the raw mix and drive off carbon dioxide and water before it is fed into the kiln. An analytical model of a generalized four-stage suspension cyclone preheater system is presented. This model was used to study the influence of waste preheater gas and dust bypass systems on preheater performance and efficiency. As the bypass size (percentage) was varied, the heat content of the bypass gas was calculated for different constant calcination degrees. The results showed that the heat content, respectively for each cyclone (I, II, III, and IV), is: 542.0, 801.9, 1034.3 and 1192.7 kJ for a calcination degree of 90% and bypass percentage of 40% bypass. Changing the calcination degree to 50% and bypass percentage to 40% resulted in gas heats of: 541.4, 801.0, 1033.2 and 1191.5 kJ, respectively for each cyclone. These results show that the calcination degree is inversely proportional to the heat content of waste preheater bypass gases. While increasing of bypass opening at constant the amount of dust kiln gas will cause decreasing of waste heat content of kiln gases.