Use of diverting_gatesfor_kiln_preheater (1)


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Use of diverting_gatesfor_kiln_preheater (1)

  1. 1. Benefits of proportional diverting gates or swivel gates in kiln preheater ( 4 th stage to Kiln inlet)
  2. 2. Proportionally operatable diverting gates TYPICAL INLINE CALCINER WITH A 5 -STAGE PREHEATER
  3. 3. Diverting gate is used to create Hot temp zone when fuels which needs long ignition and combustion time for fuels like Petcoke ,anthracite and shredded tires are used.( very low volatile) Diverting gate is used when there is tendency to form coating esp when high ash coal is used or petcoke with sulfur is used. When sulfur cycle is more than 150% or the Evoporation factor is > 1.5 then raw meal can be diverted to reduce Stickiness of raw meal thereby reduces the coating tendency. For alkalis the Effect is less. Hot zone 1100 To 1150 deg C
  4. 4. Coal firing nozzles Area prone for Coating formation Raw meal diverting gate -2 for diverting ( proportioning) 4 th stage raw meal to kiln inlet and calciner cone
  5. 5. When coal has more ash, it can fuse at the firing point when the hot zone is clear without raw meal cloud and can stick to the refractory walls of the kiln inlet or on the cone of the Calciner .This reduces the gas flow and the production too. When raw meal is diverted from 4 stage it absorbs the ash and reduces the coating formation. When we fire pet coke Or when hot meal has alkalis or sulfur,coating forms. By all means diverting material from 4 th stage to kiln inlet is beneficial. Good oxidising conditions and intense short flame are favorable to reduce the coating tendency. CO formation enhance the volatile cycle and makes the raw meal sticky. Moreover the CO burns at the inlet and shoot up the inlet gas temperature. If it is more than > 1000 deg C hot clogging takes place. Reasons for coating formation at kiln inlet
  6. 6. ILLUSION There is an apprehension or illusion ( created by old timers), that raw meal drops into the kiln when 4 th stage material Is diverted to kiln inlet and the kiln runs dusty . The gas velocity at kiln inlet is > 15 m/s and it can lift the entire quantity of material to the calciner . If the illusion is true, then in calciner where the velocity is 6 to 7 m/s , all the material must drop Into the kiln inlet . Mind that, there are kilns operated with 80 to 90 % cross over feeding comfortably. Curved castable l ining will not allow drop out Of raw meal into the inlet. Moreover the velocity of gases Is > 15 m/s Raw meal flow profile
  7. 7. Molar ratio( clinker basis) K2O = 0.5 SO3 = 0.3 C l =0.015 ASR = 0.541 This shows there will be excess alkalis which has volatile recycle. The excess alkali melts in transition zone,volatilize and condense at the kiln inlet called the transition chamber. Over a period of time it builds and blocks kiln inlet. Hence diversion of the 4 th stage to kiln inlet will reduces the coating formation.Or to reduce the coating we can use petcoke with little high S ie., 4 to 5 % to make the ASR to 1. ASR ,Alkali – sulfur ratio
  8. 8. Conclusion Advantages on the operation of 4 th stage material diversion to kiln inlet . It reduces the coating formation which is due the melting of high ash content of the coal or the excess alkali or sulfur . It increases the retention time of raw meal by 0.4 secs as it travels 5 to 6 meter extra apart from the entire calciner. This will reduce fuel marginally, being fired in calciner.