Ours is a 6 stage pre-heater with ILC.We have a problem of PC outlet temp. shooting up to 1100/1150 deg. C. against to normal design temp. of 870 deg. C. Kiln feed rate will come down from 110 to 40 TPH when PC outlet temperature shooting up.
Our observations are as follows while higher temperature at PC outlet.
1) Bottom stage (6th Cyclone) degree of calcination is 60% as against 92 %.
2) Static pressure in 5th cyclone feed pipe is coming down from 100 mmwg to 30 mmwg. (5th cyclone feed pipe discharges material in to PC inturn this material conveys to 6 th cyclone from there it enters in to kiln)
3) Feed will rushup to burning zone and forced to reduce the kiln feed and kiln rpm.
4) At this time we are getting dusty clinker with less nodules.
5) The calcination profile up to 4 th cyclone from top are normal.
What are the reasons for the above and what are your suggestions to come out of this
Short pass of feed in pre heater
Taking account of the data you wrote I can only suppose that there is some draft failure in the preheater - PC system. There maybe occur material direct flows from 2 nd to 4 th to 6th and 1st to 3th to 5th stage cyclones. In that case, if you measure material flow rate from 6th cyclone feed pipe, the feed rate must come down, because part of the material doesn't enter 6th stage cyclone ant enters to the kiln from PC, so it erroneously seems that material is less. From the other flow the badly calcined material enters from 3th to 6th cyclone and then to the kiln. Because of that failure in your kiln calcining zone prolongs and unprepared material rushs up to burning zone and because of unsufficient sintering clinker becomes dusty and with small nodules. I think that in your clinker free CaO quantity will rise also.
You have to dataily investigate your system draft. Maybe you've changed your raw meal composition and in preheaters occur some build-up growings and collapse (the case we've seen in our plant) or maybe there is problem with your ID Fan.
If I'm wrong, you can send me more detaily data and I'll try to help you out.
Regards. Davit Babayan.
This seems from the data, material is not entering the PC , shortcircuiting is taking place.You can check the material movement in lower cyclones by inspecting the flaps if you have.Material is coming from 4th to 6th stage surely.That is why no pressure in 5th stage feed pipe and also there is no material gng to PC and temp. in PC shootingup.
As such there is no problem with the stages 4th and above check feed pipes and cyclones thoroughly at stage 5.And also leakages.
hey;
Our plant is a 2000 tpd kiln with 5 stages preheater and PC, last year we faced exactly the same problem you mentioned here ... our feed dropped from 143 to 110 tph, due to high temp at PC several red spots damaged our PC shell, and etc. I agree with AN-kuwiat answer but disagree with him in that material was not entering the PC (part should be entered), because if no materials enter PC, PC temp will increase very quickly and melt its shell in few hours as we faced last year ( I have photos but i couldn't download them). The main problem of this phenomenan is LEFTING OF THE MATERIAL TO PC. After 3 months of inspection we found that part of the material was not lefting to PC due to bad draft, bad draft means: lefting gas to PC couldn't hold up ALL the materials to PC; so part of material will slip to rizer duct or kiln inlet (depend on the design).
Our observations were:
Rizer duct diameter increased 2 meter.
When the dia increased the lose of heat through PH becames more and that answered our question why PH outlet temp increased (from 330 C to 370).
When PH outle temp increase; ID fan draft through PH becomes less.
When draft in the preheater become less; draft in the tertiary duct becomes less.
When draft in tertiary duct become less; lefting of material becomes weak (only part of material will pass through PC while other part rush in to the kiln inlet)
When draft in TD become less; teriary air temp comes down.
When T.air temp come down, combustion in P.C disturbs and etc..
Dear BLM; if you are still facing this problem contact me to tell you how we solved 75% of this problem without repairing rizer duct area.
Best Regard