Hey; Our plant is an offline PC kiln with 5 stages preheater and bypass system. Last week a big explosion happened in our preheater riser duct towards Cyclone-5. The results of this explosion are:

1- Riser duct towards cyclone-5 damaged completely (Bricks and castable pieces found 1000 meter far from the preheater)

2- In several areas bricks and castable damaged.

4- Conditioning tower damaged.

5- Of course we have also small damages in each cyclone, damages in most of riser duct expansion joints and etc.

6- (One thing more) Two bird died.

As you see it is a big accident and maybe the damage of preheater is bigger than we think ... it will be clear later after checking the preheater inside.

How & why this explosion happened! I would like to share with all of you the reasons of this accident to avoid it in the future especially it is the first time (as I know) such type of accident happening in a new and modern cement plant.

Last week and after the annual shutdown; kiln feeding was started (after 24 hours heating) but after few hours the feed was stopped due to upset condition of the kiln (dusty & cold).

3 hours before the explosion: (End of the shift) Kiln operator kept the fire on for heating the kiln again.

2 hours before the explosion: Next Shift Kiln operator wanted to increase the heating rate by increasing the gas flow rate and at the same time increased ID fan rpm from 300 to 500 and again to 300 (in one minute). Here the problem started because when he took this action disturbance happened in hood pressure (+2 to -6 mbar) and as a result flame cut-off (BUT FLAME INDICATOR WAS SHOWING ON). Smoke chamber temperature started dropping. (Note: kiln camera was out of order)

1 hour before the explosion: Smoke chamber temperature still dropping very fast, the kiln operator didn’t observe the cut-off of the flame (due to false indication of flame) so he increased the gas flow more and more and at the same time reduced ID fan to the minimum. (Fresh air damper was 100% close).

10 minutes before the explosion: The kiln operator didn’t put in his mind that flame may cut-off so in order to increase the heating he stopped ID fan, due to interlock between ID fan and kiln gas; gas flow stopped and at that time the false flame indication disappeared from the monitor. Immediately he started the gas again and gave order to the kiln field operator to torch the kiln manually.

1 minute before the explosion: Preparing the manual torch took several minutes (Note that at this time gas is on, ID fan is off, and fresh air damper is close). When the torch was inserted to the kiln hood; back fire with dust puffing from the hood injured one person but fortuity his injury was only in his eyes and not serious. After 30 seconds the explosion occurred in the preheater and again fortuity all kiln field stuff were near the cooler and nobody was in preheater or around it (Note that the accident happened after midnight).

I know the kiln operator did very big and crazy mistakes and these mistakes will cost us minimum three months stoppage and  millions EUR lost. The kiln operator may be will be terminated and maybe others also but I don’t think only the termination will reduce our lost or give guaranty it will not happen again. 

Best Regard