2 replies to this topic

[aliadnan]

Hi All


During this turn around we changed the refractory of the secondary reformer. But after only 3 days of operations, hot spot was observed (the green heat sensitive paint on secondary reformer changed to white color) between the point on secondary reformer where nozzles for waste heat boilers emerge (this point is just at the bottom of the secondary reformer). On temperature monitoring of the shell, we found that the temperature of the hot spot is 650 C (the design temp of secondary reformer shell is 343 C). So immediately we shutdown the plant on 1/06/07 (still the plant is shutdown and we are breaking the refractory from the place where hotspot was observed and have decided to fill that portion by new refractory of same material).

After opening the vessel and visual inspection it was seen that normal cracks were present (which all refractories have) and no deep cracks, displaced or fallen refracory was observed. The plant at time was running at 120% load (based on 1270 MTD) and the usual temperature at the burner is 1008 C and at the bed is 930 C. The hotspot is below the catalyst bed.

Now investigation are underway but still there is no clue of what happened. I would like to have comments of people who have witnessed such type of refractory failure during their careers. I am also trying to search on the internet about such kind of failures in worldwide and I have been able to find only two incidents which occured in India. If someone has any literature about the such type of failure and what actions were taken, please share it with me.

Regards,

Ali

Attached Files

•  Refractory_Specifications___Secondary_Refromer_Sketch.doc   103KB   171 downloads

[Sujit Chakrabarti]

Dear Ali,

You are right. Such type of incidence had occured in India. Among them, I was the person who attended one of such problem as consultant Refractory Engineer of my past employer Engineers India Limited to the client Indian Farmer and Fertilizer Company’s plant at Aonla. However the problem there was not at the outlet line like in your case, but near transfer line inlet from primary reformer. But the nature of problem was similar. The hot gas penetrated through refractory lining and cracked the steel shell by hydrogen attack. Since there was water cooling from outside, hotspot was not noticed.

The secondary reformer is high pressure equipment with reducing condition inside (because of presence of gas with high percentage of hydrogen). With such condition, presence of any silica (SiO2) in the refractory are leached by hydrogen attack and make the lining porous and permeable. Since the pressure of the equipment is very high (about 40 bar), the gas penetrate through the lining and come in contact with steel shell and make either hot spot or crack the steel with prolonged contact.

To overcome this problem, it is always recommended to use refractory material with minimum silica content generally should be in the range of <0.2% for hot-face materials. Also use of very dense monolithic concrete as hot-face without joints will reduce such problem.

Sujit Chakrabarti,
The Hague, Netherlands

[rezairan]

Dear Ali

I think that portion of the secondary reformer which hot spot occurs had some contaminants.Or the thickness of the refractory is not sufficient to cover that area.
Make a radiography on that portion and see if something is wrong of course if hammer test does not work.
Maybe a careless worker has left something inside the refractory during pouring in that end point of the secondary reformer.

Good luck
Reza

Hi All


During this turn around we changed the refractory of the secondary reformer. But after only 3 days of operations, hot spot was observed (the green heat sensitive paint on secondary reformer changed to white color) between the point on secondary reformer where nozzles for waste heat boilers emerge (this point is just at the bottom of the secondary reformer). On temperature monitoring of the shell, we found that the temperature of the hot spot is 650 C (the design temp of secondary reformer shell is 343 C). So immediately we shutdown the plant on 1/06/07 (still the plant is shutdown and we are breaking the refractory from the place where hotspot was observed and have decided to fill that portion by new refractory of same material).

After opening the vessel and visual inspection it was seen that normal cracks were present (which all refractories have) and no deep cracks, displaced or fallen refracory was observed. The plant at time was running at 120% load (based on 1270 MTD) and the usual temperature at the burner is 1008 C and at the bed is 930 C. The hotspot is below the catalyst bed.

Now investigation are underway but still there is no clue of what happened. I would like to have comments of people who have witnessed such type of refractory failure during their careers. I am also trying to search on the internet about such kind of failures in worldwide and I have been able to find only two incidents which occured in India. If someone has any literature about the such type of failure and what actions were taken, please share it with me.

Regards,

Ali