recfractory anchor brick failure - could water cause this? 2

[RCMRon]

We have an indurating furnace operating at 2300 deg F as part of making iron ore pellets. the roof is a castabel refractroy 9Vesuvius) and is held in suspension by anchor bricks. We experienced a roof failure where all of the achnors broke at hte interface with the refractory. 14 inch achnor bolts and 9 inches of cast refractory. all that was left was the 5 inches of the bolt that was suspended from free moving steel achors on the beams.
Can anyone shed some light into what would have caused such a failure (Machine had just been cooled down)and does water impregnation affect the tensile strength of the anchor brick to the point of breaking? there were signs of excesive water being directed to the area of the roof colapse. it was a hole in the building roof and all of the water was aimed at the location of failure.

Any help is much appreciated

 

[TVP]

If water is making contact with ceramic/refractory materials, then brittle fracture due to thermal shock/fatigue is a possibility. What is the temperature of the refractory material near the anchors supposed to be?

 

[RCMRon]

We operate the inside of the furnace at 2200 degF so I would suspect that a tthe point wher the anchor meets the refractory is is very close to this.

large quantities of water laned in the area of the colapse s=due toa hole in the roof although there were signs of longer term thermal crack in the refractory itself.

Appreciate all the help i can get on this one

Ron

 

[TVP]

Ron,

Refractory bricks like that are not supposed to be subjected to rapid temperature changes. Large amounts of water will suddenly cool the outside of the bricks causing thermal strains to occur. These thermal strains cause the bricks to crack, which expose the anchor to extremely high temperatures. High temperatures soften the anchors causing failure.

 

[metengr]

I can tell you that with boiler cyclone refractory (higher service temperatures than would be seen in your furnace) there needs to be a curing time after initial installation to allow moisture used for mixing to escape. If not cured properly, I have seen refractory literally peel and split over time. If the bricks were not properly cured from original, this could lead to failure as indicated.

 

[RCMRon]

Thanks for the insight. What you all described above fits perfect with the failure.

Even without water, can i assume that quick heat up and cool down caused by othe reason such as a burner gun flame directed right at the refractory, would have the same result?

Is there a better way these days to hold a refractory roof? I have added a picture of the repairs that show the brick anchor system. Is there somthing else that could be used to hold the roof that is less suceptible to temperature variations?

 

[diskullman]

You may want to try a different anchor brick design, such as pictured

I can supply these

Russell Giuliano

 

[RCMRon]

Russell, would these bricks me more tolerant to water caused thermal streesses and if so , how?

They are different.

Ron

 

[diskullman]

No, they would not be any more tolerant, as the materials would be similar. The angular ridges provide a better surface area to hold castables better.

Russell Giuliano

 

[tc002]

Ron, Your question and problem area was interesting information for me. I have spent the greater part of my career almost 40 years involved in the business of shaft furnace engineering and operation including the shaft furnaces for pelletizing induration. There aren't but a few in operation around the world. The last one built was done on a project I directed in India in the 1990's.
As to your problems of refractory failure in the roof, I can say that it looks like you had a thermal shock failure from the water which probably caused the anchors to fail at the weld and the weight of the saturated refractory just gave away.
This seems to be an enormous amount of refractory for the roof and it doesn't look like it is necessary given the normal temperatures of operation as it should be. The temperature of the gases in the roof area should not be as much as 500 to 700 degrees F. I would certainly like to know more about your operation. I may have suggestions.
My background for your Info in shaft furnace induration started in 1969 with the construction of a 500K plant in the US along with startup engineering and operational management. From there I was involved in the design, construction and startup of plants in Argentina, and Morocco, evaluation of plants in Sweden, evaluation of plants in US, Minnesota, and Australia and project management, design, construction and startup of a plant in India. These also included upgrading plants and design modifications for a number of the installed ones up to as late as 2005. I believe my company is the last of its kind in the world in shaft furnace pelletizing.

Tom