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Posted by Joseph Markowski on August 14, 2009 at 11:32:00:
on 8.11.09 I experienced a violent rumble and vibration in my N0.2 boiler a 700 hp CB-LE. After shutting down and pulling the burner for inspection it was found that the inner door and Head had seperated along with breaking a stabelizing strut losing the seal for the windbox causing an extremly rich fuel mixture into the furance. The furance area has high concenstration of soot and broken refractory from the cone and the right side tube sheet tubes on the second pass has heavy deposits of soot. This was caused by the failure of the windbox seal. When we found this problem I was in the process of testing the boiler(s) to show the saving that adding new controls to boiler would have, at the time of the event we were reading excessive O2 levels in the stack (which would be an indicator of the seal failure). This is an early version of the LE model manufactured between 1993 and early 1995. The factory formed this seal for the FG damper to introduce flue gas back into the combustion chamber to reduce NOx emmissions. the original attempt used zip screws which failed, the retro fit repair used high temperature silocone and nut and bolts tie the doors together and form the seal. This was done to my boilers in 1994; which I was unaware of this as there were no records of the repair in the plant file and was done under the installtion of the boilers when the plant was rebuilt in 1993-94. This problem was eliminated in 1995 when the factory change it's method of forming the seal by using a continous weld process to form the sealing area. If you have a CB-LE boiler of this vintage please inspect this area as soon as possible. You can pull the burner assembly and look at the seal to find the gap. I now will have to replace the head on this boiler and possible on my 400 and remaining 700 hp boilers as you cannot access the seal area to rebolt the doors.
Hope this helps you to be safe