Re: steam Boiler

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Posted by james hanna CVA on December 13, 2001 at 09:26:26:

In Reply to: Re: steam Boiler posted by Clifford Weir on November 13, 2001 at 22:32:00:

I found the problem , or at least most of it . The last several vibration reading showed a very minor change and I figured that even though there had been a resonance change due to speed change .
That this resonance should reamin the same over the next few months. However the bearing vibration data was increasing with no exact bearing frequency defects present. So I determined it must be some form of minor looseness with in the bearing . I told customer that the supporting vibration data indicated an internal problem with - in the bearing . And recommended the bearing be changed with in the next 6 months. They changed the bearing and split casing bearing housings . There was some indication of minor bearing wear , but the most wear was in the bearing housing ( fan end ) showing that the bearing was spinning in housing and was allowed to move in all directions due to the worn bearing housing.
Vibration returned to normal .

james hanna CVA
Certified Vibration Analysis

: : Hello:
: : A valued customer of ours has a large wood fired steam boiler . We were having repeat bearing failures on the OFA ( over fire air fan ) I had suggested that they insulate under the frame work to reduce some of the heat comming from the boiler . This reduced the OFA bearing temperature from about 350 degrees to under 200 degrees. I had also suggested the OFA fan speed be reduced , because the shaft speed was 2080 rpm's which was over the recommended rpm for this bearing when grease lubricated. My thoughts were the reduced speed would reduce the bearing temperature. We had noticed belt squeel on several ocasions . We checked the belt sheaves and found excessive wear on both belt sheaves.
: : The belt sheaves and belts were replaced. Through human error the new sheaves were put on the wrong location , They had the right sheaves ,but put wrong one on motor and wrong one on fan . Well this reduced the rpm from 2080 rpm's down to 1563 rpm's , which is about 33% speed reduction.
: : They changed the OFA damper setting to compensate . The problem I'm concerned with now is there is a resonance vibration on the FD ( Forced Draft Fan ) . Finally my question , could the reduced rpm on the OFA fan cause this resonance vibration on the FD fan
: : Thanks
: : james w hanna
: : Certified Vibration Analyst

: Just a few questions James,

: 1)Did you do a fan balance analasis.
: 2)Are the bearings installed and aligned properly.
: 3)Do you have blades that may be suffering from errosion due to particulate in the air from in coming ducts etc.
: 4)Is there an oil cooler for the bearings, and is the flow of cooling water adequate.
: 5)What type of boiler are you using and why is your overfire air so high, if it is great what is your O2 percentage in excess air. It should be less than eight. I have seen boilers in excess of 15 percent excess air, and this creates all types of problems.
: 6)Your ash should tell you alot about your combustion in the furnace, if you have a lot of unburned fuel in the ash perhaps its not a case of overfire air and the amount should be greatly reduced, and the source my be your undergrate air distribution chambers (dampers in the incorrect position or stuck open or even a breach in the chambers them selves.
: You might even take the unit down and inspect the entire boiler there may be a access door accidentally left open causing unwanted troubles for you.

: Well hopefully all this might help and may-be it's all completely useless, well any way your welcome to email me and let me know how you made out.
: Take care.

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