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Posted by Amy on June 02, 2004 at 14:43:55:
In Reply to: Re: Boiler priming and carry over posted by Ken on June 01, 2004 at 15:45:33:
: My thinking would be to look at anything new that was changed, particularly if you have never encountered this problem before. You said you replaced your level controls. Is there a chance that the float could be sticking in the low position? I've had that happen before. The level controller would continue to call for feedwater, the boiler would end up with high water, and at times, if the load was high at the time, the boiler would end up in a low water condition, because the feedwater supply would be exhausted from supplying so much at one time. Just a thought. Wishing you luck...Amy
: : : Both of these guys are giving you some great information. Did this problem first reveal itself after the overhaul/inspection?? Were the level controls taken apart or adjusted in any way?? Maybe you are running high water, and the carryover is happening at high loads. You did say that this occurs at high fire...maybe you are overfiring your boiler. Did this problem happen on days when the load was unusually high? Also, were the combustion controls adjusted during the downtime? What did you mean when you said that you had a problem getting water into one of the boilers during startup?? What was the problem? If your boiler is tripping on low water when this happens, I would definitely look at the possibility of overfiring these boilers. Wish I could see the conditions when this happens, and I wish you lots of luck in figuring this out. Like I said...those guys are giving you great info...they know what they are doing. Let us know how it turns out for you.
: : : : At christmas time we opened all of our boilers for annual inspection. everything was great. We closed the boilers and started up on monday. We had trouble getting water into the boiler at one plant. After much inspection, it was determined,(by the carryover in the system) that it wasn't a feedwater problem, but a priming problem. This happened to a 600HP Superior Seminol firetube boiler which is fired at full rate most of the time. We also have a 500HP Superior Seminol boiler that is at a different location in the same town. When this Boiler was fired at a high rate, it did the same thing. We removed all of the chemicals, and started with a new source and one at a time. It will go fine for weeks and then upset. We have went through all of the water sofner valves and thought this might have the problem solved. Well, not so. I have checked all that I know. My TDS reading is below 1500. One question is can a small amount of water sofneer brine upset this boiler that bad and not have any effect on my TDS in the boiler. When the upset happens, my boiler shuts down on low water and when the TDS's are checked, they are just fine. I have zero condensate return. I have called the manufacture of the boiler and the DA tank and everyone else that I know and some that I don't know. Thanks
: : : Excerpt from the Association of Water Technology training manual: There are seven reasons for mechanical carryover and only one of them can be corrected by chemical means. 1. Improper boiler design. 2. Improper maintenance 3. High water level in boiler or steam drum 4.Exceeding operational limits 5. Extreme or sudden load surges 6.Uneven firing 7.Improper water composition.
: : : Excerpt: Priming is a form of mechanical carryover. This is caused by gross surges of water in the steam drum that literally throws water into the steam space, where it can be carried into the steam header. This can be caused by either improper design or improper operation. It sometimes can be corrected by changing the firing pattern, correcting false level indicators, or installing vertex breakers.
: : : I don't think the small amount of brine you mentioned will cause the large carryover you are experiencing. Take chloride tests of the boiler water and compare the results with previous results to determine if you are getting brine to the boiler. Check to see if your boiler is overfull at startup. The boiler can pull a vacuum after it cools and suck process water back to the boiler. Possibly that could cause carryover. Good luck.
: Amy, The problem started after we opened for the inspection, however, there was no work done. We just opened and closed the boilers. The level controls are McDonald Miller 7B controllers. They were opened and checked, and after we started up with problems, replaced. I called Superior Boiler and they gave me the normal water level over the top tubes and I have set the water level to this level. None of the combustion controls were changed and there has been no load change in the plant that is found. When the low water condition and carryover happens, the feedwater valve is wide open and we will go down with low water. Is it possible that an orfice in the steam discharge of the boiler for 600HP would help cure this condition? I have set and watched this boiler run at 110PSI for hours and not have any problems in the past. This is why I am so confused. Thank you for the advice. Ken
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