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Gallo22 (Military) (OP)
19 Feb 11 15:10
What would cause a a pulsating effect in a boiler would it be a faulty atomizer or oil temperature being to low? What does the excess air curve chart look at exit gas temperature or the air to fuel ratio? What type of heat transfer is taking place in a surface condenser radiant conduction or convection?
unclesyd (Materials)
19 Feb 11 15:55
Someone else may have a better answer but the times I've been involved with pulsation was related to the burner.  The problem was the location of the spud.  If you the freedom to move the stud in and out while firing you might stop the pulsing.  I would check other parameters and if possible reset the to the OEM settings.  

Are you under or over firing?
 
hacksaw (Mechanical)
19 Feb 11 17:56
What would cause a a pulsating effect in a boiler would it be a faulty atomizer or oil temperature being to low? What does the excess air curve chart look at exit gas temperature or the air to fuel ratio? What type of heat transfer is taking place in a surface condenser radiant conduction or convection?

1. Pulsation in the combustion chamber can be do to poor air distributions, improper atomization, fluctuations in fuel content, control mis-operation, etc.

2. if the oil temperature is too low you won't be able to make full load, and atomization will be almost non-existant

3. Depending on the size of the boiler and its class, the controls will monitor air flows, fuel flows, steam flows, feedwater flows, , gas temperature, stack O2, sometimes CO. Air/Fuel ratio is commonly controlled with O2 trim, lead-lag control of the firing rate, and tied into the feed water controls.

Suggest you determine if you have a control cycling issue, or if it is a burner instability.

Put the fuel flow in manual and see if the pulsation goes away.

Most power boilers have both convection and radiant sections, with several forms of preheat.

You need to be more specific about the boiler(capacity), steam pressure, etc. They are complex systems, so you have to work your way through the checks carefully, and hopefully with some good techs.

Some of the smaller boilers may have none of the fancy controls, but they are not usually classified as power boilers.

 
davefitz (Mechanical)
21 Feb 11 13:31
The furnace pressure pulsation in an oil fired furnace is related to the combination of the structural steel/furnace fundamental frequency, the windbox to furnace pressure drop, the flame instability ( related to flame speed). It is not an easy phenomena to describe, but changing any one of those 3 items can reduce or amplify the pulsation. There are some old 1980's asme papers on the subject ( some by F.L. Eisinger) , and recent work on the subject has been adapted by gas turbine mfr's to address similar issues with gas turbines.

Excess air - perhaps better named excess O2 at the furnace outlet ( if hot O2 probes are used) or at the economzier outlet- several items neeed to be nmanaged as load drops- flame stability, reheat steam temperature, fan control stability, and ability to isolate burner air registers as the burner is removed from service, each factor into the etabilishment of a recommended excess air vs load curve. The air/fuel ratio  is direclty related to excess air only if all burners with air flow are combusting fuel.

The surface condenser primarily uses condensation heat trasfer on the steam side and used convection heat transfer on the tube side.

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