Question Regarding "A" Type Water Tube Boilers 1

[Franc]

The "A" Type boiler consists of a steam drum and two mud drums; my question is regarding the flow of water between the three drums...Is the flow produced by natural draft(natural flow)? If so, is this natural draft occuring due to different temperatures at different locations within the tubes which produces differential pressure causing a flow?


Thanks for the help.

 

[spector]

That's exactly what happens and why except it's not pressure related, but due to the force of gravity.

Your boiler is a natural circulation type. Circulation occurs due to differing density of water in the hotter generating tubes and the cooler downcomer tubes. It's the product of uneven heating between the generating tubes and the downcomer tubes. Tube location in the boiler determines which absorb more heat. Cooler water is heavier. Hotter water is lighter. The differance in density/weight by volume causes the hotter water to rise and the cooler water to fall.

If your generating tubes slant sharply upwards, you can describe your boiler as an accelerated natural circulation boiler. This design is best for boilers that operate at high rates of steam production.

 

[jehar]

Hi,
The process is also called thermosyphon, and as stated is due to differences in the water density in the downcomers and the density of the water/vapor mixture in the risers. A full explanation of this and a simply JavaScript calculator can be found at the site for Waste Heat Boiler and HRSG design at

http://www.HRSGdesign.com

Thanks,
Jack Hardie

 

[Franc]

Thanks again for the help and have a "Happy New Year"!

 

[ease]

how do i get hold of ASME SECTION VIII DIV I
on the net they are too expensive???

 

[dfurey]

This is my first time on this sight. I had a chance to read your comments wrt "A" boilers or "Admirality three drum". I have steamed these boilers on an old Navy ship. These boiler (marine) were not equiped with downcomers. The flow of water was from the outboard generating tubes (ones closest to the two economizers). This is concidered a cooler section and allowed the heavier (dense) water to travle down the tubes and replace the less dense hotter water. Additionally the side which had the superheater had a large diameter superheater support tube which would distribute water. I am not sure whether a comm. boiler of the same type is equiped in this fashion.
Dave Furey
BTCM USN

 

[Rhanns]

ease,

You can go to the National Board web Site and order them. They are expensive anywhere you go.

Rex