Watertube Boiler Question 1

[Rebecca Hannah]

Hi all,

I don't have so much experience on steam boilers and interested to know more.

Is there a type of water-tube boiler which has its steam drum or water drum exposed to heat (either radiation or convection)?

Thanks very much for your help.

Aida Hanani

 

[crshears]

Hello Rebecca/Aida,

I have not seen every type of water tube boiler in existence, but in my experience only a nominal to minimal amount, if any at all, of any of the drum surfaces are normally "exposed to heat," as the ligaments between tubes are of a relatively low proportion of that part of the surface of the drum that faces the furnace.

Depending on design, generally one half or more of the drum surfaces are lagged, as this lagging together with that on the waterwalls comprises the cladding which encloses and seals the furnace / combustion space / gas passages against leakage.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[0707]

Normally steam drum or water drum is exposed to heat of convection.

luis

 

[0707]

Rebecca Hannah see the video bellow. The other doesn´t work. Sorry

luis

https://www.youtube.com/watch?v=kxI0tlivmzo

 

[hacksaw]

Water tube boilers are the most common.

 

[0707]

hacksaw

the most common I think, unless those of the old steam train machines.

 

[MJCronin]

IMHO, it is important to remember the purpose and function of the steam drum to answer your question.

The steam drum provides a volume where the steam-water influent (from the boiler tubes) can disengage and the steam can shed some water droplets. The steam drum also directs effluent flow into the downcomers thereby allowing thermal circulation through the system.

The steam drum also contains a maintained volume of water that will permit system upsets and changes in steam demand.

Finally, the steam drum also becomes a place where solids collect for that all-important continuous blowdown housekeeping requirement.

Sooooo.... With all of these requirements, it makes more sense to consider the function of the steam drum to be anything but as additional heat transfer area.

Structurally, the weakest point in any water-tube boiler is the location where the tubes penetrate the shell of the steam drum, To further stress this area by subjecting it to the ever changing heat of the fuel seems very unwise

Purchasing this book is money well spent:

https://www.babcock.com/resources/steam-its-generation-and-use

MJCronin
Sr. Process Engineer

 

[hacksaw]

my 40th Ed, still gets a bit of use, and a lot of the content is helpful beyond, just boilers.

 

[davefitz]

A thin walled drum probably would not have much of a problem as long as it was always filled halfway with water, but a thick walled drum cannot be permitted to absorb a lot of heat from the combustion gases, as it would generate a thermal stress that would bow or bananna the drum. For that reason steam drums either have insulation under them or at least a radiation shield, and large thick drums are normally located separate from the furnace in a penthouse. A dry drum asorbing heat would fail, as would the waterwalls, if there was heat transfer occurring while it was empty. Another issue is that small low pressure boilers usually have rolled tube to drum attachments, and the thermal stress could fail the rolled joints.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[Raai2015]

@ Davefitz , if i remember correctly , most of the Bi-drum Boiler (Industrial Boiler)Bottom of the top drum is in the flue gas path??Further Ligament effeciance is much small in the range of 45-60%

 

[davefitz]

True, but the mud drum is always 100% full so there is no oeverheat of the top surface, and the flue gas temperature is relatively low. In the convective pass that temp may be 1200-500F while the furnace exit temp may be 2200F or more, with significant radiant heat flux..

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[Raai2015]

@ Davefitz. Agreed. If i understand the Question correctly '' Is there a type of water-tube boiler which has its steam drum or water drum exposed to heat (either radiation or convection)?''
the Answer is 'Yes' . to my Knowledge not by Radiation but by Convection - and not in the power Generation Boilers but in the Industrial Boilers.