Newer Steel boiler outlet piping design

The Steam Whisperer

I've been looking at a number of newer, compact steel boilers and the manufacturer's claim they produce dry steam with very high velocities at the nozzles. I am currently looking at a 125 HP Hurst with a 6 inch nozzle and they say it produces dry steam for both low and high pressure applications, so there is no need for a boiler header. This sounds pretty fishy to me. As an added challenge, this particular system is vacuum so the velocity out the boiler is double that of a typical low pressure heating boiler. What is your opines, ladies and gentlemen? In this case the velocity at the nozzle is about 161 ft/sec with 0 psi steam. It will be higher, of course in vacuum.

Jamie Hall

You're way out of my league so far as any practical thoughts I might have! But theory now... it would depend on the boiler internals. If they are set up so there is a whirling -- cyclonic -- motion from internal baffles, I can see how it would work. If anything, dryer at higher velocities.

jumper

Depends on steam space size as well. Both height and water steam interface. Kettle boilers advertised 99.75% dry. Love to learn what's involved in derating a pressure boiler.

EBEBRATT-Ed

I rely on Sarco "steam utilization book". Their MAXIMUM velocity for steam piping (any pressure) is 120'/sec (most design for 80'/sec)

125hp must be around 4,200lb/hr

And note, this is for steam piping not boiler takeoffs or headers.

As @Jamie Hall said if the boiler is designed for it internally it may be ok. I am sure most boilers MFG. today are not considered for vacuum service. Low pressure nozzles are always larger. I have seen many Scotch Marines installed without equalizers or headers

I would be very cautious. Mother Nature and Physics do not like to be toyed with. I know this is nothing new to you. I would give the boiler MFG your design pressure etc. and get them to sign off on the application

The Steam Whisperer

This is a scotch marine.....Hurst 400 series. It an existing boiler they have had problems with since installed. Water level is very unstable and often trips the safeties, lock outs and the boiler ends up overfilled. We are looking at doing some surface blow out to remove any oils ( there are no conventional side skim ports), but the lack of header is troubling too. May also put in a surge column( never did one before) to see if we can stabilize the water levels in the controls.

EBEBRATT-Ed

Just a few Ideas:

Surge column is probably a good idea

Maybe reduce the firing rate if possible

Flame pattern in furnace tube (sometimes you can't do much about it) but a longer flame if nozzle changes or other adjustments permit may help

Condensate temperature. If you fire the boiler at it's maximum rating and the condensate is hotter than the rated temperature you could be technically be over firing.

And this goes against everything but the higher the pressure the lower the velocity of the steam.

You may wan't to raise the pressure, not to leave it that way but just to see if it stabilizes things.


I had a job that the engineer undersized the boiler so much that on a cold start and a system full of cold pipe the boiler couldn't make steam fast enough to stabilize. The steam hitting all the cold pipe created a vacuum out in the system that sucked the steam (and water) out of the boiler. tripping low water etc.

they had an automation system with a pressure transducer on the header. As soon as the header got to +.2psi thew water line calmed down and everything was ok........but it was a fight to get there. On a normal start with warm pipe it was ok.

I often wondered about a steam orifice between orifice flanges or throttle the gate valve.........just something to try

nicholas bonham-carter

Is this boiler used for heating?
A good surge column over time will trap any oil on the surface, If piped properly. Then when the LWCO is blown down, the oily water in the column will be emptied out. Making the top connection as large a diameter would help.—NBC