Boiler room steam distribution header

[josemg]

What are the most important things to consider when designing the boiler room steam header?
Should velocities be the same as the boiler discharge outlet? Should the spacing of the discharge and inlet pipes be the same as pipe rack spacing? Should the header have a slope for draining of condensate?

 

[TBP]

The steam velocity is pretty high between the boiler and the header. If you have boilers with the safety valves set for 150 PSIG, they'll normally fire to maintain a header pressure of 125 PSIG. At low loads, the boiler and head pressure will be almost the same. As the load increases though, the boiler pressure rises - it has to to put more steam through the same size steam lead. At high fire, the boiler drum pressure might be 140 or 145 PSIG. The header pressure should be a constant 125. There's no way you can (or should) have the velocity of steam in the header the same as the steam leads. New headers are often oversized initially anyway, to allow for future additions. This also gives water droplets that have been carried over, out of the boiler, a low velocity area to drop out of the steam flow. The header should be slightly sloped to a drip leg. You should try to allow some space between inlets and outlets on the header, but in practice, space is usually a consideration, so things typically get kind of jammed in.

 

[josemg]

What steam velocity will keep the water drops on the bottom of the steam header?

How much distance should be allowed between the steam header inlets and steam header outlets?

For example: I have three boilers 600hp 125psig 8inch steam outlet is 10inch size
steam distribution header is 12inch size
drip legs qty.2 each 6inch diameter

 

[josemg]

Correction
boiler steam outlet 8 inch
steam header 12 inch
steam outlet to system 10 inch
drip legs qty. 2 size 6 inch each.

 

[TBP]

You won't have much of a pressure drop in the steam leads from the boilers - they're pretty big. Did the boilers come from the factory with 8" connections? (That would be for hot water or low pressure steam service.) At your operating pressure, you could probably run 4" from each boiler to the header. In addition to being a lot cheaper, a 4" stop & check will last far longer because it will drive full open, and stay there. An 8" will likely crack open, flutter up and down like a flag in the wind, and wear out long before it should.

The boilers can make about 60,000 lbs per hour, in total. You can push that much at 125 through a short run (maybe 100 - 200 feet or so) of 8", and still live with the pressure drop. 10" would likely be the right size to run in a factory, being fed off a 12" header. I'd slope the header slightly to one drip & trap. If you figure out the condensate you'll have to handle at the header, it'll be pretty small.

Remember that to run a header pressure of 125 PSIG, the boilers will likely have 150 PSIG safety valves on them. Please don't fill your steam system with 125# cast iron valves, stainers and trap bodies.

 

[abcmex]

Josemg,
there is agood information on the learning center from Spirax Sarco (

http://www.spiraxsarco.com)

regarding the details of the headers for a Boiler.

One detail that they mentionend was to avoid, in boiler operating at the same time, that the pressure lost of from each boiler to the header is not even! I could tell you more but they already write it so good luck.