500# steam vs 15 #

[IanMiller]

Alright this is a dumb newbie question, but I never learned anything about boilers in school. I've just been asked to evaluate our heat tracing at one of our sites. There we generate steam with 2 500 hp Kewanne units. I talked to an engineer today at our maintenance contractor about all of our problems and a few options. He mentioned these units produce 500# steam, but on the units themselves it rates them at 15#. What is the difference and what does it mean to boiler performance?

I'm sure I'll have a lot of these questions as I go along, but I'm learning.

Thanks in advance
Ian Miller

 

[LSThill]

Hi IanMiller (Mechanical)

A good reference Book:
"BOILER OPERATIOR'A BUIDE" BY ANTHONY L. KOHAN, fourth Edition, ISBN #0-07-036574-1.

Leonard@thill.biz

http://www.thill.biZ

 

[quark]

"He mentioned these units produce 500# steam, but on the units themselves it rates them at 15#" What does this mean? You should be more patient in telling us what exactly # stands for.

If you are not clear with your problem (and for some basics) this link will help you and it is free.

http://www.armstrong.be/pdf/N_101.pdf

And these two are not free (see the warning in the first page of these two documents)

http://www.spiraxsarco.com/us/assets/uploads/PDFs/HookUp.pdf

http://www.spiraxsarco.com/us/assets/uploads/PDFs/Steam.pdf

These links will provide you with every sort of details you required.

 

[aybee]

he probably means it is rated at 500pounds (#) per hour at 15pounds per square inch (also sometimes denoted as # just to confuse the unwary)...AYBEE

 

[TD2K]

I'd ask Kewanne but my guess is that the units you have are rated for a specific duty. That translates into a specific steam production when making 15 psig steam (saturated I assume) based on some BFW temperature.

If you make 500 psig steam, you need to add more energy to make a pound of 500 psig steam versus 15 psig steam so your steam production will be decreased. Plus the heat transfer in the boiler will be reduced (since 500 psig steam is hotter than 15 psig steam) so again less steam production.

Still, if the boilers are actually designed to make 500 psig steam, it's odd they rate them as 15 psig. I suspect the 2500 hp are boiler Hp (which I've never worked with) and again, this might be tied back into the 15 psig steam energy content.

I'd just find the name of your local rep and ask the question. Be interested in hearing their answer myself.

 

[KeItSiSt]

It sounds as though these are a couple of 500HP low pressure steam boilers. 15# means 15 psig which is the design of the boiler and would be an ASME Section IV unit. This should be found on the ASME data plate with a little "H" in the clover leaf that is on the ASME nameplate. Quick way of telling if that is not readily accessible is to look at the pressure gauge on the boiler. If its in the range of 0-30 PSIG then its a 15 psig boiler. If the boilers are 500HP then this means they will produce approximately 17,000 pph (pounds per hour) of steam. I am not sure what your engineer meant by 500#...that doesn't equate to any other information you have given us. These two terms mean two different things to boiler performance. The pressure is the maximum pressure this boiler is designed to produce and the maximum setting of the relief valve. Actually, this boiler will only produce a maximum of around 12-13 psig because of the relief valve setting being 15 psig but thats for another thread. The HP rating of the steam boiler is its output capacity (energy or amount of steam) and this is based on feeding the boiler with water "from and at 212F" for all boiler companies that I can think of. This means the boiler will put out 500HP of energy if fed water at 212F and does not consider having to heat the water up to 212F. This is done for some conformity among boiler manufacturers. And don't feel bad...not too many people know anything about boilers and is a dying art especially on the steam side of things.