Design and sizing of Natural Gas line to burner of steam boiler

[sizgalil]

Hi there.

Does anyone know if the flow of natural gas to a steam boiler should be determined by the boiler's capacity or rather by it's burner's capacity which is usually substantially bigger? Will the burner not operate at a higher capacity than that of the boiler in order to overcome losses?

Thanks.

sizgalil

 

[katmar]

Unfortunately sometimes the flow of NG through a pipe is gien in btu/hr, and because a boiler can be rated in btu/hr it looks as though you are comparing like with like but this is not so. The boiler's btu/hr is a steam rating, not a gas flow. Size your pipe according to the gas requirement of the burner.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[sizgalil]

Thanks Katmar. I will try clarify my question.
The boilers are actually rated in steam output such as 10 ton of steam per hour. This is equivilent to about 6,500,000 kcal/hr. Now often I notice that such size boilers are equipped with a 10,000,000 kcal/hr burner. Why is this and should the gas lines be designed according to the boiler rating or the burner rating?

Thanks again.

 

[LittleInch]

How about thermal efficiency of the boiler??

An efficency of 65% looks a little low, but will at best be 85 to 90% so gas flow in BTU/hr will always be higher than steam output. Also depnds on how the burner control system is arranged (simple on/off or a more modualting system) and how the boiler heats up. It will need a alrge heat inout during start up to start generating steam as well as the steady state heat input ot priduce the steam.


If your burners are rated at 10 million, then unless you know for sure they're never going to be run flat out, then you need to size your gas flow for 10 million.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[sizgalil]

Thanks Littleinch.
Can't a burner much larger than a boiler burn the boiler to ashes?

 

[LittleInch]

Yes,

But that's why you install a control system and experienced vendors know how to design it properly. A 6.5 million output versus a potential 10 million input looks Ok to me. If you don't size your gas supply to the burners correctly you might not generate the steam you need or it could tske a long time to "fire up"....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[sizgalil]

So let me see if I've got this right.
A boiler needs a burner larger than its capacity in order to overcome the efficiency of the boiler.
Wouldn’t it be necessary to also account for the burners efficiency? So that if the burner is 10 million, the gas flow should actually be let say 11 million?

 

[LittleInch]

Yes, basically you have it right. I would have said "due to the inefficiency of the boiler", rather than "overcome", but that's semantics.

Maybe, depending on whether your 10 million is its rated output or input. It's not uncommon for this type of capacity to be non specific unless you ask the specific question. Usually you find someone has done it for you and given you a gas supply you need to supply...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[sizgalil]

I'm pretty sure it's output but will make sure.
Thanks so much.

 

[katmar]

The boiler steam rating is also more of an "average" rating, while the burner will be a peak rating. The burner needs to cope with start-up and various fluctuations. This is a general problem in plant sizing - average vs peak. I like to use the analogy of a car. If you only ever did steady highway driving then a 30 HP engine would be just fine. But you have to deal with starting, driving up hills and overtaking slower traffic. So we don't have many 30 HP cars anymore. And the fuel pump must be able to deliver the gas when you need to use the 100 HP (or more!) that you have.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"