natural gas emergency generators

[wwhitney]

another way to look at it is equivalent lengths
assume 1000' pipe
900 of 2"
100 of 1"
it's not a 1" restriction or drop
it's a 1000' pipe of 900/1000 x 2" + 100/1000 x 1" = 1.9" pipe

Internal diameter D and pressure drop H are not related that way.

For a gas piping systems with smooth walls and a pressure of 1.5 psi or less, 2015 International Fuel Gas Code Equation 4.1 says D is proportional to H^-0.206, which means that H is proportional to D^-4.85.

Assuming in your example that 1" and 2" are the internal diameters (for ease of calculation), then the equivalent diameter would be given by D_equiv^-4.85 = 0.9 * 2^-4.85 + 0.1 * 1^-4.85, which implies D_equiv = 1.52".

Cheers, Wayne

 

[strap89]

I have in the past sought approval from the AHJ in accordance with Article 700.12 and utilized natural gas generators without issue.

A colleague under similar circumstances has specified gas generators for Article 700 applications only to find that the gas pressure has proven to be problematic. i.e. at certain times of the day, it's fine. At other times, it's a problem. The problem is not that the unit won't run but that it won't start up in the requisite 10 seconds.

He claims he's seen this scenario multiple times and that specifying gas generators for Emergency applications is a bad idea - should never be done - etc.. This seems a bit extreme. I was wondering what the experience has been of this group of "know it alls "

SIAP...I'll chime in and add 708.20 (F)(3) to the discussion. When designing distribution required to meet Article 708 COPS (Critical Operations Power System), this section clearly states the public utility gas shall not be the only fuel source...this to me sets a standard to consider with all generators powering emergency and life safety loads, even when not applying article 708. I recommend not using natural gas gens for life safety or emergency loads.

 

[gadfly56]

SIAP...I'll chime in and add 708.20 (F)(3) to the discussion. When designing distribution required to meet Article 708 COPS (Critical Operations Power System), this section clearly states the public utility gas shall not be the only fuel source...this to me sets a standard to consider with all generators powering emergency and life safety loads, even when not applying article 708. I recommend not using natural gas gens for life safety or emergency loads.

You could always spec a dual-fuel generator. It can run on natural gas with a small injection of diesel or run 100% diesel. That way if you anticipate a case where you are likely to go beyond the minimum storage requirement of 48 hours for your outage, you can run on NG and stretch the diesel. If the NG fails, you still have your minimum diesel run time. See here for an abstract on a paper on this.

 

[strap89]

You could always spec a dual-fuel generator. It can run on natural gas with a small injection of diesel or run 100% diesel. That way if you anticipate a case where you are likely to go beyond the minimum storage requirement of 48 hours for your outage, you can run on NG and stretch the diesel. If the NG fails, you still have your minimum diesel run time. See here for an abstract on a paper on this.

This is correct, you could specify a dual fuel genset provided the system is capable of switching fuel sources automatically when one proves unreliable or depleted.