Safety location for natural gas vent line or discharge locally?

[Frankcliu2009]

I am doing pipe design for natural gas vent from separator, performance heat exchanger, scrubber for a combined cycle power plant. Those natural gas process equipment have multiple vents and relife vents and most of those are 1" line with 600psi design pressure. The equipment vendor provide the hazardus map based on NFPA codes and they require them to be discharged separately. One of the option is to routed those 1" lines to a commone open and safety place, I just feel it is not a typical way to route more than 10 pieces 1" line to a location. As all the equipment are outside, maybe all the vents can be discharged at the equipment location with extending to a safety height. Which is the typical way to do the design? Thanks!

 

[dcasto]

If they are vents from thermal relief valves, then they could be tied together as long as the credible scenario back pressure on them is acceptable to api 520 521

System vents that cannot have back flow from other sources should be vented away from ignition sources and personnel. Things like packing or seal gas systems are included. I'm not sure which NFPA standard they were using, I'd be interested in looking at it.

 

[EmmanuelTop]

Both ways are correct, having provided that vapor cloud(s) will not reach potential ignition sources or accumulate at ground level, in concentrations that can cause either explosion or other harm to the personnel/environment. If you are dealing with non-toxic gas, dispersion study accounting for 1) maximum flow and strongest wind, and 2) 10% of the maximum flow at static weather conditions, should give you a feeling of how vapor cloud will behave. I would look for 1/2 LEL and 10% LEL curves.

Having a common vent stack seems like a better idea, rather than having individual relief/discharge lines rising from the equipment sources.

Other important issues I would look at, are:
- Whether the cold relief could cause any problems with the Environmental permit of your facilities,
- If you are supposed to report cold venting of Hydrocarbons to any legal entity (certain threshold discharged to atmosphere)




Dejan IVANOVIC
Senior Process Engineer

 

[BigInch]

you can usually vent them at 8 ft above ground or skid level. Bundling them and running long distances will increase backpressure and force the line diameter to increase. then what.

you must get smarter than the software you're using.