Cooling Tower Piping Challenge for New Power Plant

[MechEng1995]

We are building a new 550MW Combined Cycle Power Plant (3 CTs on 1 Steam Turbine). We have been planning on using a 10 Cell (Back to back), Mechanical Draft, FRP cooling tower with undergound circulating (cooling) water piping to the tower. This piping feeds each cell from a riser stub up from the groung. This method is very clean and has worked very well in the past. However, we can not bury the cooling water piping this time, and in fact, we have to elevate the piping (78" steel pipe) on supports to maintain site access. As it turns out, the elevation of the pipe will be right at the deck elevation. The challenge is this: We need to find a way to run the 78" pipe directly onto the deck of the cooling tower, divide it as necessary for distribution, and incorporate an isolation valve for each cell. We must do this without increasing the footprint of the tower or making the tower so robust that is becomes cost prohibitive.

Does anyone have a cooling tower that is similar to this? Any studies? Any pictures?

Thanks,

Brett

 

[MJCronin]

1995...

It has been my experience that cooling water lines are always run underground. Typically, FRP piping is used.

Just a few more questions:

- Has there been an economic analysis of the operating and maintenance costs associated with running this 78" steel line above ground ? The operating costs associated with the additional pump head, larger pump size etc. can be massive over a number of years. There will be additional steel costs with supports, maintenance etc. UG piping can save costs here.

- Have you considered the massive transient forces on the pipe support frame when pumps start and stop ? This makes the steel big....not a problem with UG piping

- There will be maintenance costs associated with coatings etc for all of this pipe and steelwork. Is the owner happy with this ?

- My thoughts only

-MJC

 

[MechEng1995]

MJCronin,

Thanks for the response. We did look at all of this. We are into rock at grade and can not blast. The excavation costs are incredible. Above ground pipe is the leading contender at this point. We have not worked out all of the details yet - Hence, my posting. I am fishing for help on the cooling tower piping arrangement before we go too far down this road.

Thanks.

 

[EOIT]

The closest solution I have seen was in south Texas where the plant had ALL of the piping in trenches. The trench was dug ~3' with concrete walls/bottom and every stick of piping was laid down in the bottom. Handrails were erected everywhere it wasn't determined necessary for a crossing and then vehicle crossings were made when needed. I asked the plant engineer about it and he said that the original designers worried about underground leaks, etc and they wanted everything exposed.

Of course with the last several excavation projects I have had at my plant I envy them with their exposed piping.

So back on topic maybe it would be cost effective to take the middle route? Not a full burial, but carve out a pipe trench in the rock and the build access as necessary. Depending on the rock you may get away with not having to pour concrete.

Regards,

EOIT