Landfill gas condensate collection

[kimawi]

Hi Folks,

I am working on a design of a buried pipe carrying landfill gas and I calculated that some condensate will form due to the cooling of the gas. The pipe is upstream a blower and hence the gas is under -ve pressure.

I am thinking that the condensate traps along the pipe will be expensive and difficult to install because we have to have a large liquid head (long drain leg) to overcome the vacuum in the pipe before the liquid can be drained from a low point in the pipe to a sump, so the sump will be too deep in the ground.
Is there a smarter way around this? and if we size the pipe so that the gas velocity is high >50 m/s can we get away without a condensate trap in the low points of the pipe? the condensate will eventually be collected in a knock-out drum just before the blower.

Thanks

 

[zdas04]

It is unlikely that you can get 50 m/sec with a blower if the suction pipe is very long. Friction losses are brutal at that velocity.

You didn't say how long the line is, what sizes you are anticipating, or what elevation changes you have to overcome. Depending on that data you might want to think about pigging instead of drips.

David

 

[kimawi]

David,
The 6" pipe is about 500m long sloping down 10m towards the blower. I expect about 30-40 l/h of condensate.

Could you please explain how pigging helps?

 

[zdas04]

Most of the condensate will run to the knockout without aide, but some will lay in sags and overbends.

Pigging helps by pushing the liquid that wants to lay in very minor dips in the piping to your knockout. With pressures as low as you are talking about I'd probably run a pig once a day. With line drips you'd have to find a way to pump them out without introducing air into the system (a pretty tough problem, not insurmountable, but tough). With pigs you can just drop a pig in the line and let the blower suck it home.

In 6-inch you could use an Argus Pigging Valve for the launcher and receiver.

David