vent sizing

[ingproc]

Hi

We are designing the steam headers for a combined cycle power plant. To avoid condensate accumulation in headers during start up (and other conditions) we are adding drip legs along the headers. Those drip legs are draining into an Atmospheric Condensate Receiver, that is pumped to other location when is required.

Our concern is about the end of the warm up; because we think steam could flow through the drip leg, and go into the Atmospheric Condensate Receiver.

We have a vent in that receiver, but we want to be sure it is enough size to avoid pressurization.

How could we estimate the maximum flow of vapor going through the drip leg (and the system)?

Thanks in advance

 

[sshep]

Hello Ingproc,

Having a drain on your main line drain boots is a great start-up feature to handle all of the condensate and any noncondensibles that may be present, but once the line is warm, you usually close these and rely on a steam trap to drain the line to your condensate system. The start-up drain valve is usually jsut to the ground due to lack of pressure at start-up as per next paragraph.

You want to warm up the line with a small valve (like 2") around your header block valve. If the line is warmed up too fast by just opening the header block valve, the amount of condensate generated will be large and the hammer from a large slug of high velocity condensate can be dangerous. The reason that your start-up drain is usually to the ground is because the steam line will not have much pressure during the warm-up (the warm up steam passing the 2" valve is condensing against cold metal). If you warm up to a condensate return as proposed, there could be difficulty overcoming any rise in the piping.

There are all sorts of good practices (boot size, trap type, piping layout) by all the major steam trap vendors. Spirax-Sarco has a "Hook-ups" book, TLV has a "Trapping Principles" book. These can probably downloaded for free, for example:

http://www.spiraxsarco.com/us/products-services/request-product-literature.asp

Hope this helps.

best wishes always,
Sean Shepherd

 

[ione]

ingproc,

You’ve been addressed to the right place by sshep. Spirax has a wealth of experience with steam plants.

http://www.spiraxsarco.com/resource...eam-distribution/steam-mains-and-drainage.asp

http://www.spiraxsarco.com/resources/calculators/pipes/start-up-and-running-losses.asp

 

[psafety]

The steam condensing on the surface of the atmospheric receiver (induced vacuum) will likely determine the vent size.