Steam Vent Overflow (associated codes?) 2

[Spud656]

The steam silencer on our LP Steam header has been overflowing and raining condensate on the ground below it during startup, and the CV controlling the flow to it is only open 35%. How would I go about solving this issue?

I have no prior experience dealing with silencers. [highlight #FCE94F]Is there some governing code that relates to silencers? if not, is there some general reference material that I could use to educate myself with that you would recommend?[/highlight]

Would a larger drain from the silencer solve the issue without adversely affecting the operation with the silencer?

 

[LittleInch]

Do you have a sectional drawing of your silencer you can post?

Is this new or has it just started happening but didn't before?

Any change in temp or pressure of the steam exiting?

Difficult to tell if a bigger drain will work or not without seeing the design of it and how the drain works - does it have a water trap?

Is it blocked with dirt or a birds nest or a dead animal?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Spud656]

Attached is a drawing of the Silencer without proprietary information.

From what I am told, it has happened with every startup since the plant was commissioned several years ago. (I only arrived here 6 months ago)

We have no pressure or temperature measuring devices locally to the steam vent piping, but upstream of the CV(globe type), it is saturated LP Steam usually at 75 psig. Piping is 24", then expands to 32" just before the silencer., and it has a 1" drain line.

looking at the iso of the drain pipe, there is no trap in it, just a 1" pipe with several twists and turns before discharging to grade.

I don't believe it is blocked with anything, but I don't know of anyone who has gone to look.


[highlight #FCE94F]Is there some governing code that relates to silencers? if not, is there some general reference material that I could use to educate myself with that you would recommend?[/highlight]

 

[TBP]

Is this the correct unit for your operating conditions? Was it installed according the manufacturer's instructions?

The "several twists and turns" on the drain piping could be an issue. Any horizontal runs that aren't sloped properly, allowing condensate to collect at the bottom of vertical drops? Is the drain arrangement configured such that it drains properly, even after all the piping heats-up and expands?

 

[mk3223]

it has happened with every startup since the plant was commissioned several years ago

Looks that the steam pipe was started with cold pipe and too much condensate at initial stage. And, the silencer drain might not be designed under this condition.

 

[FacEngrPE]

The silencer depicted apears to be one intended to reduce noise. This type is not good at separating out water from steam. Usually these silencers are design to operate at 1/2 psi differential from the inlet to outlet at design flow. If you flow rate is higher first the mufflers become nosier than the specification states. If the DP gets large enough sometimes the baffles get damaged. The drain is intended for draining water out of the silencer, as if you do not drain the silencer the resulting water hammer can destroy it.

If you has a separator vent, those have baffles that spin the flow, it will sort liquid from steam, but for the situation you describe the drain probably needs to be close to the steam inlet size. This inquiry form lists the parameters needed for design

https://wright-austin.com/INQUIRYFORM.html.

Disclaimer - while I have installed some exhaust hoods (one incorrectly) - I have never worked for Wright Auston, there are other suppliers, and it is possible to do this with a knockout drum.

Here are the startup procedure we used to solve this problem.

Open the system drains - ALL of them, including all of the trap strainers.
Open the end of line vent valves wide open.
Warm the boiler plant up with the distribution stop valves closed. Once the boiler plant is operating stably, if the distribution stop valves have warmup bypasses open them. Not too fast, as the goal now is to heat the distribution pipe slowly, measured by freely flowing steam at the system drains, and steam trap strainers. We found we needed to add bypasses as the original design did not size the bypasses to pass an appropriate steam flow for system warmup.
You or the responsible engineer needs to figure our the appropriate sequence to close the valves down. Too slow, delays warmup. Too fast creates water hammer. This part of the sequence is site specific, be aware that water hammer on startup can create enormous shock load forces. 500 lb water slugs flying down the pipe at near sonic velocities is capable of rupturing most piping, often anchors get damaged.

 

[KevinNZ]

I would guess the steam flow inside the silencer is very turbulent. Condensate that reaches the silencer will not fall to the bottom and drain out.

The condensate needs to be removed from the upstream piping before entering the silencer.

 

[LittleInch]

As far as I know, there is no industry standard or code for these sort of items which are officially low pressure fabricated components.

It seems pretty clear that your issue is an overload of condensate during the warm up and start-up as MK3223 says.

Looking at your drawing the drain hole looks very small, but this unit is not designed to handle two phase flow.

You need to introduce a condensate know out drum just before the silencer.

General reference material would be steam process orientated, noting that what you're looking at appears to be a transient issue which is not simple to model or design and needs input from operations to describe in detail what is happening with the start up in terms of flows and temperatures.

Options would seem to be start up slower, increase drain hole size, introduce a condensate KO drum u/s the silencer, add more silencers to distribute flow more, put a bigger silencer on with more room for condensate.

If you can get hold of anyone in technical sales of a vendor you will probably learn more than any code, standard or general material.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Spud656]

Thanks everyone for the helpful responses!
Looks like the next step is to find a vendor to contact. The one that supplied this one is in Austria, so having an American contact would be nice.
I believe we are already opening all the system drains, not sure about the bypasses.
Will definitely look at the KO drum option.

 

[FacEngrPE]

The problem you are encountering also leads to condensation induced water hammer. As this is a known serious safety hazard, with a little additional effort you will significantly improve your system safety. Some references are linked and attached.

http://www.kirsner.org/pages/forensicResAlt.html

https://www.hse.gov.uk/safetybulletins/phenomenon-of-condensate-induced-water-hammer.htm