BREATHER VALVES - AUTOMATIC BLEEDER VALVES- API STANDARD 2000

[Epicuro]

I would like to ask your opinion about the following issue
(API 650 floating roof tanks):

1) BREATHER VALVES (RIM VENT): the API STANDARD 2000 allows to calculate venting requirements (Inbreath/Outbreath) in term of Nm3/h. The standard also allow to size the venting devices ie: number and size.

2) AUTOMATIC BLEEDER VALVE: comes into operation either when the floating roof is being landed, and the tank is drained down, or when an empty tank is being filled.

Can be sized withthe API STANDARD 2000

3)During normal operation the only devices responsible for Inbreath/Outbreath venting (caused both by liquid movements and thermal effects) are BREATHER VALVES (RIM VENT)
and NOT automatic bleeder Valves

Are my statements above correct?

thank you

regards

 

[IFRs]

Don't use API 2000 for sizing floating roof P/V vents. Use the manufacturer's recommendations. If not available, calculate the size and quantity using the maximum upset fill and suction rates and the weight of the floating roof. Then if your budget allows, add an extra one. Don't forget to specify at what elevation they open.

 

[Epicuro]

Thank you!

How can I do " calculate the size and quantity using the maximum upset fill and suction rates and the weight of the floating roof." ?

I don´t need detailed explanation just reference of some book/norm where I can read on my own.

Thank for yor kind reply!

 

[bimr]

Talk to the process engineer and obtain the design conditions. Convert the liquid flow rates to cubic meters/hour for the volume rates. The tank erector/designer should be able to tell you the floating roof weight.

 

[IFRs]

Try Mark's Standard Handbook for Mechanical Engineers, 9th edition, page 12-96 and 12-97 or a basic flow equation: velocity = loss factor x square root of ( 2 x head / density ). Then use the area of the vent x velocity = flow. For head use some percentage of the floating roof weight for pressure, and some fraction of its design live load for vacuum. For density use air at STP for vacuum and the same for pressure unless you want to correct for a vapor saturation factor. For the loss factor, if it can be said to be a short, round, sharp edged duct 0.60 is probably OK.

 

[e43u8]

1) Rim Vent...is reqiuired
2) Automatic Bleeder Valve or PVRV...is required
3) Vent for normal liquid movement and thermal effects...isn't required; because there is no space between liquid level and the roof.

 

[IFRs]

In my opinion, rim vents are vestigial, proven over time to be not required. I don't think there is any meaningful pressure increase or decrease in the annular space where the seal is and rim vents are just a source of emissions, something to go wrong and a potential safety hazard. I'm often wrong so consider this simply an opinion you found on the wild wild web.

In my opinion, non-contact floating roofs do not need vents even though there is space between the liquid level and the roof, for essentially the same reasons.

 

[Epicuro]

Thanks all for your reply!

@IFRs :"Mark's Standard Handbook for Mechanical Engineers, 9th edition, page 12-96 and 12-97" -> I got only 10th and 11th Edition.
Section 12 is "12. Building Construction and Equipment ." Could you write me title of the subsection so I can search in a different edition?

I wanted then to ask the following :
1) if I get some venting requirement (regardless of the determining criteria : API 2000 vs other methods) I suppose both automatic bleeder
and breather valves need to fullfill them. is it right?
In other words :
2)venting requirements are the same both when the floating roof is been landed and when is floating over liquid just in the first case AUTOMATIC BLEEDER
VALVE are involved in letting air to flow in/out whereas in the second PV breather valves are responsible for this flow. Is this statement right?

Again in other terms :
3) if I have outbreathing venting requirement, let´s say of 18000 Nm3/h the requirement is the same for both Bleeder and PV-Breather , right?

All the story starts because I am reviewing design where they sizes automatic bleeder for 18000 Nm3/h and PV breather for 9000 Nm3/h .
This doesn´t sound well for me.
4) Both of types should be sized for 18000 Nm3/h not 9000 Nm3/h

 

[e43u8]

@IFR
What do you mean by: "non-contact floating roofs" in your last post?

 

[IFRs]

Don't confuse PV vents for the tank and PV vents for the floating roof.

API 2000 helps you size vents for fixed roof tanks and for internal floating roof tanks when API 650 Annex H circulation vents are not used.

The tank needs protection from excessive pressure or vacuum, from normal operations and emergency situations. This includes effects including fill and empty activities and also other conditions that can cause pressure or vacuum.

The floating roof needs a PV vent for when it is taken off float or during initial fill before it is floating.
The floating roof needs protection only from fill and empty activities.

The tank protection is installed in the fixed roof, the floating roof protection is installed in the floating roof. Neither affects or contributes to the other.

Note: the names you use for the vents ("PV Breather" or "Automatic Breather") may to add confusion.

Does this help?

 

[IFRs]

Internal floating roofs can be grouped into two broad categories:

1) Those whose deck is intended to be in full contact with the liquid surface. This includes most if not all steel floating roofs and some aluminum floating roofs. These would be called "full-contact" floating roofs. One example is easy to visualize - one that looks like a kitchen frying pan.

2) Those whose deck is above the liquid surface. These are generally aluminum floating roofs whose buoyancy is mostly supplied by parallel rows of hollow pontoons that support the deck. This deck is not in contact with the liquid, only the pontoons are in contact with the liquid. These would be called "non-contact" floating roofs.

API 650 Annex H offers descriptions of these types of floating roofs.

You can probably see images or other descriptions using Google to search for "full-contact floating roof" and "non-contact floating roof"

 

[e43u8]

@IFR,

You mentioned:
"The floating roof needs a PV vent for when it is taken off float or during initial fill before it is floating.
The floating roof needs protection only from fill and empty activities."

As i realized from your above statement and your other relevant statements, you believe the floating roofs needs protection only for parts of filling and enptying activities limited to:

1- Part of emptying stage just after the roof sits idle
2- Part of filling stage just before the roof get started to go upside

Is my understanding correct?

 

[IFRs]

You undersea it perfectly.