API 2000 or 2557: Vapour treatment flow calculation 1

[willem79]

Hi all,
Im trying to calculate the amount of vapour expected from several tanks filled with Methanol to size the vapour treatment header. API 2000 does mention thermal outbreathing but i'm in doubt if this is referring to normal flows or sizes to maximum emergency scenarios. Does API 2557 elaborate on this? I'd like to know befor i buy a publication that is of no use to me

 

[IFRs]

You might try API MPMS Chapter 19 and/or Tanks4 from the US EPA.

 

[skearse]

API 2000 Section 4.3 covers calculations for "normal" venting (including pump-in and pump-out and thermal in & out breathing) as well as "emergency" venting (fire exposure).

 

[chicopee]

Willem79, Is your question for a methanol vapor recovery system?

 

[willem79]

Yes, it is a methanol vapour recovery system. Methanol is not "recovered" though in the sence of reusing it but disposed of. When i calculate thermal + pump-in outbreathing according to api2000 section 4.3, the flow is 3 times that we see on any tank elsehwere in the company or any vapour treatmet system flow. I'me curious if there is any way to calculate flow under normal conditions because I suspect that API calculates at worst case conditions and the flow concerns PVRV total capacity. For instance a tank has two PVRV's. one set at 100 mmwk and one at 120 mmwk. sizes are identical. the first is connected to the vapour treatment system. the second is set to "das blauwe hinein" for safety. Not on any tank ever has the second PVRV opened. My point is that i dont want to over design the vapour treatment system.

 

[chicopee]

To figure out vapor quantity, you need to know the amount of heat transfer(Btu/Hr) between environment and product in the tank. Knowing allowable tank pressure and expected vapor temperature, you can figure out the enthalpy (Btu/Lbm) needed to evaporate the methanol. Evaporation rate (Lbm/Hr)= Heat transfer/Enthalpy. Of course you'll need to set initial and final conditions.

 

[TD2K]

As said, API 2000 has tables for inbreathing and outbreathing for pumping in and out of the tank as well as for thermal effects (both inbreathing and outbreathing).

For filling or emptying a tank, for high flash point materials, the outbreathing is a little bit more than volume for volume, inbreathing is volume for volume. For low flash point materials, the outbreathing volumes are higher.

API 2000 also has the relieving capacity for fire, should that be necessary.

There's a discussion how the thermal outbreathing volumes were established in one of the appendixes. If I remember correctly, they were based on hot gasoline entering a hot tank resulting in some of the gasoline flashing and having to be relieved. The thermal inbreathing is based on a rainshower on a hot tank cooling and contracting the vapor contents.

Shand and Jurs or Protectoseal who sell tank breathing valves, pad gas systems, etc usually have exerpts from API 2000 in their catalog. You could look at them and see if it meets your needs.