5 replies to this topic

[Lizette Process Engineer]

How does one go about designing a vapour balancing system to be installed on 14 raw material storage tanks?

 

The storage tanks are each kept between 60 and 80 degrees Celcius, each currently with vents to atmosphere, holding product of an average density of 1.1kg/L at 25 degrees Celcius.

 

The aim is to connect all 14 tanks in a vapour balancing system to ensure no vapours/ fumes escape to atmosphere.

 

What are the safety and technical considerations to keep in mind while designing?

 

Any references?

 

[ankur2061]

Lizzette,

 

Are you trying to design a Vapor Recovery Unit abbreviated as "VRU" or for your storage tanks since you are saying that the aim is not to vent to atmosphere?

 

I am providing some general guidelines for design of such a system:

 

1. If it is practically feasible (no complicated loops or bends in piping) you direct the the vent pipes from each of the tanks to a common pipe manifold. The pipe manifold then gets routed to the vapor recovery unit or if you plan to destroy the vapors then to a flare or incinerator.

 

2. The individual vent connection / pipes from the individual tanks to be sized for the maximum filling rate of the tanks multiplied by the vapor growth factor (generally 1.2 to 1.3)

 

3. The common manifold pipe to be sized based on the maximum simultaneous filling of your 14 tanks. If we assume that 8 tanks are being filled simultaneously at identical filling rates then the design flow rate to the common manifold would be:

 

8*Max. filling rate of one tank*vapor growth factor

 

4. Now coming to the pressure drops in your system. There will be 15 pipe and piping components, inline equipment such as flame arresters and inline instrumentation. Let us say P1 is the pressure drop for your tank 1 vent line, P15 is the pressure drop in the common manifold, P_equip the pressure drop for the in-line equipment and Pi_nst the pressure drop for the in-line instruments. Then

 

P1 + P15 + P_equip + Pi_nst = 'Tank backpressure'

 

This calculated backpressure should be less than the design pressure of your tank for the selected vapor piping size. If it is not, increase the vapor line size and / or the manifold size and re-check. Keep on repeating this exercise till the calculated BP is less than the tank design pressure.

 

5..If the True Vapor Pressure (TVP) of your products is very low, then the possibility that the flow might not be adequate to operate the VRU or incinerator or flare. In such  a case a blower or fan may be required to be installed at the inlet of the VRU / incinerator which will suck the vapors from the tanks subjecting the tanks and vapor piping to vacuum. You need to check whether your tanks are also designed for vacuum.

 

The aforementioned are some overall guidelines for design of VRUs. Some well know international companies in Oil & Gas / Refining / Petrochemicals have developed standards for Vapor Recovery units which include vapor recovery from tank farm installations. Try to find them out.

 

Hope this helps.

 

Regards,

Ankur. 

Edited by ankur2061, 26 February 2014 - 07:53 AM.

[Art Montemayor]

I’ve modified a group of storage tanks for controlled vapor emissions in the past, so I’ll give you my idea of how I would go about doing what you propose.  My tanks were for finished product, not raw material; however, it shouldn’t make a difference.

 

Firstly, I don’t understand why you give us the density at 25 oC when the material is at 80 ^oC.  What is the purpose of this?

 

14 tanks is a lot of tanks and the finished modification is not going to be very pretty.  I have to make a series of assumptions because of your failure to furnish the detailed basic data:

• All the material in the tanks is the same in composition and temperature;
• The material will not polymerize or react in the tanks or vapor space;
• Each tank will have redundant maximum and minimum level controls and alarms.
• Each tank will be liquid-independent of the others – i.e., the tanks will not be connected to each other through their liquid contents.  Only the vapor spaces will be connected and equalized.

Refer to the attached workbook for the tank arrangement.

 Storage Tank Emission Controls.xlsx   12.87KB   159 downloads

[aqdal]

Thank you All for the detailed step by step guidelines.

Ankur, my question is related to your point number 4. (pressure drop vent piping system).   Tanks Drawings.pdf   156.22KB   62 downloads

 

I have an existing tank of chlorinated hydrocarbons, which has an split range control system with N2 sypply same as shared by the by Montemayor with additional protection of PVRV and Hatch.

 

immediate vent line is of 20" that connects with a glycol condenser, and vapor line from condenser i.e.of 3" on pressure controller goes to a blower which then sends to the incinerator system.

Now i am installing another tank in parallel as standby tank, considering that, above tank does not remain in operation and glycol remain isolated in the HEX. I have to utilize the existing blower for both the tanks (considering only one tank will remain in operation). Tie-in is are required. I was wondering for the pressure drop as the existing immediate line is of 20" and i cannot connect both tanks 20" header at height of 10m.
For new tank, I don't have Condenser/cooler and blower,
Detailed drawing has been attached, if any document/standad guideline is with you, appreciate if you could share.

 

 

[Art Montemayor]

AQ:

 

Do not be surprised if Ankur doesn't respond.

 

It has been 7 months since this thread was started -- and you are not the Original Poster (OP).  Ankur may not be looking for this post any longer.

You should always start your own, specific thread and not jump in on another member's thread with your topic.  This sky jacking someone else's thread for your own purpose.

 

It is much more efficient and easier to accommodate your needs and requests if you start your own specific thread with your own specific topic.  That way we don't confuse the responses with the different topics.  Please start your own thread; that will make life easier for all of us.

[aqdal]

Art M:

 

 

Ok, thanks,  I got it.