14 replies to this topic

[Ankit_Kumar]

Hi there,

 

I need to measure flow of vapors generated during filling of a tanker at atm pressure. Liquid being used is Methanol. Flow, temperature and pressure of methanol is known.

Kindly guide which standard to be used for calculation of vapor flow???

[gegio1960]

not sure what you're exactly asking for... but maybe this document could help you

http://people.clarks...gn/stortank.pdf

good luck

[breizh]

Hi ,

Seems to be a displacement problem !

Probably a sketch will help .

Breizh

[Zauberberg]

As a reference, get a copy of API 2000 and there you can find all factors contributing to vapor flow generation such as: volume displacement (liquid inflow), storage ambient heat, heat from the loading pump and piping, etc. You can then see what applies to your case.

 

Look out for most recent version of API 2000. Here is the first revision: https://law.resource...i.2000.1998.pdf

[Ankit_Kumar]

Dear Zauberberg

 

Can we apply the atmposheric storage tank case to the atm tanker? 

[Ankit_Kumar]

Dear Breizh Gegio

 

Rough sketch is provided below.

I need to do line sizing from vapor hose to flame arrestor, PSV for flame arrestor, RO (to ensure N2 flow is enough to dilute LEL value of vapor) and flame arrestor. (2^nd pic is showing almost all these things)

 

The tankers are coming of different size but biggest tanker is 27 MT capacity. Appreciate if you can give answers of following questions:

 

How to calculate vapor flow?

As filling is done in an open tanker so pressure of vapor will be almost 0.5 bar (against 50 ⁰C)? Right?

PSV will be required or not? For flame arrestor usually it is provided (in case of chocking) but I don’t the criteria for need of PSV?

 

[Ankit_Kumar]

Guys, kindly reply

[shahid780812]

Dear Ankit,
I have few doubts about your scheme...
1. The tank vent is open without flame arrestor whereas the tanker vent is provided with flame arrestor, why so?
In my opinion, you can consider a vapor balancing line between tanker and storage tank to prevent losses of methanol vapors.
The balancing line shall be sized based on the maximum filling rate of liquid to either storgae tank or to tanker, whichever is higher.

[Ankit_Kumar]

I hv drawn simple sketch for the basic need otherwise there r many supply from the storage tank.

 

Appreciate if u can guide regarding vap generation calculation due to filling of tanker.

[Ankit_Kumar]

Can anyone tell me for vapor flow out from the tank, do i need to calculate Normal Outbreathing (by reffering API 2000) or just vapor generation due to volatile liquid will be enough? 

 

As per API-2000 7th Edition, Annex A (A.3.2.3)

 

"For typical petroleum fluids, a liquid having a flash point less than 37.8 °C (100 °F) may be considered volatile. In the absence of flash point characteristics, the atmospheric boiling point may be used. 

For typical petroleum fluids, the vapor generation rate may be estimated as 0.5 % of the incoming liquid."

 

Kindly advice vapor generation by using this criteria is enough or i need to do complete calculations for Normal Out Breathing?

[fallah]

Anit_Kumar,

 

To calculate outbreathing rate, you should consider summation of outbreathing due to liquid movement (here tank filling rate) and outbreathing due to vapor movement by expansion and liquid vaporization as a result of weather changes...

[breizh]

Ankit_Kumar ,

 

Consider the scanned document attached to understand the philosophy about outbreathing .

 

Breizh

Edited by breizh, 18 October 2015 - 05:06 AM.

[gegio1960]

Anit_Kumar,

I didn't provide you with more details because I have no direct experience with methanol.

If it can help, I can mention the rules used for gasoline/naphtha loading/unloading that I've read in a very recent basic design package for a VRU (vapor recovery unit).

They used a vapor flow 25% higher than the max volumetric filling rate and a max hydrocarbon concentration of 40%.

These two figures were supported/justified by the rules of a specific international code, not API, that, unfortunately, I don't remember exactly.

Good luck!

[Ankit_Kumar]

to calculate vapor flow generated during filling of liquid methanol in the tank. For this I refer, Annex A of API-2000 7^th Edition.

In continuation of below mail, please find calculations for your review, if possible.

 

As per Annex A, for a liquid flash point < 38 ⁰C, Normal Out-breathing for liq movement in will be 2.02 from table.

 

As its units are 2.02 Nm3/hr of air per m3/hr of liquid flow according to the table (top right side  of table), so liq. movement in this case will be

2.02 * 46.8 (filling rate) = 94.536 m3/hr of air

 

For thermal Effects, as per A.3 table, column 4, Thermal Inbreathing is 16.9 m3/hr

 

As for volatile liq. vapor generation rate may be considered to be estimated as 0.5% of incoming liquid.

So 0.5 % of 46.8 m3/hr = 0.234 Nm3/ hr of CH3OH (Kindly check the units)

= 0.234/1.5 (For 1.5 BASIS, it is written in API 2000 A.3.2.3)

= 0.156 Nm3/hr of Air

 

Btw Total Out-breathing will be = 96.9 + 16.9 + 0.156 = 113.956 Nm3/hr of Air

= 1.5 * 114 = 171 Nm3/hr of CH3OH

[Ankit_Kumar]

I have calculated vapor generated from the filling of tanker. Now the issue is I have calculated that a line of 2" 40 SCH will be required for this vapor flow. So vapor at u/s of pipe is 196 m3/hr (171 Nm3/hr) 50 C and 1.05 bar.a (vapors are at slightly above atm pressure) (Kindly confirm if it is right to assume 1.05 value or something else should be taken)

When i calculate lenght of the pipe for specs of flame arrestor, it is only 0.03 meter which seems either there is something wrong with my calculations or it is practically impossible to have such system.

Calculations are as below

 

Flow of vap at u/s pipe = 196 m3/hr

Temp. at u/s = 50 ⁰C

Pressure at u/s = 1.05 kg/cm2.a

 

Now for gases, pipe dia was calculated by using following website with a velocity 15-25 m/s for gases. Hence 2” dia of 40 SCH was most appropriate.

From this calculation, for a flow of 196 m3/hr

Dia of 2” 40 SCH line = 52.5 mm = 0.0525 mm

Velocity of fluid = 22 m/s

 

For length of pipe, following formula is applied

L    =

∆P 2 D_in

f ρ V^2

 

 

 

here,

∆P = 0.04

D_in  = 0.0525 m

V = 22 m/sec

ρ = 0.77 kg/cm3 (vap density of methanol at 50 C) http://www.engineeri...ies-d_1209.html

Viscosity = 104 cP 

 

It is requested to kindly advice after reviewing the calculations and suggest some alternatives if flame arrestor seems impossible.