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# Calculating Storage Tank Evaporation Losses

## Calculating Storage Tank Evaporation Losses

(OP)
Hi All,

I need to calculate evaporation losses for an non-insulated Naphtha storage tank in a climate where temperatures can be 35-40C throughout summer. Significant proportion of n-pentane and iso-pentane in the fuel. Would preferably like to use HYSYS for this, the current model I've done models steady state with inflow and outflow and the level in the tank makes no difference. I'd like to model a static tank with no in/out flow and get a vapour loss rate at different fill levels and ambient temps. Any ideas?

Thanks,
PR

The scientist describes what is; the engineer creates what never was.

### RE: Calculating Storage Tank Evaporation Losses

in most countries there are Environmental Laws which define emission limits etc.
you can simply adopt the described procedures,
also API, EPA etc. distribute free software and documents,
see for example
https://www3.epa.gov/ttnchie1/ap42/ch07/final/c07s...
not sure if you wish to create a complex model with hysys,
in most cases I am able to solve these problems in Excel (I use Prode Properties for vapor pressures and a few other properties, but most standards include tables etc. with the values to apply..).

### RE: Calculating Storage Tank Evaporation Losses

The tank vapor composition, at any given temperature, can be calculated by combining Roult's and Dalton's laws.

Yi = (Xi*Pi)/Ptot

That's very easy. The hard part is determining how much volume gets expelled from the tank due to in/out flow, and the atmospheric thermal effects on the tank. That requires making assumptions based on knowledge about the specific operation of that tank, and the set pressure of the vent device. Depending on the assumptions made, the resulting values can range from very low to very high vapor losses. For that reason, it's important to qualify your answers with the specific assumptions that were made to generate those answers.

As mentioned by apetri, governmental agencies enforce uniform methodologies (uniform set of assumptions) when these calculations are done for reporting/permitting purposes. For any given tank, that may result in a close approximation of the correct valve, or it may be way off the mark.

### RE: Calculating Storage Tank Evaporation Losses

If you are making the calculation yourself, I would think that solar loading is the factor that controls the amount of evaporation occurring when the tank is just sitting there with no flow in or out.

I would also look to the epa information to get a solid start on this.

Regards

StoneCold

### RE: Calculating Storage Tank Evaporation Losses

(OP)
Thanks folks. I've had a read at the EPA method and it looks like it will work for me.

FYI I'm not so interested in filling/offloading losses as the purpose of the calculation is whether or not to insulate the tank for cold conservation so solar radiation of static tank is what I'm most interested in.

Regards,
PR

The scientist describes what is; the engineer creates what never was.

### RE: Calculating Storage Tank Evaporation Losses

I do not know where in the States you are located, however, in my State you have to follow their own guideline which to my understanding is much stricter than the Feds EPA.

### RE: Calculating Storage Tank Evaporation Losses

(OP)
Chicopee,

I'm not based in the states, based in Europe. This is not an environmental issue, its a product loss issue.

Regards,
PR

The scientist describes what is; the engineer creates what never was.

### RE: Calculating Storage Tank Evaporation Losses

Then you have to contact the European jurisdiction because whatever you use for formulae your jurisdiction may have a different way of determining evaporation losses. In my State, we had a client who had developed an excellent program, however, it was rejected by our State environmental people.

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