Hydrocarbons evaporation reduction
Hydrocarbons evaporation reduction
(OP)
Dear all,
I have sometimes heard that increasing the storage pressure of a tank containing hydrocarbons (i.e with inert blanketing) can help to reduce emissions but I don't understand it.
As far as I know, a liquid contained in a tank will evaporate until the partial pressure of that component in the vapor space above reaches its vapor pressure. If it is so, in my understanding, the mass of hydrocarbon vapor in the vapor space doesn't depend on the storage presuure, therefore the mass of hydrocarbon vapors which are expelled to the atmosphere whenever there is an increase in liquid level is the same.
Is my understanding correct? Increasing the storage pressure of a hydrocarbon can reduce the amount of hydrocarbon vapor in the vapor space?
Thank you for your help.
I have sometimes heard that increasing the storage pressure of a tank containing hydrocarbons (i.e with inert blanketing) can help to reduce emissions but I don't understand it.
As far as I know, a liquid contained in a tank will evaporate until the partial pressure of that component in the vapor space above reaches its vapor pressure. If it is so, in my understanding, the mass of hydrocarbon vapor in the vapor space doesn't depend on the storage presuure, therefore the mass of hydrocarbon vapors which are expelled to the atmosphere whenever there is an increase in liquid level is the same.
Is my understanding correct? Increasing the storage pressure of a hydrocarbon can reduce the amount of hydrocarbon vapor in the vapor space?
Thank you for your help.





RE: Hydrocarbons evaporation reduction
Now, without detailed compositions and pressure, there maybe a point where you can add N2 and vent it as needed and vent the dissolved N2 from the liquid later and have a net zero change to emissions. My recommendations is to recovery the HC' vapors when you vent them to lower your emissions. Charcoal, refrigerations, compressions, incineration,......
RE: Hydrocarbons evaporation reduction
There are a couple of things I am afraid I don't understand very well:
- You mention that the liqid phase will be 5% N2. Does it mean that some nitrogen can become liquid or what you mean is that it is dissolved in the HC liquid?
- In your example at 1000 psi in the equilibrium there is 1% HC's. In my understanding, if the pressure was 500psi the HCs content would be 2% so when there was an increase in liquid level the amount of HCs expelled would be the same (the HC content, 2%, would be the double than in the case of 1000 psi storage but the total amount of gases expelled would be half that in the case of 1000 psi because of being at a lower pressure, so the amount of HCs would remain the same). Is it wrong?
- Finally, could you please explain a bit your last sentence "there maybe a point where you can add N2 and vent it as needed and vent the dissolved N2 from the liquid later and have a net zero change to emissions"? Do you mean that it is possible to achieve a zero emission of HCs through the venting?
Thank you
RE: Hydrocarbons evaporation reduction
I did some quick simulations of a mixed HC stream and N2. At 1000 psig, the HC stream was 11% N2 and the vapor stream was 98% N2. At 500 psig, the HC liquid was 65 N2 and the vapor stream was 97.5% N2.
putting N2 in the N2 will stop a large amount of HC's from venting on your site. When you move the liquid HC's and their pressure is reduced, then at that time HC's will also leave with the vented N2. I do not believe that the amount of lost HC's when you put N2 into the tank will be less than if you didn't put N2 in, when you include venting at your site and the site where the HC's are used assumeing they are used at low pressure (less than 15 psig).
RE: Hydrocarbons evaporation reduction
Finally, could you please tell me the software or documentation you usually use for this type of calculations?
Thank you
RE: Hydrocarbons evaporation reduction