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# Peak Thermal Tank Venting Of Water Tank

thermal api 2000 water tank

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### #1 kowalskidl

kowalskidl

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Posted 09 March 2016 - 07:14 PM

Trying to estimate the peak thermal out breathing flow rate for a 500 BBL produced water tank. API 2000 gives guidance of 300 SCFH (FP > 100F) & 500 SCFH (FP < 100F). Pretty sure the API 2000 was written assuming that these are petroleum products in the tank and as a result will produce vapors at a higher rate than water.  The air above the water will certainly expand as an ideal gas with the addition of heat from the sun's radiation and the ambient temperature.

We have tried to model the tank as a building and apply ASHRAE recommendations which account for Lat Long, Sun Angles, reflectively of the tank, etc, We have gotten to the point that we are predicting a tank outer skin temperature, but then don't have a solid way to predict the temperature of the air above the water, in the tank. If we assume the air in the tank rises to the temperature of the skin, then we are predicting max flow rates of 310 cubic feet per hour, in November in the morning. We are using the ideal gas equation to say that V2=T2/T1 * V1

Each hour the skin temperature increase a certain number of degrees F.  This is dT/dt.  using the previously stated ideal gas T to V relationship, we can determine dV/dt, which is essentially SCFH.

There are also approaches for predicting thermal expansion and vapor loss in the EPA's AP 42, however this approach can only predict total losses (mass) over a month (30 thermal cycles). This doesn't help determine the max instantaneous flow that would need to be handled by a combustor or out of a thief hatch.

Don't want to buy more combustors than needed, but don't want to pop a thief hatch either.

-Dave

Process / Mechanical Engineer

### #2 shantanuk100

shantanuk100

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Posted 19 March 2016 - 10:09 PM

Hello Dave,

1. I would suggest you use the following spreadsheet and find out the relevant outbreathing.

It is based on API 2000, 14th edition.

2. The API 2000 breathing also accounts for volatility of the fluid. So it is not always with petroleum products in mind, because the volatility of the liquid is all that matters. So it doesn't matter if it is a petroleum or non petroleum product since the breathing produced by both will be the same by accounting for their volatility and flash points.

3. So even though petroleum products might produce higher vapour rates, we can calculate the same for water by accounting for the vapor pressure of water, as in the spreadsheet. API gives sufficient calculations for this.

4. Also, the temperature of the vapour above water will be the same as the liquid water since the two, i.e the vapor above the water and the water, can be considered to be in equilibrium depending on the conditions. So, rather than take the vapor temperature as the tank skin temp, I would suggest considering it as the water temp due to its equilibrium with it.

Regards,

Shantanu Kallakuri

Edited by shantanuk100, 19 March 2016 - 10:18 PM.