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Vapor Emissions

Tuesday, April 24, 2018   By: Dunedin [1843] 1 Stars
Does anyone know the amount of emission of hydrocarbon vapor from above ground vertical storage tanks operating at ambient temperature and atmospheric pressure that is permitted by local or international requirements.

I know that this is a very complicated and controversial issue but surely somewhere the limits are defined in terms that most of us would understand and hopefully comply with?

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Friday, April 27, 2018   By: DavidR@Fast.net [39] 5 Stars
The limits are set by the local environmental protection or air quality agency that has jurisdiction in the area the tank is in, often guided by the rules set down by larger entities Province, State, Federal etc . There is no one size fits all. A single tank in the middle of nowhere has different limits that a tank in the middle of a big city. If the air quality of the area where the tank is is terrible, the tanks limits may be lower, etc. The limits are often set for the overall facility that the tank is in. One tanks contribution to the overall emissions profile of the facility is fairly easy to estimate although the tools available are generally more accurate as the number of tanks increases and the period of time increases. Regulatory limits are one factor. Safety and operational issues also affect the control systems used of a tank or tank farm. In some situations you can buy or trade emissions so a particular tank can have lower control effectiveness than one might expect.

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Saturday, April 28, 2018   By: Dunedin [1843] 1 Stars
Thanks for the response. However can you explain how we measure the emissions and what are the UNITS of Measurement so that we can compare it to the required emission level for a like for like tank in like for like circumstances?

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Saturday, April 28, 2018   By: DavidR@Fast.net [39] 5 Stars
The units of measure are ultimately pounds per year. Typically int he USA and in many other countries, emissions are not measured although they can be but they are estimated using methods developed in the USA 20 years ago by the API end EPA Google AP-42 and you can read up on it. This is not the only method but it is used a lot.

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Saturday, April 28, 2018   By: DavidR@Fast.net [39] 5 Stars
You know, I really get tired of this forum eliminating punctuation, parenthesis, line breaks, etc and making my posts read like an 8-year old wrote them. Just sayin...

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Sunday, April 29, 2018   By: Dunedin [1843] 1 Stars
David Thanks, I have now had a look at this AP42 it is far from straight forward and, I doubt even possible, to determine the emissions from any specific tank and find out it it meets the requirements - whatever they may be!

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Sunday, April 29, 2018   By: DavidR@Fast.net [39] 5 Stars
Its not really that bad. Just knowing the details of the tank and product, then entering a bunch of loss factors lengths and other data. To make it easier the EPA wrote a program called Tanks4 - google is your friend again - but beware that it has not been updated and there are some errors and deficiencies that may or may not apply to your situation. See the white papers on the tanks4 web site.

There are other - not free - programs out there that have been written to keep up to date and make it easier for owners of multiple tanks and situations, again google will find them for you.

Do not despair !!

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Monday, April 30, 2018   By: ITS [1678] 4 Stars
Hello David and Dunedin,

I attached the AP-42 pdf Chapter 7 for Aboveground Storage Tanks. Hope this helps.


Click on picture for full size view or to view PDF!

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Tuesday, May 01, 2018   By: BABRTs 973 [53] 5 Stars
Unless you are a environmental engineer or something of that ilk or are the designated inmate, you really need to go out and have this done for you. There are companies who will take you tanks and based on product, gravity, TRVP, H2S roof vapor prevention appurtenances, location, tank setting cleaning and other things I am just beginning to find out will determine your pounds per year the tank emits.
This is then judged against the operating permit which in Texas is PBR and then Title V. I am presently working for a company who due to permit expiration will fall into Title V. I am having to inventory all the owned tanks in the area for roof accessories on the roof which will allow emissions. These are primary and secondary seals slotted gauge poles roof legs gauge wells hatches gauge hatches ladder boxes on IFRs seals there is a whole list of items that are taken into consideration.
What is interesting after primary and secondary seals the highest emitter is the gauge pole. And a simple gauge pole sleeve fitted around the gauge pole and liquid mounted eliminates at huge percentage of emissions. The floats everyone sells is only a marginal improvement. And these floats are a operational nightmare. The gauge pole covers offer some improvement but you need to run the modeling with and without the cover before spending the money for these. We found the gauge pole sleeves themselves lowered the numbers to a point where the covers were not necessary.
HMT has a EnviroSleeve that is probable one of the best alternatives to the cover and includes the gauge pole sleeve. But they build these in the Netherlands and has a long lead time. It is quite disappointing them having this, promoting it then finding out how ling it takes to get them.
If you will be attending ILTA and need a excuse to go Rob Ferry will be presenting there. This guy KNOWS tanks and tank emissions. I would highly recommend his classes or one of his seminars as he will lead you down the right path.

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Wednesday, May 02, 2018   By: Dunedin [1843] 1 Stars
Interesting to read your comments. It still seems to me that there are too many variables to be used in any calculation that the result is seriously wrong. Even taking the readings five minutes could effect the emissions ambient temperature or wind speed, not to mention any variance in the surface area of the tank shell at different levels affects seals and clingage. I am inclined to the view that common senses is still the best guide.

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Wednesday, May 02, 2018   By: BABRTs 973 [53] 5 Stars
That goes out the window with emissions.
You take the API numbers and plug them into your model and it gives a pounds of emissions number. Seems EPA buys off on it. You just better have the controls on the tank you say you do. And document you inspect them on a regular basis usually one year or 12 calendar months.
Job security

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Thursday, May 03, 2018   By: DavidR@Fast.net [39] 5 Stars
My opinion - advertising is best left out of engineering discussions. Gauge pole sleeves are easily added to sliding covers / well gaskets / pole wipers to reduce slotted gauge pole emissions, many companies make them but may not have fancy names for them. Almost any shop with a box and pan break can make them. I have worked on gauge poles with double sleeves double wipers and covers. Many owners recognize that the AP-42 / Tanks4 model is limited and feel strongly that for instance, full-contact floating roofs are logically better than non-contact even though the US EPA numbers dont distinguish between them. Emissions is exactly as you stated - an inventory. You count your sources and apply a factor to estimate each, then justify the calculation to a regulator. I think industry is obligated to do at least that much, to protect my family from extra air pollution and I think the money is well spent. My opinions only, of course.

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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