One of the biggest challenges for any site that uses tanks – including those in the Oil & Gas industry and chemical manufacturing – has been that the long-standing industry standard tool, EPA TANKS 4.09D, turned out to be not that reliable after all. The EPA is no longer supporting the further development of TANKS and some state agencies are rejecting hot and heated tank emission estimations made using the tool, since it was found to underestimate those types of emissions.
It was discovered that TANKS 4.09D is incapable of accurately estimating emissions from hot and heated tanks. Although the tool works well for many other operating scenarios and tank types, any business using tanks to store heated products that will slowly cool down and/or that uses tanks to keep a product at a certain temperature must find an alternate means of tracking and reporting air emissions from tanks.
Recently, at a petrochemical industry conference, the Texas Commission on Environmental Quality (TCEQ) clarified some guidelines regarding hot and heated tanks to help smooth the transition away from TANKS 4.09D. They provided some simple best practices that should be followed when reporting emissions from hot and heated tanks for your emissions inventory reporting. We’ll list them out below and explain them in a bit more detail.
It’s also worth noting that the TCEQ is known for its stringent approach to emission reports, so it’s often the case that by following TCEQ recommendations you’ll be more than meeting the minimum requirement for your own state regulator. However, always check with your own regulatory bodies about the exact requirements for air emission determinations in your region.
Follow the Gold Standard
First and foremost, the most important rule is to follow the AP-42 Chapter 7 guidelines for hot and heated tanks. TANKS 4.09D is unable to follow the AP-42 calculations fully, which is why is has been disqualified by some state regulatory agencies... TANKS uses average temperature values, which results in underestimated emissions in regions where temperatures fluctuate widely throughout the year.
AP-42 is the gold standard for tank emissions. No matter what the situation, there are AP-42 emission calculations that can be applied. AP-42 Chapter 7 outlines the base equation for estimating emissions from hot and heated tanks - in total there are over 30 different calculations in the document.
The general rule is that hot & heated tanks remain at a stable temperature and so there should be little to no breathing losses taking place. Primarily, hot/heated tanks generate working losses. A well-insulated tank will produce little breathing losses, though a poorly-insulated tank will produce more breathing losses.
However, TCEQ research suggests hot and heated tanks all emit some amount of breathing losses. We’ll cover this concern in an upcoming article.
AP-42 equations are not necessarily the most complex an EH&S manager will encounter in their careers, but the AP-42 Chapter 7 procedure does require meticulously accurate record keeping and can become quite time consuming when performed manually for numerous tanks.
Use Vapor Pressure Based on Real-World Storage Temperature in Your Tank
Determining the True Vapor Pressure (TVP) of any material in a hot or heated tank can be a challenge, but it is imperative that you use only accurate TVP values when performing AP-42 calculations.
That’s no small feat for some materials, like asphalt, for which the complete chemical composition of each batch of the material can’t ever be fully known. Nonetheless, the TCEQ directs all petrochemical manufacturers to use the best available methodology to determine an accurate TVP value based on the temperature of the product in the tank.
ERA has written about the topics of True Vapor Pressure and partial speciation (determining emissions from a chemical with partially unknown chemical components) elsewhere on this blog (click the links to read the full articles), so we’ll just provide a recap of the best practices here:
- The best practice is to go straight to the source and get TVP data from your supplier. Obviously this isn’t always possible, but getting a TVP value from your supplier can save a lot of time and effort.
- If your supplier can’t provide TVP data, the next step is to use either the Riedel or Antoine factors combined with known product chemical data.
Using American Society for Testing and Materials Method for TVP
TCEQ has also advised reporters that for heavy liquids in storage tanks it is possible to use the American Society for Testing and Materials (ASTM) method D2879. This methodology can be used to determine TVP for heavy liquids stored at a particular temperature.
ATSM also provides other methodologies for determining TVP based on material type (i.e. crude oils, petroleum products, pure liquids, etc.).
Like other resources, there is a small price to purchase access to the ASTM’s intellectual property. You can find the resources for D2879 (and others methods) online here: http://www.astm.org/Standards/D2879.htm.
Do Not Use AP-42 Default Values
The TCEQ has also urged reporters not to use the AP-42 default values for vapor pressure or liquid composition unless you’ve done the calculations to verify they accurately represent the materials in your tanks.This is not to say that AP-42 default values are not accurate or acceptable in some cases, but determining chemical properties for your specific case will result in more accurate results.
And finally, ERA would like to add our own fifth step for achieving flawless hot & heated storage tank emission estimations.
Stop Using Spreadsheets for Tank Emission Determinations
This goes for using spreadsheets to store your tank parameter data & chemical data and for using spreadsheet formulas to perform tank emission calculations.
Since EPA TANKS 4.09D is no longer viable for hot & heated tanks, many manufacturers are striking out on their own and using spreadsheet calculations to try to replace the EPA tool. However, spreadsheets, even when built by the pros, don’t have the capacity or intelligence to be a sustainable tool choice.
There are numerous other reliable tools that are specifically designed to handle hot & heated tank calculations. The key is to find tanks emissions software that offers functionality for all your types of tanks and processes rather than just focusing on one type of material (i.e. crude oil) or one type of emission (i.e. flashing losses).
July 22, 2015