A common assumption when dealing with hot and heated tanks is that their insulation protects them from the ambient heat fluctuations occurring throughout the day. This often leads reporters to assume that hot and heated tanks generate zero breathing losses.
However, a heated tank with insulation can still generate breathing losses: if a tank is only semi-insulated (i.e. no insulated roof) some breathing losses may occur. There is also the possibility for a fully insulated tank to generate standing emissions through the tank’s heating cycle.
Both of these possibilities should be accounted for in your emissions reports for any petrochemical liquid storage tanks used to heat materials or store heated products.
This short article will lay out a basic methodology for estimating insulated tank emissions.
At the moment there’s not a standardized guide for insulated tank breathing losses, but our own environmental scientists have developed a straightforward methodology for semi-insulated tanks we’re sharing here today. The Texas Commission on Environmental Quality (TCEQ) have also presented a methodology for estimating emissions from fully-insulated heated tanks.
Below we'll explore how to estimate emissions from insulated and semi-insulated tanks... if you want to learn more, download your free copy of the Hot and Heated tank Guidebook here.
Some hot and heated tanks are insulated well enough to maintain an internal temperature but may have an uninsulated roof. Or the tank may be poorly-insulated overall. In these cases, ERA applies this standard methodology:
If the ambient temperature is lower than the tank’s liquid storage temperature then there would be no breathing losses generated. Use the tank temperature for working loss estimations.
If the ambient temperature is higher than the tank’s liquid storage temperature then account for the difference in temperatures using the following calculations:
- Tmax = max(Tmax-amb, Ttank)
- Tmin = max(Tmin-amb, Ttank)
The TCEQ has recommended instructions for estimating breathing losses for fully-insulated tanks.
These breathing losses are the result of the tank’s heating cycles. TCEQ uses the heating cycle’s temperature range, frequency, and duration.
Using these variables, you can modify the basic AP-42 emission calculations for breathing losses following this TCEQ methodology:
- Replace 365 days with the number of heating cycles.
- Replace daily temperature range with the temperature range of the stored liquid.
It's worth noting that these modifications assume that all heating cycles will be uniform - it means your final emission estimation will be skewed based on the difference between your real world heating cycles and the assumed average. It's possible to use a better system that individually tracks the heating cycles and uses this more accurate data instead of averaging.
Dealing with Tank Regulation Uncertainty
Tank emission management and reporting is an evolving practice for Oil & Gas professionals: new tools are being rolled out, new emission standards are getting tested, and state regulatory agencies are always conducting studies on potential new emission sources.
Insulated tank emissions are a reality, but the exact methodology is still in development. In the meantime, reporters are being asked to put their best efforts into determining insulated tank emissions.
The only 100% reliable method of keeping up with upcoming and uncertain regulatory requirements is to get back to the basics: focus on getting solid data about your materials and keep good records about your throughput and heating cycles. That way you’ll have the data you’ll need for any type of calculations being asked of you.
ERA has prepared a free downloadable guide on tank emissions from hot and heated tanks that will be a useful resource and compliment to the information in this article. It outlines the essential methodology for hot and heated tank emissions, and delves into more advanced techniques for managing petroleum products like asphalt and crude oil.
July 28, 2015