API TR 2568

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This Technical Report provides guidance for estimating emissions that result from removing the liquid heel (free-standing stock liquid) and cleaning the remaining deposits of stock liquid mixed with residue and water (sludge) from the bottoms of aboveground storage tanks.

The emissions addressed in this report are those that leave the tank during the tank cleaning process. This report does not address:

• the fate of vapors after they have left the tank (other than accounting for the efficiency of a control device),
• the fate of sludge after it has left the tank (or emissions that may occur during sludge treatment or disposal), or
• emissions that may be expelled by the vacuum pump of a vacuum truck or suction pump, if such devices are used in the tank cleaning process.

In other words, this report addresses the estimation of the mass of volatile organic compounds that leave the tank as vapor during the tank cleaning process. It does not address emissions that may result from the handling of liquids or sludge after such materials have been removed from the tank. Tank cleaning is a non-routine event for which there are presently no emission factors. While a given tank may be cleaned only once every 10 to 20 years, regulations may require reporting the resulting emissions when this does occur. Furthermore, petroleum industry facilities may be required to estimate emissions from all sources within their plant sites. Gven these requirements to report emissions, there is a need for guidance on how to estimate them.

Emission factors have been developed for most of the routine sources of emissions from petroleum-related facilities, but little guidance has been available for estimating emissions from non-routine sources. When non-routine events occur, companies often expend a significant effort in preparing a good faith estimate of the resulting emissions. In the absence of any industry-wide practice or guidance, however, these estimates may vary widely.

This report is intended to reduce the effort required to generate a good faith estimate of tank cleaning emissions, and to result in more uniformity in the resulting emission estimates.