Guidelines Will Enable Determination of Unknown Loss in Refineries and Terminals Promoting Closure of Mass/Volume Balances

By Srini Sivaraman

Refineries and terminals undertake mass (volume) balances every month. After accounting for all known losses, adjustments for bias errors, and other known procedural errors, they report a net loss under the name of “Unknown” loss or “Unaccounted for” loss, as the net loss could no longer be explained. This Unknown loss is no longer a mystery.

The concepts summarized herein provide a tool and a methodology to account for most of the currently reported Unknown loss in most locations. This would enable the local management to bring a closure (or almost a closure) to their monthly mass (volume) balances.

In essence, the concept calls for the use of a systematic error component of a measuring device to explain the unknown loss, while the random errors in themselves will be used for total System Capability determination. This is a deviation from the conventional approach of combining both random and systematic errors.

Inclusion of systematic errors with the random components (that has been the industry practice thus far) has masked the impact of the systematic component in the net loss or gain. This phenomenon could aptly be classified as the Systematic Syndrome (SS) factor, resulting in a net unknown loss or gain.

The Systematic Syndrome (SS) factor of the measurement systems thus identified should be used as a reconciliation of monthly net loss or gain. In theory, once this concept is applied properly, and all other measurement systems carry just residual errors, with physical losses fully accounted, for a system free from bias errors, refineries and terminals alike should be able to close their books to near zero balance every month.