15-05-2025

Using mass balance as a refinery KPI: Why accuracy matters

The use of mass balance as a measure of refinery loss control performance has been debated for years. While mass (or weight) is generally a better indicator of performance than volume (or liquid) balance, its effectiveness as a KPI depends on a few critical considerations.

Key Considerations When Using Mass Balance

- Accuracy of Underlying Data: Mass balance is derived from volumetric data using density conversions. Therefore, it is essential that all volume measurements—whether directly measured or estimated—are accurate. Many modern refinery accounting systems (such as Honeywell, Aspen, or Haverly) automate this conversion, but if the base volume data is inaccurate, the resulting mass balance will be unreliable.

- Correct Density Conversion: Once volume accuracy is verified, the next crucial step is converting it using correct and current product densities. In some cases, densities have not been updated for weeks or months, distorting the mass balance and potentially leading to incorrect management decisions. This requires coordination between operations, accounting, and laboratory teams to ensure density data is regularly updated, particularly during month-end closing.

- Adjustments Outside the System: Despite the capabilities of modern refinery IT systems, some material movements and losses are not directly captured—such as sulfur extraction, CO₂ venting, hydrogen diffusion, and evaporation losses. Refinery accounting must work closely with process engineers to identify and indirectly account for these elements through estimations or calculations.

Developing a reliable mass balance KPI takes effort, but it is essential for accurately measuring refinery loss control efficiency. However, it's important to note that mass balance alone doesn't reduce hydrocarbon losses—the real value lies in the process of refining its accuracy to identify and manage unknown losses more effectively.

An accurate mass balance is a foundational step in optimizing refinery performance—and one that directly supports broader margin improvement initiatives.

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