Using Mass Balance as a Refinery KPI
Discussions about using mass balance as a measure of refinery loss control performance have been ongoing for many years. While in our view mass (or weight) is definitely a better measure of a refinery’s performance than volume (or liquid) balance, there are some important aspects that need to be taken into consideration.
Critical Aspects Of Using Mass Balance as a KPI
- Accuracy of underlying data: Mass (or weight) balance is not created by itself, it is being calculated from volumetric balance, using density conversion. It is therefore extremely important to make sure that all volume measurements that go into volumetric balance are correctly measured or calculated (if the measurement of a particular stream or volume is not possible). Many modern refinery accounting systems (like Honeywell, Aspen, and Haverly) are capable of automatically converting volume balance to mass. However, if the correctness of volume measurement is not verified, your mass balance will be grossly misleading.
- Density conversion: After the accuracy of volume, data is verified to a known degree, it is important to ensure that volume is converted to weight using correct product densities. We have seen cases where tank or stream densities were not updated in the systems for weeks or months, leading to a very distorted picture of mass balance, and, consequently, to wrong management decisions. Refinery operations, accounting, and lab must work hand in hand to develop a program, that will ensure that tank and stream densities are updated in the system on a frequent basis, especially towards the end of month closing.
- Out of system adjustments: While modern refinery IT systems are capable of capturing a vast amount of process data in real-time, there is still a lot of information, that is left out for different reasons – lack of measurement instrumentation, complex processes that cannot be directly measured, cost, refinery configuration, etc. Those include items such as sulfur extractions to sulfur plants, CO2 venting, hydrogen diffusion loss, tank evaporation loss, process sewer evaporation, etc. Refinery accounting should work closely with process engineers to identify those sources of material movements and losses and develop indirect ways of accounting for them – calculations or engineering estimations.
These steps may take significant effort and time to get developed, but they will ensure that the resulting mass balance KPI can be used to measure the refinery loss control efficiency and drive correct management decisions.
It is also important to remember that developing mass balance in itself does not lead to the reduction of refinery hydrocarbon losses. It is the continuous process of identifying unknown losses through the process of creating an accurate mass balance that will allow to eventually better control and minimize those losses.
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The author of this blog Anas Dabbakh is a Senior Consultant at Trindent Consulting.