When transporting multiple products in a pipeline, it is important to always know the location of the head and tail of each batch. The operator, informed on where batch interfaces are in real-time, will be ready to swing the valve at the exact time a batch arrives at a station to deliver product to the right storage tank or an end-customer with minimal contamination. The commercial department can use the accurate visual display of batch locations to optimize sales revenues.
It is relatively easy to track multiple batches in a pipeline with no elevation changes, and a fixed internal diameter. However, it is far more complex to track multiple batches in a pipeline with drastic elevation changes and many different sizes in diameter. When the pipeline operational pressure, temperature, or both, drop below the liquid critical point in a specific area of the pipeline the liquid can gasify causing vapor pockets. This changes the volume of liquid within the pipeline segment, moving the physical position of the batch head and tail interfaces, and reducing the accuracy of the corresponding Estimated Times of Arrival at stations. Draining or filling a pipeline section by delivering product at a higher rate than what is injected, or vice-versa causes the same effect.
A scientific approach calculates the areas of slack and volume contained within a pipeline and provides sufficient information to track batches with a high degree of accuracy. However, it is neither simple nor straightforward to simulate this phenomenon offline, and it is much more challenging in an online, real-time environment. Online, additional complexities can affect how batches and their interfaces are tracked, causing a big discrepancy between Estimated and Actual Time of Arrivals.
Atmos International this year successfully implemented a batch tracking system using an empirical approach to calculate the volume contained within a pipeline segment by tracking the volume entering and leaving that segment. Estimated and Actual Times of Arrival are within a 15-minute time window after a batch traveled over 1,000km in a pipeline with drastic elevation changes along its route.
This method has proven that batch tracking can be highly accurate and reliable with less of the theoretical assumptions used in a hydraulic simulation package, with no need to model every single characteristic of the pipeline in detail. This technique removed the uncertainties that attend those assumptions and allowed this system to perform well on a pipeline with severe slack flow and draining/filling operations.