Steady state computations have traditionally been used for liquid pipeline hydraulic design. The hydraulic behavior of multiproduct pipelines is more complex than single-product lines because the throughput varies with time as the different batches move through the system. Designing a multiproduct pipeline involves hydraulic simulation to ensure that the system can meet a specified time-average throughput for the design batch line-up. To calculate the time-averaged throughput, the hydraulic simulation determines the total time it takes to ship the complete design batch cycle and the methodology must account for the time-varying throughput of the pipeline. Two basic methods available to accomplish this are: the fully-transient method, and the simpler succession-of-steady-state method. A fully-transient model would rigorously solve the time-dependent equations of energy, mass and momentum conservation to determine operating capacity. A succession-of-steady-state (SSS) model is one where batches are moved through the system in small volume increments, and the steady-state capacity is calculated at each step. Fully-transient type software models are powerful, but expensive, complex and usually require lengthy simulation run times. An SSS spreadsheet model would not be used to evaluate transient phenomena, but is adequate for determination of nominal pipeline capacities. This paper discusses the development of a trans-thermal, SSS spreadsheet based model that was created as a design tool to determine pipeline capacity and evaluate the impact of design alternatives or changes.

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