Abstract
When dealing with transient conditions, standard process design approach may lead to poor equipment specification or even to a complete failure in evaluating the design reference conditions.
The three presented case-histories highlight the importance of dynamic process simulation as a design tool that allows both a targeted definition of the design conditions for equipment and an accurate prediction of the system behavior during transient operations thus enabling a predictive evaluation and validation of operating procedures. The three case-histories refer to different fields of application and to different levels of complexity, but in all the cases the power of the design approach based on dynamic simulation is demonstrated.
The first case-history is relevant to the design of instrumentation and relevant control scheme on a pump discharge. In a floating LNG regasification terminal, a small flow and high pressure pump used for header pressurization and vaporizers cooldown faced severe damage due to peak flow conditions during the initial phase of operation. Dynamic process simulation was used to design the flow orifice, the discharge maximum flow valve and to define the header’s pressurization procedure.
The second case-history is relevant to the behavior prediction of a complex compressor system during the start-up phase. A large propane compressor in a multilevel refrigeration cycle is currently operated with a steam condensing turbine allowing smooth start-up. The plant’s owner planned the turbine’s replacement with an electric motor, reducing the start-up ramp from several minutes to few seconds. Dynamic model, following a field data tuning phase, was used to evaluate the behavior of the compressor system during the sharp start- up ramp and to validate the Compressor’s vendor design for the control system.
The third case-history is relevant to the development of an innovative design approach. Following Techint’s design and construction experience in LNG regasification terminal, a rigorous dynamic model has been developed in order to study the behavior of the Boil Off Gas (BOG) handling system during transient operations (LNG unloading and LNG Carrier reloading). The model can be tuned on existing terminals and used in identifying the real system bottlenecks during revamp studies as well as to optimize transient operation management. As a design tool, the model can be used in the future to optimize the BOG system design.
