HF Alkylation Rapid Acid Transfer System (RATS)
Chief tasks in execution of this project included:
- Development of a dynamic process model that included piping hydraulics for the existing HF Alkylation Unit and support systems.
- Evaluation of different HF leak scenarios and operating modes using the dynamic model to define required pipe sizes and operating issues.
- Preparation of P&ID and Cause & Effect Matrix for project, including interfacing with existing piping and instrumentation systems.
- Evaluation of required system and valve testing and integration with existing flushing systems.
- Evaluation of potential failure modes and determination of best backup system for valves.
The RATS was required as a result of an updated Quantitative Risk Analysis (QRA) for the site that showed potential offsite impact from a leak of HF from the unit. With a rapidly approaching turnaround, the client wanted the process design performed quickly so that tie-in points could be identified and detailed engineering performed for the tie-ins as needed. A dynamic process model using HYSYS was build and this model used to determine the time for transfer of acid from the reactor system to the acid storage drum, and whether this time was less than that needed by the QRA.
Multiple scenarios were evaluated with the model to determine the impact on leak location on transfer time, as well as the impact of other operational considerations (i.e. storage drum pressure) on transfer time. The model was also used to estimate the quantity of acid that would be vented through the acid relief neutralizer (ARN) during a transfer, and the required caustic strength and circulation rate in the ARN to ensure complete neutralization of acid.
A full process design specification was generated, including P&ID markups, C&E Matrix, and testing guidelines for the system. An evaluation was performed and the hydraulic model used to identify impact on acid transfer time for various valve failure scenarios, and a review with plant personnel conducted to identify potential backup actuation for the valves. A backup nitrogen system was eventually selected for use in operating critical valves during RATS activation in the event of a plant air failure.
The process design was completed on schedule and used as the basis for detailed engineering of the required tie-ins so that they could be installed during the upcoming turnaround. Full installation of the system is planned for the next turnaround, with Norton Engineering anticipating to provide procedure reviews, Operator Training, and startup support.