Development of HF Alkylation Unit Water Spray Mitigation Auto-Start Technology

摘要

A dispersion modeling and wind tunnel analysis was conducted to develop a system that would automatically initiate a water spray mitigation system for HF alkylation units at two oil refineries. Dispersion modeling was used to determine the importance of the response time of the mitigation system. Modeling was then used to define release scenarios that could result in a significant offsite consequence. This modeling defined an assumed rupture size or release rate that could result in significant offsite consequences for which the mitigation system should be automatically started. The next step was to locate HF detectors within the unit. The detectors needed to be capable of identifying a wide range of releases and needed to be placed to insure that no significant release could pass between them. The siting of the detectors was done using boundary layer wind tunnel modeling for each alkylation unit. The detector siting accounted for site specific, near field dispersion within the process unit. It was found that the presence of the process unit had a very profound effect on cloud dispersion near the point of release. The boundary layer wind tunnel data were also used to determine how many detectors would experience elevated concentrations for the release of concern. Using this information, a logic system was developed to detect and distinguish the presence of a significant release. This information was programmed into the process logic controller (PLC) on the unit to control the mitigation system. As part of the logic system, a wind persistence algorithm was developed to determine which portions of the water spray system should be activated. The development of this system has allowed for the water spray mitigation system to be used in an optimum manner with a minimum amount of intervention from the unit operators.