As a result of recent industrial incidents, a petroleum company desired to ensure the effluent from all relief devices in toxic or flammable service were routed to flares and/or another safe locations. The client wanted to evaluate the adequacy of the existing flare systems with the effluent from the atmospheric relief valves included, mitigate all existing flare systems issues, estimate the cost associated with modified piping, and evaluate potential high-integrity protection systems (HIPS).
ioMosaic first sought to understand the relief systems requiring evaluation and then to establish appropriate project guidelines to ensure the design met applicable codes and standards. After ensuring the corporate standards and project guidelines were in agreement with current industry practice, a team of ioMosaic engineers collected the necessary information to evaluate the relief and flare system including photographing relief valve locations and field verifying relief device identification tags, equipment nameplates, and relief system piping. Additionally, piping isometrics to most conveniently route effluent from the relief devices to a flare system were developed.
Using the previously documented relief system design adequacy calculations, ioMosaic performed dispersion estimates using Process Safety Office® SuperChems™. The results of the dispersion estimates were used to categorize the atmospheric discharges based on risk.
The existing flare system calculations and documentation were reviewed for accuracy and for conservative assumptions. Where appropriate, ioMosaic performed more rigorous dynamic simulations to better understand the relief requirements including depressuring loads to the flare header, which resulted in reduced relief loads to the flare system. Along with reducing relief requirements through rigorous analysis, other mitigation options to alleviate concerns with previously documented potential deviations for the effluent handling system included: installation of different types of relief devices (replacing conventional valves with bellows devices for example), changing the set pressure of relief devices where appropriate, and modifying operating procedures to ensure appropriate pump line-ups were utilized thus limiting the effect of power failure contingencies.
The overpressure scenarios resulting in simultaneous discharge from more than one relief device were then reevaluated to include systems whose relief devices discharge to atmosphere. The flare system was evaluated first with the inclusion of the high risk atmospheric relief devices and then with all atmospheric relief devices.
Where flare system hydraulics proved to adversely impact the performance of relief devices, consideration was again given to modifying the relief device type and revising the relief requirements through more rigorous analysis. Additionally, candidates for HIPS installations were identified to eliminate severe relief loads from the flare system.
ioMosaic concluded that the existing flare systems could accommodate the relief from all atmospheric relief devices with the installation of HIPS to ensure safe shutdown of the heat medium supply to reboilers on three (3) column systems. Additionally, as the subheaders necessary to route some large atmospheric relief devices to the flare system were impractical to install, HIPS installations were also evaluated to reduce or eliminate the relief load on two (2) fractionation systems. ioMosaic provided a report to the client using Process Safety Enterprise® Emergency Relief System Design Workflow with our assessment, all documentation details, mitigation options, along with an Executive Summary section directed at a technical audience that is not a subject matter expert in relief devices. The detailed report also contained the list of all relief devices and the schematic drawings.