Project SynopsisPerform a flare header and flare system capacity evaluation study at a petrochemical manufacturing complex.
FLARE AND FLARE HEADER CAPACITY EVALUATION STUDY
Process Engineering Associates, LLC (PROCESS) was contracted to provide a Flare and Flare Header Capacity Evaluation Study for one of the client’s petrochemicals production facilities along the U.S. Gulf Coast. The purpose of this work was to develop credible global relieving scenarios and perform hydraulic analysis of the flare and flare header system under worst-case scenarios to help ensure that the systems are correctly designed to handle these relieving events in a safe and controlled manner.
PROCESS performed pressure relief device calculations for the client as part of a large (on-going) project to validate existing relief devices in service. An integral part of a correctly sized pressure relief system is an adequately sized flare header and flare. The client had requested PROCESS to provide a proposal to evaluate the adequacy of both their flare headers and flare stack given the fact that multiple changes to the process have been made over time which may have impacted point sources that feed into the flare header.
Project tasks included:
- Evaluation Basis Preparation that involved generating a tabular summary of the assumptions and data that were used in the subsequent project tasks. As part of this task, PROCESS generated a list of relief devices feeding into the flare header, as well as other information related to the flare, flare header, etc. This document was submitted to the client for review.
- Flare Loading Scenario Identification Analysis Report Preparation that involved preparing a report explaining which scenarios were explored and why the governing (worst-case) scenarios were selected. There were nine (9) scenarios. A report was created and provided to the client documenting the results. This report identified relief scenarios that could potentially cause hydraulic bottlenecking in the plant or liquid flare headers. These scenarios were carried forward in the study.
- Flare Header Blower sizing involved sizing a liquid knockout drum and blower to handle the worst-case relieving scenario and limit the header pressure to six (6) inches WC in order to help ensure the proper operation of the relief devices which discharge into the header. Also, blower controls and operation were presented.
This work builds on the results of PROCESS’ previous work. PROCESS utilized licensed computer process simulation software to model the portions of the flare systems involved in each of the relief scenarios identified. Each flare model started at the source of the flare load (e.g., relief valves, tank vents, dump valves, etc.) and extended to the flare tip. Isometric drawings provided by the client were used to construct the flare system models. Flow inputs to the models included existing relief loads and chemical compositions determined by PROCESS or others during previous PSV studies. After constructing each model and evaluating the anticipated back-pressures in the flare network, PROCESS identified and presented alternatives that could be utilized to help protect the affected pressure vessels which are determined to have excessive back pressure. These alternatives included:
- Modifications to the flare system
- Increasing the pressure rating of vessels
- Decreasing the set pressure of relief valves, increasing relief valve orifice sizes, or replacing conventional relief valves with bellows or pilot-operated valves
- Installing a blower in the relief header to limit the header pressure to an acceptable value.
A project report was submitted to the client that summarized the project methodology, conclusions, and recommendations. The notebook was organized by flare loading scenarios. The following tasks were required to complete the flare capacity evaluation:
- Review Flare System Information that involved PROCESS reviewing the information collected and developed for the project. This information included P&IDs, PFDs, plot plans, isometric drawings, additional mass and energy balance information (including detailed stream compositions), and equipment and flare design information.
- Simulation Model Development for the Facility Flare System that involved PROCESS building and testing the basic flare system model using licensed commercial process simulation software. PROCESS was able to draw from its experience in performing other flare header studies to help expedite the task.
- Perform Process Simulations of Flare System Loading Scenarios which involved PROCESS executing the flare system loading simulation for all scenarios identified in the scope of work. PROCESS also pinpointed bottlenecks to the flare system as appropriate and identified recommendations to eliminate the bottleneck or otherwise protect the affected pressure vessels.
- Flare System Study Report Preparation involved preparing a report summarizing the findings for the Project. The report included sections for each scenario with design basis, simulation outputs, and recommended flare system modifications as appropriate.
- Petrochemicals Processing
- Flare system analysis
- Process simulation
- Pressure relief device evaluation and sizing
- Process design