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Pressure Relieving System Design
The Flare is a major part of the pressure relieving system for hydrocarbon processing plants. For most plants it is the last line of defense against potential hazards. Flare design should include thermal radiation limits, explosion hazards, liquid carryover, noise, temperature limits, and ground level concentrations of combustion products.
In Hydrocarbon Service there has been several flare line ruptures, therefore it is something each Processing Plant should review, particularly at every revamp or expansion.
Pressure Relieving and Flare Design
Process Flare Studies
It is very important that when this system is designed or modified that the design team understand the fundamentals of pressure relieving system design and the critically of this system. Having the correct components of a system, does not necessary mean the the sum of the parts will have the desired result. The total system should be reviewed.
For example the relief valves may be sized correctly utilizing the plant's original flare design. But the plant has been revamped for more capacity and now the flare header may not give the designed back pressure. In this case the relief valves and flare header may now be undersized.
This system includes;
1. Pressure Relief Valves
2. Flare Header
3. Flare Knock Out Pot
4. Flare Liquid Pumps
5. Flare Stack
6. Flare Seal
7. Flare Tip
A typical Pressure Relieving Flare System Design or Review includes;
1. Develop Pressure Relief Valves design for multiple cases
A. Gather Relevant data - PSV Data Sheets, P&IDs, Piping Isometrics
B. Develop Creditable Relief Scenarios, Power Failure, Cooling Water Failure, ect
C. Calculate Correct Relief Valve Size after steps 2 and 3 are completed, for proper
calculation of back pressure
2. Complete Relieving System Heat and Material Balances with thermodynamic packages in Process Design Simulator such as PRO II, which includes condensation and two phase flow affects for the correct back pressure calculations
A. Physical properties generated for each stream
B. Calculate heat released from the Flare Header
3. Development of Flare Header hydraulics and sizing utilizing the Heat and Material Balance Corrected Flows
A. Calculation of flare header hydraulics for back pressure calculation.
4. Development of Flare Knock Out Pot sizing and velocities
5. From the Heat and Material Balance develop KO Pump sizing
6. Review Flare Seal Design from Vendor
7. Review Flare Tip Design from Vendor
8. Develop Flare Radiation Heat Circles and Required Stack Heights
Additional Items that can be developed or reviewed include;
1. Reduced Flaring Systems by the use of High Integrity Protection Systems (HIPS)
2. Evaluation of maximum flaring cases with existing flare system
3. Revamp strategies and modifications for existing flare systems
4. Generate all required documentation or OSHA or internal company requirements
KLM's Team of highly experienced engineers can assist your team in developing the basic design or detailed design of a Pressure Relieving System.
Pressure Reliving and Flare System White Papers