Guideline on Quick Determination of Flare Stack Support Type

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In recent project, we worked on a project involved in flare system design with reasonable large flaring load (about 1200 mmscfd). During design phase, we have been asked to provide the structure type of the flare stack support and sterile area diameter as project would like to fix the plot plan. Normally, this information is provided by the flare tip vendor. We have received information from several flare tip vendors. The tricky part is some vendor indicated that guyed wire and some indicated derrick type. As the cost of construction and plot area requirement for every type of support are pretty much different, this has given us some level of challenge.

Conventionally three main type of flare stack support structure have been used. There are self support (SS), guyed wire (GW) and derrick support (DS). The following photos shown different types of flare support.

General rule of thumbs for each support type are :

a) Self support (SS)

• lease land area
• KOD and/or seal drum can be attached at the bottom of flare stack
• Wall thickness increases with flare stack height. Maximum recommended height about 76 m (250 ft) [Ref.: JohnZink Combustion handbook, chap 20].
• API Std 521 has recommended 60 - 90m (200-300 ft).
  
• Low in construction cost
  

b) Guyed wire support (GW)

• most land area
• GW type can goes as height as 180 m (600 ft) [Ref.: JohnZink Combustion handbook, chap 20]. API Std 521 has recommended 180-250m (600-800 ft).
• reasonable construction cost

c) Derrick Support (DS)

• lease land area
• height is more than 200 m [Ref.: JohnZink Combustion handbook, chap 20].
• High construction cost

There is a simple guideline provided in the JohnZink Combustion handbook. We have used it as a quick guide and pretty supportive and informative. The following image shows the guideline.

Above image has been programed in EXCEL sheet for ease of future used. If you are interested, download from HERE. If you have any comments or improvement, please drop me a note.

Update
Feb 24, 2008 : I have missed the definition of parameter used in the Excel spreadsheet. It has been updated. Thanks to Michael.


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