FLARE SYSTEMS
The flare is the last line of defence in the safe emergency release
system in a chemical plant or refinery.
It is a fail-safe option used in the disposal of purged and
wasted products from refineries, vented gases from blast furnaces, gaseous
water from chemical industries, unrecoverable gases from oil wells etc.
 |
| Typical Flare Stack During Operation |
The flare
provides a means of safe disposal of the vapor streams from its facilities, by
burning them under controlled conditions such that adjacent equipment or
personnel are not exposed to hazards, and at the same time obeying the
environmental regulation of pollution control and public relations requirements.
 |
| Process Flow Scheme Of A Typical Oil & Gas Facility |
The most
common utilized flare systems are elevated flares.
They
include:-
1.
Self-Supported Flare System
2.
Guy-Wired Flare System
3.
Derrick Flare System
 |
| Types Of Elevated Flare Systems |
i.
SELF
SUPPORTED FLARE SYSTEM
Self-supporting Flares offer excellent alternatives to guy wire
supported, or derrick-supported structures, for flares up to 16m tall.
Self-supporting stacks are typically larger at the base, then transition to
gradually smaller diameters as they ascend.
They are referred to as self-supported, largely due to the fact
that there is absolutely no need for additional support. They minimal height
makes them more than able to withstand wind loads.
They are extremely easy to maintain compared to other flare
stacks, they are also relatively cheaper and mostly used for on-shore projects.
 |
| Typical Model Of A Flare Stack |
ii.
GUY-WIRED FLARE SYSTEM
They are generally much more preferable for use when a relatively
tall flare is required. Guy-wired flares can be as high as 50-60m above ground
level.
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| Flare System Design Model |
They are relatively cheaper than the Derrick flare and mostly preferred
for on-shore projects.
 |
| Typical Section Drawings of a Guy-Wired Flare |
 |
| High Pressure & Low Pressure Flare System |
They however require a whole lot of space, due to the
guy support system.
iii.
DERRICK FLARE SYSTEM
They are the most expensive of all the flare systems. They however
are preferable for projects (especially off-shore) where there are space
constraints.
 |
| Derrick Flare |
Derrick flare system are relatively easy to maintain and can go as
high as required without worrying too much about the effect of wind loads.
 |
| Typical Derrick Flare System |
Flare System
Selection Criteria
Selection of
the type of flare is influenced by several factors, such as availability of
space, the characteristics of the flare gas (composition, quantity and
pressure), economics, investment and operating costs, public relations and
regulation etc.
Besides that,
the design should be based on the considerations bellow as well,
11. Flare Spacing, Location, and Height
22. Radiant heat
33. Burning liquid fall out
44. Pollution limitations
55. Flare Capacity and Sizing
66. Flare design capacity is design to handle
largest vapor release from pressure
77. Relief valve, vapor blow down and other
emergency system
88. Flashback Seals -flashback protection, which
prevents a flame front from traveling back to the upstream piping and
equipment.
Stress
Analysis of Flare Lines
Flare line
are “high-pressure & temperature” lines, and as such are classified as “Critical
Lines”.
This makes
it absolutely paramount to carry out a detailed stress analysis on all flare
lines.
As a rule of
thumb, it is important to introduce an “Expansion loop” to cater for
temperature expansion in steel pipes.
 |
| 3D Model Showing an Expansion Loop |
For more on Stress Analysis of Flare Lines, click here
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