November
2016
67
HYDROCARBON
ENGINEERING
P
ressure assisted multipoint ground flares (MPGF) have long been
used in the petrochemical industry, as well as gas plants and
refineries, for the safe disposal of vent gases during upset
conditions. A properly designed MPGF can achieve 100% smokeless
operation under all flow conditions for which it has been designed. This
type of flare has a low public profile compared to a typical elevated flare
because these systems may have no visible flame outside the plant.
Additionally, the higher destruction efficiency of an MPGF can significantly
reduce continuous plant emissions.
These flare systems are comprised of a radiation fence – also known as a
wind fence – a distribution manifold with fail-open valves, multiple smaller
manifolds (or runners), which terminate in flare burners, and a control
system that operates the staging valves based on the supply pressure.
Figure 1 shows the interior of an MPGF field. Surrounding the field is the
radiation fence. In the foreground, the elevated and shielded horizontal
pipes (just above grade) are the runners, and the burners are mounted on
the smaller vertical pipes.
Increased smokeless turndown capability
Pressure-assisted flare burners rely on high velocity vent gas jets for the
entrainment of combustion air to provide smokeless operation. The
minimum pressure, and therefore minimum port exit velocity, at which the
burner can operate without producing smoke from the flame, is a critical
design feature.
A lower smokeless operating pressure for a flare burner results in a wider
operating range for a given stage, therefore the number of stages required
for a properly functioning smokeless flare field can be reduced. There is an
Matthew Martin and Bryan Beck,
Honeywell UOP's Callidus
Technologies Business, USA,
discuss
how multipoint ground flares can
help downstream companies achieve
smokeless operations, and improve
burner cross-lighting and flame length.
