Note: Descriptions are shown in the official language in which they were submitted.
CA 02505536 2005-04-28
"FLARE STACK SAFETY SYSTEM AND METHOD OF USE"
FIELD OF THE INVENTION
The field of present invention relates generally to flare systems used
at oil and gas well sites and, more particularly, to flare stack safety
systems for use
during snubbing operations, well testing and other well completion operations.
BACKGROUND OF THE INVENTION
During the insertion of piping and tools into live well bores, and the
extraction of piping and tools from live well bores, known as "snubbing", it
is
conventional that a flare stack is often burning nearby, to receive gases from
the
well and thereby relief the well pressures that are present during the
snubbing
operations.
However, at times failures occur in pressure control systems due to
equipment malfunction or, more commonly, human error. During such an event,
large plumbs of flammable gas or fluids may escape from the pressure control
equipment and/or blow out from the well and drift or move towards the flare
stack -
occasionally with disastrous results such as a well fire initiated by the
flare system.
Undesirable gas plumes due to failures can also occur during numerous other
operations, such as during piping wash-outs, coil tubing operations, rig blow
out
preventor (BOP) failures, or wellhead equipment failures.
Flare stacks for oil and gas well operations tend to be fairly simple
systems with basic controls. Typically, an ignition source such as a pilot
flame is
CA 02505536 2005-04-28
provided at the outlet of the flare stack. Such a pilot flame is typically
left on
constantly so that, in the event that flammable gases are vented to the flare
stack,
the ignition source will start combustion of such vented gases. In case of an
emergency, quickly shutting off the pilot may not be sufficient to avert
disaster
because the remaining fuel (typically propane) in the line to the pilot would
still have
enough pressure to keep the pilot flame burning for a short time (often few
minutes).
A further complicating factor is that during workover and completion
operations is it generally not desirable to shut off the flow of gases to the
flare
system when the pressure control equipment has failed. Shutting off the flow
of
venting flammable flare gases, from the well to the flare stack, would only
exaggerate the well pressure that would be desirable to relieve. However, such
a
continued flow of gases through the flare stack would also allow the flare to
continue burning, long after the fuel to the pilot flame is shut off and the
pilot flame
itself has extinguished.
What is needed is a safety system which will eliminate the danger of
ignition of escaping flammable vapors, by the flare stack system, while still
allowing
the flow of vented gases out through the flare stack.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of one embodiment of a flare
stack safety system;
Figure 2 is a schematic representation of a second embodiment of a
flare stack safety system;
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Figures 3a and 3b are perspective views of the embodiment of Figure
1;
Figure 4 is a schematic representation of a third embodiment of a flare
stack safety system; and
Figure 5 is a schematic representation of a fourth embodiment of a
flare stack safety system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is to be had to the Figures in which identical reference
numbers identify similar components.
Figures 1, 3a and 3b show one embodiment of a flare stack safety
system 10. A flare line 12 carries flammable flare gases from the well to a
flare
stack 14 for combustion. Preferably, the flare line 12 enters the flare stack
14
substantially near the bottom. The flare stack 14 has an ignition source 16 to
initiate the combustion of the flammable flare gases. The ignition source 16
can be
electronic, a pilot light or pilot flame operated with a fuel gas, or any
other
equivalent ignition source. In this embodiment the ignition source 16 is a
pilot
flame created by a burner 18 supplied with fuel gas through a pilot line 20.
A purge line 22 connects a source of purge gas 30 (which in this
embodiment is a storage vessel 30 containing said purge gas) to the flare line
12
just prior to the junction of the flare line 12 with the flare stack 14. In
another
embodiment (not shown) the source of purge gas 30 connects directly to the
flare
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line 12. In yet another embodiment (also not shown), the source of purge gas
30
connects directly to the flare stack 14. In the preferred embodiment, the
purge line
22 branches and also connects to the pilot line 20.
Preferably, check valves 24 are mounted in the purge line 22 to direct
the flow of purge gas such that when actuator means or purge valve 32 is
actuated
or opened, flow of purge gas commences from the source 30 into the flare line
12
and pilot line 20. More, preferably, a check valve 24 is mounted in the flare
line 12
to direct the flow of flammable flare gas from the well into the flare stack
14. These
check valves 24 are illustrated schematically as a spring-loaded balls and
also
function to prevent flare gases from entering purge line 22 and prevent purge
gasses from backing up into the flare line 12 towards the well. The check
valves 24
can be any suitable check valve, including ball and seat style valves or
flapper style
valves.
The purge valve 32 is preferably a quick opening valve which is left
closed during normal operations and opened to actuate the system 10 during an
emergency. More preferably, the purge valve 32 is left in a normally closed
position
during normal operations. A suitable valve would be a butterfly valve or ball
valve.
Alternatively the purge valve 32 could be a pressure activated valve or an
electronically actuated valve that can be opened from a variety of locations
on the
well site.
Storage vessel 30 contains a purge gas, preferably a non-combustible
pressurized inert gas, more preferably nitrogen (N2). Another suitable purge
gas
would be carbon dioxide (C02). Preferably, storage vessel 30 further comprises
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bottles 34 of purge gas connected to lengths of pre-charge piping 36. The pre-
charge piping 36 may be connected in a line (see FIG. 3b) or it may be looped
and
in the form of a bundle (not shown). Advantageously, the pre-charged piping 36
stores the desired volume of purge gas under pressure. Typically, the amount
of
purge gas required to extinguish the flare stack 14 is dependent upon the rate
or
velocity of the flammable flare gas flow from the flare line 12. Other
variables may
also impact the amount of purge gas required in a particular situation.
OPERATION
Referring to the preferred embodiment (see FIGS. 1, 3a and 3b), and
during normal well operations, the purge valve 32 is closed or in its non-
actuated
state, thereby keeping the pressurized purge gas in the storage vessel or
source
30. In the event of an emergency at the well site involving a flammable gas or
liquid
release, purge valve 32 is actuated. Flow of purge gas, from the source 30, is
immediately begun into the flare line 12 and pilot line 20 through the purge
line 22
and past the check valves 24.
The flow of purge gas from the purge line 22 through the flare line 12
and then into the flare stack 14 mixes with, or displaces, the combustible
flare
gases and extinguishes the pilot light 16 and flare stack 14, so as to
eliminate the
undesirable ignition sources. Advantageously, the flow of purge gases mixing
with
the flare gases makes the mixture non-combustible, typically by reducing the
concentration of flare gases below that of their lower explosive limit (LEL).
More
advantageously, in a low flammable gas rate situation, the purge gases may
even
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create an area which moves along the stack 14 where the concentration of
flammable flare gases is at or near zero. Even more advantageously, the flow
of
purge gases also cools the flare stack 14 down.
What results is a quick, within a few seconds, purging of flare stack 14
and pilot line 20 with purge gas from the source 30. Advantageously, the
ignition
source 16 is also cut off from its fuel gas by the entry of purge gas into the
pilot line
20, and is thereby extinguished and cooled. The purging and extinguishing of
the
flare stack 14 and burner 18 precludes the availability of either as a further
source
of ignition to escaping flammable gases or fluids from the well. More
advantageously, because the vented gases are still able to flow from the well,
through the flare line 12, into the flare stack 14, the well pressure can be
relieved
while having eliminated the danger of igniting the escaped flammable vapors
from
the well.
SECOND EMBODIMENT
Figure 2 illustrates a second, slightly different, embodiment wherein
the ignition source 16 is an electronic igniter 50 maintained constantly in
the on
position through use of switch or control labeled A. Accordingly there is no
pilot line
nor does the purge line 22 connect to the ignition source. The purge valve 32
is
controlled by switch B. When switch B is actuated, it accomplishes the
following
tasks: the purge valve 32 is opened and the ignition source 16 is cut off.
Accordingly, in the event of an emergency at the well site switch B is
actuated which overrides the ignition source 16, closing it off while at the
same time
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opening the purge valve 32. Switch B can be manually activated or it can be
tied
into a flammable gas detector which will set off switch B automatically as
well as
sound an audible alarm.
THIRD EMBODIMENT
Figure 4 illustrates a third embodiment of the flare stack safety system
10, wherein a plurality of flare stacks 14a, 14b are shown, each connected to
the
purge line 22 of the flare stack safety system 10.
FOURTH EMBODIMENT
Figure 5 illustrates a fourth embodiment of the flare stack safety
system 10 wherein the purge line 22 connects directly to the flare stack 14
(rather
than to the flare line 12 as in the previous embodiments). In the event of an
emergency at the well site involving a flammable gas or liquid release, purge
valve
32 is actuated to open. Flow of purge gas, in this embodiment, is immediately
begun into the flare stack 14 and also the pilot line 20 through the purge
line 22 and
past the check valves 24.
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