CA2505536A1

CA2505536A1 - Flare stack safety system and method of use

Info

Publication number: CA2505536A1
Application number: CA 2505536
Authority: CA
Inventors: Ian Pickles
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-29
Filing date: 2005-04-28
Publication date: 2005-10-29

Abstract

In the context of an oil or gas well site flare system, a safety system is provided so that in the event of a flammable gas release at the well, the safety system can be activated to extinguish the sources of ignition. Activation of the safety system does not prevent the continued venting or exiting of flare gases from the flare stack. In a system aspect, the safety system comprises a source of purge gas connected to a flare stack and actuator means. When the actuator means is actuated, a flow of purge gas commences from said source info said flare stack while allowing said flammable gases to continue to exit out said flare stack.
Other system and method aspects are also provided.

Description

"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 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;

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 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 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 line 12. In yet another embodiment (also not shown), the source of purge gas 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 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 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 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 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.

Claims

1. A flare stack safety system, for connection to a flare line carrying flammable gases from a well to a flare stack, the safety system comprising:
a source of purge gas connected to said flare line; and actuator means;
wherein when the actuator means is actuated, a flow of purge gas commences from said source into said flare line while allowing said flammable gases to continue to exit out said flare stack.

2. The system of claim 1 wherein the source of purge gas comprises a storage vessel containing a purge gas.

3. The system of claim 1 further comprising a purge line connecting said source of purge gas to said flare line.

4. The system of claim 2 further comprising a purge line connecting said source of purge gas to said flare line.

5. The system of claim 1 wherein the actuator means comprises a normally closed purge valve.

6. The system of claim 4 wherein the actuator means comprises a normally closed purge valve.

7. The system of claim 3 further comprising at least one check valve mounted in the purge line.

8. The system of claim 6 further comprising at least one check valve mounted in the purge line.

9. The system of claim 1 further comprising at least one check valve mounted in the flare line.

10. The system of claim 8 further comprising at least one check valve mounted in the flare line.

11. A flare stack safety system, for connection to a flare stack receiving flammable gases from a well, the safety system comprising:
a source of purge gas connected to said flare stack; and actuator means;
wherein when the actuator means is actuated, a flow of purge gas commences from said source into said flare stack while allowing said flammable gases to continue to exit out said flare stack.

12. The system of claim 11 wherein the source of purge gas comprises a storage vessel containing a purge gas.

13. The system of claim 11 further comprising a purge line connecting said source of purge gas to said flare stack.

14. The system of claim 12 further comprising a purge line connecting said source of purge gas to said flare stack.

15. The system of claim 11 wherein the actuator means comprises a normally closed purge valve.

16. The system of claim 14 wherein the actuator means comprises a normally closed purge valve.

17. The system of claim 16 further comprising at least one check valve mounted in the purge line.

18. A method of preventing well fires caused by gases or fluids inadvertently discharged around a well, comprising:
sensing a gas or fluid leak at the well;
turning off an ignition source adjacent a flare stack;
purging said flare stack by injecting a purge gas into said stack; and allowing well gases to continue to exit out said flare stack.