AU2007293762A1

AU2007293762A1 - Ignition system

Info

Publication number: AU2007293762A1
Application number: AU2007293762A
Authority: AU
Inventors: Stephen Percy Kendall
Original assignee: STEPHEN KENDALL
Current assignee: STEPHEN KENDALL
Priority date: 2006-09-06
Filing date: 2007-08-03
Publication date: 2008-03-13
Also published as: NZ549704A; WO2008030107A1

Description

WO 2008/030107 PCT/NZ2007/000204 TITLE: IGNITION SYSTEM FIELD OF THE INVENTION 5 The present invention is a fuel ignition device, more specifically a device that provides an essentially continuous ignition source for an oilrig burner. BACKGROUND 10 On an oilrig it is often necessary to carry out well testing, this involves sampling hydrocarbons at the choke manifold. The hydrocarbons not required after testing are produced to the burner for flaring purposes. The hydrocarbons produced to the burner are mixed with compressed air and passed 15 through the burner head where they are atomised. This atomised hydrocarbon mixture is then ignited by a propane fed single shot ignition system. The present ignition systems are described as 'single shot' as a pulse of propane is ignited by one of two methods, both of which provide an intermittent ignition source for the burner. The two most commonly used methods are the Lodge method and a fireball system. 20 The Lodge method uses a spark generator to ignite the pulse of propane. The fireball system uses an air/gas mixture to generate a fireball that is used to ignite the pulse of propane. Both of these methods pulse, that is, they do not provide a continuous ignition source for the burner, which- means there is the potential for the burner to go out. 25 Many of the oilrigs are located in the most inhospitable locations, for example the North Sea. These locations have high winds, low temperatures, rain, sleet, snow and heavy seas so the conditions are not ideal for the burner to operate. To keep the rig safe the burner is located on a boom that extends about 90 feet from the oilrig, which 30 makes it difficult to intervene manually, should the ignition system fail. In addition the oilrig may be thermally separated from the burner by water curtains, all fed with salt water, which can increase the maintenance requirements. If the burner goes out even for a short period of time the hydrocarbons that should be 35 flared fall into the sea or surrounding area. These hydrocarbons pose an environmental and safety hazard and may result in the rig being shut down. The cost 1 WO 2008/030107 PCT/NZ2007/000204 to clean up any environmental damage can be expensive and, given the location of many oilrigs, not possible until the hydrocarbons hit land. OBJECTS OF THE INVENTION 5 One object of the present invention is to provide an essentially continuous ignition system for hydrocarbons produced to a burner. The invention also aims to meet one or more of the following objectives: 10 1. Provide an ignition system that reduces the possibility of an environmental or safety incident. 2. Provide a useful choice in ignition systems. DISCLOSURE OF THE INVENTION 15 The present invention provides an essentially continuous ignition system for a burnable mixture that includes a fuel/air mixer, an ignition chamber and an ignition device, wherein the fuel/air mixer is adapted to mix fuel from a fuel source with air in the correct ratio to create a combustible mixture, the ignition chamber includes a fuel 20 burner head adapted to feed the combustible mixture into the interior of the ignition chamber, the ignition device is adapted to provide essentially continuous ignition of the combustible mixture from the fuel burner head to create a burning gas which exits the ignition chamber and, in use, ignites the burnable mixture. 25 In a highly preferred form the ignition device includes two or more electrodes connected to a high voltage source, said high voltage source being adapted to provide a sufficient potential difference between said electrodes to cause an essentially continuous arc to form between them. It is preferred that the arc is created inside the ignition chamber close to the fuel burner head. In a highly preferred form the or each 30 electrode is a rod. In a highly preferred alternative form the electrodes are part of a spark plug. Preferably there are two or more spark plugs. In a highly preferred form each spark plug is attached to a separate high voltage source. 35 2 WO 2008/030107 PCT/NZ2007/000204 In a highly preferred form the ignition chamber includes a casing, a baffle and one or more connectors, the casing includes a first end into which the fuel burner head is attached and a second end which is open. The baffle is attached to the second end by the or each connector such that the baffle nearly closes off the second end leaving 5 only a narrow annular gap between the baffle and the second end for the burning gas to exit. Preferably the baffle is adapted to-increase the pressure inside the casing above atmospheric. In a highly preferred form the fuel is gaseous, and in a highly preferred form propane. 10 Preferably the burnable mixture is an atomised hydrocarbon plume. Preferably the atomised hydrocarbon plume is produced by an oilrig burner. It is preferred that the fuel/air mixer is a Venturi mixer. 15 Preferably the high voltage source is one of the following:- a DC source, a low frequency AC source or a high frequency AC source. Preferably the ignition system includes one or more sensors to monitor one or more of the ignition system parameters in the following list: temperature, pressure, 20 composition, flowrate and moisture content. Preferably ignition system includes a control system that is adapted to control the ignition system based on the readings received from the or each sensor and preset control parameters. DESCRIPTION OF THE DRAWINGS 25 By way of example only a specific embodiment of the present invention will now be described in detail with reference to the accompanying drawings in which: Figure 1 is a diagrammatic elevation of the ignition system and oilrig burner. 30 Figure 2 is a side pictorial view with the ignition chamber partially cut away to show the interior details. Figure 3 is a side pictorial view of a second embodiment ignition system with the ignition chamber partially cut away to show the interior details. 3 WO 2008/030107 PCT/NZ2007/000204 Referring to the drawings, an ignition system (1) is shown, said ignition system includes an ignition chamber (2), a propane/air mixing device (3) and a high voltage source (4). 5 The propane/air mixing device (3) includes a fuel/air mixing device (not shown) of known type, for example a Venturi. The propane/air mixing device (3) is adapted to draw propane from a set of propane bottles (5) through a first pipe (6) and mix it with air drawn in via an air inlet (7) and form a combustible mixture (8). The combustible mixture (8) then exits the propane/air mixing device (3) through a second pipe (9) that 10 is connected to the ignition chamber (2). Referring to Figure 2, the ignition chamber (2) is shown in more detail, said ignition chamber (2) includes two electrodes (10,11), a propane burner head (12), a casing (13) and a baffle (14). Each electrode (10,11) is a thin rod of an electrically conducting 15 material, such as a metal. The casing (13) is a cylindrical drum (15) that includes a base (16) and an open end (17). The base (16) and open end (17) are at opposite ends of the cylindrical drum (15). The baffle (14) is rigidly attached to the casing (13) at the open end (17) by 20 connectors (21), such that the baffle (14) is spaced away from the peripheral edge of the open end (17) forming a chamber outlet (31). The baffle (14) is a disc with a diameter greater than the casing (13) diameter; said baffle (14) lies in a plane perpendicular to the central axis of the casing (14). The dimensions of the chamber outlet (31) are such that a positive pressure is maintained inside the casing (13) whilst 25 the combustible mixture (8) is fed to the ignition chamber (2). The second pipe (9) feeds the combustible mixture (8) to the propane burner head (12) that opens into the interior (22) of the casing (13). The ignition chamber (2) includes an insulated holder (20) adapted to electrically separate, and mechanically 3o retain, the two electrodes (10,11). The insulated holder (20) is also configured to hold each of the electrodes (10,11) such that an end (1Oa,11 a) of each electrode (10,11) is exposed to the interior (22) of the casing (13). Each of the two electrodes (10,11) is connected to the high voltage source (4) by a separate cable (23,24). The high voltage source (4) is adapted to create a sufficiently high potential difference between 35 the two electrodes (10,11) so as to create an essentially continuous spark (29) between said electrodes (10,11) when the ignition system (1) is in use. The 4 WO 2008/030107 PCT/NZ2007/000204 essentially continuous spark (29) generated is of sufficient intensity to ignite the combustible mixture (8), causing it to burn inside the ignition chamber (2) creating a burning gas (30). 5 In operation the ignition system (1) creates the combustible mixture (8), feeds this combustible mixture (8) to the propane burner (12) where it is ignited by the essentially continuous spark (29) creating the burning gas (30). The burning gas (30) passes through the interior (22) of the casing (13) and exits the ignition chamber (2) by the chamber outlet (31). This burning gas (30) provides an essentially continuous -ignition 10 source for a plume of atomised hydrocarbons (40), a burnable mixture, produced by an oilrig burner (41) of known type. The oilrig burner (41) is used to flare off the hydrocarbons produced during well testing. A further embodiment (not shown) has more than two electrodes (10,11), these 15 electrodes may be pins, concentric circles of conductive material or something similar. In a still further embodiment (not shown) the electrodes (10,11) are adapted to be continuously fed into the chamber to maintain the optimum dimensions for creating the spark (29). 20 Referring to figure 3, a second preferred embodiment of the ignition system (1) is shown. In this embodiment the ignition chamber (2) includes a socket (50) adapted to retain a spark plug (5.1). The socket (50) is attached to the base (16) and dimensioned to retain the spark plug (51) with its electrodes (52) within the ignition chamber (2), 25 close to the propane burner head (12). The socket (50) retains the spark plug (51) sufficiently close to the propane burner head (12) such that in use the spark plug can ignite the combustible mixture (8). The electrodes (52) of the spark plug (51) are connected to a high voltage source (4) by cables (23, 24). The high voltage source (4) is adapted to create a sufficiently high potential difference between the electrodes (52) 30 of the spark plug (51) so as to create an essentially continuous spark (29) between said electrodes (52) when the ignition system (1) is in use. The essentially continuous spark (29) generated is of sufficient intensity to ignite the combustible mixture (8), causing it to burn inside the ignition chamber (2) creating the burning gas (30). 5 WO 2008/030107 PCT/NZ2007/000204 In a further embodiment a sensor (60) is fitted to the second pipe (9), this sensor (60) is adapted to provide pressure, temperature and other data regarding the condition of the combustible mixture (8). 5 Though it is expected that the burning gas (30) will provide the continuous ignition source for the plume of atomised hydrocarbons (40) it is also likely that parts of the ignition chamber (2) may also reach sufficiently high temperatures to provide alternative ignition sources. 10 In a further modification of the second preferred embodiment there is a second socket (55) which retains a second spark plug (56) within the ignition chamber (2). With this arrangement if the first spark plug (51) fails an alternative ignition source is present. This provides an additional level of redundancy. As a further level of redundancy the second spark plug (56) can be connected to a second high voltage source (57), but 15 equally both spark plugs (51, 55) can be fed from a single high voltage source (4). In a further modification (not shown), of the second embodiment, more than two spark plugs (51, 55) can be used to provide additional redundancy. 20 In a further embodiment the ignition system (1) includes a control system (not shown) adapted to accept readings from monitoring sensors (not shown) and activate control valves (not shown) or other devices (not shown) to optimise the performance of the ignition system (1): 25 Though propane is mentioned it should be understood that other combustible fluids could be used and still fall within the scope of the invention. In addition various safety devices, such as flashback arrestors, may be fitted without falling outside the scope of the invention. 3o Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field. 6

Claims

1. An essentially continuous ignition system for a burnable mixture that includes a fuel/air mixer, an ignition chamber and an ignition device, wherein the fuel/air 5 mixer is configured to mix fuel from a fuel source with air in the correct ratio to create a combustible mixture, the ignition chamber includes a fuel burner head configured to feed the combustible mixture into the interior of the ignition chamber, the ignition device is configured to provide essentially continuous ignition of the combustible mixture from the fuel burner head to create a burning 10 gas which exits the ignition chamber and, in use, ignites the burnable mixture.

2. The ignition system as claimed in claim 1 characterised in that the ignition device includes two or more electrodes connected to a high voltage source, said high voltage source being configured to provide a sufficient potential difference 15 between said electrodes to cause an essentially continuous arc to form between them.

3. The ignition system as claimed in claim 2 characterised in that the arc is created inside the ignition chamber close to the fuel burner head. 20

4. The ignition system as claimed in claim 2 or 3 characterised in that at least one electrode is a rod.

5. The ignition system as claimed in claim 2 or 3 characterised in that at least one 25 electrode is part of a spark plug.

6. The ignition system as claimed in claim 5 characterised in that there is more than one spark plug. 3o

7. The ignition system as claimed in claim 6 characterised in that each spark plug is connected to a separate high voltage source.

8. The ignition system as claimed in any one of claims 1 to 7 characterised in that the ignition chamber includes a casing, one or more connectors and a baffle, the 35 casing includes a first end into which the fuel burner head is attached and a second end which is open. 7 WO 2008/030107 PCT/NZ2007/000204

9. The ignition system as claimed in claim 8 characterised in that said baffle is attached to the second end by the or each connector, such that the baffle nearly closes off the second end leaving only a narrow annular gap between the baffle 5 and the second end for the burning gas to exit.

10. The ignition system as claimed in claim 8 or 9 characterised in that the baffle is configured to increase the pressure inside the casing above atmospheric. 10

11. The ignition system as claimed in any one of claims 1 to 10 characterised in that the fuel is gaseous.

12. The ignition system as claimed in 11 characterised in that the fuel is propane. 15

13. The ignition system as claimed in any one of claims 1 to 12 characterised in that the burnable mixture is an atomised hydrocarbon plume produced by an oilrig burner.

14. The ignition system as claimed in any one of claims 1 to 13 characterised in that 20 the fuel/air mixer is a Venturi mixer.

15. The ignition system as claimed in any one of claims 2 to 7, or any one of claims 8 to;14 when dependent upon claim 2, characterised in that the high voltage source is selected from the group consisting of:- a DC source, a low frequency 25 AC source and a high frequency AC source.

16. The ignition system as claimed in any one of claims 1 to 15 characterised in that it includes one or more sensors to monitor one or more of the ignition system parameters selected from the group consisting of: temperature, pressure, 30 flowrate, composition and moisture content.

17. The ignition system as claimed in 16 characterised in that it includes a control system that is adapted to control the ignition system based on the readings received from the or each sensor and preset control parameters. 35 8