Patent Application
20130330675
1. Field of the Invention
This invention pertains to ignition and sensing systems and more particularly to flame ignition and flame detecting or sensing systems. Even more particularly, the invention pertains to such systems having a spark type ignition.
2. Description of the Related Art
A gas pilot burner is a device used to create a stable pilot flame by combustion of a low flow rate (relative to the main burner) gaseous fuel-air mixture. The pilot flame is used to light a larger main burner, or a difficult to light fuel. Gas pilot designs normally include an ignition system and a flame detection system. The two most common types of ignition systems used in gas pilot burners are high tension (HT) and high-energy ignition (HEI). Flame detection is typically by a flame ionization detection (FID) system.
An HT flame ignition system typically utilizes a high voltage source and an HT spark plug or spark rod. The high voltage source provides high voltage, low current pulses. Often, such pulses will be 15 kV or greater and from about 10 to about 50 mA. HT systems create low amperage sparks that bridge an air gap created in a spark plug or between a spark rod and the grounded pilot frame. This spark is used to ignite the fuel-air mixture and, thus, generate the pilot flame. While this type of ignition can be low cost, it can be inconsistent when ignition conditions are not ideal. Moisture from steam or rain, contamination and heavy fuel can all generate ignition problems when using an HT system.
An HEI system typically utilizes a capacitive discharge exciter to pass large current pulses to a spark rod. The large current pulses are often greater than 1 kA. The spark rod or igniter probe for an HEI system is generally constructed using a center electrode surrounded by an insulator and an outer conducting shell over the insulator such that, at the ignition end of the spark rod, a high-energy spark can pass between the center electrode and outer conducting shell. HEI systems have the ability to maintain powerful high energy sparks in adverse conditions such as cold temperatures, heavy fuels (heavy gases or oils), contamination of the igniter plug with coking or other debris and moisture presence due to steam purging or rain.
For safety considerations, it is important that the ignition system ignites the fuel-air premix as soon as possible after the main fuel gas valve opens. It is also important that the flame ionization detection system registers the flame signal as soon as possible after the flame is established. Together, rapid ignition and flame detection help minimize the chance of explosion due to raw fuel being pumped into a burner. Typically, there is a burner management system (BMS) that controls the fuel and ignition systems while monitoring the flame ionization detection system. Often, the burner management system will give five seconds or less of fuel flow time before closing the fuel valve if flame is not proven. The window for ignition and detection is therefore very short.
Most prior HT ignition systems have used a combined HT and flame detection system wherein ignition must occur and then an electromechanical switch de-energizes the exciter and energizes the flame detector. This means ignition and detection are sequenced into two distinct time periods, each occupying a portion of the maximum limited allowable fuel valve open time window. HT or HEI systems allowing for simultaneous ignition and flame detection have relied on using completely separate ignition and detection systems. It would be beneficial to have a powerful ignition system, such as an HEI system, and a flame detection system that can operate simultaneously through the entire window where the flame detection system is an integral part of the HEI systems; that is, without utilizing completely separate ignition and detection systems.
In accordance with one embodiment of the present invention, there is provided a pilot burner comprising a source of electrical energy, a spark rod and a housing. The spark rod has a first end, a second end and a flame rod connected thereto at the second end. The spark rod is connected to the source of electrical energy at the first end such that the electrical energy causes a spark at the second end. The housing has a fuel flow passage, which contains the second end of the spark rod. The position of the flame rod in the housing and the connection of the spark rod to the source of electrical energy is such that when no flame exists adjacent to the second end of the spark rod, no current flows between the flame rod and the housing and when a flame exists adjacent to the second end of the spark rod, current flows between the flame rod and the housing. The source of electrical energy and the pilot burner are capable of simultaneously generating the spark and providing the current.
In another embodiment of the invention, there is provided an apparatus for ignition and flame detection comprising a first electrode, a second electrode and a third electrode. The first electrode and second electrode each have a first end and a second end. The first electrode and the second electrode are positioned and electrically insulated from each other such that a spark tip is formed by the second ends so that, when the first ends are connected to a source of electrical energy, a spark can pass between the second end of the first electrode and the second end of the second electrode. When fuel is adjacent to the second end of the second electrode, the spark ignites the fuel and produces a flame. The second electrode is configured and positioned relative to the third electrode such that, when the flame is present between said second electrode and said third electrode, electricity is conducted between the second end of the second electrode and the third electrode but, when no flame is present, electricity is not conducted between the second electrode and the third electrode.
In a further embodiment, there is provided an ignition device comprising a source of rectified current, a flame detection circuit, a fuel source, a housing, an electrode, an insulating sleeve, an electrode tube and a controller. The source of rectified current has a high potential terminal and a low potential terminal. The housing has an electronics enclosure and a tube portion forming a longitudinal passage that is in fluid flow communication with the fuel source such that fuel from the fuel source flows through the longitudinal passage. The electronics enclosure and the longitudinal passage are sealed such that the fuel cannot pass between them. The housing is electrically grounded and the electronics enclosure contains the source of rectified current and flame detection circuit. The electrode has a first end and a second end. The first end is in the electronics enclosure and is connected to the high potential terminal. The electrode extends into the longitudinal passage. The insulating sleeve extends over at least a portion of the electrode. The electrode tube has a first end and a second end, wherein the first end is in the electronics enclosure and connected to the low potential terminal. The electrode tube extends into the longitudinal passage and is positioned around the insulating sleeve such that the electrode and the electrode tube are positioned so that a spark can pass between the second end of the electrode and the second end of the electrode tube to ignite the fuel and, thusly, produce a flame. The first end of the electrode tube is connected to the flame detection circuit. The flame detection circuit provides a current to the electrode tube. The second end of the electrode tube is configured such that, when the flame is established, current is conducted between the second end of the electrode tube and the housing but, when no flame is present, current is not conducted between the electrode tube and the housing. The controller is connected to the electrode tube, the fuel source and the source of electrified current. The controller detects the flow of current between the second end of the electrode tube and the housing and stops the flow of rectified current to the first terminal if current flow occurs.
In yet another embodiment, there is provided a process for simultaneous ignition and flame detection in a high energy igniter of the type that has a fuel channel having a grounded wall and a spark rod located therein with the spark rod being a type that has a center electrode and an electrode tube where the center electrode and electrode tube form a spark tip. The process comprises:
The description below and the figures illustrate a pilot burner or ignition system of the type used in a furnace having a main burner that supplies a fuel and air mixture to the furnace and a pilot burner adjacent to the main burner for igniting the fuel and air mixture. While the invention is described in the context of a pilot burner for such a furnace, it will be appreciated that the inventive ignition device is more broadly applicable as an ignition and flame detection system for fuels.
Referring now to
Fuel introduction pipe 18 is in fluid flow communication with a fuel source 19 and longitudinal fuel flow passage 26 of tube portion 14. Generally, a fuel-air mixture will be introduced into passage 26 through pipe 18 such that the fuel-air mixture will flow in a generally longitudinal direction towards second end 24 and out opening 28.
Extending longitudinally along longitudinal passage 26 is a spark rod 31. Spark rod 31 has a first end 32 extending into electronics enclosure 16 and a second end 33 located near the second end of tube portion 14. Spark rod 31 is comprised of a center electrode 34, an insulating sleeve or tube 37 and an outer shell or electrode tube 40. Center electrode 34 has a first end 35 located within electronics enclosure 16 and a second end 36 located near, but spaced away from, second end 24 of tube portion 14 so that it is inside tube portion 14. Electrode tube 40 has a first end 41 located within electronics enclosure 16 and a second end 42 located near, but spaced away from, second end 24 of tube portion 14 so that it is inside tube portion 14. Insulating sleeve 37 has a first end 38 located within electronics enclosure 16 and a second end 39 located near second end 24 of tube portion 14 and, as shown, just short of the second ends of center electrode 34 and electrode tube 40 so as to form a well 54. Second ends of center electrode 34, insulating sleeve 37 and electrode tube 40 form spark tip 43 of spark rod 31 (as best seen in
As illustrated, spark rod 31 extends through a second insulating sleeve 44 that isolates spark rod 31 from housing 12, which is connected to ground wire 29 so that housing 12 is at ground potential. Generally, spark rod 31 is held in place by second insulating sleeve 44. While spark rod 31 can be attached to second insulating sleeve 44, it is preferred that they be slidingly engaged so that spark rod 31 can be removed from second insulating sleeve 44 at either first end 32 or second end 33. Second insulating sleeve 44 is held in place by sealing device 30 and structural supports 46, which are connected to second insulating sleeve 44. Optionally, structural supports 46 can be made from insulating material and connected directly to spark rod 31 without use of second insulating sleeve 44; however, this can hamper removal of spark rod 31 from first end 32 and/or second end 33.
Additionally, at second end 33 spark rod 31 has a flame rod 48 attached to electrode tube 40. Flame rod 48 is a conducting material that extends towards wall 20 of housing 12 but is not in contact with housing 12. Additionally, flame rod 48 is positioned such that when spark rod 31 has ignited the fuel-air mixture to produce a flame 50, flame rod 48 will be located within the flame.
As illustrated, spark rod 31 is a high-energy igniter (HEI) probe. Accordingly, spark rod 31 should be suitable to pass large current pulses (often greater than 1 kA) from an energy source, further described below, to the spark tip and, thereby, generate a spark at the spark tip. The purpose of an HEI probe is to provide high ignition power. In applications with low temperatures, heavy fuels (heavy gases or oils), contamination of the igniter plug with coking or other debris, or moisture presence due to steam purging or rain, the main fuel may be difficult to light but an HEI system has the ability to maintain powerful high energy sparks in these adverse conditions.
As described above, the HEI igniter probe is generally constructed using a center electrode 34, an insulation system (typically comprising insulation sleeve or tube 37) and outer shell or electrode tube 40. Outer electrode tube 40 is generally about 0.25 to 0.75 inches in diameter. In the past electrode tube 40 has been grounded and not isolated from the pilot frame or housing 12; however, it is an advantage of the current invention that electrode tube 40 not be grounded and be isolated from the housing and, hence, from ground, as is further described herein.
Additionally, a semiconductor material 52 (see
Turning now to electronics enclosure 16, it has at least partially located therein a source of electrical energy, which includes a power supply 56, exciter 58 and flame detection circuit 60. Power supply 56 (as shown located outside of electronics enclosure 16) provides electrical power to both exciter 58 and flame detection circuit 60. A controller 62, sometimes referred to as a burner management system (BMS), is operationally connected to the source of electrical energy.
Exciter 58 can be any high-energy exciter known in the art and suitable to provide a rapid electrical pulse to spark rod 31 and, thus, cause a spark at spark tip 43. Accordingly, exciter 58 will typically be a capacitive discharge device. In an exemplary exciter, exciter 58 has a transforming element 64, diode 66 and capacitor 68. Terminals 70 and 72 are in electrical connection with capacitor 68. Additionally, terminal 70 is connected to center electrode 34 at first end 35 and terminal 72 is connected to electrode tube 40 at first end 41. Terminal 72 is also connected to terminal 74 of flame detection circuit 60.
Electrical input to exciter 58 can by controlled by switch 76, which is operationally connected to controller 62 (connections not shown). Accordingly, when controller 62 activates switch 76, transforming element 64 steps up the incoming voltage and diode 66 rectifies it such that capacitor 68 is charged by the step up transformer. When a predetermined threshold voltage is reached, switch 78 is closed by the exciter's controller (not shown). This causes the spark gap, between center electrode 34 and electrode tube 40 at spark tip 43, to connect to the potential deference stored on the capacitor 68 and create an arc. Thus, energy in capacitor 68 flows through terminal 70 (in this case the high potential terminal) through center electrode 34, across well 54 (spark gap), through electrode tube 40 and terminal 72 (in this case the low potential terminal) and back to the capacitor 68. This large capacitive current results in a powerful spark across well 54.
Accordingly, for the illustrated exciter, it can be said that terminal 70 has a high potential and terminal 72 has a low potential with low potential terminal 72 having an electrical potential below the potential of high potential terminal 70 but above ground potential. This is achieved through galvanic isolation in the transforming element 64 and by electrical connection to terminal 74 of flame detection circuit 60.
While the embodiment illustrated in
As previously mentioned, flame detection circuit 60 is supplied power by power supply 56 through terminals 80 and 82. Flame detection circuit 60 is connected to ground wire 84 and is connected to low potential terminal 72 and electrode tube 40 through terminal 74. As mentioned above, terminal 70, electrode 34, terminal 72 and electrode tube 40 are all isolated from ground. Tube portion 14, however, is grounded. Accordingly, when flame detection circuit 60 is activated, there is potential across the gap 51 between flame rod 48 and tube portion 14. As explained below, only when a flame is present and extends between flame rod 48 and tube portion 14, will there be a conductive pathway between flame rod 48 and tube portion 14. However this pathway only conducts current from flame rod 48 to tube portion 14; hence, if the current applied is an alternating current, only a rectified current is passed, similar to that illustrated in
Flame detection circuit 60 provides a signal 86 to controller 62. Controller 62 is operationally connected to switch 76, flame detection circuit 60 and the fuel source 19 such that, based upon signals 86 received from flame detection circuit 60, controller 62 can start or stop either the exciter 58 or the fuel-air mixture flowing into pipe 18 or both, as further explained below.
The tip of pilot burner 10 can be better seen with reference to
Referring now to
In operation, fuel and air are introduced into longitudinal passage 26. The fuel and air may be introduced from a fuel-air mixture source 19 into fuel introduction pipe 18 or may each be introduced from separate sources into fuel introduction pipe 18. Fuel introduction pipe 18 is in fluid flow communication with longitudinal passage 26 and the fuel and air in pipe 18 is under positive pressure so that fuel and air within pipe 18 flows into longitudinal passage 26. Within longitudinal passage 26, the fuel and air flows in a generally longitudinal direction through passage 26 around spark rod 31 and around and through structural supports 46. Structural supports 46 can be perforated and can be shaped into swirling or diffusion elements to induce premixing of fuel and air within longitudinal passage 26 and prior to reaching the second end 33 of spark rod 31. Whether mixed within longitudinal passage 26 or mixed prior to introduction to fuel introduction pipe 18, the air and fuel should be adequately mixed upon reaching the second end 33 of spark rod 31 to produce a flame upon exposure to a spark from spark tip 43.
Prior to spark initiation, flame detection circuit 60 is powered up. Terminal 74 of flame detection circuit 60 is connected to potential terminal 72 of exciter 58 and electrode tube 40, thus supplying a small current potential to both. While this current can be direct current or alternating current, the operation will be described with respect to alternating current, except where indicated. Spark is initiated by closing switch 76; thus providing power to exciter 58. Center electrode 34 is connected to terminal 70 of exciter 58 and, as previously indicated, electrode tube 40 is connected to the terminal 72 of exciter 58 and flame detection circuit 60. Accordingly, in the embodiment of
When the exciter 58 provides a sufficiently large potential difference, an electrical pulse will jump between electrode 34 to electrode tube 40 at the spark tip 43 of spark rod 31; preferably, the current will follow the ionized path created by the semiconductor 52. This electrical pulse will be in the form of a spark and can ignite the fuel-air mixture around second end 33 of spark rod 31.
A flame produces free ions in the vicinity of the flame envelope that form an electrically conductive pathway. By placing two electrodes in the flame and applying a voltage between them, a small current will result (less than 10 μA). If one of the electrodes is much larger than the other, current will flow more easily from the small electrode to the large electrode than vice-versa. By applying an AC voltage between the electrodes, a current rectifying property will result and a current will flow across the gap between the two electrodes similar to the rectified current illustrated in
In the invention, tube portion 14 is electrically grounded and serves as a third electrode. Flame rod 48 is designed to be much smaller than tube portion 14 and, when no flame is present, is electrically isolated from tube portion 14 of the housing 12, and hence from ground. Accordingly, if no flame is present, then no current will flow from flame rod 48 to tube portion 14. If the spark generated at second end 33 of spark rod 31 creates a flame, flame rod 48 is positioned to be in the flame. In other words, the flame rod 48 is positioned so that the flame 50 will bridge the gap 51 so that spark rod 31 is no longer electrically isolated from tube portion 14 and a rectified current (similar to that illustrated in
Detection circuit 60 sends a signal to controller 62 based on the establishment of a current between flame rod 48 and tube portion 14. When a rectified current is established, detection circuit 60 sends a signal to controller 62. In response to the signal, controller 62 opens switch 76 to shutdown exciter 58 and, hence, stop spark rod 31 from generating sparks. If controller 62 does not receive the signal that a rectified current is established within a predetermined period of time (the timeout period), then controller 62 will shutdown exciter 58 and stop fuel introduction into pipe 18. Additionally, in the case of a short or ground failure, an alternating current can be established between flame rod 48 and tube portion 14, similar to the current illustrated in
In one embodiment, an inventive integrated high energy ignition (HEI) and flame ionization detection (FID) device operates as follows:
For safety considerations, it is important that the ignition system ignite the fuel-air mixture as soon as possible after introduction of fuel into pipe 18 has commenced. Accordingly, the timeout period is typically set very short, often five (5) seconds or less. Accordingly, it is important that the flame detection system registers positive flame signal as soon as possible after flame is established. As will be realized from the above description, the current invention has the advantage of being capable of simultaneous rapid ignition and flame detection utilizing an integrated ignition and flame detection system. The term simultaneous refers generally to flame detection during the period that the exciter is energized and the spark rod is sparking. In a system with sequential flame detection, the ignition attempt (sparking of the spark rod) is made, then the exciter is de-energized, and then the flame detector is energized to detect flame. If no flame is detected, the flame detector is de-energized and the exciter re-energized to initiate another spark. In a system with simultaneous flame detection, there is no de-energizing of the exciter for the spark rod before flame detection.
Together, this simultaneous rapid ignition and flame detection help minimize the chance of explosion due to raw fuel being pumped into a burner. Prior art systems have not been able to achieve simultaneous ignition and flame detection in an integrated system. They instead relied on either sequenced ignition and flame detection or completely separate ignition and detection systems.
Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.
