Patent Application
20180283686
The present invention relates generally to gas burner flame rectification, and especially to flame rectification (sensing) for pipe, ribbon, line, or other types of burners.
In many parts of the world, including Canada and the United States, fuel safety Standards, Codes, Acts, etc. require that a burner with a flame space greater than a certain distance be sensed at the farthest point of the ignition. For example, in some jurisdictions, “when a burner has a flame width (or runs the length of a burner) in excess of 3 ft (900 mm) from the source of the burner ignition, (a) the main burner flame shall be proven at the farthest point(s) along its base from the source of ignition; (b) the source of ignition shall be located in the combustion zone adjacent to the entry of the fuel or fuel/air mixture to the burner; and (c) the main burner flame shall be proven at a location providing the most stable flame detection at all firing rates and not affected by the source of ignition.” It is also required that line, pipe, ribbon, and radiant burners that are installed adjacent to one another or connected with flame-propagating devices, shall be considered to be a single burner and shall have at least one flame detector installed to sense burner flame at the end of the assembly farthest from the source of ignition.
One well known technique for detecting the presence of a flame is by using a flame rod, which works based on electrical properties associated with the flame. As a flame burns, it produces an ionized region in its vicinity, thereby providing an electrically conductive medium. This property can be utilized in conjunction with a probe placed into the flame, and a grounded metal burner to produce a usable electrical signal. If such apparatus is constructed with an effective grounded burner area greater than the effective probe area, typically in at least a 4 to 1 ratio, the flame will exhibit electrical characteristics somewhat similar to those of a diode in series with a 10 Mega-ohm resistor. If an alternating current signal is injected into the flame by the probe, the signal will be rectified by the flame. Appropriate filtering and amplification circuitry may then be employed to extract the rectified signal
In the line, pipe, ribbon and radiant heaters, special flame rods are fabricated and fastened to the body of the burner. These rods run the length of the burner body, and at the end of the flame space the rods protrude into the flame. Flame rods can be fabricated into various lengths to suit the application.
Typically flame rods are made using a conductor, such as a high temperature alloy like Kanthal, Stainless Steel, and Inconel rod. The rod is usually surrounded by an insulator (ceramic, steatite etc.) to protect the rod from grounding. The principles of flame rectification require that flame sensing rod is to tell the controller that the main gas burners have ignited and a flame is present. If no flame is present after a certain amount of time, the controller needs to close the gas valves to the burners.
Typically, a burner or multiple burners are installed in a chamber and there is no direct access to the opposite end of the burner assembly. Thus, sensing the flame at the farthest point from ignition becomes very difficult. If a flame rod is mounted at the end of a burner, service and maintenance become very difficult.
The problem is that most currently available devices are not reliable for numerous reasons. They use a stainless steel, Kanthol or Inconel rods that run the length of the burner. Along the way the rod has several ceramic insulators that are fastened to brackets that allow the rod to remain fixed. At the end of the rod a portion is positioned into the flame. These ceramic insulators often move or crack, and as a result, the flame rod grounds and can no longer send an electrical signal to the burner flame safeguard. In addition, depending on who makes the assembly, some providers add extra steel over the area of the flame. This is in hopes that by providing a greater surface area over the flame it will sense better. Often, during operation as the steels expands when heated, it can touch the burner surface, causing it to ground out and not sense the flame. In this case, it will not re-ignite as the flame relay will not hold open, as when it is grounded the flame cannot sense during the trial for ignition period. In order to fix a failed flame rod, the burner needs to be removed from the chamber and a new assembly be installed, in the hopes that when reinstalled it will work. If not, the burner needs to be removed and process repeated.
Most manufacturers of such components are always pushing the envelope with the design of flame rods and only try to reduce the amount of ceramic (insulators) used. In addition, developers look for more robust materials or alloys that can handle exposure to high temperatures.
The present invention replaces the flimsy and problematic flame rod, with an insulated electric element to provide a robust and reliable flame sensor. The present flame sensing element can be extended along a long length of any burner without any grounding problem. Therefore, it is ideal for use in pipe, line, ribbon, infrared and tube burners that require to have a flame sensor at the opposite or farthest end from the burner's point of ignition.
One object of the present invention is to provide a sensor to sense flames at the farthest distance from the ignition point in various burners.
Another object of the present invention is to provide a remote sensing rod that solves the issue of flame rods, related to their material being consumable and after a short time will no longer sense a flame.
Another object of the present invention is to replace the currently used flame rods, which are flimsy stainless steel rods, which will be damaged over time, with a more robust systems.
Another object of the present invention is to reduce or rid the reliance on ceramic insulators as part of the flame sensing apparatus.
Embodiments herein will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which:
The figures are not intended to be exhaustive or to limit the present invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the disclosed technology be limited only by the claims and equivalents thereof.
The device disclosed herein, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the disclosed technology. These drawings are provided to facilitate the reader's understanding of the disclosed technology and shall not be considered limiting of the breadth, scope, or applicability thereof. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.
The remote flame sensing device of the present invention is illustrated in
The preferred embodiment of the present flame sensing device comprises of a rod-element 110, which extends from the proximal end 103 of the burner towards the distant 104 of the burner. The structure of the rod-element 110 is illustrated in
The outer rod can also be from other high temperature metal alloys such as Incoloy 800 or Inconel 601. The outer sheath can withstand prolonged operation at high temperatures.
In one embodiment of the present invention, as illustrated in
Two brackets, 130 and 140, rigidly hold the flame sensor and the rod-element, where the two are attached to each other. Therefore, the sensor 150 is connected to a main controller through the rod-element 110, which is attached to the burner body (on the sides of the pipe) 100 by a set of brackets 180, 181.
A long rod-element 110 is attached to one end 141 of the flame detector 150, extending from the distal end of the burner to the proximal end of the burner. In addition, a shorter rod-element 112 is connected to the second end 131 of the flame detector 150 to firmly hold the flame detector. The length of the rod-element depends on the burner length, and it can be any length. More commonly used lengths are 42″, 48″, 60″, 72″ and 144″. The outer diameter is preferably 0.246″.
In another embodiment of the same invention, as illustrated in
In another embodiment of the same invention, flame sensor is an integral part of the rod element, as illustrated in
As illustrated in
In operation, a controller applies alternating voltage between the flame sensing rod and the base of the flame (ground). The ions in the flame provide a high resistance current path between the two. Because the surface of the base flame is larger than the sensing flame rod, more electrons flow in one direction than the other, resulting in a very small DC offset current. If there is a flame present, the DC offset is detected by the controller, which tells the gas valve to remain open. If there is no current flow, the controller will close the gas valve and the system will purge itself of any remnant gas before trying to reignite or lockout.
The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
With respect to the above description, it is to be realized that the optimum relationships for the parts of the invention in regard to size, shape, form, materials, function and manner of operation, assembly and use are deemed readily apparent and obvious to those skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
