Patent Application
20220390108
Furnaces are a major component of many central heating systems that are used to heat large interior spaces, such as houses and other buildings, and to provide heat in industrial applications. Furnaces are also used in utility and chemical industries to provide heat for steam generation and to facilitate the generation of chemical products. The typical operation of a furnace includes the burning of fuel and the resulting movement of an intermediary substance (e.g., air, steam, hot water, etc.) to disperse heat throughout the boilers or to specific areas for work (e.g., applying heat for metallurgy purposes and chemical processing). Fuel sources can include natural gas, liquefied petroleum gas, oil, wood, and coal, among others.
Many types of furnaces utilize a burner to burn the aforementioned fuels to provide heat. However, some burners, such as coal-fired burners, cannot be lit by themselves and rely on an igniter to provide ignition of the fuel. As long as a sufficient amount (depending on the size of the furnace and other relevant specifications) of air is provided and maintained, the fire within the burner is maintained, and thus operation of the furnace is maintained. Because of the popularity of number 2 oil in the U.S., oil-fired burners have historically been employed in furnaces and were generally rated between at about 3-10% of burner capacity. Burner capacity is the capability of the burner to generate heat and is typically measured in MBTU/hr (mega British thermal unit per hour); a normal burner capacity is around fifty to two hundred fifty MBTU/hr. In addition, oil-fired burners require a fairly high temperature to maintain burning, which necessitated large amounts of energy. As natural gas became cheaper and more readily available for mass use, gas burners began to overtake oil burners.
However, because both gas from external gas lines and external air (i.e., “combustion air,” as described herein) are needed for combustion, gas igniters can be quite expensive. In addition, especially in the case of use in buildings with limited space (e.g., older buildings), there can be significant physical constraints on how much combustion air can be accessed. For example, in older coal and oil burners, the internals of these burners pose a physical limitation on the size of the igniter that can be used. This can limit the cost and efficiency of these burners.
In one embodiment, a furnace igniter system is provided. The system comprises a guide tube comprising an end to be positioned within a furnace; the guide tube is configured to receive gas from a gas inlet and air from an air inlet and provide the gas and air to the furnace; and an igniter tip connected to the end of the guide tube to be positioned within the furnace. The igniter tip comprises first and second sets of holes, holes of the first set of holes having a size and orientation different than a size and orientation of holes of the second set of holes, the first and second set of holes being configured to provide the gas to the furnace.
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the applications of its use.
Embodiments of the present disclosure relate to an improved and high capacity gas igniter for furnaces and burners. The disclosed igniter can include an igniter tip that is annular in shape (i.e., ring-like), which includes various holes of different sizes and angular projections distributed throughout. Typically, igniter tips are not annular and do not include holes of different sizes or angular projections. Combustion via standard igniters relies on pumping air and fuel (external combustion air or air from outside the furnace) to a pilot at the end of an igniter tip. The disclosed igniter tip, because of its annularity and hole design, can be uniquely connected to the gas line used by the burner and pilot. The disclosed holes cause radial gas dispersion, which increases mixing with the surrounding air (e.g., internal combustion air or air from inside the furnace). Increased mixing can cause more robust and reliable combustion. The holes in the igniter tip can be in a variety of configurations and patterns and are described in more detail with respect to
In addition, embodiments of the present disclosure relate to a safety-mechanism that can prevent damage to igniters and igniter tips. Because of the extreme conditions at the inside of a furnace, igniters can often fail and/or break when the igniter tip breaks off from the igniter. Many igniters include concentric tubes, such as an outer and an inner tube. The tubes are often welded together, and the igniter tip is welded or attached at the end. The outer tube is in direct contact with the furnace air, which can reach temperatures up to 650° F., while the inner tube is usually at a much lower temperature because of the gas it transports. In some cases, such as during the winter, the transported gas and inner tube can be as low as 25-30° F. This difference in temperature can cause the outer tube to undergo higher degrees of thermal expansion than the inner tube. Because of such non-uniform expansion, significant stresses can be put on the igniter tip, which can detach from the system and potentially cause explosions and other damage. In one or more embodiments, the igniter tip disclosed herein utilizes a slip-joint-like mechanism or sleeve that connects the inner and outer tubes; this allows the inner tube to slide when undergoing thermal expansion, which alleviates stress from building up on the inner tube and igniter tip, preventing damage. In addition, the sleeve can employ Labyrinth teeth to control leakage from the slip-joint. This is a major improvement over existing ignitor systems.
Accordingly, as will become apparent, the disclosed igniter offers various advantages, such as a diminished physical footprint, high turn-down capability, improved reliability in ignition in both cold and hot boilers, increased flame stability, a reduced requirement in terms of combustion air and cooling air, and greater robustness against damage.
The second portion 130 of igniter 100 can include a common gas inlet 108, pilot gas regulator 110, spark rod 112, pilot air branch 114, common air inlet 116, various manual valves 118, a primary air source 120, a secondary air branch 122, and a pilot gas branch 124. During operation, a fraction of the gas from the common gas inlet 108 can be controlled by the pilot gas branch 124 and pilot gas regulator 110 and sent to a protective environment to create a small stable flame (e.g., pilot 102). In some embodiments, the common gas inlet 108 can provide gas at around five to twenty pounds per square inch (PSI). In some embodiments, the pilot gas regulator 110 can be set at two PSI. The pilot 102 can be ignited by the spark rod 112. In some embodiments, the pilot 102 can be continuously lit to ignite and stabilize the main flame of the igniter. A continuously lit pilot 102 can enable a high turndown capability, between around fifteen to fifty MBTU/hr. In some embodiments, the turndown ratio (i.e., the ratio of minimum load to maximum load) can be around 1:3 to 1:4, whereas many igniters have zero turndown ratio.
In some embodiments, a majority of the gas from the common gas inlet 108 can be sent to igniter tip 104, which is configured to provide a flame for ignition of the furnace. In some embodiments, combustion air is provided by the common air inlet 116, and the manual valves 118 can split the combustion air into primary and secondary combustion air (e.g., primary air source 120 and secondary air branch 122). In some embodiments, the common air inlet 116 can have a diameter of around three inches. The primary combustion air is provided to igniter tip 104. Pilot air branch 114 can provide air from the common air inlet 116 to the pilot 102. In some embodiments, igniter tip 104 and pilot 102 together can use about 240 standard cubic feet per minute (SCFM) of combustion air for ignition. The primary combustion air exits igniter tip 104 through an annular area between the igniter inner wall and the pilot 102 to create a flammable mixture of air and fuel at the core of the main flame.
Secondary combustion air is routed through secondary air branch 122 and provided at a different point to igniter 104. Air can be routed directly from the burner wind box and used as both secondary combustion air and tertiary combustion air. In some embodiments, secondary combustion air can include both air from the burner wind box and air from the common air inlet 116 that is routed through secondary air branch 122. A burner wind box is a part of the furnace that provides combustion air to the burner and is not shown in the figures. Additional details on the secondary and tertiary combustion air flows are discussed below with respect to
The holes 402, 404, 406 can be configured to project gas outward in the various directions to increase mixing between the combustion air and the fuel (e.g., the gas). Arrow 408 illustrates the flow of pilot air (e.g., from pilot air branch 114), while arrow 410 illustrates the flow of pilot gas (e.g., from pilot gas branch 124). Arrows 412 illustrate the flow of gas directed outward within the furnace from holes 402; arrows 414 illustrate the flow of gas directed outward within the furnace from holes 404; and arrows 416 illustrate the flow of gas directed outward within the furnace from holes 406. Arrow 418 illustrates the flow of primary combustion air in the annular area between the pilot 102 and the outer tube (not shown).
The disclosed high capacity igniter can fire up to 50 MBTU/hr of natural gas through a small guide tube (around six inches in diameter) with one gas supply line and one common air inlet. A small fraction of the gas is taken from the gas supply line, controlled, and sent to a protective environment to create a small, stable flame, which acts as a pilot for the main igniter. The pilot flame can be ignited by a high energy spark rod. The continuously lit pilot ignites and stabilizes the igniter main flame at all times. A continuously lit pilot flame enables a high turndown capability (fifteen to fifty MBTU/hr).
A majority of the gas is sent to the main igniter tip, which has multiple holes with different sizes and projection angles to ensure good mixing with the air and thus a stable igniter flame. The combustion/cooling air is split between the pilot and the main igniter, and the split ratio is controlled via manual valves. The igniter needs only 240 SCFM of combustion/cooling air for both the pilot and the igniter primary combustion air. Secondary and tertiary combustion air are taken directly from the burner wind box. Some of the secondary combustion air can be taken from the primary combustion/cooling air and is controlled via a manual valve. The primary combustion air exits the igniter through an annular area between the igniter inner wall and the pilot to create a flammable mixture of gas and fuel at the core of the main flame. The igniter tip has a unique controlled-leak sliding mechanism to avoid stress due to differential thermal expansion between the inner and outer tube delivering gas to the igniter tip.
While various embodiments have been described above, it should be understood that they have been presented by way of example and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail may be made therein without departing from the spirit and scope. In fact, after reading the above description, it will be apparent to one skilled in the relevant art(s) how to implement alternative embodiments. For example, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.
In addition, it should be understood that any figures which highlight the functionality and advantages are presented for example purposes only. The disclosed methodology and system are each sufficiently flexible and configurable such that they may be utilized in ways other than that shown.
Although the term “at least one” may often be used in the specification, claims and drawings, the terms “a”, “an”, “the”, “said”, etc. also signify “at least one” or “the at least one” in the specification, claims and drawings.
Finally, it is the applicant's intent that only claims that include the express language “means for” or “step for” be interpreted under 35 U.S.C. 112(f). Claims that do not expressly include the phrase “means for” or “step for” are not to be interpreted under 35 U.S.C. 112(f).
