Patent Description:
Oxides of nitrogen in the form of nitrogen oxide (i.e., NO) and nitrogen dioxide (NO<NUM>) that can collectively be referred to as NOx, are generated by the burning of fossil fuels in the air which provides the nitrogen and the oxygen in the form of diatomic gases for forming NOx. Along with NOx emitted from motor vehicles, NOx from fossil fuel-fired industrial and commercial heating equipment (e.g., furnaces, ovens) is known to emit NOx and thus, besides motor vehicles, is also recognized to be a major contributor to poor air quality and also smog.

Recycling of combustion exhaust gas (also known as flue gas) commonly known as exhaust gas recycling (EGR) is a known method to achieve lower NOx emissions in fossil fuel-fired combustion applications. Numerous studies have evidenced the beneficial effect of recycling combustion exhaust gas using a variety of external piping arrangements. However, the addition of EGR to any fired chamber application generally involves increased equipment complexity, capital, and/or operational expense.

One conventional method to achieve EGR for industrial fuel-fired burners is to have the exhaust gas externally piped back from the exhaust stack to the combustion air intake where it can enter the combustion air fan to be mixed with the combustion air, where this exhaust gas and air mixture is sent to an air inlet of the burner. This known EGR arrangement needs additional piping and apparatus around (external to) the fuel-fired burner. This known EGR arrangement also involves an enlargement (or up-sizing) of the combustion air fan to handle the increased volume of the added flue gas. Larger air fans result in increased cost and also use more electricity per unit of heat produced. Moreover, the fan materials of construction generally need upgrading to higher temperature capable alloys needed to handle the additional temperature and corrosive compositions generally present in the exhaust gas. <CIT> discloses a fuel fired burner and method of its operation. The burner features a refractory lined burner housing having a fuel inlet coupled to a fuel pipe coupled to a burner nozzle. The burner features a hot flue gas recycle port and a combustion air inlet coupled to a combustion air nozzle. The combustion air nozzle circumscribes the fuel nozzle. The combustion air nozzle is configured to direct the combustion air into a chamber, thereby sucking flue gas through an annular gap into the chamber using a jet pump effect.

This Summary is provided to introduce a brief selection of disclosed concepts in a simplified form that are further described below in the Detailed Description including the drawings provided. This Summary is not intended to limit the claimed subject matter's scope.

The method and the burner according to the invention recognize in order to more economically implement EGR for fuel-fired burners, what is needed is a fuel-fired burner arrangement that lowers capital and operating costs by reducing the complexity of the EGR for the burner. The method and the burner according to the invention accomplish this by utilizing a jet pump arrangement that is located entirely inside the burner housing which eliminates the previously needed externally positioned hot exhaust gas piping, as well as the special fan and associated controls needed to mix the exhaust gas and the combustion air in proper proportions.

The invention comprises a fuel-fired burner that includes a combustion air inlet for receiving combustion air coupled to a combustion air nozzle at an input to a second chamber within a burner housing spaced apart from a third chamber that is within the second chamber. The combustion air nozzle directs the combustion air into the third chamber. A fuel pipe having a fuel inlet is coupled to a burner nozzle secured to a burner mounting plate having a recycle port(s) for receiving hot exhaust gas provided to the second chamber. A jet pump located entirely inside the burner housing is configured to receive the exhaust gas from the second chamber. The jet pump operates by flowing the combustion air through the combustion air nozzle which suctions in the hot exhaust gas through the recycle port into an exhaust gas path bounded by the second chamber then into a gas mixing zone extending from an output of the combustion air nozzle to an input end of the third chamber for mixing the hot exhaust gas and the combustion air.

Disclosed aspects of the invention are described with reference to the attached figures, wherein
like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate certain disclosed aspects. Several disclosed aspects are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the disclosed invention.

The invention comprises a fuel-fired burner including EGR including a jet
pump arrangement located entirely inside the burner housing that mixes exhaust gas with combustion air. As used herein the term "jet pump" refers to a passive pump (meaning the pump is not supplied any electrical power), where the jet pump is configured so that a small jet of a fluid that is in rapid motion lifts or otherwise moves by its impulse a large quantity of the fluid with which it mingles, in this case, exhaust gas. A jet pump thus operates by what is more generally called the Venturi effect.

<FIG> depicts a cross-sectional view of an example fuel-fired burner <NUM> shown as a fuel burner, according to an embodiment of the invention, including EGR comprising a jet pump arrangement provided entirely inside the burner housing <NUM> that mixes hot exhaust gas (also known as flue gas) received through a recycle port <NUM> formed (such as cut) in a burner mounting plate <NUM> to a recycled exhaust gas path (exhaust gas path) <NUM>. The exhaust gas path <NUM> is bounded by an outside of a third chamber <NUM> and an inside of a second chamber <NUM> which enables the exhaust gas to flow into a gas mixing zone <NUM> as shown between the combustion air nozzle <NUM> and the input to the third chamber <NUM>. The burner mounting plate <NUM> closes and seals the burner housing <NUM> (sealed other than the recycle port <NUM>) on the side of the fuel-fired burner <NUM> having the burner nozzle <NUM>. A fuel pipe <NUM> having a fuel inlet <NUM> is coupled to the burner nozzle <NUM>.

The fuel-fired burner <NUM> also includes another plate shown as a wall plate <NUM> that can represent a mounting wall in the customer's application for the fuel-fired burner <NUM>. <FIG> shows the burner discharge sleeve <NUM> connected to the third chamber <NUM> by a weld region <NUM>. The wall plate <NUM> is shown provided with a hole in its center region to enable insertion and thus the connection of the burner discharge sleeve <NUM> two the third chamber <NUM>. A wall plate <NUM> with a hole in the center region is generally provided by the customer. For example, enabled by the hole in the wall plate <NUM>, the burner discharge sleeve <NUM> can be connected (e.g., welded) to the third chamber <NUM> as shown in <FIG>. Alternatively, the burner discharge sleeve <NUM> can be connected (e.g., welded) to the portion of the burner mounting plate <NUM> radially inside the recycle port <NUM>. Both of these options allow for the fuel-fired burner <NUM> to be inserted into the customer's application chamber, such as a boiler, furnace or a heater, as a single unit.

The wall plate <NUM> comprises a generic plate that represents the wall of another apparatus that receives heat from combustion performed by the fuel-fired burner <NUM>, such as a boiler, furnace, or heater. The wall plate <NUM> generally has an opening large enough for the burner discharge sleeve <NUM> to pass through for mounting and still have enough surface area to place welded mounting studs on the wall plate <NUM>. The burner mounting plate <NUM> generally includes mounting holes in the flange portion and the recycle port(s) <NUM> in the central area as shown in <FIG> described below. The burner mounting plate <NUM> is generally welded to the third chamber <NUM> as shown in <FIG>, and the burner housing <NUM>, and the burner mounting plate <NUM> generally has a dimension generally being a diameter that is larger than the burner housing <NUM> (and the opening in the application wall) to create a mounting flange with holes for the studs of the wall plate <NUM> to pass through.

The gas mixing zone <NUM> is between an output of a combustion air nozzle <NUM> and the burner mounting plate <NUM>. The gas mixing zone <NUM> is for mixing hot exhaust gas with combustion air propelled by a combustion air fan <NUM> through ducting <NUM> to a combustion air inlet <NUM> that flows through the combustion air nozzle <NUM> to provide an internal EGR.

Although shown as an external combustion air fan <NUM> coupled by ducting <NUM> to the combustion air inlet <NUM>, the combustion air fan <NUM> can also be located in other locations.

For industrial fuel-fired burners that generally need large volume combustion air flows at a relatively high pressure, the combustion air fan <NUM> is generally mounted away from the fuel-fired burner <NUM> and is ducted to the combustion air inlet <NUM> as shown in <FIG>. In some other arrangements, particularly if the air flow and pressure needs of the fuel-fired burner are lower, the combustion air fan <NUM> can be mounted directly onto the combustion air inlet <NUM> of the fuel-fired burner <NUM> so that no ducting <NUM> is needed.

In another arrangement, the burner discharge sleeve <NUM> can be made of a refractory material, such as configured as a block. In the case the burner discharge sleeve <NUM> comprises a block of generally a refractory material, the third chamber <NUM> would be extended slightly past the plane of the burner mounting plate <NUM> to slide as an open cylinder into an opening of this block. The internal flared shape for the burner discharge sleeve <NUM> is generally maintained whether the burner discharge sleeve <NUM> comprises a block or comprises sheet metal. The burner discharge sleeve <NUM> can represent any firing chamber that such a fuel-fired burner can fire into, such as a boiler or a heater.

There is no requirement to electronically control the exhaust flow entering through the recycle port(s) <NUM> into the jet pump because passive control can be used since variations in the flow of combustion air from the combustion air fan <NUM> will cause the amount of suction in the jet pump to vary to automatically increase or decrease the amount of exhaust gas being suctioned through the recycle port(s) <NUM> via the exhaust gas path <NUM> into the jet pump. The size of the recycle port(s) <NUM> can be designed to determine the amount of exhaust flowing into the exhaust gas path <NUM> to be utilized by the jet pump. The recycle port(s) <NUM> can be sized and fixed in their size based on the amount of suction that is produced by the jet pump at a given combustion air flow rate.

The materials of construction for the combustion air fan <NUM> can vary, but most combustion fans comprise steel. The size of the combustion air fan <NUM> is selected by the fuel-fired burner designer to meet the pressure and volume requirements for the combustion air. The design of the combustion air fan depends on the rotations per minute (rpm), wheel (or blower impeller) diameter, and the wheel width. A bigger wheel in the combustion fan provides a higher volume of combustion air.

A combustion air fan <NUM> provides the proper combustion air volume and pressure through the combustion air inlet <NUM> into the burner housing <NUM>, which is connected to the jet pump nozzle. Although not shown in <FIG>, the fuel, and the air can be controlled using individual valves on the air and fuel lines that are driven by a control signal from the system that monitors the stack exhaust oxygen level. Alternatively, such valves can be driven by controllers for measuring the air and fuel flow and holding these flows to a preset ratio. As described above, the air exiting the combustion air nozzle <NUM> functioning as a jet pump nozzle drives the jet pump to suck in exhaust gas from the recycle port <NUM> through the exhaust gas path <NUM> to the gas mixing zone <NUM>.

In operation of a disclosed fuel-fired burner, the jet pump, utilizing a centrally positioned combustion air nozzle <NUM> creates a negative pressure condition when the combustion air fan <NUM> is operating. This negative pressure is operable to pull hot exhaust gas from the exhaust gas path <NUM> into the gas mixing zone <NUM> without the use of an additional fan or the need to up-size the combustion air fan <NUM>. The exhaust gas enters the burner housing <NUM> as described above through the recycle port <NUM> in the burning mounting plate <NUM> of the burner, where the exhaust gas is suctioned into the exhaust gas path <NUM> then into the gas mixing zone <NUM> where it is mixed with the combustion air, and then passes through the third chamber <NUM> into the burner discharge sleeve <NUM> where the exhaust gas and air mixture can be mixed with fuel in various ways to provide a flame emerging from the burner nozzle <NUM>.

The resulting mixture of combustion air, exhaust gas, and fuel gas, results in a combustion which produces a flame with a lower level of NOx emissions as compared to a flame without EGR. It is this lower level of NOx emissions provided by disclosed fuel-fired burners that is believed to make disclosed fuel-fired burners and related aspects particularly valuable. Disclosed aspects create this low NOx emissions result without the use of external hot exhaust gas piping, without the need for an upsized and/or upgraded combustion air fan, or additional controls, and without the associated safety concerns of having external hot exhaust piping running through the work area of a plant.

As described above, the disclosed fuel-fired burner comprising a jet pump arrangement are sized and located entirely inside the burner housing <NUM>. The combustion air fan <NUM> provides the proper combustion air volume and pressure into the burner housing <NUM>, which is connected to the combustion air nozzle <NUM>. The combustion air nozzle <NUM> ejects high velocity combustion air outward from its outlet including into the third chamber <NUM>. The high velocity combustion air exiting the combustion air nozzle <NUM> drives the jet pump. The jet pump, which can include more than one combustion air nozzle <NUM>, creates a negative pressure condition when the combustion air fan <NUM> is operating that suctions in hot exhaust gas through the recycle port <NUM> through the exhaust gas path <NUM> to the gas mixing zone <NUM>.

There can optionally be a butterfly type control valve in the combustion air and fuel supply lines with control by a control system in the plant where the fuel-fired burner <NUM> is installed, where the control system can provide air and fuel ratio control for the fuel-fired burner <NUM>. In that case the fuel-fired burner <NUM> is connected to the plant's fuel and air control system. described combustion air blowers connected to the burner, and combustion air blowers connected via duct work. This is an alternative to the ducted air arrangement shown in <FIG> including ducting <NUM>, where control valve for the air would typically be placed in the ducting <NUM> either by the manufacturer of the fuel-fired burner <NUM>, or by others.

This negative pressure, suctions exhaust gas from the recycle port <NUM> to the exhaust gas path <NUM> into the gas mixing zone <NUM> without the use of an additional fan or the need to up-size the combustion air fan. The exhaust gas thus enters the burner housing <NUM> through recycle port(s) <NUM> in the burner mounting plate <NUM> which is transported by an interior sleeve referred to herein as the exhaust gas path <NUM>, and is mixed in the gas mixing zone <NUM> with the combustion air, and then passes into the burner discharge sleeve <NUM> where it can be mixed with fuel in various ways to provide a flame at the burner outlet around the burner nozzle <NUM>.

<FIG> depicts a generalized jet pump, with the various regions of the jet pump with their respective reference numbers shown in <FIG> added to so that the jet pump can be considered to be a disclosed internal jet pump now shown as fuel-fired burner portion <NUM>. A high velocity jet of gas shown as q<NUM> at a pressure of Pi corresponds to combustion air propelled by the combustion air fan <NUM> shown in <FIG> after it exits a combustion air nozzle <NUM> positioned in the burner housing <NUM> with an arrow depicting this combustion air <NUM> flowing in the gas mixing zone <NUM> as shown in <FIG>.

The combustion air when flowing left to right in <FIG> between an output of the combustion air nozzle <NUM> and the burner mounting plate <NUM> creates an impulse sufficient to suction in a second gas (shown in <FIG> as q<NUM> at a pressure of P<NUM>), in this case being the hot exhaust gas entering through the recycle port <NUM> to the gas mixing zone <NUM>, to mix with air from the combustion air fan (see the combustion air fan <NUM> in <FIG>), so that the gas mixing zone <NUM> creates a larger combined volume of the mixed gas as compared to the volume of the combustion air supplied by the combustion air fan <NUM>. The "qd" in <FIG> shown at a pressure of Pd at an output of the fuel-fired burner portion <NUM> is the mixed gas (combustion air mixed with the hot recycled exhaust gas).

<FIG> depict various views of the example fuel-fired burner including EGR comprising a jet pump arrangement provided inside the burner housing that mixes hot exhaust gas with combustion air to provide internal exhaust gas recycle as shown in <FIG>, according to an embodiment.

<FIG> depicts a back view looking at the burner mounting plate <NUM> of an example fuel-fired burner and the wall plate <NUM> attached (shown as bolted on by bolts <NUM>) to the burner mounting plate <NUM> that closes the burner housing <NUM>. The recycle ports <NUM> are generally cut into the burning mounting plate <NUM>, where the recycle ports <NUM> are shown only by example as being an annular-shaped region.

<FIG> depicts a fuel-fired burner taken along the cut line B-B shown in <FIG>. depicts the direction of flow for the combustion air and the hot exhaust gas. The hot exhaust gas can be seen to make a turn inwards after flowing past the third chamber <NUM>. <FIG> depicts a side cut view of the fuel-fired burner shown in <FIG>. The third chamber <NUM> can be seen to be fully open on its side facing the output of the combustion air nozzle <NUM>.

A further benefit disclosed fuel-fired burners is that combustion air in the burner housing <NUM> cools the exhaust gas in the exhaust gas path framed by the second chamber <NUM>. As a result, because the second chamber <NUM> generally comprises steel which is known to be thermally conductive, the combustion air also cools the second chamber <NUM>. This cooling of the hot exhaust gas also transfers heat to the combustion air used for combustion, which in turn, increases the overall thermal efficiency of the combustion process for the fueled-fired burner <NUM> compared to a conventional "piped" EGR system.

Computational Fluid Dynamics (CFD) Simulation is one method that can be used to determine at least one design parameter for the fuel-fired burner <NUM>. For example, design parameters for simulation for a disclosed fuel-fired burner can include the internal geometry, sizes of the recycle ports <NUM>, and an orientation of the combustion air nozzle <NUM> relative to the third chamber <NUM>.

Disclosed fuel-fired burners can be constructed of rolled and formed sheet metal, tubing, pipe such as comprising steel which can be welded, or can use another suitable high temperature tolerant material. For example, the burner housing <NUM> generally comprises shaped sheet-metal. The various connections between components can be made by bolting on with flanches or by welding, such as bolting on with flanches of the burner mounting plate <NUM> to the end of the burner housing <NUM>, and securing the combustion air nozzle <NUM> to the second chamber <NUM> using a weld.

Disclosed invention's aspects that as described above build entirely inside the burner housing
<NUM> a jet pump that implements EGR can be applied to generally essentially any fuel-fired burner. A variety of fuel gases, such as natural gas or propane, or fuel liquids can be used.

Claim 1:
A method, comprising:
providing a fuel-fired burner (<NUM>) comprising a burner housing (<NUM>) having a fuel inlet (<NUM>) coupled to a fuel pipe (<NUM>) coupled to a burner nozzle (<NUM>) secured to a burner mounting plate (<NUM>) that has at least one recycle port (<NUM>), a combustion air inlet (<NUM>) for receiving combustion air coupled to a combustion air nozzle (<NUM>) positioned beginning at an input to a second chamber (<NUM>) within the burner housing (<NUM>), the combustion air nozzle (<NUM>) having an output spaced apart from a third chamber (<NUM>) also within the second chamber (<NUM>), wherein the combustion air nozzle (<NUM>) is configured to direct the combustion air into the third chamber (<NUM>), and a jet pump, comprising the combustion air nozzle (<NUM>), second chamber (<NUM>) and third chamber (<NUM>), is located entirely inside the burner housing (<NUM>);
directing the combustion air using a combustion air fan (<NUM>) from the combustion air inlet (<NUM>) through the combustion air nozzle (<NUM>);
directing fuel through the fuel pipe (<NUM>) to the burner nozzle (<NUM>) to implement a combustion process that generates a flame originating at the burner nozzle (<NUM>) which generates a hot exhaust gas, and
operating the jet pump by flowing the combustion air through the combustion air nozzle (<NUM>) with a sufficient velocity for creating an impulse that suctions in the hot exhaust gas through the recycle port (<NUM>) into the second chamber (<NUM>) then into a gas mixing zone (<NUM>) extending from an output of the combustion air nozzle (<NUM>) to an input end of the third chamber (<NUM>) which mixes the hot exhaust gas suctioned in with the combustion air received from the combustion air nozzle (<NUM>).