Compact low NOx gas burner apparatus and methods

Compact burners that produce low NOx and how to do so

Full description

Background of the invention

The present invention relates to gas burner apparatus and methods for burning mixtures of fuel gas and air by which flue gases with low NOx contents are produced.

Government authorities continually impose emission standards that limit the amounts of gaseous pollutants such as oxides of nitrogen (NOx) that can be emitted into the atmosphere. Such standards have led to the development of different and improved gas burner designs that reduce the production of NOx and other polluting gases. For example For example, methods and devices have been developed where all the air and some fuel are in a first zone while the remaining fuel is burned in a second zone. In this staged fuel combustion method, an excess amount of air in the first zone acts as a diluent - the temperature of the combustion gases and thus reduces the formation of NOx. Other methods and devices have been developed in which flue gases are mixed with fuel gas and/or mixtures of fuel gas and air in order to dilute the mixtures, lower their combustion temperatures, and form NOx.

Although the methods and combustion devices according to the previous technology described above used to produce flue gases with low NOx contents have achieved varying degrees of success, there is still a need to improve gas combustion devices and the methods used to burn fuel gas, where a device is used. Simple burning is economical and produces flue gases with low NOx contents.

The burners used so far to perform the methods described above are generally large, produce long flames, and have low turn-down ratios.

Therefore, there is a need for improved combustion devices and methods that produce flue gases with low NOx contents. The combustion devices are compact, produce short flames and have high fold rates.

General description of the invention

The present invention provides compact gas burners that produce low NOx and methods for doing so that meet the requirements described above and overcome the shortcomings of the prior art. That is, the present invention provides improved gas burning devices and improved methods for discharging mixtures of fuel gas and air into furnace spaces where the mixtures are burned and form flue gases with low NOx contents. The compact burning devices according to this invention are smaller in size than most burning devices according to the previous technology, have high folding ratios and produce short flames.

A combination gas burning device according to this invention primarily includes a housing with an open end connected to a furnace space and a means for introducing an air flow at a controlled rate into the housing to which it is connected. A refractory burner tile is attached to the open end of the can and an opening is formed in it to allow air to pass from the can into the furnace space. The burner tile includes a wall surrounding the opening, which is located inside the furnace space and forms a mixing zone inside and above the wall. The outer sides of the wall are divided into sections by several connected baffles arranged radially, where alternating sections have the same or different heights and lean toward the opening at the same or different angles. Some or all of the sections, preferably one section after the other, contain passageways formed to transport primary fuel gas from outside the sections to inside the wall. Optionally, a primary fuel gas nozzle connected to a fuel gas source may be arranged within the opening and the slab wall.

burner tile, in order to mix an additional amount of primary fuel gas with the air flowing through the burner tile. One or more fuel gas nozzles are provided, preferably one nozzle for each external inclined wall section, connected to a fuel gas source and arranged outside the burner wall in order to drain secondary fuel gas next to one or more sections. One or more fuel gas nozzles, preferably one fuel gas nozzle after the other, also discharge the primary fuel gas and flue gases into and through the primary fuel gas passages, thus mixing the secondary fuel gas with the flue gases into the furnace space, and mixing. The mixture of secondary fuel gas and flue gases with both unburned air, primary fuel gas and flue gases flows through the opening and wall of the burner slab and the resulting mixture is burned in the furnace space.

Folded flame pattern.

Using improved methods according to the present invention, a mixture of fuel gas and air is discharged into a furnace space, where the mixture is burned in a folded flame pattern and flue gases with low NOx contents are formed. A method according to this invention primarily includes the following steps: discharging air to a mixing zone within and adjacent to a wall extending within a space

The oven has external sides divided into successive sections by several connected beams arranged radially. Successive sections have the same or different heights and lean towards the opening at the same or different angles. One or more sections, preferably one section after another, contain passages formed in it to transport a mixture of primary fuel gas and flue gases from outside the sections to inside the wall. An initial portion of the fuel gas is discharged from locations outside the wall and next to one or more sections of the wall that have passages formed in them, so that the initial portion of the fuel gas is mixed with the flue gases in the furnace space, and the resulting mixture of the primary fuel gas and the flue gases flows toward the mixing area inside the wall through a passage. One or more passages to form a mixture of primary fuel gas, flue gases, and air flowing into the furnace space. At the same time, a secondary portion of the fuel gas from one or more locations is exhausted

The wall and next to one or more sections of the wall so that the secondary fuel gas mixes with the flue gases in the furnace space, and the mixture of the secondary fuel gas and flue gases drains into the mixture of the primary fuel gas, flue gases and air in several separate streams that enter and mix with the primary fuel gas, flue gases and air to form A mixture of fuel gas and flue gases

Highly mixed air burns in a folded flame pattern.

The objectives, features and advantages of the present invention will become readily apparent to those skilled in the art when reading the description of the following preferred embodiments in conjunction with the accompanying drawings. Brief explanation of the drawings

A - Figure 1: shows a perspective drawing of the incendiary slab according to the present invention which includes

On a wall divided into sections by several radial beams so that successive sections have different heights and lean towards the opening at different angles.

Figure 2: shows a side view of a cross-section of the burning device according to the present invention

It is connected to the wall of a furnace containing the burning slab according to Figure 1, and the view of the burning slab is taken along line 2-2 of Figure 1.

Figure 3: shows an upper view of the burner according to Figure 2 taken along the line

3-3 for Figure 2.

Figure 4: shows a side view of a cross-section of the burner slab taken along the length

Line 4-4 of Figure 3.

Figure 5: Shows an image of the folded flame pattern produced by burning devices

And methods according to this invention.

Detailed description:

Referring now to the figures, shows a compact gas burner device that produces low NOx according to the present invention and is generally referred to as 10. As best shown in Figure 2, the burner device 10 is hermetically attached to the bottom wall 12 of a furnace space above an opening formed therein. Although it typically installs a gas burner device

Vertically and ignite upward, as shown in Figure 2. However, it should be understood that the burning device can also be installed horizontally and ignited horizontally, or installed vertically and ignited downward. The burning device 10 consists of a box 14 that has an open end 16 and an open end 18. The box 14 is connected to the oven wall 12 by means of a flange. 20 and several bolts 22 extending through complementary holes in the flange 20 and the wall 12. A control device for regulating the air flow rate regulating register 24 is connected to the box 14 at its open end 16 to regulate the flow rate of combustion air entering the box 14. The furnace wall 12 includes an internal layer of insulating material 26 attached to it, and the open end 18 of the box 14 includes a Burning slab 28 made of flame and heat resistant refractory material attached to it. As shown in Figure 2, the inner surface of the insulating material 26 attached to the furnace wall 12 and the upper surface of the base portion 30 of the burner slab 28 define a furnace space within which the fuel gas and air exhausted by the combustor 10 are burned. The incendiary slab 28 contains a central opening 32 formed in its base part 30 through which the air that is entered into the box 14 is drained by the air entry control device 42. The incinerator slab also includes a wall portion 34 that includes a hollow inner surface 33 that surrounds the opening 32 and forms a circular ledge that extends into the furnace space. The incendiary slab 28, the inner surface 33 of the wall part 34 and the central opening 32 in the basal part 30 of the incendiary slab 28 as well as the enclosure 14 can take different shapes, for example, a circular, rectangular, square, triangular, polygonal or other shape. However, the burning device 10 preferably includes a circular burning slab 28 containing a circular opening 32 formed therein and a circular wall portion 34. It is also preferable for the box 14 to include a circular hole 18 formed in it, and it is preferable for the box to be cylindrical in shape. However, the enclosure may also include a square-shaped opening 18 formed therein and may have square or rectangular sides 15. In a preferred embodiment as shown in Figure 2, the circular opening 32 in the circular burner slab 28 is smaller

A size of the inner surface 33 in its wall 34 is provided so as to provide a circular protruding edge 35 in the slab 28 that acts as a surface to stabilize the flame.

Referring now to Figure 1, a perspective drawing of Al-Harqa slab 28 and its wall 34 is shown. The inner sides of the wall 34 are vertical as best shown in Figure 2. The outer sides of the wall 34 are divided into several sections 36 and 38 by beams arranged radially 0 4 where the successive sections 36 and 38 have the same or different heights and lean toward the opening 32 at the same or different angles. It is preferable that successive sections have different heights and lean at different angles, as shown in the drawings.

Referring now to Figure 4, it can be seen that the sections 36, in a preferred embodiment, have lower elevations and lean toward the opening 32 in the burner slab 34 at larger angles compared to the sections 38 that have higher elevations and lean toward the opening 32 at smaller angles. As will now be understood and as shown in Figures 1-4, sections 36 and 38 alternate between beams 40 around wall 34. In the embodiment shown in the drawing, there are four sections 36 and four sections 38. Depending on the size of the burner, there can be a greater or lesser number of successive divisions, such that the total sum is even numbers, e.g., 8, 6, 4, 10, etc.

The successive sections 36 have heights ranging from about 0 to about 40.64 cm (16 inches) and are inclined toward opening 32 at an angle ranging from about 0 to about 90. The successive sections 38 can have the same or different heights as the successive sections 36 ranging from about 5.08 cm (2 inches) to about 40.64 cm (16 inches) and lean toward the slot 32 at the same or different angles ranging from about 0 to about 60. Preferably, the 36 successive sections have heights ranging from about 0 to about 40.64 cm (16 inches) and are inclined at an angle ranging from about 0 to about 90 degrees, while the 38 successive sections have different heights ranging from about 5.08 cm (2 inches) to about 40.64 cm (16 inches) and tilt at different angles ranging from about 0 to about 60. As best shown in Figures 2-4, each section includes:

Sections 36 on a passage 42 extending from outside to inside wall 34 through which fuel gas mixed with flue gases flows as further described below.

In a currently preferred arrangement, the first of the successive sections has a height of about 17.78 cm (7 in) and leans toward the opening at an angle of about 20, while the second of the successive sections has a height of about 22.86 cm (9 in) and leans toward The opening is at an angle

It is about 10.

As shown in Figures 1 and 2, a central primary fuel gas nozzle 44 may optionally be arranged within the opening 32 near the bottom of the burner slab 28. When used, connect the nozzle 44 to the fuel gas manifold 48 via a channel 46 . Channel 46 is connected to the manifold 48 using a union connection 50, and channel 52 connected to the manifold 48 is connected to a source of compressed fuel gas. As shown in Figures 2 and 3, a venturi tube 37 may optionally be arranged around and above the nozzle 44 so as to form a thread of fuel gas and air

It is poor in fuel gas and burns in the fuel tube 37 and above it. It may also include

The burner 14 is optional with several nozzles 44 and venturi tubes 37 instead of a single nozzle 44 and a single venturi tube 37.

As best shown in Figures 2 and 3, several secondary fuel gas discharge nozzles 54 are spaced apart on the surface 30 of the burner slab 28 adjacent to the bottoms of the sections 36 and 38 of the wall 34. The nozzles 54 are arranged adjacent to the intersection points of the sections 36 and 38 with the surface of the basal portion 30 of the incendiary slab 28. The nozzles 54 are connected to fuel gas channels 56 (see Figure 2) which are connected to the fuel gas manifold 48 by means of connections 58. The nozzles 54 arranged adjacent to the sections 38 include fuel gas discharge holes through which secondary fuel gas is discharged in fan shapes parallel to and substantially adjacent to the outer surfaces of the sections 38. The nozzles 54 arranged next to the sections 36 include holes for the fuel gas discharge formed through which the secondary fuel gas is discharged in fan shapes parallel to the external surfaces.

Essentially for Sections 36 and adjacent thereto. When the secondary fuel gas discharged through the nozzles 54 flows onto the surfaces of the sections 36 and 38, the flue gases in the furnace space outside the burner slab 28 are mixed with the secondary fuel gas.

The passages 42 are arranged in sections 36 adjacent to the nozzles 54 as best shown in Figure 3. In addition to the fuel gas discharge holes used to discharge secondary fuel gas along the surfaces of the sections 36, the fuel gas nozzles 54 adjacent to the sections 36 and the passages 42 formed therein include primary fuel gas discharge holes to drain the primary fuel gas to the interior of the opening 32 and the wall 34 of the burner slab 28. Due to the flow of primary fuel gas streams through the openings 42, the flue gases in the furnace space are drawn outside the burner slab 8 2 into the openings 2 4 and made to flow through them with the primary fuel gas towards the inner part of the opening 32 and the wall 34 of the burner slab 28.

While it is preferable that the passages 42 through which the primary fuel gas and flue gas streams flow are located in each section after another as described above, it should be understood that one or more of the passages 42 through which the primary fuel gas and flue gas streams flow may be used in the wall 34 for the burning slab 28.

In addition to defining sections 36 and 38, the beams separate the secondary fuel gas and flue gases into several separate streams that enter and mix harmoniously with the mixtures of primary fuel gas, flue gases and air discharged from inside the wall 34 of the burner slab 28. The mixtures of primary fuel gas, flue gases, and air formed inside the wall 34 are ignited while inside the wall 34 and then flow out. Collisions between streams of secondary fuel gas and flue gases with mixtures of primary fuel gas, flue gases and air result in several flames 60 in the shape of the letter &U& or folded, as shown in Figure 5. As is well known to those versed in the technique, one of the main mechanisms that produce NOx in a combustion process is the thermal mechanism of NOx production, i.e. the higher the flame temperature, the greater the amount of NOx formed. In the incinerator according to this invention, the multiple folded flames 60 shown are produced

In Figure 5, the fuel gases quickly with the flue gases before and during combustion with air, thus reducing NOx production. The high surface area of ​​the folded and coiled flames 60 also causes the flue gases to mix with the flames more efficiently, and the gaps 62 in the flames that exist between the folds allow the flue gases to also penetrate between the flames and mix with them, and all of this contributes to the production of NOX in a very low amount.

When the burner device 10 is operated, the fuel gas is introduced into the furnace space to which the burner 10 is connected and burned therein at a flow rate that results in the release of the desired amount of heat. Air is also introduced into the burner box 14 and a column of air flows into the furnace space. The air flow rate introduced into the furnace space exceeds the air flow rate necessary to form a controlled mixture of air and fuel gas by a rate ranging from about 0% to about 100%. It is preferable that the air flow rate exceed the controlled air flow rate by about 15%. In other words, the mixture of fuel gas and air exhausted into the furnace space contains an excess amount of air from about 0% to about 100%. As shown in Figure 2, the air column flows through the enclosure 4 1 and through the opening 32 in the burner slab 28 toward the mixing zone formed inside and above the wall 34. While within the mixing zone, the air mixes with the primary fuel gas and exhaust flue gases within the mixing zone via passages 42 and fuel gas nozzles 54 arranged adjacent to the passages 42 and optionally via the fuel gas nozzle 44 . The resulting mixture of the fuller fuel gas, flue gases and air containing a large excess of air is burned in and adjacent to the upper part of the burner slab 28 and the flue gases formed from it have very low NOx contents as a result of diluting the fuel gas with the excess amount of air and flue gases.

The discharged secondary fuel gas is mixed in directions parallel to the surfaces of the sections 36 and 38 through the nozzles 54 with the flue gases surrounding the burner slab 28. The resulting mixtures of secondary fuel gas and flue gases are discharged to the mixture of primary fuel gas and air flowing from inside the wall 34 in several separate streams that form a folded flame pattern and are mixed

With the mixture of primary fuel gas and air to form a highly mixed mixture of fuel gas, flue gases and air. The mixture of fuel gas, flue gases, and air burns in multiple folded flames in the furnace space and produces flue gases with low NOx contents as a result of dilution of the fuel gas with a relatively cool excess amount of air and flue gases.

Although it is preferable to discharge the secondary fuel gas through the nozzles 44 adjacent to the surfaces of each of the sections 36 and 38, it should be understood that the secondary fuel gas may be discharged from one or more of the nozzles 44 adjacent to one or more of the sections 36 and 38.

It includes a method according to this invention for discharging a mixture of fuel gas and air into a furnace space where the mixture is burned in a folded flame pattern and from which flue gases with low contents are formed from the following steps: (a) Air discharge to a mixing area inside and adjacent to a wall that extends into the furnace space and has external sides divided into successive sections by several connected beams arranged radially. The successive sections have the same or different heights and lean toward the opening at the same or different angles, and one contains or more successive sections on corridors formed to transport a mixture of primary fuel gas and flue gases from outside the section to inside the wall; (b) Discharge an initial portion of fuel gas to locations outside the wall and adjacent to one or more containing wall sections Passages formed such that the primary fuel gas portion is mixed with the flue gases in the furnace space and the resulting mixture of the primary fuel gas and flue gases flows toward the mixing area inside the wall through the aforementioned passages to form a mixture of primary fuel gas, flue gases, and air flowing toward the furnace space; (c) Discharge a secondary portion of the fuel gas from one or more locations outside the wall and adjacent to one or more sections of the wall such that the secondary portion of the fuel gas mixes with the flue gases in the furnace space and the mixture of the secondary fuel gas and the flue gases drains into a mixture Primary fuel gas, flue gases and air in one or more separate streams formed by radially arranged baffles, enter and mix with the fuel gas mixture

Primary, flue gases and air are used to form a highly mixed mixture of fuel gas, flue gases and air that burns in a folded flame pattern.

The above method may also include the optional step that includes introducing a portion of the primary fuel gas into the mixing area inside the wall of the burner slab, thus mixing the primary fuel gas with the air in it.

The mixture of fuel gas, flue gases and air exhausted into the furnace space according to step (b) may contain an excess amount of air from about 0 to about 100%. The primary part of the fuel gas used according to step (b) constitutes a percentage ranging from about 2% to about 40% of the total volume of fuel gas drained into the furnace space, while the secondary part of the fuel gas used according to step (c) constitutes a percentage ranging from about 60% to about 98% of the total fuel gas volume drained into the furnace space.

Another method according to this invention includes discharging a mixture of fuel gas and air into a furnace space where the mixture is burned in a folded flame pattern and from which flue gases with low contents are formed from the following steps: (a) Exhaust column of air into the oven space; (b) directing a first portion of the fuel gas mixed with the flue gases from the furnace space towards the air column; and (c) directing a second portion of the mixed fuel gas with the flue gases from the furnace space toward the air column containing the first portion of the mixed fuel gas with the flue gases in several separate streams from widely spaced locations around the column, the separate streams entering the column radially. It burns with the first part of the fuel gas in the form of separate folded flames surrounded by and mixed with the flue gases and air.

Another method according to this invention for discharging a mixture of fuel gas and air into a furnace space where the mixture is burned in a folded flame pattern and from which flue gases with low NOx contents are formed includes the following steps: (a) discharging said air into said furnace space; and (b) draining said fuel gas mixed with flue gases from the furnace space

The said into the said air in two or more separate streams entering the air and burning therein in the form of one or more folded flames surrounded by and mixed with the flue gases and air.

To further illustrate the device according to this invention, its operation and the methods of the invention, the following two examples are provided. Example 1

A combustor 10 designed to release heat at a rate of 2,016,000 kcal/hour (8,000,000 Btu/hour) is ignited by burning natural gas with a calorific value of 8,125 kilocalories/standard m3 (913 Btu/standard cu ft) within a space oven. Compressed fuel gas was supplied to manifold 48 of the burner 10 at a pressure of approximately 227.5 kPa (33 psi) and a flow rate of approximately 248.3 m3/hour (8765 standard cu ft/hour). A portion of the fuel gas (flow rate of 49.65 m3/hour (1,753 standard cu ft/hour)) amounting to 20% by volume was used as primary fuel gas and drained into the opening 32 and the wall 34 of the burner slab 28 via the fuel gas discharge nozzle 44 and the fuel gas discharge nozzles 54 The mattress next to the openings 42 in the wall 40 of the burning slab 28. The tip of the remaining portion bleeds the fuel gas, i.e., the secondary portion (at a rate of 198.6 m3/hour (7.12 standard cu ft/hour)) into the furnace space by means of nozzles 54 in separate fuel gas streams mixed with the flue gases.

The air flow rate entering the furnace space through the air intake control device 4 2, the canister 4 1 and the burner slab 28 exceeded the controlled air flow rate by at least 15% in relation to the total fuel gas flow rate. The mixture of primary fuel gas, flue gases and air began burning near passages 2 and 4 and the upper part of the incendiary slab wall 34. The mixtures of fuel gas and flue gases discharged at different angles towards the partially burned mixture of fuel gas, air and flue gases at the upper part of the wall of the burner slab 34 mixed in a synergistic manner with the flue gases from the furnace space and the remaining air in it and burned above the burner slab in the form of a short flame with a folded flame pattern. . Given the relief

Primary and Secondary Fuel Gases With the excess amount of air and the monolithic mixing of the mixture of fuel gas, air, and flue gases, the burner had a high fold ratio and produced very low NOx emissions. Finally, the burner had compact dimensions (much smaller than other low-NOx burners) and could be easily installed in existing furnaces. Example 2

Use a computer simulation program to see the flame pattern produced by the burner 10 when operated as described in Example 1 above. The software used was obtained from Fluent Inc. Of Lebanon Fluent Inc. of Lebanon, New Hampshire. The burner was redesigned in the simulation program with a fully detailed 3D drawing including all important features such as the slab faces, fuel gas outlet holes, the ledge in the slab that maintains the flame and the entire shape of the air-filled space.

Then a three-dimensional model of the furnace in which the incinerator was tested was prepared, and the incinerator model was installed in the furnace model exactly like the incinerator and test furnace used in Example 1, except that air entered the can from the side instead of the bottom. The flow areas in the burner model were partitioned into small volumes using the finite volume method and boundary conditions were applied, e.g., fuel pressure, flow rates, etc. At the entrances to the incendiary model. The software then calculated and predicted the flow patterns, in addition to the values ​​for the combustion reactions and the resulting flame pattern, by iteratively calculating the values ​​for all the combustion and flow media in each of the small sizes.

The calculations were repeated until the expected error was reduced to a desired level and the output (a table of values ​​for each size) was then fed to a graphing software package that produced static temperature profiles at levels cut through the flame at the intended verticals. One of these vertical projections is shown in Figure 5. As shown in Figure 5, the flame pattern ignites on eight folded flames 60 corresponding to the eight sections 36 and 38 of a slab.

The incendiary device contains 62 gaps between the folds. The central flame 64 is produced by burning the fuel drained from the fuel gas nozzle 44.

As mentioned earlier in this statement, the separate folded flames 60 allow the fuel gas to be rapidly mixed with the flue gases before being burned with air thereby reducing the flame temperature and NOx production. The high surface area of ​​the folded flames 60 and the gaps 62 that exist between the folds allow flue gases to penetrate the flames and mix with them to a greater extent than has been possible so far. As a result, the proportion of NOx emissions in flue gases released into the atmosphere is very low.

Thus, the present invention is well suited to achieve the aforementioned goals, objectives and advantages in addition to those inherent in it. While many changes can be made by those skilled in the art, such changes are covered by the principle of this invention as defined by the appended claims.