Patent Application
20130104783
1. Field of the Invention
Embodiments of the present invention generally relate to a burner assembly and methods of manufacturing and operating the same. More specifically, embodiments of the present invention relate to burner assembly for use in an aggregate drying facility having requisite ultra-low nitrogen oxide emissions.
2. Description of the Related Art
High capacity fuel and/or gas burners are often utilized in industries requiring extreme drying of various materials. Such burners are often utilized in conjunction with large rotary aggregate dryers for the processing of cement, coal, sand, lime and similar materials.
In drying aggregate, a typical unit may have a rotating horizontal drum 60 feet in length and 10 feet in diameter. Wet rock, or similar material, is introduced into one end of the drum, carried to the top of the drum and dropped back. The material is gradually carried to the opposite end of the drum and removed by a conveyor. A high capacity fuel and/or gas burner, which may have an outlet chamber of from one to two feet in diameter, is placed at one end of the drum. The hot gases and air emanating from the burner are directed through the falling aggregate and serves to evaporate all moisture from the material. Typically, an exhaust fan at the output end of the drum draws the heated air therethrough. The gas temperature at the burner input end may be on the order of 1200 to 2400 degrees Fahrenheit dropping to about 250 to 350 degrees Fahrenheit at the opposite end of the drum. For large dryers, the burners may be required to produce as much as 200 million BTU per hour.
As with any high temperature process, there are often undesirable emissions resulting from the burning of fuels and/or gases. With regard to industrial burners, one of the larger concerns surrounds the level of nitrogen oxides (NOx) emissions. Science has shown that excessive NOx emissions add to problems surrounding acid rain, global warming, plant and folliage growth, and in conjunction with other pollutants, NOx may form toxic chemicals.
Due to these concerns, the Environmental Protection Agency (EPA), as well as many states, have enacted specific guidelines with respect to acceptable NOx emissions being generated by aggregate dryers located at asphalt pavement production plants. For example, the State of New Jersey has set out certain “State of the Art” performance levels for all burners utilized in conjunction with aggregate dryers within the state. In particular, the allowable emissions must be kept below: 35 ppmvd @7% O2 using a single natural gas burner; 75 ppmvd @7% O2 using a dual fuel burner with natural gas; 100 ppmvd @7% O2 using a dual fuel burner with No. 2 fuel oil; and 125 ppmvd @7% O2 using a dual fuel burner with any of No. 4 fuel oil, No. 6 fuel oil, or other approved fuel oils. While these limits may not be considered overly excessive regulation, they are generally too difficult to achieve with standard burners alone.
One solution to achieve the requisite NOx emissions is to modify a standard burner assembly to allow for flue gas recirculation (FGR).
In its simplest form, FGR operates by using a combustion air blower to suck the flue gases out of the stack and blend them with fresh air before they go into the burner. The technique is also known as air vitiation, and it has been applied to many types of burners without any other modifications. Another way to create a FGR burner is to use a separate blower to pull the flue gases from the stack and push them through some sort of manifold or bustle ring into the flame. However, most FGR burners require industrial fabrication of many components to become suitable to operate at extremely high temperatures and to handle the type of flue gases that are produced in such processes. As such, the cost of FGR burner assemblies does not always justify the benefits achieved.
Another solution to achieve the requisite NOx emissions is to utilize a burner assembly having a primary burner work in conjunction with specific premix burners. For example, U.S. Pat. No. 6,575,734 describes a combination premix and diffusion burner. As described by the reference, traditional diffusion-type burners typically have substantial NOx emissions, but by combining a diffusion burner and a premix burner, where the diffusion burner operates at reduced capacity and its flame serves primarily to stabilize the premix burner flame during main or high firing, reduced NOx emissions are realized. However, the issues with such type of burner assembly is the intricate nature of the structural array of premix burners, as well as the operable parameters required to maintain the primary heat source as the premix burners with the diffuser burner merely acting to stabilize the heat output of the premix burners. Achieving such results requires a very costly and difficult to maintain burner assembly purchased from one of a few manufacturers.
Thus, there is a need for a cost effective burner assembly for use in an aggregate drying facility having requisite ultra-low nitrogen oxide emissions and methods of manufacturing and operating the same.
Embodiments of the present invention generally relate to a burner assembly and methods of manufacturing and operating the same. More specifically, embodiments of the present invention relate to burner assembly for use in an aggregate drying facility having requisite ultra-low nitrogen oxide emissions.
In one embodiment of the present invention, a burner assembly comprises a single burner apparatus having a centrifugal blower, a transition section, and a frustoconical stabilizer cone from which a flame may exit the burner assembly; a combustible fuel line having a first end connected to a fuel source, and a second end connected to a nozzle for delivering fuel to a combustion chamber within the single burner apparatus; a compressed air line having a first end connected to a compressed air source, and a second end connected to a nozzle for delivering compressed air to the combustion chamber; and a water line having a first end connected to a water source and a second end connected to a nozzle for delivering water to the combustion chamber.
In another embodiment of the present invention, a method of using a burner assembly for aggregate drying while producing low NOx emissions comprises: providing a burner assembly comprising: a single burner apparatus having a centrifugal blower, a transition section, and a frustoconical stabilizer cone from which a flame may exit the burner assembly; a combustible fuel line having a first end connected to a fuel source, and a second end connected to a nozzle for delivering fuel to a combustion chamber within the single burner apparatus; a compressed air line having a first end connected to a compressed air source, and a second end connected to a nozzle for delivering compressed air to the combustion chamber; and a water line having a first end connected to a water source and a second end connected to a nozzle for delivering water to the combustion chamber; supplying fuel to the combustion chamber via the combustible fuel line; supplying air to the combustion chamber, the air coming from at least a combination of the centrifugal blower and the compressed air line; combusting the fuel and air in the combustion chamber; and introducing water via the water line to the combustion chamber.
In yet another embodiment, a method of creating a burner assembly for aggregate drying while producing low NOx emissions comprising: providing a dual fuel, single burner apparatus having a centrifugal blower, a transition section, a frustoconical stabilizer cone, a compressed air line, and first and second fuel lines for providing a first and second fuel to a combustion chamber within the burner assembly, respectively; removing the second fuel line from the apparatus; and replacing the second fuel line with a water line.
So the manner in which the above recited features of the present invention can be understood in detail, a more particular description of embodiments of the present invention, briefly summarized above, may be had by reference to embodiments, which are illustrated in the appended drawings. It is to be noted, however, the appended drawings illustrate only typical embodiments of embodiments encompassed within the scope of the present invention, and, therefore, are not to be considered limiting, for the present invention may admit to other equally effective embodiments, wherein:
The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word may is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures.
Embodiments of the present invention generally relate to a burner assembly and methods of manufacturing and operating the same. More specifically, embodiments of the present invention relate to burner assembly for use in an aggregate drying facility having requisite ultra-low nitrogen oxide emissions.
Embodiments of the present invention may be applied to nearly any type of existing burner assembly utilizing a single fuel and/or gas burner. For example, certain embodiments of the present invention may be combined with a swirl-type burner, a high or low pressure combustion burner, or the like. In one embodiment, many the basic structural components of a burner assembly in accordance with embodiments of the present invention can be found in a commercially available burner sold by Gencor, Inc., of Florida, under the brand name Ultraflame. As embodiments of the present invention will support, any of such types of single burners can benefit from the structural and functional applications disclosed herein for achieving acceptable NOx emission reductions.
The centrifugal blower 210 any type of blower suitable for embodiments of the present invention. In many embodiments, the centrifugal blower 210 provides air flow of between about 20 osig (ounce/square inch guage) to about 40 osig. In some embodiments, the centrifugal blower 210 may comprise a structure similar to the devices disclosed by U.S. Pat. Nos. 3,572,963 and 3,572,967, the disclosures of which are incorporated by reference herein in their entireties.
In many embodiments, there are three primary inputs into the burner 200. The first input is a fuel input. The burner 200 is arranged to burn either gas (i.e., natural gas) or a liquid fuel such as no 2. fuel oil. As shown, the gas supply to the burner is introduced through gas line 270. A gas control valve 272 controls the amount of gas being provided to the burner 200 from a gas source (not shown). The gas source may generally comprise a tank, a municipal gas line, or the like, provided such output is suitable for embodiments of the present invention. In certain embodiments, where fuel oil is used instead of gas, a similarly structured fuel oil line may be provided. In additional embodiments, multiple types of gas and/or fuel oil may be utilized by the burner 200, and additional lines may be provided as necessary.
A second input into the burner 200 is a compressed air input. In many embodiments, a compressed air line 250 may also be provided to the burner assembly 200. The compressed air line 250 may be connected to a compressed air source, such as a tank or a device for compressing air (i.e., a pump or the like) (not shown). The compressed air line 250 may generally comprise compressed air at pressures of between about slightly greater atmospheric pressure (i.e., 14.7 psi) to about 100 psi. In many embodiments, the compressed air may be pressurized to between about 25 psi to about 50 psi. In one embodiment, the compressed air may be introduced to the burner at about 40 psi.
A third input into the burner, which is unique to embodiments of the present invention, is a water line 260. The water line 260 may generally be connected to a water source, such as a tank or the like (not shown). In many embodiments, water may be provided through the water line 260 at a pressure ranging from between about slightly greater atmospheric pressure (i.e., 14.7 psi) to about 100 psi. In many embodiments, the water may be pressurized to between about 25 psi to about 50 psi. In one embodiment, the water may be introduced to the burner at about 40 psi. In addition to being pressurized, the water may be provided in a volumetric flow rate of between about 1 gal/min to about 10 gal/min. In some embodiments, the volumetric flow rate of the water is between about 2 gal/min to about 6 gal/min. In one embodiment of the present invention, the volumetric flow rate of the water is about 4 gal/min through the water line 260.
Generally, each of the compressed air line 250, the water line 260 and the gas line 270 terminate via one or more respective nozzles (not shown) into a combustion chamber 280, which is generally located near the interface of the transition section 220 and stabilizer cone 230. Within the combustion chamber 280 is a reaction zone, where the actual chemical combustion of gas/fuel and air takes place. In many embodiments, the compressed air line 250, the gas line 270 and a source of air generated from the centrifugal blower 210 meet within the combustion chamber 280, along with a flame or heat source (e.g., a pilot light) (not shown), to ignite the gas. In accordance with embodiments of the present invention, the pressurized water from the water line 260 is also provided into the combustion chamber at the reaction zone.
In accordance with embodiments of the present invention, there may be numerous other components to the burner assembly 200 commonly utilized with known burners, not described herein for sake of convenience. However, many of such common components (e.g., air intake valves, control mechanisms, etc.) are described in references such as U.S. Pat. No. 4,298,337, as introduced above, the disclosure of which has already been incorporated by reference in its entirety.
At step 320, either gas and/or fuel oil is supplied to the burner assembly via a gas/fuel line as described herein. In many embodiments, the gas comprises a natural gas, where supplying the natural gas comprises opening a valve on a gas line connected to a gas source. Similarly, in embodiments where fuel oil is provided, the fuel oil may comprise any of number 2, number 4 or number 6 fuel oil, and supplying such oil may comprise opening a valve on the fuel line connected to a fuel tank or similar source. Supplying the gas/fuel comprises delivering the gas and/or fuel to a combustion chamber within the burner assembly via an exit nozzle.
At step 330, air is supplied to the burner assembly. In accordance with embodiments of the present invention, for purposes of combustion, air may be obtained from multiple sources: air from the centrifugal blower, compressed air from the air line, air entering through the stabilizer cone from the environment, and optionally, air entering through one or more inlets at or near the combustion chamber. In many embodiments, the compressed air may be pressurized to between about 25 psi to about 50 psi. In one embodiment, the compressed air may be introduced to the burner and delivered into the combustion chamber at about 40 psi.
At step 340, the gas and/or fuel is combined with the air and is combusted within the combustion chamber to create an external flame. In many embodiments, once the gas and/or fuel is provided to the combustion chamber along with the air, a pilot light or similar type of heat/energy source (e.g., a spark plug) causing ignition of the flammable materials in the combustion chamber.
At step 350, at either the time of combustion or shortly thereafter, water is introduced to the combustion chamber. Generally, the water is delivered directly to the reaction zone where the combustion occurs via a nozzle on the end of the water line. In many embodiments, supplying the water comprises opening a valve on the water line connected to a water source. In many embodiments, the water may be pressurized to between about 25 psi to about 50 psi, having a volumetric flow rate of between about 2 gal/min to about 6 gal/min. In one embodiment, the water may be introduced to the burner at about 40 psi, having a volumetric flow rate of about 4 gal/min through the water line.
By combining the combustible gas/fuel with the air and water, the resulting flame burns sufficiently hot to remove moisture from drying aggregate as commercially intended, but without producing dangerous levels of NOx emission. In one exemplary and experimental embodiment of the present invention, the resulting NOx emissions were kept under about 75 ppm. In other exemplary embodiments, the resulting NOx emissions we kept under about 50 ppm. In addition to the NOx emissions, embodiments of the present invention keep other dangerous emissions such as CO and VOC underneath 250 ppm and 125 ppm, respectively.
The method 300 ends at step 360.
In accordance with embodiments of the present invention, as fuel (e.g., oil, gas, etc.) costs increase, the need for dual fuel sources in a burner becomes less desirable. As such, at step 430 the second fuel line of the burner assembly may be removed. In many embodiments of the present invention, the removal of the fuel line may only comprise removal of the fuel source, such as disconnection from a tank or other source. As the type of fuel considered primary and secondary may vary from application to application, the determination of which fuel line should be removed may also be dependent upon the nature of the application. Thus, in some embodiments, a gas line may be considered the second fuel line to be removed, and in other embodiments, the fuel oil line may be considered the second fuel line to be removed.
At step 440, the removed second fuel line may be replaced with a water line. In accordance with various embodiments of the present invention, the act of replacing the second fuel line with the water line may comprise connecting a water source to the lines that originally existed for the second fuel. In many embodiments, the water source comprises a tank or similar source that is capable of providing pressurized water at a set volumetric flow rate to the burner assembly when in use. Generally, the water is provided to the burner assembly at the combustion chamber via a nozzle.
The method 400 ends at step 450.
In one alternative embodiment of the method 400, a method of creating a burner assembly may comprise keeping both a first and second fuel line within a burner. Thus, rather than replacing the second fuel line with a water line, the water line is added to the burner assembly, having a nozzle for providing water to the combustion chamber when in use. While such an embodiment is within the scope of embodiments of the present invention, it may not be the most cost-effective means to achieve the desired result of lowered NOx emissions.
It should be emphasized that the above-described embodiments of the present invention are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
