Patent Description:
The invention relates generally to burners. More particularly, the present invention relates to modular gas- and oil-fired burners having adjustable heat outputs.

It is known to use a fuel burner assembly to heat and dry aggregate materials used in connection with the production of hot mix asphalt. <CIT> and <CIT> disclose burner assemblies according to generic state of the art. However, conventional burner assemblies suffer from several disadvantages. For example, as industrial production needs change, the heat output requirements for existing on-site burners often change as well. Conventionally, such a change would require the purchase of an entirely new burner assembly that was sized appropriately for the new production requirements. Often, modifying the heat output of a burner requires changing or resizing multiple components of the assembly, including fan size and geometry, airflow rate, etc..

It would be desirable, therefore, if the heat output of a fuel burner assembly could be adjusted as needed such that a single burner could be reconfigured with minimal changes to meet various heat output requirements.

The use of the terms "a", "an", "the" and similar terms in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising", "having", "including" and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. The terms "substantially", "generally" and other words of degree are relative modifiers intended to indicate permissible variation from the characteristic so modified. The use of such terms in describing a physical or functional characteristic of the invention is not intended to limit such characteristic to the absolute value which the term modifies, but rather to provide an approximation of the value of such physical or functional characteristic.

Terms concerning attachments, coupling and the like, such as "connected" and "interconnected", refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both moveable and rigid attachments or relationships, unless specified herein or clearly indicated by context. The term "operatively connected" is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship.

The use of any and all examples or exemplary language (e.g., "such as" and "preferably") herein is intended merely to better illuminate the invention and the preferred embodiment thereof, and not to place a limitation on the scope of the invention. Nothing in the specification should be construed as indicating any element as essential to the practice of the invention unless so stated with specificity.

The above and other needs are met by a burner assembly in accordance with claim <NUM>. In certain preferred embodiments, the burner assembly includes two or more interchangeable airflow restrictor plates. Each of the airflow restrictor plates has openings with different cross-sectional areas such that airflow through the housing may be varied by replacing one of the two or more airflow restrictor plates with another one of the two or more airflow restrictor plates.

In order to facilitate an understanding of the invention, the preferred embodiments of the invention, as well as the best mode known by the inventor for carrying out the invention, are illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiments described or to use in connection with the apparatus illustrated herein. The inventor expects skilled artisans to employ such variations as seem to them appropriate, including the practice of the invention otherwise than as specifically described herein.

The presently preferred embodiments of the invention are illustrated in the accompanying drawings, in which like reference numerals represent like parts throughout, and in which:.

This description of the preferred embodiments of the invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawings are not necessarily to scale, and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness.

Referring now to <FIG>, there is provided burner assembly <NUM> according to an embodiment of the present disclosure. Preferred burner assembly <NUM> includes housing <NUM> having air inlet and nozzle end <NUM> having opening <NUM> that functions as an air outlet. The preferred burner assembly <NUM> also includes a motor such as variable speed motor <NUM> for driving inline centrifugal fan <NUM> located near fan end <NUM> of housing <NUM>. Radial damper <NUM> is located at outlet side of fan <NUM>. Preferred longitudinal axis <NUM> generally extends from fan end <NUM> towards nozzle end <NUM>. Preferred housing <NUM> extends generally along longitudinal axis <NUM> and includes first tubular housing portion <NUM> that is located nearest fan <NUM> and that is removably mounted to second tubular housing portion <NUM>, which is located further downstream from fan <NUM> than the first housing portion. Gaseous fuel line <NUM>, which includes a gas injection nozzle (not shown), and igniter line <NUM> each extend along an outer surface of the housing <NUM>. Similarly, liquid fuel guide tube <NUM> and compressed air tube <NUM> extend through housing <NUM> inside of center tube <NUM> to nozzle end <NUM> and atomizing nozzle <NUM>.

When the burner assembly <NUM> is in operation, the fan <NUM> is configured to create an airflow within the housing <NUM>, which airflow is modulated by the damper <NUM>. The damper <NUM> includes multiple vanes that can be moved between an open position, where airflow from the fan <NUM> through the housing <NUM> is maximized, and a closed position, where airflow from the fan can be minimized or eliminated entirely. The damper <NUM> also has a number of intermediate positions between the open and closed positions that permit varying amounts of airflow through the housing <NUM>. Typically, the damper is set by selecting one of the several discrete set points that range from fully open and fully closed. For example, a typical damper might have <NUM> total positions that range from "<NUM>" to "<NUM>," where position "<NUM>" is fully or mostly closed and produces the least amount of airflow and position "<NUM>" is fully open and produces the greatest airflow. The airflow created by the fan <NUM> is carried through the first and second housing portions <NUM>, <NUM> and exits through the opening <NUM> at the nozzle end <NUM>, where it is mixed with gaseous fuel and/or liquid fuel. Gaseous fuel is conveyed to the nozzle end <NUM> via gaseous fuel line <NUM>. Liquid fuel and compressed air are conveyed to the nozzle end <NUM> inside of the center tube <NUM> by the liquid fuel guide tube <NUM> and compressed air tube <NUM>, respectively, where the liquid fuel is atomized by the atomizing nozzle <NUM>. The air and fuel combination is ignited at the nozzle end <NUM> to create a flame.

Burners, such as burner assembly <NUM>, are often used as part of a large industrial or commercial dryer that is used to dry and process materials, such as aggregate material used in road construction. These dryers typically include large rotary drums that are placed around and extend outwards from the nozzle end <NUM> of the burner assembly <NUM>. Preferably, the flame produced by the burner assembly <NUM> extends out through the nozzle end <NUM> via opening <NUM> and into the drum to heat and dry the material that is being turned within the drum. Changes to the industrial or commercial processes that require the use of burners typically result in increased heating needs and, therefore, the replacement of a smaller burner with a larger one. For that reason, when initially sizing a burner for a particular application, it would be advantageous to size the burner to provide a heat output that is greater than the heat output that will initially be required by that application. This would allow for the heat output to be increased as the heating needs increased without requiring the burner to be replaced. However, oversizing a burner in this manner can create issues that must be corrected.

First, sizing a burner with the capacity to provide the large amount of fast-moving airflow required to produce high heat output makes adjusting the burner at low airflows more difficult. In particular, if the damper is sized for high amounts of airflow, the damper position required to achieve low airflows is achieved very quickly (e.g., at damper positions "<NUM>" or "<NUM>"), which limits the adjustability of the burner at low airflow rates. Another issue that may be caused by oversizing a burner is that the flame produced may damage portions of the dryer shell or other surrounding equipment and the temperature of the process and material being heated may be too high. For that reason, the burner assembly <NUM> of the present invention provides means for increasing and decreasing the heat output of a burner that is also easily adjusted at different airflows.

With reference to <FIG>, the burner assembly of the present invention is provided with an airflow restrictor plate <NUM> that may be used to selectively restrict airflow through the housing in order to vary the heat output of the burner assembly at the nozzle end. The restrictor plate <NUM> is placed inside of the housing to restrict a portion of the airflow, as shown in <FIG>, and to reduce the airflow velocity at the nozzle end of the burner assembly. When more airflow is needed to produce a greater heat output, a less restrictive airflow restrictor plate <NUM> can be placed into the housing. Eventually, to have maximum airflow and heat output, the restrictor plate <NUM> can be removed entirely from the burner assembly, as shown in <FIG>. Thus, an advantage of the restrictor plate <NUM> of the present design is that heat output can be modified very easily by exchanging a minimal number of components.

In preferred embodiments, the restrictor plate <NUM> is mounted within the housing <NUM> between the first housing portion <NUM> and the second housing portion <NUM>. The restrictor plate <NUM> is provided with an opening <NUM> through which airflow must pass in order to pass from the first housing portion <NUM> to the second housing portion <NUM> and to exit the housing. Preferably, the perimeter edge of the opening <NUM> in the restrictor plate <NUM> is smaller than the inside of the housing <NUM>, including the first housing portion <NUM> and the second housing portion <NUM>, in order to restrict the air flowing through it. Therefore, preferred restrictor plate <NUM> redirects (and slows) at least a portion of the airflow away from an inner wall surface of the first housing portion <NUM>, through the opening <NUM>, and into the second housing portion <NUM>.

In certain preferred embodiments, the burner assembly <NUM> includes two or more airflow restrictor plates <NUM> that are interchangeable with one another. In <FIG>, the nozzle end of a burner assembly having three restrictor plates 134A-C of varying sizes is shown.

The restrictor plate 134A shown in <FIG> has an opening 136A with a radius R1 and is the most restrictive of the three (e.g., <NUM> MMBTU/hr plate) (e.g., <NUM> MW plate). Airflow passes by restrictor plate 134A through the ring-shaped opening 136A that is formed between the restrictor plate and the center tube 128A. A less restrictive restrictor plate 134B having an opening 136B with a radius R2 is shown in <FIG> (e.g., <NUM> MMBTU/hr plate) (e.g., <NUM> MW plate). Lastly, the least restrictive restrictor plate 134C having an opening 136C with a radius R3 is shown in <FIG> (e.g., <NUM> MMBTU/hr plate) (e.g., <NUM> MW plate). Each of the restrictor plates 134A-C can be removed and exchanged as the heat output needs of the burner change. Alternatively, in other embodiments, the size of the opening in the airflow restrictor plate may be selectively adjusted to provide an opening having two or more different cross-sectional areas. For example, instead of using multiple different restrictor plates 134A-C with a fixed opening, a single restrictor plate having a re-sizeable opening (e.g., a mechanical iris) could be used.

<FIG> illustrate two restrictor plates 234A, 234B that are each configured to bolt onto the burner assembly shown in <FIG>. Each of the restrictor plates 234A, 234B is provided with a flange <NUM> that surrounds the opening 136A, 136B which includes a series of fastener openings <NUM>. Additionally, one or more cutouts <NUM> may be provided to receive the gaseous fuel line <NUM> and igniter line <NUM>. To removably secure the restrictor plates 234A, 234B to the burner assembly <NUM>, the restrictor plate is placed against an end of the first housing portion <NUM> and openings <NUM> in the restrictor plate are aligned with corresponding openings formed in a corresponding flange of the first housing portion. Next, the second housing portion <NUM> is placed against the restrictor plate 234A, 234B so that the restrictor plate is located between the first housing portion <NUM> and the second housing portion. Openings formed in a corresponding flange of the second housing portion <NUM> are aligned with the previously-aligned openings in the restrictor plate 234A, 234B and first housing portion <NUM>. Fasteners are then passed through first housing portion <NUM>, restrictor plate 234A, 234B and second housing portion <NUM> and are fixed in place with threaded nuts. Lastly, the gaseous fuel line <NUM> and igniter line <NUM> are placed into the cutouts <NUM> and their ends are fitted into the second housing portion <NUM>.

In preferred embodiments, in order to minimize equipment changes as process needs change, a damper having a high airflow capability may be initially selected for the burner assembly. The airflow may initially be adjusted downwards with the damper in order to limit the heat output to the then-required amount of heat. As heating needs increase, the damper may be opened to allow for greater airflow and to increase heat output. However, using a damper that is sized to provide high amounts of airflow in a low airflow situation causes the airflow required for that application to be achieved very quickly. For example, the needed airflow might be reached by position "<NUM>" of the damper, which leaves four additional positions (i.e., positions "<NUM>" through "<NUM>") that are not used. This limits the user's ability to make downward adjustments to the damper to reduce or moderate the airflow.

Accordingly, with reference to <FIG>, preferred embodiments of the burner assembly of the present invention also include removable fan blocking plate <NUM> that is mounted adjacent the outlet side (downstream) from the damper <NUM>. The fan blocking plate <NUM> is formed by two semi-circular halves <NUM>. Each half <NUM> of fan blocking plate <NUM> has flat side <NUM> that includes semi-circular cutout <NUM>. When burner assembly <NUM> is in low airflow mode, one of halves <NUM> is placed adjacent damper <NUM> and the cutout is positioned on one side of center tube <NUM>. Next, second half <NUM> is placed adjacent damper <NUM> such that flat sides <NUM> are aligned and cutouts <NUM> encircle center tube <NUM> (<FIG>). Fan blocking plate <NUM> blocks a portion of damper <NUM> and reduces the velocity of airflow passing through the damper and housing. Reducing the velocity of the airflow when low airflow is required improves the ability of burner assembly <NUM> to achieve the desired flow and heat output and increases the adjustability between its maximum and minimum airflow rates. Once airflow needs are increased, fan blocking plate <NUM> could be removed in order to increase velocity of the airflow and provide a higher heat output (<FIG>).

Typically, when comparing airflow to damper position, louvered dampers exhibit an airflow characteristic that is similar to a "quick open" valve, and airflow rate initially increases very rapidly as the damper is opened and then increases more slowly as the damper continues to be opened. This characteristic shape is illustrated, for example, in the upper curve in <FIG> (with data points denoted by diamond-shaped icons), which illustrates the air flowrates for a burner assembly that does not have a fan blocking plate at damper positions "<NUM>" thru "<NUM>. " However, burners with fan blocking plate <NUM> exhibit an airflow characteristic that is much flatter and linear. This characteristic shape is illustrated, for example, in the lower curve (with data points denoted by triangle-shaped icons), which illustrates the air flowrates for an identical burner assembly having a fan blocking plate <NUM> at the same damper positions as above. In both cases, the flowrate ranges from about <NUM>,<NUM> standard cubic feet per hour (SCFH) to about <NUM>,<NUM> SCFH (about <NUM> to <NUM> SCMH). When the burner assembly has no fan blocking plate, it achieves approximately <NUM>% of its maximum flowrate range when the damper is at position "<NUM>. " This provides only <NUM> damper positions for adjusting the flowrate downwards. On the other hand, when the burner assembly is equipped with a fan blocking plate, the flowrate curve is much flatter and the burner reaches approximately the same percentage of the maximum flowrate range (~<NUM>%) when the damper is at position "<NUM>. " This provides a total of <NUM> damper positions for adjusting the flowrate downwards. Thus, a burner assembly equipped with a fan blocking plate according to the current invention has a greater amount of adjustability at low and mid-range airflow rates than an equivalent burner assembly that does not have a fan blocking plate. This adjustability enables a user to more easily obtain the desired airflow and to more precisely control the air-to-fuel ratio than in conventional burner systems.

Claim 1:
A burner assembly (<NUM>) comprising:
a housing (<NUM>) having an air inlet and an air outlet and configured to guide an airflow from the air inlet and out of the housing via the air outlet; an airflow restrictor plate (<NUM>, <NUM>) for selectively restricting an amount of airflow passing out of the housing in order to adjust a heat output of the burner assembly, the airflow restrictor plate having a single opening (<NUM>) through which the airflow must pass in order to exit the housing via the air outlet;
an inline centrifugal fan for generating the airflow;
a motor (<NUM>) for powering the fan (<NUM>); and
a damper (<NUM>) for modulating the airflow having an inlet side that is disposed at an outlet of the fan (<NUM>) that the airflow flows into and an outlet side that the airflow exits out of.