FIELD OF THE INVENTION
This application claims the priority of provisional application serial No. 06/239,983, filed Oct. 16, 2000.
This inventions relates to regenerative burners, and more particularly to an improved method and apparatus for recovering exhaust for use in preheating the air used for combustion in the burner.
Regenerative burners are used on furnaces to improve efficiency because they recover sensible heat that would otherwise be wasted. Generally a regenerative burner captures waste heat from the exhaust gasses that leave a furnace and uses the heat to preheat combustion air. The use waste heat to preheat combustion air improves the efficiency of the furnace or process in which the burner is used.
- SUMMARY OF THE INVENTION
One common type of regenerative burner requires the use of a pair of burners in tandem. One burner is ignited at a time and while it is burning the exhaust gases from the furnace are routed through a heat exchange media associated with the second burner which captures heat from the furnace exhaust. The first burner is then extinguished and the second burner is ignited. Combustion air for the second burner is routed through the heated media and becomes preheated as it approaches the burner. The use of the preheated combustion air improves the efficiency of the burner. While the second burner is burning, exhaust gasses from the furnace are routed through heat exchange media associated with the first burner. The process is then repeated, each burner using preheated combustion air. The timing of the switch from one burner to the other is commonly controlled to maximize the efficiency of the furnace or process to which the burner is attached by recovering the maximum practical amount of waste heat.
The present invention is an improvement in the design of a regenerative burner, to the method for its operation and, in particular, the design of the heat exchange media bed associated with the burner. One embodiment of the invention has a regenerative burner, or heat exchanger, with a housing containing a removable media bed. Heat exchange media is carried by the bed, and the bed can be removed from the housing, with the media, for regeneration, replacement or other treatment of the media. Preferably, the heat exchanger has a spare media bed that can be prepared with new, renovated or otherwise treated media, ready to replace the bed in the heat exchanger with minimal delay when the heat exchange media needs replacement, renovation or other treatment.
In another embodiment, the heat exchanger housing has a detachable lower section. The lower section contains heat exchange media, and can be moved for regeneration, replacement or other treatment of the media.
Other features and advantages of this invention will be apparent from the accompanying drawings and the following detailed description.
FIG. 1 is a cross-sectional view of a conventional regenerative burner.
FIG. 2 Figure is a cross sectional side elevation view of a regenerative burner embodying the present invention.
FIG. 3 is cross sectional end elevation view of the regenerative burner shown in FIG. 2.
FIGS. 4-9 provide plan, elevation and sectional views of a removable cassette or bed for the regenerative heat exchanger shown in FIGS. 2 and 3.
FIGS. 10-13 provide elevation and sectional views of a second embodiment of this invention.
The conventional regenerative burner shown in FIG. 1 has a burner, generally indicated as 1, and an associated heat exchanger, generally indicated as 2. This burner is used in tandem with an identical or other similar burner. During operation one burner is ignited and burned for a predetermined period of time. During this time exhaust air from the furnace is routed through the heat exchange media of the second burner. The exhaust gases leave the furnace and enter the burner housing at 3 and pass down through pipe section 4, through heat exchange media 5 and out through port 6. From this point the exhaust gases are routed to auxiliary pollution control equipment (not shown) or directly to the atmosphere. More than one port may be provided, however only one is required for operation. Additional ports may be connected to alternate exhaust gas pipes and controlled by valves or merely covered or have optional apparatus such as vibratory cleaning devices attached to them. Depending on the contents of the furnace a small amount of material from the furnace may become entrained in the stream of exhaust gases and be deposited in the heat exchange media bed. This material is solid, liquid or gaseous initially but all of the material deposited in the heat exchange media will be either solid or liquid. Gases will continue through the heat exchange media with the exhaust stream. After a period of time that is typically less than a minute, the first burner is extinguished and the second burner is ignited. When this occurs the combustion air for the second burner is routed so that it enters the media bed associated with the second burner where it is preheated, passes into the burner housing and takes part in the combustion process. At the same time the exhaust from the furnace is routed out through the first burner in the same manner described above preheating the heat exchange media associated with the first burner.
The heat exchanger design shown in FIG. 1 is provided with two access doors 8 and 9 to permit the periodic maintenance and cleaning of the heat exchange media. As mentioned above, material from the furnace may be entrained in the exhaust gases and deposited on the media. During routine maintenance, the heat exchanger is allowed to cool down and door 9 is opened and the media is raked or shoveled from the heat exchanger. Conventional heat exchange media can be used. The media typically comprises ceramic balls of a single size or a mixture of various sizes. The media may be other shapes as well. The composition of the media can be selected based on the environment to which it will be exposed. However, in all cases the media must be able to withstand high temperatures and sudden thermal shocks. High alumina ceramic balls of about 1 inch in diameter are a convenient and effective material for use as heat exchange media.
After the media is removed from the heat exchanger bed it is cleansed by tumbling or scrubbing to remove the deposited materials. After cleaning the media may be reused if it is still in satisfactory condition. It is not unusual for media to be reused many times depending on the environment to which it is exposed. Door 9 is then closed and clean media is charged into the heat exchanger bed through door 8. The newly charged media should be leveled in the heat exchanger bed after charging to insure proper exhaust gas flow through the bed of media.
The above described routine cleaning and maintenance can require several hours to complete and requires workers to perform many operation in close proximity to hot furnace surfaces.
The present invention comprises improvements to the design of the heat exchanger portion of a regenerative burner to permit easier and faster maintenance and cleaning of the heat exchanger media.
The redesigned heat exchanger permits the media and the supporting carrier, cassette or other bed in which it rests to be removed from the heat exchanger housing as a unit. One embodiment of the improved design is shown in FIGS. 2 and 3. FIG. 2 shows a side view of a cross section of a regenerative burner with a heat exchanger cassette, carrier or other bed modified in accordance with the present invention. FIG. 3 is an end view of a cross section of the regenerative burner shown in FIG. 2. The media bed is no longer an integral part of the heat exchanger housing, but has been redesigned as a removable cassette shown more clearly in FIGS. 4-9. To maintain the heat exchanger with this new configuration, door 10 is opened and media bed 11 is removed as a unit. Because of the size of some of these units, a forklift or similar device may be required to remove the media bed 11, and rectangular tubes 12 are provided to facilitate such removal. Tubes 12 are adapted to receive the forks of a forklift and provide a convenient mechanism for removal of the media bed. After removal, the media is dumped from the bed and replaced with clean media. As with conventional regenerative burners, the media can be cleaned and reused. A forklift equipped with rotary forks can be used to facilitate the dumping of the media bed.
In one embodiment of the invention, the media bed is tapered from a smaller end, designed to be inserted into the heat exchanger housing first, to a larger end as shown in FIGS. 5 and 9. This permits easy insertion of the media bed into the heat exchanger housing and helps insure that a good seal is established around the media bed and the housing so exhaust gas does not leak around the media and escape without passing through the media bed. Gasket material may be placed around the top of the media bed to help form a good seal with the heat exchanger housing. Optionally, gasket material may be used at other locations as required or desirable. However, it is still desirable to have the media in the bed filled to a uniform level to improve the performance of the heat exchanger. To achieve this uniform level with the tapered bed shown, rigid combustible boards can be placed along the inside of the vertical walls of the media bed to extend the effective height of the media bed walls to a uniform level. Media can then be placed in the bed to a level approximately equal to the height of the combustible boards and will retain the boards in place during insertion of the bed. After the burners operate for a short period, the combustible boards will burn up and the media will settle slightly in the bed forming a level bed well sealed to the heat exchanger housing. Media 7 filled to a uniform level in a tapered bed is illustrated in FIG. 2.
A further technique for obtaining a good seal between the media bed and the heat exchanger housing is to precompress the gasket material and retain it in the compressed state with adhesive tape while the media bed is inserted into the heat exchanger housing. The tape can be any common paper, plastic film or cloth backed tape. After the burners operate for a short period, the tape will burn away and release the gasket material to expand and form a good seal.
The media bed shown in FIGS. 4-9 comprises a rectangular vertical front wall 12, a rectangular back wall 13 and two tapered side walls 14. Each of the walls is lined with a refractory material 18 and terminates at the bottom with a horizontal flange 15 that supports a perforated grate 16. The grate 16 both supports the media and permits the exhaust gasses to pass through. If equipped with optional forklift tubes 16, the tubes may have holes 17 to permit exhaust gasses to also pass through this portion of the media bed.
A second embodiment of the invention is shown in FIGS. 10-13. In this embodiment, the heat exchanger housing is split into two pieces along a horizontal plane. The lower section contains the heat exchanger media and is fastened to the upper section by detachable fasteners. Screw jacks 24 are illustrated for this purpose.
The regenerative burners shown in this embodiment also operate in pairs as described above. The exhaust passes out of the furnace through pipe 19, down through media bed 20, along passage 21, up through passage 22 and out through exhaust port 23.
During routine cleaning and maintenance, the lower section of the heat exchanger housing is detached from the upper section. Optionally, it may be convenient to support the lower section using a forklift. If a forklift is used, the forks are inserted in optional rectangular tubes 24. The media is then dumped from the media bed located in the lower section of the heat exchanger housing and replaced with clean media. After a uniform layer of clean media has been placed in the media bed, the lower section of the heat exchanger is reattached to the upper section. Again, gasket material may be used to seal the joint between the upper and lower sections.
The furnace down time required for the periodic cleaning and maintenance of the media in the heat exchangers may be further reduced by the use of a spare media bed or lower section. In this case the spare can be prepared and equipped with clean media and set aside until it is needed. Then, when the cleaning and maintenance function is performed, the media bed may be removed as described above, and immediately replaced with the prepared spare media bed. (Or, in the case of the regenerative burner shown in FIGS. 10-13, the lower section can be removed and replace with a spare prepared lower section.) The burners can then be reignited. At some time between maintenance intervals, the media bed, or lower section, as appropriate, can be dumped, refilled with clean media and set aside until needed.
As those skilled in the art will readily appreciated, the embodiments described above proved dramatic improvements in regenerative burners or heat exchangers, and their operations. The time required to replace a removable, bed of heat exchange material is significantly reduced, in comparison to current methods for treating regenerating or otherwise treating heat exchange material in burner or heat exchanger. In addition, hazards and inconvenience associated with current methods are largely avoided.
Of course, those skilled in the art will also appreciate that numerous modifications can be mad to the equipment and methods defined above within the scope of this invention, which is defined by the following claims.