Stoves and furnaces – Liquid heater – Fluid fuel burner for other than top-accessible vessel
Reexamination Certificate
2003-03-11
2004-08-17
Yeung, James C. (Department: 3749)
Stoves and furnaces
Liquid heater
Fluid fuel burner for other than top-accessible vessel
C126S350100
Reexamination Certificate
active
06776153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high efficiency hybrid atmospheric water heater that overcomes many of the problems of current water heaters. Specifically, the present invention is capable of achieving approximately 99% efficiency, can be operated on a wide variety of fuel types, is capable of achieving low nitrogen oxides (NO
x
) emissions, can be built to any size, operates with consistent burner performance and low noise and vibration, and is constructed of economical materials.
2. Description of the Related Art
Applicant's water heater is a combination of a direct contact water heater, i.e. a water heater where the combustion gases come into direct contact with the water that is being heated, and an indirect contact water heater, i.e. a water heater where the combustion gases are contained within a combustion chamber and exhaust tubes and do not come into direct contact with the water that is to be heated which is located on an opposite side of the combustion chamber wall and on an outside surface of the exhaust tubes.
The present invention combines a direct contact water heater portion and an indirect contact water heater portion to create a new and better type of water heater. Current water heater designs have three areas where improvement can be made. These areas where improvement is needed are in the location of the water inlet, the design of the combustion chamber, and the exit of the exhaust tubes.
The first problem with current water heater designs is in the location of the water inlet. The optimum location for the makeup water inlet in a direct contact water heater is at the top of the unit. By adding the cooler makeup water at the top of the unit, maximum heat exchange can occur between the downwardly cascading makeup water and the upwardly flowing combustion gases. Water heaters with the makeup water inlet located at the bottom of the unit are less efficient, able to achieve only approximately 91% efficiency as compared to approximately 99% heat transfer efficiency in the present invention.
Although makeup water to the heater is introduced through the makeup water inlet, the present invention is also provided with a separate water recirculation inlet at the top of the indirect contact water portion. This water recirculation inlet is for recirculating water within the lower indirect contact portion of the water heater whenever the temperature of the water to be reheated is greater than or equal to 150 degrees Fahrenheit. In the case of recirculation water temperatures that are less than 150 degrees Fahrenheit, the recirculation water is distributed by the upper makeup water inlet along with any makeup water that is needed.
Prior art water heaters teach a single water distribution location for water to be heated. This single water distribution location on prior art water heaters is always located at the top of the heating tower for both cold makeup water and for hotter recirculation water. Entry of hotter recirculation water to the upper portion of the water heaters, i.e. the direct contact portion, creates a high degree of vaporization of the distributed water stream. This vaporization cools down the water stream, making the overall efficiency of water heaters that move hotter recirculation water up to the top portions of the unit, i.e. the direct contact portion, lower than can be achieved when limiting the flow of hotter recirculation waters only to the lower sections, i.e. the indirection contact portions.
The second problem with current water heater designs is in the design of their combustion chamber. Prior art water heaters with the combustion chamber under the water line employ as their combustion chamber either a small diameter immersion tube or open bottom atmospheric combustion burner box instead of the large diameter, forced draft, firing chamber of the present invention. Both the small diameter firing tube and the open bottom atmospheric burner limit the amount of energy that can be burned to approximately 3 million BTUs/hr., thereby limiting the size of the water heater that can be produced when it employs one of these two types of combustion chamber. The present invention, on the other hand, employs a large diameter firing chamber that does not limit the size of the water heater unit with which it is employed. The present invention employs a forced draft combustion burner which allows efficient and clean combustion of liquid fuels. In addition to giving clean, efficient combustion, the firing chamber is large enough to allow the flame to be fully developed without impinging on any wall structure of the fire box. The combustion chamber of the present invention allows for adequate combustion space to burn large BTU energy releases of either gaseous or liquid fuels. Also, because the combustion chamber is circular when viewed from a top perspective, this makes the fire box more economical to produce than the square and rectangular prior art fire boxes and also minimizes the creation of thermal hot spots that produce NO
x
, thus making the present invention a lower NO
x
producing device than prior art rectangular fire box designs.
Also, both a small diameter firing tube and an open bottom atmospheric burner are not designed to produce low NO
x
emissions at the concentration of 20 ppm or less. Therefore, a water heater employing either of these two types of combustion chambers could not be used in California or Texas or anywhere that is designated by the EPA as a non-attainment zone and requiring 20 ppm NO
x
or less. The present invention, in contrast, is able to achieve low NO
x
emissions less than 20 ppm due to its use of a larger diameter firing chamber.
In addition, both a small diameter firing tube and an open bottom atmospheric burner can only be used with gaseous fuels, and neither can be employed with fuel oil or other combustible liquid fuel. The inability to burn oils severely limits the use of water heaters with these two types of combustion chambers, particularly in the eastern states in the United States and in foreign countries both of which are heavily dependent on liquid heating fuels. The present invention does not have this limitation because its large diameter firing chamber can easily burn either gaseous or liquid fuel sources. The large diameter firing chamber of the present invention has a plurality of exhaust tubes as the only exit out of the chamber for combustion gases.
The third problem with current water heater designs is in the exit of the exhaust tubes. Current gas fired water heaters, such as for example the one taught in U.S. Pat No. 4,658,803 to Ball et al., employ an overhead canopy or cover above the exit of the exhaust tubes. The purpose of the overhead canopy is to prevent water from entering the exhaust tubes. Exhaust tubes which have an overhead canopy experience two problems: overheating of the dry portion of the metal tubes located above the water line and below the canopy and sporadic backpressure created by a water curtain that is created by the canopy. Also the cost of manufacturing units with canopy style designs is higher than production of the present invention.
The immediate metal surfaces of the metal tubes, i.e. those portions of the metal tubes that are located above the water contained in the water chamber which surrounds the tubes and also located under the canopy where falling water cannot contact their exterior surfaces, remain dry and tend to overheat since they are not cooled by contact with the water. This results in overheating of the metal tubes and possible metal failure or at least greatly reduced tube life. One solution to this problem is to add an elaborate water cooling system to cool this portion of these metal tubes, however this type of cooling system is expensive to manufacture.
The solution that is normally employed to address this problem is to utilize expensive metal, i.e. special steel, which is capable of withstanding the elevated temperatures when manufacturing those dry portions of the metal tubes. Because of the ex
Mundt Keith John
Walker B. Keith
McKay Molly D.
Yeung James C.
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