Stoves and furnaces – Stoves – Heating
Reexamination Certificate
2000-04-28
2001-09-25
Yeung, James C. (Department: 3743)
Stoves and furnaces
Stoves
Heating
C126S0920AC, C126S101000, C431S116000, C431S215000
Reexamination Certificate
active
06293275
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a heat source and, more particularly to a heat source for generating of high-temperature heat.
BACKGROUND OF THE INVENTION
Heat sources for temperatures up to approximately 1000° C. are needed particularly in the technology of block-type thermal power stations for transforming fuel energy into current and heating warmth in small decentralized units. In such cases, the object is high efficiency with small units. Furthermore, low emissions (NO
x
and CO) are desirable. Specifically, a heat source with high dependability and a useful life with simple installation and little maintenance are desirable for use in building heating systems. Furthermore, it must be possible to economically manufacture the heat sources in large runs.
U.S. Pat. No. 5,003,349 discloses a Stirling motor with a combustion chamber surrounded by an annular waste gas/air heat exchanger, which is also designated as a recuperator and serves the purpose of transferring exhaust gas heat to fresh air in counterflow. The recuperator is surrounded with a pot-type thermal insulation.
For a high total efficiency, recuperators should be as efficient as possible. If the gas heater is to be used in small block-type thermal power stations, a compact, simple and sturdy construction is required.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, in view of the foregoing, a general object of the present invention is to provide a compact heat source with good efficiency.
The present invention provides these and other advantages and overcomes the drawbacks of the prior art by providing a heat source which includes a combustion chamber and an exhaust gas/air heat exchanger (recuperator), the diameter of which increases in axial direction. The recuperator can be, for example, conical, truncated conical, bell-shaped or cone-shaped. The bell form provides the advantage that, in the conical portion, gap widths in the millimeter range (less than 5 mm, below 2% of the mean recuperator diameter) can be achieved with tolerances of 10% of the gap width, which permits a uniform flow at the circumference of the recuperator. The partition wall of the recuperator is suitably to be provided on its inside and/or outside with knobs or burls, which establish the gap width. Despite this fitting accuracy, which is important for the convective heat transition, because of the conical portion of the bell form, the individual parts of the recuperator can be inserted into one another simply and also disassembled. Alpha-values are possible of up to 150-250 W/k.m
2
. The recuperator can be implemented in a compact form and with low weight; it consists only of a few simple parts (e.g., merely three substantially conical parts), and it is self-adjusting.
In the domed portion of the bell, the heat transition takes place at high temperatures, predominantly by radiation; as the gap width plays a subordinate role. In contrast, the considerable amount of the recuperator parts that are disposed in this area an be contained best by the domed construction form.
The small size and precise maintenance of the gap geometry permits low pressure losses on the exhaust-gas and the air-side as well as intensive heat exchange with a small heat-exchanger surface and thus a small volume. Moreover, arranging the combustion chamber at least partly in the interior space enclosed by the recuperator produces a compact construction. The combustion chamber can be designed to accommodate both combustion with flames, and also with flameless combustion, which allows particularly low NO
x
and CO values. An adjustable jet nozzle permits the flameless operation even with a partial load. With regard to the flameless combustion, reference is made to DE 44 19 332 Al and to patent application P 198 56 933.
Insulating the combustion chamber against the recuperator and insulating the recuperator to the outside provides thermal advantages. Insulating material can be provided in, for example, an evacuated space which is built in the outer wall of the recuperator. A domed outer form protects against deformation by air pressure. While the thickness of the outer insulation decreases toward the cold end of the recuperator, in an advantageous embodiment, the thickness of the inner insulation, as measured in radial direction, increases in the same direction. Thus, the heat losses of the combustion chamber and the heat losses of the recuperator can be minimized with a small structural volume.
The combustion chamber functions so as to generate a high temperature level, for example, to execute chemical reactions, as a gas mixture induced through the combustion chamber is heated therein. The reaction is set weakly exothermally (partial oxidation) in order to make up for wall losses. In this manner, the gas heater can serve without a separate high temperature heat exchanger, for example as a gas generator for a fuel cell.
A high temperature heat transfer device can also be connected to the combustion chamber. This can be in the form of one or more channels, for example tubes, which extend through the combustion chamber or through a space traversed by exhaust gas. In the combustion chamber high-temperature heat can be drawn off, for example for a thermal power apparatus (block-type thermal power technology). Furthermore, the gas can comprise a gas which is to be altered chemically. The gas heater, therefore, can serve also as a hydrogen generator in the vapor reforming process of fossil fuels or methanol.
Hot exhaust gas drawn off from the combustion chamber can be used to heat a steam generator in order, for example, to recover vapor needed for a vapor-reforming process. By controlling or regulating the exhaust gas streams between the recuperator and the steam generator, the distribution of the energy flows of the steam from the steam generation and from the vapor-reforming process can be adjusted very rapidly to changing loads. This enables their use in hydrogen generation for the operation of fuel cells in motor vehicles. Likewise, for use in power-heat coupling, a variable distribution of heat generation and mechanical energy generation is possible. Thus, in addition to the warmth given off by a Stirling motor, heating warmth can be derived.
For removing low-temperature warmth a coil-type condenser can be provided at the cold end of the recuperator in or on the exhaust gas channel. Because of the large diameter of the recuperator, the flaw speed is not too large in this location, so a few tube turns suffice for a good heat transfer. The pressure loss is also low.
In close proximity, an air filter can be provided in front of the entrance to the air channel. The result is a compact component that contains all of elements essential for the gas heater. Flow speed and pressure loss are low.
In the combustion chamber, catalysts can be arranged, for example, on the heat consuming elements (fluid-conducting tubes). As a result, the oxidation of the fuel takes place at lower temperatures directly on the heat sinks (tubular heaters). Improved heat transition can result and overheating of the catalysts can be prevented. Further, catalysts can be arranged in the exhaust gas channel of the recuperator, for example, on the inner wall of the recuperator, in order to reduce emissions.
In the combustion chamber, an electrically driven heat source can be provided, such as, for example, an incandescent heater. This allows a simple starting operation and a large regulating range. Moreover, the combustion chamber can be particularly laid out in combination with a catalyst and an adjustable jet nozzle so as to allow for different temperatures and loads, which can likewise facilitate the starting, and produces a good regulating range. The jet nozzle permits an internal recirculation in the combustion chamber to be maintained, even with a small load. The recuperator is well suited to be constructed of a ceramic material.
The present invention can provide the following advantages:
high efficiency, i.e. low exhaust gas and wall losses;
low combustion-caused emissions (NO
x
and CO)
Leydig , Voit & Mayer, Ltd.
Yeung James C.
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