Combustion – Heated line section feeds flame holder – Housing encloses heated section and flame area
Patent
1986-12-02
1989-07-25
Makay, Albert J.
Combustion
Heated line section feeds flame holder
Housing encloses heated section and flame area
431215, 431247, 431248, 431243, 431 5, 431 11, 422203, 422204, F23D 1144
Patent
active
048508578
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for the combustion of oxidizable substances, suspended in a carrier gas, and comprises of a gas inlet and gas outlet, a burner to which a high velocity mixing pipe is connected, a primary combustion chamber, a heat exchanger consisting of heat exchange tubes placed around the high velocity mixing chamber which transports the unprocessed gas in counter-flow to the already incinerated gas. These tubes are bent at one end.
2. Description of The Prior Art
An appropriate device of this type is described in German DE No. 30 43 286, Oct. 22, 1981 and corresponding EP No. 0 040 690 Dec. 2, 1981. Here the heat exchange tubes are bent inwardly on the high-temperature-side of the apparatus, i.e. curved inwardly in the vicinity of the burner and connected into a drum which encompasses the burner concentrically. Admittedly, this design offers the advantage that, different expansions of individual tubes, caused by temperature, do not lead to damage during process dependent applications, such as cracking.
This, however requires a considerable manufacturing effort in order to weld the inwardly bent tubes to the drum, due to the fact that, the space between the tubes is small. The drum as such cannot contribute to the compensating of tube expansions occuring from temperature differentials, because its relatively large wall thickness is necessary to prevent contraction and distortion during welding, which would in turn subject the tube bends to undue stress and strain.
Furthermore, the heat exchange tubes do not effectively transfer heat over their entire length, because the hot exhaust gas does not impinge directly on the curved ends, but is deflected and diverted away, so that it misses these parts of the tubes.
Moreover, the occurrence of scale formation in the vicinity of the tube bends is inavoidable, because these bends are located within the hottest part of the appliance. Scale build-up however can cause increased erosion of the tube walls when the tubes are subjected to large rates of change of expansion in this region. Such rates of change of expansion are more often than not characteristic of a particular process.
SUMMARY OF THE INVENTION
The object of this invention is to improve upon the device as previously described in such a fashion that, the heat exchanger and its components can be protected against varying expansions and surface damage due to temperature, utilizing simple design methods.
In accordance with the objects of this invention the problem is addressed by allowing the cold ends of the heat exchange tubes to curve outwardly. The immediated advantage is that the tube ends are connected to an circumferential area substantially larger than that required for inwardly curved tubes, thereby making welding easier and even making automatic welding possible.
As these welded ends may be spaced much further apart in such fashion that the shell housing the tube ends need not be an extra component such as a drum as prescribed by state of the art, what is more, the inside wall of the outer annular chamber, through which the combustible laden carrier gas is fed from the inlet nozzle to the heat exchanger tubes, is used as a wall to which the tubes are welded in a preferred embodiment of the invention.
As there is no danger of contraction and distortion during welding of the tubes due to the wider spacing, a thinner shell wall may also be chosen, and this consequently increases the overall flexibility of the region of thermal compensation.
As the available space for the outwardly curved heat exchange tube ends may be made as large as necessary, another resulting advantage is the number of consecutive tube rows may be increased with increasing number of tubes at the other tube rows in comparison to the arrangement in accordance with EPO No. 040 690.
In combination with this the flow of the gas around the tubes becomes increasingly more turbulent.
This ultimately enables the number of cross-flow heat exchange passes to be
REFERENCES:
patent: 1881206 (1932-10-01), Magis et al.
patent: 3549333 (1970-12-01), Tabak
patent: 3806322 (1974-04-01), Tabak
patent: 3838975 (1974-10-01), Tabak
patent: 3898040 (1975-08-01), Tabak
patent: 4364724 (1982-12-01), Alpkvist
patent: 4365951 (1982-12-01), Alpkvist
Katec Betz GmbH & Co.
Makay Albert J.
Price Carl D.
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