Combustion – Flame holder having protective flame enclosing or flame... – Including means feeding air axially spaced points of the flame
Reexamination Certificate
1999-11-22
2001-02-27
Lazarus, Ira S. (Department: 3743)
Combustion
Flame holder having protective flame enclosing or flame...
Including means feeding air axially spaced points of the flame
C431S008000, C431S010000, C431S353000, C431S190000, C239S132000, C239S427300, C060S758000, C060S760000
Reexamination Certificate
active
06193502
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a burner for fuels suitable for spraying, in particular gaseous fuels, having a substantially cylindrical fire tube, a fire tube cover arranged on the upstream end of the fire tube, a fuel nozzle terminating centrally in the fire tube cover and means to feed the combustion air into the fire tube.
Such designs are used above all as standard burners for gas turbines.
Furthermore, the invention relates to a method for burning the fuel suitable for spraying, in particular gaseous fuel, which is fed centrally into a combustion zone where it is mixed with combustion air.
A major objective of modern combustion technology is to produce low-pollutant waste gases. In addition to complete burnout to avoid carbon monoxide, low NO
x
values are a particular objective.
Normally, a combustion zone is formed at the burner head, into which combustion zone the combustion air is blown through corresponding openings in the fire tube cover and in the fire tube, thus cooling the fire tube material. Further combustion air is fed in through scale-like openings which are distributed along the entire fire tube.
It has been found that such devices and methods can be improved on. The object of the present invention was therefore to achieve even temperature distribution in the fire tube and thus a reduction in the amount of pollutants produced.
This object is achieved by the device of the aforementioned type in that the means to feed the combustion air into the fire tube exhibit a plurality of first and second air line nozzles, that the first and second air line nozzles are inclined in the direction of counterflow at an angle to the axis of the fire tube, that the first air line nozzles end at the fire tube whilst the second air line nozzles extend into the fire tube and that a first air line nozzle is assigned to each second air line nozzle and arranged upstream directly adjacent thereto.
The method of the aforementioned type to achieve the desired objective is characterised in that the combustion air is blown into the combustion zone in such a manner that a highly turbulent toroidal eddy forms in a plane perpendicular to the direction of flow of the combustion zone, the direction of rotation of said turbulent toroidal eddy inside being against the direction of flow of the combustion zone.
SUMMARY OF THE INVENTION
Major embodiments of the present invention result from the dependent claims.
The toroidal eddy or eddy ring generated at the burner head generates a very intensive turbulent circulation and thus a good mixing of fuel and air. Due to the higher degree of homogeneity of the fuel-air mixture, the number of local areas, which exhibit stoichiometric or near-stoichiometric mixture concentrations and, due to their extreme temperatures, are the main source of NO
x
emissions, is reduced.
The combustion chamber of the invention is a so-called diffusion chamber in which the speed of the combustion process is governed by the speed of the fuel-air swirling and not by the speed of the chemical reactions. Therefore, the higher degree of mixing caused by the highly turbulent toroidal eddy in the upstream area of the fire tube leads to a shorter residence period of the combustion products in the high-temperature range, which reduces the amount of NO
x
emissions generated.
Furthermore, the invention leads to an increased penetration of the fuel flow by the air streams exiting through the first and second air line nozzles, said air streams preferably forming a major part of the entire combustion air. The second air line nozzles extending into the inside of the fire tube contribute particularly to the formation of the eddy. This achieves an even distribution of air across the fire tube cross-section and in this manner reduces the unevennesses of the gas temperature field in the combustion zone. This is particularly of substantial importance when the combustion chamber is used as the turbine combustion chamber, which is in fact one of its main fields of application. Temperature peaks constitute a considerable load for turbine blades and shorten their service life.
The air streams exiting through the second air line nozzle penetrates deep into the hot gas flow. It therefore cools the high-temperature range up to the axis of the fire tube.
Although the second air line nozzles extend into the combustion zone, the temperature loading is controlled in that an upstream first air line nozzle and preferably also a downstream third air line nozzle is assigned to and arranged directly adjacent to each second air line nozzle. The second air line nozzles are therefore cooled by the air exiting through the first air line nozzles and optionally through the third air line nozzles. The number of similar first and third air line nozzles can be increased even further by similar fourth air line nozzles which, viewed in the circumferential direction, are arranged between adjacent second air line nozzles. It has been found that the cross-section distribution between the two types of air line nozzles substantially increases the evenness of temperature distribution at the combustion chamber outlet.
In addition to the arrangement of the air line nozzles, a critical value for formation of an optimal highly turbulent toroidal eddy is the angle of incline of the air line nozzles to the axis of the fire tube. An angle of incline of 55 to 60° has proved to be very favourable. Furthermore, the axial distance between the first air line nozzles and the fuel nozzle is also of critical importance. It has been found that this distance depends on the diameter of the fire tube and is preferably approx. 0.70 times to 0.85 times the diameter of the fire tube.
The invention not only permits more intensive swirling of the fuel-air mixture and thus a more intensive combustion process but also at the same time permits a high stabilisation of the pilot flame in all load ranges.
Apart from the arrangement of the air line nozzles, the distance of the air line nozzles to the axis of the fire tube is of critical importance for a favourable air distribution across the fire tube cross-section and thus for a very even gas temperature field at the combustion chamber outlet. These values also depend on the diameter of the fire tube. Whilst the discharge openings of the first and optionally the third and fourth air line nozzles are flush with the fire tube, the discharge openings of the second air line nozzles should be at a distance to the fire tube and said distance should preferably be approx. 0.15 times to 0.18 times the fire tube diameter. The ratio between the total cross-sections of the two types of air line nozzles is also critical in this connection. It has proved to be particularly advantageous for the total cross-section of the second air line nozzles to be approx. 0.6 to 0.7 times the total cross-section of the first and optionally the third and fourth air line nozzles.
Additional combustion air can be supplied in the area of the fire tube cover and thereby cool said fire tube cover. Furthermore, it is possible to feed in combustion air through openings in the fire tube wall downstream of the air line nozzles. This measure proves to be advantageous for reducing the generation of carbon monoxide.
REFERENCES:
patent: 2974485 (1961-03-01), Schiefer
patent: 3643430 (1972-02-01), Emory, Jr. et al.
patent: 3751911 (1973-08-01), De Tartaglia
patent: 3831854 (1974-08-01), Sato et al.
patent: 4054028 (1977-10-01), Kawaguchi
patent: 4301657 (1981-11-01), Penny
patent: 5984662 (1999-11-01), Barudi et al.
Peters Karl
Poslusny Gustav
Scholz Karl-Heinz
Sudarev Anatolij Vladimirovic
Vesely Stanislav
Blakely & Sokoloff, Taylor & Zafman
Cocks Josiah C.
Lazarus Ira S.
Ruhrgas Aktiengesellschaft
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