US2941361A - Combustion apparatus having a flame stabilizing baffle - Google Patents

Description

June 21, 1960 COMBUSTION APPA Filed Oct. 12, 1955 D: g kmms I 2,941,361

RATUS HAVING A FLAME STABILIZING BAFFLE I v 3 Sheets-Sheet 1 A I? arm J41 June 21, 1960 D. B. SPALDING 2,941,351

COMBUSTION APPARATUS HAVING A FLAME STABILIZING BAFFLE Filed Oct. 12,' 1953 3 Sheets-Sheet 2 fizzoz fxma cr/on/ PUMP AWE/wpe J23 0. M mid June 21, 1960 D. B. SPALDING 2,941,361

COMBUSTION APPARATUS HAVING A FLAME smsmzmc mm: 'FiledOct. 12, 1953 5 Sheets-Sheet s Amewrok kw QM 1. 77' ORNE Y] COMBUSTION APPARATUS HAVING A FLAME STABILIZING BAFFLE Dudley B. Spalding, Cambridge, England, assignor to National Research Development Corporation, London, England, a British corporation Filed Oct. 12, 1953, Ser. No. 385,663 Claims priority, applicationGreat Britain Oct. 15, 1952 '3 Claims. (Cl. 60-3952) The invention relates to equipment for burning vaporific fuel in a ducted stream of combustion-supporting gas and is particularly applicable in circumstances where the velocity of the gas stream is high, as in the case of continuous combution gas turbine plant for example.

In combustion'systems for such plants it has been previously proposed to place a baflle in the stream in the wake of which the gases have a recirculating motion. Fuel is burnt in the wake of the baffle and the flame there is stabilized because the recirculation draws hot burnt gases upstream to mix with and ignite the unburnt fuel and air flowing around the bafile edge. If the recirculating gases are insufficiently hot to cause suificient fresh reaction for the supply of such recirculating gases to be maintained, then the flame would be extinguished. Extinction is aided by a high velocity gas stream, by small baffle dimensions and by unduly low temperatures and pressures. An object of the present invention is to arrange the combustion system in such manner that flames are less easily extinguished than heretofore.

Broadly stated, the present invention provides a combustion system for burning vaporific fuel in a ducted stream of fast moving combustion-supporting gas comprising a duct defining a path for the said gas stream, a flame-stabilizing bafile positioned in the duct, means for introducing fuel into the duct for combustion in the gas stream, and means for encouraging the complete combustion, in a sheltered region afiorded by the bafiie, of some of the said gas before that gas comes into contact with unburnt gas which has flowed past the baffle.

According to one aspect of the invention the baflie is so shaped and positioned in the duct that some of the gas flowing past the batfle is recirculated in the wake thereof to form the aforesaid sheltered region. The aforesaid means for encouraging complete combustion may be constituted by an open-ended tube extending lengthwise in the wake of the baflie and so positioned that burnt gas is recirculated through the tube from a downstream part of the combustion zone to an upstream part near the bafile. This tube discourages the recirculation of incompletely burnt gasesby virtue of the position of its downstream end and therefore tends to ensure that only burnt gas comes into contact with unburnt gas which has flowed past the baffle. Alternatively or additionally to the inclusion of the aforesaid tube, the downstream surface of the baffie may be catalytic, the catalyst causing partly burnt recirculated gas to complete its combustion at the said surface before the partly burnt gas comes into contact with unburnt gas which has flowed past the bafiie. Following the recirculation of the burnt gas and its mixing with unburnt gas which has flowed past the baflie, it is desirable that ignition should occur; but it is possible that the bafile may have chilled the recirculated burnt gas, thereby preventing ignition. According to an embodiment of the invention, therefore, means are provided for extracting from the system the surface layer of burnt gas contacting the downstream surface of the bafiie. The baffle may be hollow and the downstream surface thereof porous or apertured and means may be provided for extracting by suction recirculated gas in contact with the said surface through the pores or apertures therein.

According to another aspect of the invention the bathe comprises an open-ended tube extending lengthwise of the duct, the inside thereof constituting the aforesaid sheltered region and an insert of refractory material contained within the tube, the insert presenting a large surface area to gas flowing through the tube for encouraging the complete combustion of the said gas, the burnt products passing from the downstream end of the tube and there mixing with and igniting the unburnt gas which has passed around the outside of the tube. The refractory insert may be impregnated with a catalyst such as platinum or palladium and may be a single body of a porous nature or having a plurality of lengthwise extending throughways.

By way of example, several embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a longitudinal sectional view of the duct showing one embodiment of the invention.

Figure 2 is a sectional view of Figure 1 in the direction of arrow II,

Figure 3 is a view similar to Figure 1 showing a modification of the embodiment,

Figure 4 is a sectional view of Figure 3 in the direction of arrow IV,

Figure 5 is a longitudinal sectional view of the duct showing another embodiment of the invention,

Figure 6 is a longitudinal sectional view of the duct showing a combination of the embodiments shown in Figures 1 and 5,

Figure 7 is a longitudinal sectional view of the duct showing another embodiment of the invention,

Figure 8 is a longitudinal sectional view of the duct showing yet another embodiment of the invention, and

Figure 9 is a sectional view of Figure 8 in the direction of arrow IX.

Considering firstly the embodiment shown in Figures 1 and 2, 1 denotes the duct through which a fast moving stream of combustion-supporting gas e.g. air is passing, the direction of flow being in the direction of arrows A. Fuel is injected into the air stream in an upstream direction by means of fuel nozzle 2. The fuel is carried by the gas stream in droplet form into the region of combustion immediately downstream of a bafile 3. The baffle 3 is of conical form and has its apex pointing upstream and is hollow. 4 denotes a support for the baflie. The bathe is so shaped that air flowing over the surface of the bafiie is little disturbed and a relatively stable and sheltered re-- gion in which recirculation of the air occurs is produced in the wake of the baffle, where it is ignited by igintion means 20, combustion occurring in this region. An openended tube 5 is mounted axially of the duct 1 on support members 6 with its upstream end in the vicinity of the baflie 3. The tube 5 is of such a length that the downstream end is in a part of the combustion region in which combustion is substantially complete. In the arrangement shown in Figures 1 and 2 the tube 5 is so positioned that the recirculated gas is encouraged to flow through the tube 5, the gas entering at the downstream end of tubes 5 and re-emerging at the upstream end of the tube where it mixes with unburnt air/fuel mixture which has flowed around the outside of bafile 3. By positioning the tube 5 so that the downstream end is in the region where v the combustion is substantially complete only burnt gas is recirculatedthr'ough the tube. This embodiment including the bafiie. and the tube therefore tends to ensure that onlysubstantially completely burnt gases mix with the fresh unburnt air/fuel mixture.

In the modification shown in Figures 3 and 4 the baflie is of annular form instead of conical form and similarly References Cited in the file of this patent UNITED STATES PATENTS Beckfeld et a1. Feb. 18, 1890 Benedict Dec. 17, 1912 Hyatt Jan. 5, 1932 Darling Mar. 27, 1951 10 6 Williams Apr. 10, 1951 Berggren et a1. Apr. 8, 1952 Clarke et a1. Dec. 23, 1952 Reid et a1. Nov. 3, 1953 Probert May 25, 1954 Harris et a1. Feb. 14, 1956 FOREIGN PATENTS Canada June 3, 1952

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