US2588833A - Fuel burning means - Google Patents

Description

March 11, 1952 J. HARVEY FUEL BURNING MEANS Filed July 23, 1948 lNvsN-roR ATTORNEY Patented Mar. 1l, 1952 agrar ori FUEL BURNING MEANS Application July 23, 1948, Serial No. 40,231

10 Claims.

My present invention relates to the burning of slag forming fuel at high rates of heat release in such a manner as to attain maximum heat release in a furnace of restricted volume.

More particularly, my invention is addressed to the dual problem of stabilizing the iiame and maintaining it at a position close to the burner ports of a pulverized fuel burner of the intertube type, ring a furnace of restricted volume at maximum firing rates. To attain these ends, my invention involves a burner outlet port construction with a sharp corner edge formation at the tubes marginal to the intertube burner ports, this construction being so related to adjacent shielded furnace space as to promote low velocity eddy currents of fuel carrying air in the shielded spaces, as a means for maintaining ignition at a position close to the discharge position of the burner port and for increasing theV flexi-' bility of operation of the furnace at a high degree of effectiveness over a wide load range with burners of a premix type.

In premix burners of the type illustrated in this application, rate of iiame propagation of the mixture delivered to the combustion space through the burner port is so related to the velocity of the mixture that back firing into the mixing passage will be avoided. While the velocity of fuel mixture introduction at high rates of fuel burning is relatively high, the intense heat of the furnace causes quick heating of the mixture to ignition temperatures even though the burner wall absorbs heat because of its Water cooled structure.

With the pertinent premix type of pulverized fuel burner to be operated with a variable rate of fuel introduction, it is desirable, particularly at the lower firing rates, to provide ignition stabilization and temperature enhancing effects to compensate for the otherwise low furnace temperature in the vicinity of the burner port.

The present invention relates to a preferred configuration of the margins of the burner ports on the furnace side thereof to induce the development of eddy currents of a combustible fuel and air mixture marginal to the main stream as it leaves the burner port, to thereby effect a secondary fuel burning in the zones laterally of the stream for the purpose of maintaining the desired ignition temperature. While this action is particularly desirable at low rates of mixture in v troduction, it is also eifective at high rates.

Such eddy currents because of the manner in which they are formed carry smaller than average size pulverized fuel particles and thus they f are constituted "of a fluid fuel mixture which is more readily ignitable because of the finer particles.

In the present invention the formation of eddy currents is insured by making the outlet port with its furnace face margin of a sharp edge or right angle construction, whereby an eddy current of fine fuel carrying air develops from the outer envelope of the stream from the port. As there is an adequate fuel-air ratio to give complete combustion because of the premix feature with which the port is associated, the burning of the fuel in the constantly replenished eddy currents increases the temperature of the zone adjacent the burner wall to enhance the heating of .the remaining portion of the fuel stream.

The described arrangement of premix burner has been found to be eiective in attaining short iiame operation, as Well as a more stable ignition condition than would be obtained without the port configuration, thus contributing to exibility and eiciencyof furnace operation.

My invention is particularly adaptable for the burning of pulverized fuel at high rates in the restricted available furnace spaces of mobile boiler units such as those adapted for steam locomotive use.

In the form of my invention indicated in the accompanying drawings, there is a downwardly fired pulverized coal burning furnace which is vertically restricted and substantially limited as to combustion space. Because of these limitations and because of the importance of obtaining the maximum heat release within this limited furnace, it is important that ignition be maintained throughout the entire furnace, including positions closely adjacent the burner ports, Also because of the wide range of load variation of suchl an installation, it is important that ignition be stabilized. This is particularly true at low loads.

The invention will be described with reference to the drawings in which,

Fig. l is a partial vertical section indicating the arrangement of burners and burner ports in the roof of a furnace having its boundary surfaces delineated by wall carrying tubes;

Fig. 2 is a partial transverse section of the Fig. l installation; l

Fig. 3 is a longitudinal vertical section of the burner and burner throat construction, upon an enlarged scale, on the line 3 3 of Fig. 2;

Fig. 4 is a detail View of the burner port edge construction involving a burner port tube with a refractory holding member secured thereto; and

Fig. is a perspective view of the metallic body which forms a part of the constructions at the edges of each burner port.

Fig. 1 of the drawings shows the burner portion of a furnace having a combustionlchamber l with its boundary surfaces defined by spaced uid conducting tubes. As an example, the front wall 2 is defined by upright wall tubes 3 which may be connected into the circulation of a steam generator, through the headers 4 and 5 and other appropriate connections.

The furnace is relatively shallow with its floor defined by the fluid conducting tubes l which may be also connected into the circulation system of a steam generator.

The furnace is downwardly fired by a plurality of pulverized fuel burners including the nozzles 8-| and the burner port constructions such as Il, l2, and i3 formed between the furnace roof tubes such as 23-28. be also connected to the circulation system of the steam generator.

The burners project burning fuel downwardly and in a direction substantially normal to the surface of the furnace floor and the furnace flames are stabilized at positions close to the furnace roof by the effect of refractory constructions disposed on the furnace sides of the roof tubes adjacent the burner ports and presenting furnace faces which are substantially normal to the direction of flow of fuel and air through the burner ports. These furnace faces also join the sides of the burner ports in subH stantially right angular edge constructions as indicated at A-F in Fig. 3, thereby providing spaces adjacent and out of alignment with the main fuel and air streams in which low velocity eddy currents of fuel carrying air burn and enhance the ignition of the main fuel and air streams at positions close to the furnace roof.

The side walls of the illustrative furnace are lined with spaced steam generating tubes such as 22, the upper portions of these tubes being bent to form `horizontally inclined furnace roof sections such as those indicated at 224-28.

The steam generating wall tubes discharge into a steam and water drum 6, and they are supplied with Awater at their lower ends through a circulatory system including downcomers such as 3S (Fig. 2), having roof sections such as 3|-33 (Fig. 3)

vThe burner ports are long narrow openings provided in the horizontally inclined portion of the furnace roof, between the groups of roof tube sections indicated in Fig. 3. For example, the burner port 35 (Fig. 3) is disposed between the group of roof tube sections 23, 24, and 33 and another group consisting` of sections 25, 2a, and 32. lThe opposite surfaces of the entrances of the mixing passages leading to the burner ports are formed by the walls of successive deiiectors Sii-33, constructed of metal plate or sheet metal and of tapered construction as indicated in the drawings. As shown, the deflectors have their vertically inclined front walls cli- 42 welded to tubes 2l, 25, and 23, and their vertically extending rear walls @l- 46 welded to the tubes 2B, 26, and 24.

The deectors dil-42 have end walls such as 48 and e9 and intermediate stiffeners such as 5G, cut out, with the surfaces of the cut out portion receiving the roof tube sections 3l, 32, and 33 of the downcomers.

The surfaces of the Amixing passages leading to the burner ports are continued downwardly These tubes may beyond the tubes (such as iii-2S) by refractory constructions secured to those tubes and having furnace faces in a plane indicated by the line Cv-K in Fig. 3, which is substantially normal to the direction of ilow of the fuel through the burner ports. One of these refractory constructions is shown on an enlarged scale in Figs. 4 and 5, this particular refractory construction being secured to the tube 23. It is in the nature of an open ended box-like metal body having opposite sides 51 and 58 welded to the lower sides of the tube 23. These sections have inwardly projecting portions such as 5e and BQ, at their lower ends to form a pocket for receiving and holding a high Atemperature refractory material 5I packed in the pockets between the sides 5l and v53 .and between the transverse walls 52-54. The latter walls have their upper edges curved to fit the surface of tube 23. Each refractory member is a unitary construction welded to its tube by such welds as those shown at 55 and 56.

Above the burner ports, there is a secondary air chamber 62, the wall of which is shown at 5s and a portion of its roof at 6c. This chamber is connected to a suitable source of preheated air under adequate pressure to cause iiow from the chamber through the mixing passages and through the burner ports and into the furnace.

Within the secondary air chamber B2, the primary air and fuel conduits {i1-2| are disposed. They correspond in number to the .number of burners utilized for firing the furnace. These conduits supply pulverized fuel and primary air, under pressure, to the burners, and for `that purpose, they are connected to an air swept pulyerizer, not shown. These tubes terminate at positions above the burner ports where they are fitted with burner tips or nozzles `such as 8--IL Each nozzle is tapered as indicated by the walls 84 and 85 of the nozzle l5 in Fig. 3. They are also tapered or flared in the opposite sense as indicated by the walls 84 and 85 in Fig. 2 lto provide a wide discharge opening 88 discharging primary air and pulverized fuel as a thin sht in a direction such as that indicated at 911 in Fig. 3.

With this construction an arrangement of burner nozzles and burner ports, a wide stream of secondary air from the chamber B2 is caused to flow along the inclined surface of the deflectors (such as the surface 42 in Fig. 3) in a direction such as that indicated by the arrow 92, and at a position between the burner nozzle outlet 88 and the inclined wall 42 of the deflector. These interposed streams of secondary air, while flowing in such relation to the stream'of primary air and fuel from the burner nozzle I0 as to promote effective mixing of fuel and air, also act to scrub and protect the inclined surface of the deflectors.

These streams ( arrows 90 and 92, Fig. 3) are subjected to a mixing flow as they pass downwardly in the converging mixing passages between successive deflectors such as 31 and 38 at increasing velocities and pass through the burner ports in the plane G-K at the furnace face of the refractory constructions on tubes 23-28.

To maintain the correct operative relationship of the burner nozzles 8-ID and the walls of the burner port, the deflectors 36-38 are rigidly connected at their upper ends with the associated burner nozzles. Such connections are indicated in Fig. 3 as including the lugs 94-96 secured to and extending rearwardly from the burner nozzles. These lugs are fixed, as indicated at H10-|02, to upstanding lugs |04-l06 welded to the tops of the deiiectors. The spaces between the end walls of the deflectors and the wall 64 on the one side, and the drum on the other, are closed by thermal insulation and refractory bodies such 'as IIB-lll to confine the ow of secondary air to the burner ports.

The eddy current zones and shielded spaces in or adjacent to the plane G-K and marginal to the burner ports function to,

(a) Maintain the flame close to the burner ports (b) Substantially increase the stability operation of the burners, and

(c) Increase the flexibility of the operation of the burners of the furnace at high rates of effectiveness, and over wide load ranges.

When the arrangement is such as indicated in Fig. 3 of the drawings, the shielded spaces in which such action occurs are augmented by the spaces between the roof tube sections and beneath the deflectors. O'ne of such spaces is indicated in Fig. 3 as the space R between the refractory constructions secured to the tubes 21 and 28. Another is the space S above the tubes 25 and 26 within the defiector 31. Similar shielded spaces exist at the positions of all of the deectors and the tube sections covered thereby.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

l. In a furnace, a pulverized fuel burner construction of the intertube type with adjacent furnace boundary tubes disposed at the `opposite sides of burner ports normally having a mixture of pulverized fuel and air owing therethrough, and refractory constructions secured to the furnace sides of said tubes and presenting fuel contacting burner port walls with sharp corner edges marginally related to the burner ports.

2. In a pulverized fuel red furnace having a boundary delineated by spaced fluid conducting tubes, some of said tubes being arranged at the sides of burner ports normally having a mixture of pulverized fuel and air flowing therethrough, and refractory constructions presenting furnace faces with substantially right angle edge constructions at the margins of the ports, said refractory constructions being secured to furnace sides of the` tubes and presenting wall surfaces of fuel and air passages terminating in said ports.

3. In a pulverized fuel fired furnace having a furnace boundary delineated by spaced fluid conducting tubes, said tubes being arranged at the opposite sides of burner ports normally having a mixture of pulverized fuel and air flowing therethrough, and refractory constructions secured to the furnace faces of said tubes and presenting furnace faces transversely disposed relative to the direction of fuel flow through said ports, the refractory constructions also presenting surfaces of fuel iiow passages leading to the ports and joining the furnace faces in sharp edges at the ports.

4. In a pulverized fuel fired furnace having a boundary surface delineated by fluid conducting Wall tubes, said tubes being arranged in spaced groups at the sides of burner ports normally having a mixture of fuel and air owing therethrough, metallic deectors disposed adjacent said tubes and forming the opposite side Walls of fuel and air mixing passages leading to the burn- 5 er ports, and refractory construction secured to the furnace faces of said tubes and presenting furnace faces substantially normal to the fuel ow through the ports, a plurality of said constructions being provided at the furnace side of each defiector with a space between the constructions and shielded by the .deflectors 5. In a pulverized fuel red furnace having a boundary surface defined by spaced fluid conducting tubes, said tubes being arranged at the sides of burner ports and with a plurality of the tubes between successive burner ports, metallic deectors disposed adjacent said tubes and forming the opposite side walls of the fuel and air passages leading to burner ports which normally have a mixture of pulverized fuel and air flowing therethrough at high velocity, and refractory constructions secured to the furnace faces of said tubes and presenting furnace faces in planes transverse to the direction of ow through said ports, said refractory constructions also presenting sharply dened edges at opposite sides of said ports and in front of the tubes.

6. In a furnace, a pulverized fuel burner construction of the intertube type with adjacent furnace wall tubes disposed at the opposite sides of burner ports normally having a mixture of pulverized fuel and air flowing therethrough, and refractory constructions secured to the furnace sides of said tubes presenting substantially right angled corner edges marginally related to the burner ports, the side parts of said refractory constructions presenting surfaces of fuel flow passages leading to the ports with the fuel passage surfaces joining furnace face portions of the refractory constructions in said corner edges, said furnace face portions being disposed in a plane at the furnace face sides of the tubes.

7. In a pulverized fuel fired furnace having a boundary surface defined by spaced uid conducting tubes, said tubes being arranged at the sides of burner ports and with a plurality of the tubes between successive burner ports, metallic deectors disposed adjacent said tubes and forming the opposite side walls of fuel and air mixing passages leading to burner ports normally having a mixture of pulverized fuel and air flowing therethrough, and refractory constructions secured to and over the furnace faces of said tubes and presenting furnace faces substantially transverse to the fuel flow through the ports, said refractory constructions including metallic bodies with non-metallic refractory furnace face portions, a plurality of said constructions being provided at the furnace side of each defiector With a space between the constructions shielded by the associated defiector.

8. In a pulverized fuel red furnace having a boundary surface defined by spaced fluid conducting tubes, said tubes being arranged at the sides of burner ports with a plurality of the tubes disposed between successive burner ports, hollow metallic defiectors secured to said tubes and forming the opposite side walls of fuel and air mixing passages leading to the burner ports, means causing a mixture of pulverized fuel and air to ow at high velocity through said passages and burner ports, and refractory constructions including recessed metallic bodies secured to the 7l furnace faces of said tubes and non-metallic re-

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