US2800092A - Burning of pulverized fuel - Google Patents

Description

July '23, 1957 H, U 2,800,092

" BURNING OF PULVERIZED FUEL Filed Feb. 8, 1952 2 Sheets-Sheet 1 In ventor Hans EURQ A tto rney July 23, 1957 H. BURG 2,800,092

' BURNING OF PULVERIZED FUEL Filed Feb. 8, 1952 V y 2 Sheets-Sheet 2 Inventor Hau i 5 wil L 1/3601 A ttorne y United States Pateag BURNING OF PULVERIZED FUEL Hans Burg, Essen, Germany, assignor of one-half to Pollopas Patents Limited, London, England, a British company The present invention relates to 'a method of and apparatus for burning pulverised fuel which enables coke, anthracite and low-grade fuels, hereinafter also jointly referred to as coke-type fuel, to be burned efficiently.

Pulverised fuel burners are already known (see French Patent No. 641,47 8) in which the pulverised fuel and air (herein called primary air) is injected into a combustion chamber through a burner orifice which imparts a rotary motion to the fuel-air mixture leaving the burner orifice, thereby to produce a turbulent flame, the surrounding walls of the combustion chamberbeing provided with air inlets distributed therearound for producing jets of air (herein called secondary air) in directions substantially tangential with the internalisurface of the combustion chamber, thereby toproducea 'sleeve of secondary air around the flame whicharotates in the same direction of rotation as a fuel-air mixture leaving the burner orifice, the secondary air fed throughthese inlets in the wall of the combustion chamberservin'g to assist in the complete combustion of the fuel.

The present invention has amongst its objects to provide an improved apparatus for burning pulverised fuel of the kind above referred to, which iscapable of. burning pulverised coke or anthracite which it has hithertont been possible to burn in pulverised fuelburners.

To achieve these results we have found that the following criteria must be observed:; 1'

l. The internal periphery of the combustion .chamber must. be substantially smooth in order that the rotation of the flame. and air sleeve therearound will not be retarded or appreciably disturbed by eddies so that'the ro v confine the burner flame to the central axial zone of the combustion chamber and away from the walls thereof. This arrangement concentrates the burner flame,which burns with a more intense heat, and furthermore protects the walls of the combustion chambers from being rapidly burned away. Preferably the direction in which the secondary air is admitted makes an angle of .about 30 to" the tangential direction of the internal surface of the combustion chamber where the air inletis located. Without secondary air, the flame would have, a diameter of approximately /3 to A of thediameter of the combustion chamber; the secondaryflair is directed tangentially to this vertical diameter and makes several'turns 'around;

the chamber in a spiral of decreasingd'iam'eter; thereby confining the flame to the central axial zone and reducing its'eifectivediameten 3. The passages defining theuinlets for=secondaryrain to the combustion chamber should maintain theirsame general direction throughout their.entiretlength so that; as the bricks of the combustion .chambenburn away the direction in which the secondary air is admitted to the combustion chamber will not substantially vary.

4. The primary air mixed with the'fuel in the burner tube and the secondary air fed to the combustion chamber must be preheated to a high temperature, the actual temperature of preheating depending upon the particular fuel being burnt and other operating conditions. In gen-' eral, for burning coke and anthracite, the temperature to which the primary and secondary air has to bespre heated before admission to the burner or the secondary air inlets must be at least 200 C. and often. considerably higher.

One aspect of the present invention therefore consists in an apparatus for burning pulverised fuel, particularly.

cokeor anthracite, comprising a substantially horizontally disposed burner tube having an orifice leading into.

fuel and air under pressure to the burner tube, means in the burner tube for imparting a rotary motion to the fuel-air mixture leaving the burner orifice, air inlets dis tributed around the peripheralwall of the combustionv chamber and inclined'at an anglerto the radial direction,

means for supplying air under pressure to said inlets to produce within the combustion chamber a sleeve ofair rotating in the same direction of rotation as the fuelair mixture leaving the burner orifice and adapted to confine the burner flame .to the central axial zone of. the combustion chamber andaway from the walls thereof, 1

and means for preheating the air supplied to the burner tube and'to the said inlets to 200 C. l r

The combustion chamber may continuously increase in diameter from the end containing the burner, orifice to the opposite endconnecting to the boiler furnace or the like, or the flared portion may lead into a substantially cylindrical portion whichconnects with the furnace or the like. Preferably the combustion chamber is constructed of a plurality of annular sections arranged end-to end, means being provided for controlling the amount of:

secondary air admitted through the air inlets comprised within each section. r r i From another aspect the invention consists in the v method of burning pulverised fuel, particularly pul-x verised coke and anthracite, which consists in injecting a' mixture of the-pulverised fuel and air which has been preheated to a temperature of at least 200 C. into a combustion chamber having a smooth internal surfaceand arranged substantially coaxial with the inletfor the fuel-air mixture, the fuel-air mixture being ignited insaid combustion chamber, impartingarotary motion to the fuel-air mixture during its admission to the combustion chamber, and in rotating around the core of the? flame a sleeve of air which hasbeen preheated to a tem-' perature of at least 200 C. and has been injected into the combustion chamber through orifices, in the wall thereof directed substantiallytangential to the-core of theflame.

Other objects and aspects of the invention will become apparent from the following description by way of example in connection'with the'accompanying drawings:

Fig.1 shows, diagrammatically, a sectional elevation of a burnerapparatus according to the invention for firing a water tube boiler.

Fig. 2 shows a section of a modified construction of combustion chamber. f

Fig. 3 shows a section on the line III-III in Fig.2. Referring to Fig. l of the drawings, 1 generally indi-' cates the' front portion of a boiler of the water-tube type 1 comprising water tubes-,2 which are heated from'theu Patented July 23, 1957 a temperature of at least" furnace chamber 3. The burner arrangement 4 according to the present invention comprises a burner tube 5 the burner orifice of which opens into a substantially coaxial combustion chamber. 6. The combustion chamber is built upfromthree sections 6a, 6b and 60 arranged endtovend, the two sections 6a, 6b closest to the burner orifice being of frusto-conical form and increasing in diameter from the end containing the burner orifice, Whilst the third section 6c is of substantially cylindrical form. The sections of the combustion chamber 6 are built up from fireproof bricks assembled with spaces therebetween through which secondary air may be admitted. The general disposition of these bricks will be understood from the crosssection shown in Fig. 3, which although actually being a cross-section of the modification shown in Fig. 2 indicates how the bricks 7 are arranged to produce the series or" secondary air inlet apertures distributed around the periphcry. of. the combustion chamber. The inlet apertures 27 taper in width from the outer periphery of the bricks to the inner periphery thereof but their general direction remains unchanged so that air admitted therethrough will be directed at angles of approximately 30 with respect tothe tangents to the internal periphery of the combustion chamber at the places where the air inlets 27 are located. In other Words the direction of each inlet, at the point at which it penetrates the combustion chamber wall, forms an angle (viz. 30 and 60 respectively) both with the tangent and with the radius of the combustion chamber.

The bricks may be held in assembled relationship in any convenient manner, for example by clamps, their external peripheries being surrounded by chambers 18, 19, 20 as shown in Fig. 1 through which secondary air can beadmitted from the air line 15 through the control valves 21, 22, 23 respectively to enable the amount of secondary air admitted through the air inlets in the three sections of the combustion chamber to be controlled.

The bottom portions of the sections 6b and 6c of the combustionchamber may be cut away as shown in Fig. l to allow slags to fall into the slag chamber 8.

Pulverised fuel is fed to the burner 5 from the fuel hopper 9 through the fuel control means 11 and the pipe 10. Primary air is also supplied to the burner tube from the air supply line 15 through the pipe 16 and control means 17. The fuel-air mixture in the burner tube 5 is injected into the combustion chamber through the burner orifice which is fitted with spirally arranged vanes 25 or the like for imparting a rotary motion to the fuel-air mixture leaving the burner orifice. The direction of rotation of this fuel-air mixture is the same as the direction of rotation imparted to the sleeve of secondary air produced by the air inlets 27 in the wall of the combustion chamber 6.

The air pressure fed to the burner tube and secondary air inlets is created by the blower 12. In order to burn coke or anthracite, the primary and secondary air is preheated. This may be elfected by connecting the air intake 13 of the blower 12 to the slag chamber 8 so as to utilise the heat from the slags for preheating the air. Preheating may be efiected in other ways, for example from any other convenient source of heat, preferably waste heat, or alternatively by a special preheating apparatus 14 connected in the air line 15.

The fuel-air mixture injected through the burner orifice 25 may be ignited in any convenient manner, for example by a gas flame. The injection velocity may be of the order of 15-20 metres per second. In a practical test of the apparatus, for burning pulverised coke of a grain size such that not more than 20% residue was left on a 70 mesh screen (70 apertures per centimetre) the primary and secondary air was preheated to 250 C. For burning pulverised coke having a grain size which left a residue of 50% on a 70 mesh screen, the air was preheated to 300 C. In both cases the fuel was completely burnt with an intensely hot flame. The ratio of primary air to secondary air was about 1:2. Similar temperatures of preheating the air are required for burning pulverised anthracite of corresponding grain size containing up to 4% of volatile materials.

It will be readily understood that with the construction described the internal surface of the combustion chamber is substantially smooth and does not restrict the rotation of the sleeve of secondary air. Furthermore, when the bricks of the combustion chamber are partly burnt away the direction in which the secondary air is admitted remains unchanged so that the operation of the apparatus remains substantially constant throughout the entire life of the combustion chamber.

Fig. 2 shows'a modified construction of the apparatus according to this invention. In this embodiment only the first section of the combustion chamber is of frustoconical form, the remaining two sections being cylindrical. The assembly of bricks forming the combustion chamber are enclosed man air jacketsub-divided into three sections 18a, 19a, 20aby the partitions 26, each section being provided with inlets 28 for the admission of preheated secondary air. With this modification the lower portions of the cylindrical sections are notcut away.

Whilst particular embodiments have been described, it will be understood that various modifications may be made without departing from the scope of the invention.

I claim:

1. The method of efliciently burning pulverised coke type fuel which consists in providing a mixture of the pulverised fuel and combustion air preheated to at least 200 C., injecting said mixture through a tubular inlet in a predominantly axial direction into a horizontal tubular combustion chamber arranged substantially coaxially with the inlet for the-fuel-air mixture, and having a smooth internal surface and a considerably greater diameter than said inlet, imparting a rotary motion to the fuel-air mixture during its admission to the combustion chamber, heating the rotating fuel-air mixture to ignition temperature and igniting said mixture and thereby producing a flame in said combustion chamber, preheating a further quantity of air to at least 200 C. and injecting under pressure said further quantity of preheated air circumferentially around said flame in controlled amounts through axially extending orifices in the wall of the combustion chamber directed substantially tangentially to a circle the diameter of which is at least 10 percent smaller than the internal diameter of the combustion chamber wall in the direction of rotation of said flame, thereby causing said further quanity of air to form a sleeve rotating around said flame in the same direction therewith and confining and concentrating it within a core portion of the combustion chamber and maintaining it at a temperature suflicient to sustain combustion, said core portion having approximately said smaller diameter, and said sleeve of air separating the flame from the wall of the combustion chamber.

2. Apparatus for burning pulverised fuel, especially pulverised coke, comprising a substantially horizontally disposed combustion chamber of smooth, substantially circularcross-section, having a flared part and a cylindrioal part joined to the wider end of the flared part, a substantially horizontally disposed burner tube disposed substantially coaxially to the combustion chamber and terminating in an orifice opening into the same at the narrower end of the flared part, and arranged to inject fuel into the combustion chamber in a predominantly axial direction, means for supplying pulverised fuel and air under pressure to the burner tube, means in the burner tube for imparting a rotary motion to the fuelair mixture leaving the burner orifice in said axial di rection, circumferentially directed air inlets distributed around the peripheral wall of both said parts of the combustion chamber from a section adjacent the burner orifice substantially throughout the length of'said chamber, the direction of each inlet at the point at which it penetrates the combustion chamber wall being tangential to a circle which is co-axial with the axis of the combustion chamber and of which the diameter is at least 10 percent smaller than the internal diameter of the combustion chamber, means for supplying air under pressure to said inlets, to produce within the combustion chamber a sleeve of air rotating in the same direction of rotation as the fuel-air mixture leaving the burner orifice and adapted to confine and concentrate the burner flame to a central axial zone of smaller diameter than the combustion chamber, and means for preheating the air supplied to the burner tube and to said inlets.

3. Apparatus as claimed in claim 2, wherein the combustion chamber is constructed of a plurality of annular sections arranged end-to-end, means being provided for difierentially controlling the amount of secondary air ladrnitted through the air inlets of different sections.

4. Apparatus as claimed in claim 2, in which the air inlets are directed inwardly of the combustion chamber so as to form an angle of about 30 with the tangents to the internal periphery of the chamber at the places where the air inlets are located.

References Cited in the file of this patent UNITED STATES PATENTS 1,618,808 Burg Feb. 22, 1927 1,762,505 Burg -1 June 10, 1930 1,910,735 Zikesch May 23, 1932 1,943,286 Burg Jan. 16, 1934 1,946,011 Burg Feb. 6, 1934 2,357,301 Bailey et a1 Sept. 5, 1944 2,413,586 Skoog Dec. 31, 1946 FOREIGN PATENTS 675,113 Germany Apr. 28, 1939 289,930 Great Britain Apr. 30, 1928 350,051 Great Britain June 11, 1931 661,472 France Mar. 5, 1929

Images