US2608168A

US2608168A - Dual nozzle burner for pulverized fuel

Info

Publication number: US2608168A
Application number: US122758A
Authority: US
Inventors: George P Jackson
Original assignee: Combustion Engineering Superheater Inc
Current assignee: Combustion Engineering Inc
Priority date: 1949-10-21
Filing date: 1949-10-21
Publication date: 1952-08-26
Anticipated expiration: 1969-08-26

Description

5 Sheets-Sheet 1 I A Q H G. PfJAcKsoN DUAL. NOZZLE BURNER FOR PULVERIZED FUEL Aug. 26, 1952 Filed Oct. 21

INVENTOR George P. Jackson Aug. 26,1952 s. P. JACKSON 2,608,168

mum. NOZZLE BURNER FOR PULVERIZED FUEL.

Filed Oct. 21, 1949 v s Shets-Sheet 2 INVENTOR George P. Jackson ATTOR EY Aug. 26, 195 e. P. JACKSON DUAL NOZZLE BURNER FOR PULVERIZED FUEL :s sheets shet 3 Filed Oct. 21, 1949 INVENTOR George P. Jackson Afloat-2% Patented Aug. 26, 1952 DUAL NOZZLE BURNER FOR PULVERIZED FUEL George 1?. Jackson, Flushing, N. Y., assignor to Combustion Engineering-Superheater, Inc., New York, N. Y., a corporation of Delaware Application October 21, 1949, Serial No. 122,758

3' Claims. (01. 110-28) This invention relates to fuel burners for use in pulverized coal burning furnaces in which the fuel is introduced by what is known as the tangential method of firing.

Coal as mined and shipped contains varying amounts of volatile matter, fixed carbon, sulphur, ash and moisture. Volatile matter is that portion which after evaporation of moisture is driven off in gas or vapor form at elevated temperatures. It consists of hydrocarbons and other gases resulting from distillation and decomposition.

From an economical standpoint it is sometimes highly desirable in the operation of steam power plants to burn coal of Widely difierent volatile content. This content may vary roughly between and 40% depending .on the location of the coal seam or mine. Accordingly coals are classified as high volatile coals, medium volatile coals and low volatile coals. Each class of coal when burned requires a definite adjustment to be made to the burner with respect to the air quantity and air pressure and air velocity in order to secure the optimum of burner and furnace performance efficiency.

If it is known to the operator that a change in coal is about to take place, for example from a high volatile to a low volatile coal, then he can adjust air quantity and :air pressure to meet the new conditions. However, such advance knowledge is generally .not available. Hence constant diligence on the part of the operator is required in order to meet changing fuel conditions so as to maintain stable ignition and to avert possible loss of fire.

The primary object of my invention is the provision of burner means adapted. to make ignition less sensitive to change of fuel.

A more specific objectis the provisionsof burner nozzle means organized to obtain a larger surface exposure of the fuel to the secondary air stream thereby stabilizing ignition.

A further object is to provide nozzle means adapted to create recirculation of hot gases and air between the fuel streams issuing from the upper branch and the lower branch of my inventive bifurcated nozzle burner tip thereby aiding in maintaining stable ignition.

How the foregoing together with such other objects and advantages as may hereafter appear or are incident to .my invention, are realized is illustrated in preferred form in the ac-. oompanying drawings wherein:

Fig. 1 is a diagrammatic plan view ofa furnace having burners equipped with nozzles of a type 2 shown in greater detail by Fig. 5 and other views and mounted for tangential firing;

Fig. 2 is an elevational cross section, taken on line 2-2 of Figs. 1 and 5, of a set of three coal burners and two oil burners, the pulverized coal burners shown illustrating a burner nozzle tip designed in accordance with my invention;

Fig. 3 represents an enlarged cross sectional view taken on line 3-3 of Fig. 4 of a burner nozzle showing the double tip feature of my invention;

Fig. 4 shows an end view of double burner tip and is taken on line 44 of Fig. 3

Fig. 5 is a plan section taken on line -5-5 of Figs. 2 and 3 indicating in greater detail than could be shown on diagrammatic Fig. 1 how this burner is organized to fire tangentially from each corner of the furnace; and

Fig. 6 illustrates a diagrammatic elevational section of the double tip burner nozzle showing flame shape and recirculation of gas or air between fuel streams issuing from upper and lower branches of the bifurcated nozzle tip.

The drawings hereof typify installations wherein it is customary to provide one or more oil burners each vertically flanked by pulverized coal burners, the tipped portions of the pulverized burners as well as the oil burners being vertically adjustable over a range of approximately deg. and being preferably coupled for simultaneous tilting, the oil burners being used in warming up the installations and bringing them to operating temperature .after which the pulverized coal burners are turned on, the pulverized The illustrative burner apparatus to be benefited Referring now to Fig. 1 the reference character A generally designates a combustion chamber such as that of a boiler furnace whose walls typically will be lined with water circulating tubes (not shown in Fig. 1 but indicated at '7 in Fig. 5), and the reference number B denotes the burner devices which are desirably located at the four corners of the combustion chamber so as to deliver their fuel and flame streams tangentially to an imaginary circle D therewithin.

As is further indicated by Fig. 2, each of the four corner-mounted burner .devices B of Fig. 1 is provided with a casing formed into compartments at, b and 0, these compartments being open at the combustion furnace side thereof so as to communicate with the interior of the furnace A.

zontal axis [2. The tip has an inner member l4 and an outer member 16 surrounding the same and spaced therefrom to provide an open channel I8.

In accordance with this invention (and for a purpose later to be made evident) said inner member l4 consists of upper channel 28 and lower channel 22 communicating with burner pipe 24 and also through the open face with furnace A; and a third channel 25 is located within said inner member Maud between

channels

28 and 22. This third or central channel 26 also communicates with the furnace through its open face and with the aforesaid open channel l8 (formed by said outer member I6) through openings 25 (see Fig. in the side walls of said channel 26.

A mixture of pulverized coal and primary air or carrying air is delivered to the burner 8 (as through a suitable fuel pipe shown at 21 in Fig. 2) and'is discharged through the channels 28 and 22 (again see Fi 3) of the inner member l4 of the tip l0. Secondary air is supplied through compartment b (Fig. 2) and passes through the outer channel [8 (Fig. 3) in surrounding relation with the fuel-air mixture delivered from the divided inner member I4. Further air may pass into the combustion chamber around the outer member iii of the tip and through said sidewall Opening 25 (see Fig. 4) into channel 26. In the multiburner organization shown by Fig. 2 still additional air is admitted through extreme top and bottom compartments a and discharged into the furnace by way of the air nozzle devices 28.

Each oil burner 9 of the Fig. 2 organization consists of a tubular member 30 and a tip member 34 which is likewise pivoted to tilt about a horizontal axis. Fuel oil is supplied through pipe 32 and is discharged in atomized form from the nozzle 36 located within the tip 34. To this end the portion 38 of the pipe32 has a flexible construction. Air enters compartment 0 and flows through the space between the inner and outer members of the tip 34 and also around the outer member of the tip; and still further air from compartment 0 flows through the tiltable nozzle device 40 of which there is one above and one below the fuel discharging tip 34.

In the illustrative assemblage shown by Fig. 2, all of the burner tips In (three for pulverized fuel) and 34 (two for oil) and air nozzles 28 (at extreme top and bottom of assemblage) and 40 (flankin the OH tips 34) are tiltable desirably through a vertical range of the order of about 60. To this end operating arms 42 (plus crank arms 44) and bell cranks 45 are provided for the ps1 verized fuel burner tips and similar operating

arms

46 and 48 and bell cranks 4! and 49 respectively, are provided for the top and bottom air nozzles 28 and for the air nozzles 40 that flank the oil burner tips 34. Each oil burner 9 is further provided with a linkage 58 causing both sets of its air nozzles 40 and its central fuel tip 34 to be tilted simultaneously when the adjusting arm 48 therefor is operated.

The aforesaid

tilt effecting arms

42, 46 and 48 ar connected through their

respective cranks

45, 41 and 49 with a common operating member 5| which when shifted upwardly imparts downward tilt adjustment to all of the burner tips and air nozzles and which when shifted downwardly imparts upward tilt adjustment to said tips and nozzles. Such upward and downward shifting in the position of member 5| may be effected either manually or automatically, as through motor driven reduction gearing 53 connected with member5| through

linkage elements

55, 51, 59 and 6|. In this manner all of the burner tips and air nozzles can simultaneously be adjusted to any desired position within their range of vertical tilt adjustment.

One example of the practical utility of such adjustment, in the case of burners installed (as indicated by Figs. 1 and 5) in the water-walled combustion chamber of a power-station type of steam generating unit, is to control (i. e., maintain constant over a wide loading range) the temperature of the superheated steam leaving the generator (not here shown) in the commercially successful and now extensively used manner taught by U. S. Patent 2,363,875 issued November 28, 1944 to Kreisinger et al. for fCombustion Zone Control and assigned to the same assignee as is this invention.

The problem involved Past practice in the firing of pulverized coal by means of tiltable burner units corresponding to elements 8 of Figs. 2 and 3 has been to provide each such unit with only a single fuel nozzle and to discharge the fuel-air mixture therefrom in but a single stream.

As earlier indicated, a certain amount of air is discharged with the pulverized coal through the fuel nozzle. The quantity and velocity of this air, which is called primary air, is governed among other factors by the volatile content of the coal. If for example the steam generating unit is operating with high volatile coal and it is intended to switch over to a coal with a medium or low volatile content, then the amount of primary air will have to be decreased so that the ratio of volatile to primary air remains about the same.

Otherwise, when using the single-nozzle burners of the prior art, ignition may be endangered and loss of fire may occur; this resulting in interruption of steam generator operation which is not only costly but also dangerous if unnoticed by the operator for some time, since unburned pulverized coal discharged into a furnace with heated air forms a highly explosive mixture.

In the operation of pulverized coal fired steam generating units where the volatile content in the fuel varies over a wide range it therefore becomes highly desirable to install burners designed so as to make ignition less sensitive to change in volatile content of the fuel.

Prior to the present invention an attempt had been made to accomplish this by increasing the number of single-nozzle fuel burner units 8 installed in each furnace corner. However such an attempt proved to be impractical due to the necessity of correspondingly increasing the fuel piping leading to such larger number of burner units from the mills or cyclone and also due to the high cost of such a design.

How the problem is solved by my invention In accordance with my invention the foregoing difficulties are overcome by equipping. each pulverized fuel burner unit 8 with a fuel discharge nozzle ll! utilizing the two separate flow channels which are shown at and 22 in Figs. 3 and 4 (and also represented in Figs. 2 and 6) and which are vertically spaced to lie above and below a central channel 26 that communicates through side openings (see Fig. 5) with the air flow space along the fuel tip sides.

This novel dual nozzle design accomplishes the desirable objectives earlier set forth and stabilizes ignition to an extent which heretofore could not be obtained in the operation of boiler furnaces burning high and low volatile coal alternatively in the same furnace. As made evident by Figs. 2, 3, 4 and 6 the inventive feature of the new burner nozzle lll consists in dividing the stream of fuel and primary air entering fuel pipe 24 into two portions, one portion Fl entering the furnace through upper channel 20 and the other portion F2 entering the furnace through lower channel 22 (Fig. 6).

This design effects an improvement in ignition for the following reasons:

Reason (a) .-The pulverized coal ignites on the surface of the coal stream leaving the nozzle. The extent of this surface is considerably increased when using two nozzles instead of one anddischarging the same amount of coal. Because of this increase in coal stream surface, ignition of the fuel is benefited and the burning process made more stable.

Reason (1)) .-In leaving the nozzle opening a high velocity jet is formed issuing from each nozzle thereby causing, due to an aspiration action, a recirculation of hot air and gases between the nozzles.

The aspiration action referred to under reason (12) has much in common with that disclosed and claimed in my co-pending application Serial No. 624,899 filed October 26, 1945, for Method of Burning Pulverized Fuel and assigned to the same assignee as is the present invention and now Patent No. 2,511,587. In accordance with that method there is induced from a burning portion of the primary fuel-air stream a reverse current of the burning mixture which hot reverse current flows transversely past a colder portion of the incoming primary stream and heats same with resultant acceleration in the ignition of the stream-laden fuel and intensification of the flame. In this way pulverized coals of exceedingly lowvolatile content can be successfully burned without loss-of-fire hazard.

In the present application of this unique principle the two closely spaced fuel-air streams Fl and F2 issuing from upper and lower nozzles 29 and 22 in the parallel relationship shown by Fig. 6 create in the cavity space 26' therebetween a region of reduced pressure into which region hot burning gases from the burning surfaces of flames Fl and F2 tend to be drawn transversely (as from the sides of the burner showing of Fig. 5 and from the inner flame surfaces between flames Fl and F2) with resultant heating to the fuel air streams issuing from

nozzles

20 and 22 and accompanying acceleration in the ignition of the fuel laden stream. This is a great aid in promoting the burning of the fuel which is substantiated in practice by observing how this triangular shaped region between flames Fl and F2 takes on a brighter color than that observed at the fringe area immediately above FI and immediately below F2, indicating a higher temperature and more active combustion created by this For a clearer understanding of the above adwithout incurring unreasonable vantages reference may again be had to Fig. 6. There the reference characters '20 and 22 desisnate the cones of unignited fuel-air mixture (shown in dot and dash) which respectively issue from the parallel nozzles and 22. The distance-from the end of each nozzle, or the base of the cone, to its apex, as it were, is a measure of the speed of ignition of the fuel. This distance or lengthof the cone can be varied by either keeping the base constant and changing the apex angle or by keeping the apex angle constant and changing the diameter of the cone base. The former, in effect takes place when the volatile content ofthe fuel is varied, and the latter when the size of the fuel nozzle tip is changed. In order to meet varying volatile contents in the fuel my invention shortens this cone of unignited fuel and thereby betters ignition, by dividing the single stream of coal and air mixture-ordinarily issuing from one nozzle into the two streams that issue'from the new dual nozzles ill-22, thereby in effect shortening the length of an equivalent single cone'by approximately 30%.

' Thus it can be appreciated how this further stabilizes the burning process and allows successful operation with coals having a wide range of volatile content.

My invention as above described and illustrated accordingly makes it unnecessary to increase the number of fuel pipes and burners at the same time making it possible to double the number of coal streams issuing into the furnace expense. WhatIclaimis: I 1. In a furnace for burning finely divided fuel, a burner comprising an air casing, means mounted in a wall of the furnace providing an air discharge outlet leading from said casing into the furnace, a fuel nozzle mounted in said casing in fixed relation thereto to discharge fuel through said air discharge outlet, tip means operatively associated with said fuel nozzle and said air discharge outlet to discharge fuel and air through said tip means and into said furnace, and means for bodily adjusting said tip means to vary the angle of discharge of fuel and air; the combination in and with said tip means of a bifurcated central fuel passage terminating in two fuel discharge branch passages and a surrounding substantially parallel air passage plus an air passage centrally located between the spaced apart branches of said bifurcated fuel passage. said air passages and fuel passages being maintained in fixed relation to each other and being constructed and arranged to separately discharge air from said surrounding and central air passage and fuel from said bifurcated fuel passage directly into the furnace with the air in substantially uniform surrounding relation to the fuel discharge from the bifurcated fuel passage, whereby the air contacting surface area of the resultant two individual fuel streams issuing from said fuel discharge branch passages is increased to aid in igniting the fuel and to stabilize burning thereof.

2. In a tangentially fired furnace for burning finely divided fuel, a burner mounted in a corner of said furnace and comprising an air casing, means providing an air discharge outlet leading from said casing into the furnace, a fuel nozzle mounted in said casing in fixed relation thereto to discharge fuel through said air discharge outlet, tip means operatively associated with said fuel nozzle and said air discharge outlet to discharge fuel and air through said tip means and into said furnace, and means for bodily adjusting said tipmeans vertically to vary the angle of dischargeof fuel and air; the combination in and'with 'said tip means-of a bifurcated central fuel passage terminating in two fuel discharge branch passages and a surrounding substantially parallel air passage plus an air passage centrally located between the spaced apart branches of said bifurcated fuel passage, said air passages and fuel passages beingmaintained in fixed relation to each other and being constructed and arranged toseparately discharge air from said surrounding and central air passages and fuel from saidbifurcated-fuel passage directly into the furnace with the air in substantially uniform surrounding relation to the fuel discharge from thebifurcated fuel passage, whereby the air contacting surface area of the resultant two individual' fuel-streams issuing from said fuel discharge branch passagesis increased to aid in igniting the fuel and to stabilize burning thereof.

In a furnace for burning finely divided fuel, a burner comprising an air casing, means mounted in a wall of the furnace providing an air discharge outlet leading fromsaid casing into the furnace, a-fuel nozzle mounted in said casing in fixed relation thereto to discharge fuel through said air discharge outlet, tip means operatively associated with said fuel nozzle and said air discharge outlet to discharge fuel and air through said tip means and into said furnace and means for bodily adjusting said tip means to vary the angle of discharge of fuel and air; the combination in and with said tip means of a central fuel passage divided into at least-two channels terminating in at least two fuel discharge branches and a surrounding substantially parallel air passage plus at least one air passage centrally located between the spaced apart branches of said divided fuel passage, said air passages and fuel passages being maintained in fixed relation to each other and being constructed and arranged to separately discharge air from said surrounding and central air passages and fuel from said divided fuel passage directly into the furnace with the air in substantially uniform surrounding relation to the fuel discharge from the divided fuel passage, whereby the air contacting surface area of the resultant individual fuel streams issuing from said fuel discharge branch passages is increased to aid in igniting the fuel and to stabilize burning thereof.

GEORGE P. JACKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,314,740 Gadd Sept. 2, 1919 1,795,347 Reese Mar. 10, 1931 1,878,926 Yarrow Sept. 20, 1932 1,961,043 Hatch May 29, 1934 2,397,793 Leach Apr. 2, 1946 FOREIGN PATENTS Number Country Date 7,591 France 'Sept. 2, 1907 407,425 Great Britain Mar. 22, 1939