US2003943A - Heating process and apparatus - Google Patents

Description

June 4, 1935. A KLEES 21,003,943

HEATING PROCESS AND APPARATUS Filed April 8, 1933 2 Sheets-Sheet l VENTO/e .4L/55H7 L. KLEE ATTORNEY June 4, 1935. A KLEES 2,003,943

HEATING PROCESS AND APPARATUS Filed April 8, 1933 2 Sheets-Sheet 2 j /52 /Jz /N VENT 0R 202 Y Afrf L /fLffs 5y A TTORNEY Patented June 4, 1935 UNITED STATES HEATING PROCESS AND APPARATUS Albert L. Klees, New York, N, Y., `assignor to Combustion Utilities Corporation, ',New York, Y N. Y., a corporation of Maine Application April 8, `1933, Serial No. 665,053

20 Claims.

The present invention relates to industrial high temperature heating and heat-treating operations, and `more especially it relates to a process and apparatus for the heating of ma- U terials in. a manner generally following the principles of diffusion combustion, but in which process pulverized solid fuels are utilized instead of the usual combustible iiuids.

The principles of diffusion combustion are now Well known. In accordance therewith, contacting parallel streams of air'and gaseous or vaporized'fuels are flowed into and through a furnacefunder conditions of velocity and temperature such that controlled progressive combustion of the fuel constituents occurs throughout the path of ow within the furnace, while turbulence is substantially reduced to a minimum. Applications of diffusion type combustion employing fluid fuel are now in successful commercial use; and these involve many improvements over prior known methods-including an increased rate of heat transfer to the material being heated with a substantially lower flame temperature. Furthermore, undue refractory wear is minimized thus greatly reducing routine repairs; and the heating process is stabilized, insuring consistent quality of product and uniform results.

'I'he usual powdered solid fuel is not normally adapted for use in a process involving diffusion combustion. Heretofore the use of powdered coal in industrial Vfurnace operation has usually involved the employment of a mixing burner design necessitating a high velocity of iloW both of the powderedfuel'andof the combustion air entering the combustion chamber. One reason for the necessity for high fioW velocities in prior processes has been that the usual type of solid fuel pulverizers employed in the past has produced a considerable amount of fuel lparticles of a sizesubstantially larger than 100 mesh; and high velocities are required to convey these large particles to and into the combustion zone. The said highvelocities were further needed in order to give an intensity of combustion which would promote the complete burning of these larger size fuel particles. Intensity and rapidity of combustion have a1- ways been desirable, in order to complete the combustion of the fuel within the smallest possible combusticn space.

The fact that these very high flow velocities haveibeen required in the past for the combustion `of powdered coal has heretofore strongly militatedxagainst its use in a combustion opera- Cil Cil

(Cl. 26S- 15) tion based in whole or in part upon the diffusion principle-such as that set out fully invpatent application Serial No. 424,280 of Stephen K P. Burke, filed Jan. 29, 1930; and in my'copending patent application Serial '-No.`f620,5'76 filed July 2, 1932. Y

Among the more important objects 1 of Vthe present invention therefore are:V To provide for a heatingfor combustion operation employing solid fuel or mixtures containing the same,;in accordance with the diffusion name Vprinciple of combustion; and to provide infnovel manner for the `preparation and regulated combustion of a fuel mixture of uniform selectedlheating value and'containing powdered solid fuel. v The present invention is basedinlsubstantial part upon the discovery that if a solid'fuel is pulverized'to a point where about r8013er cent or more thereof will pass through a4 20G-imesh sieve, and 99 per centplus will pass -through a 100 mesh sieve,-and if the thusepulverized sold fuel is dilutedlwith,and-suspended in-Suflicient hot inert gases or ue gases to produce afcom.- bustible mixture having a heating value of :from 200 to 3000 Brt; u. per cu. ft. and is then introduced into a combustion chamber'or furnace yin a series of spaced parallelr streams or sheets, interspersed with flowing streams of acombustion-supporting gas such'as airthe combustion of the solid fuel in the streams of iiue gases occurs'progressively -as the latter flow through the furnace toward the furnace outlet; Because ofthe fine division of the pulverized solid fuel, the minute particles of fuel and of ash therefrom are in major part carried along in suspensionin the stream of'combustion gases', the ash "beingv discharged throughk the stack; lso that substantially no contamination of f the materials being heatedY occurs; In .manytypes of heating operations, the presence -of small amountsof ash upon the' material being heated is immaterial, as'is'rtheyrcase in'the production of steel in an open-hearth furnace such as here# inafter described. y Referring now to the accompanyingv drawings illustrating certainfeatures of; the presenting vention: v

Fig. l'is a side elevation, partly in section;- of a billet heating furnace; Fig. 2 iS a transverse sectiontaken along vthe line 2-2 of Fig. 1,1lcoking in the directionof thearrows; Fig. 3 is a perspective view of one -form 'of burnerassembly, partsbeing broken away Figfiis a vertical-section through another form of burner assembly, taken along the line 4-4 of Fig. 5, looking in the direction of the arrows;

Fig. 5 is an end elevation of the burner assembly of Fig. 4;

Fig. 6 is a somewhat diagrammatic view, partly in section, showing an open-hearth furnace and associated parts; and Fig. 7 is a corresponding view, partly in section, of another form of open-hearth furnace and associated parts.

Referring to the drawings, numeral IU designates a furnace suitably lined with a refractory material. An elongated heating and combustion chamber I2 of approximately uniform crosssection throughout its length has a work-receiving end wall I4, provided with an opening controlled by a door I6.

`The opposite end of the chamber I2 has a throat I8, the floor of which preferably is disposed above the floor 20 of the chamber I2 a distance approximately equal to the height of the work to be heated therein. A work charging device 22 is provided at the end I4 of the furnace for introducing into the chamber I2 materials to be heated. Work-supporting tracks 24 are provided, which may be hollow and water-cooled. An inclined work-discharge chute 26 having therein a pair of spaced closing members 28, 30, is adapted to permit removal of the work while preventing substantial fluid flow between the furnace and the outer atmosphere.

For removing the products of combustion from the chamber I2, a flue 32 is provided in one or both side walls of the furnace adjacent the work-receiving end-the same communicating through passageway 34 with a horizontal flue or recuperator heating chamber 36 disposed below the chamber I 2,-the opposite end of the chamber 36 being connected with a stack 38 controlled by stack valve 40.

Referring now to the form of burner construction more particularly set out in Figs. 1 and 3, there is provided a burner tube assembly comprising an elongated hollow rectangular casing 42 of heat resistant material such as high melting point oxidation resistant metal or alloy, preferably lined or coated with non-metallic refractory material, such as that disclosed in the copending application, Serial No. 417,391 of John D. Morgan, filed December 30, 1929. The interior of the casing is divided into a plurality of spaced, parallel superposed fuel passageways or ducts 44, interspersed with a plurality of air passageways or ducts 46,-by means of respective pairs of partition members 48, 50, disposed adjacent each other and having theirside margins provide a gas-tight flt with the side walls of the casing 42. A tapered fuel mixture distributing member 52 is secured to one end of the casing 42 for distributing fuel mixture to the respective fuel ducts. The members 48 and 50 are respectively ared or curved in a. direction away from each other at their inlet ends adjacent the distributing member 52, so that the curved forward margins of each member 48, 5I) excepting the top-most and lower-most ones, engages the next adjacent member and is sealed thereto. By this construction the fuel mixture flowing through the member 52 is uniformly distributed within the respective fuel ducts 44. The forward part of each fuel duct 44 is provided with a constricted section tending to locally increase the rate of flow of the fuel suspension and correct for any undue lack of uniformity of the powdered coal-flue gas mixture flowing thereto from member 52. The portions of the members 48 and 50 at the outlet ends.

of the fuel ducts are substantially parallel thus serving to discharge the fuel mixture from the furnace in parallel spaced streams.

For introducing air or other combustion-supporting gas into the burner ducts 48, 46, and for distributing it therein in uniform manner, the casing 42 adjacent the fuel inlet end has its width increased as shown at 54 to form vertical air passageways 55 each connected with a conduit 58 leading to the outlet of an air pump or fan 66. Each passageway 56 is in permanent communication with each of the air ducts 46, 46 as shown; but the closed side Walls of the respective fuel ducts 44, 44 prevent access of the air to the space within the same, as clearly indicated in the drawings. A series of screens 62 may, if desired, be positioned within the respective air ducts 46, 46 for further facilitating the uniform distribution of air around the respective fuel streams leaving the burner,-although such screens are not necessary to the practice of the invention.

The various parts of the burner are preferably made out of heat-resistant metal or alloys similar to that forming the casing 42. The surfaces forming the inner walls of the respective air ducts 46, 46 preferably are provided with refractory coating applied and secured thereto in any well known manner, such as that disclosed in the aforementioned copending patent application of John D. Morgan. The total crosssectional area of the air ducts 46, 46 is of course much greater than that of the fuel ducts 44, 44, since a much larger volume of air than fuel mixture is required for the substantially complete combustion of the latter.

The lowermost slot or duct in the burner assembly is preferably a fuel duct 44 adapted to provide a flowing blanket of pulverized solid fuel in inert or reducing gases or flue gases,- which blanket flows over the work in the heating chamber in a direction generally parallel to the longitudinal axis of the furnace and forms a protective atmosphere between the work and the actively combusting fuel. The burner construction may be modified to adjust the thickness of this flowing blanket of floating solid fuel.

For grinding and pulverizing the solid fuels to be utilized, such as bituminous coal, anthracite coal, petroleum coke, ordinary coke, lignite, etc., to a suitable degree of ineness whereby it may be utilized properly in connection with the present invention, there is provided,-in the modification of the invention illustrated,-an impact mill of well known type in the nature of a ball mill 10, adapted to be rotated by a motor I2 through suitable gearing 'I4v at a speed which causes steel balls therein to be carried around by centrifugal force to a point where they are thrown down on the material within the mill, whereby there is a continuous cascade of these balls, delivering thousands of impacts per second, and serving to reduce the solid fuel to a neness such that over per cent, and generally around to 95 per cent thereof, will pass through a 20D-mesh sieve, and around 60 to '75 per cent thereof will pass through a 300- mesh sieve.

The solid fuel to be ground is fed from a hopper 16 to the inlet end of the ball mill 'l0 by a disc or other feeder I8 preferably driven i2;oo'3;94'3

by as mall variable speed motor v(not shown). eration, forcontinuous'lyand -uniformlyadjustuAn enclosed fan 89 isconnecte'd with -the discharge -end of Athe mill 15D and is driven :by a v-variable vspeed motor 6|. The fan 'draws flue Vgases or other inert or reducing gases through the pulverizer 1) at a rate vadapted to remove `from the latter only the impalpable l'powder of the size herein indicated, which Vflows in suspension past the fan and is discharged 'to and through conduits 82 and V84 to the flared fuelkdistributing member 52 mounted or formed in 'thelrefractory lining of the furnace l0.

For :producing continuously a uniform mix- Iture of Vthe finely pulverized fuel and for sus- ;.pending the latter in substantially inert flue :gases 1in accordance with'this form of 4the invention, lthe interior of the ball mill during 'operation is continuously swept by a stream or" flue gases, preferably those withdrawn from'the stack 38. For this purpose a lagged valve-controlled conduit 8S leads from the stack v38 directly to the inlet end of the ball mill T0. A

valve-controlled 'bypass line 88 having therein la blower S directly connects the conduit S6 with the 4fuel-distributing member 52 of the burner assembly, bypassing the ball mill, and facilitates regulated dilution with inert gases of the .fuel suspension flowing from the Vball mill 10, when this is desired. A valve-controlled conduit S2, connected with the conduit 33, is

adapted to supply combustible gas or a corn- Abustible mixture to the burner for heating up the furnace when starting up or to dilute the Vpowdered fuel mixture flowing to the burner when desired.

For introducing hot air into the air-distributing -passageways or headers 56 at a regulated urate and temperature, there is provided a fan S having its discharge Voutlet connected with conduit 58. The inlet end of the ian is connected through a valved recuperator conduit 94 lwith theouter atmosphere, the said conduit'extending through the heatingchamber 3S for the purpose of preheating the air. The inlet end of the fan 5t is also connected with a valved cold Aair conduit 95 for introducing cold 'air into the burner housing, or for tempering the preheated air entering the fan through conduit 94.

The fan 60 preferably is driven by a constant speed motor, (not shown) and regulation of `the air now is by the valves in the air conduits 94 and 96.

VFor bringing the cold furnace up to the -desired operating temperature and for initially producing flue gases having sufcient heat and lthe desired composition for the practice of the process, a combustible gas or .gas mixture may be introduced into the furnace through the burner vfrom line SZ,-air being supplied to the furnace at the same time by means of the blower. 5D, or through the air conduit 98 leading to a burner |59. Fuel gas, or oil, or both, may be introduced for the same purpose into the combustion chamber through one or more valved conduits |62 and combusted with air introduced to the burner through the said conduit 98 vor in other suitable manner.

YAs soon as the furnace has reached the desired operating temperature and hot flue gases are being generated, the now of oil or gas and air through the conduits 92, 98 and |02 preferably is discontinued-although a lean natural gas or an artificial gas such as coke-oven gas, cracking still gas, or water gas, may, Yif desired, be introduced through conduit 92 during opthe flared inlet.

lar members and all portions rearwardly there- -of have substantially parallel walls as shown enlarged or iiared mouth portion H4; and each tube is provided with a constriction forming a Venturi orifice 556 immediately rearwardly of The mid-portion of the tubuin Fig. fi. Surrounding each tubular member H2 is a larger concentric tubular member H8, each opening into the furnace at its outlet end, and at its other end being in permanent communication with a nue-gas header I2@ which is` fed by iiue gas iiowing through valve-controlled conduit 22 connected with a suitable source of flue gas under pressure, such as conduit 85.

This forms a plurality of annular flue gas Spassageways or ducts |23 surrounding each tubular member H2. An annular air passageway |2 is provided 'which extends around each of 'the flue gas ducts |23 and is fed with air from the air' conduit 58.

In the modification of the invention illustrated in Fig. 6, an open-hearth furnace |553 having the usual hearth |5| is provided with the check- Aerwork regenerators |52, |52', respectively con- Y nected with opposite ends of a' melting and refining chamber |54 through suitable waste gas nues i, |55 controlled by dampers |58, '|58'. The lower parts of the respective regenerators |52, lili are connected with a lstack conduit |69 by means of the respective branch conduits |62, |62' and damper 164,-the arrangement being such thatJ when flue gases Yare flowing to the stack from one 'of the regenerators, the gas outlet from the other regenerator is closed.

`For introducing air for combustion into the regenerators, there is provided air conduit |55 through which air under suitable pressure flows from an external source. The conduit |653 is adapted to be selectively connected with either of the regenerators |52, |52' through the respective conduits |63, |8 and the damper i'. Mounted in the upper part of the furnace at opposite ends of the hearth or combustion and melting zone i5! is a pair of opposed burner assemblies of the diffusion type, such as heretofore described. The casing 42 of each burner has its outlet end located somewhat distant from the respective waste gas iiues ISE, |55 to prevent or limit actual contact therewith cf the hot combustion gases flowing through these flues at certain stages in the operation of thev furnace. The respective Yfuel distributing members '52 are selectively-connected through conduits |12, 12' and valve VM with the pulverizer 10.'

For introducing a regulated amount of flue gases at suitable velocity and temperature into the pulverizeig and for providing a fuel mixture of regulated heating value,-a conduit |16 having therein rbiower or pump |78 connects stack conduit |56 with aval'ved branch conduit 88 communicating with the inlet end of the pulveriser and with a valved conduit IB leading directly to the inlet of fan 8e.

For Vconducting air ata regulatedv rate vto Y the 'airheader Sebi each burner assembly'there are provided valve-controlled air conduits |84, |84', connecting each air header with a corresponding regenerator |52, |52', and adapted to function upon proper adjustment of the respective valves or dampers |56, |58. According to this modification, a single pulverizer serves each of the opposed burners of a single open-hearth furnace.

The form of the invention illustrated in Fig. 7 is adapted for the operation' of open-hearth furnaces, whereby a separate pulverizer successfully feeds fuel mixture to each burner of the furnace. This modification is in most respects similar to that illustrated in Fig. 6, with the following exception: air for combustion is fed through the conduit 200, and is directed by damper 202 selectively to one of the regenerators |52, |52. The damper 202 concurrently connects the other of the regenerators with a waste gas duct 204 leading to a stack (not shown). Preheated air is delivered to the respective air headers 56 of each burner assembly through valve-controlled air conduits 205, 206 having therein blowers 208, 208.

In the ordinary practice of the present invention, in connection with the form of apparatus shown in Fig. 1, a suitable solid fuel such as anthracite, semi-bituminous, or bituminous coal, metallurgical coke, petroleum coke, lignite char and the like, is subjected to a high degree of pulverization in the puverizer or mill 10; and the pulverized fuel is suspended in a current of inert or substantially inert gases to form a fuel suspension continuously having a uniform regulated heating value, preferably within the range of from 200 to 3000 B. t u. per cu. ft.

Assuming the furnace to be at a high operating temperature, fuel to be pulverized is fed from the hopper 16 by the disc feeder 'I8 at a uniform regulated rate to the inlet of the mill where it is nely pulverized generally to a degree whereby 60 per cent thereof passes through a 3D0-mesh, over 80 per cent passes through 200- mesh, 99 plus per cent passes through 100-mesh and 100 per cent passes through a 50-mesh screen. The higher the degree of diffusion ame combustion desired, the more finely should the material be pulverized; so that fora very high type of diffusion combustion operation the material should be'pulverized to a point where 99 plus per cent passes through a 20D-mesh sieve; and in some cases even to a point where 99 plus per cent of the pulveried material passes through a B25-mesh screen.

During pulverization of the solid fuel, a stream of hot flue gases withdrawn from the stack 38 or from other suitable source of supply is passed through the pulverizer l0 and serves as a hot carrier fluid for the material drawn from the pulverizer under the action of fan for discharge to the burner assembly. These hot iiue gases may be replaced if desired, by any other hot inert or relatively inactive gas such as nitrogen, or water vapor andthe like. In some instances a small amount of air may be added to the flue gases. The temperature of the flue gases passing to the pulverizer 'l0 preferably is within the range of 650 to 800 F. Temperatures substantially higher than this are not recommended. Any hydrocarbon gases or vapors released from the solid fuel during its pulverization and suspension in the hot carrier gases flow with the suspension of fuel in iiue gases to the burner assembly. For the regulated dilution of the pulverized fuel suspension whenE desired,

prior to the passage thereof into the burner assembly in order to control the velocity of flow of the pulverized fuel mixture through the burner assembly to the furnace independently of the amount and size of the pulverized fuel particles being produced in' the pulverizer, a regulated portion of the hot flue gases may be forced by fan 9 0 through the Valve-controlled conduit 88 directly into the fuel suspension flowing in conduit 82. In this manner a fuel suspension of uniform B. t. u. value is caused to flow continuously through the distributing header 52 into and through the burner ducts. The Venturi-shaped constriction in the forward portion' of each of the fuel ducts in the burner is adapted still further to increase the velocity of the fuel mixture within the fuel ducts to maintain the intimacy of the intermixture and to prevent the deposit of solid fuel within' these tubes.

Y Where 350-mesh pulverized fuel is employed, the conditions preferably are so selected that thn fuel suspension flows within the burner ducts at a velocity of around l0 to 15 ft. per second; while if fuel is employed of a size such that per cent will pass through a 20G-mesh sieve and 99 plus per cent passes through a 100-mesh sieve, a somewhat higher velocity of around 25 ft. per second through the burner tubes is more desirable.

When once the solid fuel enters the highly heated combustion chamber of the furnace, the ratel of fiow of the fuel may be safely increased in the practice of the invention; and in long combustion or work-heating chambers, flow velocities of from 25 to 100 ft. per second are desirable, depending upon whether the neness of pulverization is such as to yield a fuel 99 plus per cent of which passes through a 325- mesh sieve,-or is such that 90 percent will pass through a 20G-mesh sieve and 99 per cent plus passes through a 3D0-mesh sieve.

Concurrently with the flow of fuel, preheated air under suitable pressure to control its velocity of flow to the furnace enters the burner casing Ythrough the conduits 50 and is uniformly diseach other as they enter the furnace throat,

and are ignited due to the high temperature therein. The velocity of flow of the fuel suspension and the air streams is preferably so regulated that these streams flow at approximately the same velocity as they enter the furnace. Gradual mixing of the streams of fuel and air thereafter occurs largely by interdiffusion as the combustion progressively proceeds at the surfaces of contact of the contiguous fuel and air streams and at the surfaces of the individual fuel particles adjacent such surfaces of contact.

The heat of the hot carrier gases serves to release combustible volatiles from the pulverized solid fuel when such is present therein-and these volatiles ow to the burner with the fuel suspension'. Due to the limited temperature of the fuel suspension and the nature of the cornponents thereof, no objectionable reactions occur between these components prior to their introduction into the furnace combustion zone.

The total transverse cross-sectional area of the fuel ducts and of the air ducts preferably is so selected as to facilitate maintenance of the respective streams at approximate equal velocisultant higher flame temperatures.

ties as they enter the furnace and inv suitable` proportions for substantially complete combustion of the fuel. While a somewhat overventilatedviiame is desired for many operaticns,-it is within the scope of the invention to use either a neutral flame or an underventilated. flame.

Duer to the high temperature of the flue gases, and toa furnace construction free from abrupt changes in transverse cross section, turbulence of the iiowing gases is still further inhibited,- thus greatly retarding the rate of intermixture of gases, While permitting the formation in the furnace of carbon particles within the fuel streams from the cracking of any hydrocarbons released from the solid fuel during or subsequent to pulverization of the fuel.` The incandescent carbon persists in the gases flowing through thefurnace so as to effectively radiateA heat to the furnace and work over a4 large portion of its path of travel therein.

VAfter the furnace has been brought to 'the temperature required for the heating operation, such as a temperature in the range from 220i)o to 290D F., the work is moved into the furnace and is exposed to the highly heated combustionfga'ses containing therein incandescent carbon, thus rapidly heating the work,-tlie gases thereafter passing to the flue 38 through theV recuperator.

When employing a pulverized fuel suspension containing fuel particles a major portion of which, range in size from 200 to 325 mesh, it is preferredto employ burner port velocities ranging from l0 to 30 ft. per second. In order to prevent these' velocities from producing an undesirable degree of turbulence within the furnace such as would serve to interfere with the desired control of the rapidity and intensity of` the combustion therein,-this tendency is. offset by, suitable adjustment of the B. t. u. value ofy the fuel suspension. Having selected. the burner port velocities required to prevent undesirable degree of turbulenca-a combustion control, to regulate the flame temperature isk ef.

fected by reducing the concentration of fuel particles in the fuel suspension moving to the furnace. This may be accomplished'by limiting the amount of hot gases drawn through the pulverizer, and by maintaining the desired Velocity of hot flue gases by diluting thefuelsuspension with hot gases flowing through the conduit 88. Furthermore, by lowering the B; t.'u. content of the fuel suspension, it is possible to satisfactorily utilize lower port velocities, since lowering4 the concentration of fuel particles in v the flue gas lowers the velocities necessary to justed; in general the lower theB. t.' u. concen. ration at a given velocity, the` slower the corn.

bustion, and the higher the B. t. u. yconcentration the more rapid the combustion with re- Where the quantity of flue gases available isunlimited, the

intensity ofthe flame may be varied as desired' by thus adjusting the concentration of the ysolid fuel in the flue gases-amore particularly Where a` highdegree` of diffusion flame combustionis desirable. In other instances Wheresuch high degreev of diffusion combustion is not. essential,

and wherev the quantity of flue gases is limited.;

the rate and intensityy of combustion. may be increased by correspondingly increasingy the f uekA and air velocities at the burner ports.

In` certain instances. it maynot bel practicable. to secure control of the rate and intensity oft combustion within desired limitseither by va. Y

rying the burner port velocities or by` adjusting.v the. B. t. u. content of the7 pulverized, fuelislusf.. pension. Under such conditions. a. further con?.r Jrol of combustion is secured by the utilization of theV type of burnerv assembly illustrated in, Figs. and 5,-in the use of which a sullOllIlClYAM ing layer or sheet of flue gases or other inertr or relatively inactiveA fluid is interposed between,k eachv stream. of pulverized fuel suspension. andV the surrounding air stream as they leave. the burner. These protective streams. or layers. of-l inert gases serve to4 keep the reacting, components of the fuel and air streams separatedfor a substantial length of time after entryinto the, combustion chamber, and providesa reasonableC degree of control of the rapidity of combustion.

This type of operation is of especial. valueim instances where it is absolutely necessaryto use;

highvelocity streams of. the pulverized fuel sus?.k

pension, or where extremely high. concentra-,

tions of. pulverized fuel'suspension influelgases.

facilitates combustion control even ininstances.

wherea considerable degree of .turbulenceoccurs.. Such. operation is especially desirablewhere insufficient pulverization. Yof, the solid,.fuel, has..

occurred with the result. thatfthel particles. re-v quire high velocity streams of flue gases for. convk veying them to the furnace. Somewhat', greater'.

controlof the intensity and rapidity of.comhus.

tionof the fuel particularly at highzvelocitiesjs. possible by this forml of ,operation Where a highdegree of diffusionflame. come bustion is necessary, it .may occurY at.ltimes,that..

the amount of fuel requiredin the fuelsuspen sion for providing a fuel mixture of desired. .te u. value cannotreadilyV be handled vat the gflue, gas. velocitiesavailable through theV pulverizer. This. can be compensated for at leastinpart by4 p ro,-. viding that thetemperature of thev flue gases,

used .be-as high as possible within the.tempera turerangefup to 900 F.

, It has been determinedthat within `reasonable.- liniits-the higher the temperature ofthe pulver ized fuel suspension in the flue gases, the larger.

the. amount of solid .fuelparticles r.whichecan Ebe..

satisfactorily carried. by the. gasstream ata.,

given velocity. The reason for. this..phenomen0n.

is not entirely. understood, but experimental work.

seems to Vindicatethat when finely` dividedicoall. particles are heated, they adsorb` gasnlms, at.'

their surfaces, which` greatly adds. to. their.

buoyancy and facilitates., the preparation` and; maintenance of a suspension of suchparticlesejgf at velocities Within the range set out here..

of time and by the temperature of these carrier gases. For instance, to provide a fuel suspension having a heating value of 600 B. t. u. per cu., ft. only approximately half the amount of flue gases is required that would be needed for the production of a300 B. t. u. per cu. ft. fuel mixture.

Of course, the total amount of flue gases put through the pulverizer must be at least the minimumamount required to carry'the desired amount of pulverized coal therefrom to the furnace burner assembly,-and this in turn depends upon the neness of pulverization.

In the utilization o-f the invention in connection with a regenerative type of heating operationysuch as carried out in an open-hearth furnace, the operationis in general the same as that previously described. A regulated ow of hot air. to the respective burners is made possible by use of the blowers 208, 208. Moreover, ablower is provided for regulating the flow of flue gases to the pulverizer and burner assembly at each end of the furnace. In open-hearth furnace operation, the combustion air is prefei'ably heated to around 1800 F. within the respective regenerators. It is particularly desirable therefore that the interior surface of the metal air ducts Within each burner assembly be refractory lined. By suitable regulation of the dampers or valves in the lagged conduits |80, |82, respectively conducting hot flue gases to the pulverizer and directly to the burner assembly, the amount flowing to the former may be adjusted to give gas velocities within the pulverizer required for the proper suspension of the fuel. The remainder of the flue gases needed to adjust the heating value is added to the pulverized fuel suspension as the latter flows from the pulverizer to the burners.

In instances where the air and fuel suspension velocities are low andthe air is preheated toa, high temperature, such as in the range of around 1800" F., it is advantageous to employ in the process solid fuels which have been treated previously as` by coking operations or by air or flue gas treatment at lower temperatures to eliminate or substantially reduce the coking properties of the material, and to reduce the combustible volatile content thereof to a selected value.

The ratio of the total air duct to total 'gas duct transverse cross sectional area will of course vary depending upon the B. t. u. value of the solid fuel suspension used, the relative velocities of the air and fuel streams, and the ratio of air to fuel used. In an instance in which the said fuel suspension had a heating value of 250 B. t. u.V per cu. ft. this ratio was approximately 2% to 1,-

thevelocities of the combustible fuel and air being approximately the same. The burners and associated parts are usually so designed that under normal operation of the open-hearth furnace a flame is produced having a general satisfactory rate of heating but which is low enough so as not to hav'ea deleterious effect 'upon the life of the lining of the furnace and adjacent parts. c

The invention is susceptible of modification within the scope of the appended claims I claim: c

1. The method of operating furnaces, which comprises pulverizing a solid fuel While so .passing a hot and substantially inert gas there* through as to suspend in said gas fuel particles of a desired neness, continuously advancing the resultant suspension at an elevated temperature toward a highly heated combustion zone of said furnace, and continuously and concurrently conducting the said hot fuel suspension and a heated combustion-supporting gas into said highly heated combustion zone in parallel superposed streams at regulated approximately equal velocities adapted to maintain in substantial degree a parallel flow of the said contacting streams within the combustion Zone.

2. The method of operating furnaces, which comprises pulverizing a solid fuel while so passing a hot and substantially inert gas therethrough as to suspend in said gas fuel particles of a desired fineness, continuously advancing the resultant suspension at an elevated tempera,-` ture toward a highly heated combustion zone, of said furnace, and continuously and concur, rently conducting the said hot fuel suspension and a heated combustion-supporting gas into said highly heated combustion zone in parallel superposed streams at regulated, approximately. equa-l velocities adapted to maintain in substantial degree the parallel flow of the said contacting streams within the combustion zone, the lowermost stream consisting of the said fuel suspension.

3. The method of operating furnaces, which comprises finely pulverizing solid fuel, suspending the pulverized fuel in a stream of hot gases low in uncombined oxygen to provide a solid fuel suspension having a regulated uniform heating` value and having a temperature near but below that at which substantial thermal decomposition of hydrocarbon in the fuel suspension occurs, thereafterfiowing the said hot fuel suspension and a combustion-supporting gas into a.

highly-heated combustion zone in parallel contacting streams at approximately equal velocities not substantially greater than 100 ft. per second.

4. The method of operating furnaces which comprises pulverizing solid fuel to a size such that the major portion thereof passes through a 30D-mesh sieve, suspending the finely pulverized fuel in a stream of hot gases low in uncombined oxygen to provide a hot fuel suspension having a uniform regulated heating Value and a temperature substantially below that at.

which interaction occurs between ingredients of the fuel, thereafter concurrently flowing the said fuel suspension while hot and a combustion-supporting gas into a combustion zone of the furnace in parallel contacting streams at respective velocities substantially below the turbulent velocity range, thereby effecting a regulated combusion of the fuel particles and the productionof flue gases.

5. The process as defined in claim 4, in accordance with which flue gases produced in the process and low in runcombined oxygen flow through the pulverizing zone, thereby producing the said suspension of the pulverized fuel.

6. 'I'he process as defined in claim 4, in accordance withwhich the said combustion-supportingv gas before its introduction vinto the combustion zone is preheated by heat regenerated from the flue gases produced in the process, and the pulverized fuel is suspended in a stream of the hot flue gases prior to the iiow of the fuel suspension to the combustion zone.

7.' The method` of operating furnaces, which comprises pulverizing solid fuel to a degree such that over 80 per cent thereof passes ,through a 200-mesh screen, continuously suspending the said finely pulverized fuel in a hot' stream of gases low in uncombined oxygen to provide a fuel suspension having a uniform regulated heating value and having a temperature near but below the carbonization temperature, thereafter con-- currently flowing the said Solid fuel suspension While hotanda combustion-supporting gas into Contact with material to be heated within a highly heated reaction zone in parallel contacting streams at approximately equal velocities, and sweeping the exposed surface of the material beingy heated with a protective layer of the said pulverized fuel suspension, flowing at approximately the same velocity as the respective streams of -fueland air, and in a direction parallel thereto.

8. The method of heating and melting materials in an open-hearth furnace, which comprises continuously suspending pulverized solid fuel in a stream of hot flue gases low in uncombined oxygen to provide a fuel suspension having a uniform regulated heating value, the said solid fuel being pulverized to suchr degree that over 80 per cent thereof passes through a ZOO-mesh sieve and atleast 6G per cent thereof passes a SOO-mesh sieve, the said fuel suspension having a-temperature near but below that at which substantial thermal decomposition of any hydrocarbon therein occurs, thereafter concurrently flowing the said solid fuel suspension while hot and a combustion-supporting gas in parallel contacting sheets flowing at approximately like velocities into a highly-heated reaction Zone containing a mass of material to be melted, each of the said sheets extending approximately the entire width of the reaction zone, periodically reversing the direction of flow within the reaction zone of the said sheets of the fuel suspension and the combustion-supporting gas, regenerating heat from the resultant flue gases formed in the last-named zone, and utilizing the hot Iiue gases for suspending pulverized fuel to be subsequently used in the process.

.9.,The process as defined in claim 8, including the step of flowing between the exposed surface of .the material being melted and the burning fuel a protective layer of finely Vpulverized solid fuel in `suspension in a stream of hot gases low in uncombined oxygen.

10. In combination a furnace having an elengated heating chamber, a burner disposed at one-end of the said chamber, the burner havingA a casing and a plurality of parallel, tubular, superposed members therein, each of said members having an inlet end ared to cooperate with like ends of adjacent tubes, the flared ends of adjacent tubes being joined to form a plurality of slots defining passage-ways tov the inlet ends of the tubular members, the outlet ends I of the tubular members being open, air passage-I Ways formed between the tubular members which are open at their outlet ends, each of said tubular members With the exception of the lowermost having air passage-way on its upper and lower sides, means for introducing air to the'air passage-ways and meansforiintroducing a controlled volume of fuel to the tubular members. v

ll. In combination ay furnace having an elongated heating chamber, a burner disposed at an end of said chamber, the burner having a casing and a plurality of parallel tubular chambers therein, each chamber having an inlet end dared to cooperate with like ends of adjacent tubes to form a plurality of slots 'defining openings to the tubular members at 'their inlet ends, said tubular members being spaced apartand open Aat .their outlet ends, a fuel .distributingv header arranged to distribute fuel to each of said slots, an exhaust gas outlet for said furnace, va conduit for conducting flue gases from said exhaust gas outlet having controlling means for Yintroducing predeterminedvolumes of flue gas to said distributing header, fuel pulverizing mechanism operatively connected with said distributing head and connected With said flue gas conduit so arranged as to be swept by a stream of flue ygas from said conduit and valve-controlled means connecting the respective spaces between the tubular members with a source of air supply. y v

i2. In combination, a furnace having an elongated heating chamben afburner assembly at an end ofthe said chamber, the said burner assembly being formed of a casing, a plurality of parallel tubular members therein, a fuel distributing header connected with the inlet ends of the ltubular members, the said inlet end of cach tubular member being dared and secured to the corresponding ends of adjacent tubular members, means for introducing air at a regulated rate within the casing and for distributing it uniformly around each of the said tubular members, a fuel-pulverizing mechanismV having a fuel inlet, `a gas inlet, and a fuel outlet, means f or feeding solid fuel at a regulated rate to the s id mechanism, a iiue gas conduit connecting the furnace outlet with the fuel pulverizer gas-inlet, means connecting the outlet of the fuel pulverizer with the said burner, and means for effecting a 'controlled flow of fiue gases from the furnace through the pulverizer to the fuel-distributing member.

13. In `combination a furnace having an elongated heating chamber of approximately uniform cross-section throughout itslength, an exhaust gas outlet for said chamber, a burner disposed at one end of said chamber, said burner comprising a casing and a plurality of spaced tubular members therein, a fuel distributing header surrounding the inlet end of the tubular members, the ends of adjacent members being secured together to form flaring inlet ends for the tubular members, said tubular members being spaced apart and open at their outlet ends to form air passages between the members, means operatively connected to the burner casing for introducing air into the air passageways, a fuel pulverizer, a conduit connected with the pulverizer and the exhaust gas outlet, means for controlling the flow of flue gas to the pulverizer, a by-pass leading from said conduit tothe distributing header, means for feeding solid fuel from the pulverizer to the distributing header at a regulated rate and means for controllingthe flow of flue gas from the conduit through the by-pass to the header.

14. In combination, a furnace having an elongated heating chamber, and a gas outlet, a burner disposed at one end of the said chamber,

the'burn'er having a Vcasing containing a plurality of parallel tubular members each having an inlet end flared to cooperate with adjacent like' ends to form an interconnected group of contiguous contacting ducts at the said inlet ends but which ducts are spaced apart at their outlet ends, a combustion air header, means connecting the latter with the spaces between the respective ducts, a fuel-distributing header connected with the said ducts, means operatively connected with the furnace gas outlet for conducting a regulated stream of furnace gases to the distributing header, fuel-pulverizing mechanism operatively connected with the lastnamed means and adapted to be swept by a stream of the furnace gases, and means for flowing flue gases at a regulated rate from the furnace through the fuel pulverizer.

15` In combination a furnace having an elongated chamber, a burner disposed at one end of the chamber and composed of a plurality of flat super-posed tubular ducts, the adjacent ducts being spaced apart and opened at their outlet ends to form tubular passage-ways for air between the ducts, a valve-controlled conduct for supplying air to the passage-ways between the ducts, a fuel distributing header arranged to supply fuel to the inlet ends of each of said ducts, means for controlling the flow of fuel through the header, an exhaust gas recuperator chamber leading from said furnace, a recuperator .conduit passing through the recuperator chamber and connected with said air supply conduit, a fuel pulverizing mechanism having l an outlet connected with said header, means for feeding fuel at a regulated rate to the pulverizer and means for introducing gases into said pulverizer for carrying fuel from the pulverizer to the header.

- 16. An open-hearth furnace comprising in combination, a hearth, regenerative chambers respectively adjacent each of two opposite ends thereof, burner means respectively mounted in each of the said ends of the furnace at opposite sides of the hearth, the said burner means includingA a casing having therein a plurality of spaced parallel fuel ducts and being of approximately the same width as the hearth, means for the regulated introduction of air selectively to either casing between the said spaced fuel ducts therein, gas outlets disposed within the furnace respectively between the hearth and a corresponding burner, the said gas outlets being in regulated communication respectively with a corresponding regenerator, at least one gasswept solid-fuel pulverizer adapted to be connected with each of the respective burners, means selectively connecting each of the regenerators with the pulverizer, and means for inducing a regulated flow of flue gases selectively from either regenerator through the pulverizer and to the corresponding burner.

17. An open-hearth furnace comprising in combination' a hearth, regenerative chambers respectively adjacent each of two opposite ends thereof, burner means including a casing having therein a plurality of spaced parallel fuel ducts respectively mounted in each of the said ends of the furnace at opposite sides of the hearth, the said burner means being of approximately the same width as the hearth, means connected with'each regenerator adapted to flow air at a. regulated rate to the corresponding casing and to distribute it between the spaced fuel ducts therein, gas outlets within the furnace adjacent the hearth and connecting the latter with corresponding regenerators, the respective burners being in regulated communication with a corresponding regenerator, at least one gas-swept solid fuel pulverizer connected with the respective burners and having an inlet and outlet end, means for feeding solid fuel at a regulated rate to the pulverizer, a flue gas conduit connecting the respective regenerators with the pulverizer, means for inducing a regulated flow of flue gases selectively from either regenerator through the pulverizer and to the corresponding burner, and means for the regulated flow of flue gases from a regenerator directly to one of the burners and bypassing the said pulverizer.

18. An open-hearth furnace comprising in combination a hearth, burner assemblies respectively disposed at two opposite ends of the hearth, each of the said assemblies occupying at least a major portion of the width of the furnace at the said ends, each burner assembly having a plurality of parallel spaced fuel ducts interspersed with air ducts and arranged in close groups, a solid-fuel pulverizer in communication with the hearth through the fuel ducts, the air ducts being in regulated communication with a source of air, regenerators each in regulated communication with the furnace adjacent the hearth, valve-controlled means connecting each regenerator with the air ducts of a corresponding burner assembly, means in regulated communication with each regenerator and adapted to force combustion gases selectively from either regenerator through the pulverizer or directly to a burner assembly, and means for feeding a suspension of solid fuel in combustion gases from the pulverizer at a uniform regulated rate to the fuel ducts of a burner assembly.

19. The method of operating furnaces, which comprises continuously flowing through a heated combustion zone a suspension of finely pulverized solid fuel in a stream of hot inert gases low in uncombined oxygen while confining the said suspension between parallel streams of an oxygen-supplying gas flowing in the same direction, the said fuel being pulverized to a point where at least 80% thereof passes through a 200 mesh sieve, and reacting the said fluid streams flowing through the combustion zone while maintaining the velocities of the respective Huid streams substantially equal and below the turbulent velocity range.

20. The method of operating furnaces, which comprises continuously flowing through a heated combustion zone a suspension of pulverized solid fuel in a stream of hot flue gases while reacting the said suspension with a parallel stream of an oxygen-supplying gas flowing in the same direction, the said fuel being pul- Verized'to a point where at least 80% thereof passes through a 200 mesh sieve, and maintaining thevelocities of the respective fluid streams substantially equal and below 100 ft. per second flowing through the combustion zone to produce diffusion flame combustion at the interface of the said streams within the said zone.

ALBERT L. KLEES.

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