US2604083A - Method of and apparatus for heattreating and burning pulverized materials - Google Patents

Description

July 22, 1952 D. DALIN 2,604,083

METHOD oF AND APPARATUS FOR HEAT-TREATING AND BURNING PULVERIZED MATERIALS Filed April l5, 1946 4 Sheets-Sheet 1 T/ 5gg,

July 22, 1952 D. DALIN 2,604,083

METHOD oF AND APPARATUS FDR HEAT-TREATING AND BURNING PDLVDRIZED MATERIALS 4 Sheets-Sheet 2 Filed April 15, 1946 l L. l

[7571/7/77` BE7/zn July 22, 1952 D. DALIN 2,604,083

METHOD OF AND APPARATUS FOR HEAT-TREATING AND BURNING FULVERIZED MATERIALS Filed April l5, 1946 4 Sheets-Sheet 3 July 22, 1952 D. DALIN 2,604,083

METHOD oF AND APPARATUS FDR HEAT-TREATING AND BURNING PULVERIZDD MATERIALS Filed April 15. 1946 4 Sheets-Sheet 4 Usl/zj 17j/1n u?.

Patented July 22, 1952 METHOD OF AND APPARATUS FOR HEAT- TREATING AND BURNING PULVERIZED MATERIALS y David Dalin, Sodertalje, Sweden- ,Application April 15, 1946,-seria1 No. 662,111 In Sweden June 1'7, 1944 4 Claims.

This invention relates to improvements in the method and apparatus for burning and heat treating powdered or pulverized materials in furnaces or ovens. More particularly, this invention concerns the regulation and control of furnace temperatures generated by the combustion of pulverized fuels and the maintenance in the furnace of' a uniform temperature most suitable for the combustion of the fuel.

Such fuels as powdered or lpulverized coal, charcoal, and peat burn at an extremely rapid rate when injected along with air into the combustion chamber of a furnace, and the excessively high temperatures generated as a result of such combustion are responsible for what is commonly known as sintering of the fuel. When sintering occurs combustion of the fuel is interfered with and rendered incomplete so that ecient combustion and liberation of all of the heat energy contained in the powdered fuel is impossible.

The `primary object of this invention is to maintain combustion chambers in which pulverized fuels are burned at a uniform temperature of a value below the sintering temperature of the fuel by leading away and utilizing for useful purposes the excessive heat generated during the combustion process so as to prevent sintering of the fuel but to assure combustion of the fuel at temperatures most suitable from the standpoint of rapid and complete combustion.

Past methods for controlling combustion temperatures of such powdered fuels as pulverized coal, charcoal, and peat relied upon admitting excessive amounts of air into the combustion chamber, or the circulation of spent combustion gases therethrough. y

While such practice affords a degree of control over the temperatures in the combustion chamber and acts to limit sintering of the materials being burned, it is nevertheless unsatisfactory for the reason that the large excesses of air and/or spent combustion gases circulated through the combustion chamber interfere with rapid* and complete combustion and efficiency suffers as a result thereof. Moreover, excesses of air and combustion gases must be forcefully circulated through the combustion chamber by means of pumps or blowers which require the expenditure of considerable power for their operation.

Hence, it is another object of this invention to provide for efficient burning of powdered fuels and heating of other materials such as pulverized ores by a method which avoids excesses of air and whichoemploys fluid cooled ducts positioned to be impinged by combustion gases in the combustion chamber to usefully .absorbl excess yli'eatrfrorn the burning or heated material.

With the above and other vobjects in View,k which will appearv as the description proceeds, lnvention resides in 'the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly dened by the appended claims, it beingv understood that lsuch changes in the precise embodiment of the hereindisclosed invention may be made as come within the'scope off the claims.

The accompanying drawings illustrate several complete examples of the physical embodiment of the invention` constructed according to the best modes so far devised for the practical ap;- plication of the principles thereof', and in which:

Figure 1 is a somewhat diagrammatic view through a furnace'in which the-combustion process of this invention may be carried out;

K Figure 2 is a crosssectional viewftlirou'g'h the combustion chamber'of' the 'furnace taken along the plane of the line 2-2 -of'ligurel Figures 3; 3a, andA 3b are diagrammatic views illustrating various ways in which the fluid cooled ducts may be shielded to prevent direct contact betweenthe same and the material being treated;

Figure 4 is a more'or'less' diagrammatic longitudinal sectional view through a furnace of slightly differentconstruction; V

Figure 511sv a cross sectional view taken through Figure 4 on the plane of the line 5 5; Figure 6 is a diagrammatic longitudinalsectional view of still anotherformof furnace by which the method of this invention may be practiced; and

Figure 7 is a sectional view taken-through Figure 6 on the plane of the line 11.

In the method of thisinvention, pulverized fuel such as c oal, charcoal, or peat i's-injected together withv air required for combustion of thefuel into the combustion chamber of a furnace to be ignited upon its entry thereto and caused to flow along a defined path through the combustion chamber.

Inasmuch as the pulverized fuel burns at an extremely rapid rate, combustion temperatures in the combustion chamber'riseto excessively high degrees aty which sinteringof the' fuel particles takes place. When sintering occurs complete combustion of the fuel particlesiis'impossible' and much heat energy is wasted.

The method of this invention1 seeks to obtain all of the heat energy available in powdered fuels by controlled combustionthereof to preclude sintering of the fuel, and sothat combustionis caro;l ried on underthe most suitable conditions.

In order to control the combustion temperature of the fuel, the excessively hot combustion gases with burning fuel particles entrained therein are caused to circulate through the combustion chamber past heat absorbing surfaces which remove excessive heat from the fuel particles andV lower their temperature to values belowthev sintering temperature of the fuel being burned.

The cooling surfaces, however, are provided by ducts through which a uid heat absorbing medium is circulated, and by which the excess heat of the burning fuel particles is led away from the combustion chamber to be utilized for useful purposes.

In the apparatus more or less diagrammatically shown in Figure 1 the furnace in .which the method of this invention may be carried outl isV provide all the primary air needed for combustion.

The air and entrained pulverized fuel entering the combustion chamber is caused to sweep along the side wall of the combustion chamber adjacent to the inlet nozzle 1. This area of the combustion chamber, designated I0, having been preheated in any suitable manner such as by directing a flame thereagainst, serves to ignite the incoming combustible material borne along with the air, and the tangential direction of injection causes the combustion gases together with the burning particles of fuel to swirl spirally around the interior of the combustion chamber toward the bottom II thereof.

vSecondary air is also injected into the combustionchamber through nozzles 'I' and I opening through the side wall of the chamber to mix with the combustion gases and enable complete combustion'of the burning fuel particles entrained therein.

As indicated in Figure 1,;-the combustion gases and entrained burning fuel particles travel completely around the interior of the combustion chamber a number of times before discharge through a substantially centrally disposed annular outlet port I2 in the bottom wall II of the chamber.

VExcessive heat generated by combustion of the material traveling through the combustion chamber may be partly carried away by means of a central cooling shaft generally designated I3. The cooling shaft I3 comprises a, cylindrical shell Idopen at its ends and mounted in an upright fashion in the combustion chamber on the central axis thereof. p y

`The walls of the cooling shaft are preferably of 4metal so as to readily absorb heat from the combustion gases and burning particles passing over its exterior exposed within the combustion chamber, 'and such absorbed heat is carried away byy air lcirculating upwardly through the open ends of the shell. The cooling effect obviously may be increased by forcefully circulating cooling air upwardly through the shaft if desired.

`fn the furnace shown, the cooling shaft l is mounted for rotation on its upright axis in suitable bearings I5 carried by the topwall 9 of the combustion chamber, and an intermediate bottom wall I6 spaced beneath the bottom'wall II. A thrust bearing Il confined between the upper bearing I5 and an overhanging flange I8 on the shaft serves to suspend the shaft inside the furnace, and rotation of the shaft may be effected through a power driven bevel pinion I9 meshing with a bevel gear 28 carried by the lower end of the shaft.

The discharge opening I2 in the bottom Wall I I of the combustion chamber surrounds the cooling shaft and also provides for the discharge of ash accumulated on the bottom wall of the combustion chamber. Such ash is collected and discharged through the opening I2 to fall onto the intermediate wall I5 by arms 2| fixed on the exterior of the rotatable cooling shaft to scrape across the bottom wall I I.

VThe combustion gases discharging from the chamber likewise enter the space between the walls I I and I5, but are lead into a dust separator generally designated 22 through a port 23 in the side wall of the furnace communicating with the space between the walls II and I6.

Any ash which deposits upon the intermediate Wall I6 is collected by a second set of scraper armsV 2!! on the cooling shaft and conducted through openings 25 in the intermediate wall near the side wall 8 of the furnace to drop onto an extreme bottom wall 23 spaced beneath the intermediate wall I6.

Scraper arms 27 carried by the cooling shaft and arranged to traverse the bottom wall 26 force the collected ash outwardly of the furnace through an annular opening 28 adjacent to and surrounding the exterior of the cooling shaft. It is to be understood, of course, that the ash discharged from the furnace in this manner drops into a suitable ash pit for subsequent removal.

Dust and ash or'other solid particles are'separated from the combustion gases in the separator 22 and collect in a bin 30 while the combustion gases discharging from the separator are caused to flow through a heat exchange apparatus indicated at 3 I, and if desired through an additional dust separator indicated at 32 and then to apparatus, not shown, such as a waste heat boiler for further utilization of the heat of the gases.

As stated previously, the cooling shaft I3 provides for a degree of control over the temperature in the combustion chamber 6. Most of the control over the temperature in the combustion chamber, however, is obtainedr by means of a series of vertical fluid cooled ducts 34. f

These ducts are positioned in the combustion chamber to provide heat absorbing and dissipating surfaces in the path of the spirally traveling combustion gases and effect removal of suflicient heat from the interior of the combustion chamber as to preclude sintering of the burning fuel particles.

With relation to the spiral path of the combustion gases and entrained burning fuel particles, it will be seen that the fluid cooled ducts nearest the inlet for the combustion chamber are located directly adjacent to the wall section 9 by which ignition is effected, so that the fuel particles impinge these ducts immediately after being ignited and started on their spiral course through the combustion chamber. The ducts thus exercise a cooling effect on the combustion gases'immediately after their ignition, but it is important to note that the ducts are so formed and positioned as to exercise their greatest cooling effect on the `hoi-combustion gases and burn ing fuel,V particles entrainedv thereinV at` the. area of "greatest heat, withthe cooling effect gradually decreasing alongthe' length of the path of' the gases. so as. to exercise the' leastv cooling effect adjacent tothefoutlet of the combustion chamber.

In thisY manner` cooling` of the combustion chamber and the'gases iiowing therethrough below a' temperature most advantageous for effl'cienti combustion ofv the fuel without sintering thereof isl avoided, and a substantially uniform temperature is maintained throughout the.` entire'Y combustion chamber with said temperature ata Value below the sintering temperature of the fuelbeing burned; f

It will be understood, ofcourse, that the temperature most suitable for the complete andefficient 'combustionoff the fuelA being burned Without sintering of the fuel may be regulated either by regulation of the volume orr temperature of the. fluid circulated; through: the ducts. The fluidcooledi ducts connect with headers 36.*for this purposeand these headers in turn may be connected with a steamv drum or the like by which the heat-,absorbed'from the burningl materials in the combustion chambery may be utilized for useful purposes.

In the event direct contact of the burningy particles with the cooling'surfaces provided bythe iiuid cooled ducts' 3.4- hasv a tendency to retard combustion, the ducts may be' provided with sleeves, such indicated at 38, 3,8', and 38 in Figures. 3, 3a, and' 3b, telescoped over theA ducts with their sidev Wallsfspaced from the exterior of the ducts.

The method of controlling combustion temperatures in the burning of pulverized fuels may also be carried out in a furnace such as that illustrated in Figure 4. Thisr furnace is in many respects similarto that described but the outlet for the combustion chamber; is provided by a vertical exhaust duct 40 extending down into the combustion chamber'from the top thereof to have its open lower end 4l providing a discharge port for combustion gases spaced a distance above a grate.42 extending across thelower portion of the furnace and deningthe bottom of the combustion chamber.

They grate provides forthe complete combustion of burning particles of fuel'which drop outof suspension at or near thev entrance 4i to. the exhaust duct v4l).- for upward travel therethrough. Ports 43 in the conical side walls of the furnace beneath the grate provide for the supply of' air to burning material resting on the grate to complete combustion thereof. It is to be understood that the grate is of the type which is movable to permit dropping of the ash intol the hopper like conical bottom portion of the furnace in the usual manner.

The exhaust duct 40 is preferably formed vof one or more circumferential rings of vertical cooling tubes 45 having their peripheries in en-y gagement with one another as shown in Figure 5 so as to provide a substantially cylindrical cooling surface about which the hot combustion gases traveling through the combustion chamber circulate to be cooled thereby.

Hence, the Walls of the exhaust duct 40 cooperate with the iiuid cooled ducts 34 inside the combustion chamber to maintain a uniform temperature in the chamber of a Valve below the sintering temperature of the pulverized fuel being burned.

The combustion gases traveling upwardly through theexhaust duct 40 may be lead through a-heatexchanger such asaV Waste-heatb'oiler of a1 superheater 46 having a multitudev of ducts41 disposed therein to be impinged by the hotV combustion Igases passing through the superheater.

Itis to be understood that the ducts 41 have a fluid such as a steam emulsion circulated therethrough and are connected with headers' 48u/nich in turn may be connectedwith a steam drum or the like.

Dust collecting` hoppers 49V arranged beneath the bank of ducts 41 Vreceive the ash which drops out of l Y suspension from the combustion gases passing;- through the superheater, and to effect furtherseparation of dust and ash the` combustion gases'discharging from the outlet 50 of the superheater are led into a dust separator 5I. Obviously, the hotlcombustion gases mayl thenbe lead to other apparatus Wherethe heat thereof isfurther utilized.

lin-the Figure 6- embodiment a substantially rectangular combustionchamber- 53 is shown as comprisingthe major partof a combined oven and boiler. The boiler tubes 54 connect to headers.v 55L and` as in the previous embodiments the tubes or ducts lie in the path of combustion gases travelinghorizontally through the combustion chamber'toward its outlet 51.

In this embodiment also, powdered fuel togetherwith air for supporting combustion of the fuel-are injected together through the inlet 56 into the combustion chamber to be ignited upon its entrance thereto; The boiler tubes 54 like- Wise exert a cooling influence upon the combustion gases and the burning particles of fuel entrained therein tocoolthev same and the interior of thecombustion chamber to a temperature below the sintering temperature of the fuel.

Dust and-ash collecting hoppersl) are likevviseV provided beneath the boiler tubes toreceive any-ash and dust which drops out of suspension during `travel' ofthe combustion gases through the chamber.

Referring to Figure 7, it will be seen that the boiler tubes 54', which provide cooling surfaces impinged by the hot combustion gases and entrained burning-fuel particles, are arranged with the'greatest number thereof adjacent to the inlet 56. These tubes also decrease in number toward the outlet 51 so that throughoutv the combustion chamber a temperature most suitable for efficient combustion of the fuel is-maintained.

Inboth the Figures 4 and 61* embodiments, it is to be--understood that the comb-ustionchamber is providedy withv openings 1 and 1"y for the injection of secondary air as described in connection with the apparatus of Figure 1.

While the method and apparatus has been described as dealing primarily with temperature control in the burning of pulverized fuels such as powdered coal, charcoal, and peat, the method and apparatus is equally as well suited for the heating and melting of the metal content of pulverized ores.

In this latter case it is also highly important that temperatures in excess of the sintering temperature of the ores being treated be avoided so as to assure eicient recovery of the metal content thereof.

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art that the method and apparatus of this invention provide for improved and highly efficient control over combustion temperatures when burning or heat treating powdered materials, and that such control is effected without waste of the excess heat removed from the materials during .their processing.

Those skilled in this art will also readily understand that the term powdered fuel encompasses a relatively wide range of particle sizes including what might be more accurately defined as granular or granulated fuel.

What I claim as my invention is: 1. A furnace for burning powdered fuel, comprising: a substantially 'cylindrical combustion chamber having an outlet adjacent to one end portion thereof; means. dening a substantially tangential inlet port in the side of the combustion chamber adjacent to the opposite end portion of the chamber and throughY which powdered fuel and air required for combustionof the fuel may be injected to burn inside the chamber while travelling in a substantially spiral path through the combustion chamber toward the outlet thereof; and iiuid cooled ducts distributed within the combustion chamber away from the walls thereof and spaced from one another to be impinged by combustion gases and burning fuel particles travelling along said spiral path, the distribution and size of the ducts being 'such that the total surface area thereof diminishes along said path of the combustion gases towards the outlet of the combustion chamber, so that the cooling influence of said ducts upon the burning particles is substantially directly proportional to the temperatures of the particles.

2. A furnace for burning powdered fuel, comprising: an upright substantially ycylindrical combustion chamber; an exhaustY duct extending down into and substantially axially of the combustion chamber through the top thereof with itsy lower end opening into the combustion chamber at the lower portion thereof and providing an outlet for said chamber; means on the side of the combustion chamber at its upper portion dening a substantially tangential inlet through which powdered fuel entrained in air required for combustion of the fuel may be injected into said chamber to be ignited uponits entrance thereto and so that the resulting combustion gases and the particles of burning fuel entrained therein travel in a substantially spiral path around the exhaust duct downwardly through the combustion chamber for discharge through the outlet port defined by the lower end of the exhaust duct; and fluid cooled heat absorbing ducts in said combustion chamber for controlling the temperature thereof, said ducts being spaced from the walls of the combustion chamber and from one another and distributed within the interior thereof to be impinged by combustion gases and burning fuel particles traveling along said spiral path, the distribution and size of the ducts being such that the total surface area thereof diminishes along said path of the combustion gases towards the outlet of the combustion chamber, so that the cooling iniiuence of said ducts upon the ,burning particles is substantially directly proportional to the temperature of the particles.

3. A furnace as set forth in claim 2 wherein said axial exhaust duct is a cooling unit comprising a group of closely adjacent fluid cooled ducts substantially forming an inner circumferential wall about which the combustion gases and burning fuel particles swirl in their travel along said spiral path.

4. The method of combusting fuel of small particle size which comprises: forcing the fuel together with air required for combustion thereof along a dened path through a combustion chamber with the fuel particles entrained in said air; igniting the fuel as itV enters the combustion chamber-so that the burning particles and the combustion gases travel along said path; circulating a fluid coolant back and forth across the path of the burning fuel particles and combustion gases in indirect heat exchange relation therewith and in diminishing effectiveness along said path of the burning fuel particles in the direction of gas flow so that the cooling effect of said fluid coolant upon the burning fuel particles is substantially directly Vproportional to the temperature of the particles.

DAVID DALIN.

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

UNITED STATES PATENTS Number Name Date 132,041 Allen Oct. 8, 1872 1,618,566 Bergh Feb. 22, 1927 1,649,121 Kreisinger Nov. 15, 1927 1,708,862 Bell Apr. 9, 1929 1,814,605 Mayr July 14, 1931 1,828,870 Lucke Oct. 27, 1931 1,886,064 Steinmuller Nov. 1, 1932 1,942,687 Daniels Jan. 9, 1934 2,167,545 Duram July 25, 1939 2,357,302 Kerr et al. Sept. 5, 1944

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