US2004916A - Recuperator for open hearth furnaces - Google Patents

Description

June 11, 1935.-

w. H. FITCH RECUPERATOR FOR OPEN HEARTH FURNACES 3' Sheets-Sheet 1 Filed July 28, 1933 WILLIAM H. m-rcn ATTORNEY.

June 11, 1935. r w. H. FITCH I RECUPERATOR FOR OPEN HEARTH FURNACES Filed July 28, 1953 :5 Sheets-Sheet 2 IIILL INVENTOR. WILLIAM H. FITCH ATTORNEY.

June 11, 1935. w. H. FITCH 2,004,916

RECUPERATOR FOR OPEN HEARTH FURNACES Filed July 28, 1933 3 Sheets-Sheet 3 INVENTOR. WILLIAM H. FITCH ATTORNEY. M

Patented June 11,1935 h 2 004 915 BECUPERATOR i on OPEN nEAn'rn' Y rsmnmcns William H. Fitch, Plainfleld, N v Application July 2s, 1933, se i l-No; 882,654 3-Claims (01; ace -15) This invention relates to furnace installations, The emciency of regenerators used in .the manner and particularly relates to one-way firing of open described is consequently quite low.- hearth furnaces in which a plurality of recupera- Again the change .O the flow of :waste gases tors ar used t preheat th i ded for cornfrom one regenerator to the other, and the sim-.-

5 bustion of the fuel. My improved furnace repreilar change o he, f w i l 't instalgents an advance in the development of open lation of valves which are expensive to install and hearth n e desigf v twhich add to the cost of upkeep of the furnace.

In the usevof open hearth furnacesit is a comow 0 t large Va ati ns in temperature mon practice to fire the fuel from each end of in the regenerative chamber n in portions of theheating chamber alternately a regenerator the combustion chamber; there is successive ex- 10' 7 being provided at either e nd of the heating champansion and contraction [of refractories With. a. I

her. or a given directionof firing onerof the 151 93 1 8 Shortening O thelifedfhthese rregenerators receives he urn d gases which heat- .t als. I up'the checker bricks or heat transfer elementsv ai o s to fl at One end 1 8 15 while the other regenerator delivers heat, pre-' furnace and distribute the heatof v dd viously stored up in the manner described, to air a v shu m temperature over the entire h h is being preheated for combustion length of the furnace. If a short flame is mainposes. Both regenerators' are alike, each having mi her appreciflble'drop ifrtempera' th same amount t transfer surface r ature at the outlet endof. the'furnace'and if a.

20 double t t requited m device operating on t long flame is maintainedthe whole temperature 20' recuperative principle if the r t of h t t is lowered, excessive fuel burned and-combusfer i t Same, p I I tion takeshplace beyond the melting chamber, an

T ere l re any di advantages connected with unecctmomicallresult in either case! t furnace arrangement just described It is v The present invention is directed to the proviobvious in the first place that thevolume of the ,sion of a furnace installationin which-thesedif- 25 very h t burned gases is much greater a given flculties are overcome and in which the recov-' pressure than thevolume of. the air which is er? of the wasteheat from the burned 8 5 needed for combustion. Hence difliculties arise emciently and eCOnOmiCaHYVAQETfied :sdthat in the regulation of the rate of flow'of the fuel the cost u Operation iS' ma e y eand en and ases produced by combustion duced- In order to accomplish'this object through'ports of one sized area in the furnace'and icordlng to, the presentmvention I 19391156, for theregenerat chambem I v example, of -xa one-way fired furnace which in n isdiflicult todistributethe flow of the burned eludes in d t to om -c s] gases and of air respectively through the checkone recuperator dividedin-two sectionsfwhmh are ersina regenerative sy tem in such a manner that sumcient in themselvesfto pr heat theairiused a large percentage of the reg-en t f c for COmbuStiOn)-t0 the extent. These.

will be utilized. Theburnedor'waste gases which recuperators are constructedlthat total are admitted at one end of the regenerator cham-' heat vt'ecovery per unit 9 e r '15 bet tend to flow through the upper p ofthe much greater than that obtained by the use of H chamber until they reach the opposite end two regenemmrs with Standard k w 40 whence they move down to the outlet. The 'Therecupemmr'armngemint uses el w checkerwork is therefore notfuniformly heated i than the f s'j pd t s v] on account of the difliculty of obtaining a well 3g andmamgaimng the equipment less distributed flow of burned gases through the e recupem wanmgempbthan is 9 case with the regenerators. checkerwork. After the direction of firmg is re,. I 1 th 15 f ed, air is admitted in a stream through a m 2 f 7 1: a WW- du'ct which previously formed the outlet for the ih 3:31 bigg gonnegtgd burned'gases. The-cold air tends'to flow along mm of b n g amteI-T thefioor of'the regenerator chamber until it is y l is pro 6 ong ends n 'Q a along the back wall. By the use of a number of do forced up by the opposite end wall. After rising burners it is T possible to mix the fueland air for tothe p 1t Chamber em! {185568 O 0 combustion in proper proportions for obtaining mix with the fuel. The path traversed by the ind maintaining the kind of" flame desired" flowing ir is therefore different from that pres throughout the length'of the furnace. -By'this viously traversed by the outfiowi'ng burned gases, method iofx-flring continuously from" a pluralit 55 s of burners (distributed along the whole length of the furnace) it is possible to regulate the areas of ports in all parts of the furnace for economical and efficient operation. .For example, larger ports are provided for the outlet of burned gases than are provided for admitting fuel and air for combustion. By maintaining uniform distribution of temperature over the back of the furnace,,minimum timeof making a heat is ob tained and production: is increased. By maintaining uniform flame temperatures the refractories are maintained in good condition for long,

periods.

My invention is illustrated by the accompany ing drawings in which:

Figure 1 is a somewhat diagrammatic .plan' view of a furnace installation constructed in accordance with the principles of my invention? Figure 2 is a sectional elevation on the .line

IIII of Fig. 1;

Figure 3 is' a sectional elevation onthe line III-III of Fig. 1; I Figure 4 is a sectional elevationonthe line IVIV of Fig. 2; i i a Figure 5 is a sectional VVofFig.3;. -y..

Figure 6 is a plan view similar to a portion-of Fig. '1,-but showing a modified arrangementof thev burners; and

Figure x7.-is a fragmentary sectional elevation on the; line.VII--'VII. of Fig. 1 showingjthe man ner in which theheat transfer elements are" mounted in place.

Referring tothe drawings-in detail 'a-furnac'e 1 chamber indicatedin transversesection in" Fig. 4. This chamber maybeof'a standard construction 1(suchas is used for melting furnacesi and it .containsa'hearth 3 withside'walls' 4 and anarch 5,; the structure being supported bymeans of buck staysi:

A charging door I- is disposed 'in' the front wall of the furnace and .a spout I is disposed in the back wall of the furnace for-tappingthe metal, At the backflwall of the furnace are Provided burners which are. conventionally 'illus trated at 8 in Fig.4. The same reference char-' acter is used to denote the location 'ofxburner's'in other views such as, Figure. 2. These burners" may use artificial or natural gas, oilj-p'ulverized ,coal or any fuel suitable for the purpose. The" flow-of the burned gases from the combustion" chamber, .then through the recuperaton'and finally to the stack'is shown by meansiof doublearrows particularly in Figures 2 and. 3; Ducts l l are provided through which the burned'gases flow. downwardlybelow, the hearth level into dust settling chambers l2; From. the upper-portion of each dust chamber a duct-l3 (following the flow ofburned'gases. on oneside of the installa-:

tion) permits the passage of the burned-gases acrossa bank of-recuperator tubes 3|. which stretchacross the chamber 14, the general. direc-: tion of the flow ofthe burned gases in this'chamher being downward; -The burnedugases then pass to a chamber l5 where ,theytfiow in a generally upward direction past another bank ofv recuperator tubes. Theburned gases'then' pass downward through a, duct. l6.(in large capacity.

furnaces tubes 7 would be jemployed :here) and horizontally through a duct" 11 .to the..stackl8- which is' sufficiently high to move the burned gases at the desiredrate;

The flow of air through the recuperatortakes place in agenerally horizontaldirection as illustrated, for example, inFig. 3 by means of 51 18 6 into the chamber 2| whence it flows through the elevation on; the line ary wall between an air chamber arid a duct" minal portions of the tubes are 'sjupported" by the tube termina'ljwalls as indicatedinFig. The. supporting blockscan be undercut adjacent their plastic cement. -As indicated-in" the dra'w'ings thex-recuperator tubes are provided with: core 'busters 33 which are made of refractory rods which are provided with legs flby 'm'earis'j:-o:f

within the, corresponding recuperator' tube; -The bustion chamber and not on :the end walls; With "theburner arrangement as-in 6'the burned a wider'distribution ofhigh temperatures in'the arrows. There are a number of air chambers 2|, 22 and 23. Air is forced by the motor driven pump I 9 (Fig. 1) through a duct 20 (following the flow of air on one side of the installation) recuperator tubes which cross the chamber IS.

a The heated air then passes'into the chamber 22 and from there through another set of recuperator tubes into the airfgchamber' 23 from whichlt flows through an ioutlet 24 intoan air duct 25 which supplies preheated air to the burners (placed at each end of the furnace and along aportion of the back wall of the furnace) I'asindicated in Fig. 2 and similarly in Fig. 1.

Each of the air chambers (2|, 22 and 23) is 15 provided with means of access, such as a door 21.

The chamber,23, which is nearest the outlet; is

"comparatively narrow. It is used at intervals for inspection of the tubular heat transfer elements.

The next chamber 22 is comparatively wide. 20

Thischamber provides space not only for inspection ofthe recuperator elements but iswide enough'to permit replacement of defectiverecuperator elements. I g V The method of support of the recuperator tubes 3l'isillustrated i'nFig. '7. The tubes arejshown" as supported adjacent their endsin tube termi' nal walls, each of which constitutes "a boundwhich is used for the "vertical flow of'bu'rned may beinserted in such a' manner that the "ter-' edges to permit calking ofthe joints around the tubes. and between the blocks by'means of a which the rodis'supported' in "a coaxial position airis :thus' forced .to flow in a-thin film between corebuster and thetube. Goodthermal con-- tact isobtained in this way between theair and the-tube; Thetubes themselves are made of a refractory material having a 'high thermal conductivity such as siliconcarbide. This material also has a low coeflicient of expansion which makes it resistant to spallingand it has great mechanical strength'lwhen:suitably bonded) at V very. high temperatures,even above 1400 de-" grees C. g

- In the modificationshownin m. 6 the bumers are mounted only in the rearwall 'of'the'comgas'es take a more direct route ,to the dust set:-' tlinglchambers than is the case when end'bumw ersare also employed. ,On the other hand the use of end'burners .as wellasback burners gives combustion chamber.

Dam'peisare shown in Fig. 25, 36 and i for regulating the flow of burned gases from either recuperator or from both recuperators taken together. Valves 38 and 39 are also shown; 7 0

i'or regulating the flow' .ofairlthrough the air chambers and connecting tubes in eachnrecuperator. I

i The provisionsfor keepingjthe space between recuperator tubes from being clogged by semi- 75 8 'gasesJ These tub'e' terminal walls are built jfr'omj 1 fireclay blocks 32 which 'areshaped" to p fovid f i openings'through which" the fr'ecuperator tubes solidemat''rial carried over by the burnedgases are indicated more particularly in Fig." 3. 'Ihe burned gases which descend through the ducts II are carried by their momentum toward the bottom of the chamber l2 before leaving the chamber by way of the outlet duct l3. The chamber I2 is provided with a door 4| for cleaning purposes. The burned gases which pass through the chamber I2 pass down the duct I4 around the recuperator tubes 3|. Dust and other semisolid materials which collect on the outer surfaces of the tubes are loosened with .an iron bar (through cleaning holes 43 seen in Fig. 4) and fall to the bottom of duct [4. A door 42 is provided for cleaning solid material from the floor of the recuperator chamber. The provisions for keeping the recuperator chamber and its connections clean are therefore unusually ood.

As indicated in Fig. 4 the burner is directed downwardly toward the charge so that the charge receives the first impact of the flame instead of the roof or sides as is the case with many open hearth furnaces. The more complete combustion obtained by the applicant (as compared with furnaces using less highly preheated air or excess fuel) enables him to obtain better contact between the flame and the charge. By directing the flame on the metal charge, the roof and side walls of the combustion chamber are saved largely from the destructive action which is produced by very hot flames.

Preheating of the air to high temperatures suitable for the rapid combustion of the fuel is made possible in the applicant's furnace by the use of bonded silicon carbide in the manufacture of the recuperator tubes. The thermal conductivity of bonded silicon carbide is several times that of fireclay and may be as high as .036 calorie/cm /C./sec.. Suitably bonded silicon carbide stands much higher temperatures than metals which are commercially available. Its high mechanical strength at temperatures as high as 1500 C. also contributes to making it a suitable material for the construction of recuperator tubes subjected to high temperatures and to various active elements and gases found in this practice.

My furnace arrangement has .a-number of advantages arising from its continuity of operation and from the maintenance of substantial constancy of temperature in various parts of the furnace with consequent long life of the refractory parts. The recuperator material and design permit very high temperature of the air leaving the recuperator and a very low average overall recuperator structure temperature. This high preheating of the air causes very complete combustion of the fuel, thus diminishing the danger of contamination of the metal.

I claim:.

1. An open hearth furnace unit adapted to continuous operation at very high temperatures for extended periods, said furnace unit comprising a combustion chamber disposed over an elongated hearth, burner inlets distributed along the back and end walls of said combustion chamber,

recuperator chamber and heated .exteriorly by the flow of burned gases in a vertically upward or downward direction, and means for compelling a flow of air through the interior of said recuperator tubes and thence to the burner inlets. 2. An open hearth furnace unit adapted to continuous operation at very high temperatures for extended periods, said unit comprising a combustion chamber disposed over an elongated hearth, burner inlets distributed over the back and end walls of said combustion chamber, a charging door in the front wall of the furnace, a'tap for molten metal in the rear wall of the furnace, a slag chamber at each end of the combustion chamber, a recuperator chamber disposed near each end of the combustion chamber and in front of the same, a plurality of burned gas outlets from each end of the combustion chamber and below the same, said outlets discharging downwardly into their corresponding slag chambers, an outlet from the upper end of each slag chamber to the adjacent recuperator chamber, horizontally disposed tubes of highly conducting refractory supported terminally by walls in each recuperator chamber and heated exteriorly by the flow of burned gases in a vertically upward or downward direction, and means for compelling a flow of air through the interior of said recuperator tubes and thence to the burner inlets.

v 3. An open hearth furnace unit adapted to continuous operation at very high temperatures for extended periods, said unit comprising a combustion chamber disposed over an elongated hearth, burner inlets distributed along the back wall of said combustion chamber, a. charging 'door in the front wall of the furnace, a tap for molten metal in the rear wall of the furnace, a slag chamber at each end of the combustion chamber, a burned gas outlet from each end of, the combustion chamber, said outlet discharging downwardly into its corresponding slag chamber, an outlet from the upper end of each slag chamber to the adjacent recuperator chamber, horizontally disposed tubes of highly conducting refractory supported terminally by walls in each recuperator chamber and heated exteriorly by the flow of burned gases in a vertically upward or downward direction, a door at the base of the slag chamber for the removal of ash, a door in the recuperator chamber for the inspection of the recuperator tubes, and means for compelling a flow of air through the interior of said recuperator tubes and thence to the burner inlets.

WILLIAM H. FITCH.

Images