US1571575A - Process of heating gases and equipment therefor - Google Patents

Description

Feb. 2 1926. 1,571,575

'Y W. A, ARRAH PROCESS OF HEATING GASES AND EQUIPMENT THEREFOR Filed April 25, y1923 2 Sheets-Sheet l,

' ,/05 OH l We /o 419 r f r 48 i V g /f; /CZgU/"G 1 I -:V:/: :KT -E 524-*- :i--sf f5 5/ l i I I I I 1 5 1 f i i. s l I l f s s i it, i923@ rear WILLIAM A. DARH/AH, OF CHICAGO, ILLINOIS.

PROCESS OF HEATING GASES AND EQUIPMENT THEREEUR.

Application iled April 25, 1923. Serial No. 634,642.

To 7l wzom/ it '7n fry concern Be it known that I, WILLrAM A. Damian, a citizen of the United States, residing at Chicago, in the county of Cook and citate of Illinois, have invented a new and useful Improvement in Processes of Heating Gases and Equipment Therefor, of which the following is the specification. v

This invention relates to methods of heating air or other gases, and equipment for carrying out said heating process effectively and economicallyv and at a reasonably small expense for equipment.

AThis invention more particularly applies to the heating of air and other gases in large quantities for industrial operations, such as the drying of salt, sugar,.s'tarch, sand, and similar materials, although the air thus heated may also be employed for the heat# 4ing of buildings, and any other applications where. a source of heated air or other gases are required. A This process and equipment is particularly related to the so-called class of indireet heaters, in "which the products of combustion do not ordinarily intermingle withv the air or gases to be heated. Provision is made, however, in this equipment, for allowing said products of combustion to intermingle with the air or gases which are heated.

Any desired source of -heatmay be employed with this equipment but the best results are ordinarily secured using fuels such as coal, oil, `gas and related products. The invention, however, is not limited to the fuel used, as any fuel orother source of heat may be satisfactorily utilized.

In the description which is here given, the specific illustration of a process and furnace for .heating air is chosen for purposes of clearness in villustrating the invention. It should be understood, however, that where the word air7 'is used throughout the speciication or claims, any other gases may be .fnbstituted. F or purposes of illustration also, the drawings show an oil heated fur-4 nace. It will be evidentthat other fuels mav be used, making simple modifications in the design. In the case of coal we prefer to use a stoker for maintaining a uniform heat. This is not essential, however,

although it is frequently of practical -advantage.

Home of the objects of this invention are to effectively and etliciently heat air or other Agates with the minimum size of heating equipment and with the minimum loss of heat. Other objects will be evident from a perusal of the specification and claims. Other objects will also be referred to in the course of the description given in this specification.

Upon referring to the drawings, Figure l shows a front elevation,v in section, of one form of device for carrying out my inven; tion. Figure II shows a side elevation of a heater built in accordance with this invention, the section being shown through the combustion chamber. Figure III shows a 79 side elevation partly in section, the elevation being taken through the air passages. Figure IV shows a plan iiiew in section.v

ln the drawings the arrows which are shown in dotted lines indicate the path of 'f5 the products of combustion, while the solid arrowsy indicate the path of the. air or other gases which are being heated.

Referring to the drawing, (l) represents the furnace foundation carrying base wall 80 `(2)which is interspersed at the necessary hot points with, highly insulating material (3). Furnace walls (4) enclose, the structure while strips of highly insulating material' (5) are placed in such position as to S5 surround the warmer parts of the furnace. Combustion chambers (G) are provided within the walls (4), and in the specific case illustrated, three chambers are shown, numbered respectively 6, 7 and 8. The walls 90 (9) of combustion chambers (6, 7 and 8) are preferably made of a highly conducting and very refractory material, such ascme borundum. They may be readily built up of carborundum brick cemented together, or 4they-may be made of tile, or formed'in a single piece.

The carborundum or highly conducting portion of combustion chamber (6) is preferably connected at one extremity with a flue member (10) .provided with battle (.11) j and carrying on its upper surface metal conducting tlues (l2, 13 and 14). These fines are arranged to connect one into thc other,

and eventually, by means of breeching lead to stack (16). 4It is desirable to make the walls (9) of combustion chamber (6) out of highly conducting refractory material, but 'for economical reasons it is not desirable to make it of sufficient strength to carry the load of the flue members ofr the. furnace.y These metal flueinembers (12, 13 and 14) therefore rest Iupon a refractory flue member (10)' which is of course subjected to less severe temperature conditions'than the combustion chambers and which because of its thicker Walls and lowergrade material is less expensive. Since the material used in the combustion chamber is differentl from the material used in the flue member (10) these two portions should preferably not be bonded together but should be closely 1s, 19, 2o and 21).

adjacent so as tb prevent leakage lfrom the combustion chamber' to the air spaces (17, The bonding together ofthese two parts would of course result in unequal eXpansi0n,Which would4 cause the .structure .to crack. Likewise, since the tem` peratures of the combustion chambers (6,-7, and 8) and lues (10, 10A and 103) are much higherv and fluctuate more Widely than the temperature of the Walls of the furnace, it is essential that the lines, combustion chambers etc., be constructed in such a Way that they are free to expand Without moving the Wall member and that they are not bonded to the Wallmember in any may.

The combustion chamber Walls, and other heat conducting Walls of the furnace, are preferably formed with many rough projections which serve toc'ause eddies in the air and gases which'move overthem, .thus maintaining the Walls at substantially the temperature of the gases. By this device it is possible' to materially increase the number of heatrunits which are convected over- -the Walls to the air or gases tobe heated, .or

conversely, to increase the number of heat units which are transmitted over theprod ucts of combustion orflame to the walls.

The effect of irregularities of thiskind are therefore to materially decrease the -surfaces necessary for handling the heatl :This-re-` duction 'in necessary surface area naturally makes the equipment much less expensive, more compact .and more effective. Typical projections on the chambers are indicated by reference numeral (22), and similar projections on the fines by numeral (23).

. In order to secure the maximum travel" for the gases Which are to give up their heatT bailles (24and 25) are placed in combustion chamber (6).` Baiiies (24 and 25) also serve to tietogether the vertical Walls (26 and 27) of combustion chamber (6). tying eifect. of baliles (24 and 25) the relatively tall thin walls of the combustion,

chamber would frequently be too unstable lVithout the tion to travel through a longer path.

Referring to Figure II, it will be evident that the flame enters through burner (28), fills combustion chan'iber (6) and travels as shown, around baffles (24 and 25) to the upper portion of flue (10) and then out through metal passageways (12,' 13 and 14) to the stack. .lVe have found it economical to .make metal luemember (12) of heat resisting alloy, While-the adjacent member,

shown in this case b r `portions' (13 and'14),

made of cast iron.

may to advantage nl ctc.. may be made The stack reaching, f

of steel plate, brick, or other desired material.

I have found it an advantagein connection with `metal lines (typified by12, 13 and 14) to form the lside walls into a corrugated or sawftoothsection such that the flue gases l are compelled to continually change their angle of flow. The continual change of the angle of flow causes the gases toimpinge alternately on -the various sides ofthe fines, thus -ma'int-aining the flues at substantially the temperature. ofv the gases. By this device it is possi-ble to materially increase the number of heat units which can be radisquare feet of flue surface. This formation also results in strength, and gives a structure vated or absorbed by a given number of Referring to Figures I, II and IH, .it will A 'be noted that the air (or other gases to be heated) enters at the top of the furnace, travels downward through the elevated portion until it encounters baille Wall (3 1), -I y which causes the air current to turn, passing along and underneath baffle wall (31) in the space betweenbaille Walls (31 and 32). The air to be heated then passes along the bottom of the furnace between the combustion chambers (6, 7 and 8) and finallyupward at the front end of the furnaceand out through opening (33) vwhich is connected with the dryer (34). A

It will. be noted, therefore, 'that the airv travels in an vopposite direction to lthe flue gasesor products of combustion. .As a re.-

sult of this arrangement, it will be evident that thev greatest average'.temperature .difference is maintained betveen the air to be heated and the ue vgases Which supply the heat. This arrangement gives the greatest possible eiliciency, and at the same time, since the amount of heat transmitted varies directly as the ten'iperature difference, it will give the most compact and therefore the most inexpensive construction.

In order to secure the most complete contact between the airto be heated and the hot'surfaces, various battles have been pro vided which serve to deflect the air'onto .the hot surfaces and at the same time to create eddies. Thus, baiiies (35 and 36) serve to direct the incoming air down between various tine members (14, 13 and 12). In the same. wayfbatlles (37 3S and 39) serve to cause the incoming air to break into eddies and to be deflected against the hot sections.

4In a similar manner the metal plate .deflectors (4t), 41 and deflect the incoming air against the hot flues and create eddies.

It will be evident that the air within the walls of the furnace portion (30) will be materially hotter than the air outside. This will tend to create a draft which would ordinarily cause .the ai'r to travel upward in the same direction as the Hue gases. Obviously this would defeat the obj ct of the device. It will of course be understood that in normal operation the air is drawn through the dryer by a fan, shown diagrammatically as (45). 'Ever-i, however, when fan (45) is in operation, the back draft caused bythe tendency of the hot gases in member 30) toI rise, would result in a loss of considerable heat. 'l

This condition is partly overcome by the shape of members (40, 41, 42) and related members; which make the passage of thev air in the normal direction easier than inthe reverse direction. This same tendency is furtherovercome by the use of the adjustable members (46 and 47), which are designed to close the opening between the breeching (15) and the brick walls (30) to, such a degree that the velocity of the incoming air (caused by the suction of the'fan) issu'tficifent to prevent the escape of any of the. heated air within the walls Heat absorbing walls (48 and 49) are' typical ofthe construction which/is placed around the highly heated portions ofthe combustion chamber in order to secure theinost effective heat transfer. Said walls (4S and 49) are not necessarily highly conducting material, and in ordinary commercial furnaces may be made of second quality fire brick. The walls should be strong, du-

rable, and preferably have a relatively roughA surface. `The advantage of the walls is de-l` rived from the fact that only a definite amount. of heat can be absorbed when a gas passes over a given number of square feet of hot surface. In other words, the amount of'heat absorbed when a gas passes over a heated surface is approximately a function of the [i1-st power of the temperature. On the other hand, the amount of heat which may be radiated lfrom a highly conductingv wall, normally varies, as the cube, oi' even higher powers of the temperature. It will be evident, therefore, that `in dealing with high temperatures, the amountof h'eatwhich is radiated will be much in excess of the amount of heat which can be absorbed by forcing air over the hot surfaces. In order, therchV re, to properly heat a stream of air (or other gases) it is necessary to provide a definite number of square feet' of' radiating surface for any given temperature.A Inesmuch, however, asv goodcondnctiiml refractl'oiies are relatively expensive. and 'further inasmuch as anair heating device becomes large and bulky (and therefore expensive) if direct contact with the conducting refractories is depended upon, itis desirable to provide other means for accomplishing'this resultm The other means vwhich I have devised are exemplified by walls (48 and 45)) which receive by radiation a large amount of heat which maintains them at a high temperature. The air passing overitlie'se walls, therefore, is heated, and the ell'cct is si'lbstantiallythe same as if the area of thehighly conducting refractory walls were doubled. Itwill be noted also/that walls (51 and 52) serve in the saine manner as walls (4t) and 48). At the same time, walls (51 and 52) act as enclosing walls Yfor the furnace.

Doors (5o and 54) are provided to permit ready access to the interiorof the conibustion chamber for cleaning, inspection or repairs. y

)Valls (48 and 49) v'also serve the further purpose of reducing the volumel of the air Space between adjacent combustion chambei's .(6, 7 and 8), thusbringing the air velocity to the desired figure. The advantage in' controlling the air velocity arid-sl from the fact that too slow an air tvelocity causes the air to absorb too little heat as it travels through the furnace. thus entailing a large and expensive furnace. (')n tin` othen hand, to'o high an air velocity throughthe furnace results in shortening the time the air is in the furnace and ii'icreac-:ing the work necessary on the fan which draws the air through the furnace. 'i

In loperating this device I have frequently.' found it of advantage to return the air which leaves the blower (l5) to the intake -of the furnace, or I may only return a portion of this air. Iliave also provided doors or outlets (55 and which may be opened` thus permitting'a portion of the flue gases to enter the heated air.

A furnace of the typehere described will readily give efficiencies under operating con' ditions ranging from 7() to 90C?. An average efficiency exceeding 80% is the rule, and* signed for handling very small amounts of air or quantities of air as great as 18,000

cu. ft. per minute. OlneV standard size which is commonly employed. will handle approximately 5,000 cu. ft. of air per minute, and will raise the temperature of this air from normal oiit-door temperature to 1000 to 1200 degrees. Such a furnace requires a consumption, when burning ordinary fuel oil, of approximately l5 gallons of oil per hour. An equivalent amount of coal will produce the same` results.

In the description which has been given of i'efiactories specilic mention has been made of carborunduin for the reasoirlhat this material is particularly suited for transmitting relatively large. quantities of heat per unitv volume and at the same time will withstand high temperatures for long periods. It is of course entirely possible to usemany other materials for this purpose, such as magnesite, alundiini, graphite, etc. Fused quartz may be employed as well 'as heat resisting alloys, such asnichrome, sil; chrome, etc. j4

4It will b-e understood that this invention is not confined 'to any specili'c material but to types of materials of the class described. The materials, however, are preferablygraded as described and shown, so that the more refractory material is subjectedto the l.high temperature, the less refractory material (resistant alloys) to the lower tein-v peratures, and cast 'iron' and ste-el to the- Ixmay rigid it advisF lowest tempgiiatii es. g .moreothe grades able to oinitanyedescribed and shown. i i

It should be understood that one object of the inclined walls shown in sections 13 and 14, is to produce a structure which will cause the gases passing through the structure to give up a maximum amount of their* heatto the walls with a minimum ofresistance to the flow of the'gases. AThis result isalso secured by the longitudinal. ribs. and

other ldevices which have been'showii and i 'described lowerheat conductivity than sai Having new disclosed my invention, what I claim as new and wish to secure by Letters Patent in the United States, is as follows:

1. A furnace for heating gases, which con-k sists of combustion chambers having walls of relatively good conducting material, fines connectingr said combustion chmbers to a stack, spaces between said combustion chambers and llues for the circulation fof said gases to beheated, andsep'aratingr walls of chamber walls located in said spaces between said combutsion chambers.

i 2. In a furnace for heating gases, a combustion chamber having walls of relatively highheat conductivity, and an adjacent wall of lower thermal conductivity arranged to be vmember and within said housing,

heated by radiation from said .combustion-i chamber wall, said, adjacent walll being placed to permit the circulation of gases to be heated in contact'with it.

3.`An air` heating furnace consisting of horizontal combustion chambers communi-- extending radiation member enclosed in a.

housing', air spaces around said radiation and bafiies 'so arranged as to oll'er the minimum retardation of air passing in one direction through said air spaces while oiferingconsiderable resistance to air traveling in the lother direction through said air spaces..

5. In an air heating furnace, vertically eX- tending radiation members enclosed in a housing, air spa-ces within said houslng adjacent to said radiation, member, air openings at the upper portion'of said housing, and

adjustable delectois at said .air opening, said delectors arranged to permit varying amount of products of combustion to enter` saidair passages. l

6. ln air heating furnace, a vertically extending radiation member, a housing surrounding said member, battles in said housing, air spaces adjacent to said radiation member and within said housing, an opening at the .upper portion of said housing to permit the entrance of air, said opening being of much smaller cross section than the air passages in said housing.

In an air heating' furnace, a. radiatio member composed of'surfaces'arranged ata slight angle to the direction of travel off gases through said radiation member and a radiation member having 'a lower thermal conductivity than said radiation member.

8. In an air heater, a combutsion chainber, a radiation meinbercommunicating thcrewitlna housing surroundingusaid com.- bustion chamber and radiation member and a radiation receiving wall oflower thermal conductivity than said radiation member, the walls of said radiation .member said ,radiation receiving member adjacent to said i radiationfreceiving walls and combustionl chamber being provided with irregularities which produce eddies in the air passing through lsaid housing. j

9. In an air heating furnace, a combustion chamber provided with. walls of high heat conductivity, and an absorbing wall of lower thermal conductivity adjacent to said combustion chamberavalls, and spaced. between said absorbing wall'and said combustion chambeii` wall, and means for circulating air ove'i'"`the surface of said' absorbing wall. '10. A furnace for heating'gases, compris ing a combustion chamber formed from carl borundum combustion chamber and an adborundum, an adjacent wall of re brick nr jcent. Wall of relatively 10W conductivity a1'- ranged to receive Lheat by vradiation' from' raned to be heated by radiation from said l0 said combustion chamber, and a path for `com ustion chamber, a circulation space bc- 5 gases to circulate between said combustion ing provided between said combustion ohnm-v chamber and said adjacent Wall. ber and said low heat conductivity Wall.

1 Tn a furnace for heating gases, a car- W. A. DARRAH.

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