US1786593A - Furnace - Google Patents

Description

; lr atenited Dec. 30, 1930 warren srnras PATENT OFFICE RAYMOND C. BENNER, F NIAGARA FAILS, NEW YORK, ASSIGNOR TO THE GAE- BORUNDUIVI COMPANY, 0F NIAGARA. FALLS, NEW YORK, A CORPORATION 0F PENN SYLVANIA EURNAGE Application filed December 13, 1927. Serial No. 239,724.

This invention relates to furnaces and to the method of operating them, and constitutes an improvement on the invention disclosed in the application of Clarence E.

Hawke, Serial No. 244,734, filed January In the said application of Clarence E. Hawke it is pointed out that with the present improved fuel burning apparatus and furnace designs the number'of B. t. u.s/cubic foot/hour in the combustion space has been increased enormously over the "rating \of boilers according to old methods of burning fuel and old designs of furnaces. This enormous increase in the rate of fuel combustion per cubic foot per hour imposes very severe operating conditions on the furnace linings.

In the said Hawke application provision is made for protecting the linings by constr'ucting the linings of a refractory material which' is many times more thermally conductive than fire clay, and which is much stronger at operating temperatures than fire clay, and the temperature of this lining is controlledby the circulation of air back of theunexposed face of the lining. By the selection of a refractorymaterial whose rate of thermal conductivity is in excess of .006 cal/cm /C./sec., designing the lining of a suitable thickness, and by forcing air back of the lining at a predetermined rate, a definite control of the temperature on the face of the lining is secured. Alt is possible to keep the exposed faceof the, lining at a temperature considerably below the flame temperature of the furnace and below the P congealing point of slag and ash. By so controlling the temperature, the ash and slag will congeal on the exposed face of the lin ing and form a protective film or coating resistant to the erosive action of hot slags and ash. "1;; V i

'It is also pointed out in said application that the control of the temperature at the face of a' fire clay lining is not practical because fire clay has a heat conductivity of less than .006 c al/cm /C./sec. and that any wall of fire Iclay thin enough to allow for any appreciablgcontrol would not have the mechanical strength to sustain itself at the operating temperature of the furnace. In 0 said application there is disclosed the provision of a lining of a refractory such as silicon carbide whose thermal conductivity ranges between .029 and .038 cal/cm /C./sec. The silicon carbide, in addition to having a high coeficient of thermal conductivity as compared with fire .cla and other materials, also has considera le strength at the,

Fused Megne' 810 Also: site may Thermal conductivity"--. Same Same. Same. Same. Thickness -2. 5 2. 5 1 Transverse strength 59, 700 1,' 250 875 200 Crushing strength 6, 300 500 125 Resistance to fused ash.-- 63 2. 5 1 1 Resistance to abrasionih. 18. 9 5 0.02 1 Resistance to spelling"--. 6. 3 1. 3 0. 7 1 Fusion p0mt. 2240 C. 1900 C. 1900 C. 1750 C.

From the fore oing it becomes appagent that vcontrol of t e temperature at the; exposed face of a fire clay wall by the circulation of fluid back of the wall is not practical.

As pointed out in the said Hawke applica- ,tion," control of the temperature at the exosed face of the refractory is highly desirable for the most eflicient conditions of operation. Not only is it ossible to afford greater protection of the re ractory by keeping this exposed face below the con ealing point of the slag, but it is also possible to keep the interior'of the furnace at a temperature sufficiently high-to secure a high rate of combustion and a thorough combustion-of the fuel. Where control of the temperature on the exposed face' of the lining is not possible, it is necessary to depress the flame temperature in the combustion" chamber by an excess amount of air, or' it is necessary to make the combustion space excessively large in order ion high

ith the practice of the invention as disclosed in the said Hawke application, a considerable degree of controlis possible, and the air which is used in cooling the furnace lining is supplied to the furnace for support-' ing combustion, thereby further increasing the efliciency of the furance. However, under some conditions of operation it is desirable to provide some means of cooling in addition to the air.

According to the present invention the air cooling ofa lining is combined with other cooling means for securing a greater degree of control. According to the 2preferred em-- bodiment of the invention the coolin means 1 may also be used to reinforce the wa l structure and thereby not only increase the degree of temperature control which may be exercised but also add to the mechanical strength of the lining.

Theinvention may be readily understood by reference to the accompanymg drawing, in which Figure 1 is a more or less diagrammatic view representing a cross section through a boiler provided with a powdered coal-burning furnace and embodying the present invention;

- Figure 2 is a detail view representing a section throu h a wall constructed according to a perferreg embodiment of my invention;

Figure 3 is a view similar to Figure 2 of a modified arrangement; and

Figure 4 is a viewsimilar to Figure 20f another modification,

The arrangement shown inFigure 1 is a typical powdered coal burning installation applied to a boiler furnace. In this view, 2

is the pulverizer fan for feeding powdered coal from a hopper 3 through a feeder pipe 4 into the combustion space 5 of the furnace, desi ated generally as. 6. The boilers are outlined at 7 The-interior of the combustion chamber 5 islined with a refractory material having a coefficient of thermal conductivity which is r elativelyhigh as compared with fire clay, its thermal conductivity being in excess of .006 cal/cm /C./sec. This lining is preferably made of silicon carbide and is designated 8. 'Betwejen the wall 8 and the outer shell 9 of the furnace is an air circulating space 10;. Air is supplied to the space 10 by a fan 11 which forces the air through a pipe 12 into an opening 13 communicating with the spacelO. The air which is forced or circulated through the space 10 at a predetermined rate, is discharged through a pipe 14 which communicates with a chamber 15 surrounding the turbulent burner 16 at the end of'the pipe 4, the arrangement being such that the air which is forced through the space 10 between the silicon carbide, wall and the outer shell of the furnace may be discharged with the fuel into the combustion chamber. The primary or compressed air line for the burner is designated 17.

So much of the arrangement as has been described is disclosed in the said I-Iawke application. According to the prevent invention, pipes or conduits are built into the air circulating passage. Fluid can be circulated through these pipes. The pipes will receive heat directly from the furnace lining by radiation, and heat will be transferred from the furnace lining to the pipes and to the fluid circulating therethrough by the air wiping against the lining and then against the pipes. The temperature of the air can thus be controlled and greater cooling SQIIIBCL The pipes may be located at certain points about the lining where there is a particular tendency of the lining to become overheated, or can be located throughout the entire lining.

In Figure 1 there is illustrated one possible arrangement wherein there-are a plurality of vertically extending pipes 18 connected to a common header 19 at the top thereof, and to a similar header 20v at the bottom thereof. Water or other cooling fluid may be supplied to the header 19 through a pipe 21 and valve 22, and water may be withdrawn from the header 20 through pipe 23 and valve 24, or thercirculation of fluid can be reversed.

Figure 2 illustrates a preferred arrangement of the pipes in the air circulating passages. In Figure 2, 25 designates a furnace lining of silicon carbide or other refractory having a high coeflicient of thermal conductivity as compared-with fire clay. The ex posed face of the lining is designated 26 and 27 designates the fire clay or other shell outside the lining 25. In the lining 25 are a plurality of air circulating passages 28 through which air (an be forced through the blower. Arranged in some or each of .the passages 28 is a pipe 29 through which water, steam or other fluid may be circulated. The pipes 29 receive heat from the refractory 25 by'direct'contact with the refractory. They also receive heatby radiation from the refractory, and the refractory is cooled by the transfer of heat fromthe air: cir

culating through the passages 28to thepipes.

Due to'the wiping action which the air has 'over the surface of the refractory material and over the surface of thepipes, the heat is transferred very efliciently. By regulating,

the flow of air and the flow of fluid the tem- 4 50 terial diife'rence between the exposed face fluid circulating pipes, designated 30, are lo-- cated in a passage 31 between the refractory lining 32 of silicon carbide .or other refractory having a highcoeficient of thermal conductivity, and the outer shell 33. The exposed face of the lining 32 is indicated by the reference numeral 34. The arrangement shown in Figure 3 is generally similar to that outlined in Figure .1. The pipes in this arrangement being staggered, impart aturbulent flow of the air so that there is a greater wiping action against the unexposed surface of the refractory 32 and against the outsides of the pipes. The pipes also receive heat by radiation directly from the refractory/.32.

In the arrangement shown in Figure 4, 35 designates the exposed surface of a furnace wall which possesses a much higher coetlicient of heat conductivity than fire clay, such for instance as silicon carbide. self is designated 36and at 37 is the usual fire clay wall at the unexposed surface. Formed in the wall 36 are water circulating pipes 38. The wall 36 also has air circulating passages 38 therein. This construction differs from that shown in Figures 2 and 3 in that the water'and air circulating passages are separated. In this construction, as in the constructions previously described, more efi'ective control of the temperature of the furnace wall can be secured than where one fluid alone is used for cooling the wall. The water pipes furthermore serve to reinforce the wall.

The invention provides for a more efiicient cooling of the refractory than is possible.-

where water cooling-or air cooling is relied upon entirely, and provides for amore accurate control of the temperature conditions at the exposed face of the lining. It is necessary in order to secure this control that the refractory lining have a high coeficient of thermal conductivity as compared with fire clay so that heat may be transferred there throughata rate sufiicient to secure a maof the lining'and the fiaine temperature. At the same time it is necessary that the wall be thick enough'to have the desired mechanical strength. The pipes for the circulation of water or other fluid can be located wherever they are needed. If additional coolin is necessary for only certain parts of the lining, the1 pipes can be disposed adjacent those parts on y.

The invention is particularly applicable to the burning of powdered coal or sus ended fuels where the most efiicient conditions of combustion are obtainable when the lining is at a temperature substantially above 400 G.

pended claims. l

The wall it-.

In the burning of such types of fuels also.

the furnace lining is subjected to the most severe conditions of operation and thecontrol of the temperature at the face of the lining is therefore more desirable.

While I have described and shown certain embodiments of the inventionit will be. understood that'this merely is byway of illustration and the invention is not confined to the; particular arrangement and construction shown as'variouslchanges and modifications may be made within the contemplation of the invention and under the scope of the ap-' I claim:

, 1. In a. furnace, a combustion chamber havin a wall, with a refractory lining comprised principally of silicon carbide, said lining having a thermal conductivity inany times that of fire clay, watertight conduits in said wall structure, an air passage in said wall structure, and means for forcing a current of air through said air passage.

2. In a furnace, a combustion chamber having a wall structure with a lining of a non.- metallic refractory, the thermal conductivity of which is in excess'of .006 cal/cm /C./sec., water-tight conduits in said wall structure, an air passage in said wall structure, and

means for forcing a current of air through said air passage, said water-tight conduits conductivity in excess of .006 cal cm (l/sed,

water-tight conduits in said wall structure, an air passagefin said wall structure, and means for forcing a current of air through said air passage, said water-tight conduits being located directly in the air passage whereby the current will wipe over the surface of said water-tight conduits.

4. In a. furnace, a combustion chamber having a. wall structure with a lining ofa retrac tory material.v comprised principally of silicon carbide the thermal conductivity of which i is in excess of -.006 cal/cm /C./sec., watertight conduits in said wall through which fluid may be circulated, an air passage in said wall back of the exposed face thereof through I which a current of air may be circulated, a blower at the input end of said air passage for blowin air through the air passage and maintaining a pressure in said passage above atmospheric pressure.

5. In a furnace, a refractory wall-structure having a liningcomprised principally of silicon carbide, the thermal conductivity of which lining is in excess of .006 ca1/cm /C./sec., a water-tight conduit in said wall structure back of the exposed face of the lining, an air passage in said wall structure back of the exposed face of the lining, means for forcing a current of air through said air passage, said water-tight conduits being located directly in the air passage, and means for conducting substantially all of the air from said passage to the combustion chamber to support combustion therein.

6. In a furnace, a wall structure having a lining comprised of a refractory material the thermal conductivity of which is in excess of .006 cal/cm /C./sec., ater-tight conduits in said wall structure, an air passage in said wall structure, and means for forcing a current of air through said air passage.

7. In the method of controlling the term perature of a non-metallic refractory furnace lining having a thermal conductivity in excess of .006 cal/c1n /./sec., the steps which comprise conducting heat from the exposed face of the refractory at a rate sufficient to keep such face below the point at which the slag in the furnace is fluid by circulating air against an unexposed face of said wall, and cooling the air as it circulates against the unexposed face to reduce the volume of air required.

8. In tne method of controlling the temperature of a non-metallic refractory furnace lining having a thermal conductivity in excess of .006 cal/cni C./sec.,-the steps which comprise conducting heat from the exposed face of the'refractory a rate sufficient to keep such face below the point at which the slag in the furnace is fluid by circulating air against an unexposed face of said wall, cooling the air as it circulates against the unexposed face to reduce the volurne'of air re qui'red, and utilizing all of the air soi circulated in the furnace to support combustion.

9. In the method of controlling the temerature of a non-metallic refractory lining an a boiler furnace wherein the lining has a high thermal conductivity as compared with a fire clay refractory and in excess of .006- cal/cm /C./sec., the steps which comprise conducting heat from the exposed face of the refractory at a rate suficient to keep such face below the point at which the slag in the furnace is fluid by circulating air a ainst an unexposed face of the wall, cooling t e air as it circulates against the unexposed face by simultaneously circulating it over conduits which contain the fluid contained in the boiler to reduce the amount of air required, and utilizing all of the air to support combustion in the furnace.

10. In the method of controlling the temperature of a non-metallic refractory furnace lining having a high thermal conductivity and in excess of 006 cal/cm /C./sec., the steps which comprise conducting heat from the'exposed face of the refractory at a rate sufficient to keep such face below the point at perature of a non-metallic refractory furnace lining formed principally of silicon carbide, the steps which comprise conducting heat from the exposed face of the silicon carbide refractory at a rate sufficient to keep such face below the point at which the slag in the furnace is fluid by transferring some of the heat from the wall to a confined fluid and transferring other heat to air wiping against an unexposed face of the wall, and maintaining the pressure of the air which wipes the unexposed face of the wall at a pressure above atmospheric pressure.

12. In the method of controlling the temperature of a non-metallic refractory furnace lining formed principally of silicon carbide, the steps which comprise conducting heat from the exposed face of the silicon carbide refractory at a rate sufficient to keep such face below the point at which the slag in the furnace is fluid by transferring some of the heat from the wall to a confined fluid and transferring other heat to air wiping against an unexposed face of the wall, and varying the volume of air circulated against the wall in accordance with the increase or decrease in the fluidity of the slag contacting with the wall.

13. A furnace wall comprising, in combination, a lining of silicon carbide on the inner side of the wall, an outer portion constructed of fire clay, ducts in the silicon carbide lining for the circulation of cooling media in heat interchanging relation, said ducts including water pipes subjected to the-wiping action of controlled current of air surrounding said pipes, and means for circulating air at controlled velocity relative to said pipes.

ll. In a furnace, a combustion chamber having a wall structure with a lining of nonmetallic refractory material the thermal conductivity of which is in excess of .006 cal/cm O./sec., water-tight conduits in said linin said conduits supporting the lining and being in substantial contact therewith for a material proportion of the area of the conduit, an air passage within the wall, and means for circulating air through said passage and in contact with said lining and said conduits.

15. In the method of controlling the tomb perature of a non-metallic refractory furnace lining formed principally of silicon carbide. the steps which comprise conducting heat from the exposed face of the silicon carbide refractory at a rate sufiicient to keep such face below the point at which the slag in the furnace is fluid by transferring some of the heat memes from the Well to e confinedl. fluifl, amt transferring other heat to air wiping against an unexposed face of the Wall, and maintaining the pressure of the air which Wipes the unexposed fece of the ell at a ptessure above the pressure within the furnace to prevent the suction of any hot furnace gases through the reflector well. v v

In testlmony whereof I have hereunto set 10 my hand.

RAYMOND G. BENNER.

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