US3563211A

US3563211A - Gas-fired boilers or the like

Info

Publication number: US3563211A
Application number: US808273A
Authority: US
Inventors: Lloyd H Hornbostel Jr
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-03-18
Filing date: 1969-03-18
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16

Abstract

A steam boiler or analogous heat exchanger is provided with a gas-fired burner comprising a plenum chamber from which a combustible gas-air mixture escapes through an inexpensive and readily replaceable burner member formed of foraminous ceramic material. The porosity and thermal conductivity of the burner member are such as to produce substantially flameless combustion toward the outer surface of the burner member, which causes that surface to incandesce and to radiate heat directly to waterfilled boiler elements facing the burner member.

Description

United States Patent 3,211,133 10/1965 Valyi 122/33 3,315,646 4/1967 Wilten, Jr. 122/235 3,418,979 12/1968 Reichmann 43 l/328X Primary ExaminerKenneth W. Sprague 38 32 2s 78 A4. 21 a 21 :3 2 l8 3- laiaii i xia 23727 Patefiied Feb; 16, 1911 3,563,211

2 Sheets-Sheet 1 INVENTOR. LLOYD HORNBOSTEL JR.

P atented Feb. 16,1971 I 3,563,211

2 Sheets-Sheet 2 INVENTOR. LLOYD HORNBOSTEL. JR.

e e 1 1 t GAS-FIRED BOILERS OR THE LIKE BACKGROUND OF THE INVENTION- 1. Field of the lnverition The present invention relates to gas-fired steam boilers or analogousheat exchangers and more particularly to such devicesemploying surface combustion radiant burners.

2. Description of the Prior Art i i ln gasfired steam generating units at least four principal heat transfer mechanisms occur simultaneously; namely, nonluminous radiation from theproducts of combustion, luminous radiation fromburning particles of suspended solids carried by the combustion gases, convection from the combustion gases and conduction between the boiler surfaces and hot particles deposited thereon during combustion. ln most types of boilers, radiation is the most significant of these mechanisms, particularly inthose portions of the boiler where the highest rate of steam generation takes place. Accordingly,

it has long been recognized that boiler efficiency can be improved by increasing theamount of available heat energy which is transferred to theboiler surfaces byradiation; which is most commonly accomplished by employing refractory firebrick furnace and boiler wall linings which reradiate energy to the boiler surfaces when they become heated to incandescent temperatures. Due to the weight and relatively low strength of such refractory firebrick.rriaterials, however, it is generally impracticable to employ such a construction to a meaningful extent in high output portable boilers, e.g. of the type employed in steam automobiles.

If a combustible mixture of air and gas is forced through a porous refractory material and ignited at the outer surface thereof while a sufficient flow velocity is maintained to prevent combustion fromflashing back through such material, the outer surface of thematerial adjacent the combustion is rapidly heated to an incandescent temperature. Thereafter, the incandescent refractory material promotes the combustion to the extent that the mixture burns with almost no visible flame but with high radiant energy output. Although such so-called surface combustion'can be produced by means of a porous mass of almost any type of refractory substance, a.

particularly desirable material for that purpose comprises a molded composition of ceramic fibers bonded together to provide a relatively light and self-supporting rigid structure of predetermined permeability and low thermal conductivity,

known means for achieving such combustion. Briefly, these objectives are accomplished in accordance with the invention by providing a boiler, preferably of the water tube-type, with a gas-fired burner comprising a plenum chamber from which a combustible gas-air mixture escapes through a burner member formed of molded ceramic material of the general type described above. When the combustible mixture is ignited at the outside surface of the burner member, the resulting previously described incandescent surface combustion phenomena imparts a high proportion of radiant energy to the boiler tubes or analogous water-filled elements spaced from but facing the burner member. Due to the low thermal conductivity of the burner member material and the homogeneous porosity thereof, the burner material adjacent the plenum chamber is kept 'at a temperature well bclowtheignition temperature of the combustible mixture by the passage of unignited air and gas therethrough. Consequently, since the burner member is devoid of any sizeable individual passageways extending between its inner and outer surfaces, the possibility of flashback into the plenum chamber is positively avoided regardless of the flow velocity through the burner member. Additionally,

this relatively cool condition of the portion of the burner member beyond its outer combustion surface allows it to be sealed in gastight cooperation with the plenum chamber structure without compensating for large differences in thermal expansion, and without subjecting the joint surfaces to high temperatures. in accordance with a preferned embodiment of the invention, this feature allows a gastigh't joint to be provided between the burner member and the mating surface of the plenum chamber structure by means of a conventional resilient O-ring gasket. Preferably, the burner element is adapted to be removed and replaced in a simple and straightforward manner without recourse to any major disassembly of the boiler or any significant interruption in its operation.

The configuration of the burner member is such as to present a maximum incandescent area thereof to the adjacent water-filled elements of the boiler. For example, the burner member may be in the form of a relatively flat disc confronting candescent burner surface may define a corresponding spiral Specific details of such materials and techniques for the production thereof are disclosed-in U.S. Pat. No. 3,l79,l56, which also illustrates and describesthe" use of that type. of material as a burner element in a reflective-type gasfired radiant space heater. An example of a commercially available material particularly suitable for such surface combustion applications in the product sold by the Babcock and Wilcox Co. of Augusta, Ga., under the trademark KAOWOOL.

At least years ago, experimental attempts were made to improve steam boiler performance by the employment of surface combustion firing. Briefly, these experiments involved filling the firetubes of firetube-type boilers with loosely packed lumps or particles of arefractory material such as firebrick and effecting combustion of an air-gas mixture introduced into the refractory mass through central jet openings in annular fireclay plugs partially closing the inlet ends of the tubes adjacent the tubesheet. While those experiments conclusively demonstrated improved heat transfer performance, and thereby potential reduction in boiler flue lengths, this technique apparently enjoyed little or not practical application, presumably because of the obvious attendant difficulties and inconvenience involved in boiler cleaning, inspection and maintenance.

SUMMARY time rNvgNrroN g I The present invention contemplates improving heat transfer rates in gas-fired steam boilers by the employment of surface combustion firing without involving any of the complications or inconveniences inherent in the above-described previously or helical recess partially surrounding the adjacent boiler tube to thereby further increase the impingement of radiant energy on that tube. In various embodiments of the invention a plurality of such burner elements of either similar or different configurations can be employed in a single boiler, in which case each of such burner members can be replaced individually whenever necessary.

Although the foregoing description refers to steam boilers, it will be apparent that the invention is equally applicable to water heaters or other analogous structures in which heat is imparted to a confined gas or liquid. Accordingly, it will be understood that the term boiler" as used herein is not confined strictly to conventional steam producing boilers but is intended also to encompass such related devices for heating various confined liquids or gases.

Various means for practicing the invention and other ad vantages and novel features thereof will be apparent from the 1 following detailed description of illustrative preferred embodiments of the invention, reference being made to the accompanying drawings in which like reference numerals identify like elements.

BRIEF DESCRlPTlON OF THEv DRAWINGS In the drawings:

F IG. 1 is an exploded perspective view of a compact boiler according to a preferred embodiment of the present invention,

FIG. 3 isa cross-sectional elevational view ofa boiler in actapered edge surfaces of those elements tightly against the cordance with an alternate preferred embodiment of the inmating surfaces of the burner seating cones. To further insure vention comprising a tubular cylindrical burner member surthe existence of a gastight seal between the edges of the rounded bya helically disposed boiler water tube. burner elements and the respective burner seating cones, a 5 heat-resistant resilient O-ring 38 is located in an annular DESCRIPTION OF THE ILLUSTRATWE PREFERRED depression 39 in each of the two cones and is slightly flattened EMBODIMENT and squeezed into the adjacent burner element when the latter The illustrative embodiment of the invention depicted in is pressed into P e y the corresponding closure member- FIGS 3 and 2 f the accompanying drawings is a very 1 Accordingly, it will be seen that the closure members pact gas-fired water tube boiler particularly suitable for steam Cooperate wlthvthe burner l to dehhe Plenum Chamautomobiles or other related applications. The boiler housing, hers 41 which Combustible mixtures of and gas are identified by numeral 12, is generally symmetrical above and mitted through mixing Valves 42 removably attached to the below its horizontal center plane and comprises a central two elesure member? cylindrical wall member 13 from which tapered burner seating the operatlhh of the holler, the comhushble h cones 14 extend outwardly to peripheral flanges 15. An annumlxture lhtmdfleed mto the Plenum chambers Permeates lar channel-shaped manifold member 16 surrounds the central threhgh the uhlformly Permeable h' elements portion of the boiler and is welded to the outer surfaces of bustle" e defined y the lhhel' fflees e the burner cones 14 to define an annular exhaust chamber 17 provided elemehts'ahd y hher g when the holler first P m with outlet tubes 18, which can also serve to support the boiler 20 Operation, this combustible mixture is ignited the unit. bustion chamber by a conventional spark plug or the like pro- I h bl d b il a combustion h b li i 19 jecting into the combustion chamber through a radial tube in fits snugly into the cylindrical wall member of the boiler housthe eXhauSt Chamber, as depleted at numeral ing and includes radial holes aligned with corresponding AS previously mentioned, the ignited mixture initially burns holes 22 in that n member This ring is made f a with a flame adjacent the inner surfaces of the burner elerefractory material, f bl f h same type f ld d ments. Under the influence of the heat thus produced adjacent ceramic fiber composition mentioned previously, which is also the inner burner Surfaces, those Surfaces S0011 become incanthe material of which the hereinafter described burner eledescent. h r up n h r ing pr m ion of the comments are f d sh ll Slots 23 are l t d i h upper bustion process causes the air and gas mixture to burn near the and lower surfaces of the liner ring to receive and position the burner Surfaces With little 0 Visible am ut with a high laterally projecting rods 24 of boiler tube support members 25 level of radiant energy emission. By virtue of the relatively nd 26, uniform porosity and low thermal conductivity of the burner The three boiler tubes of the illustrative boiler are identified element material, however, those portions of the

burner eleby numerals

27,28 and 29 and are all of flat spiral configuraments beyond the regions of surface combustion are maintion. The

primary boiler tubes

27 and 28 are supported tained at a relatively cool temperature, well below the ignition respectively by

support members

25 and 26 above and below temperature of the combustible gas mixture, by the cooling inthe planes defined by the upper and lower faces of the liner fluence of the unignited gases constantly permeating ring. The secondary boiler tube 29 is supported between the therethrough. Consequently, this mode of burner construction primary tubes in generally parallel relation thereto. in FIG. 1, positively avoids the danger of combustion flashback through both ends of all three tubes are shown extending outwardly the burner elements and also eliminates the exposure of the through the boiler housing so that they can be connected exburner sealing rings to potentially destructive temperatures. ternally to one another, as well as to a feedwater pump and Due to the conformation of the combustion surfaces of the control valve unit and to a stream manifold or the like. Howburner elements with the configuration of the corresponding ever, it will be apparent thatthe three boiler tubes could be boiler tubes, it will be apparent that radiant energy is impinged connected within the boiler housing in any desired fashion so onto approximately half the total surface area of those tubes that only a single water inlet tube and single steam outlet tube from the closely adjacent burner surfaces generally parallel would emerge through the housing. Preferably, the three tubes thereto. Additionally, the remaining surfaces of the tubes are are connected in series to provide a so-called monotube-type of course also exposed to less concentrated but nevertheless boiler in which the secondary tube functions as a superheater very intense radiation, both directly from the burner elements or economizer. and also by reflection from the refractory liner ring. Ac-

Burner elements 31 are in the form of generally flat discs cordingly, very high rates of heat transfer are achieved, resultwith tapered edge surfaces 32 which conform to the conical ing in a correspondingly high level of boiler efficiency as comconfiguration of the internal surfaces of the boiler seating pared to previously known boilers of comparable simplicity cones 14. The smaller diameter faces of the burner elements 5 5 and compactness. By way of example, a simple small scale exare provided with spiral grooves 33 conforming to the spiral perimental boiler comprising a single flat spiral water tube form of the adjacent primary boiler tubes. As previously heated by a flat gas-fired surface combustion burner accorddescribed, the burner elements are made of a gas-permeable ing to the present invention was found to produce at least 30 composition of bonded refractory fibers, Preferably, the percent more power in terms of steam output compared to its burner elements are produced in finished form bymolding corresponding power output when heated with a similarly techniques, but it is also possible to machine such elements located conventional multiple orifice burner burning gas at from blocks or slabs of the above-identified KAOWOOL the same rate ofconsumption. material or some other analogous material. To further improve the thermal efficiency of the boiler illus- In the assembled boiler, burner elements 31 are supported trated in FIGS. 1 and 2, a feedwater tube, not shown, can surby the mating engagement of their tapered edge surfaces with round manifold member 16, whereby some of the heat energy the tapered internal surfaces of the burner seating cones and of the exhaust gases within chamber 17 is devoted to preheatare oriented such that the primary boiler tubes are partially ing the boiler feedwater. Similarly, if the boiler is tired by a received in the corresponding burner element grooves 33 with vaporized liquid fuel such as gasoline, a vaporizer or preheater the internal surfaces of those grooves in spaced confronting tube can also be provided within the annular exhaust relation to the adjacent external tube surfaces. Peripheral chamber. Appropriate insulative lagging obviously can also be flanges 34 of closuremembers 35 are attached to the corprovided about the outer periphery of the boiler, but in auresponding flanges 15 by bolts 36 extending through gaskets l, tomotive applications it may be preferable to surround the 37. Flanges 34 overlap the adjacent surfaces of the outer faces manifold member 16 with an air duct from which hot air can of the corresponding burner elements and thereby hold the 1 be obtained to supply heat to the interior of the automobile.

If it should be necessary to replace one of the burner elements of the boiler, this can be, accomplished simply by shutting off the flow of combustible gases to the boiler, disconnecting the mixing valve from the corresponding closure member, and then unbolting and removing that closure member from the boiler housing. Therefore, if the boiler is mounted in such a manner as to provide suitable access to both of its closure members, such replacement of the burner elements can be accomplished rapidly and conveniently without removing the boiler from its mountings or disconnecting steam or water lines.

The monotube boiler shown in FlG. 2 to illustrate an alternate embodiment of the invention comprises a generally cylindrical housing member 45 provided with an upper exhaust stack 46 and with a peripheral lower flange 47. A tubular combustion chamber liner 48, similar to the previously described liner ring 19, fits into the boiler housing and is held in place by disc member 49; the latter being provided with appropriate annular gaskets and sandwiched tightly between flange 47 and the similar flange 51 of plenum chamber member 52 by bolts 53. Beyond bolts 53, holes 54 are provided through the two flanges and the disc member for the purpose of mounting the boiler in a stationary support frame, not shown.

In accordance with this embodiment of the invention, burner element 55 is formed of the same type of bonded fibrous ceramic material previously described and is in the form of a cylindrical tube closed at its upper end 56 and provided with a conical. lower flange 57. A metal support tube 58, closed at its top end, extends upwardly with the upper face 59 of its enlarged base portion 61 seated against the lower face 62 of the flanged lower end of the burner element. The portion of the support tube within the burner element is uniformly perforated with a pattern of narrow vertical slots 63, or the equivalent, whereas the larger base portion of the support tube is provided with a plurality of larger radial holes 64.

When the burner element is installed in the boiler it is positioned in coaxial relation with the helical boiler tube 65 by the mating engagement of the conical burner element flange 57 with a correspondingly tapered lip 66 defining a central opening in disc member 49 and by the reception of the base portion of the support tube in central opening 67 in the bottom wall 68 of plenum chamber member 52. A removable cover plate 69 is attached to the bottom wall of the plenum chamber with a gastight gasket by means of nuts 71 threaded onto studs 72. When this cover plate is in place, it engages the lower end of support tube 58 so that the latter forces the conical flange of the burner element into tight engagement with the mating tapered surface of disc member 49 and with O-ring 73, corresponding to the previously mentioned O-ring 38. Accordingly, when a combustible gaseous mixture is introduced into the plenum chamber member through a mixing valve connected to inlet tube 74, it passes into the support tube through radial holes 64 and then permeates outwardly through the perforated upper portion of the support tube and through the adjacent cylindrical wall of the burner element. Upon being ignited in the combustion chamber 75, the gaseous fuel mixture therefore burns at the surface of the burner element in the same manner described above, thereby imparting heat energy to the boiler tube both by direct and reflected radiation.

Although the boiler depicted in H0. 3 is somewhat less compact and efficient than the one illustrated in FIGS. 1 and 2, its very simple construction may offset those comparative disadvantages in various applications; for example, in domestic steam or water heatingunits. Additionally, it will be apparent that maintenance of this unit is even more straightforward than in the case of the previously described unit inasmuch as only one element, namely cover plate 69, need be removed to provide access to the removable burner element and support tube.

The invention has been described in detail with particular reference to illustrative preferredembodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A boiler comprising:

a. a housing;

b. a water tube coil of generally flat spiral configuration supported in said housing;

c. a disc-shaped burner element "made of porous refractory material of such porosity and relatively low thermal conductivity that a combustible gas mixture supplied to one surface of said burner element will permeate through said element to the opposite surface thereof and when ignited adjacent said opposite surface will produce substantially flameless surface combustion of high radiant energy output at said opposite surface;

d. means for supplying a combustible gas mixture to said one surface of said burner element; and

e. support means supporting said burner element in said housing with said opposite surface thereof generally parallel to and in direct confronting relation to adjacent external surface areas of said water tube coil.

2. A boiler according to claim 1 in which said burner element includes a peripheral conical surface, said housing including means defining a plenum chamber and a conical support surface adapted to mate with the conical peripheral surface of said burner to support said burner element in communication with said plenum chamber so that a combustible gas mixture within said plenum chamber is supplied to said one surface of said burner element and permeates through said burner element to said opposite surface thereof.

3. A boiler according to claim 2 including a burner seating member engageable with said burner element adjacent said conical surface thereof to seat said conical surface of said burner element firmly in mating contact with said conical support surface.

4. A boiler according to claim 3 including an annular O-ring seal adapted to be compressed between said mating conical surfaces of said burner element and said support member.

5. A boiler according to claim 1 in which said opposite surface of said burner element is provided with a generally semicylindrical groove conforming to the configuration of said coil, said coil being partially received in said groove out of contact with said burner element.

6. A boiler comprising:

a. a boiler tube element including a pair of generally flat tubular coils substantially parallel to one another,

b. a housing laterally surrounding said boiler tube element,

c. a pair of generally flat surface combustion burner elements supported in said housing at opposite sides of said boiler tube element in parallel confronting relation to the adjacent ones of said tubular coils,

d. plenum chamber means defining plenum chambers in communication with the outwardly facing surfaces of said burner elements, and

e. means for introducing into said plenum chambers a combustible mixture of gases which permeates through said burner elements and after being ignited adjacent the inwardly facing surfaces of said burner elements produces surface combustion at those surfaces.

7. A boiler comprising:

a. a housing including opposed conical housing sections tapering outwardly from each end of a generally cylindrical central housing section,

b. a boiler tube element including a pair of opposed generally flat tubular coils substantially parallel to one another,

0. means supporting said boiler tube element within said central housing section in substantially normal relation to the axis of said housing,

d. a pair of generally flat round surface combustion burner elements having tapered peripheral surfaces adapted to mate with said conical sections of said housing to support said burner elements respectively in parallel confronting bustible mixture of gases which permeates through said burner elements and after being ignited at the inwardly facing surfaces of said burner elements produces surface combustion at those surfaces, and

g. exhaust means for conducting exhaust gases out of the boiler combustion chamber defined within said central housing section between said burner elements and occupied by said boiler tube element.

Claims

1. A boiler comprising: a. a housing; b. a water tube coil of generally flat spiral configuration supported in said housing; c. a disc-shaped burner element made of porous refractory material of such porosity and relatively low thermal conductivity that a combustible gas mixture supplied to one surface of said burner element will permeate through said element to the opposite surface thereof and when ignited adjacent said opposite surface will produce substantially flameless surface combustion of high radiant energy output at said opposite surface; d. means for supplying a combustible gas mixture to said one surface of said burner element; and e. support means supporting said burner element in said housing with said opposite surface thereof generally parallel to and in direct confronting relation to adjacent external surface areas of said water tube coil.

6. A boiler comprising: a. a boiler tube element including a pair of generally flat tubular coils substantially parallel to one anotheR, b. a housing laterally surrounding said boiler tube element, c. a pair of generally flat surface combustion burner elements supported in said housing at opposite sides of said boiler tube element in parallel confronting relation to the adjacent ones of said tubular coils, d. plenum chamber means defining plenum chambers in communication with the outwardly facing surfaces of said burner elements, and e. means for introducing into said plenum chambers a combustible mixture of gases which permeates through said burner elements and after being ignited adjacent the inwardly facing surfaces of said burner elements produces surface combustion at those surfaces.

7. A boiler comprising: a. a housing including opposed conical housing sections tapering outwardly from each end of a generally cylindrical central housing section, b. a boiler tube element including a pair of opposed generally flat tubular coils substantially parallel to one another, c. means supporting said boiler tube element within said central housing section in substantially normal relation to the axis of said housing, d. a pair of generally flat round surface combustion burner elements having tapered peripheral surfaces adapted to mate with said conical sections of said housing to support said burner elements respectively in parallel confronting relation to the corresponding ones of said tubular coils located between said burner elements, e. cover members peripherally engageable with the outwardly facing surfaces of said burner elements to urge said burner elements into tight supported mating engagement with said corresponding conical housing sections and to define respective plenum chambers in communication with the outwardly facing surfaces of said burner elements, f. means for introducing into said plenum chambers a combustible mixture of gases which permeates through said burner elements and after being ignited at the inwardly facing surfaces of said burner elements produces surface combustion at those surfaces, and g. exhaust means for conducting exhaust gases out of the boiler combustion chamber defined within said central housing section between said burner elements and occupied by said boiler tube element.