US 3850146 A
A shielding or insulating wall of discrete tiles is removably secured in front of the impingement surfaces of boiler tubes in the burner region of the boiler furnace chamber for shielding the lower regions of the boiler tubes against excessive heating in order to force combustion gases to rise into the superheat and reheat regions of the boiler to develop and maintain required higher temperatures in such latter regions, or to protect the boiler tubes from direct impingement of burner flames which tend to generate and accelerate their premature deterioration. The shielding wall of tile is free-floating with the expansion and contraction of the boiler tubes, whose load and temperature variation in the burner region of the furnace area normally results in cracking and decay of a fixed continuous shielding wall material as currently practiced.
Claims available in
Description (OCR text may contain errors)
United States Patent Graham et a1.
[451 Nov. 26, 1974 BOILER TUBE SHIELDING WALL  Inventors: Robert G. Graham, 2433 N. Nine Primary Exammer Kenneth Sprague Mile Rd., Sanford, Mich. 48657; Douglas J. Frame, 3774 Lancaster 57 ABSTRACT Dr., Sterling l-le1ghts, Mich. 48077 I A shielding or insulating wall of discrete tiles lS remov-  Flledl 1974 ably secured in front of the impingement surfaces of  APPL No; 444,855 boiler tubes in the burner region of the boiler furnace chamber for shielding the lower regions of the boiler Related -S- Application Data tubes against excessive heating in order to force com-  Division of Ser. No. 323,872, Jan. 15, 1973. bustion gases to rise into the superheat and reheat regions of the boiler to develop and maintain required  US. Cl. 122/6 A, 110/98 R higher temperatures in such latter regions, or to pro  Int. Cl. F22b 37/66 tect the boiler tubes from direct impingement of  Field of Search 110/98; 122/6 R, 6 A, 235 A burner flames which tend to generate and accelerate their premature deterioration. The shielding wall of [5 6] References Cited tile is free-floating with the expansion and contraction UNITED STATES PATENTS of the boiler tubes, whose load and temperature varial 738 283 l2/l929 Carlson 110,98 tion in the burner region of the furnace area normally 1 775 4 4 22 results in cracking and decay Of a fiXd continuous 1:955:7o0 4/1934 Snow 122/6 Shielding Wall material as Currently practiced- 2,086,940 7/1937 Kuhner et al... 122/6 2,705,476 4/1955 Hardgrove 122/6 23 Clams 10 D'awmg Flgures l8 I8A l 28 82 8O 82 8O 28 2 8O PATENTEL wave- 3.850.146
SHEET 10F 2 PATENIEL, HUYZS I974 sum 2 BF 2 FIGS FIG. IO
REFERENCE TO PRIOR APPLICATION This application is a division of our earlier copending application Ser. No. 323,872 filed Jan. 15, 1973, bearing the same title, and the benefit of that filing date is claimed.
BACKGROUND OF THE INVENTION The invention pertains to a heat shielding wall tile and system for securing such tile in a free-floating relationship to boiler tubes in a boiler tube furnace which has been converted from coal firing to oil firing burners. Most utility boiler tube furnace structures were originally designed for and operated over a long period of time with coal-fired burners. Because of the distinctive nature of coal firing, the character and distribution of its flame and combustion gases, the relatively moderate volumes of excess air utilized by these burners, the design and organization of the lower regions and the upper superheat andreheat regions of the boiler tubes, such utility furnaces developed superheat temperatures and pressures adequate to meet specified output requirements. However, today, in view of the ecological and environmental need to reduce air pollution as an important if not a vital operating factor, utility companies have been gradually converting their coal-fired burners to oil-fired burners. Such conversions have unfortunately also been attended by a consequent reduction in the necessary specified elevated temperatures in the superheat regions of the boiler unless substantial additional excess air is provided to the oil-fired burners. As a result, operating costs of such boiler tube furnaces have increased markedly due to accelerated corrosion of the boiler tubes and the quantity of input oil fuel required in comparison with previously used lower cost coal. More frequent down-time and inspections have also occurred, adding to the cost factor.
ln evaluating the problem of such conversion to oilfiring burners, it was found that spray coating the lower regions ofthe boiler tubes with a wall ofa suitable insulating shielding ceramic material, operating as an insulating wall while still transmitting a required amount of heat to the boiler tubes in such lower region; caused a deflection upwardly into the superheat and reheat regions of the boiler of the combustion gases sufficient to maintain the required elevated temperatures in the latter regions. But the difficulty with such a continuous sprayed wall coating upon the heat impinging surfaces of the boiler tubes was an expected cracking, separation and decay of such coating material because of the variation in temperatures in various regions of the coated tubes due to load variations and expansion and contraction characteristics, whether such coating material was anchored by mechanical means to the boiler tubes or not so anchored. The load variation in the impingement area of the oil-fired flameand combustion gases resulted directly in thermal variations which occasioned the destructive cracking, separation and decay of the continuous sprayed-on wall coating material. Once cracking and separation were initiated, the wall crumbled and decayed with consequent loss of shielding to the boiler tubes in their lower regions, ,a lower temperature in the superheat and reheat regions of the boiler, an increased cost factor, and more frequent shut-down for inspection and repair. The primary difficulty, as observed, appeared to be the variation in thermal expansion and contraction of the-boiler tubes.
BRIEF GENERAL DESCRIPTION OF THE INVENTION The invention herein disclosed provides for a shielding wall of discrete ceramic tiles which moves and floats relatively freely with the boiler tubes and thus avoids the primary difficulties occasioned by the expansion and contraction factors of the tubes in continuous substantially solid wall surfacing. Individual tiles of a suitable high temperature resistant ceramic material are shaped and designed to dovetail with adjacent lateral, superior and inferior tiles to form a shielding wall of relative insulation for the lower regions of the boiler tubes against impinging oil-fired flames and combustion gases. The lowest course of such tiles is supported upon the metallic angle or clips permanently secured to two or more adjacent boiler tubes, and a plurality of horizontal courses of these tiles are laid against the tubes and secured thereto by free-floating retaining members that hold the tiles to and against the boiler tubes by means of double or duplex bar devices removably secured to and between vertically spaced apart tile supporting angles or metallic clips fixedly attached to the boiler tubes, as above, while allowing the tubes to expand and contract without disturbing the relationship of the courses of tile resting freely against the tubes. A second superior bank of such tiles can be secured above the first bank and separated slightly therefrom by a second course of permanently attached clip members supporting the courses of tile forming such second bank. The horizontal gap between the two banks of tiles is filled with a heat insulating type of material such as Kaowool, a readily installed and removable material adapted to shield the boiler tubes in the area of the gap. Where required or desired, third, fourth and additional superior banks of the ceramic tile can be applied to the water wall boiler tubes until the lower region of the boiler tube furnace has been sufficiently shielded to obtain the required temperature distribution from the lower region to the upper superheat region of the boiler unit.
PURPOSES AND OBJECTS OF THE INVENTION It is therefore an object of the invention to provide a relatively free-floating wall of ceramic tile secured to boiler tubes in an oil-fired boiler tube furnace. Another object is the provision of vertically arranged files of the ceramic tile supported upon clip members permanently secured to the boiler tubes. A further object is to provide free-floating tile retaining means anchoring superior courses of the tile to double or duplex bar members removably secured to and between horizontal rows of the clip members. Yet another object is to provide, where desired or required, a plurality of banks of such tiles arranged in horizontal courses, the banks being spaced slightly vertically apart from each other and the horizontal gap therebetween filled with a suitable readily removable insulating filling material. Still a further object is to provide a shielding wall of ceramic tile secured to the boiler tubes to form a shielding insulating wall for the lower regions of the tubes in order to obtain required elevated temperatures in the superheat and reheat regions of the boiler. Yet a further object is to provide a shielding wall of insulating tile which is free-floating vertically and laterally, the tiles being readily individually removable if necessary for replacement without a major repair of the wall. Still another object is to provide a free-floating bank of tiles to protect the boiler tubes from direct impingement of burner flames and combustion gases, wherein the boiler tubes are in contiguous tangent relationship, or closely adjacent but spaced apart relationship, or widely or substantially widely spaced apart relationship. Still a further object is to maintain and improve high boiler output efficiencies in a boiler tube furnace converted from coal-tired to oil-fired burners, and if possible to effect fuel cost savings.
Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example a preferred form of the invention. Reference is here made to the drawings annexed hereto and forming an integral part of this specification, in which DRAWINGS FIG. 1 is a front elevational view of a portion of a bank of tiles forming a shielding wall in front of closely adjacent continuous tangent boiler tubes, embodying features utilizing the inventive system.
FIGS. 2 and 3 are to and bottom perspective views respectively to the tile illustrated in FIG. 1.
FIG. 4 is a horizontal sectional view taken substantially on the line 44 of FIG. 5.
FIG. 5 is a side vertical sectional view taken substantially on the line 55 of FIG. 6.
FIG. 6 is a horizontal sectional view taken substantially on the line 6-6 of FIG. 5.
FIG. 7 is a perspective view showing the free-floating tile retaining clip positioned before insertion'between the two bars of the free-floating duplex bar member, for the construction illustrated in FIGS. 5 and 6.
FIG. 8 is a perspective view similar to that illustrated in FIG. 7 but showing the free-floating tile retaining clip engaged with the free-floating duplex bar member, as in FIG. 5. v
FIG. 9 is a perspective view of the free-floating duplex bar member.
FIG. 10 is a fragmentary enlarged horizontal sectional view. similar to FIG. 4, illustrating the conjunctive relationship of the duplex bar member and the tile supporting clip.
SPECIFIC DESCRIPTION One modern boiler design specifies that the boiler tubes be brought into contiguous or tangent parallel contact with each other to form a solid water wall toward and against which the burner-generated flames and combustion gases are directed. Such boiler tubes, of conventional tubular shape, are provided on their outer surfaces with longitudinally extending lateral flanges or ribs, substantially 180 apart, which are welded, or otherwise fixedly secured, to the body of the boiler tube. When these flanged tubes are installed, adjacent abutting edges of the flanges are welded to each other to form a continuous uninterrupted wall of boiler tubes. A modified preferred form of the invention disclosed in our co-pending application Ser. 'No. 323.872, of which this application is a division, to accommodate such wall of boiler tube construction is described below and illustrated in the drawings. The drawing views correspond to FIGS. 23-30 inclusive of the aboveidentified co-pending parent application.
The heat shielding wall 10 comprises one or more banks 12 of ceramic tiles 14 arranged in horizontal courses 16 one above the other, to shield the boiler tubes 18 therebehind. Water filled tubes 18, at least in the lower region of the boiler furnace area, are disposed in vertical closely adjacent contiguous tangent parallel aligned relationship to form a water wall" against and upon which the combustion gases discharged by the burners would normally impinge to heat the water therewithin to the elevated temperatures required for the generation of steam which rises from these lower tube regions into the superheat and reheat regions of the boiler unit. Because the superheat and reheat regions of the boiler tubes are substantially elevated above the burner portion of the boiler furnace, the rising combustion gases operate to increase the temperature of the steam to superheat temperatures in the upper regions of the boiler tubes due to the shielding effect of the ceramic tile wall 10.
The tiles 14 comprise a heat resistant ceramic fire brick body 19 having a substantially planar distal front hot face wall surface 20, adjacent lateral side walls 22,22 extending rearwardly from the wall surface 20 and having a longitudinally extending rib portion 24 on one wall and a complementary recess 26 on the opposite lateral wall, an upper slot 28 extending transversely of the tile from one side edge to the other rearwardly of the rib 24 and recess 26, a first distal top surface 30 intermediate the side walls 22,22 and extending from the front facing wall 20 to the depending wall 32 defining one side of the slot 28, a second proximal top surface 34 extending from inner wall 36 of the slot 28 to the arcuate edges of the longitudinally extending closely adjacent concavely curved wall surfaces 38,38 intermediate the side walls 22,22 and spaced apart from each other by the proximal medial web surface 40 having a longitudinally extending groove or slot 41 substantially medially between the arcuate concavely curved wall surfaces 38,38, and a first distal bottom surface 42 extending from the front facing wall 20 to a vertically depending stop wall surface 44, and a second proximal bottom surface 46-extending from the latter wallsurface 44 to the lower edges of the arcuate wall surfaces 38,38 and to the web surface 40 and slot 41 between the lateral walls 22,22, the second bottom surface 46 being disposed substantially parallel to and below the adjacent first bottom surface 42.
The ceramic tile 14 is formed of a fire clay type of material suitable for use in the furnace region of the boiler unit in which substantial elevated temperatures are achieved, often of the order of more than 2,000F. The hot face 20 of the ceramic tile is positioned in a plane forwardly of the boiler tubes 18 against which the tiles are designed to rest, to receive the impinging effect of the burner flame and combustion gases. The
arcuate wall surfaces 38,38 have a curvature complementary to the cylindrical configuration of the water tubes 18 so that substantially optimum contact can be made between such tile surfaces and the tubes against which they rest.
To support the courses 16 of the tiles in each bank 12 upon the boiler tubes and in relatively free-floating relationship thereto, support angle clips and freefloating tile retaining clips are used to retain the ceramic tile 14 adjacent and against the boilertubes 18.
The permanently affixed support clip 60 comprises a plate portion 62 having arcuate edges 64,64 spaced apart by a medial portion 66 and intermediate substantially co-planar lateral outer edge portions adjacent the lateral sides 68,68 of the plate portion 62, and an upstanding tile retaining flange 72 at its distal edge. The
I arcuate edges 64,64 have a curvature complementary to the cross-sectional curvature of the outer surface of the cylindrical boiler tubes 18,18 (FIG. 4), to which they are permanently affixed by welding as at 74,74.
The supporting clips 60 are shown (FIG. 1) positioned in spaced apart substantially horizontal alignment so that the first course 16 of tiles 14 will rest thereon in a substantially straight row, although a less regular arrangement and organization may also be adopted. The tile depending face 44, bottom face 46, the lower region of the arcuate wall surfaces 38,38, and proximal web 40 and slot 41 define the proximal lower flange portion 76 of the tile'positioned inwardly of the retaining flange 72 of clips 60, the arcuate surfaces 38,38 lying substantially closely adjacent or abutting the cylindrical outer wall surface of the adjacent boiler tubes 18,18. The proximal bottom surface 46 of the tile 14 rests directly upon the plate portion 62 of the clip 60 (FlG. 5). The proximal upper flange portion 78 of tile 14 is defined by the transverse slot wall surface 36,
the lateral walls 22,22, the concavely curved proximal wall surfaces 38,38, and the portion of proximal web 40 and slot 41 lying in the horizontal planeof the slot 28.
As shown particularly in FlG. l, in a single course 16, a single tile 14 rests medially between adjacent boiler tubes 18,18, allowing portions of adjacent lateral tiles 14,14 to rest in part upon lateral portions of the plate portion 62 ofa single supporting angle clip 60, thus distributing the weight of one full tile and portions of two adjacent lateral tiles upon a single clip 60. The adjacent tiles of each course aredisposed in very slightly spaced apart relationship, with the lateral ribs 24 and recesses 26 of adjacent tiles dovetailing each other in similar spaced relationship (FIG. 6).
The boiler tubes 18a comprise the tubes 18 and outer longitudinally extending flanges or ribs 79 at each side thereof, substantially l80apart, which are welded to the tubes 18. When installed, the tube ribs 79 are welded to each other at their abutting edges or surfaces to form a continuous imperforate wall or boiler tubes 18a.
Since tiles 14 are of substantially identical shape and size, superior courses of tiles also rest on inferior tile courses in substantially straight lines. To support the tiles 14 in horizontal courses and vertical files in a bank l2,'the angle clip 60 is further provided with an intermediate medial notch 256 adjacent plate portions 257,257 between the arcuate edges 64,64, lateral end portions 258,258 each having a corner notch 260 adjacent plate portion 259 which, in complement with the adjacent corner notch 260 of the next adjacent clip 60, forms a notch substantially equivalent to the medial notch 256, between the boiler tubes 18a,18a where the lateral edges of the clips 60,60 are present. The lateral edges of adjacent clips 60,60 are preferably spaced apart to allow for some movement toward each other without contact under the expansion/contraction movements of the adjacent boiler tubes l8a,l8a (HO. 4).
Freefloating tile retaining clips are used with the tile retaining parallel duplex bar device 272 which comprises a pair of bars 274,274 secured together in parallel spaced apart relationship at one end by a pin 276 having an intermediate web section 278 and laterally outwardly extending end portions 280,280 and at the other end by a pair of spacer bars 282,282 secured to and between the bars 274,274 in a plane normal to the axis of the pin 276 and having depending end portions 284,284 extending beyond the lower ends of the bars 274,274. As will be described below, the bar device 272 is free-floating in the tile supporting clip notches 256 and adjacent corner notches 260,260 of adjacent supporting clips 60.
The free-floating tile retaining clip 80 comprises a distal tile anchoring plate member 82, a stem or post 84 having one end secured substantially central of and to the rearward side of the plate member 82 and its other end to a proximal retaining member 86. The thickness or diameter of the stem 84 and the proximal retaining member 86 is such as to pass these components easily and freely between the bars 274,274 of the duplex bar device 272, and the length and width of the retaining member 86 are such as to clear without engagement the outer surfaces of the boiler tubes 18,18 next thereto adjacent, while great enough to engage the bars 274,274 when rotated into a plane normal to the axis of the bars.
The retaining member 86 is first presented to the duplex bar device 272 as illustrated in FIG. 7, the member being aligned with and in the plane of the open space between the bars 274,274 of the bar device 272, then inserted therebetween until the proximal retaining member 86 clears the back side of the device 272. When the distal plate portion 82 is rotated 90 so that the member 86 lies in a plane normal to the axis of the bars 274,274, the tile retaining clip 80 is engaged for tile retention (FIG. 8).
As will be seen more particularly in FIGS. 5 and 6, the tile retaining duplex bar device 272, which is preferably of a length sufficient to accommodate a plurality of horizontal courses 16 of tiles 14 between vertically spaced apart supporting clips 60 provided for each bank oftiles (FIG. 5), is first supported upon a superior supporting tile clip 60 in each notch 256 and adjacent corner notches 260,260, disposed between the boiler tubes 18,18, by the outwardly extending lateral end portions 280,280 of cross pin 276 which engage the plate portions 257,257 on either side of and adjacent the medial notch 256, or engage the lateral plate portion 259,259 adjacent the corner notches 260,260 of adjacent tile supporting clips 60.
Generally, more than one horizontal course of tiles is laid up in a bank. Since the dimensions of these tiles are approximately 12 inches high by about 3 inches wide, their width depending substantially upon the center to center relationship of the boiler tubes taken in horizontal section, several horizontal courses of tiles 14 can be supported upon the clips 60. The length of the bar device generally corresponds to the height of the bank 12 of tiles 14.
Once the duplex bar devices 272 are supported upon the superior clips 60, the tiles 14 are laid up upon the supporting clips in a horizontal course, and the freefloating tile retaining clips 80 for each tile are presented to the bar devices 272 as above described, inserted between the bars 274,274 and rotated for engagement therewith, the distal plate portions 82 being dropped into the transverse slot or groove 28 of the tiles as the post or stem portion 84 rests upon the tile proximal upper wall surface 34. After a full bank 12 of the tiles 14 has been laid up upon the clips 60 and retained by the clips 80 and the duplex bar device 272, the next superior bank of tiles is laid up upon the next superior supporting clips 60 (FIG. The tile retaining duplex bar devices 272 for the superior bank are now supported by pins 276 upon the next superior supporting clips 60 within the notches 256 and 260,260, and depend toward and substantially in alignment with the duplex bar devices 272 of the inferior laid up bank of tiles. The duplex bar devices 272 now line up by virtue of the spacer bar portions 284,284 which depend from the lower ends of the bar members 274,274, and these portions pass into the space between the bar members 274,274 and about each side of the pin medial web portion 278 at the upper end of the next inferior duplex bar device 272, to form a continuous aligned engaging duplex bar device for the free-floating clips 80. Each duplex bar device 272 is free-floating for its bank 12 of tiles 14, being suspended by the pin 276 from the next superior supporting clip 60.
It will of course be recognized that, although the boiler tubes 18 of the combination tubes 18a, the latter being the tubes 18 with their lateral flanges 79, are very closely adjacent each other, they are not in fact touching each other, the space therebetween being filled by the adjacent attached flanges 79,79, so that the boiler tubes 18 are slightly spaced apart from each other to permit some relative expansion and contraction movement ofthe tubes. Conductionof heat through the tube flanges 79 provides means for more rapid heat transmission and thermal equalization in the water wall, a stabilization factor that reduces the range of expansion and contraction movement.
Alternate Application of the Invention Although the heat shielding wall described above was designed and developed for the purpose of'deflecting heat generated by burner produced combustion gases into the upper superheat'and reheat'region of the boiler, there are instanceswhere the wall of tiles can be used to protect the lower regions of boiler tubes against direct burner generated flame impingement while absorbing the heat of the combustion gases to transmit them by conduction, radiation or convection directly to the lower regions of the boiler tubes where that is the desired or required purpose. Because direct flame impingement upon the boiler tubes, particularly in coilfired furnaces, can result in accelerated deterioration of the boiler tubes, it is most desirable to shield such tubes from direct flames. To effect this result, the tiles 14 can be made of a silicon carbide composition which is a very good ceramic heat conductor. Such tiles will absorb heat generated by the burners and at the same time protect the boiler tubes from direct flame impingement, thereby extending their useful life in the boiler unit.
The tiles l4 disclosed herein are preferably made of ceramic or equivalent materials according to conventional fire-brick manufacturing practice. The tile supporting clips 60 are preferably made of sheet stock stainless steel or equivalent alloys such as for example the No. 309 alloy, or they may be cast. The tile retaining clips 80 and the tile retaining duplex bar device 272 are preferably made of sheet, or sheet and rod, or bar stock, or cast stainless steel or equivalent alloys, such for example as the NO. -12 alloy. The selection of proper and suitable materials for the tiles, clips and duplex bar device will of course vary in some measure according to engineering preference and standards, and in view of particular boiler furnace and tube conditions and the firing equipment being used therein, such selection being well within the competence of persons skilled in the art and having the foregoing disclosure available to them.
It will be at once observed that the system of this invention, while providing a more satisfactory solution to the problems of heat distribution first above described, also permits a selective replacement, removal or repair of damaged tiles without in any way affecting adjacent portions of the shielding wall 10 not involved in such damage. Thus, the costs in labor and materials to repair any damaged portion of the shielding wall 10 is substantially and materially reduced, by comparison with present day practices referred to generally above. In
' addition, of course, the advantages of free-floating movement of the shielding wall 10 upon general or 10- calized expansion and contraction of the boiler tubes, varying from region to region in the boiler tube furnace and from portion to portion in the boiler tube, are of paramount importance and should contribute substantially to an improvement in the cost factor.
Although a certain particular embodiment of the invention is hereindisclosed for purposes of explanation, further modifications thereof, after study of this specification, may or will become apparent to those skilled in the art to which the invention pertains. Reference should be had to the appended claims in determining the scope of the invention.
1. In a wall of ceramic fire brick or tile to shield at least a portion of a water wall of substantially parallel closely adjacent but spaced apartboiler tubes, secured together to form an impenetrable water wall by lateral rib members affixed to saidboiler tubes and to each other, and extending vertically upwardly in and from the burner region of a boiler tu'be furnace area, from direct impingement 'of burner-produced flames and combustion gases upon the facing exposed surfaces of said boiler tubes, and to deflect a significant portion of the heat generated by said flanges and combustion gases into the superheat region of the boiler unit thereabove, the improvement combination comprising at least one pair of said parallel closely adjacent but spaced apart vertically extending boiler tubes, a plurality of shielding tiles for said boiler tubes, means to support said plurality of shielding tiles in substantially vertical files adjacent the said facing exposed surfaces of said boiler tubes, said support means being fixedly secured to said boiler tubes, and free-floating tile retaining means comprising a bar device manually removably engageable with said support means and a free-floating tile retaining clip manually removably engageable with an upper portion of each said tile in said files and with said bar device, to secure each said tile in shielding relationship to said boiler tubes, each of said tiles comprising a unitary ceramic body having a distal front face, lateral side walls,
a proximal rear face, and a top wall surface having a transverse slot therein, one of said side walls having a longitudinally extending rib portion and the other of said side walls having a longitudinally extending recess complementary to said rib portion, said rib portion and recess being aligned with each other transversely of said body, whereby said tiles are relatively free-floating with the expansion and contraction movements of said boiler tubes, and said rib portions and recesses of laterally adjacent tiles dovetail with each other when said tiles are arranged in parallel side-by-side relationship. 2. The structural combination defined in claim 1, wherein said means to support said plurality of shielding tiles comprises a plate portion disposed at an angle to the plane of said boiler tubes and fixedly secured to said boiler tubes, and a tile retaining portion at the distal edge of said plate portion to engage said tile resting upon said plate portion and retain the same thereon. 3. The structural combination defined in claim 2, wherein said plate portion is provided with a proximal edge substantially complementary to the facing exposed surfaces of said boiler tubes, portions of said proximal edge being welded to said boiler tube surfaces. 4. The structural combination defined in claim 2, wherein said plate and tile retaining portions comprise a unitary angle plate. 5. The structural combination defined in claim 3, wherein said boiler tubes are cylindrical and have convexly v curved outer facing surfaces extending axially of said tubes, and said plate portion proximal edge is provided with concavely arcuate portions complementary to said boiler tube convexly curved outer facing surfaces. 6. The structural combination defined in claim 5, wherein said arcuate edge portions are at least in part welded to said boiler tube surfaces. 7. The structural combination defined in claim 5, wherein said plate portion proximal edge is further provided with a notch in the web portion intermediate said concavely arcuate edge portions, and a notch at each corner of said proximal edge. 8. The structural combination defined in claim 7, wherein said tile support means further comprises a plurality of said plate portions arranged in horizontal alignment and secured to a plurality of pairs of said boiler tubes, said notches at adjacent corners of each plate portion proximal edge forming a combination notch substantially equal in width and depth to said web portion notch. 9. The structural combination defined in claim 2, wherein said distal tile retaining portion comprises an upstanding flange.
10. The structural combination defined in claim 1, wherein said tile ceramic body top wall surface transverse slot extends from one side wall to the other, said transverse slot being spaced from and extending substantially parallel to said distal front face. 11. The structural combination defined in claim 10, wherein said tile body further comprises a distal undercut bottom wall surface extending rearwardly to a depending proximal lower flange portion. 12. The structural combination defined in claim 10, wherein said proximal rear face comprises a pair of substantially adjacent longitudinally extending substantially parallel concavely curved wall surfaces, said concavely curved wall surfaces being spaced apart by a medial longitudinally extending web portion therebetween, said concavely curved wall surfaces having a transverse curvature substantially complementary to the adjacent portion of the outer facing surfaces of said boiler tubes. 13. The structural combination defined in claim 10, wherein said tile body further comprises a proximal upper flange portion extending rearwardly of said slot and being lower in height than said top wall surface. 14. The structural combination defined in claim 12, wherein said web portion intermediate said concavely curved wall surfaces is provided with a longitudinal slot extending the length of said proximal rear face. 15. The structural combination defined in claim 8, wherein said bar device comprises a pair of parallel bars, a pin securing said parallel bars in spaced apart relationship and fixedly positioned adjacent one end of said parallel bars, said pin having end portions extending laterally outwardly from said parallel bars at each side of said bar device, and a pair of spacer bars securing said parallel bars in spaced apart relationship and fixedly positioned at the opposite end of said parallel bars and therebetween. 16. The structural combination defined in claim 15, wherein said spacer bars lie in a plane normal to the axis of said pin, and in spaced apart relationship a distance substantially equal to and slightly greater than the diameter of said pin, said spacer bars extending longitudinally from and beyond the ends of said parallel bars. 17. The structural combination defined in claim 16, wherein said pin and said spacer bars secure said parallel bars in substantially parallel spaced apart relationship throughout their longitudinal extent. 18. The structural combination defined in claim 16, wherein each said bar device is longitudinally alignable and removably engageable with substantially identical bar devices upon inter-engagement of the spacer bars of a superior bar device with the intermediate web portion of the pin between said parallel bars of an inferior bar device. 19. The structural combination defined in claim 15, wherein each said bar device is engageable with and supportable from said support means plate portions by said pin end portions, said parallel bars extending through said medial plate portion notch or said combination notch at the proximal corners of adjacent plate portions.
21. The structural combination defined in claim 20,
wherein said stem and said bar device engaging member each have a cross-sectional thickness no greater than the free clear distance between said bar device parallel bars, said bar device engaging member having a transverse width substantially greater than such free clear distance between said bar device parallel bars, whereby the proximal portion of said stem and said bar device engaging member are insertable between said parallel bars and, upon rotation of said stem and bar device engaging member, said free-floating tile retaining means is engaged with said parallel bars.
22. The structural combination defined in claim 21, wherein said bar device engaging member is planar and, when rotated into engagement with said parallel bars, lies in a plane substantially normal to the axis of said bar device. 23. The structural combination defined in claim 1, wherein each said tile comprises a unitary ceramic body of silicon carbide.