US2931345A - Vapor generating units - Google Patents

Description

April 1960 A. E. RAYNOR ETAL 2,931,345

VAPOR GENERATING UNITS Filed March 26, 1957 7 h tsh 2 FIG. 2

I INVENTORS 24E Arrhur E. Raynor BY eorge W. Bouion ATTORNEY April 5, 1960 A. E. RAYNOR ETAL VAPOR GENERATING UNITS Filed March 26, 1957 FIG.3

7 Sheets-Sheet 3 Arrhur E'Raynor orge W. Bouron ATTORNEY April 5, 1960 A. E. RAYNOR ETAL 2,931,345

VAPOR GENERATING UNITS Filed March 26, 1957 7 Sheets-Sheet 4 FIG. 4

INVENTORS Arrhur E. Raynor BY George W. Boufon ATTORNEY April 5, 1960 Filed March 26, 1957 A. E. RAYNOR EI'AL VAPOR GENERATING UNITS 7 Sheets-Sheet 5 N INVENTORS Arthur E. Raynor urge W. BouTon WM ATTORNEY April 1960 A. E. RAYNOR ETAL I 9 2,931,345

VAPOR GENERATING UNITS Filed March 26, 1957 7 Sheets-Sheet 6 INVENTORS Arrhur E. Raynor BY orge W. Bouion AT TORNEY p i 1960 A. E. RAYNOR ETAL 2,931,345

VAPOR GENERATING mms 7 Sheets-Sheet '7 Filed March 26, 1957 (NNIK INVENTORS Arrhur E. Raynor BY eorge W. Bouion ATTORNEY United States Patent VAPOR GENERATING UNITS Arthur E, Raynor, Rockville Centre, N.Y., and George W. Bouton, Hohokus, NJ., assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Application March 26, 1957, Serial No. 648,573 12 Claims. (Cl. 122479) This invention relates to the construction and operation of vapor generating units, and more particularly, to a natural circulation high capacity high pressure steam generator designed for superheating and reheating steam to high temperatures, e.g. in the range of l0001l00 F., by the burning of a slag-forming solid fuel at mean furnace temperatures above the fuel ash fusion temperature in cyclone type furnaces.

The main object of the invention is the provision of a natural circulation type vapor generating unit of the character described in which such fuels can be efiiciently burned over a wide load range while removing a major portion of the ash or slag produced in a molten condition, and having substantially all of the vapor generating tubes of the unit arranged in the walls of the cyclone furnaces and in a communicating gas cooling section to provide a relatively large amount of radiant heat absorbing surface, which in conjunction with gas tempering provisions, will be suflicient to reduce the gas temperature at and above an intermediate point in said load range to a value at which the slag particles in suspension in the gases will be in a solidified condition when the gases enter a convection heating section of the unit in which the vapor superheating and reheating surface is located.

A further object of the invention is the provision of a vapor generating unit of the character described in which such fuel can be burned in a plurality of cyclone furnaces positioned at opposite sides of the unit, with the cyclone furnaces arranged, and the adjoining gas receiving section of the unit constructed, to produce a stable gas fiow distribution throughout the substantially open top of said adjoining section and at the entrance to the convection heating section.

A further object is an improved arrangement and location of gas tempering ports in the gas radiant cooling section of a unit of the character described by which effective gas tempering is obtainable with a reasonable number of gas tempering ports at all loads at which the slag particles reaching the convection section would be otherwise in a molten or sticky condition.

A further object is the provision in a vapor generating unit of the character described having a plurality of cyclone furnaces at opposite sides of a common gas receiving chamber, of a special arrangement of vapor generating tubes defining slag screens and a chamberdividing partition which permits equalization of gas pressure throughout the chamber and a stable distribution of heating gases even when cyclone furnaces on only one side are in service.

In the drawings:

Fig. 1 is a partly diagrammatic'sectional elevation of a specific embodiment of the instant invention;

Fig.2 is a vertical section view taken on line 22 of Fig. l; i

' Fig. 3 isfan enlarged view of the lower portion of the construction shown in Fig. 2;

Fig. 4 is an enlarged view of the upper portion of the construction shown in Fig. 2;

2.9 3134% Patented Apr. 5, 1960 ice Fig. 5 is a sectional plan view taken on line 5-5 of Fig. 2;

Fig. 6 is a sectional plan view taken on line 6-6 of Fig. 2;

Fig. 7 is a sectional plan view taken on line 7--7 of Fig. 2;

Fig. 8 is a detail sectional view taken on line 8-8 of Fig. 1; and

Fig. 9 is a schematic sectional plan-view taken along line 9-9 of Fig. 2.

In the drawings the invention is illustrated as embodied in a high capacity high pressure natural circulation type unit designed for central station use. The illustrated embodiment has a maximum continuous steam generating capacity of approximately 2,200,000 lbs. of steam per hour, a designed boiler pressure of 2,375 p.s.i., and a total steam temperature at the superheater outlet of approximately 1055 F. at a pressure of 2100 p.s.i. The instant unit also includes a steam reheater capable of producing reheat steam temperatures in the order of 1005" F.

The unit illustrated has a vertically elongated setting 20 having front, rear, and side walls 21, 22 and 23, respectively, defining a lower furnace and gas cooling section 24 and a superposed vertically extending heat absorbing section 25, both of rectangular horizontal crosssection. The lower setting section 24 includes a common gas mixing or primary radiation chamber 24A of substantially reduced rectangular cross-section formed by the lower portions of the setting side walls 23 and inwardly offset vertical portions of the front and rear walls 21 and 22 respectively. The lower chamber 24A is open throughout its upper end and connected by a transition section 24C formed by outwardly diverging portions 21A and 22A of the front and rear walls respectively to an upper radiation chamber 24B occupying the full crosssectional area of the setting.

A plurality of cyclone type furnaces 26 of the general construction disclosed in U.S. Patent 2,357,301 and adapted to be independently fired by relatively low quality, high ash content, coarsely pulverized or'granulated coal, are arranged to separately discharge hot gaseous products of combustion and molten slag into the common intervening chamber 24A. Each of the cyclone furnaces 26 is substantially of circular cross-sectional area having the barrel portion thereof defined by steam generating tubes 27, which with the front wall tubes 28, rear wall tubes 28A, and side wall tubes 29, constitute the steam generating surface of the unit. As shown in Fig. 5, five horizontally arranged laterally spaced cyclone furnaces 26 discharge through the front wall 21 of the chamber 24A and four similar cyclone furnaces 26 discharge through the rear wall 22, the cyclone furnaces in the two walls being in staggered relation. It has been found advantageous to arrange all of the cyclone furnaces so that their discharged gases are rotating towards the longitudinal center line of the chamber 24A. With an equal number of cyclone furnaces in both the front and rear walls, the cyclone furnaces may be either opposed or in staggered relation, but in either case, for optimum gas distribution, the cyclone furnaces are preferably arranged so as to have the gas streams discharged from all of the furnaces rotating in the same direction when viewed by an observer from within the chamber 24A and successively facing each row of discharge throats.

- Three slag discharge openings 24D are symmetrically transverse header 30.

With the steam generating section of the unit constituted by the relatively large number of cyclone furnace wall and riser tubes and the tubes lining the wallsofthe setting 2%, there are difficult problems in locating the riser 'or upflow portions of the natural circulation circuits within the setting; As shown in Fig.1, a transverse steam and water drum 40 is arranged at the top of the unit to receive the steam and water mixtures discharged by the steam generating section tubes. The tubes 27 defining the circumferential wall ofeach cyclone furnace are connected at their upper ends to a longitudinal header 26A from which riser tubes 27A extend upwardly externally of the setting until reaching the bottom level of the upper radiation chamber- 2413', at which point the risers from the two rows of cyclone furnaces extend through the Figs. 3 and 6, into a single transverse row defining the partition 35C which is normal to the planes of the slag screen platens. Each of the sidewalls 23 of the setting extends in a single vertical plane and is lined with 'vertically extending steam generating tubes 29 connected to front and rear walls and thence upwardly along those walls to the transverse headers 3 1,and 34' respectively, at the topof the unit. The headers 31'and 34 are connected as shown in Figure l to the drum '40. The tube rows defining the front and rear walls of the lower radiation chamber 24A have their lower ends connected to a bottom The tubes 28 extend across the floor 32 of the chamber 24A, and then upwardly to define the inner end walls and re-entrant throats of the front Wall cyclone furnaces. The tubes 28A extend directly upward to define the inner end walls and throats of the rear wall cyclone furnaces. Half of these tubes 28 and 28A continue upwardly along the diverging wall portions 21A, 22A. Adjacent pairs of tubes are connected by inverted Y-fittings, and theconjoined tubes then continue along the front and rear walls 21, 22 of the chamber 24B and convection section 25 to the headers-31, 3-1- respectively. The wall 'spacesb'etw'een the spaced upper portions of the tubes 28, 28Aare'occupied by the cyclone furnace riser tubes 27A.

As shown in Figs. 1 and 5', the remaining tubes 28 and 28A are bent'in groups laterally and thence inwardly and upwardly to 'form oppositely arranged L-shaped platens 315 spaced transversely of the chamber 24A (e.g. on 3' centers) from a level intermediate the height thereof to 'a level corresponding to the upper end of the transition section 240. As shown in Fig. 8, the lower inclined legs A of the tube platens are covered with studs and refractory material to form solid members converging upwardly in the same vertical plane from the front and rear Walls of the chamber 24A. These transversely spaced refractory covered inclined tube platens form a slag screen across the path of the slag-carrying gases flowing upwardly from the oppositely arranged cyclone vection heating section of th'e unit. As shown in Fig; 2,

the tubes forming the'partitionSSC are spaced apart at' transversely. spaced intervals to 'form verticallyelon'gated narrow pressure-equalizing slots 38 in the-partition. The

partition slots 33, as well as the spaces between the L- shaped'tube platens, 35, insure uniform gas pressures throughout the ems-sectional "areas of thetransition section and upper radiation chamber and contribute to maintaininga stable gas distribution pattern therein regardless of the number of cyclone furnaces being fired or their particular location. j

Thus the front and rear walls of the lower radiation lower and upper side wall headers 42 and 43 respectively which are supplied by the cross header 30." The side wall tubes 29, front and rear wall tubes 28, 28A respectively, in the area of the lower radiation chamber 24A up to the slag screen level are provided with studs and refractory, while the wall tube segments disposed thereabove are left bare.

The vapor generating tubes defining the front, rear and, side walls and partition are connected into a natural circulation circuit separate from the circuit including the cyclone furnace wall and riser tubes. This is accom-v plished by connecting the ring header 44 circumscribing the lower portion of the setting and the cross header 30 independently and separately to the steam and water drum by separate pairs of downcom'ers. Accordingly, a inrality of downcomcrs are longitudinallyspaced along the drum so that the outermost pair, 45 connects the drum 40 to the ring header 44 and the innermost pair 46 connects the drum 40 to the cross header 30. The ring header 44 in turn sup lies the wall tubes of the cyclone furnaces by "means ofsupply tubes 47, while the cross header 3i) supplies the front, rear, and side wall and the partition tubes. With this arrangement the flow resis'tances in the'sepa'rate circuits are substantially balanced providing optimum fiuid =fiow conditions in the" steam generating'tubes.

The tubes forming the partition 35C continue upwardly in the setting and are bent out of the plane of the partition into two side-by-side rows of spaced tube portions 52, as shown in Figs. 1 and 6, to permit the passage be tween'the tubes of superheater and reheater tubes, as hereinafter described. Above this level the tubes are bent back into a single tube-to-tube contacting row and connected at their upper ends to a header 39, which in turn is connected by riser tubes 41 to the drum 40. This-tube arrangement divides the convection heating section 2'5 of the unit into parallel gas flow passages 36 and 37. An

, L-shaped partition 71 provides a lateral continuation of the passages to a lateral gas' exit 62, with dampers 68 and 69 at the end of the passages arranged to proportion the gas flow therethrough. V I

A pair of economizer tube sections 48 are arranged in parallel in the upper ends of the gas passes 36, 37 for are bent into a single row of aligned tubes to form a a transverse vertical partition 35C extending from the upper end of the tube platens 353 to the bottom of the con-' bank 49A and a reheater tube. bank 50A,, both. newbies supplying feed water to the drum 40. In the portion of the convection heating section 25 below the economizers 48. there are located several sections A, B, C, of superposed steam superheating tube banks. Each tube bank is made up of a piurality of nested return bend tube rows, the transverse spacing between the tubes being progressively decreased in each ascending tube bank.

' The uppermost section A includes a group of rimarysuperheater tube banksv49' in gas pass 36 and a group of steam rehe'ater tube banks 50 disposed in pass 37. The primary superheater and. reheater tubes 49 and, 50 in the upper section A are. preferably 2%" QDftubes on 4 /2" centers. The next intermediate section B of the gas passes includes an additional. primary superheater are formed by 2%" OD. tubes on '9" centers. Travers- 7 ing the full depth of the setting is a primary superheater 5., tube bank 493 extending between the partition tubes. The tubes 4913 making up this portion of the primary superheater constitute a plurality of transversely extend ing return bend tube rows of 2%" OD. tubes on 9" centers.

The lowermost section C consists of a plurality of superposed secondary superheater tube banks 51. The tube banks 51 extend across the full depth of the setting and the tube rows thereof are formed by 2%" OD. tubes on 27" centers. The secondary superheater tubes 51 and the primary superheater tube 493 are arranged in the spaces 52 formed by the offset adjacent tubes in the partition 35C, the intermediate portions of the horizontally extending tubes 49B and 51 being supported therebetween in a manner similar to that disclosed in a co-pending application of L. M. Fink et al., Serial No. 666,657, filed June 19, 1957. In operation the steam separated in the steam and water drum 40 is directed through a steam conduit 53 to a primary superheater inlet header 54. From the inlet header 54 the steam flows serially through the primary superheater banks 49, 49A, 498 to an outlet header 55, i.e. in counter tlow heat transfer relation to the gas flow. From the outlet header 55 the stream flows through a conduit 56 and suitable spray attemperator 57 to the secondary superheater inlet header 58. In the secondary superheater the steam is heated to its final temperature, e.g. 1055 F., at the outlet header 59, the steam flow being generally parallel to the gas flow.

The steam to be reheated flows from the inlet header 60 downwardly through the tube banks 50 and 50A in counter flow heat transfer relation to the gas fiow, to the reheater outlet headers 61.

In accordance with the invention, provisions are made for variably introducing relatively cool gases into the fresh gaseous products of combustion at positions relative to the cyclone furnaces and slag screen platens and in a manner providing an effective intimate mixing of the recirculated gas with the fresh combustion gases from the cyclone furnaces to reduce the temperature thereof to a desired value at which the gases, after passing through the upper radiant chamber and on reaching the convection heating section, will have a temperature below the fuel ash softening temperature, so that any suspended slag particles will then be in a solidified condition. For this purpose gas is withdrawn by a controllable recirculating gas fan (not shown) from the gas exit fiue 63 leading to an air heater 70 through a duct 63A. The gases are delivered by the fan through a duct controlled by a damper 67 to a distributing manifold 64 extending along the front Wall of the setting at a level between the lower ends of the slag screen platens 35 and the lower end of the transition section 24C. A plurality of spaced gas inlet ports or nozzles 65 in each of the front and rear walls are provided for introducing into the setting the recirculated gases delivered to the manifold 64, Side wall ducts 66 connect the front wall manifold 64 to a similar manifold 64A extending along the rear wall of the setting. As diagrammatically indicated in Fig. 9, each of the front and rear walls and corresponding manifolds have vertically elongated gas inlet ports, e.g. 6%" x 3 6", constructed therein, with the vertical center line of each port in the same vertical plane as the longitudinal axis of a corresponding cyclone furnace at the opposite side of the unit. Accordingly the front wall 21 is provided with four gas inlet ports 65, each above the level, but whose vertical center line is in line with the longitudinal axis, of a corresponding cyclone furnace 26 discharging through the rear wall. The rear wall 22 is similarly provided with five recirculating gas inlet ports 65 having a similar arrangement relative to the five cyclone furnaces 26 of the front wall.

With this arrangement the main stream'of gaseous products of combustion flowing upwardly from each cyclone furnace in the chamber 24A will be impacted by a horizontally directed relatively high velocity stream at low temperature gas from the opposite side of the furnace, the open formation of the L-shaped platens 35 at the level of the recirculating gas inlets permitting the recirculated gas streams to mix with the rising gases either between the vertical legs 353 or above the inclined legs 35A of the platens. This intimate mixing of the streams of high temperature slag-carrying gases and tempering recirculated gas adjacent but above the slag screen platens causes a rapid decrease in gas temperature as the gases reach the bare tube wall portions of the setting. The turbulent gas conditions resulting in the spaces be-. tween the vertical tube platens also facilitates the separation of slag particles at this level. The unit is designed to attain the desired superheat and reheat conditions at approximately 85% of full load without gas recirculation. To insure the desired slag conditions however the unit is desirably operated in the range of -100% load with 20% gas recirculation. In the 80-85% range the increased heat content of the gases clue to such gas recirculation results in some increase in superheat and reheat temperatures. The final control of these temperatures is effected by the operation of the steam attemperator 57 and proportioning dampers 68, 69.

Combustion air for the cyclone furnaces is supplied by means of a forced draft fan (not shown) through the air heater 70 connected to individual air supply ducts (not shown) supplying each of the cyclones. Relatively low quality high ash content slag-producing fuel can be efficiently burned while at the same time permitting the slag to be tapped in molten form at minimum load conditions. In operation relatively low quality coarse or crushed coal is independently and controllably delivered to the separate furnaces and burned in a helical flame path therein under normal mean temperatures above the fuel ash fusion temperature. The fuel ash separates as molten slag from the combustion gases, depositing on the walls thereof and flowing along the bottom of each cyclone furnace to discharge into the lower radiation chamber 24A, from which it is discharged through slag openings 24D into the slag tanks 24E. The gaseous products of combustion discharge through the gas outlet throats of the individual cyclone furnaces and into the unobstructed lower chamber 24A. The spacing between the front and rear wall 21, 22 of the lower chamber 24A is sufficiently wide so as to prevent the combustion products issuing from the individual cyclone furnaces on one side of the chamber from carrying over into anyof the cyclone furnaces in the opposite wall which may be out of operation, but narrow enough to cause efiec tive mixing of the gas streams from opposite sides.

The refractory lining of the walls of the chamber 24A and slag screen platens 35A and location of the cyclone furnaces relative to the floor 32 jointly contribute to maintaining the slag reaching the floor 32 in a molten condition.

Another significant advantage is in the positioning of the screen 35 immediately ahead of the gas tempering ports 65. By positioning the slag screen below the gas ports 65, the slag screen portion 35A is not subjected to the cooling effect of the tempering gases. Also because the slag screen 35A is covered by refractory and is positioned in a high temperature zone, the screen portion 35A tends to produce a hot spot on which the slag is collected in a molten and flowable state. The inclination-of the screen 35A causes any slag accumulating thereon to flow therealong and down the walls of chamber 24A. A sub stantial percentage of the entrained molten particles of slag suspended in the upfiowing gases are thus collected on the screen and subsequently returned to the chamber while still in a flowable condition. As a result any tendency of the entrained slag particles to stick or plug the gas ports downstream of the slag screen is substantially eliminated.

As the upper radiant chamber is relatively large in tubes in addition to the partition of steam generating tubes disposed therebetween, the upwardly flowing gases become further cooled by radiant heat transmission to these tubes. Thus any slag particles entrained in the upwardl'y flowing gases will be solidified within the upper chamber. 24B and carried out of the unit.

- The introduction of the recirculated gases into the gas cooling chamber 24 between 'the transition section 240 and the screen platens 35A further enables the tempering gas and upwardly flowing combustion gas to be readily mixed due to the subsequent expansion thereof as the gases fiow upwardly through the transition section 24C. As result the gas exits from the upper chamber 243 and enters into the convection passes as a substantially uniform mixture and at a controlled temperature depending upon the rate of gas recirculation. The screen platens 35 are suificiently spaced so as to materially contribute to the mixing of the gases in the transition section 240. The gases leaving the chamber 24B at a predetermined temperature pass into the convection section 25 and over the widely spaced secondary superheater tubes 51. The

' gases continue their upward flow passing over the priinary superheater bank 49B. Thereabove the upwardly flowing gas stream is divided into a pair of parallel streams, flowing through the respective convection passes 36, 37 and simultaneously transmits heat to the reheater 50, 50A and primary superheater 49, 49A disposed in the respective passes.

Certain novel structural features disclosed herein are disclosed and claimed in said application of L. M. Fink ct aLSerial No. 666,657, filed June 19, 1957.

While the instant invention has been disclosed with reference to a particular embodiment thereof, it is to be, appreciated that the invention is not to be taken as limited to. all of the details thereof as modifications and variations thereof may be made without departing from the, spirit or scopeof the invention.

We claim: 7

1. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its open end, a superposed intermediate radiation chamber forming a transition section, and an upper radiation chamber connected for gas flow serially therethrough, the lower portions of said front and rear walls defining said upper radiation chamber having downwardlyzconvergingrportions defining said transition section and inwardly offset vertical portions defining said lower radiation chamber so that said lower radiation chamber hasa cross-sectional area which is less than that of said 7 8' 1y converging portions defining said tion chamber so that said lower radiationrchamber has a cross-sectional area which is less than that of said upper radiation chamber, vertically extending vapor generating tubes lining said walls, a plurality of cyclone furnaces for burning a slag-forming solid fuel at temperatures above the fuel ash fusion temperature and discharging slag-carrying gases through the front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the from. and rear walls-of said lower radiation chamber being bent inwardly and upwardly, said inwardly and upwardly bent tubes forming groups of laterally displaced tubes to define oppositely inclined tube platens extending upwardly into saidtransition section at spaced intervals transversely of said setting, said platens converging upwardly to form a partition in said upper radiation chamber, and means for introducing tempering gas through the front and rear walls of said lower radiation chamber at a level above the lower ends of said platens and below said diverging transition section.

3. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber'having a gas outlet throughout its open end, a superposed intermediate radia-,

burning a slag-forming solid fuel at temperatures above r the fuel ash fusion temperature and discharging slag carrying gases through the front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly, said inwardly and upwardly bent tubes forming groups of laterally displaced tubes to define oppositely arranged upper radiation chamber, vertically extending vapor gencrating tubes lining said walls, means for burning a slagforming solid fuel at temperatures above the fuel ash fusion temperature and discharging slag-carrying gases through the front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly andupwardly, said inwardly and upwardlyfbent tubes forming groups of laterally displaced tubes to define oppositelyinclined' tube platens converging upwardly in the upper part of said lower radiation chamber at spaced intervals transversely of said setting, and means for introducing tempering, gasthrough the front and rear walls of said lower radiation chamber at a level above the lower ends of said tube platens and below said diverging transition section.

7 2.1 1 vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout iisope'n end, ;a superposedintermediate radiachamber :formin'ga transition section, and an upp r I radition chamber connected for gas flow serially there-g through, the lower portions of said front and rear walls defining said upper radiation chamber having downward L-shaped tube platens extending upwardly into said transi-, tion section, the tubes of said platens then converging upwardly to form a partition in a plane normal to :said tube platens in said upper radiation chamber, and means: for introducing low temperature gases through the front and rear walls of said lower radiant chamber at a level above the lower endsof said L shaped tube platens and below said diverging transition section.

4.'A vapor generating and superheating unit compris ing vertical front, rearjand side walls defining a setting enclosing a lower radiation chamber having a gas outlet "throughout its open end, a superposed intermediate .radia:

tion chamber forming a transition section; and an upper radiation chamber, the lower portions of said front and rear walls defining said upper radiation chamber having downwardly converging portions defining said transition section and inwardly offset vertical portions defining said lower radiation chamber so that said lower radiation chamber has a cross-sectional area which is less than that of said upper radiation chamber, vertically extending vaporgeneratin-g tubes lining said walls, meansifor burning .a slag-forming solid fuel at temperatures "above the fuel ash fusion temperature and "discharging slag carrying gases through the front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly, said inwardly and upwardly bent tubes forming groups of laterally displaced tubes to define oppositely arranged L-s'haped tube platens extending upwardly transition'seetion and; inwardly offset vertical portions defining said lower radia-' having spaced pressure equalizing openings thereim'and leans for introducing low temperature heating gases through the front and rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section.

5. A Vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its open end, a superposed intermediate radiation chamber forming a transition section, and an upper radiation chamber, the lower portions of said front and rear walls defining said upper radiation chamber having downwardly converging portions defining said transition section and inwardly offset vertical portions defining said lower radiation chamber so that said lower radiation chamber has a cross-sectional area which is less than that of said upper radiation chamber, vertically extending vapor generating tubes lining said walls, a plurality of cyclone furnaces burning a slag-forming solid fuel at temperatures above the fuel ash fusion temperature and discharging slag-carrying gases through the front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly, said inwardly and upwardly bent tubes forming groups of laterally displaced tubes to define oppositely arranged L-shaped tube platens extending upwardly into said transition section at spaced intervals transversely of said setting, the tubes of said platens converging to form a partition in said upper radiation chamber in a plane normal to said tube platens, and means comprising wall inlets having their vertical center lines in the same vertical planes'as the longitudinal axis of said cyclone furnaces in the opposite wall for introducing low temperature heating gases through the front and rear walls of said lower radiation cham ber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section.

6. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section receiving heating gases from said subjacent lower radiation chamber and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower portions of said front and rear walls having downwardly converging portions defining the front and rear walls of said subjacent transition section and inwardly offset vertical portions defining the front and rear walls of said lower radiation chamber, vertically extending vapor generating tubes lining all of said walls, means for burning a slag-forming solid fuel at temperatures above the fuel ash fusion temperature comprising a plurality of cyclone furnaces arranged to discharge slag-carrying gases through the front and rear walls of said lower radiation chamber, a slag discharge opening in said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly to define oppositely arranged laterally spaced L-shaped tube platens extending inwardly in vertical planes and projecting into said transition section to a level approximating the'upper end of said section and a partition in said upper radiation chamber in a plane normal to the planes of said tube platens, the tubes defining said partition being arranged to form spaced pressure-equalizing openings, refractory material covering the lower oppositely inclined legs of said platen tubes to form a slag screen, and means for introducing low temperature heating gases through the front and rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section. i

it) I 7. A vapor generating and superheating unit compris' ing vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section receiving heating gases from said subjacent lower radiation chamber and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower portions of said front and rear walls having downwardly converging portions defining the front and rear walls of said subjacent transition section and inwardly offset vertical portions defining the front and rear walls of said lower radiation chamber, vertically extending vapor generating tubes lining all of said walls, means for burning a slag-forming solid fuel at temperatures above the fuel ash fusion temperature comprising a plurality of cyclone furnaces arranged to discharge slag-carrying gases through the front and rear walls of said lower radiation chamber, a slag dis charge opening in said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly to define oppositely arranged laterally spaced L-shaped tube platens extending inwardly in vertical planes and projecting into said transition section to a level approximating the upper end of said section and a partition in said upper radiation chamber in a plane normal to the planes of said tube platens, the tubes defining said partition being arranged to form spaced pressure-equalizing openings, refractory material covering the lower oppositely inclined legs of said platen tubes to form a slag screen, and means for introducing low temperature heating gases through the frontand rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section comprising vertically elongated wall inlets having their vertical center lines in the same vertical planes as the longitudinal axis of cyclone furnaces in the opposite wall.

8. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section receiving heating gases from said subjacent lower radiation chamber and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower portions of said'front and rear walls having downwardly converging portions defining the front and rear walls of said subjacent transition section and inwardly offset vertical portions defining the front and rear walls of said lower radiation chamber, vertically extending vapor generating tubes lining all of said walls, means for burning a-slag-forming soli fuel at temperatures above the fuel ash fusion temperature comprising a plurality of cyclone furnaces arranged to discharge slag-carrying gases through the front and rear walls of said lower radiation chamber, a slag discharge opening in said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly to define oppositely arranged laterally spaced L-shaped .tube' platens extending inwardly in vertical planes and projecting into said transition section to a level approximating the upper end of said section and a partition in said upper radiation chamber in a plane normal to the planes of said tube platens, the tubes defining said partition being arranged to form spaced pressure-equalizing openings, means for introducing low temperature heating gases through the front and rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section comprising vertically elongated wall inlets having their vertical center lines "in the'sarne veri tical planes. asthc. longitudinal axis of cyclone furnaces V in the opposite, wall, a convection fluid heating section in superposed relation to said upper radiation chamber, and means for withdrawing heating gas after passing through said convection heating section and recirculating said gas to said gas introducing means.

9. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section receiving heating gases from said subjacent lower radiation chambe: and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower portions of said front and rear walls having downwardly converging portions defining the front and rear walls of'said subjacent transition section and inwardly offset vertical portions defining the front and rear walls of said lower radiation chamber, vertically extending vapor generating tubes l ning all of saidwalls, means for burning a slag-forming solid fuel at temperature above the fuel ash fusion temperature and arranged to discharge slag-cart lng gases through the front and rear walls :of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of s id lower radiation chamber being bent inwardly and upwardly to define oppositely arranged laterally spaced L-shaped tube platens'extending inwardly in vertical planes and projecting into said transition section to alevel approximating the upper end of said section and a partition in said upper radiation chamber in'a plane normal to the planes of said tube platens, the tubes defining said partition being arranged to form spaced pressure-equalizing openings, refractory material covering the lower oppositely inclined legs or" said platen tubes to form a slag screen, means for in troducing low temperature heating gases through the front and rear 'walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section'ya convection fluid heating section in superposed relation to said upper radiation chamber, and means for withdrawing heating gas after passing through said convection heating section and recirculating said gas to said gas intr'oducing means.

1 0. A vapor generating and superheating unit comprising vertical front, rear and side walls defining a setting enclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section Ieceiving heating gases from said subjacentlower radi ation chamber and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower, portions of said front and rear walls having downwardly converging portions defining the front and .rear walls of said ,subjacent transition section and inwardly offset vertical portions definingthe front and rear walls of said lower radiation chamber, vertically extendingvapor generating tubes lining all of said walls, means for burning a slag-forming soiid fuel at temperature comprising a plurality of cyclone furnaces arranged to discharge slag-carrying gases through the -ront and rear walls of said lower radiation chamber, a slag discharge opening in said lower radiation chamber, some of the vapor generating tubes liningthe front and rear walls of said lower radiation chamber being bent inwardly and upwardly to define oppositely arranged laterally "spaced L-shaped tube platens extending inwardly vertical planes and projecting .into said transition section to a level approximating the upper end of SBidiSCCIlOfl-Bild .apartitionin said upper radiation chamher in a plane normal to the planes of said tube platens, tubes defining said partition being arranged to form spaced pressure-equalizing openings, refractory material temperatures above the fuel ash fusion covering the lower oppositely inclined legs of said platen tubes to form a slag creen, means for introducing low temperature heating gases through the front and rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and below said diverging transition section comprising vertically elongated Wall inlets having their vertical center lines in the same vertical planes as the longitudinal axes of cyclone furnaces in the opposite wall, a convection fluid heating section in superposed relation to said upper radiation chamber, and means for withdrawing heating gas after passing through said onvect on heating section and recirculating said gas to said gas introducing means 11. In a vapor generating and superheating unit, a setting having front, rear and side walls of closely spaced vapor generating tubes defining a radiation section including a lower radiation chamber open throughout its upper end, a connected superposed upwardly diverging transition chamber, and an upper radiation chamber connected thereto, and a superposed heat absorbing section having vapor heating means disposed therein, fuel burning means disposed in opposite walls of said radiationchamber wherein the hot gaseous products of combustion generated by said opposed fuel burning means are discharged directly into the lower radiation chamber common to said opposed fuel burning means, gas recirculation means for withdrawing lower temperature gases after transfer of heat therefrom to said vapor heating'means and recycling the same through the radiation section, said recirculation means including gas discharge ports disposed in the walls ofthe setting downstream of said fuel burning means and below the transition chamher, and a portion of said front and rear wall tube being inwardly bent to form a screen between said'gas ports and fuel burning means, the tubes of said screen being laterally offset to form tube platens at spaced intervals transversely of said setting. 7

12. A vapor generating and 'superheating unit comprising vertical front, rear and side walls defining a settingenclosing a lower radiation chamber having a gas outlet throughout its upper end, a superposed intermediate radiation chamber forming a transition section receiving heating gases from said subjacent lower radiation chamber and open throughout its upper end, and a superposed upper radiation chamber receiving heating gases from said transition section, the lower portions of said front and rear walls having'downwardly converging portions defining the front and rear Walls of said subjacent transition section and inwardly offset vertical portions defining the front and rear walls of said lower radiation chamber having a gas outlet throughout its open end, vertically extending vapor generating tubes lim'gg all of said walls, fuel burning means arranged to discharge combustion gases through the. front and rear walls of said lower radiation chamber, some of the vapor generating tubes lining the front and rear walls of said lower radiation chamber being bent inwardly and upwardly, said inwardly and upwardly bent tubes forming groups of laterally displaced tubes to define oppositely arranged laterally spaced'L-shaped tube platens extending inwardly in vertical planes and projecting into said transition section to a level approximating the upper end of said section and apartition in said upper radiation chamher in a plane normal to the planes of said tube platens, the tubes defining said partition being arranged to form spaced pressure-equalizing openings, refractory material hovering the lower oppositely inclined legs of said platen tubes to form a slag screen, and means for introducing low temperature heating gases through the front and rear walls of said lower radiation chamber at a level above the lower ends of said L-shaped tube platens and 'be'low'said diverging'transition section.

(References on following page) References Cited in the file of this pate UNITED STATES PATENTS Rowand et ai Mar. 13, 1956 Sifrin May 29, 1956 5 Lotz June 5, 1956 Junkennann Dec. 18, 1956 '14 5 Armacost et a1. Feb. 19, 1957 Chan et a1. July 23, 1957 FOREIGN PATENTS France Dec. 22, 1956 Italy Mar. 27, 1954

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