US2884909A

US2884909A - Vapor generating and superheating unit having multiple entry of returned heating gases

Info

Publication number: US2884909A
Application number: US278872A
Authority: US
Inventors: Paul H Koch
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1952-03-27
Filing date: 1952-03-27
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

May 5, 1959 P. H. KOCH 2,

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES Filed March 2'7, 1952 4 Sheets-Sheet 1 IN V EN TOR.

7 FIG-1 BY Jazz/fife]:

ATTORNEY P. H. KOCH May 5, 1959 2,884,909 VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES 4 SheetsSheec 2 Filed March 2'7. 1952 www I In I I INVENTOR, azzi L h ATTORNEY y 5, 1959 P. H KOCH 2,884,909

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES Filed March 27, 1952 4 Sheets-Sheet 3 FIGS IN VEN TOR.

F l s. 5

ATTORNEY y 5, 1959 P. H. KOCH 2,884,909

VAPOR GENERATING AND SUPERHEATING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES Filed March 27, 1952 4 Sheets-Sheet 4 INVENTOR.

BY 6 z ATTORNEY United States Patent VAPOR GENERATING SUPERHEAT- ING UNIT HAVING MULTIPLE ENTRY OF RETURNED HEATING GASES Paul H. Koch, Bernardsville, N.J., assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Application March 27, 1952, Serial No. 278,872 13 Claims. (Cl. 122-478) This invention relates to improvements in combined vapor generating and superheating units.

The invention is more particularly concerned with the vapor generating and superheating units which are utilized to supply high pressure and highly superheated vapor to prime movers, in central power stations and methods of operating such units. The overall efiiciency of such installations is, of course, of paramount importance, and it is recognized that the employment of high pressure vapor at the highest optimum temperature promotes such efliciency. When it is desired to maintain high superheat it is necessary to dispose the tubular elements of the superheater at a position at which the heating gas is of high heat content and temperature. This is particularly true when a predetermined superheat is to be maintained over a wide load range including very low loads. A problem in the attainment of the optimum high superheat arises in connection with the burning of slag forming fuel. When the pertinent superheater elements are disposed in a high temperature zone to attain the optimum high superheat, the superheater elements accumulate slag coatings which reduce the heat absorption rates of the superheater elements. Hence, the slagging of the superheated tubes must be controlled from the standpoint of attaining optimum high superheat.

This invention involves heating gas recirculation which is utilized for gas tempering for slag control under some conditions.

.In a more specific sense, the invention involves fuel burning means exemplified by a cyclone furnace construction burning a slag forming fuel at temperatures above the slag fusion temperature, and the disposition of at least parts of superheater platens in the path of the combustion products and at such a position that the pertinent superheater parts are, at times, contacted by slag particles in such condition with respect to fusion that these particles accumulate upon the pertinent superheater parts. In a preferred embodiment of the invention the superheater elements are arranged as pendent sup'erheater platens disposed within a vertically elongated secondary funnace chamber receiving the combustion products from a cyclone furnace arrangement burning crushed coal at temperatures above the ash or slag fusion temperatures of the coal. Parts of the dependent superheater platens are disposed in a part of the secondary furnace chamber receiving combustion products including high temperature heating gases with particles of fused slag suspended therein. In this arrangement; there is a recirculated furnace gas system including fan and ductw'orlc' having its inlet downstream gas-flowwise with respect to the superheat'er and having its tempering gas outlet ingas" mixing cornmunication with the secondary furnace chamber at a position upstream of the superheater.

This recirculated gas system also has a recirculated gas outlet incommunication with the primary furnace chamber of' the cyclonefurnace arrangement and associated with gas flow controls to the end that the'flow of recirculated gas to the primary furnace chamber may be in- 2,884,909 Patented May 5, 1959 creased as the load decreases. In this manner, the optimum high superheat is maintained by decreasing the ratio of furnace absorbed heat to the total heat absorbed in superheating the vapor. Such action includes an increase in the proportion of the heat of the fuel in the gases carried to the superheater.

Due to concurrent increase in heat content of the gases entering the superheater, and due to the increase in gas mass flow over the convection superheater, the overall Vapor heating is increased.

To control slagging conditions over the superhcater, the invention also involves means for returning the heating gases from a point downstream gas-flowwise of the superheater and causing the entry of those gases as tempering gases into the secondary furnace chamber at a position upstream of the superheater. The invention involves variation of the rate of flow of such tempering gases in accordance with changing slagging conditions involved 'in changing load or changing fuel, as well as changing superheat and reheat requirements.

In a vapor generating and superheating unit of the pertinent type, where the superheating is accomplished by the combination of a predominantly radiant superheater and a predominantly convection superheater, and where the reheater is a predominantly convection heater adjacent the convection superheater, the use of returned furnace gases as tempering gases to effect a lowering of the gas temperature to the radiant superheater while maintaining the heat content, is effective in reducing the otherwise inherent divergence of reheater and superheater temperatures, with reducing load. This is particularly true where the convection re'heater and the superheate'r section are arranged in series as to gas flow at a position downstream of the radiant superheater.

The type of unit involved in the invention is one in which substantially all of the vapor is generated in tubes defining or constituting parts of the walls and other boundaries of the furnace chambers and the cyclones burning the slag forming fuel. Advantageously, the heating gases are returned from a position downstream gasfiowwise of the superheater to a zone adjacent the top of the primary furnace chamber and also adjacent a pos tion through a wall of the secondary furnace chamber ahead of or below the superheater platens. In this zone the outlet of the system for returning furnace gases may be considered as having a tempering gas chamber adapted to be placed in communication with the secondary furnace, and a recirculating gas chamber adapted to be placed in controlled communication with the upper part of the primary furnace chamber. Gas flow control devices are associated therewith to control and vary the flow of returned heating gases to either one orboth of these chambers. In addition, the communication between the tempering gas chamber and the secondary furnace chamber takes place through a plurality of openings distributed along the wall of the furnace gas chamber, and in these openings there are disposed multiple louver gas flow control devices which are independently adjustable and therefore adapted to direct the incoming tempering gases transversely of gas flow in the secondary furnace chamber and at different angles in order that adequate mixing of the tempering gases with the other gases may be attained.

The invention also contemplates the use of an automatic control system for maintaining a predetermined superheatover a wide load range. It contemplates the control or variation of tempering gas flow from indications related to furnace gas temperature or from load, subject to possible modification by control elements resp'onsive to final vapor temperatures and/or responsive to intermediate vapor temperature at the attemperat'or,

disposed between a predominately convectional primary superheater and the predominately radiant secondary superheater.

The invention also contemplates control of vapor generation over a wide load range, in accordance with vapor demand and the variation and control of the flow of recirculating gas to the primary furnace chamber from representations of steam flow-airflow, vapor temperatures, and the characteristics of the devices for directly controlling the recirculated gas flow. The automatic control system contemplated by the invention is of the nature of that disclosed in the pending patent application of W. H. Rowand, Serial No. 250,268, filed October 8, 1951, now Patent No. 2,840,054 issued June 24, 1958, for Power Generating and Superheating Method and Apparatus Therefor.

The invention contemplates the described units and their methods of control which may render it advantageous to continue (in regulated degrees) the introduction and mixing of tempering gas over a major part of the entire load range. Such wide range use of tempering gas flow has been found to be advantageous in increasing the availability of the unit by reason of beneficial effect upon slagging conditions. One such beneficial effect resides in what may be termed the cumulative effect of the tempering gas flow upon slag accumulations resulting from the continuance of such flow even after and beyond the periods during which the gas temperatures in front of the superheater are such as would not maintain slag particles in such condition that they would accumulate.

Such continued flow might be said to have a cumulative mechanical effect in dislodging slag accumulations which had previously been deposited.

Advantageous regulation of vapor heating may be effected by the simultaneous entry and control of recirculating gas flow and tempering gas flow, the former introduced at a position within a water-cooled furnace, remote from the super-heater and the latter introduced at a position ahead of the superheater and intermediate the position of recirculating gas introduction and the superheater.

The invention also contemplates the coordination of tempering gas flow and recirculating gas flow to maintain optimum high superheat and reheat over wide load range in a unit which involves a predominantly radiant secondary superheater and a predominantly convection heated reheater disposed in a convection gas pass beyond a secondary furnace chamber in which the secondary superheater is disposed. Such unit may involve the disposition of the reheater in one or more of two parallel sub-divisions of the convection gas pass, the remaining sub-division or sub-divisions of that gas pass including a convection primary superheater. Because reheat, in an installation of this type, tends to fall at a greater rate than superheat, the gas flows in the parallel subdivisions of the convection gas pass are dampered so as to substantially maintain optimum reheat at low loads by increasing gas flow over the reheater at the expense of gas flow over the primary superheater. This substantially eliminates any necessity for reheat attemperation. However, such control of reheat involves an increase in draft loss which can be reduced or minimized by the use of the present invention. The invention accomplishes such control by its effectiveness in the distribution of superheater and reheater heat absorption.

This is particularly accomplished by reason of the marked effect of the variation of tempering gas flow upon the secondary superheater which is predominantly of radiant heat absorption. When the gas temperature within the effective range of the radiant superheater is varied that temperature efiect has an increased effect upon the thermal action of the secondary superheater by reason of the fourth power characteristic of its radiant heat absorption. For example, when the tempering gas flow is increased, the temperature of the gas eifective upon the The invention also contemplates a unit of the pertinent.

type in which optimum reheat and superheat control may be effected, in part, by selective multiple level fuel burner control. As an example of the components of the unit promoting this control, the fuel burning devices include rows of cyclone fuel burners at different levels and discharging high temperature combustion products into a primary furnace chamber and toward a wall of vapor generating tubes common to the primary furnace chamber and the secondary furnace chamber. In this aspect of the invention, the flow of recirculated furnace gases in the primary furnace chamber and along the surface of that common wall, combines with the multiple level row of burners in a cumulative effect upon the ratio of furnace absorbed heat to the heat absorbed in reheating and superheating. For example, when only the burners of the lower row are employed and with a substantial flow of recirculated gas along the common wall, the effect is such as to produce a marked decrease in furnace absorbed heat, and a marked decrease in the ratio of furnace absorbed heat to the heat absorbed by reheating and superheating.

The terms recirculated gas or recirculating gas, or similar terms, and the term tempering gas or tempering gas flow refer, respectively, to returned gas flow to the primary furnace chamber and returned gas flow to the secondary furnace chamber.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification, but, for a better understanding of the invention, its operating advantages and the specific objects attained by its use reference should be had to the accompanying drawings and descriptive matter which disclose several embodiments of the invention.

In the drawings:

Fig. 1 is a side sectional view, or vertical section of a vapor generating and superheating unit constituting a preferred embodiment of the invention;

Fig. 2 is a diagrammatic view in the nature of an elevation, looking toward the cyclone burners of the Fig. 1 unit;

Fig. 3 is an enlarged vertical section through one of the multiple louver damper constructions for controlling and directing the flow of tempering gases into an upper part of the secondary furnace chamber;

Fig. 4 is a horizontal section of the Fig. 3 construction on the line 44 of Fig. 3;

Fig. 5 is a detailed view of the tempering gas outlet indicated in Fig. 3;

Fig. 6 is a diagrammatic view in the nature of a side sectional view of a vapor generating and superheating unit of modified construction.

The main components of the Fig. 1 unit include cyclone burner arrangements with upper and lower rows of cyclones A and B. They burn crushed coal, with the products of combustion discharging into a common primary furnace chamber 10 from which the combustion gases with the small remainder of the suspendedslag particles therein pass into the lower end of a vertically elongated secondary combustion chamber 12. In this combustion chamber gases contact the superheater including the

dependent platens

14 and 16. The combustion gases pass through the outlet 18 at the upper right hand part of the secondary combustion chamber to the the top of that wall. -.tubes continue as upright circulators 66 having end pordampered parallel heating gas :passes, tone of which preferablycontains one or-moreibanksof tubes forming :a convection vapor reheater, with the other parallel passes having therein .banks of tubes constituting the primary vapor superheater including the tubes or banks aof tubes 118-123 inclusive.

The gases'fiowing through the lower part of the downflow gas pass, flow over the-elements of a bank 26 of economizer tubes into .ductwork or abreeching 28 leading to the inlet 30 of a tubular air heater 32.

In communication with the breeching 28 is the inlet 34 of the ductwork 36 of a heating gas recirculation system which has one outlet formed by a tempering gas chamber 38 at the front wall 40 ofthe secondary combustion chamber 12 and at .a position just above the primary furnace chamber 10. Another outlet for the recirculated gas system is formed by the recirculating gas chamber 42 which is disposed below .the tempering gas chamber and in ,such position that'itis conveniently incommunication with the upper part ,ofthe primary furnace chamber 10.

Substantially, all if the vapor generation of the illustrative unit takes place in vapor generating wall tubes which are included in the walls and other boundaries of the :cyciones, furnace chambers, andthe convection gas :pass. In the natural circulation system of the unit these -vapor generating tubes have their lower ends either di- .rectly connected to the liquid drum 44 at the bottom of the installation, or connected to said drum through the intermediacy of appropriate headers and tubes. The upper ends of the vapor generating tubes are similarly connected to the liquid and vapor drum 46. Appropriate downcomers lead from the liquid space of the upper drum to the lower drum. .Such downcomers are formed bythe conduits 147 and associated tubular connections.

Some of the vapor generating tubes lead to the left from the lower drum, with their initial portions 50 included in a fluid cooled slagging bottom disposed between the slag pit 52 and the primary furnace chamber, portions of these tubes being bent aside over the slag pit to form an opening 54 through which slag flows to the pit. Beyond the floor 56 of the primary furnace chamber, these tubes continue in the left hand wall 58 of that chamber and then around the outlets of the cyclones, one of said outlets being indicated at 60. Thence, these tubes continue upwardly at '62 along the same wall of the primary combustion chamber, and thereafter, along the left hand wall of the secondary combustion chamber to At this position some of these tions 68 bent to the right for direct communication with the liquid and vapor drum '46. Others of these wall tubes continuealong the roof 70 of the secondary combustion chamber and then along the roof 72 of the convection gas pass 22 to a position 74 near the rear wall 76 of that gas pass. From this point they are bent to extend to direct communication with the liquid and vapor drum, as at 78.

The opposite or right hand wall 80 of the secondary combustion chamber includes Wall tubes 82 extending directly from the upper part of the lower drum 44 with some of these tubes having their lower parts associated with refractory material to form a part of the rear wall '80 of the secondary furnace chamber. These wall tubes continue upwardly to form parts of a division wall 86 between the convection gas pass 22 and the upper part of the secondary combustion chamber 12. Above the level of the reheater and primary superheater 24, some of these wall tubes are bent out of their wall formation to provide a screen 88 across the gas inlet to the convection 'gas pass. These bent out tubes preferably continue along the roof 72 of the gas pass and thence are bent upwardly to direct communication with the liquid and vapor drum 46. Others of these wall tubes continue through 'theroofof the unit, as at 90, to communication with the liquid and vapor drum 46.

The fluid cooled wall 92 which divides the primary and secondary combustion chambers includes fluid cooled tubes leadingdirectly from the lower drum 44 and having lower parts which form the tubular slag screens 94 and 96 extending across the flow of, gases from the primary furnace chamber to the secondary furnace chamber. Beyond these tubular screens, the tubes have portions forming the upright common wall extending to alevel just below the level of the header 98 which is disposed near the top of the primary furnace chamber, and externally thereof. This header has riser connections (ineluding risers 100) with the drum 46. Along opposite side walls of the secondary combustion chamber are upper and lower

side wall headers

102 and 104 connected by upright vapor generating tubes 106. The

headers

102 and 104 have appropriate connections withthe drums 44 and 46.

The rear wall 76 of the convection gas pass'22 includes primary superheater inlet tubes 108 with their inlet ends connected to the upper header 109 which in turn receives vapor from the vapor chamber of the liquid and vapor drum 46 through conduits 112. These Wall tubes .108 discharge superheated vapor to the lower'header 114 at the right hand lower corner of the convection gas pass. From other parts of this header, tubes 116 leading to the various return bend components of the "banks 118- -123- of primary superheater, extend. The outlet portions of these tubes, after forming the upper bank 123 of the primary superheater, extend along the rear wall of the inlet chamber, or gas mixing chamber 20 at the top of the convection gas pass, to an upper superheater header 126.

The cyclone furnaces A and B and other closely associated components are constructed and arranged in a manner similar to that indicated in the US. patent .to Bailey et al. 2,357,301, September 5, 1944, the walls of the cyclones including vapor generating tubes having their inlet ends leading directly from the lowermost header which is, in turn, appropriately connected to the lower drum 44. In conforming to the cylindrical or circular walls of the cyclones, the fluid cooling system includes appropriate lower and

upper headers

132 and 134 for each cyclone with connecting tubular elements 136 of substantially semi-circular formation. From the upper cyclone headers, risers 138 lead directly upwardly to junction with horizontal circulators 140 which have direct communication with the liquid and vapor drum.

Supenheated vapor from the outlet header of the primary superheater flows through

conduits

142, 144 to the inlet header 146 at the upper left hand part of the secondary superheater. This superheater is constructed in accordance with the detailed description of the common ass'ignees co-pending application of J. E. Black, Serial No. 277,831 filed March 21, 1952, now Patent No. 2,809,- 616, issued Oct. 15, 1957. It includes a number of U-bent tubes leading downwardly from the inlet header and then upwardly to form the first row 14 of the long platens. The lower parts of these platens below the lower ends of the interposed short platens 148 have the adjacent tubes arranged in a closely contiguous manner and in what may be termed a tu-be-to-tube relationship to limit slag accumulation and enhance periodic slag removal. The upper parts of these long platens have their tubes somewhat spaced so that their width corresponds to the width of the shorter platens. From the outlet ends of the tubes of the long platens of the first row, crossover tubes 150 extend to downfiow parts of the platens of the second row, these second row long platens being constructed in a manner similar to that of the first row of long platens. The vapor flows downwardly to the lower ends of the long platens of the second row and then upwardly through the return bend legs of the U-tubes to an intermediate header 152 at the upper right hand part of the secondary superheater, with the outlet ends of the tubes of the longer platens connected in circumferential rows to this header. From -heater. inlet 34 of the recirculating gas system through the inlet flow in the secondary furnace chamber.

positions between these rows the tubes of the shorter platens 148 extend downwardly to a position about half 'these upfiow portions, crossover tubes similar to those above referred to lead to the downflow tubes of the similarly constructed short platens of the remaining row. The outlet ends of the tubes of these platens are in alignment with the inlet tubes of the secondary superheater -to a position somewhat above the roof of the secondary combustion chamber. to the right to connections with the outlet header 154 From that position they extend for the secondary superheater. This outlet header has a conduit 156 connected thereto for conducting the superheated steam to a point of use.

The longer superheater platens are arranged on 24" bridging across these parts of the platens by accumula- -tions of slag particles which are deposited thereon during the operation of the unit, the slagging characteristics of this zone of the superheater being controlled by the introduction of tempering gas into the secondary furnace chamber at a position just below the secondary super- This tempering gas flows from the breeching ductwork 36 to the inlet of the fan 158 and thence through other ductwork 160 to the zone which includes the tempering gas inlet chamber 38 disposed adjacent the front wall 40 of the secondary furnace chamber 12. Fig.

' 2 shows this chamber as well as the chamber 42 as having and directed by multiple louver damper constructions,

each including a plurality of louvers or dampers 174-179 fixed to pintles 180185 the outer ends of which have the crank arms 186 fixed thereto. The louvers 174179 of each construction are manually adjustable so that they may be fixed in closed position, open position, or at any intermediate position directing the tempering gases in different directions at different angles transversely of gas The manually operable adjusting mechanism for these louvers includes parallel connections for the louvers. These connections include the bar 190 which is pivotally connected to each of the crank arms 186. At its upper end this bar is pivoted to the crankarm 192 at 194, this crank arm being fixed to a shaft 196 geared to a countershaft 198 upon which a hand wheel 200 is mounted. The louvers for each of the outlets 164169 may be independently adjusted. In this way, the gases through one outlet may flow at an upwardly inclined direction across the secondary furnace chamber while the gases of the adjacent outlet flow obliquely downwardly across the gas flow of the secondary furnace chamber in order that adequate mixing of the gases may take place upon entry into the slagging Zone of the secondary superheater.

The outlets for tempering gas are completed by

fiat plate studs

202 and 204 welded to the

tubes

206 and 208,

similar studs

210 and 212 welded to the

tubes

170 and 172,

side wall members

216 and 214 welded to

tubes

170 and 172, and associated refractory 218.

As shown in Fig. 1, some of the rear wall tubes 82,

chamber preferably takes place over the upper part of 'the total load range of the unit with the flow of tempering gas increasing as the load increases, from a fractional load to full load, the flow of tempering gas being controlled by an automatic control system which may be influenced primarily from steam fiow, or load. Thus, the gas temperatures at positions below the lower parts of the short superheater platens are kept at such values that the solid particles of incombustible residue of the fuel are generally not in a sticky or slagging condition beyond that point.

To maintain a predetermined superheat, recirculated gas is caused to enter the upper part of the primary furnace chamber from the recirculating gas inlet chamber 42 directly below the tempering gas inlet chamber, the walls of these chambers being formed by appropriate heat resisting material and insulating material. At the opposite inlet ends of the recirculating gas chamber 42 there are control dampers 162 similar to those provided for the ends of the tempering gas chamber 38. These dampers may be automatically controlled from representations of load, with or without modification by final steam temperature, and intermediate steam temperature at the attemperator. Recirculating gas flows from the inlet chamber 42 through openings provided in the left hand wall of the primary furnace chamber. These openings are provided by the bending of selected wall tubes out of their wall formation.

The Fig. 6 unit involves one or more cyclone burners 250 from which high temperature furnace gases are discharged through the outlet 252 into the primary furnace chamber 254. The furnace gases with the residual suspended slag particles therein pass across

tubular screens

256 and 258 into the secondary furnace chamber 260.

The Fig. 6 embodiment has its superheater 262 formed by upright tubular sections connected for series flow and pendently supported across gas flow in the gas outlet 264 of the secondary furnace chamber 260. The gases then proceed into the inlet 266 of the downflow gas pass 268 wherein they first flow across the transverse tubes of the reheater 270 and then across the banks of tubes constituting the primary superheater 272, the inlet header 274 receiving steam through the conduit 276 from the steam and water drum 278.

Below the primary superheater 272 the gases pass across the transversely disposed tubes of the economizer 280, thence into the breeching 282 leading to the air heater.

Communicating with the breeching 282 between the economizer and the air heater is the inlet 284 of a recirculated gas system including inlet ductwork 286, the fan 288, and the outlet ductwork 290. This outlet ductwork leads to a recirculated gas chamber 292 from the upper part of which controlled flow of the gases may pass through the tempering gas duct 294 into the upper part of the secondary furnace chamber 260. From the lower part of the chamber 292, controlled flow of the returned gas may be recirculated through the duct 296 through openings in the left hand wall 298 of the secondary furnace chamber. These openings will be formed by bending some of the tubes of the wall 298 to the right toward the secondary furnace chamber in spaced relation to the tubes of the wall 300 so as to form the recirculated gas duct or passage 302. The position of the tubes forming the right hand wall of this passage is indicated at 304 and 306 above the position at which these tubes fan out to form the screen 258. The associated screen 256 is similarly formed by the fanning out of the tubes forming the right hand wall 300 of the primary furnace chamber 254.

Tempering gas fiow through the duct .294'is controlled by a damper 310, and the control "of recirculated gas to the duct 296'to'the inlet of the secondary furnace chamber is controlled by the damper 312. The vapor genera- 'tion in the Fig. 6 unit takes place in the furnace wall tubes, and aside from the above described construction, the other pertinent features of the Fig. 6 modification correspond with the structure of the Fig. 1 unit.

In the operation of the'Fig. 6 unit sufiicient gas is recirculated at full load, and introduced through duct 294 near the outlet of the secondary furnace chamber to re- ,duce the gas temperatures to values of the order of 2000 F. at positions entering outlet 264. This may take about 20% recirculation. As the load drops, only suflicient gas 'is recirculated through the duct 294 to hold the gas temperature entering the superheater down to values of the order of 2000 F. To maintain good mixing, the entry of the tempering gas through the duct 294 may be directed or controlled as described above with reference to the Fig. 1 unit. This duct may be divided so that it has divisions leading to apart of the ductwork forming a tempering gas chamber similar to chamber 38 of Fig. 1, or a part ofthe duct extending across the furnace chamber :may have a series of vaned outlets similar to those described relative to chamber 38.

As the load drops, the amount of recirculated gas flow -'to-the primary furnace is increased to maintain desired vapor heating. Superheat is controlledby an interstage spray attemperator (not shown) functioning between the primary'superheater 272 and the secondary superheater "262. Only a small amount of attemperation isnecessary at full load, with the amount increasing as the load -drops. Therecirculation of gas through the duct 294 :near the "outlet of the secondary furnace chamber is for the purpose of reducing the gas temperature entering the superheater.

While the 'Fig. '1 unit and the Fig. 6 unit are disclosed as involving cyclone furnaces, it is to'be appreciated -that some features of the invention maybe employed "with other types of fuel burners, the primary requisite of such other fuel burners being that they afford the pertinent high temperatures of the combustionproducts in order thatthe'pertincnt high superheat may be attained.

'With the predominantly radiant superheater of the Fig. 'lunit, the gas tempering feature of the invention is particularly effective as compared to any similar installation employing a radiant superheater-of the wall tube rtype,:and the gas tempering feature of the invention is also particularly effective in the distribution of superheater and reheaterheat absorption (between the reheat- =er andthe secondary superheater) to maintain reheat at an optimum value at low loads while simultaneously 'minimizing draft loss which would otherwise be occa- --sioned by increased damper control to effect increased gas flow over the reheater-component of the convection gas pass. This effect exists where dampers are employed to increase gasflow through a reheater gas pass with respect to parallel gas passes inwhichthe primary superiheater isdisposed. A somewhat similar effect is pro- 'duced as to the distribution of superheater absorbed heat :and reheater absorbed heat in the pertinent type of installation which includes convectionreheater surface'di'sposed in aconvection gas pass in advance of primary superheater surface in that gas pass. At a fractional load, if the tempering gas flow is increased, the radiant secondary'superheater heat absorption decreases because of the ilowered gas temperatures and the convection reheater'heat absorption increases because of the higher gas mass flow.

' Certain features of this invention are disclosed in my prior-copending joint application with A. E. Raynor, filed December -6, 1950, which has issued as US. Patent No.

*While in accordance .with the provisions of the statutes "have illustrated and described herein the best. forms of myinvention now known to me, those skilled in the cart will understand that the changes maybe made in the forrnof the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of-my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of predominantly radiantly heated secondary vapor superheating tube platens spaced across the upper part of said radiant chamber, a furnace constructed to burn a slagforming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carying heating gases through one of said walls into the lower end of said radiant chamber, means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and mixing one portion of the withdrawn gases with the heating gases as they discharge from said furnace, and means for introducing another portion of the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said-vapor superheating tube platens.

2. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arrangedto receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor. generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of predominantly radiantly heated secondary vapor superheating tube platens spaced across the upper part of said radiant chamber, a furnace constructed to burn a slagforming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, means forming a verticallyextending baflle extending inwardly and downwardly from said last named wall to a level adjacent the level of ,the heating gases discharging from said furnace anddefining a primary furnace chamber therebetween opening to the lower end of said radiant chamber, means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing one portion of the withdrawn gases into said primary furnace chamber above the level of the heating gases discharging from said furnace, and means for introducing another portion of the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said vapor superheating tube platens.

3. A vapor generating and superheating unit comprising vertically extending'walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens spaced across the upper part of said radiant chamber,a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said Walls, means forming a vertically extending bafile extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging from said cyclone furnace and defining a primary furnace chamber therebetween opening to the lower end of said radiant chamber, meansfor withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing one portion of the withdrawn gases into said primary furnace chamber above the level of the heating gases discharging from said cyclone furnace, means for introducing another portion of the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens, and means for independently varying the amount of withdrawn gases introduced at each location.

4. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens spaced across the upper part of said radiant chamber, a plurality of vertically spaced rows of cyclone furnaces constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, means including a row of vapor generating tubes forming a vertically extending baflle extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging from the lowermost row of cyclone furnaces and defining a primary furnace chamber therebetween opening to the lower end of said radiant chamber, means for withdrawing heating gases from said convection heatmg pass downstream of said primary superheating tubes and introducing one portion of the withdrawn gases into said primary furnace chamber above the level of the heating gases discharging from the uppermost row of cyclone furnaces, and means for introducing another portion of the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens.

5. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens spaced across the upper part of said radiant chamber, a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, means including a row of vapor generating tubes forming a vertically extending baflle extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging from said cyclone furnace and defining a primary furnace chamber therebetween opening to the lower end of said radiant chamber, means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing one portion of the withdrawn gases into said primary furnace chamber above the level of the heating gases discharging from said cyclone furnace, means for introducing another portion of the withdrawn gases in laterally spaced streams into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens, means for independently varying the amount of withdrawn gases introduced at each location, and means for separately varying the angle of entry of said laterally spaced streams relative to said wall.

6. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of convection heated vapor superheating tubes in said heating pass, means for burning a slag-forming fuel at temperatures above the fuel ash fusion temperature and discharging slag-carrying heating gases through one of said walls, means including a row of vapor generating tubes forming a vertically extending fluid cooled bafile extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging through said wall and defining a primary furnace chamber therebetween opening at its lower end to the lower end of said radiant chamber, and means for withdrawing heating gases from said convection heating pass downstream of said vapor superheating tubes and introducing the withdrawn gases into said primary furnace chamber at a location above the level of the heating gases discharging thereinto and at points distributed over a major portion of the width of said primary furnace chamber.

7. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of convection heated vapor superheating tubes in said heating pass, a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, means including a row of vapor generating tubes forming a vertically extending fluid cooled baflle extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging from said cyclone furnace and defining a primary furnace chamber therebetween opening at its lower end to the lower end of said radiant chamber, and means for withdrawing heating gases from said convection heating pass downstream of said vapor superheating tubes and introducing the withdrawn gases into said primary furnace chamber at a location above the level of the heating gases discharging thereinto from said cyclone furnace and at points distributed over a major portion of the width 0 said primary furnace chamber.

8. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of convection heated vapor superheating tubes in said heating pass, a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, baflie means including a row of vapor generating tubes and extending inwardly and downwardly from said last named wall to a level adjacent the level of the heating gases discharging from said cyclone furnace and defining a recirculated gas chamber opening at its lower end to the lower end of said radiant chamber, means for withdrawing heating gases from said convection heating pass downstream of said vapor superheating tubes and introducing the withdrawn gases into said recirculated gas chamber at a location above the level of the heating gases discharging from said cyclone furnace and at points distributed over a major portion of the width of said primary furnace chamber and downwardly along said baffle means, and means for varying the amount of withdrawn gases so introduced.

9. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of convection heated vapor superheating tubes in said heating pass, a plurality of vertically spaced rows of cyclone furnaces constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls, means including a row of vapor generating tubes forming a vertically extending bafile extending inwardly and down wardly from said last named wall to a level adjacent the level of the heating gases discharging from the lowermost row of said cyclone furnaces and defining a primary furnace chamber therebetween opening at its lower end to the lower end of said radiant chamber, and means for withdrawing heating gases from said convection heating pass downstream of said vapor superheating tubes and introducing the withdrawn gases into said primary furnace chamber at a location above the level of the heating gases discharging thereinto from the uppermost row of cyclone furnaces and at points distributed over a major portion of the width of said primary furnace chamber.

10. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens laterally spaced across the upper part of said radiant chamber, means for burning a slag-forming fuel at temperatures above the fuel ash fusion temperature and discharging slag-carrying heating gases through one of said walls into the lower end of said radiant chamber, and means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens.

11. A vapor generating and superheating unit com prising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens spaced across the upper part of said radiant chamber, means for burning a slag-forming fuel at temperatures above the fuel and ash fusion temperature and discharging slag-carrying heating gases through one of said walls into the lower end of said radiant chamber, and means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens comprising a series of vertically elongated openings in one of said radiant chamber walls, a series of multiple louver dampers in each of said openings, and means for independently adjusting the series of dampers in said wall openings with respect to the vertical angle thereof relative to said wall.

12. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall or" s'aid radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens laterally spaced across the upper part of said radiant chamber, a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slagcarrying heating gases through one of said walls into the lower end of said radiant chamber, means for withdrawing heating gases from said convection heating pass downstream of said primary superheating tubes and introducing the withdrawn gases in streams through one of said vertical Walls into said radiant chamber at a level closely subjacent to the lower ends of said pendent vapor superheating tube platens in intimate mixing relation With the heating gases flowing to said heating gas outlet, and means forming a gas-defiecting arch on the vertical wall opposite said last named wall and arranged to deflect the heating gases into mixing relation with said recirculated gas streams.

13. A vapor generating and superheating unit comprising vertically extending walls defining a vertically elongated radiant chamber arranged to receive heating gases at its lower end and having a heating gas outlet at its upper end, vapor generating tubes lining a wall of said radiant chamber, means defining a convection heating pass connected to said gas outlet, a bank of primary vapor superheating tubes in said heating pass, a plurality of pendently supported secondary vapor superheating tube platens spaced in parallel vertical planes across the upper part of said radiant chamber, alternate tube platens terminating at their lower ends at substantially different levels in said radiant chamber, a cyclone furnace constructed to burn a slag-forming fuel at temperatures above the fuel ash fusion temperature and arranged to discharge slag-carrying heating gases through one of said walls into the lower end of said radiant chamber, means for withdrawing heating gases from said convection heat* ing pass downstream of said primary superheating tubes and introducing the withdrawn gases into said radiant chamber at a level closely subjacent to the lower ends of the lowermost pendent vapor superheating tube platens, and means for varying the amount of withdrawn gases so introduced.

References Cited in the file of this patent UNITED STATES PATENTS 1,828,483 Wood Oct. 20, 1931 1,964,149 Frisch June 26, 1934 2,100,190 Jackson Nov. 23, 1937 2,109,840 Gordon Mar. 1, 1938 2,685,279 Caracristi Aug. 3, 1954 2,730,080 Stallkamp Jan. 10, 1956 2,737,930 Rowand et a1 Mar. 13, 1956 FOREIGN PATENTS 523,870 Great Britain July 24, 1940 504,114 Great Britain Apr. 14, 1939 OTHER REFERENCES B & W Bulletin G67-A of 1950 page 41.