US2891522A - Vapor generating, superheating and reheating unit - Google Patents

Description

June 23, 1959 W. H. R OWAND ETAL Filed May 10, 1955 FIG WILL H. ROWAND CHARLES L. MARQUEZ BY CLYDE B. BAVER ARTHUR J. HUGHES TTORNEY United States Patent F VAPOR GENERATING, SUPERHEATING AND REHEATING UNIT Will H. Rowand, Short Hills, Charles L. Marquez, Jersey City, Clyde B. Bayer, Fanwood, and Arthur J. Hughes, Packanack Lake, N.J., assignors to The Babcock 8: Wilcox Company, New York, N.Y., a corporation of New Jersey Application May 10, 1955, Serial No. 507,346

9 Claims. (Cl. 122-481) This invention relates toa high capacity and high pressure vapor generating unit having therein a high temperature vapor superheater and a high temperature vapor reheater so constructed and arranged as to closely approach optimum vapor superheat temperatures and vapor reheat temperatures, over a wide range of vapor generating load.

The components of the vapor superheater and the vapor reheater are preferably arranged in series as to gas flow, and the superheater and the reheater each involves a section which is predominantly convectionally heated, and another section which is predominantly heated by radiantly transmitted heat, the inherent tendencies of the convection sections and the radiant sections tending to balance or compensate each other over a wide range of vapor generating load to approach the optimum reheat and superheat temperatures over the wide load range.

More specifically, the invention involves a vapor generating unit which has incorporated therein a high temperature vapor superheater and a high temperature vapor reheater, both the superheater and the reheater having widely spaced platens of tubes disposed in the upper part of a vertically elongated secondary furnace chamber which is fired at its lower part at temperatures above the fusion temperatures of the slag forming fuel used in the firing means. A convection gas pass leads laterally from the upper part of the vertically elongated secondary furnace chamber, and within this gas pass there is disposed a convection heated section of the reheater connected in a series as to vapor fiow with the radiantly heated section of the reheater. Within the gas pass and beyond the convection reheater section there is a bank of tubes constituting a convection section of the secondary superheater, of which the superheater platens at the upper part of the secondary furnace chamber are a part. This bank of tubes within the gas pass is arranged in series as to vapor flow with the secondary superheater platens disposed in the upper part of the vertically elongated furnace chamber. Beyond the bank of tubes constituting the convection section of the secondary superheater is arranged the convection section of a primary vapor superheater including banks of tubes which extend entirely across the gas flow from one side of the gas pass to the other, without any partition or division wall disposed within that section of the gas pass. The vaporizable fluid circuit of the unit includes a vapor and liquid drum in which the generated vapor is separated from the vapor and liquid mixtures entering the drum. The generated vapor passes through appropriate connections to the convection section of the primary superheater, which preferably includes a plurality of banks of tubular sections connected in series as to vapor flow. From the outlet of the convection section of the primary superheater the superheated vapor flows through an attemperator on its way to the first stage of the secondary superheater, which includes the widely spaced superheater tube platens disposed in the upper part of the secondary furnace chamber. From the outlet of this first stage of the secondary ice superheater the superheated vapor flows to the inlet of the second stage of the secondary superheater, which is formed by the bank of closely spaced convection heated tubes of a dependent section disposed within the gas pass. From the outlet of that section the superheated vapor flows to the high pressure stage of a prime mover. From the exhaust of this high pressure stage the vapor flows to the inlet of the first stage of the reheater which is formed by the widely spaced reheater tube platens disposed in the upper part of the secondary furnace chamber and between the first stage of the secondary superheater and the remaining superheater and reheater sections. From the outlet of this first stage of the reheater, the reheated steam flows to the inlet of a convection section of the reheater which is formed by -a bank of closely spaced tubes disposed within the gas pass. From the outlet of this second stage of the 'reheater, the reheated vapor flows to the inlet of a lower pressure stage of the prime mover.

The invention also includes the method of attaining superheat and reheat control effected by the illustrative unit. The method involves the passage of the steam to be superheated through a zone which is predominantly convection heated, and then through a zone which is predominantly radiantly heated. The method also involves a similar procedure as to the convection heating and radiant heating of the reheated vapor.

The invention will be concisely set forth in the claims appended hereto, but for a complete understanding of the invention, its uses and advantages, recourse should be had to the following description which refers to a preferred embodiment of the apparatus of the invention, as shown in the accompanying drawings.

In the drawings:

Fig. 1 is a sectional elevation diagrammatically indicating the pertinent features of the illustrative vapor generating, superheating, and reheating unit; and

Fig. 2 is a plan section of the Fig. 1 unit on the line 22 of Fig. 1, and looking in the direction of the arrows.

Fig. 1 of the drawings shows a high capacity vapor generating, superheating and reheating unit including a vertically elongated secondary furnace chamber 10. The boundaries of this chamber, such as the front wall 12 and the rear wall 14, preferably include upright vapor gen erating tubes connectedinto a fluid system including the vapor and liquid drum 16 at the upper part of the unit, and the liquid drum 18 at the lower part of the unit. Such vapor generating wall tubes are connected at their upper ends to the drum 16 to discharge vapor and liquid mixtures into the drum for separation of the generated vapor from the liquid. In the operation of the unit the inlets of the vapor generating tubes are supplied with liquid through the lower drum 18 and one or more large diameter downcorners 20 leading from the liquid space of the drum 16 to the lower drum 18.

The vertically elongated secondary furnace chamber 10 is normally supplied with high temperature gases having temperatures of the range of 230.0 F. to 3300 F. by burning slag forming fuel at the lower part of the unit, in a cyclone furnace 22, the structure and arrangement of which may be of the nature indicated in the US. patent to Kerr et al. 2,594,312 of April 29, 1952. This cyclone furnace normally burns a slag forming fuel such as particle form coal, at temperatures above the fusion temperature of the slag in the fuel. The combustion chamlber 24 of the cyclone furnace is supplied withhig-h temperature secondary air in such a manner that cyclonic action of the burning fuel and gases therefrom is'se't up" within the combustion chamber. The gaseous products of combustion flow through the cyclone furnace tliioat 26 into the primary furnace chamber '28. From primary furnace chamber 28 the combustion gases with a small percentage of suspended particles therein pass over the screen formed by the vapor generating tube sections 30 and 32 into the lower part of the seconday furnace chamber 10. The upper part of the secondary furnace chamber, by reason of the disposition therein of widely spaced vapor superheater platens and reheater platens, constitutes aradiant vapor heating zone which will be later referred to.

High temperature secondary air for the cyclone furnace 22 is supplied through appropriate ductwork 34 leading from a high temperature air heater (not shown). During the operation of the cyclone furnace molten slag collecting in the bottom of the combustion chamber 24 flows through a slag opening 36 to the floor 38 of the primary furnace chamber 28, and thence passes into a slag pit 40.

Leading laterally fiom the radiant vapor heating zone at the upper part of the secondary furnace chamber 10 is a convection gas pass in which the gases flow substantially horizontally to a turning space 42. From this turning space the gases flow downwardly through the downfiow section 44 of the convection gas pass, and thence through breeching 46 and ductwork 48 leading to a high temperature air heater, and thence to a stack.

Within the vapor and liquid drum 16 there are two rows of cyclone steam separators 50, each of which is preferably of the type indicated in the US. patent to Fletcher and Rowand 2,289,970. These devices receive the vapor and liquid mixtures from the vapor generating wall tubes of the secondary furnace chamber, and discharge the separated vapor into the upper part of the drum. The separated vapor thence proceeds through a series of conduits 52 along the roof 54 of the unit to the header 56 at the top of the downflow section of the convection gas pass. Two rows of superheater supply tubes lead from the header 56 downwardly. The tubes '58 of one row lead directly downwardly along the left hand side of the downflow section of the convection gas pass and thence in spaced relationship across the lower part of the gas pass as indicated at 60. Their lower ends are connected to the header 62. The tubes 64 of the other row leading from the header 56 lead across the roof of the convection gas pass as indicated at 66, and thence downwardly along the right hand wall 68 to connection with the header 62. From the header 62 rows of tubes 70 lead upwardly to a position beyond the economizer 72 where they form the banks 7477 of spaced tubes of the primary superheater, thence the outlet portions of these tubes 80 lead directly upwardly to the out let header 82 of the primary superheater. From the header 82 the steam flows through one or more conduits 84 to an attemperator which may be of the type indicated in the patent to Fletcher et al. 2,550,683 of May 1, 1951. This attemperator operates to control the final steam temperature by the injection of spray water into the steam in quantities controlled automatically from a plurality of variables, the most important one of which may be the final temperature of the steam. From the attemperator the steam passes through conduits 88 and 90 to a secondary superheater inlet header 92' preferably extending entirely across the width of the unit. From the inlet header 92 and its companion outlet header 94 depend a series of widely spaced platens of superheater tubes constituting the first stage of the secondary superheater, disposed in a high temperature gas region constituting the radiant vapor superheating and reheating zone. One of these platens is indicated at 96, and the spacing in these platens transversely of the unit is indicated in Fig. 2 of the drawings. The spacing of these platens transversely of the unit is preferably 24 inches or more in order to form this stage of the secondary superheater in such a manner that it is predominantly radiantly heated, and in order to promote optimum conditions' as to heattran sfenparticularly with respect to slagging conditions and the removal of deposits upon these platens.

From the first and radiant stage of the secondary superheater the superheated vapor passes from the outlet header 94 throuh a series of conduits 98 to the inlet header 100 of the second stage of the secondary superheater. This stage is formed by a hank of closely spaced upright tubular sections 102 pendently arranged within the upper part of the convection gas pass for transverse flow of the heating gases thereover. This stage of the secondary superheater, because of the gas flow conditions and the close spacing of the component tubes, constitutes a secondary superheater section which is predominantly convection heated. From this second stage of the superheater the superheated vapor passes through the outlet tubes 104 to the outlet header 106, and thence through one or more conduits 108 to the inlet of a high pressure stage 110 of a prime mover. From the exhaust 112 of this prime mover stage the vapor, reduced in pressure, passes through one or more lines 114 to the inlet header 116 of the first stage or radiantly heated section of the reheater. This radiantly heated stage of the reheater is formed by a plurality of pendent platens 118 which are disposed in the upper part of the secondary furnace chamber 10, which constitutes the radiant vapor heating zone. These platens are constructed and arranged in a manner similar to the construction and arrangement of the platens 96 of the first stage of the secondary superheater.

The outlets of the tubes constituting the platens 118 of the first stage of the reheater are connected to the outlet header 120 from which reheated vapor flows through one or more conduits 122 to the second and predominantly convection heated stage of the reheater. In this stage of the reheater pendently supported and closely spaced tube sections constitute the convection heated banks of tubes 124 and 126.

The side spacing of the tubes of the banks of tubes 124 and 126 of the predominantly convection heated section of the reheater is much less than the spacing of the tubes or the platens in the predominantly radiantly heated section of the reheater, as indicated particularly in Fig. 2 of the drawing. From the outlets of the tubes constituting the predominantly convection heated stage of the reheater, reheated steam passes to the outlet headers 128 and 130, and thence through conduits 132 to the inlet 134 of a lower pressure stage 136 of the prime mover.

The predominantly radiantly heated first stage of the secondary superheater has such an inherent heat transfer characteristic that the vapor temperature at the outlet of this section falls below an optimum value as the vapor generating load increases, and the predominantly convection heated second stage of the superheater has such a heat transfer characteristic that it has an inherent tendency to effect superheated vapor temperatures increasing above an optimum value as the load increases. Therefore, the present invention involves such proportioning of the extent of the surfaces in the predominantly radiantly heating stage, and the predominantly convection heating stage that these two opposing tendencies tend to balance each other and therefore promote the maintenance of a predetermined superheated vapor temperature over a wide range of rate of vapor generation.

Conditions such as those referred to in the immediately preceding paragraph also pertain to the radiantly heated and the convection heated sections of the reheater. However, the reheater, because of its connections with the prime mover, and the different temperatures and pressures of the vapor entering the reheater, with respect to similar conditions of the vapor entering the superheater, the reheater is subject to an additional inherent tendency wherein the reheat effect of the convection section of the reheater is such that if the same proportionate arrangement of surfaces was involved in the combined reheater as in the superheater, the reheat temperature would tend to depart from a predetermined value when the vapor generating load decreases. This invention therefore involves a differential proportioning of the convection heating surfaces and the radiantly heated surfaces of the reheater, with respect to the proportioning of the Corresponding surfaces of the superheater, for overcoming this differential tendency.

Preferably, aspray attemperator similar to the ratternperator above referred to, is incorporated in the reheater circuit.

A temperature control range on both the superheater and the reheater can be obtained by varying the excess air to the cyclone burner. At control load the excess air may be increased, from 10% to 30% to obtain full steam temperature, and this results in 1.5% spray on the reheater, which is equivalent to approximately 30 F. safety. If at control load, the excess air is increased from 30% to 40%, then the superheat temperature is increased 30 F. (due to the fact it is mostly convection surface), but the reheat temperature only increases F.

With the illustrative superheat and reheat control system, full steam and reheat' temperatures may be controlled from 6Q% to 100% of full load, and at full load there is only 2% spray water required on the reheater.

For controlling the gas temperature conditions within the secondary furnace chamber 10, particularly with respect to maintaining s lagging conditions within an optimum range, and for maintaining the gas temperatures within such a range that they will promote a high degree of availability of the unit, from the standpoint of allowable gas temperatures with respect to the metal of the radiantly heated heated platens of the secondary superheater land the reheater, the gases flowing upwardly in the lower part of the secondary furnace chamber may have their temperature reduced by mixing therewith lower temperatureheating gases withdrawn from a pos'ition in the gas flow path beyond the economizer 72, and introduced into the lower portion of the secondary furnace chamber. These results may be effected by a recycling gas system including a fan 150- having appropriate ductwork 152 connecting the inlet of the fan with an opening 154 in the fine or ductwork 48 leading from the lower part of the convection gas pass. The outlet of the fan 150 is connected by ductwork 156 to a transverse distributing duct 158, from which the lower temperature gases flow through the ductwork 160 through a plurality of outlets preferably distributed across the width of the wall .14 of the secondary furnace chamber. To appropriately form such a series of outlets, alternate vapor generating tube's along the secondary furnace chamber wall 14 may be bent out of their wall forming alignment over the vertical extent of the ductwork 160.

In the illustrative unit the reheater and thesuperheater components are arranged throughout the full width of the unit, thus reducing the number of flow circuits. This is not only of importance with respect to the original cost of the unit, by reducing the complexity of the multifarious tubular connections to the various headers employed in an arrangement wherein the superheater and the reheater; components are divided transversely of the unit. This arrangementof the illustrative unit is also of particular importance with. respect to the functioning of the reheater. This results from the particularly low pressure drop of the illustrative arrangement.

7 Additional vapor generating surface for the Fig. 1 unit is provided by wingWaHs of vapor generating tubes, the lower parts of which are disposed within the lower part of the secondary furnace chamber 10. Such tubes lead through the wall 14 of the secondary furnace chamber from headers 170 which are appropriately connected into the circulation system of the unit. The main parts of these tubes 173 and 174 are closely spaced and disposed in upright position in the right hand part of the secondary furnace chamber. Just below the arch 176 these tubes have upwardly inclined or offset portions 178- 480 which lead to other upright portions, extending in division will formation through that part of the convectional gas pass in which the banks of reheater tubes 124 and 126 are disposed. The partition or division walls formed by these tubes are indicated at 190 and 192 in Fig. 2. At the roof of the gas pass these tubes are bent to be appropriately connected to the vapor and liquid drum 16. They may combine with the upper parts of the rear wall tubes 200 to extend to the left at the upper part of the secondary furnace chamber, as indicated at 202. Intermediate parts of the rear wall furnace tubes form the lower and upper parts 204 and 206 respectively of the arch 176, and the parts of these tubes above the arch extend upwardlyin spaced relation to the superheater supply tubes 58 to form a screen extending across the convection gas pass at a position ahead of the convection stage of the secondary superheater. I

The vapor generating tubes 210 for the front wall of the secondary furnace chamber have lower parts bent out of their wall alignment as indicated at 212, so as to form the upper part of the wall dividing the primary furnace chamber from the lower part of the secondary furnace chamber. Beyond this inclined wall the tubes extend as indicated at 30 and 32, and thence to a connection with the drum 18. Others of the secondary furnace chamber front wall tubes extend along the upright wall of the cyclone furnace as indicated at 214 and 216, and thence along the primary furnace chamber floor 38 to the header or drum 18. Some of these tubes are bent to define the throat 26 of the cyclone furnace.

The Fig. 1 unit is preferably rectangular in horizontal cross-section and the reheater and superheater headers, as well as the vapor and liquid drum 16 are supported by suitable hangers from rectangular steelwork, including such beams as the beams 218 supported by columns such as 220224 inclusive. The hangers for supporting the drum 16 from the beams 218 include a plurality of U- shaped members cradling the drum between upwardly extending legs, such as 230 and 232.

The attainment of a constant reheat temperature over a wide range of vapor generating load is effected in the illustrative unit by taking advantage of the radiant heat absorption characteristics of the radiant platens, and proportioning the radiant heating surface to the convection heating surfaces to supply additional heat absorption reqnired by the reheat vapor, with decreasing load, such additional heat absorption required by the reheater being an increasing function with decreasing load.

The feature of the invention whereby the heat absorption characteristics of the combination of radiant and convection reheater surface results in a pat-tern of operati-ve results whereby the steam temperatures are maintained constant over a wide load range, also results in minimizing the amount of spray water required for attemperation, and maintaining the spray water requirements substantially constant over a wide load range.

The superheater surface of the illustrative unit is so proportioned between its first and second stages that the total superheating effect is obtainable by radiant heat absorption and convection absorption, and through the use of increased excess air to the cyclone furnace, full effect can be obtained on the superheater with a minimum amount of increase in excess air.

In the operation of the illustrative unit with recycled gases used for controlling the gas conditions within the secondary furnace chamber, gas temperatures entering the convection section may be maintained at a low value and yet the heat absorption to the convection vapor heating components disposed midway and further downstream in a gas-flow sense in the convection gas pass, is increased as a result of the increased mass flow of gases through the convection section.

the invention is not to be taken as limited to all of the details thereof. It is rather to be taken as of a scope commensurate with the scope of the subjoined claims.

What is claimed is:

l. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber, vapor generating tubes lining the Walls of said furnacechamber, a high temperature vapor superheater comprising a bank of primary superheater tubes in said gas pass, a bank of pendent secondary superheater tubes arranged in vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber in the space between said secondary superheater tube platens and said gas pass, and a bank of pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of said gas pass, and means for passing vapor to be reheated serially through said reheater tube banks in the order named, said superheater and reheater radiantly heated tube platens being formed solely by superheater and reheater tubes respectively.

2. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of pendent secondary superheater tubes arranged in vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical radiantly heated platens Widely spaced transversely of the upper part of said furnace chamber and in spaced alignment with said secondary superheater tube platens, and a bank of pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of the horizontal section of said gas pass, and means for passing vapor to be reheated serially through said reheater tube banks in the order named, said superheater and reheater radiantly heated tube platens being formed solely by superheater and reheater tubes respectively.

3. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of pendent secondary superheater tubes arranged in vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical radiantly heated platens wide- I ly spaced transversely of the upper part of saidfurnace chamber, and a bank of pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of the horizontal section of said gas pass, means for passing vapor to be reheated through said reheater tube banks in the order named, and both of said reheater tube banks being'positioned in the space between said secondary superheater tube platens and said gas turm g space. a a

4. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning a'slag-forming fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of multi-looped pendent secondary superheater tubes arranged vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical radiantly heated platens widely spaced transversely of the upper part of said furnace chamber and in spaced alignment with said secondary superheater tube platens, and a bank of multi-looped pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of the horizontal section of said gas pass, means for passing vapor to be reheated through said reheater tube banks in the order named, and both of said reheater tube banks being positioned in the space between said secondary superheater tube platens and said gas turnin space.

5. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, Walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls. of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of multi-looped pendent secondary superheater tubes arranged in vertical radially heated platens Widely spaced transversely of the upper part of said furnace chamber, a bank of multi-looped pendent secondary superheater tubes arranged in closely spaced vertical parallel .planes across the entire width of the gas turning space of said heating gas pass, means for passing vapor to be superheated through said primary and plurality ofsecondary superheater tube banks in the order named, and a high temperature vapor reheater comprising a bank of multilooped pendent vapor reheating tubes arranged in parallel vertical platens across theentire width of the horizontal section of said gas pass positioned in the space between said secondary superheater tube platens and said bank of secondary superheater tubes in said gas turning space, said superheater and reheater tube platens being formed solely by superheater and reheater tubes respectively.

6. A vapor generating, superheatingand-reheating unit comprising walls defininga vertically elongated furnace chamber having means for burning a slag-forming fuel in suspension at its lower end, 'walls'definin'g a convection heating gas pass opening to one sideof the upper end of said furnace chamber }and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of multi-looped pendent secondary superheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber, a bank of multi-looped pendent secondary superheater tubes arranged in closely spaced vertical parallel planes across the entire width of the gas turning space of said heating gas pass, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, and a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber and in spaced alignment with said secondary superheater tube platens, and a bank of multi-looped pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of the horizontal section of said gas pass, means for passing vapor to be reheated through said reheater tube banks in the order named, and both of said reheater tube banks being positioned in the space between said secondary superheater tube platens and said bank of secondary superheater tube platens in said gas turning space.

7. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber, vapor generating tubes lining the walls of said furnace chamber, a vapor superheater comprising a bank of primary superheater tubes in said gas pass, a bank of multi-looped pendent secondary superheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber, a vapor reheater comprising a bank of multi-looped pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of said gas pass, said reheater tube bank being positioned in the space between said secondary superheater tube platens and said bank of primary superheater tubes, and vapor generating tubes arranged in a plurality of wing walls having lower portions spaced transversely of the furnace chamber below the level of said superheater tube platens and upper portions extending vertically through said gaspass intermediate the width of said reheater tube bank therein.

8. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass, a bank of pendent secondary superheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber, and a bank of pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of said gas pass, and both of said reheater tube banks being positioned in the space between said secondary superheater tube platens and said bank of primary superheater tubes, and vapor generating tubes arranged in a plurality of wing walls having lower portions spaced transversely of the furnace chamber below the level of said superheater and reheater tube platens and upper portions extending vertically through said gas pass intermediate the width of said reheater tube bank therein.

9. A vapor generating, superheating and reheating unit comprising walls defining a vertically elongated furnace chamber having means for burning a slag-forming fuel in suspension at its lower end, walls defining a convection heating gas pass opening to one side of the upper end of said furnace chamber and having serially connected horizontal and vertical gas flow sections connected by a gas turning space, vapor generating tubes lining the walls of said furnace chamber, a high temperature vapor superheater comprising a bank of horizontally extending primary superheater tubes in said gas pass vertical section, a bank of multi-looped pendent secondary superheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber, a. bank of multi-looped pendent secondary superheater tubes arranged in closely spaced vertical parallel planes across the entire width of the gas turning space of said heating gas pass, means for passing vapor to be superheated through said primary and secondary superheater tube banks in the order named, a high temperature vapor reheater comprising a bank of pendent reheater tubes arranged in vertical platens widely spaced transversely of the upper part of said furnace chamber and in spaced alignment with said secondary superheater tube platens, and a bank of multi-looped pendent vapor reheating tubes arranged in parallel vertical planes across the entire width of the horizontal section of said gas pass, means for passing vapor to be reheated through said reheater tube banks in the order named, and both of said reheater tube banks being positioned in the space between said secandary superheater tube platens and said bank of secondary superheater tube platens in said gas turning space, and vapor generating tubes arranged in a plurality of wing walls having lower portions spaced transversely of the furnace chamber below the level of said superheater and reheater tube platens and upper portions extending vertically through said gas pass horizontal section intermediate the width of said reheater tube bank therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,279 Caracristi Aug. 3, 1954 2,737,930 Rowand et a1. Mar. 13, 1956 FOREIGN PATENTS 1,046,913 France July 15, 1953

Images