US2798464A - Vapor generators having vapor heaters - Google Patents

Description

July 9, 1957 s m 2,798,464

VAPOR GENERATORS HAVING VAPOR HEATERS Filed Feb. 6. 1953 Tici. K

2 Sheets-Sheet l INVENTOR.

July 9, 1957 H. SEIDL Filed Feb. 6. 1953 2 Sheets-Sheet 2 Tic-14.

JUL un INVENTOR. J/erer Said! United States Patent O ice VAPOR GENERATORS HAVING VAPOR HEATERS Herbert Seidl, Oberhausen, Germany, assiguor to The Babcoclt & Wilcox Company, New York, N. Y., a corpo= ration of New Jersey Application February 6, 1953, Serial No. 335,494

4 Claims. (Cl. 122-478) tion, tube metal failures may result and, in cases where a slag-forming fuel is burned, the tubes may become fouled with slag. Such accumulations of slag soon re duce the heat transfer rate to a point at which the advantages of placing the elements in a high temperature section may even be overcome.

The primary object of my invention is the provision of a fluid heater with an improved arrangement of a radiant draining type vapor heater therein providing a high rate of heat transfer without danger of tube damage or excessive tube slagging.

A more specific object is to provide a radiant draining type vapor heater, the tubes of which are arranged vertically for gas flow parallel to the tubes over the greatest part of their length and protected from the direct heat of the gaseous products of combustion by an improved arrangement of fiuid heating screen tubes- A further object is the provision of a fluid heater with a radiant type vapor heater disposed in a recessed position therein in combination with an improved arrangement of gas tempering means for protecting the vapor heater from excessive gas temperatures and slagging.

For a better understanding of the invention, its operating advantages and specific objects attained by its use,

reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of my invention.

In the drawings:

Fig. 1 is a partly diagrammatic sectional elevation of a steam generating unit constructed in accordance with my invention;

Fig. 2 is a view similar to Fig. 1 showing a modified arrangement of the superheater and screen tubes;

Fig. 3 is a vertical section taken on the line 33 of Fig. 2; and I Fig. 4 is a view similar to Fig. l of a further modification. In the steam generating unit shown in Fig. 1, pulverized fuel and combustion air are introduced into the lower portion of a vertically elongated furnace 10 through pulverized fuel burners lit. The fuel and air are ignited and burn in the lower section 10, generating a stream of high temperature gases flowing upwardly therein. The front and rear walls of the furnace chamber 12 and 17 are bent forwardly at the upper end thereof to form a forwardly offset vertically elongated high temperature gas pass 10A having about half the depthofthe furnace Patented July 9, 1957 2 chamber. The upper end of the gas pass llllA opens laterally at the rear side thereof into a rearwardly inclined gas pass 40 defined by an inclined roof 15 and floor 15A. The front wall 12 contains steam generating tubes 13, some of which run directly vertically into the steam drum 14 while others 1413 first extend along the roof 15. Some of tubes 16 lining the rear furnace wall 17 run vertically through gas pass 40, while the others 16A are bent forwardly to line the rear wall of the gas pass 10A, thence along the floor 15A and up through a short vertical partition 19 to the drum 14. Some of the furnace side wall tubes 20 lead directly to the drum 14 while others lead first to an upper header 21. The water downcorners from the drum 14 to the lower ends of the wall tubes have been omitted for clarity.

vIn the steam generator illustrated the steam generating section is defined by the wall tubes described while the pressure parts located in the high temperature gas passes 10A and 40 and a rear vertical gas pass 26 opening to the rear end of the gas pass 40 are employed for superheating the steam generated to a high. temperature. Saturated steam flows from the drum 14 through spaced rows of superheater supporting tubes 22 in the gas pass 26 on which are suspended vertically spaced groups 23, 2 iof convection heated superheater tubes, through tubes which line the rear wall of the pass 26, and through tubes 27 which line the side walls of the pass 26, to a common header 28, thence through the tubes 29 to an inlet header 30 of the radiant superheater section 31. The radiant superheater 31 occupies substantially the whole height of the gas pass 10A from the exit of the furnace chamber It) to the upper end of the entrance to the gas pass 40 and is made in the form of transversely spaced platens of nested inverted hairpin tubes with their ends connected to the header 30 and a vertically adjacent outlet header 32. The steam then flows from each header 32 through a tube 33 to a common collecting header 34, from which the steam is conducted to a corn vection heated superheater section in the downflow gas pass 26. The convection section is formed by vertically spaced serially connected banks of looped horizontal tubes 23 and 24 supported on the tubes 22. The uppermost tube legs of the bank 23 are connected to a common outlet header 35. The steamleaving the header 35 passes to an inlet header 38 of a secondary convection super heater section either directly or through a regulable steam attemperator of any suitable type (not shown); The secondary convection section is formed by two laterally spaced pendant superheater sections 36 and 37 in the gas pass 40. i

With the described arrangement of superheater sections, the steam to be superheated first flows parallel to the gas flow in the gas pass 26 through the wall tubes 25 and 27 and support tubes 22, is then mixed in the header 23, delivered to the inlet headers 30 of the predominantly radiant section 31, where it first flows parallel to the gas flow in the pass 10A and then counter to the gas flow to the headers 32. The steam is then mixed in the header 34 and delivered to the primary convection sections 24 and 23, flowing upwardly therein counter to the, gas flow in the pass 26. The superheated steam, attemperated if desired, then flows through the pendant sections 36 and 37 counter to the gas flow in the gas pass 40 wherein it receives its final superheating.

In accordance with my invention, the radiant superheater section 31 is constructed and arranged in the gas pass 10A to provide a high rate of heat transfer thereto predominantly by radiation from the high velocity high temperature gases flowing upwardly therein and with a minimum deposition of slag thereon. For this purpose the surface is arranged in platens spaced transversely at least several tubes diameter, as indicated inFig. 3, with the platens having a special configuration in the gas pass A and the inlet and outlet headers and 32 positioned externally of the gas pass.

The upper half of the tube platens of the radiation superheater 31 occupy the rear half of the gas pass 10A directly in front of the gas pass 40. At the lower level of the gas pass the superheater tubes are bent at an angle downwardly and forwardly substantially parallel to the angle of the roof 15 and floor 15A, and then downwardly so that the lower vertical half of the platens occupy the forward half of the gas pass 10A adjacent the front wall 12. The lower end portions of the superheater tube platens are again bent forwardly through the front wall 12 to the external headers 30 and 32. Some of the steam generating tubes 13A of the front wall 12 are bent inwardly from the wall and extend upwardly along the inner side of each superheater platen so as to protect the superheater tubes from direct impact of the furnace gases. Hangers support corresponding superheater platens from the roof 15. Access openings, 42, 43 and 44 in the front wall 12 are arranged to permit cleaning of the lower half of the superheater platens 31 where the tubes are subject to the highest gas temperatures and where slagging is likely to occur. Tube blowing devices 46 are also located in this section.

As shown in Fig. l the superheater is arranged close to the front wall in the lower portion of the gas pass 10A where the gas temperatures are highest. The gases tend to be hottest toward the center and rear of the furnace. The gases flowing upwardly between the platens 31 pass along the vertical length of the tubes with relatively small heat transfer by convection in proportion to their temperatures. A high rate of heat transfer by gaseous radiation provides a. substantial steam superheating effect. The provision of the rear wall forward extension and the forwardly offset upper portion of the superheater platens causes the hot gases to flow over the bent portions of the tubes and then partly in back of the upper half of the platens before passing forwardly over the upper half of the platens. This arrangement provides a superheater section of high superheating capacity without the likelihood of overheating the tubes or excessive slagging.

In the construction shown in Figs. 2 and 3 the lower vertical portions of the superheater platens 31 are continued along the front wall 12 to the inclined wall section 12A below the gas pass 10A and then bend through the inclined wall section to the external headers 32A and 30A. The gas flow characteristics are improved by eliminating the lower horizontal stretches of the tubes in the gas pass adjacent the headers in Fig. 1. Besides eliminating the possibility of a slag collecting pocket, the Fig. 2 arrangement permits a continued straight vertical extension of some of the wall tubes in the front wall 12 along the rear side of the lower half of the platens. Some of these tubes 13C may be bent around the inclined sections of the platens, as shown in Fig. 3, to extend along the forward side of the upper half of the platens, while the remaining tubes 13A are bent rearwardly along the rear sides of these platen sections.

Referring to Fig. 4 where additional superheating surface is necessary, a supplementary radiant superheating surface 47 may be placed in a recess 55 formed in the rear wall 52 by vertically spaced inwardly projecting wall portions and 51. The radiant superheater 47 is formed by C-shaped tubes nested to form transversely spaced platens, each connected to headers 48 and 49. The tubes 52A along the rear wall are carried across the wall projections 50 and 51 to protect corresponding tube platens of the superheater 47. V f Ducts 53 and 55 to which either recirculated flue gas or air may be supplied are located below the radiant superheaters 31 and 47. Sets of nozzles 54 and 56 are connected to the ducts 53 and 55 respectively and are provided to discharge the recirculated gas or excess air, or a mixture of thetwo,.ata downward angle, into the 4 upwardly flowing stream of the gaseous products of combustion.- The velocity of the gas or air directed into the furnace through either set of nozzles may be used to vary the position of the stream of hot gases of combustion relative to the corresponding radiant superheater and thus the rate of heat transfer thereto.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of 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 the use of other features.

I claim:

1. A fiuid heating unit comprising front, rear and side walls, defining a vertically elongated chamber, a lat erally disposed gas outlet in the upper portion of said chamber, said front wall being inclined from the vertical for a portion of its height below said lateral gas pass with the upper and lower portions of said front wall being substantially vertical, means for burning fuel in the lower portion of said chamber and producing a heating gas flow upwardly therein and thence laterally through said gas outlet, said chamber having a narrow well section formed by an outward extension of the rear wall from a position above said fuel burning means to a position subjacent said lateral gas outlet, a projection in the rear of said chamber above said fuel burning means formed by a forward extension of said rear wall, said rear wall being formed to present a recessed portion extending above said projection to the bottom of said gas outlet, a radiant vapor heater disposed in said recess having a plurality of tube platens spaced across said chamber and having ends extending through said rear wall, external headers connected to the tube ends of each platen, a fluid inlet means arranged in said front and rear walls subjacent said radiant vapor heater and arranged to impinge fluid jets against the stream of heating gases, a series of vapor generating tubes extending across said recess in front of each of said platens, a radiant vapor heater having a plurality of inverted hairpin-tube parallel platens spaced transversely across said narrow upper section, each of said platens having a substantially vertical upper portion positioned a substantial distance away from said front wall and forwardly of said lateral gas opening, a middle portion bent at an angle downwardly and forwardly towards said front wall, a lower substantially vertical portion arranged close to said front wall and extending downwardly to the inclined portion of said front wall with each end bent at an angle through said inclined portion of said front wall, and external inlet and outlet headers connected to the tube ends of each platen.

2. A fluid heating unit comprising front, rear and side walls defining a vertically elongated furnace chamber; a laterally disposed gas outlet in the rear wall of the upper portion of said chamber; means for burning fuel in the lower portion of said chamber and producing a heating gas flow upwardly therein and thence laterally through said gas outlet; a radiant vapor heater having a plurality of parallel tubular platens formed of side by side tubes in panel formation and spaced transversely across said chamber; each of said platens being parallel to each other and the chamber side walls and having a lower substantially vertical portion positioned in the forward section of the furnace chamber with its for ward edge immediately adjacent said front wall to minimize radiant heat input to that portion, a middle portion bent at an angle upwardly and rearwardly towards said rear wall, and a substantially vertical upper portion positioned in the rear section of said chamber immedi* ately adjacent said lateral gas outlet and extending sub stantially throughout the height of said gas outlet; and external inlet and outlet headers connected to the tube ends of each platen.

3. A fluid heating unit comprising front, rear, and side walls defining a vertically elongated furnace cham ber; a laterally disposed gas outlet in the rear wall of the upper portion of said chamber; means for burning fuel in the lower portion of said chamber and producing a heating gas flow upwardly therein and thence laterally through said gas outlet; said chamber having a narrow upper section formed by a forward extension of the rear wall from a position above said fuel burning means to a position subjacent said lateral gas outlet; a radiant vapor heater having a plurality of parallel tubular platens formed of side by side tubes in panel formation and spaced transversely across said chamber; each of said platens being parallel to each other and the chamber side walls and having a lower substantially vertical portion positioned in the forward section of the furnace chamber with its forward edge immediately adjacent said front wall to minimize radiant heat input to that portion, a middle portion bent at an angle upwardly and rearwardly toward said rear wall, and a substantially vertical upper portion positioned in the rear section of said chamber immediately adjacent said lateral gas outlet and extending substantially throughout the height of said gas outlet; and external inlet and outlet headers connected to the tube ends of each platen.

4. A fluid heating unit comprising front, rear, and side walls defining a vertically elongated furnace chamher; a laterally disposed gas outlet in the rear wall of the upper portion of said chamber; said front wall being inclined from the vertical having a portion of its height below said lateral gas outlet with the upper and lower portion of said front wall being substantially vertical; means for burning fuel in the lower portion of said chamber and producing a heating gas flow upwardly therein and thence laterally through said gas outlet; said chamber having a narrow upper section formed by a forward extension of the rear wall from a position above said fuel burning means to a position subjacent said lateral gas outlet; a radiant vapor heater having a plurality of inverted hairpin tube parallel platens formed of side by side tubes in panel formation and spaced transversely across said chamber; each of said platens being parallel to each other and the chamber side walls and having a lower substantially vertical portion positioned in the forward section of the furnace chamber with its forward edge immediately adjacent said vertical front wall to minimize radiant heat input to that portion, a middle portion bent at an angle upwardly and rearwardly towards said rear wall forward extension, and a substantially vertical upper portion positioned in the rear section of said chamber immediately adjacent said lateral gas outlet and extending substantially throughout the height of said gas outlet; and external inlet and outlet headers connected to the tube ends of each platen.

References Cited in the file of this patent UNITED STATES PATENTS 1,826,029 Smith Oct. 6, 1931 1,944,234 Hardgrove Jan. 23, 1934 2,685,279 Caracristi Aug. 3, 1954 FOREIGN PATENTS 373,860 Great Britain June 2, 1932 274,037 Italy May 9, 1930 OTHER REFERENCES B and W Central Station Boilers Bulletin G67-A of D 1950, page 41.

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