US2737160A - Steam generators employing radiant superheaters and reheaters - Google Patents

Description

March 6, 1956 w. H. ARMACOST ET AL 2,737,160

STEAM GENERATORS EMPLOYING RADIANT SUPERHEATERS A-ND REHEATERS Filed May 29, 1951 3 Sheets-Sheet l 25 37 36 40 43 25b T0 Drum l7 4L'IIIIIIIIIIllllllIIIIIIIIIIIIIIIIIIIIIIIIIIIA(IIIIAWIIIIIIII l9 3/ 'INVENTORS 3 Wilbur H. Armocost BY Z153? Leonard J. Marshall' March 1956 w. H. ARMACOST ET AL STEAM GENERATORS EMPLOYING RADIANT SUPERHEATERS AND REHEATERS 3 Sheets-Sheet 2 Filed May 29, 1951 Fig. 4.

March 6, 1956 Filed May 29, 1951 w. H. ARMACOST ET AL 2,737,160

STEAM GENERATORS EMPLOYING RADIANT SUPERHEATERS AND REHEATERS 3 Sheets-Sheet 3 Fig; 5.

l I l i I l I l i 20 46 INVENTORS l9 Wilbur H. Armocpst 22 BY Leonard J. Marshall United States Patent '0 STEAM GENERATGRS EMPLGYING RADIANT SUPERHEATERS AND REHEATERS Wilbur H. Armacost, S'carsdale, N. Y., and Leonard J.

Marshall, T'enafly, N. 5., assignors to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Application May 29, 1951, Serial No. 228,944

3 Claims. (Cl. 122-478) This invention relates to large steam generators for delivering steam at high pressures and temperatures.

In such high capacity steam generators delivering steam at high temperatures it is essential in many in stances (as when the generator serves a steam turbine) to use radiant superheaters and/ or reheaters lining a wall or walls of the generator furnace. However, experience has indicated that cracks occur in the tubular elements of such superheaters when they are exposed to the region of high heat absorption within the furnace and when the steam temperatures and consequently the metal temperatures of said elements are relatively high. Such cracks are the result of thermal stresses caused by a too high rate of heat absorption occurring on one side of the tube.

One object of this invention is to overcome the above ditlicnlties by providing improved arrangements and organizations of radiant superheaters and/or reheaters upon a wall or Walls of the furnace which the steam generator comprises.

Another object is to provide a novel combination of such superheaters with additional heat absorbing elements adjacent the streams of fuel entering the furnace.

Additional objects and advantages will become apparent from the following description of illustrative embodiments of the invention when taken in conjunction with the accompanying drawings, wherein:

Fig. l is a vertical cross section through a steam gencrating unit embodying the invention;

Fig. 2 is a horizontal cross section through the Fig. 1 furnace taken on line 22 of Fig. 1;

Fig. 3 is a fragmentary vertical cross section taken on line 3--3 of Fig. 1 showing how radiant superheater and reheater tubes are arranged on the rear Wall of the furnace;

Fig. 4 is a vertical cross section through a steam generating unit embodying a modified form of the invention shown in Fig. 1;

Fig. 5 is a partial vertical cross section taken on line 55 of Fig. 4 and showing the tube arrangement comprising the rear wall of the furnace;

Fig. 6 is a modification of the tube arrangement Fig.

Figs. 7 and 8 are partial vertical cross sections simila to a corresponding portion of Fig. 4 and showing two possible forms of the partition walls dividing the furnace into compartments C.

In Figs. 1, 2 and 4 the furnace A is enclosed by front and rear walls 1 and 2 plus side walls 3 and roof 4 all of which walls are lined with fluid cooled tubes. At the furnace bottom the front and rear walls 1 and 2 slope inwardly and downwardly to form a hopper 5 with an opening 6 at the botom for the withdrawal of ash from the furnace. At the top of the furnace A an oiftake 7 is provided for conveying the hot products of combustion out of the furnace.

Patented Mar. 6, 1955 A multiplicity of burners 8 project fuel and air (from sources not shown) into an offset portion at the front of the furnace in parallel streams in a downwardly direction adjacent the front furnace wall as shown by the arrow. As the streams of burning fuel approach the furnace bottom, they turn toward the rear of the furnace (again as indicated by the arrow) then flow upwardly adjacent the rear wall 2 and finally, when combustion is complete, leave the furnace at a high temperature through the furnace offtalce 7. Air conduits 9 adjacent the front wall 1 deliver additional air through apertures provided therefor in the front wall 1, where shown by the arrows, into the descending fuel and air stream to aid in the combustion of the fuel.

The hot furnace-leaving gases in passing through the oiftake 7, flow over banks of tubular superheater elements, generally designated as S in Fig. l, thence flow downwardly through the conduit 10 containing banks of tubular economizer or evaporator elements generally designated as E, and thence continue through conduit 10 and through the gas side of the air heater AP, here shown as the well known regenerative type, and finally through the breeching 11 to exhaust fan and chimney (not shown). The air for combustion is delivered by forced draft fan 12 via duct 13 through the air side of thea'ir heater AP, thence in heated condition through duct 14 into the air conduits 9 and to the burners 8 via ducts 15 and 15a.

Even though not shown in Fig. 4, an economizer, an air heater, forced draft and exhaust fans and interconnecting conduits and ducts may also be associated with the Fig. 4 furnace as shown and described above for Fig. 1.

In Fig. l the fluid cooled tubes lining the rear wall 2 of the furnace A are all steam heating elements (see Fig. 3) to be described below, while those lining the front wall 1 and the two side walls 3 are all steam generating tubes 16. The steam generating tubes 16, in Fig. 1, receive water from the steam and water drum 17 via downco'mer pipes 18, 180, which connect into the main supply header 19, thence via connecting pipes 20 and 21 to the respective headers 22 and 23 to which the steam generating tubes 16 of the front and side walls are respectively connected. The front wall tubes 16 deliver their steam and water mixture'via the roof tubes 24, which are the continuations of tubes 16, and via the header and connecting pipes 25 into the steam and water separating drum 17.

The side wall tubes 16 within the main portion of the furnace discharge their steam and Water mixture into the top header 25a which is connected to the steam drum 17 by pipes 25b. The side wall tubes 16 within the offset portion of the furnace beneath the burners 8 discharge their steam and water mixture into the header 25c adjacent the burners 8 and thence into the riser tubes 25d. These riser tubes 25d bend upwardly toward the front wall 1 and rise in alignment with the tubes 16 up said wall to the roof and thence continue under the roof and to the steam drum 17 in the same manner as do tubes 16 and in alignment with tubes 24, through header and pipes 25.

As shown in Fig. 3, portions of the steam heating tubes lining the outer portions of the rear wall '2, are groups of superheater elements 26, while those lining the middle portion of the rear wall 2 are reheater elements 27. The elements 32 of superheater groups 26, following the direction of steam flow, leave the steam and water drum 17 intwo groups of aligned spaced tubes, thence pass forwardly beneath the roof 28 of conduit 10 above the eeonomizer E, thence pass downwardly in offset open formation as shown at 29, thence pass downwardly and forwardly in alignment on the bottom wall 30 of offtake 7, thence pass down the face of the rear wall 2 in spaced alignmentin the two spaced apart groups 26, Fig. 3, and connect into the headers 31 adjacent the outlet 6 of hopper 5.

There are two headers 31 in Fig. 3 which accommodate the two groups 26, one adjacent each of the furnace side walls 3. Each group 26, see Fig. 3, contains the spaced superheater tubes 32 carrying the down flow steam from the drum 17 to the headers 31, as described, and also contains the superheater tubes 33 carrying the up flow steam from the headers 31 to the top of the furnace. The down flow tubes 32 and up flow tubes 33 alternate in side by side arrangement as the arrow markings of Fig. 3 indicate. When the up flow superheater tubes 33 reach the bottom wall 30 of the oiftake 7, they offset into an open formation, as shown at 34, and continue upwardly through the furnace roof 4 to headers 35 of which there are two, one adjacent each of the side walls 3, similarly arranged as headers 31 shown in Fig. 3. From headers 35 the steam flows serially via connectors 36 and header 37 through the convection banks of tubes 38 and 39 of superheater S, in counterfiow to the flow of gases through the oiftake 7 and thence into the superheater oiftake header 40. Said convection superheater S extends across the entire width of the offtake 7.

The tubular reheater elements 27, Fig. 3, lining the rear wall 2 occupy the central portion of the wall between the two groups of superheater tubes 26. The supply header 42, which lies between the headers 31, delivers steam from the turbine (not here shown) into the bottom of all reheater elements 27. These elements 27 rise in alignment along the rear wall 2 and when they reach the bottom wall 30 of the oiftake 7, they ofiset into an open formation, as shown at 34, and continue upwardly through the furnace roof 4 to a central offtake header 43 whence the reheated steam returns to the turbine. Said central header 43 lies between the two outer headers 35 earlier mentioned.

Each of the furnaces shown by Figs. 1 and 4 has its front portion provided with a multiplicity of banks of aligned vertical steam generating tubes 44, here represented as three, Figs. 2, 7, 8, extending into the furnace from a point spaced from the front wall 1 toward the rear wall 2. These banks of tubes 44 form partitions which divide the furnace below the burners 8 into compartments C, here shown as four (see Fig. 2), each compartment C receiving the fuel and air streams descending from a group of said burners. As the burning fuel streams turn toward the rear of the furnace in the lower portions of the compartments C, they leave the compartments and then turn upwardly into the open portion of the furnace and rise to leave the furnace through the oiftake 7.

As shown in Figs. 7 and 8, the banks of tubes 44 each receive water from a bottom header 45 (likewise represented in Fig. 2) which is supplied by feeder tubes 46 from the supply header 19 (fed from downcover 18 as indicated by Fig. l). The upper ends of these dividing wall tubes 44 discharge in the design of Fig. 7, their steam and water mixture into the header 47 whence the riser tubes 48 convey the mixture along the upper portion of the front furnace wall 1, across beneath the furnace roof 4 to header 25, Fig. 1, and thence via header and tubes 25 into the steam and water separating drum 17. In the design represented by Fig. 8, the banks of partition tubes 44 deliver through bifurcated ends into the riser tubes 48 as shown, and these convey the steam and water mixture to the steam drum 17 as described above, thereby dispensing with the header 47 and reducing the resistance to fluid flow through the circuit.

Said banks of partition tubes 44 supply additional heat absorbing surface for the furnace A and consequently provide a relatively lower furnace temperature which permits the use of the radiant superheaters 26 and 27 upon the rear wall 2 of the furnace while maintaining a favorable combustion rate within the furnace. Taking advantage of the above, the arrangement of the superheaters as disclosed provides the added improvements of having the relatively cool steam flowing through the superheater or reheater tubes adjacent the bottom of the furnace where the furnace gases are hot, but cooler than beneath the burners 8, and having the hotter steam flowing through said tubes adjacent the top of the furnace where the furnace leaving gases are coolest.

By arranging said tubes in open formation at the offtake 7, as shown at 34, the relatively cool furnace gases heat said tubes over their entire circumference and thereby relatively improve the heat absorption at that location. Moreover, because of the cooler temperatures of the furnace leaving gases flowing over the superheater tubes which are spaced across the offtake 7, and because of the relatively lower unit heat transfer rate there, the metal temperatures of said tubes remain generally about or perhaps below the temperature of the superheater tubes in the lower portion of the furnace so that none of said metal temperatures become unsafe. In the case of the superheater elements 32-33, the final high temperature is then added to the steam by the convection superheater S in a relatively cool gas zone. By the disclosed arrangement of the radiant superheater tubes 32 upon the face of the bottom wall 30 of the otftake 7, that portion of the wall is protected thereby and precludes the necessity of locally using a special heat resisting construction or the special use of steam generating tubes.

In the modified form of the invention shown in Fig. 4, the rear wall 2 is lined only with superheater tubes 26 (3233), as shown in Fig. 5, the reheater tubes 27, shown in Fig. 3, being omitted from this wall. The return header 31 and the collector header 35 now extend for the full width of the furnace wall 2. The routing of the superheater tubes is, with respect to steam flow, the same as that in Fig. 1, that is, from steam drum 17, the elements 32 pass beneath roof 28, across offtake 7 in open formation, down floor 30, down the face of wall 2 to header 31, thence the elements 33 pass up the face of wall 2, in alternation with the down going elements 32, across oiftake 7 in open formation, through roof 4, into header 35, thence serially through banks 39, 38 of convection superheater S (see Fig. 1). and into outlet header 40.

Obviously, if the superheater bank of tubes 26 need not be the full furnace width, it may be reduced in width as shown in Fig. 6 and water wall tubes 49 may occupy the remaining wall space. These will be supplied with water from bottom header 50, Figs. 4, 6, and may follow paths similar to tubes 32 of superheater 26 with upflowing steam and water discharging into the drum 17. Header 50 may receive water from header 19 via tubes 50a, Fig. 4.

In the modification of the invention shown in Fig. 4, the tubes of the reheater (corresponding to 27 in Figs. 1 and 3) line the two side walls 3 in two groups. In each reheater one group of tubes 51 extends from a steam supply header 52 downwardly, with respect to steam flow, to bottom header 53 and the other group of tubes 54 extends upwardly from header 53 to the offtake header 55. The coolest steam from the turbine passes through tube groups 51 adjacent the end chambers C and its temperature rise is effected by the radiation of heat from the fuel streams of the burners 8 discharging into the end chambers C. Regulation of the temperature of the steam passing through the tube groups 51 may be effected by varying the amount of fuel burned in the said end chambers C.

Again as in the reheater of Fig. 1, the coolest steam flows through the tubes 51 and through the lower portions of tubes 54 where the furnace gases are hottest, and the hottest steam flows through the upper portions of tubes 54 where the furnace gases are coolest. The combustion rates may be moderated in said end chambers C and proportionately increased in the remaining chamhers C. Such placing of the hotter superheater tubes in the cooler furnace gas zone eliminates the danger of cracks due to thermal stresses which have occurred in the tubes when heated mostly on one side in the region of high heat absorption and high metal temperatures. As a result of the improved arrangement of superheater tubes, the locally high metal temperatures heretofore encountered have been eliminated and safe metal temperatures are achieved throughout the extent of the tubular ele ments of said superheaters.

As shown in Fig. 1, the downcomer 18, 18c, conducts water from the steam and water drum 17 directly into the bottom supply header 19. Should conditions prevail where the use of smaller steam generating tubes would be advantageous, a controlled or forced circulation of the boiler water may be employed by directing the downcomer water from drum 17 through pipe 18a, through pump 55, through pump discharge pipe 18b and thence through pipe 180 again to the main supply header 19.

While only illustrative embodiments of this invention have been here shown and described, it will be understood that changes in construction, combination and arrangement of parts may be made without departing from the spirit and scope of the invention as claimed.

What we claim is:

1. In a steam generator having a steam and water separating drum and a vertically extending furnace with front, rear and side walls and a furnace offtake adjacent the top of the furnace with the bottom of said oiftake extending forwardly to the rear wall of the furnace; fluid cooled tubes lining the walls of the furnace including superheater elements organized to conduct steam away from said drum; a multiplicity of fuel burners adjacent the front wall delivering fuel into the lower portion of said furnace to cause the burning products of combustion to rise to said offtake; a superheater having an intermediate header and an outlet header and including the aforesaid wall-lining tubular elements disposed in said furnace to receive heat at least in part by radiation from the aforesaid burning fuel, said elements being arranged to convey the steam in parallel paths from said steam and water separating drum downwardly across the rearward opening of said offtake in spaced relation, thence forwardly upon the floor of said ofltake, thence downwardly upon a portion of the rear wall of said furnace in spaced parallel paths, thence upwardly upon said rear wall in spaced parallel paths alternating with said downward paths, thence upwardly across the forward opening of said oiftake in spaced relation and thence into said intermediate header; a superheater finishing-0E section receiving heat from said products of combustion mainly by convection and disposed above the bottom of said offtake, said convection superheater comprising tubular elements spacedly arranged across the width of said offtake and being connected on the steam inlet side thereof to said intermediate header and on the steam outlet side thereof to said outlet header, a reheater having an inlet header adjacent the bottom of the furnace and an outlet header above the furnace, said reheater having tubular elements that extend from said inlet header upwardly upon the remaining portion of the rear wall of said furnace in parallel relation, thence upwardly across the forward opening of said offtake in spaced relation and thence into said reheater outlet header; means to supply fuel and air to said burners.

2. In a steam generator having a steam and water separating drum and a vertically extending furnace with front, rear and side walls and a furnace ofitake adjacent the top of the furnace with the bottom of said oflitake extending forwardly to the rear wall of the furnace; fluid cooled tubes lining the walls of the furnace some of which are steam generating tubes connected to deliver steam into said drum and some of which are superheater elenients organized to conduct steam away from said drum; a multiplicity of spaced banks of aligned steam generating tubes within the furnace forming division walls that extend from adjacent said front wall rearwardly toward said rear wall for a portion of the depth of the furnace and to the bottom thereof and that form compartments bounded by said banks and said front wall and portions of the side walls, said compartments being open towards the rear of the furnace; groups of fuel burners adjacent the front wall of said furnace each group serving one of said compartments and projecting streams of fuel and air toward the lower portion of that compartment to flow therethrough while burning and thence continue to flow through the main furnace while rising to said otftake; a superheater having an outlet header and including the aforesaid wall-lining tubular elements disposed in said furnace to receive heat at least in part by radiation from the aforesaid burning fuel, said elements being arranged to convey the steam in parallel paths from said steam and water separating drum downwardly across the rearward opening of said oiftake in spaced relation, thence forwardly upon the floor of said ofi'take, thence downwardly upon a portion of the rear wall of said furnace in spaced parallel paths, thence upwardly upon said rear wall in spaced parallel paths alternating with said downward paths, thence upwardly across the forward opening of said offtake in spaced relation; banks of tubular convection elements of said superheater located in said oiftake, tubular connections between said aforementioned radiant-heat-receiving elements and said convection elements and said outlet header whereby the steam leaving said aforementioned elements flows through said convection elements into the outlet header; a reheater having an inlet header adjacent the bottom of the furnace and an outlet header above the furnace, said reheater having tubular elements that extend from said inlet header upwardly upon the remaining portion of the rear wall of said furnace in parallel relation, thence upwardly across the forward opening of said oiftake in spaced relation and thence into said reheater outlet header; means to supply fuel and air to said burners; and means to supply water from said steam drum to said steam generating tubes.

3. In an upright elongated furnace for the heating of high temperature high pressure steam having a gas off take adjacent the upper end thereof and including a furnace side wall exposed to a rising stream of hot combustion gases the temperature of said gases decreasing from that prevailing in a high temperature gas zone adjacent said walls lower end to that prevailing in a relatively low temperature gas zone adjacent said walls upper end; fiuid cooling means for said Wall comprising radiant reheater tubes lining an inner vertical surface portion of said wall said tubes having an inlet adjacent said walls lower end for receiving relatively cool steam and an outlet adjacent said walls upper end for discharging relatively hot steam, said tubes conducting the steam upwardly in parallel paths from said high temperature zone to said low temperature zone whereby the cold ends of said reheater tubes are exposed to relatively hot gases and the hot ends to relatively cool gases; and other fluid cooling means comprising radiant superheating tubes lining the remaining inner surface of said wall a first half of said tubes having inlets adjacent said walls upper end and outlets adjacent said walls lower end, a second half of said superheater tubes having inlets adjacent said walls lower end and outlets adjacent said walls upper end, and conduit means connecting said outlets of the first half of said radiant superheating tubes with the inlets of the second half of said tubes; and convection superheater tubes communicating with the outlets of said second half tubes for receiving steam partially heated by flow through said radiant superheater tubes, said convection tubes being disposed adjacent said gas offtake within a zone of said gas stream that is remote and downstream of said high temperature gas zone, whereby extreme temperature differences are substantially prevented Within the struc ture of said furnace wall and unsafe metal temperatures avoided in the hot end portions of said radiant superheating and reheating tubes.

References Cited in the file of this patent UNITED STATES PATENTS Armacost Sept. 3, 1940 Drewry June 3, 1941 Krug et a1 Aug. 4, 1942 Bailey' Sept. 5, 1944 Woolley May 15, 1951

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