US3796195A - Circuit arrangement for once through vapor generator - Google Patents

Circuit arrangement for once through vapor generator Download PDF

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Publication number
US3796195A
US3796195A US00247068A US3796195DA US3796195A US 3796195 A US3796195 A US 3796195A US 00247068 A US00247068 A US 00247068A US 3796195D A US3796195D A US 3796195DA US 3796195 A US3796195 A US 3796195A
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United States
Prior art keywords
panel
downflow
header
flow
generator
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Expired - Lifetime
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US00247068A
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English (en)
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W Gorzegno
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Foster Wheeler Inc
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Foster Wheeler Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B29/00—Steam boilers of forced-flow type
    • F22B29/06—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes
    • F22B29/061—Construction of tube walls
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B29/00—Steam boilers of forced-flow type
    • F22B29/06—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes
    • F22B29/061—Construction of tube walls
    • F22B29/062—Construction of tube walls involving vertically-disposed water tubes

Definitions

  • ABSTRACT A once-through vapor generator in which the roof and heat recovery area rear wall comprise a single continuous downflow pass feeding the generator primary superheater.-An outlet header for the pass, at the lower end of the pass, also serves as the inlet header for the primary superheater, flow from the header being upwardly in the superheater. A plurality of diaphragms at spaced intervals along the axis of this common header divide the header into a plurality of separate sections which in turn form in the downflow pass and superheater a plurality of narrow-width parallel downup flow circuits. The invention prevents the occurrence of recirculation of flow at low loads within the roof and heat recovery area rear Wall.
  • a plurality of mix headers maybe employed in each down-up flow circuit, at a midpoint in elevation in the heat recovery area rear Wall. This reduces the possibility of recirculation within a particular down-up flow circuit. in large sized units having a large difference in elevation between the roof inlet header and the lower common header.
  • the invention is particularly applicable to a supercritical once-through vapor generator of the Benson design, and will be described with reference thereto, although it will be appreciated that the invention has broader application, such as with the Sulzer design or with a recirculation type of generator.
  • a generator with which the present invention can be employed is described in prior Gorzegno et al. US. Pat. No. 3,556,059, patented Jan. 19, l971, assigned to assignees of the present application.
  • the vapor generator of this patent is provided with a plurality of successive passes, in series, for the flow of the fluid being heated.
  • the first three passes of the generator define the generator furnace enclosure and part of the heat recovery area enclosure.
  • the fourth pass constitutes the roof and heat recovery area rear wall, the flow from this pass then being into the generator primary superheater and finishing superheater in that order.
  • the arrangement of surfaces in the generator is such that the roof and the heat recovery area rear wall form a single continuous downflow pass between an upper roof inlet header and a lower outlet header located in the plane of the rear wall.
  • the primary superheater is located physically above the lower header, so that the latter can thus be employed as the inlet header for th superheater, as well as the outlet header for the downflow pass; i.e., the header serves as a common header for both surfaces.
  • the pass at full load, has a pressure drop of at least 50 psi, with an inlet orifice pressure drop of at least psi.
  • the pass is located upstream of the start-up bypass and pressure reducing station so that it receives at all times the full flow in the generator, which is at least the minimum 25 percent start-up flow.
  • Pressure within the pass is at about full generator pressure, for instance about 3,550 psi for a supercritical unit.
  • the invention comprises the features hereinafter fully described and particularly pointed out in the .claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but several of the various ways in which the principles of the invention may be employed.
  • FIG. 1 is an elevation, partial section view of a .vapor generator in accordance with the concepts of the present invention
  • FIG. 2 is a schematic flow diagram showing the sequence of passes of a part of the vapor generator of FIG. .1;
  • FIG. 3 is an enlarged, partial, section, elevation view showing a part of the heat recovery area of the vapor generator of FIG. 1, illustrating the concepts of the present invention
  • FIG. 4 is an elevation view of the generator heat recovery area taken along the rear side of FIG. 3;
  • FIG. 5 is an enlarged, detailed, section view of a part of the heat recovery area illustrated in FIG. 4;
  • FIG. 6 is a rear, elevation view of the heat recovery area illustrated in FIG. 5;
  • FIG. 7 is a section view taken along line 7-7 of FIG. 6;
  • FIG. 8 is a graph showing circuit characteristics of the tube circuits of FIG. 3 illustrating advantages of the invention.
  • the vapor generator comprises an upright, rectangular, furnace enclosure 12 extending from a lower hopper 14 to a roof l6. Burners 18 immediately above the hopper provide a heat input into the fluid cooled tubes of the enclosure. Near the top of the enclosure, below the roof 16, the tubes of the rear wall 20 are branched at 22 to provide a gas pass 24 leading to the generator convection area 26.
  • the generator In the convection area, frequently referred to as the heat recovery area, the generator is provided with a plurality of banks of superheating and reheating tubes, plus banks of economizer tubes.
  • the only bank illustrated is primary superheater 28 being the bank with which the present invention is primarily concerned.
  • the convection or heat recovery area 26 also is provided with a plurality of panels of tubes which form the heat recovery area enclosure and which also divide the heat recovery area enclosure into at least two gas passes or cells one of which houses the primary superheater. Only the roof l6 and rear wall 30 of the enclosure are illustrated, as these are the portions of the enclosure with which the present invention is concerned.
  • the roof 16 is comprised of a plurality of parallel tubes connected to an inlet header 32 which is located near the front upper corner of the genrator, parallel to the generator front wall.
  • the tubes emanating from the header 32 extend downwardly and then into the plane of the roof. The latter is sloped in a slightly downward direction towards the rear wall 30.
  • the tubes are then bent downwardly to define the rear wall, and in this way, the roof and rear wall tubes form a continuous net downflow pass, identified with the numeral 33, terminating in a lower pass header 34 positioned well below the elevation of the roof.
  • the primary superheater 28 comprisies a plurality of multilooped horizontally disposed spaced tubes which extend across the depth ofa convection pass of the generator adjacent to the rear wall 30.
  • the particular configuration of the primary superheater is not critical, except that the tubes of the superheater are connected at their lower ends with the roof-heat recovery area outlet header 34, and at their upper ends with headers 36 disposed above the roof 16.
  • the header 34 serves as a common header for both the downflow pass 33 and the superheater 28.
  • FIG. 2 Flow from the generator enclosure walls is through a fan-mix arrangement 38 into downcomers 40 to surfaces of the heat recovery area including vestibule side walls 42, convection area enclosure front and side walls 44, and a convection area partition wall 46.
  • the flow from these walls is collected in the inlet header 32 which feeds the roof 16 and heat recovery area rear wall panel 30, identified as downflow pass 33, the latter leading to outlet header 34.
  • the primary superheater panels 28 are shown schematically connected between the header 34 and superheater outlet headers 36.
  • the flow from the primary superheater headers 36 is then in succession through a platen superheater (not shown) and a finishing superheater (not shown) to a point of use.
  • a start-up bypass system may be employed between the platen superheater and the finishing superheater to bypass the point of use during start-up of the generator.
  • a pressure reducing station functioning to reduce the pressure of the flow to a pressure more suitable for the start-up of the turbine, may be positioned in the bypass system.
  • the circuitry illustrated in FIG. 2 is at the full operating pressure of the generator.
  • the circuit is located in the generator to receive the full flow in the generator which is at least the minimum 25 percent flow during start-up.
  • the downflow pass 33 will have a substantial pressure drop, for instance a full load pressure drop of at least about 50 psi, plus an inlet orifice drop of at least about 10 psi, which will insure a stable circuit or pass characteristic for all normal loads.
  • the downflow pass may be sensitive to certain transient conditions at start-up andlow loads, such as a fluid enthalpy unbalance at the roof inlet header 32, or an extreme firing unbalance resulting in extreme absorption input to the pass, which may cause certain tubes in the pass to recirculate and overheat at the furnace roof boundary location.
  • the outlet header 34 which is also the inlet header for the primary superheater 28, is sectioned, along its length, into a plurality of successive short header sections 47. Preferably this is accomplished by positioning a plurality of impervious diaphragms 48 at spaced intervals within the header.
  • the generator is approximately 50 feet in width, and the outlet header is divided into approximately 10 sections e achof about 5 feet in length:
  • outlet header 34 of the roof heat recovery area rear wall circuit is also the inlet header of the primary superheater
  • diaphragming the header 34 forces all of the flow from a particular five foot wide section of the downflow pass to enter a corresponding section of the superheater. This establishes in these two surfaces a plurality of narrow-width, parallel, down-up flow circuits which extend the full distance between the roof inlet header 32 and the primary superheater outlet headers 36.
  • FIG. 2 This is diagrammatically illustrated in FIG. 2, the multiple circuits being indicated by the parallel dashed lines identified with the numeral 50. As shown in FIG. 2, the dashed lines extend in a continuous fashion from the inlet header directly to the superheater outlet headers, with no reverse flow.
  • the flow in this part of the generator will be controlled by the circuit characteristics of the multiple down-up flow circuits, rather than by the circuit characteristic of the single wide down-flow pass between the roof header 32 and rear wall header 34.
  • the lowergraph of the figure contains a set of curves which give the circuit characteristics for the downflow pass alone when the lower header 34 is not diaphragmed.
  • the upper graph of FIG. 8 contains a set of curves which give the circuit characteristics of the individual down-up flow passes when the header 34 is diaphragmed.
  • Both sets of curves were plotted at start-up or low load transient conditions. Specifically, the conditions selected were an inlet fluid enthalpy, at the roof inlet header 32, of approximately 500 BTUs per pound (a sub-cooled condition); percent minimum flow during start-up; and full generator pressure of 3,550 psi.
  • the abcissa or x axis represents the flow in the pass.
  • the ordinate or y" axis gives the total pressure drop which occurs, or pressure difference which exits, between the roof inlet header and the heat recovery area rear wall outlet header 34.
  • the ordinate or v" axis gives the pressure drop which occurs, or pressure difference which exists, between the roof inlet header and the superheater outlet headers 36.
  • point b is that point representing an eixsting total pressure drop for a flow of 25 percent of full flow, for average absorption conditions.
  • This system total pressure drop is represented by line E in FIG. 8.
  • the curve line B shows the change in total pressure drop, with average absorption conditions. which occurs in the pass with increased or decreased flow through ,the pass. Line B intersects the abcissa at point b.
  • curves A andC represent abnormal conditons, namely50 percent less absorption and 50 percent greater absorption, respectively. These curves show that for the existing total pressure drop in the downflow pass, there is less flow with 50 percent greater absorption, as indicated by the location of point c, and greater flow with 50 percent less absorption, as indicated by the location of point a. These flow changes occur because of the relative variation of hydrostatic head and friction pressure drop in the circuit for the absorption and flow conditions imposed. Yet with 50 percent less absorption or 50 percent greater absorption, the curves indicate that there is still a positive flow in a downward direction in the pass, at the pressure drop in the pass, as evidenced by the intersection of curves A and C with the abcissa at points a and 0.
  • Curve D represents the circuit characteristics which would exist with extreme absorption upset, for instance 200 percent greater absorption. As shown, this curve does not intersect the abcissa, indicating that at the total pressure drop existing there will be no downward flow. In fact, a reverse flow will exist (in the tubes subjected to 200 percent greater absorption), the amount of the reverse flow being indicated by point d on the reverse side of the ordinate line or y axis. Point d is the point of intersection of the abcissa with a line D" representing recirculated flow. If total pressure drop for the system is increased from E to F then downward flow for condition D would be re-established.
  • horizontal line X represents an existing total pressure drop in the down-up circuit comprised of the roof, heat recovery rear wall pass, and primary superheater for average flow condition B" and average absorption B.
  • the intersection of curve B with line x' at b indicates the flow that ocurs with average absorption, namely B". This is the same flow that would occur for average absorption conditions in the roof-heat recovery area rear wall alone, without a diaphragmed header, as shown by vertical line B.
  • Curves A and C for 50 percent less absorption and 50 percent greater absorption, intersect horizontal line x at points a and c, indicating that in the down-up flow circuits, there is the compensating effect of more flow with greater absorption and less flow with less absorption.
  • curve D shows that there is a significant increased flow in the down-up flow circuits (as compared to the reverse flow of the lower set of curves with this absorption). This increased flow with greater absorption is the result of the driving force stemming from the heat input into each up-flow superheater portion of the individual down-up flow circuits.
  • a principal advantage of the invention should be apparent from the curves of FIG. 8. Because the greater part of absorption upsets in a generator will be between different sections of the unit, such as a center section versus an end section, arranging the circuitry in accordance with the concepts of the invention, better circuit characteristics and more stable flow is obtained.
  • FIG. 5, 6 and 7 An embodiment of the present invention is illustrated in FIG. 5, 6 and 7.
  • the difference in elevation between the common outlet header 34 and the roof inlet header 32 may be about 55 feet.
  • the same elevation for larger coal fired steam generators may be as much as to feet, because of the larger size of these generators.
  • extreme absorption differences tube-tube may result in recirculation within each diaphragmed header section, in particular with a very low enthalpy input flow into the roof header 32.
  • This recirculation is prevented by employing mix headers for each down-up flow section.
  • these headers are employed at a midpoint in elevation in the roof-heat recovery area rear wall panel to mix the fluid within each section and to re-introduce an orifice pressure drop in the succeeding down-flow portion of the section.
  • FIGS. 5, 6 and 7, the mix header arrangement is illustrated. These mix headers are disposed outside of the rear Wall 30, horizontally across the face of the wall. Two headers 52 and 54 are employed for each section, the headers being at spaced elevations along the wall. Alternate tubes of each section are bent outwardly at a first elevation 56' and are connected with feeders 57 which lead to the upper header.
  • the header is provided with a longitudinally extending diaphragm 58 with an opening 60 in the center (FIG. 7), and the flow is from one side of the diaphragm to the other through the opening; Return feeders 62 transmit the flow back into tubes in the plane of the rear wall along the same centers occupied by the alternate tubes feeding the header.
  • the lower header 54 is fed by the remaining alternate tubes of the rear wall section, this header also being provided with a diaphragm 58 and mixing occurring in the same way as with the flow in the upper header.
  • An advantage of this aspect of the invention is that it can be applied readily to existing units. It is a simple matter to modify the rear wall panel to include the mix headers.
  • a once-through vapor generator comprising:
  • thermoelectric recovery area means defining a furnace enclosure and a heat recovery area, said heat recovery area including a downflow panel which forms a wall of the area, the tubes of the wall being closely spaced, parallel and welded together along their lengths to form a gastight construction;
  • said outlet header means being divided into a plurality of sections which establish in the downflow panel and further upflow heat absorption surface a plurality of adjacent parallel down-up flow circuits each having a downflow portion arid an upflow portion and each being of substantially smaller dimension, width-wise, than said panel, wherein the circulation in the downflow portion of each circuit is considerably enhanced by the driving force in such cicuit upflow portion.
  • a once-through vapor generator comprising:
  • an enclosure including a roof and a heat recovery area rear wall forming a single continuous downflow panel, the tubes of the panel being parallel and closely spaced together;
  • a primary upflow superheater positioned in the generator heat recovery area above said outlet header; said downflow panel being of sufficient width and having sufficient heat absorption surface whereby recirculation could occur in the panel;
  • said partitioning means comprises a plurality of diaphragms disposed in the outlet header at regularly spaced intervals along the axis of the header.
  • a once-through vapor generator comprising:
  • an enclosure including a roof and a heat recovery area rear wall forming a single continuous downflow panel, the tubes of the panel being parallel and closely spaced together;
  • a primary upflow superheater positioned in the generator heat recovery area above said outlet header; said downflow panel being of sufficient width and having sufficient heat absorption surface whereby recirculation could occur in the panel;
  • the generator of claim 4 wherein the tubes of the down-flow panel are welded together along the lengths thereof to form a gas-tight enclosure; said generator being top supported, further including two mix headers for each down-up flow circuit at spaced elevations in the downflow panel, alternate tubes of each downflow panel being connected to the upper mix header of the mix header pair, the remaining tubes being connected to the lower header of the mix header pair, thereby defining a substantially continuous load bearing tube surface.
  • said mix headers include a diaphragm means longitudinally disposed therein, an opening in said diaphragm means located axially in about the center of the diaphragm means, and means communicating the downflow panel tubes with opposite sides of the diaphragm means whereby the fluid flow in said tubes is through said opening causing mixing thereof.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
US00247068A 1972-04-24 1972-04-24 Circuit arrangement for once through vapor generator Expired - Lifetime US3796195A (en)

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US24706872A 1972-04-24 1972-04-24

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AU (1) AU465725B2 (xx)
CA (1) CA971444A (xx)
ES (1) ES414504A1 (xx)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5669333A (en) * 1996-02-13 1997-09-23 The Babcock & Wilcox Company Once-through steam generator furnace outlet fluid mix to minimize the number of headers and riser materials

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4244327A (en) * 1979-06-11 1981-01-13 Combustion Engineering, Inc. Steam generator arrangement

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2962005A (en) * 1958-05-16 1960-11-29 Babcock & Wilcox Co Forced flow vapor generating unit
US3001514A (en) * 1959-05-13 1961-09-26 Babcock & Wilcox Co Support and expansion apparatus for a vapor generating and superheating unit
US3050042A (en) * 1958-04-11 1962-08-21 Combustion Eng Steam generator organization

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3556059A (en) * 1969-01-28 1971-01-19 Foster Wheeler Corp Two-pass furnace circuit arrangement for once-through vapor generator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3050042A (en) * 1958-04-11 1962-08-21 Combustion Eng Steam generator organization
US2962005A (en) * 1958-05-16 1960-11-29 Babcock & Wilcox Co Forced flow vapor generating unit
US3001514A (en) * 1959-05-13 1961-09-26 Babcock & Wilcox Co Support and expansion apparatus for a vapor generating and superheating unit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5669333A (en) * 1996-02-13 1997-09-23 The Babcock & Wilcox Company Once-through steam generator furnace outlet fluid mix to minimize the number of headers and riser materials

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JPS5138361B2 (xx) 1976-10-21
JPS4941702A (xx) 1974-04-19
AU5482473A (en) 1974-10-31
ES414504A1 (es) 1976-05-01
CA971444A (en) 1975-07-22
AU465725B2 (en) 1975-10-02

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