US3344777A

US3344777A - Once-through vapor generator furnace buffer circuit

Info

Publication number: US3344777A
Application number: US501168A
Authority: US
Inventors: Walter P Gorzegno
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1965-10-22
Filing date: 1965-10-22
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03
Also published as: GB1163554A

Description

Oct. 3, 1967 w. P. GORZEGNO ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFER CIRCUIT 3 Sheets-Sheet 1 Filed Oct. 22, 1965 lNVENTOR WAIT/F1? P GORZEG/VO ATTORNEY Oct. 3, 1967 ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFER CIRCUIT Filed Oct. 22, 1965 3 Sheets-Sheet 2 U1 5 gIZO Z I U] E 0 MI 1::

LU so E E r r 5 so Q E 40 A if I s 5 I 2o- W U ll. E: O

0 2o 40 so so PERCENT LOAD F/g.4

oowucouen T0 PASS4\ BUFFER BUFFER cmcun' CIRCUIT PASS 3 I as 44 2 26 46 4 \L k 26 I [4 RISER FROM PASS l.

INVENTOR WAL 767? f GORZEG/VO BY @4144, A PZ ATTORNEY Oct. 3, 1967 w. P. GORZEGNO 3,344,777

ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFER CIRCUIT Filed Oct. 22, 1965 3 Sheets-Sheet 5 Fig.5

er to Pass 4 INVENTOR WAL 75,? F? GO/QZEG/VO ATTORNEY United States Patent Ofiiice 3,344,777 Patented Oct. 3, 1967 3,344,777 ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFER CIRCUIT Walter P. Gorzegno, Florham Park, N.J., assignor to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Oct. 22, 1965, Ser. 501,168 6 Claims. (Cl. 122-406) ABSTRACT OF THE DISCLOSURE A forced-flow once-through vapor generator wherein the furnace is an all-welded enclosure comprising a plurality of upright tube panels welded together, each of the tube panels having parallel tubes welded together. The panels are serially connected, with panels at different temperature levels being separated from each other by an intermediate panel. The fluid entering the intermediate panel is a mixture of the fluids entering the separated panels.

This invention relates to a forced-flow supercritical or subcritical once-through vapor generating unit.

A vapor generating unit, of the type to which the present invention is applicable, is described in co-pending application, Ser. No. 370,604, filed May 27, 1964, by Walter P. Gorzegno et al.

In this type of a unit, the furnace wall enclosure is divided vertically into upper and lower portions, the lower portion constituting a high temperature radiant heat zone contaning the burners for the unit. The lower portion itself is divided peripherally into a plurality of pass sections, each pass section comprising parallel finned tubes welded along their lengths into vertically oriented sideby-side panels. Inlet and outlet headers serve each pass section separately, and are connected so that the flow in the lower enclosure wall is in series through the successive pass sections. From the lower portion of the furnace and pass sections therefor, the fluid flows to the upper portion constituting at least one additional flow pass in the furnace area.

The circuits in both the upper and lower portions of the furnace are divided into as many passes as the needed to meet minimum velocity and enthalpy pick-up requirements. Since the burners are located in the vicinity of the lower passes, where high local heat inputs can be expected, the lower portion of the furnace is generally provided with a greater number of passes than the upper portion.

The arrangement offers many advantages. Flow is always up in the furnace tubes. Frequent mixing resulting in low fluid anthalpy pick-up for a circuit gives good circuit characteristics and eliminates the need for using orifices for uniform distribution of flow. A desired flexibility in design is available, and the use of excessively small diameter tubes, subject to plugging, is avoided.

Since the enthalpy of the fluid increases from pass to pass in the furnace periphery, a temperature differential exists between passes. If the tubes of one pass panel are welded directly to those of another, the higher the temperature differential, the higher the stresses will be in the panel joints. It is advantageous to provide a means to reduce these stresses to lowest levels.

In accordance with the invention, this means is provided, in a once-through vapor generator which includes a plurality of the vertically oriented adjacent tube panels welded together into a gas-tight enclosure, a header means connecting the panels so that the fluid makes successive flow passes in the generator with the panels of successive passes remote from each other, and at least one additional header arrangement adapted to transmit predetermined portions of the flow from the inlet ends of said remote panels to a panel intermediate the remote panels. The intermediate panel, which can be termed a buffer pass, thus contains a mixture of fluid taken from the two successive passes and is at an average temperature intermediate those of the successive passes. In practice, a temperature differential exists, between adjacent welded tubes of the in-series pass panels and the panel of the buffer pass, less than F., a generally accepted limit based on weld and tube strength design criteria.

The invention and advantages thereof will become more apparent on consideration of the following description, and accompanying drawings in which:

FIGURE 1 is an oblique view of a portion of a forced flow once-through vapor generator illustrating the invention;

FIGURE 2 is a schematic diagram of the generator of FIG. 1 illustrating the invention;

FIGURE 3 is a reduced size schematic oblique diagram illustrating the full furnace circuitry and invention of the generator of FIG. 1;

FIGURE 4 is a load versus differential temperature graph illustrating advantages of the invention; and

FIGURE 5 is a cross-section elevation view of the generator of FIG. 1.

eferring to FIGS. 1 and 5, the vapor generator furnace is of the flat-bottom type with fluid from an economizer (not shown) passing through a floor pass 12 of the generator to an outlet header 14 parallel to the front wall 16 of the furnace. From the header l4, risers 18 transmit the partially heated fluid to an inlet header 20, which feeds the tubes of a panel 22 making up the middle portion of the front wall 16. The tubes of this panel constitute the furnace second pass, the floor panel being a first pass. The tubes of panel 22 exit in an upper header in the front wall (not shown in FIG. 1) and the fluid from this header is transmitted by parallel downcomcrs 24 to L-shaped headers 26 in opposite front corners of the furnace periphery. These headers feed the tubes of L-shap-ed panels 28 (also in the front corners of the generator) constituting pass 3 for the furnace circuitry.

It is apparent that the tube of pass 2 will be at a temperature different from those of pass 3. Since the furnace tubes are welded together along their lengths to form a gas-tight enclosure, a stress would be set up in the joint between

passes

2 and 3 if the tubes of these passes were joined together. To reduce this thermal stress, a buffer circuit is provided comprising headers 30 positioned on opposite sides of the front wall second pass header 20, between this header and the L-shapcd headers 26 for pass 3. On opposite sides of the second pass panel 22 between this panel and the panels 28 for the third pass, buffer circuit panels 32 receive fluid from the headers 30. The buffer circuit, comprising the headers 30 and panels 32, receive fluid from the second pass downcomers 24 (or third pass inlet) via small diameter lines 34, and also receive fluid from risers 18, or the second pass inlet, through orifice valves 36. By proper proportioning of the lines 34 and orifice valves 36, the buffer circuit receives predetermined proportions of fluid from the inlet ends of both passes 2 and 3, to attain a temperature which is intermediate the temperatures of the

pass

2 and 3 circuits.

The remainder of the side walls and the rear wall of the furnace enclosure are made up of tubes of a pass No. 4 (item 40), receiving fluid from pass No. 3 via the U- shaped header 42. The dimensions of pass No. 4 are consideraly greater than those of prior passes, to accommodate design requirements.

Butler circuits could also be disposed between the tubes of

passes

3 and 4. However, in this example, the passes are sized in such a way that the temperature differential between these two passes is substantially less than 100 R, an accepted limit, obviating the need for the buffer circuit.

FIGURE 2 provides a clear illustration of the fluid flow in the furnace circuitry. From the downcomer and floor pass 1, the fluid is transmitted to the pass No. 2 header, designated item 20. Downcotners 24 transmit the pass No. 2 flow to headers 26 for pass No. 3. At

connections

44 and 46, predetermined proportions of the flows to both pass Nos. 2 and 3 are transmitted to the butter circuit passes, items 32. Orifices 36 and line sizing establish the proportions obtained. The proportions of each flow are usually kept at 50-50. The butler circuit outlet corresponds to the outlet of pass 3, and the fluid is then transmitted to pass No. 4, not shown in FIG. 2.

From pass No. 4, the fluid follows the circuitry set forth in the co-pending application mentioned above, being transmitted to a U-shaped pass No. 5 making up the entire front and side wads of the upper part of the furnace. This is shown in FIG. 3, connections 48 serving to transmit the flow.

As a general rule, the buffer circuit will comprise at least 5% of the tubes in the applicable wall width to achieve a practical reduction of joint longitudinal thermal stress. A typical temperature differential between passes 2 and 3 may be in the range from 100 F. to 135 F. By use of the buffer circuit, the temperature differential be tween tubes at the joint will be reduced in half. Experimental stress analyses have shown that longitudinal thermal stresses between tube vertical joints are reduced by approximately when the butter circuit is about 12.5% of the total panel width. Geometry is im portant, the more tubes employed in the buffer circuit for a constant wall dimension, the greater will be the reduction in longitudinal thermal stress.

FIG. 4 is from a particular example in accordance with the invention. The graph shows that the largest temperature differentials occur at load. With a maximum pass 2 and a pass 3 temperature differential of about 106 F.. a butler circuit of 1?. tubes was used. Headers for the buffer circuit provided an equal flow from both

passes

2 and 3. sufficient to have the same flow in pounds per hour-tube as in

passes

2 and 3. This resulted in a temperature differential of 50 F. between the buffer circuit inlet and the

pass

2 and 3 inlets, at 30% load. For the geometry involved, that is, buffer circuit width vs. Wall applicable width, a 15% reduction in joint longitudinal thermal stress is predicted.

Although the invention has been described with respect to specific embodiments, many variations within the spirit and scope of the invention as defined in the following claims will be apparent to those skilled in the art.

What is claimed is:

1. A once-through vapor generator which includes a plurality of parallel vertically oriented tubes welded into laterally adjacent panels to define an essentially gas-tight furnace enclosure, and header means connecting panels laterally remote from each other to define at least two upfiow flow passes in series so that fluids entering said panels are at different enthalpies, the improvement comprising at least one additional header means connected to the panel intermediate said remote panels; and

means for transmitting to said additional header means predetermined portions of the flow to said remote panels, the enthalpy of the fluid entering said intermediate panel thereby being intermediate the enthalpies of the fluids entering said remote panels.

2. A once-through vapor generator comprising a rectangular vertically oriented furnace enclosure; the enclosure comprising sideby-side panel sections defining a plurality of laterally adjacent upflow flow passes; each panel section comprising parallel vertically oriented finned tubes welded together along their lengths; the panel sections being welded together lengthwise thereof so that the enclosure is essentially gas tight; burner means radiantly heating said enclosure; header means connecting at least two of the flow passes in series, the enthalpy of the fluid increasing in the Successive passes; and second header means adapted to receive predetermined portions of the flow from the inlet ends of both said flow passes and to mix and feed said portions to a pass the tubes of which define a panel section intermediate the panel sections of said two flow passes. 3. A once-through vapor generator comprising a rectangular vertically oriented furnace enclosure having front, rear and side walls; the enclosure being divided vertically into upper and lower portions; burner means in the lower portion front and rear walls radiantly heating said enclosure; the lower portion of the enclosure comprising a plurality of side-by-side panel sections each panel section comprising tubes welded together along their lengths, the panel sections being welded together lengthwise thereof so that the enclosure is essentially gas tight; header means connecting the panel sections into at least three successive flow passes in series whereby the first pass constitutes a portion of the front wal the third pass constitutes portions of the side walls and the rear Wall, and the second pass constitutes portions of the front and side walls in the front corners of the enclosure, the panels being sized so that the temperature difference between the first and second flow passes is more than F.; the enclosure comprising two buffer panel sections inter mediate the panel section for the first pass and those for the second pass; and second header means adapted to receive and mix predetermined portions of the flow from the inlet ends of the first and second passes and to pass said portions to the inlet ends of said buffer panel sections. 4. A once-through vapor generator according to claim 3 wherein the panels are sized such that the temperature difference between the second and third pass inlets is less than 100 F.

5. A once-through vapor generator according to claim 4 wherein at least one additional upflow pass comprises the side and rear walls of the lower portion of the furnace enclosure, and header means connecting the third pass to said additional upflow fluid pass, the passes one to four being progressively larger in number of tubes with increasing enthalpy of the fluid flow.

6. A once-through vapor generator according to claim 3 wherein the buffer panel sections comprise at least 5% of the tubes in the applicable wall width.

References Cited UNITED STATES PATENTS CHARLES I. MYHRE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,344,777 October 3, 1967 Walter P. Gorzegno It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1 line 33 "contaning" should read containing line 45 "the", second occurrence should read are line 54 "anthalpy" should read enthalpy Column 2 line 45 "tube" should read tubes Column 3, line 42 after "and" cancel "a"; line 47 "50 F. should read 53 F. line 62, after "thgf" cl'lnsert the Column 4 line 53 after "upflow" insert H u1 Signed and sealed this 29th day of July 1969 (SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,344,777 October 3, 1967 Walter P. Gorzegno It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 33, "contaning" should read containing line 45, "the", second occurrence, should read are line 54, "anthalpy" should read enthalpy Column 2, line 45, "tube" should read tubes Column 3, line 42, after "and" cancel "a"; line 47, "50 F." should read 53 F. line 62, after "thafif'wiinsert the Column 4, line 53, after "upflow" insert L11 --f.

Signed and sealed this 29th day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM Attesting Officer Commissioner of Patents

Claims

1. A ONCE-THROUGH VAPOR GENERATOR WHICH INCLUDES A PLURALITY OF PARALLEL VERTICALLY ORIENTED TUBES WELDED INTO LATERALLY ADJACENT PANELS TO DEFINE AN ESSENTIALLY GAS-TIGHT FURNACE ENCLOSURE, AND HEADER MEANS CONNECTING PANELS LATERALLY REMOTE FROM EACH OTHER TO DEFINE AT LEAST TWO UPFLOW FLOW PASSES IN SERIES SO THAT FLUIDS ENTERING SAID PANELS ARE AT DIFFERENT ENTHALPIES, THE IMPROVEMENT COMPRISING AT LEAST ONE ADDITIONAL HEADER MEANS CONNECTED TO THE PANEL INTERMEDIATE SAID REMOTE PANELS; AND MEANS FOR TRANSMITTTING TO SAID ADDITIONAL HEADER MEANS PREDETERMINED PORTIONS OF THE FLOW TO SAID REMOTE PANELS, THE ENTHALPY OF THE FLUID ENTERING SAID INTERMEDIATE PANEL THEREBY BEING INTERMEDIATE THE ENTHALPIES OF THE FLUIDS ENTERING SAID REMOTE PANELS.