Two-pass furnace circuit arrangement for once-through vapor generator

Claim 2

A once-through vapor generator comprising: a plurality of parallel vertically oriented tubes defining an upright furnace enclosure including front, rear and sidewall panels; header means dividing said furnace enclosure into first and second flow passes in series flow relationship; and one of said flow passes constituting substantially the full expanses of the front and rear wall panels of the furnace enclosure, the other of said flow passes occupying substantially the full expanses of the sidewall panels of the furnace enclosure.

Claim 3

The generator of claim 1 wherein said furnace enclosure comprises an upper gas exit and a lower high-absorption zone; further including: convection surface enclosure means in gas flow communication with said furnace enclosure gas exit; burner means in said lower high-absorption zone; said furnace enclosure panels being limited in dimension so that the gas temperature adjacent said gas exit is substantially the maximum value permissible for the fuel fired.

Claim 4

The generator of claim 2 wherein said burner means are positioned in both the front and rear wall panels of said furnace enclosure; said first and second flow passes extending the full height of said furnace enclosure, the first flow pass constituting said front and rear wall panels.

Claim 5

The generator of claim 3 wherein said furnace includes an upper zone in addition to said lower high-absorption zone, the tube diameters in said upper zone being greater than the diameters in said lower zone to reduce the pressure drop in said passes, the tube diameters in the lower zone being sufficiently small to maintain mass flow rates in said high-absorption zone at above acceptable minimum levels.

Claim 6

The generator of claim 2 wherein said front, rear and sidewall panels are substantially flat defining a rectangular furnace enclosure; further including buffer circuit panels each comprising a plurality of parallel tubes defining upright corners of said furnace enclosure, between said front, rear and sidewall panels; header means arranged to distribute to said buffer circuit panels substantially equal portions of the flow being distributed to said first and second passes, so that the temperatures in said buffer circuit panels are intermediate the temperatures in the panels of said first and second passes.

Claim 7

The generator of claim 5 wherein said furnace enclosure is substantially all-welded to provide a gastight membrane wall construction.

Claim 8

The generator of claim 2 further including primary and finishing superheater passes, said primary superheater pass including pendant radiant heat transfer surface adjacent the gas exit of said furnace enclosure, said finishing superheater pass comprising heat transfer surface positioned on the convection side of said gas exit, adjacent thereto.

Claim 9

The generator of claim 1 further including a third flow pass comprising wall panels in end-to-end relationship with the wall panels of said second flow pass; said third flow pass panels being laterally substantially coextensive with the second flow pass panels but above the latter so that said second and third pass panels together have about the same height as said first pass panels; mix header means between said second and third pass panels; burner means in the lower portion of said furnace enclosure, said burner means being predominantly oil fired; said furnace enclosure defining gas exit means adjacent the top thereof; and the temperature of the flue gas adjacent said gas exit means being the maximum permissible value for the fuel fired.

Claim 10

The generator of claim 1 further including downcomer means between said first and second passes; horizontal exit header means for said first pass panels; said downcomer means cOmprising a horizontal manifold extension above said furnace enclosure substantially parallel with said header means and downwardly extending side connections connected to said manifold extension on opposite sides of said enclosure; fan-mix connection means between said header means and said downcomer means horizontal extension; and said fan-mix connection means comprising connections between said exit header means and said manifold extension which lead from one end of each header means to a corresponding end of the manifold extension and alternately to an opposite end of the extension, connected to the latter near the center of said manifold extension, more centered header connections leading to portions of the manifold extension more removed from the center of the latter.

Claim 11

The generator of claim 3 further including a division wall panel, said division wall panel being parallel to the sidewall panels, coextensive in height therewith, and having the same geometry, said header means connecting said division wall panel so that the flow therein is in parallel with the flow in the sidewall panels.

Claim 12

A once-through vapor generator comprising: an upright substantially rectangular furnace enclosure including a plurality of parallel vertically oriented tubes defining front, rear and sidewall panels; said enclosure comprising a lower high absorption zone and an upper gas exit; header means connecting said tubes to define first and second flow passes in series, the first flow pass constituting substantially the full periphery of the front and rear wall panels of said enclosure and the second flow pass constituting substantially the full periphery of the sidewall panels of said enclosure, at least in said high-absorption zone; burner means positioned in the front and rear wall panels in said lower high-absorption zone; a plurality of parallel upright tubes defining buffer circuit panels positioned in said enclosure between the front, rear and sidewall panels of said first and second passes; header means for said buffer circuit panels; connections between said header means and said first and second passes whereby the flow to said buffer circuit panels comprises substantially equal amounts of the flows at fluid conditions existing at the first and second pass inlets; and said furnace enclosure panels being limited in dimension so that the gas temperature adjacent said gas exit is substantially the maximum value permissible for the fuel fired.

Claim 13

A once-through vapor generator comprising: an upright substantially rectangular furnace enclosure including a plurality of parallel vertically oriented tubes defining front, rear and sidewall panels; said enclosure comprising a lower high absorption zone and an upper gas exit; header means connecting said tubes to define first and second flow passes in series, the first flow pass constituting substantially the full periphery of the front and rear wall panels of said enclosure and the second flow pass constituting substantially the full periphery of the sidewall panels of said enclosure, at least in said high-absorption zone; burner means positioned in the front and rear wall panels in said lower high-absorption zone; a plurality of parallel upright tubes defining buffer circuit panels positioned in said enclosure between the front, rear and sidewall panels of said first and second passes; header means for said buffer circuit panels; connections between said header means and said first and second passes whereby the flow to said buffer circuit panels comprises substantially equal amounts of the flows at fluid conditions existing at the first and second pass inlets; and said furnace enclosure panels being limited in dimension so that the gas temperature adjacent said gas exit is substantially the maximum value permissible for the fuel fired.

Claim 14

The generator of claim 11 wherein said furnace enclosure includes an upper gas exit zone in addition to said lower high-absorption zone; the tube diameters of said first and second passes being increased in said upper gas exit zone reducing the pressure drop therein, but maintaining minimum required mass flow rates in said lower high-absorption zone.

Claim 15

The generator of claim 12 wherein said furnace enclosure is all-welded to provide a membrane wall-type construction.

Claim 16

A once-through vapor generator comprising: a plurality of parallel vertically oriented tubes defining an upright furnace enclosure including front, rear and sidewall panels; header means dividing said furnace enclosure into first and second flow passes in series flow relationship; and one of said flow passes constituting substantially the full expanses widthwise of the front and rear wall panels of the furnace enclosure, the other of said flow passes occupy substantially the full expanses widthwise of the sidewall panels of the furnace enclosure, said passes constituting a substantial portion of the furnace enclosure.

Claim 17

A once-through vapor generator comprising: a plurality of parallel vertically oriented tubes defining an upright furnace enclosure including front, rear and sidewall panels; header means dividing said furnace enclosure into first and second flow passes in series flow relationship; and one of said flow passes constituting substantially the full expanses widthwise of the front and rear wall panels of the furnace enclosure, the other of said flow passes occupy substantially the full expanses widthwise of the sidewall panels of the furnace enclosure, said passes constituting a substantial portion of the furnace enclosure.