Gas screen arrangement for a vapor generator

A vapor generator which includes an upright furnace section the boundary walls of which are formed by a plurality of tubes for passing fluid through the length of the furnace section to convert a portion of the fluid to vapor or to heat the fluid. One portion of the tubes forming one of the boundary walls are bent out of the plane of the latter wall for connection to a plurality of headers. A single tube extends upwardly from each of the headers in fluid communication with the other tubes connected to said header, with the single tubes being disposed in a spaced relationship to form a screen for the passage of combustion gases from the furnace section to a heat recovery section disposed adjacent the furnace section.

BACKGROUND OF THE INVENTION 
This invention relates to a vapor generating system and, more particularly, 
to a sub-critical or super-critical once-through vapor generating system 
for converting water to vapor. 
In general, a once-through vapor generator operates to circulate a 
pressurized fluid, usually water, through a vapor generating section and a 
superheating section to convert the water to vapor. In these arrangements, 
the water entering the unit makes a single pass through the circuitry and 
discharges through the superheating section outlet of the unit as 
superheated vapor for use in driving a turbine, or the like. 
These arrangements provide several improvements over conventional drum-type 
boilers, and although some problems arose in connection with early 
versions of the once-through generators, such as excessive thermal losses, 
mismatching of steam temperature, the requirement for sophisticated 
controls and additional valving during startup, these problems have been 
virtually eliminated in later generation systems. 
For example, the system disclosed in U.S. Pat. No. application Ser. No. 
713,313 filed on Aug. 10, 1976, now U.S. Pat. No. 4,099,384, and assigned 
to the assignee of the present invention, includes a plurality of 
separators disposed in the main flow line between the vapor generating 
section and the superheating section and adapted to receive fluid flow 
from the vapor generating section during startup and full load operation 
of the system. This arrangement enables a quick and efficient startup to 
be achieved with a minimum of control functions, and without the need for 
costly valves. Also, the turbines can be smoothly loaded at optimum 
pressures and temperatures that can be constantly and gradually increased, 
without the need of boiler division valves or external bypass circuitry 
for steam dumping. Also, according to this system operation can be 
continuous at very low loads with a minimum of heat loss to the condenser. 
In the latter arrangement, the walls of the furnace section of the 
generator are formed by a plurality of vertically extending tubes having 
fins extending outwardly from diametrically opposed portions thereof, with 
the fins of adjacent tubes being connected together to form a gas-tight 
structure. During startup the furnace operates at constant pressure and 
super-critical water is passed through the furnace boundary walls in 
multiple passes to gradually increase its temperature. 
In this arrangement the upper portions of some of the tubes forming the 
rear boundary wall of the furnace section are bent out of the plane of the 
lateral wall and upwardly to form a gas screen for the passage of gases 
from the furnace section to a heat recovery area disposed adjacent the 
furnace section. However, this design requires precision and tedious 
fabrication which is difficult and time-consuming and, therefore, 
expensive. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a vapor 
generator which incorporates the features of the arrangement discussed 
above and yet enables a gas screen to be formed in a relatively simple yet 
effective manner. 
It is a further object of the present invention to provide a vapor 
generator of the above type in which a portion of the tubes forming the 
rear wall of the furnace section of the vapor generator are bent out of 
the plane of the lateral wall for connection to a plurality of headers. 
It is a still further object of the present invention to provide a vapor 
generator of the above type in which a single tube extends upwardly from 
each of the headers in fluid communication with the other tubes connected 
to the header, with the single tubes being disposed in a spaced 
relationship to form a gas screen. 
It is a still further object of the present invention to provide a vapor 
generator of the above type in which the boundary walls of the furnace 
section of the vapor generator are formed by a plurality of finned tubes, 
with the fins of adjacent tubes being interconnected to render the furnace 
section gas-tight. 
It is a still further object of the present invention to provide a vapor 
generator of the above type in which the fluid passes through the boundary 
wall circuitry of the furnace section in one single complete pass. 
Towards the fulfillment of these and other objects, the vapor generator of 
the present invention comprises a vapor generator comprising an upright 
furnace section the boundary walls of which are formed by a plurality of 
tubes through which fluid is passed to apply heat to the fluid. A 
plurality of headers are provided and are connected to the upper portions 
of a plurality of tubes forming one of the boundary walls. A single tube 
extends upwardly from each of the headers in fluid communication with the 
other tubes connected to said header, and are disposed in a spaced 
relationship to form a screen for the passage of combustion gases from the 
furnace section.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring specifically to FIG. 1 of the drawings, the reference numeral 10 
refers in general to a vapor generator utilized in the system of the 
present invention and including a lower furnace section 12, an 
intermediate furnace section 14, and an upper furnace section 16. The 
boundary walls defining the furnace sections 12, 14, and 16 include a 
front wall 18, a rear wall 20 and two sidewalls extending between the 
front and rear wall, with one of said sidewalls being referred to by the 
reference numeral 22. The lower portions of the front wall 18 and the rear 
wall 20 are sloped inwardly to form a hopper section 23 at the lower 
furnace section 12 for the accumulation of ash, and the like, in a 
conventional manner. 
As better shown in FIG. 2, each of the walls 18, 20, and 22 are formed of a 
plurality of tubes 24 having continuous fins 26 extending outwardly from 
diametrically opposed portions thereof, with the fins of adjacent tubes 
being connected together in any known manner, such as by welding, to form 
a gas-tight structure. 
Referring specifically to FIGS. 1 and 3, in the lower furnace section 12 
the tubes 24 in the sidewalls 22 extend vertically up to a horizontal 
plane P1 located at the upper portion of the hopper section 23, while the 
tubes 24 in the front wall 18 and the rear wall 20 are sloped inwardly 
from the latter plane to form the hopper section 23. The tubes 24 forming 
the walls 18, 20, and 22 in the intermediate section 14 extend from the 
plane P1 to a plane P2 disposed in the upper portion of the vapor 
generator 10, with these tubes extending at an acute angle with respect to 
the planes P1 and P2. The tubes 24 in the intermediate section 14 wrap 
around for the complete perimeter of the furnace section at least one time 
to form the corresponding portions of the walls 18, 20, and 22 before they 
terminate at plane P2. 
The tubes 24 forming the walls 18, 20, and 22 of the upper furnace section 
16 extend vertically from the plane P2 to the top of the latter section 
with the exception of a portion of the tubes in the rear wall 20 which 
will be discussed in detail later. 
Each angularly extending tube 24 in the intermediate furnace section 14 
registers with two tubes 24 in the upper furnace section 16 and with two 
tubes 24 in the lower furnace section 12. The connection between each tube 
24 in the intermediate furnace section 14 and its two corresponding tubes 
in the upper furnace section 16 and in the lower section 12 can be made by 
a plurality of bifurcate connections between the respective tubes as 
disclosed in detail in the U.S. application Ser. No. 791,830, filed on 
Apr. 28, 1977 and assigned to the same assignee as the present invention. 
A plurality of burners 28 are disposed in the front and rear walls 18 and 
20 in the intermediate furnace section 14, with the burners being arranged 
in this example in three vertical rows of four burners per row. The 
burners 28 are shown schematically since they can be of a conventional 
design. 
A heat recovery area, shown in general by the reference numeral 30, is 
provided adjacent the upper furnace section 16 in gas flow communication 
therewith and includes a vestibule section 32 and a convection section 34. 
As better shown with reference to FIGS. 1 and 3, portions of the tubes 24 
forming the rear wall 20 of the furnace section 12 are bent outwardly as 
shown by the reference numeral 24a at an angle to the plane of the latter 
wall and are connected to a plurality of cylindrical headers 36 which 
extend in a coaxial relationship in a row extending parallel to the plane 
of the rear wall 20. 
A portion of the cylindrical headers 36 are depicted in detail in FIGs. 4 
and 5 along with their respective connections to the tubes 24a. Each 
header 36 has two rows of two inlet counterbores which are adapted to 
receive the corresponding ends of four of the tubes 24a, with two of the 
latter being bent slightly as shown to register with their respective 
inlet counterbore. As shown in FIG. 5 each bottle 36 is hollow and each 
inlet counterbore 36a extends for a short radial distance into the wall of 
each bottle 36 and communicate, via a radial passage 37 formed through the 
latter wall, with the interior of the header. The ends of the tubes 24a 
are secured to the headers 36 in any known manner such as by welding. 
It is noted that for each five consecutive vertically extending tubes 24 in 
the upper furnace section 16, four are bent outwardly to form the portions 
24a while the remaining one continues upwardly vertically for connection 
to an upper header with the latter tube being shown by the reference 
numeral 24b in FIGS. 1 and 3. As shown in FIG. 4, the tubes 24a are 
uniformly spaced in a lateral direction and form the floor of the 
vestibule section 32. Although not shown in the drawings it is understood 
that the tube portions 24a have continuous fins 26 connected thereto with 
the fins of adjacent tubes being connected together in a manner similar to 
that of the tubes 24 to render the floor gas-tight. 
A vertically extending tube 38 extends upwardly from each header 36 to an 
upper header and is welded to the header over an outlet opening 36b formed 
through the header in communication with the interior of each header to 
put the tube 38 in fluid communication with each of the tubes 24a. 
The tubes 38 are of a larger diameter than the tubes 24 and extend in a 
spaced relation to form a gas screen for permitting the combustion gases 
from the upper furnace section 16 to pass through the vestibule section 32 
and into the convection section 34. 
The convection section 34 includes a front wall 40 the upper portion of 
which is formed by a plurality of tubes extending in a spaced relationship 
to form an additional screen adjacent the screen formed by the tubes 38. 
The heat recovery area 30 also includes a rear wall 41 and two sidewalls 
42, with one of the latter being shown in FIG. 1. It is understood that 
the rear wall 41, the sidewalls 42, and the lower portions of the front 
wall 40 are formed of a plurality of vertically extending, finned, 
interconnected tubes 24 in a similar manner to that of the upper furnace 
section 16. Also, to insure gas tightness it is understood that a seal 
plate, or the like, (not shown) will extend from the area in which the 
tubes 24a are connected to the bottles 36 to the front wall 40. 
A partition wall 44, also formed by a plurality of finned interconnected 
tubes 24, is provided in the heat recovery area 30 to divide the latter 
into a front gas pass 46 and a rear gas pass 48. An economizer 50 is 
disposed in the lower portion of the rear gas pass 48, a primary 
superheater 52 is disposed immediately above the economizer, and a bank of 
reheater tubes 54 is provided in the front gas pass 46. 
A platen superheater 56 is provided in the upper furnace section 16 and a 
finishing superheater 57 is provided in the vestibule section 32 in direct 
fluid communication with the platen superheater 56. 
As better shown in FIG. 3 a plurality of division walls 58 are provided 
with each having a portion disposed adjacent the front wall 18. The 
division walls 58 penetrate a portion of the tubes 24 of the latter wall 
in the intermediate furnace section 14 and extend upwardly within the 
upper furnace section 16 as shown in FIG. 1. 
The upper end portions of the tubes 24b and 38 as well as the walls 18, 20, 
and 22 of the furnace section 12, the division walls 58, and the partition 
wall 44, sidewalls 42 and rear wall 41 of the heat recovery area 30 all 
terminate in substantially the same general area in the upper portion of 
the vapor generating section 10. 
A roof 60 is disposed in the upper portion of the section 10 and consists 
of a plurality of tubes 24 having fins 26 connected in the manner 
described above but extending horizontally from the front wall 18 of the 
furnace section to the rear wall 36 of the heat recovery area 30. 
It can be appreciated from the foregoing that combustion gases from the 
burners 28 in the intermediate furnace section 14 pass upwardly to the 
upper furnace section 16 and through the screens defined by the tubes 24b 
and 38 and the tubes forming the upper portion of the wall 40 and through 
the heat recovery area 30 before exiting from the front gas pass 46 and 
the rear gas pass 48. As a result, the hot gases pass over the platen 
superheater 56, the finishing superheater 57 and the primary superheater 
52, as well as the reheater tubes 54 and the economizer 50, to add heat to 
the fluid flowing through these circuits. 
Although not shown in the drawings for clarity of presentation, it is 
understood that suitable inlet and outlet headers, downcomers and 
conduits, are provided to place the tubes 24 of each of the aforementioned 
walls and heat exchangers as well as the roof 60 and the tubes 24a and 38 
in fluid communication to establish a flow circuit that will be described 
in detail later. 
A plurality of separators 64 are disposed in a parallel relationship 
adjacent the rear wall 41 of the heat recovery area 30 are disposed 
directly in the main flow circuit between the roof 60 and the primary 
superheater 52. The separators 64 may be identical to those described in 
the above mentioned patent application and operate to separate the fluid 
from the roof 60 into a liquid and vapor. The vapor from the separators 64 
is passed directly to the primary superheater 52 and the liquid is passed 
to a drain manifold and heat recovery circuitry for further treatment as 
also disclosed in the above mentioned application. 
For the purposes of example, the diameter of tubes 24 in the upper furnace 
section 16 and the lower furnace section 12 can be 11/8 inch, the diameter 
of the tubes in the intermediate furnace section 14 can be 13/8 inch and 
the diameter of the tubes 38 can be 3 inches. Also, the angle that the 
tubes 24 in the intermediate furnace section extend with respect to the 
planes P1 and P2, can be between 20.degree. and 25.degree., and in the 
example just described is 22.degree.. 
The fluid circuit including the various components, passes and sections of 
the vapor generating section of FIG. 1 is shown in FIG. 6. In particular, 
feedwater from an external source is passed through the economizer tubes 
50 to raise the temperature of the water before it is passed to inlet 
headers (not shown) provided at the lower portions of the furnace walls 
18, 20, and 22. All of the water flows upwardly and simultaneously through 
the walls 18, 20, and 22 and the screen formed by the tubes 38 to raise 
the temperature of the water further to convert at least a portion of same 
to vapor, before it is collected in suitable headers located at the upper 
portion of the vapor generator 10. The fluid is then passed downwardly 
through a suitable downcomer, or the like, and then upwardly through the 
division walls 58 to add additional heat to the fluid. The fluid is then 
directed through the walls 40, 41, 42, and 44 of the heat recovery area 30 
after which it is collected and passed through the roof 60. From the roof 
60, the fluid is passed via suitable collection headers, or the like, to 
the separators 64 which separate the vapor portion of the fluid from the 
liquid portion thereof. The liquid portion is passed from the separators 
to a drain manifold and heat recovery circuitry (not shown) for further 
treatment, and the vapor portion of the fluid in the separators 64 is 
passed directly into the primary superheater 52. From the latter, the 
fluid is spray attemperated after which it is passed to the platen 
superheater 56 and the finishing superheater 57 before it is passed in a 
dry vapor state to a turbine, or the like. 
FIGS. 7 and 8 depict an alternate embodiment of a header which functions in 
an identical manner to the header 36 of the previous embodiment. The 
header of the embodiment of FIGS. 7 and 8 is shown in general by the 
reference numeral 70 and includes a hollow body member 72 which has a 
circular cross section and which is tapered from an inlet end 72a of a 
relatively large diameter to an outlet end 72b of a relatively small 
diameter. 
As shown in FIG. 8, the inlet end 72a of the body member 72 is provided 
with four inlet openings disposed in an angularly spaced relationship and 
adapted to receive the corresponding end portions of the tubes 24a in any 
known manner such as by welding, or the like, with the tubes being bent as 
necessary to align with the openings. 
The hollow portion of the body member 72 is in communication with the inlet 
openings via a plurality of passages 74, and an outlet opening 76 is 
formed through the outlet end portion 72b of the body member 72 in 
communication with the hollow portion of the body member. A tube 38 is 
connected to the outlet end portion 72b in communication with the outlet 
76 for receiving the fluid from the body member 72. 
As a result, fluid flow from the tubes 24a passes into and through the body 
member 72 and through the tube 38 as described in connection with the 
previous embodiment. 
The headers 70 are located in a row and each receives four adjacent tubes 
24a with each fifth tube 24 staying in the plane of the rear wall 20 in 
the same manner as discussed in connection with the previous embodiment. 
It is understood that the portions of the tubes 24a forming the floor of 
the vestibule portion 32 are provided with interconnected fins and that a 
seal plate (not shown) extends from the area in which the tubes connect 
with the header 70 to the wall 40 as discussed in connection with the 
previous embodiment. 
It is understood that while the preferred embodiments described above 
include a furnace having a substantially rectangular shaped 
cross-sectional area, other cross-sectional configurations, such as those 
having a circular or elliptical patterns, may be utilized. For example, 
the furnace may have a helical configuration in a pattern conforming to 
the cross-sectional shape of the furnace. (In this context, it should be 
noted that the type of boiler covered by the present invention in which 
the tubes are angularly arranged in the furnace boundary wall is commonly 
referred to by those skilled in the art as a "helical tube boiler," 
notwithstanding the fact that a true mathematical helix is not generated 
in a boiler which has a substantially rectangular cross-sectional area.) 
It is also understood that the tubes may wrap around the furnace for more 
than one complete revolution, depending on the overall physical dimensions 
of the furnace. Further the tubes forming the boundary walls of the 
furnace section, including those in the intermediate section described 
above, may extend vertically for the entire length of the wall. 
It is further understood that portions of the vapor generator have been 
omitted for the convenience of presentation. For example, insulation and 
support systems can be provided that extend around the boundary walls of 
the vapor generator and windbox, or the like, may be provided around the 
burners 28 to supply air to same in a conventional manner. It is also 
understood that the upper end portions of the tubes 24 forming the upper 
furnace section 16 and the heat recovery area 30 can be hung from a 
location above the vapor generating section 10 to accommodate thermal 
expansion in a conventional manner. 
A latitude of modification, change and substitution is intended in the 
foregoing disclosure and in some instances some features of the invention 
will be employed without a corresponding use of other features. 
Accordingly, it is appropriate that the appended claims be construed 
broadly and in a manner consistent with the spirit and scope of the 
invention herein.