[0001] This invention relates to air-cooled steam condensing systems, and is concerned with
air-cooled vacuum steam condensers serving steam turbine power cycles or the like
and, more particularly, apparatus for condensing steam or other vapors and draining
the condensate over a wide range of loads, pressures and ambient air temperatures
and also completely removing the steam-transported, undesirable, non-condensible gasses
that migrate and collect at the end of the steam condensing system.
[0002] One technique for generating mechanical energy is the use of a turbine, boiler and
an array of coupling conduits. Water is first converted to steam in the boiler. The
steam is then conveyed to the turbine wherein the steam is expanded in its passage
through rotating blades thereby generating shaft power. An array of conduits couple
the turbine and the boiler and also define a working fluid return path from the turbine
back to the boiler through steam condenser mechanisms in a continuing cycle of operation.
[0003] Steam condenser mechanisms include air-cooled vacuum steam condensers which may be
considered as being comprised of four basic elements or systems: the steam condensing
system, the air moving system, the condensate drain system and the non-condensible
gas removal system.
[0004] The main problems plaguing the industry today are in the condensate drain and non-condensible
gas removal systems that result in condensate freezing followed by the rupturing of
bundle drains and heat exchanger tubes. The reasons for their failures can be traced
to faulty condensate-drain hydraulic-design, the trapping of non-condensible gasses
in the rear headers of the heat exchanger bundles and inadequate freeze protection.
The problems are aggravated further by the wide range of plant operating conditions
imposed upon the equipment and by low ambient air temperatures coupled with high winds.
[0005] Various approaches are disclosed in the patent literature to improve the efficiency,
hydraulics, freeze protection and control of air-cooled vacuum steam condensers and
related devices. By way of example, note U.S. Patents Numbers 2,217,410 to Howard
and 3,289,742 to Niemann. These patents disclose early versions of heat exchangers
for use in turbine systems. Other patents relating to improving air-cooled system
steam condensers include U.S. Patents Numbers 2,247,056 to Howard and 3,429,371 to
Palmer. These patents are directed to control apparatus for accommodating pressure
variations. In addition, U.S. Patent Number 4,585,054 to Koprunner is directed to
a condensate draining system. The linear arrangement of tubes in A-frame steam condensers
is disclosed in U.S. Patents Numbers 4,177,859 to Gatti and 4,168,742 to Kluppel while
U-shaped tubes are disclosed in U.S. Patents Numbers 3,705,621 and 3,887,002 to Schoonman.
In addition, applicant Larinoff describes a wide variety of improvements in air-cooled
heat exchangers in his prior U.S. Patents Numbers 3,968,836; 4,129,180; 4,240,502
and 4,518,035. Such improvements relate to condensate removal, air removal, tube construction,
cooling controls and the like. Lastly, various improvements in mechanisms for non-
analogous technologies are disclosed in U.S. Patents Numbers 2,924,438 to Malkoff;
3,922,880 to Morris and 4,220,121 to Maggiorana.
[0006] As illustrated by the great number of prior patents and commercial devices, efforts
are continuously being made in an attempt to improve air-cooled vacuum steam condensers
having particular utility in systems configuration with steam turbine cycles.
[0007] US-A-2 217 410 (see also US-A-2 247 056) discloses an air-cooled steam condensing
system comprising:-
a plurality of lower headers, arranged to receive steam as well as non-condensible
gasses to be removed;
a plurality of inclined (vertical, after-cooler) condensing tubes, the tubes being
arranged in bundles and in rows within each bundle, the tube bundles being connected
to respective lower headers;
a plurality of upper headers, which are rear and final headers, arranged above
the lower headers; connected to respective tube bundles, with the condensing tubes
rising up from the lower headers to the upper headers, whereby steam may flow upwardly
from the lower headers into the tubes for being condensed, with the condensate flowing
back downwardly into the lower headers and then drained therefrom, while the non-condensible
gasses may flow from the lower headers upwardly into the tubes and then be fed upwardly
therefrom to the upper headers, the upper headers serving for the receipt and collection
of the non-condensible gasses, and
gas removal means, employing vacuum suction, connected to each upper header for
removal of collected non-condensible gasses from within each of the upper headers.
[0008] In the system of US-A-2 217 410 the lower headers (34) are middle headers, which
can only pass to the tubes steam which has not already been condensed in preceding
condenser tubes, and non-condensible gasses carried along with that un-condensed steam.
The tubes are merely after-coolers.
[0009] In the system of US-A-2 217 410, upon entry into the condensing system, steam is
first fed to a plurality of first and front headers, above the lower headers, and
from the front headers to the tops of respective bundles of down-pass condensing tubes.
The bottoms of the bundles of down-pass condensing tubes are connected to the respective
middle headers. Thus, steam must flow downwardly from the front headers into the condensing
tubes, with the condensate flowing downwardly into the middle headers to be drained
therefrom. The non-condensible gasses must also flow downwardly from the front headers
downwardly into the condensing tubes, and then be fed downwardly from the tubes to
the middle headers. The non-condensible gasses must then be carried with un-condensed
steam through the middle headers, to the after-cooler tubes, to rise in those tubes
to the rear and final headers for removal from the system.
[0010] In the system of US-A-2 217 410, the after-cooler tube rows in each bundle are connected
to a common upper (rear and final) header, used by all the tubes in the bundle. The
upper (rear and final) headers are open headers.
[0011] In the system of US-A-2 217 410 the gas removal means comprise connections to each
open upper (rear and final) header, for receiving non-condensible gasses from those
headers, and an extraction conduit and a vacuum pump.
[0012] The system of US-A-2 217 410 is thus a two-pass system, and non-condensible gasses
must be carried with steam on a first, downward pass through down-pass condensers,
and then on a second, upward pass through up-pass after-coolers, via front, middle
and rear headers, before they can be removed from the system.
[0013] FR-A-1 386 255 discloses (see Figs. 1 and 2 thereof) an air-cooled steam condensing
system comprising:-
a plurality of lower headers, arranged to receive steam as well as non-condensible
gasses to be removed;
a plurality of inclined dephlegmators, belonging to respective bundles (see below),
connected to respective lower headers, the dephlegmators rising up from the lower
headers, whereby steam may flow upwardly from the lower headers into the dephlegmators
for being condensed, with the condensate flowing back downwardly into the lower headers
and then drained therefrom, while the non-condensible gasses may flow from the lower
headers upwardly into the dephlegmators and then be fed upwardly therefrom for removal;
and
gas removal means, employing vacuum suction, for removal of collected non-condensible
gasses.
[0014] In the system of FR-A-1 386 255 the lower headers are middle headers, which can only
pass to the dephlegmators steam which has not already been condensed in preceding
condenser tubes, and non-condensible gasses carried along with that un-condensed steam.
[0015] In the system of FR-A-1 386 255 upon entry into the condensing system, steam is first
fed to a common front header, above the lower headers, and from the front header to
the tops of respective bundles (c.f. the left and right sides of Fig. 2 of FR-A-1
386 255) of down-pass condensing tubes.
[0016] In Fig. 1 of FR-A-1 386 255, the down-pass condensing tubes are arranged in groups
of eight each, and each group is divided into two bundles of four condensing tubes.
A dephlegmator is associated with each bundle. Other arrangements are disclosed.
[0017] The bottoms of the bundles of down-pass condensing tubes are connected to the respective
middle headers. Thus, steam must flow downwardly from the front header into the condensing
tubes, with the condensate flowing downwardly into the middle headers to be drained
therefrom The non-condensible gasses must also flow downwardly from the front header
downwardly into the condensing tubes, and then be fed downwardly from the tubes to
the middle headers. The non-condensible gasses must then be carried with un-condensed
steam through the middle headers, to the dephlegmators, to rise therein for removal
from the system.
[0018] In the system of FR-A-1 386 255 Figs. 1 and 2, the top ends of the dephlegmators
are connected in common to gas removal means comprising pipes, a common pipe, a sub-cooler
and a vacuum pump.
[0019] The system of FR-A-1 386 255 is thus a two-pass system, and non-condensible gasses
must be carried with steam on a first, downward pass through down-pass condensers,
and then on a second, upward pass through up-pass dephlegmators and through headers,
before they can be removed from the system.
[0020] US-A-3 968 836 discloses an air-cooled steam condensing system having an inlet header
for receiving both steam to be condensed and non-condensible gases, a plurality of
condensing tubes arranged in rows and grouped in bundles, the tubes being coupled
at their input ends to the inlet header, a plurality of outlet headers coupled to
the output ends of the tubes, each tube row having its own individual outlet header.
[0021] In US-A-3 968 836, both condensible and non-condensible gasses are received in the
outlet headers.
[0022] According to the present invention there is provided an air-cooled steam condensing
system comprising:-
a front header for receiving both steam to be condensed as well as non-condensible
gasses to be removed;
a plurality of inclined condensing tubes arranged in rows and grouped in bundles,
the tubes being coupled at their lower ends to the front header whereby steam may
flow from the front header into the tubes for being condensed with the condensate
flowing back into the front header and then drained therefrom while the non-condensible
gasses flow from the front header into the tubes and then upwardly;
a plurality of rear headers coupled to the upper ends of the tubes for receiving
the non-condensible gasses from the tubes, each tube row having its own individual
rear header for the receipt and collection of the non-condensible gasses; and
vacuum piping with gas inlets in communication with the interior of each rear header
for evacuating the collected non-condensible gasses from within each of the rear headers
along its full length.
[0023] An embodiment of the invention can provide a condensing and draining mechanism which
avoids the drawbacks of the state of the art and which allows proper and complete
drain of condensate from air cooled steam condenser systems which protects said systems
from freezing, which avoids corrosion problems and which allows complete removal of
undesired gasses from the terminal points of the condensing system.
[0024] For a fuller understanding of the nature and objects of the invention, reference
should be had to the following detailed description taken in conjunction with the
accompanying drawings in which:
Figure 1 is a simplified version of a steam power cycle that is a partially schematic
and a partially diagrammatic illustration of a boiler, turbine, pumps, coupling conduits
and an air-cooled steam condenser. The condenser shown is an "A" frame design with
steam flowing upward in the finned tubes while condensate drains downward to the steam
supply duct in a counter-flow manner. It is mechanical forced draft with condensate
drain to a storage tank and a two stage steam operated air removal system.
Figures 2 and 3 are elevational drawings with vertical sections through the bundles
and with a forced draft fan in the middle serving both banks;
Figure 4 is a view of the front header showing its tube holes where the exhaust steam
enters to be condensed.
Figure 5 is a sectional view through the bundle showing finned tubes attached four
rows deep. It also shows the evacuation piping placed inside the bundle channel frame.
Figure 6 is a sectional view across a bundle showing the air-cooled pre-condenser
set on top of the frame with piping leading to the rear headers.
Figure 7 is a view looking into the rear header end of the bundle. It shows the vent
manifolds inside each of the four rear manifolds.
Figure 8 is a sectional view of a rear header showing the placement of the vent manifold
and its orifices.
Figure 9 is a flow diagram of the gas removal vacuum system. It shows the pre-condenser
resting on top of the bundles close to the steam supply duct.
Figure 10A, 10B, 10C and 10C are simplified versions of bundle gas removal designs
that have been used in the past and compared to the proposed system.
[0025] Similar referenced characters refer to similar parts throughout the several Figures.
[0026] With reference to Figure 1, there is shown a power system 10 for converting thermal
energy into mechanical energy. The system includes a boiler 12 for generating steam
and a turbine 14 which expands the high pressure steam thereby converting its energy
into shaft power. The waste steam exhausted from the turbine is condensed in an air-cooled
steam condenser 18 and the condensate is returned to the power cycle via conduits
16 and auxiliaries. The steam condensing mechanism 18 consists of sub-systems which
may be considered as including a steam condensing system 22, an air moving system
24, a condensate drain system 26 and a gas removal vacuum system 28.
[0027] The steam condensing mechanism consists of a main steam duct 33 feeding a steam supply
duct 35 to which the steam condensing bundles 56 are attached at the front header
34. The exhaust steam flows upward through a plurality of parallel finned tubes 32
where it is condensed and the condensate runs downward in the same tubes in counter-flow
manner back into the steam supply duct 35. In the disclosed embodiment, the bundles
56 are arranged in two banks 46 and 48 in an A-frame configuration with the front
header 34 on the bottom and the rear headers 36, 38, 40 and 42 on the top with a bundle
air seal 164 at the apex. The tubes 32 are provided with fins 52 to facilitate and
promote more efficient heat transfer. The heat transfer involves the flow of ambient
air 50 over the finned tubes for cooling purposes to condense the steam into water.
The condenser tubes of each bank are separated into a plurality of bundles 56 as shown
in Figures 1 and 9. Within each bundle, the tubes are arranged in a plurality of rows
60, 62, 64 and 66, four in the disclosed preferred embodiment as shown in Figure 5.
The four parallel rows are symmetrically positioned in the bundle with the cold ambient
air striking row 60 first while the heated air leaving row 66 is discharged back into
the atmosphere.
[0028] Each row of tubes has its own rear header 36, 38, 40 and 42 which are the terminal
points of the steam condensing system and therefore the gathering points for all the
non-condensible gasses released by the condensing steam. While the steam moves upward
through the tubes, the condensate flows downward by gravity in the same tubes and
drains into the steam supply duct 35.
[0029] The steam condensing system may be considered as consisting of a single-pass, multi-row,
extended surface, air-cooled, heat exchanger bundles with a separate rear header for
each row. The tubes are in a single pass arrangement in relation to the air flow on
the outside and the steam flows counter to its condensate inside the tubes. The bundle
arrangement must be inclined toward the front header 34 sufficiently so that the condensate
can drain by gravity back into the steam supply duct 35. From that minimum position
it can be tilted upward until it is completely vertical to meet design/installation
requirements.
[0030] The important advantages of this new steam condensing system can be set forth as
follows. A. This design does not require additional devices for the withdrawal of
condensate from the bundles. B. The counter-flow movement of steam and condensate
inside the same tubes produces a condensate temperature close to the saturation temperature
of the steam. C. Final condensate saturation temperature can be achieved by the use
of a separate reheating element installed in the steam supply duct. D. Most importantly,
this design has a low internal steam pressure drop because of its short steam-condensing
path length. This means the condenser can operate with a lower turbine exhaust pressure
during cold weather which is very desirable from a plant thermal efficiency aspect.
[0031] The air moving system 24 is the conventional industry type shown in the patent literature.
It preferably employs either mechanical draft fans 86, natural draft or some combination
of both. The fan arrangements can be either of the induced or forced draft type. In
all cases the forced air flow 50 across the outside of the finned tubes is the cooling
medium that condenses the steam inside the tubes.
[0032] It should be noted here that, although the bundles show four rows, all the disclosures
in this patent apply to bundles of one or more rows.
[0033] The condensate drain system starts at the point where the condensate flows out of
the finned condensing tubes 32 into the steam supply duct 35 by gravity as shown in
Figure 2. Its vertical fall is intercepted by a condensate reheating element 166.
During cold weather the condensate is subcooled by its contact with the metal walls
of tube 32 but it can be readily reheated to the steam saturation temperature by breaking
it up into droplets and thin films and delaying its fall. The condensate reheating
element 166 can do this with an interwoven mesh material or some other such device
that is at saturation temperature being suspended in this steam atmosphere. The reheating
element can also be constructed of trays and baffles similar to designs presently
employed in commercial heaters. This element provides the added contact surface area
and time delay that is necessary to bring the condensate back up to the desired saturation
temperature.
[0034] Returning to Figure 1, condensate flow from steam supply duct 35 is via pipe manifold
82 into drain pipe 83 and then into tank 84. The steam pressure inside tank 84 is
the same as that in supply duct 35 because of piping connection 100. The condensate
flow from supply duct 35 to storage tank 84 is entirely by gravity. Condensate pumps
88 take suction from the storage tank and return the condensate back to the power
cycle to repeat the process.
[0035] For a better understanding as regards the removal of non-condensible gasses from
air-cooled steam condensers, a short review of past arrangements and problems is helpful.
[0036] First, to answer the question as to what are these non-condensible mixed gasses in
the exhaust steam of power cycles. These inert gasses are the result of boiler water
treating chemicals that are continually injected into the boiler feed water system.
They vaporize in the boiler drum but do not all condense when cooled down. They also
are the result of air leakage around shaft seals such as the turbine, condensate pumps
and valve stems. Air leakage also occurs at the welded joints of the steam condensing
system which includes steam ducts, manholes, bundles, tanks, condensate piping, etc.
There could be a large presence of inert gasses in the turbine exhaust steam.
[0037] The second question that arises is why are they important in the design consideration
of steam condensers. These inert gasses can cause tube corrosion, but more importantly,
tube failures resulting from freezing. These gasses are frequently trapped in stagnant
pockets in rear headers which then grow in size and progress down into the condensing
tubes. If there is condensate present, it can freeze because the stagnant gas pockets
become cold, having displaced the steam. Frozen condensate can rupture tubes and pipes
that will shut down the power generating unit. During the summer these same gas pockets
will blanket finned-tube heat-transfer surfaces thereby degrading the plant's thermal
performance.
[0038] Knowing what these inert gasses are and what they do, we can now examine how they
have been handled in the past and compare that with what is now being proposed. Figures
10A, 10B, 10C and 10D present the various design attempts in removing the undesirable
gasses from the condenser. The IDEAL gas removal design shown in Figure 10A would
be a cone-shaped bundle where steam (S) enters the cavity and is condensed leaving
the gasses behind. As more steam enters and condenses, the gasses are pushed further
and further ahead until finally they reach the tip of the cone where there is practically
no steam and all gas. The first-stage ejector then "sucks" out nearly pure gas and
discharges it from the system. There are no stagnant pockets in the IDEAL design because
of its cone shape, however, this bundle cannot be built and remains only as an ideal
concept.
[0039] Scheme A, Figure 10B, shows past attempts by industry at solving this problem. The
total steam condensing surface is built in two sections or zones. They could be separate
bundles as shown or they could be incorporated in the same bundle. The attempt here
is to try to concentrate the inert gasses before they are withdrawn at point Y. The
two sections could have the same heat transfer capacity or the second section could
be as small as five per cent of the heat transfer surface area of the first section.
The rear header 36 of the first section may or may not be the cavity which serves
as the front header 34 for the second section. There are many design variations on
this connection. The patent literature shows the following names for the first section:
Main Condenser, Primary Condenser, First Condensing Zone and First Plurality Tubes.
The second section names have been shown as: Dephlegmator, Vent Condenser, Secondary
Condenser, After Condenser, After-cooler Section, Second Condensing Zone, Second Plurality
of Tubes and Reflux Condenser.
[0040] Regardless of the name, bundle size, shape, tube passes, tube arrangement, configuration,
etc., the design aim is always to drive the gasses toward the terminal end (E) of
the condenser and then remove them with an ejector system. A typical rear header length,
which is the bundle width (W), could be as large as ten feet. There could be fifty
finned tubes in this width all discharging gasses into the rear header. However, the
gas quantities entrapped in the steam are minute by comparison to the total mass of
steam being condensed. Typically in a small condensing system for every 454 kg/hr
(1000 lbs/hr) of steam entering a bundle with a fifty tube row there is less than
0.454 kg/hr (1.0 lbs/hr) of gas vapor mixture that is sucked out of the rear header
at point Y by the first stage ejector. Considering the internal volume of a rear header
that is 3.1m (ten feet) long, a 0.454 kg/hr (1.0 lb/hr) flow withdrawal rate toward
the one pipe connection (Y) is very, very small.
[0041] With this arrangement where there is but one pipe connection from the rear header
to the ejector, it is quite obvious that there will be stagnant pockets of inert gasses
in the rear header as shown in Figure 10B. In fact, the real danger is that these
pockets will extend down into the finned tubes along both sides of the bundle where
freeze damage then occurs. The vapor/gas fluid being withdrawn by the ejector is that
which comes mainly from the finned tubes in the immediate vicinity of the suction
opening (Y). These few tubes opposite opening (Y) bring in a continual supply of additional
steam and gas into the withdrawal area where all the action takes place. The remaining
tubes, which are the majority, merely stagnate with gas movement created mainly by
molecular diffusion and small eddies rather than pressure gradients. The inert gasses
keep accumulating and concentrating inside the tubes along the sides of the bundle
with very slow movement toward the suction opening (Y). That is the nature of fluid
movements with the type of containment and withdrawal arrangements presently practiced.
[0042] Scheme B, Figure 10C, has a main condenser where each bundle rear header 36 has a
vent tube or tubes. This vent tube 170 is finned similar to the main condenser. It
is in essence a pre-condenser to the first stage ejector which is built into the same
bundle as the main condenser. This scheme does a better scavenging job of the rear
header than does Scheme A. The mass volume of gas/vapor mixture leaving the bundle
at (Y) and entering the ejector at (Z) is the same for both Scheme A and B. The mass
volume of gas/vapor leaving the rear header of Scheme B at point (X) is considerably
larger than that leaving at point (Y), Scheme A, due to the condensation of steam
vapor in the vent tube. Since the mass volume flow at point (X), Scheme B, is larger,
the flow volumes and velocities around suction opening (X) are higher. However, this
design has the same basic flaw that Scheme A has in that the flow into suction opening
(X) comes mostly from tubes in the immediate vicinity of the opening. The rest of
the rear header and the tubes along the sides to the bundle stagnate.
[0043] Scheme C, shown in figure 10D, is a gas removal system with its suction sparger that
shows how it proposes to scavenge the rear header by the vary nature of its construction.
[0044] The purpose of this system is to remove all of the non-condensible gasses from the
bundle rear headers 36, 38, 40 and 42. These non-condensible gasses are part of the
normal steam cycle vapor system and become the gas residue when the vapors are condensed.
A flow diagram of the gas removal vacuum system 28 is shown in Figures 1 and 9. The
gas removal starts with the suction sparger 116 installed in all rear headers; then
piping 121, 123, 125 and 127 connecting the suction spargers to pre-condensers 120,
122, 124 and 126; then additional piping connects the pre-condensers to a liquid/vapor
separator 128 where the liquid flows to the condensate storage tank 84 by gravity
while the gasses and vapors flow to the first-stage ejectors; then the gasses and
vapors enter the steam jet air ejector package 130 where the gasses are further concentrated
and then ejected from the system into the atmosphere at point 134 while the condensate
from the steam vapors is returned to the cycle. A more detailed explanation of each
of these gas removal steps follows.
[0045] As was stated earlier, the inert gasses all end up in the rear headers 36, 38, 40
and 42. To remove them from the rear headers, it is necessary to create a higher vacuum
which is a lower absolute pressure than that which exists in the rear headers. This
is accomplished by the first-stage ejectors 144 and completed by the remainder of
the steam jet air ejector package 130. The suction sparger 116 is the starting point
for the gas removal process. Each rear header, of which there are four per bundle,
has its own suction sparger running the full length of the rear header as shown in
Figure 7. The spargers have orifices 114 drilled along the entire length through which
the gasses and vapors enter. Any condensate which enters the sparger either flows
out of a single small drain hole 136 shown in Figure 8 and located at the closed end,
or it flows into connecting piping 121, 123, 125 and 127 and then drains into the
pre-condenser. The vapor/gas flow from the rear header through the orifices is induced
by the action of the steam jet ejectors. The orifices are positioned such that they
face a calm area 138 as shown in Figure 8 and are located midway between two adjacent
tubes 32. The other side of the sparger pipe faces the heat exchanger tube 32 openings
which is the turbulent zone or area 140. It is turbulent because there is some steam
flow in the rear header between tubes in the same row. This steam interchange amongst
tubes 32 occurs as a result of uneven cooling air velocities across the face of the
bundle. Locating the suction orifices in the calm zone of the rear headers insures
a more effective scavenging job. Since each condensing tube 32 discharges some gas,
the multiplicity of suction orifices 114 means that the gasses have only to travel
a few inches in the rear header before they enter an orifice in the suction sparger
116. This is unlike the usual steam condenser bundle rear header which has but one
suction pipe connection where the gasses must travel from a minimum of a few inches
to a maximum of five to ten feet, depending on the suction pipe location.
[0046] The orifices 114 vary in diameter (a) along the length of the suction sparger 116,
(b) among each of the rear headers 36, 38 40 and 42 and (c) from bundle 56 to adjacent
bundle 56. These orifices are sized to perform several important flow-equalizig functions.
The national steam condenser code specifies the required evacuation capacity (kg/hr)
((lbs/hr)) of the steam jet air ejector package 130 based on the size of steam condenser,
i.e., mass quantity of steam condensed (kg/hr) ((lbs/hr)). Hence, the orifices are
sized to flow the code mandated capacity plus the steam vapor capacity condensed in
a pre-condenser, if used. In this first calculation step an orifice diameter is found
for each row knowing total flow quantities, total bundles and total orifices. Now
since the bundles close to the first-stage ejectors will have less piping pressure
drops, they would normally flow a larger amount of gas/vapors than the bundles located
at the end of the tower. Hence, the first adjustment to the orifice diameters is to
equalize the flows irrespective of the bundle location in the tower structure. That
means that bundles located close to the first-stage ejectors will have smaller orifices
than the bundles located at the end of the tower. With this adjustment all bundles
will now deliver the same mass quantity of gas/vapor to the evacuation system. There
is a second adjustment to be made to the orifice diameters which concerns operations
inside the rear headers. Flow through the sparger orifices must be equalized along
its entire length. This will insure that each increment of length along the rear headers
is being evacuated evenly since each finned tube 32 is discharging very nearly the
same quantity of gas. The orifice 114 openings near the front end of the sparger 116
will be slightly smaller than the orifices near the closed end which are further away
and therefore have a larger piping pressure drop. A third ajustment concerns the individual
rows. They each condense different quantities of steam, and therefor have different
quantities of vapor/gas to be evacuated through different size orifices.
[0047] The rear header evacuation piping 121, 123, 125 and 127 is run inside the bundle
channel frame 148 as shown in Figures 3, 5, 6 and 7 and then brought outside with
piping 30 running on top of the bundle frames near the steam supply duct 35 as shown
in Figures 1, 2, 3, 6 and 9. By installing fins 53 on pipes 30, low-cost air-cooled
pre-condensers 120, 122, 124 and 126 can be made to serve the first-stage ejectors
144. Such a pre-condenser increases the scavenging rate of the rear headers by the
amount of steam vapor it condenses. In the process of doing that, it provides a more
concentrated inert gas mixture to the ejectors which makes them more efficient.
[0048] The steam vapor condensing capability of this air-cooled pre-condenser is dependent
upon, amongst other things, the temperature of the cooling air 50 passing through
its fins 53 as it lies on top of the main steam condensing tubes 32. This air temperature
in turn is controlled by the number of fins 52 installed on tubes 32 located directly
below the pre-condensers. As the fins are stripped back along the tubes as shown in
Figure 2 the temperature of the air reaching the pre-condensers drops and then more
steam vapor is condensed. Figure 2 shows the top row fins stripped to a distance L
while the bottom row is left intact; rows 2 and 3 are stripped varying amounts. This
control of the number of heat dissipating fins built into the path of this small segment
of cooling air gives the designer flexibility to maximize the steam vapor condensing
capability of the pre-condenser and minimize the potential for freezing.
[0049] The air-cooled pre-condenser is installed in the warm air stream of the bundle air
discharge to protect it from freezing. The vapor/gas mixture flowing in the pre-condenser
tubes 30 does not carry much steam so that it does not have the self protection features
as does the regular steam condensing tube 32. Although the pre-condenser is protected
by being surrounded with heated air, it is still subject to freezing if it is not
protected from cold blasting winds. In cold climate installations a removable, sheet-metal,
protective wind shield 162, would be installed to partially cover the pre-condenser.
[0050] The pre-condenser is shown installed on the bottom of the bundles 56 near the steam
supply duct 35 to achieve greatest freeze protection. In warmer climate installations
the pre-condenser could be installed near the top of the bundles just below rear header
42. This would save piping costs for items 121, 123, 125 and 127.
[0051] Steam vapors condensed in connecting piping 121, 123, 125 and 127 and in pre-condensers
120, 122, 124 and 126 all drain by gravity toward the fluid separating connection
128. This is a "T" pipe connection installed in a vertical position as shown in Figures
1 and 9. The condensate flows downward through pipes 71, 73, 75 and 77 by gravity
into the condensate storage tank 84, while the vapors and gasses flow upward through
the tees toward the first-stage ejector 144. The condensate pipes 71, 73, 75 and 77
terminate below the water level in the tank because they also serve as water-leg seals.
Condensate levels in these water legs are above the water level in the tank and each
is at a different height because they all have different internal vapor pressures.
In cold climate installations, the small condensate pipes 71, 73, 75 and 77 are fastened
to the much larger and warmer pipe 83 and then all five pipes are wrapped with heat
insulation as a single line.
[0052] The vapors and gasses leaving the fluid separator 128 enter the first-stage ejectors
144 of which there are four; one for each bundle row because they all have different
pressures and cannot be tied together. The use of multiple first-stage ejectors discharging
into a common inter-condenser is generally known in the existing art in the process,
petrochemical, pharmaceutical and related industries. The process cycles generally
have several points, at different pressures, which must be evacuated with their own
first-stage ejectors which then discharge into the shell of a common condenser. As
shown in Figures 1 and 9, the first-stage ejectors then discharge their mixture into
inter-condenser 150 and the second-stage ejector 154 withdraws that shell mixture
and discharges it to the after-condenser 152. The after-condenser condenses the remaining
steam vapor and discharges the residue of inert gasses into the atmosphere via vent
134. This air ejection package 130 is a conventional steam operated 132 two-stage
steam ejector unit with inter and after-condensers. Motor driven vacuum pumps with
or without air ejectors could be readily substituted for the steam operated device
shown.
[0053] The low-cost pre-condenser 120, 122, 124 and 126 would be installed when operating
conditions indicated the need for additional scavenging of the rear headers. If they
were not needed, then there would be some cost savings by eliminating the fins 53
on piping 30, the fluid separating connection 128 and the four condensate drain lines
71, 73, 75 and 77 and running the extraction piping 30 in the cavity below bundle
air seal 164 Figures 2 and 3.
[0054] Although the preferred arrangement as illustrated in the drawings of this invention
shows four rows of tubes, all of the disclosure in this invention apply to bundles
constructed with one or more rows. Similarly, each row may have a different finned
tube diameter such as, the first row could be 3.8 cm (one and one-half inch) in diameter,
the second row 3.2 cm (one and one-forth inch) in diameter and the third row 2.54
cm (one inch) in diameter.
1. Luftgekühltes Dampfkondensatorsystem, umfassend einen Vorsammler (34), der sowohl
zu kondensierenden Dampf als auch zu entfernende, nicht-kondensierbare Gase empfängt;
eine Anzahl geneigter Kondensationsrohre (32), die in Reihen (60, 62, 64, 66) angeordnet
und zu Bündel (56) gruppiert sind, wobei die Rohre an ihren unteren Enden mit dem
Vorsammler (35) gekoppelt sind, so daß Dampf vom Vorsammler in die Rohre fließt und
mit dem Kondensat, das in den Vorsammler zurückfließt, kondensiert und dann von dort
abgezogen wird, während die nicht-kondensierbaren Gase vom Vorsammler in die Rohre
strömen und dann nach oben;
eine Anzahl von Nachsammlern (36, 38, 40, 42), die an die oberen Enden der Rohre
gekoppelt sind und die nicht kondensierbaren Gase aus den Rohren empfangen, wobei
jede Rohrreihe (60, 62, 64, 66) ihren eigenen - individuellen - Nachsammler (36, 38,
40, 42) zum Empfang und zum Sammeln der nicht-kondensierbaren Gase besitzt; und
einem Vakuumrohrsystem (121, 123, 125, 127) mit Gaseinlässen (114), die mit dem
Inneren des jeweiligen Nachsammlers in Verbindung stehen und das die gesammelten,
nicht-kondensierbaren Gase aus den jeweiligen Nachsammlern längs deren ganzen Länge
evakuiert.
2. System nach Anspruch 1, wobei das Vakuumrohrsystem im jeweiligen Nachsammler (36,
38, 40, 42) über dessen ganzer Länge innenseitig installiert ist und jeweils eine
Anzahl von Öffnungen (114) besitzt, die in unmittelbarer Nachbarschaft zu den Rohrenden
(32) angeordnet sind, damit durch Flüssigkeitsdruckunterschiede die verbliebenen nicht-kondensierbaren
Gase veranlaßt werden, das jeweilige Rohrende zu verlassen und gleichmäßig und stetig
direkt in die Öffnungen (114) zu strömen, welche durch weitere Rohrleitungen (120,
122, 124, 126) stromab der vakuumschaffenden Ausstoßer (144) verbunden sind, wodurch
die Gase unmittelbar über die gesamte Länge der Nachsammler (36, 38, 40, 42) und der
Bündel (56) sauber entfernt werden.
3. System nach Anspruch 1, das weiter innen im Vorsammler (35) eine Einrichtung (166)
zum Aufheizen des Kondensats besitzt, die auf der Strecke des fallenden Kondensats
angeordnet ist, so daß deren Verweilzeit in der Dampfatmosphäre verlängert ist und
sie das überkühlte Kondensat zurück auf seine Sättigungstemperatur bringt.