Note: Descriptions are shown in the official language in which they were submitted.
406~
¦ _ BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to gas
turbine engine systems, and more particularly, to methods
and appar~tus for treating and recovering energy from hot
gases, such as primary gas turbine exhaust gases, to improve .
the overall efficiency of the gas turbine engine, heating
or power generating system in which the gases are employed.
Prior Art
The use of high pressure gas turbine engines moti-
vated by combustion product gases to produce mechanical
shaft energy, which is convertible into electrical energy,
~1 117~06~ I
is common in modern day power plants. In recent years,
due in part to increasing fuel costs, there has been an
especially intensive effort by designers to increase the
thermodynamic efficiency of the gas turbine. It is generally
accepted that the efficiency of such a turbine is a function
of the turbine operating temperature (To) and turbine exhaust
gas temperature (Tx) and that the efficiency relationship
may be expressed as: To _ Tx
efficiency T
Thus, in a typical situation, where To = 1,073K and
Tl = 773K, the turbine efficiency is only 27.8%. Most
efforts to improve turbine efficiency have focused on increasing
To/ the turbine operating temperature. However, increased
temperatures necessitate the use of improved materials,
which are generally more costly, while the exposure to
higher temperatures shortens the lifetime of the equipment.
-Thus, on an overall economic basis, it is doubtful that
merely increasing To is a productive approach to improving
turbine efficiency.
-- Designers have had very little success in lower-
ing Tx, the turbine exhaust gas temperature. As a result,
the relatively low pressure, relatively high thermal content
turbine exhaust gases are typically used as the thermal
source in conventional heat exchangers and passed in indirect
heat exchange relationship with water or compressed air
to produce steam or combustion chamber feed air before being
disposed of by exhausting them to atmosphere through tall
himneys or stacks. It has also been suggested that overall
11~40~1
t rbine system efficie~cy could be increased by condacting
the relat,ively high thermal content exhaust gases to a low
pressure turbi-ne to produce additional mechanical shaft
work before passing the resulting exhaust gases, in typical
manner, through conventional heat exchangers to indirectly
heat water or compressed air before discharging the gases
to atmosphere through tall chimneys or stacks.
The problem with either of the foregoing approaches
to utilizing the exhaust gases is that they typically contain
harmful contaminants yet must be discharged through stacks
to the atmosphere. The disadvantages of this method of
disposal include resulting air pollution and its harmful
effects on the environment, a waste of recoverable heat
energy, and the high cost of constructing and maintaining
tall stacks. Loss of recoverable heat energy is unavoidable
because gases discharged into a stack must be substantially
hotter than ambient air to produce an up-draft in the stack
and to avoid condensation in the chimney. Moreover, the
latent heat of steam in flue gases is not generally recovered
in order to avoid condensation and the attendant corrosion,
as a result of which additional, available heat energy is
being wasted.
Where the latent heat of steam is not recovered,
the system designer must work with "low heating values"
of the fuels rather than "high heating values". Low and
high heating values for fuels are given in such handbooks
as the John N. Perry Engineering Manual, published in 1959
by McGraw Hill, where the following typical heating values
are given:
406 1
High ~eating Low ~eating
Gas Value Value
Hydrogen60,958 Btu/lb51,571 Btu/lb
Methane23,861 Btu/lb21,502 Btu/lb
Octane20,510 Btu/lb 19,150 Btu/lb
Methyl10,270 Btu/lb 9,080 Btu/lb
alcohol
(vapor)
As will be apparent from these heating values, about 18
percent more Btu/lb can be recovered from hydrogen if its
high heating value can be utilized, about 11 percent more
from methane, about 13 percent more from methyl alcohol
vapor and about 7 percent more from octane "gasoline".
Prior systems have not been able to utilize the high heating
value of such gases.
As the public concern about air pollution has
increased, stack heights have been increased to affect
better dispersion of pollutants. However, increasing stack
heights adds to the cost of constructing and maintaining
stacks, yet provides no solution to the underlying problem,
i.e., avoiding emission in the first instance of harmful
substances such as sulfur oxides, chlorine gases, phosphor
oxides, etc.
A significant factor in air pollution is the incre-
asing level of gaseous airborne pollutants which combine
with moisture in the air to produce acids, e.g., carbon dioxide,
sulfur dioxide, and oxides of chlorine and fluorine. The carbon
dioxide content in some industrial districts is as h~gh
as ten times normal. Acid forming pollutants have been
found in some instances to increase the acidity of rainwater
rom its normal p~ of about 6.9 to values of 4Ø ~ainwater
~-~ 1174061
.
having a pH of 5.5 or lower less will destroy aquatic life
and can do substantial harm to buildings, monuments, and
other structures. -
One proposal for removing acid forming componentsfrom exhaust gases is to scrub the entire flow of exhaust
gases with water and caustic prior to discharging them
through a stack. However, scrubbing the entire exhaust
gas flow requires large quantities of water, which are not
always available, and requires costiy, large capacity scrubbing
equipment. Indeed, scrubbing the entire flow of exhaust
gases from some incinerators requires at least half the
amount of water, by weight, of the solid wastes burned in
the incinerator. Treating the large volume of scrub water
needed in such a process is very costly and contributes
to the impracticality of scrubbing as a total solution to
the acid pollutant problem.
Another difficult pollutant to deal with effec-
tively is sulfur in the exhaust gases. One proposal for
the desulfurization of exhaust gas utilizes a series of
heat exchangers to extract heat energy from the gas prior
to a scrubbing operation. Heat extracted from the gas is
returned to the gas following desulfurization and the gas
is exhausted through a tall stack for diffusion into the
atmosphere. This proposal has the disadvantages of wasting
heat energy recovered from the gases, requiring large volumes
of scrubbing water, requîring the use of a tall stack, and
polluting the air with such noxious components as are not
removed during scrubb~ng.
1~ 1174~6~ 1
- 6 -
The problem of disposing of exhaust gases is now
recognized as a major concern in industrial countries through-
out the world. Dispersing emissions through the use of
tall stacks is no longer regarded as an acceptable solution.
Applicant's U.S. Patent 3,970,524 discloses a system for
gasification of solid waste materials and a method for treat-
ing the resulting gases to produce commercially useable
gases in such a manner that dispersion through stacks is
not necessary. A feature of one embodiment of this patent
is pressurization of a combustion zone to such pressures
as will permit blower and/or compression units to be eli-
minated from the gas treatment system. Another feature
is the use of a multichamber gas treatment unit in which
noxious gas components are sublimed or "frozen out" and
thereby separated from the clean useable gas components.
A problem not addressed by U.S. Patent No. 3,970,524 is
that of providing a system for treating combustion exhaust
gases and productively reclaiming heat energy from the hot
gases. This problem is, however, dealt with in applicant's
U.S. Patent No. 4,126,000 which teaches reclamation of
heat energy by the transfer of the sensible and latent heat
of the gases to a power fluid in indirect heat exchange
relationship therewith, as in a conventional heat exchanger.
~owever, the economics of indirect heat exchange at the
lower temperature levels are very poor and reduce the over-
all desirability of such a system. Applicant's U.S. Patent
No. 4,265,088 discloses a system which utilizes
1174051
direct heat exchange between the hot gases and a power fluid
to improve the economics and thermal efficiency of the
system.
SUMMARY OF THE INVENTION
It is therefore an object of the present inven-
tion to overcome the foregoing economic and other drawbacks
of the prior art, and to provide unique and improved methods
and apparatus for improving the overall operating efficiency
of a gas turbine system by purifying relatively hot turbine
exhaust gases to remove harmful components therefrom, by
converting a portion of the thermal energy of the exhaust
gases to mechanical work and by transferring a portion of
the thermal energy of the exhaust gases to other fluids.
Another object of the invention is to provide
unique and improved methods and apparatus for converting
a portion of the thermal energy of the relatively~hot exhaust
gases to mechanical work by expanding relatively hot compressed
air in a helper turbine.
Still another object of the invention is to provide
improved systems and methods for treating relatively hot
turbine exhaust gases for economically removing harmful
components and recovering heat energy therefrom to permi~t
their discharge to atmosphere without the need for expensive
gas treatment equipment or tall chimneys or stacks.
Other objects and advantages will become apparent~
~ 1~74061
- 8 -
from the following description and appended claims.
In accordance with the foregoing objects the pre-
sent invention provides a method for improving the overall
efficiency of a gas turbine power plant system whereby re-
latively hot turbine exhaust gases, generally at about 300
to 600C, containing such components as nitroge~ carbon
dioxide, carbon monoxide, sulfur dioxide,
hydrocarbon gases, and the like, are treated by cooling
in regenerators in heat-exchange relationship with solid
materials having relatively high heat capacitance and re-
latively large surface area to volume ratios, processing
to remove the noxious, generally less volatile components
of the exhaust gases, and exhausting the resulting purified
gases (generally comprising the more volatile components
of the exhaust gas) to atmosphere without using a tall stack.
The less volatile components, comprising the environmental
pollutants, may be removed in known manner, preferably by
subliming or "freezing out" such harmful, less volatile
components of the qases for subsequent scrubbing, neutra-
lization or utilization. Heat values in the relatively
hot turbine exhaust gases are removed, at least in part,
by cooling the gas in regenerators and recovered by passing
a heat exchange fluid, preferably a gas such as steam, com-
pressed air, or the like, through the regenerators. The
resulting heated heat exchange fluid is utilized to operate
at least one auxiliary or helper gas turbine, with the re-
ult that the over~ll ermodynamic efficiency o~ the ga~
- 1174061
turbines comprising the power plant system is improved.
If compressed air is used as the heat exchange fluid, at
least a portion of the heated air may advantageously be
used as the combustion air fed to the exhaust gas source,
i.e., the gas turbine combustion chamber or the combustion
unit. The heat values remaining in the purified exhaust
gas, if sufficient, may also be utilized, e.g., to heat
water (or other fluid) which, in turn, may be used for ge-
nerating steam, preheating boiler feed water, domestic
heating or other purposes. Likewise, the heat values remaining
in the auxiliary or helper turbine exhaust may be ut;lized
to heat water or other fluid.
In one embodiment of the invention the relatively
hot turbine exhaust gases are purified in regenerators,
i.e., less volatile components are sublimed or condensed.
The gases are cooled prior to subliming using regenerators
as heat exchangers and transfer their heat to the packing
of the regenerators. The cooled and purified gas may be
used to reclaim a portion of the heat originally transferred
to the regenerators. The balance of the heat energy transferred
from the gases is recovered from the -regenerators by passing
a heat exchange fluid, such as compressed air, therethrough.
In a particularly desirable form of this embodiment a first
plurality of regenerators arranged in series are used to
perform the cooling and gas purifying functions and a second
plurality of regenerators arranged in series are used to
perform the purified gas reheating and heat reclamation
117~0~1
- 10 -
functions.
One noteworthy advantage of the various purifi-
cation systems of the present invention is that they are
able to process relatively hot turbine exhaust gases, i.e.,
gases having a temperature of 300C or higher, to convert
the gases to a form suitable for venting while at the same
time preserving the thermal values present in the gases~
Heat reclamation is effected in regenerators which operate
at a thermal efficiency of 90% or better compared with con-
ventional indirect heat exchangers which operate at thermal
efficiencies in or below the 50-60~ range. Another impor-
tant advantage is that the present systems also obviate
the need for costly stacks. Still another advantage of the
present invention is that the systems consume none or only
a small fraction of their power output. Yet another advantage
is that the systems of the present invention may, if desired,
utilize a sublimation or "freezing out" process to separate
out harmful, less volatile gas components which can then
be recovered and treated for utilization or neutralized,
as by scrubbing, with far less water than would be required
if the entire flow of exhaust gases were to be scrubbed
as in prior proposals. The small volume of scrub water, if at all
required for this operation can be treated at minimal cost
with scrubbing equipment having a much smaller capacity
than is required where the entire flow of exhaust gas is
scrubbed. Substantial savings are achieved over prior
processes inasmuch as large capacity scrubbing equipment
1~`740~1 1
is not required. The ability to atilize smaller capacity
eguipment is important also from~the standpoint of minimizing
the amount of expensive corrosion resistant material needed.
As is well known, all scrubbing systems experience a severe
corrosion problem requiring the provision of expensive
corrosion resistant materials. In the present systems,
where small scale rather than large scale equipment can
be used due to the limited scrubbing volume, the amount
of expensive corrosion resistant material needed is minimized.
If the exhaust gases are to be treated for utilization,
an absorption or adsorption system can be applied which
will yield a concentrated stream of SO2 ready for use in
the chemical process industry. Such utilization obviates
the use of water for scrubbing in a neutralization system.
Gas treatment methods and apparatus of the type
described in U.S. Patent No. 3,970,524 may advantageously
be used to effect a separation of harmful, less volatile
exhaust gas components by the sublimation or "freezing out"
process. The apparatus includes an arrangement of valve
interconnected, packed, refrigerated towers through which
exhaust gas passes to e-ffect sublimation or "freezing out"
of harmful components. Components which can be removed
by this process include CO2, HCl, H2S, SO2, C2H2, HCN, SO3,
and the like. It is noteworthy that this type gas treatment
process is primarily of a physcial nature. Chemical treatment
is not utilized until noxious gas components, which comprise
only a small fraction of the total gas flow, are separated
1 ~740B ~
out.
Inasmuch as the system of the present invention
provides a relatively simple and inexpensive method of puri-
fying turbine exhaust gases, it also permits the use of cheap
fuels having a relatively high sulfur content. The savings
which result from the use of cheaper fuels, the elimination
of tall stacks, the ability to recover thermal energy from the gases
and to convert it to mechanical energy, the elimination of large uses
of scrub water, and the reduction in size of required scrubbing
equipment make the system economically attractive for installatio ~s
oE a wide range of sizes. Moreover, where the exhaust gases
being treated contain a relatively high concentration of
sulfurous compounds, elemental sulfur and/or sulfuric acid
may be obtained from the compounds, thereby adding to the
economy of operation of the system.
BRIEF DESCRIPTION OF THE DRAWINGS _
A fuller understanding of the invention may be
had by referring to the following description and claims
taken in conjunction with the accompanying drawings in
which:
FIGURE 1 is a schematic flow diagram of a system
for practicing one embodiment of the present invention;
FIGURE 2 is a schematic flow diagram of an ill-
ustrative turbine exhaust gas separation and heat reclama-
tion unit for use in the Figure 1 embodiment of the present
invention
~ 1174061
FIGURE 3 is a schematic flow diagram of ~n illus-
trative helper turbine exhaust gas heat reclamation unit
for use in the Figure l embodiment of the present invention.
FIGURE 4 is a schematic flow diagram of an illus- ¦
trative helper turbine exhaust gas heat reclamation unit
for use in the Figure l embodiment of the present invention;
and
FIGURE 5 is a schematic flow diagram of an illus-
trative turbine exhaust gas heat reclamation unit for use
in the Figure l embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, a gas turbine power plant
is indicated generally by the numeral 10. The power plant
10 can include one or more gas turbines for the production
of shaft work which are motivated by hot exhaust gases
emitting from a fuel combustor associated with or separate
from the gas turbine. The hot exhaust gases typically con-
tain such components as nitrogen, carbon dioxide, sulfur
dioxide, carbon monoxide, nitrogen oxides,
and-hydrocarbon components.
In the embodiment illustrated in Figure l, the
gas turbine power plant 10 comprises a primary or high pres- .
SUre turbine 12 having assocîated therewith a combustion
chamber 14 and a compressor 16. Fuel is supplied to the
74061
combustion chamber 14 as indicated by arrow 15. In pre-
ferred operation the fuel used is inexpensive liquid
fuel or gas having a relatively high sulfur content. This
fue; is preferred due to its low cost and because the sulfur
content is easily separated out of the exhaust gases, as
will be explained more fully hereinafter. Air or even oxygen
enriched air is supplied to the combustion chamber 14 for
reaction with the fuel. In preferred practice, a compressor
16 is used to pressurize the air supply furnished via air
line 17 such that the combustion chamber operates under
pressure. ~here available, heated air may be supplied to
combustion chamber 12 via air line 17. In a preferred form
of the invention, the combustion chamber 12 is operated
under sufficient pressure that the exhaust combustion gases
can efficiently operate high pressure turbine 12 yet still
have sufficient head to pass through the exhaust gas separation
and heat reclamation unit. If the pressure of exhaust gas
is not sufficient to pass it through the separation and
reclamation unit a blower is incorporated into the system
design.
Exhaust gases generated in the combustion chamber
14 are ducted through high pressure turbine 12 wherein they
are expanded to a lower, substantially ambient, pressure
and, in expanding, produce a net shaft work output. To
convert the shaft work to a more useful form of energy,
a power generator 18 is coupled to the drive shaft 20 of
turbine 12. Generally, compressor 16 may likewise be coupled
1 17~06~
to drive shaft 20 to provide the energy for operation of
the compressor. The gases exiting high pressure turbine
12 are led into gas feeder conduit 153 which directs the
gases to gas separation and heat reclamation unit 158.
These gases have a reduced pressure compared to the combustion
chamber exhaust gases, due to pressure losses in turbine
12, but are "relatively hot", at temperatures of about 400-
600C, and still contain a great deal of thermal energy.
The unit 158 is operable: (1) to cool the relatively hot
gases and separate them into condensable components of
relatively low volatility and more volatile components
having similar vapor pressures, such as C3 and C4 fractions; ,
and (2) to reheat the more volatile components and to heat
a heat exchange fluid, such as compressed air, to a temperature
which may be as high as within a few degrees of the temperature
of the relatively hot exhaust gases which entered unit 158
through feeder conduit 153. The more volatile, noncondensed
or clean components of the gas exit unit 158 via purified
gas (off gas) discharge conduit 172. The heated heat ex-
change fluid exits unit 158 via heated air discharge conduit
170 and is used to operate low pressure helper or auxililary
gas turbine 22, which may be coupled via drive shaits 24
and 20 to power generator 18, to improve the overall thermo-
dynamic efficiency of the gas turbine power plant system.
Although one auxiliary or helper gas turbine is shown, a
plurality of such turbines arranged in series or parallel
could, if desired, be employed. It will be appreciated
that if helper turbine 22 is motivated by a flow of 5-6
ar compressed air at about 760K and expands the air, at
1 1740~1
- 16 -
substantially constant entropy, to about 1 bar and 500K,
an enthalpy change from about 800 kJ/kg to 500 kJ/kg is
realized, which enthalpy change is recoverable as subtantial
shaft work. The ambient pressure, but still hot at 500K
air exits helper turbine 22 via heated air discharge conduit
171. As will become clear, this stream of hot air can be
charged to a gas turbine and to enhance the turbine's thermal
efficiency or directed to the combustion chamber of a boiler.
Referring to Figure 2 there is shown an illus-
trative gas separation and heat reclamation unit 158, useful,
for example, in the embodiment of Figure 1. The unit of
Figure 2 uses separate regenerators to perform the four
essential functions of unit 158, i.e., to cool the relatively
hot exhaust gas, to separate components of the gas, to re-
heat the relatively cool purified off gas prior to venting
or utilizing, and to reclaim thermal energy transferred
from hot exhaust gas to the regenerator packing by heating
the compressed air heat transfer fluid. Unit 158 of Figure
2 accomplishes its functions with a first heat exchange
zone comprising a plurality (two are illustrated) of series
arranged regenerator units 301, 361 to cool the relatively
hot exhaust gas and separate it into its components and
a second heat exchange zone comprising a plurality (two
are illustrated) of series arranged regenerator units 303,
363 to reheat the relatively cool purified off gas and to
reclaim thermal energy by heating a heat transfer fluid.
Either set of series arranged regenerator units 301, 361
or 303, 363 can serve as the first heat exchange zone and
perform the functions of that zone. Likewise, either set
an serve as the second heat exchang- zone and pe}Eorm the
11740~1
functions of that zone. Thus, regenerators 301, 303, com-
prising a first heat exchange sub-zone, are arranged in
parallel relationship to allow the relatively hot exhaust
gas to be introduced initially into either one of regenera-
tors 301, 303 and to allow either one to perform the hot
exhaust gas cooling function while the other performs the
heat reclamation function. Likewise, regenerators 361,
363, comprising a second heat exchange sub-zone, are arranged
in parallel relationship to allow either one to perform
the component separation function while the other performs
the off gas reheating function.
Relatively hot exhaust gases from primary turbine
12 are led into gas feeder conduit 153 from which they pass
into exhaust gas separation and heat reclamation unit 158.
Unit 158 includes at least four similar packed towers or
columns 301, 303, 361, 363. Towers 301 and 303 are arranged
in parallel relationship to each other, as are towers 361,
and 363. However, towers 301, 303 are arranged in series
relationship to towers 361, 363. Each of the towers 301,
303, 361, 363 is similar in constuction and content to the
regenerators shown as 59, 61, 63 in Figure 1 of U.S. Patent
No. 4,126,000 and each is similar to a regenerator described
by Russell B. Scott at pages 29-31 of CrYogenic Engineering,
published in 1959 by D. Van Nostrand Co., Princeton, N.J.
Each of the towe~rs contains loose solids, for example,
ceramic balls, quartzite pebbles, steel shot, etc., pancakes
wound from thin corrugated aluminum ribbon, or other solids
1174~61
- 18 -
having relatively large surface area to volume ratios,
relatively high heat capacitances and the capability of
storing heat and resisting corrosion. Typically, the packing
for the regenerator towers has a surface area to volume
ratio and packing capability sufficient that the regenerator
has a surface density of 1000 to 2000 s~uare ft. per cubic
foot.
Automatic switch valves 305a, 305b are provided
at the end of towers 301, 303 adjacent to feeder conduit
153 with valves 305a connecting thereto. Tower connection
conduits 307 communicate the towers 301, 303 with the valves
305a, 3d5b. Tower connection conduit 309 through cross
conduit 315 communicates with towers 301, 303 and connects
towers 301, 303 with feed conduit 353 and automatic switch
valves 364a, 364b provided at the end of towers 361, 363
adjacent feed conduit 353. Tower connection conduit 367
communicates the towers 361, 363 with the valves 364a, 364b.
Tower connectlon conduit 368 communicates the towers 361,
363 with automatic switch valves 365a, 365c. A pair of
transfer conduits 373, 374 connect valves 365a, 365c of
towers 361, 363 with a cooling means, preferably an expansion
turbine 375. An expansion turbine has the advantage that
it cools the gas more efficiently by substantially isentropic
expansion while at the same time it produces useful shaft
work. A power generator 376 may be coupled to turbine 375
to convert the shaft work to a more useful form of energy.
In an alternative embodiment (not shown), transfer conduits
~ 11740~1
-- 19 --
373,374 could connect the valves 365a, 365c with a noxious
gas removal system, such as a system which removes environmental
pollutants by use of conventional absorption, extraction
and/or adsorption means and which operates at relatively
low temperatures, e.g., about 5 to ~50C. In the illustrated
system, purified off gas is discharged following component
separation in tower 361 and reheating in tower 363 through
purified off gas discharge conduit 172. A preheated compressed
air discharge conduit 170 connects with the valves 305b.
A compressed air feed line 321 having a compressor 322 therein
supplies a cooling heat exchange fluid to towers 301, 303.
A compressor 313 is included in tower connection conduit
309 to provide the positive pressure in the system which
may be required when very large exhaust gas volumes are
passed.
The manner by which gases are treated in unit
158 may be visualized as that of subjecting the gases in
successive like cycles to cooling in towers 301, 303 and
reheating and/or cool ng in towers 361,363~ During each
cycle, a different step is being conducted in each of to-
wers 301, 303. While a first tower is serving as the cool-
ing tower to cool the hot gases, the other tower is serving
to heat the compressed air flowing therethrough via air
feed line 321. In the next cycle, the roles of the respective
towers 301, 303 are reversed. Likewise with towers 361,363.
While one of these towers is serving as the component separa-
tion tower t~ seQ rate the le5s volatile gas Components
~ 174061
- 20 -
by sublimation or condensation from the cooled gases flowing
from towe,rs 301, 303, the other tower serves to reheat the
more volatile, noncondensed or clean components of the gas
passing out of the component separation tower. In the next
cycle, the roles of the respective towers 361, 363 are re-
versed.
Thus in a first cycle one of the towers 301, 303
is selected as the cooling tower into which the hot particle
free exhaust gases are ducted and the corresponding valve
305a is opened. If tower 301 is to serve as the cooling
tower, valve 305a associated therewith and valve 305b assoc-
iated with tower 303 are opened while valve 305b associated
with tower 301 and valve 305a associated with tower 303
remain closed. The hot exhaust gases flow from feeder
conduit 153 through valve 305a into tower 301 in which the
gases are cooled prior to compression in compressor 313.
At the same time the tower 301 is heated by the hot gases
in preparation for serving as the air heating tower in the
next cycle. The compressed gases are then directed by con-
duit 309 to feed conduit 353 for component separation in
towers 361 or 363. When tower 361 is to serve as the com-
ponent separation tower valve 364a associated therewith
and valve 364b associated with tower 363 are opened while
valve 364b associated with tower 361 and valve 364b assoc
iated with tower 363 remain closed. The relatively cooled
compressed exhaust gases flow from feed conduit 353 through
valve 364a into tower 361 in which the gaseous components
~ 117~061
are further cooled and separated by sublimation or conden-
sation with the less volatile components remaining in tower
361 while the more volatile or purified components pass
through the tower. (It is assumed here that towers 301
and 361 had already been precooled in a previous cycle so
that the gases will be cooled in tower 301 and less vola-
tile gas components loaded into tower 361 will be sublimed
or "frozen out".) At the same time the tower 361 is heated
by the relatively cool exhaust gases in preparation for
serving as the purified gas reheating tower in the next
cycle. The gas, freed of the less volatile components,
flows via valve 365a and transfer conduit 373 through turbine
375 wherein the gas is further cooled. The exhaust gases
are allowed to flow through towers 301 and 303 in this
manner for a short period of time, for example, for about
6 to 10 minutes. Energy extracted from the gases by turbine
375 is used to drive the generator 376. The gases expand
in the turbine and are cooled as they expand. The expan-
sion pressure ratio in the turbine need only be sufficient
to accomplish the desired cooling. In view of this addi-
tional pressure drop, a system which u~ilizes an expansion
turbine will generally operate at a somewhat higher com-
bustion system pressure as compared to a system which uti-
lizes some other means of cooling the èxhaust gas, such
as a conventional heat exchanger.
The further cooled purified gases are re~urned
through tower 363 via transfer conduit 374 and valve 365c.
1174061
.
In tower 363 the purified gases are reheated to the relatively
cool condition while the tower is cooled (it is assumed
that tower 363 had been pre-heated in a previous cycle by
passage of relatively cool exhaust gases therethrough).
The relatively cool purified gases leave tower 363 through
tower connection conduit 367 and valve 364b and are dis-
charged via purified off gas discharge conduit 172. If
the off gas contains sufficient thermal energy values, as
will hereinafter be discussed, then its thermal content
may be reclaimed. If the off gas contains insufficient
thermal energy it is generally vented to ambient.
It will be appreciated that in the immediately
previous cycle, tower 361 had been used for the sublimation
or "freezing out" step" and the less volatile components
of the gas had been condensed or converted into the solid
phase and had remained within tower 361, i.e., the tower
was loaded. Therefore, in the next cycle, loaded tower
361 is cleaned by revaporizing the "frozen out", sublimed
or condensed components from the prior cycle to form an
acid gas. In one embodiment of the invention, the initial
flow of purified gas which passes through loaded tower 361
may be used to purge the tower. The mixed flow of purified
gas and revaporized components, i.e., acid gas, as shown
in Figure 1, are ducted through compressor 182 via purified
gas discharge conduit 172 and valve 169a into the blowdown
conduit 193a. The acid gas typically consists mainly of
S2 and C02 with small amounts of S03 and other noxious
gases. Inasmuch as exhaust gas discharge restrictions
p clade emission o~ these gases, mcst noxious componen~s
~174061
in the blow-down gases are neutralized by scrubbing or are
otherwise separated out to permit exhausting the cleansed
blowdown gas. Cleaning of the loaded tower in this manner
can be accomplished during each cycle by switching the
initial purified gas flow to the blowdown line 193a via
valve 169a for just enough time to purge the tower an~ then
switching the purified gas flow back through valve 169b
to either be vented via gas path 193b, valve 183a, line
195 and vent line 194 or, if the purified off gas contains
sufficient thermal energy to be used as a thermal source
for heating water or other heat exchange medium, utilized
via heat exchanger 196, as will be discussed more fully
hereinafter. In another embodiment of the invention, loaded
tower 361 may be cleaned using vacuum revaporization system
330, shown in phantom in Figure 1, alone or in combination
with the purified gas purge flow into the blowdown conduit
as previously described. To use vacuum revaporization
system 330, at the beginning of each cycle, just before
exhaust gas flow is switched from tower 301 to tower 303
(or vice versa), the valves are realigned to allow flow
into the new hot exhaust gas receiving tower and the tower
to be cleaned of sublimed or condensed components is isolated
and momentarily (up to about 5 seconds) connected to the
vacuum revaporization system to substantially instantaneously
equalize pressure therebetween and to substantially completely
revaporize the sublimed or condensed components. In the
stance, for example, where hot exhaust yas flow is switcheù
7406~
- 24 -
to tower 303 and compressed air flow is initiated through
tower 301, valve 305a associated with tower 303 and valve
305b associated with tower 301 are opened as are valves
364a and 365a associated with tower 363 and valves 364b
and 365c associated with tower 361. At the same time valve
305a associated with tower 301, valve 305b associated with
tower 303, valves 364a and 365a associated with tower 361
and valves 364b and 365c associated with tower 363 are
closed to complete the realignment of the system valves.
Valve 36~c associated with tower 361 is closed to momentarily
(up to about 5 seconds) isolate tower 361, which contains
the sublimed or condensed components from the previous
cycle, from turbine 375. Vacuum revaporization system 330
is connected to tower 361 via valve 364b and purified gas
discharge conduit 172 by opening valve 332 in vacuum line
331 which opens a flow path between tower 361, vacuum chamber
334 and compressor 340. Vacuum pump 336 operates to reduce
the p~essure in chamber 334 by a ratio of about 10 to 1.
When chamber 334 is connected to tower 361 the pressure
in tower 361 instantaneously drops to equalize with the
reduced pressure in chamber 334 and the "frozen out", sublimed
or condensed components in tower 361 are revaporized to
form an acid gas which is drawn out of tower 361. The withdrawn
acid gas is compressed by compressor 340 and is discharged
into acid gas discharge conduit 338 from which it may be
directed, in the same manner as is gas in blowdown conduit
193a, to scrubbing or other noxious component separation
apparatus to recover S~ as a co~dity.
1174061
-25-
The heat energy stored in tower 303 i~s recovered
by passing compressed air through air feed line 321 and
compressor 322 into and through tower 303 in which the air
is hea~ed ~ihile the solid packing in tower 303 is cooled
(it is assumed that tower 303 had been pre-heated in a
previous cycle by passage of hot exhaust gases therethrough).
The heated air leaves tower 303 by way of tower connection
conduit 307 through valve 305b and conduit 170 and may be
utilized, such as by expanding through helper turbine 22
to produce useful shaft work, by ducting the air to serve
as the preheated combustion air fed to chamber 14 via pre-
heated air line 26 and flow control valve 28 therein, as
shown in Figure 1, and/or for other purposes, as will be
more fully discussed hereinafter. It is the flow of cool
compressed air through tower 303 which readies that tower
for the next cycle during which gas cooling will take place
therein.
As can be seen most clearly in Figure 1, the
helper turbine exhaust air in conduit 171 can be diverted
through optional air supply line 320 (shown in phantom)
to serve as an air feed source for line 321. Alt-ernatively,
the helper turbine exhaust air can be diverted through one
or more optional expansion turbines 130 (shown in phantom)
to generate additional shat work or electrical ènergy via
optional power generator 132 (shown in phantom). The further
expanded and cooled air exiting turbine 130 is generally
discharged to ambient, but could be reused if desired.
40~1
- 26 -
In still another alternative or additional use,- the helper
turbine exhaust air may be used as a thermal energy source
in a heat exchanger to directly heat water or other heat
exchange fluid in heat reclamation unit 100. For example,
heat reclamation unit 100 may comprise an optional heat
exchanger 185 into which cold water is fed via feed line
184 by pump 192. The water is heated by closing or throttl-
ing valve l90b and directing the helper turbine exhaust
air via line 171a into heat exchanger 185 through valve
l90a and heating coils or sparger 186. The co`oled air is
vented from heat exchanger 185 through vent line 191.
Heated water is pumped from heat exchanger 185 through line
187 by pump 188 to be used for district heating, and the
like. In another embodiment shown in Figure 3, heat re-
clamation unit 100 may be used to directly heat water or
other heat exchange fluid. For example, optional heat .
exchangers 444, 445 may be provided into which cold water
is fed via feed line 447. The water is intially heated
at ambient pressure almost to its vaporization point by
direct heat exchange in heat exchanger 445 and the thus
heated water is pumped from heat exchanger 445 via line
487 and pump 488 into heat exchanger 444. Heat exchanger
444 is maintained at an elevated temperature and pressure .
for further heating and degassing of the water prior to
utilization, for example as feed water to the economizer
section of a steam generator or to a district heating system,
or for conversion of the water into steam. The helper
1 174061
turbine exhaust air is fed initially through heat exchanger
444 by closing or throttling valve l90b and directing the
exhaust air via line 171a into the heat exchanger via valve
l90a and line 489. From heat exchanger 444 the exhaust
air is directed into heat exchanger 445 via line 448 and
sparger 446. Cooled air is vented as necessary from heat
exchanger 445.
It will, of course, be appreciated that the heat
content of the helper turbine exhaust air can be used
to heat a recyclable, preferably water immiscible, inter-
mediate heat exchange fluid, which can then be used to heat
water or other medium. Such an embodiment is shown in
Figure 4 wherein heat reclamation unit 100 comprises optional
heat exchangers 544 and 545 for exchanging heat between
the recyclable heat exchange fluid and the helper turbine
exhaust air, turbine 543 and power generator 542 for extracting
useful mechanical work from the heat exchange fluid and
converting it to electrical energy and a condenser 541 for
condensing the turbine exhaust heat exchange fluid and
returning it to heat exchanger 545. To aid in better under-
standing the embodiment of Figure 4 the flow of helper
turbine exhaust air through heat reclamation unit 100 is
shown as dashed lines and the flow of recyclable heat exchange .
fluid is shown as dot-dash lines. By closing switch
valve l90b, conduit 171a directs the helper turbine exhaust
air via valve l90a and line 589 into, through and out of
heat exchanger 544, and, then, into heat exchanger 545 via
~ ~4061
- 28 -
line 548 and sparg~r 546. Cooled air is vented as necessary
from heat exchanger 545. Liquid recyclable heat exchange
fluid fed via line 539 is initially heated almost to its
vaporization point by direct heat exchange with helper tur-
bine exhaust air in heat exchanger 545 (which may comprise
an injection drum in which a power fluid is sprayed into
direct contact with the helper turbine air) and the thus
heated heat exchange fluid is pumped from heat exchanger
545 via line 587 and pump 588 into heat exchanger 544.
In heat exchanger 544 the heat exchange fluid is vaporized
by heat exchange with he~per turbine exhaust air and the
vapors are ducted through conduit 537 to an expansion tur-
bine 543 in which the vapor expands and cools. The work
done by the vapors on the turbine is manifested as turbine
shaft energy. Coupled to the output shaft of turbine 543
is a power generator 542. The cooled exhaust vapor exiting
the turbine 543 is carried via duct 538 into condenser 541
where a flow of a heat exchange cooling medium, such as
water, through coils 540 causes the recyclable heat exchange
fluid to condense. The condensed heat exchange fluid is
returned to heat exchanger 545 through return conduit 539
and the cycle is repeated.
In a typical system such as shown in Figure 2
the hot gases entering the cooling tower 301 are at a tempera-
ture of about 400-600C and are cooled in the tower to
about 40-130C (relatively cool condition) at which tempera-
ture the gases are compressed and passed to tower 361 in
hich the~ are co~led to about -100 to -1-0C, the te~pera-
11~40~1 ~
- 2~ -
ture at which component separation occurs. The purified
gases leaving tower 361, which may be further cooled in
turbine 375, are reheated in tower 363 to within 5 to 10C
of the temperature of the gases entering tower 361 prior
to discharge through line 172 for heat reclamation, venting,
etc. If the purified gases leaving tower 361 are in the
range of 40C to less than about 70C, then the purified off
gas will not contain sufficient heat values to be useful
and will likèly have to be vented. On the other hand, if
the gases are in the range of 70C to 130C, then the puri-
fied off gas generally contains sufficient residual heat
for use, such as the heat source in a heat exchanger. The
compressed air entering tower 303 via air feed line 321
may be heated in tower 303 to within 5 to 10C of the
temperature of the gases entering tower 301. If for some
reason it is not desired to reclaim the bulk of the heat
energy of the towers with a heat transfer fluid such as
compressed air, then provision can be made for directing
the purified gases through heat energy-containing tower
303 wherein the gases are reheated. The heat energy would
then have to be-reclaimed from the heated purified gas
exiting the system through conduit 170, e.g., as is described
in Applicant ' s U . S . Patent No . 4, 265, 088 .
Thus it can be seen that the system of the present
invention offers a choice in the manner of reclaiming the
heat energy of the exhaust gases. Heat energy may be re-
~174081
- 30 -
claimed by thermal exchange between the compressed air flow
passed through the tower and the relatively hot tower solids.
~lternatively or concurrently, heat energy may be reclaimed
from the relatively cooled purified off gases exiting the
system through discharge conduit 172 if they have been
reheated sufficiently to achieve a temperature range at
which the heat values of the gases may usefully and efficiently
be reclaimed. If it is not desired to reclaim heat energy
via the purified off gas, the purified off gas flow may
be vented. On the other hand, heat energy may usefully
be reclaimed if the off gas is at a temperature in the range
from about 70C to 130C. Thus, as shown in Figure 1, the
purified off gas may be ducted through valve 169b, line
193b and valve 183b into heat exchanger 196 where the gas
gives up its heat energy in coils or sparger 179 before
being vented from the heat exchanger via vent line 194 as
cooled off gas. In this case it is desirable to retain
as much heat energy as possible in the pufified off gas.
Thus, compressor 182 may be operated without the conventional
after cooler in order that the heat energy added to the
exhaust gas by the compressor is retained in the system -~
and ultimately reclaimed from the purified off gas. Cold
water, for example, may be fed to heat exchanger 196 via
line 177 and pump 178 to absorb the heat energy from the
off gas and heated water pumped from heat exchanger 196
via line 180 and pump 181. It will, of course, be appre-
ciated that the heating values of the off gas can be used
~174061
to heat other l~quids, air or other gases or may be use~
to heat a recyclable, preferably water immiscible, inter-
mediate heat exchange fluid which can then be recycled or
used to heat water, air or other medium. The balance of
the heat energy in towers 301, 303, i.e., the portion not
absorbed by the purified gas, is removed directly from the
heated tower solids using a heat transfer fluid, e.g., com-
pressed air, other than the purified gases. The heated
fluid exiting the towers via line 170 may be utilized in
the manners previously described herein.
The next cycle is like the one just described
except that tower 303 serves as the exhaust gas cooling
tower and tower 301 as the air heating tower. It will be
appreciated that following the previous cycle, tower 301
was left in a relatively heated state by the passage of
hot exhaust gases therethrough whereas tower 303 was left
in a relatively cooled state by virtue of having given up
its heat content to the compressed air passing therethrough.
Just before the hot exhaust gas flow from feeder conduit
153 is directed through valve 305a into tower 303, but after
valves 305a, 305b, 364a, 364b, 365a and 365c have been
realigned to allow gas flow, sequentially, through towers
303, 363 and 361 and compressed air flow through tower 301,
valve 365c associated with tower 361 is momentarily closed
(up to 5 seconds) to isolate tower 361 in communication
with the previously described vacuum revaporization system
for ~ubstantially c-m~letely cleaning loaded tower 361 of
~1~4061
sublimed or condensed componen-s. Then valve ~65c associated
wlth tower 361 is reopened and hot exhaust gas flow is
directed through valve 305a into tower 303 in which the
gases are cooled while the tower is heated. They are then
ducted via cross conduit 315 to compressor 313 in which
they are compressed. The compressed gases are ducted through
conduit 309 to feed conduit 353 for component separation
in tower 363 prior to further cooling in turbine. It will
be appreciated that following the previous cycle, tower
361 was left in a relatively heated state by the passage
of the relatively cooled exhaust gases therethrough whereas
tower 363 was left in a cooled state by virtue of having
given up its heat content to the cold purified gases passing
therethrough. The relatively cooled exhaust gases flow
from feed conduit 353 through valve 364a into tower 363
in which the gaseous components are further cooled and separated
by sublimation or condensation while the tower 363 is heated.
Following processing in tower 363 the purified gases are
ducted through turbine 375, wherein they are still further
cooled, to tower 361 wherein they are reheated to the relatively
cool condition, while the tower is cooled and purged of
any remaining "frozen out", sublimed or condensed components
from the prior cycle. The purified or mixed gases are then
discharged from the system via purified off gas discharge
conduit 172 for further processing of revaporized components,
venting, heat reclamation, and the like. At the same time,
the thermal energ~ st red in tower 301 is reclaimed by passing
1174061
compressed air from air f;ed l;ne 321 therethrough. Heated
air leaving tower 303 flows via conduit 170 to and through
helper turbine 22 to produce shaft work, via preheated air
line 26 to chamber 14 as preheated combustion air and/or
is used for other purposes. It will be appreciated that
as the heated air source switches between towers 301 and
303 there is a momentary interruption in motivating air
flow to helper turbine 22. In order to prevent instability
and to reduce the shock as flow falls off then resumes then
falls off again, a flywheel is provided, in conventional
manner, on helper turbine 22.
The use of regenerators for the purpose of cooling
the primary turbine exhaust gas prior to purification and
reclaiming the heat energy of the exhaust gas prior to dis-
charge adds to the overall thermodynamic efficiency of the
gas turbine power plant system by utilizing heat exchange
equipment which operates at thermal efficiencies in the
90% range while it simplifies the design and reduces capital
costs. Capital costs can be further reduced by utilizing
a gas separation and heat reclamation unit 158 which employs
only two towers, each necessarily serving a dual function.
Each tower is effectively a split regenerator wherein separate
upper and lower portions perform separate functions. Thus,
while a first tower is being cooled in an upper portion
thereof by a flow of relatively cool compressed air and
in a lower portion thereof by the flow of cold purified
off gas, initial cooling of the hot exhaust gas is taking
place in an apper portion cf the second tower and component
~174061
- 34 -
separation by sublimation or condensation is taking place
in a lower portion of the second tower. Condensed or sub-
limed components are removed from the lower portion of the
second tower at the beginning of the next cycle by the
initial flow of purified gas therethrough.
With minor modification the system of Figure 1
is equally useful for heat reclamation from a hot clean
exhaust gas, see Figure 5, such as a gas resulting from
combustion of a clean fuel such as CH30H or clean natural
gas, which contain no harmful contaminants. Such a gas
would not require purification and could pass from the gas
turbine 12 to a heat reclamation unit, 158, there being
no need for a gas separation function. Therefore, regen-
erator towers 459, 463 could serve exclusively as highly
efficient heat transfer units for the reclamation of thermal
energy from the hot exhaust gas.
In the operation of the embodiment illustrated
in Figure 5 the clean, hot, substantially ambient pressure
primary turbine exhaust gases from turbine 12 pass via gas
feeder conduit 153 into one of towers 459, 463 wherein the
hot gases give up heat to the high heat capacitance solids
therein and become cooled, preferably to about ambient
temperature. At the same time, the thermal energy content
of the other tower 459, 463 (it having been heated by the
passage of hot exhaust gases therethrough in a previous
cycle) is recovered by passage of a heat exchange fluid,
e.g., compressed air, therethrough. A first step of one
1174061
- 35 -
i cycle is carried out by opening the valves 464a, 465a at
each end of tower 459 and valves 464c, 465c at each end
of tower 463. The hot exhaust gases will then flow from
feeder conduit 153 via valve 464a through tower 459 in which
the gases cool. The cooled gases exit tower 459 via valve
465a and off gas discharge line 172. As shown and discussed
in connection with Figure 1 the cooled off gas may either
be vented or utilized to reclaim heat values therefrom.
It will, likewise, be appreciated that as the
exhaust gases cool in passing through tower 459, the tower
solids are heated. The heat stored in the tower solids
may be recovered by feeding a cool heat exchange fluid,
such as ambient temperature compressed air, from air feed
line 321 and compressor 322 into tower 463 (it is assumed
here that the tower 463 had been preheated in a previous
cycle by the flow of hot exhaust gases therethrough). The
flow of air cools the solid packing in tower 463 as it
passes therethrough and becomes heated itself as it does _
so. It is the flow of cool compressed air through tower
463 that readies the tower for the next cycle during which
exhaust gas cooling will take place therein. The heated
air may be used to operate one or more helper gas turbines
as already described herein or a portion may be used as
preheated combustion air. The helper turbine exhaust air
may be used to operate a power turbine or as the thermal
energy source in a heat exchanger, as shown and discussed
in connection with Figures 1, 3 and 4, to directly heat
water, air or other heat exchange fluid.
While the invention has been described with re-
ference to particular embodiments thereof it will be under-
- 36 ~ 4 0 6 1
stood that numerous modifications may be made by those skilled
in the art without actually departing from the scope of
the invention. For example, the methods and systems illus-
trated in Figures 1-5 are effective to reduce the impurity
levels in the purified gas to trace levels. Should it be
desired to completely remove all sulfurous compounds and
other harmful components, adsorption or absorption systems
can be linked, in known manner, to the systems of Figures
1-5. Accordingly all modifications and equivalents may
be resorted to which fall within the scope of the invention
as claimed.
