Note: Descriptions are shown in the official language in which they were submitted.
z~o
CROSS REFERENCE
The present application is related to co-pending
Canadian Application No. 316,491, filed November 20, 1978,
and to Canadian Patent No. 1,044,895, issued December 26,
1978.
BACKGROUND OF THE INVENTION
1. Field of the Inventio_
The present invention relates generally to the
treatment of exhaust gases for discharge to the atmosphere,
and more particularly to methods and apparatus for treating
and recovering energy fro~ hot exhaust gases.
Exhuast gases suitable for treatment by the system
of the present invention include combustion exhaust gases
produced in fuel burning furnaces, roasters and the like,
exhaust gases such as .those produced in cement kilns and
the like, and exhaust
Z~6~)
~ases containing such componellts ~s nitrogen, carbon
dioxide, carbon monoxide, hydrogen chloride, hydro-
gen sul~ide, h~drocarbon gases, and the like. The
exhaust gases are prefera~ly cssentially inert but
include noxious components and traces of combustible
gases.
2. Prior Art
. _ _
Hot exhaust gases generated during the combus-
tion of fuel have commonly been disposed of by ex-
hausting them to atmosphere through tall chimneysor stacks. Disadvantages of this methoa of disposal
include resulting air pol:Lution and its harmful
effects on the environmen1:, a waste of recoverable
heat energy, and the high cost of constructing and
lS 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 ec~vered
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 valuesn.
Low and high heating values for fuels are given in
_ . .. , . .. ._ , . , . .. ,.. , . .. _ .. _ _ _.. _ _ _ . .. . .. . .... .... . . . . .. ..
- .
f~6(~
--3--
such handbooks as the Jolhn N. Perry En ineerin~_Manual,
published in 1959 by ~cGraw Hill, where the following
typical heating values are given:
High Heating Low Heating
Gas Value Value
Hydrogen60,958 Btu/lb 51,571 Btu/lb
Methane 23,~61 Btu/lb 21,502 Btu/lb
Methyl alcohol 10,:270 Btu/lb 9,080 Btu/lb
(vapor3
~ As will be apparent from t:hese heating values, about
18 percent more Btu/lb cam be recovered from hydrogen
if its high heating value can ~e utilized, about
11 percent more from methane, and about 13 percent
more from methyl alcohol vapor. Prior systems have
not been able to utilize the hig~l heating value of
such gases.
As the public concern about air pollution has
increased, stack heights have been increased to af-
fect better dispersion of E~ollutants. However, in-
creasing stack height adds to the cost of construc-
ting and maintaining stacks, yet provides no solu-
tion to the underlying prohlem, i.e., avoiding emis-
sion in the first instance of harmful substances
~ such as sulfur oxides, chlorine gases, phosphor
o~ides, etc.
A significant factor in air pollution is the
increasing level of gaseous airborne pollutants which
~2
4--
combine with moisture in ~he air to produce acids,
e.g. carbon dioxicle, sulfur dioxide, chlorine and
fluorine. The carbon diox.ide content in some indus-
trial districts is as high as ten times normal.
Acid forming pollutants have been found in some in-
stances to increase the acidity of rainwater from
its normal pH of about 6.9 to values of 4Ø Rain-
water having a pH of 5.5 or less will destroy aquatic
life and can do substantial harm to buildings, monu-
ments, and other structures.
One proposal for removing acid forming componentsfrom exhaust gases is to SC1. ub the entire flow of
exhaust gases with water ancl caustic prior to dis-
charging them through a stack. ~owever, scrubbing
the entire exhaust gas flow requires large ~uantities
of water, which are not always available, and re-
~uires costly, large capacity scrubbing e~uipment.
Indeed, scrubbing the entire flow of exhaust gases
from some incinerators requires at least half the
amount o water, by weight, of the solid wastes
burned in the incinerator. l'reating 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 flue gases. One proposal
. , . , . ~ . _ . ... , . . _ . . _ _ , _ . _ ., _ _ _ . _ _ _ , . _ , .. .
32~:~60
for the desulfurization of flue gas utilizes a series
of hcat exchangers to extract heat energy from the
flue gas prior to a scrubbing operation. Hcat ex-
tracted 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, requiring the use of
a tall stack, and polluting the air with such noxious
components as are not removed during scrubbing.
The problem of disposing of exhaust gases is
now recognized as a major concern in industrial coun-
tries throughout the world. Dispersing emissions
through the use o tall stacks is no longer regaraed
as an acceptable solution. Applicant's U.S. Patent
3,970,524 discloses a system for gasification of
solid waste materials and a method or treating the
resulting gases to produce commercially useable gases
in such a manner that dispersion through stacks is
not necessary. A feature o' one embodiment o' this
patent is pressurization o a combustion zone to
such pressures as will permit blower and/or compres-
sion units to be eliminated from the gas treatment
system. Another feature is the use o~ a multichamber
gas treatment unit in which noxious gas components
are sublimed or r'frozen outr' and thereby se,parated
O
from the clean useable yas components. A problem not
addressed by U.S. Patent No. 3,970,524 is that of pro-
viding a system for treating combustion exhaust gases
and productively reclaiming heat energy from the hot
gases. ~his 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 ex-
change relationship therewith, as in a conventional hea~
exchanger. However, the economics of inairect heat ex-
change at the lower temperature levels are very poor
and reduce the over-all desirability of such a system.
Applicant's copencling Application Ser;al No. 316,491
filed November 20, 1978, discloses a system which
utilizes direct heat exchange between the hot gases
and a power fluid to improve the econornics and thermal
efficiency of the system.
Notwithstanding the improvements in exhaust
gas pollutant control and heat reclamation economics
made possible by the systerns disclosed in applicant 15
prior patents and copending application, a major
problem not dealt ~with is the thermal inefficiency
resulting frorn use of conventional combustion or
other gas producing systems. A large amount of avail-
able power today is derived from fossil fuel firedfurnace units which provide the thermal energy for
steam generation in boiler units. In a conventional
~t~ 60
steam generating boiler system, preheated feed water
is treated in a series of heat exchange sections to
ultimately produce steam a~ ~he desired temperature
and pressure for driving power generating stcam turbines
and the like. The boiler feed water is typically
converted to high temperature, high pressure steam by
initial heating in an eccnomizer section, by subsequent
passage through various superheater sections, often
through a reheater sectic,n and subsequently through
boiler convection and radiation sections. The fossil
or manufactured fuel fired to produce the thermal ~/
energy which is transferred to the boiler feed water
to produce the high temperature and pressure steam
is converted to a hot exhaust gas which typically
exits the furnace through an air preheater as its
final stage. In this final stage, combustion gases
having temperatures of about 300-350C exchange their
thermal energy with compressed ambient air with the
result that the gases exhaust the unit at about 130C
to 180C and the air is heated to about 200C. The
130 to 180C exhaust gas is urther processed to
separate pollutants and reclaim heat values while
the heated air is utilized, serving, for example,
as the combustion air fed to the boiler or combustion
unit. Air preheaters are well known to require from
60% to 70% of the boiler's heat exchange surface
area and to operate at thermal efficiencies in the
Z~6~
--8--
.
50-60~ range. See, Hicks, Standard Handbook of Engineer-
ing Calculations (1972). Accordingly, if the preheater
could be eliminated without a corresponding loss in heat
reclamation capacity, a su~stantial cost and energy
savings could be achieved.
SUMMA~Y OF l'HE 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 purifying
hot exhaust gases to remove harm~ul components there-
from and for recovering and using the thermal energy
therein.
Another object is to provide unique and improved
methods and apparatus for purifying at least 300C
and preferably 300 to 350C exhaust gases and, thereby,
permit use of boilers or combustion units having
substantially less surface area.
Still another object is l-o provide improved
~0 systems and methods for treati.ng hot exhaust gases
for removing harmful components and recovering heat
energy therefrom to permit their discharge to atmos-
phere without the need for tal.L chimneys or stacks.
Other objects and advantaqes will become ap-
parent ~rom the following description and appended
claims.
In accordance with the for~egoing objects the
present invention provides a method whereby hot ex-
2~60
--9--
haust gases, generally at about 300 to 350C, whichhave not been subjected to a flow of cooling air such
as typically occurs in a conventional air preheater,
are treated by separating out solid particles, cooling
S in regenerators in heat-exchange relationship with
solid materials having relatively high heat capa-
citance and relatively large surface area to volume
ratios, processing to remove the noxious, generally
less volatile components of the exhaust gas, and
exhausting the resulting purified gases (generally
comprising the more volatile components of the ex-
haust gas) to atmosphere without using a stac~.
The less volatile components, comprising the environ-
mental pollutants, may be removed in known manner,
preferably by subliming or "~reezing out" such harm-
ful, less volatile components of the gases for subse-
quent scrubbing, neutra]ization or ut:ilization. Heat
values in the hot exhaust gas are removed, at least
in part, by cooling the gas in regenerators and
recovered by passing a heat exchange fluid, prefer-
ably a gas such as steam, compressed air, or the
like, through the regenerators. The resulting heated
heat exchange fluid may be utilized for any purpose.
Ho~ever, if compressed air is used, the heated air
'5 is particularly suitable for use as the combustion
air fed to the exhaust gas source, iOe., the boiler
or combustion unit. The heat values remaining in
--10-
Z~60
the exhaust gas, i suficient:, may also be utilized,
e.g., to heat water which, in turn, may be used for
preheating hoiler feed water, domestic heating or
other purposes.
In one embodiment oE the invention the exhaust
gases, after removal of solid part;cles therefrom,
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 transfe!r their heat to the
packing o 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 of the gases is recovered
from the regenerators by passing a heat exchange
fluid, such as compressed air, therethrough. In
another embodiment of the invention the exhaust gases
are cooled, less volatile comE)onents are sublimed,
purified gases are reheated and heat energy is re-
claimed, all using a single pair of regenerators,i.e., each regenerator performs multiple functions.
` In still another embodiment a irst plurality of
regenerators arranged in series are used to perform
the cooiing and gas purifying functions and a second
plurality of regenerators arranged in series are
used to perform the purified gas reheat;ng and heat
reclamation functions.
,
~ ~2~60
One noteworthy advar~ta~e of the var.ious systems
of the present invention is that they are able to process
hot exhaust gases, i.e., gases having a temperature of
300C or higher, obviating the need for the air preheater
stage of conventional boiler and combustion units and
thus effecting a savings of at least 60~-70~ of the
heat transfer surface area o~ such units. Heat reclama-
tion is effected, instead, :in regenerators which operate
at a thermal efficiency of '30~ or better compared with
conventional boiler air preheaters which operate at
thermal efficiencies in the 50-60~ rangeO Another impor-
tant advantage is that they also obviate the need for
costly stacks. Still another advantage of the present
invention is that the systems consume only a small frac-
tion of their power output as compared with conventionalsystems which utilize up to :L0~ of their power output.
Yet another advantage is that the systems of the present
invention may, if desired, ut:ilize a sublimation or
"freezing out" process to separate out harmful, less
volatile gas components which can then be r~covered
and treated for ut.ilizat;on 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 required for this operation can be treated
at minimal cost with scrllbbinq equipment having a
much smaller capacity than is required where the
Z~
-12-
entire flow of ~Yhaust gas is scrubbed. Su~stantial
savings are achieved over prior processes inasmuch
as large capacity scrubbincl equipment is not required.
The ability to utilize smaller capacity equipment 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 concent'rated stream of SO2 ready
Eor use in the chemical process industry. Such v/
utilization obviates the use of water for scrubbing
' in a neutraliæation system.
Gas treatment methods and apparatus of the ~ype
described in U.S. Patent No. 3,970,524 may advan-
; tageousl~ be used to ef~ect a separation of harmful,
less volatile exhaust gas components by the sublima-
tion or "freezing out" process. The apparatus in-
' 25 cludes an arrangement of valve interconnected, packed,
refrigerated towers through which exhaust gas passes
~' to effect sublimation or "freezing out" o~ harmful
components. Cornponents which can be removed by this
process include C02, HCl, H2S, S02, C2~2, HCN,
; 0 SO3, and the like. It is noteworthy that this type
gas treatment process is primarily o~ a physical
. .
.
z~
--13-
nature. Chemical treatment is not utilized until
noxious gas components, which comprise only a small
fraction of the total gas flow, are separated out.
A particularly useful aspect of this type of gas
treatment is that it permit:s noxious gases from many
sources to be treated concurrently, thereby obviating
the need for several separate gas treatment apparatus
installations. Off gases from refinery equipment
and the like can be collected and transferred through
a sewer-like system of conduits and treated at a
single installation with apparatus embodying the
invention.
Inasmuch as the system o the present invention
provides a relatively simple and inexpensive method
lS o purifying flue gases, it also permits the use
of cheap fuels having a relatively high sulfur con-
tent. The savings which result from the use of
cheaper fuels r the elimination of tall stacks, the
ability to recover energy from the gases, the elimi-
nation of need for the air preheater section ofboilers, the elimination of large uses of scrub
water, and the reduction in size of required scrubbin~
e~uipment make the system economically attractive
for installations o a wide range of sizes. More-
over, where the exhaust gases being treated containa relatively high concentration of sulfurous com-
pounds, elemental salfur and/or sulfuric acid may
.. . .
2~160
be obtained from the compounds, thereby adding to
the economy of operation c~f the system~
In the desired practice of the present ;nven-
tion, exhaust gases are generated in the firebox
of a combustion system, and the irebox is operated
under sufficient pressure to obviate the need for
blowers and compressors in the exhaust gas treatment
system. By pressurizing t:he combined combustion and
gas treatment system with a compressor upstream of
the combustion system, the need for compression equip-
ment downstream from the combustion system is elimi-
nated. However, as a practical matter, where large
gas volumes are generated, the combustion system
cannot maintain much of a positive pressure and at
least one downstream compressor is generally necessary.
BRIEF DESCRIPT]:ON OF TME DRAWINGS
.
A fuller understanding of the invention may
be had by referring to the following description
and claims taken in conjunction with the accompany-
ing drawings in which:
FIGURE 1 ;s a schematic flow diagram of a system
for practicing one embodiment o the present invention;
FIGURE 2 is a schematic flow diagram of a system
for practicing another embodiment of the present
invention;
FIGURE 3 is a schematic flow diagram of an il-
lustrative gas separation and heat reclamation unit-
.
o
--15--
for use in the Figure 2 embodiment of the present
invention; and
FIGURE 4 is a block diagram of a hot exhaust
gas producing combustion system in combination with
a steam generating boiler for use in connection with
the systems of the present invention.
FIGURE 5 iS a schematic flow diagram of a system
or practicing still another embodiment o~ the present
invention.
DFSC]RIPTION OF THE P:REFERRED EMBODIMENTS
Referring to Figure 1, a cornbustion or other
gas producing system is indicated generally by the
numeral 10. The system 10 can include one or more
fuel burning furnaces, roasters, cement kilns and
the like which emit hot exhaust gases as a product
of fuel combustion and/or other chemical process
which discharge hot exhaust gases containing such
components as nitrogen, carbon d;oxide, sulfur di-
oxide, hydrogen chloride, hydrogen sulfide, carhon
monoxide, nitrogen oxide, h~drogen c~anide, and hy-
drocarbon components. A typical combustion system
in combination with a suitable steam generating
boiler is illustrated in Figure 4. It can be seen
from Figure 4 that the hot gases produced in com-
bustion system 10 pass in heat exchange relationshipwith boiler feed water and steam in convection-radia-
tion sections, superheater sections, reheater sec-
tions and economizer sections of steam boilers before
being discharged for clean-up and/or heat reclamation
to the systems o~ the present invention.
. . .
f~
- 16-
Fuel is supplied to the combustion s~stem 10
as indicated by an arrow 11. In preferrcd operati~n,
the fuel used in the system 10 is ;nexpensive solid
or liquid fuel having a relatively high sulfur con-
tent. This fuel is preferred due to its low costand because the sulfur content is easily separated
out of exhaust yases as will be explained.
Air or oxygen enriched air is supp]ied to the
combustion system 10 as indicated by an arrow 12.
In preferred practice, a compressor 13 is used to
pressurize the air supply 12 such that the combustion
system operates under pressure. Where available,
heated compressed air is supplied to combustion sys-
tem 10 via air line 14. Depending on the magnitude
of the pressure maintained in the system 10, one
or more downstream gas com]pression units may be elimi-
nated from the exhaust gas treatment system of the
present invention, as will be explained. In a pre-
ferred form o the invention, the combustion system
10 is operated under sufficient pressure ~at least
about 28 psig) to obviate the need for blowers and
compressors in the exhaust gas treatrnent s~stem.
By pressurizing the system with a compressor upstream
of the combustion system llD, the need for compression
equipment downstream from the combustion s~stem is
diminished or eliminatea. As a practical matter,
however, where the configuration of Figure 1 is used
.,
, .. ... ... _ ...
17-
in connection with very large exhaust gas volumes (e~g.,
2,500,~00 Nm3/hr or more), the combustion system can- '~
not generally maintain much of a positive pressure.
Therefore, at least one downstream compressor, such as
compressor 213, is generally necessary.
Exhaust gases generated by the comhustion sys-
tem 10 are ducted via conduits 15, 16, 17 to, through
and from a series of particle separation units 20,
21, 22. The separation unit 20 is preferably a c~-
clone separator, and particulate matter as small
as 50 microns in size is separated out of the gases,
as indicated by an arrow 24. The separation units
21, 22 house filters which remove smallex particles
as inclicated by arrows 25, 26. The units 20, 21
22 are insulated to avoid heat loss.
' Exhaust gases which have been cleaned of par-
ticulate matter are ducted through feed conduit: 17a
into exhaust gas cooling and heat reclamation unit
200. Unit 200 is operable: (1) to cool the exhaust
gases prior to duct:ing them to compressor 213 and
gas treatment and separation unit 58 which may op-
erate, for example, by separation of the cooled gas
into condensable and noncondensable components by
subliming or "freezing out"; (2) to receive the puri-
fied gases exiting gas treatment and separation unit58 and to discharge or direct them to a point of
utilization; and (3) to heat a heat exchange fluid,
. _ . _ .. _ .. _ .
a60 l8- .
which or purposes of descriptive simplicity will
be identi~ied herein as compressecl air, to within
a ~ew degrees of the temperature of the exhaust gases
which entered unit: 200 through feed conduit 17a.
5 Unit 200 includes two similar packed towers or col-
umns 201, 203. Each of the towers 201, 203 is simi-
lar in construction and content to the regenerators,
described more fully hereinaftert shown as 59, 61,
63. Automatic switch valves 205a, 205b~ are provided
at the end of towers 201, 203 adjacent feed conduit
17a. Feed conduit 17a connects with the valves 205a.
Tower connection conduits 207 communicate the towers
` 201, 203 with the valves 205a, 205b. Tower connec-
tion conduit 209 communicates the towers 201, 203
15 with feed conduit 53 of the gas treatment and separa-
tion unit 58. Purified gas return conduit 210 returns
purified gas from unit 58 to unit 200. A heated
air discharge conduit 211 connects with the valves
205b A compressor 213 is included in tower connec-
20 tion conduit 209 to provide the positive pressurein the system which is almost invariably required
when very larye exhaust gas volumes are passed through
the Figure 1 system. Conduits 209 and 210 are cross
connected throuyh conduits 215 and 217 tWhich contain
25 appropriate flow control valves) upstream of the
compressor 213 to allow either tower 201 or 203 to
-~ function as the air heating or exhaust gas cooling
,. .
,
:. .
' .
.. . . .. , . , .. .. , .. ... . . . . . . .. ., . .. . . . . . .. . ... .. . ~ . .. . ~ .. . .. . . ....
O
--19-- .
tower.
The manner by which gases are treated in unit
200 may be visualized as that of subjecting the gases
in successive like cycles to cooling in towers 201,
203. During each cycle, a different step is being
conducted in each of towers 201, 203. While a first
tower is serving as the cooling tower to cool the
hot gases, the other tower is serving to heat the
compressed air fecl therethrough via air feed line
221. In the next cycle, the roles of the respec-
, tive towers are reversed.
¦ Thus in a first cycle one of the towers 201~
203 is selected as the cooling tower into which the
hot particle free exhaust gases are ducted and the
corresponding valve 205a is opened. If tower 201
! iS to serve as the cooling tower, valve 205a assoc-
ia~ed therewith and valve 205b associated with tower
203 are opened while valve 205b associated with tower
201 and valve 205z, associated with tower 203 remain
closed. The hot exhaust gases flow from feea conduit
17a through valve 205a into tower 201 in which the
gases are cooled prior to compression in compressor
213. At the same time the tower 201 is he~ted by
the hot gases in preparation for servin~ as the air
heating tower in the next cycle. The compxessea
~ases are directed via cross conduit 215 through
conduit 209 to feed condu;t 53 for processing in
. , .. , . ..... . . . . . .... . . . .... . .. ~ . . . . . .... .. . . . . ... .... . . .
)60
-20-
gas treatment and separation unit 58. Xf desired,
other noxious gases may be mixed with ~he compressed
exhaust gases entering conduit 209 (optional add;tion
indicated by broken line 90). Following processing
in unit 58, the purified gases leaving towers 59,
61, 63 through valves 64c are ducted via purified
gas return conduit 210 through purified gas discharge
conduit 220. The heat energy stored in tower 203
is recovered by passing compressed air through air
feed line 221 into and through tower 203 in which
the air is heated while the tower is cooled (it is
assumed that tower 203 had been pre-heated in a pre-
vious cycle by passage of hot exhaust gases there-
through). The heated air leaves tower 203 by way
of tower connection conduit 207 through valve 205b
and conduit 211 and may be utilized, such as by duct-
ing the air to serve as the preheated combustion
air fed to system 10 via preheated air line 14~
In a typical system the hot gases entering the cool-
ing tower 201 are at a temperature of about 300-350~C
and are cooled in the tower to about 40-130C, the
precise temperature range selected depending upon
whether or not it is desired to retain heat energy
in the purified off gas for subsequent use. Stated
otherwise, the temperature range to which the gas
is cooled in tower 201 is approximately the tempera-
ture range at which the purified yases return from
.. , , . . . . ... . ... .. , .. .. . , .. , . ... , .. ,. . ,, .,, , .,_ , . , . . ,, , _ . _
Z~`61~
-21-
unit 58. If the gases are cooled to the range 40C
to less than about 70C, then the purified off gas
at 40-70C will not contain sufficient heat values
to be useful and will have to be vented. On the
other hand if the gases are cooled to the range 70C
to 130~C then the purified off gas at 70-130C con-
tains sufficient residual heat for use, such as in
a heat exchanger as shown in Figure 2. Thus, in
the operation of the system of the present invention,
there is a built-~in option to retain sufficient resi-
dual heat energy in the purified off gas for sub-
seguent use. In this connection, particularl~ where
it is desirable t:o retain heat energy in the purified
off gas, compressor 213 may be operated without the
conventional after cooler in order that the heat
energy added to t:he exhaust ~as by the compressor
is retained in the system and ultimately reclaimed
from the puri~ied off gas.
The exhaust gases from towers 201, 203 at 40-
130C are compres.sed in compressor 213 and enter .
unit 58. The cooled purified gases leaving unit
58 are discharged~ via line 220 and, depending upon
their temperature, are either vented or utilized,
such as in a heat. exchanger shown in Figure 2. The
compressed air entering tower 203 via air feed line
221 is reheated i.n tower 203 to within 5 to 10C
of the temperature of the gases enterin~ tower 201.
2~60
-22-
If for some reason it is not desired to reclaim the
heat energy of the towers with a heat transfer fluid
such as compressed air, instead of discharging the
purified gases via line 220, the purified gases may
be allowed to pass through the heated tower 203 wherein
the gases would be reheated. The heat energy would
then have to be reclaimed from the heated purified
gas exiting the system through condui, 211, e.g.,
as is described ili connection with copending applica-
tion Serial No.316,491 filed November 20, 1978.
The next cycle is like the one just describedexcept that tower 203 now serves as the exhaust gas
cooling tower and tower 201 as the compressed air
heating tower. It will be appreciated that following
the previous cycle, tower 201 was left in a relatively
heated state by the passage of hot exhaust gases
therethrough whereas tower 203 was left in a rela-
tively cooled state by virtue of having given up
its heat content to the compressed air passing there-
through. In this next cycle the hot exhaust gasesflow from feed conduit 17a through valve 205a into
tower 203 in which the gases are cooled while the
tower is heated. They are then ducted via cross
conduit 215 to compressor 213 in which they are com-
pressed. The compressed gases are ducted throughconduit 209 to feed conduit 53 for processiny in
gas treatment and separation unit 58. Follot~ing
,, .. .. , .. ., , . . . . . .. .... ... ....... . .. . _ ~ ... . . . .. .
~23-
~Z~60
processing in unit S~, the purifi.cd cJases leaving
to~ers 59, 61, ~3 t:hrouyh valves 64c are ducted via
purified gas returrl conduit 210 and cross conduit
217 to discharge via line 220. The compressed ~ir
entering tower 201 via air feed line 221 is heated
while the tower is cooled and the resulting heated
air leaving tower 201 may be utilized if desired,
as the combustion air fed to system 10 via preheated
air line 14.
By feeding towers 201, 203 wi~h exhaust ~ases
at such high temperature levels of up to about 350C,
the boiler or combustion unit may eliminate the air
preheater which t~pically occupies ~0%-70% of the
heat exchange surface of the unit (see Figure 4).
Moreover, the use of high thermal efficiency regen-
erators for the purpose of cooling the gas prior
to purification and! reclaiming the heat energy of
the exhaust gas prior to discharge adds to the over-
all thermodynamic efficiency of the s~stem while
20 it simplif ies the design and rcduces capital costs.
Gas treatment and separation unit 58 is prefer-
ably of the same type described in U.S. Patent No.
3,970,524 and is operable to separate the gases into
condensable and non.condensable components by subliming
25 or "freezing out" n.oxious, condensable components of
relatively low vola.tility and components having similar
vapor pressures, such as approximately between C
_, , , .. _ .. ~ . _ . ..... ... _ . -- _
24-
3l~52~60
and C~ fractions. The unit 58 includes three similar
packed towers or columns 59, 61, 63. Each o~ t-he
towers 59, 61, 63 is similar to a regenerator de-
scribed by ~ussel]L B. Scott at pages 29-31 of Cryo-
qenic En~ineerinq, published in 1959 by D. Van NostrandCo., Princeton, N. J. Each of the towers 59, 61t
63 contains loose solids, for example, ceramic balls,
quartzite pebbles, steel shot, etc., pancakes wound
from thin corrugated aluminum ribbon, or other solids
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 suffi-
cient that the regenerator has a surface of 1000to 2000 square ft. per cubic foot.
Automatic switch valves 64a, 64b, 6~c, and 65a,
65c are provided at opposite ends of the towers 5g,
61, 63. Tower connection conduits 67, 68 communi-
cate the towers 59, 61, 63 with the valves 64a, 64b,64c and 65a, 65c, respectively.
The gas feeder conduît S3 connects with the
valves 64a. An acid gas conduit 70 connects with
the valves 64b. A vacuum pump 79 communicates with
the acid gas conduit 70. A transfer conduit 80 com~
municates the pump 79 with a compressor 81. An acid
gas discharge conduit 82 communicates with the com-
., .. , .,, ... . . .. .. , .. .. , .. .... . ... . ... .... . ... . .... . .. . . ,, .. _ . . ... . .. .. .. .....
... . . ..
-25-
~ ~ ~2~60
pressor 81. A pUI. ified gas discharge conduit 210
connects ~ith the valves 64c.
A pair of transfer conduits 73, 74 connect with
the valves 65a, 65c~ A cooling means, which could
be a heat exchanger, but, if gas pressure is high
enough is preferably an expansion turbine 75, com-
municates the transfer conduits 73, 74. An expan-
sion turbine has the advantage that it cools the
gas more efficiéntly by substantially isentropic
10 expansion while at the same time it produces use- -
ful shaft work. To convert the shaft work to a more
useful form of energy, a power generator 76 is coupled
to the drive shaft of the turbine 75.
The manner b~r which gases are treated in the
unit 58 may be visualized as that of subjecting the
gases to several like cycles repeated time after
time as long as exhaust gases are being produced
by system 10. During each cycle, a different step
is conducted simultaneously in each of the towers
59, 61, 63. While one of the towers is being cooled
by a flow of cooled purified gas, separation is taking
place in another l:ower, and condensed or sublimed
components are be;ng removed from the third tower.
A first step of one cycle is carried out b~
opening the valves 64a, 65a at each end of tower
59 and valves 64c, 65c at each end of tower 63.
Gases will then flow through tower 59, will drive
-26-
~ 60
the turbine 75, and will flow throuyh the tower 63.
The gases expand in the turbine 7S and, as the gases
expand, they are cooled. It is the flow of these
cooled gases through the tower 63 that readies the
tower 63 for a subsequent gas separation step. (It
is assumed here t:hat the tower 59 has already been
pre-cooled in this manner in a previous cycle so
that less'volatile gas components loaded into the
tower 59 will be sublimed or "frozen outnr) The
gases are allowed to flow in this manner for a short
period of time, or example, for about 6 to 8 minutes.
Energy extracted from these gases by the turbine
75 is used to drive the generator 76.
Gas cools in tower 59 due to contact with the
large surface ar,ea of the cooler solids in the tower.
Less volatile components of the gas are condensed
or converted into the solid phase and remain in tower
5~. The more volatile, noncondensed or clean compo-
nents o the gas pass out of tower 59 and, via tur-
bine 75, through tower 63. This clean gas is puri-
fied in the sense that it has been freed from the
"rozen out", sublimed or condensed components.
The turbine 75 expands the gas, thus further cooling
it, and delivers the gas at a pressure of typically
about S psig into tower 63. The pressure at which
the gases enter the tower 63 is not critical. What
is re~uired is that the pressure ratio reduction
effected in the turbine 75 is o~ sufficient ma-3nitude
to adequately cool the ~ases so the gases can properly
chill the tower 63.
A second step (which is carried out simultan-
eously with the loading of exhaust gas into the tower
59 and the cooling of the tower 63j is that of clean-
ing a loaded tower by revaporizing the "frozen out,"
sublimed or condensed components remaining in that
tower from a prior cycle. This step is carried out,
for example in connection with tower 61, by closing
the valves 65a and 65c at the lower end of tower
61 and by connecting the other end of that tower
through valve 64b to the vacuum pump 79 and compres-
sor 81. The pump 79 operates to reduce the pressure
in the tower 61 by a ratio of about 10 to 1. As
pressure in the tower is reduced, the "frozen out,~
sublimed or condensed components are revaporized
to form an acid gas which is drawn out of the tower
61. The wîthdra~n acid gas is compressed by the
compressor 81 and is discharged into the acid gas
discharge conduit 82. The acid gas typically con-
sists mainly of C02 with small amounts of H2S, S02,
S03, HCN and other noxious gases. Noxious gases,
containing chlorine, sulfur, and the like, may be
neutralized, as by scrubbing with caustic solution.
Combustible components of the neutralized gases are
preferably separated out and retained for useO Such
.. . . . . . . . . . .. . . ... ... .. .. .. . .. ... ..... ... . .. ........ . ... . . .. . . ..
2~
-28-
gases can be burned ;n the combustion system 10.
The next cycle is like the one j~st described
and consists of a first step of passing gases from
the conduit 53 through one o the valves 64a into
the cooled tower 63, separating, by "freeæing out"
or subliming, components of the gases in that tower,
cooling the separated clean gas leaving tower 63
in the turbine 75 and passing the cooled, expanded
clean gas through the recently cleaned tower 61 to
chill that tower in preparation for receiving the
next charge of exhaust gases from conduit 53. A
second step is that of simultaneously revaporizing
the "frozen out", sublimed or condensed components
which remain in the tower 59 from the prior cycle
to clean that tower in preparation for chilling dur-
ing the next cycle.
The next cycle is like the two foregoing cycles
Its first step is that of passing gases from the
c~nduit 53 into the tower 61 to separate out gaseous
components and coc,ling the just cleaned tower 59
.with the separatedl clean gas fraction from tower
61 and turbine cooling means 75. A second step is
to clean tower 63 by revaporizing components remain-
ing in the tower 63 from the previous cycle by with-
drawing them through vacuum pump 79 and compressor81.
The purified gases, which are relatively cool.,
5~6U
-29-
discharged through valves 64c into the conAuit 210
are discharged from tlle system via purified gas dis-
charge conduit 220. These yases can, if desired,
be exhausted to atmosphere without the use of a flue
gas stack. Alternatively, if they contain sufficient
heat values, e.g., their temperature is in the range
70C to 130~C, they can be used as a heat source
in a heat exchangec, e.g., for preheating boiler feed
water, domestic heating, etc. Even if the gases
do not contain sufEicient heat value5, inasmuch as
they are dry, they can be used to advantage in evap-
orative cooling towers and the like.
Noxious gases created in chemical proccsses
other than combustion can be mixed with gases in -
the tower connection conduit 209 and treated in theunit S8. The optional addition of such gases is
indicated by broken line 90 in Figure 1. A sewer-
like blow down sysl:em of gas collection conduits
101 can be used to collect exhaust gases from a plu-
rality of gas producing apparatuses 102. Suitablecompression equipment (not shown) can be included
in the conduit sysl:em 101 to transfer the collected
gases into the conduit 53.
Referring to Figure 2, another embodiment of
the present invention is illustrated in which the
exhaust gases are subjected to treatment to separate
them into condensable and noncondensable components
-30-
l~SZ1~60
by subliming or "reezing out". The combustion sys-
tem and particulate matter separation uni~s ~hown
in Fig~re 2 may ~e just like their countcrpart units
in ~igure 1. Thus, ~ombustion system 110 is fueled
from a fuel supply source 111 and air or oxygen is
supplied to the combustion system 110 through air
or oxygen supply line 112. Preferably air supply
line 112 includes a compressor 113 to pressurize
the air supply and to maintain the combustion system
110 operating under a positive pressure. Where avail-
able, preheated c~mpressed air is supplied to combus-
tion system 110 via air line 114. In this embodiment
of the invention, where hot gases are treated through-
out, downstream compressors are inefficient and,
hence, undesirable. Therefore it is desirable that
the gases in the ~as treatment system are maintained
under sufficient pressure by a compressor in the
combustion system 110, such as compressor 113, or
by a compressor located upstream of the combustion
system 110.
Exhaust gases generated by the combustion sys-
tem 110 are ductecl via conduits 115, 116, 117 to,
through and from a series of particle separation
units 120, 121,`122. The separation unit 120 is
preferably a cyclc,ne separator, and particulate
matter as small as 50 microns in s;ze is separated
out of the gases as indicated by an arrow 12~. The
6(~
-31-
separation unit:s 121, 122 house filters which remove
smaller particl.es as indicated by arro~s 125, 126.
The units 120, 121, 122 are insulated to avoid heat
loss.
Exhaust gases, which have been cleaned of par-
ticulate matter are led from conduit 117 into gas
feeder conduit 153 which directs the hot gases to gas
I separation and heat reclamation unit 158. These gases
¦ have a slightly reduced pressure due to pressure losses
in the filters, but are at substantially the same temp-
erature, as high as about 300-350C, as when they exited
the combustion system 110. The unit 158 is operable:
(1) to cool the 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.l)e as high as within a few
~ degrees of the temperature of the exhaust gases which
entered unit 158 through feeder conduit 153. The
more volatile, noncondensed or clean components of
the gas exit unit 15~ via purifie~ yas (off gas)
discharge conduilL 172. The heated heat exchange
fluid exits unit 158 via heated air.discharge conduit
171.
Reerring to Figure 3 there is shown an illus-
~ Z~6l~
trative gas separation and heat reclamation unit
15~, useful, for example, in the embodiment o Figure
2. The unit of Figure 3 uses separate regenerators
to perform the four essential functions of ~nit 15~,
i.e., to cool the hot exhaust gas, to separate compo-
nents of the gas, to reheat the relatively cool puri-
fied off gas prior to venting or utilizing, and-to
reclaim thermal energy by heating the compressed
.~ .
air heat transfer fluid. Unit 158 of Figure 3 ac-
complishes its functions with a first heat exchange
zone comprising a plurality (two are illustrated)
of series arranged regenerator units 301, 361 to
cool the exhaust gas and separate it into its com-
ponents and a sec:ond heat exchange zone comprising
a plurality (two are illustrated) of series arranged
re~enerator units 303, 363 to reheat the relatively
cool purified off gas and to reclaim thermal energy
by heating a beat 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 can serve as the second heat exchange zone and
perform the functions of that zone. Thus, regen-
erators 301, 303 comprising a first heat exchange
sub-zone are arranged in parallel relationship to
allow the exhaust gas to be introduced initially
into either one o~ regenerators 301, 303 and to allow
. . , .. .. . . _ .... .. .. ... . ...... .... . . .. , . . " , . . , ,, , _
2~60
either one to perform the hot e~haust gas cooling
function while the other performs the heat reclama-
tion function. rJikewiser regenerators 361r 363
comprising a sec~nd heat exchange sub-zone are ar--
ranged in parall~el relationship to allow either one
to perform the component separation function while
the othe perform, the off gas reheating function.
~haust gases which have been cleaned o~ parti-
culate matter are led into gas ~eeder conduit 153
from which they pass into exhaust gas separation
and heat reclamat:ion unit 158. Unit 158 includes
at least four similar packed towers or columns 301,
303, 361, 363. Towers 301 and 303 are arranged în
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 con-
struction and content to the regenerators shown as
59, 61, 63 in Figure 1. 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,
305b. 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
-3~-
~ 6~
end o towers 361, 363 adjacent feed conduit 353.
Tower connection conduit 367 communicates the to~ers
361, 363 with the valves 364a, 36~b. Tower connec-
tion conduit 36g communicates tle towers 361, 363
with automa~ic switch valves 365a, 365c. A pair
of transfer conduits 373, 37~ connect valves 365a,
365c of towers 361, 363 with a cooling means, pref-
erably ~ expansion turbine 375. An expansion turbine
has the advantage that it cools the gas more effi-
ciently 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 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
2Q low temperatures, e.g., about -40 to -50C. In
the illustrated system, purified of~ gas is discharged
following component separation in tower 361 and re-
heating in tower 363 through purified of gas dis-
charge conduit 172. A preheated compressed air dis-
charge conduit 171 connects with the valves 305b.
A compressed air feed line 321 and compressor 322
supply a cooling heat exchange fluid to towers 301,
o
303. A compressor 313 is included in tower connec-
t;on conduit 309 to provide the positive pressure
in tl-e system which is almost invariably re~uired
when very large exhaust gas volumes are passed.
The ~anner by which gases are treated in unit
158 may be visualized as that of subjecting the gases
in successive 1~ ~ cycles to cooling in towers 301,
303 and reheating and/or cooling in towers 361, 363.
During each cycle, a different step is being con-
ducted in each of towers 301, 303. While a first
tower is serving as the cooling tower to cool the
hot gases, the cther tower is serving to heat the
compressed air flowing therethrough via air feed
line 321. In the next cyc]e, the roles of the re-
spective towers 301, 303 are reversed. Likewise
with towers 361, 363. While one of these towers
-is serving as the component separation tower to sep-
arate the less volatile gas components by su~blima-
tion or condensation from the cooled gases flowing
from towers 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 reversed.
Thus in a first cycle one of the towers 301,
303 is selected as the cooling tower into wh;ch the
hot particle free exhaust gases are ducted and the
.. . . ... ;.. ..... ., . .. , ;.. ., .. ~ . ..... ,. ...... ,, . ... . . .;.. .... . .. . . .. ... ...
-36
~:~l5;2~60
corresponding valve 305a is opened. If tower 301
is to serve as the cooling tower, valve 305a associated
therewith and valve 305b associated 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~fro~ feeder con-
duit 153 throug'h valve 305a into tower 301 in wh;ch
the gases are cooled prior to compression in com-
pressor 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 conduit 30
to feed conduit 353 for component separation in
towers 361 or 363. rJhen tower 361 is to serve as
the component separation tower valve 364a associated
therewith and valve 364b associated with tower 363
are opened while valve 364b associated with tower
361 and valve 364a associated with tower 363 remain
closed. The relatively cooled compressed exhaust
gases flow from feed conduit 353 through valve 364a
into tower 361 it'l which the ~aseous components are
further cooled and separàted by sublimation or con-
densation with the less volatile components remaining
in tower 361 while the more volatile or purified
2s components pass through the tower. (It is assumed
here that towers 301 and 361 had already been pre-
cooled in a previous cycle so that the gases will
16~
be cooled in tower 301 and less volatile gas compo-
nents loaded into tower 361 will be sublimed or "fro%en
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, flo~ via valve 365a and transfer conduit
373 through turbine 375 wherein the gas is further
cooled. The exllaust gases are allowed to flow through
towers 301 and 3~3 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
expansion pressure ratio in the turbine need only
be sufficient to accomplish the desired cooling.
In view of this additional pressure drop, a system
which utilizes an expansion turbine will generally
operate at a somewhat higher combustion sys~em pres-
sure as compared to a ~ystem which utili~es some
other means of cooling the exhaust gas, such as a
conventional heat exchanger.
The further cooled purified gases are returned
through tower 363 via transfer conduit 374 and valve
365c. 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
-3g-
~ L~Z~60
pre-heated in a previous cycle by passage of rela-
tively cool exhaust gases therethrough). The rela-
tively cool purified gases leave tower 363 through
tower connection conduit 367 and valve 364b and are
discharged via purified off gas discharge conduit
172. If the off gas ~ontains sufficient thermal
energy values, as will hereinafter be aiscussed,
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 imrnediately
previous cycle, tower 363 had been used ~or the sub-
limation or "~reezing out" step and the less volatile
cornponents of the gas had been condensed or converted
into the solid phase and had remained withi-n tower
363, i.e., the tower was loaded. To clean loaded
tower 363 by revaporizing the "frozen out", sublimed
or condensed components from the prior cycle to form
a~ acid gas, the initial flow o~ puri~ied ~as which
passes through loaded tower 363 is used to purge
the tower. The mixed flow of purified gas and re-
vaporized components, i.e., acid gas, as shown in
Figure 2, are ducted through compressor 182 via puri-
fied gas discharge conduit 172 and valve 169a into
the blowdown conduit 193a. The acid gas typically
consists mainly of SO2 and CO2 with small amounts
of H2S, SO3, HCN and other noxious gases~ Inasmuch
~39--
as flue gas discharge rcstrictions preclude emission
.
of these gases, most noxious components in the blow-
clown gases are neutralized by scrubbing or are other-
wise separatea out to permit exhausting the cleansed
blowdown gas. Cleaning of the loaded to~er in this
manner can be accomplished during each cycle by switch-
ing the initial purified gas flow to the blo~down
lîne 193a via valve 169a for just enough time to
purge the tower and 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 1~4 or, if the purified off gas contains suffi-
cient thermal energy to be used as a thermal source
for heating water or other heat exchange medium,
via heat exchanger 196, as will be discussed more
fully hereinafter.
The heat energy stored in tower 303 is recovered
by passing compressed air through air feed line 321
and compressor 322 into and through tower 303 in
which the air is heated while 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 171 and may be
utilized, such as by ducting the air to serve as
the preheated combustion air fed to system 110 via
.. .. .. . .. . .. . . . . . .
--~10--
~152~6V
~preheated a;r line 114 as shown in ~ig-lre 2 and/or
for other purposes, as will be more fully discusse2
hereinafter It is the flow of cool compressed air
! through tower 303 which readies that tower for the
next cycle during which gas cooliny will ta'~e place
therein.
As can be seen most clearly in Figure ~, the
heated compressed air in conduit 171 can be diverted
through optional expansion turbine 130 (shown in
phantom) to generate shaft work or electrical energy
via optional power generator 132 (shown in phantom).
The expanded and cooled air exiting turbine 130 is
generally discharged to ambient, but could be reused
if desired. In still another alternative or addi-
tional use, the heated air may be used as a thermalenergy source in a heat exchanger to directly heat
water or other heat exchange fluid. For example,
an optional heat exchanger 185 may be provided into
l~7hich cold water is ~ed via feed line 18~ by pump
192. The water is heated by closing or throttling
valve 190b and directing the heated compressed a;r
into heat exchanger 185 through valve 190a and heating
coils or sparger 186. The cooled air is vented from
heat exchanger 185 through vent line 191. Heated
water is pump~d from heat exchanger 185 through line
187 by pump 188. It will, of course~ be appreciated
that the heating values ~f the heated air can be
. _ . . . . . . .
used~to heat a ~ecyclable, preferably water imrnis-
ciblc, intermediate heat exchange fluid/ which can
then be used to heat water or other meclium.
In a typical system the hot gases entering the
cooliny tower 301 are at a temperature of about 300-
350C and are cooled in the tower to about 40-130C
(relatively cool condition) at which temperature
the gases are compressed and passed to tower 361
in which they are cooled to about -100 to -140C
the temperature at which component separation occurs.
The purifi~d 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
40C to less than about 70C, then the purified off
gas will not cont:ain sufficient heat values to be
useful and will ]ikely have to be vented. On the
other hand, if the gases are in the range oL 70C
to 130C, then the purified off gas yenerally con-
tains 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
25 in tower 303 to within 5 to 10C of the temperature
of the gases entering t~wer 301. If for some reason
it is not desired to reclaim the bulk of the heat
.. . . , . .. , . .. , ,.. ,, . . .. , , . , . , ., , , , . , .,, , . . , . . .. _ .... _.. .. .. . .
.
~2-
1 ~2~ 6~
energ~ of the towers with a heat transfer fl~id such
as compr~ssed air, then provision can be made for
directing the purified gases through heat energ~-
containing tower 303 wherein the gases would be re-
heated. The heat energy would then have to be re-
claimed from the heated purified gas exiting the
system through conduit 171, e.g., as is described
in connection with copending application Serial No.
316,491 filed November ~, 1978.
Thus it can be seen that the system o the present
invention offers a ~hoice in the manner of re~laiming
the heat energy of the exhaust gases. Heat energy
may be reclaimed by thermal exchange bet~een the
compressed air flow passed through the tower and
the relatively hot tower solids. Alternatively,
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 effi-
ciently 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 70~ to 130~C.
Thus, as shown in Figure 2r the purified off gas
may be duc~ed through valve 169b, line 193b and valve
--~3
3L~L5~60
183b into heat exchanger 196 where the gas ~iv~s
up its heat energy in coils or sparger 179 b~fore
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 eneryy as possible in the
purified off gas. Thus, compressor 182 may be op-
erated 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 ulti-
mately reclaimed from the purified off gas. Cold
water, for example, may be fed to heat exchanger
196 via line 177 and p~mp 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 appreciated that the heating
values of the off gas can be used to heat a re-
cyclable, preferably water immiscible, intermed;ate
heat exchange fluid which can then be recycled or
used to heat water 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 usillg a heat
transfer fluid, e.g., compressed air, other than
the purified gases. The heated fluid exiting the
towers via line L71 may be utiliæed in the manners
previously described herein, such as for combustion
feed air or as a thermal energy source in a heat
.... ., . , ., ... .... .. . _ ., . .. ~ ... _ . _ ., ..... _ . . . . . .... . . . . . .. . ... . . .. .
. -~4-
~ Z~60
exchanger.
The next cycle is like the one jU5t described
except that tower 303 serves as the exhaust gas cool-
ing 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 there-
through whereas tower 303 was left in a relatively
cooled state by virtue o~ having given up its heat
content to the compressed air passing therethrough.
The hot exhaust gases flow from feeder conduit 153
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 compres~sor 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 375. 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
~5 exhaust gases flo~ from feed conauit 353 through
valve 364a into tower 363 in which the gaseous com-
ponents are further cooled and separated by sublima-
.. . . . . . . .
_~5_
~ ~ ~2~ ~0
tion or condensation while the tower 363 is heated.Following proccssing in tower 363 t}-~e purified gases
are ducted through turbine 375, wherein thcy are
still further cooled, to tower 361 wherein they are
reheated to the relatively cool condition, while
the tower is cooled and purged of "frozen out",
sublimed or conaensed components from the prior
cycle. The purified or mixed gases are then dis-
charged from the system via purified off gas dis-
charge conduit 1-/2 for further processing of revaporized
components, vent;ng, heat reclamation, and the like.
By feeding towers 301, 303 with exhaust gases
at such high temperature levels of up to about 350C,
the boiler or combustion unit may eliminate the air
preheater which typically occupies 60%-70% of the
heat exchange surface of the unit. The use of regen-
erators for the purpose of cooling the gas prior
to purification and reclaiming the heat energy of
the exhaust gas prior to discharge adds to the thermo-
dynamic efficienc:y of the system while it simpllfiesthe design and reduces capital costs. Capital costs
can be further reduced by utilizing a gas ~cparation
and heat reclamation unit 15~ which employs only
two towers, each necessarily serving a dual function.
Each tower is effectively a split regenerator wherein
separate upper and lower portions perforrn separate
functions. Thus, while a first tower is being cooled
.. . . ~ .. . . . . .. ... .. . .. . ... . . . . . . . . . . .. . .. .. . ... . .. .. ..
.. . . . .
-46-
Z~6~
in an upper port;on thereof by a flow of relatively
cool compressed air and in a lower portion thereof
by the flow of cold purified off ~as, initial co~ling
of the hot exhaust gas is taking place in an upper
portion of the second tower and component separation
by sublimation or condensation is taking place in
a lower portion of the second to~er. Condensed or
sublimed 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.
~ ith minor modification the system of Figure 2
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 particle separation units and could
pass from the combustion s~stem 410 directly to a
heat reclamation unit 458, there being no need for
a gas separation i-unction. Therefore, regenerator
t~wers 459, 463 could ~,erve 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 exhaust gases from combus-
tion system 410 pass via conduit 415 into gas feeder
conduit 453 and then into one of to~ers 459, 463
wherein the hot gases give up heat to the high heat
47
~ 6~
capacitance solids therein and become cooled, prefer-
ably 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 therethro-lyh in a previous cycle) is
recovered by passage of a heat exchange fluid, e.g.,
compressed a~r, therethrough. A first step of one
cycle is carried out by opening the valves 464a,
465a at each end of tower 459 and valves ~64c, 465c
at each end of l-ower 463. The hot exhaust gases
will then flow from feeder conduit 453 via valve
464a through tower 459 in which the gases cool.
The coolea gases exits tower 459 via valve 465a and
off gas discharge line 472. The cooled off gas may
either be vented throuyh valve 483a or utilized to
reclaim heat values therefrom. To recover heat
values from the off gas, the gas may be ducted through
compressor 482, valve 483b and line 493 into heat
eYchanger 496 where the yas gives up its heat energy
in coils or sparger 479 before being vented from
the heat exchanger via vent line ~9~. In this case
it is desirable to retain as much heat as possible
in the off gas. Thus, compressor 482 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
.
. . .
~ 60
for example may be fed to heat exchan4er 496 via line
- 477 to absorb lhe heat energy from the o~f gas and
heated water pumped frorn heat exchanger 496 via line
480 and pump 4~1. It will, of course, be appreciated
that the heating values of the off gas can alternatively
be used to heat a recyclable, pre~erably water immiscibie,
intermediate heat exchange ~luid which can then be re-
cycled or used lo heat water or other medium.
It willr likewise, be appreciated that as the ex-
haust 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 434 and compressor 436 into tower 463. The
flow of air cool~; the solid packing in tower 463 as it
passes therethrough and becomes heated itself as it does
so. (It is assumed here that the tower 463 had been pre-
heated in a previous cycle by the flow o~ hot exhaust
gases therethrough). 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 as preheated combus-
tion air in the combustion system 41Q, to operate a power
turbine tnot shown) or as the thermal energy source in a
heat exchanger to directly heat water or other heat ex-
change fluid. For example, optional heat exchangers 444,
445 may be provided into which cold water is fed via
feed line 447. The water is initially heated at ambient
pressure almost to its vaporization point by direct heat
exchange in heat exchanger 445 and the thus heated water
~-~9-
2~60
is pulnped from heat exchanger 4~5 via line 487 and pump
488 i.nto heat exchanger 444. Ileat exchan~er 444 is main-
tained at an elevated pressur~, e.cJ., 28 psig, and a
temperature of about 130~C, for further hecl-ting and de-
gassing of the water prior to utilization, for exampleas feed water to the economizer section of a steam genera-
tor or to a district heating system. The heated com-
pressed air is fed initially through heat exchanger 444
by closing or throttling valve 490b and directing the
air into the heat exchanger via valve 490a and line 489.
From heat exchanger 444 the 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 app.reciated that the heating values of the
heated air can be used to heat a recyclable, preferably
water immiscible, intermediate heat exchange fluid, which
can then be use~ to heat water or other medium.
While the inv~ntion has been de~cribed with re~erence
to particular embodirnents thereof it will be understood
that numerous modifications may be mad~ by those skilled
in the art without actually departing from the scope of the.
invention. For e~ample, the methods and systems illus-
trated in Figures 1, 2 and 3 are effective to reduce the
impuxity levels in the purified gas to trace levels. Should
it be desired to completely remove all sulfurous cornpounds
and other harmful components, adsorption or absorption
systems can be linked, in known manner, to the systems of
Figures 1, 2 and 3. Accordingly all modifications and
equivalents may be resorted to which fall within the scope
of the ;nvention as claimea.
