CA1152060A - Method and apparatus for treating exhaust gases - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method and apparatus for treating hot exhaust gas to purify the gas and/or to recover the heat values therein includes removing particulate matter from the gas, cooling the gas by transferring its heat to regenerators and purifying the cooled gas by subliming or "freezing out" harmful, less vola-tile components. The heat energy of the exhaust gas may be recovered by passing a heat exchange medium, such as compressed air and/or purified cooled gas, through the heated regenerators. A major advantage of this method and apparatus is that exhaust gases at 300-350°C may be purified and the heat energy recovered using thermodynamically efficient regen-erators. As a result the air preheater stage of conventional boilers or combustion units, which com-prise 60% to 70% of the heat exchange surface area, may be eliminated.

Description

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 _ . .. , . .. ._ , . , . .. ,.. , . .. _ .. _ _ _.. _ _ _ . .. . .. . .... .... . . . . .. ..

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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 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~

.

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 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 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~

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 . .
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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 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.

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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 ., , .. ... ... _ ...

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 ,. .

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.. . . .. , . , .. .. , .. ... . . . . . . .. ., . .. . . . . . .. . ... .. . ~ . .. . ~ .. . .. . . ....

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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 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~

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 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

_, , , .. _ .. ~ . _ . ..... ... _ . -- _ 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-., .. , .,, ... . . .. .. , .. .. , .. .... . ... . ... .... . ... . .... . .. . . ,, .. _ . . ... . .. .. .. .....
... . . ..

~ ~ ~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 ~ 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~

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

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 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(~

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 .. . . ... ;.. ..... ., . .. , ;.. ., .. ~ . ..... ,. ...... ,, . ... . . .;.. .... . .. . . .. ... ...

~:~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 .. . . ~ .. . . . . .. ... .. . .. . ... . . . . . . . . . . .. . .. .. . ... . .. .. ..
.. . . . .

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 ~ 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.

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for generating power from steam including the steps of combusting a fuel for producing thermal energy containing hot gases, passing said gases in heat exchange relationship with feed water to transfer heat from said gases to said water for converting said feed water to steam and reclaiming the residual thermal energy of said hot gases by heat exchange between said gases and relatively high heat capacitance solid material to concurrently cool said gases and heat said solid materials, the improvement comprising passing said gases into heat exchange relationship with said solid materials while said gases have a temperature in excess of 300°C.

2. In a process for generating power from steam including the steps of combusting a fuel in a furnace to produce thermal energy containing hot gases, passing said gases in heat exchange relationship with feed water in boiler means consisting essentially of economizer means, superheater means, reheater means, convection and radiation heating means to transfer heat from said gases to said water for converting said feed water to steam and reclaiming the residual thermal energy of said hot gases by heat exchange in regenerator means between said gases and relatively high heat capacitance solid material to concurrently cool said gases and heat said solid materials, the improvement comprising passing said hot gases into said regenerator means directly from said economizer means without substantial cooling therebetween.

3. In a power generating system for producing energy from steam, including furnace means for generating thermal energy containing hot gases, boiler means consisting essentially of economizer means, superheater means, reheater means, convection and radiation heating means for utilizing said thermal energy for converting feed water to steam and heat reclamation means for recovering residual thermal energy from said hot gases using regenerators containing relatively high heat capacitance solid materials to concurrently cool said gases and heat said solid materials, the improvement comprising means for directing said hot gases from said economizer means to said heat reclamation means without substantial cooling therebetween.