US3656915A

US3656915A - Catalytic exhaust gas treatment apparatus

Info

Publication number: US3656915A
Application number: US33359A
Authority: US
Inventors: John F Tourtellotte
Original assignee: Chemical Construction Corp
Current assignee: Chemical Construction Corp
Priority date: 1970-04-30
Filing date: 1970-04-30
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: GB1328454A; FR2140737A5; DE2121158A1; CA966277A

Abstract

An apparatus for catalytically treating the exhaust gas from internal combustion engines in two stages, with the first catalyst stage reducing nitrogen oxides, and the second stage oxidizing hydrocarbons and carbon monoxide. Preheated air is injected into the exhaust gas stream between the stages, and the final hot fully reacted exhaust gas serves to preheat the air. The entire apparatus is disposed in a single container having flat inclined catalyst beds and a central co-axial heat exchange section.

Description

11 nlted States Patent 1151 3,656,91 Tourtellotte [45] Apr. 18, 1972 541 CATALYTIC EXHAUST GAS 3,176,461 4/1965 Calvert ..60/30 R TREATMENT APPARATUS 3,203,168 8/1965 Thomas ..23/288 F X 3,228,746 1/1966 Howk et a1... ..23/2 E Invenwrr John Toumllofle, Weslfield, 3,255,123 6/1966 Haensel ..23/288 F ux z N 3,380,810 4/1968 Hamblin ..23/288 F [73 1 Ass'gnee $fif jgi' f Cmmmn ew 3,544,264 12/1970 Hardison ..23/288 F x [22,] Filed: Apr. 30, 1970 Primary Examiner-Morris O. Wolk Assistant Examiner-Barry S. Richman [2]] Appl 33359 Attorney-J. L. Chaboty [52] U.S. Cl. ..23/288 F, 23/2 E, 60/30 R, [57] ABSTRACT I 5 1 1 Int Cl 5 853 1 An apparatus for catalytically treating the exhaust gas from in- 58] Fie'ld 3] ternal combustion engines in two stages, with the first catalyst stage reducing nitrogen oxides, and the second stage oxidizing hydrocarbons and carbon monoxide. Preheated air is injected [56] References Cited into the exhaust gas stream between the stages, and the final UNITED STATES PATENTS hot fully reacted exhaust gas serves to preheat the air. The entire apparatus is disposed in a single container having flat gi g inclined catalyst beds and a central co-axial heat exchange 0C a ection 3,168,806 2/1965 Calvert.... ..23/288 F X 3,172,738 3/1965 Houdry ..23/288 F 12 Claims, 6 Drawing Figures PATENTEDAPR 18 I972 SHEET 10F 3 JOHN F. TOUR TELLOTTE IN VENTOR.

PATENTED RWBIZ Y 3 656,915 SHEET 20F 3 JOHN F. TOURTELLOTTE INVENTOR.

AGENT PATENTEDAFR 18 I872 SHEET 30F 3 JOHN F. TOUTELLOTTE I IN VENT OR. BY a m' AGENT BACKGROUND OF THE INVENTION some areas a so-called smog is generated due to atmospheric inversions and accumulation of such exhaust gases in the atmosphere. Recent attempts to prevent such air pollution have concentrated on the destruction or elimination of noxious components by catalysis, especially by admixture of secondary air into the exhaust gas followed by catalytic oxidation of residual hydrocarbons, carbon monoxide, etc., in various types of apparatus specially designed for this purpose. Improvements in active catalytic agents for this function are described in U.S. Pat. Nos. 3,053,773; 3,429,656; 3,316,057; 3,398,101; 3,477,893 and 3,476,508 and prior art apparatus for carrying out the procedure are described in U.S. Pat. Nos. 3,380,810, 3,325,256; 3,255,123; 3,222,140; 3,186,806; 3,180,712; 3,169,836; 3,168,806, 3,146,073 and 3,086,839.

SUMMARY OF THE INVENTION In the present invention, a catalytic apparatus for treating exhaust gas from internal combustion engines is provided, in which catalysis is effected in two stages within the same unitary container, which also accommodates for preheating of air which is then employed as an additive to the exhaust gas between the initial reduction stage, in which nitrogen oxides are catalytically reduced, and the second catalytic stage in which residual hydrocarbons and carbon monoxide are catalytically oxidized to innocuous components such as carbon dioxide and water vapor. The apparatus includes inclined upper and lower catalyst beds for first and second stage reactions, and conventional catalysts may be employed for each stage, such as those described in the U.S. patents mentioned supra. Different catalysts may be used for each stage, but the same catalytic agent is preferably employed in both catalytic stages, for reasons of economy and simplicity. The flat inclined catalyst beds are aligned within the same container and are preferably substantially parallel, and the indirect heat exchange section, for preheating of reaction air by indirect heat exchange with hot fully reacted exhaust gas, is disposed centrally in the container and aligned coaxially with the central axis of the substantially horizontal container.

The principal advantage of the apparatus of the present invention is that a unitary apparatus combination is provided which is readily fabricated and easy to assemble, and which accomplishes in a single apparatus unit the combined functions of catalytic reduction, preheating of air, injection of preheated air into the catalytically reduced exhaust gas, and catalytic oxidation. Another advantage is that the apparatus has a low overall gas pressure drop, and thus does not entail the provision of a high initial exhaust gas pressure or high back pressure. A further advantage is that the apparatus also has a dampening effect on sounds and pulsations of exhaust gas from the internal combustion engine, and thus the apparatus also functions as a muffler.

It is an object of the present invention to provide an improved apparatus for catalytically treating the exhaust gas from internal combustion engines.

Another object is to remove the noxious components from engine exhaust gases by means of an improved apparatus.

An additional object is to prevent air pollution by preventing the discharge of engine exhaust gases, containing deleterious components such as nitrogen oxides, carbon monoxide and residual hydrocarbons, into the atmosphere.

A further object is to provide an improved catalytic apparatus for removing noxious components from the exhaust gas from internal combustion engines, using two stage catalysis with interstage injection of preheated air.

These and other objects and advantages of the present invention will become evident from the description which follows.

DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS Referring now to the drawings,

FIG. 1 is a sectional elevation view of one embodiment of the invention,

FIG. 2 is an elevation view of one end of the FIG. 1 embodiment, taken on section 2-2 and showing internals,

FIG. 3 is a sectional elevation view of an alternative embodiment of the invention,

FIG. 4 is an elevation view of one end of the FIG. 3 embodiment, taken on section 44 and showing exhaust gas and air inlet members,

FIG. 5 shows the two air inlet pipes in plan view, and is taken on section 5-5 of FIG. 4,

FIG. 6 is a sectional elevation view of the FIG. 3 embodiment, taken on section 6-6 and showing internals.

Referring now to FIG. 1, hot exhaust gas stream 1 is derived from an internal combustion engine such as a gasoline-burning automobile or truck engine or the like. Stream 1 typically contains noxious components such as nitrogen oxides, residual hydrocarbon vapor, and carbon monoxide, as well as carbon dioxide and nitrogen. Stream 1 is passed via inlet pipe 2 into the generally horizontally oriented container defined by one end wall 3, side or top and bottom wall 4 and the other end wall 5. A vertically oriented fluid closure partition 6 depends from the top wall 4 external to pipe 2, and directs the exhaust gas stream 1 through enclosure screen 7 and into the initial catalyst bed 8, in which the selective reduction of all or most of the nitrogen oxides in the gas stream to elemental nitrogen takes place. Catalyst bed 8 may typically consist of any known catalytic agent for the treatment of exhaust gases, such as those agents, compounds or compositions described in the U.S. patents cited supra. Bed 8 preferably consists of elemental metallic zinc, nickel, platinum, copper, manganese, vanadium, cobalt, chromium or iron, or mixtures thereof, or mixtures including oxides thereof, which may be suitably promoted by alkali or alkaline earth metal oxides or carbonates or the like, such as the oxides or carbonates of sodium, potassium, calcium, magnesium, etc., and which are preferably deposited on a suitable carrier such as kaolin, silica, alumina, zeolite or the like. A catalytic reduction of nitrogen oxides takes place by the reaction of nitrogen oxides in bed 8 with reducing components in the gas stream, to yield nitrogen and water vapor and/or carbon dioxide. Bed 8 is preferably substantially flat and inclined at an angle of 2 to 45 to the horizontal, and extends upwards from partition 6 to a terminus at end wall 5.

The downflowing hot partially reacted gas stream is discharged below bed 8 and is now substantially free of nitrogen oxides, however the gas stream contains other noxious components as mentioned supra which are destroyed by a high temperature oxidation reaction. The downflowing gas stream is diverted horizontally and laterally below bed 8 by the substantially horizontal partition 9, which extends through the container from a fluid-impervious connection with the lower end of partition 6. A preheated hot air stream is discharged into the partially reacted exhaust gas between wall 5 and the end of partition 9 adjacent to and spaced from the wall 5, via the flared outlet of transition duct 10. The resulting hot mixture of exhaust gas and air flows downwards between wall 5 and the gas diversion bafile 11, which depends from the end of the partition or baffle 9 adjacent to wall 5. The hot gaseous mixture next flows through catalyst retention screen 12 and upwards through oxidation catalyst bed 13, which is of known composition to catalyze the oxidation of hydrocarbon vapor, carbon monoxide etc. in the exhaust gas to innocuous components such as carbon dioxide and water vapor, and which may be one of the compositions or catalysts mentioned supra, such as those described in the US. patents cited supra.

The resulting hot fully reacted exhaust gas stream discharged upwards from bed 13 is now of a suitable composition substantially free of noxious components, and may be safely discharged to atmosphere without causing air pollution. The hot fully reacted gas is diverted laterally and horizontally towards end wall 3 below partition 9, and the hot gas next flows into the substantially horizontal duct 14 which is generally coaxial with the substantially horizontal container defined by the wall 4 and end walls 3 and 5. As will appear infra, the hot gas flowing through duct 14 is cooled by indirect heat exchange with air flowing external to duct 14 and the cooled fully reacted and innocuous exhaust gas is discharged from duct 14 via stream 15, which may pass via a tailpipe to an auxiliary muffler, not shown, or directly to atmospheric discharge.

The air stream which is preheated in accordance with the present invention is derived as stream 16 from a suitable blower or the like, not shown, which may be driven by a pulley rotated by the fanbelt of the motor or engine. In any case, stream 16 is passed into the device, via transition pipe or element 17, which passes the preferably ambient air stream 16 tangentially via a tangential transition piece into an annular passage defined between duct 14 and outer concentric duct 18, so that the air flows through the annular passage between ducts 14 and 18 in a spiral flow path. The spirally flowing air is heated by indirect heat exchange with the hot fully reacted exhaust gas flowing within duct 14, and the resulting preheated air is removed from the annular passage between ducts 14 and 18 via a tangential transition piece or section of pipe 10, with tangential removal of preheated air via aiding in maintaining the spiral flow pattern of the air. The heated air is discharged from the pipe or duct 10 into the partially reacted exhaust gas, as described supra.

Referring now to FIG. 2, a sectional elevation view of the front end of the FIG. 1 device is shown, with selected internal elements being illustrated as seen through front wall 3. FIG. 2 shows the generally elliptical cross-section of the device via wall element 4, with the vertical axis of elliptical element 4 being longer than the horizontal axis. Tangential entry of stream 16 via pipe 17 into the annular passage between ducts l4 and 18 is shown, as well as tangential removal of preheated air from the tangential passage via pipe 10. Finally, FIG. 2 shows horizontal partition 9 extending between outer duct 18 and wall 4. Portions of the catalyst bed 8 and screen 7 have been omitted in FIG. 2, in the interest of clarity. In this respect, it will be evident from FIG. 2 that elements 8 and 7 may extend downwards laterally between the upper half of duct 18 and wall 4 to a lower terminus of partition 9. Similar considerations apply to the upper rear section of catalyst bed 13 and screen 12, which may extend to an upper terrninus which is contiguous to partition 9 on each side between the lower half of duct 18 and wall 4, adjacent to baffle 11.

FIG. 3 shows an alternative and simplified embodiment of the invention, in which rectangular elements and passages are provided. Unit 19 is an internal combustion engine or motor such as the motor of a gasoline-burning automobile, and exhaust gas stream 20 passes from unit 19 into pipe 21, which extends through front wall 22 and discharges the exhaust gas into the rectangular device of this embodiment of the present invention, which is defined by front wall 22, top wall 23, bottom wall 24 and rear wall 25. The exhaust gas passes downwards through flat inclined inlet screen 26, which extends upwards between

walls

22 and 25 at an angle which is typically 2 to 45 from the horizontal. Reducing catalyst bed 27 extends between screen 26 and lower screen 28 which is preferably substantially parallel with screen 26, and the nitrogen oxides content of the hot exhaust gas flowing downwards through bed 27 is catalytically reduced to innocuous components such as elemental nitrogen and water vapor and/or carbon dioxide.

The resulting exhaust gas discharged downwards from screen 28 is diverted laterally and horizontally by the substantially horizontal partition 29 and towards the rear of the device, where the exhaust gas flows downwards between the end of partition 29 and wall 25, and external to discharge pipe 30 and downwards between the substantially vertical baffle 32 and wall 25. Baffle 32 depends from the end of partition 29. A preheated air stream is injected into the downflowing exhaust gas via pipe 31. The resulting downflowing mixture of hot exhaust gas and preheated air flows downwards and horizontally below the lower end of baffle 32, and is diverted upwards by floor or bottom wall 24. The hot gaseous mixture next flows laterally and upwards through screen 33 and oxidizing catalyst bed 34, in which noxious components such as hydrocarbon gases or vapors and carbon monoxide are oxidized to innocuous components such as water vapor and carbon dioxide. The resulting hot gaseous mixture flows upwards from catalyst bed 34 through upper retention screen 35. Screens 34 and 35 are preferably parallel, and may be inclined at a greater angle to the horizontal than screens 26 and 28, or screens 34 and 35 may in some cases be substantially parallel to screens 26 and 28. In any case, screens 34 and 35 extend from the lower front end wall 22 upwards and laterally to the lower end of baffle 32.

The hot gaseous mixture discharged upwards from screen 35 is now suitable for discharge to the atmosphere, and may be discharged without causing air pollution, however the hot gaseous mixture is utilized in accordance with the present invention to preheat reaction air by indirect heat exchange. The rising hot gaseous mixture is diverted horizontally below the lower substantially horizontal partition 36, and flows upwards between the end of partition 36 and front wall 22. The hot gaseous mixture next flows horizontally through the passage defined between

partitions

36 and 29, and heats the air flowing within pipe 31, which is disposed between

horizontal partitions

36 and 29, so that preheated air is discharged from pipe 31 as described supra. The somewhat cooled gaseous mixture is discharged from the passage between

partitions

36 and 29 via pipe 30, which discharges the gaseous mixture 37 to atmosphere or to an auxiliary mufiler or tailpipe, not shown.

The preheated air is derived from ambient air stream 38, which is passed via fan or blower 39 as stream 40 to the main inlet pipe 41, from which a portion of the air is conducted by shoulder pipe connection 42 to pipe 31, for preheating and usage as described supra.

Referring now to FIG. 4, an elevation view of the front end, or exhaust gas and air inlet end of the device is shown. FIG. 4 shows top wall 23, bottom wall 24, and

side walls

43 and 44 of the rectangular device of FIG. 3. In addition, FIG. 4 illustrates a second air preheating pipe or tube 45, which is parallel with pipe 31 and receives air for preheating via central pipe 41 and shoulder pipe connection 46.

FIG. 5 is a sectional plan view of FIG. 4, taken on section 5-5, and shows the parallel

air preheat pipes

31 and 45 which receive air stream 40 via pipe 41 and shoulder pipe connections or

transition members

42 and 46, and which discharge hot air into the partially reacted hot exhaust gas between baffle or partition 32 and the rear wall 25. One or more than two air preheat pipes such as

elements

31 and 45 may be provided in practice. Pipe 30, which serves to discharge the fully reacted and innocuous exhaust gas from the device external to rear wall 25, is also shown.

FIG. 6 is a sectional elevation view of a portion of the FIG. 3 device, taken on section 6-6, and shows the arrangement of

pipes

31 and 45, central exhaust gas discharge pipe 30, all disposed between

horizontal partitions

29 and 36.

Numerous alternatives within the scope of the present invention, besides those alternatives mentioned supra, will occur to those skilled in the art. As mentioned supra, the air blower may be driven by the fan belt of the motor, thus the fan belt or auxiliary gearing of motor 19 may drive blower 39. The catalyst beds could be inclined in the opposite direction, sloping downwards from the front wall of the device to the rear wall.

An example of testing of a fabricated device according to FIG. 1, as applied to a commercial gasoline-buming truck engine, will now be described.

EXAMPLE The device according to FIG. 1 was fabricated and tested on a commercial truck engine. The reducing section catalyst area was 0.625 square feet, catalyst volume was 0.156 cubic feet. The oxidizing section catalyst area was 0.58 square feet, catalyst volume was 0.144 cubic feet. The catalyst composition was composed of a reduced mixture of the oxides of nickel, cobalt and manganese deposited on particles of alpha alumina, with the preliminary reduction by means of hydrogen serving to reduce a portion of the oxides to the metallic state. The same catalyst composition was used in both the reducing and oxidizing catalyst beds. Following are the test results.

Reducing Section Engine speed, m.p.h Gas volume, c.f.m Velocity thru catalyst, f Space velocity per hour. AI, inches water M.p.h.=miles per hour (equivalent) C.f.m.=cubic feet per minute F.p.s.=feet per second AP =pressure drop In the test runs, all surfaces were insulated with 0.5 inches of insulation.

The inlet exhaust gas contained 1,040 ppm of nitrogen oxides, which was reduced to less than 75 ppm in the final exhaust gas. Essentially complete destruction of hydrocarbon vapors and carbon monoxide was attained in the oxidizing section, and the final exhaust gas was essentially devoid of these components.

lclaim:

1. An apparatus for catalytically treating the exhaust gas from an internal combustion engine which comprises a container, a first inclined catalyst bed disposed in said container, means to pass an exhaust gas stream from an internal combustion engine into said container, whereby said exhaust gas stream flows through said first catalyst bed and at least a portion of the nitrogen oxides in said exhaust gas stream are catalytically reduced, means within said container to pass a preheated air stream into the exhaust gas stream discharged from said first catalyst bed, means to pass the resulting exhaust gasair mixture through a second inclined catalyst bed disposed in said container, whereby said exhaust gas stream containing injected air flows through said second catalyst bed and at least a portion of the hydrocarbons and carbon monoxide in said exhaust gas stream are catalytically oxidized and a final hot exhaust gas stream substantially free of noxious components is discharged from said second catalyst bed, means within said container to pass said final hot exhaust gas stream in indirect heat exchange with an air stream, whereby said air stream is heated to form said preheated air stream, and means to remove the resulting cooled final exhaust gas stream from said container.

2. The apparatus of claim 1, in which said container is horizontally oriented and provided with substantially vertical front and rear end walls, said exhaust gas is passed through the front end wall of said container adjacent to said first bed, said first catalyst bed is disposed above and spaced from said second catalyst bed, said means to pass a preheated air stream into the exhaust gas stream discharged from said first catalyst bed within said container is disposed adjacent to said rear end wall of said container, and said means to pass said final hot exhaust gas stream in indirect heat exchange with an air stream within said container is disposed between said first catalyst bed and said second catalyst bed.

3. The apparatus of claim 2, in which said first catalyst bed and said second catalyst bed are inclined and slope upwards from said front end wall to said rear end wall.

4. The apparatus of claim 3, in which said first catalyst bed and said second catalyst bed are inclined at an angle in the range of 2 to 45 from the horizontal.

5. An apparatus for catalytically treating the exhaust gas from an internal combustion engine which comprises a horizontally oriented container, an upper exhaust gas inlet at one end of said container, means to pass an exhaust gas stream from an internal combustion engine to said exhaust gas inlet, whereby said exhaust gas stream flows into the top portion of said container, a first flat inclined catalyst bed disposed in the upper section of said container, said first catalyst bed being inclined at an angle in the range of 2 to 45 from the horizontal and extending upwards from below said exhaust gas inlet at said one end of said container to the opposite other end of said container, whereby said exhaust gas stream flows downwards through said first catalyst bed and at least a portion of the nitrogen oxides in said exhaust gas stream are catalytically reduced, a substantially horizontal partition disposed in said container below said first catalyst bed, said partition extending from one fluid-impervious terminus contiguous with said one end of said container to another terminus spaced from and adjacent to said other end of said container, whereby said exhaust gas stream flowing downwards from said first catalyst bed is diverted horizontally towards said other end of said container by said partition and flows downwards between said other terminus of said partition and said other end of said container, means to inject a preheated air stream into said downflowing exhaust gas stream adjacent to said other terminus of said partition, a second flat inclined catalyst bed disposed in the lower section of said container below said partition, said second catalyst bed being inclined at an angle in the range of 2 to 45 from the horizontal and extending upwards from the lower portion of said one end of said container to a terminus adjacent to said other terminus of said partition, whereby said exhaust gas stream containing injected air flows upwards through said second catalyst bed and at least a portion of the hydrocarbons and carbon monoxide in said exhaust gas stream are catalytically oxidized and a hot exhaust gas stream substantially free of noxious components is formed above said second catalyst bed at said one end of said container, means to pass said hot fully reacted exhaust gas stream coaxially from said one end of said container, and between said first catalyst bed and said second catalyst bed, through said container to an exhaust gas outlet at said other end of said container, and means to pass air from said one end of said container through said container between said first catalyst bed and said second catalyst bed and in indirect heat exchange with said hot fully reacted exhaust gas stream, whereby said air is heated by said hot exhaust gas stream and is discharged into said exhaust gas stream between said first catalyst bed and said second catalyst bed as said preheated air stream.

6. The apparatus of claim 5, in which said container is substantially elliptical in vertical cross-section, said elliptical cross-section having a vertical axis which is longer than the horizontal axis.

7. The apparatus of claim 5, in which said container is rectangular in vertical cross-section, said partition is an upper partition which defines the upper side of a central rectangular passage for flow of said hot fully reacted exhaust gas stream between said first catalyst bed and said second catalyst bed, a second horizontal partition is spaced below said upper partition to define the lower side of said central rectangular passage for flow of said hot fully reacted exhaust gas stream, and said air is preheated by passing air through at least one pipe disposed within said central rectangular passage, said pipe discharging preheated air into the partially reacted exhaust gas stream discharged from said first catalyst bed adjacent to said other end of said container.

8. The apparatus of claim 5, in which said first bed and said second bed are inclined at substantially the same angle to the horizontal and are substantially parallel.

9. The apparatus of claim 5, in which said hot fully reacted exhaust gas stream flows centrally and axially through said container from said one end of said container to discharge at said other end of said container through a first central substantially horizontal duct, said first duct being coaxial with said container and disposed between said first catalyst bed and said second catalyst bed, and said air is preheated by providing a second outer duct concentrically disposed external to said first duct, and providing means to pass said air through the annular passage defined between said first duct and said second duct.

10. The apparatus of claim 9, in which said means to pass air into the annular passage defined between said first duct and said second duct is substantially tangential to said annular passage, and the resulting preheated air is tangentially removed from said annular passage by said means to inject a preheated air stream into said exhaust gas stream, whereby said air is preheated while flowing in a spiral flow path through said annular passage.

11. The apparatus of claim 5, in which said first catalyst bed and said second catalyst bed are composed of the same active catalytic agent, deposited on a suitable carrier.

12. The apparatus of claim 11, in which said active catalytic agent is selected from the group consisting of zinc, nickel, platinum, copper, manganese, vanadium, cobalt, chromium, iron, catalytically promoted mixtures thereof, and catalytically promoted oxides thereof, deposited on a suitable carrier,

Claims

2. The apparatus of claim 1, in which said container is horizontally oriented and provided with substantially vertical front and rear end walls, said exhaust gas is passed through the front end wall of said container adjacent to said first bed, said first catalyst bed is disposed above and spaced from said second catalyst bed, said means to pass a preheated air stream into the exhaust gas stream discharged from said first catalyst bed within said container is disposed adjacent to said rear end wall of said container, and said means to pass said final hot exhaust gas stream in indirect heat exchange with an air stream within said container is disposed between said first catalyst bed and said second catalyst bed.
3. The apparatus of claim 2, in which said first catalyst bed and said second catalyst bed are inclined and slope upwards from said front end wall to said rear end wall.
4. The apparatus of claim 3, in which said first catalyst bed and said second catalyst bed are inclined at an angle in the range of 2* to 45* from the horizontal.
5. An apparatus for catalytically treating the exhaust gas from an internal combustion engine which comprises a horizontally oriented container, an upper exhaust gas inlet at one end of said container, means to pass an exhaust gas stream from an internal combustion engine to said exhaust gas inlet, whereby said exhaust gas stream flows into the top portion of said container, a first flat inclined catalyst bed disposed in the upper section of said container, said first catalyst bed being inclined at an angle in the range of 2* to 45* from the horizontal and extending upwards from below said exhaust gas inlet at said one end of said container to the opposite other end of said container, whereby said exhaust gas stream flows downwards through said first catalyst bed and at least a portion of the nitrogen oxides in said exhaust gas stream are catalytically reduced, a substantially horizontal partition disposed in said container below said first catalyst bed, said partition extending from one fluid-impervious terminus contiguous with said one end of said container to another terminus spaced from and adjacent to said other end of said container, whereby said exhaust gas stream flowing downwards from said first catalyst bed is diverted horizontally towards said other end of said container by said partition and flows downwards between said other terminus of said partition and said other end of said container, means to inject a preheated air stream into said downflowing exhaust gas stream adjacent to said other terminus of said partition, a second flat inclined catalyst bed disposed in the lower section of said container below said partition, said second catalyst bed being inclined at an angle in the range of 2* to 45* from the horizontal and extending upwards from the lower portion of said one end of said container to a terminus adjacent to said other terminus of said partition, whereby said exhaust gas stream containing injected air flows upwards through said second catalyst bed and at least a portion of the hydrocarbons and carbon monoxide in said exhaust gas stream are catalytically oxidized and a hot exhaust gas stream substantially free of noxious components iS formed above said second catalyst bed at said one end of said container, means to pass said hot fully reacted exhaust gas stream coaxially from said one end of said container, and between said first catalyst bed and said second catalyst bed, through said container to an exhaust gas outlet at said other end of said container, and means to pass air from said one end of said container through said container between said first catalyst bed and said second catalyst bed and in indirect heat exchange with said hot fully reacted exhaust gas stream, whereby said air is heated by said hot exhaust gas stream and is discharged into said exhaust gas stream between said first catalyst bed and said second catalyst bed as said preheated air stream.
6. The apparatus of claim 5, in which said container is substantially elliptical in vertical cross-section, said elliptical cross-section having a vertical axis which is longer than the horizontal axis.
7. The apparatus of claim 5, in which said container is rectangular in vertical cross-section, said partition is an upper partition which defines the upper side of a central rectangular passage for flow of said hot fully reacted exhaust gas stream between said first catalyst bed and said second catalyst bed, a second horizontal partition is spaced below said upper partition to define the lower side of said central rectangular passage for flow of said hot fully reacted exhaust gas stream, and said air is preheated by passing air through at least one pipe disposed within said central rectangular passage, said pipe discharging preheated air into the partially reacted exhaust gas stream discharged from said first catalyst bed adjacent to said other end of said container.
8. The apparatus of claim 5, in which said first bed and said second bed are inclined at substantially the same angle to the horizontal and are substantially parallel.
9. The apparatus of claim 5, in which said hot fully reacted exhaust gas stream flows centrally and axially through said container from said one end of said container to discharge at said other end of said container through a first central substantially horizontal duct, said first duct being coaxial with said container and disposed between said first catalyst bed and said second catalyst bed, and said air is preheated by providing a second outer duct concentrically disposed external to said first duct, and providing means to pass said air through the annular passage defined between said first duct and said second duct.
10. The apparatus of claim 9, in which said means to pass air into the annular passage defined between said first duct and said second duct is substantially tangential to said annular passage, and the resulting preheated air is tangentially removed from said annular passage by said means to inject a preheated air stream into said exhaust gas stream, whereby said air is preheated while flowing in a spiral flow path through said annular passage.
11. The apparatus of claim 5, in which said first catalyst bed and said second catalyst bed are composed of the same active catalytic agent, deposited on a suitable carrier.
12. The apparatus of claim 11, in which said active catalytic agent is selected from the group consisting of zinc, nickel, platinum, copper, manganese, vanadium, cobalt, chromium, iron, catalytically promoted mixtures thereof, and catalytically promoted oxides thereof, deposited on a suitable carrier.