US 3224842 A
Description (OCR text may contain errors)
Dec. 21, 1965 w. J. MANSKE 3,224,842
WASTE GAS INCINERATING AFTERBURNERS Filed Jan. 10, 1963 4 Sheets-Sheet 1 ENGINE J EXHAUST FIG. I
CONDUIT IN VEN TOR.
S PPLEME TAL Fl WENDELL J. MANSKE AIR AND EXHAUST BY couourr W mm, and A42 ATTORNEYS Dec. 21, 1965 w. J. MANSKE WASTE GAS INCINERATING AFTERBURNERS 4 Sheets-Sheet 2 Filed Jan. 10, 1963 FIG. 5
WENDELL J. MANSKIE ATTORNEYS Dec. 21, 1965 w. J. MANSKE WASTE GAS INCINERATING A F'IERBURNERS 4 Sheets-Sheet 3 Filed Jan. 10, 1963 FIG. 7
IN VEN TOR.
WENDELL J. MANSKE a n, m mwm,
ATTORNEYS United States Patent 3,224,842 WASTE GAS INCINERATING AFTEREEURNERS Wendell .l. Manske, Birchwood, Minn, assignor to Minnesota Mining and Manufacturing Qompany, St. Paul, Minn a corporation of Delaware Filed .lan. it), 1963, Ser. No. 25tl,7il2 7 Claims. (Cl. 23-277) The instant application is a continuation-in-part of application Serial Number 62,972, filed Oct. 17, 1960 and now forfeited.
This invention relates to devices for the incineration of exhaust gases incorporating recuperative heat exchangers and more particularly to exhaust afterburn-ers for internal combustion engines.
The exhaust gases from the operation of internal combustion engines are known to contain products of incomplete combustion of fuel such as carbon monoxide and hydrocarbons. As used herein, the term hydrocarbons will be understood to comprise a large number of materials such as alcohols, ketones, acids, esters and the like which are formed under particular conditions of combustion of hydrocarbon fuels. The total amount of hydrocarbons present can be as much as 0.1 percent by volume or more of the exhaust gases. It is apparently the cumulative effect of large scale production of this hydrocarbon fraction by numerous vehicles which is responsible, at least under certain conditions, for the unpleasant atmospheric condition known as smog. It is certain that the odors caused by exhaust are likely to be unpleasant and even nauseating. Furthermore, the production of carbon monoxide is even greater, sometimes approaching percent by volume of the exhaust gases. While carbon monoxide is odorless, it is pe rniciously toxic. It is therefore apparent that the exhaust gases from internal combustion engines are a form of atmospheric contamination which should be eliminated if possible or at least brought to a minimum value, particularly in larger cities.
The exhaust gases from other operations are also frequently unpleasant in various ways such as being malodorous, sooty or otherwise objectionable, for example, the exhaust gases from incomplete incineration of waste and oltgases from industrial processes such as varnish manufacture. The term waste gases will be understood to include fumes, vapors and gaseous products having no economic value which are desirably dissipated in the atmosphere as being valueless and includes not only off-gases from processes which may be diluted with air and/or oxygen from ventilation operations but also exhaust gases which are commonly discharged directly into the atmosphere.
The most effective way of disposing of undesirable exhaust products of the type described is by combustion or incineration, and considerable effort has been devoted to this end, particularly with respect to devices using catalytic units. Such devices as described heretofore so far as known always suffer from possible inactivation of the catalyst such as poisoning by lead compounds or other gasoline additives or contaminants in the case of automobile exhaust afterburners, or by inefiiciencies in design, particularly where wholly metallic constructions are employed.
It is an object of this invention to provide an exhaust incinerator or afterburner wherein exhaust gases can be burned to substantially non-toxic and innocuous products. A further object is to provide an afterburner unit for internal combustion engines in which there is reduced high-ternperature corrosion.
Other objects will become evident hereinafter.
in accordance with the above and other objects of this invention it has been found that an especially useful exhaust afterburner is provided by positioning at least iCe one cross-flow honeycomb ceramic heat exchanger unit of substantially parallelepipedal configuration in contact with the walls of a suitable casing on at least three corner edges, the spaces thus formed between adjacent isolated faces and the walls of the casing forming plenums for the entering and exiting exhaust gases, while the other two faces of at least one of the heat exchanger units together with the remainder of the casing wall define a combustion chamber space which is fitted with ignition means.
In further explanation of the invention, drawings are provided herewith, wherein:
FIGURE 1 is a view in perspective of an embodiment of an afterburner of generally cylindrical shape of the present invention with the wall partially broken away to show the honeycomb ceramic heat-exchanger unit and the battles employed.
FIGURE 2 is a top view of an afterburner of the type shown in FIGURE 1 with the top end removed and look ing down on the top of the heat exchanger unit.
FIGURE 3 is a view in perspective of another embodiment of the invention, one end being removed to show details of internal construction.
FIGURE 4 is a View in cross-section transversely and approximately through the midpoint of another embodiment of the invention.
FlGURE 5 is another View in cross-section through the midpoint of another embodiment of the invention in which exhaust gases enter from one end of the afterburner.
FEGURE 6 is a View in cross-section transversely through the midpoint of an afterburner embodying the principles of the invention in which two heat-exchanger units are employed in series arrangement, the exhaust gases being admitted at one end of the afterburner.
FIGURE 7 is a view in crosssection transversely through the midpoint of another embodiment of the invention in which two heat exchangers are employed in parallel arrangements, the combustion chamber being centrally located in the afterburner.
FIGURE 8 is a view in perspective of an embodiment of the invention for incineration of off-gases, one portion being broken away to show internal structure.
Referring again to the drawings, the devices of the invention and their operation will be described in greater detail, as follows:
Referring to FIGURES 1 and 2, the after-burner casing 10 is provided with tubular inlet Ill, and tubular outlet 12 at one end and ignition means 15, here shown as a spark plug in the other end cover 16. A portion of the casing is shown cut away so that the ceramic honeycomb heat exchanger unit 18 is visible. The heat-exchanger unit 18 is made up from corrugated sheets 19 and at right angles (only two of the sheets in each direction being numbered). The corner edges between the faces of the heat exchanger are joined to the casing ill, as by means of high-temperature cement.
The edges of adjacent faces, together with that part of the casing which connects them, form inlet and outlet manifolding means for the exhaust gases. Supplementary air is supplied to the device at a point (not shown) in the inlet tube, immediately before the portion illustrated or by means of a port 14 into the combustion chamber 24. A battle 23 closes the ends of the inlet and outlet manifolds, forcing the gases through the heat exchanger passages before and after they traverse the combustion chamber 24, formed by the portions of the casing 10 not occupied by the heat exchanger 18 and the semicircular baffle 23. Each corrugated sheet of the heat exchanger unit together with the fiat sheets above and below it forms a rank of passageways, successive ranks being at right angles separated by the divider sheets. In operation, exhaust gases (flow of which is also indicated by arrows) enter the combustion chamber 24 at the face of the channel 25 between the face of the heat exchanger opposite to the inlet manifold after passing from inlet lll (shown in dotted lines in FIGURE 2) through the parallel passageways of the heat exchanger. They are prevented from entering the exit manifold by the semi-circular baffle 23 and are compelled to flow turbulently through the combustion chamber 24 before entering the channel at 26 between the face of the heat exchanger opposite the outlet manifold and the casing because of the triangular bafile 28. This baffle is not absolutely necessary for operation of the unit, but serves to promote eflicient operation of the device by preventing channelled flow through the combustion chamber. While in the combustion chamber oxidation takes place exothermically. Initially, when the engine or other source of objectionable off-gases has just been started and is cold, temperatures are not high enough for oxidation, and self-sustaining combustion is initiated by supplemental additions of fuel, e.g. by choking the engine for a time, and igniting the thus-enriched exhaust gases by the ignition means indicated at 15. This can be a spark plug or glow plug of conventional construction, connected respectively to sparking coil means or to a battery. Alternatively, the action of these devices is augmented by providing adjacent to them a burner nozzle supplied with a fuel and air mixture which can preheat the assembly by combustion. Other means, such as arrangements for blowing hot air through the heat exchanger unit so that self-supporting combustion can begin more rapidly, can also be used. It is believed that such ignition means and/or preheating means are sufficiently well-known to the art that they need not be further characterized herein and are repre sented only schematically. Such means can be collectively termed igniters.
As a result of the combustion, the exhaust gases are heated and in passing from the combustion chamber through channel 26 and through the heat exchanger unit to the outlet manifold and the outlet tube 12, heat is given up to the heat exchanger and to the entering exhaust gases flowing from inlet 11 through the heat exchanger passageways at right angles to the exiting gases. In this way the exhaust gases are continually being heated so that combustion of carbon monoxide and hydrocarbons can be maintained. When industrial off-gases (including incompletely incinerated gases) are to be incinerated, a small addition of fuel may be necessary continuously. This will be evident from analysis of the offgases involved.
The corrugated sheets employed in constructing these heat exchangers should have a frequency of corrugations, e.g. peak to peak, of about 3 to about 10 corrugations per inch and preferably about 3 to about 7 per inch. It is advantageous to employ corrugated sheets having slightly lower corrugation frequencies for the outlet side of the heat exchanger unit since this effectively reduces back pressure between the atmosphere and the combustion chamber. Likewise, heat exchanger chambers of larger dimensions can be used on the outlet side for this purpose. In all cases as shown in FIGURE 2 through 8, the heat exchangers unit or units extend the entire length of the casing and are sealed to the casing as by the use of high temperature ceramic cement to prevent leakage of gases past the end. It will be apparent, however, that internal leakage, if small, results only in slight losses in efficiency.
FIGURE 3 shows a schematic cross-section of an embodiment of the invention having a metal casing 3t) provided with ceramic lining 311, inlet for exhaust gases and supplementary air 32 to inlet manifold 33 and heat exchanger unit 34 (constructed as described hereinabove) having contact with the walls of the casing at 35, 36 and 37.
The near end cover plate of the device, which is a fiat metal piece of the same shape as the external configuration of the body of the casing, and which is provided with holes for inlet tube 32 and outlet tube 39, has been removed to show detail of the device. The end cover plate is provided with a ceramic liner and is tightly fitted to the various parts to prevent leakage of gases. The combustion chamber 40 has an igniting means (not shown) in the far end of the cover plate of the device, in the combustion chamber. Baffies 42 and 44 provide for mixing of the gases during incineration and before the exit of the gases through the passageways (not shown) of the heat exchanger to the outlet manifold 38 and outlet tube 39. The operation of the device is the same as that of the afterburner illustrated in FIGURES l and 2.
In FIGURES 4, 5, 6 and 7 which are schematic transverse cross-sections through the approximate midpoint of each device depicted, the lines on the cross-section of the heat exchanger units indicate inlet passageways of each heat exchanger. In each case, the heat exchanger unit (constructed as described hereinabove) contacts the walls of the casing 52 and is held in place by means of angular mounting brackets 54, which extend across the length of the casing. Inlets for exhaust gases are indicated at 55 and inlet manifolds at 56. After passing through the combustion chamber and heat exchanger, the incinerated exhaust gases pass through exit manifolds 57 and outlet tube 59. In FIGURE 4 the flow of gases is indicated by arrows. In FIGURES 5 and 6, inlets 55 and inlet manifolds 56, and outlet manifolds 57 are shown, but the outlet tube in each of these cases is located in the end of the device which is not shown. In FIGURE 7, a pair of inlets 55 and inlet manifolds 56 are used, with a corresponding pair of outlet manifolds 59 and outlets 57. Combustion chambers are indicated at 60 in all of these cases.
FIGURES 6 and 7 show the embodiments of the invention in which a plurality of heat exchanger units (crossflow units construction as herein described) are employed and illustrate the manner in which such a plurality of units may be arranged in accordance with the invention. Arrangements of any number of such units in series can of course be provided. The parallel arrangement of two heat exchanger units as shown in FIGURE 7 will be seen to be comparable to two separate units of the type shown, for example, in FIGURE 3 except for the central, rather than lateral, combustion chamber 60.
Referring to FIGURE 6, and as indicated by arrows, exhaust gases and any added supplementary air and/or fuel enter at inlet 55 to the inlet manifold 56 pass through the first heat-exchanger unit 50 into the intermediate space 51 and thence into the inlet side of the second heat-exchanger unit 56, from which the gases pass into the combustion chamber 60 provided with ignition means 15. On leaving the combustion chamber the gases pass in the opposite direction through the second heat-exchanger unit 50, into the intermediate space 53 and through the first heat exchanger unit 50 to the outlet manifold 57, and are then dissipated through the outlet tube (not shown). The intermediate chambers serve as alternative positions for combustion or partial combustion when gas pressures are reduced or increased so that the flame may pass out of the normal combustion chamber and as such serve as an additional safeguard against unsatisfactory combustion.
Referring to FIGURE 7, as shown by arrows, the exhaust gases and supplementary air are admitted at the dual inlets 55 to the dual inlet manifolds 56 and pass through the heat-exchanger units 50 to the central combustion chamber 66) provided with ignition means 15, where they mingle turbulently and are incinerated. The gases then pass cross-wise out through the heat-exchanger units 50 (any difference in back pressure determining volume of outflow), into the dual outlet manifolds 57 and are discharged through the outlet tubes 5?, either separately or after recombination into a common duct. The central combustion chamber permits a somewhat more rapid warm-up of the afterburner and better conservation of heat since there is less chance for dissipation of heat, and, in addition, offers the advantage of two units in that, for example, if one becomes plugged, the other is still functional.
Referring to FIGURE 8, as shown by the arrows, diluted process off-gases containing oxygen sufficient for combustion of the combustible portions thereof (as a result of the ventilation system employed) are introduced at into header 72 and distributed among the ports '74- into inlet plenum space '76 and then pass through heat exchanger where they are heated as described below into combustion chamber 82 having wall 84 and top 35 of steel which may be lined with a refractory material if desired. Simultaneously an auxiliary gas burner or igniter means is operated in combustion chamber 82 by means of a flammable gas-air mixture introduced through header 92 and inlet connections 93. In passing burner 90, the diluted process off gases are further heated and combustible components are oxidized during the period the said gases are resident in the combustion chamber so that by the time the gases pass through heat exchanger fill in the cross direction they are at an elevated temperature. A portion of their sensible heat is transferred to further incoming gases in heat exchanger 80. The partially cooled gases emerge from the heat exchanger into outlet plenum 86 and pass through outlet ports 88 into outlet header 89 and are vented to the atmosphere containing substantially only carbon dioxide and water as oxidation products of carbon and hydrogen present originally in combustible forms. It will be seen that heat exchanger 80 contacts simicircular blister 78 at three edges and is positioned by receiving guides which effect sealing between chambers 82 and inlet plenum '76 and outlet plenum 86 as well as between the latter two. Suitable means (not shown) are provided for initial ignition of the gas flame of gas burner 90.
Formation of the heat exchanger structures as illus trated in the drawings is readily accomplished according to the following procedure.
A plasticized raw material mix containing finely divided sinterable particles, plasticizing ingredients (as, for example, organic polymeric resins) and volatile viscosity adjusting media, is formed into a thin film or sheet material. Such film may be formed as by knife-coating or a temporary support, extrusion or the like, as long as it possesses sufficient body when free of viscosity adjusting fluids to retain its integrity after corrugation. The thick ness of the films employed for the purposes of this invention can range from 1 to 25 mils although films as thick as about 50 mils can be made and used if other dimensions are increased correspondingly. At least about 80 percent by weight of sinterable particles and sufficient organic polymeric plasticizing ingredients to lend a degree of flexibility to the film are used. The thin films used in the heat exchangers contribute to the thermal shock resistance of the fired structures, permitting them to Withstand a multitude of rapid and severe fluctuations in temperature without fracture, as well as permitting rapid heat transfer.
In the step of corrugation itself, it is preferable to support very thin plasticized green ceramic films on a thin sheet of metal foil, for example, aluminum foil, preferably of a thickness on the same order of magnitude as the film to be corrugated (but usually not greater than about 0.01 inch), or to sandwich the green ceramic film between two such metal foil sheets as it is passed between the corrugating rolls, suitably at room or elevated temperatures. While not absolutely necessary in all cases, the foil advantageously serves as a carrier to distribute corrugation stresses uniformly, aiding in obviating cracking or rupture of the films. Also, in the case of these film plasticized with ingredients which impart an elastic memory property to the film, at least one sheet of metal foil corrugated with the film is desirably left in position for a short time so as to maintain the corrugations in the film and prevent reversion to a fiat sheet.
Corrugations of the flexible films may be accomplished using standard corrugating equipment, and without undue pressure at low temperatures. Usually corrugations of uniform periodicity are formed, for example, corrugations of repetitive and uniform Wave shape, amplitude, and pitch. The corrugations most frequently employed are those of standard curved ridges and grooves; however, other wave shapes or configurations may be useful, as a minimum requirement, the amplitude of corrugations (that is, the elevation distance between the peak of a ridge and the lower-most portion of an adjacent groove) is at least as great as the thickness of the film that is corrugated, which means that the elevation distance between the peak of a ridge on one side of a corrugated film and the peak of a ridge on the opposite side of the film is at least twice as great as the thickness of the film itself. However, the heat exchangers employed for purposes of this invention generally utilize sheets having corrugations with amplitudes at least about five to ten times greater than the thickness of the film, and up to about twenty to thirty times this thickness.
While the sinterable flexible plasticized corrugated films and fiat sheets are in the green unfired state, they are sawed, cut and fabricated into heat exchanger assemblies such as illustrated in the drawings. Where the ridges of corrugated film are to be welded to a sinterable flat sheet member or panel, the basic raw material mix from which the sinterable film or sheet material was formed is diluted with organic solvents or fluids to adjust viscosity, and then painted over the ridges of the corrugations as a glue media for affixing a sinterable sheet member thereto. The solvent of the applied glue media between the ridges of corrugations and the sheet member may tend to solvate a portion of the adjacent film and sheet member before volatilizing into the air. In any event, once the structure is dried, a temporary bond between the ridges and the sheet member is formed, which, after the structure is fired to sintering temperatures, turns into a strong and rigid weld.
In the green unfired state, the corrugated structures and assemblies can easily be cut or sawed to shape, for example, trimmed to dimensional requirements; as well as bonded to elements which are intended to form part of the heat exchanger structure such as bafilles, locating studs and the like, as desired, using cement media or heat sealing as previously described.
Where solvent bonding is employed, the completed structural article is allowed to dry in air so as substan tially to remove volatile solvents or organic iiuids from its joints. Then the structures are fired using temperatues suitable for the sintering of the particular sinterable ingredients in the corrugated films and other portions of the structure, as well understood in the ceramic art.
Representative ceramic powders which are can be used to form heat exchanger units as used in the afterburner devices described herein include alumina, beryllia, zirconia, titania, petalite, cordierite, mullite and the like. It will be understood by those skilled in the art that the ceramic material used can be selected upon the basis of the service for which the heat exchanger is to be employed, and the known properties of the ceramic materials. Such factors as shrinkage on firing can be determined by simple empirical tests when not already known. Temperatures of firing and coefficients of expansion, melting points etc. are of course well known to ceramicists and need not be further elaborated here. It is preferable to use materials having low coeificients of expansion, such as coordierite and petalite, to eliminate problems connected with heat shock. Other ceramic materials can be used by properly designing the cross-flow heat exchanger to minimize stresses.
Polymers suitable as temporary binders include acrylates such as polymethyl methacrylate, polyacrylonitrile and polyacrylic acid; polyvinyl chloride, phenolformaldehyde resins and the like.
To further illustrate the invention, the construction and operation of the embodiment of the invention shown in FIGUKE l is described.
A casing of silicon carbide one-half inch thick and 7% inches internal diameter is provided with silicon carbide end plates about one-half inch thick. One of the end plates is fitted with inlet and outlet tubes of stainless steel cemented in place using a high temperature-resistant cement containing silicon carbide. The other is provided with an opening in which ignition means is attached. The combustion chamber need not necessarily be cylindrical but can be hemispherical or a combination of the two. The ignition means provided consists of a device supplied with raw fuel and air in correct proportions, a sparking means and means for blowing the hot gaseous products through the afterburner unit.
Since this unit is intended to demonstrate operating conditions it is also provided with means for removal of gases from various positions, for analysis and measurement of temperatures as described hereinbelow. It is found highly advantageous to provide an opening for admission of supplementary air to the combustion chamber and also a means for shutting off the flow of air when excessive temperatures are reached. Provision for supplementary fuel is made as will be evident when necessary as shown by analysis of the gases to be incinerated.
In producing a cross-flow heat exchanger for use in the automobile exhaust afterburner device of the invention, portions of green sheet material made from powdered cordierite with a temporary organic polymer binder are corrugated to 3 corrugations per inch, and other portions to 4 /2 corrugations per inch and a portion is retained flat. Squares of each shape are cut 6 inches on a side and assembled as follows: A flat Sheet is laid down and a 4 /2 corrugated sheet attached to it by means of a thin slurry of cordierite in the same binder dissolved in a volatile solvent therefor as a cement followed by a flat sheet, a 3 corrugated sheet at right angles to the first corrugated sheet and another flat sheet, etc. All the sheets are cemented as at first. This sequence is repeated, all of the corrugated sheets of same caliper opening on one face, until a block about 7 inches high is formed and finished off with a fiat sheet. The block is trimmed as needed to produced a shape 5% inches square and to give approximately straight sides and fired by heating it to 1650 C. over a period of 4 hours and then cooling it to room temperature over a period of 4 hours, without holding the article any extended time at the maximum temperature. The resultant ceramic unit, after cooling, is mounted with a high-temperature cement containing silicon carbide in the silicon carbide casing and the semicular bafiie of one-half inch thick silicon carbide and the ends are likewise cemented in place. The inlet opening gives access to the face of the heat exchanger where the corrugations are 4 /2 to the inch and the outlet to the other face with 3 corrugations per inch. While it is not essential to the success of this afterburner that the corrugations be different, there is somewhat less back pressure and better performance under these conditions particularly in view of the volume of supplementary air introduced. In general about 3 to 7 corrugations per inch are preferred for the cross-wise heat exchangers employed in the afterburner of the invention. However, since the corrugations serve to channel the flow of gases it will be apparent that other expedients, such as straight-walled partitions or the like, will serve for this purpose.
After assembly, the whole assembly is fired at 2100 F. to set the cement. This is done under conditions of slow heat-up and cooling, to minimize heat-shock.
As stated above certain provisions are made in this unit for testing purposes and supplementary air is admitted to 8 the combustion chamber through the base of the manifold supplying preheated exhaust gas thereto. The volume of supplementary air is of the order of magnitude of 20 per cent of the volume of exhaust gases. This is substantially in excess of the theoretical amount necessary. The engine employed for testing purposes produces about 32 to 35 standard cubic feet per minute (s.c.f.m.) of exhaust at 35 miles per hour and about 6 to 8 standard cubic feet per minute of supplementary air is sutficient for substantial incineration of the exhaust products under these conditions. For example, the hydrocarbon content (measured as n-hexane by a non-dispersive infra-red gas analyzer) drops from about 300 to about 40 parts per million. This figure does not take into account lower hydrocarbons or hydrogen which may be present, but these are apparently also reduced substantially. Carbon monoxide also drops by about percent from roughly 6 percent to about 0.5 percent. It is found that unless an excess of suppleientary air is available, incineration is less complete. The excess is such that considerably greater concentrations of combustiblcs than the usual limits can be burned at least partially with a resultant surge of total heat and temperature. Such concentrations may be reached during deceleration or engine malfunctioning. If this perists for long with temperatures above about 1800 F. there is considerable likelihood of fusing the ceramic heat exchanger. Accordingly, a limit device on the temperature is introduced in the combustion chamber which shuts off the flow of supplementary air when the temperature rises above 1850 F. and restores it when the temperature drops again. Because of the large volume of gas passing through this chamber, cooling occurs rapidly and the overall eficiency is still good although puffs of unincinerated exhaust pass through. For purposes of demonstration, the conditions necessitating this cut-off may be shown, if while the engine is running and the afterburner operating on exhaust gases containing about 300 p.p.m. of hydrocarbons, one ignition wire is removed so that one cylinder no longer fires. The hydrocarbons content of the gas rapidly rises to over 800 p.p.m. and the temperature in the combustion chamber of the afterburner rises and the cutoff operates to protect the ceramic from excessive temperatures. Outlet gases contain about p.p.m. of hydrocarbons. It is informative of the engine condition to have the cutoff switch also flash a light on the dashboard when supplementary air is off since repeated display of this signal indicates wasteful malfunctioning of the engine.
Provisions of the unit for testing purposes consist of thermocouples and tubes for gas sampling. The thermocouples are placed to measure temperatures as follows:
T Exhaust entering afterburner T --Exhaust plus supplementary air after preheating 3 Different locations in the combustion chamber 4 T Burned gases entering heat exchanger T Outlet from heat exchanger.
It will be noted that T T and T are substantially checks on one another varying mostly as a result of inherent errors in the individual thermocouples.
Gas samples are taken from the inlet (near T from the reactor (near T and from the outlet (near T The gases are analyzed for hydrocarbon content by use of a non-dispersive infra-red gas analyzer. The amount of hydrocarbons is expressed in parts per million of hexane. This neglects H and lower hydrocarbons, but these are included in the determination of total combustibles. The total amount of combustibles including carbon monoxide is determined by a total combustible analyzer calibrated as percent CO in N The gas samples are analyzed in an Orsat apparatus for carbon dioxide, oxygen and carbon monoxide. The carbon dioxide varies from about 11% to about 15%. Oxygen in the inlet gas (the engine exhaust) varies from about 1% downward to about 0.2%.
It is thus apparent that supplementary air is normally necessary.
Operation of the afterburner constructed as described above with the thermocouples and other accessories is demonstrated by mounting on the exhaust line from a 1957 Chevrolet 6 cylinder engine near the exhaust manifold to take advantage so far as possible of the higher temperasuch as acceleration and deceleration by these methods. In View of the consistent performance of the afterburner over this run of about 100 hours, it is apparent that it will adapt to transient conditions as well as other speeds and exhaust conditions to effect a substantial incineration of combustible components of exhaust gases from internal combustion engines using hydrocarbon fuels.
Table 1 Carbon Hydrocarbons 2 Total Secondary Monoxide Combustiblcs 3 Mileage 1 air it. 3/min. T T 'I T" Back Rpm. Pressure,
cm. 11g. Inlet Outlet Iniet Outlet Inlet Outlet 7. 5 780 1, 270 1, 770 1, 280 6. 7 3. 9 1. O 220 48 10 1. 3 1, 6110 7. 5 800 1, 320 1, 790 1, 3110 6. 7 4. 8 0. 7 272 48 9. 7 0.8 1, 600 7. 5 790 1, 320 1, 770 1, 280 6. 7 4. 9 O. 7 272 48 9. 5 0. 7 1, 600 7. 5 810 1, 350 1, 770 1, 290 6. 5 4. 9 0.8 272 40 10 1. 1 1, (500 Engine shut down for 8.5 hours 7. 5 800 1, 790 1, 280 5. 5 5. 4 0.7 304 40 10 1. 1, G00 7. 5 780 1, 390 1, 770 1, 260 5. 5 4. 9 0.7 256 32 1. 0 l, 500 7. 5 760 1, 390 1, 730 1, 240 5. 2 4. 8 0. 7 2 10 32 10 1. 0 1, 1100 7. 5 770 1, 140 1, 740 1, 260 5. 3 6. 8 0.8 10 2. 6 1, i300 Valves ground 7. 5 760 1,180 1, 760 1, 860 4. 2 5. 6 0.9 80 16 10 1. 6 1, 600 7. 5 790 1, 450 1,800 1, 290 3. i 4. 5 0. 9 136 48 10 1. 7 1, 690 7. 5 800 1, 500 1, 760 1, 300 2. 9 =1. 6 0. 7 160 32 10 1. 3 1, 600 6 680 1, 350 1, 580 1,100 1. 8 4. 3 1.1 152 32 10 2.0 1, 300 6 690 1, 390 1, 600 1, 120 1. 9 5. 4 1. 0 132 10 10 2. 1 1, 310 5 720 1, 550 1, 690 1, 0 1. 5 6. 3 1. 3 160 10 2. 0 l, 100 5 680 l, 580 1, 040 1. 3 6. 0 1. 1 168 64 1O 2. 1 1, 100 Adjust carburetor to leaner mixture (less eonibustlbles), no shut down 7. 5 l 750 1, 240 l ,680 I 1, 320 6. 0 5. 6 I 1.1 158 24 1O 1 75 1, 600
1 Initial odometer reading: 54,850. 7 Parts per million determined as n-hexane by infrared absorbtion.
3 Determined as percent CO in Nitrogen, by a. Total Combustibles Analyzer.
ture of exhaust at that point. Supplementary air is provided by compressed air supply. The engine is arranged to drive a generator to simulate the load of driving and is provided with manual throttle. During testing, the engine is stopped and the afterburner allowed to cool while maintenance on the engine is carried out, e.g. grinding valves. The engine is run under cruising conditions which are varied for times as shown. The table below shows temperature conditions and gas analyses at various times. The data have been consolidated by omission of non-material results, thus only T is given since T and T are substantially the same, and analytical results are confined to combustible substances omitting carbon dioxide and oxygen. Cruising speed is indicated as revolutions per minute. For this engine 1100 r.p.m.-25 m.p.h. 1300 r.p.rn.- m.p.m. 1600 r.p.m.- m.p.h.
In starting the operating of the afterburner, exhaust gases are passed through the device while choking the engine for several minutes and operating the ignition means. In this way, the afterburner is heated to about 1500 F. The choke is then opened and the incineration of the exhaust gases passing through the afterburner is self-sustaining. Obviously at low ambient temperatures operating conditions would require a longer preheat time. The results of a run are summarized in Table 1. It will be noted that these results all refer to cruising conditions since it is not feasible to anaylze relatively transient conditions An afterburner as shown in FIGURE 3 is constructed using a cross-flow ceramic heat exchanger made from alternating corrugated and flat plates composed of cordierite, in a manner similar to that described above. The overall length of the casing is 15 inches, the height overall 13 inches and the width 7 inches. The heat exchanger is about 5 inches on each side and about 15 inches long. Provision is made to insert three thermocouples in each of the plenum places opposite each of the four faces of the heat exchanger. These are numbered from 1 through 12 progressing in counterclockwise fashion from the upper battle. In each group the uppermost is positioned toward the back of the unit, the lowest near the forward end and the other at an intermediate position.
The unit is mounted on a 6 cylinder overhead valve engine of 235 cubic inches displacement (30.4 AMA horsepower) and after starting by use of the ignition means to bring the temperature of the combustion chamber to 1500 F. when self-sustained combustion com- 0 mences, the engine is run to establish equilibrium conditions at cruise speeds corresponding to about 30 or 35 miles per hour.
Those thermocouples in the inlet plenum space (numbers 7, 8 and 9) show no variations in temperature indicating good distribution of the entering gas. The data are further presented for each of 5 sets of results in the following tables 2 and 3. Supplementary air (about 8 s.c.f.m.) is introduced upstream of the afterburner except in set 2 when it is introduced in the combustion chamber.
Table 2 PHYSICAL MEASUREMENTS Temperatures Back M.p.l1. Run Combustion Chamber Pressure R.p.m. (approxi- Inlet Outlet to Atmosphere across unit mate) 7-9 cm. of Hg.
Inlet Outlet 1 Not measured.
aaagsaa These results show that the gases entering the afterburner at about 400-800 F. are heated by the gases passing toward the outlet. The afterburner does in fact usefully and significantly reduce the content of undesirable constituents of the exhaust gases.
The afterburners of the invention are useful in processing of industrial ofi-gases, for example, from varnish cooking. When varnishes are prepared, heating of the resins results in off-gases containing considerable concentrations of organic substances comprising, among other things, acrolein, phthalic and maleic anhydrides and fumaric acid. The total amounts and concentrations vary during the operation and some of the materials can be removed using a water scrubber. Incomplete combustion of the remaining substances may result in the formation of even, more undesirable substances. It will therefore be evident that adequate oxygen or air for complete combustion or incineration is necessary. Such exhaust gases from varnish making are commonly at about 80 F. as a result of scrubbing and dilution with air in the ventilation system and therefore it may be necessary to add supplementary fuels or employ auxiliary burners as shown in FIGURE 8 when simple combustion is used for their disposal, to provide the extra heat so that the exhaust gases have a dwell time of at least 0.5 second at 1200 F. or higher, which has been determined empirically to be necessary for complete incineration. Inasmuch as no useful products result from the incineration, the fuel costs represent an economic drain on the varnish cooking operation.
In an afterburner which is essentially a cylindrical refractory lined space 37 /2 inches in diameter and about 60 inches high (which provides a dwell time of 0.7 second) the fuel requirements to raise the temperature from 80 F. to 1220 F. of 950 standard cubic feet per minute of diluted off-gases are found to be about 33,000 B.t.u./ min. of which about one quarter represents heat losses through the Walls of the afterburner.
By making an afterburner of the invention incorporating a heat exchanger as shown in FIGURE 8, considerable saving in fuel consumption is possible. For this purpose a vertical semicircular blister is provided along the side of a vertical cylindrical steel chamber of the above dimensions, which may have a refractory lining, in which a ceramic heat exchanger as described above is positioned along three edges as shown in the figure. A heat exchanger having a square cross section nine inches on a side and 60 inches long, the height of the cylindrical chamber, provides significant recuperative effect. The diluted off-gas (collected along with large amounts of air from the cooking vessels) is supplied to one side of the heat exchanger and natural gas, i.e. methane, is introduced and burned in the combustion chamber near the opposite face. The gases pass the burner and peripherally around the chamber and leave through the heat exchanger in the crosswise direction. The diluted off-gas (at 80 F.) is heated to about 945 F. in passing through the heat exchanger and is further heated by the burner and by combustion in the combustion chamber to about 1500 F. before leaving. The heat consumption, not counting heat losses, is about 12,000 Btu/min. This compares with 24,500 B.t.u./ min. heat consumption for the afterburner in which heat is not recovered. A substantial economy is thus possible with a relatively simple construction. It will be evident that the burning natural gas is an effective igniter means for the combustible portions of the diluted off-gas and that supplementary oxygen or air for combustion of the combustible components or portions of the 0&- gases may be provided thereto in amounts at least sufficient for oxidation of the combustible components either upstream from the afterburner or in the combustion chamber.
What is claimed is:
1. A device for the incineration of combustible portions of waste gases containing at least sutficient oxygen for the oxidation of said combustible portions comprising in combination, a casing having at least one crossflow heat exchanger of generally parallelepipedal configuration positioned therein so that at least three corner edges of the heat exchanger contact the walls of the said casing and the spaces formed by the walls of the said casing connecting the corner edges of adjacent faces of the heat exchanger block form inlet and outlet plenums for the said waste gases and the space encompassed by the walls of the said casing not occupied by the said heat exchanger forms a combustion chamber; and ignition means in said combustion chamber.
2. An afterburner for combustible portions of the exhaust gases of internal combustion engines, comprising in combination, a casing having at least one crossflow heat exchanger of generally parallelepipedal configuration positioned therein so that corner edges of the heat exchanger contact the walls of the casing and the spaces formed by the walls of the said casing connecting the corner edges of adjacent faces of the heat exchanger block form inlet and outlet plenums for the exhaust gases and the space encompassed by the walls of the said casing not occupied by the said heat exchanger forms a combustion chamber; an igniter in said combustion chamber and means providing supplementary air to said exhaust gases for combustion thereof in said combustion chamber.
3. An afterburner for combustible portions of the exhaust gases of internal combustion engines, comprising in combination, a casing having at least one crossfiow heat exchanger of generally parallelepipedal configuration positioned therein so that at least three of the corner edges of the heat exchanger contact the walls of the casing and the spaces formed by the walls of the said casing connecting the first and second corner edges and the second and third corner edges, respectively, form inlet and outlet plenums for the exhaust gases and the space formed by the walls of the said casing connecting the third and first corner edges and any portion of the said casing not occupied by the said heat exchanger forms a combustion chamber; an igniter in said combustion chamber and means providing supplementary air to said exhaust gases for combustion thereof in said combustion chamber.
4. An afterburner for combustible portions of the exhaust gases from internal combustion engines, comprising, in combination, a generally cylindrical casing having at least one cross-flow heat exchanger block of generally parallelepipedal configuration coextensive with the length of said casing but having a diagonal dimension smaller than the largest diameter of said casing positioned therein so that two adjacent corner edges of the heat exchanger contact the part of the wall of the casing to form with one face of the said heat exchanger an inlet plenum, one of said corner edges and the next adjacent corner edge contacting another adjacent part of the wall of said casing to form with an adjacent face of said heat exchanger an outlet plenum, and the other corner edge of said heat exchanger being spaced from the wall of said casing, whereby the remainder of the casing wall and the other two adjacent faces of the heat exchanger form a combustion chamber; an igniter positioned in said combustion chamber and means providing supplementary air to said exhaust gases for combustion thereof in said combustion chamber.
5. An afterburner for combustible portions of the exhaust gases from internal combustion engines, comprising, in combination, a generally cylindrical casing having at least one cross-flow ceramic honeycomb heat exchanger block of generally parallelepipedal configuration coextensive with the length of said casing but having a diagonal dimension smaller than the largest diameter of said casing positioned therein so that two adjacent corner edges of the heat exchanger contact the part of the wall of the casing to form with one face of the said heat exchanger an inlet plenum, one of said corner edges and the next adjacent corner edge contacting another adjacent part of the wall of said casing to form with an adjacent face 01: said heat exchanger and outlet plenum the remainder of the casing wall and the other two adjacent faces of the heat exchanger forming a combustion chamber; an igniter positioned in said combustion chamher and means providing supplementary air to said exhaust gases for combustion thereof in said combustion chamber.
6. An automobile exhaust afterburner for the substantial incineration of combustible constituents of automobile exhaust gases comprising, in combination, 21 Casing having inlet and outlet means, ignition means, a combustion chamber, means providing supplementary air to said exhaust gases for combustion thereof in said combustion chamber and at least one cross-flow honeycomb ceramic heat exchanger unit of generally parallelepipedal configuration and coextensive in length with the said casing positioned therein in contact with portions of the walls of said casing on at least three corner edges whereby the faces included together with the wall portions connecting them from manifolding means to the said inlet and outlet means, and two faces of at least 14 one heat exchanger unit opening on said combustion chamber.
7. An afterburner for combustible portions of the exhaust gases of internal combustion engines, comprising in combination, a casing having at least one crossflow heat exchanger of generally parallelepipedal configuration positioned therein so that the corner edges of the heat exchanger contact the walls of the casing and the spaces formed by the walls of the said casing connecting the corner edges of adjacent faces of the heat exchanger block form inlet and outlet plenums for the exhaust gases and the space encompassed by the walls of the said casing not occupied by the said heat exchanger forms a combustion chamber, an igniter in said combustion chamber, and means for introducing supplemental air required for combustion of the said gases into the combustion chamber.
References Cited by the Examiner UNITED STATES PATENTS 3,086,353 4/1963 Ridgway 23288 FOREIGN PATENTS 1,090,466 10/1960 Germany.
References Cited by the Applicant UNITED STATES PATENTS 1,825,498 9/1931 Wogan. 2,03 3,402 3/ 1936 Smith. 2,946,651 7/ 1960 Houdry.
FOREIGN PATENTS 479,840 2/1938 Great Britain.
MORRIS O. WOLK, Primary Examiner.
JAMES H. TAYMAN, Examiner.