SE443830B - PROCEDURE FOR TREATING A GAS FLOW FROM A COMBUSTION ENGINE, INTERMITTENT CATALYTIC COMBUSTION OF PARTICLES, AND THEIR EQUIPMENT - Google Patents

Description

§ -; a2o11zo-5, n 2. which promotes the combustion of retained particles.

It must be taken into account that the generation of carbon particles is common under all operating conditions of a diesel engine. Furthermore, it is to be expected that the quantity and quality of an exhaust stream generated in an arbitrary internal combustion engine will vary according to the operating characteristics of the engine. The temperature range exhibited by an exhaust stream from a diesel engine can e.g. vary between slightly above ambient air temperatures and temperatures above 6500 C (1200 ° F).

When the exhaust gas is hot enough, carbon particles trapped in a filter will be burned. However, engine operating conditions in which this renewal can occur cannot always be achieved in diesel-powered passenger cars, buses or similar vehicles.

In cases where it has been found that the engine is constantly operating under such conditions that particles are continuously produced and accumulated in the filter, the particle collection filter bed must be rejuvenated at regular intervals.

When the exhaust gas is hot enough, rejuvenation or regeneration simply consists of introducing the hot exhaust stream, which contains enough oxygen, into the filter belts to be able to burn xvarnaiina carbon particles to ash in contact. However, the combustion of a potentially large, entrapped carbon pool can produce temperatures in excess of that of the exhaust gas. The result is that at such excessively high temperatures, the filter bed is sensitive to heat shock, damage or deformation.

An object of the present invention is to provide a method and apparatus capable of retaining combustible particles from an exhaust stream in a filter and periodically regenerating the filter by incinerating the retained particles to ash. This is to achieve a regulated speed for removing carbon from an exhaust stream with minimal damage to the filter. In a first aspect, the present invention relates to a method of treating an exhaust stream from an internal combustion engine, the exhaust stream being passed through a filter bed to retain combustible particles from the exhaust stream, the filter bed comprising a catalytic member to facilitate combustion. combustion, periodically burns the retained particles to ash in the filter bed by periodically heating the exhaust stream upstream of the filter bed to a temperature above the temperature at which the catalyst can initiate combustion of the particles, before fuel in the exhaust stream to produce a heated gas. and fuel mixture and passing the heated gas and fuel mixture through the catalytic portion to ignite the mixture and thus induce periodic combustion of the retained particles in the filter bed, which process is effected by dividing the exhaust stream upstream into the filter bed. part and a main part, that heating s The process comprises heating the smaller part to said temperature above the temperature at which the catalyst can initiate combustion of the retained particles and that the fuel is introduced into the heated smaller part of the exhaust gas stream.

Preferably, the smaller part constitutes between 1 and 10% by volume of the exhaust gas stream.

In a second aspect, the invention further relates to a device for treating an exhaust gas stream from an internal combustion engine "f _......'- .. '.:. ~ ......' _ '-.a .__' '___._ ..,; _;' s2o11so-s 10 15 20 25 30 35 with the features specified in claim S.

The invention thus provides a reaction chamber containing a filter bed, which includes a catalytic part, through which the exhaust gas stream passes. This catalytic surface may be incorporated into the filter bed, or it may be located at its upstream end.

To ensure that the main filter bed becomes functional regardless of the operating conditions of the engine, a part of the exhaust stream is preheated periodically by means of a heating device, e.g. an electric heater. This stream is passed into contact with the catalytic part, whereby the catalyst is raised to a temperature above the temperature at which the catalyst can initiate combustion of the particles.

Extra fuel is preheated by bringing it into contact with a hot surface of the filter.

The hot fuel is then injected into the heated part of the exhaust gas to form a fuel / exhaust mixture.

When the latter mixture comes in contact with the catalyst, it will ignite. When the oxidizing effect in the catalyst part becomes self-sustaining, the electric heating of the exhaust stream used in the initial stage can be interrupted. In some embodiments, the additive fuel does not need to be preheated, but preheating is preferred.

In summary, the main filter bed will be regularly flushed or rejuvenated by hot exhaust gas from the catalyst section. Such treatment, if repeated at predetermined times, will preclude carbon accumulations which, if not removed, may otherwise lead to thermal stress or damage to the filter bed at such times when the accumulated material is incinerated. Embodiments of the invention are described in more detail below in an exemplary form with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of a diesel engine. , provided with exhaust gas treatment according to the present invention; Fig. 2 is a partially sectioned view of the treatment apparatus; Fig. 3 is a more detailed sectional view of the apparatus; Fig. U is a diagram illustrating the operation of the apparatus; Fig. 5 is a partially sectioned view of a second embodiment and Fig. 6 is a more detailed sectional view of the second embodiment.

Referring to Fig. 1, in order to facilitate the description of the present system, an internal combustion engine 10 or other exhaust source is considered to be of the diesel type. In the latter, air is introduced in a continuous sequence from an air filter II by means of suction pipes 12 to the various combustion chambers. '' Diesel fuel is then injected in controlled quantities into each combustion chamber from a fuel pump 13. The flow rate of the fuel is regulated by means of accelerator pedal lü.

The hot exhaust stream is led from the exhaust manifold 16 and led via an exhaust pipe 18 to a smoke filter 17. Although a muffler can be inserted into the exhaust pipe, such an element is of secondary importance and not essential for the system and operation in question. * a2o113o-s 10 15 20 25 30 35 The exhaust gas stream, after leaving the exhaust manifold 16, will be at a temperature in a range from about 95 ° C to 65 ° C (about 120 ° F). The exact temperature will depend on the operating conditions of the engine.

At low speeds and idling, e.g. the exhaust gas to be relatively cold or only moderately heated. In connection with the particle quantity exhaust gas stream entering filter 17, the particles will as a result be retained along the many different channels inside the filter bed 19.

Although the exhaust gas is primarily composed of a combination of gases, it usually contains enough oxygen to support at least a limited degree of combustion in the stream as such.

Referring to Fig. 2, in one embodiment, filter 17 comprises an elongate metallic sheath 21, which at opposite ends has walls 22 and 23 which define an inner reaction chamber 2h. The latter chamber is to a large extent occupied by at least one filter bed 19, formed of a material which is particularly suitable for accommodating a large number of irregular flow channels through it.

The function of bed 19 is to delimit a series of channels, along which the exhaust gas will flow. During such a passage, particulate matter carried by the exhaust stream will be retained on the walls of the various ducts.

Bed 19 may preferably be formed of a metallic, mesh-like mass, such as e.g. steel wool, metal wires or similar material, which mass is designed to substantially fill the reaction chamber 2ü. Bed 19 is preferably supported at its ends upstream and downstream by means of perforated discs 26 and 27, gratings or other similar rigid, gas-permeable, transverse parts. The latter are located at the casing wall 21 to support the bed or beds 19 contained therein, in particular when the latter are weakened by heat.

The upstream filter wall 22 is provided with an inlet opening 28 for preheating and then the introduction of exhaust gas to the upstream side of bed 19. Similarly, wall 23 is terminated with an exhaust line 29 for discharging particle-free gases leaving bed 19.

In order to best achieve the gas filtration effect, bed 19 may comprise, as pointed out, a suitable, gas-permeable medium or matrix which is capable of retaining solid, particulate material from the exhaust gas stream. To facilitate the combustion of the retained particles into the ash, chamber exhaust gas entering the filter initially heats the catalyst-containing conical segment 32 of the filter by contact. With catalyst portion 32 then heated to "lightoff" temperature, additional fuel can be added to the heated exhaust gas to form a combustible fuel / gas mixture.

A portion of the catalyst bed 32, now at a temperature of about 230 to 300 ° C (60 ° C to 55 ° C), will feed the fuel-gas mixture. The fuel component, whether in liquid or gaseous form, together with the combustion-supporting oxygen in the exhaust stream will thereby ignite when it comes in contact with the hot catalyst surface.

By the time the fuel mixture begins to burn, the catalyst bed 32 will no longer require any preheating energy. As the combustion of the fuel-gas mixture continues in bed 19, the latter degree will gradually rise to about 70 ° C (120 ° F).

In connection with the heated exhaust gas stream entering main filter bed 19 from catalyst segment 32, the gas will have an elevated temperature of the same order of magnitude as in the catalyst bed. In an environment with such an elevated temperature, the particulate material retained on the main filter will be incinerated to ash and bed 19 will be left relatively particle-free.

In a preferred embodiment of the apparatus, the front end or upstream end of filter bed 19 is arranged adjacent to catalyst segment 32. The latter includes a matrix or filter medium with a thin layer of an oxidizing catalyst material located on the surface.

Although not shown here, catalyst segments 32 may be arranged at intervals to and upstream of filter bed 19, although not at such a distance that the exhaust gas will undergo cooling before it reaches bed 19.

In the present embodiment, as pointed out, catalyst segment 32 is located in the front part or upstream part of jacket 21. It extends perpendicular to the latter, so that it substantially comes into contact with the hot exhaust gas stream 1 in its entirety. .

To achieve preheating of at least a part of the exhaust gas stream, filter inlet 28 is provided with an electrically heated heating device 36. Included in this exhaust preheating section is also a supplementary fuel injection system. The latter comprises a fuel line part for transporting a stream of extra fuel, as described in more detail below, before it is injected into the hot exhaust gas stream. Referring to Fig. 3, inlet port 28 of filter 17 consists of a generally elongate tubular conduit which communicates with and limits a continuation. to the end wall 22. A second or inner conduit 37 is located internally in the conduit 28 to define between them an annular channel 38, through which a major part of the exhaust stream passes.

Although both parts, 28 and 37, are described as annular, the exact shape or cross-sectional contour of these is of relatively little importance, since it is only necessary for the respective ducts to direct the divided exhaust stream towards the catalyst bed 32. The second line 37 is supported at its opposite ends by means of a transverse sleeve 39 at the front end, which is attached with its periphery to the inside of conduit 28. The downstream end of conduit 37 is supported by a generally conically shaped gas deflector ül, the edge of which is round the periphery is connected to the inside of jacket 21.

The deflector U1 defines a successively tapered passage ü2 together with the adjacent filter end wall 22. A series of openings H3, arranged at intervals in both the longitudinal direction and around the periphery, allow untreated exhaust gas flowing through the annular passage 38 to be successively introduced into the catalytic segment 32.

The downstream end of the inner tubular member 37 is terminated by a gas diffuser NH. The latter includes a central chamber 36, delimited by an outer wall, in which a series of outlet openings H7 are formed. Chamber H6 is located to receive the hot stream of fuel / exhaust mixture and discharge this mixture radially by means of openings H7 into catalyst bed 32. In the latter case, the fuel / gas mixture comes into contact with the catalyst surface immediately. to ignite, if the surface temperature is at, or above the "ignition" temperature. Heating element 36 is located inside the inlet line 28 with a generally circular cross-section and placed to be in contact with at least a small or insignificant part of the exhaust stream coming from line 18. In the embodiment shown here, the heating device 36 consists of an elongate, band-like part, which is designed to delimit a substantially cylindrical passage H8 through the conduit.

Heating element 36 may alternatively be designed to define a helically shaped path, through which a part of the exhaust gas flows, the latter being heated as a result of contact with the guiding heating element walls.

In the embodiment shown, heating elements 36 extend longitudinally in inlet conduit 28 and are preferably coaxial therewith. In both cases, the exhaust stream entering the upstream end of inlet line 28 will divide into two branches. The main part of the flow passes into the annular passage 38. A small proportion flows into the inner passage NB, which is delimited by the heating element.

The heating element 36 is in one embodiment, and as shown in Fig. 3, in contact with the insides of the second tubular conduit 37. The latter will thereby cause radiant energy to be deflected inwards, in order thereby more efficiently. heat the gaseous flow flowing towards the diffuser NOW. In one embodiment and to enclose the gaseous stream, adjacent loops of the heating element 36 may be wound sufficiently close together to define a substantially closed central passage RB.

In terms of function, the main stream of exhaust gas, which comprises approximately 90 to §9 vol-1 and which enters the annular passage 38 from pipeline 18, will flow into the tapered passage H2 and thus through openings H3 10 15 20 25 30 35 8201130 -5 11_ in deflector Ål. The gas will then flow into the catalyst bed} 2.

In the latter, this unheated gas segment will be reunited with the insignificant, heated gas stream to thereby stabilize or lower the temperature of the latter. The smaller gas stream may comprise between about 1 and about 10 vol-1 of the total exhaust gas stream.

Although the heating element 36 is illustrated herein as a single, helically wound electrical element, the specific shape thereof may assume any of a number of embodiments. In addition, although the present embodiment of the heating unit delimits a passage H8 with a substantially constant cross-section, such a design is not necessarily necessary but rather is so that it is efficient.

For example. as mentioned heating element 36 can be designed so as to limit a passage with gradually decreasing cross-section. Furthermore, it may extend longitudinally in the second conduit 37 to define heated walls against which the exhaust stream flows. In all conditions, it is arranged so that it cooperates with diffuser NN to emit a hot gas stream to the latter for continued spreading. heating element 36 is operated between the on and off position by means of a suitable connection 33. The latter is connected through the wall of the line 28 to a timer 56 and from there to an electrical energy source SH.

The downstream end of passage H8 is provided with fuel injection details which are adapted to introduce a regulated flow of a liquid or gaseous fuel into the exhaust stream. At least one injection device 51 is arranged in connection with the NOW inlet of the diffuser and is provided with a nozzle 52 which terminates in the central passage H8. 10 15 20 25 30 35 8201130-5 12.

Fuel injection device 51 runs across the wall of the inlet line 28 and communicates therewith at an end outlet 53. The latter in turn communicates with a supply 57 of the supplementary fuel.

The fuel used to heat the exhaust gas may consist of a suitable liquid, such as diesel oil, kerosene or in the case of a gaseous fuel, propane. Furthermore, virtually any liquid capable of forming the desired fuel / exhaust mixture capable of being combustibly controlled can be utilized in the present case. e The supplemental fuel cycle, outside the filter, includes a pump ÉU or similar device capable of metering the required, regulated fuel flow to the injectors 51. The timing or metering mechanism 56 operates periodically affects the pump. The filter purge cycle can thus be programmed to allow the injection of a predetermined amount of supplemental fuel into the exhaust gas at desired time intervals.

Operationally, the filter flushing cycle begins in response to the on-B action of the timing mechanism, which affects the heating element 36. The exhaust gas stream flowing from line 18 is divided. Some of this enters the passage H8, which is limited by the heating element, and its temperature is further satisfied.

This exhaust heating step continues for as long as is necessary to bring the temperature of the exhaust gas at the downstream end of the heating element 36 to a predetermined temperature level before introducing the gas mixture into catalyst bed 32.

Since the catalyst bed surrounding diffuser NN must be raised to an "ignition" temperature of about 290 ° C tf 'rr-f- fl ëïï wf- * if-.L i 10 15 20 25 30 35 8201130-5 13 (550 ° F) the initial heating of the exhaust stream by means of heating element 36 will continue until such a state is reached in the catalyst bed 32.

Maintenance of the exhaust gas heating period can be established in a programmed time-controlled process. Alternatively, it may occur in response to a rise in temperature in the catalyst bed 32, determined by means of a suitable sensing body or thermocouple, which may be located in bed 17 and connected to timing or control mechanism 56.

When catalyst bed 32 has reached the desired temperature level, the control device 56 will initiate a flow of fuel through pump Sü and into the injector or devices 51. Thereafter, sufficient fuel flow is fed into the heated exhaust stream to provide a combustible fuel / exhaust mixture upon entry into diffuser section H6. From the latter, the heated fuel / exhaust mixture is fed by means of outlet openings H7 into the catalyst bed 32, where it is immediately ignited. The resulting combustion successively raises the temperature in the filter bed 19 to a level at which the retained particles will be combusted. Referring to Fig. 3 and Å, the diagram in the latter figure illustrates a compilation of data taken during a test run for to demonstrate the invention. During the experiment, a stream of hot exhaust gas 215 ° C (ü20 ° F) was introduced to filter inlet 28 (Fig. 3). Temperature measurements were made at points a and b (Fig. N) by means of thermocouples, which were located in the filter inlet 28 as well as in the filter bed. .

Supplementary fuel in the form of propane was added to the smaller segments of the exhaust stream, so that a combustible mixture was formed. This fuel was injected into the hot gas stream at a rate of 7.5 liters per minute beginning at time B. The smaller, heated exhaust gas stream was then allowed to pass in. in the catalytic segment of the filter together with the majority of the exhaust gas stream.

From Fig. N it can be seen that the thermocouple attached to a registers a steady increase in temperature starting at point A, when the electric heating element was started, and during the subsequent time period of 1.5 minutes to point B.

During this time period, the electric heater 36 was affected by the timing mechanism 56. The temperature in the smaller proportion of the exhaust gas rose from 2150 ° C (U20 ° F) to about 27 ° C (52 ° F).

At point B, the supply of electricity to heating element 36 was interrupted, and the introduction of propane fuel by injector 51 was initiated. When the heated fuel gas mixture came in contact with the heated catalyst bed 32, the latter present at "ignition" temperature caused the mixture to ignite immediately.

As can be seen from the diagram in Fig. H, the temperature in point a and as illustrated on curve a 'dropped sharply when the propane fuel was introduced into the gas stream. However, this sudden drop in temperature was only the result of cooling of the thermocouple as a result of its proximity to the nozzle 52, and not of a cooling of the entire fuel gas mixture.

With the heating element 36 disconnected, and with only the combustion of the fuel / gas mixture, the temperature in the main filter bed rose sharply. This increase was obtained as a result of combustion of particles retained in the filter beds and continued until a maximum temperature of about 650 ° C (1200 ° F) was reached.

To avoid excessive heating and possible damage to the filter bed, the flow of propane to the heated gas stream was regulated. The fuel supply (C) may have been interrupted, at which time the filter bed temperature dropped sharply.

Thereafter, the temperature in the bed was maintained at about the temperature of the exhaust stream. Operationally, the cyclic preheating of a portion of the exhaust stream is preferably repeated over a constant period of time. Thus, even though no significant amount of carbon particle material has been retained in the filter, the latter is nevertheless flushed periodically.

The amount of electrical energy used by heating elements 56 to preheat a portion of the exhaust stream is suitably reduced to a minimum. However, tank 57 with supplementary fuel is normally exposed to the effects of the environment and the fuel contained therein will consequently vary within a wide temperature range.

During periods of cold weather, the supplementary fuel can reach fairly low temperatures. When injected into the heated exhaust stream, it therefore tends to cool the latter too much, thereby prolonging the preheating period or cooling down the catalyst bed 52.

In order to avoid or reduce the degree of such cooling to a minimum, the supply of supplementary fuel can be initially brought into heat exchange contact with the filter 17 itself.

This will be described below with reference to the second embodiment of the invention shown in Figs. 5 and 6, where corresponding details are denoted by the same reference numerals as those used in Figs. 1 to 3. Preferably, heat energy, which is normally radiated from the filter body, is used to raise the supplementary fuel to a desired temperature. In addition, this fuel can be conducted in close proximity to heating element 36 to be indirectly heated by contact with the latter. e 10 15 20 25 30 35 8201130-5 .16 As shown in Fig. 5, supplementary fuel from tank 57, after leaving pump SN, is passed through a heat exchanger set or loop 62 by means of line 61. Loop 62 is preferably arranged in direct contact with the outside of jacket 21 in order to utilize as much heat as possible which is dissipated and radiates from the latter as far as possible.

Heat exchanger loop 62 may comprise one or more lengths of pipe, which are drawn in the longitudinal direction along the jacket 21. Alternatively, the heat exchanger device may comprise a single loop, which as shown is wound around and in contact with the wall of the jacket 21. In both cases, in order to minimize the heat loss to the atmosphere, the entire filter 21, or only the area outside the heat exchanger loop 62, can be lined or otherwise provided with an insulating layer 6ü.

As shown in Fig. 6, the initially preheated fuel, after being fed into the interior of the filter, is passed on through a second heat exchanger loop or set 63.

The latter is arranged in direct contact with the heating element 36.

The second heat exchanger set 63 may consist of a loop which is wound simultaneously with the loops in heating element 36 and in line contact with the latter. Alternatively, the second heat exchanger set 63 can be guided in the longitudinal direction along passage H8 to be in point contact with the respective heating element loops.

After the heated supplementary fuel has passed through heating set 63, it is in any case led to the fuel nozzle 52. The heated fuel stream then goes into the passing exhaust stream, so that a heated fuel / gas mixture is formed. This preheating of the supplementary fuel, before it later enters the exhaust gas stream, has the task of maintaining the temperature in the exhaust gas in connection with the latter leaving heating passage H8. When the fuel gas mixture enters diffuser RU, it will then be at a desired ignition temperature for the catalyst bed 32, so that the mixture can be safely guided radially outwards into the catalytic section 32 for ignition therein in a manner similar to that of the first embodiment.

Claims (10)

'' izw fi ïïñ fl Wr »" “a2o11so-s, 8 10 15 20 25 30 35 ggtentkrav A method of treating an exhaust stream from an internal combustion engine, wherein the exhaust stream is passed through a filter bed to retain combustible particles from the exhaust stream, the filter bed comprising a catalytic portion to facilitate combustion, periodically burning the retained particles to ash in the filter bed by periodically heating the exhaust gas stream upstream of the filter bed to a temperature above the temperature at which the catalyst can initiate combustion of the particles, introducing fuel into the exhaust stream to produce a heated gas and fuel mixture and conducting the heated gas and fuel mixture. the fuel mixture through the catalytic part to ignite the mixture and thus induce periodic combustion of the retained particles in the filter bed, characterized in that the exhaust stream upstream of the filter bed is divided into a smaller part and a main part, that the heating step comprises heating the smaller the part to said tempe above the temperature at which the catalyst can initiate combustion of the retained particles and that the fuel is introduced into the heated smaller part of the exhaust gas stream. 2. A method according to claim 1, characterized in that the smaller part constitutes between 1 and 10% by volume of the exhaust gas stream. 3. A method according to claim 1 or 2, characterized in that the catalytic part is arranged in the upstream end of the filter bed and that the main part of the exhaust gas stream is led into the catalytic part parallel to the passage of the smaller, heated gas and fuel mixture part into in the catalytic part. 4. A method according to one or more of claims 1 - 3, characterized in that the fuel is preheated through a heat exchange contact, before the fuel is introduced into said heated smaller part of the exhaust gas stream. .l%,% uß & ¿mrm » An apparatus for treating an exhaust stream from an internal combustion engine, comprising a jacket (21) defining a chamber (24) between an inlet (28) and an outlet opening (29) for the exhaust stream, a filter bed (19, 32). ) in the chamber for retaining combustible particles from the exhaust stream, which filter bed comprises a catalytic part (32) for facilitating combustion. In a heating element (36) which is arranged in the inlet (28) and can operate periodically for heating the exhaust stream to a temperature above the temperature at which the catalyst can initiate combustion of the particles, means (51, 52) for introducing fuel into the inlet (28) to provide a heated gas and fuel mixture and device (46) for feeding the heated gas and fuel mixture through the catalytic part to ignite the mixture and thus induce periodic combustion of the retained particles in the filter bed, provided that the inlet (28) limits a mi lower, inner flow passage (48) and a separate, larger, annular, outer flow passage (38), the heating element (36) being arranged in the characteristic - smaller flow passage (48) for heating the smaller part of the exhaust gas stream to said temperature above the temperature at which the catalyst can initiate combustion of the retained particles and that the fuel introduction means (51, 52) are arranged to introduce fuel into the heated, smaller part of the exhaust gas stream. Device according to claim 5, characterized in that the devices for introducing fuel comprise a fuel supply line (62, 63), arranged in heat exchanger contact with the device for preheating the fuel, before it is introduced into the inlet (28). Device according to claim 6, characterized in that the M k * * 10 15 8201130-5 80 fuel line (62) is in heat exchanger contact with an outer surface of the jacket (21). Device according to Claim 6 or 7, characterized in that the fuel line (63) is in contact with a heat exchanger with the heating element (36). Device according to one or more of Claims 6 to 8, characterized in that the fuel line (63) extends into the inlet and is provided with a nozzle (52), the opening of which is directed downstream in relation to the heating element. (36). Device according to one or more of claims 5 - 9, characterized in that the heating element (36) comprises an elongate electrical element, designed to delimit a gas flow passage (48) in the inlet opening. : IW '