SE1251468A1 - Process and system for desulphurizing a post-treatment system - Google Patents

Abstract

The present invention relates to a method for desulfurizing a finishing system, said finishing system being adapted to treat an exhaust stream resulting from a combustion at an internal combustion engine, and wherein said finishing system comprises at least a first component. The method comprises, if sulfur has accumulated in said first component of said finishing system: - raising a temperature of said first component by supplying to said exhaust gas fuel for oxidation in said finishing system, - when said temperature of said first component reaches a first temperature, interrupting said supply of fuel to said exhaust gas stream, and - resuming supply of fuel for oxidation to said finishing system when said temperature of said first component has dropped to a second, compared to said first temperature, lower temperature.Fig. 5

Description

l0 l5 soot particles. Particulate filters are used to capture these soot particles, and work in such a way that the exhaust stream is led through a filter structure where soot particles are captured from the passing exhaust stream and stored in the particulate filter.

The particulate filter is filled with soot as the vehicle is driven, and sooner or later the filter must be emptied of soot, which is usually accomplished by means of so-called regeneration.

Regeneration means that the soot particles, which mainly consist of carbon particles, are converted to carbon dioxide and / or carbon monoxide in one or more chemical processes, and regeneration can take place in different ways.

Regeneration can e.g. happen with the help of s.k. N02-based regeneration, often also called passive regeneration. In passive regeneration, nitrogen monoxide and carbon monoxide are formed by a reaction between carbon and nitrogen dioxide. The NO 2 -based regeneration has the advantage that desired reaction rates, and thus the rate at which the filter is emptied, can be achieved at relatively low temperatures, which is advantageous especially when the finishing system comprises temperature sensitive components.

However, the N02-based regeneration is strongly dependent on the availability of nitrogen dioxide. If the supply of nitrogen dioxide is reduced, the regeneration rate will also be reduced.

The supply of nitrogen dioxide can e.g. is reduced if the formation of nitrogen dioxide is inhibited, which e.g. can occur if one or more components of the after-treatment system are poisoned by sulfur, when said sulfur normally occurs in at least certain types of industries, such as e.g. Diesel.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for desulfurizing at least one 10 15 component of a finishing system. This object is achieved by a method according to the characterizing part of claim 1.

The present invention relates to a method for desulfurizing an after-treatment system, said after-treatment system being arranged for treating an exhaust stream resulting from a combustion at an internal combustion engine, and wherein said after-treatment system comprises at least a first component and a second component. The method comprises, if sulfur has accumulated in said first component of said finishing system: - raising a temperature of said first component by supplying to said exhaust gas fuel for oxidation in said finishing system, - when said temperature of said first component reaches a first temperature, said first temperature being a temperature in excess of a temperature tolerance for at least one second component arranged downstream of said first component in said after-treatment system, interrupting said supply of fuel to said exhaust gas stream, and - resuming supply of fuel for oxidation to said after-treatment system when said temperature for said after-treatment system first component has dropped to a second, compared to said first temperature, lower temperature.

If e.g. a vehicle is used for a long time in such a way that the exhaust gas temperatures are kept relatively low, such as below 300-350 ° C, the sulfur fuel such as e.g. Diesel normally contains to chemically react with the active coating, often consisting of precious metals or other metals, which components of the finishing system usually include. In this reaction, sulfur molecules, e.g. in the form of sulphates to l0 l5 metal atoms / ions, whereby these metal atoms / ions can no longer participate in desired chemical reactions, ie. the component is poisoned by sulfur storage.

This poisoning takes different lengths of time depending on e.g. prevailing temperature in the after-treatment system, the exhaust gas flow and the purity of the fuel, ie. in this case the presence of sulfur.

The effect of sulfur storage can be exacerbated if regeneration is imminent. As mentioned, NO2-based regeneration is dependent on nitrogen dioxide NO2, and the sulfur poisoning results in the properties of the after-treatment system with respect to NO2 conversion, ie. conversion of nitrogen monoxide NO to nitrogen dioxide NO2 is adversely affected. This in turn means that the rate of NO2-based regeneration will decrease. In unfavorable conditions from a sulfur storage point of view, there is also a continuous further poisoning. In the worst case, a passive regeneration will be so slow that the filter, instead of being emptied, is filled up with additional soot so that the vehicle is eventually forced to stop to carry out a so-called parked regeneration, resulting in unwanted costs in time and fuel consumption.

The reduced NO2 conversion, i.e. the changed balance between N0 and N02 in the exhaust stream can also have a negative effect on exhaust gas purification in other ways. For example. the after-treatment system may comprise an SCR catalyst, e.g. downstream of a particulate filter, which is dependent on NO2 formation for the total NOX conversion.

The present invention reduces problems with sulfur poisoning of components in the aftertreatment system by, when sulfur poisoning is detected, cyclically raising the temperature of the component where sulfur storage has been detected. By cyclically raising the temperature and lowering the temperature, the temperature of components in the finishing system is “pulsed”. The component that is primarily exposed to the poisoning is the, seen from the internal combustion engine, the first (precious) metal-coated component meets the exhaust gas flow, such as e.g. an oxidation catalyst. The cyclic increase in temperature has the advantage that when the desulphurisation is strongly temperature dependent, a high temperature can be achieved in the component which is mainly poisoned, and by then allowing the temperature to drop to a lower level before the temperature is raised again, the temperature in subsequent components of the finishing system will not increase. to the same extent due to the thermal inertia of the components. Thus, the temperature of a sulfur poisoned component can be raised to a significantly higher temperature compared to what subsequent components have as a tolerance, which means that a good desulfurization can be obtained without risking damage to the subsequent components.

Additional features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

Brief Description of the Drawings Fig. 1A schematically shows a vehicle in which the present invention can be used.

Fig. 1B shows a control unit in the control system of the vehicle shown in Fig. 1.

Fig. 2 shows the finishing system in more detail for the vehicle shown in Fig. 1.

Fig. 3 shows an example of the regeneration (soot burn-out) rate as a function of the amount of soot in the particle filter, and its temperature dependence.

Fig. 4 shows the temperature dependence of oxidation of nitric oxide to nitrogen dioxide in an oxidation catalyst and the temperature dependence of the reaction rate on oxidation of carbon by means of NO 2.

Fig. 5 shows a method according to an exemplary embodiment of the present invention.

Fig. 6 shows a temperature diagram of a desulfurization process according to the present invention.

Detailed Description of Embodiments Fig. 1A schematically shows a driveline in a vehicle 100 according to an embodiment of the present invention. The vehicle 100 schematically shown in Fig. 1 comprises only one axle with drive wheels 113, 114, but the invention is also applicable to vehicles where more than one axle is provided with drive wheels, as well as to vehicles with one or more additional axles, such as one or more several support axles. The driveline comprises an internal combustion engine 101, which is connected in a conventional manner, via a shaft outgoing on the internal combustion engine 101, usually via a flywheel 102, to a gearbox 103 via a clutch 106.

The internal combustion engine 101 is controlled by the control system of the vehicle via a control unit 115. Likewise, the clutch 106, which e.g. may be an automatically controlled clutch, and the gearbox 103 of the vehicle control system by means of one or more applicable control units (not shown). Of course, the driveline of the vehicle can also be of another type such as of a type with conventional automatic transmission etc.

A shaft 107 emanating from the gearbox 103 drives the drive wheels 113, 114 via an end gear 108, such as e.g. a conventional differential, and drive shafts 104, 105 connected to said final gear 108.

The vehicle 100 further includes an after-treatment system (exhaust purification system) 200 for treating (purifying) exhaust emissions resulting from combustion in the internal combustion engine 101 combustion chamber (eg, cylinders).

The after-treatment system is shown in more detail in Fig. 2. The figure shows the combustion engine 101 of the vehicle 100, where the exhaust gases generated during combustion (exhaust gas flow) are led via a turbocharger 220. In turbocharged engines, the exhaust gas resulting from combustion often drives a turbocharger the air for the combustion of the cylinders. Alternatively, the turbocharger can e.g. be of compound type. The function for different types of turbochargers is well known, and is therefore not described in more detail here. The exhaust stream is then led via a pipe 204 (indicated by arrows) to a diesel particulate filter (DPF) 202 via a diesel oxidation catalyst (DOC) 205.

The oxidation catalyst DOC 205 has several functions, and is normally used primarily to oxidize residual hydrocarbons and carbon monoxide in the exhaust stream to carbon dioxide and water during the post-treatment. During the oxidation of hydrocarbons (ie oxidation of fuel) heat is also formed, which can be used to raise the temperature of the particle filter during emptying, so-called regeneration, of the particle filter.

The oxidation catalyst can also oxidize a large proportion of the nitrogen monoxides (NO) present in the exhaust stream to nitrogen dioxide (NO2). This nitrogen dioxide is used in e.g. N02-based regeneration. Additional reactions may also occur in the oxidation catalyst.

Furthermore, the after-treatment system comprises a SCR (Selective Catalytic Reduction) catalyst 201 arranged downstream of the particulate filter 202. SCR catalysts use ammonia (NH3), or composition from which ammonia can be generated / formed, as an additive for reducing the amount of nitrogen oxides NOX in the exhaust stream. However, the efficiency of this reduction depends on the ratio of NO to NO 2 in the exhaust gas stream, which is why this reaction is also adversely affected by reduced NO 2 conversion.

In the embodiment shown, the components DOC 205, DPF 202 and SCR catalyst 201 are integrated in one and the same exhaust gas purification unit. It should be understood, however, that these components do not have to be integrated in one and the same exhaust gas cleaning unit, but the components can be arranged in another way where it is convenient, and one or more of said components can e.g. consist of separate units. Fig. 2 also shows temperature sensors 210-212 and a differential pressure sensor 209, respectively.

In general, control systems in modern vehicles consist of a communication bus system consisting of one or more communication buses for interconnecting a number of electronic control units (ECUs) such as the control units, or controllers, 115, 208, and various components arranged on the vehicle. Such a control system can comprise a large number of control units, and the responsibility for a specific function can be divided into more than one control unit.

For the sake of simplicity, in Figs. 1A-B only the control units 115, 208 are shown.

In the embodiment shown, the present invention is implemented in the control unit 208, which in the embodiment shown above is responsible for other functions in the finishing system, such as e.g. regeneration (emptying) of the particle filter 202, but the invention can thus also be implemented in a control unit dedicated to the present invention, or in whole or in part in one or more other control units already present in the vehicle, such as e.g. motor control unit 115.

The function of the control unit 208 (or the control unit (s) to which the present invention is implemented) according to the present invention will, in addition to being dependent on sensor signals from one or more of temperature sensors 210-212, be likely to e.g. depend on information such as received from the control unit (s) controlling motor functions, ie in the present example the control unit 115.

Control units of the type shown are normally arranged to receive sensor signals from different parts of the vehicle. The control unit 208 can e.g. further receive sensor signals as above, as well as from other control units other than the control unit 115. Such control units are furthermore usually arranged to emit control signals to various vehicle parts and components. For example. the control unit 208 can emit signals to e.g. motor control unit 115.

The control is often controlled by programmed instructions. These programmed instructions typically consist of a computer program, which when executed in a computer or controller causes the computer / controller to perform the desired control, such as method steps of the present invention.

The computer program usually forms part of a computer program product, the computer program product comprising an applicable storage medium 121 (see Fig. 1B) with the computer program 109 stored on said storage medium 121.

Said digital storage medium 121 may e.g. consists of someone from the group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk drive, etc., and be arranged in or in connection with the control unit, the computer program being executed by the control unit. By following the instructions of the other computer program, the behavior of the vehicle in a specific situation can thus be adapted.

An exemplary control unit (control unit 208) is shown schematically in Fig. 1B, wherein the control unit may in turn comprise a calculation unit 120, which may consist of e.g. any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP), or an Application Specific Integrated Circuit (ASIC). The computing unit 120 is connected to a memory unit 121, which provides the computing unit 120 e.g. the stored program code 109 and / or the stored data calculation unit 120 need to be able to perform calculations. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit is provided with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals may contain waveforms, pulses, or other attributes, which of the input 122 devices 125, 125 may be detected as information for processing the computing unit 120. The output signals 123, 124 for transmitting output signals are arranged to convert calculation results from the computing unit. 120 to output signals for transmission to other parts of the vehicle control system and / or the component (s) for which the signals are intended. Each of the connections to the devices for receiving and transmitting input and output signals, respectively, may consist of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport), or any other bus configuration; or by a wireless connection. l0 l5 ll As mentioned, soot particles are formed during the combustion of the internal combustion engine 101. These soot particles should not, and in many cases should not, be released into the vehicle's environment. Diesel particles consist of hydrocarbons, carbon (soot) and inorganic substances such as sulfur and ash. As mentioned above, these soot particles are captured by the particulate filter 202, which works by directing the exhaust stream through a filter structure where soot particles are captured from the passing exhaust stream and then stored in the particulate filter 202. By means of the particulate filter 202 a very large proportion of the particles separated from the exhaust stream.

Thus, as particles are separated from the exhaust stream by means of the particle filter 202, the separated particles accumulate in the particle filter 202, this being filled up with soot over time. Depending on factors such as current driving conditions, the driver's driving style and vehicle load, a larger or smaller amount of soot particles will be generated, so this soot / particle filling takes place more or less quickly, but once the filter is filled to a certain level the filter must be "emptied". If the filter is met to too high a level, the vehicle's performance can be affected, at the same time as the risk of fire, due to soot accumulation in combination with high temperatures, may occur.

According to the above, emptying of particle filter 202 is performed by means of regeneration where soot particles, carbon particles, in a chemical process. Over time, the particulate filter 202 is regenerated at more or less regular intervals, and determining the appropriate time for regenerating the particulate filter can e.g. performed by means of a control unit 208, which e.g. can perform determination of the appropriate time (s) at least in part by means of signals from a pressure sensor 209, which measures the differential pressure across the particle filter. The more 10 l1 l2 the particle filter 202 is filled, the higher the pressure difference across the particle filter 202 will be.

Regeneration can take place in essentially two different ways. Partly through so-called oxygen (O2) -based regeneration, also called active regeneration, where a chemical process takes place mainly according to C + O2 = QO2 + heat. Thus, in oxygen-based regeneration, carbon plus oxygen is converted to carbon dioxide plus heat. This chemical reaction is highly temperature dependent and requires high particulate filter temperatures for a significant reaction rate to occur at all. At the same time, the temperature tolerance of the components included in the exhaust system is often limited, which means that the active regeneration can have a maximum permissible temperature which is low in relation to the temperatures required for the desired reaction rate to be achieved. The temperatures required for this type of regeneration for the desired reaction rate may thus be too high in relation to temperature tolerances for the components included in the finishing system. For example. often the particulate filter 202 and / or (where applicable) subsequent SCR catalyst 201 have design limitations with respect to the maximum temperature to which they may be exposed.

For this reason, NO2-based regeneration is often applied to such systems. In NO 2 -based regeneration, in particular, nitric oxide and carbon monoxide are formed in a reaction between carbon and nitrogen dioxide according to: NO 2 + C = NO + CO. Ie. the N02-based regeneration is strongly dependent on N02. The NO 2 -based regeneration has the advantage that desired reaction rates, and thus the rate at which the filter is emptied, can be achieved at significantly lower temperatures. Typically, particle filter regeneration occurs at NO 2 -based regeneration at temperatures 13 in the range of 200 ° C - 500 ° C, although temperatures in the greater part of the range are normally preferred.

This thus constitutes a significantly lower temperature range compared with active regeneration, which can completely fall below the minimum temperature desired during active regeneration. This is a great advantage in e.g. the presence of SCR catalysts, since the risk that such a high temperature level that damage to the SCR catalyst can occur can in principle be completely avoided. However, it is still important that a relatively high temperature is obtained.

Fig. 3 shows an example of the regeneration (soot burn-out) rate in NO 2 -based regeneration as a function of the amount of soot in the particulate filter 202, and for operating cases at two different temperatures (350 ° C and 450 ° C, respectively).

The regeneration rate is also exemplified for low and high concentrations of nitrogen dioxide, respectively. As can be seen in the figure, the burnout rate is low at low temperature (350 ° C) and low concentration of nitrogen dioxide. The temperature dependence of the regeneration rate is evident from the fact that the burn-out rate is relatively low even at a high concentration of nitrogen dioxide as long as the filter temperature is low. The burn-out rate is significantly higher at 450 ° C even in the case of a low concentration of nitrogen dioxide, but a high temperature in combination with high levels of NO2 is preferred.

Thus, the passive regeneration, in addition to being dependent on the temperature and amount of soot of the particulate filter according to Fig. 3, and as can be seen from the chemical processes above, is also dependent on the availability of nitrogen dioxide. Normally, however, the proportion of nitrogen dioxide NO2 in the total amount of nitrogen oxides NOX generated during the combustion of the internal combustion engine is only 0 -% of the total amount of nitrogen oxides NOX in the exhaust gas stream. When the 14 internal combustion engine is heavily loaded, the proportion of NO2 can even be as low as 2 - 4%. Thus, in order to obtain a rapid regeneration of the particulate filter, there is a desire that the proportion of nitrogen dioxide in the exhaust gas stream is as high as possible at the entry of the exhaust gas stream into the particulate filter 202.

Thus, there is also a desire to increase the amount of nitrogen dioxide NO2 in the exhaust gas stream resulting from the combustion engine combustion. This conversion can be performed in several different ways, and can be accomplished as above by means of the oxidation catalyst 205, where nitrogen monoxide can be oxidized to nitrogen dioxide.

However, oxidation of nitrogen monoxide to nitrogen dioxide in the oxidation catalyst also constitutes a highly temperature-dependent process, as exemplified in Fig. 4.

As can be seen in the figure, at favorable temperatures, the proportion of nitrogen dioxide in the total amount of nitrogen oxides in the exhaust stream (solid line) can be increased to up to 60%. As can also be seen in the figure, it would thus be optimal to have a temperature in the order of 250 ° C - 350 ° C during the passive regeneration in order to obtain as high an oxidation of nitrogen oxide to nitrogen dioxide as possible.

As described above, however, a completely different temperature condition applies to the burnout process itself. This temperature ratio is indicated by a dashed line in Fig. 4, and as can be seen, the reaction rate is in principle non-existent at temperatures below a particle filter temperature of 200-250 ° (the temperature indications shown are illustrative only, and actual values may deviate from these. the way in which the temperatures are determined / calculated can have an effect on the temperature limits (some ways to determine the temperature of the filter are exemplified below). l0 l5 The burn-out rate (regeneration rate) thus increases with the amount of NOx in the exhaust gas stream, the temperature of the exhaust gas stream (particulate filter) and the prevailing amount of soot in the particulate filter. Thus, the NO 2 -based regeneration requires a good supply of NO 2. As shown above, the NO 2 content of the total amount of NO X in the exhaust gas stream can be markedly increased by the oxidation catalyst 205, where the resulting NO 2 content after the oxidation catalyst 205 is strongly dependent on the temperature. However, the conversion of NO to NO 2 by means of the oxidation catalyst is not only dependent on the temperature of the oxidation catalyst, but also on whether the oxidation catalyst has been poisoned by undesired coating.

Depending on how a vehicle is driven, the temperature of the exhaust gas resulting from the combustion will vary. If the internal combustion engine is working hard, the exhaust gas flow will maintain a higher temperature, while, conversely, in the driving of the vehicle where the load on the internal combustion engine is relatively low, the temperature of the exhaust gas flow will be significantly lower. If the vehicle is driven for a long time in such a way that the temperature of the exhaust stream maintains relatively low temperatures, such as e.g. temperatures below 300-350 ° C, a degradation of the function of the oxidation catalyst will occur due to the fact that the sulfur commonly present in the fuel reacts in various forms with the active coating, usually comprising one or more noble metals or other applicable metals such as e.g. aluminum. This in turn adversely affects the properties of the oxidation catalyst with respect to the NO 2 conversion. The sulfur can react with the coating and e.g. form sulphates such as e.g. aluminum sulphate, platinum sulphate and palladium sulphate depending on the type of metal present in the coating. These 10 15 l 16 sulphates take up the surface of the active coating and prevent desired reactions, such as oxidation of NO to NO 2. Compared with NO 2 conversion in an unaffected oxidation catalyst, the NO 2 conversion in an oxidation catalyst with sulfur coating will thus give off a lower proportion of NO 2 under otherwise equal conditions.

This reduction in NO 2 conversion of the oxidation catalyst thus means that a smaller amount of NO 2 is available in the NO 2 -based regeneration of the particulate filter, thereby reducing the conversion of soot and thus the regeneration rate.

In severe cases of sulfur coating in the oxidation catalyst, a NO 2 -based regeneration, when carried out, will in the worst case proceed so slowly that the filling of soot is higher than the burn-out, which will lead to the filter being filled to such a high level that the vehicle is forced to stop to perform a so-called parked regeneration. According to the above, this gives rise to a loss of time with associated costs and also an increased consumption of fuel.

The reduced NO2 conversion can also have additional disadvantages. The after-treatment system may, as above, comprise an SCR catalyst, which is usually located downstream of the oxidation catalyst and the particulate filter. The SCR catalyst, for its function, depends on a good supply of NO 2 for the overall NO 2 conversion in the after-treatment system to meet set requirements.

According to the present invention, there is provided a process for effectively reducing problems arising from sulfur coating in the oxidation catalyst without the risk of subsequent temperature sensitive components being damaged. This is accomplished by a process 500 shown in Fig. 5. The process begins in step 501, where it is determined whether undesired sulfur coating of the oxidation catalyst has occurred. This determination can be performed in several different ways. For example. during an ongoing NO 2 -based regeneration, it can be determined that the regeneration rate is undesirably slow.

This determination can e.g. is performed by means of the differential pressure sensor 209 shown in Fig. 2, which measures the differential pressure across the particle filter 202. During regeneration, the differential pressure across the particle filter will decrease as the filter is emptied of soot particles and the flow resistance thereby decreases. If this differential pressure reduction decreases more slowly than expected during regeneration, which e.g. can be determined by comparing the rate at which the differential pressure decreases in relation to prevailing regeneration conditions, it can be determined that the regeneration rate is undesirably slow despite prevailing temperature conditions, thus indicating sulfur coating in the oxidation catalyst.

Whether or not sulfur coating has formed can also be determined in other ways. By e.g. based on the type of fuel used and a temperature history of a temperature representing e.g. the temperature of the oxidation catalyst, it is possible to estimate a degree of sulfur occupancy with the aid of applicable models. As mentioned above, the lower the temperature of the oxidation catalyst, the faster the sulfur coating will occur. The rate of sulfur coating also depends on the exhaust gas flow, and the higher the flow, the faster the active surfaces of the oxidation catalyst will be coated with sulfur. Sulfur coating of the oxidation catalyst can also be determined in other applicable ways.

Thus, when in step 501 it is determined that sulfur coating in the oxidation catalyst has occurred, e.g. to any applicable extent, where this e.g. can be controlled by regeneration rate, calculated coating or the like as above, the process proceeds to step 502, where a temperature T of the finishing system 200, such as e.g. a temperature representing the temperature of the oxidation catalyst 205. This determined temperature is then compared in step 503 with a minimum temperature T3, which is a temperature at which oxidation of unburned fuel is considered to be possible to the desired extent in the oxidation catalyst. If the post-treatment system temperature T (oxidation catalyst temperature) is below said temperature T3, the process proceeds to step 504 to attempt to achieve this oxidation catalyst temperature by motor control. In principle, it is sufficient for the oxidation catalyst to reach a temperature of approx. 250 ° C. Once engine control has begun, the process returns to step 502 to see if the desired temperature has been reached.

If, on the other hand, the oxidation catalyst temperature exceeds said minimum temperature T3, which can thus be in the order of approx. 250 ° C, and oxidation of unburned fuel in the oxidation catalyst is thus considered to be possible to the desired extent, the process proceeds to step 505.

In step 505, an increase of the temperature of the oxidation catalyst 205 is started, where the temperature increase can be effected as described below. The temperature of the oxidation catalyst should reach temperatures above 400 ° C for the accumulated sulfur to react with the passing exhaust gas stream. The bond of the sulfur with the metals of the coating can thus be broken, which can take place at least in part by the oxidation of hydrocarbons (fuel) reacting with oxygen atoms in e.g. sulfates so that sulfur in new molecular form detaches from the catalyst coating and is then passed with the exhaust stream 19 through the after-treatment system and / or re-solidifies downstream of the previous position. The chemical process in this respect can take place in several ways and is not described in more detail here, but when the binding of the sulfur with the coating metal is broken, the liberated / newly formed sulfur molecule, such as e.g. sulfur dioxide, sulfuric acid, or sulphite, with the exhaust gas stream to be removed from the oxidation catalyst or recaptured. One and the same sulfur atom can become trapped and released a large number of times during movement through the finishing system.

Heating thus means that the oxidation catalyst can be detoxified and its original NO2 conversion performance can be restored.

The desulphurisation process follows Arrhenius' equation and the process speed thus increases with increasing temperature. In other words, for best desulfurization efficiency, as high a temperature as possible should be achieved in the oxidation catalyst 205. As mentioned above, however, there are often different temperature tolerances with respect to the components included in the finishing system 200.

The temperature increase is achieved by supplying unburned fuel to the exhaust gas stream, where the unburned fuel then, thanks to the temperature T of the oxidation catalyst exceeding said minimum temperature T3, is at least partially oxidized, with associated heat evolution. In step 505, therefore, an applicable amount of fuel is determined for supply to the exhaust gas stream, whereby fuel injection is then started. The amount of fuel supplied can e.g. depend on the temperature of the oxidation catalyst 205, the actual flow in the exhaust stream, the internal combustion engine load, the actual vehicle speed, etc., or also constitute a constant predetermined amount of fuel, then the supply of fuel is controlled l0 l5 based on the oxidation catalyst temperature T in order to achieve a first and where the supply of fuel is interrupted when a desired first oxidation catalyst temperature T1 is reached or will be reached.

The supply of the unburned fuel to the exhaust gas stream can be carried out in several different ways. For example. For example, the aftertreatment system 200 may include an injector (not shown) in the exhaust system upstream of the oxidation catalyst 205, wherein fuel may be injected into the exhaust stream by the injector.

Alternatively, fuel may be supplied to the exhaust gas stream by injection into the combustion chamber of the internal combustion engine 11 (such as the cylinders of the internal combustion engine) so late in the combustion cycle that no or only parts of the regeneration fuel are burned in the cylinders. The present invention is applicable to both types of fuel injection.

When fuel supply has then been started according to any applicable model as above, the process proceeds to step 506, where it is determined whether the temperature T of the oxidation catalyst exceeds a first, compared with said minimum temperature T3, substantially higher temperature T1. This first temperature T1 consists of a temperature which would cause subsequent components to be damaged when heated to this temperature. According to the present invention, a cyclic increase of the temperature is performed for the component where sulfur storage has been found, i.e. in this case the oxidation catalyst 205, and due to the cyclic temperature rise, raising the temperature of subsequent components to undesirable levels will not occur.

As long as the temperature T1 is not reached, the process 21 returns to step 505 for continued fuel supply. If the temperature T1 has been reached, the supply of fuel to the exhaust gas stream is interrupted and the process proceeds to step 507. In step 507, it is determined whether the temperature T has dropped to a lower temperature T2 compared with the temperature T1. As long as this is not the case, the process remains in step 507, and then, when the temperature T has dropped to the temperature T2, proceeds to step 508.

Said first temperature T1 and said second temperature T2 are determined / selected so that the temperature at components downstream of the oxidation catalyst 205, such as e.g. the particulate filter 202 and the SCR catalyst 201, respectively, will not exceed impermissible levels.

Said first temperature T1 is preferably set to as high a level as possible, but which, in combination with the lowering of the temperature T1 of the oxidation catalyst 205 to the selected second temperature T2, ensures that the temperature arranged at the downstream oxidation catalyst 205, such as e.g. the particulate filter 202 and the SCR catalyst 201, respectively, will not exceed impermissible levels. For example. For example, the most temperature sensitive component in the present example may be the SCR catalyst 201, and according to the process of the invention it can be ensured that the temperature after the particle filter / at the inlet 203 of the SCR catalyst 201 does not reach undesirable levels.

Said second temperature T2 can be determined / selected based on a calculation / modeling of a temperature course of the temperature T of the oxidation catalyst 205 and / or the applicable temperature at components arranged downstream of the oxidation catalyst 205, such as e.g. the particulate filter 202 and the SCR catalyst 201, respectively. The said second temperature T2 may alternatively, or in combination with the above, be determined / selected based on measurements of temperature profile of the oxidation catalyst 205 temperature T and / or applicable temperature at downstream oxidation catalyst 205 arranged components, such as for example the particulate filter 202 and the SCR catalyst 201, respectively.

Said second temperature T2 is determined / selected so as to ensure that the temperature at components arranged downstream of the oxidation catalyst 205, such as e.g. the particulate filter 202 and the SCR catalyst 201, respectively, when using the process according to the invention will not exceed impermissible levels.

In step 508, it is determined whether the desulfurization is complete. If so, the procedure is terminated in step 509. This determination can be performed in any applicable manner, e.g. by determining for how long t desulphurisation has been going on, and interrupting the desulphurisation when the desulphurisation has been going on at least for an applicable first time tl. Alternatively, this can be determined e.g. in that heating to the temperature T1 must take place a certain number of times. The determination can also be performed based on the differential pressure change across the particle filter in a regeneration test. Ie. in this case, the differential pressure reduction obtained during regeneration during e.g. a certain time to at least some applicable level, otherwise the regeneration rate is considered to be too slow, and desulphurisation is thus not performed to the desired extent.

The desulphurisation can also be terminated based on another applicable parameter.

As long as desulfurization is to continue, the process returns to step 502 from step 509.

If fuel were to be supplied continuously to keep the oxidation catalyst 205 at a constant temperature, the temperature in the subsequent components would also rise to correspondingly high levels. Thus, a constant maintenance of the temperature T1 of the oxidation catalyst 205 at the level T1 would cause the temperature in subsequent components to become impermissibly high. The process of the present invention has the advantage that a higher desulfurization rate can be achieved by raising the temperature T of the oxidation catalyst 205 to a first temperature T1 exceeding a temperature tolerance of at least one of the components provided downstream of the oxidation catalyst 205, such as the particulate filter 202 and the SCR catalyst system. 200. By interrupting this temperature rise when the temperature T1 has been reached, i.e. interrupt the fuel supply, and allow the temperature T5 of the oxidation catalyst 205 to drop to said second temperature T2, the temperature in the components arranged downstream of the oxidation catalyst 205 will not have time to rise to impermissibly high levels before the temperature starts to drop again. Thus, by pulsing the temperature T of the oxidation catalyst 205, significantly higher temperatures can be allowed locally, with an associated increase in reaction rate, at the same time as this heat wave will be attenuated by the subsequent part of the oxidation catalyst 205 and e.g. a particle filter 202 so that e.g. an SCR catalyst 201 arranged downstream of the particulate filter is exposed to a substantially lower temperature compared to the oxidation catalyst 205. By means of the process of the present invention it is thus possible to raise the maximum temperature in the oxidation catalyst 205 by a relatively large number of degrees without sacrificing other requirements. , thereby also creating an opportunity to desorb as much as possible of stored sulfur. Fig. 6 shows an example of a temperature diagram for a part of a desulphurisation process according to the invention in a system of the type shown in Fig. 2, where a fuel supply according to step 505 is started at t = t0. The solid curve 601 represents the oxidation catalyst temperature, which is pulsed between the temperature T1-T2 as above, and the curve 602 represents the temperature after the particle filter 202, and thus the input to the SCR catalyst 201. At t = t1, fuel supply is interrupted and then resumed again at t = t2. to be interrupted again at t = t3 etc. As can be seen, the SCR catalyst 201 will be exposed to a significantly lower temperature compared to the oxidation catalyst 205 due to the attenuation due to the thermal inertia of the components to which the heat wave is exposed.

The process shown can also be further improved. During the pulsation of the temperature T above, the internal combustion engine 101 can also be adjusted to be operated with different lambda values. As is well known, lambda = 1 means a fuel / air ratio where stoichiometric combustion is obtained, and where larger and smaller lambda values mean an excess of air and a deficit of air, respectively, during combustion. The composition of the exhaust stream can be controlled against near stoichiometric conditions (ie lambda = 1) when fuel is added. Ie. in this case, the internal combustion engine is operated with the smallest possible lambda, whereby fuel is then supplied as far as possible without exceeding temperature requirements in order to end up close to stoichiometric conditions.

In this case, the oxygen level at the entrance to the oxidation catalyst 205 can be kept to a minimum, whereby hydrocarbons will react as far as possible with oxygen atoms in sulfur-metal bonds. According to one embodiment, said combustion engine and / or supply of fuel is controlled in such a way that a lambda value of less than 1.5 is obtained at the input of the oxidation catalyst 205.

When the fuel supply is switched off and the temperature eats down, the settings of the internal combustion engine 101 can be changed so that a considerably higher lambda is used and a rich excess of oxygen instead occurs in the system. In this way, it is possible to vary the conditions in the finishing system to optimize the desorption of sulfur bound in different compounds. The advantage of varying conditions in this way is that different sulfur compounds such as base metal-sulfur and precious metal-sulfur dissociate and desorb at different speeds.

The rate at which the temperature T is raised, which can be varied with the rate at which fuel is supplied, and lambda values can be adapted to the metals present in the finishing system in order to achieve as optimal a desulphurisation as possible.

The invention has been exemplified above in connection with the system shown in Fig. 2. The after-treatment system set-up shown in Fig. 2 is common in heavy vehicles, at least in jurisdictions where stricter emission requirements apply.

According to one embodiment, the particle filter instead comprises noble metal coatings so that the chemical processes present in the oxidation catalyst instead occur in the particle filter, the after-treatment system thus not comprising any DOC. However, the invention is also applicable here, whereby e.g. the temperature T1 is adapted to this system instead.

Furthermore, the finishing system 200 may also comprise more components than those exemplified above. For example, the after-treatment system in addition to, or instead of, the DOC 205 and / or SCR 201 may comprise an ASC (ammonia slip) catalyst (not shown), whereby the applicable temperature adjustment can also be performed here. Furthermore, the present invention has been exemplified above in connection with vehicles. However, the invention is also applicable to arbitrary vessels / processes where finishing systems as above are applicable, such as e.g. water or aircraft with combustion processes as above.

Further embodiments of the method and system according to the invention are found in the appended claims. It should also be noted that the system can be modified according to various embodiments of the method according to the invention (and vice versa) and that the present invention is thus in no way limited to the above-described embodiments of the method according to the invention, but relates to and includes all embodiments within the appended independent the scope of protection of the requirements.

Claims (17)

A method for desulphurizing an after-treatment system (200), said after-treatment system (200) being arranged to treat an exhaust stream resulting from a combustion at an internal combustion engine (101), and said after-treatment system (200). 200) comprises at least a first component (205, 202) and a second component (201), characterized in that the method comprises, if sulfur has accumulated in said first component (205, 202) at said finishing system (200): - raising a temperature (T) for said first component (205, 202) by supplying to said exhaust gas fuel for oxidation at said after-treatment system (200), - when said temperature (T) for said first component (205, 202) amounts to a first temperature ( T1), said first temperature (T1) being a temperature exceeding a temperature tolerance of at least one second component (201) arranged downstream of said first component (205, 202) in said after treatment system (200), interrupting said supply of fuel to said exhaust gas stream, and - resuming supply of fuel for oxidation to said after-treatment system (200) when said temperature (T) of said first component has dropped to a second, compared to said first temperature ( T1), lower temperature (T2). The method of claim 1, further comprising: - before said raising of said temperature (T), determining whether said temperature (T) of said first component (205, 202) exceeds a third, compared to said first temperature (T1) , lower temperature (T3), said fuel supply being started if said temperature (T) exceeds said third temperature (T3). 10 15 20 25 30 28 The method of claim 2, wherein said third temperature (T3) is an applicable temperature in excess of 250 ° C. A method according to any one of claims 2-3, wherein the method further comprises, if said temperature (T) is below said third temperature (T3), controlling said combustion motors (101) in such a way that a high exhaust temperature is generated. A method according to any one of the preceding claims, wherein said first temperature (T1) constitutes an applicable temperature in excess of 400 ° C. A method according to any one of the preceding claims, wherein said supply and interruption in supply of fuel to the exhaust gas stream is repeated until said first component (205, 202) has been desulfurized to the desired level, or the desulfurization is interrupted for other reasons. A method according to any one of the preceding claims, wherein said supplied fuel is at least partially oxidized in said first component (205, 202). A method according to any one of the preceding claims, further comprising directing said combustion motors (101) towards a first lambda value at said fuel supply, and towards a second, compared to said first lambda value, higher lambda value when said fuel supply is interrupted. A method according to claim 8, wherein said combustion meetings and / or supply of fuel are controlled in such a way that a lambda value of less than 1.5 is obtained at said first component (205, 202) at said fuel supply. A method according to any one of the preceding claims, wherein said combustion mats (101) comprise at least one combustion chamber, and wherein fuel for oxidation in said after-treatment system (200) is supplied to said after-treatment system (200) via supply via said combustion chamber. 11. ll. A method according to any one of the preceding claims, wherein said desulphurisation is interrupted when any of the following conditions are met: - a first time since the desulphurisation began has elapsed, - a regeneration rate exceeds a first regeneration rate. 12. l2. A method according to any one of the preceding claims, wherein fuel is supplied to said after-treatment system (200) by means of an injector arranged downstream of the combustion chamber of said internal combustion engine. A process according to any one of the preceding claims, wherein said at least one first component consists of at least one of an oxidation catalyst (205) and a particulate filter (202). 14. l4. Computer program comprising program code, which when said program code is executed in a computer causes said computer to perform the method according to any one of claims 1-13. A computer program product comprising a computer readable medium and a computer program according to claim 14, wherein said computer program is included in said computer readable medium. Sat. A system for desulfurizing an after-treatment system (200), said after-treatment system (200) being arranged to treat an exhaust stream resulting from a combustion at an internal combustion engine (10), and said after-treatment system (200) comprising at least a first component (205). , 202) and a second component (201), characterized in that the system comprises means for, if sulfur has accumulated in said first component (205, 202) at said finishing system (200): - raising a temperature (T) for said first component (205, 202) by supplying to said exhaust gas fuel for oxidation at said after-treatment system (200), - interrupting said supply of fuel to said exhaust gas when said temperature (T) of said first component (205, 202) amounts to a first temperature (T1), said first temperature (T1) being a temperature in excess of a temperature tolerance of at least one downstream of said first component (205, 202). arranged second component (201) in said finishing system (200), and - resume supply of fuel for oxidation to said finishing system (200) when said temperature (T) of said first component has dropped to a second, compared to said first temperature (T1). ), lower temperature (T2). Vehicle (100), characterized in that it comprises a system according to claim 16.