FIELD OF THE INVENTION

The present invention relates to a method and system for cleaning filters, and in particular filters for exhaust particles from combustion engines, such as diesel particle filters.

BACKGROUND OF THE INVENTION

There is an increasing demand on the environmental aspects of pollution to decrease the negative effects and thus the amount of pol lution . One source of poll ution of the environment is exhaust gases from combustion engines in vehicles such as cars, buses and the like.

The exhaust gases have become less harmful during the last two decades thanks to more advanced emission control and catalysts. Also diesel engines have become cleaner thanks to catalysts. During recent years, many diesel powered engines have also been equipped with particle filters, for further reducing the amount of pollutants in the exhaust gases.

The particle filters are very efficient in collecting particles and many vehicles have a certain cleaning procedure at certain intervals, wherein the filter is heated in order to try and remove the collected particles. However, even if some of the particles are burnt off during this procedure it is not so efficient as to completely clean the filters, and thus after a certain time the filter has to be replaced. The replacement of the filter is rather costly for the vehicle owner and the filter should be able to be used further if cleaned because the material of the filter, stainless steel and ceramics, have not been degraded during use, if the filter has not been exposed to physical damage, and thus the filter could be reconditioned. This would in turn mean cheaper spare parts for the owners as well as reduced use of material resources.

To service a device such as a diesel particulate filter, it is known to manually move a focused stream of pressurized air back and forth across the outlet side of the filter to loosen soot/ash that has collected on the filter. For example, a dry air gun (e.g., 50-100 psi) can be used as a source of pressurized air. WO2008091218A1 discloses a method of cleaning a particle filter, in particular for combustion engines, comprising the steps of: - a) applying heat to the interior of the particle filter during a certain time period for burning the trapped particles, - b) removing the burnt particles from the particle filter, - c) measuring the particle filter, wherein the measurements are compared to values of an unused filter of the particular type, and if the measured values deviate from the values of the unused filter by a predetermined amount, steps a) to c) are repeated until the measured values are within an approval range. It is mentioned that the removal of burnt particles is performed by blowing air into the particle filter.

WO06096244A1 discloses an apparatus for combusting soot from a diesel engine exhaust aftertreatment device. The apparatus includes a cabinet having a housing, a heating element positioned within the housing of the cabinet, and a mounting arrangement for securing the diesel engine exhaust aftertreatment device above the heating element. The apparatus also includes an ash collection container mounted beneath a floor of the housing for collecting ash that falls from the diesel engine exhaust aftertreatment device during heating.

EP1698765A1 discloses a pulse cleaner for cleaning a diesel exhaust treatment device. The pulse cleaner includes a cabinet, a diesel exhaust treatment device positioned within the cabinet, and a collection filter positioned within the cabinet for collecting material displaced from the diesel exhaust treatment device during cleaning. The pulse cleaner also includes a pulse generator for generating pulses that are each directed at a majority of a face of the diesel exhaust treatment device when the diesel exhaust treatment device is mounted at the diesel exhaust treatment device mount. The pulse generator includes a pressure tank for accumulating pressurized air, and a valve arrangement that flushes the pressurized air from the tank. A pulse of air for cleaning the diesel exhaust treatment device is generated each time the tank is flushed. What is needed is an improved method for servicing overloaded diesel particle filters or other exhaust aftertreatment devices. SUMMARY OF THE INVENTION

The present invention solves the above mentioned problems associated with prior art methods of cleaning diesel particle filters. Specifically the present invention provides a method for cleaning a diesel particle filter, in particular for combustion engines, comprising the steps of:

• positioning the diesel particle filter within a cleaning cabinet, said particle filter positioned upright with the outlet side upwards and the inlet side downwards;

• applying a flow of hot air to the interior of the particle filter from the outlet side, wherein

o the flow of hot air is generated by blowing ambient air at a flow between 10 and 100 m ³ /hour through a heating element with an effect of 6-24 kW to increase the temperature of the air to 600 C-700 C; and

o the flow is increased to compensate for thermal buoyancy resulting from heating the particle filter;

• continuing the flow of hot air for 30 to 90 minutes, preferably 30 to 60 minutes, wherein the flow of hot air is briefly increased with 50 to 100% for at least 10 seconds at least every 15 minutes;

• applying a flow of ambient air at a temperature of between 10 and 40 C for less than an hour;

• removing the diesel particle filter from the cleaning cabinet after cleaning.

In a preferred embodiment of the present invention the flow of hot air is generated by blowing ambient air at a flow between 30 and 70 m ³ /hour through a heating element with an effect of 9-18 kW.

In a particularly preferred embodiment of the present invention the flow of hot air is generated by blowing ambient air at a flow between 40 and 60 m ³ /hour through a heating element with an effect of 10-14 kW.

Preferably the diesel particle filter includes a ceramic substrate having a honey-comb configuration of plugged passages. More preferably the diesel particle filter includes silicon carbide or cordierite. In one embodiment of the present invention the diesel particle filter includes a wire mesh. In a preferred embodiment the diesel particle filter includes corrugated metal foil. In order to establish the flow of hot and cold air a blower is used to blow air through the diesel particle filter.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a flow chart of the method according to the invention. Fig. 2 shows schematically a setup for cleaning particle filters for vehicles according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, references are made to the accompanying drawings that depict various embodiments which are examples of how certain inventive aspects may be practiced. It is to be understood that other embodiments may be utilized, and structural and functional changes may be made without departing from the broad scope of the inventive aspects.

The present disclosure relates to a method for efficiently and effectively cleaning diesel particle fi lters (DPF) or other exhaust aftertreatment devices. I n one em bodiment compressed air is used to back flush collected material (e.g. , soot, ash or other material captured from engine exhaust) from DPF.

Throughout the specification, cleaning devices and methods are described primarily with respect to cleaning diesel particulate filters. However, it will be appreciated that the same methods can be used to clean other types of engine exhaust aftertreatment devices as well. Other example aftertreatment devices that may require servicing include catalytic converters, lean NOx catalyst devices, selective catalytic reduction (SCR) catalyst devices, lean NOx traps, or other devices for removing pollutants from the exhaust stream. The methods and cleaners can also be used to clean other types of filters/treatment devices, and are not limited exclusively to engine exhaust aftertreatment devices. Diesel particulate filter substrates can have a variety of known configurations. An exemplary configuration includes a monolith ceramic substrate having a "honey-comb" configuration of plugged passages as described in U .S. Patent no. 4,851 ,015. This type of filter can be referred to as a wall-flow trap or filter. Common materials used for wall-flow filters include silicon carbide and cordierite. Wire mesh, corrugated metal foil and other flow-through type filter configurations can also be used. I n certain embodiments, the filter substrate can include a catalyst. Exemplary catalysts include precious metals such as platinum, palladium and rhodium, and other types of components such as base metals or zeolites.

As described herein, DPF or aftertreatment devices are described as having inlet sides or faces and outlet sides or faces. The inlet side or face of an aftertreatment device is the side that faces the incoming flow of exhaust when installed in an exhaust system. The inlet side can be referred to as the "dirty" side since it is the side at which material filtered from the exhaust stream collects. The outlet side or face of an aftertreatment device is the side that faces away from the incoming flow of exhaust when installed in an exhaust system. The outlet side can be referred to as the "clean" side.

Figure 1 shows a schematic flowchart of the method according to the present invention. The particles filter to be cleaned is first visually inspected for visual defects such as cracks, damaged fittings and the like.

The next step is then to clean the interior of the particle filter. According to the present invention this is performed by burning off the soot and carbon compounds that have been deposited on the filter surfaces.

Finally the particle filter is cooled with a flow of ambient air and ultimately mounted in an exhaust system of a vehicle. The particle filter is connected to a flow of heated air. A mass flow controller is arranged to control the air flow. Then the air is preheated before entering the particle filter. The particle filter is heated to temperatures above the exothermic reaction of the soot when it is burnt off, but not too high, thereby avoiding damaging the ceramic filter surfaces. Temperature sensors are arranged to monitor the temperatures. During this step the carbon compounds are burnt off the filter surfaces during which the flow is increased to compensate for thermal buoyancy resulting from heating the particle filter. Typically the temperature of the hot air is increased in accordance with a predetermined heating curve, which curve dictates the applied temperature at a given time. The end of the process could be performed in a few different ways. The most simple is to end the heating after a predetermined time period, which time period is based on empiric studies of different types of particle filter. Another way is to measure the amount of burnt particles during the heating process. In that aspect, the particle filter may be subjected to bursts of air injection through it with certain time intervals. The air bursts cause the burnt particles to be ejected from the filter. The amount of particles could then be used as a measurement of when the burning process can be terminated.

Figure 2 shows an apparatus (1 ) for cleaning a particle filter (2) according to the present invention. The outlet (clean) side of the particle filter is releasibly attached to a pipe (3) comprising a heating element (6). The pipe (3) is connected to an air source (5) and a fan (4), where incoming air is heated by the heating element (6) before entering the particle filter (2). The air (containing burnt particles) leaving the inlet (dirty) side of the particle filter (2) enters a mixing chamber (7), wherein the air is mixed with (cold) ambient air (9) blown into the apparatus through a second fan (8). The mixed air is then forced through a filter (10) before leaving the apparatus (1) as clean air (1 1).

Even though some examples have been mentioned above, it is to be understood that other types of equipment, systems and principles can be utilized for performing the method according to the present invention. Therefore the embodiments described and shown in the figures are to be regarded as only non-limiting examples of the present invention and that it may be modified within the scope of the patent claims.