Device for cleaning of air filters

TECHNICAL AREA

The present invention relates to a method and system for cleaning of filter and in particular filter for exhaust particles from combustion engines. The present invention also relates to methods for measuring of the cleaning result.

TECHNICAL BACKGROUND There is a growing demand on the environmental aspects of pollutions in order to reduce the negative effects and thus the amount of pollution. A source of pollution in the environment is the exhausts from combustion engines in vehicles such as cars, lorries, busses and the like.

The exhausts have been less harmful during the last two decades thanks to more advanced emission control and catalysts. Also diesel engines have been cleaner thanks to catalysts. During the recent years many diesel engines have been equipped with particle filters in order to further reduce the amount of pollution in the exhausts.

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

A method and a system has been developed by the applicant of the present application, which is described in the patent application No. PCT/SE2008/050082. This highly effective method comprises heating of a particle filter and supply of oxygen in order to remove soot in the clogged filters by burning. The method has received a lot of attention from the vehicle industry where reconditioning is a steadily growing sector.

BRIEF DESCRIPTION OF THE INVENTION In order to meet the demands on reconditioned particle filters the present invention has been developed and in particular to clean clogged particle filters in a more automated way and on a larger scale.

The present invention is characterised by the features of the independent patent claims. Preferable embodiments of the invention are characterised by the dependent patent claims.

According to a main aspect of the invention it is characterised by a device for cleaning of particle filters, comprising an enclosure in which at least a number of particle filter can be placed, heating means for heating of the enclosure, means for air supply into the interior of the filters to be cleaned, heat exchange means arranged in said enclosure for heating of the air that is supplied to the particle filters, which air is used for burning of particles in the filters.

According to another aspect of the invention, the air supply means comprises an air pipe conduit, that the heat exchange means comprises a number of loops of the air pipe conduit, which loops are arranged in the enclosure.

According to a further aspect of the invention, the air supply means further comprises a source of pressurized air and means for controlling the air to the filters.

According to a further aspect of the invention it further comprises temperature sensors for the respective filter, for sensing the temperature inside the filters during burning.

According to yet an aspect of the invention, data from the temperature is used for controlling the amount of air to the filter for controlling the burning.

According to another aspect of the invention it further comprises a source of carbon dioxide, connections between the carbon dioxide source and the respective particle filter and control means for controlling the supply of carbon dioxide to the filters for controlling the burning.

The advantages with the present invention are several. Due to that the heat exchange means are arranged inside the heated enclosure, where air to the burning of soot and other particles in the filters pass through the heat exchange means, a heating of the air is obtained in a very simple and yet reliable way. No complicated equipment or components are required in the oven.

Because each filter is connected to an air supply loop of its own and that this is arranged with flow controlling means, the amount of air can be controlled individually to each filter, which is an advantage when all filters behave somewhat differently during burning. When also each filter is arranged with a temperature sensor that controls the temperature during burning, the air supply may be controlled in a very reliable way, whereby too high temperatures may be avoided, which otherwise would risk damaging the filters.

If however there is a risk that the temperature should reach critical levels despite the throttling of the air supply, it is possible with the device to supply carbon dioxide in order to reduce the burning and thereby lower the temperature.

Preferably a control system is arranged that automatically handles the burning of all filters in the oven with the aid of sensors and control means for supply of air or carbon dioxide.

These and other aspect of and advantages with the present invention will be apparent from the following detailed description of the invention and from the attached drawings.

SHORT DESCRIPTION OF THE INVENTION In the following detailed description of the invention, reference will be made to drawing 1 which schematically shows a system for cleaning of particle filters in which the present invention is comprised.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows schematically a system for cleaning of a particle filter. The system comprises an enclosure 10 arranged with a heating unit 12, such as a heating furnace, in which a number of particle filters 14 can be placed.

The system further comprises a circuit 16 for supply of air or oxygen to each filter. Each branch 20 comprises an adjustable valve 22 for controlling the air to the filter and a flow meter 24. Inside the oven each branch is arranged as a loop 26 with a length of a number of meters, the function of which will be explained below.

Each particle filter is further arranged with a temperature sensor 28 placed inside the filter. Also a pressurised container is arranged which contains carbon dioxide. The carbon dioxide container is connected to a circuit 32. The circuit contains a number of branches 34 where each branch is

arranged with a control valve 36. Each branch is connected to the branch 20 for the air downstream its control valve 22.

The system is intended to function as follows. First a blowing or suction process is preferably performed in order to remove loose particles in the filter in order to perform a pre-cleaning in a first step. In this aspect it is conceivable to perform measures against the type of ash plugs 2 that often occur in the innermost part of a channel in the filter, Fig. 2, which ash plugs often are somewhat more homogenous and which are difficult to remove with pressurized air or vacuum because the streams tend to take the easiest path past the ash plugs. In this respect the filter may be filled from one side with soot 4, after which a blow- or suction process is started. Because of the soot the air flow 6 is forced to work on the ash plugs, whereby these are removed effectively. Then loose soot may be removed. Eventual remaining added soot is burnt in the preceding burning process.

The particle filters 14 that are to be cleaned are placed in the oven. Each particle filter is connected to a pipe loop 20 and the temperature sensor 28 is placed inside the respective particle filter. After this the oven is heated with the heating unit up to suitable temperature, that can be in the area of 400 - 600 ⁰ C depending on the type of filter. After this the control valves 22 for the air are opened so that the air is flowing through each branch 20 and each loop 26. The air in the loop will be heated to the same temperature as the oven when it then is fed into the particle filter. The air in the filter gives that a burning is performed whereby the particles in the filter are burnt away. Suitably the air flow in the loop up to the filter is so low that the burning does not become so intense that the temperature is raised too much in the filter, which otherwise could damage the filter. The flow is measured by the flow meter 24 and is controlled by the control valve 22. Further the temperature sensor 28 is continuously measuring the temperature so that it does not become too high.

If the temperature however is in the progress of reaching an upper acceptable limit despite the air flow being throttled completely, carbon dioxide may be fed into the filter in order to reduce the burning. The control valve 36 to the respective filter of the circuit 32 with carbon dioxide is opened whereby carbon dioxide is fed into the filter in order to reduce the burning and thereby the temperature. It is to be understood that other gasses can be used that are capable of reducing the burning in the filters. It is thus possible to control the burning process by controlling the supply of air, carbon dioxide, oxygen and other gasses as well as controlling the flow of gas in order to obtain an optimal cleaning process.

Because the burning processes in the filters are exothermic, i.e. heat is produced, not so much power input is required in order to keep the oven at work temperature. The oven is only switched on full power when it is to be heated. When the process then is running, the oven is only to be kept at constant temperature, whereby only about 25% of available power is utilized.

Apart from pipe loops it is possible to have other variants and designs of the heat exchanging means. For example "heat exchangers " such as plate heat exchangers may be used, the important thing is that the air is given time to be heated to the proper work temperature when it reaches the filter.

When the filter has been treated during a certain time period the particles have been burnt and are to be removed. This can either be done by blowing air into the filter whereby the burnt away particles are removed. It is however to be understood that vacuum can be used instead, whereby the burnt away particles are sucked away by suitable suction means. According to the above the flow of gas through the filters may be controlled in many ways in order to obtain an optimal result. Thus it is conceivable to increase the flow during the burning process during maintaining of a proper burning temperature in order to remove burnt particles such that a preceding blow or suction process becomes unnecessary or at least is reduced.

After this the filter is preferably measured and checked regarding degree of purity after cleaning and that there are no cracks or other damages. One way is measuring the differential pressure over the particle filter where high values of the differential pressure is an indication of a dirty filter because the filter is clogged with soot and other carbon compounds. The measured differential pressure is compared with the differential pressure of a clean unused filter of the specific type. Pressure sensors 20, 22 are then placed at the inlet and the outlet of the filters and a pressure source (not shown) is used in order to induce pressure to the filter. The pressure sensors are connected to suitable means for handling of the signals from the sensors and for comparing them with predetermined pressure values.

Another way of measuring the result of the heating process is to measure the opacity through the particle filter where Fig. 3 shows a measuring unit comprising two inlet pipes 10, 12 connected to a three-way valve 14 where one of the inlet pipes is connected to an air source and a fan (not shown) and the other is connected to a smoke generator. A further pipe is connected to the three-way valve. To this pipe, the inlet of a particle filter 18 may be releasably attached.

The outlet of the filter is connected to a straight pipe 24. The pipe is in one end arranged with a light transmitter 26, for example a strong LED and the other end is arranged with an optical receiver 28. The light transmitter is attached to suitable drive means in order to drive this and the optical receiver is connected to signal handling means. An outlet pipe 30 is attached to an end of the straight pipe and arranged to a valve 32. A gas meter 34 is further arranged to the particle filter.

The system is intended to function as follows. The tree-way valve 14 is positioned such that the inlet pipe 10 for smoke is connected to the further pipe 16. Smoke generated by the smoke generator is then fed through the

inlet and fills the particle filter 18 and the straight pip 24. The outlet valve 32 is closed.

The gas meter 34 is activated and measures gas content such as CO, CO2, HC and O2. The gas meter can also check if a catalyst is functioning, if the particle filter is combined with a catalyst, which some vehicles have.

The light source 26 is activated and when a stable concentration of gas is obtained, the strength of the transmitted light is measured through the smoke-filled straight pipe by the receiver 28 as a measure of the opacity. The measured opacity is then compared with the values of a clean unused filter.

The opacity measurement provides an indication that the filter is cracked which gives high values. A combination of dirty filter having cracks can give normal values of the differential pressure measurements but will have high values of the opacity measurements.

When the measurements have been performed the three-way valve 14 is positioned such that the air intake 12 is connected to the further pipe and the outlet valve 32 is opened. The system is now cleaned from smoke and is ready to test a subsequent filter.

When a combined filter and catalyst is to be measured, the catalyst has to be lit and heated in order to have the correct operating conditions.

Other measuring means may include laser scanning and in particular for locating cracks and clogged channels in the filter. It is also possible to use optical and/ or image processing devices for inspecting the cleaning result inside the filter.

As mentioned above, the measured values are compared with previously measured values and predetermined values of a new filter. If the measured

values deviate from the predetermined values with a certain amount, this indicates that the heating step has not been completely successful. In this case the filter is exposed to a further cleaning.

The above described process of cleaning particle filters is preferably controlled and supervised by a suitable control equipment. This may e.g. be a PLC or an industrial computer that via the different sensors can monitor the process and via the control valves control the burning processes for the separate filters.

It is to be understood that the embodiment that is described above and shown in the drawings only is to be regarded as a non-limiting example of the invention and that it is only limited by the scope of protection of the patent claims.