WO2013004914A1

WO2013004914A1 - New purifying apparatus

Info

Publication number: WO2013004914A1
Application number: PCT/FI2012/050713
Authority: WO
Inventors: Teuvo Maunula
Original assignee: Ecocat Oy
Priority date: 2011-07-07
Filing date: 2012-07-06
Publication date: 2013-01-10
Also published as: CN204386703U; EA201490049A1; FI20115731A0; EA031848B1; EP2729673A4; EP2729673A1

Abstract

The invention relates to a purifying apparatus for use in the treatment of particulate-containing fluids. In order to provide a high particle separating capacity and the ability to remain substantially block-free in operating conditions, a purifying apparatus (PUL) of the invention comprises for a fluid through flow at least one main particle separator (PPE) and alongside that is at least one bypass particle separator (OPE), and that the main particle separator (PPE) has a higher relative particle separating capacity and pressure loss than those of the bypass particle separator (OPE), and that the bypass particle separator (OPE) is substantially less susceptible to blocking and dimensioned in such a way that, upon a total blockage of the main particle separator (PPE), it is capable of undertaking the treatment of fluids in the purifying apparatus (PUL), and that the flow of fluids through the main particle separator (PPE) and the bypass particle separator (OPE) is arranged to be controlled by means of relative back pressures of the separators.

Description

NEW PURIFYING APPARATUS

Field of the invention

The invention relates to a purifying apparatus for use in the treatment of particu- late-containing fluids. The invention relates also to a method for the manufacture, regeneration and operation of such a purifying apparatus.

Background technology

The exhaust gas emission limits for vehicles, machines and engines become increasingly stringent year by year, which is why the use of aftertreatment methods is unavoidable for maintaining emissions below limit values. The most difficult task in diesel automobiles is to achieve particle (PM = particulate matter) and NO_x emission standards, while carbon monoxide and hydrocarbon emission standards are reasonably easy to reach by using oxidation catalysts. In engines, the reduction of NO_x can be effected by lowering the combustion temperature with methods of engine technology (e.g. EGR = Exhaust Gas Recirculation), which nevertheless have an increasing effect on CO, HC and PM emissions. Diesel particulate filters (DPF = Diesel Particulate Filter) are generally used in vehicle applications for reducing harmful particles with over 90% conversion. Conventional filters are of a wall-flow type (forced flow through a porous wall), based on skin filtration, wherein a particulate layer builds up on the wall of a flow channel and very few particles accumulate within the porous wall after the initial buildup. Such skin filtration- based filters have a mean pore size in the wall of about 8-25 μιη, which in ordinary sizing is sufficient to remove over 95% of particulate mass. These full filters can be replaced with partial filters, which are also known as POC (Partial Oxidation Catalyst) and which provide a filtering efficiency of about 40-70%. An advantage offered by partial filters is maintenance freedom with non-combusted ash and excess particles being able to depart from the assembly without the use of external energy, as opposed to full filters in which most of the ash and non-combusted material remain trapped on the filter's surface. With full filters, the pressure loss tends to increase during operation even though a complete removal of combustible soot/carbon is achieved. The reason for this is just this buildup of non-combusted ash. Roughly between skin and partial filtration in terms of the separation efficiency thereof are found filters based on deep filtration, which usually have the separation efficiency within the range of 50-90%, the estimated optimum from the standpoint of practical use being about 60-80%. The deep filtration-based filters are usually manufactured from ceramic or metallic fibers or foam or sintered metal. The fibers in a filter can take the form of a mattress or pleated mats. By maximizing the filtering area (thin mats in pleated configuration similar to air or oil filters), it is possible to maximize the relationship between efficiency and pressure loss. The essential difference between partial filters and full filters is that in full filters the fluid is forced all the way through a filtering/collecting layer while in partial filters there is also an unimpeded passage through the filter. Often employed in partial filters are screens, fibrous mats or perforated plates, onto which particles may mi- grate in response to pressure differences and turbulence in various channels. It is the working mechanism and construction which distinguishes deep and partial filters from each other, even if nominally the same materials were used in both. A fibrous mat, for example, may function as a honeycomb by forcing a flow through the mat (deep filtration), or as a cell by having a main flow proceed through chan- nels of the cell made of a corrugated and smooth fibrous mat, with some of the particles nevertheless remaining on wall surfaces (partial filter). In filters, which are based on the use of fibers, the filtration is based on a diameter of the fibers favorable from the standpoint of filtration. There is typically a very high proportion of void (>90% porosity) in fiber layers or mats, while in typical skin filtration-based fil- ters (e.g. cordierite, SiC or Al-titanate), the porosity in a filtering wall is typically 40- 50% and in special high porosity filters as high as 60-70%. Also in deep filtration, more particles start building up downstream on the filter surface the same way as in skin filtration.

Ordinarily, the filtered carbon matter (soot) of particles is subjected to thermal combustion by means of supplemental heat. Soot can be oxidized by an intense combustion reaction with oxygen at over 550 tempe rature, or slowly at lower temperatures (250-350Ό) by means of NO 2· The NO2, generated in an oxidation catalyst, oxidizes soot at reasonably low temperatures (>250-300Ό) as long as the oxidation catalyst is sufficiently effective. Effective oxidation catalysts enable removing a large portion of the hydrocarbon- containing evaporating fraction (VOF = volatile organic fraction or SOF = soluble organic fraction) of PM. Usually the proportion of VOF is 10-40%, but with certain engines and in certain driving conditions the VOF of particles can be as high as 70-90%. Such conditions are generated, among others, in city driving, with out- dated engines and/or with certain fuels. Hence, there is no way of explicitly categorizing the oxidation catalyst, partial filter and full filter according to separation ef- ficiency as their separation efficiencies overlap in terms of conversion rates, depending on the operating condition. In addition, the separation efficiency of filters, wherein particles accumulate inside a filter phase (deep filtration), not on the surfaces of channels, is highly dependent on flow rate and linear velocity. The sepa- ration efficiency of deep filters commonly decreases as the linear velocity increases and the efficiency of typical partial filters increases as the linear velocity increases (filtration is based on enhanced material transfer), which makes a clear functional difference therebetween. Many deep-filtering filters start allowing particles through at higher flow rates. The separation efficiency depends also on parti- cle size.

The removal of carbon fraction calls for a longer dwell time in the filter or catalyst. A prior known CRT method (Continuous Regenerating Trap) comprises a Pt- containing oxidation catalyst, followed by an uncoated or catalyst-coated DPF (EP 341 ,832). The problems of a passive method with a conventional full filter are re- lated to situations in which N0₂ is not generated in a sufficient amount, e.g. in congested city driving, and the method requires a very low-sulfur fuel (S<10 ppm) for minimizing sulfate formation in the effective and expensive Pt-containing oxidation catalyst. In the event of using a fuel richer in sulfur, the increasing formation of sulfates (SO₂ - S0₃ -> S0₄ catalyzed by a Pt-catalyst) wipes out the benefits gained by a filter, or the filter fills up too quickly which increases regeneration frequency and blocking risk. The blocking of a full filter (DPF) is unacceptable in any event as it brings the driving to a halt. It is for this reason that most particle filters feature active regeneration, which type of principle has already been practiced for several dozen years. Modern control engineering and engine control enables ac- tive regeneration to be conducted in a DPF. In new modern diesel automobiles, the active filter regeneration can be arranged by a periodically conducted temperature rise, usually to the range of 60Ό-650 . I f the filter has a sufficient buildup of soot, the start of combustion supplies supplemental heat which assists in a complete combustion of soot. Despite the regeneration of carbon, the full fil- ters gather non-combusted ash, the amount of which must be considered in sizing, lubricant recommendations, and in possible maintenance procedures.

In addition to a conventional wall-flow type particle filter, there are prior known assemblies made from steel wool, ceramic foam, a candle structure, a fiber-coated pipe structure to make use of electrostatic separation or water scrubbers. In prior known filter assemblies, perforated pipe structures have been wrapped in a fibrous mat or metal wool, and one or more of these structures can be installed in a full filter assembly. What is typical is that the fibrous structure is homogeneous without interspaces and the flow is channeled randomly in the assembly, dodging the fiber filaments and the main direction being averagely radial. These aspects are typical for deep filtration-based filters, wherein some of the particles accumu- late within the filter material. Ordinarily, the exhaust gas flows in these filters in radial direction towards the pipe interior, whereby there is enough room for the particles to accumulate inside, on the surface and in the open space of the assembly upstream of the filter. There are also metallic full filters, using e.g. sintered metal or porous metal foam. The structure of partial filters has been remodeled from oxidation catalyst, such that the separation of particles is improved by replacing a ceramic or metal cell with structures which feature various penetrations, claws or protrusions in the walls, and constrictions or filtering elements in the cell's flow channels. The penetrations or filtering elements have been constructed by using ceramic or metal screens, wools or porous materials instead of ordinary metal or ceramic walls. Partial filters are usually provided with a cell assembly, which in a main flow direction comprises an axial open channel system. The main flow is similar to what occurs in ordinary catalyst assemblies, but the particle separation has been enhanced by forcing the flow to partially proceed in radial direction through screens, fibers, or meshes in the wall, while being regulated by pressure difference. The radial direction flow is nevertheless haphazard in various directions, the vector consistent with main flow being averagely axial. Another underlying principle is that the flow comes in at one end and out from the opposite side at the other end of a cell, which is usually round or angular. The regeneration of particle filters has been conducted by using not only the combination of engine throttling (adjustment of air/fuel ratio to the proximity of a stoichiometric condition) and supplementary fuel injection but also electric heating, plasma (SAE Paper 1999-01-3638) or burners, which enable bringing supplemental heat and combusting soot (EP 0070619-1982 and Emissionminderung, Autobilabgase, Dieselmotoren, Nurnberg 15-17 Oct 1985, Kurzfassungen, VDI 1985). The supplementary fuel can be injected either into the cylinder (post- injection) or into the exhaust system upstream of an oxidation catalyst and/or a catalyzed particle filter. Combustion can also be enhanced with additives to be injected into the fuel and containing e.g. Ce, Fe or Sr, which, upon dispersing on the surface of soot, decrease the combustion temperature e.g. to about 500Ό and also enhance the regeneration taking place with NO₂. Especially in stationary projects, it is possible to use adjacent particle filters, some of the filters being in filtration and some in regeneration mode. The filter loaded with particles is transferred to regenerate and returned after regeneration back to the filtration mode. The flow of fluids is regulated by valves, the employment of which may nevertheless be problematic and defects may occur in dirty projects. Such structures also require large extra filter volumes compared with a single-line system.

The catalytic coating of particle filters can be used for promoting the catalytic combustion of soot (SAE Paper 8500015, 1985), the formation of N0₂, or for oxi- dizing the fuel injected in a purpose of raising temperature. The catalysts, which are most effective in the oxidation of hydrocarbons (from fuel), carbon monoxide and NO, and which are most durable, are based on the use of platinum (Pt). The formation of a high NO₂ content calls for the use of Pt in particular, while in the oxidation of hydrocarbons and CO, also palladium (Pd) is active. The catalytic com- bustion of soot has been conducted by using various catalysts, which are coated on a filter and which contain for example vanadium, copper, potassium, molybdenum and compounds of the like elements. These catalysts typically exhibit good mobility to the surface of solid soot or contain mobile oxygen.

As opposed to full filters, the regeneration of partial filters has been primarily based on passive regeneration with NO2. It has also been possible to use partial filters, without blocking, with fuels richer in sulfur and ash, because the non- combusted impurities and sulfates emerge out of the partial filter immediately or after a while. A requirement from the standpoint of regeneration has been that temperatures and the NO_x/C ratio be sufficiently high on average, whereby it is possible to form an adequate amount of NO2 and the NO₂+C reaction is sufficiently fast to impede the cumulative buildup of particles. In terms of their construction and particulate buildup, the partial filters are different from full filters, which is why different conditions prevail in regeneration. In the early 2000s, the efficiency of partial filters was just slightly better than that of oxidation catalysts, but subse- quently it has been desirable to raise the PM efficiency of this open filter up to the level of about 60-70%. As such, the PM emissions are still more than 5-20 fold with respect to full filters (conversion more than 95-98%), and these filters can be rated in different categories. Therefore, the blocking conditions and regeneration strategies of partial filters are still totally different from those in full filters based on skin filtration. As compared to these, very sparse oxidation catalysts provide still a grade lower blocking risk or back pressure. In full filters, the rise of back pressure is sufficiently considerable to be measured with conventional pressure sensors. In partial filters, on the other hand, there is a much lesser and slower increase in pressure loss. The significant rise of back pressure is already an indication of blocking. Initially, in the early 2000s partial filters were quite open with a PM conversion just slightly higher than (30-40%) than those of DOC or than the VOF fraction. As partial filters have been enhanced (PM conversion 60-70%) by developing more closed structures, the risks of blocking have risen at the same time and there has even been a desire to use also active regeneration methods not originally associ- ated therewith. If it is absolutely necessary to employ active regeneration methods with partial filters, some of the advantages gained by using partial filters will be lost and the threshold to take up the use of full filters will be lowered.

Description of the invention

It is an objective of this invention to provide a purifying apparatus for use in the treatment of particulate-containing fluids, which possesses a high particle separation capacity and remains as block-free as possible in operating conditions. In order to achieve this objective, the invention is characterized by features presented in the independent claims. Other claims present a few preferred embodiments of the invention. The purifying apparatus according to the invention comprises at least one main particle separator PPE, and alongside that is at least one bypass particle separator OPE, and the main particle separator PPE has a higher relative particle separation capacity and pressure loss than those of the bypass particle separator OPE. The bypass particle separator OPE is substantially less susceptible to blocking and dimensioned in such a way that, upon a total blockage of the main particle separator PPE, it is capable of undertaking the treatment of fluids for a purifying apparatus PUL, and the flow of fluids through the main particle separator and the bypass particle separator is arranged to be controlled by means of relative back pressures of the separators. The apparatus is preferably completely passive, when compared to prior known systems which may include e.g. valves in the regulation of flows. Preferably, alongside the full or partial filter is at least one partial filter or cell catalyst, which is substantially less prone to blocking and dimensioned for a capacity to handle the treatment of the system's fluids in case of a total blockage of the main unit. In comparison with ordinary full or partial filters based on the prior art, the novel type assembly, regeneration method and system enabled maintenance-free operation, regeneration in all working conditions, and low energy consumption in regeneration. The assembly enables the use of a coating with catalytically active components for the oxidation of carbon monoxide, hydrocarbons, nitric oxide (NO), and particles. A non-blocking quality for the purifying apparatus and a low pressure loss therein practically over its entire service life are attained by an assembly, which has at least two different filters or catalysts side by side, such that the sparser structure functions in the situation in which the more effective unit is completely obstructed. The flow distribution is obtained totally without valve adjustments or other regulations, since the flow through the assemblies becomes channeled in response to relative back pressures of the separators. Another benefit offered by the apparatus according to the invention is its modest manufacturing and operating costs. According to one object of the invention, the main particle separator PPE and the bypass particle separator OPE are coated with a catalyst, which catalyzes the oxidation of hydrocarbons, carbon monoxide, hydrogen, oxides of nitrogen, ammonia and/or particles, and/or the reduction of oxides of nitrogen with hydrocarbons, ammonia and the like reducers, and/or adsorbs oxides of nitrogen. The purifying apparatus (PUL) according to one object of the invention is further preceded by a cleaning catalyst, which is active in the oxidation of hydrocarbons, carbon monoxide, oxides of nitrogen and/or particles, and/or in the catalytic removal of oxides of nitrogen.

The fields of use for the invention include, among others, exhaust, flue gas and ef- fluent gas applications in mobile or stationary projects. Generally, the gas mixture is such that it contains excess oxygen continuously or averagely. In the combustion, the result of which is exhaust gas, it is possible to use any type of gaseous (for example methane, propane, biofuels, gasification gases), liquid (light or heavy fuel oil, diesel, gasoline or biofuels) or solid fuel. The filter according to the invention can be used e.g. in totally lean conditions (excess oxygen), or conditions in which from time to time is conducted a short-term mixture ratio adjustment for a stoichiometric or rich ratio. The purpose of a mixture ratio adjustment, and a temperature rise resulting therefrom, is a complete or partial regeneration of the filter from particles and built-up toxins or adsorbents. An- other possible reason for a mixture ratio adjustment is that the system comprises other catalysts (e.g. NO_x adsorption catalyst), which from time to time require stoichiometric or rich conditions for regeneration.

The use of full and partial filters has been expanded to projects, in which temperatures are quite low, for example in constant city driving, nor are the conditions suf- ficient for passive regeneration, and hence the high performance filters may begin to block or, in the case of partial filters, particles are slipping in a larger amount into the exhaust gas. In this event, the risk of blockage is imminent, especially in full filters using regeneration based on NO₂. Full filters become in any case inevitably completely obstructed even with active regeneration, because non-combusted ash cannot be removed without maintenance and cleaning. This maintenance cycle depends also on the properties of fuel and lubricant (ash matter). In a malfunction incident (non-standard fuel, other impurities, faulty engine operation), the blocking may also occur quite abruptly.

A few solutions according to the invention are depicted in the accompanying fig- ures:

Fig. 1. A purifying apparatus, comprising a main particle separator and a bypass particle separator.

Fig. 2. A purifying apparatus, further comprising a cleaning catalyst upstream, and optional perforated plate members. Fig. 3. An assembly with a bypass particle separator in the middle.

Fig. 4. An assembly with three nested separators having a stepwise changing relative pressure loss.

Fig. 5. An assembly with 2 different separators one after the other in its bypass and/or main channel.

Fig. 6. An assembly with two structures of the invention one after the other, such that the first has its main cell located in the middle and the latter on the outer periphery.

Fig. 7. A channel system made up by a pair of screens, wherein the flow is able to proceed also in lateral direction.

Fig. 8. A partial filter structure made up by a pair of walls or a plurality of walls. Fig. 9. Regeneration of an assembly according to the invention by using passive (NO₂ in both separators) and active regeneration (in main particle separator).

Fig. 10. The effect of particle layer thickness in an open particle separator, the effect on pressure loss and on the size of a bypass. Abbreviations used in figs. 1-10:

1 = inbound fluid,

2 = outbound (treated) fluid,

3 = main particle separator (PPE)

4 = bypass particle separator (OPE)

5 = flow through the main particle separator

6 = flow through the bypass particle separator

7 = perforated plate

8 = reactor/housing

9 = cleaning catalyst

10 = additional energy, such as fuel or electric power, for raising temperature ES = energy supply One assembly according to the invention is shown in fig. 1. A fluid (1 ) (usually exhaust gas) enters a reactor provided with one or more main particle separators PPE (3) and one or more bypass particle separators OPE (4). The main particle separator has a higher particle separation capacity and relative pressure loss than those of the bypass particle separator. The flow control among the separators (5 and 6) is principally determined in a totally static manner based on the separators' relative back pressure, size, and degree of filling, without regulating valves. Thus, the apparatus is preferably completely passive in terms of flow control. It is also essential that the bypass channel be defined as a separator, instead of being just a void bypass. In addition, the configuration may incorporate a perforated plate 7 upstream and/or downstream of the separator in the service of regulating/controlling the flow and functioning as a coarse filter. The apparatus is accommodated in a reactor/housing (8) (fig. 2). The basic structure may also be preceded by a cleaning catalyst (9) in a purpose of effectively oxidizing gaseous impurities, such as carbon monoxide, hydrocarbons, carbon (particles) and NO, into water, CO2, and NO₂ which can be utilized in the regeneration of a partial filter or in the actual cleaning catalyst, and which can also possibly have an active role in the reduction of oxides of nitrogen (NO_x adsorption reduction (NO_x trap), SCR in which the reducer is ammonia and/or its derivatives, and hydrocarbons).

Hence, the assembly according to the invention comprises a nested structure of two or more cells, wherein the flow is distributed through various cells on the basis of a relative back pressure. The back pressure in each cell, and thereby the distri- button of flow, will be determined on the basis of a principal configuration (ordinary cell, POC configuration (partial filter, even full filter), sizing (face area, length, aperture number, wall thickness), and a soot/ash loading amount. In dense and solid cells, the back pressure rises faster than in open sparse cells, which remain open even in harsher conditions. Indeed, several diesel services may be subjected to conditions, in which the full filter does not become regenerated or fills up with ash, and the driving stops as the filter becomes obstructed. Therefore, a small bypass channel through the bypass cell is a good precaution in the system.

Hence, the basic structure comprises a dense and a sparse separator/cell. The dense cell stands for a cell which has a higher particle separating capacity (APE cell with a higher mesh number) and back pressure. The sparse cell stands for a cell with a lower particle separating capacity and back pressure. The assembly and method thus include a denser and a sparser cell. If the dense cell is a full filter, the sparser cell can be an open particle structure (APE). In case the denser one is an APE structure, the sparser is e.g. a conventional flow-through converter or open straight-channel cell. The flow-through converter is for example an ordinary oxidation catalyst, which, when working as a bypass cell, is preferably a metallic ring element. Essentially, in this case, the flow-through converter collects fewer particles and is less prone to blocking than PPE. If the dense cell is an ordinary flow-through converter with a mesh number 1200 cpsi, the sparser one is e.g. a 400 cpsi ordinary flow-through converter. The particle separating efficiency and the back pressure correlate with each other, but at the same time the cell blockage increases in direct proportion to separation efficiency and back pressure. The cell lengths may also be different in a dense and a sparse cell.

One special solution is such that the cells are similar, but the "sparse cell" is considerably shorter for not blocking so easily, and as the longer cell is obstructed, more and more fluid starts flowing through the shorter one. There is more turbulence in the shorter cell. This concept can be applied primarily in open structures, because the filtration efficiency and blocking susceptibility of full filters result from a closed design.

The purifying apparatus can be housed in a reactor (8, fig. 2), which is e.g. a conventional mantled catalytic converter in which the cell can be uninsulated or wrapped in an insulation/installation mat and/or heat shields. The reactor may also be integrated with a muffler, which may also include other functional units (oxida- tion or deNO_x catalyst (SCR, LNT), a full filter, and additional units associated with the operation of these units). The cell shape can be round, oval or racetrack and, in all these, the flow can be axial or radial, or in some the cells axial and in some other radial. According to one object of the invention, the main particle separator PPE is a full filter, such as a wall-flow filter, and the bypass particle separator OPE is an open particle separator APE, which has a cell structure provided with permeable walls with open channels therebetween. In one object of the invention, the main particle separator PPE is an open particle separator and the bypass particle separator OPE is a flow-through converter.

In one object of the invention, the main particle separator PPE is dimensioned for having a through flow of more than 70%, preferably more than 85%, in unloaded condition and/or with normal particle loadings.

In one object of the invention, the main particle separator PPE has a particle sep- arating efficiency within the range of 50-100%, preferably 60-99%, and the bypass particle separator OPE has an efficiency within the range of 20-90%, preferably 30-70%. The main particle separator (PPE, 3) is for example a full filter, a skin filter or a deep filter with a high particle separating efficiency (usually within the range of 80-100%), or an open particle separator whose PM efficiency (e.g. 50- 80%) is higher than that of the bypass particle separator (OPE, 4, PM efficiency 20-70%).

In one object of the invention, the main particle separator PPE is a ceramic wall- flow filter and the bypass particle separator OPE is a metallic and/or ceramic open particle separator (APE). The full filter is typically a cell type filter, wherein the fluid is compelled to pass through a filtering wall. The material consists of cordierite, silicon carbide or aluminum titanate or the like ceramic material or a mixture thereof. The full filter may also be a deep filter made of ceramic foam, fiber (metal, ceramics, metal oxides or mixtures thereof), sintered metal or the like effective particle filters. When the PPE is an open particle separator, there is alongside another open particle separator as an OPE, whose relative PM efficiency and back pressure are lower than those of the PPE.

The bypass particle separator OPE is generally a particle separator with a back pressure per unit volume substantially lower than that of the main particle separator. This is realized, among others, in such a way that OPE is an open particle separator while PPE is e.g. a cell type full filter. The open particle separator has through-cell open channels keeping the structure unobstructed even if PPE begins to clog. The flow control in the apparatus is completely passive. Since the relative back pressure of OPE is lower than that of PPE, a remarkably small volume of OPE is needed to ensure operation of the bypass structure and to make sure that the back pressure does not become too high even if PPE were totally obstructed. Since the OPE is small and has only a fraction of the fluid flowing therethrough in normal condition, the PM efficiency of the whole system remains at a high overall level. The invention differs from other bypass-equipped systems, in which the flow is commonly regulated with valves. Structures, which include a void bypass channel or pipe, are likewise substantially different from the invention, because the bypass channel is intended to have collecting efficiency/surface, catalytic surface, and a particle separator/catalyst cell. The most stripped-down, bypass-equipped struc- ture would of course be such that the bypass comprises a void pipe or annular channel, but even then it is essential to adjust relative back pressures by dimensioning the system's flow distributions as presented in the invention, such that the back pressure stays within limits and does not prevent continued driving.

The open particle separator (APE) refers to structures, which instead of a dense pore or fiber pattern of full filters are provided with open channels, wherein the adherence of particles to flow walls has been accelerated by using tortuous, occasionally contracting and expanding channel sections with penetration paths through the walls, contributing to the equalization of pressure difference between adjacent channels. These conditions promote the adherence of particles to the walls, which function as collecting surfaces and which are preferably made of screens, membranes or fibrous mats (or combinations thereof) that are metallic or ceramic. Typically, the collecting efficiency lies within the range of 40-80%, which is distinctly lower than what is obtained with cell type full filters.

One assembly of the invention is depicted in fig. 3 with a bypass in the middle of the main cell. In this case, the more collecting main cell lies on the outside, whereby it is easier to cool, and heat propagates more easily outwards. In technical sense, it may be easier to make a small sparse cell in the middle than a cell with a corresponding face surface on the outer periphery.

In one object of the invention, the main particle separator PPE has a middle loca- tion in the structure, and the metallic bypass particle separator OPE is arranged around the main particle separator PPE structure in parallel with respect to the direction of flow. According to the invention, it is also possible to arrange more than two separators in parallel (fig. 4). In this case, the density, separating efficiency and/or relative back pressure of the cells become stepwise less intense, whereby through the densest separator in a void condition passes first most of the flow, but, as the denser ones are filling up, the flow diverts more and more into the next sparser one and finally into the sparsest separator. It is also common that relative volumes and collecting areas also diminish as the separating efficiency decreases. This type of apparatus could be made up for example of a structure, in which the main particle separator comprises a full filter, the 1^st bypass particle separator comprises a dense APE, and the 2^nd bypass particle separator comprises a sparse APE or a flow-through cell or a void bypass channel, which would remain open in all situations.

The main and/or bypass channel can also be provided successively with separa- tors of different properties (fig. 5). This also enables a more accurate regulation of back pressure and flow distribution. Up front can be for example a sparse cell with a denser one on its downstream side, whereby an appropriate back pressure is obtained and more particles are collected on the dense downstream section. Hence, the particles do not fill up the separator from the front but from the rear, whereby, when the upstream section becomes clogged, there is still room in the front for collecting and storing particles. If a denser cell is located upstream in this structure, more particles are collected in the upstream section of the cell, whereby it can be more easily regenerated with external energy supplied to the front thereof (heating solutions based on electricity or heating solutions based on fuel injec- tion). In succession can also be an APE and a full filter, for example as a PPE. Successive structures also enable using a catalytically more active coating in the upstream section, which enables producing in a downstream dense cell, specifically in that particular channel, more NO2, or the upstream catalyst is an effective oxidizer of HC in connection with active regeneration. Thus, the upstream separa- tor may also be a flow-through cell. It is possible that this structure be used to replace an upstream cleaning catalyst.

In one solution of the invention, the flow is channeled through the cells under the regulation of totally static sections of the cells. Regeneration would also happen without external flow adjustments. If a cell is in the process of blocking, there is less through-going flow, which makes its heating easier. In addition to a static condition, it is also possible to use flow or regeneration controls, e.g. electric heat- ing in a dense cell. External heating is particularly suitable for this system as normal heating, conducted by fuel enrichment, is more difficult to convey through a totally obstructed cell. Additional energy enables the entire system, the main particle separator as a whole, a part of the PPE at a time to be heated, or the carbon- containing matter present in the main particle separator to be ignited. The particles consist mostly of carbon and hydrocarbons, the ignition of which is possible to achieve with additional energy or spark. Hydrocarbons may ignite locally if temperature rises to more than 150-300°C, and the same applies to carbon if temperature rises locally to more than 400-600°, dependin g on the structure of soot and possible catalytic activities in the combustion of carbon. A concurrent high NO2 content may also promote this ignition. Regeneration may of course be based on completely or partially passive regeneration with NO2.

In one object of the invention, the purifying apparatus PUL is dimensioned such that the pressure loss may increase 5 to 50 fold, preferably 10 to 20 fold, with the entire flow proceeding by way of the bypass particle separator OPE, when compared to a purifying apparatus PUL which is free of particles. The objective in a purifying apparatus is of course to maintain the overall back pressure as low as possible, but the apparatus according to the invention has its sections dimensioned this way by means of relative back pressures. Flow rates through the cells are designed in such a way that the main flow in normal condition proceeds through a more effective, denser cell, whereby this cell must be considerably larger in volume than the sparser cell. The sparser cell is smaller, yet designed in such a way that the back pressure allows for the engine to run and the driving even if nearly all or completely all of the flow should be therethrough. However, the back pressure would be several hundred mbar in normal sizing in case the main cell is clogged. Of course, a small sparse cell cannot be provided with a major soot storage capacity, whereby the PM conversion remains at a relatively low level (30-50%) in case the entire flow deflects to stream through the bypass cell. The bypass particle separator can also be used for ensur- ing operation of the engine/apparatus without a stop and for conducting e.g. active regeneration whenever it is possible. The regulation of flows can of course be conducted by using actuators and valves, working e.g. on the basis of back pressure, in which case the system is no longer passive. In one application according to the invention, the adjustment of flow would be totally passive, but the PM re- generation can be carried out by using either active or passive methods. Special solutions could be those with cell sizes closer to each other. One such system could comprise a full filter (PM conversion >98%) and an open particle separator (PM conversion 40-50% with this particular sizing) side by side, whereby the PM overall conversion would be higher (e.g. 80-90%) with the flow for the most part through the full filter and lower with (60-70%) with the flow for the most part through the open particle separator. This would provide time and a chance to perform regeneration or maintenance on the system without interrupting the drive and whenever an access to maintenance is possible. There is a possibility of the OBD (On-Board Diagnostic) system activating when most of the flow proceeds through the bypass filter, nor can regeneration by conducted in field conditions. This way, the purifying apparatus guarantees an access to maintenance.

One open particle separator applied in the examples is composed of corrugated screens, wherein the corrugation of a screen deviates from the main flow direction and the adjacent/superimposed screens are at mutually different angles relative to the main flow direction (figs. 7 and 8). The corrugation useful in a partial filter can have its height (hi and h2) selected to suit the purpose in terms of design, back pressure and emission regulations (fig. 8) The corrugation height can be equal or unequal in various screens. The height can be varied over the range of 0.2 to 200 mm, preferably it is within the range of 0.8 to 3 mm. The angle of diagonal corru- gation can also be varied within the range of -90 to +90 degrees, preferably it is within the range of -60 to -20 and +20 to +60 degrees. The minus and plus sign angles refer to angles in opposite directions relative to the main flow direction. It is practical to use one diagonally corrugated screen material, make a pair of screens thereof by turning one of the screens inside out, such that the corrugation crests extend in diverse directions and provide support against each other. This preferably results in an APE constructed from one and the same screen. The corrugation height and width ratio can be varied over a very extensive range by using either low and wide corrugations or high and narrow corrugation crests. These diagonally corrugated screens are made by running a straight screen through helical gears, which results in a corrugated finish employed in the invention as a PPE or an OPE. Between two diagonally corrugated screens can also be an uncorrugated screen or a permeable wall, whereby a reduction of the channel size enhances material transfer and collecting capacity. Between the permeable walls can also be an impermeable foil or wall for the encasement of components to prevent the same from blending with each other. This enables regulating active or passive regeneration. It is possible to optimize the corrugation height according to project: very dirty projects -> major corrugation height, very clean projects - minor corrugation height.

In the APE depicted in figs. 7 and 8, the screen filament thickness is within the range of 0.01-5 mm, preferably within the range of 0.1-1 mm. The size of meshes in the screen is within the range of 0.05-10 mm, preferably within the range of 0.1- 2 mm. The screen can be woven or otherwise coherent. The extensive range is due to the existence of highly diverse projects or purposes. In very dirty projects the screen is sparser and the corrugation has a major height, and in clean projects the screen is denser and the corrugation has a minor height. It is possible to use a screen of very thin filament and/or with large meshes for the corrugated screen and a very dense screen for the flat screen, making it possible to roll up the screen even at quite a major corrugation angle (40-80 degrees). Instead of or together with the screen, it is also possible to use fiberboards or membranes processed for a corresponding structure, which features respective mesh- es/thicknesses in the walls and which is partly permeable to fluid. The assembly shown in figs. 7 and 8 may further comprise extra or optional flow barriers, constrictions/enlargements or claws/vanes, which enhance material transfer and collecting efficiency and create an open particle separation assembly.

In the event that the PPE is ceramic (cordierite, SiC, silicon nitride, aluminum ti- tanate or the like), the OPE can be a metallic APE, the structure thus having side by side a more effective ceramic and a less effective metallic particle separator, through which the flow adjusts primarily in a static fashion, without active adjustment, on the basis of pressure loss. The ceramic cell would be preferably in the middle, and around it is an annular, metallic OPE which can be made, as de- scribed in previous paragraphs, from corrugated metal structures (screens). The ceramic particle filter is not easy to construct as a ring structure, nor does it have a good strength as a thin ring structure. This enables making use of the good qualities of each structure. Such a structure also enables the use of different regeneration practices for different separators. The PPE can be subjected to active regen- eration based in fuel injection and/or raising temperature by electric power. At the same time, also the setting of A/F ratio can be made lower, which also raises temperature.

The PPE and the OPE can be completely or partially coated in the flow direction with a porous support medium, functioning as a primer for active compounds which oxidize CO, hydrocarbons, hydrogen, ammonia or carbon. The hydrocarbons may also include functional groups containing oxygen, nitrogen or halogens. The coating of an APE has preferably been conducted in such a way that the screen meshes remain at least partially open at least in one of the screens. Alternatively, there is no coating at all in the structure, which therefore only serves as an APE and a muffler. Additionally or optionally, the catalyst may catalyze the re- duction of NO_x with hydrocarbons or ammonia, absorb oxides of nitrogen (reduction in rich conditions), or oxidize ammonia. Typically, the catalyst contains aluminum, silicon, titanium oxides and/or zeolites in a support medium. The coating has a thickness within the range of 1-500 micrometers, preferably within the range of 5-40 micrometers. The coating surface area is determined by the employed raw materials, and it is within the range of 1-1000 m²/g, usually within the range of 20- 300 m²/g. The coating can be applied to separators from various slurries, sols and/or solutions by dipping, pumping, sucking and/or spraying. The screens can be coated in an open condition by spraying while the screens of a pair of screens are separated from each other, and only then rolled up to form a screen and APE assembly established by the APE. This makes it possible to ensure that the screen meshes remain open. As for the APE, it is provided with a mechanically durable coating, which nevertheless leaves the screen meshes open. The coating can also be conducted entirely or partially by means of evaporable starting materials (CVD, Ale techniques). The active metals employed in catalyst coatings comprise e.g. precious metals, such as platinum (Pt), palladium (Pd), iridium (Ir) and/or rhodium (Rh) and/or iridium (Ir) and/or ruthenium (Ru). The active components can be added into the coated catalyst composition by absorption (dry, wet or chemisorption methods) or by being blended within a coating slurry, solution or sol. The active components can be pre-absorbed into the raw material particles of a catalyst prior to mixing and coating the slurry. The coating and/or absorption processes involve the use of water or other solvents or mixtures thereof, generally in liquid phase.

The amount of active metal (e.g. precious metal) is 0.01-10 g/dm³, preferably 0.1- 3 g/dm³. If there are several structures in succession, the amount of active metal in the first upstream one can be preferably 0.8-2 g/dm³ and in the next downstream one/ones 0-0.8 g/dm³. An objective is to supply one and the same structure e.g. with more Pt on what is the inlet side in the flow direction, thus producing more NO₂ there. On the outlet side, there is no time for Pt to catalyze as much the oxidation of NO for passive regeneration, whereby the charge there is lower. On the outlet side may also be present other active components, such as Pd. This structure can be used jointly with a cleaning (oxidation) catalyst located upstream thereof.

The active component is selected according to usage. The platinum-containing catalyst coatings with a suitable support medium can be used for promoting the formation of NO₂, which promotes the combustion of particles and the regenera- ^, tion of a purifying e.g. in diesel projects. All Pt-containing catalysts do not provide a high NO₂ content, because the use of suitable additives (e.g. vanadium) in the support medium enables preventing the formation of NO2 and thereby sulfates. The reduction of N0₂ formation is intended for projects, wherein the regeneration is conducted in a completely active manner (fuel injection and/or by engine throttling) and when the objective is to minimize NO₂ emissions. Pd can be used as an active component, when the catalyst coating is intended for catalyzing the oxidation of CO and HC without the formation of NO₂ and when temperatures are high in working or regeneration conditions. Promoters employed in the support medium may comprise e.g. vanadium (V), tungsten (W), iron (Fe), zirconium (Zr), cerium (Ce), lanthanum (La), manganese (Mn), cobalt (Co), barium (Ba), strontium (Sr) and/or nickel (Ni). The support medium may also consist for the most part of these compounds of promoters. Into the coating can be added, e.g. by absorption, typical NO_x adsorption compounds, enabling oxides of nitrogen to be adsorbed in a lean mixture and to reduce the same during a rich mixture.

In full filters according to the invention can be used similar type coatings as in APE or a coating, added preferably in the form of sol, which coats the fibers or pores of a collecting unit with a thin catalyst layer without blocking the channels or raising the back pressure at that location. The sol refers to a liquid, in which are dispersed small particles having an average diameter within the range of 5-1000 nm, preferably within the range of 15-100 nm, which particle size enables even small pores and fibers to be uniformly coated. The particles can be e.g. Al, Si Ti, Zr, Ce, Mn, V, Cr, Co, Sr, La, Y, Pr oxides. The amount of coating is typically 0.1-30% of the weight of a full filter, and the active component is typically a precious metal such as Pt, Pd, Rh or a mixture thereof. Otherwise can be used the same promoters, active metal charges/addition practices and treatments as those used for other catalyst coatings.

In separators can be used compounds (V, Cr, Mn, Co, Sr) promoting the catalytic combustion/ignition of soot, and thermally stable oxides (La, Y, Zr) which protect separators from thermal stress. One application of the invention is such that the full filter is coated with sol, and the APE with normal catalyst slurry which contains larger particles (»100 pm). This results in an optimum coating on both separators. The slurry, which contains large particles, e.g. blocks small-pore full filters, or the coating becomes undesirably filtered only on the separator surface. The use of normal catalyst slurry (e.g. oxidation catalyst) enables providing a thicker catalyst layer on the surface of a flow-through cell.

One coating strategy of the invention is such that on the separators is applied a thermally durable coating and/or a coating catalyzing the combustion of soot di- rectly or indirectly (by way of NO₂ formation). The main and bypass particle separators can also be provided with different coatings. For example, a thermally durable coating (contains e.g. La and/or Zr) can be on the main particle separator because, upon blocking and subsequent combustion of particles, it heats more than the bypass particle separator. At the same time, the bypass particle separator can be provided with a coating which catalyzes the combustion of soot directly or indirectly (with the assistance of ΝΟ₂, higher Pt content, nor compounds impeding the formation of NO₂).

The cleaning catalyst upstream of the separators involves the use of coating compositions similar to those used in the APE. The cleaning catalyst differs typically from the APE in the sense that the amount of coating is typically larger, i.e. about 50-500 g/L, and the amount of active metal is also larger, typically 1-5 g/L. The cleaning catalyst body is a ceramic or metallic cell with a mesh number within the range of 1-2000 cpsi, preferably within the range of 50-600 cpsi.

The units coated with catalysts can be treated during a manufacturing process in static or dynamic conditions with oxidizing and/or reducing gas mixtures, which may include air, oxygen, hydrogen, carbon monoxide, ammonia, exhaust gas, hydrocarbons, water or some inert gas. The treatments can also be used for preparing various mixed oxides between the coating compounds by using suitable starting materials, particle sizes and finishing conditions. The APE has its screen secured by welding, soldering, or around the screen cell is stuck a metal nail or spike, which can be in attachment with the inner pipe. Heat sources (electrically working heating systems or devices), associated with active regeneration, can also be integrated with these structural elements responsible for mechanical attachment. If the PPE comprises a ceramic full filter, it is supported on the skin or mantle with a flexible installation mat capable of withstanding high temperatures. Thus, around the cell in the middle is an installation mat and a mantle, and the APE present around it does not need a separate, bulky installation mat, thus facilitating the structure manufacturing process.

Thus, the apparatus according to the invention enables especially the amount of particulate emissions to be cut down from effluent gases. The assembly is a separating apparatus, among others, for diesel projects, wherein the success of passive or active regeneration is ensured by making more use of a bypass particle separator whenever the conditions are not always suitable for regeneration. Particularly well this structure suits the projects, wherein temperatures are low e.g. in city driving, nor can regeneration be guaranteed with passive, or even with active regeneration, all of the time. The regeneration of separators (main and/or bypass particle separator) is preferably carried out by using as much as possible the passive regeneration for optimum fuel efficiency. The purifying, or parts thereof, may also replace some of the ordinary elements used in muffling. The purifying can be accommodated in a muffler similar to those used for ordinary oxidation catalysts and particle separators.

Hence, the particles collected on the separators are regenerated passively and/or actively by using external energy (fuel, electricity, etc.). In the case of exhaust gases containing excess oxygen, upstream of the apparatus can be installed a cleaning catalyst (e.g. DOC = Diesel Oxidation Catalyst), which oxidizes CO, HC and NO. The resulting NO2 slowly oxidizes carbon-based particles. The DOC can be located in the same canister or as a separate unit upstream of the reactor The DOC can also be inside an inlet pipe. The temperature of separators can be raised externally by burning hydrocarbons or by using other exothermic (heat gen- erating) reactions, which take place in (catalyzed) separators or in a cleaning catalyst. Additional heat is generated by feeding fuel into the exhaust gas and/or by post-injection into the engine. At the same time, the amount of combustion air can also be reduced (by reducing the A/F ratio). Additional heat for the regeneration of a catalyst structure can be generated by electric heating, burners and/or plasma and/or some other method capable of heating the structure and/or soot. The buildup of particles can also be enhanced by electrostatic methods, by using pairs of screens in a charged state as collecting screens and by isolating the screens from the rest of the structure and from each other. The regeneration of particles with an assembly of the invention can also be enhanced by using additives, which promote the combustion of soot (FBC = Fuel-Born Catalyst) and which contain for example Fe-, Sr- and/or Ce-based compounds. By feeding additives and using ac- tive regeneration at the same time, the carbon of particles can be ignited more easily.

From the combustion of particles must be obtained such an amount of heat that the separator temperature rises momentarily to more than 500-600Ό, which is sufficient for thermal combustion which can also be assisted by a catalyst present in the separators or entrained in the exhaust gas. If the thermal energy of particles present in a separator is to be exploited, it is essential that the separators will have collected thereon an amount of particles sufficient for heating and sustaining combustion for as long as it takes to have the separator regenerated entirely or for a sufficient part thereof.

One advantage of the invention is gained in a structure, wherein the denser separator (cell) is located in the middle and the bypass is present around it on the outside. In this case, heat losses are small because the external cell functions as an insulator and the oxidation of particles present in the middle separator can be commenced with as little additional energy as possible as opposed to systems which only have a particle filter in direct communication with ambient air by way of the skin. Thus, the regeneration functioning with external energy can be applied on the middle separator, whereby the external energy and the combustion heat are spreading and become focused in a concentrated manner for enhanced re- generation.

Of course, the described structure can be implemented not only in a nested configuration but also by using adjacent separators, which are e.g. round or angular, and in which the flow can be axial and/or radial.

Hence, the idea is that separators, which are different from each other in terms of particle separating capacity (filtering capacity), will be arranged side by side in such a way that, when the more effective one becomes obstructed, the flow is diverted through the less effective separator under the control of a natural change in pressure loss, as described. Thus, units which can be installed side by side in the order of diminishing separation efficiency are 1) wall-flow based filters, 2) deep fil- ters made of fibers, sintered metal, ceramic/metal foam, 3) open particle separators (APE), and/or 4) conventional catalyst cells (ceramic or metallic, flow through). A fifth one may also be present in the form of a void bypass pipe and channel. In parallel can be provided also structures of a similar type, but the separation efficiency is regulated by the length of a cell, the pore size of a wall, the size/shape of channels, or by other variables with an effect on filtration. The relative separation efficiency stands for an efficiency which would be attained with corresponding designs or separator size, filtering area, and/or weight. The separation efficiencies can be rated as disclosed above or even more precisely within each category. In wall-flow filters, for example, the separation efficiency in- creases as the wall thickness increases and as the pore size of a wall decreases. In the APE, the separation efficiency can be regulated with a channel size/shape/material and volume. The particulate separation efficiency of wall-flow filters is high, i.e. 90-100%, usually about 97-99.8%. In deep filters, the PM separation efficiency is about 50-95%, usually 70-90%. In open particle separators, the PM separation efficiency is 30-80%, usually 40-70%. In ordinary catalyst cells, the PM conversion follows the VOF content and is about 10-60%, usually about 20- 40%. Accordingly, the assembly according to the invention can be defined on the basis of these PM conversion ranges and the relative back pressure.

Linear velocities are typically unequal in various separators: in full filters, the rela- tive pressure loss is higher and thereby the linear velocity is lower than in open separators or catalyst cells. In the invention, all units have been defined as particle separators, because even the fully open catalytic cell has some oxidation activity, which promotes the removal of hydrocarbons and thereby a VOF fraction from the particles. Should the bypass cell be just an empty pipe without catalyst material, it would not be possible to remove even this VOF fraction in normal operating conditions, resulting in a system which is different in comparison with the solution of the invention. The VOF fraction can be quite substantial and fluctuates over an extensive range: about 10-85%, usually about 15-40%, which makes a difference in particle separating efficiency. The apparatus according to the invention is preferably intended for conditions with nothing but low temperatures for quite long periods, whereby the passive regeneration of separators is deficient. Such a condition, e.g. with vehicles, is constant city driving or some other type of driving at low speeds. As opposed to the full filter, the correctly designed open filter does not block even then, but the collecting capacity decreases and more particles come through as the flow is diverting more towards the bypass channel. The use of a bypass particle separator enables the main particle separator to be regenerated from time to time, even if the speeds are continuously low.

The passive regeneration of separators calls for the use of high Pt charges with a suitable support medium composition in the large oxidation catalyst upstream and in the separators. Since blockage of the entire apparatus can be prevented by us- ing a bypass feature, the amount of expensive precious metal can be reduced to some extent, which provides a major commercial benefit obtained from saving strategic raw materials. Most of the Pt is needed for raising the NO2 content within the range of 20Ό-300 . The use of slightly lower P t charges further enables the separators to be regenerated at over 300 as the b ypass enables the effect of conditions to be equalized. This also enables reducing NO2 emissions, and the smaller oxidation catalyst produces less back pressure for further reduced fuel consumption. One objective is to combine the benefits of using a passive method and a filtering bypass feature in the apparatus of the invention. Being in operation whenever possible, the passive regeneration maintains the back pressure at low level, nor consumes external energy.

Although the APE is not as sensitive as full filters, and especially CRT systems, to the sulfur of fuel (<10 ppm S), it is beneficial for its operation that the fuel should contain as little sulfur as possible. However, this is not possible in all intended ser- vices. The use of a bypass particle separator enables a reduction in the activity of an oxidation catalyst (lower Pt loading), whereby the formation of sulfates decreases at the same time. Therefore, the apparatus according to the invention is useful also for fuels richer in sulfur, since the PPE can be dense and effective, yet the OPE serves to ensure the passage of fluid through and the back pressure re- striction, even in the event that particles would accumulate rapidly in the PPE and its back pressure would rise. The regulation strategy must be worked out according to driving (operating) conditions and fuel.

The regulation of active regeneration in full filters has been effected by using pressure sensors upstream and downstream of the filter, and temperature sensors in assistance. Combining a pressure difference datum with engine map data makes it possible to commence active regeneration at such a moment that it is most easily possible and energy efficient. It is of course possible to use these methods also with an apparatus of the invention or with parts thereof. In the case of a full filter (PPE) this is natural, but the APE presents quite a low back pressure even at high particulate loadings, whereby the accuracy of pressure sensors may become a limiting factor. Hence, the apparatus can be provided with back pressure sensors across the entire system, or across the main particle separator which in practice is the same thing. The use of active regeneration jointly with a full filter is most sensibly carried out by means of a previously worked out strategy. Pres- sure and temperature sensors can also be used for OBD purposes to notify whether the apparatus is in the process of blocking or overheated, and requires maintenance.

Upstream of the purifying apparatus it is also possible to feed not only hydrocarbons and known fuels but also other oxidizing and reducing compounds, such as ammonia, urea, ozone, hydrogen peroxide, air, oxygen and/or water, pure or in mixtures. This enables promoting the reaction of NO_x and/or particles and maintenance of the purifying, and adjusting the stoichiometry of reactions.

The structure according to the invention can be subjected to regeneration passively and/or actively (fig. 9). In the main filter, with more propensity of blocking and more need for regeneration, can be applied active regeneration based on the use of external energy (fuel or electricity). When the main particle separator becomes obstructed, less and less fluid is flowing therethrough with less thermal energy required for heating the separator and the fluid in comparison with the condition in which most of the fluid flows through and cools the separator during regeneration. At the same time with the use of external energy, it is possible in lean mixture engine projects to make a change of the A/F ratio to the proximity of λ-value 1. whereby the temperature of exhaust gas rises. Thus, the regeneration of a main particle separator would be based on the adjustment of A/F ratio and on simultaneous additional heating, and the regeneration of a bypass particle separator would be enhanced by virtue of the A/F ratio adjustment and the temperature rise caused thereby. Otherwise, the regeneration of both separators occurs passively whenever the NO₂/C ratio and the temperature are suitable (>250'C) for an NO2+C reaction.

Example 1 Exemplary assemblies and flow distribution can be simulated on the basis of what is known about the back pressures of prior art cells. For each cell type there are parameters defined into calculation equations, wherein the pressure loss experienced by exhaust gas depends on cell configuration, cell dimensions, mesh number, the amount of support medium, temperature and flow rate. These pressure loss equations for catalyzer cells are common knowledge. Exemplary calculations comprise iterating the flow rates for establishing an equal pressure loss across adjacent cells, an effect which by nature equalizes the flow in these structures. Blockage can be observed in the equations purely in terms of geometry by treating soot the same way as a support medium and varying the support medium thick- ness. The latter calculation is probably suitable only for small PM loadings. The it- erative calculation for adjacent cells has been conducted on Excel-based spreadsheets, incorporating pressure loss equations for each cell type.

In exemplary calculation, the amount of exhaust gas from a given engine is 770 kg/h. The maximum temperature in exhaust gas is 500Ό and operating conditions fluctuate from the temperature of outside air to this maximum at which the pressure loss calculations were conducted.

Case 1 : The main cell was an open particle separator made of diagonally corrugated metal screens with a corrugation height corresponding to mesh number 400 cpsi, the filament thickness was 110 pm and the amount of support medium 10 g/m². The bypass cell was a straight channel 400 cpsi metal cell, wherein the foil thickness was 50 pm and the amount of support medium 40 g/m². Preliminary calculation and iteration were conducted regarding dimensions of the main cell and the bypass cell. Pressure loss for an annular bypass cell can be calculated on the basis of a round cell with the matching face surface. The main cell diameter was set at 230 mm, whereby the use of a 10.4 mm (70 mm round equivalent) annular bypass cell around the main cell results in a flow distribution of 90.8% through the main cell and 9.2% through the bypass cell to start with (pressure loss 16.9 mbar). In the event that the entire flow should be diverted to pass through the bypass cell, the pressure loss would be 543 mbar, which is thus the worst case. When the size of a bypass cell was smaller than this (<70 mm equivalent), the pressure loss in the entire flow situation increased to excessive magnitude: 7366 mbar if bypass D30 mm equivalent, 1662 mbar if bypass D50 mm equivalent. Even these structures (narrower channels) can possibly be used for as long as there is certainty of the main particle separator never becoming completely obstructed, whereby this extreme worst case scenario shall never occur.

Case 2: Conditions as in case 1. but the employed bypass cell is an Ecocat™ cell (foil 50 pm, support medium 40 g/m²), containing tortuous channels. The bypass channel's face surface was maintained as before (D70 mm), whereby the main flow was 90.3% and through the bypass cell passed 9.7% (pressure loss 16.7 mbar). With the flow passing entirely through the bypass cell, the pressure loss would be 501 mbar. If the amount of support medium in a bypass cell is dropped by 50%, i.e. 20 g/m², the flow distribution would be 89.3%/10.7% (16.4 mbar and max. 424 mbar).

Case 3: Simulating the buildup of particles with the premise of their impact being similar to the addition of support medium in case 2. It is presumed that an open bypass cell does not collect particles at all. If the APE has collected a 40 μιη layer of particles, the flow distribution has changed for the ratio of 88.3%/11.7% (21.9 mbar, max. 501 mbar). Respectively, with a 100 pm particulate layer, the flow distribution will be 85%/15% (31.5 mbar, maximum remaining the same, i.e. 501 mbar).

Case 4: The situation of case 3 was also calculated with a straight-channel bypass cell (400 cpsi, foil thickness 50 pm, amount of support medium 40 g/m²). On the basis of calculation was obtained the correlation of particle layer thickness to by- pass-% and to the system's pressure loss (fig. 10). This clearly indicates that the main flow, and thereby the PM efficiency, remains on the main particle separator side up to particle layers of moderate thickness. The bypass is about 40% with a 500 pm particle layer.

The corresponding practice can be applied for simulating and dimensioning, with respect to pressure loss and flow distribution, also structures in which the main particle separator is a cell type full filter and the bypass particle separator is for example an open particle separator as presented in the previous examples.

The bypass cell D70 is a reasonably good size in terms of practical applications: 9.2% through the bypass cell, max. Δρ 543 mbar. Thus, a main portion of the flow, i.e. about 80-91 % thereof, would proceed through the main cell which is dimen- sioned for the PM conversion of about 50-70%. If blockage should start to occur, the back pressure across the bypass cell all the way would be in the same order as maximum Ap's often in DPF projects. The same principle can also be applied in dimensioning for slightly different back pressures or flow distribution. In simulation and design, it could also be relevant to consider a situation in which the bypass cell's back pressure had also slightly increased as a result of blocking.

Claims

1. A purifying apparatus (PUL) for use in the treatment of particulate-containing fluids, characterized in that, in order to provide a high particle separating capacity and the ability to remain substantially block-free in operating conditions, the purify- ing apparatus (PUL) comprises for a fluid through flow at least one main particle separator (PPE) and alongside that is at least one bypass particle separator (OPE), and that the main particle separator (PPE) has a higher relative particle separating capacity and pressure loss than those of the bypass particle separator (OPE), and that the bypass particle separator (OPE) is substantially less suscepti- ble to blocking and has been dimensioned in such a way that, upon a total blockage of the main particle separator (PPE), it is capable of undertaking the treatment of fluids in the purifying apparatus (PUL), and that the flow of fluids through the main particle separator (PPE) and the bypass particle separator (OPE) is arranged to be controlled by means of relative back pressures of the separators.

2. A purifying apparatus (PUL) according to claim 1 , characterized in that the main particle separator (PPE) is a full filter such as a wall-flow filter, and the bypass particle separator (OPE) is an open particle separator (APE), having permeable walls in a cell structure and open channels between said walls.

3. A purifying apparatus (PUL) according to claim 1 or 2, characterized in that the regulation of fluid through flow between the separators main particle separator

(PPE) and bypass particle separator (OPE) is primarily determined in a completely static manner on the basis of the separators' relative back pressure, size and degree of filling, without regulating valves.

4. A purifying apparatus (PUL) according to any of the preceding claims, char- acterized in that the main particle separator (PPE) is an open particle separator and the bypass particle separator (OPE) is a flow-through cell.

5. A purifying apparatus (PUL) according to any of the preceding claims, characterized in that the main particle separator (PPE) has been dimensioned for a through flow of more than 70%, preferably more than 85%, in a empty condition and/or with normal particle loadings.

6. A purifying apparatus (PUL) according to any of the preceding claims, characterized in that the purifying apparatus (PUL) has been dimensioned in such a way that, when the entire flow proceeds by way of the bypass particle separator (OPE), the pressure loss can increase to 5-50 fold, preferably 10-20 fold, in comparison with the purifying apparatus (PUL) free of particles.

7. A purifying apparatus (PUL) according to any of the preceding claims, characterized in that the main particle separator (PPE) and the bypass particle sepa- rator (OPE) have been coated with a catalyst, which catalyzes the oxidation of hydrocarbons, carbon monoxide, hydrogen, oxides of nitrogen, ammonia and/or particles, and/or the reduction of oxides of nitrogen with hydrocarbons, ammonia and the like reducers, and/or which adsorbs oxides of nitrogen.

8. A purifying apparatus (PUL) according to any of the preceding claims, char- acterized in that the main particle separator (PPE) has a particle separating efficiency within the range of 50-100%, preferably 60-99%, and that the bypass particle separator (OPE) has its efficiency within the range of 20-90%, preferably within the range of 30-70%.

9. A purifying apparatus (PUL) according to any of the preceding claims, char- acterized in that the main particle separator (PPE) is a ceramic wall-flow filter and the bypass particle separator (OPE) is a metallic and/or ceramic open particle separator (APE).

10. A purifying apparatus (PUL) according to any of the preceding claims, characterized in that the main particle separator (PPE) is located in the middle of the structure and the metallic bypass particle separator (OPE) lies around the main particle separator's (PPE) structure parallel thereto in the direction of flow.

11. A purifying apparatus (PUL) according to any of the preceding claims, characterized in that upstream of the purifying assembly (PUL) is further provided a cleaning catalyst, which is active in the oxidation of hydrocarbons, carbon monox- ide, oxides of nitrogen and/or particles, and/or in the catalytic removal of oxides of nitrogen.

12. A method for the manufacture of a purifying apparatus (PUL) for use in the treatment of particulate-containing fluids, characterized in that, in order to provide a high particle separating capacity and the ability to remain substantially block-free in operating conditions, the purifying apparatus (PUL) is provided for a fluid through flow with at least one main particle separator (PPE) and alongside that with at least one bypass particle separator (OPE), the flow of fluids through both being arranged to be controlled by means of relative back pressures of the separators, and that the main particle separator (PPE) has a higher relative particle separating capacity and pressure loss than those of the bypass particle separator (OPE), and that the bypass particle separator (OPE) is substantially less susceptible to blocking and dimensioned in such a way that, upon a total blockage of the main particle separator (PPE), it is capable of undertaking the treatment of fluids in the purifying apparatus (PUL), and that the flow of fluids through the main particle separator (PPE) and the bypass particle separator (OPE) is arranged to be controlled by means of relative back pressures of the separators.

13. A method for the regeneration of a purifying apparatus (PUL) according to any of claims 1-11 , characterized in that the regeneration of particles is based on passive regeneration with NO₂.

14. A method for the regeneration of a purifying apparatus (PUL) according to any of claims 1-11 , characterized in that the regeneration of particles is based on passive regeneration with NO₂, and on active regeneration by means of heating based on additional energy, such as fuel injection and/or electricity.

15. A method for the regeneration of a purifying apparatus (PUL) according to any of claims 1-11 , characterized in that the regeneration of particles is based on passive regeneration with NO₂, and on active regeneration by raising temperature in the separators with an A/F adjustment for λ-value to the proximity, such as 1.0- 1.2, of the stoichiometric condition of combustion, and by using at the same time additional energy, such as fuel injection and/or electricity, in the separator or upstream thereof or upstream of the cleaning catalyst.

16. A method for the regeneration of a purifying apparatus (PUL) according to any of claims 1-11 , characterized in that the regeneration (oxidation) of the main particle separator's (PPE) particles is based on passive regeneration by means of NO₂, and on active regeneration by means of additional energy, and the regeneration (oxidation) of the bypass particle separator (OPE) is based on passive regeneration relying on the presence of NO₂.

17. The use of a purifying apparatus (PUL) according to any of claims 1-11 in exhaust, flue gas and effluent gas applications in mobile or stationary projects.

18. The use of a purifying apparatus (PUL), according to claim 17, characterized in that the fluid contains oxygen continuously or averagely in excess, the λ- value being > 1.0.