JP3462731B2 - Maintenance method of high temperature bag filter and filter membrane - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature bag filter that physically collects and removes soot and dust in high temperature exhaust gas generated in a waste treatment furnace such as a refuse incinerator and an ash melting furnace by a filter membrane. And a method of maintaining the filter membrane.

[0002]

2. Description of the Related Art Generally, a bag filter of this type is provided with a plurality of cylindrical filter units in an exhaust gas treatment chamber, and the exhaust gas supplied into the exhaust gas treatment chamber passes through a filter membrane of each filter unit and passes therethrough. Sometimes, soot and the like in the exhaust gas are removed, and after passing through the opening for exhaust gas after the soot and the like of each filter unit is removed, it is sucked and discharged to the outside of the exhaust gas processing chamber. Also,
In order to clean and remove soot and dust adhering to the filter membrane of each filter unit, a back pressure cleaning pipe is arranged along the opening of each filter unit, and an air ejection port provided in the back pressure cleaning pipe. There is a back pressure cleaning device having a structure in which is installed so as to face each of the openings.
Specifically, the compressed air supplied to the back pressure cleaning pipe is ejected from the air ejection port toward each of the openings, so that the air is opposite to the flow of the exhaust gas during normal exhaust gas treatment. In a direction from the inside to the outside of each filter unit, the soot dust and the like adhering to the filter film and sprayed on the filter film are back-pressure washed.

By the way, conventionally, an ordinary bag filter in which a cloth made of natural fiber, synthetic fiber, inorganic fiber or the like is used for the filter membrane has been generally popular. Due to the heat resistance of the filter membrane, the maximum inlet temperature is 150 to 200 ° C.
Had to be limited to. Therefore, 500 ℃ to 60
Exhaust gas having a high temperature of about 0 ° C. is temporarily supplied at 150 ° C. to 200 ° C. in a gas cooling tower or the like before being supplied to the normal bag filter.
It is necessary to cool to a low temperature of about ℃, and to raise the temperature of the combustion exhaust gas after removing the dust again to remove nitrogen oxides, dioxins, etc. which are harmful substances in the combustion exhaust gas in the catalytic reaction tower etc. However, since such a cooling / heating process is required, there is a problem that an excessive heat loss is caused for the treatment of combustion exhaust gas.

Further, when cooling the high temperature exhaust gas by water injection in the gas cooling tower or the like, a large amount of water vapor is generated, so that the absolute amount of the exhaust gas is increased and it is necessary to increase the capacity of the suction blower. In addition, the amount of heat per unit amount of exhaust gas of the combustion exhaust gas after the dust removal has decreased, which has been a factor of decreasing the waste heat utilization efficiency. Further, in the cooling process, the exhaust gas temperature is lowered by passing through the dioxin resynthesis temperature of 300 ° C., so that a large amount of dioxin is contained in the dust and the like collected by the normal bag filter, and the recovery is performed. It was necessary to separately perform chelating treatment on the generated dust and so on.

In order to deal with the above problems of the ordinary bag filter, recently, the filter film is provided with 700 ° C.
A high-temperature bag filter that uses a heat-resistant filter membrane made of an inorganic material such as ceramic fiber or a metal-based porous membrane that can be used under moderately high temperatures has been proposed, and high-temperature exhaust gas such as combustion exhaust gas is directly removed without cooling treatment. A processable configuration is adopted.

[0006]

However, fly ash in exhaust gas generated in a waste treatment furnace such as a refuse incinerator or an ash melting furnace has a low melting point substance having a low melting point of around 350 ° C to 400 ° C. The low melting point substance was deposited on the surface of the filter membrane, causing the filter membrane to be clogged, resulting in deterioration of the filter dust collecting function. Further, the low melting point substance deposited on the surface of the filter film cannot be removed from the surface of the filter film by normal back pressure cleaning, and the operation of the high temperature bag filter is stopped to cool the surface of the filter film once. Since the low melting point substance must be removed, the operating efficiency and maintenance work efficiency of the high temperature bag filter are significantly impaired, resulting in a sharp rise in equipment maintenance cost.

The present invention has been made in view of the above problems, and an object thereof is to provide a high-temperature bag filter capable of easily cleaning and removing the low melting point substance deposited on the surface of the filter film, and a maintenance method thereof. However, it is the point that the features of the high temperature bag filter are fully realized.

[0008]

The first characteristic constitution of the present invention for attaining this object is a high temperature formed by forming a peelable porous thin film layer on the surface of the filter membrane on the exhaust gas intake side of the filter unit. It is a bag filter,
Form the porous thin film layer toward the filter membrane surface on the inlet side.
The point is that the first injection mechanism for injecting the releasing agent is formed.

The second characteristic structure is added to the first characteristic structure.
Another point is that a thin film layer removing mechanism for peeling and removing the porous thin film layer is provided.

The third characteristic configuration is the first or second characteristic configuration.
In addition to the characteristic structure, the porous thin film layer is composed of diatomaceous earth, Ca
This is because a stripping agent composed of fine powder particles such as (OH) ₂ , CaO, or CaCO ₃ is attached to the surface of the filter membrane on the exhaust gas suction side.

[0011] The same fourth characteristic configuration of, addition to the third feature configuration
Ete has a plurality of exhaust gas treatment chamber, each exhaust gas treatment chamber,
At least one filter unit and a second injection mechanism for injecting the release agent from outside the exhaust gas treatment chamber toward the exhaust gas treatment chamber are provided.

The fifth aspect of the present invention for achieving this object
The characteristic configuration is the high temperature bar according to any one of the first to fourth characteristic configurations.
Concerning the maintenance method of the filter film of the filter, at the time of cleaning the filter film, at the same time as removing the dust and the like adhering to the filter film surface, the porous thin film layer and the dust and the like adhering to the porous film layer are removed from the filter film surface is there.

[0013] the sixth characterizing feature of having a plurality of exhaust gas treatment chamber, what the first third characterizing feature in the exhaust gas treatment chamber
A high-temperature bag filter provided with at least one of the above filter units, or a high-temperature bag filter of the fourth characteristic configuration.
Concerning the maintenance method of the filter membrane of the filter , a part of the plurality of exhaust gas treatment chambers is selected, and only the other exhaust gas treatment chambers that are not selected are subjected to normal filter dust collection treatment, and the selected exhaust gas treatment chambers For the filter unit,
At the same time as removing dust and the like adhering to the filter membrane surface,
A cleaning step of peeling and removing the porous thin film layer and dust and the like adhering to the porous thin film layer from the filter membrane surface is performed, and a new porous thin film layer is formed on the filter membrane surface after the porous thin film layer is peeled and removed. The point is to execute the porous thin film layer forming step.

[0014] the seventh characterizing feature, relative to all of the plurality of exhaust gas treatment chamber, lies in performing maintenance method of the sixth characterizing feature of the filter membrane sequentially.

The operation and effect will be described below. According to the first characteristic configuration, the low-melting point substance is not directly welded to the filter membrane surface but is welded to the porous thin film layer, so that even if the low-melting point substance is welded, the filter film surface is clogged. Even if occurs, the low melting point substance deposited by the filter film cleaning such as the normal back pressure cleaning as in the fifth characteristic configuration is peeled off from the filter film surface together with the porous thin film layer in the welded state. Can be done.

[0016] According to a first characterizing feature, further, a low-melting substance the welding in a conventional counter-pressure washing after the filter membrane surface than peeled off together with the porous thin film layer, new to the filter membrane surface The porous thin film layer can be easily formed. In this case, when a part of the plurality of filter units is selected to wash the filter membrane by, for example, back pressure cleaning, the supply of exhaust gas into the exhaust gas treatment chamber may be temporarily stopped, or even after back pressure cleaning. By controlling the ejection amount of the back pressure cleaning air to the filter unit, only the release agent can be attached to the filter film surface while suppressing the suction of the exhaust gas to the filter film surface of the filter unit. Of. As a result, the features of the high-temperature bag filter are maximized without sacrificing the operating efficiency and maintenance work efficiency of the high-temperature bag filter significantly compared to the normal low-temperature bag filter by the porous thin film layer forming process. It can be done.

Furthermore, according to the second characterizing feature, by a thin layer removal mechanism and the filter membrane cleaning mechanism and shared mechanisms or dedicated mechanism, a low-melting substance the welding at the time of peeling removal of said porous thin layer It can be peeled and removed together with the porous thin film layer in the welded state. As a result, since it becomes possible to remove the low melting point substance in the normal back pressure washing step, the operation efficiency and maintenance work of the high temperature bag filter as compared with the normal low temperature bag filter by the treatment of removing the low melting point substance. The features of the high temperature bag filter can be maximized without sacrificing efficiency. That is, since it is not necessary to cool the exhaust gas before the high-temperature bag filter, re-synthesis of the dioxin can be avoided, and steam is not generated due to the cooling, so that the induction blower can be downsized. Moreover, since the amount of heat per unit amount of exhaust gas is high, waste heat can be reused with high efficiency.

According to a third characterizing feature, the release agent is particularly attached to the filter membrane surface without requiring binder or the like, fine particles of the release agent is greater than the mesh of the filter membrane the release agent itself It is possible to form a porous thin film layer that is rougher than the filter film on the surface of the filter film without passing through or clogging the filter film. Therefore, the porous thin film layer can prevent the low melting point substance from adhering to the filter film without impairing the filter dust collecting function of the filter film. In particular, when diatomaceous earth, for example, is used as a stripping agent, it does not have a neutralizing effect on corrosive gases such as hydrogen chloride contained in the exhaust gas, but it has a remarkable adsorption and stripping effect, and its effect is great. Further, as a release agent, for example, Ca (O
H) ₂ , CaO, or CaCO ₃ or the like uses an alkaline powder, which has a neutralizing effect on corrosive gases such as hydrogen chloride, so that chlorine is fixed (CaCl ₂ ) and harmful dioxins are generated. It is possible to avoid the formation of the connected precursor and prevent the re-synthesis of dioxin downstream of the high temperature bag filter. Furthermore, the desalted high-temperature, clean exhaust gas discharged from the high-temperature bag filter corrodes the heat transfer tubes of the equipment even when directly used as the heat source of the waste heat recovery device such as the heat source for heating the rotary kiln. It is possible to improve the waste heat recovery efficiency without worrying about it. As the stripping agent, it is necessary to use a stripping agent that does not react with the exhaust gas-containing component to produce a harmful gas component.

According to the fourth or sixth characteristic configuration, the removal and removal of the porous thin film layer by back pressure cleaning and the formation of a new porous thin film layer can be selectively performed independently for each exhaust gas treatment chamber unit, Since it is not necessary to stop the normal dust removal processing in another exhaust gas processing chamber, the continuous operation as a whole can be maintained with a simple configuration. Further, in the process of forming the porous thin film layer, the fine powder of the release agent injected from the second injection mechanism floats in the exhaust gas processing chamber, and the fine powder of the release agent is sucked by a normal exhaust gas to cause the fine powder of the release agent to flow through the filter film surface. It is attracted to and adheres to and forms the new porous thin film layer. Note that it is necessary to stop the supply of exhaust gas into the exhaust gas processing chamber. When the fine powder of the release agent is attached to the filter membrane surface in a state of being mixed in the exhaust gas,
This is because the low melting point substance also adheres to the surface of the filter film, and the original effect of providing the porous thin film layer is significantly impaired.

According to the seventh characteristic configuration , the filter film surface condition can be always maintained at a certain quality or higher for all the filter units, and high operating efficiency is maintained without deteriorating the processing characteristics of the high temperature bag filter. You can do it.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a high temperature bag filter according to the present invention (hereinafter, simply referred to as an apparatus of the present invention) will be described below with reference to the drawings.

As shown in FIG. 1, the apparatus of the present invention, like a general bag filter, has an exhaust gas treatment chamber 6 of the apparatus of the present invention.
The high-temperature combustion exhaust gas that has been sucked into or fed into a and has not been filtered yet has passed through the filter membranes 8 of the plurality of substantially cylindrical filter units 1 having vertical axis cores to remove soot and then the soot removal. The combustion exhaust gas afterward is discharged through the opening 9 located above the filter unit 1 outside the exhaust gas treatment chamber 6b.
Is configured to be discharged to. Further, each of the filter units 1 is configured by mounting the filter membrane 8 made of ceramic fiber from the outside on a frame 10 configured by combining metal annular and linear members, and a ceiling partition wall of an exhaust gas treatment chamber. Ceiling opening 12 provided at 11
And the opening 9 are aligned with each other, and the periphery of the opening 9 is subjected to an appropriate sealing treatment and is suspended and supported from the ceiling partition wall 11.

The apparatus of the present invention comprises a back pressure cleaning mechanism 13 for back pressure cleaning of the filter membrane 8 and a diatomaceous earth toward the filter membrane surface 2 facing the exhaust gas suction side on the outer surface of the filter membrane 8. Ca (OH) ₂ , CaO, or CaC
First, a release agent 4 composed of fine powder particles such as O _{3 is} sprayed from the side to form a porous thin film layer 3 on the filter film surface 2.
The injection mechanism 5 is provided.

In the back pressure cleaning mechanism 13, a back cleaning pipe 13a for conveying compressed air for back pressure cleaning is piped above the ceiling partition wall 11 along the ceiling opening 12, and inside the filter unit 1. An injection nozzle 13b for injecting the compressed air for backwashing toward the backwash pipe 13a is separately connected to the backwash pipe 13a above the ceiling opening 12 via a solenoid valve 13c.

Further, in the first injection mechanism 5, a ceramic release agent injection pipe 14 having a large number of ejection openings 14a on one side closed at one end is provided around the filter membrane surface 2 around the axis of the filter unit 1. A plurality of pipes are provided so as to penetrate through the ceiling partition wall 11 in parallel with the core, and the open end sides of the release agent injection pipes 14 are gathered together above the ceiling partition wall 11 and compressed air is supplied through the solenoid valve 15. Together with the release agent delivery pipe 16 for delivering the release agent 4,
A release agent adding device 17 for adding the release agent 4 is provided in the middle of the release agent transport pipe 16.

In the apparatus of the present invention, before the filter dust collecting process of soot and dust in the exhaust gas, the first spraying mechanism 5 is used to physically remove the release agent 4 onto the filter membrane surface 2 of each filter unit 1 in advance. The porous thin film layer 3 is formed by being adhered by mechanical engagement, and is included in the fly ash in the exhaust gas.
A low-melting substance having a low melting point of around 50 ° C. to 400 ° C. is prevented from directly adhering to the filter film surface 2. Specifically, soot and the like adhering to the filter membrane surface 2 and the porous thin film layer 3 and soot and low melting point substances adhering to or adhering to the porous thin film layer 3 are washed by the back pressure washing mechanism 13. After being removed, the solenoid valve 15 connected to each of the stripping agent injection pipes 14 arranged around the cleaned and removed filter unit 1 is selectively opened, and the stripping agent 4 is sent together with compressed air, The release agent 4 is sprayed from the ejection port 14a toward the filter membrane surface 2. The above operation is executed for all of the filter units 1. The stripping agent 4 may be mixed fine powder particles of a part or all of diatomaceous earth, Ca (OH) ₂ , CaO, CaCO ₃ or the like, or any one kind of fine powder particles. I do not care.

The back pressure cleaning of the filter membrane surface 2 is carried out by a known means such as a pulse jet method and a known method. Specifically, for some of the filter units 1, some of the filter units 1 are sequentially selected, and the injection nozzle 13b corresponding to the selected filter unit 1 is selected.
The solenoid valve 13c connected to the compressed air is opened in order to blow compressed air from it. Since the porous thin film layer 3 is adhered only by physical engagement without using a binder or the like, the surface of the filter film is easily caused by the passage of backwash air through the filter film and the accompanying vibration of the filter film. It can be peeled off from 2. As a result, the back pressure cleaning mechanism 13 also functions as a thin film layer removing mechanism for peeling and removing the porous thin film layer.

Another embodiment will be described below. <1> The first injection mechanism 5 is not necessarily limited to the structure, form, and material shown in FIG. For example, as shown in FIG. 2, instead of the plurality of release agent injection pipes 14, a plurality of annular release agent injection pipes 18 having a shape that annularly surrounds the periphery of the filter unit 1 may be provided by being fixed vertically. Alternatively, it is also a preferable mode that one of the annular release agent injection pipes 19 is attached so as to be vertically movable. The porous thin film layer 3 does not necessarily have to be formed by the first injection mechanism 5. The forming material and forming means can be changed appropriately.

<2> For cleaning the filter membrane surface 2, a cleaning mechanism of another cleaning method such as mechanical vibration may be used in addition to the back pressure cleaning mechanism 13. Further, the back pressure cleaning method in the back pressure cleaning step may be another method.

<3> In the above embodiment, it is not particularly limited whether the exhaust gas treatment chamber 6a is a single exhaust gas treatment chamber or one of a plurality of exhaust gas treatment chambers. As another embodiment, as shown in FIG. 3, it has a plurality of exhaust gas processing chambers 6, and each exhaust gas processing chamber 6 has at least one filter unit 1 and the exhaust gas processing chamber outside 6b to the exhaust gas processing chamber. Release agent 4 toward 6a
A second structure having a structure different from that of the first injection mechanism 5 for injecting
It is also a preferable embodiment that the injection mechanism 7 is provided. Here, since the stripping agent 4 is sprayed to form the porous thin film layer 3, the exhaust gas processing chamber 6a into which the stripping agent 4 is sprayed has a space for containing exhaust gas before dust removal processing. Point to. As shown in FIG. 3, each of the exhaust gas processing chambers 6 is provided with an exhaust gas inlet 20, an exhaust gas outlet 21, and the second injection mechanism 7 separately. Each of the second injection mechanisms 7 is connected to a stripping agent transport pipe 23 that transports the stripping agent 4 together with compressed air via the solenoid valve 22 outside the exhaust gas treatment chamber 6b, and the stripping agent transport pipe 23 is provided with the stripping agent transport pipe 23 in the middle thereof. The peeling agent adding device 24 for adding the peeling agent 4 is provided. The reason why each of the second injection mechanisms 7 is provided independently of the exhaust gas inlet 20 is to inject the release agent 4 into the exhaust gas processing chamber 6a together with clean air. If the low melting point substance in the exhaust gas is also adhered to the surface of the filter film when it is injected together with the exhaust gas from the exhaust gas inlet port 20, the original effect of providing the porous thin film layer is significantly impaired. Because.

In the present embodiment, at the same time as removing the dust and the like adhering to the filter membrane surface 2, the porous thin film layer 3 and the dust and the like adhering thereto are removed from the filter membrane surface 2.
Back pressure cleaning step for further peeling and removal, and the porous thin film layer 3
The porous thin film layer forming step of forming a new porous thin film layer 3 on the filter membrane surface 2 after the peeling and removal is continuously performed for the specific filter unit 1. The selection of the specific filter unit 1 is performed by selecting a part of the plurality of exhaust gas treatment chambers, and the other exhaust gas treatment chambers that are not selected are subjected to a normal filter dust collection treatment, whereby the entire apparatus of the present invention is provided. As a result, the operating state can be maintained at all times. Here, as a method of selecting a part of the exhaust gas processing chambers from the plurality of exhaust gas processing chambers 6, the attachment state of the dust or the like on the filter membrane surface 2 or the filtering ability is detected by some means, and the detection is performed. Based on the result, the exhaust gas treatment chambers determined to require the back pressure cleaning step may be sequentially selected, or simply a predetermined number of exhaust gas treatment chambers may be selected in a predetermined order. I do not care.

In the step of forming the porous thin film layer, the fine powder of the stripping agent 4 sprayed from the second spraying mechanism 7 floats in the exhaust gas processing chamber 6a, and the fine powder is sucked by a suction mechanism for sucking normal exhaust gas. It is attracted to and adheres to the filter membrane surface 2 to form the new porous thin film layer 3. In addition, the back pressure cleaning method in the back pressure cleaning step may be the same method as the previous embodiment or another method.

<4> The shape, structure, dimensions of the filter unit 1 or the material of the filter film 8 in each of the above-described embodiments can be appropriately changed within a range in which the original function as a high temperature bag filter can be exhibited. It is natural. For example, a metal-based porous membrane may be used as the material of the filter membrane 8, and in that case, it is necessary to appropriately change the support structure and the like in consideration of its weight, shape and the like.

<5> The identification of the components of the low melting point substance and the effect of the present invention are not directly related. As a result of the experiment according to the present invention, a melting point of 3 was found from the DTA analysis of exhaust gas.
The presence of low melting point substances such as 59.1 ° C., 420.9 ° C., 470.2 ° C. has been confirmed, and Pb, PbCl ₂ ,
The melting points of Zn and ZnCl ₂ are 329 ° C., 501 ° C., and 4 respectively.
Since the temperature is 19 ° C. and 365 ° C., it is presumed that these low melting point substances or compounds similar in composition to them are contained in fly ash and the like in the exhaust gas.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing an embodiment of a high temperature bag filter according to the present invention.

FIG. 2 is a perspective view of a main part for explaining another embodiment of the first injection mechanism according to the present invention.

FIG. 3 is a perspective view showing another embodiment of the high temperature bag filter according to the present invention.

[Explanation of symbols]

1 Filter unit 2 Filter membrane surface 3 Porous thin film layer 4 Release agent 5 First injection mechanism 6 Exhaust gas treatment room 6a Exhaust gas treatment room 6b Outside the exhaust gas treatment room 7 Second injection mechanism 8 filter membrane 9 openings 10 frames 11 ceiling partition 12 Ceiling opening 13 Back pressure cleaning mechanism (thin film layer removal mechanism) 13a Backwash pipe 13b injection nozzle 13c, 15,22 solenoid valve 14 Release agent injection pipe 14a spout 16, 23 Release agent carrier pipe 17, 24 Stripping agent adding device 18, 19 Annular release agent injection pipe 20 Exhaust gas inlet 21 Exhaust gas outlet

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-79130 (JP, A) JP-A-8-103617 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 61/00-65/10 B01D 46/00-46/54 B01D 53/22

Claims (7)

(57) [Claims] 1. A high-temperature bag filter obtained by forming a freely porous thin film layer peeled off the exhaust gas inlet side of the filter membrane surface of the filter unit (1) (2) (3), of the flue gas suction side filter Forward towards the membrane surface (2)
The release agent (4) forming the porous thin film layer (3) is sprayed.
High temperature bag filter comprising a first injection mechanism (5). 2. The high temperature bag filter according to claim 1, further comprising a thin film layer removing mechanism (13) for peeling and removing the porous thin film layer (3). 3. The stripping agent (4) is diatomaceous earth, Ca (O).
The high temperature bag filter according to claim 1 or 2, which is made of fine powder particles such as H) ₂ , CaO, or CaCO ₃ . 4. A plurality of exhaust gas treatment chambers (6), wherein each exhaust gas treatment chamber (6) includes at least one filter unit (1) and the exhaust gas treatment chamber (6b) to the exhaust gas treatment chamber (6). The second injection mechanism (7) for injecting the release agent (4) toward 6a) is provided .
The high temperature bag filter according to any one of items . 5. A method of maintaining a filter film of a high temperature bag filter according to any one of claims 1 to 4 , wherein dust and the like adhering to the filter film surface (2) is removed during cleaning of the filter film. At the same time, a method for maintaining a filter membrane, characterized in that the porous thin film layer (3) and soot and dust adhering thereto are peeled off from the filter membrane surface (2). 6. A plurality of exhaust gas treatment chambers (6), wherein each exhaust gas treatment chamber (6) is provided with at least one filter unit (1) according to any one of claims 1 to 3. A certain high-temperature bag filter or a high-temperature bag filter according to claim 4 , wherein a part of the plurality of exhaust gas treatment chambers is selected, and only the other exhaust gas treatment chambers that are not selected are subjected to normal filter dust collection treatment, With respect to the filter unit (1) of the selected exhaust gas treatment chamber, at the same time as removing the dust and the like adhering to the filter membrane surface (2), the porous thin film layer (3) and the dust and the like adhering thereto are removed. A cleaning step of peeling and removing from the filter membrane surface (2) is performed, and the porous thin film layer (3)
A method for maintaining a filter film, which comprises performing a porous thin film layer forming step of forming a new porous thin film layer (3) on the surface of the filter film after the film has been removed by peeling. 7. For all of the plurality of exhaust gas treatment chamber (6), the filter membrane method maintenance and executes the service method of the filter membrane of claim 6, wherein sequentially.