Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1999-07-01
2001-07-31
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
active
06267890
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of operating a spiral wound type membrane module used in a membrane separation device including a microfiltration device, ultrafiltration device, and reverse osmosis membrane separation device.
BACKGROUND OF THE INVENTION
As a membrane module used for a membrane separation device, there has been known a spiral wound type membrane module in which separation membranes are wound around the outer circumference of a water collection pipe.
FIG. 5
is a perspective view, partly exploded, showing a structure of a conventional spiral wound type membrane module.
A plurality of envelope-shaped membranes
2
having a shape of an envelope are wound onto a water collection pipe
1
with mesh spacers (outer spacers)
3
being interposed between the membranes.
The water collection pipe
1
is provided with a slit-like opening for allowing communication between the outside and the inside of the pipe. Inside of the membrane
2
formed in an envelope shape, communicates with the inside of the water collection pipe
1
. Inserted into each envelope-shaped membrane
2
is an inside spacer
4
including mesh-like spacer, for forming a channel inside the membrane, so that the inside of the envelope-shaped membrane (hereinafter, sometimes referred to as just “membrane”)
2
constitutes a permeated water channel.
The opposite ends of a roll
5
of the membranes
2
are closed with a top ring
6
and an end ring
7
at its edges and brine seals
8
are fitted around the top ring
6
and the end ring
7
.
Feed water (raw water) flows from the front end of the membrane roll
5
into a feed water channel(raw water channel) between the membranes
2
and further flows in the longitudinal direction of the membrane roll
5
. Nonpermeated water is outputted from outlets of the rear end of the membrane roll
5
. While the water passes in the feed water channels, the water permeates through the membranes
2
and flows into the pipe
1
and is taken out from the rear end of the pipe
1
as permeated water.
The spiral wound type membrane module is easily clogged and it is difficult to operate in such a manner to keep a flux of the permeated water at a high rate for a long period.
The conventional spiral wound type membrane module has also the following detects:
1) The water collection pipe
1
must have larger diameter to obtain a great flux within the pipe
1
. However, this also makes the diameter of the spiral wound type membrane module larger.
2) The permeated water flows in each membrane spirally to the water collection pipe
1
, so that a flow resistance increases in the membrane. A flow resistance is also high around the slit-like openings through which the permeated water flows from the inside of the membrane
2
into the water collection pipe
1
.
3) A volume of the feed water flowing in the feed water channels decreases as the feed water flows to the outlet by permeation into the membranes, and a flow velocity of the feed water becomes small in a downstream region of the feed water channels whereby the membranes are easy to be fouled therearound.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of operating a spiral wound type membrane module capable of producing permeated water at a high rate.
It is another object of the present invention to provide an improved method of operating a spiral wound type membrane module which has a roll of a membrane wound spirally and is improved in such a manner to separate feed water into permeated and nonpermeated water by supplying the feed water between the membranes.
The module is operated, according to the present invention, such that a differential pressure between the feed water flowing into feed water channels and the nonpermeated water flowing out from the channels is 0.3 kg/cm
2
or less, particularly 0.15 kg/cm
2
or less, more particularly 0.10 kg/cm
2
or less.
In the method of operating the spiral wound type membrane module of the present invention, as the differential pressure across the permeating process (the above differential pressure between the feed water and the nonpermeated water) is suitable, the permeate flux is kept at a relatively high rate for a long period and the feed water is membrane-separated efficiently for the total running time.
In one embodiment of the present invention, the spiral wound type membrane module has envelope-shaped membranes, a permeated water spacer for forming permeated water channels disposed inside each envelope-shaped membrane and a feed water spacer for forming feed water channels disposed between the membranes. Each membrane may be formed in a substantial rectangle having first, second, third and fourth sides. The first, second and third sides are closed and the fourth side is partly opened to have an opening and closed at the rest thereof to have a blocking portion. The membranes are wound onto a shaft of the module to form a membrane roll in such a manner that the first sides perpendicular to the fourth sides are in contact with the shaft and the fourth sides are exposed on the rear end of the membrane roll, and the second sides opposite to the fourth sides are exposed on the front end of the membrane roll. Each feed water channel between the membranes is closed along the entire of the third side, closed to have a blocking portion along a portion of the fourth side corresponding to the opening of the membrane, and opened to have an opening along a portion of the fourth side corresponding to the blocking portion of the membrane.
In the thus constituted spiral wound type membrane module, raw water flows from the front end of the roll into the feed water channels. The raw water flows in the feed water channels in a direction substantially parallel to the axis of the membrane roll and is taken out as nonpermeated water from the openings of the feed water channels on the rear end of the roll.
Water permeated through the membranes flows in the membranes in a direction substantially parallel to the axis of the roll and is taken out from the opening formed on the rear end of the roll.
Since the permeated water flows in the membranes in the direction parallel to the axis of the roll as mentioned above, a water collection pipe used in a conventional spiral wound type membrane module is no longer necessary. This can avoid the flowing resistance of the water when flowing from the membranes into the water collection pipe, thereby significantly reducing the flowing resistance of the permeated water.
As the water collection pipe can be eliminated, the length of the membrane in the winding direction can be increased so as to increase the membrane area. Even with the membrane having increased length in the winding direction, the flowing resistance of the permeated water is not grown up. This allows greater flux to be obtained.
Each feed water channel is opened just along a portion of the rear end of the roll so that the flow rate of feed water (nonpermeated water) at the downstream of the feed water channel can be higher than that of the conventional one, thereby also preventing the fouling at the downstream of the feed water channel.
In one embodiment of the invention, the openings of the membranes are positioned in one of outside and inside annular portions of the rear end of the roll, and the openings of the feed water channels are positioned in the other portion of the rear end of the membrane roll. A ring member is connected to the rear end of the roll for separating permeated water flowing out from the openings of the membranes and nonpermeated water flowing out from the openings of the feed water channels. The ring member defines the rear end of the roll to distinguish an outlet area for permeated water from an outlet area for nonpermeated water.
REFERENCES:
patent: 4814079 (1989-03-01), Schneider
patent: 5069780 (1991-12-01), Thalmann et al.
patent: 5460720 (1995-10-01), Schneider
patent: 5858229 (1999-01-01), Uemura et al.
patent: 0 347 174 (1989-12-01), None
patent: 0 819 466 (1998-01-01), None
patent: 54-3
Shigemi Hirotake
Uemura Keiji
Fortuna Ana
Kanesaka & Takeuchi
Kurita Water Industries Ltd.
Ward Richard W.
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