Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-01-20
2003-03-18
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S650000, C210S321740, C210S090000, C210S097000, C210S257200
Reexamination Certificate
active
06533937
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spiral wound type membrane element employed for a membrane separation device such as a low-pressure reverse osmosis membrane separation device, an ultrafiltration device or a microfiltration device and methods of running and washing a spiral wound type membrane module.
2. Description of the Background Art
With recent applications of the membrane separation technology to water purification, the membrane separation technology is now applied as pretreatment for reverse osmosis membrane separation systems used desalination of seawater, for example. While a microfiltration membrane and an ultrafiltration membrane attaining high permeate flow rates are generally used for such membrane separation, a reverse osmosis membrane attaining a high permeate flow rate under ultra-low pressures of not more than 10 kgf/cm
2
has recently been developed.
As a membrane element used for membrane separation, a hollow fiber membrane element is generally used in consideration of the membrane area (volumetric efficiency) per unit volume. However, the membranes of the hollow fiber membrane element are easy to break, and when the membranes are broken, raw water is mixed into the permeate to disadvantageously lower the separating performance.
On the other hand, a spiral wound type membrane element can provide a large, membrane area. The spiral wound type membrane element, which can maintain high separating performance, is superior in reliability to the hollow fiber membrane element.
FIG. 25
is a partially fragmented perspective view of a conventional spiral wound type membrane element
21
, and
FIG. 26
is a perspective view showing the appearance of the conventional spiral wound type membrane element
21
.
As shown in
FIG. 25
, the spiral wound type membrane element
21
is formed by superposing separation membranes
26
on both surfaces of a permeate spacer (permeate passage forming member)
25
and bonding three sides thereby forming an envelope-like membrane (bag-like membrane)
23
, mounting an opening of the envelope-like membrane
23
on a water collection pipe
22
formed by a perforated hollow pipe and spirally winding the envelope-like membrane
23
on the outer peripheral surface of the water collection pipe
22
with a netty raw water spacer (raw water passage forming member)
24
.
The raw water spacer
24
is provided for forming a passage for the raw water along the envelope-like membrane
23
. If the thickness of the raw water spacer
24
is small, the separation membranes
26
are clogged with suspended substances although the charging efficiency thereof is increased. In general, therefore, the thickness of the raw water spacer
24
is set to about 0.7 to 3.0 mm.
In relation to treatment of raw water such as river water containing a large quantity of suspended substances, a spiral wound type membrane element employing a zigzag corrugated sheet type raw water spacer (the so-called corrugated spacer) is already known in the art.
As shown in
FIG. 26
, the outer peripheral surface of the spiral wound type membrane element
21
is covered with a protective sheath
27
made of FRP (Fiber-Reinforced Plastics) or formed by a shrink tube, while packing holders
28
called anti-telescopes are mounted on both ends thereof respectively.
FIG. 27
is a sectional view showing an exemplary method of running the conventional spiral wound type membrane element
21
. As shown in
FIG. 27
, a pressure vessel (pressure-resistant vessel)
30
is formed by a tubular case
31
and a pair of end plates
32
a
and
32
b.
The end plate
32
a
is provided with a raw water inlet
33
, and the other plate
32
b
is provided with a concentrate outlet
35
. The end plate
32
b
is provided on its center with a permeate outlet
34
.
The spiral wound type membrane element
21
having a packing
37
mounted on a portion close to an end of the outer peripheral surface is introduced into the tubular case
31
, and both opening ends of the tubular case
31
are sealed with the end plates
32
a
and
32
b
respectively. One opening end of the water collection pipe
22
is engaged with the permeate outlet
34
of the end plate
32
b,
while an end cap
36
is attached to the other opening end thereof.
In order to run the spiral wound type membrane element
21
, raw water
51
is introduced into a first liquid chamber
38
from the raw water inlet
33
of the pressure vessel
30
. As shown in
FIG. 27
, the raw water
51
is supplied from one end of the spiral wound type membrane element
21
. The raw water
51
axially flows along the raw water spacer
24
, and is discharged as concentrate
53
from the other end of the spiral wound type membrane element
21
. The raw water
51
permeating through the separation membranes
26
along the raw water spacer
24
flows into the water collection pipe
22
as permeate
52
along the permeate spacer
25
, and is discharged from the end of the water collection pipe
22
.
The permeate
52
is taken out from the permeate outlet
34
of the pressure vessel
30
shown in FIG.
27
. The concentrate
53
is taken out from a second liquid chamber
39
of the pressure vessel
30
through the concentrate outlet
35
.
When the spiral wound type membrane element
21
is run, the membrane
23
is clogged with suspended substances contained in the raw water
51
, to reduce the membrane flux. Therefore, chemical washing is performed for eliminating such clogging and recovering the membrane flux. However, such chemical washing requires much labor and a high cost. In order to prevent clogging, therefore, back wash reverse filtration is periodically performed with permeate or air in a hollow fiber membrane element, for example.
In the conventional spiral wound type membrane element
21
, however, back wash reverse filtration results in the following problems:
FIG. 28
is a partially fragmented perspective view showing back wash reverse filtration in the conventional spiral wound type membrane element
21
. As shown in
FIG. 28
, the permeate
52
is introduced from an end of the water collection pipe
22
. Since the outer peripheral surface of the envelope-like membrane
23
wound around the water collection pipe
22
is covered with the protective sheath
27
, the permeate
52
derived from the outer peripheral surface of the water collection pipe
22
permeates through the envelope-like membrane
23
and axially flows in the spiral wound type membrane element
21
along the raw water spacer
24
, and is discharged from the end of the spiral wound type membrane element
21
. Despite back wash reverse filtration, therefore, contaminants such as turbid substances causing clogging of the membrane
23
are readily captured by the raw water spacer
24
before discharged from the end of the spiral wound type membrane element
21
and insufficiently removed.
As shown in
FIG. 27
, further, the clearance between the inner peripheral surface of the tubular case
31
of the pressure vessel
30
and the spiral wound type membrane element
21
defines a dead space S, to cause residence of the fluid (fluid residue). When the spiral wound type membrane element
21
is used over a long period, the fluid residing in the dead space S is denatured. Particularly when the fluid contains organic matter, germs such as microorganisms may propagate to decompose the organic matter and give off a bad smell or decompose the separation membranes
26
, leading to reduction of reliability.
In addition, the raw water
51
is supplied from one end of the conventional spiral wound type membrane element
21
and discharged from the other end, and hence the conventional spiral wound type membrane element
21
requires the packing holders
28
for prevent the envelope-like membrane
23
wound around the water collection pipe
22
from being deformed in the form of a bamboo shoot. Further, pressure loss caused by the raw water spacer
24
as well as by clogging results in pressure difference between thee raw water inlet side and the concentrate
Adachi Tetsurou
Andou Masaaki
Hisada Hajimu
Kawada Ichirou
Kawashima Toshiyuki
Akin Gump Strauss Hauer & Feld L.L.P.
Fortuna Ana
Nitto Denko Corporation
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