U.S. patent application number 13/186177 was filed with the patent office on 2012-03-15 for membrane filtration system.
Invention is credited to Yuka Hiraga, Futoshi Kurokawa, Koichi Matsui, Takeshi Matsushiro, Seiichi Murayama, Ryo Namba, Hiroyuki Tokimoto, Hideaki Yamagata, Katsuya Yokokawa.
Application Number | 20120061300 13/186177 |
Document ID | / |
Family ID | 45805625 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120061300 |
Kind Code |
A1 |
Matsushiro; Takeshi ; et
al. |
March 15, 2012 |
MEMBRANE FILTRATION SYSTEM
Abstract
According to one embodiment, a membrane filtration system
includes a raw water tank, a pretreatment membrane module, a raw
water feed line, a high-pressure RO membrane module, a
high-pressure line, a preceding power recovery unit which
pressurize the pretreated water by transmitting the pressure of the
concentrate to the pretreated water, a succeeding power recovery
unit which pressurize the raw water by transmitting a remaining
pressure of the concentrate to the raw water, a concentrate
discharge line, a first pressure transmission line communicating to
the power recovery unit by being branched from the high-pressure
line, a second pressure transmission line communicating to the
power recovery unit by being branched from the raw water feed line,
and a valve provided in the drain line to regulate a discharge of
the concentrate from the power recovery unit in accordance with a
pressure loss in the pretreatment membrane module.
Inventors: |
Matsushiro; Takeshi;
(Yokohama-shi, JP) ; Yokokawa; Katsuya;
(Fuchu-shi, JP) ; Kurokawa; Futoshi;
(Tachikawa-shi, JP) ; Namba; Ryo; (Fuchu-shi,
JP) ; Matsui; Koichi; (Tokyo, JP) ; Yamagata;
Hideaki; (Urayasu-shi, JP) ; Hiraga; Yuka;
(Tokyo, JP) ; Murayama; Seiichi; (Fuchu-shi,
JP) ; Tokimoto; Hiroyuki; (Kawasaki-shi, JP) |
Family ID: |
45805625 |
Appl. No.: |
13/186177 |
Filed: |
July 19, 2011 |
Current U.S.
Class: |
210/137 |
Current CPC
Class: |
B01D 61/58 20130101;
B01D 61/04 20130101; C02F 1/444 20130101; C02F 2303/10 20130101;
B01D 61/14 20130101; C02F 2209/03 20130101; B01D 61/022 20130101;
B01D 61/025 20130101; B01D 2313/243 20130101; C02F 1/441 20130101;
C02F 2103/06 20130101; B01D 61/10 20130101; Y02A 20/131 20180101;
Y02W 10/30 20150501; C02F 2103/08 20130101; B01D 2311/14 20130101;
B01D 61/08 20130101; B01D 61/12 20130101; B01D 61/06 20130101 |
Class at
Publication: |
210/137 |
International
Class: |
B01D 61/12 20060101
B01D061/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2010 |
JP |
2010-207175 |
Claims
1. A membrane filtration system, comprising: (A) a raw water tank
configured to accommodate a raw water containing solutes and
insoluble components; (B) a pretreatment membrane module that
separates and removes the insoluble components from the raw water
fed from the raw water tank; (C) a raw water feed line having a raw
water feed pump to feed the raw water from the raw water tank to
the pretreatment membrane module; (D) a high-pressure reverse
osmosis membrane module provided in a subsequent stage of the
pretreatment membrane module to separate and remove the solutes
from pretreated water providing treated water as permeate and
concentrate as retentate; (E) a low-pressure reverse osmosis
membrane module provided in the subsequent stage of the
high-pressure reverse osmosis membrane module and to which a
pressure lower than that applied to the high-pressure reverse
osmosis membrane module is applied to separate and remove remaining
solutes from the treated water; (F) a high-pressure line having a
high-pressure pump to feed the pretreated water to the
high-pressure reverse osmosis membrane module at predetermined high
pressure; (G) a preceding power recovery unit having a
positive-displacement pump to which a portion of each of the brine
and the pretreated water are fed and which pressurize the
pretreated water by transmitting the pressure of the concentrate to
the pretreated water; (H) a succeeding power recovery unit having a
positive-displacement pump to which a portion of each of the
concentrate from the preceding power recovery unit and the raw
water are fed and which pressurize the raw water by transmitting a
remaining pressure of the concentrate to the raw water; (I) a
concentrate discharge line through which the concentrate discharged
from the high-pressure reverse osmosis membrane module flows to
transmit the pressure of the discharged concentrate to the
positive-displacement pump of the preceding power recovery unit;
(J) a communicating line communicating the preceding power recovery
unit and the succeeding power recovery unit and through which the
concentrate from the preceding power recovery unit flows; (K) a
first pressure transmission line branched from the high-pressure
line and communicating to the preceding power recovery unit and
through which a portion of the pretreated water to be fed to the
high-pressure reverse osmosis membrane module flows; (L) a second
pressure transmission line branched from the raw water feed line
and communicating to the succeeding power recovery unit and through
which a portion of the raw water to be fed to the pretreatment
membrane module flows; (M) a drain line to discharge the
concentrate from the succeeding power recovery unit; and (N) a
pressure regulating valve provided in the drain line to regulate a
discharge of the concentrate from the succeeding power recovery
unit in accordance with a pressure loss in the pretreatment
membrane module.
2. The system according to claim 1, further comprising: a first
manometer that measures a pressure in upstream of the pretreatment
membrane module; a second manometer that measures a pressure in
downstream of the pretreatment membrane module; and a controller
that determines a membrane differential pressure .DELTA.P of the
pretreatment membrane module from measured pressures of the first
and second manometers, regulates the pressure of the concentrate
discharged from the high-pressure reverse osmosis membrane module
by opening the pressure regulating valve if the determined membrane
differential pressure .DELTA.P is smaller than or equal to a set
pressure value Pc, and maintains the pressure regulating valve
closed if the determined membrane differential pressure .DELTA.P is
larger than the set pressure value Pc.
3. The system according to claim 1, further comprising: a treated
water tank arranged in a subsequent stage of the pretreatment
membrane module to accommodate the pretreated water having passed
through the pretreatment membrane module; a water conveyance line
having a conveying pump to feed the pretreated water from the
treated water tank to the high-pressure pump; and a back washing
line branched from the water conveyance line and communicating to
the pretreatment membrane module, to guide the pretreated water to
the pretreatment membrane module by driving of the conveying
pump.
4. The system according to claim 1, further comprising: a direct
transfer line connected to the high-pressure line to directly guide
the pretreated water having passed through the pretreatment
membrane module to the high-pressure reverse osmosis membrane
module; a treated water tank that accommodates the treated water
having passed through the high-pressure reverse osmosis membrane
module; a water conveyance line having a conveying pump to feed the
treated water from the treated water tank to the low-pressure
reverse osmosis membrane module; and a back washing line branched
from the water conveyance line and communicating to the
pretreatment membrane module, to guide the treated water to the
pretreatment membrane module by driving of the conveying pump.
5. The system according to claim 1, wherein there are a plurality
of succeeding reverse osmosis membrane modules, and the system
further comprises: a treated water tank that accommodates product
water having passed through the last stage, succeeding reverse
osmosis membrane module; a water conveyance line having a conveying
pump to send out the product water from the treated water tank; and
a back washing line communicating to the pretreatment membrane
module by being branched from the water conveyance line to guide
the treated water to the pretreatment membrane module by driving of
the conveying pump.
6. The system according to claim 1, further comprising: a
concentrate tank that accommodates the concentrate discharged from
the reverse osmosis membrane module; and a back washing line having
a washing pump to feed the concentrate from the concentrate tank to
the pretreatment membrane module.
7. The system according to claim 1, further comprising: a hot water
tank that accommodates hot water; a washing line provided between
at least one of the pretreatment membrane module, the high-pressure
reverse osmosis membrane module and the low-pressure reverse
osmosis membrane module, and the hot water tank and having a
conveying pump to feed the hot water to at least one of the
high-pressure reverse osmosis membrane module and the low-pressure
reverse osmosis membrane module; and a controller that controls
driving of the conveying pump at preset intervals or in preset
timing to cause the conveying pump to feed the hot water to at
least one of the high-pressure reverse osmosis membrane module and
the low-pressure reverse osmosis membrane module.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2010-207175,
filed Sep. 15, 2010, the entire contents of which are incorporated
herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a membrane
filtration system that filters brackish water, sea water, ground
water, landfill leachate, industrial wastewater and the like
containing a solute such as ions and salts by a reverse osmosis
membrane module.
BACKGROUND
[0003] In the field of water treatment, membrane filtration by a
reverse osmosis membrane module is used as a method of obtaining
domestic water, industrial water, and agricultural water from
brackish water, sea water, ground water, landfill leachate,
industrial wastewater and the like containing a solute such as ions
and salts. The reverse osmosis membrane (RO membrane) is a membrane
having a property of allowing water molecules to pass through, but
does not allow impurities such as ions and salts to pass through
and separates water from solutes by a pressure equal to or more
than the osmotic pressure in accordance with the solute density
being applied thereto. A membrane filtration system that uses such
an RO membrane provides pretreatment to remove insoluble components
such as turbidity, algae, and microbes contained in the intake sea
water before desalination by passing the sea water through an RO
membrane module. The sand filtration in which sea water is caused
to permeate through a sand filled layer is commonly used for the
pretreatment. However, if an attempt is made to obtain clearer
pretreated water to maintain permeation performance of an RO
membrane module, the sand filtration has low clarification
performance and is not effective.
[0004] As an effective pretreatment method in a water treatment
system, a membrane module having a microfiltration membrane (MF
membrane) and/or an ultrafiltration membrane (UF membrane) is
used.
[0005] In a conventional system, however, if a membrane module such
as an MF membrane or UF membrane is used for pretreatment of an RO
membrane module, a pressure pump to feed sea water to the MF
membrane/UF membrane module (pretreatment membrane module) by
applying pressure is further needed. Thus, power costs of the added
pressure pump are further added to a system that uses a membrane
module for pretreatment and therefore, compared with a system that
uses the sand filtration for pretreatment, power costs become
higher, increasing total operation costs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a configuration block diagram showing a membrane
filtration system according to a first embodiment;
[0007] FIG. 2 is a block circuit diagram showing a hydraulic
circuit containing a preceding power recovery unit;
[0008] FIG. 3 is a block circuit diagram showing the hydraulic
circuit containing the preceding power recovery unit when a channel
is switched;
[0009] FIG. 4 is a block circuit diagram showing the hydraulic
circuit containing the power recovery unit in a subsequent
stage;
[0010] FIG. 5 is a flow chart illustrating control of a line
pressure by switching control of a pressure regulating valve;
[0011] FIG. 6 is a configuration block diagram showing the membrane
filtration system according to a second embodiment;
[0012] FIG. 7 is a configuration block diagram showing the membrane
filtration system according to a third embodiment;
[0013] FIG. 8 is a configuration block diagram showing the membrane
filtration system according to a fourth embodiment;
[0014] FIG. 9 is a configuration block diagram showing the membrane
filtration system according to a fifth embodiment; and
[0015] FIG. 10 is a configuration block diagram showing the
membrane filtration system according to a sixth embodiment.
DETAILED DESCRIPTION
[0016] Various embodiments will be described hereinafter with
reference to the accompanying drawings.
[0017] (1) A membrane filtration system according to an embodiment
includes
[0018] (A) a raw water tank 2 configured to accommodate a raw water
containing solutes and insoluble components,
[0019] (B) a pretreatment membrane module 3 that separates and
removes the insoluble components from the raw water fed from the
raw water tank,
[0020] (C) a raw water feed line L2 having a raw water feed pump P1
to feed the raw water from the raw water tank to the pretreatment
membrane module,
[0021] (D) a high-pressure reverse osmosis membrane module 6
provided in a subsequent stage of the pretreatment membrane module
to separate and remove the solutes from pretreated water providing
treated water as permeate and concentrate as retentate,
[0022] (E) a low-pressure reverse osmosis membrane module 10
provided in the subsequent stage of the high-pressure reverse
osmosis membrane module and to which a pressure lower than that
applied to the high-pressure reverse osmosis membrane module is
applied to separate and remove remaining solutes from the treated
water,
[0023] (F) a high-pressure line L5 having a high-pressure pump P4
to feed the pretreated water to the high-pressure reverse osmosis
membrane module at predetermined high pressure,
[0024] (G) a preceding power recovery unit 7 having a
positive-displacement pump (71,72) to which a portion of each of
the concentrate and the pretreated water are fed and which
pressurize the pretreated water by transmitting the pressure of the
concentrate to the pretreated water,
[0025] (H) a succeeding power recovery unit 8 having a
positive-displacement pump (81,82) to which a portion of each of
the concentrate from the preceding power recovery unit and the raw
water are fed and which pressurize the raw water by transmitting a
remaining pressure of the concentrate to the raw water,
[0026] (I) a concentrate discharge line L61 through which the
concentrate discharged from the high-pressure reverse osmosis
membrane module flows to transmit the pressure of the discharged
concentrate to the positive-displacement pump of the preceding
power recovery unit,
[0027] (J) a communicating line L7 communicating the preceding
power recovery unit 7 and the succeeding power recovery unit 8 and
through which the concentrate from the preceding power recovery
unit flows,
[0028] (K) a first pressure transmission line L52 branched from the
high-pressure line L5 and communicating to the preceding power
recovery unit 7 and through which a portion of the pretreated water
to be fed to the high-pressure reverse osmosis membrane module
flows,
[0029] (L) a second pressure transmission line L22 branched from
the raw water feed line L2 and communicating to the succeeding
power recovery unit 8 and through which a portion of the raw water
to be fed to the pretreatment membrane module flows,
[0030] (M) a drain line L8 to discharge the concentrate from the
preceding power recovery unit 8, and
[0031] (N) a pressure regulating valve V1 provided in the drain
line L8 to regulate a discharge of the concentrate from the
succeeding power recovery unit in accordance with a pressure loss
in the pretreatment membrane module.
[0032] In the membrane filtration system in an embodiment, a feed
pressure of the pretreated water by the high-pressure pump P4 is
transmitted to the power recovery unit 7 in the previous stage via
the first pressure transmission line L52, the transmitted pressure
is recovered by the power recovery unit 7, and the recovered
pressure is provided to the pretreated water flowing through the
high-pressure line L5 upstream of the high-pressure reverse osmosis
membrane module via the first pressure transmission line L52. The
remaining pressure of the concentrate from the power recovery unit
7 in the previous stage is transmitted to the power recovery unit 8
in the subsequent stage via the communicating line L7 and the
transmitted pressure is recovered by the power recovery unit 8. The
recovered pressure is provided to the raw water flowing through the
raw water feed line L2 upstream of the pretreatment membrane module
via the second pressure transmission line L22 (FIGS. 1 and 4 to
10).
[0033] According to the membrane filtration system in an
embodiment, the pressure recovered from the preceding power
recovery unit 7 is applied to an upstream line of a reverse osmosis
membrane module to reduce power of the high-pressure pump P4 and
also the recovered pressure recovered from the succeeding power
recovery unit 8 is applied to the upstream line of the pretreatment
membrane module to reduce power of the raw water feed pump P1 and
therefore, total running costs can significantly be reduced. In
this case, switching control of the pressure regulating valve V1 is
exercised in accordance with a pressure loss .DELTA.P in the
pretreatment membrane module 3, the pressure of the concentrate
discharged from the succeeding power recovery unit 8 is regulated
to regulate the recovered pressure transmitted from the succeeding
power recovery unit, and the regulated recovered pressure is added
to increase the feed pressure of raw water.
[0034] (2) In the membrane filtration system described in (1), it
is preferable to further include a first manometer G1 that measures
a pressure P17 upstream of the pretreatment membrane module, a
second manometer G2 that measures a pressure P18 downstream of the
pretreatment membrane module, and a controller 20 that determines a
membrane differential pressure .DELTA.P of the pretreatment
membrane module from measured pressures of the first and second
manometers, regulates the pressure of the concentrate discharged
from the high-pressure reverse osmosis membrane module by opening
the pressure regulating valve V1 if the determined membrane
differential pressure .DELTA.P is smaller than or equal to a set
pressure value Pc, and maintains the pressure regulating valve V1
closed if the determined membrane differential pressure .DELTA.P is
larger than the set pressure value Pc.
[0035] In the membrane filtration system in an embodiment, the
pressure P17 upstream of the pretreatment membrane module is
measured by the first manometer G1 and the pressure P18 downstream
of the pretreatment membrane module is measured by the second
manometer G2 to determine a differential pressure of the both
measured pressures P17, P18 and if the determined membrane
differential pressure .DELTA.P is smaller than or equal to the set
pressure value Pc, the pressure regulating valve V1 is opened to
regulate the pressure of the brine discharged from the reverse
osmosis membrane module to a desired value (FIGS. 5, 1). If the
determined membrane differential pressure .DELTA.P is larger than
the predetermined set pressure value Pc, pressures on the upstream
and downstream sides are measured again while the pressure
regulating valve V1 is closed to continue the calculation of the
membrane differential pressure.
[0036] If the solute concentration of the concentrate upstream of
the high-pressure reverse osmosis membrane module increases with
the passage of processing time, the osmotic pressure rises and both
the load of the RO membrane and the load of the high-pressure pump
P4 become excessive. However, according to the membrane filtration
system in the present embodiment, the concentrate can be discharged
from the high-pressure reverse osmosis membrane module at
appropriate solute concentration so that processing efficiency of
the high-pressure RO membrane module can be improved without
damaging the RO membrane and the high-pressure pump P4.
[0037] (3) In the membrane filtration system described in (1), it
is preferable to further include a treated water tank arranged in
the subsequent stage of the pretreatment membrane module to
accommodate the pretreated water having passed through the
pretreatment membrane module, a water conveyance line L4 having a
conveying pump P3 to feed the pretreated water from the treated
water tank to the high-pressure pump, and a back washing line L42
branched from the water conveyance line L4 and communicating to the
pretreatment membrane module, to guide the pretreated water to the
pretreatment membrane module 3 by driving of the conveying pump
P3.
[0038] In the membrane filtration system in the present embodiment,
the pretreated water is temporarily accommodated in a treated water
tank 4, the channel is switched from the water conveyance line L4
to the back washing line L42 by a switching valve, and the
pretreated water is fed from the treated water tank 4 to the
pretreatment membrane module 3 through the back washing line L42 by
driving of the conveying pump P3 to reversely clean a membrane
filter in the pretreatment membrane module by the pretreated water
(FIG. 6).
[0039] According to the membrane filtration system in an
embodiment, the pretreated water generated in a system can be used
as back washing water without newly introducing back washing water
from outside the system and therefore, the membrane filter in the
pretreatment membrane module can be cleaned at low cost.
[0040] (4) In the membrane filtration system described in (1), it
is preferable to further include a direct transfer line L31
connected to the high-pressure line to directly guide the
pretreated water having passed through the pretreatment membrane
module to the high-pressure reverse osmosis membrane module, a
treated water tank 9 that accommodates the treated water having
passed through the high-pressure reverse osmosis membrane module, a
water conveyance line L91 having a low-pressure pump P6 to feed the
treated water from the treated water tank to the low-pressure
reverse osmosis membrane module, and a back washing line L92
branched from the water conveyance line and communicating to the
pretreatment membrane module, to guide the treated water to the
pretreatment membrane module by driving of the conveying pump.
[0041] In the membrane filtration system in an embodiment, the
treated water having passed through the reverse osmosis membrane
module is sent from the high-pressure reverse osmosis membrane
module 6 to the treated water tank 9 via the direct transfer line
L31 to temporarily accommodate the treated water in the treated
water tank 9, the treated water is sent to the reverse osmosis
membrane module 10 in the second or subsequent stage via the water
conveyance line L91 by driving of the low-pressure pump P6 for
normal treatment, and the channel is switched from the water
conveyance line L91 to the back washing line L92 and the treated
water is sent to the pretreatment membrane module 3 via the back
washing line L92 by driving of the low-pressure pump P6 to
reversely clean the membrane filter of the pretreatment membrane
module 3 for back washing treatment (FIG. 7).
[0042] According to the membrane filtration system in an
embodiment, the pretreated water generated in a system can be used
as back washing water without newly introducing back washing water
from outside the system and therefore, the membrane filter in the
pretreatment membrane module can be cleaned at low cost.
[0043] (5) In the membrane filtration system described in (1),
wherein there are a plurality of succeeding reverse osmosis
membrane modules, and it is preferable to further include a treated
water tank 11 that accommodates product water having passed through
the last stage, succeeding reverse osmosis membrane module 10; a
water conveyance line L111 having a conveying pump P7 to send out
the product water from the treated water tank; and a back washing
line L112 communicating to the pretreatment membrane module by
being branched from the water conveyance line to guide the treated
water to the pretreatment membrane module by driving of the
conveying pump.
[0044] In the membrane filtration system in the present embodiment,
the product water is temporarily accommodated in the treated water
tank 11 and the product water is fed to the pretreatment membrane
module 3 from the treated water tank 11 via the back washing line
L112 by driving of the conveying pump P7 to reversely clean the
membrane filter in the pretreatment membrane module by the product
water (FIG. 8).
[0045] According to the membrane filtration system in an
embodiment, the product water produced in a system can be used as
back washing water without newly introducing back washing water
from outside the system and therefore, the membrane filter in the
pretreatment membrane module can be cleaned at low cost.
[0046] (6) In the membrane filtration system described in (1), it
is preferable to further include a concentrate tank 23 that
accommodates the concentrate discharged from the high-pressure
reverse osmosis membrane module and a back washing line L82 having
a washing pump P8 to feed the concentrate from the concentrate tank
to the pretreatment membrane module.
[0047] In the membrane filtration system in an embodiment, the
concentrate discharged from the reverse osmosis membrane module is
temporarily accommodated in the concentrate tank 23 and the
concentrate is fed from the concentrate tank 23 to the pretreatment
membrane module 3 through the back washing line L82 by driving of
the washing pump P8 to reversely clean the membrane filter in the
pretreatment membrane module by the concentrate (FIG. 9).
[0048] According to the membrane filtration system in an
embodiment, the concentrate generated in a system can be used as
back washing water without newly introducing back washing water
from outside the system and therefore, the membrane filter in the
pretreatment membrane module can be cleaned at low cost.
[0049] (7) In the membrane filtration system described in (1), it
is preferable to further include a hot water tank that accommodates
hot water, a cleaning line provided between at least one of the
pretreatment membrane module, the high-pressure reverse osmosis
membrane module and the low-pressure reverse osmosis membrane
module, and the hot water tank and having a conveying pump to feed
the hot water to at least one of the pretreatment membrane module,
the high-pressure reverse osmosis membrane module, and the
low-pressure reverse osmosis membrane module, and a controller that
controls driving of the conveying pump at preset intervals or in
preset timing to cause the conveying pump to feed the hot water to
at least one of the pretreatment membrane module, the high-pressure
reverse osmosis membrane module, and the low-pressure reverse
osmosis membrane module.
[0050] In the membrane filtration system in an embodiment, the
channel is switched from the water conveyance line L111 to the back
washing line L112 by a switching valve and the hot water is fed
from a hot water tank 27 to the pretreatment membrane module 3
through the back washing line L112 by driving of the conveying pump
P7 to reversely clean the membrane filter in the pretreatment
membrane module by the hot water (FIG. 10).
[0051] According to the membrane filtration system in an
embodiment, by doing, in addition to normal cleaning, back washing
with hot water whose temperature is higher than that of normal
cleaning water periodically, clogging of the membrane filter can
efficiently be eliminated in a short time so that total running
costs can be reduced by reducing the rise in pressure of the
pretreatment membrane module and the reverse osmosis membrane
module.
[0052] Various embodiments will each be described hereinafter with
reference to the accompanying drawings.
First Embodiment
[0053] The first embodiment will be described with reference to
FIGS. 1 to 5.
[0054] As shown in FIG. 1, a membrane filtration system 1 according
to the first embodiment includes a raw water tank 2, a raw water
feed pump P1, a pretreatment membrane module 3, a first treated
water tank 4, a conveying pump P3, a protector filter 5, a
high-pressure pump P4, a high-pressure reverse osmosis membrane
module 6 in the first stage, a second treated water tank 9, a
low-pressure pump P6, a low-pressure reverse osmosis membrane
module 10 in the second stage, a third treated water tank 11, and a
conveying pump P7. These apparatuses and devices are arranged in
series in order from the upstream side on the main lines L1 to L11.
Further, the membrane filtration system 1 includes, as peripheral
equipment, a compressor C1, a first manometer G1, a second
manometer G2, a washing pump P2, a preceding power recovery unit 7,
a succeeding power recovery unit 8, a booster pump P5, a pressure
regulating valve V1, various valves (not shown), and a controller
20. The membrane filtration system 1 is controlled by the
controller 20 in a unified fashion.
[0055] The raw water tank 2 accommodates sea water pumped up from
the sea by driving of a storage pump (not shown) via the like L1
communicatively connected into the sea as the raw water. The
pressure line L2 having the pump P1 is connected to the outlet of
the raw water tank 2 so that the raw water is sent at predetermined
pressure from the raw water tank 2 to the pretreatment membrane
module 3 via the line L2 by driving of the raw water feed pump
P1.
[0056] The pretreatment membrane module 3 contains an MF membrane
or UF membrane that partitions the inside thereof into the
retentate side and the permeate side. On the retentate side of the
pretreatment membrane module 3, the raw water feed line L2, a
compressed air feed line from the compressor C1, and a discharge
line L32 are each communicated. The direct transfer line L31 is
directly communicated to the permeate side of the pretreatment
membrane module 3. The raw water is introduced into the
pretreatment membrane module 3 through the raw water feed line L2
and passed through the MF membrane or UF membrane before being sent
to the first treated water tank 4 through the direct transfer line
L31 as pretreated water from which solid content (such as sand and
suspended solids) has been removed.
[0057] The first manometer G1 is mounted on the line L2 on the
upstream side (retentate side) of the pretreatment membrane module
3. The first manometer G1 measures the pressure P17 on the upstream
side of the pretreatment membrane module 3 and sends a measurement
signal S1 thereof to the controller 20. The second manometer G2 is
mounted on the line L31 on the permeate side of the pretreatment
membrane module 3. The second manometer G2 measures the pressure
P18 on the downstream side (permeate side) of the pretreatment
membrane module 3 and sends a measurement signal S2 thereof to the
controller 20. Based on the input signals S1, S2, the controller 20
determines the upstream side measured pressure P17 and the
downstream side measured pressure P18, respectively, calculates the
difference .DELTA.P from the both measured pressures P17, P18, and
sends a control signal S3 corresponding to the calculated
difference .DELTA.P to a drive power supply of the pressure
regulating valve V1 described later.
[0058] The first treated water tank 4 is a reservoir to accommodate
the pretreated water membrane-filtered by the pretreatment membrane
module 3. The outlet of the first treated water tank 4 is connected
to the water conveyance line L4 having the pump P3 and communicates
to the protector filter 5 via the line L4. A back washing line L12
having the pump P2 is connected to a lower part of the first
treated water tank 4. The back washing line L12 is connected to an
appropriate position of the direct transfer line L31. The
pretreated water from the first treated water tank 4 is fed to the
downstream side of the pretreatment membrane module 3 by passing
through the lines L12.fwdarw.L31 by driving of the washing pump P2
so that the clogged MF membrane or UF membrane is reversely
cleaned.
[0059] The protector filter 5 is provided between the first treated
water tank 4 and the high-pressure reverse osmosis membrane module
6 to remove foreign matter from the pretreated water sent from the
first treated water tank 4 so that foreign matter such as solid
content is prevented from infiltrating into the high-pressure
reverse osmosis membrane module 6. The protector filter 5 is filled
with filter elements, the water conveyance line L4 is connected to
the inlet of the protector filter 5, and the high-pressure line L5
is connected to the outlet of the protector filter 5.
[0060] The high-pressure pump P4 is mounted on the high-pressure
line L5 so as to feed water having passed through the protector
filter 5 to the high-pressure reverse osmosis membrane module 6 at
predetermined high pressure P4 (for example, 6 MPa). Various types
of pumps such as a reciprocating pump and volute pump can be used
as the high-pressure pump P4.
[0061] The high-pressure reverse osmosis membrane module 6 contains
a RO membrane that partitions the inside thereof into the retentate
side and the permeate side. The high-pressure line L5 and the
concentrate discharge line L61 are connected to the retentate side
of the high-pressure RO membrane module 6. A water conveyance line
L62 is connected to the permeate side of the high-pressure RO
membrane module 6.
[0062] The high-pressure line L5 is branched into two. That is, a
line L51 is branched from the main line L5 communicating to the
high-pressure RO membrane module 6 via the high-pressure pump P4.
As shown in FIGS. 2 and 3, the branch line L51 communicates to a
high-pressure side chamber (space on one side inside cylinders 71a,
71b partitioned by pistons 72a, 72b) of the positive-displacement
pumps 71, 72 of the preceding power recovery unit 7 in the previous
stage and forms a first transmission line to transmit pressure from
the pretreated water (pretreated sea water) to the pistons 72a,
72b.
[0063] Another first pressure transmission line L53 communicates to
a low-pressure side chamber (space on the other side inside the
cylinders 71a, 71b partitioned by the pistons 72a, 72b) of the
cylinders 71a, 71b of the preceding power recovery unit 7. The
first pressure transmission line L53 merges with the high-pressure
line L5 via a pressure transmission circuit 79 and the other
pressure transmission line L52 to transmit the recovered pressure
to the upstream side of the high-pressure RO membrane module 6. The
booster pump P5 of the line L52 supplements an insufficient
pressure of the recovered pressure by the power recovery unit 7 in
the previous stage and is an optional device that can be omitted if
a sufficient pressure can be recovered by the preceding power
recovery unit 7.
[0064] The concentrate discharge line L61 communicates to a 4-port
switching valve 61 of the preceding power recovery unit 7 in the
previous stage. The concentrate discharge line L61 guides
concentrate discharged from the upstream side of the high-pressure
RO membrane module 6 to the preceding power recovery unit 7 so that
high pressure held by the concentrate is transmitted to the pistons
72a, 72b.
[0065] The communicating line L7 is provided between the 4-port
switching valve 61 of the preceding power recovery unit 7 and a
4-port switching valve 62 of the succeeding power recovery unit 8.
The communicating line L7 is a pressure transmission channel to
cause raw water on the side of the succeeding power recovery unit 8
to recover pressure energy of concentrate (brine) discharged from
the preceding power recovery unit 7.
[0066] The second pressure transmission line L22 is provided
between the low-pressure side chamber of the succeeding power
recovery unit 8 and the line L2 downstream of the pump P1. A raw
water introduction line L21 is provided between the line L2
upstream of the pump P1 and the low-pressure side chamber of the
succeeding power recovery unit 8. The raw water introduced into the
low-pressure side chamber of the succeeding power recovery unit 8
from the line L21 has pressure energy transmitted from a
pressurized fluid (brine) in the high-pressure side chamber via the
pistons 82a, 82b and the pressure energy is given to the raw water
flowing through the line L2 via the second pressure transmission
line L22.
[0067] The drain line L8 is provided between the high-pressure side
chamber of the succeeding power recovery unit 8 and a concentrate
tank (not shown) via the pressure regulating valve V1. The drive
power supply of the valve V1 is controlled by the controller 20.
That is, when the control signal S3 from the controller 20 is
received, the valve V1 opens to discharge concentrate into the
atmospheric pressure. The pressure control signal S3 is determined
by the controller 20 based on the two pressure measurement signals
S1, S2. Details thereof will be described later with reference to
FIG. 5.
[0068] A permeate side space of the high-pressure RO membrane
module 6 communicates to the second treated water tank 9 via the
water conveyance line L62. That is, primary treated water having
permeated through the RO membrane is sent from the RO membrane
module 6 to the second treated water tank 9 via the line L62.
[0069] The second treated water tank 9 is a reservoir to
accommodate primary treated water having been membrane-filtered by
the high-pressure RO membrane module 6. The outlet of the second
treated water tank 9 is connected to a line L9 having the
low-pressure pump P6 and communicates to the upstream side of the
low-pressure RO membrane module 10 via the line L9. The
low-pressure pump P6 applies a pressure lower than the
predetermined high pressure P4 (6 MPa) applied to a fluid by the
high-pressure pump P4 to a fluid.
[0070] Two lines L101, L102 communicate to the permeate side of the
low-pressure RO membrane module 10. One line L101 communicates to
the first treated water tank 4. The other line L102 communicates to
the third treated water tank 11.
[0071] The third treated water tank 11 is a reservoir to
accommodate product water (treated water in low solute
concentration) treated by the low-pressure RO membrane module 10.
The outlet of the third treated water tank 11 is connected to the
line L11 having the conveying pump P7 and communicates to a fresh
water clarification tank of a product water treater (not shown) via
the line L11.
[0072] The power recovery unit in two stages will be described in
detail with reference to FIGS. 2 to 4.
[0073] As shown in FIGS. 2 and 3, the preceding power recovery unit
7 includes a pressure regulating valve PV1, the 4-port switching
valve 61, a pair of the positive-displacement pumps 71, 72, two
sets of rod position detectors (77a, 78a), (77b, 78b), and the
pressure transmission circuit 79 having four check valves CV1, CV2,
CV3, CV4. These elements function as a pressure conversion unit
that converts the pressure P6 of the concentrate discharged from
the high-pressure RO membrane module 6 into an additional pressure
P11 added to the pretreated water fed to the high-pressure RO
membrane module 6. Of these elements, the pressure regulating valve
PV1 and the 4-port switching valve 61 are each controlled by the
above controller 20 in operation.
[0074] The pressure regulating valve PV1 is provided on the
concentrate discharge line L61 upstream of the 4-port switching
valve 61 and controls the concentrate (brine) pressure P7 delivered
to the 4-port switching valve 61 by limiting the pressure P6 of the
brine (high-concentration sea water) discharged from the
high-pressure RO membrane module 6. The concentrate discharge
pressure P6 from the high-pressure RO membrane module 6 falls with
clogging of the RO membrane after long-term usage of the RO
membrane. The pressure regulating valve PV1 is used to regulate a
decrease of the concentrate discharge pressure P6. With the
pressure regulating valve PV1 being controlled by the controller
20, the pressure P11 of the pretreated water output from the power
recovery unit 7 in the previous stage and the pressure P4 of the
pretreated water output from the high-pressure pump P4 are
controlled so as to be always equal.
[0075] The 4-port switching valve 61 is arranged on the line L61
downstream of the pressure regulating valve PV1 and switches the
inflow of concentrate into the positive-displacement pumps 71, 72
and the discharge of concentrate from the positive-displacement
pumps 71, 72 according to the control signal from the controller
20. As the system of switching the 4-port switching valve 61, the
pneumatic system, hydraulic system, oil pressure system or solenoid
coil based system can be used.
[0076] One pair of the positive-displacement pumps 71, 72 is
communicatively connected to the retentate side of the
high-pressure RO membrane module 6 via the pressure regulating
valve PV1 of the line L61 and the 4-port switching valve 61. The
first positive-displacement pump 71 and the second
positive-displacement pump 72 have substantially the same
configuration. The input channel to the pumps 71, 72 is switched by
the 4-port switching valve 61 so that the first
positive-displacement pump 71 and the second positive-displacement
pump 72 are alternately loaded with the concentrate pressure P7.
FIG. 2 shows a state in which the first positive-displacement pump
71 is loaded with the concentrate pressure P7. FIG. 3 shows a state
in which the second positive-displacement pump 72 is loaded with
the concentrate pressure P7.
[0077] The first positive-displacement pump 71 includes the
cylinder 71a, the piston 72a, and a rod 73a. The cylinder 71a is
composed of a container in a cylindrical or rectangular pipe shape
to form an enclosed space and the container has a total of three
openings, that is, an inlet and an outlet of a pressurized fluid
and an insertion port of the rod 73a, formed therein. The piston
72a is supported reciprocatingly slidably inside the cylinder 71a
and partitions an internal space of the cylinder 71a into a first
space and a second space. A seal ring (not shown) is fitted to an
outer circumferential surface of the piston 72a for fluid-tight
sealing so that a fluid is not leaked from the first space to the
second space in the cylinder 71a. Concentrate (brine) is to be
introduced into the first space of the cylinder 71a through the
4-port switching valve 61 of the line L61. Pretreated water is to
be fed into the second space of the cylinder 71a through the line
L51.
[0078] On end of the rod 73a is joined to the piston 72a from the
side of the second space and the other end projects to the outside
through a seal hole of the cylinder 71a. Because the rod 73a is
joined to the piston 72a from the side of the second space of the
cylinder 71a, an area A2 where the piston 72a faces the second
space of the cylinder 71a is smaller than an area A1 where the
piston 72a faces the first space of the cylinder 71a (A2<A1).
The ratio of the areas A1, A2 is preset based on the pressure of
concentrate from the high-pressure RO membrane module 6, pressure
of pretreated water from the high-pressure pump P4, frictional
force between the cylinder 71a and the piston 72a, and frictional
force between the cylinder 71a and the rod 73a.
[0079] One side of the pressure transmission circuit 79 is
connected to the protector filter 5 by the branch line L51 and the
other side is connected to the cylinders 71a, 71b by the line L53.
The pressure transmission circuit 79 includes a loop circuit
through which the pretreated water passes from the first treated
water tank 4 via the protector filter 5 and four check valves CV1,
CV2, CV3, CV4 mounted on the loop circuit. These four check valves
CV1, CV2, CV3, CV4 open and close independently in accordance with
a pressure difference therearound.
[0080] One pair of the detectors 77a, 78a is position detection
sensors that detects the position of the rod 73a projecting to the
outside from the cylinder 71a of the first positive-displacement
pump 71. One detector 77a is mounted in a position allowing the
detector 77a to detect the rod 73a when the piston 72a comes close
to the left end of the cylinder 71a. The other detector 78a is
mounted in a position not allowing the detector 78a to detect the
rod 73a when the piston 72a comes close to the right end of the
cylinder 71a. When one detector 77a is in a position enabling
detection of the rod 73a or the other detector 78a is in a position
disabling detection (non-detection state) of the rod 73a, a signal
thereof is sent to the controller 20.
[0081] The detectors 77b, 78b of the second positive-displacement
pump 72 have substantially the same configuration as that of the
detectors 77a, 78a of the first positive-displacement pump 71
described above and detect the position of the rod 73b projecting
from the cylinder 71b. When one detector 77b is in a position
enabling detection of the rod 73b or the other detector 78b is in a
position disabling detection (non-detection state) of the rod 73b,
a signal thereof is sent to the controller 20.
[0082] An overview of the operation of the preceding power recovery
unit 7 will be described.
[0083] The controller 20 calculates the position of the piston 72a
inside the first cylinder 71a based on a signal sent from the first
detectors 77a, 78a, and also calculates the position of the piston
72b inside the second cylinder 71b based on a signal sent from the
second detectors 77b, 78b. Based on the calculated positions of the
first and second pistons 72a, 72b, the controller 20 determines
whether to cause the 4-port switching valve 61 to perform a
switching operation and if the controller 20 determines to cause
the 4-port switching valve 61 to perform a switching operation, the
controller 20 sends an instruction signal thereof to the 4-port
switching valve 61.
[0084] If detection signals are received from the detectors 77a,
78b, the controller 20 determines that the first piston 72a is
positioned near the left end of the first cylinder 71a and the
second piston 72b is positioned near the right end of the second
cylinder 71b and outputs a signal to the switching valve 61 to
cause the switching valve 61 to discharge concentrate from the
first positive-displacement pump 71 and to feed the concentrate to
the second positive-displacement pump 72. The transmission path of
concentrate pressure in this operation is: module 6.fwdarw.line
L61.fwdarw.switching valve 61.fwdarw.second pump 72.fwdarw.line
L53.fwdarw.check valve CV3.fwdarw.line L52.fwdarw.line
L5.fwdarw.module 6 (FIG. 3).
[0085] On the other hand, if detection signals are received from
the detectors 78a, 77b, the controller 20 determines that the first
piston 72a is positioned near the right end of the cylinder 71a and
the second piston 72b is positioned near the left end of the
cylinder 71b and outputs a signal to the 4-port switching valve 61
to cause the switching valve 61 to feed concentrate to the first
positive-displacement pump 71 and to discharge the concentrate from
the second positive-displacement pump 72. The transmission path of
concentrate pressure in this operation is: module 6.fwdarw.line
L61.fwdarw.switching valve 61.fwdarw.first pump 71.fwdarw.line
L53.fwdarw.check valve CV2.fwdarw.line L52.fwdarw.line
L5.fwdarw.module 6 (FIG. 2).
[0086] Next, the succeeding power recovery unit 8 will be described
with reference to FIG. 4.
[0087] The succeeding power recovery unit 8 is connected to the
preceding power recovery unit 7 by the communicating line L7. That
is, the outlet of the switching valve 61 of the preceding power
recovery unit 7 communicates to the inlet of the switching valve 62
of the succeeding power recovery unit 8 via the communicating line
L7 so that a remaining pressure P9 of concentrate having passed
through the preceding power recovery unit 7 is transmitted to raw
water of the succeeding power recovery unit 8.
[0088] The succeeding power recovery unit 8 includes a pressure
transmission circuit 89 having the 4-port switching valve 62, a
pair of the positive-displacement pumps 81, 82, two sets of rod
position detectors (87a, 88a), (87b, 88b), and four check valves
CV5, CV6, CV7, CV8. These elements function as a pressure
conversion unit that converts the remaining pressure P9 of the
concentrate into an additional pressure P15 added to the raw water
fed to the pretreatment membrane module 3. Of these elements, the
4-port switching valve 62 is controlled by the above controller 20
in operation.
[0089] In the succeeding power recovery unit 8, the 4-port
switching valve 62 has substantially the same configuration as that
of the 4-port switching valve 61 in the previous stage described
above, but the positive-displacement pumps 81, 82 have a different
type from that of the positive-displacement pumps 71, 72 in the
previous stage described above. That is, the positive-displacement
pump 81 (82) has a connecting rod 83a (83b) having pistons 82a, 84a
(82b, 84b) of different diameters mounted on both ends. The first
positive-displacement pump 81 includes a set of the large-diameter
cylinder 81a/piston 82a, a set of the small-diameter cylinder
85a/piston 84a, and the connecting rod 83a connecting the
large-diameter piston 82a and the small-diameter piston 84a.
[0090] The both cylinders 81a, 85a are composed of a container in a
cylindrical or rectangular pipe shape to form an enclosed space and
one end thereof is open and the other end is closed. The openings
of the both cylinders 81a, 85a are opposite to each other. The
cylinders 81a, 85a have the inlet/outlet of a pressurized fluid
(concentrate or raw water) and an insertion port of the connecting
rod 83a formed therein.
[0091] The large-diameter piston 82a is attached to one end of the
connecting rod 83a and the small-diameter piston 84a is attached to
the other end of the rod 83a. That is, the two pistons 82a, 84a
share one rod 83a. A dog 86a is formed in the center in the
longitudinal direction of the connecting rod 83a. The
large-diameter piston 82a is arranged slidably inside the
large-diameter cylinder 81a by being supported by the rod 83a and
the small-diameter piston 84a is arranged slidably inside the
small-diameter cylinder 85a by being supported by the rod 83a.
[0092] The high-pressure side chamber is formed from the
large-diameter piston 82a and the large-diameter cylinder 81a. A
seal material (not shown) is inserted between the large-diameter
piston 82a and the large-diameter cylinder 81a. One opening of the
large-diameter cylinder 81a communicates to the communicating line
L7 so that concentrate is introduced into the high-pressure side
chamber from the preceding power recovery unit 7 in the previous
stage. The area of the plane of the large-diameter piston 82a
receiving pressure from the concentrate introduced into the
high-pressure side chamber is A3.
[0093] On the other hand, the low-pressure side chamber is formed
from the small-diameter piston 84a and the small-diameter cylinder
85a. A seal material (not shown) is inserted between the
small-diameter piston 84a and the small-diameter cylinder 85a. One
opening of the small-diameter cylinder 85a communicates to the line
L21 so that raw water is introduced into the low-pressure side
chamber from the raw water tank 2. The area of the plane of the
small-diameter piston 84a receiving pressure from the raw water
introduced into the low-pressure side chamber is A4. The area A3 is
larger than the area A4 (A3>A4). The ratio of the area A3 to the
area A4 is preset based on the remaining pressure P9 of concentrate
from the preceding power recovery unit 7, feed pressure P16 of raw
water from the raw water tank 2, raw water feed pressure P17 from
the pump P1, frictional force between the large-diameter cylinder
81a and the large-diameter piston 82a, and frictional force between
the small-diameter cylinder 85a and the small-diameter piston
84a.
[0094] The second positive-displacement pump 82 includes a set of
the large-diameter cylinder 81b/piston 82b, a set of the
small-diameter cylinder 85b/piston 84b, and the connecting rod 83b
connecting the large-diameter piston 82b and the small-diameter
piston 84b.
[0095] The both cylinders 81b, 85b are composed of a container in a
cylindrical or rectangular pipe shape to form an enclosed space and
one end thereof is open and the other end is closed. The openings
of the both cylinders 81b, 85b are opposite to each other. The
cylinders 81b, 85b have the inlet/outlet of a pressurized fluid
(concentrate or raw water) and an insertion port of the connecting
rod 83b formed therein.
[0096] The large-diameter piston 82b is attached to one end of the
connecting rod 83b and the small-diameter piston 84b is attached to
the other end of the rod 83b. That is, the two pistons 82b, 84b
share one rod 83b. A dog 86b is formed in the center in the
longitudinal direction of the connecting rod 83b. The
large-diameter piston 82b is arranged slidably inside the
large-diameter cylinder 81b by being supported by the rod 83b and
the small-diameter piston 84b is arranged slidably inside the
small-diameter cylinder 85b by being supported by the rod 83b.
[0097] The high-pressure side chamber is formed from the
large-diameter piston 82b and the large-diameter cylinder 81b. A
seal material (not shown) is inserted between the large-diameter
piston 82b and the large-diameter cylinder 81b. One opening of the
large-diameter cylinder 81b communicates to the line L8 so that a
pressurized fluid (concentrate) is discharged from a third space.
The area of the plane of the large-diameter piston 82b receiving
pressure from the pressurized fluid (concentrate) introduced into
the third space is A3.
[0098] On the other hand, the low-pressure side chamber is formed
from the small-diameter piston 84b and the small-diameter cylinder
85b. A seal material (not shown) is inserted between the
small-diameter piston 84b and the small-diameter cylinder 85b. One
opening of the small-diameter cylinder 85b communicates to the line
L22 so that raw water is introduced into the low-pressure side
chamber from the raw water tank 2. The area of the plane of the
small-diameter piston 84b receiving pressure from the raw water
introduced into the low-pressure side chamber is A4. The area A3 is
larger than the area A4 (A3>A4). The ratio of the area A3 to the
area A4 is preset based on the pressure P9 of concentrate from the
power recovery unit 7 in the previous stage, pressure P17 of raw
water from the conveying pump P1, frictional force between the
large-diameter cylinder 81b and the large-diameter piston 82b, and
frictional force between the small-diameter cylinder 85b and the
small-diameter piston 84b.
[0099] The first set of the detectors 87a, 88a detects the position
of the dog 86a in the first connecting rod 83a. One detector 87a is
mounted in a position allowing the detector 87a to detect contact
of the dog 86a when the piston 84a comes close to the left end of
the cylinder 85a. On the other hand, the other detector 88a is
mounted in a position allowing the detector 88a to detect contact
of the dog 86a when the piston 82a comes close to the right end of
the cylinder 81a. When the detectors 87a, 88a detect the dog 86a,
detection signals are sent to the controller 20 and accordingly,
the positions of the both pistons 82a, 84a in the first
positive-displacement pump 81 are grasped.
[0100] The second set of the detectors 87b, 88b detects the
position of the dog 86b mounted on the second connecting rod 83b.
The second set of the detectors 87b, 88b has the same configuration
as that of the first set of the detectors 87a, 88a and detects the
position of the dog 86b in the rod 83b. When the detectors 87b, 88b
detect the dog 86b, detection signals are sent to the controller 20
and accordingly, the positions of the both pistons 82b, 84b in the
second positive-displacement pump 82 are grasped.
[0101] The controller 20 outputs a switching signal to the
switching valve 62 in accordance with a detection signal from the
detectors 87a, 88a, 87b, 88b. That is, if detection signals are
received from the detectors 87a, 88b, the controller 20 determines
that the piston 84a is positioned near the left end of the cylinder
85a and the piston 82b is positioned near the right end of the
cylinder 81b. Then, the controller 20 sends a switching signal to
the switching valve 62 so that concentrate is discharged from the
first positive-displacement pump 81 and also the concentrate is fed
to the second positive-displacement pump 82. If detection signals
are received from the detectors 88a, 87b, the controller 20
determines that the piston 82a is positioned near the right end of
the cylinder 81a and the piston 84b is positioned near the left end
of the cylinder 85b. Then, the controller 20 sends a switching
signal to the switching valve 62 so that concentrate is fed to the
first positive-displacement pump 81 and also the concentrate is
discharged from the second positive-displacement pump 82.
[0102] In the above embodiment, a case when a 2-cylinder power
recovery unit is used is described, but the power recovery unit is
not limited to such a structure and a 3-cylinder system can also be
adopted. In the power recovery unit in the embodiment, a case when
a piston rod is used as a pressure transmission mechanism is
described, but a crank shaft as a different pressure transmission
mechanism can also be used.
[0103] An overview of the operation of the power recovery unit 8 in
the subsequent stage will be described.
[0104] The controller 20 calculates the positions of the first and
second pistons 82a, 85a inside the first and second cylinders 81a,
85a based on signals sent from the first detectors 87a, 88a, and
also calculates the positions of the third and fourth pistons 82b,
84b inside the third and fourth cylinders 81b, 85b based on signals
sent from the second detectors 87b, 88b. Based on the calculated
positions of the pistons 82a, 84a, 82b, 84b, the controller 20
determines whether to cause the 4-port switching valve 62 to
perform a switching operation and if the controller 20 determines
to cause the 4-port switching valve 62 to perform a switching
operation, the controller 20 sends an instruction signal thereof to
the 4-port switching valve 62.
[0105] If detection signals are received from the detectors 87a,
88b, the controller 20 determines that the first piston 82a is
positioned near the right end of the cylinder 81a and the fourth
piston 84b is positioned near the left end of the cylinder 85b and
outputs a signal to the 4-port switching valve 62 to cause the
4-port switching valve 62 to feed concentrate to the first
positive-displacement pump 81 and to discharge the concentrate from
the second positive-displacement pump 82. The transmission path of
concentrate pressure in this operation is: the power recovery unit
7.fwdarw.line L7.fwdarw.switching valve 62.fwdarw.first pump
81.fwdarw.line L23.fwdarw.check valve CV6.fwdarw.line
L22.fwdarw.line L2.fwdarw.module 3 (FIG. 4).
[0106] On the other hand, if detection signals are received from
the detectors 88a, 87b, the controller 20 determines that the
second piston 84a is positioned near the left end of the second
cylinder 85a and the third piston 82b is positioned near the right
end of the third cylinder 81b and outputs a signal to the 4-port
switching valve 62 to cause the 4-port switching valve 62 to
discharge concentrate from the first positive-displacement pump 81
and to feed the concentrate to the second positive-displacement
pump 82. The transmission path of concentrate pressure in this
operation is: preceding power recovery unit 7.fwdarw.line
L7.fwdarw.switching valve 62.fwdarw.second pump 82.fwdarw.line
L23.fwdarw.check valve CV7.fwdarw.line L22.fwdarw.line
L2.fwdarw.module 3.
[0107] Next, an overview of the operation of a membrane filtration
system according to an embodiment will be described.
[0108] Raw water is fed to the pretreatment membrane module 3 by
the pump P1 at predetermined pressure P17 and passed through an MF
membrane or UF membrane to become pretreated water from which a
portion of solutes is removed before being stored in the first
treated water tank 4. The pretreated water in the first treated
water tank 4 is conveyed to the high-pressure pump P4 and the
preceding power recovery unit 7 in the previous stage by the
conveying pump P3 and the high-pressure pump P4 increases the
pressure of the water to the predetermined high pressure P4 (about
6 MPa) before conveying the water to the high-pressure RO membrane
module 6. The high-pressure RO membrane module 6 removes solutes
such as ions and salts contained in the raw water to generate
primary treated water whose solute concentration is lowered. The
generated primary treated water is stored in the second treated
water tank 9. To get better water in quality, the water in the
second treated water tank 9 is conveyed to the low-pressure RO
membrane module 10 by the low-pressure pump P6. In the low-pressure
RO membrane module 10, solutes such as ions and salts remaining in
the water are further removed to generate secondary treated water
(product water) whose solute concentration is further lowered. The
generated product water is stored in the third treated water tank
11.
[0109] On the other hand, brine (concentrated sea water) discharged
from the high-pressure RO membrane module 6 is sent to the
preceding power recovery unit 7. The preceding power recovery unit
7 has the first positive-displacement pump 71 to which the brine is
fed and the second positive-displacement pump 72 from which the
brine is discharged. The preceding power recovery unit 7 recovers
the pressure of brine and transmits the recovered pressure to the
pretreated water on the route of the line L53.fwdarw.the pressure
transmission circuit 79.fwdarw.the line L52.fwdarw.the
high-pressure line L5. The pretreated water to which the recovered
pressure is added is further pressurized by the booster pump P5 to
push the high-pressure pretreated water of the high-pressure line
L5.
[0110] On the other hand, the pretreated water from the protector
filter 5 passes through the main line L5 before being fed to the
high-pressure pump P4 at, for example, 0.2 MPa and also passes
through the check valve CV4 from the branch line L5 before being
fed to the second space of a cylinder of the second
positive-displacement pump 72 (FIG. 2).
[0111] The pretreated water whose pressure is increased to, for
example, 6.0 MPa by the high-pressure pump P4 is merged with the
pretreated water from the preceding power recovery unit 7 before
being introduced into the RO membrane module 6. In this case, the
pretreated water from the preceding power recovery unit 7 is water
discharged from the second space of the cylinder 71a of the first
positive-displacement pump 71 and having passed through the check
valve CV2. The RO membrane module 6 discharges the treated water
and brine.
[0112] The brine discharged from the RO membrane module 6 passes
through the pressure regulating valve PV1 and the switching valve
61 before flowing into the first space of the cylinder 71a of the
first positive-displacement pump. At this point, the second space
of the cylinder 71a of the first positive-displacement pump is
filled with pretreated water. The brine pushes the piston 72a
inside the cylinder 71a in the direction of the second space to
discharge the pretreated water from the second space while
pressurizing the pretreated water.
[0113] The area where the piston 72a faces the first space is A1
and the area where the piston 72a faces the second space is A2 and
thus, the pressure P8 of the pretreated water discharged from the
second space of the cylinder 71a is calculated as
P8=P7.times.(A1/A2) by using the brine pressure P7 from the
switching valve 61. Accordingly, the pressure P8 is a pressure
equivalent to the pressure P4 introduced into the high-pressure RO
membrane module 6 or a little higher.
[0114] The pretreated water from the protector filter 5 passes
through the check valve CV4 before flowing into the second space of
the cylinder 71b of the second positive-displacement pump 72. At
this point, the first space of the cylinder 71b of the second
positive-displacement pump 72 is filled with brine.
[0115] The pretreated water having passed through the fourth check
valve CV4 has the pressure of, for example, 0.2 MPa and pushes the
piston 72b inside the cylinder 71b in the direction of the first
space. The movement of the piston 72b in the direction of the first
space discharges the brine from the first space of the cylinder 71b
via the 4-port switching valve 61.
[0116] Accordingly, if the above operation is maintained, the one
piston 72a moves closer to the left end of the cylinder 71a and the
other piston 72b moves closer to the right end of the cylinder 71b.
Then, the rod 73a comes into contact with the first detector 77a
and a detection signal (contact signal) thereof is sent to the
controller 20. Also, the rod 73a moves away from the fourth
detector 78b and a detection signal (non-contact signal) thereof is
sent to the controller 20. If detection signals from the first and
fourth detectors 77a, 78b are received, the controller 20 sends a
control signal to the 4-port switching valve 61 to switch the
direction of inflow and discharge of brine. Accordingly, the inflow
and discharge of brine are switched and the pistons 72a, 72b move
in arrow directions. That is, as shown in FIG. 3, the brine is
introduced into the second positive-displacement pump 72 and the
brine is discharged from the first positive-displacement pump
71.
[0117] The brine discharged from the high-pressure RO membrane
module 6 passes through the pressure regulating valve PV1 and the
4-port switching valve 61 before flowing into the first space of
the cylinder 71b of the second positive-displacement pump 72. At
this point, the second space of the cylinder 71b of the second
positive-displacement pump 72 is filled with pretreated water. The
brine pushes the piston 72b inside the cylinder 71b in the
direction of the second space to discharge the brine from the
second space while pressurizing the pretreated water.
[0118] The area where the second piston 72b faces the first space
is A1 and the area where the second piston 72b faces the second
space is A2 and thus, the pressure P10 of the pretreated water
discharged from the second space of the cylinder 71b is calculated
as P10=P7.times.(A1/A2) by using the brine pressure P7 from the
switching valve 61. Accordingly, the pressure P10 is a pressure
equivalent to the pressure P4 introduced into the RO membrane
module 6 or a little higher.
[0119] The brine from which the pressure is recovered from the
preceding power recovery unit 7 is further sent to the succeeding
power recovery unit 8. The remaining pressure P9 of the brine is
recovered by the succeeding power recovery unit 8 and the recovered
pressure is transmitted to the raw water in the downstream line L2
of the pump P1. The raw water to which the additional pressure is
added is sent to the pretreatment membrane module 3. For the rise
in pressure, the pressure regulating valve V1 is controlled in
accordance with a difference (inter-membrane differential pressure)
LP between the measured pressure P17 at upstream of the membrane
module 3 measured by the first manometer G1 and the measured
pressure P18 at downstream of the membrane module 3 measured by the
second manometer G2 to obtain the pressure necessary to feed raw
water to the pretreatment membrane module 3. One end of the
pressure regulating valve V1 is open to the air and thus, the gauge
pressure of the first space of the cylinder 71b of the second
positive-displacement pump 72 is approximately zero. The pretreated
water having passed through the fourth check valve CV4 has the
pressure of, for example, 0.2 MPa and moves the piston 72b inside
the cylinder 71b in the direction of the first space. The
pretreated water pushes the piston 72b in the direction of the
first space to discharge the brine from the first space.
[0120] The washing pump P2 is driven periodically at predetermined
intervals to cause the pretreated water in the first treated water
tank 4 to flow backward to the pretreatment membrane module 3 via
the back washing line L12 for back washing of the MF membrane or UF
membrane in the module. In this case, bubbling to feed a compressed
air into the membrane module 3 from the compressor C1 may be used
in combination.
[0121] Next, an overview of the operation of the pressure
regulating valve V1 will be described with reference to FIG. 5.
[0122] The pump P1 is activated to start feeding of raw water from
the raw water tank 2 to the pretreatment membrane module 3. The
pump P3 is activated to start feeding of pretreated water from the
first treated water tank 4 to the protector filter 5 and further,
after water having passed through the protector filter 5 being fed
to the power recovery line L52 by activating the booster pump P5,
the high-pressure pump P4 is activated to apply a high pressure to
the water having passed through the protector filter 5 to feed the
water to the high-pressure RO membrane module 6 and also a
supplementary pressure is applied to a fluid passing through the
pressure transmission like L52 by the booster pump P5 to start
treatment (step K1). When the treatment is started, the pressure
regulating valve V1 is open.
[0123] After the pressure regulating valve V1 is closed (step K2),
the pressure P17 upstream of the pretreatment membrane module 3 is
measured by the first manometer G1 (step K3). After the pressure
regulating valve V1 is closed (step K2), the pressure P18
downstream of the pretreatment membrane module 3 is measured by the
second manometer G2 (step K4). The controller 20 calculates the
differential pressure LP between the both measured pressures P17,
P18 (step K5) and compares the calculated differential pressure LP
with a preset permissible pressure Pc to determine whether the
differential pressure .DELTA.P is equal to or less than the
permissible pressure Pc (step K6). If the determined membrane
differential pressure .DELTA.P is smaller than or equal to the
predetermined set pressure value Pc, the pressure regulating valve
V1 is opened to adjust the brine pressure P6 discharged from the
high-pressure RO membrane module 6 to a desired value. If the
determined membrane differential pressure LP is larger than the
predetermined set pressure value Pc, the pressure P17 in the
upstream side and the pressure P18 on the downstream side are
measured again while the pressure regulating valve V1 is closed to
continue the calculation of the membrane differential pressure LP.
That is, if the determination result of process K6 is NO, the
operation of the steps K2 to K6 is repeated by returning to before
the step K2. If the determination result of step K6 is YES
(.DELTA.P.gtoreq.Pc), the pressure regulating valve V1 is opened
(step K7) and the operation of the steps K3 to K6 is repeated by
returning to after the step K2.
[0124] The back washing operation of the pretreatment membrane
module 3 will be described.
[0125] The washing pump P2 is driven periodically at predetermined
intervals to cause the pretreated water in the first treated water
tank 4 to flow backward to the pretreatment membrane module 3 via
the back washing line L12 for back washing of the MF membrane or UF
membrane in the pretreatment membrane module 3. In this case,
bubbling to feed a compressed air into the membrane module 3 from
the compressor C1 is used in combination. Accordingly, foreign
matter such as solid content adhering to the MF membrane or UF
membrane is removed so that membrane clogging is eliminated.
[0126] According to the membrane filtration system in the
embodiment, pump power supplied to the RO membrane module can be
reduced and also pump power supplied to the pretreatment membrane
module can be reduced so that total running costs can be
reduced.
Second Embodiment
[0127] Next, a membrane filtration system according to the second
embodiment will be described with reference to FIG. 4. The
description of a portion of the present embodiment that is common
to the above embodiment is omitted.
[0128] A membrane filtration system 1A in the second embodiment has
a configuration in which the washing pump P2 is omitted from the
system 1 in the first embodiment. Instead, the back washing line
L42 is provided between immediately the downstream side of the
conveying pump P3 and the downstream side of the pretreatment
membrane module 3.
[0129] In the embodiment, the pretreated water is sent from the
first treated water tank 4 to the pretreatment membrane module 3
through the back washing line L42 by a driving force of the
conveying pump P3 to backwash the MF membrane or UF membrane in the
membrane module 3.
[0130] According to the above-mentioned embodiment, total equipment
costs and running costs can be reduced by omitting a washing pump
dedicated to back washing.
Third Embodiment
[0131] Next, a membrane filtration system according to the third
embodiment will be described with reference to FIG. 5. The
description of a portion of the present embodiment that is common
to the above embodiments is omitted.
[0132] A membrane filtration system 1B in the third embodiment has
a configuration in which the first treated water tank 4, the
washing pump P2, the conveying pump P3, and the protector filter 5
are omitted from the system 1 in the first embodiment. Instead, the
back washing line L92 is provided between immediately the
downstream side of the low-pressure pump P6 and the downstream side
of the pretreatment membrane module 3.
[0133] In the embodiment, the primary treated water is sent from
the treated water tank 9 to the pretreatment membrane module 3
through the back washing line L92 by a driving force of the
low-pressure pump P6 to reversely clean the MF membrane or UF
membrane in the membrane module 3.
[0134] According to the above-mentioned embodiment, total equipment
costs and running costs can be reduced by omitting the first
treated water tank 4, the washing pump P2, the conveying pump P3,
and the protector filter 5.
Fourth Embodiment
[0135] Next, a membrane filtration system according to the fourth
embodiment will be described with reference to FIG. 6. The
description of a portion of the present embodiment that is common
to the above embodiments is omitted.
[0136] A membrane filtration system 10 in the fourth embodiment has
a configuration in which the first treated water tank 4, the
washing pump P2, the conveying pump P3, and the protector filter 5
are omitted from the system 1 in the first embodiment. Instead, the
back washing line L112 is provided between immediately the
downstream side of the conveying pump P7 and the downstream side of
the pretreatment membrane module 3.
[0137] In the embodiment, the product water is sent from the
treated water tank 11 to the pretreatment membrane module 3 through
the back washing line L112 by a driving force of the conveying pump
P7 to reversely clean the MF membrane or UF membrane in the
membrane module 3.
[0138] According to the above-mentioned embodiment, total equipment
costs and running costs can be reduced by omitting the first
treated water tank 4, the washing pump P2, the conveying pump P3,
and the protector filter 5.
Fifth Embodiment
[0139] Next, a membrane filtration system according to the fifth
embodiment will be described with reference to FIG. 7. The
description of a portion of the present embodiment that is common
to the above embodiments is omitted.
[0140] A membrane filtration system 1D in the fifth embodiment has
a configuration in which the brine tank 23, the washing pump P8,
and the back washing line L82 are added to the system 1 in the
first embodiment.
[0141] In the embodiment, the product water is sent from the brine
tank 23 to the pretreatment membrane module 3 through the back
washing line L82 by a driving force of the washing pump P8 to
backwash the MF membrane or UF membrane in the membrane module
3.
[0142] According to the above-mentioned embodiment, total running
costs can be reduced by washing the membrane filter with brine to
improve the recovery of a system.
Sixth Embodiment
[0143] Next, a membrane filtration system according to the sixth
embodiment will be described with reference to FIG. 8. The
description of a portion of the present embodiment that is common
to the above embodiments is omitted.
[0144] A membrane filtration system 1E in the sixth embodiment has
a configuration in which the hot water tank 27 with a heater 28 and
the washing lines L112, L121, L122, L123 are added to the system 1
in the first embodiment. As a unit to produce hot water, instead of
the heater 28, an energy-saving heat pump or natural energy may be
used.
[0145] In the embodiment, the product water is sent from the third
treated water tank 11 to the hot water tank 27 by a driving force
of the conveying pump P7 and further, the hot water is sent to the
pretreatment membrane module 3 through the washing lines L112, L123
for, in addition to normal washing, backwashing of the MF membrane
module or UF membrane module with water whose temperature is higher
than that of normal washing water at periodic frequency. Also, the
product water is sent from the third treated water tank 11 to the
hot water tank 27 by a driving force of the conveying pump P7 and
the hot water is sent to the reverse osmosis membrane module 6 in
the first stage through the washing lines L112, L122 to wash the RO
membrane and also, the hot water is sent to the reverse osmosis
membrane module 10 in the second stage through the washing lines
L112, L121 to wash the RO membrane.
[0146] According to the above-mentioned embodiment, total running
costs can be reduced by washing the MF membrane or UF membrane and
the RO membrane with hot water to improve the recovery of a
system.
[0147] According to the embodiments, total running costs can be
reduced by reducing power of a raw water feed pump and a
high-pressure pump.
[0148] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *