U.S. patent application number 14/394519 was filed with the patent office on 2018-01-25 for method and apparatus for effecting high recovery desalination with pressure driven membranes.
The applicant listed for this patent is Ben Gurion University of the Negev Research and Development Authority, Mekorot Water Company Ltd.. Invention is credited to Sivan BLEICH, Jack GILRON, Yevgeny GOLDKINE, Dan PELED.
Application Number | 20180021733 14/394519 |
Document ID | / |
Family ID | 52666994 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180021733 |
Kind Code |
A2 |
GILRON; Jack ; et
al. |
January 25, 2018 |
METHOD AND APPARATUS FOR EFFECTING HIGH RECOVERY DESALINATION WITH
PRESSURE DRIVEN MEMBRANES
Abstract
A system and method for switching between flows of water
solutions passed in groups of blocks of membrane pressure vessels
arranged in parallel in a tapered flow system, wherein the system
comprises a system inlet feed line, a system outlet flow line, high
pressure booster pumps configured to provide a high pressure feed
stream to the system; blocks of membrane pressure vessels arrayed
in parallel, and a first and second bypass line each parallel to
said blocks.
Inventors: |
GILRON; Jack; (Beer-Sheva,
IL) ; PELED; Dan; (Kiryat Tivon, IL) ;
GOLDKINE; Yevgeny; (Beer-Sheva, IL) ; BLEICH;
Sivan; (Karkur, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ben Gurion University of the Negev Research and Development
Authority
Mekorot Water Company Ltd. |
Beer-Sheva
Tel-Aviv |
|
IL
IL |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150076063 A1 |
March 19, 2015 |
|
|
Family ID: |
52666994 |
Appl. No.: |
14/394519 |
Filed: |
April 15, 2013 |
PCT Filed: |
April 15, 2013 |
PCT NO: |
PCT/IL2013/000040 PCKC 00 |
371 Date: |
October 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61624305 |
Apr 15, 2012 |
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Current U.S.
Class: |
210/636 ;
210/130; 210/139; 210/650 |
Current CPC
Class: |
B01D 65/027 20130101;
B01D 65/02 20130101; C02F 2103/08 20130101; C02F 1/441 20130101;
B01D 61/022 20130101; B01D 65/08 20130101; B01D 63/00 20130101;
B01D 2321/40 20130101; C02F 1/44 20130101; B01D 2317/04 20130101;
B01D 2313/48 20130101; C02F 2209/03 20130101; C02F 1/442 20130101;
B01D 2317/027 20130101; C02F 1/008 20130101; C02F 2303/22 20130101;
Y02A 20/131 20180101; B01D 61/12 20130101 |
International
Class: |
B01D 65/02 20060101
B01D065/02; B01D 61/00 20060101 B01D061/00; C02F 1/44 20060101
C02F001/44; B01D 63/00 20060101 B01D063/00 |
Claims
1. A tapered flow desalination system comprising: a system inlet
feed line coupled to a first high pressure booster pump configured
to provide a high pressure feed stream to the system; blocks of
membrane pressure vessels arrayed in parallel, wherein the outlet
of said first booster pump is coupled by means of flow lines to
said blocks at first opening sides of said blocks; a second booster
pump, coupled at its inlet by a first bypass line parallel to said
blocks, to said first booster pump outlet, wherein said second
booster pump outlet and inlet are also coupled by means of flow
lines to said blocks at second opening sides of said blocks and
wherein said first bypass line is also coupled by means of flow
lines to said blocks at said second opening sides of said blocks; a
system outlet flow line coupled to said first opening sides of said
blocks, coupled to said second opening sides of said blocks and to
the second booster pump outlet, wherein said system outlet flow
line is coupled to said second opening sides of said blocks and to
said second booster pump outlet by means of a second bypass line;
wherein the first bypass line comprises a valve and wherein the
second bypass line comprises a valve; wherein at least two of the
lines coupling between said first booster pump outlet and said
first opening sides of said blocks each comprise a valve; wherein
at least two of the lines coupling between said second booster pump
outlet and said second opening sides of said blocks each comprise a
valve; wherein at least two of the lines coupling between said
second opening sides of said blocks and said second booster pump
inlet each comprise a valve; and wherein at least two of the lines
coupling between said first opening sides of said blocks and said
system outlet flow line each comprise a valve.
2. The system according to claim 1 wherein said system comprises
three blocks, and wherein the lines coupling between said first
booster pump and said first opening sides of said blocks each
comprise a valve; wherein the lines coupling between said second
booster pump and said second opening sides of said blocks each
comprise a valve; wherein the lines coupling between said second
opening sides of said blocks and said first bypass line each
comprise a valve; and wherein the lines coupling between said first
opening sides of said blocks and said system outlet flow line each
comprise a valve.
3. The system according to claim 1, wherein the system comprises
one or more control elements selected from the group of additional
valves, check valves and sensors.
4. The system according to claim 1, wherein each pressure vessel
block is coupled to a permeate product line.
5. A method for switching between flows of water solutions passed
in groups of blocks of membrane pressure vessels arranged in
parallel in a tapered flow system, wherein said method comprising
the steps of: A) passing feed water solution through one or more of
said system blocks in a first stage and the concentrated water
solution exiting said blocks of the first stage is passed through
one or more of the system blocks in a second stage and the
concentrated water solution exiting the blocks of the second stage
is passed through a system concentrate outlet; B) slowing the
stream(s) passed in said second stage by bypassing a portion of the
concentrated water solution exiting the blocks of the first stage
to the system concentrate outlet; C) stopping the slowed stream(s)
of a first group of blocks being of one or more of the blocks of
the second stage; D) slowing the stream(s) passed in the first
stage by bypassing a portion of said feed water solution, to the
system concentrate outlet; E) stopping the slowed stream(s) of a
second group of blocks being of one or more of the blocks of the
first stage, wherein said second group of blocks comprise the same
number of blocks as in said first group of blocks; and passing a
portion of the feed water solution through said first group of
blocks; F) stopping the bypassing of step D and passing a portion
of the concentrated water solution exiting the blocks of the first
stage through said second group of bocks; G) stopping the bypassing
of step B.
6. A method according to claim 5, wherein the number of blocks in
the first group of blocks is 1.
7. A tapered flow desalination system comprising: a system inlet
feed line coupled to a first high pressure booster pump configured
to provide a high pressure feed stream to the system; a first group
of blocks of membrane pressure vessels arrayed in parallel, wherein
the outlet of said first booster pump is coupled by means of flow
lines to said first group of blocks at first opening sides of said
first group of blocks; a second booster pump, coupled at its inlet
by means of flow lines to said first group of blocks at second
opening sides of the first group of blocks; and coupled at its
outlet to a second group of blocks of membrane pressure vessels
arrayed in parallel at first opening sides of the second group of
blocks; a third booster pump, coupled by means of flow lines to
said second group of blocks at second opening sides of the second
group of blocks; and coupled by means of flow lines to said first
group of blocks at said second opening sides of said first group of
blocks; a system outlet flow line coupled by flow lines to said
first opening sides of said first group of blocks, coupled to said
second opening sides of said first group of blocks and to the third
booster pump, wherein said system outlet flow line is coupled to
said second opening sides of said first group of blocks and to said
third booster pump by means of a bypass line; wherein the bypass
line comprises a valve; wherein at least two of the lines coupling
between said first booster pump and said first opening sides of
said first group of blocks each comprise a valve; wherein at least
two of the lines coupling between said second booster pump and said
second opening sides of said first group of blocks each comprise a
valve; wherein at least two of the lines coupling between said
third booster pump and said second opening sides of said first
group of blocks each comprise a valve; wherein at least two of the
lines coupling between said first opening sides of said first group
of blocks and said system outlet flow line each comprise a
valve.
8. The system according to claim 7 wherein the first group of
blocks comprise at least 4 blocks and the second group of blocks
comprise, at most, two less blocks than the first group.
9. The system according to claim 7, wherein the system comprises
one or more of the control elements selected from the group of
additional valves, check valves and sensors.
10. The system according to claim 7, wherein each pressure vessel
block is coupled to a permeate product line.
11. A method for switching between flows of water solutions passed
in groups of blocks of membrane pressure vessels arranged in
parallel in a tapered flow system, wherein said method comprising
the steps of: A) passing feed water solution through one or more of
said system blocks in a first stage and the concentrated water
solution exiting said blocks of the first stage is passed through
one or more blocks in a second stage and the concentrated water
solution exiting the blocks of the second stage is passed through
one or more blocks in a third stage and the concentrated water
solution exiting the blocks of the third stage is passed through a
system concentrate outlet; B) slowing the stream(s) passed in said
third stage by bypassing a portion of the concentrated water
solution exiting the blocks of the second stage to the system
concentrated outlet; C) stopping the slowed stream(s) of a first
group of blocks being of one or more of the blocks of the third
stage; D) stopping the stream(s) of a second group of blocks being
of one or more of the blocks of the first stage, wherein said
second group of blocks comprise the same number of blocks as in
said first group of blocks; and passing a portion of the feed water
solution through said first group of blocks; E) passing a portion
of the concentrated water solution exiting the blocks of the second
stage through said second group of blocks; F) stopping the
bypassing of step B.
12. A method according to claim 11, wherein the initial number of
blocks in the third stage is at most, one less than , the number of
blocks in the second stage and the number of blocks in the second
stage is at most, one less than the number of blocks in the first
stage.
13. A flushing loop system for periodically flushing a concentrate
removal line with undersaturated solution comprising: a flushing
undersaturated solution feed tank coupled to a recycle line ending
back at said feed tank; wherein said recycle line comprises a
recirculation pump configured to drive said undersaturated solution
from said feed tank and back to said feed tank; wherein a portion
said recycle line is connected in parallel with said concentrate
removal line.
14. A flushing loop system for periodically flushing a concentrate
removal line with undersaturated solution comprising: a flushing
undersaturated solution feed tank coupled to a recirculation pump
by a flow line; wherein a first portion of the concentrate removal
line is coupled to a third portion of the concentrate removal line
by two parallel flow lines, one being a second portion of the
concentrate removal line and the other being a flush removal line;
wherein said recirculation pump is coupled to the second portion of
the concentrate removal line by two parallel flow lines; and
wherein said feed tank is coupled to the second portion of the
concentrate removal line by two parallel flow lines.
15. The flushing loop system according to claim 14, wherein said
recirculation pump is coupled to a first three-way valve by a flow
line; wherein said first three way valve is coupled to a second
three way valve by a flow line and to the second portion of the
concentrate removal line by a flow line; wherein said second three
way valve is also coupled to said second portion of the concentrate
removal line; wherein said second portion of the concentrate
removal line is also coupled to a third three way valve and to a
fourth three way valve; wherein said third three way valve is also
coupled to said fourth three way valve by a flow line; wherein said
flushing removal line is coupled to said first three way valve,
said second three way valve, said third three way valve and said
fourth three way valve; wherein said fourth three way valve is
coupled to the feed tank; wherein said third three way valve is
coupled to the first portion of the concentrate removal line;
wherein the second three way valve is coupled to the system third
portion of the concentrate removal line; and wherein said portion
of the concentrate removal line and said flushing removal line each
comprise a two way valve.
16. A method for flushing a portion of a concentrate removal line,
comprising: A) passing a concentrated solution through a portion of
a concentrate removal line; B) redirecting the concentrated
solution and passing it through a flow line parallel to said
portion of the concentrate removal line; and passing a flow of
undersaturated solution through said portion of the concentrate
removal line; C) stopping the passing of the undersaturated
solution; and redirecting the concentrated solution and passing it
back through said portion of the concentrate removal line; D)
periodically repeating steps B-C.
17. The method according to claim 16, wherein: step A further
comprises passing an undersaturated solution through the flow line
parallel to the portion of the concentrate removal line; and
wherein step B further comprises redirecting the undersaturated
flow of step A and passing it through the portion of the
concentrate removal line; and wherein step C further comprises
redirecting the undersaturated flow of step B and passing it back
to the flow line parallel to the portion of the concentrate removal
line.
18. A flushing loop system for periodically flushing a concentrate
removal line with undersaturated solution comprising: a flushing
undersaturated solution feed tank coupled to a recirculation pump
by a flow line; wherein a first portion of the concentrate removal
line is coupled to a third portion of the concentrate removal line
by two parallel flow lines, one being a second portion of the
concentrate removal line and the other being a flush removal line;
wherein said recirculation pump is coupled to the second portion of
the concentrate removal line by two parallel flow lines; and
wherein said feed tank is coupled to the second portion of the
concentrate removal line by two parallel flow lines, wherein said
first portion of the concentrate removal line is the system outlet
flow line of a tapered flow desalination system in accordance with
claim 1.
19. A flushing loop system for periodically flushing a concentrate
removal line with undersaturated solution comprising: a flushing
undersaturated solution feed tank coupled to a recirculation pump
by a flow line; wherein a first portion of the concentrate removal
line is coupled to a third portion of the concentrate removal line
by two parallel flow lines, one being a second portion of the
concentrate removal line and the other being a flush removal line;
wherein said recirculation pump is coupled to the second portion of
the concentrate removal line by two parallel flow lines; and
wherein said feed tank is coupled to the second portion of the
concentrate removal line by two parallel flow lines, wherein said
first portion of the concentrate removal line is the system outlet
flow line of a tapered flow desalination system in accordance with
claim 7.
Description
BACKGROUND
[0001] In cross-flow pressure driven membrane desalination systems,
the feed stream is typically fed into a high pressure feed inlet of
a pressure vessel that leads the pressurized saline solution on a
flow path parallel to the membrane in the membrane element and a
portion of the water passes through the membrane and exits by a low
pressure connection from the same pressure vessel. The remaining
saline solution with increased concentration of the retained
solutes can exit from a second high pressure connection from the
pressure vessel which is denoted as the concentrate port (see FIG.
1).
[0002] FIGS. 1A and 1B relate to prior art (EP1691915) The
crossflow pressure vessel for pressure-driven membrane desalination
showing the flow arrangement during forward flow (1A) and reverse
flow (1B) in which the high pressure connections of stream Q1 and
stream Q4 are switched between the left (L) side and the right (R)
side of the pressure vessel, while continuing to remove the low
pressure product stream (Q3) which passed through the membrane.
[0003] It has been shown (I&EC v 46, EP1691915) that in such
pressure driven cross-flow desalination systems that by reversing
the flow of a stream to be desalinated by switching the feed and
concentrate connections to the high pressure ports of the pressure
vessel, mineral scaling can be prevented by carrying this out
before the induction time has been completed. This allows the use
of no or little antiscalant to prevent the precipitation in the
membrane elements. Furthermore it is a common practice that in high
recovery pressure driven membrane desalination processes that one
or more desalination membrane elements are placed in pressure
vessels in stages such that more pressure vessels are in an
upstream stage and that they communicate their concentrate stream
to the feed ports of a fewer number of pressure vessels in the
downstream stage. This is called a tapered flow arrangement of
pressure vessels. This practice preserves a minimum cross-flow rate
in the downstream pressure vessels that helps to prevent fouling by
colloids, organics and biomaterials as well as to reduce the
concentration of salts at the membrane surface. It has been
revealed (European Patent Publication No. EP1893325, the entire
disclosure of which is incorporated herein by reference) that by a
particular use of valves arrangement, that the block of pressure
vessels can be repositioned from downstream stage to an upstream
stage and exchanged with block of similar number of pressure
vessels from the upstream stage which are moved to the downstream
stage while at the same time switching the concentrate and feed
connections on the blocks of pressure vessels being repositioned.
By so doing the end of the membrane element in the downstream stage
that saw the highest concentration concentrate will now be exposed
to the feed solution which has the lowest concentration and also
the lowest concentration of sparingly soluble salts. This will
allow a zeroing of the induction time as described in I&EC v46
and EP1691915, the entire disclosure of which is incorporated
herein by reference.
[0004] In both flow reversal arrangements described in I&EC v46
and in the patent application concerning repositioning of the
pressure vessels in the tapered flow arrangement EP1893325, all the
membrane elements in the pressure vessels are periodically exposed
to undersaturated solutions. On the other hand, the piping
downstream of the switching valves of the second stage pressure
vessels (e.g. V.sub.Bf, V.sub.Af and V.sub.Cb in FIG. 2, when these
valves are downstream of the second stage pressure vessels) always
see supersaturated solutions, that may be with little or no
antiscalant. Therefore while scaling is prevented on the membranes
in the pressure vessel, it may not be prevented in the piping
downstream of these switching valves. Such scaling is particularly
a possibility downstream of the pressure maintenance devices P/FV,
when these are pressure reducing valves that could cause cavitation
downstream where the pressure is released, as shown in stream 14 of
FIG. 2. It is a common practice to place flow, conductivity and
other composition sensors on the concentrate line downstream of the
pressure maintenance device and scaling of these sensors could
cause them to malfunction and misreport. This in turn could
interfere with the appropriate control strategy of the plant. It is
a purpose of the present invention to provide a practical solution
to this problem that does not require the wasting of permeate and
does not interrupt the smooth operation of the desalination system
with flow reversal or repositioning of pressure vessels.
[0005] In EP1893325 a particular embodiment was described for
repositioning pressure vessels by the use of three-way valves (see
FIG. 2, wherein BW refers to Brackish water, P-I refers to Permeate
(step I), P-II refers to Permeate (step II) and CT refers to
Concentrate). While this method is effective, it can be problematic
because of the brief time during which those valves must switch
between one port and the other port of the three-way valve.
Furthermore it does not easily allow for complete isolation of one
block of pressure vessels which may be desirable for maintenance or
diagnostic purposes while operating the rest of the desalination
unit. Furthermore, while an auxiliary bypass valve (AV) was
provided for taking part of the flow from the downstream block of
elements when they were being switched to an upstream stage, the
particular embodiment did not describe such a bypass valve for the
upstream block of elements, so that during the brief time when a
fewer number of blocks of pressure vessels was being operated in an
upstream stage until a new block of pressure vessels could be
repositioned into that block, it would see a much larger flow that
could exceed the flow allowed. At the same time when a new block of
pressure vessels was repositioned into the first stage, if all of
its designed flow was immediately fed to this re-positioned block,
it may be subject to water hammer or other mechanical stresses that
could be harmful.
SUMMARY OF INVENTION
[0006] A method and apparatus are provided for repositioning blocks
of pressure vessels between one or more stages of a desalination
train operating at high recovery so that mineral scaling of the
membranes can be achieved with no or little use of antiscalant.
This improved method solves the challenge that in re-positioning
blocks of pressure vessels between a last stage and previous stage
in staged desalination by pressure driven membranes there is a risk
of: a) water hammer due to changing flows in each stage; and a risk
of b) scaling of the concentrate line downstream of the device
maintaining pressure in the feed side of the membrane elements. The
present invention addresses these problems by incorporating a 2-way
bypass valve across each stage and not just the last stage. In
addition, the invention applies a series of valves to periodically
flush with undersaturated solution the concentrate line downstream
of the device maintaining pressure in the feed side of the
membranes. The desalination membranes can be of the type of reverse
osmosis or nanofiltration in order to retain one or more of the
scaling species such as ions of calcium, carbonate, sulfate,
fluoride, barium, strontium or neutral species such as silica.
[0007] In one aspect the present invention is directed to a method
for repositioning membrane block(s) of pressure vessels arranged in
a tapered flow structure between an upstream stage and a downstream
stage, and between a downstream stage and an upstream stage, such
that sudden changes of flow in the upstream stage are prevented,
the method comprising: bypassing at the beginning of any membrane
block(s) repositioning process in which membrane block(s) are moved
out of, or into, the upstream stage, the membrane block(s) in the
upstream stage, by means of a bypass stream of the feed stream; and
stopping the bypass of the membrane block(s) in the upstream stage
after the membrane block(s) repositioning process is completed. A
particular embodiment of the method which helps prevent water
hammer involves slowing the opening and closing of two-way valves
on the bypass and entrance and exit ports of the membrane blocks so
that there is time for pressures to equilibrate.
[0008] The invention is also directed to a method for keeping lines
of concentrate in a pressure driven membrane desalination process
free of scaling from a supersaturated solution of sparingly soluble
minerals that is not stabilized with antiscalant, the method
comprising periodically flushing the concentrate line with
undersaturated solution, and concurrently streaming the concentrate
through a removal line with appropriate pressure maintenance
devices and concentrate monitoring sensors to allow the membrane
desalination process to keep operating while the concentrate line
is being flushed. The sparingly soluble minerals can be any soluble
species whose activity exceeds its thermodynamic solubility in the
concentrate based on the concentrate's composition, temperature and
pressure.
[0009] The opening and closing of the various valves in the tapered
flow arrangement may be operated by means of control means (e.g.,
PLC, microcontroller, personal computer--PC) adapted to determine
the timing to effect the opening and closing. Optionally, the
frequency of the flushing may be as high as once every hour.
Alternatively the frequency of the flushing may be as low as once
every time that any particular block of pressure vessels is moved
to the most downstream stage of multi-stage membrane desalination
process. In yet another alternative, the frequency of the flushing
may be set to any time between the once every hour and every time
that any particular membrane block of pressure vessels is moved
into the most downstream stage.
[0010] Optionally, the desalination permeate may be used for the
undersaturated solution. Alternatively, the undersaturated solution
may be the treated feed supplied to the entrance of the
desalination process. Advantageously, the undersaturated solution
is continuously recirculated in a separate flushing loop while the
membrane desalination process and concentrate line are in normal
operation.
[0011] Preferably, while the concentrate line is being flushed the
concentrate from the desalination process is sent to a bypass line,
wherein the bypass line is part of the flushing loop during the
normal operation before the flushing of the concentrate line, and
wherein the bypass line comprises a pressure maintenance device
which is set to maintain the pressure in the high pressure lines of
the membrane desalination plant during the flushing of the
concentrate line. Alternatively, when the concentrate line is being
flushed, the concentrate from the desalination process may be sent
out via a bypass line, without maintaining pressure in the
desalination process and the flushing may be effected for a short
time e.g., about 1-5 minutes. Optionally, only the concentrate line
downstream of the pressure maintenance device is flushed with
undersaturated solution.
[0012] In another aspect the invention is directed to a tapered
flow desalination apparatus comprising: a high pressure pump
configured to provide a high pressure feed stream to the apparatus,
wherein the outlet of the high pressure pump is connected by means
of a feed line to block(s) of membrane pressure vessels arrayed in
parallel, wherein one set of high pressure ports of the block(s) of
membrane pressure vessels are connected to the feed line by inlet
valves, and another set of high pressure ports of the block(s) of
membrane pressure vessels are connected to the inlet of an
interstage booster pump by means of another set of outlet valves;
and a bypass line parallel to the block(s) of membrane pressure
vessels comprising a controllable bypass valve, wherein the bypass
line connects between the feed high pressure pump outlet and the
interstage booster pump inlet. In certain embodiments of the
invention the apparatus may be implemented without the interstage
booster pump, and in this case the high pressure outlet of the
block(s) of membrane pressure vessels is connected by means of
outlet valves directly to a manifold of second stage inlet valves
leading to a second stage block(s) arrangement comprising block(s)
of parallel membrane pressure vessels, and wherein the bypass valve
connects between the outlet of the feed high pressure pump and the
manifold of second stage inlet valves. The bypass valve may be
implemented by means of a simple on-off valve. Optionally, the
bypass valve may be implemented by means of a proportional valve.
Preferably, the bypass valve is controlled by pneumatic actuators,
or alternatively, by means of electric actuators.
[0013] The apparatus may comprise a flushing loop comprised of a
flushing solution feed tank, recirculation pump, and a recycle line
connecting the flushing solution feed tank and recirculation pump
to form a circulation line, wherein a portion of the recycle line
of this flushing loop is connected in parallel with the concentrate
removal line. Preferably, the portion of the flushing loop
connected in parallel to the concentrate line is equipped with a
pressure maintenance device. Additionally, or alternatively, the
part of the flushing loop that is connected in parallel to the
concentrate line is connected to that line by means of directional
control valves installed at each end of the parallel section so
that flushing solution can be sent alternately through the
concentrate line, and alternately recirculate in the flushing loop
parallel to the return line. Advantageously, another set of
directional control valves may be used to collect the flushing
solution from either the concentrate line or from the flushing loop
bypass line. Yet, another set of directional control valves may be
utilized to send the desalination concentrate through the regular
concentrate line or through the flushing loop bypass line.
[0014] In yet another aspect the present invention is directed to a
method for repositioning blocks of pressure vessels arranged in a
tapered flow structure between a downstream stage and an upstream
stage by means of pairs of two-way valves connected in parallel,
wherein the two-way valves are installed at each end of each of the
blocks of pressure vessels and configured to communicate with a
high pressure port on that end of the pressure vessels. The time
for repositioning blocks of pressure vessels may be determined
according to the induction time for sparingly soluble salts at the
composition found at the exit stream of the most downstream block
of pressure vessels. Optionally, the induction time may be
determined by an in-situ sensor. Alternatively, the induction time
may be determined by previous laboratory experiments or pilot
facility experiments. Advantageously, the composition of the feed
stream may be used for calculating the induction time based on an
empirical correlation between composition and induction time.
[0015] The method may be implemented by an apparatus comprising a
manifold of pairs of 2-way valves with each pair of valves of the
said manifold attached in parallel to one high pressure port of a
block of pressure vessels and a second manifold of pairs of two-way
valves wherein each corresponding pair of valves in this second
manifold is attached in parallel to the other high pressure port of
the same block of pressure vessels, and wherein for each pair of
two-way valves connected in parallel to the first high pressure
port, one of the pair is connected at its other end to the high
pressure feed pump outlet and the other member of the pair is
connected to the pressure maintenance device, and wherein for each
pair of two-way valves connected in parallel to the second high
pressure port of a block of pressure vessels one of the pair is
connected at its other end to the inlet of an interstage booster
pump and the other member of the pair is connected at its other end
to the outlet of the same interstage booster pump. The apparatus
may be equipped with check valves in appropriate places to prevent
flows in unintended directions.
[0016] The present invention relates to a method for repositioning
membrane block(s) of pressure vessels arranged in a tapered flow
structure between an upstream stage and a downstream stage, and
between a downstream stage and an upstream stage comprising: [0017]
a) bypassing the membrane block(s) in the upstream stage, at the
beginning of any membrane block(s) repositioning process in which
membrane block(s) are moved out of, or into, the upstream stage, by
means of a bypass stream of the feed stream, and [0018] b) stopping
the bypass of the membrane block(s) in the upstream stage after the
membrane block(s) repositioning process is completed.
[0019] The present invention relates to a method for keeping lines
of concentrate in a pressure driven membrane desalination process
free of scaling from a supersaturated solution of sparingly soluble
minerals that is not stabilized with antiscalant, comprising
periodically flushing the concentrate line with undersaturated
solution, and concurrently streaming the concentrate through a
removal line with pressure maintenance devices and concentrate
monitoring sensors to allow the membrane desalination process to
keep operating while the concentrate line is being flushed.
[0020] The present invention relates to a method for repositioning
blocks of pressure vessels arranged in a tapered flow structure
between a downstream stage and an upstream stage by means of pairs
of two-way valves connected in parallel, wherein said pairs of
two-way valves are installed at each end of each of the blocks of
pressure vessels and configured to communicate with a high pressure
port on one end of the pressure vessels.
[0021] The present invention relates to a tapered flow desalination
apparatus comprising: a high pressure pump configured to provide a
high pressure feed stream to the apparatus, wherein the outlet of
said high pressure pump is connected by means of a feed line to
block(s) of membrane pressure vessels arrayed in parallel, wherein
one set of high pressure ports of the block(s) of membrane pressure
vessels are connected to the feed line by inlet valves, and another
set of high pressure ports of the block(s) of membrane pressure
vessels are connected to the inlet of an interstage booster pump by
meams of another set of outlet valves; and a bypass line parallel
to said block(s) of membrane pressure vessels comprising a
controllable bypass valve, wherein said bypass line connects
between said feed high pressure pump outlet and said interstage
booster pump inlet.
[0022] The present invention relates to a flushing loop for
periodically flushing a concentrate removal line with
undersaturated solution comprising a flushing solution feed tank,
recirculation pump, and a recycle line connecting said flushing
solution feed tank and said recirculation pump to form a
circulation line, wherein a portion said recycle line is connected
in parallel with said concentrate removal line.
[0023] According to a preferred embodiment, the apparatus comprises
pairs of two-way valves connected in parallel, wherein said pairs
of two-way valves are installed at each end of each of the blocks
of pressure vessels and configured to communicate with a high
pressure port on one end of the pressure vessels.
[0024] The present invention relates to a tapered flow desalination
system comprising:
[0025] a system inlet feed line coupled to a first high pressure
booster pump configured to provide a high pressure feed stream to
the system;
[0026] blocks of membrane pressure vessels arrayed in parallel,
wherein the outlet of said first booster pump is coupled by means
of flow lines to said blocks at first opening sides of said
blocks;
[0027] a second booster pump, coupled at its inlet by a first
bypass line parallel to said blocks, to said first booster pump
outlet, wherein said second booster pump outlet and inlet are also
coupled by means of flow lines to said blocks at second opening
sides of said blocks and wherein said first bypass line is also
coupled by means of flow lines to said blocks at said second
opening sides of said blocks;
[0028] a system outlet flow line coupled to said first opening
sides of said blocks, coupled to said second opening sides of said
blocks and to the second booster pump outlet, wherein said system
outlet flow line is coupled to said second opening sides of said
blocks and to said second booster pump outlet by means of a second
bypass line (which is also actually parallel to said blocks);
[0029] wherein the first bypass line comprises a valve and wherein
the second bypass line comprises a valve;
[0030] wherein at least two of the lines coupling between said
first booster pump outlet and said first opening sides of said
blocks each comprise a valve;
[0031] wherein at least two of the lines coupling between said
second booster pump outlet and said second opening sides of said
blocks each comprise a valve;
[0032] wherein at least two of the lines coupling between said
second opening sides of said blocks and said second booster pump
inlet each comprise a valve; and
[0033] wherein at least two of the lines coupling between said
first opening sides of said blocks and said system outlet flow line
each comprise a valve.
[0034] Preferably, said system comprises three blocks, and
[0035] wherein the lines coupling between said first booster pump
and said first opening sides of said blocks each Comprise a
valve;
[0036] wherein the lines coupling between said second booster pump
and said second opening sides of said blocks each comprise a
valve;
[0037] wherein the lines coupling between said second opening sides
of said blocks and said first bypass line each comprise a valve;
and
[0038] wherein the lines coupling between said first opening sides
of said blocks and said system outlet flow line each comprise a
valve.
[0039] Preferably, the system comprises one or more control
elements selected from the group of additional valves, check valves
and sensors.
[0040] Preferably, each pressure vessel block is coupled to a
permeate product line.
[0041] The present invention relates to a method for switching
between flows of water solutions passed in groups of blocks of
membrane pressure vessels arranged in parallel in a tapered flow
system, wherein said method comprising the steps of: [0042] A)
passing feed water solution through one or more of said system
blocks in a first stage and the concentrated water solution exiting
said blocks of the first stage is passed through one or more of the
system blocks in a second stage and the concentrated water solution
exiting the blocks of the second stage is passed through a system
concentrate outlet; [0043] B) slowing the stream(s) passed in said
second stage by bypassing a portion of the concentrated water
solution exiting the blocks of the first stage to the system
concentrate outlet; [0044] C) stopping the slowed stream(s) of a
first group of blocks being of one or more of the blocks of the
second stage; [0045] D) slowing the stream(s) passed in the first
stage by bypassing a portion of said feed water solution, to the
system concentrate outlet; [0046] E) stopping the slowed stream(s)
of a second group of blocks being of one or more of the blocks of
the first stage, wherein said second group of blocks comprise the
same number of blocks as in said first group of blocks; and passing
a portion of the feed water solution through said first group of
blocks; [0047] F) stopping the bypassing of step D and passing a
portion of the concentrated water solution exiting the blocks of
the first stage through said second group of bocks; [0048] G)
stopping the bypassing of step B. [0049] Preferably, the number of
blocks in the first group of blocks is 1.
[0050] The present invention relates to a tapered flow desalination
system comprising:
[0051] a system inlet feed line coupled to a first high pressure
booster pump configured to provide a high pressure feed stream to
the system;
[0052] a first group of blocks of membrane pressure vessels arrayed
in parallel, wherein the outlet of said first booster pump is
coupled by means of flow lines to said first group of blocks at
first opening sides of said first group of blocks;
[0053] a second booster pump, coupled at its inlet by means of flow
lines to said first group of blocks at second opening sides of the
first group of blocks; and coupled at its outlet to a second group
of blocks of membrane pressure vessels arrayed in parallel at first
opening sides of the second group of blocks;
[0054] a third booster pump, coupled by means of flow lines to said
second group of blocks at second opening sides of the second group
of blocks; and coupled by means of flow lines to said first group
of blocks at said second opening sides of said first group of
blocks;
[0055] a system outlet flow line coupled by flow lines to said
first opening sides of said first group of blocks, coupled to said
second opening sides of said first group of blocks and to the third
booster pump, wherein said system outlet flow line is coupled to
said second opening sides of said first group of blocks and to said
third booster pump by means of a bypass line;
[0056] wherein the bypass line comprises a valve;
[0057] wherein at least two of the lines coupling between said
first booster pump and said first opening sides of said first group
of blocks each comprise a valve;
[0058] wherein at least two of the lines coupling between said
second booster pump and said second opening sides of said first
group of blocks each comprise a valve;
[0059] wherein at least two of the lines coupling between said
third booster pump and said second opening sides of said first
group of blocks each comprise a valve;
[0060] wherein at least two of the lines coupling between said
first opening sides of said first group of blocks and said system
outlet flow line each comprise a valve.
[0061] Preferably, the first group of blocks comprise at least 4
blocks and the second group of blocks comprise, at most, two less
blocks than the first group.
[0062] Preferably, the system comprises one or more of the control
elements selected from the group of additional valves, check valves
and sensors.
[0063] Preferably, each pressure vessel block is coupled to a
permeate product line.
[0064] The present invention relates to a method for switching
between flows of water solutions passed in groups of blocks of
membrane pressure vessels arranged in parallel in a tapered flow
system, wherein said method comprising the steps of: [0065] A)
passing feed water solution through one or more of said system
blocks in a first stage and the concentrated water solution exiting
said blocks of the first stage is passed through one or more blocks
in a second stage and the concentrated water solution exiting the
blocks of the second stage is passed through one or more blocks in
a third stage and the concentrated water solution exiting the
blocks of the third stage is passed through a system concentrate
outlet; [0066] B) slowing the stream(s) passed in said third stage
by bypassing a portion of the concentrated water solution exiting
the blocks of the second stage to the system concentrated outlet;
[0067] C) stopping the slowed stream(s) of a first group of blocks
being of one or more of the blocks of the third stage; [0068] D)
stopping the stream(s) of a second group of blocks being of one or
more of the blocks of the first stage, wherein said second group of
blocks comprise the same number of blocks as in said first group of
blocks; and passing a portion of the feed water solution through
said first group of blocks; [0069] E) passing a portion of the
concentrated water solution exiting the blocks of the second stage
through said second group of blocks; [0070] F) stopping the
bypassing of step B. [0071] Preferably, the initial number of
blocks in the third stage is at most, one less than, the number of
blocks in the second stage and the number of blocks in the second
stage is at most, one less than the number of blocks in the first
stage.
[0072] The present invention relates to a flushing loop system for
periodically flushing a concentrate removal line with
undersaturated solution comprising:
[0073] a flushing undersaturated solution feed tank coupled to a
recycle line ending back at said feed tank;
[0074] wherein said recycle line comprises a recirculation pump
configured to drive said undersaturated solution from said feed
tank and back to said feed tank;
[0075] wherein a portion said recycle line is connected in parallel
with said concentrate removal line.
[0076] The present invention relates to a flushing loop system for
periodically flushing a concentrate removal line with
undersaturated solution comprising:
[0077] a flushing undersaturated solution feed tank coupled to a
recirculation pump by a flow line;
[0078] wherein a first portion of the concentrate removal line is
coupled to a third portion of the concentrate removal line by two
parallel flow lines, one being a second portion of the concentrate
removal line and the other being a flush removal line;
[0079] wherein said recirculation pump is coupled to the second
portion of the concentrate removal line by two parallel flow lines;
and wherein said feed tank is coupled to the second portion of the
concentrate removal line by two parallel flow lines;
[0080] Preferably, the recirculation pump is coupled to a first
three-way valve by a flow line;
[0081] wherein said first three way valve is coupled to a second
three way valve by a flow line and to the second portion of the
concentrate removal line by a flow line;
[0082] wherein said second three way valve is also coupled to said
second portion of the concentrate removal line;
[0083] wherein said second portion of the concentrate removal line
is also coupled to a third three way valve and to a fourth three
way valve; wherein said third three way valve is also coupled to
said fourth three way valve by a flow line;
[0084] wherein said flushing removal line is coupled to said first
three way valve, said second three way valve, said third three way
valve and said fourth three way valve;
[0085] wherein said fourth three way valve is coupled to the feed
tank;
[0086] wherein said third three way valve is coupled to the first
portion of the concentrate removal line;
[0087] wherein the second three way valve is coupled to the system
third portion of the concentrate removal line; and
[0088] wherein said portion of the concentrate removal line and
said flushing removal line each comprise a two way valve.
[0089] The present invention relates to a method for flushing a
portion of a concentrate removal line, comprising: [0090] A)
passing a concentrated solution through a portion of a concentrate
removal line; [0091] B) redirecting the concentrated solution and
passing it through a flow line parallel to said portion of the
concentrate removal line; and passing a flow of undersaturated
solution through said portion of the concentrate removal line;
[0092] C) stopping the passing of the undersaturated solution; and
redirecting the concentrated solution and passing it back through
said portion of the concentrate removal line; [0093] D)
periodically repeating steps B-C.
[0094] Preferably, step A further comprises passing an
undersaturated solution through the flow line parallel to the
portion of the concentrate removal line;
[0095] and wherein step B further comprises redirecting the
undersaturated flow of step A and passing it through the portion of
the concentrate removal line;
[0096] and wherein step C further comprises redirecting the
undersaturated flow of step B and passing it back to the flow line
parallel to the portion of the concentrate removal line.
[0097] The present invention relates to a system wherein the first
portion of the aforementioned concentrate removal line is the
aforementioned system outlet flow line.
[0098] According to another embodiment of the present invention,
all the system embodiments as disclosed herein do not necessarily
need to have a second booster pump (or third booster pump), such as
when the streams have adequate pressure provided by the first
pressure pump (at the inlet feed line) of the system invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0099] The present invention is illustrated by way of example in
the accompanying drawings, in which similar references consistently
indicate similar elements and in which:
[0100] FIGS. 1 and 2 illustrates a prior art inventions.
[0101] FIG. 3 illustrates the flushing of the concentrate line
embodiment of the present invention.
[0102] FIGS. 4, 5A-5G illustrate the two stage with AVF bypass line
embodiment of the present invention.
[0103] FIG. 6 illustrates an example of a general overview of an
embodiment of the present invention.
[0104] FIGS. 7A-7F illustrate the three stage embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0105] One of the objects of the present invention is to provide
technological solutions to several possible operational problems
that may arise in the practice of EP1691915 and repositioning of
pressure valves as taught in EP1893325, by means of a novel valve
arrangement. In particular, the apparatus of the present invention
is designed to prevent scaling in the lines of the downstream of
the positioning valves downstream of the pressure vessels in the
last stage that always see supersaturated concentrate. The present
invention further provides an improved design for preventing water
hammer effects or other hydraulic shock to membrane elements in the
pressure vessels in the upstream stage when repositioning blocks of
pressure vessels into and out of this stage. In both cases a novel
valve arrangement is used in ways that would not be anticipated or
practiced by those versed in the art of membrane systems.
[0106] The novel valve arrangement of the invention on the
concentrate line allows flushing of the concentrate line only
without losing time to production while the flushing solution
flushes the whole membrane train. In the past, it has been the
practice of some operators of membrane desalination plants to
periodically (e.g. once every day) flush their lines with feed
water or saline water (see Liberman et al.), but this involves
cessation of the membrane operation and loss of production. In the
case of Liberman et al. it also involves the use of saline
solutions that carry both a chemical expense and an environmental
penalty because of the need to dispose of these hypersaline
solutions.
[0107] FIG. 6 shows a general flowsheet of the tapered flow
desalination apparatus according to an embodiment of the invention.
The apparatus illustrated in FIG. 3 (an expansion of a portion of
the apparatus of FIG. 6) exemplifies one preferred embodiment of
the invention and a method for carrying it out. The concentrate
stream [4] can be directed by one or more valves (here XV-4 and
XV-5) between a flushing solution recycle line (FRL) and the
concentrate removal line (CRL). Both the CRL and FRL are equipped
with devices (in this embodiment back pressure valves P/FV and
P/FV2 respectively) to maintain the pressure in the
feed/concentrate side of the membrane elements. However the
pressure maintenance devices could also be pressure exchangers or
other energy recovery devices. During normal operation (indicated
by reference numerals 3n), the concentrate stream [4] flows through
the concentrate removal line (CRL) sent out of the system while a
stream of flushing solution [5] is recycled between the CIP tank
and the FRL through valves XV-6 and XV-7 while P/FV2 is completely
open. Periodically (for example, as frequently as once every hour
up to as infrequently as the same time period as used for flow
reversal or for repositioning pressure vessels between the stages
to prevent scaling) the valves XV-4 and XV-5 (in this particular
embodiment 3-way valves but it could be a manifold of two-way
valves or slide valves) valve positions are switched to direct the
concentrate stream [4] as indicated by the arrows referenced by
numerals 3p so that the concentrate stream [4] is sent through the
FRL, and the position of valves XV-6 and XV-7 are also switched
such that the flushing solution [5] flowing in the direction of the
arrows referenced by numerals 3r is sent through the CRL before
returning to the CIP tank (TK-1). In this way, all the surfaces of
the CRL that were exposed to supersaturated concentrate are now
exposed to undersaturated flushing solution. At the same time the
back pressure device P/FV is completely opened and the back
pressure device P/FV2 is set to the same setting as previously held
by the P/FV to maintain the same back pressure in the feed lines of
the pressure vessels. In this case a limited volume of flushing
solution which can be feed water or permeate is held in a tank such
as a clean-in-place (CIP TK-1) tank and it is re-used over and over
for periodically flushing the concentrate line. This can continue
to be the case until the residual concentration of scaling ions in
the flushing solution reaches their saturation limit and a new
batch of flushing solution may be then introduced.
[0108] According to an embodiment of the invention, the time during
which the CRL is flushed (stream [5] going in the direction of
arrows 3r) can be as short as one minute or twice the hydraulic
residence time in the CRL, whichever is shorter, and as long as the
time that a particular block is positioned in the downstream stage
or that one direction of a flow reversal cycle is being operated.
Once the flushing is complete, the valve positions are returned to
their original position (3n).
[0109] Some of the advantages of this approach are: the system
never stops operating and producing permeate while the concentrate
line is flushed; a limited amount of volume is repeatedly used
(volume of the CIP tank TK-1) and therefore little permeate is
wasted; and any sensors on line CRL are kept free of scaling so
they will operate properly.
[0110] Other embodiments for flushing the CRL concentrate line
involve briefly (for a time as little as two hydraulic residence
times of the normal concentrate stream) sending all of the permeate
to a point downstream of P/FV which may be used for simplicity but
does involve wasting a certain amount of permeate, but does allow
keeping sensors on CRL to be maintained scale-free. Another
embodiment involves bypassing the 2nd stage and lowering
recovery-opening P/FV (+ adding acid/AS) temporarily to get
concentrate conditions to undersaturated conditions. This has the
advantage of rinsing the P/FV without a separate line while
maintaining production from the first stage. It has the
disadvantage of losing production from the second stage. However if
the time is short this may not be too bad a disadvantage.
[0111] The present invention further provides a two-way valve
arrangement for effecting repositioning of pressure vessels between
the stages of a membrane desalination plant, wherein the valve
arrangement employs a bypass valve on the first stage to prevent
sudden changes in hydraulic flows on pressure vessels in the first
stage. One preferred embodiment of this solution of the invention
is shown in FIG. 4. In this embodiment, the apparatus 40 the pairs
of 2-way valves (AFI/ARO, BFI/BRO, CFI/CRO) have replaced the
two-way upstream valves V.sub.1A, V.sub.1B, V.sub.1C, and three-way
valves V.sub.Af, V.sub.Bf, and V.sub.Cb, shown in FIG. 2, and the
pairs of two-way valves (ARI/AFO, BRI/BFO, CRI/CFO) have replaced
two-way valves V.sub.2A, V.sub.2B, V.sub.2C, and three-way valves
V.sub.Ab, V.sub.Bb and V.sub.Cf shown in FIG. 2. In addition, an
additional bypass valve AVF has been added to link the outlet of
the high pressure pump to the inlet of the interstage booster pump
to take the excess flow from the high pressure feed pump when only
one block of pressure vessels is operative in the first stage, and
to reduce the initial flow on re-introducing a block of pressure
vessels into the first stage after repositioning. A particular
embodiment can include partially opening the proportional back
pressure valve P/FV when the flow rate increases as a result of
using the bypass AV and/or AVF. By doing this, an increase in
pressure can be prevented from the increase in flow to the P/FV
when feed flows through the second stage and/or first stage bypass
line.
[0112] According to an embodiment of the present invention, the
tapered flow desalination system and method are as follows. The
system comprises two stages in which the concentrate exiting the
first stage becomes the feed entering the second stage. The system
comprises I membrane block pressure vessels having feed water pass
through them during the first stage and J membrane block pressure
vessels having feed (concentrate exiting the I first stage blocks)
pass through them during the second stage, wherein preferably
I>J. A feed high pressure pump is connected to the flow line at
a portion of the line wherein the incoming inlet feed flows through
a single line before being split into the lines of the blocks into
the next stage.
[0113] An interstage booster pump is connected between the blocks
of both stages. The flow direction in block(s) of the second stage
can be reversed and become part of the first stage and the flow
direction in block(s) of the first stage can be reversed and become
part of the second stage.
[0114] Additional elements (e.g. valves or control elements such as
check valves or sensors) are connected to the system. Each pressure
vessel is coupled to a permeate product line wherein the permeate
filtered exits the pressure vessel through it. The permeate product
lines coming out of the pressure vessels are coupled to one main
system outlet permeate product line.
[0115] According to an embodiment, an AV bypass line (with an AV
valve) couples between the concentrate outlet of the system and the
second stage booster pump. The bypass line AVF line (with the AVF
valve) couples between the first stage booster pump and the second
stage booster pump.
[0116] FIG. 4 shows an embodiment with two vessel blocks in the
first stage (A and B), and one vessel block (C) in the second
stage. The first booster pump is connected to the system incoming
feed inlet line 60.
[0117] The blocks of pressure vessels A,B, and C have been
connected to the flow manifold so that they can either operate in
parallel and as part of stage one (the bottom stage) or as part of
stage two (the top stage). When the valves connected to a block and
labeled with the symbol FI and FO are open (open symbols) then that
block is parallel to and part of the first stage. When the valves
connect to a block and labeled with the symbols RI and RO are open
(open symbols) then that block is part of the second stage.
[0118] The valves AFI, BFI and CFI are each coupled by flow lines
to the first booster pump 51, to the valves ARO, BRO and CRO
respectively, to the inlets/outlets of blocks A, B and C
respectively, to the AVF valve 54 and to one another.
[0119] The valves ARO, BRO and CRO are also coupled to the
inlets/outlets of each of the blocks A, B and C respectively, to
the AV valve 55, to the system outlet concentrate outlet line 70
(of the system) and to one another.
[0120] The valves AFO, BFO and CFO are each coupled by flow lines
to the second booster pump 52, to the valves AM, BRI and CRI
respectively, to the inlets/outlets of blocks A, B and C
respectively, to the AVF valve 54 and to one another.
[0121] The valves AM, BRI and CRI are also coupled to the
inlets/outlets of blocks A, B and C respectively, to the second
booster pump 52, to the AV valve 55 and to one another.
[0122] The first booster pump 51 is also coupled to the AVF valve
54.
[0123] The second booster pump 52 is also coupled to the AV valve
55 and to the AVF valve 54.
[0124] The AV valve 55 is also coupled to the concentrate outlet
line 70 of the system. (which according to an embodiment is line
[4] of FIG. 3).
[0125] A particular method for operating apparatus 40 is
illustrated in FIGS. 5A to 5G comprising the same structure as in
FIG. 4. Though not shown in the figures, check valves may be
installed on each of the lines to prevent short-circuiting and
bypassing during the transition process. Dotted lines refer to
lines in which feed solution is flowing between the feed high
pressure pump and the interstage booster pump. Dashed lines refer
to lines in which interstage concentrate or final concentrate is
flowing between the interstage booster pump and the back pressure
valve or device (P/FV) and onward to the concentrate outlet line.
Thin lines refer to process lines in which no flow is occurring.
Apparatus 40 comprises pairs of 2-way valves on each high pressure
port of the pressure vessels to effect repositioning of membrane
blocks A B and C of pressure vessels between a first and second
membrane stages. The sequence to effect this change is illustrated
in FIGS. 5A to 5G. Table 1 summarizes a sequence of steps needed to
reposition block C from the second stage to the first stage, and
block B from the first stage to the second stage. In particular,
this highlights the role of the bypass valve AVF in the first
stage.
[0126] In yet another preferred embodiment of the invention, the
apparatus is configured to switch blocks by placing all three
blocks in the first stage to slow the flow rate to each one in
preparation for switching. Then one of the block's valving is
changed so that it is moved into the second stage.
[0127] In yet another preferred embodiment of the invention, the
apparatus is configured to switch one of the two blocks in the
first stage with the block of the second stage, slowing the flow
rate to each one in preparation for switching. The steps performed
in this embodiment are demonstrated in table 2. This embodiment has
the advantage of eliminating the need for the first stage bypass
valve, AVF. On the other hand it could lead to too high recovery
being obtained in the first stage unless applied feed pressures are
adjusted during the transition.
[0128] In both embodiments (with AFV and without), there is an
advantage to increasing the time to effect the opening and closing
of the two-way valves to between 5 and 30 seconds (and preferably
between 5 and 15 seconds) in order to reduce the increase in
pressure even further.
[0129] In the method, as explained in FIGS. 5A-5G, the initial
working mode (FIG. 5A) is wherein at a first stage incoming feed
water is passed through blocks A, B. The concentrated liquid coming
out of those four blocks is passed in the second stage though block
C, and from there out of the system. The method comprises switching
the roles between block B and block C. After the switching, block C
is connected to the feed line 60 (at its opposite side), and block
B becomes the second stage vessel block. This is done by
opening/closing the appropriate valves. The working modes are
switched periodically.
[0130] Thus in FIG. 5A, block C is in the third stage and blocks A
and B are in the first stage. In FIG. 5G, block B is in the second
stage and blocks A and C are in the first stage.
[0131] The following table clarifies the switching procedure step
by step.
TABLE-US-00001 TABLE 1 Valve steps in moving from configuration
with blocks A and B in stage I to blocks A and C in stage I
(switching blocks B and C between stages), as illustrated in FIGS.
5A to 5G. STEPS Start End (FIG. 5A) Iv (FIG. 5G) A, B 1.sup.st Iii
(FIG. 5E) V A, C 1.sup.st stage C I Ii (FIG. 5D) B (FIG. 5F) stage,
2.sup.nd (FIG. 5B) (FIG. 5C) Stage 1 stopped, B slowed, B 2.sup.nd
Valves stage C slowed C stopped slowed C forward C forward stage
BLOCK AFI On On On On On On On A AFO On On On On On On On ARI Off
Off Off Off Off Off Off ARO Off Off Off Off Off Off Off BLOCK BFI
On On On On Off Off Off B BFO On On On On Off Off Off BRI Off Off
Off Off Off On On BRO Off Off Off Off Off On On BLOCK CFI Off Off
Off Off On On On C CFO Off Off Off Off On On On CRI On On Off Off
Off Off Off CRO On On Off Off Off Off Off Auxiliary AVF Off Off Off
On On Off. Off Bypass AV Off On On On On On Off Valves Comments A,
B in C C Stage I B B rev., A, C 1.sup.st 1.sup.st stage slowed
stopped Slowed stopped slow stage C, in 2nd C C for., B, 2nd stage
forward fast stage slow
[0132] The following items indicated in FIGS. 5A-5G refer to:
[0133] FW--Feed Water
[0134] C1-LP--Low Pressure Concentrate 1st stage
[0135] C1-HP--High Pressure Concentrate 1st stage
[0136] C1--1st stage Concentrate
[0137] C2--2.sup.nd stage
[0138] PP--Permeate Product
TABLE-US-00002 TABLE 2 Alternate way to switch blocks B and C
between stages I and II eliminating need of valve AVF STEPS Valves
Start I ii Iii Iv v End BLOCK AFI On On On On On On On A AFO On On
On On On On On ARI Off Off Off Off Off Off Off ARO Off Off Off Off
Off Off Off BLOCK BFI On On On On Off Off Off B BFO On On On On Off
Off Off BRI Off Off Off Off Off On On BRO Off Off Off Off Off On On
BLOCK CFI Off Off Off On On On On C CFO Off Off Off On On On On CRI
On On Off Off Off Off Off CRO On On Off Off Off Off Off Auxiliary
AVF Off Off Off Off Off Off Off Bypass AV Off On On On On On Off
Valves Comments A, B 1.sup.st C C All B B Rev., A, C 1st stage
slowed stopped blocks Stopped slow B, 2nd st C, 2nd on stage A, C
For. stage I and Fast slow
[0139] According to another embodiment of the present invention,
the tapered flow desalination system and method are as follows. The
system comprises three stages in which the concentrate exiting one
stage becomes the feed entering the next stage. The system
comprises K membrane block pressure vessels having feed water pass
through them during the first stage, L membrane block pressure
vessels having feed (concentrate exiting the K first stage blocks)
pass through them during the second stage and M membrane block
pressure vessels having feed (concentrate exiting the L second
stage blocks) pass through them during the third stage, wherein
preferably K>L>M. A booster pump is preferably connected to
the flow lines at a portion of the line wherein the incoming feed
at each stage flows through a single line before being split into
the lines of the blocks of the next stage. The flow direction in
block(s) of the third stage can be reversed and become part of the
first stage and the flow direction in block(s) of the first stage
can be reversed and become part of the third stage.
[0140] Additional elements (e.g. valves or control elements such as
check valves or sensors) are connected to the system in a similar
manner as explained hereinabove regarding the 2 stage embodiment.
Each pressure vessel is coupled to a permeate product line wherein
the permeate filtered exits the pressure vessel through it. The
permeate product lines coming out of the pressure vessels are
coupled to one main system outlet permeate product line.
[0141] According to an embodiment, the AV line (with the AV valve)
couples between the concentrate outlet of the system and the third
stage booster pump, in a similar manner as explained hereinabove
regarding the 2 stage booster pump. Optionally, the AVF line (with
the AVF valve) couples between the first stage booster pump and the
second stage booster pump, as explained hereinabove regarding the
second stage embodiment.
[0142] FIG. 7A-7F show an embodiment with six vessel blocks in the
first stage (B, C and four more), three vessel blocks in the second
stage and one vessel block (A) in the third stage. The system
valves are connected to the system in a similar manner as in FIGS.
4-5.
[0143] The first booster pump is connected to the system incoming
feed line 60.
[0144] The valves AFI, BFI and CFI are each coupled by flow lines
to the first booster pump 51, to the valves ARO, BRO and CRO
respectively, to the inlets/outlets of blocks A, B and C
respectively, to the inlet of the four additional first stage
blocks and to one another.
[0145] The valves ARO, BRO and CRO are also coupled to the
inlets/outlets of each of the blocks A, B and C respectively, to
the AV valve 55, to the system outlet concentrate outlet line 70
(of the system) and to one another.
[0146] The valves AFO, BFO and CFO are each coupled by flow lines
to the second booster pump 52, to the valves ARI, BRI and CRI
respectively, to the inlets/outlets of blocks A, B and C
respectively, to the outlets of the four additional first stage
blocks and to one another.
[0147] The valves ARI, BRI and CRI are also coupled to the
inlets/outlets of blocks A, B and C respectively, to the third
booster pump 53, to the AV valve 55 and to one another.
[0148] The second booster pump 52 is also coupled to the outlets of
the four additional first stage blocks and to the inlets of the
three second stage blocks.
[0149] The third booster pump 53 is also coupled to the outlets of
the three second stage blocks and to the AV valve 55.
[0150] The AV valve 55 is also coupled to the concentrate outlet
line 70 of the system.
[0151] Each pressure vessel is coupled to a permeate product line
wherein the permeate filtered exits the pressure vessel through it.
The permeate product lines coming out of the pressure vessels are
coupled to one main system outlet permeate product line 80.
[0152] The method of this embodiment comprises switching roles
between two pressure vessel blocks, one in the first stage and the
other in the third stage. Thus the third stage block which is most
exposed to scaling/membrane fouling because the feed entering it is
highly concentrated (supersaturated) after passing two vessel
blocks (of the first stage and second stage). Therefore this method
of switching is a very efficient because after switching, the
former third stage vessel is exposed to under saturated feed water
which washes out all the minerals and materials that accumulated on
the former third stage vessel, and this is done without water
hammering.
[0153] The initial working mode is wherein at a first stage
incoming feed water is passed through blocks C, B and through 4
additional blocks. The concentrated liquid coming out of those four
blocks is passed in the second stage through three blocks. The
concentrated liquid coming out of those three blocks is passed in
the third stage though block A, and from there out of the system.
The method comprises switching the roles between block A and block
B. After the switching, block A is connected to the feed line 60
(at its opposite side), and block B becomes the third stage vessel
block. This is done by opening/closing the appropriate valves. In
this example a further switch can be made in which block C becomes
the third stage vessel block and the vessel blocks A and B are part
of the 6 blocks of vessels in the first stage. The working modes
are switched periodically. Alternatively there can be only blocks A
and B which are switched between the first and third stages,
without any block C being connected to a manifold for switching as
described in the previous paragraph.
[0154] The blocks of pressure vessels A,B, and C have been
connected to the flow manifold so that they can either operate in
parallel and as part of the first stage or as part of the third
stage . When the valves connected to a block and labeled with the
symbol FI and FO are open (open symbols) then that block is
parallel to and part of the first stage. When the valves connect to
a block and labeled with the symbols RI and RO are open (open
symbols) then that block is part of the third stage. Thus in FIG.
7A, block A is in the third stage and blocks B and C are in the
first stage. In FIG. 7F, block B is in the third stage and blocks A
and C are in the first stage parallel to the rest of the pressure
vessels in the first stage. This arrangement has the advantage that
because the blocks are being switched into and out of the first and
last stage, the change in the number of pressure vessels in
parallel in the first stage during the switching is relatively
minor and this minimizes any hydraulic upset. The steps described
hereinabove that are used in switching between the first and second
stage, are similar to those taken here as well to minimize any
hydraulic shocks.
[0155] The following table clarifies the switching procedure step
by step.
TABLE-US-00003 TABLE 3 Valve steps in moving from configuration
with block A in stage III (while blocks B and C are together with
rest of stage I) to block B in stage III (while blocks A and C are
together with rest of stage I), as illustrated in FIGS. 7A to 7F.
(C does not change stages) STEPS Start (I) II III IV V End (VI)
Valves (FIG. 6A) (FIG. 6B) (FIG. 6C) (FIG. 6D) (FIG. 6E) (FIG. 6F)
BLOCK AFI Off Off Off On On On A AFO Off Off Off On On On ARI On On
Off Off Off Off ARO On On Off Off Off Off BLOCK BFI On On On Off
Off Off B BFO On On On Off Off Off BRI Off Off Off Off On On BRO
Off Off Off Off On On BLOCK CFI On On On On On On C CFO On On On On
On On CRI Off Off Off Off Off Off CRO Off Off Off Off Off Off
Bypass AV Off On On On On Off Valves Comments B, C 1.sup.st A
slowed A A in 1.sup.st B B in 3.sup.rd stage stopped stage reversed
stage A, 3rd and B in 3.sup.rd and stage stopped stage regular and
slow speed A, C 1.sup.st A, C 1.sup.st stage stage Fast Fast
[0156] While some of the embodiments of the invention have been
described by way of illustration, it will be apparent that the
invention can be carried into practice with many modifications,
variations and adaptations, and with the use of numerous
equivalents or alternative solutions that are within the scope of a
person skilled in the art, without departing from the spirit of the
invention, or the scope of the claims.
* * * * *