Title of Invention

A METHOD OF ESTIMATING A MAXIMUM FLUX DURING STABLE OPERATION OF A MEMBRANE FILTRATION PLANT

Abstract It is an object of the present invention to provide a method of estimating the maximum value of the flux during long-term stable operation including cleaning of a membrane filtration plant based on measured data of a membrane filtration characteristic during initial membrane filtration. The present invention provides a method in which the maximum flux during stable operation of a new membrane filtration plant for which a membrane module and operating conditions have been specified is estimated from a measured value A of an initial membrane filtration characteristic measured using a liquid to be treated in and a membrane of a membrane module of the new membrane filtration plant, an empirical value of a maximum flux during stable operation of each of a plurality of existing membrane filtration plants having the same or a similar membrane module and operating conditions, and a measured value B of the initial membrane filtration characteristic measured using a liquid to be treated in and a membrane of a membrane module of each of the existing membrane filtration plants.
Full Text A0501 UP30W/AYK
METHOD OF ESTIMATING
STABLE STATE MEMBRANE FILTRATION FLUX
Technical Field
The present invention relates to a method of estimating the value
of a membrane filtration flux in its stable state, required for designing a
new membrane filtration plant, based on initial membrane filtration test
data.
Background Art
In a membrane filtration plant that uses filtration membranes such
as ultrafiltration membranes or precise filtration membranes, a liquid to
be separated is passed through a membrane module, and pressure is
applied to the liquid from outside the membrane module. Desired
filtration is then carried out under conditions at which a certain flux can
be obtained, based mainly on the size of the pores in the membranes.
The nature of the liquid to be treated in a membrane filtration
plant varies between membrane filtration plants, and it is often the case
that various substances contained in the liquid cause so-called fouling
such as clogging of the membranes so that the flux decreases rapidly or
gradually. In a membrane filtration plant, physical cleaning such as air
bubbling, or flushing is thus carried out repeatedly at relatively short time
intervals to restore the membrane performance to some extent.
Moreover, within a condition assuming chemical cleaning that thoroughly
restores the membrane performance to be carried out, for example, once
every six months, and within a range of possible operating conditions, a
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state under which operation can be carried out stably over the six months,
by the next chemical cleaning, is determined, and out of such conditions,
operation is generally carried out using conditions for which the
efficiency is best.
Typical behavior of the operating pressure during stable operation
under the condition of constant flow rate in a membrane filtration plant is
shown in FIG. 10(a). In FIG. 10(a), the horizontal axis shows the
operating time in days, and the vertical axis shows the operating
pressure. An enlarged view of the portion enclosed by the circle in FIG.
10(a) is shown in FIG. 10(b). FIG. 10(b) shows the short-term pressure
change associated with periodic cleaning. As can be seen from FIG.
10(a), the operating pressure rises rapidly at the start of operation.
However, once the initial period has elapsed, a stable period begins and
the operating pressure gradually rises with a constant gradient with the
operating time. After the stable period, a final period begins and the
operating pressure rises rapidly approaching the operating limit of a
liquid feeding pump, whereupon chemical cleaning of the filtration
membranes becomes necessary.
As the conditions of the operation of the membrane filtration plant,
when assuming in advance that an operation time period is from this
initial period to this final period and that the short-term cleaning is
carried out, it is most efficient to operate at the maximum flux at which
operation can be carried out stably at a constant flow rate over this time
period. Therefore, when designing the membrane filtration plant, the
maximum value of the flux in a stable state is estimated, taking the fixed
short-term cleaning conditions and an operating time period between the
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chemical cleanings into consideration, and the design scale of the
membrane filtration plant is determined accordingly.
However, the stable state flux during actual operation is affected
by the type of substances contained in, the nature of particles in, and the
concentration and so on of the liquid to be treated with pre-treatment
included, and furthermore is considered to be affected in a complex way
by various conditions such as the filtration membrane characteristics,
interaction between substances contained in the liquid to be treated and
the filtration membranes, the filtration membrane cleaning conditions, the
operating conditions, and so on. Conventionally, due to such complex
interactions, it has been considered to be completely impossible to
estimate the stable state flux value in advance.
As an attempt to estimate this, there has been proposed, for
example, a method known as the SDI (silt density index) measurement
method in which the liquid to be treated is subjected to filtration for a
fixed time at a constant pressure using a certain filtration filter, and it is
attempted to determine the stable state flux value from the measured
value of the flow rate at the time of starting the filtration and the time of
ending the filtration. However, this method can only be used in a very
narrow water quality range, and hence is not very practicable. Moreover,
in Japanese Patent Application Laid-open No. 2001-327967 (Patent
Document 1), there is described a method in which it is attempted to
optimize a membrane filtration flux, a physical cleaning interval, a
chemical cleaning timing, pre-treatment and so on from a function of
measured values of a turbid matter amount and a soluble organic carbon
amount, and the membrane filtration flux. However, in that invention,
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DOC, E260, and turbidity must be analyzed, which is complicated.
Moreover, the cause of organic contamination is specified as being humic
matter, the extent of contamination being calculated purely from the ratio
between DOC and E260, and hence in the case that organic matter other
than humic matter contributes to membrane contamination, the effect
thereof cannot be properly evaluated.
Conventionally, when designing a new membrane filtration plant, it
has thus generally been the case that membrane module(s) with one type
or a plurality of types of candidate membrane(s) is/are used, and while
using various combinations of pre-treatment and membrane module
empirically or through trial and error, long-term operation for from a
minimum of approximately one month to a maximum of approximately one
year including seasonal variations is carried out in advance by actually
passing the liquid to be treated through the membrane module, and it is
tested through trial and error what is the maximum value of the flux that
can be obtained stably. For example, in Non-Patent Document 1
(Advanced Aqua Clean Technology for 21st Century (ACT 21) New
Development of City Water Membrane Filtration Technology, published by
the Japan Water Research Center, December 2002, pages 200-204,
227-230, 257-271, 272-274, 277-279), various similar test results are
reported, including a report of results of tests in which the long-term
stability of a membrane water purification treatment system was
investigated while testing various types of pre-treatment using an
ultrafiltration (UF) membrane at Gifu Prefecture Yamanouchi Water
Purification Plant.
Alternatively, in the case that such a long time cannot be taken for
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testing, it has been the case that empirical values for past membrane
filtration plants for which the composition of the liquid to be treated is
thought to be relatively similar are consulted, and thus the stable state
flux value for the new membrane filtration plant is assumed empirically,
and then a safety factor larger than usual is applied thereto so as to
obtain the design value.
Disclosure of Invention
It is an object of the present invention to provide a method of
estimating the maximum value of the flux during long-term stable
operation including short-term cleaning of a membrane filtration plant
based on measured data of a membrane filtration characteristic during
initial membrane filtration.
The present invention is method of estimating a maximum flux
during stable operation of a membrane filtration plant for which a
membrane module and operating conditions have been specified, the
estimating method comprising: a step of obtaining a measured value A of
an initial membrane filtration characteristic for the membrane filtration
plant using a liquid to be treated in and a membrane of a membrane
module of the membrane filtration plant; a step of obtaining a maximum
flux value during stable operation of each of a plurality of existing
membrane filtration plants having a membrane module and operating
conditions the same as or similar to the aforementioned membrane
module and operating conditions; a step of obtaining a measured value B
of the initial membrane filtration characteristic for each of the existing
membrane filtration plants using a liquid to be treated in and a membrane
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of a membrane module of that one of the existing membrane filtration
plants; and an estimating step of estimating a maximum flux for the
aforementioned membrane filtration plant from the measured value A
based on a relationship between the maximum flux values and the
measured values B for the existing membrane filtration plants.
Here, the estimating step is preferably a step of representing by a
formula or on a graph a relationship between the logarithm of the
measured values B of the initial membrane filtration characteristic and
the maximum flux values, and estimating the maximum flux for the
membrane filtration plant by extrapolating or interpolating for the
measured value A using the formula or graph.
Moreover, the operating conditions preferably comprise at least
filtration time or membrane cleaning pattern conditions. Furthermore,
the initial membrane filtration characteristic is preferably selected from
the group consisting of a constant pressure simple filtration resistance, a
quantitative simple filtration resistance, a cleaning-included constant
pressure filtration resistance, and a cleaning-included quantitative
filtration resistance. Moreover, the measured values of the initial
membrane filtration characteristic, and the empirical values of the
maximum flux during stable operation are preferably linked to one
another by through a semi-log graph with the measured values on the log
side.
Advantageous Effects of the Invention
It becomes possible to estimate the maximum value of the flux
during long-term stable operation including cleaning conditions of a
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membrane filtration plant very simply from liquid flow data for a short
initial membrane filtration period. As a result, there is no longer any
need to carry out long-term test operation when designing a new
membrane filtration plant.
Brief Description of Drawings
FIG. 1 is a schematic drawing showing schematically an example
of the construction of an apparatus for measuring an initial membrane
filtration characteristic;
FIG. 2 is a diagram showing an example of experimental results
for determining the maximum value of the flux in a stable state for an
existing membrane filtration plant (A);
FIG. 3 is a diagram showing an example of experimental results
for determining the maximum value of the flux in a stable state for an
existing membrane filtration plant (B);
FIG. 4 is a diagram showing an example of experimental results
for determining the maximum value of the flux in a stable state for an
existing membrane filtration plant (C);
FIG. 5 is a diagram showing an example of a graph for determining
a quantitative simple filtration resistance;
FIG. 6 is a diagram showing the concept of a cleaning-included
constant pressure filtration resistance;
FIG. 7 is a diagram showing the concept of a cleaning-included
quantitative filtration resistance;
FIG. 8 is a diagram showing an example of the relationship
between a K value and the maximum value of the flux in a stable state;
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FIG. 9 is a diagram showing an example of experimental results
for determining the maximum value of the flux in a stable state for a new
membrane filtration plant; and
FIGS. 10 are diagrams showing an example of the typical behavior
of the operating pressure for a membrane filtration plant.
Best Mode for Carrying Out the Invention
Following is a description of embodiments of the present invention
with reference to the drawings. In the present invention, first, the
membrane module and operating conditions for a membrane filtration
plant to be newly established are determined. Then, using a membrane
to be used in the membrane module, and a liquid planned to be treated
using the new membrane filtration plant, an initial membrane filtration
characteristic such as the filtration resistance of the membrane (this
value is taken as a measured value A) is measured. The measurement
is completed in a short time of approximately 10 minutes to 1 hour.
Next, at least two existing membrane filtration plants with a
membrane module and operating conditions the same as or similar to
those of the membrane filtration plant to be newly established are
selected, and empirical data on the maximum value of the flux at which
operation can be carried out stably within an operating time range up to
planned chemical cleaning is gathered. Such empirical values are
gathered through trial and error by changing operating conditions such
as the operating pressure in each plant. Moreover, using a membrane
of the membrane module used in each of the existing membrane filtration
plants and the liquid to be treated in that existing membrane filtration
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plant, the same initial membrane filtration characteristic as above is
measured (each such value is taken as a measured value B).
Next, the empirical values of the maximum value of the flux for
each of the existing membrane filtration plants, and the measured values
B are plotted on a semi-log graph with the measured values B on the log
side. The points are then joined by a straight line, and the point
corresponding to the measured value A on this straight line is identified.
If the flux value at this point is read off, then the maximum value of the
flux at which operation can be carried out stably for the membrane
filtration plant to be newly established can be obtained.
That is, surprisingly, regardless of what the liquid to be treated is,
so long as there is data on the maximum value of the flux for each of a
plurality of existing membrane filtration plants each having the same or
similar membrane module and operating conditions, then by measuring
the initial membrane filtration characteristic for the membrane of each of
the existing membrane filtration plants and the initial membrane filtration
characteristic for the membrane of the membrane filtration plant to be
newly established, the maximum stable flux value for the membrane
filtration plant to be newly established can be estimated forthwith.
Note that in the above, for convenience of explanation, the various
steps of the estimating method according to the present invention have
been described in the order measured value A, measured values B,
maximum flux values, but the estimating method according to the present
invention is not necessarily limited to this order. For example, the
above may be determined in the order measured value A, maximum flux
values, measured values B, or even the order maximum flux values,
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measured values B, measured value A.
The present invention was accomplished upon discovering, while
carrying out various data analysis by trial and error based on empirical
values for numerous existing membrane filtration plants constructed for
various types of liquids to be treated, that if the above semi-log graph is
plotted, then surprisingly, regardless of the nature of the liquids to be
treated, the data for the various existing membrane filtration plants lies
substantially on a single straight line for which the membrane module
and operating conditions are specified.
As a result, it has become possible to carry out estimation of
design conditions for a new membrane filtration plant very easily and in a
short time and moreover highly accurately, whereas conventionally this
has required long-term test operation for from one month at the shortest
to approximately one year in general. Following is a more detailed
description.
First, the new membrane filtration plant referred to here means a
membrane filtration plant that is at the planning stage but has not yet
been constructed, although this may also be an existing membrane
filtration plant, i.e. a membrane filtration plant that has been constructed
without long-term testing having been carried out in advance but rather
with design values having been assumed based on data for another
existing membrane filtration plant for which the nature of the liquid to be
treated is similar, or a plant for which the work of finding out the
maximum flux empirically has not been carried out. With such a plant,
there is a possibility that optimal design has not been necessarily been
carried out, and hence estimating the maximum value of the flux is
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worthwhile.
Next, the membrane module and operating conditions to be used
in the new membrane filtration plant are specified. This is because
these are parameters that specify different straight lines when the
semi-log graph described above is created. Here, the type of the
membrane module is, as a rule, judged by the material of the membranes,
the form of the membranes such as whether the membranes are hollow
fibers or flat membranes, the diameter of the pores, the number of pores,
in the case of hollow fibers the diameter of the fibers, the length of the
fibers, the packing ratio of the fibers in the module, in the case of flat
membranes the dimensions of the membranes, the distance between
membranes, and the form of the module such as whether the module is
spiral type, filter press type or the like, and so on. In the case that the
above differ, the performance of the membrane module differs, and hence
as a rule a different membrane module is specified.
In actual practice, carrying out the judgment in accordance with
the product classification of the membrane module is simple and thus
preferable. That is, judging products of the same grade as being the
same membrane module, and products of different grades as being
different membrane modules is simple. This is because it is considered
that if different grade numbers have been assigned, then membrane
modules have different specifications and performance to one another.
In the case that more than one grade is assigned to one product, the
judgment is preferably carried out by returning to the above principles.
Moreover, membrane modules being "similar" means that to a certain
specified membrane module, the various specifications and
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characteristics described above are close, and hence the membrane
modules can be used as alternatives for one another. A characteristic
being "close" means that even if numerical values of the characteristic
differ, the numerical values are within a range of ±30%. Within this
range, characteristics are judged as being similar or substantially the
same operating condition. More preferably, the numerical values are
within ±20%, yet more preferably ±10%.
Moreover, operating conditions mean the filtration time comprising
the sum of, in actual operation, (i) the time for the filtration process in
which the liquid to be treated is treated, (ii) the time for a cleaning
process in which the membranes are cleaned, and (iii) the time for a
flushing process in which a turbid component is flushed out as required
(i.e. the time required for carrying out a repeat unit process in actual
operation), a membrane cleaning pattern comprising, for example, the
form of the membrane cleaning, the air flow rate in the case of using air
scrubbing in the membrane cleaning, and the backwashing time, and so
on. In the case that these are the same, it is judged that the operating
conditions are the same. Moreover, even if the numerical values thereof
differ, so long as the numerical values are within a range of ±30%, the
operating conditions are judged to be similar or within a range of being
substantially the same. More preferably, the numerical values are within
±20%, yet more preferably ±10%. Note that pre-treatment conditions
need not be included in the operating conditions. This is because,
although the nature of the liquid to be treated is changed by such
pre-treatment, the present invention can be applied regardless of the
nature of the liquid to be treated.
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Next, using a membrane of the membrane module to be used in
the new membrane filtration plant, and the liquid to be treated in the new
membrane filtration plant, the measured value A of an initial membrane
filtration characteristic of the membrane is measured. Here, "initial
membrane filtration characteristic" means a membrane characteristic
within a time period from treatment of the liquid to be treated being
started using a new unused filtration membrane up to a stable state
being reached as shown in FIG. 1, but in actual practice, it is sufficient to
measure the membrane characteristic over a time interval of from
approximately 10 minutes from the treatment being started up to at the
longest a time including approximately 2 to 3 cleaning steps. Examples
of the item measured as the initial membrane filtration characteristic are
the constant pressure simple filtration resistance, the quantitative simple
filtration resistance, the cleaning-included constant pressure filtration
resistance, the cleaning-included quantitative filtration resistance, and so
on; in the following, the case that the constant pressure simple filtration
resistance is used as the initial membrane filtration characteristic is
described. Description will be given for other initial membrane filtration
characteristics later.
FIG. 1 is a schematic drawing of an apparatus for measuring the
initial membrane filtration characteristic. A membrane module, which is
central to the apparatus, is a mini-module 1 in which a single hollow fiber
2 of length approximately 20 cm is housed in a housing. As the hollow
fiber 2, there is used an unused hollow fiber the same as a hollow fiber
to be used in the membrane module planned to be used in the new
membrane filtration plant, although the length of the hollow fiber is made
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to match the housing. One end of the hollow fiber 2 is closed off by a
stopper 5, and the other end is made to be an open end 6 such that
liquid that has permeated through the membrane can flow out. The
liquid to be treated enters into the housing from an inlet 3 on the side of
the mini-module, and only liquid that permeates through the membrane
flows out from the open end 6. An outlet 4 on the side of the
mini-module leads to a closed off end 63 via a line 62.
The liquid 70 to be treated in the new membrane filtration plant,
which is in a vessel 11, is sucked in from the vessel 11 via a line 60 by
an extruding roller 21 of a pump 20 while being stirred by a stirrer 10,
and is fed to the inlet 3 on the side of the mini-module via a line 61. A
filtration pressure is applied to the mini-module 1 through rotation of the
pump 20. Pressure gauges 50 and 51 are provided in the line 61 and
the line 62 respectively, and so long as the measurement is being carried
out normally, the pressures indicated by the two pressure gauges are
substantially the same value.
A vessel 31 for receiving membrane-permeated liquid 71 flowing
out from the open end 6 of the mini-module 1 is placed below the open
end 6. The vessel 31 is further placed on an electronic balance 30
capable of sequentially measuring the weight of the
membrane-permeated liquid 71 for each vessel 31. Cumulative data on
the weight measured by the electronic balance 30 is sent to a computer
40 and subjected to data processing, whereby the constant pressure
simple filtration resistance K is computed.
Here, the constant pressure simple filtration resistance K will now
be described. K is also known as the Ruth constant pressure filtration
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coefficient, being a coefficient obtained from studying cake filtration
under a condition of constant pressure filtration. Taking the filtration
time from starting filtration as 0, and the amount of filtrate as V, K is
defined as the gradient 9/V2 of a straight line obtained by plotting a
graph of 0/V on the vertical axis against V on the horizontal axis on
ordinary graph paper. This graph of 0/V on the vertical axis against V
on the horizontal axis is shown on the computer 40 portion in FIG. 1. A
program for computing K is stored in the computer 40. When
determining K, so that the pressure gauges 50 and 51 are at constant
pressure, the measurement is preferably carried out under the condition
of the rotational speed of the roller 21 being constant. The
measurement of the constant pressure simple filtration resistance can
easily be completed within approximately 10 minutes. The measured
value A of the constant pressure simple filtration resistance K using the
membrane and the liquid to be treated to be used in the membrane
module of the new membrane filtration plant is thus obtained.
Note that any of various modifications may be made to the
apparatus for measuring the initial membrane filtration characteristic, the
apparatus not being limited to that shown in FIG. 1. For example, there
is no limitation to one hollow fiber being housed in the mini-module, but
rather a mini-module with a flat membrane may be used instead.
Moreover, the measurement may instead be carried out by making the
flow rate constant and measuring the variation in pressure.
Next, from out of existing membrane filtration plants, a plurality of
ones each having a membrane module and operating conditions the
same as or similar to those of the new membrane filtration plant are
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selected (in actual practice, the membrane module and operating
conditions for the new membrane filtration plant are selected by
consulting the membrane module and operating conditions for the
existing membrane filtration plants). When selecting the existing
membrane filtration plants, there is no need for the nature of the liquid to
be treated to be similar to for the liquid to be treated in the new
membrane filtration plant.
Next, data on the maximum value of the flux in a stable state as
measured by trial and error is gathered for each of the plurality of
existing membrane filtration plants. In general, with an existing
membrane filtration plant, the flux is changed by varying the filtration
pressure as appropriate so as to optimize the operating conditions for a
while after starting operation, and then operation is carried out in this
state for a certain time period, and the behavior over time of the filtration
pressure is studied. Examples of situations in which this was carried
out are shown in Tables 2 to 4.
FIG. 2 shows results of an experiment in which the flux was
increased in stages for a certain existing membrane filtration plant (A),
carried out with the purpose of determining at up to what flux the
filtration pressure could be maintained in a stable state, i.e. the
maximum value of the flux in a stable state. Here, the flux is the volume
of membrane-permeated liquid obtained per unit area of the membrane
per day, m3/m2/d = m/d being used as the units thereof. In an initial
period of the experiment, it was started from a small flux of 4 m/d, and it
was ascertained that a stable state was obtained in this case. The flux
was thus next increased to 6 m/d, whereupon the gradient of the
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pressure increase was too high, and hence it was ascertained that stable
operation was not possible. It can be seen from this that at 6 m/d, the
maximum value of the flux at which a stable state can be obtained has
been exceeded. In actual fact, through subsequent tests, it was
ascertained that the maximum value of the flux is 4.7 m/d.
FIG. 3 shows the results of an experiment for determining the
maximum stable flux value for another existing membrane filtration plant
(B). Operation was carried out at 2.9 m/d initially, whereupon the
gradient of the pressure increase was too high, it being ascertained that
200 kPa, which is the upper limit of the operating pressure for the plant,
was exceeded before completing an operating time period up to planned
chemical cleaning. That is, a stable state was not obtained. The
membrane was thus then subjected to chemical cleaning so as to return
the membrane to a state like that of a new article, and operation was
carried out again with the flux reduced to 2.4 m/d, whereupon it was
ascertained that a stable state with a small pressure increase gradient
could be obtained. Next, the membrane was again subjected to
chemical cleaning so as to return the membrane to a state like that of a
new article, and operation was carried out with the flux increased to 2.6
m/d, whereupon it was ascertained that a stable state could be obtained
even at this flux. Furthermore, from the results of experiments, not
shown, in which the flux was adjusted more finely between 2.6 m/d and
2.9 m/d, it was verified that the maximum value of the flux for the
existing membrane filtration plant (B) is 2.7 m/d.
FIG. 4 shows the results of an experiment for determining the
maximum value of the flux in a stable state for yet another existing
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membrane filtration plant (C). First, operation was carried out under the
condition of a flux of 1.5 m/d, it being ascertained that a stable state
could be obtained in this case. Next, the flux was increased to 3 m/d,
whereupon the filtration pressure increased rapidly, 200 kPa, which is the
upper limit of the pressure for operation of the plant, being exceeded at
times. That is, a stable state was not obtained. From subsequent
experiments, not shown, divided into finer stages, it was verified that the
maximum value of the flux at which a stable state can be obtained for
this membrane filtration plant is 2.8 m/d.
That is, the maximum stable flux value is determined empirically in
stages through trial and error, i.e. first filtration operation is carried out
for a certain time period at a flux value assumed to be on the stable side,
the extent of the pressure increase is investigated, and it is judged
whether or not a pressure increase gradient within a desired range is
obtained; in the case that a desired gradient is obtained, this is taken as
a stable state, and then the flux is further changed and it is judged
whether or not a stable state is obtained. In this way, data on the
maximum value of the flux in a stable state measured individually for
each of the existing membrane filtration plants is gathered (in actual
practice, from out of existing membrane filtration plants for which such
data has been assembled, a plurality of existing membrane filtration
plants that can be consulted when setting the conditions for the new
membrane filtration plant are selected).
Next, using a membrane of the membrane module used in one of
the existing membrane filtration plants, and the liquid to be treated in
that existing membrane filtration plant, the constant pressure simple
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filtration resistance K is measured as described above with reference to
FIG. 1. The membrane used is a membrane having the same
specification characteristics (or the same grade) as a membrane housed
in the membrane module used in the existing membrane filtration plant,
but being an unused membrane. Note that there is no need for the
length of the membrane or the number of such membranes to be the
same. For each of the remaining existing membrane filtration plants out
of the plurality selected, the constant pressure simple filtration resistance
K is similarly measured using the liquid to be treated in that plant, and an
unused membrane having the same specification characteristics as a
membrane housed in the membrane module of that plant. The plurality
of measured values thus obtained are taken as the measured values B.
As in the case of the new membrane filtration plant described above, this
measurement can be completed in at most approximately 10 minutes for
each of the membranes. Note that the measured value of the initial
membrane filtration characteristic is intrinsic to each plant, and hence in
the case that the measured value B has already been obtained, this
measured value may be used.
Next, the maximum value of the flux in a stable state is estimated
for the new membrane filtration plant from the data obtained as described
above. First, the plurality of measured values B of K, and the maximum
values of the flux in a stable state, for the existing membrane filtration
plants obtained as described above are plotted on a semi-log graph, the
K values being on the log side. Next, a straight line passing through the
plotted points is drawn. As already described, it has been discovered
that, regardless of the nature of the liquid to be treated, if the membrane
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module and operating conditions are specified, then even if the points
have been measured for different membrane filtration plants, the points
all lie on the same straight line. That is, it can be estimated that a point
also exists on this straight line for the new membrane filtration plant.
Accordingly, if the measured value A of K for the new membrane
filtration plant obtained as described above is plotted on the straight line,
and the value of the membrane filtration flux is read off from the vertical
axis, then this value can be estimated as being the maximum value of the
flux at which a stable state can be obtained for the new membrane
filtration plant in question. That is, estimation of the stable state for the
new membrane filtration plant can be carried out by extrapolating or
interpolating from the data for the existing membrane filtration plants.
In this way, based on empirical values for existing membrane
filtration plants, and an initial membrane characteristic that can easily be
measured, regardless of any difference in the nature of the liquid to be
treated, the desired maximum flux value can be obtained highly
accurately. There is thus no longer any need for long-term test
operation which has been necessary for new membrane filtration plants
hitherto, or for test operation through trial and error for determining the
maximum value of the flux after the plant has been constructed,.
Conversely, if the initial membrane filtration characteristic of
membranes used in each of various membrane modules is measured with
the liquid to be treated in the new membrane filtration plant, then it can
be identified in advance the membrane module and operating conditions
like which existing membrane filtration plant to use so as to obtain the
highest flux in the new membrane filtration plant, i.e. the optimum
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conditions.
That is, if a database having stored therein data on the initial
membrane filtration characteristic and the maximum flux value for
existing membrane filtration plants under various conditions is created,
then merely by measuring the initial membrane filtration characteristic for
each of various membranes using the liquid to be treated in the new
membrane filtration plant, the optimum membrane module and operating
conditions for the new membrane filtration plant can be determined
forthwith.
Next, as initial membrane filtration characteristics that can be
used, other than the simple filtration resistance K described above,
examples include the quantitative simple filtration resistance, the
cleaning-included constant pressure filtration resistance, and the
cleaning-included quantitative filtration resistance. Note, however, that
the initial membrane filtration characteristic is not limited thereto, but
rather may be any parameter enabling an initial membrane characteristic
to be identified.
For example, the quantitative simple filtration resistance is defined,
from the variation over time in the membrane-permeated amount and the
operating pressure as measured using an apparatus as in FIG. 1 under
the condition of constant flow rate, as the gradient of a straight line
obtained in the case of plotting the cumulative value V of the
membrane-permeated volume (which corresponds to the time) on the
horizontal axis and the operating pressure P on the vertical axis on a
graph on ordinary graph paper. This is shown in FIG. 5. This
quantitative simple filtration resistance is practical from the viewpoint
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A0501 UP30W/AYK
that a membrane filtration plant is operated under quantitative operating
conditions in actual practice. However, on the other hand, the
apparatus for measuring the initial membrane filtration characteristic
becomes complex since there arises a need to control operation of the
pump through signals from the pressure gauges.
Moreover, as the initial membrane filtration characteristic, there
can also be used one including up to approximately two to three cleaning
steps, although the measurement becomes more complex. K under the
condition of constant pressure with cleaning conditions added is referred
to as the cleaning-included constant pressure filtration resistance. This
is shown in FIG. 6. The solid line is the actual measurement data, it
being possible to use the gradient of the straight line shown by the
broken line as the initial membrane filtration characteristic.
Similarly, when measuring the quantitative simple filtration
resistance, that with the addition of up to approximately two to three
cleaning steps can also be used. This resistance under the quantitative
condition with cleaning conditions added is referred to as the
cleaning-included quantitative filtration resistance. This is shown in FIG.
7. The solid line is the actual measurement data including the cleaning,
it being possible to use the gradient of the straight line shown by the
broken line as the initial membrane filtration characteristic.
Furthermore, regarding the temperature during operation, it is
preferable to establish in advance a standard reference temperature from
the operating temperature for an existing membrane filtration plant, and
handle the shift therefrom by conversion using the temperature variation
of the viscosity of the liquid to be treated. Following is a more detailed
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A0501 UP30W/AYK
description of the present invention through a working example; however,
the scope of the present invention is not limited by this working example.
Example 1
For a certain sand filtration facility for river water, before
constructing a new membrane filtration plant for filtering wastewater
during backwashing, the maximum stable flux value was estimated. The
turbidity of the wastewater was relatively high at 100 degree. It was
decided to select a hollow fiber type precise filtration membrane module
made by Asahi Kasei Chemicals Corporation (model number UNA-620A,
membrane area 50 m2) as the membrane module, which was considered
to be suitable from the required throughput and so on, and the stable
operating time period up to chemical cleaning was set to 6 months.
Moreover, a total of 30 minutes comprising 28.5 minutes of filtration
operation, 1 minute of air scrubbing with backwashing, and 30 seconds of
flushing was taken as a unit process, this constituting standard operating
conditions, and operation was carried out by repeating this unit process.
During the air scrubbing with backwashing, sodium hypochlorite was
added to a concentration of 1 to 5 mg/l to the filtrate water used in the
backwashing. Using an unused membrane to be used in the membrane
module, the apparatus shown in FIG. 1, and the wastewater for when
carrying out the backwashing in the sand filtration, the constant pressure
simple filtration resistance K of the membrane was measured. The
measured value was relatively high at 0.35. This was taken as the
measured value A.
Next, three plants were selected that used a membrane module
having the same model number as the membrane module selected above
23

A0501 UP30W/AYK
and the same operating conditions. One was the membrane filtration
plant (A) for which some of the experimental results were shown in FIG. 2,
being a plant that carries out filtration of river water of turbidity 0.03
degree. Using an unused membrane the same as a membrane used in
the membrane module of the membrane filtration plant (A), and the river
water treated by the membrane filtration plant (A), the constant pressure
simple filtration resistance K was measured at a temperature of 20 °C
using the apparatus of FIG. 1, being 0.00033. This was taken as one of
the measured values B.
The second plant was the membrane filtration plant (B) for which
some of the experimental results were shown in FIG. 3, being a plant that
carries out filtration of industrial water of turbidity 1 degree. The
membrane module and operating conditions used in this membrane
filtration plant (B) were the same as for the membrane filtration plant (A).
Using the industrial water and membrane for the membrane filtration
plant (B), the constant pressure simple filtration resistance K was again
measured using the apparatus of FIG. 1, being 0.022. This was taken
as the second one of the measured values B.
The third plant was the membrane filtration plant (C) for which
some of the experimental results were shown in FIG. 4, being a plant that
carries out filtration of river water that has been made to have a turbidity
of 0.14 through the addition of pre-treatment comprising coagulating
sedimentation and sand filtration on the raw water. The membrane
module and operating conditions used in this membrane filtration plant
(C) were the same as for the membrane filtration plant (A). Using the
pre-treated water and membrane for the membrane filtration plant (C),
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A0501 UP30W/AYK
the constant pressure simple filtration resistance K was again measured
using the apparatus of FIG. 1, being 0.0187. This was taken as the third
one of the measured values B.
Next, the maximum stable flux value, which had been previously
identified, and the constant pressure simple filtration resistance K for
each of the membrane filtration plants (A) to (C) are shown in Table 1.
Table 1

K value Membrane filtration flux (m/d)
0.00033 4.7
0.022 2.7
0.0187 2.8
A graph of these values plotted as white circles (o) on a semi-log
graph with the constant pressure simple filtration resistance on the log
side is shown in FIG. 8. It can be seen that, as a result, the three points
lie on a single straight line as shown in FIG. 8. The point for the
measured value A described above (K value = 0.3500) is plotted on the
straight line as a black square (■), and reading off the flux value at this
point gives 1.4 m/d. This is the estimated value of the maximum stable
flux value.
Next, after the new membrane filtration plant had been
constructed based on the selected membrane module and operating
conditions, while carrying out filtration operation on river water made to
have a turbidity of 100 degree through the addition of pre-treatment, the
flux was changed in steps, so as to measure the maximum stable flux
value. An example of the behavior of the filtration pressure during the
25

A0501 UP30W/AYK
measurement is shown in FIG. 9. It can be seen that a stable state was
obtained at up to 1.39 m/d, but at 1.74 m/d the pressure increase was too
rapid and hence a stable state was not obtained. The measured value
of the maximum stable flux value from more detailed experiments was 1.4
m/d, and hence it was possible to obtain a result that matched the
estimated value well within the range of measurement error.
Reference Example 1
26
It was attempted to estimate the maximum value of the flux in a
stable state using the SDI (silt density index) measurement method.
Using a precise filtration filter of pore size 0.45 |j,m (made by Millipore,
trade name HAWP 47 mm §) as a filter, the liquids to be treated in the
membrane filtration plants (A), (B) and (C) in working example 1 were
each subjected to filtration. As the filtration conditions, the filtration
pressure was made to be fixed at 210 kPa, and the filtration flow rate
measurement time interval was made to be 15 minutes. First, the time
required to filter 500 ml of the liquid to be treated at the start of the
filtration was measured. This was taken as to. Next, the filtration was
continued, and after the measurement time interval of 15 minutes had
elapsed from the start of the filtration, the time required to filter 500 ml of
the liquid to be treated was again measured. This was taken as t15.
The SDI was calculated from these measured values and the following
formula:

The SDI in the case of using the liquid to be treated in the


A0501 UP30W/AYK
membrane filtration plant (A) was 0. Moreover, the SDI in the case of
using the liquid to be treated in the membrane filtration plant (B) was 3.8.
Furthermore, the SDI in the case of using the liquid to be treated in the
membrane filtration plant (C) was 6.5. Even though the maximum stable
flux values were close to one another for the membrane filtration plant
(B) and the membrane filtration plant (C), the result was that the SDIs
differed greatly. Moreover, using the liquid to be treated in the new
membrane filtration plant of working example 1, the SDI was similarly
measured, but membrane-permeated liquid could not be obtained
because the turbidity was high. That is, the filtration flow rate was zero,
and hence measurement was impossible.
According to the present invention, when designing a new
membrane filtration plant, the maximum value of the flux during long-term
stable operation including short-term cleaning of a membrane filtration
plant can be easily estimated, without carrying out long-term test
operation, from measured data of a membrane filtration characteristic
during initial membrane filtration, which can be determined in a short
time.
27

A0501 UP30W/AYK
CLAIMS
We claim:
1. A method of estimating a maximum flux during stable
operation of a membrane filtration plant for which a membrane module
and operating conditions have been specified, the estimating method
comprising:
a step of obtaining a measured value A of an initial membrane
filtration characteristic for said membrane filtration plant using a liquid to
be treated in and a membrane of a membrane module of said membrane
filtration plant;
a step of obtaining a maximum flux value during stable operation
of each of a plurality of existing membrane filtration plants having a
membrane module and operating conditions the same as or similar to
said membrane module and operating conditions;
a step of obtaining a measured value B of the initial membrane
filtration characteristic for each of said existing membrane filtration
plants using a liquid to be treated in and a membrane of a membrane
module of that one of said existing membrane filtration plants; and
an estimating step of estimating a maximum flux for said
membrane filtration plant from said measured value A based on a
relationship between the maximum flux values and the measured values
B for said existing membrane filtration plants.
2. The estimating method according to claim 1, characterized
in that said estimating step is a step of showing by a formula or on a
graph a relationship between the logarithm of the measured values B of
said initial membrane filtration characteristic and the maximum flux
28

A0501 UP30W/AYK
values, and estimating the maximum flux for said membrane filtration
plant by extrapolating or interpolating for said measured value A using
the formula or graph.
3. The estimating method according to claim 1 or 2,
characterized in that said operating conditions comprise at least filtration
time or membrane cleaning pattern conditions.
4. The estimating method according to any of claims 1 to 3,
characterized in that said initial membrane filtration characteristic is
selected from the group consisting of a constant pressure simple
filtration resistance, a quantitative simple filtration resistance, a
cleaning-included constant pressure filtration resistance, and a
cleaning-included quantitative filtration resistance.

It is an object of the present invention to provide a method of
estimating the maximum value of the flux during long-term stable
operation including cleaning of a membrane filtration plant based on
measured data of a membrane filtration characteristic during initial
membrane filtration. The present invention provides a method in which
the maximum flux during stable operation of a new membrane filtration
plant for which a membrane module and operating conditions have been
specified is estimated from a measured value A of an initial membrane
filtration characteristic measured using a liquid to be treated in and a
membrane of a membrane module of the new membrane filtration plant,
an empirical value of a maximum flux during stable operation of each of a
plurality of existing membrane filtration plants having the same or a
similar membrane module and operating conditions, and a measured
value B of the initial membrane filtration characteristic measured using a
liquid to be treated in and a membrane of a membrane module of each of
the existing membrane filtration plants.

Documents:

01834-kolnp-2007-abstract.pdf

01834-kolnp-2007-claims.pdf

01834-kolnp-2007-correspondence others 1.1.pdf

01834-kolnp-2007-correspondence others.pdf

01834-kolnp-2007-description complete.pdf

01834-kolnp-2007-drawings.pdf

01834-kolnp-2007-form 1.pdf

01834-kolnp-2007-form 18.pdf

01834-kolnp-2007-form 2.pdf

01834-kolnp-2007-form 3.pdf

01834-kolnp-2007-form 5.pdf

01834-kolnp-2007-international publication.pdf

01834-kolnp-2007-international search report.pdf

01834-kolnp-2007-pct request form.pdf

01834-kolnp-2007-priority document.pdf

1834-KOLNP-2007-ABSTRACT.pdf

1834-KOLNP-2007-AMANDED CLAIMS.pdf

1834-KOLNP-2007-CORRESPONDENCE OTHERS 1.2.pdf

1834-KOLNP-2007-CORRESPONDENCE.pdf

1834-KOLNP-2007-DESCRIPTION (COMPLETE).pdf

1834-KOLNP-2007-DRAWINGS.pdf

1834-KOLNP-2007-EXAMINATION REPORT.pdf

1834-KOLNP-2007-FORM 1.pdf

1834-KOLNP-2007-FORM 18.pdf

1834-KOLNP-2007-FORM 2.pdf

1834-KOLNP-2007-FORM 3-1.1.pdf

1834-KOLNP-2007-FORM 3.pdf

1834-KOLNP-2007-FORM 5-1.1.pdf

1834-KOLNP-2007-FORM 5.pdf

1834-KOLNP-2007-FORM-27.pdf

1834-KOLNP-2007-GPA.pdf

1834-KOLNP-2007-GRANTED-ABSTRACT.pdf

1834-KOLNP-2007-GRANTED-CLAIMS.pdf

1834-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

1834-KOLNP-2007-GRANTED-DRAWINGS.pdf

1834-KOLNP-2007-GRANTED-FORM 1.pdf

1834-KOLNP-2007-GRANTED-FORM 2.pdf

1834-KOLNP-2007-GRANTED-LETTER PATENT.pdf

1834-KOLNP-2007-GRANTED-SPECIFICATION.pdf

1834-KOLNP-2007-INTERNATIONAL SEARCH REPORT.pdf

1834-KOLNP-2007-OTHERS-1.1.pdf

1834-KOLNP-2007-OTHERS.pdf

1834-KOLNP-2007-OTHERS1.2.pdf

1834-KOLNP-2007-PA.pdf

1834-KOLNP-2007-PETITION UNDER RULE 137.pdf

1834-KOLNP-2007-REPLY TO EXAMINATION REPORT-1.1.pdf

1834-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

abstract-01834-kolnp-2007.jpg


Patent Number 247785
Indian Patent Application Number 1834/KOLNP/2007
PG Journal Number 20/2011
Publication Date 20-May-2011
Grant Date 18-May-2011
Date of Filing 23-May-2007
Name of Patentee ASAHI KASEI CHEMICALS CORPORATION
Applicant Address 1-2, YURAKU-CHO 1-CHOME, CHIYODA-KU, TOKYO
Inventors:
# Inventor's Name Inventor's Address
1 TAKASHI OGAWA 1-2, YURAKU-CHO 1-CHOME, CHIYODA-KU, TOKYO 100-8440
2 YOSHIHIKO MORI 1-2, YURAKU-CHO 1-CHOME, CHIYODA-KU, TOKYO 100-8440
PCT International Classification Number B01D 65/00
PCT International Application Number PCT/JP2005/022016
PCT International Filing date 2005-11-30
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2004-350897 2004-12-03 Japan