.* CA 02769064 2012-02-24
/1
Description
Method of recovering oil from extra heavy oil layer
Technical Field
[0001]
The present invention relates to a method of recovering
extra heavy oil from Canadian oil sands or a Venezuelan extra
heavy oil layer (hereinafter, referred to as "extra heavy oil
layer") by employing a steam assisted gravity drainage (SAGD)
method.
Background Arts
[0002]
In recovering extra heavy oil from an extra heavy oil layer,
an SAGD method including injecting steam into the extra heavy
oil layer to recover the extra heavy oil as a mixture of oil
and water has been put into practical use in Canada. More
specifically, the following recovery process is conducted.
[0003]
The extra heavy oil contained in the extra heavy oil layer
is present as high-viscosity oil which does not flow at normal
temperature. Therefore, high-temperature steam is injected
under pressure for heating so as to reduce the viscosity of the
oil. In this manner, a mixture of high-temperature water, which
is formed by condensation of the steam, and oil is recovered.
The mixture is separated into the oil and the high-temperature
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water in a facility located on the ground.
[0004]
The oil obtained by the separation is shipped as a product,
whereas the high-temperature water is heated again in a boiler
and converted to steam to be reused in the SAGD method. At this
time, the high-temperature water contains silica, a hardness
component such as a calcium salt and a magnesium salt, metal
ions, and a water-soluble organic substance mainly containing
a humic substance, which are eluted from the extra heavy oil
layer, and the like. Therefore, when the high-temperature water
is to be reused in the SAGD method, those substances are required
to be removed.
[0005]
Patent Document 1 discloses a method of treating an organic
substance, including adsorbing the organic substance to an
adsorbent and desorbing the organic substance from the adsorbent
by electrolysis. Activated carbon and zeolite are described
as examples of the adsorbent (Examples 1 and 2, paragraphs 0082
and 0083) .
Patent Document 2 discloses an invention in which bitumen
is extracted from a bitumen-mixed fluid recovered from the ground
and heated oil-containing water separated from the mixed fluid
is treated with a microfiltration membrane (MF membrane) made
of polytetrafluoroethylene when bitumen is produced from oil
sands. In paragraph 0028, it is described that a UF membrane,
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5702-562 CA 02769064 2012-02-24
an RO membrane, and an NF membrane are not preferred.
Patent Documents 3 and 4 each disclose a method of treating
heated oil-containing water, similar to that disclosed in Patent
Document 2. FIG. 1 illustrates a flow diagram including
subjecting high-temperature water with an anionic flocculant
or a cationic flocculant treatment to form coagulation solid
under an acidic conditionandcooling the acidic high-temperature
water to a temperature close to normal temperature, followed
by a membrane treatment in which a UFmembrane 1034, an NFmembrane
1036, and an RO membrane 1118 are connected in series.
[0006]
The above cited Patent Document 1 is JP-A2008-279435, Patent
Document 2 is JP-A 2010-248431, Patent Document 3 is CA 2673981
Al and Patent Document 4 is CA 2673982 Al.
Summary of the Invention
[0007]
The present invention relates to a method of recovering
oil from an extra heavy oil layer, including a process for
separating and recovering oil and high-temperature water from
a mixture of the oil and the high-temperature water, which is
obtained by injecting high-temperature steam into the extra
heavy oil layer, and the reusing the high-temperature water
to generate the high-temperature steam, the process including
subjecting the high-temperature water to a softening
treatment and a coarse filtration treatment, followed by
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65702-562 CA 02769064 2012-02-24
ultrafiltration using an ultrafiltration membrane equipment,
thereby removing a hardness component, a suspended substance,
and a water-soluble organic substance dissolved in the
high-temperature water at such a high removal rate that enables
the reuse of the high-temperature water.
[0008]
The present invention relates to a method of recovering
oil from an extra heavy oil layer, including separating and
recovering oil and high-temperature water from a mixture of
the oil and the high-temperature water, which is obtained by
injecting high-temperature steam into the extra heavy oil
layer, and then reusing the high-temperature water to
generate the high-temperature steam,
the method including the step of subjecting raw water, which
is obtained by cooling the high-temperature water to a
temperature of 60 to 90 C, to ultrafiltration by feeding the
raw water to an ultrafiltration membrane equipment, thereby
providing permeated water with a reduced content of a
water-soluble organic substance,
in which:
the permeated water is reused to generate the
high-temperature steam; and
the ultrafiltration membrane equipment used in the
ultrafiltration step includes an ultrafiltration membrane
module filled with a hollow fiber membrane or hollow fiber
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55702-562 CA 02769064 2012-02-24
membranes which are made of a heat-resistant resin and have a
molecular weight cut-off of 8,000 to 30,000.
[0009]
The present invention relates to a method of recovering
oil from an extra heavy oil layer, including separating and
recovering oil and high-temperature water from a mixture of
the oil and the high-temperature water, which is obtained by
injecting high-temperature steam into the extra heavy oil
layer, and then reusing the high-temperature water to
generate the high-temperature steam,
the method including the steps of:
charging the high-temperature water separated from the
mixture of the oil and the high-temperature water into a raw-water
tank;subj ecting the high-temperature water in the raw-water tank
to a softening treatment by delivering the high-temperature water
to a softener;
subjecting the alkaline high-temperature water obtained
by the softening treatment in the previous step to a coarse
filtration treatment;
subjecting raw water, which is obtained by cooling the
high-temperature water to a temperature of 60 to 90 C, to
ultrafiltration process, thereby providing ultrafiltration
permeated water with a reduced content of a water-soluble organic
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substance; and
subjecting the permeated water from which the water-soluble
organic substance is removed in the previous step to an ion
exchange treatment,
in which:
the permeated water obtained by the ion exchange treatment
is reused to generate the high-temperature steam; and
the ultrafiltration membrane equipment used in the
ultrafiltration step includes an ultrafiltration membrane
module filled with a hollow fiber membrane or hollow fiber
membranes which are made of a heat-resistant resin and have a
molecular weight cut-off of 8,000 to 30,000.
[0010]
In other words, the invention relates to a method of
recovering oil from an extra heavy oil layer, including
injecting high temperature steam into the extra heavy oil layer
and separating and recovering oil and high-temperature water
from a mixture of the oil and the high-temperature water, further
including cooling the high-temperature water to a temperature
of 60 to 90 C to obtain raw water, subjecting the raw water to
ultrafiltration by feeding the raw water to an ultrafiltration
membrane device, thereby providing permeatedwater with a reduced
content of a water-soluble organic substance (s) , heating the
permeated water to generate the high-temperature steam to reuse
the high-temperature water to generate the high-temperature
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steam, in which the ultrafiltration membrane equipment includes
an ultrafiltration membrane module filled with a hollow fiber
membrane or hollow fiber membranes which are made of a
heat-resistant resin and has a molecular weight cut-off of 8,000
to 30,000.
According to the method of recovering oil from an extra
heavy oil layer of the present invention, the ultrafiltration
membrane equipment is provided in the recovery step. Therefore,
the following effects can be obtained.
(I) By the operation of the ultrafiltration membrane
equipment, the permeated water with a lowered concentration of
a humic substance can be fed to a boiler. Therefore, the
frequency, and cost of maintenance for maintaining a normal
operation of the boiler are reduced.
(II) The operating time of the boiler can be increased
because the frequency and cost of maintenance for maintaining
the normal operation of the boiler are reduced. Therefore, an
operating rate of the boiler can be increased.
(III) Concentrated water and back-pressure washing waste
water generated by the operation of the ultrafiltration membrane
equipment are recycled. Therefore, a recovery rate of water
used for recovering the oil from the extra heavy oil layer is
improved. Moreover, a supply water amount of river water or
well water can be saved.
(IV) Auxiliary equipments for treatments, which are
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CA 02769064 2012-02-24
provided downstream of the ultrafiltration membrane equipment,
are fed with the permeated water with the concentration of the
humic substance lowered by the operation of the ultrafiltration
membrane equipment. Therefore, a load on the auxiliary
equipment is reduced to further enhance treatment capability.
(V) When the amount of an impurity is further reduced by
providing an NF-membrane equipment or an RO-membrane equipment
downstream of the ultrafiltration membrane equipment device,
a stable membrane treatment operation can be performed because
the concentration of the humic substance which causes fouling
in the membrane treatments is reduced.
The method of recovering oil from an extra heavy oil layer
of the resent invention can be used as a method including injecting
steam into the extra heavy oil layer to recover extra heavy oil
as a mixture of oil and water when the extra heavy oil is recovered
from the extra heavy oil layer.
Brief Description of the Drawings
[0011]
FIG. 1 is a flow diagram for conducting a method of recovering
oil from an extra heavy oil layer of the present invention.
FIG. 2 is a flow diagram of another embodiment for conducting
the method of recovering oil from an extra heavy oil layer of
the present invention.
FIG. 3 is a flow diagram of still another embodiment for
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conducting the method of recovering oil from an extra heavy oil
layer of the present invention.
FIG. 4 is a schematic view of an ultrafiltration membrane
equipment in each of the flows illustrated in FIGS. 1 to 3.
FIG. 5 is a diagram illustrating an ultrafiltration method
of Example.
FIG. 6 is a graph showing changes with in permeated water
amount (flux) when filtration is performed using hollow fiber
membranes having molecular weight cut-offs of 10,000 and 30,000
in Example.
FIG. 7 is a graph showing change with time in water flux
when filtration is performed using a hollow fiber membrane having
a molecular weight cut-off of 150,000 in Comparative Example.
FIG. 8 is a graph showing changes with time in removal rate
of a humic substance when filtration is performed using hollow
fibermembranes havingmolecular weight cut-offs of 5,000,10,000,
30,000, and 150,000 in Example and Comparative Example.
In the drawings, reference Numerals are:
1 boiler
2 steam separator
3 wellhead separator
4 separator
oil tank
6 separator
7 raw-water tank
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8 softener
9 after filter
ultrafiltration equipment
11 ultrafiltration membrane module
12 permeated-water tank
13 ion exchange equipment
14 tank for boiler feed water
21 crystallizer
Detailed description of embodiments of the invention
[0012]
A method of recovering oil from an extra heavy oil layer
is described referring to FIG. 1. Note that, in FIG. 1, a process
flow except for an ultrafiltration membrane equipment 10 and
lines provided therewith is the same as a process flow executed
in a known SAGD method.
Steam is supplied from a boiler 1 through a line la to a
steam separator 2.
The steam separator 2 can recover part of the steam as
condensed water.
High-temperature steam separated by the steam separator
2 is injected under pressure from a line 2a into an extra heavy
oil layer.
[0013]
Extra heavy oil contained in the extra heavy oil layer is
reduced inviscositybythe high-temperature steaminjectedunder
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pressure to give a mixture of high-temperature water, which is
obtained by condensation of the steam, and oil.
The mixture of high-temperature water and oil is recovered
from a line 3a to be delivered to a wellhead separator 3 where
a gas component is separated.
The mixture of high-temperature water and oil, from which
the gas components are separated away, is delivered through a
line 3b to a separator 4 where the mixture is separated into
the high-temperature water and the oil.
The oil obtained by the separation in the separator 4 is
delivered through a line 4a to an oil tank 5 so as to be recovered
as oil from a line 5a.
[0014]
The high-temperature water obtained by the separation in
the separator 4 still contains oil therein and therefore is
delivered through a line 4b to a separator 6 (for separating
oil) to separate residual oil.
The high-temperature water after the oil is separated by
the separator 6 (for separating oil) is delivered through a line
6a to a raw-water tank 7. Raw water in the raw-water tank 7
has a pH of about 6 to 7.
[0015]
The raw water at a high temperature (about 90 to 100 C)
in the raw-water tank 7 is delivered through a raw-water line
7a to a softener 8. In the softener 8, a softening treatment
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corresponding to a step of removing a hardness component such
as calcium and magnesium, silica, and the like is conducted.
Although the raw water is cooled even in a process for the
softening treatment by the softener 8, river water or well water
can be fed from a line 7b for further cooling as needed.
As a method for the softening treatment, a precipitation
method with a coagulant, an adsorption method with an adsorbent,
or the like can be employed.
When the precipitation method with a coagulant is employed,
a method including adding, for example, calcium hydroxide (lime)
and magnesium oxide can be employed.
[0016]
The raw water subjected to the softening treatment in the
softener 8 is delivered through a line 8a to an after filter
9 where a coarse filtration treatment is performed.
The after filter 9 can remove larger impurities such as
suspended solids by filtration.
[0017]
The raw water subjected to the coarse filtration by the
after filter 9 is delivered through a line 9a to the
ultrafiltration equipment 10 where a filtration treatment is
performed.
When a temperature of the raw water fed to the
ultrafiltration membrane equipment 10 is too high, an
ultrafiltration membrane module is deteriorated, resulting in
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the need of early replacement of the module. Therefore, it is
preferred that the temperature of the raw water be cooled to
be in the range of 60 to 90 C.
The adjustment of the temperature of the raw water is
sometimes performed by natural cooling when the raw water passes
through each of the lines in the course through the softener
8 and the after filter 9 described above to the ultrafiltration
membrane equipment 10. Besides, an air-cooling zone including
air-cooling means or a water-cooling zone including
water-circulating type water-cooling means can be provided in
each of the lines (for example, the lines 6a and 7a) to the
ultrafiltration membrane equipment 10.
[0018]
Any ultrafiltration membrane equipment may be used as the
ultrafiltration membrane equipment 10 as long as the
ultrafiltration membrane equipment includes an ultrafiltration
membrane module 11, a permeated-water tank 12 for storing the
permeatedwater after the ultrafiltration therein, and a pressure
pump. The one as illustrated in FIG. 2 can be used.
Although the ultrafiltration membrane equipment 10
including the ultrafiltration membrane module 11, the
permeated-water tank 12, and the pressure pump which are combined
into one equipment is preferred, an ultrafiltration membrane
equipment including the components provided separately may also
be used.
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[0019]
A pressure pump 10A is provided between the line 9a and
the ultrafiltration membrane module 11 illustrated in FIG. 1.
The raw water whose pressure is boosted to a predetermined
pressure by the pressure pump 10A is fed to the ultrafiltration
membrane module 11 where an ultrafiltration treatment is
performed.
Permeated water obtained by the filtration treatment in
the ultrafiltration membrane module 11 is delivered through
permeated-water lines ha and llf (Fig4) which are opened by
operating three-way valves 10a and 10b to a permeated-water tank
12 so as to be stored therein.
Concentrated water generated during the filtration
treatment conducted in the ultrafiltration membrane module 11
is delivered through the line llb (Figl) to the raw-water tank
7 or the line 6a (or the line 7a) before or after the raw-water
tank 7 where a circulation process is performed. By the
circulation process, a recovery rate of water is increased to
save a supply water amount of the river water or well water.
[0020]
During a filtration operation of the ultrafiltration
membrane module 11, back-pressure washing is conducted so as
to maintain filtration performance.
The back-pressure washing is performed by actuating a
back-pressure washing pump 10B to feed the permeated water in
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the permeated-water tank 12 through a back-pressure washing line
12b and the permeated-water line ha which is opened by operating
the three-way valve 10b (the permeated-water line lib is closed)
to the ultrafiltration membrane module 11. (Fig4)
Intervals of conducing the back-pressure washing can be
appropriately set in accordance with the degree of decrease of
a permeated-water amount. For example, by the back-washing for
about 30 to 90minutes for each interval, a stable permeated-water
amount can be kept. A time period for one back-pressure washing
is, for example, 0.5 to 2 minutes.
It is preferred to perform the back-pressure washing under
a pressure of 0.1 to 0.2 MPa.
Washing waste water after the back-pressure washing is
partially delivered, by operating a three-way valve 10c, through
a line lid to the raw-water tank 7 or the line 6a or 7a before
or after the raw-water tank 7 so as to be subjected to the
circulation process. At this time, the washing waste water can
also be delivered to the raw-water tank 7 or the line 6a or 7a
before or after the raw-water tank 7 so as to be subjected to
the circulation process after being subjected to a coagulation
sedimentation treatment by adding a coagulant or an adsorption
treatment using an adsorbent (such as activated carbon or
anthracite) . By conducting the treatments under an acidic
condition with a pH of 4 to 6, the efficiency of removal of a
humic substance contained in the washing waste water can be
CA 02769064 2012-02-24
enhanced. By the circulation process, the water recovery rate
can be increased to save the water intake amount.
The remaining washing waste water is drained from a line
lie by operating the three-way valve 10c. Tn he drained washing
waste water can also be used in the water-circulating type
water-cooling zone.
[0021]
A structure itself of the ultrafiltration membrane module
11 is well known and is such that a case housing including a
raw-water inlet, a permeated-water outlet, and a
concentrated-water outlet is filled with the ultrafiltration
membrane.
A hollow fiber membrane made of a heat-resistant resin is
preferred as the ultrafiltration membrane because a temperature
of the raw water to be treated is high. As the hollow fiber
membrane, any of an internal-pressure type one and an
external-pressure type one may be used. In view of washing
performance of the back-pressure washing, the internal-pressure
type one is preferred. In the case of the internal-pressure
type hollow fiber membrane, an inner diameter of 0.5 to 1.2 mm
and an outer diameter of 0.8 to 2.0 mm are preferred, and an
inner diameter of 0.8 to 1.0 mm and an outer diameter of 1.3
to 1.6 mm are more preferred. When the inner diameter is 0.5
mm or more, a permeation flow rate is prevented from being lowered
owing to clogging of the hollow fiber membrane. On the other
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hand, when the inner diameter is 1.2 mm or less, an effective
membrane area per module can be increased to save the cost.
[0022]
Further, a main component of the water-soluble organic
substance (s) contained in the raw water is the humic substance.
Therefore, in order to efficiently separate the humic substance
and the raw water, the hollow fiber membrane having a molecular
weight cut-off of 8,000 to 30,000 is preferred.
When the molecular weight cut-off exceeds 30,000, the
removal of the humic substance becomes insufficient, resulting
in a risk of difficulty of the reuse of water. On the other
hand, when the molecular weight cut-off is less than 8,000, the
amount of permeated water through the membrane becomes smaller
even though the removal of the humic substance is sufficient.
As a result, the size of the ultrafiltration membrane equipment
becomes large by increasing a membrane area or increasing a
operation pressure of the pump. As a result, there is a risk
in that the equipment becomes economically inadequate.
The molecular weight cut-off is determined from a permeation
rate and a rejection rate for solutes when a membrane filtration
test is conducted using a dilute solution containing
polyethyleneglycol and a trypsin inhibitor having predetermined
molecular weights as the solutes. In the case of the present
invention, a UF membrane having a molecular weight cut-off with
a permeation rate of 20% or more for polyethyleneglycol
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(molecular weight cut-off of 12,000) and a rejection rate of
90% or more for the trypsin inhibitor (molecular weight cut-off
of 28,000) is preferred.
As the hollow fiber membrane made of a heat-resistant resin,
a polysulfone, a polyethersulfone, a polyvinylidene fluoride,
a polytetrafluoroethylene and the like are preferred. Of those,
polyethersulfone which allows low molecular weight cut-off
ultrafiltration and has heat resistance is more preferred.
As the ultrafiltration membrane module 11, for example,
an FE10 module and an FW50 module manufactured by Daicen
Membrane-Systems Ltd. can be used.
As the hollow fiber membrane made of the polyethersulfone
membrane, for example, FUS0181, FUSO1C1, and FUS0382
manufactured by Daicen Membrane-Systems Ltd. can be used.
[0023]
Operating conditions of the ultrafiltration module 11 can
be set as described below.
An operation pressure is 0.02 to 0.08 MPa, preferably 0.03
to 0.06 MPa in terms of a transmembrane pressure obtained by
subtracting a permeation pressure from an average value of an
inlet pressure and an outlet pressure of themodule . Across-flow
velocity is preferably 0.1 to 0.6 m/s, more preferably 0.1 to
0.3 m/s.
It is preferred to perform the filtration operation at a
permeation flow rate of about 1.0 to 1.5 m/day. Further, a
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recovery rate of the permeated liquid is preferably 80 to 95%.
[0024]
It is preferred that 70% or more of an organic substance
(humic substance) be removed from the permeated water obtained
by the ultrafiltration treatment in the ultrafiltration membrane
module 11 as compared with the raw water before being subjected
to the filtration treatment. It is more preferred that 80% or
more thereof be removed, and it is even more preferred that 85%
or more thereof be removed.
[0025]
In the permeated water subjected to the ultrafiltration
treatment of the present invention a humic acid is removed.
Therefore, even when the NF-membrane equipment or the RO-membrane
equipment are provided downstream of the ultrafiltration
treatment so as to perform the membrane treatment, a
concentration of the humic substance which causes fouling of
the NF membrane or the RO membrane is kept low. Accordingly,
the stable membrane treatment operation can be performed. Thus,
the acquisition of treatedwater substantially free of impurities
is expected.
[0026]
The permeated water in the permeated-water tank 12 is
delivered through a line 12a to an ion exchange equipment 13
where an ion exchange treatment is performed, and is then
delivered through a line 13a to a tank for boiler feed water
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14, to be stored therein.
The ion exchange equipment 13 includes an ion exchange
membrane, an ion exchange resin, or a combination thereof as
an ion exchanger. In the ion exchange equipment 13, the permeated
water subjected to the filtration treatment by the
ultrafiltration membrane equipment10 is treated as water to be
treated. Therefore, a load on the ion exchange equipment 13
is reduced. Accordingly, a time period in which the ion exchanger
is available can be further increased (the frequency of
replacement of the ion exchanger can be reduced) .
[0027]
Thereafter, the permeated water in the tank for boiler feed
water 14 is delivered through a line 14a to the boiler 1 to become
high-temperature steam, which is then delivered through the line
la to the steam separator 2.
In the boiler 1, the permeated water with the concentration
of the humic substance sufficiently lowered by the
ultrafiltration membrane equipment 10 is used. Therefore, a
problem of precipitation of the humic substance in the boiler
1 is remarkably improved. Therefore, an interval between works
for stopping the operation of the boiler 1 to remove coke inside
a heating tube can be further increased. As a result, a workload
therefor is reduced, while the operating time period of the boiler
1 can be further increased. Therefore, an operating rate can
also be enhanced.
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[0028]
Note that, in the case where part of the steam is recovered
as condensed water (condensed water mainly containing sodium
chloride) in the steam separator 2, the condensed water is
delivered through a line 2b to a crystallizer 21 to remove the
impurity (sodium chloride) and the like by crystallization.
When the amount of the humic substance remaining in the
condensed water is large in this process, the humic substance
disturbs crystal precipitation of sodium chloride and the like
to lower the efficiency of removal of the impurity by the
crystallization. In the present invention, however, the humic
substance is removed in the ultrafiltration membrane equipment
10. Therefore, the efficiency of crystallization in the
crystallizer 21 is improved to enhance a removal rate of the
impurity (sodium chloride) as well.
The removed impurity is drained from a line 21a. Water
after the removal of the impurity is delivered through a line
21b to the line 7a so as to be subjected to the circulation process .
By the circulation process, the water recovery rate can be
enhanced to save the water intake amount.
[0029]
Next, another embodiment of a process flow illustrated in
FIG. 1 is described referring to FIG. 2.
In the process flow illustrated in FIG. 2, when part of
the steam is recovered as the condensed water (condensed water
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mainly containing sodium chloride) in the steam separator 2,
the condensed water is delivered through the line 2b to an
ultrafiltration membrane module 11' where the ultrafiltration
treatment is performed.
A filtrate obtained in the ultrafiltration membrane module
11' is delivered through a line 2d to the crystallizer 21 where
the impurity (sodium chloride) and the like are removed by the
crystallization.
A concentrated liquid generated in the ultrafiltration
membrane module 11' is returned to the line 6a to be then delivered
to the raw-water tank 7 or is directly returned to the raw-water
tank 7.
The impurity removed by the crystallizer 21 is drained from
the line 21a. Water after the removal of the impurity is
delivered from the line 21b to the line 7a so as to be subjected
to the circulation process.
By providing the ultrafiltration membrane module 11', a
load on the crystallizer 21 can be reduced to enhance the effect
of saving the water intake amount.
[0030]
Next, still another embodiment of the process flow
illustrated in FIG. 1 is described referring to FIG. 3. In the
process flow illustrated in FIG. 3, when part of the steam is
recovered as the condensed water (condensed water mainly
containing sodium chloride) in the steam separator 2, the
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condensed water is delivered through the line 2b to a multieffect
evaporator 22, the ultrafiltration membrane module 11 ' , and the
crystallizer 21 in the stated order so as to be treated.
A treated liquid in the multieffect evaporator 22 is
delivered through the line 2d to the ultrafiltration membrane
module 11 ' . An distillate liquid from the top is delivered
through a line 2e to the line 7a.
The treated liquid (filtrate) in the ultrafiltration
membrane module 11' is delivered through a line 2g to the
crystallizer 21. A concentrated liquid is returned through a
line 2f to the line 6a to be then delivered to the raw-water
tank 7 or is directly returned to the raw-water tank 7.
The impurity removed by the crystallizer 21 is drained from
the line 21a. Water after the removal of the impurity is
delivered through the line 21b to the line 7a so as to be subjected
to the circulation process.
By providing the multieffect evaporator 22 and the
ultrafiltrationmembranemodule 11' , the load on the crystallizer
21 can be reduced to enhance the effect of saving the water intake
amount.
Examples
[0031]
Example and Comparative Example
An evaluation was made for each sample obtained in the flow
illustrated in FIG. 1 when ultrafiltration was conducted.
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[0032]
<Raw-water sample>
For raw water for the UFmembrane treatment, a treated liquid
obtained by subjecting the high-temperature water from the
raw-water tank 7 to the softening treatment in the softener 8
and then subjecting the resultant to the coarse filtration
treatment with the after filter 9 was used as the raw water.
[0033]
<Ultrafiltration membrane equipment>
An experimental filtration equipment illustrated in FIG.
was used.
A hollow fiber membrane 102 was provided between a container
101 corresponding to the raw-water tank (containing a raw-water
sample) and a container 104 corresponding to a concentrated-water
tank. Membrane-permeated water was obtained by an
internal-pressure filtration method.
A container 103 corresponding to a permeated-water tank
was provided just below the hollow fiber membrane 102 so as to
be able to store the permeated water treated by the hollow fiber
membrane (UF membrane) 102.
[0034]
<Types of membrane>
As the hollow fiber membranes made of polyethersulfone (PES)
and having molecular weight cut-offs of 10,000, 30,000, and
150,000, FUS0181, FUS0381, and FUS1581 manufactured by Daicen
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Membrane Systems Ltd. were used, respectively.
In a permeation test illustrated in FIG. 5, one hollow fiber
membrane having a length of 1 m was used. The UF membranes used
each had an inner diameter of 0.8 mm and an outer diameter of
1.3 mm.
As the membrane having a molecular weight cut-off of 5,000,
a flat membrane made of PES (Microdyn UP005 manufactured by
Microdyn-Nadir GmbH) was used and provided in accordance with
the equipment illustrated in FIG. 4.
[0035]
<Operating conditions>
(Hollow fiber membrane)
Pressure at membrane inlet 102a: 0.050 MPa
Pressure at membrane outlet 102b: 0.035 MPa
Recovery rate (permeated-water amount/raw-water amount) :
30 to 50%
Temperature of raw-water sample: 25 C or 65C
Filtration method: internal-pressure cross-flow
filtration
(Flat membrane)
Pressure at membrane inlet: 1 MPa
Filtration method: dead-end filtration
Raw-water circulating amount: 1.2 L/min
Temperature of raw-water sample: 25 C
[0036]
25
CA 02769064 2012-02-24
The results with the OF membranes with the respective
molecular weight cut-offs are shown in FIGS. 6 and 7.
With the OF membranes with molecular weight cut-offs of
10,000, 30,000, and 150,000, a flux of 1.2 to 1.5 m3/m2.day was
obtained even under a low pressure of 0.05 MPa. On the other
hand, as shown in FIG. 6, when the flat membrane having a molecular
weight cut-off of 5,000 was used, the membrane permeation became
unavailable immediately after the start owing to fouling of the
surface of the membrane. Even after the operation for 3 hours,
the permeated liquid was not, successfully obtained. The reason
is believed that the humic substance clogged the surface of the
membrane.
[0037]
Next, when the organic substance to be removed was the humic
substance in the membrane permeation experiment shown in FIGS.
6 and 7, a removal rate of the humic substance was defined by
the following equation because a concentration thereof can be
represented by an absorbance at the wavelength of 465 nm due
to an aromatic ring of the humic substance ("Effect of the
fractionation and immobilization on the sorption properties of
humic acid", Soil Biology and Biochemistry volume 21, issu 2,
1989, Pages 223-230) . The results are shown in Table 1 and FIG.
8.
Removal rate of humic substance: R= (absorbance of permeated
water at 465 nm/absorbance of raw water at 465 nm) x100
26
* CA 02769064 2012-02-24
[0 0 3 8]
[Table 1]
Removal rate (%) of humic substance
Example 1 PES membrane (molecular weight cut-off of 10,000) 90
- 95
Example 2 PES membrane (molecular weight cut-off of 30,000)
80
Example 3 PES membrane (molecular weight cut-off of 150,000)
67
Example 4 PES membrane (molecular weight cut-off of 5,000)Unmeasurable
because of unavailability
of permeated liquid
[0039]
As clear from Table 1 and FIG. 8, it was confirmed that
about 80% of the humic substance was able to be removed by using
the UF membrane having a molecular weight cut-off of 30,000 and
90% or more of the humic substance was able to be removed by
using the UFmembrane having a molecular weight cut-off of 10,000.
Moreover, as understood from FIG. 8, with the UF membrane having
a molecular weight cut-off of 10,000, the result that the removal
rate of the humic substance at as high a temperature as 65 C
was slightly larger than that at 25 C was obtained.
On the other hand, with the UF membrane having a molecular
weight cut-off of 150,000, the removal rate of the humic substance
was only 70% or less . Therefore, the removal rate is insufficient.
With the UF membrane having a molecular weight cut-off of 5,000,
the membrane was clogged immediately after the start of the
filtration experiment as shown in FIG. 6. Therefore, the
permeation experiment was not successfully conducted.
27
