Note: Descriptions are shown in the official language in which they were submitted.
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WATER TREATMENT SYSTEM
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a water treatment system which purifies
wastewater by coagulation and magnetic separation, in which a flocculant and a
magnetic
powder are added to wastewater.
Description of the Related Art
As techniques for purifying wastewater, there is a coagulation and magnetic
separation method, in which a flocculant and a magnetic powder are introduced
into
wastewater to produce magnetic flocs, and the magnetic flocs are collected by
a magnetic
force to thereby obtain purified water. In this method, a sludge containing
the magnetic
powder is produced, and the sludge produced must be disposed of as industrial
waste.
The sludge disposal costs lead to an increase in running costs. If the amount
of the
sludge can be reduced, it is possible to reduce the running costs and the
amount of sludge
produced.
As a technique for solving the above problem, a technique is proposed in which
a sludge containing a magnetic powder is decomposed by a hydrothermal reaction
so that
the sludge is reduced in volume, as disclosed in Japanese Patent Application
Laid-Open
Nos. 11-123399 and 11-207399.
SUMMARY OF THE INVENTION
In the inventions disclosed above, wastewater is purified by coagulation and
magnetic separation, a sludge produced in the purification process is
hydrothermally
treated under high temperature and high pressure conditions, and the magnetic
powder is
collected by magnetic separation in the high temperature-high pressure line.
Therefore,
a magnetic separation device used in the process must have a structure with
strong heat
resistance and high strength. Accordingly, the structure of the magnetic
separation
device is complicated, a large amount of production costs are incurred, and
the
maintenance thereof is troublesome.
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Meanwhile, in the inventions disclosed above, since the total amount of sludge
produced is decomposed by a hydrothermal treatment under high temperature and
high
pressure conditions, the amount of energy introduced into the device is large.
In order to solve the above problems, the presently disclosed subject matter
aims to
provide a water treatment system which is capable of reducing the volume of
sludge and
cutting the running costs by purifying wastewater, collecting magnetic powder
from a
sludge produced and recycling the sludge with a simple device configuration at
low
running costs.
Certain exemplary embodiments can provide a water treatment system comprising:
at least one flocculant-injection device which injects a flocculant into
wastewater to be
treated; a magnetic-powder injection device which injects a magnetic powder
into the
wastewater; at least one agitation device which agitates the flocculant and
the magnetic
powder contained in the wastewater to form magnetic flocs; a magnetic floc
separating
device which separates the produced magnetic flocs from the wastewater; a
first pressure
pump which feeds a sludge which is an aggregate of the separated magnetic
flocs and
pressurizes the sludge to have a pressure equal to or more than a saturated
vapor pressure;
a first reactor in which the pressurized sludge is heated to have a
temperature of 200 to
300 C by a heater and subjected to a hydrothermal treatment while passing
therethrough;
a first heat exchanger which performs heat exchange between a low-temperature
sludge
before the hydrothermal treatment and a high-temperature sludge after the
hydrothermal
treatment; a first back pressure regulating valve which discharges the sludge
under
atmospheric pressure while maintaining a pressure in the first reactor equal
to or more than
the saturated vapor pressure; a magnetic separation device which collects the
magnetic
powder from the discharged sludge; and a conveying device which conveys the
collected
magnetic powder to the magnetic-powder injection device.
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2a
According to a second aspect, the water treatment system according to the
first
aspect of the presently disclosed subject matter, further includes: a solid-
liquid separation
device which is provided downstream of the first reactor and which separates a
supernatant
fluid from the heated sludge; a second back pressure regulating valve which
discharges the
supernatant fluid; and a second reactor in which the sludge after the
separation of the
supernatant fluid is heated again.
According to a third aspect, the water treatment system according to the first
aspect of the presently disclosed subject matter, further includes: a solid-
liquid
separation device which is provided downstream of the first reactor and which
separates
a supernatant fluid from the heated sludge; a second pressure pump which feeds
the
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sludge after the separation of the supernatant fluid; and a second reactor in
which the
sludge pressurized by the second pressure pump is heated again.
According to a fourth aspect, the water treatment system according to the
first
aspect of the presently disclosed subject matter, further includes: a solid-
liquid
separation device which is provided downstream of the first reactor and which
separates
a supernatant fluid from the heated sludge; a second back pressure regulating
valve
which discharges the supernatant fluid; a second pressure pump which feeds the
sludge
after the separation of the supernatant fluid; and a second reactor in which
the sludge
pressurized by the second pressure pump is heated again.
According to a fifth aspect, the water treatment system according to the first
aspect of the presently disclosed subject matter, further includes: a third
back pressure
regulating valve provided downstream of the first reactor; a solid-liquid
separation
device which is provided downstream of the third back pressure regulating
valve and
which separates a supernatant fluid from the heated sludge; a second pressure
pump
which feeds the sludge after the separation of the supernatant fluid; and a
second reactor
in which the sludge pressurized by the second pressure pump is heated again.
According to the presently disclosed subject matter, in water treatment for
removing impurities from wastewater, a flocculant and a magnetic powder are
introduced
into wastewater, magnetic flocs produced are removed by a magnetic floc
separating
device, a sludge produced in the magnetic separation is decomposed by a
hydrothermal
treatment, the magnetic powder is collected from the sludge after cooling and
depressurization, and the collected magnetic powder is reused. Therefore, it
is possible
to provide a water treatment system which is capable of reducing production
costs by
allowing the magnetic separation device to have pressure resistance
performance and
heat resistance performance at normal temperature and normal pressure, and
capable of
reducing the amount of waste and running costs by reusing the magnetic powder.
In addition, in a stage before the hydrothermal treatment for decomposing a
sludge, since the sludge is preliminarily made compact (consolidated), and
moisture is
removed from the sludge, it is possible to reduce an amount of energy
necessary for the
hydrothermal treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a schematic diagram for illustrating one example of a configuration
of a
water treatment system according to the present embodiment;
Fig. 2 is a schematic diagram for illustrating another example of a
configuration
of a water treatment system according to the present embodiment;
Fig. 3 is a schematic diagram for illustrating still another example of a
configuration of a water treatment system according to the present embodiment;
Fig. 4 is a schematic diagram for illustrating yet another example of a
configuration of a water treatment system according to the present embodiment;
Fig. 5 is a schematic diagram for illustrating still yet another example of a
water
treatment system according to the present embodiment;
Fig. 6 is a graph for illustrating a saturated vapor pressure curve of water;
and
Fig. 7 is a schematic diagram for illustrating an exemplary configuration of
water treatment according to the present embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(First Embodiment)
Fig. 1 illustrates one example of a water treatment system provided in the
present invention. The water treatment system illustrated here has a
configuration of a
water treatment system employing a coagulation and magnetic separation method.
Wastewater to be treated is accumulated in a raw water tank 101. This
wastewater is fed into an agitation device 103 by a pump 102. Into the
agitation device
103, a flocculant is introduced from a flocculant tank 104 and a magnetic
powder
dispersed in water is introduced from a magnetic powder tank 105, and these
components
are agitated so as to form magnetic flocs composed of contaminants and the
magnetic
powder. Wastewater in which the magnetic flocs are formed is fed into a
magnetic
separation device 106, and then magnetic flocs are collected from the
wastewater to
obtain purified water. The collected magnetic flocs are fed into a sludge tank
1.
A sludge which is an aggregate of the magnetic flocs is then fed by a pump 2
and receives heat from a high-temperature sludge which has been hydrothermally
treated,
by a heat exchanger 5 for preheating. Next, the sludge introduced in a reactor
4 is
heated by a heater 3 so as to maintain an intended temperature and to degrade
the
function of the flocculant, thereby decomposing the sludge into the magnetic
powder and
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other impurities. The decomposed sludge is discharged from the reactor 4 and
then heat
exchanged with a low-temperature sludge , by the heat exchanger 5 to be cooled
to a
temperature equal to or lower than the boiling temperature of the sludge at
atmospheric
pressure. The cooled sludge is depressurized to atmospheric pressure by a back
5 pressure regulating valve 6 and is then supplied to a magnetic separation
device 7. At
this time, the pressure of the sludge from when the time the sludge is
pressurized by the
pump 2 till when the sludge is depressurized to atmospheric pressure by the
back
pressure regulating valve 6 must be set to a pressure equal to or higher than
a saturated
vapor pressure of the sludge at a temperature in the reactor 4. The sludge
supplied to
the magnetic separation device 7 is separated into magnetic powder and sludge
residues
by a magnetic force, and the magnetic powder is collected. It is so designed
that the
collected magnetic powder is conveyed to the magnetic powder tank 105 to be
used
again for coagulation and magnetic separation.
As a condition for the above hydrothermal treatment, the heating temperature
of
sludge is preferably set in the range of from 200 C to 300 C. This is because
when the
sludge is heated at 200 C or higher, it can be decomposed in a short time;
however when
the sludge is heated 300 C or higher, a change in magnetic powder composition
rapidly
proceeds, and the saturation magnetization decreases.
As described above, in the water treatment system of the present embodiment,
magnetic separation for collecting magnetic powder, which is performed after
decomposition of sludge by a hydrothermal treatment at high temperature and
high
pressure, can be carried out at normal temperature and normal pressure, and
thus the
pressure resistance performance and heat resistance performance of the
magnetic
separation device 7 can be set at normal temperature and normal pressure, and
the
production cost can be reduced. Further, the magnetic powder which has been
disposed
as a sludge in a conventional device can be efficiently collected, and thus
the amount of
sludge produced can be reduced. Furthermore, since the magnetic powder
collected can
be reused in the coagulation-magnetic separation device, it is possible to
provide a water
treatment system having low running costs.
In the present embodiment, the term "high temperature" means a temperature
equal to or higher than the boiling point of sludge at atmospheric pressure,
and the term
"high pressure" means a pressure equal to or higher than atmospheric pressure.
Further,
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in this embodiment, although one type of flocculant is used, the number of
types of
flocculants may be increased as required, and a neutralizer and the like may
be added.
(Second Embodiment)
Fig. 2 illustrates another example of a water treatment system provided in the
present invention. The water treatment system illustrated here has a system
configuration in which the decomposition reaction described in the first
embodiment is
carried out in two stages, at high temperature and at low temperature,
respectively, and
by separating the sludge into solid and liquid after the decomposition
reaction at the first
stage, an amount of sludge to be fed to a high-temperature decomposition
reaction at the
second stage can be reduced.
Firstly, similarly to the first embodiment, a sludge containing a magnetic
powder, which is produced in purification of wastewater, is accumulated in a
sludge tank
1. This sludge is fed by a pump 2 and receives heat from a high-temperature
sludge
which has been hydrothermally treated, by a heat exchanger 5 for preheating.
Next, the
sludge introduced into a reactor 4 is heated at 150 C or lower by a heater 3
to degrade
the function of the flocculant, and thereby the sludge can be made more
compact
(consolidated) than untreated sludge. This sludge is fed to the heat exchanger
5 to
perform heat exchange and then introduced into a solid-liquid separator 10 so
as to be
separated into a supernatant fluid and a sludge containing the magnetic
powder. The
supernatant fluid is discharged through a back pressure regulating valve 16,
and the
sludge receives heat from a high temperature sludge which has been
hydrothermally
treated, by a heat exchanger 15 for preheating. Next, the sludge introduced
into a
reactor 14 is heated so as to maintain an intended temperature by a heater 13
and to
degrade the function of the flocculant, thereby the sludge being decomposed
into a
magnetic powder and other impurities. The decomposed sludge is discharged from
the
reactor 14 and then heat exchanged with a low-temperature sludge , by the heat
exchanger 15 to be cooled to a temperature equal to or lower than the boiling
temperature
of the sludge at atmospheric pressure. It is so designed that the cooled
sludge is
depressurized to atmospheric pressure by a back pressure regulating valve 6
and the
magnetic powder is collected from the sludge by a magnetic separation device 7
and
conveyed to a magnetic powder tank 105. At this time, the pressure of the
sludge from
when the sludge is pressurized by the pump 2 till when the sludge is
depressurized to
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atmospheric pressure by the back pressure regulating valve 6 must be set to a
pressure
equal to or higher than a saturated vapor pressure of the sludge at a
temperature in the
reactor 14.
Meanwhile, by setting the temperature of the reactor 4 to about 50 C to about
150 C, it is possible to efficiently compact (consolidate) the sludge and to
substantially
remove moisture in the sludge therefrom in the solid-liquid separator 10.
As described above, according to the present embodiment, the sludge introduced
into the reactor 14, which is set in a state of high temperature and high
pressure, is
condensed, and an amount of sludge to be treated can be considerably reduced,
and
thereby an amount of energy required to be introduced into the heater 13 can
be reduced.
The solid-liquid separator 10 is employed mainly for separating a magnetic
power having a high specific gravity from water. Therefore, as a configuration
of the
solid-liquid separator 10, a gravity setting chamber, a cyclone, a centrifugal
separator, a
magnetic separation device or the like may be used instead thereof.
(Third Embodiment)
Fig. 3 illustrates still another example of a water treatment system provided
in
the present invention. The water treatment system illustrated here has a
system
configuration in which the first stage decomposition reaction described in the
second
embodiment can be performed at a temperature equal to or lower than the
boiling point
of the sludge at atmospheric pressure.
Firstly, similarly to the first embodiment, a sludge containing a magnetic
powder, which is produced in purification of wastewater, is accumulated in a
sludge tank
1. This sludge is fed by a pump 2 and receives heat from a high-temperature
sludge
which has been hydrothermally treated, by a heat exchanger 5 for preheating.
Next, the
sludge introduced into a reactor 4 is heated at a temperature equal to or
lower than the
boiling point of the sludge at atmospheric pressure by a heater 3 so as to
degrade the
function of the flocculant, and thereby the sludge can be made further compact
(consolidated). This sludge is passed through the heat exchanger 5 and then
introduced
into a solid-liquid separator 10 so as to be separated into a supernatant
fluid and a sludge
containing the magnetic powder, under atmospheric pressure, and then the
supernatant
fluid is discharged. The sludge that has been subjected to the solid-liquid
separation is
then pressurized by a pump 22. In the water treatment system, the zone located
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downstream of the reactor 14 is so designed that the sludge is treated
similarly to the
second embodiment, so that the magnetic powder is collected and conveyed to a
magnetic powder tank 105.
A different point of the third embodiment from the second embodiment is that
the first stage decomposition reaction which proceeds in the reactor 4 is
carried out under
substantially atmospheric pressure. According to the water treatment system of
the
present embodiment, internal pressures of the reactor 4, the heat exchanger 5
and the
solid-liquid separator 10 are substantially atmospheric pressure, and thus it
is possible to
set the pressure resistance performance of these system components at
atmospheric
pressure and to reduce the production costs.
In some cases, a production ratio between water and solids in the solid-liquid
separator 10 changes due to a change in composition of a sludge to be treated.
In this
case, a sensor for measuring a production ratio between water and solids in
the solid-
liquid separator 10 is disposed beforehand, and by installing a controller
which changes
the liquid feeding rate of the pumps 22 and 2 and the output power of the
heaters in
response to the production ratio, the water treatment can be efficiently
carried out.
Further, if the operation speed of the reactor 4 or reactor 14 is
insufficient, the operation
speed can be made higher by increasing the reaction temperature.
(Fourth Embodiment)
Fig. 4 illustrates yet another example of a water treatment system provided in
the present invention. The water treatment system illustrated here has a
system
configuration in which the pressure in the reactor 4, in which the first stage
decomposition reaction described in the second embodiment is performed, can be
reduced.
Firstly, similarly to the first embodiment, a sludge containing a magnetic
powder, which is produced in purification of wastewater, is accumulated in a
sludge tank
1. This sludge is pressurized by a pump 2 and receives heat from a high-
temperature
sludge which has been hydrothermally treated, by a heat exchanger 5 for
preheating.
Next, the sludge introduced into a reactor 4 is heated at 150 C or lower by a
heater 3 to
degrade the function of the flocculant, and thereby the sludge can be made
further
compact (consolidated). This sludge is introduced into a solid-liquid
separator 10 so as
to be separated into a supernatant fluid and a sludge containing the magnetic
powder.
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The supernatant fluid is discharged through a back pressure regulating valve
36. The
sludge that has been subjected to the solid-liquid separation is then
pressurized by a
pump 22. In the water treatment system, the zone located downstream of the
reactor 14
is so designed that the sludge is treated similarly to the second embodiment,
so that the
magnetic powder is collected and conveyed to a magnetic powder tank 105.
A different point of the fourth embodiment from the second embodiment is that
the first stage decomposition reaction which proceeds in the reactor 4 is
carried out at a
pressure lower than that of the reactor 14.
A saturated vapor pressure curve of water is illustrated in Fig. 6. As can be
seen from Fig. 6, the higher the temperature is, the more rapidly increases
the saturated
vapor pressure of water. Therefore, if the reaction temperature can be lowered
only to a
certain extent, the pressure applied in the reaction can be considerably
reduced. For
that reason, according to the water treatment system of the present
embodiment, the
internal pressure of the solid-liquid separator 10 can be set to be lower than
that in the
second embodiment, and thus it is possible to set the pressure resistance
performance of
the system components including the reactor 4, the heat exchanger 5 and the
solid-liquid
separator 10 can be set to be low and to reduce the production costs.
In some cases, a production ratio between water and solids in the solid-liquid
separator 10 changes due to a change in composition of a sludge to be treated.
In this
case, a sensor for measuring a production ratio between water and solids in
the solid-
liquid separator 10 is disposed beforehand, and by installing a controller
which changes
the liquid feeding rate of the pumps 22 and 2 and the output power of the
heaters in
response to the production ratio, the water treatment can be efficiently
carried out.
Further, if the operation speed of the reactor 4 or reactor 14 is
insufficient, the operation
speed can be made higher by increasing the reaction temperature.
(Fifth Embodiment)
Fig. 5 illustrates still yet another example of a water treatment system
provided
in the present invention. The water treatment system illustrated here has a
system
configuration in which the pressure of the sludge flowing through the solid-
liquid
separator 10 described in the second embodiment can be reduced.
Firstly, similarly to the first embodiment, a sludge containing a magnetic
powder, which is produced in purification of wastewater, is accumulated in a
sludge tank
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1. This sludge is pressurized by a pump 2 and receives heat from a high-
temperature
sludge which has been hydrothermally treated, by a heat exchanger 5 for
preheating.
Next, the sludge introduced into a reactor 4 is heated at 150 C or lower by a
heater 3 so
that the function of the flocculant degrades and the sludge can be made
compact
5 (consolidated). The pressure in the reactor 4 is kept at a pressure equal to
or higher than
the saturated vapor pressure by a back pressure regulating valve 46, and the
sludge that
has passed through the back pressure regulating valve 46 is then introduced
into a solid-
liquid separator 10 at atmospheric pressure. In the solid-liquid separator 10,
the sludge
is separated into a supernatant fluid and a sludge containing the magnetic
powder. The
10 supernatant fluid is disposed of, and the sludge is again pressurized by a
pump 22. In
the water treatment system, the zone located downstream of the reactor 14 is
so designed
that the sludge is treated similarly to the second embodiment, so that the
magnetic
powder is collected and conveyed to a magnetic powder tank 105.
By way of example, the following describes the flow of substances. When
polyaluminum chloride and polyacrylamide are used as the flocculant, magnetic
flocs
composed of contaminants, magnetic powder, polyaluminum chloride and
polyacrylamide are produced in the agitation device 103. The magnetic flocs
are
collected in the magnetic separation device 106 to be a sludge and accumulated
in the
sludge tank 1 as a sludge. When this sludge is heated at about 150 C and
allowed to
stand still, the solid content in the sludge is made compact (consolidated)
and the sludge
is separated into a supernatant fluid and solids. The supernatant fluid is
disposed of.
When the solids containing a small amount of moisture are hydrothermally
treated at
200 C or higher in the reactor 14, the solids are decomposed, whereby a
magnetic
powder can be collected. The collected magnetic powder is conveyed again to
the
magnetic powder tank 105, thereby making it possible to achieve reuse of
magnetic
powder and reduction in the amount of sludge discharged, which leads to a
reduction in
running costs.
As described above, according the water treatment system of the present
embodiment, the internal pressure of the solid-liquid separator 10 can be set
at
substantially atmospheric pressure, and thus it is possible to set the
pressure resistance
performance of the solid-liquid separator 10 low and to reduce the production
costs.
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Fig. 7 illustrates system components of each of the embodiments 2, 3, 4 and 5
described above and the pressure applied to each of these system components.
Note
that in Fig. 7, the second embodiment is designated with Example 2, the third
embodiment is designated with Example 3, the fourth embodiment is designated
with
Example 4, and the fifth embodiment is designated with Example 5.
As can be seen from Fig. 7, in Example 2, the pressure applied to components
from the pump 2 to the back pressure regulating valve 6 is 1 MPa or higher.
Whereas,
in Example 3, only the pressure applied to from the pump 22 to the back
pressure
regulating valve 6 is 1 MPa or higher. In Examples 4 and 5, the pressure in
the reactor
4 is pressurized to 1 MPa or lower (more than 0.1 MPa). Examples 4 and 5 are
utilized
in the case where the temperature required for compaction (consolidation) for
reducing
the volume of the sludge at atmospheric pressure is higher than the boiling
point of the
sludge at atmospheric pressure.
