1. A support system for production schedule planning of desalination process for use in a desalination plant which has 5 a freshwater tank serving as a buffer for storing therein freshwater produced from raw water, comprising: a salt concentration time change estimation unit that computes a salt concentration estimated value of the raw water; a water temperature time change estimation unit that 10 computes a water temperature estimated value of the raw water; a production schedule computation unit that calculates a power cost of the desalination plant, based on the salt concentration estimated value, the water temperature estimated value, an electricity rate unit price per time zone in an area 15 in which the desalination plant is installed, a freshwater tank maximum capacity which is an upper limit value of a water volume stored in the freshwater tank, a freshwater tank minimum capacity which is a lower limit value of a water volume stored in the freshwater tank, a current freshwater volume in 20 freshwater tank which is a freshwater volume currently stored in the freshwater tank, and a demand for freshwater, and thereby computes a water desalination schedule; and a water desalination schedule display unit that displays the computed water desalination schedule. 25

2. The support system for production schedule planning of 63 desalination process according to claim 1, further comprising a freshwater demand estimation unit that computes the demand for freshwater based on weather prediction data and temperature prediction data. 5

3. The support system for production schedule planning of desalination process according to claim 1 or 2, wherein the production schedule computation unit calculates a power cost of the desalination plant, based on a 10 distribution reservoir maximum capacity of a distribution reservoir connected downstream of the freshwater tank, a distribution reservoir minimum capacity of the distribution reservoir, and a current freshwater volume in distribution reservoir indicating a freshwater volume currently reserved in 15 the distribution reservoir, in addition to the salt concentration estimated value, the water temperature estimated value, the electricity rate unit price per time zone, the current freshwater volume in freshwater tank, and the demand for freshwater, and thereby computes a water desalination 20 schedule.

4. The support system for production schedule planning of desalination process according to any one of claims 1 to 3, wherein the production schedule computation unit 25 calculates a power cost of the desalination plant, based on a residual salt concentration tolerance in freshwater and a 64 freshwater tank salt concentration, in addition to the salt concentration estimated value, the water temperature estimated value, the electricity rate unit price per time zone, the current freshwater volume in freshwater tank, the demand for 5 freshwater, the freshwater tank maximum capacity, and the freshwater tank minimum capacity, and thereby computes a water desalination schedule.

5. The support system for production schedule planning of 10 desalination process according to any one of claims 1 to 4, further comprising: a freshwater consumption actual value acquisition unit that acquires an actual value of freshwater consumption; an additional freshwater necessary amount calculation 15 unit that calculates an additional freshwater necessary amount which is an amount of freshwater to be additionally produced, by subtracting the actual value of freshwater consumption from a value of the demand for freshwater; a production schedule computation unit that calculates a 20 power cost of the desalination plant, based on the salt concentration estimated value, the water temperature estimated value, the electricity rate unit price per time zone, the freshwater tank maximum capacity, the freshwater tank minimum capacity, the current freshwater volume in freshwater tank, and 25 the additional freshwater necessary amount, and thereby computes a water desalination schedule on a real time basis; 65 and a water desalination schedule display unit that displays the computed water desalination schedule. 5 6. A support system for production schedule planning of desalination process, substantially as herein described with reference to accompanying drawings and examples.

SUPPORT SYSTEM FOR PRODUCTION SCHEDULE PLANNING OF
DESALINATION PROCESS
BACKGROUND OF THE INVENTION
5 1. Field of the Invention
[0001]
The present invention relates to a support system for
production schedule planning of desalination process which has
a function of changing a volume of desalinated water to be
10 produced, to an appropriate value in a desalination plant in
which a membrane for obtaining freshwater from seawater or
brine water is used.
2. Description of the Related Art
[0002]
15 More and more seawater or brine water desalination
apparatuses have been recently used which perform filtration
treatment using semipermeable membrane. The semipermeable
membrane includes reverse osmosis membrane and forward osmosis
membrane by differences in structure and usage. The
20 semipermeable membrane is made of such material as cellulose
and polyamide. The reverse osmosis membrane can be used for
obtaining freshwater by applying a pressure in excess of an
osmotic pressure of seawater, which does not allow salt to
permeate through the membrane but allows desalinated seawater
25 to permeate therethrough.
[0003]
2
If, for example, seawater is used as raw water in a
desalination process, since an osmotic pressure thereof is
about 2. 4 MPa, a pump typically needs to supply a pressure about
more than twice the seawater osmotic pressure. Power cost of
5 the pump accounts for a significant percentage of an operating
cost. Reduction in the power cost has been thus attempted by
developing a highly-efficient pump or using a large-size pump
having high efficiency. There is a limit, however, to the
above-described hardware measures, and further, those measures
10 disadvantageously increase initial cost.
[Related Art Documents]
[Patent Documents]
[0004]
[Patent Document 1] Japanese Laid-Open Patent Application,
15 Publication No. 2009-000580 (to be referred to as Patent
Document 1 hereinafter)
[Patent Document 2] Japanese Laid-Open Patent Application,
Publication No. Hll-033360 (to be referred to as Patent
Document 2 hereinafter)
20 [Patent Document 3] Japanese Laid-Open Patent Application,
Publication No. 2011-240234 (to be referred to as Patent
Document 3 hereinafter)
[Patent Document 4] Japanese Laid-Open Patent Application,
Publication No. 2011-120988 (to be referred to as Patent
25 Document 4 hereinafter)
3
SUMMARY OF THE INVENTION
[0005]
Freshwater production performance of the above-described
semipermeable membrane is influenced by some external
5 conditions. In a case of a seawater desalination plant, for
example, if a temperature of seawater is high, more freshwater
can be obtained. If a salt concentration of seawater is high,
less freshwater is obtained. Such conditions naturally vary
from season to season. In particular, if there is a river near
10 an intake of the seawater desalination plant, the performance
is greatly influenced by weather or tide. Power required for
obtaining a desired amount of freshwater thus changes with time.
Therefore, if more freshwater is produced when power required
for the freshwater production is small, and in turn, less
15 freshwater is produced when power required for the freshwater
production is large, then the power cost can be reduced,
resulting in a reduction in tan operating cost.
[0006]
A seawater desalination plant typically has a freshwater
20 tank downstream thereof, from which freshwater is delivered to
outside of the plant. If an operation of the plant is performed
such that more freshwater is produced when a power required for
the freshwater production is small, and in turn, less
freshwater is produced when the power required for the
25 freshwater production is large, there is a possibility that the
freshwater tank overflows exceeding an upper limit water level
4
thereof or that the freshwater tank becomes empty falling below
a lower limit water level. It is thus necessary to set a
prescribed volume of freshwater to be produced, taking the
water levels (or a water volume) into consideration.
5 [0007]
Further, there are some regions to which a time load tariff
that is applied in which an electricity rate unit price varies
according to season or time zone. In order to lower an operating
cost, such an operation is also effective that more freshwater
10 is produced in a time zone in which the electricity rate unit
price is inexpensive, and less freshwater is produced in a time
zone in which the electricity rate unit price is expensive. It
is however difficult to plan a production schedule with the
minimum operating cost, taking into consideration all of a
15 water quality condition changing over time, an electricity rate
unit price, and a water level (or a water volume) of a freshwater
tank serving as a buffer. To solve the problems, related art
techniques have been proposed as follows.
[0008]
20 Patent Document 1 describes a technique relating to an
operation support apparatus of a membrane filtration treatment
device for use in a water treatment plant. Patent Document 1
discloses, in particular, that a recommended operation
condition is presented based on information on turbidity of raw
25 water or the like. The inventions of Patent Document 1 are not
however directed to seawater or brine water rich in salt and
5
cannot be applied to a support for a desalination plant
operation. As described above, this is because the power cost
of the desalination apparatus using membrane is largely
affected by a change in salt concentration.
5 [0009]
Patent Documents 2 to 4 are all directed to a seawater
desalination plant. Patent Document 2 describes a technique
relating to an operation controller of a water producing plant
using a reverse osmosis membrane module. Patent Document 2
10 discloses, in particular, calculation of a producible water
quantity range based on a temperature or a concentration of
supplied water. The inventions of Patent Document 2, however,
fail to disclose how to appropriately manage an electricity
rate unit price which varies according to time zone or how to
15 create an operation plan taking into consideration a freshwater
tank serving as a buffer.
[0010]
Patent Document 3 describes a technique relating to a
seawater desalination apparatus in which proper running
20 conditions of a power recovery device are set and an electric
power amount is reduced. The inventions of Patent Document 3
use information on seawater temperature, but fail to draw up
an operation plan taking into consideration a freshwater tank
serving as a buffer for an electricity rate unit price which
25 varies according to time zone.
[0011]
6
Patent Document 4 describes a water desalination device
provided with a reverse osmosis membrane device. Patent
Document 4 discloses that a temperature of raw water is measured
and the measured temperature is fed back to a setting of an
5 operation condition, but fails to disclose how to plan an
appropriate operation schedule, or an efficient use of a buffer
function of a freshwater tank, or consideration to an
electricity rate by time zone or season. Patent Document 4
cannot thus solve the above-described problems.
10 [0012]
The present invention has been thus made in an attempt to
provide a support system for production schedule planning of
desalination process in which a buffer function of a freshwater
tank can be efficiently used taking into consideration a water
15 quality changing over time or an electricity rate unit price,
to thereby allow a reduction in power cost.
[Means for Solving the Problems]
[0013]
A support system for production schedule planning of
20 desalination process is used for a desalination plant which has
a freshwater tank serving as a buffer for storing therein
freshwater produced from raw water. The support system
includes: a salt concentration time change estimation unit that
computes a salt concentration estimated value of the raw water;
25 a water temperature time change estimation unit that computes
a water temperature estimated value of the raw water; a
7
production schedule computation unit that calculates a power
cost of the desalination plant, based on the salt concentration
estimated value, the water temperature estimated value, an
electricity rate unit price per time zone in an area in which
5 the desalination plant is installed, a freshwater tank maximum
capacity which is an upper limit value of a water volume stored
in the freshwater tank, a freshwater tank minimum capacity
which is a lower limit value of a water volume stored in the
freshwater tank, a current freshwater volume in freshwater tank
10 which is a freshwater volume currently stored in the freshwater
tank, and a demand for freshwater, and thereby computes a water
desalination schedule; and a water desalination schedule
display unit that displays the computed water desalination
schedule.
15 [Advantageous Effects of the Invention]
[0014]
In this embodiment, even without a large amount of
hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
20 software measures. This allows a supply of freshwater lower in
price. In this embodiment, power itself can also be reduced.
This allows a reduction in cost as well as in a volume of
greenhouse gas emission.
25 BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
8
FIG. 1 is a block diagram illustrating a support system
for production schedule planning of desalination process
according to a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a desalination
5 plant to which the first embodiment of the present invention
is applied.
FIG. 3 is a diagram illustrating an example of a change
in salt concentration over time according to the first
embodiment of the present invention.
10 FIG. 4 is a diagram illustrating an example of an
electricity rate unit price per time zone according to the first
embodiment of the present invention.
FIG. 5A and FIG. 5B are diagrams each illustrating a
calculation result of a water desalination schedule according
15 to the first embodiment of the present invention.
FIG. 6 is a block diagram illustrating a support system
for production schedule planning of desalination process
according to a second embodiment of the present invention.
FIG. 7 is a block diagram illustrating a support system
20 for production schedule planning of desalination process
according to a third embodiment of the present invention.
FIG. 8 is a block diagram illustrating a desalination
plant to which the third embodiment of the present invention
is applied.
25 FIG. 9 is a block diagram illustrating a support system
for production schedule planning of desalination process
9
according to a fourth embodiment of the present invention.
FIG. 10 is a block diagram illustrating a support system
for production schedule planning of desalination process
according to a fifth embodiment of the present invention.
5
DETAILED DESCRIPTION OF EMBODIMENTS
[0016]
Embodiments of the present invention are described with
reference to related drawings.
10
[0017]
FIG. 1 is a block diagram illustrating a configuration of
a support system for production schedule planning of
desalination process 1 according to a first embodiment of the
15 present invention. FIG. 2 is a diagram illustrating a portion
of a configuration of a desalination plant 6. The support system
for production schedule planning of desalination process 1
according to this embodiment is configured to plan a production
schedule of the desalination plant 6 shown in FIG. 2.
20 [0018]
As shown in FIG. 2, the desalination plant 6 includes: a
high pressure pump 58 that pumps taken raw water 62 to a reverse
osmosis membrane device (which may also be referred to as a
reverse osmosis membrane) 60; the reverse osmosis membrane
25 device 60 that produces freshwater from the raw water 62; a
power recovery device 56 that recovers a concentrated
10
wastewater 72 from the reverse osmosis membrane device 60; and
a freshwater tank 4 that stores freshwater 2 obtained by the
reverse osmosis membrane device 60. The raw water 62 includes,
for example, seawater and brine water. The reverse osmosis
5 membrane device 60 is disposed downstream of the high pressure
pump 58. The reverse osmosis membrane device 60 is connected
to the power recovery device 56 and the freshwater tank 4. The
reverse osmosis membrane device 60 is made of such material as
cellulose and polyamide. Application of a pressure higher than
10 an osmotic pressure of the raw water 62 to the reverse osmosis
membrane device 60 allows the raw water 62 to be recovered as
the concentrated wastewater 72 by the power recovery device 56,
without allowing salt contained in the raw water 62 to permeate
the membrane. The freshwater 2 permeating the reverse osmosis
15 membrane device 60 is stored into the freshwater tank 4.
[0019]
As shown in FIG. 1, the support system for production
schedule planning of desalination process 1 includes: a salt
concentration time change estimation unit 8, a temperature time
20 change estimation unit 10, a storage unit (which may also be
referred to as a memory) 11, a water level gauge 9, a production
schedule computation unit 28, and a water desalination schedule
display unit 30.
[0020]
25 The salt concentration time change estimation unit 8
estimates a change in salt concentration of the raw water 62
11
over time and outputs information on an estimated value of the
change in salt concentration over time (an estimated salt
concentration value) 12 to the production schedule computation
unit 28 . The salt concentration time change estimation unit 8
5 according to this embodiment accumulates data on the raw water
62 and estimates a time change in salt concentration using the
accumulated data. For example, the salt concentration time
change estimation unit 8 estimates a temporal change in salt
concentration of raw water based on data on a day or days
10 previous to a day when the planning is made. If a mouth of a
river is not so far away from an intake of the desalination plant
6, tide affects on the estimated salt concentration value 12.
The salt concentration time change estimation unit 8 may use
data on the tide in estimating the salt concentration. FIG. 3
15 illustrates an example of a change in salt concentration over
time because of tide.
[0021]
The water temperature time change estimation unit 10
estimates a change in temperature of the raw water 62 over time
20 and outputs information on a value of the estimated water
temperature (which may also be referred to as a water
temperature estimated value) 14 to the production schedule
computation unit 28. The water temperature time change
estimation unit 10 according to this embodiment accumulates
25 data on the raw water 62 and estimates a change in the water
temperature using the accumulated data. For example, the water
12
temperature time change estimation unit 10 estimates a temporal
change in water temperature of raw water based on data on a day
or days previous to day when the planning is made. The water
temperature time change estimation unit 10 may estimate a
5 change in a water temperature taking into consideration
information on weather on the target day.
[0022]
The storage unit 11 stores therein: electricity rate unit
price information by time zone (which may also be referred to
10 as a electricity rate unit price per time zone) 16 in an area
where the desalination plant 6 is established; information on
a maximum capacity of freshwater which the freshwater tank 4
can store therein (freshwater tank maximum capacity) 18;
information on a minimum capacity of freshwater which the
15 freshwater tank 4 can store therein (freshwater tank minimum
capacity) 20; and information on demand for freshwater (demand
for freshwater) 24. The production schedule computation unit
28 receives the information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, the
20 freshwater tank minimum capacity 20, and the demand for
freshwater 24 from the storage unit 11.
[0023]
The water level gauge 9 measures a water volume of
freshwater stored in the freshwater tank 4 of the desalination
25 plant 6 on a real time basis and transmits information on the
measured freshwater volume to the production schedule
13
computation unit 28. The production schedule computation unit
28 receives the information on the freshwater volume stored in
the freshwater tank 4, from the water level gauge 9 on a real
time basis.
5 [0024]
This embodiment describes a case in which the production
schedule computation unit 28 computes a single water
desalination schedule 26 and displays the single schedule 26
in the water desalination schedule display unit 30. However,
10 the production schedule computation unit 28 may compute a
plurality of water desalination schedules 26 and displays the
plural schedules 26 in the water desalination schedule display
unit 30. If a plurality of the water desalination schedules 26
are displayed, an operator of the desalination plant 6 selects
15 any one of the plural water desalination schedules 26 and inputs
information on the selected water desalination schedule via an
input device (not shown) of the support system for production
schedule planning of desalination process 1. Based on the
inputted water desalination schedule, the support system for
20 production schedule planning of desalination process 1
supports planning of a production schedule of the desalination
plant 6.
[0025]
The electricity rate unit price per time zone 16 is a time
25 load tariff in which an electricity rate unit price is more
inexpensive in nighttime during which less power is consumed
14
in a day, compared to a power production capability, and also
in daytime during which more power is consumed in the day. FIG.
4 is a diagram illustrating an example of a change in the
electricity rate unit price per time zone 16. A value of the
5 electricity rate unit price per time zone 16 may change not only
with time but also with season.
[0026]
As described above, the desalination plant 6 includes the
freshwater tank 4. This embodiment is characterized in that the
10 freshwater tank 4 serves as a buffer responding to a condition
changing over time such as the estimated salt concentration
value 12, the estimated water temperature value 14, and the
electricity rate unit price per time zone 16, based on which
the production schedule computation unit 28 computes an
15 appropriate production schedule. The production schedule
computation unit 28 computes the water desalination schedule
26 of the desalination plant 6 such that the desalination plant
6 is operated as little as possible or as little freshwater as
possible is produced at a time when: the estimated salt
20 concentration value 12 of raw water is high; the estimated water
temperature value 14 of the raw water is low; and the
electricity rate unit price per time zone 16 is high. In terms
of operating cost, the desalination plant 6 is preferably
operated based on the water desalination schedule 26 as
25 described above. On the other hand, the production schedule
computation unit 28 computes the water desalination schedule
15
26 of the desalination plant 6 such that the desalination plant
6 is operated as much as possible or as much freshwater as
possible is produced at a time when: the estimated salt
concentration value 12 of raw water is low; the estimated water
5 temperature value 14 of the raw water is high; and the
electricity rate unit price per time zone 16 is low. In terms
of operating cost, the desalination plant 6 is preferably
operated based on the water desalination schedule 26 as
described above.
10 [0027]
Nevertheless, if too much freshwater is produced compared
to the demand for freshwater 24, there is a possibility that
the freshwater tank 4 overflows. On the other hand, if too
little freshwater is produced compared to the demand for
15 freshwater 24, there is a possibility that the freshwater tank
4 becomes empty. In this case, the freshwater 2 in response to
the demand for freshwater 24 cannot be supplied, resulting in
an unsatisfactory performance of the desalination plant 6.
[0028]
20 It is thus indispensable for the production schedule
computation unit 28 to use the freshwater tank maximum capacity
18 and the freshwater tank minimum capacity 20 as constraint
conditions and plan a schedule of a volume of freshwater to be
produced, setting an initial value to the current freshwater
25 volume in freshwater tank 22 at a present point of time. Hence,
in this embodiment, information on the freshwater tank maximum
16
capacity 18, the freshwater tank minimum capacity 20, and the
current freshwater volume in freshwater tank 22 is used in
addition to the information on the estimated salt concentration
value 12, the estimated water temperature value 14, and the
5 electricity rate unit price per time zone 16, based on which
the production schedule computation unit 28 appropriately
computes the water desalination schedule 26.
[0029]
Next is described a specific method of computing the water
10 desalination schedule 26 by the production schedule
computation unit 28. It is assumed herein that the desalination
plant 6 plans an hourly volume of freshwater to be produced for
the next 24 hours once a day. This embodiment exemplifies
planning on an hour to hour basis. However, the planning may
15 be computed on a 30 minutes, a 10 minutes, or any other different
time period basis, using a similar technique.
[0030]
At a time of planning, let volumes of demand for freshwater
Q2 [m3/h] at respective hour-by-hour times, namely, time 1,
20 time 2, time 3, ..., and time 24, be as follows:
time 1 : Q2 [1] , time 2 : Q2 [2] , time 3 : Q2 [3] , ..., and time
24 : Q2[24]
Also, let a freshwater volume in the freshwater tank 4 be
V[0] at the time of planning, and let a set value of the
25 freshwater volume in the freshwater tank 4 after a lapse of the
24 hours be V[24] . V[24] is set to a value equal to V[0] if there
17
is no specific reason. This makes the freshwater volume in the
freshwater tank 4 the same at the time of planning every day,
resulting in an easy management of the planning.
[0031]
5 In the first embodiment, a freshwater production schedule
corresponds to the water desalination schedule 26. The water
desalination schedule 26 used herein includes a set value of
a volume of freshwater produced at the desalination plant 6.
Further, let freshwater volume Ql [m3/h] beQl[l], Ql[2], Ql[3] ,
10 ..., and Ql [24] at respective hourly times of time 1, time 2, time
3, ... , and time 24. This embodiment attempts to determine
appropriate values of the described-above.
[0032]
Relationship among the above-described demand for
15 freshwater Q2 [m3/h] , the set value V of the freshwater volume
in the freshwater tank 4, and the freshwater volume Ql [m3/h]
is represented by Expression (1) . £ used herein means a sum of
volumes at time i which is varied from time 1 to time 24.
SQl[i]-SQ2[i]=V[24]-V[0] ...Expression (1)
20 Expression (1) is deformed to obtain Expression (2) as
follows:
EQl[i]=EQ2[i]+V[24]-V[0] ...Expression (2)
In this embodiment, the production schedule computation
unit 28 sets Ql[i] to a value which satisfies the relationship
25 represented by Expression (2), and calculates, in that case,
whether or not the current freshwater volume in freshwater tank
18
22 is larger than a freshwater tank maximum capacity Vmax or
is smaller than a freshwater tank minimum capacity Vmin. The
value of Ql[i] may be set using, such as, but not limited to,
all possible regression, and Monte Carlo method with a random
5 number. As an example, procedures (a) to (d) of setting Ql[i]
in which the Monte Carlo method is used are shown below:
(a) Calculate a value of SQ2[i]+V[24]-V[0] according to
Expression (2);
(b) Prepare 24 random numbers;
10 (c) Distribute the value of SQ2[i]+V[24]-V[0] according
to ratios of respective values of the 24 random numbers prepared
in (b); and
(d) Obtain the distributed value as a value of Ql[i].
[0033]
15 Using Ql[i] set as described above, a freshwater volume
V[i] in the freshwater tank 4 can be calculated with expressions
as follows:
V[1]=V[0]+Q1 [1]-Q2[1] ...Expression (3)
V[2]=V[1]+Q1[2]-Q2[2] ...Expression (4)
20
V[24]=V[23]+Q1[24]-Q2[24] ...Expression (5)
The production schedule computation unit 28 compares each
of V[i] obtained as above, to the freshwater tank maximum
capacity Vmax as well as the freshwater tank minimum capacity
25 Vmin. If any one of V[i] is beyond a range between the freshwater
tank maximum capacity Vmax and the freshwater tank minimum
19
capacity Vmin, the production schedule computation unit 28
returns the processing to the procedure (b) and recalculates
V[i] using another random numbers. On the other hand, if all
of 24 V[i] are within the range, the production schedule
5 computation unit 28 advances the processing to the next step
and calculates hourly power cost as shown below.
[0034]
In the desalination plant 6 using the reverse osmosis
membrane 60, an osmotic pressure n [Pa] determined by a salt
10 concentration has an affect on pump power. The osmotic pressure
is represented by the following expression:
Osmotic pressure n=nxRxT ... Expression (6)
Herein, n represents a solute molar concentration
[mol/L]; R, a gas constant [L-kPa/K-mol]; and T, a water
15 temperature [K]. The solute molar concentration n is
proportional to the salt concentration. Expression (6)
demonstrates that the osmotic pressure is related to the salt
concentration and the water temperature. The estimated salt
concentration value 12 and the estimated water temperature
20 value 14 as described above are entered in Expression (6).
Pressure [Pa], a required pressure of a high pressure pump 58
which supplies the raw water 62 to the reverse osmosis membrane
60 at high pressure is represented by Expression (7) using a
value of the osmotic pressure n.
25 Pressure=n+Jv/Lv ... Expression (7)
Herein, Jv is a filtration flux [m/sec] , and Lv is a pure
20
water permeability coefficient [m/secPa]. A value of Jv can
be calculated by the following Expression (8) wherein A [m2]
is an membrane area of the reverse osmosis membrane 60:
Jv=Ql/3600/A ... Expression (8)
5 Since a volume of water for a given one hour is Ql [m3/h] ,
if a recovery rate is designated as a [%] , a supplied water
volume Q [m3/h] which is supplied by the high pressure pump 58
is represented by Expression (9) as follows:
Q=Qlxl00/a ... Expression (9)
10 At this time, a pressurization power of the high pressure
pump 58 is represented by Expression (10) as follows:
PowerPump[kWh]=0.163x(Q/60)x(Pressure/10000)/RatePump
... Expression (10)
Herein, RatePump is a pump efficiency [-].
15 [0035]
Of the supplied water volume Q, the concentrated
wastewater 72 other than the freshwater volume Ql is supplied
to the power recovery device 56 and typically covers a portion
of pressurization power required for the high pressure pump 58.
20 A flow rate Qpx [m3/h] of the concentrated wastewater 72
supplied to the power recovery device 56 is represented by
Expression (11) as follows:
Qpx=Qx(100-a) /100 ... Expression (11)
A value of an inlet pressure Ppx [Pa] of the power recovery
25 device 56 is calculated by subtracting a value of a flow channel
resistance, channelLoss [Pa] , on a concentrated liquid primary
21
side of the reverse osmosis membrane 60 from the required
pressure Pressure of the high pressure pump 58.
Ppx=Pressure-channelLoss ... Expression (12)
Herein, channelLoss is a pressure loss [Pa] due to the flow
5 channel resistance.
[0036]
Herein, let a conversion efficiency of the power recoverydevice
56 be called pxEfficiency [-]. A power, PowerRecovery
[kWh], which can be recovered by the power recovery device 56
10 is represented by Expression (13) as follows:
PowerRecovery=0.I63x(Qpx/60)x(Ppx/10000)xpxEfficiency
... Expression (13)
A power consumed, PowerConsumption [kWh], can be then
calculated by Expression (14) as follows:
15 PowerConsumption=PowerPump-PowerRecovery ... Expression
(14)
By multiplying an electricity rate unit price per time
zone, which is UnitPrice [yen/kWh], by PowerConsumption, an
hourly power cost P, which is PowerCost [yen/h] can be
20 calculated.
PowerCost=UnitPricexPowerConsumption ... Expression (15)
Let a value summing up the power cost for 24 hours,
PowerCost [yen/h], be called CostSum [yen]. In a calculation
of the summed value performed for the first time, the production
25 schedule computation unit 28 stores therein the value of
CostSum. In and after the calculation for the second time, the
22
production schedule computation unit 28 returns to the
procedure (b).
[0037]
At each time of the calculation of CostSum [yen], if a
5 calculated result is smaller than a previously-calculated
CostSum, the production schedule computation unit 28 replaces
the previously-calculated CostSum by the currently-calculated
smaller CostSum and stores Ql[i] corresponding to the smaller
CostSum. In this example, the Monte Carlo method is used in
10 which a number of the calculations are repeated. As a result,
regardless of whether or not there is a local minimum, an
operating condition with smaller and smaller power cost can be
obtained. Such iterative calculations may be stopped when the
calculations are performed a prescribed total number of
15 repetitive times, or when a frequency of replacing CostSum or
a degree of variation of CostSum becomes small.
[0038]
The production schedule computation unit 28 transmits the
information on the water desalination schedule 26 computed as
20 described above, to the water desalination schedule display
unit 30. The water desalination schedule display unit 30
displays the received water desalination schedule 26 to an
operator. This can support a production schedule planning by
the operator. An operation in accordance with the water
25 desalination schedule 26 makes it possible to efficiently use
the desalination plant 6 while the freshwater tank maximum
23
capacity 18 and the freshwater tank minimum capacity 20 of the
freshwater tank 4 disposed downstream in the desalination plant
6 are kept within an appropriate range, and to minimize power
cost.
5 [0039]
As an example, FIG. 5A and FIG. 5B illustrate results of
the water desalination schedule 26 calculated according to this
embodiment which can minimize the power cost when the
electricity rate unit price per time zone 16 shown in FIG. 4
10 is applied. FIG. 5A is a diagram illustrating a volume of
freshwater produced by the desalination plant 6 in a case where
the desalination plant 6 is operated appropriately such that
the produced freshwater volume is constantly maintained. FIG.
5B is a diagram illustrating a freshwater volume in the
15 freshwater tank 4 in a case where the desalination plant 6 is
operated appropriately such that the produced freshwater
volume is constantly maintained. The water desalination
schedule display unit 30 displays contents at least shown in
FIG. 5A in form of a graphic, a table, or a numerical value.
20 This makes it possible for the operator to check a change in
a volume of freshwater produced by the desalination plant 6.
Further, the water desalination schedule display unit 30 may
receive information on the freshwater tank maximum capacity 18,
the freshwater tank minimum capacity 20, and an estimated value
25 of a freshwater volume in the freshwater tank 4 when the
desalination plant 6 is operated such that the produced
24
freshwater volume is constantly maintained, from the
production schedule computation unit 28, and may display the
information therein. FIG. 5B is an example of a diagram
illustrating the freshwater tank maximum capacity 18, the
5 freshwater tank minimum capacity 20, and a time change in an
estimated value of freshwater in the freshwater tank 4. Note
that, in the example calculated as described above, the power
cost was found to be reduced by about 10%, compared to a case
in which the freshwater volume Ql is maintained constantly in
10 a day.
[0040]
A certain type of the desalination plant 6 is designed not
to change the freshwater volume Ql gradually but to, for example,
start or stop an operation thereof unit by unit. Further, if
15 an inverter is used to control a rotation speed, efficiency of
the inverter may different from that of another according to
a load factor. In that case, an appropriate constraint
condition corresponding to the inverter efficiency is added to
the above-described calculation operation performed by the
20 production schedule computation unit 28. Only when such a
constraint condition is satisfied, the minimum value of power
cost can be calculated.
[0041]
In this embodiment, even without a large amount of
25 hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
25
software measures. This allows a supply of freshwater lower in
price. In this embodiment, power itself can also be reduced.
This allows a reduction in cost as well as in a volume of
greenhouse gas emission.
5
[0042]
FIG. 6 is a block diagram illustrating a support system
for production schedule planning of desalination process 1
according to a second embodiment of the present invention. The
10 support system for production schedule planning of
desalination process 1 according to this embodiment plans a
production schedule of desalination process of the
desalination plant 6 shown in FIG. 2. In this embodiment,
description of a configuration similar to that in the first
15 embodiment is omitted herefrom, and description of a
configuration different from that in the first embodiment is
made in detail below.
[0043]
The support system for production schedule planning of
20 desalination process 1 according to this embodiment includes:
the salt concentration time change estimation unit 8, the water
temperature time change estimation unit 10, a first storage
unit 11, the water level gauge 9, a second storage unit 13, a
freshwater demand estimation unit 36, the production schedule
25 computation unit 28, and the water desalination schedule
display unit 30. The first storage unit 11 stores therein
26
information on the electricity rate unit price per time zone
16, the freshwater tank maximum capacity 18, and the freshwater
tank minimum capacity 20. The second storage unit 13 stores
therein information on a weather prediction data 32 and a
5 temperature prediction data 34.
[0044]
The production schedule computation unit 28 receives
information on the estimated salt concentration value 12 of raw
water from the salt concentration time change estimation unit
10 8, and information on the estimated water temperature value 14
of the raw water from the water temperature time change
estimation unit 10. The production schedule computation unit
28 also receives information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, and
15 the freshwater tank minimum capacity 20 from the storage unit
11. The water level gauge 9 measures a freshwater volume in the
freshwater tank 4 on a real-time basis and transmits
information on the measured current freshwater volume in
freshwater tank 22 to the production schedule computation unit
20 28. The freshwater demand estimation unit 36 computes the
demand for freshwater 24 based on the information on the weather
prediction data 32 and the temperature prediction data 34. The
freshwater demand estimation unit 36 outputs information on the
computed demand for freshwater 24 to the production schedule
25 computation unit 28.
[0045]
27
In this embodiment, the support system 1 includes two
storage units, namely, the first storage unit 11 and the second
storage unit 13. However, the support system 1 may include one
storage unit (for example, the storage unit 11) . If the support
5 system 1 includes one storage unit, for example, the storage
unit 11, then the storage unit 11 stores therein information
on the electricity rate unit price per time zone 16, the
freshwater tank maximum capacity 18, the freshwater tank
minimum capacity 20, the weather prediction data 32, and the
10 temperature prediction data 34. In this case, the freshwater
demand estimation unit 36 receives the information on the
weather prediction data 32 and the temperature prediction data
34 from the storage unit 11.
[0046]
15 In this embodiment, let volumes of demand for freshwater
[m3/h] at respective hour-by-hour times be as follows:
time 1 : Q2 [1] , time 2 : Q2 [2], time 3 : Q2 [3], ..., and time
24 : Q2[24]
The support system for production schedule planning of
20 desalination process 1 according to this embodiment includes
the freshwater demand estimation unit 36 and can thus compute
the demand for freshwater 24 more accurately. Next is described
a specific method of computing the demand for freshwater 24 by
the freshwater demand estimation unit 36.
25 [0047]
The freshwater 2 obtained in the desalination plant 6 can
28
be used as domestic water, industrial water, or agricultural
water. Of these, usage of the industrial water is greatly
influenced by an operating schedule or an operating rate of a
factory or the like. Meanwhile, usage of the domestic water or
5 the agricultural water is greatly influenced by weather or
temperature. In addition to the above-described, usage of the
domestic water is also influenced by a day of the week and a
specific day such as the New Year holidays. In general, however,
there is more demand for the domestic water when the weather
10 is clear and the temperature is high. By contrast, there is less
demand for the domestic water when it rains and the temperature
is low, which may be called a qualitative tendency. The
qualitative tendency cannot be represented by a physical
formula. The freshwater demand estimation unit 36 thus applies
15 a technique using a multiple correlation formula to compute the
demand for freshwater 24. One example is described next in which
the freshwater demand estimation unit 36 computes the demand
for freshwater 24.
[0048]
20 In computing the demand for freshwater 24, first, the
weather prediction data 32 is quantified. For example,
appropriate numbers are put into different statuses of weather,
such as fair as 4, cloudy as 3, rainy as 2, and snowy as 1. The
demand for freshwater 24 statistically processes and computes
25 coefficient values CI to C3 in the following expression such
that the obtained values are most consistent with previous data
29
on the demand for freshwater 24 as well as information on the
temperature prediction data 34.
Demand for freshwater =C1+C2xweather+C3xtemperature
By using the demand for freshwater 24 computed by the
5 freshwater demand estimation unit 36 as described above, the
freshwater 2 in a volume closer to an actual demand can be
produced. An irregular or idle operation of the desalination
plant 6 can also be reduced. This can result in a further
reduction of power cost.
10 In this embodiment, even without a large amount of
hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
software measures. This allows a supply of freshwater lower in
price. In this embodiment, power itself can also be reduced.
15 This allows a reduction in cost as well as in a volume of
greenhouse gas emission.

[0049]
FIG. 7 is a block diagram illustrating a support system
20 for production schedule planning of desalination process
according to a third embodiment of the present invention. FIG.
8 is a block diagram illustrating a portion of a configuration
of the desalination plant 6. The support system for production
schedule planning of desalination process 1 according to this
25 embodiment plans a production schedule of operating the
desalination plant 6, a portion of which is illustrated in FIG.
30
8. In this embodiment, description of a configuration similar
to that in the first embodiment is omitted herefrom, and
description of a configuration different from that in the first
embodiment is made in detail below.
5 [0050]
As shown in FIG. 8, the desalination plant 6 includes: the
high pressure pump 58 that pumps the taken raw water 62 to the
reverse osmosis membrane device (which may also be referred to
as a reverse osmosis membrane) 60; the reverse osmosis membrane
10 device 60 that produces freshwater from the raw water 62; the
power recovery device 56 that recovers the concentrated
wastewater 72 from the reverse osmosis membrane device 60; the
freshwater tank 4 that stores therein the freshwater 2 obtained
by the reverse osmosis membrane device 60; and a water delivery
15 pump 64 that delivers the freshwater stored in the freshwater
tank 4 to a distribution reservoir 38. The freshwater tank 4
can be used as a buffer in response to a condition changing over
time, such as a salt concentration contained in the raw water
62, a temperature of the raw water 62, and an electricity rate
20 per time zone.
[0051]
If the freshwater 2 is further supplied as domestic water
or agricultural water, the freshwater 2 is in some cases
tentatively pumped to the distribution reservoir 38 using the
25 water delivery pump 64. The distribution reservoir 38 is
typically installed at a high place such that the freshwater
31
2 stored therein is appropriately supplied by just flowing down
by itself. Thus, power for the water delivery pump 64 also
affects operating cost considerably.
[0052]
5 As shown in FIG. 7, the support system for production
schedule planning of desalination process 1 according to this
embodiment includes: the salt concentration time change
estimation unit 8, the water temperature time change estimation
unit 10, the storage unit 11, the water level gauge 9, the
10 production schedule computation unit 28, the water
desalination schedule display unit 30, and a water delivery
schedule display unit 68. The storage unit 11 stores therein
information on the electricity rate unit price per time zone
16, the freshwater tank maximum capacity 18, the freshwater
15 tank minimum capacity 20, the demand for freshwater 24, a
distribution reservoir maximum capacity 40, and a distribution
reservoir minimum capacity 42. The distribution reservoir
maximum capacity 40 is an upper limit of a volume of freshwater
which the distribution reservoir 38 can store therein. The
20 distribution reservoir minimum capacity 42 is a lower limit of
a volume of freshwater of the distribution reservoir 38. A
current freshwater volume in distribution reservoir 44 is a
volume of freshwater currently reserved in the distribution
reservoir 38. The water level gauge 9 measures a volume of
25 freshwater stored in the freshwater tank 4 of the desalination
plant 6 on a real time basis and transmits information on the
32
measured freshwater volume to the production schedule
computation unit 28. The production schedule computation unit
28 receives the information on the freshwater volume stored in
the freshwater tank 4, from the water level gauge 9 on a real
5 time basis.
[0053]
Another water level gauge 19 measures a volume of
freshwater stored in the distribution reservoir 38 on a real
time basis and transmits information on the measured freshwater
10 volume to the production schedule computation unit 28. The
production schedule computation unit 28 receives the
information on the volume of the freshwater stored in the
distribution reservoir 38, from the water level gauge 19 on a
real time basis.
15 The production schedule computation unit 28 receives
information on the estimated salt concentration value 12 of raw
water from the salt concentration time change estimation unit
8, and information on the estimated water temperature value 14
of the raw water from the water temperature time change
20 estimation unit 10. The production schedule computation unit
28 also receives information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, the
freshwater tank minimum capacity 20, the demand for freshwater
24, the distribution reservoir maximum capacity 40, and the
25 distribution reservoir minimum capacity 42, from the storage
unit 11. The production schedule computation unit 28 receives
33
the information on the volume of freshwater stored in the
freshwater tank 4, from the water level gauge 9 on a real time
basis, and information on a volume of freshwater stored in the
distribution reservoir 38, from the water level gauge 19 on a
5 real time basis.
[0054]
The production schedule computation unit 28 computes a
power cost or an operating cost of the desalination plant 6,
based on the above-described information and appropriately
10 determines the water desalination schedule 26 and the water
delivery schedule 66. This embodiment illustrates an example
in which the production schedule computation unit 28 computes
and displays one optimum water desalination schedule 26 in the
water desalination schedule display unit 30 and also computes
15 and displays one optimum water delivery schedule 66 in the water
delivery schedule display unit 68. However, the production
schedule computation unit 28 may compute and display a
plurality of water desalination schedules 26 and a plurality
of water delivery schedules 66 in the water desalination
20 schedule display unit 30 and the water delivery schedule
display unit 68, respectively. If a plurality of the water
desalination schedules 26 and a plurality of the water delivery
schedules 66 are displayed, an operator of the desalination
plant 6 selects any one of the displayed water desalination
25 schedules and any one of the displayed water delivery schedules,
and enters information on the selected water desalination
34
schedule and the selected displayed water delivery schedule
into the support system for production schedule planning of
desalination process 1 via an input device (not shown). The
support system for production schedule planning of
5 desalination process 1 supports production schedule planning
of the desalination plant 6, based on the entered water
desalination schedule and water delivery schedule.
[0055]
The production schedule computation unit 28 computes the
10 water desalination schedule 26 of the desalination plant 6 such
that the desalination plant 6 is operated as little as possible
or as little freshwater as possible is produced at a time when:
the estimated salt concentration value 12 of raw water is high;
the estimated water temperature value 14 of the raw water is
15 low; and the electricity rate unit price per time zone 16 is
high. In terms of the operating cost, the desalination plant
6 is preferably operated based on the water desalination
schedule 26 as described above. On the other hand, the
production schedule computation unit 28 computes the water
20 desalination schedule 26 of the desalination plant 6 such that
the desalination plant 6 is operated as much as possible or as
much freshwater as possible is produced at a time when: the
estimated salt concentration value 12 of raw water is low; the
estimated water temperature value 14 of the raw water is high;
25 and the electricity rate unit price per time zone 16 is low.
In terms of the operating cost, the desalination plant 6 is
35
preferably operated based on the above-described water
desalination schedule 26. From a viewpoint of the water
delivery pump 64, the production schedule computation unit 28
preferably computes the water delivery schedule 66 of the
5 desalination plant 6 such that the water delivery pump 64 pumps
as little water as possible at a time when the electricity rate
per time zone is high and such that the water delivery pump 64
pumps as much water as possible at a time when the electricity
rate per time zone is low. In terms of the operating cost, the
10 desalination plant 6 is preferably operated based on the water
desalination schedule 26 as described above.
[0056]
Nevertheless, if too much freshwater is produced compared
to a volume of delivered water, there is a possibility that the
15 freshwater tank 4 overflows. On the other hand, if too little
freshwater is produced compared to a volume of the delivered'
water, there is a possibility that the freshwater tank 4 becomes
empty. If too much water is delivered compared to the demand
for freshwater 24, there is a possibility that the distribution
20 reservoir 38 overflows. On the other hand, if too little water
is delivered compared to the demand for freshwater 24, there
is a possibility that the distribution reservoir 38 becomes
empty. In this case, the freshwater 2 in response to the demand
for freshwater 24 cannot be supplied, resulting in an
25 unsatisfactory performance of the desalination plant 6.
[0057]
36
The production schedule computation unit 28 thus uses the
distribution reservoir maximum capacity 40 and the
distribution reservoir minimum capacity 42 as constraint
conditions, in addition to the freshwater tank maximum capacity
5 18 and the freshwater tank minimum capacity 20, and plans a
schedule of a volume of freshwater to be produced, setting
initial values to the current freshwater volume in freshwater
tank 22 and the current freshwater volume in distribution
reservoir 44 at a present point of time. Hence, in this
10 embodiment, information on the freshwater tank maximum
capacity 18, the freshwater tank minimum capacity 20, the
current freshwater volume in freshwater tank 22, the
distribution reservoir maximum capacity 40, the distribution
reservoir minimum capacity 42, and the current freshwater
15 volume in distribution reservoir 44 is used in addition to the
information on the estimated salt concentration value 12, the
estimated water temperature value 14, and the electricity rate
unit price per time zone 16, based on which the production
schedule computation unit 28 appropriately computes the water
20 desalination schedule 26 and the water delivery schedule 66.
[0058]
Next is described a specific method of computing the water
desalination schedule 26 and the water delivery schedule 66 by
the production schedule computation unit 28. It is assumed
25 herein that the desalination plant 6 plans hourly volumes of
freshwater to be produced and water to be delivered for the next
37
24 hours once a day. This embodiment exemplifies planning on
an hour to hour basis. However, the planning may be on a 30
minutes, a 10 minutes, or any other different time period basis,
using a similar technique.
5 [0059]
At a time of planning, let volumes of demand for freshwater
Q2 [m3/h] at respective hour-by-hour times, namely, time 1,
time 2, time 3, ..., and time 24, be as follows:
time 1 : Q2 [1] , time 2 : Q2 [2] , time 3 : Q2 [3] , ..., and time
10 24 : Q2[24]
Also, let a freshwater volume in the freshwater tank 4 at
the time of planning be V[0] , and let a set value of a freshwater
volume in the freshwater tank 4 after a lapse of 24 hours from
the planning time be V[24]. V[24] is set to a value equal to
15 V[0] if there is no specific reason. This makes the freshwater
volume in the freshwater tank 4 the same at the time of planning
every day, resulting in an easy management of the planning.
[0060]
Similarly, let a freshwater volume in the distribution
20 reservoir 38 at the time of planning be VR[0], and let a set
value of a freshwater volume in the distribution reservoir 38
after a lapse of 24 hours from the planning time be VR[24].
VR[24] is set to a value equal to VR[0] if there is no specific
reason. This makes the freshwater volumes in the freshwater
25 tank 4 the same at the time of planning every day, resulting
in an easy management of the planning. Thus, this embodiment
38
aims that the production schedule computation unit 28
determines appropriate values of hourly volumes of freshwater
of the desalination plant 6 which are represented by Ql [m3/h]
and are specifically Ql[l], Ql[2] , Ql[3] , ..., and Ql[24], as
5 well as appropriate values of hourly volumes [m3/h] of water
delivered by the water delivery pump 64 which are specifically
QR[1], QR[2], QR[3], ..., andQR[24].
[0061]
Relationship among the above-described demand for
10 freshwater Q2 [m3/h] , the set value V of the freshwater volume
in the freshwater tank 4, the freshwater volume Ql [m3/h] , and
the freshwater volume in the distribution reservoir 38 is
represented by Expression (16), based on a balance of the
freshwater volume.
15 SQ1 [i]-SQ2[i] = (V[24]-V[0] )+(VR[24]-VR[0] ) ...Expression
(16)
Expression (16) is deformed to obtain Expression (17) as
follows:
ZQl[i]=SQ2[i] + (V[24]-V[0]) + (VR[24]-VR[0]) ... Expression
20 (17)
Expression (18) below also holds because of the balance
of the freshwater volume in the freshwater tank 4.
ZQl[i]-EQR[i]=(V[24]-V[0]) ...Expression (18)
Expression (18) is deformed to obtain Expression (19) as
25 follows:
SQR[i]=EQl[i]-(V[24]-V[0] ) ...Expression (19)
39
A value of SQR[i] can be obtained by substituting 2Ql[i]
obtained in Expression (17).
In this embodiment, the production schedule computation
unit 28 sets Ql[i] to a value which satisfies the relationship
5 represented by Expression (17) and sets QR1 [i] to a value which
satisfies the relationship represented by Expression (19) . The
production schedule computation unit 28 computes whether or not
the current freshwater volume in freshwater tank 22 is larger
than a freshwater tank maximum capacity Vmax or is smaller than
10 a freshwater tank minimum capacity Vmin and whether or not the
current freshwater volume in distribution reservoir 44 is
larger than a distribution reservoir maximum capacity VRmax or
is smaller than a distribution reservoir minimum capacity VRmin.
The values of Ql[i] and QRl[i] may be set using, such as, but
15 not limited to, all possible regression, and Monte Carlo method
with a random number. As an example, procedures (a) to (h) of
setting Ql [i] and QRl [i] by the production schedule computation
unit 28 in which the Monte Carlo method is used are shown below:
(a) Calculate a value of
20 EQ2[i] + (V[24]-V[0] ) + (VR[24]-VR[0] ) according to Expression
(17);
(b) Prepare 24 random numbers;
(c) Distribute the value of
SQ2[i]+(V[24]-V[0])+(VR[24]-VR[0]) according to ratios of
25 respective values of the 24 random numbers prepared in (b);
(d) Obtain the distributed value as a value of Ql[i];
40
(e) Calculate a value of SQ1[i]-(V[24]-V[0]) according to
Expression (19);
(f) Prepare 24 random numbers;
(g) Distribute the value of SQ1[i]-(V[24]-V[0]) according
5 to ratios of respective values of the 24 random numbers prepared
in (f); and
(h) Obtain the distributed value as a value of QRl[i].
[0062]
The production schedule computation unit 28 uses Ql [i] and
10 QR[i] set as described above to compute the current freshwater
volume in freshwater tank V[i] and the current freshwater
volume in distribution reservoir VR[i] by the following
expression:
V[1]=V[0]+Q1[1]-QR[1] ...Expression (20)
15 V[2]=V[1]+Q1[2]-QR[2] ...Expression (21)
V[24]=V[23]+Q1[24]-QR[24] ... Expression (22)
VR[1]=VR[0]+QR[1]-Q2[1] ...Expression (23)
VR[2]=VR[1]+QR[2]-Q2[2] ...Expression (24)
20
VR[24]=VR[23]+QR[24]-Q2 [24] ...Expression (25)
The production schedule computation unit 28 compares each
V[i] with the freshwater tank maximum capacity Vmax and also
with the freshwater tank minimum capacity Vmin and also
25 compares each VR[i] with the distribution reservoir maximum
capacity VRmax and also with the distribution reservoir minimum
41
capacity VRmin. If even one of the plural V[i] and VR[i] is
beyond the above-described capacities, the production schedule
computation unit 28 returns the processing to the
above-described procedure (b) and computes V[i] andVR[i] again
5 using another random numbers. On the other hand, if all of V[i]
in the 24 hours are within the range between the freshwater tank
maximum capacity Vmax and the freshwater tank minimum capacity
Vmin, and at the same time, if all of VR[i] in the 24 hours are
within the range between the distribution reservoir maximum
10 capacity VRmax and the distribution reservoir minimum capacity
VRmin, the production schedule computation unit 28 advances the
processing to the next step and calculates hourly power cost
as shown below.
[0063]
15 Operating cost in a case where the reverse osmosis
membrane 60 is used can be calculated with the above-described
Expressions (6) to (14). The production schedule computation
unit 28 can thereby compute a consumed power, Poweronsumption
[kWh] . In this embodiment, it is necessary to add a power
20 consumed at the water delivery pump 64, PowerTransmission [kWh] ,
to the power cost.
PowerTransmission=0 .163x (QR/60) xHead/RatePump ...
Expression (26)
Herein, QR is a volume of delivered water [m3/h] , Head is
25 a head difference at a time of delivering water [m], and
RatePump is a pump efficiency [-].
42
[0064]
Power cost, PowerCost [yen/h], can be then calculated by
multiplying an electricity rate unit price per time zone,
UnitPrice [yen/kWh], by the operating cost plus the power
5 consumed in the water delivery pump 64.
PowerCost=UnitPricex(PowerConsumption+PowerTransmissio
n) ... Expression (27)
Let a value summing up the power cost for 24 hours,
PowerCost [yen/h], be called CostSum [yen]. In a calculation
10 performed for the first time, the production schedule
computation unit 28 stores therein the value of CostSum. In and
after a calculation for the second time, the production
schedule computation unit 28 returns to the procedure (b).
At each time of the calculation of CostSum [yen], if a
15 calculated result is smaller than a previously-calculated
CostSum, the production schedule computation unit 28 replaces
the previously-calculated CostSum by the currently-calculated
smaller CostSum and stores Ql[i] corresponding to the smaller
CostSum. In this example, the Monte Carlo method is used in
20 which a number of the calculations are repeated. As a result,
regardless of whether or not there is a local minimum, an
operating condition with smaller and smaller power cost can be
obtained. Such iterative calculations may be stopped when the
calculations are performed a prescribed total number of
25 repetitive times or when a frequency of replacing CostSum or
a degree of variation of CostSum becomes small.
43
[0065]
The production schedule computation unit 28 transmits the
water desalination schedule 26 computed as described above, to
the water desalination schedule display unit 30 and also
5 transmits the water delivery schedule 66 to the water delivery
schedule display unit 68. Since the water desalination schedule
display unit 30 displays the received water desalination
schedule 26 and the water delivery schedule display unit 68
displays the water delivery schedule 66 to an operator, the
10 operator in planning a production schedule is thereby supported.
An operation in accordance with the water desalination schedule
26 and the water delivery schedule 66 makes it possible to
efficiently operate the desalination plant 6 while keeping an
appropriate range of the freshwater volume in the freshwater
15 tank 4 disposed downstream in the desalination plant 6, between
the freshwater tank maximum capacity 18 and the freshwater tank
minimum capacity 20, and also to minimize the power cost.
[0066]
In this embodiment, even without a large amount of
20 hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
software measures. This allows a supply of freshwater lower in
price. In this embodiment, power itself can also be reduced.
This allows a reduction in cost as well as in a volume of
25 greenhouse gas emission.

44
[0067]
FIG. 9 is a block diagram illustrating a configuration of
a support system for production schedule planning of
desalination process according to a fourth embodiment of the
5 present invention. The support system for production schedule
planning of desalination process 1 according to this embodiment
plans a production schedule of desalination process which is
performed by the desalination plant shown in FIG. 2. In this
embodiment, description of a configuration similar to that in
10 the first embodiment is omitted herefrom, and description of
a configuration different from that in the first embodiment is
made in detail below.
[0068]
As shown in FIG. 9, the support system for production
15 schedule planning of desalination process 1 according to this
embodiment includes the salt concentration time change
estimation unit 8, the water temperature time change estimation
unit 10, the storage unit 11, the water level gauge 9, the
production schedule computation unit 28, and the water
20 desalination schedule display unit 30. The storage unit 11
stores therein information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, the
freshwater tank minimum capacity 20, the demand for freshwater
24, a residual salt concentration tolerance 46, and a
25 freshwater tank salt concentration 70.
[0069]
45
The production schedule computation unit 28 receives
information on the estimated salt concentration value 12 of raw
water from the salt concentration time change estimation unit
8 and receives information on the estimated water temperature
5 value 14 of raw water from the water temperature time change
estimation unit 10. The production schedule computation unit
28 receives the information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, the
freshwater tank minimum capacity 20, the demand for freshwater
10 24, the residual salt concentration tolerance 46, and the
freshwater tank salt concentration 70, from the storage unit
11. The water level gauge 9 measures a volume of freshwater
stored in the freshwater tank 4 of the desalination plant 6 on
a real time basis and transmits the information on the measured
15 freshwater volume to the production schedule computation unit
28.
[0070]
The production schedule computation unit 28 receives the
information on the freshwater volume stored in the freshwater
20 tank 4, from the water level gauge 9 on a real time basis.
[0071]
The production schedule computation unit 28 computes a
power cost or an operating cost of the desalination plant 6,
based on the above-described information and appropriately
25 determines the water desalination schedule 26 and the water
delivery schedule 66. This embodiment illustrates an example
46
in which the production schedule computation unit 28 computes
and displays one optimum water desalination schedule 26 in the
water desalination schedule display unit 30 and also computes
and displays one optimum water delivery schedule 66 in the water
5 delivery schedule display unit 68. However, the production
schedule computation unit 28 may compute and display a
plurality of water desalination schedules 26 and a plurality
of water delivery schedules 66 in the water desalination
schedule display unit 30 and the water delivery schedule
10 display unit 68, respectively. If a plurality of the water
desalination schedules 26 and a plurality of the water delivery
schedules 66 are displayed, an operator of the desalination
plant 6 selects any one of the displayed water desalination
schedules and any one of the displayed water delivery schedules,
15 and enters information on the selected water desalination
schedule and the selected displayed water delivery schedule
into the support system for production schedule planning of
desalination process 1 via an input device thereof (not shown) .
The support system for production schedule planning of
20 desalination process 1 supports production schedule planning
of the desalination plant 6, based on the entered water
desalination schedule and water delivery schedule.
[0072]
The desalination plant 6 has the freshwater tank 4
25 disposed downstream therein. This embodiment is characterized
in that the freshwater tank 4 serves as a buffer in response
47
to a condition changing over time, such as the estimated salt
concentration value 12 of raw water, the estimated water
temperature value 14 of the raw water, the electricity rate unit
price per time zone 16, based on which the production schedule
5 computation unit 28 computes an appropriate production
schedule.
[0073]
The production schedule computation unit 28 computes the
water desalination schedule 26 of the desalination plant 6 such
10 that the desalination plant 6 is operated as little as possible
or as little freshwater as possible is produced at a time when:
the estimated salt concentration value 12 of raw water is high;
the estimated water temperature value 14 of the raw water is
low; and the electricity rate unit price per time zone 16 is
15 high. In terms of operating cost, the desalination plant 6 is
preferably operated based on the water desalination schedule
26 as described above. On the other hand, the production
schedule computation unit 28 computes the water desalination
schedule 26 of the desalination plant 6 such that the
20 desalination plant 6 is operated as much as possible or as much
freshwater as possible is produced at a time when: the estimated
salt concentration value 12 of raw water is low; the estimated
water temperature value 14 of the raw water is high; and the
electricity rate unit price per time zone 16 is low. In terms
25 of operating cost, the desalination plant 6 is preferably
operated based on the water desalination schedule 26 as
48
described above.
[0074]
Nevertheless, if too much freshwater is produced compared
to the demand for freshwater 24, there is a possibility that
5 the freshwater tank 4 overflows. On the other hand, if too
little freshwater is produced compared to the demand for
freshwater 24, there is a possibility that the freshwater tank
4 becomes empty. In this case, the freshwater 2 consistent with
the demand for freshwater 24 cannot be supplied, resulting in
10 an unsatisfactory performance of the desalination plant 6. The
production schedule computation unit 28 thus uses the
freshwater tank maximum capacity 18 and the freshwater tank
minimum capacity 20 as constraint conditions and plans a
schedule of a volume of freshwater to be produced, setting an
15 initial value to the current freshwater volume in freshwater
tank 22 at a present point of time.
[0075]
In the desalination plant 6, a salt concentration
remaining in the freshwater 2 becomes a problem in some cases.
20 In particular, if the salt concentration in the freshwater 2
for use in industrial water or the like is too high, products
or piping may be damaged. In that case, the production schedule
computation unit 28 plans the water desalination schedule 26
also taking into consideration a water quality of the
25 freshwater 2.
[0076]
49
A salt concentration TDS [mol/m3] contained in the
freshwater 2 is influenced by a water quality and a filtration
flux Jv of supplied water.
[0077]
5 TDS=Js/Jv ... Expression (28)
Herein, Js is a solute permeation flux [mol/ (m2,sec) ] and Jv
is a filtration flux [m/sec] . The solute permeation flux Js can
be obtained by Expression (29) as follows:
Js=Psx(Cm-Cp) ... Expression (29)
10 Herein, Ps is a solute permeation coefficient [m/sec], Command
is a salt ion concentration [mol/m3] of a membrane surface, and
Cp is a salt ion concentration [mol/m3] of permeated water.
[0078]
The estimated salt concentration value 12 of the supplied
15 water may be given as the salt ion concentration Cm [mol/m3]
of the membrane surface. Or, actually, a concentration
polarization phenomenon occurs, and thus, an appropriate value
obtained by an elaborate calculation taking concentration
polarization into consideration may be given as the salt ion
20 concentration Cm. Meanwhile, it is contemplated that the salt
ion concentration Cm [mol/m3] of the permeated water is
sufficiently lower than that of the supplied water and that the
concentration polarization is also small. Hence, the salt ion
concentration Cm is considered to be zero. The value of TDS
25 obtained by Expression (29) and Expression (28) is a function
of Jv which is likely to vary every hour. The salt concentration
50
of the freshwater 2 desalinated by the reverse osmosis membrane
60 has a possibility of varying hour by hour. As described above,
the freshwater tank 4 is disposed downstream of the reverse
osmosis membrane 60. The freshwater 2 filtered by the reverse
5 osmosis membrane 60 becomes mixed with the freshwater 2
remaining in the freshwater tank 4. Then, when the mixed
freshwater 2 flows out from an outlet of the freshwater tank
4, the freshwater 2 has an averaged salt concentration.
[0079]
10 Let a salt concentration of the freshwater tank 4 at the
time of planning be called C[0]. Let an hourly salt
concentration in the freshwater 2 filtered by the reverse
osmosis membrane 60 be called TDS[i]. An averaged salt
concentration C[i] in the freshwater tank 4 can be calculated
15 as follows:
C [ 1 ] = ( C [ 0 ] x V [ 0 ] + T D S [ 1 ] x Q l [ 1 ] - C [ 0 ] x Q 2 [ 1 ] ) / ( V [ 0 ] + Q 1 [ 1 ] -Q
2 [ 1 ] ) ... E x p r e s s i o n (30)
C[2] = ( C [ l ] x V [ l ] + T D S [ 2 ] x Q l [ 2 ] - C [ l ] x Q 2 [ 2 ] ) / ( V [ l ] + Q l [ 2 ] -Q
2 [ 2 ] ) ... E x p r e s s i o n (31)
20
C[24] = (C[23]xV[23]+TDS[24]xQl[24]-C[23]xQ2 [24] )/(V[23]
+Q1 [24]-Q2 [24] ) ...Expression (32)
Next is described a specific method of computing the water
desalination schedule 26 by the production schedule
25 computation unit 28. It is assumed herein that the desalination
plant 6 plans an hourly volume of freshwater to be produced for
51
the next 24 hours once a day. This embodiment exemplifies
planning on an hour to hour basis. However, the planning may
be computed on a 30 minutes, a 10 minutes, or any other different
time period basis, using a similar technique.
5 [0080]
At the time of planning, let volumes of demand for
freshwater [m3/h] at respective hour-by-hour times be as
follows:
time 1: Q2[l], time 2: Q2[2], time 3: Q2[3], ..., and time
10 24: Q2[24]
Also, let a freshwater volume in the freshwater tank 4 at
the time of planning be V[0] , and let a set value of a freshwater
volume in the freshwater tank 4 after a lapse of 24 hours be
V[24] . Further, let hourly freshwater volumes [m3/h] be Ql[l],
15 Ql[2] , Ql[3] , ..., and Ql[24]. This embodiment attempts to
determine appropriate values of those described-above.
Relationship among the above-described demand for
freshwater Q2 [m3/h] , the set value V of the freshwater volume
in the freshwater tank 4, and the freshwater volume Ql [m3/h]
20 is represented by Expression (33). £ used herein means a sum
of volumes at time i which is varied from time 1 to time 24.
EQl[i]-EQ2[i]=V[24]-V[0] ...Expression (33)
Expression (33) is deformed to obtain Expression (34) as
below:
25 SQ1 [i]=SQ2 [i]+V[24]-V[0] ...Expression (34)
In this embodiment, the production schedule computation
52
unit 28 sets Ql[i] to a value which satisfies the relationship
represented by Expression (34), and determines, in that case,
whether or not the current freshwater volume in freshwater tank
22 is larger than a freshwater tank maximum capacity Vmax or
5 is smaller than a freshwater tank minimum capacity Vmin and also
whether or not an average salt concentration in the freshwater
tank 4 is higher than a residual salt concentration tolerance
46 TDSmax. The value of Ql[i] may be set with, such as, but not
limited to, all possible regression, and Monte Carlo method
10 using a random number. As an example, procedures (a) to (d) of
setting Ql [i] in which the Monte Carlo method is used are shown
below:
(a) Calculate a value of SQ2[i]+V[24]-V[0] according to
Expression (2);
15 (b) Prepare 24 random numbers;
(c) Distribute the value of £Q2[i]+V[24]-V[0] according
to ratios of respective values of the 24 random numbers prepared
in (b); and
(d) Obtain the distributed value as a value of Ql[i],
20 [0081]
Using Ql[i] set as described above, a freshwater volume
V[i] in the freshwater tank 4 can be calculated by Expression
(35) to Expression (37) as follows:
V[1]=V[0]+Q1[1]-Q2[1] ...Expression (35)
25 V[2]=V[1]+Q1 [2]-Q2[2] ...Expression (36)
53
V[24]=V[23]+Q1[24]-Q2[24] ...Expression (37)
Further, according to Expression (30) to Expression (32) ,
the production schedule computation unit 28 calculates average
salt concentration C[i] in the freshwater tank 4. The
5 production schedule computation unit 28 compares each of V[i]
obtained as described above, to the freshwater tank maximum
capacity Vmax and the freshwater tank minimum capacity Vmin as
well as the TDSmax as the residual salt concentration tolerance
46 in terms of a salt concentration. If any one of V[i] is beyond
10 a range described above, the production schedule computation
unit 28 returns the processing to the procedure (b) and
recalculates V[i] using another random numbers. On the other
hand, if all of 24 V[i] are within the range defined by the
freshwater tank maximum capacity Vmax, the freshwater tank
15 minimum capacity Vmin, and the residual salt concentration
tolerance 4 6, the production schedule computation unit 28
advances the processing to the next step and calculates an
hourly power cost.
[0082]
20 The power cost required for the reverse osmosis membrane
60 can be calculated by the above-described Expression (6) to
Expression (15). Let a value summing up the power cost,
PowerCost [yen/h], for 24 hours be called CostSum [yen]. In a
calculation of CostSum performed for the first time, the
25 production schedule computation unit 28 stores therein the
value of CostSum. In and after the calculation for the second
54
time, the production schedule computation unit 28 returns the
processing to the procedure (b). The production schedule
computation unit 28 then calculates CostSum [yen] each time.
If a calculated result is smaller than a previously-calculated
5 CostSum, the production schedule computation unit 28 replaces
the previously-calculated CostSum by the currently-calculated
smaller CostSum and stores Ql[i] corresponding to the smaller
CostSum. In this example, the Monte Carlo method is used in
which a number of the calculations are repeated. As a result,
10 regardless of whether or not there is a local minimum, an
operating condition with smaller and smaller power cost can be
obtained. Such iterative calculations may be stopped when the
calculations are performed a prescribed total number of
repetitive times or when a frequency of replacing CostSum or
15 a degree of variation of CostSum becomes small.
[0083]
The production schedule computation unit 28 transmits the
information on the water desalination schedule 26 computed as
described above, to the water desalination schedule display
20 unit 30. Since the water desalination schedule display unit 30
displays the received water desalination schedule 26 to an
operator, the operator in planning a production schedule can
be supported. An operation in accordance with the water
desalination schedule 26 makes it possible to efficiently use
25 the desalination plant 6 while satisfying conditions for the
freshwater tank maximum capacity 18 and the freshwater tank
55
minimum capacity 20 of the freshwater tank 4 disposed
downstream in the desalination plant 6 as well as the residual
salt concentration tolerance 46, and also to realize an
operation with the minimum power cost.
5 [0084]
In this embodiment, even without a large amount of
hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
software measures. This allows a supply of freshwater lower in
10 price. In this embodiment, power itself can also be reduced.
This allows a reduction in cost as well as in a volume of
greenhouse gas emission.

[0085]
15 FIG. 10 is a block diagram illustrating a configuration
of a support system for production schedule planning of
desalination process according to a fifth embodiment of the
present invention. The support system for production schedule
planning of desalination process 1 according to this embodiment
20 plans a production schedule of desalination process of the
desalination plant 6 shown in FIG. 2. In this embodiment,
description of a configuration similar to that in the first
embodiment is omitted herefrom, and description of a
configuration different from that in the first embodiment is
25 made in detail below.
[0086]
56
The support system for production schedule planning of
desalination process 1 according to this embodiment includes
the salt concentration time change estimation unit 8, the water
temperature time change estimation unit 10, the first storage
5 unit 11, the water level gauge 9, the second storage unit 15,
a freshwater consumption actual value acquisition unit 48, an
additional freshwater necessary amount calculation unit 54,
the production schedule computation unit 28, and the water
desalination schedule display unit 30. The storage unit 11
10 stores therein information on the electricity rate unit price
per time zone 16, the freshwater tank maximum capacity 18, and
the freshwater tank minimum capacity 20. The storage unit 15
stores therein information on the demand for freshwater 24. In
this embodiment, the support system 1 includes two storage
15 units, namely, the first storage unit 11 and the second storage
unit 13. However, the support system 1 may include one storage
unit (for example, the storage unit 11) . If the support system
1 includes one storage unit, for example, the storage unit 11,
then the storage unit 11 stores therein information on the
20 electricity rate unit price per time zone 16, the freshwater
tank maximum capacity 18, the freshwater tank minimum capacity
20, and the demand for freshwater 24. In this case, the
additional freshwater necessary amount calculation unit 54
receives the information on the demand for freshwater 24 from
25 the storage unit 11.
[0087]
57
The production schedule computation unit 28 receives
information on the estimated salt concentration value 12 of raw
water from the salt concentration time change estimation unit
8 and information on the estimated water temperature value 14
5 of the raw water from the water temperature time change
estimation unit 10. The production schedule computation unit
28 also receives the information on the electricity rate unit
price per time zone 16, the freshwater tank maximum capacity
18, and the freshwater tank minimum capacity 20 from the storage
10 unit 11. The water level gauge 9 measures a volume of freshwater
stored in the freshwater tank 4 of the desalination plant 6 on
a real time basis and transmits information on the measured
freshwater volume to the production schedule computation unit
28. The production schedule computation unit 28 receives the
15 information on the volume of the freshwater stored in the
freshwater tank 4 from the water level gauge 9 on a real time
basis. The additional freshwater necessary amount calculation
unit 54 calculates an additional freshwater necessary amount
52 based on the freshwater consumption actual value 50 and a
20 value of the demand for freshwater 24. The freshwater
consumption actual value 50 is measured by the freshwater
consumption actual value acquisition unit 48. The production
schedule computation unit 28 receives the additional
freshwater necessary amount 52 from the additional freshwater
25 necessary amount calculation unit 54.
[0088]
58
A person in charge of planning a production schedule or
the water desalination schedule 26 of the desalination plant
6 may draw the schedules for the next 24 hours, for example,
first thing in the morning every day. An operation of the
5 desalination plant 6 is then started based on the demand for
freshwater 24 for the next 24 hours estimated early in the
morning. An actual demand for freshwater 24 does not, however,
always match an estimated value. Though such a production
schedule planned early in the morning is optimum at the time
10 of planning, the production schedule may not be optimum along
a lapse of the 24 hours. In a case where a total volume of the
demand for freshwater 24 is not specifically determined, for
example, the demand for freshwater 24 estimated in the morning
of the day may not be the same as the freshwater consumption
15 actual value 50 along the lapse of the 24 hours due to a change
of weather or temperature. In that case, the additional
freshwater necessary amount calculation unit 54 calculates,
before the lapse of the 24 hours, the additional freshwater
necessary amount 52 to be required thereafter compared to the
20 first estimated demand for freshwater 24, based on the
freshwater consumption actual value 50 and gives information
on the additional freshwater necessary amount 52 to the
production schedule computation unit 28. This makes it possible
for the production schedule computation unit 28 to plan the
25 water desalination schedule 26 further corresponding to the
actual demand for freshwater 24.
59
[0089]
One of methods of calculating the additional freshwater
necessary amount 52 is that: a ratio between the demand for
freshwater 24 and the freshwater consumption actual value 50
5 is calculated; the ratio is multiplied by the demand for
freshwater 24 thereafter; and the obtained result is given to
the production schedule computation unit 28 as the additional
freshwater necessary amount 52.
[0090]
10 On the other hand, in a case where the total volume of the
demand for freshwater 24 for the next 24 hours is specifically
determined, the production schedule computation unit 28
performs a calculation in which the freshwater consumption
actual value 50 is subtracted from the total volume to obtain
15 the updated demand for freshwater 24, and the updated demand
for freshwater 24 is appropriately divided by remaining hours.
This makes it possible for the water desalination schedule 26
to plan the more suitable water desalination schedule 26. Also,
an operator can acquire such information using the water
20 desalination schedule display unit 30 and can perform a
suitable operation in line with a change in a demand-side state
of affairs.
[0091]
In this embodiment, even without a large amount of
25 hardware investment such as a highly-efficient pump and a
large-size pump, a power cost can be reduced by means of
60
software measures. This allows a supply of freshwater lower in
price. In this embodiment, power itself can also be reduced.
This allows a reduction in cost as well as in a volume of
greenhouse gas emission.
5 DESCRIPTION OF REFERENCE CHARACTERS
[0092]
1 support system for production schedule planning of
desalination process
2 freshwater
10 4 freshwater tank
6 desalination plant
8 salt concentration time change estimation unit
10 water temperature time change estimation unit
11 storage unit
15 12 estimated salt concentration value
13 storage unit
14 estimated water temperature value
16 electricity rate unit price per time zone
18 freshwater tank maximum capacity
20 20 freshwater tank minimum capacity
22 current freshwater volume in freshwater tank
24 demand for freshwater
26 water desalination schedule
28 production schedule computation unit
25 30 water desalination schedule display unit
32 weather prediction data
61
34 temperature prediction data
36 freshwater demand estimation unit
38 distribution reservoir
40 distribution reservoir maximum capacity
5 42 distribution reservoir minimum capacity
44 current freshwater volume in distribution reservoir
4 6 residual salt concentration tolerance
48 freshwater consumption actual value acquisition unit
50 freshwater consumption actual value
10 52 additional freshwater necessary amount
54 additional freshwater necessary amount calculation unit
56 power recovery device
58 high pressure pump
60 reverse osmosis membrane
15 62 raw water
64 water delivery pump
66 water delivery schedule
68 water delivery schedule display unit
70 freshwater tank salt concentration
20 72 concentrated wastewater
62

WE CLAIM:
1. A support system for production schedule planning of
desalination process for use in a desalination plant which has
5 a freshwater tank serving as a buffer for storing therein
freshwater produced from raw water, comprising:
a salt concentration time change estimation unit that
computes a salt concentration estimated value of the raw water;
a water temperature time change estimation unit that
10 computes a water temperature estimated value of the raw water;
a production schedule computation unit that calculates a
power cost of the desalination plant, based on the salt
concentration estimated value, the water temperature estimated
value, an electricity rate unit price per time zone in an area
15 in which the desalination plant is installed, a freshwater tank
maximum capacity which is an upper limit value of a water volume
stored in the freshwater tank, a freshwater tank minimum
capacity which is a lower limit value of a water volume stored
in the freshwater tank, a current freshwater volume in
20 freshwater tank which is a freshwater volume currently stored
in the freshwater tank, and a demand for freshwater, and thereby
computes a water desalination schedule; and
a water desalination schedule display unit that displays
the computed water desalination schedule.
25
2. The support system for production schedule planning of
63
desalination process according to claim 1, further comprising
a freshwater demand estimation unit that computes the
demand for freshwater based on weather prediction data and
temperature prediction data.
5
3. The support system for production schedule planning of
desalination process according to claim 1 or 2,
wherein the production schedule computation unit
calculates a power cost of the desalination plant, based on a
10 distribution reservoir maximum capacity of a distribution
reservoir connected downstream of the freshwater tank, a
distribution reservoir minimum capacity of the distribution
reservoir, and a current freshwater volume in distribution
reservoir indicating a freshwater volume currently reserved in
15 the distribution reservoir, in addition to the salt
concentration estimated value, the water temperature estimated
value, the electricity rate unit price per time zone, the
current freshwater volume in freshwater tank, and the demand
for freshwater, and thereby computes a water desalination
20 schedule.
4. The support system for production schedule planning of
desalination process according to any one of claims 1 to 3,
wherein the production schedule computation unit
25 calculates a power cost of the desalination plant, based on a
residual salt concentration tolerance in freshwater and a
64
freshwater tank salt concentration, in addition to the salt
concentration estimated value, the water temperature estimated
value, the electricity rate unit price per time zone, the
current freshwater volume in freshwater tank, the demand for
5 freshwater, the freshwater tank maximum capacity, and the
freshwater tank minimum capacity, and thereby computes a water
desalination schedule.
5. The support system for production schedule planning of
10 desalination process according to any one of claims 1 to 4,
further comprising:
a freshwater consumption actual value acquisition unit
that acquires an actual value of freshwater consumption;
an additional freshwater necessary amount calculation
15 unit that calculates an additional freshwater necessary amount
which is an amount of freshwater to be additionally produced,
by subtracting the actual value of freshwater consumption from
a value of the demand for freshwater;
a production schedule computation unit that calculates a
20 power cost of the desalination plant, based on the salt
concentration estimated value, the water temperature estimated
value, the electricity rate unit price per time zone, the
freshwater tank maximum capacity, the freshwater tank minimum
capacity, the current freshwater volume in freshwater tank, and
25 the additional freshwater necessary amount, and thereby
computes a water desalination schedule on a real time basis;
65
and
a water desalination schedule display unit that displays
the computed water desalination schedule.
5 6. A support system for production schedule planning of
desalination process, substantially as herein described with
reference to accompanying drawings and examples.