US 12,390,768 B2 · Bimodal reverse osmosis and pressure retarded osmosis framework

Abstract

A method of operating a dual reverse osmosis/pressure retarded osmosis plant, including when electricity costs less than a first predetermined price, moderate salinity water is pumped into the first portion of a pressure vessel having first and second portions separated by a water permeable/salt impermeable osmotic membrane to yield desalinated permeate in the second portion and brine in the first portion. Further, when electricity costs greater than the first predetermined price, low salinity water is pumped into the second portion and brine is pumped into the first portion to yield pressurized moderate salinity water in the second portion which is run through an energy recovery device to generate electricity. The salinity of the low salinity water is lower than the salinity of the moderate salinity water, and the salinity of the moderate salinity water is lower than the salinity of the brine.

A method of operating a dual reverse osmosis/pressure retarded osmosis plant, comprising:

a) when electricity costs less than a first predetermined price, moderate salinity water is pumped into the first portion of a pressure vessel having first and second portions separated by a water permeable/salt impermeable osmotic membrane positioned in a membrane module to yield desalinated permeate in the second portion and brine in the first portion;
and
b) when electricity costs greater than the first predetermined price, low salinity water is pumped into the second portion and brine is pumped into the first portion to yield pressurized moderate salinity water in the second portion which is run through an energy recovery device to generate electricity;
and
c) flushing all pipes and vessels when switching between steps a and b;
wherein steps a and b are controlled by a microprocessor and occur automatically;
wherein step a is defined as RO mode and step b is defined as PRO mode;
wherein flux across the water permeable/salt impermeable osmotic membrane is automatically calculated using
J
w
≈
A
⁡
(
Δ
⁢
π
-
Δ
⁢
P
)
=
A
⁡
(
π
f
⁢
e
-
J
w
⁢
s
D
-
π
p
⁢
e
J
⁢
w
k
1
+
B
J
⁢
w
[
e
J
w
⁢
s
D
-
e
J
⁢
w
k
]
-
ΔP
)
;
wherein Jw is the flux of water across the membrane, A is the membrane permeability to water, Δπ is the osmotic pressure difference, and ΔP is the hydraulic pressure difference across the membrane, S is the membrane support layer structural parameter, k is the mass transfer coefficient in the membrane module, B is the membrane permeability to salts, and D is the diffusivity of salt in water;
wherein power density W* of step a is automatically calculated using
W*=JwΔP;
wherein exergetic efficiency ηII is automatically calculated as a function of the process net work Wnet and the respective process least work Wleast using
η
II
,
RO
=
W
l
⁢
e
⁢
a
⁢
s
⁢
t
W
net
,
RO
;
wherein exergetic efficiency ηII is automatically calculated as a function of the process net work Wnet and the respective process least work Wmax using
η
II
,
PRO
=
W
net
,
RO
W
max
;
wherein least work of reverse osmosis Wleast is defined as the minimum energy of separation using
W
least
=
m
p
[
(
g
p
-
g
b
)
-
1
r
⁢
(
g
f
-
g
b
)
]
;
wherein m represents the mass flow rate, the recovery ratio is represented by a ratio of permeate to feed flow rates
r
=
m
p
m
f
,
and g is the Gibbs free energy of the respective solution;
wherein PRO mode operates at the max power density of 0.5Δπ and RO mode operates at a pressure associated with a standard recovery of r=0.5;
wherein net work is automatically calculated as a summation of the input and output work using
W
n
⁢
e
⁢
t
=
V
f
⁢
Δ
⁢
P
HPP
η
HPP
+
η
ERD
⁢
V
b
⁢
Δ
⁢
P
ERD
;
wherein Vis the volumetric flow rate and subscripts b, HPP, and ERD represent the brine in RO mode and outlet concentrate in PRO mode, high pressure pump, and energy recovery device, respectively;
wherein
Wmax,PRO=−Wleast,RO;
wherein relative economic profit of each respective mode is automatically calculated for a given combination of system operational inputs as costs and economic inputs (price of pure water and price of electricity) as revenue using
R
R
⁢
O
,
n
⁢
e
⁢
t
=
(
C
p
⁢
m
p
+
C
b
⁢
m
b
)
-
(
W
l
⁢
e
⁢
a
⁢
s
⁢
t
η
II
,
RO
⁢
C
e
+
C
f
⁢
m
f
)
;
and
RPRO,net=(WmaxηIICe+Cfmf)−(Cpmp+Cbmb);
where R and C represent the net revenue and cost or selling price associated with the respective water or electricity source, respectively;
wherein a peak price ratio PPRe is defined as the ratio between the sale price of electricity for producers and the baseload cost of electricity for consumers where the economic surplus from RO and PRO are equal and accounts for any additional incentives for producing electricity during peak hours, where the PPRe is automatically calculated using
P
⁢
P
⁢
R
e
=
1
W
max
⁢
η
II
⁢
C
e
[
R
R
⁢
O
,
n
⁢
e
⁢
t
+
(
C
p
⁢
m
p
+
C
b
⁢
m
b
-
C
f
⁢
m
f
)
]
;
wherein the dual reverse osmosis/pressure retarded osmosis plant operates in RO when hydraulic pressure is sufficiently high to force pure water across the water permeable/salt impermeable osmotic membrane;
wherein the dual reverse osmosis/pressure retarded osmosis plant operates in PRO when hydraulic pressure is be half the osmotic pressure;
wherein the salinity of the low salinity water is lower than the salinity of the moderate salinity water;
and
wherein the salinity of the moderate salinity water is lower than the salinity of the brine.

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Bimodal reverse osmosis and pressure retarded osmosis framework

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Bimodal reverse osmosis and pressure retarded osmosis framework

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Abstract

Claims3