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Energy recovery pump in reverse osmosis desalination plants
Desdination, 54(1985)117-126
117
Elsevier Science Publishers B.V.,Amsterdam-PrintedinThe Netherlands
ENERGY RECOVERY PUMPS IN REVERSE OSMOSIS DESALINATION PLANTS P. Goubeau, Pompes Guinard, 45, Av. du Pont, De Tasset, 74000 Annecy, France
INTRODUCTION
I.
With the fresh water supply critically low in many places, and with the quality and availability of fresh water decreasing, desalination is a vital solution to this major problem. Of the many desalting processes existing today, reverse osmosis (R/O) is growing fast, and although it is still being developed and improved, it is already a leading method of desalination. The reason for this is that R/O meets two of the most important requirements for desalination: low running cost and low energy consumption. These advantages of reverse osmosis can be further improved by using an energy recovery device. There are several ways of reducing running cost and energy consumption, and the choice of the right one is very important. There is now enough experience in the different aspects of energy recovery to allow comparison of the different systems. The following presentation will include, after a quick review of desalination requirements, a description of the integrated energy recovery pumping system and a comparison of the two major technologieswhich take advantage of the remaining energy of the concentrated brine of the R/O process.
II.
THE REQUIREMENTS OF DESALINATION BY REVERSE OSMOSIS
1) Desalination of sea water Desalination is a vital problem for the user countries. The local activity, whether it is industry or tourism, very often relies on the fresh water supply. Thus, the first priority is to produce fresh water reliably. The second point is that these plants are generally in very remote areas, so maintenance should be as infrequent and as simple as possible. Lastly, the users, except in the Middle East, generally have high energy costs. 2)
Advantages of reverse osmosis vs thermal process:
Lower running costs (especially energy consumption), shorter delivery time and some technical aspects like low temperature, and all the energy being in tha. form of pressure. In reverse osmosis, three main points have to be considered: a) salted water pretreatment: This problem is now well known and many companies have good experience in this matter. Improper pretreatment can
118 shorten the life of the membranes and reduce the quality of the produced fresh water. b) Membranes: There are several different kinds of membranes on the market now, some of which are new, and others which have been in use for a long time. The result of membrane failure is poor fresh water quality and membrane replacement costs. c) The high pressure pumping or energy recovery pumping system: The result of failure is non-production. Thus it is vital for the customers, consultants and contractors to choose the most suitable equipment for the high pressure pumping system. 3)
Requirements for reverse osmosis plant equipment
In the view to save, even to improve the advantages of the reverse osmosis vs thermal processes, all the equipment has to meet the following requirements Producing water "any way": high reliability.
: low maintenance
Low running cost
low energy consumption. Flexibility to adapt to the needs of the users, including winter-summer (intake water temperaturevariations) long term : especially for brackish water because of TDS variation and generally because of modification of the membrane characteristics, Possibility of modification to meet new data (as the pumping equipment is generally designed for a 20 years running time, one can expect that new membranes will be available by this time, and the pumping equipment should meet the new data requirements with as few modifications as possible.) Simple running procedure and regulation. Short deliveries.
REVERSE OSMOSIS DESALINATION
REQUIREMENTS
LOWRUNNING
,
HIGH EFFICIENCY LOW MAINTENANCE
FLEXISILITY
>
HYDRAULIC
DESIGN
LONG RANGE FLEXIBILITY
>
EVOLUTING
DESIGN
RELIABILITY
_ ..___
COST
ANSWERS
*
DESIGN CRITERIA
----.-
119 III. THE ENERGY RECOVERY PUMPING SYSTEMS There are two ways to meet the requirements of the reverse osmosis process: 1) to use standard water or petroleum pumping equipment for this particular application. 2) to design and develop a complete system exactly adapted to this application. Our experience in
standard energy recovery pumping system (we have
been supplying energy recovery equipments for petro-chemical industry for the past 20 years) showed that this standard systems may not be well adapted to all sizes of R/O plants, especially regarding cost, maintenance and flexibility. Then, POMPES GUINARD decided to put its experience in the service of the development of an adapted energy recovery pumping system, known under the name of "TPMDX".
INTEGRATED SYSTEM T?MDX
PUMP + TURBINE
SEPARATED UNITS
THE ENERGY
RECOVERY
PUMPING SYSTEMS
For that POMPES GUINARD used: 1)
Its nuclear experience for safety and reliability
Medium high speed (4000 to 9000 RMP) Oil lubrication systems Type of bearing (tilting pad oil lubrication or hydrostatic bearings). This experience is the result of
25
years
of development and technical impro-
vement, proven by 200 high pressure feed pumps or safety pumps class II running on about 50 nuclear sites and cautioned by the N stamp of the American Society of Mechanical Engineers.
120 2)
Its experience in the petroleum industry and water reinjection environmental conditions.
-
Labyrinth seal instead of mechanical seal
-
Choice of environmental equipment and instrumentation
-
Extra safety equipment (especially for lubrication)
We have 35 years of experience in petrochemical processes and 10 years in hi& pressure water reinjection. 3)
Its experience in'turbine design and regulation to design high
efficiency turbine hydraulics, and about 17 years of industrial applications. 4)
Its experience in sea water pumping for the choice and especially the
utilization /of the right materials and the design (40 years in the Middle East and Latin America including off-shore for reinjection, fire pumps, etc.)
IV. THE
1)
TPMDX
Description:
The TPMDX unit is composed of : -
the turbopump TPMDX,
-
the heat exchanger,
-
the gear increaser,
-
the complete lubrication system,
-
the high speed coupling,
-
the low speed coupling,
-
the set of instrumentation,
-
the common baseplate with or without motor,
-
the coupling guards.
The TPMDX turbopump is composed of.: -
one multistage pump (multi-bladenozzle hydraulics),
-
one multistage turbine (multi-bladenozzle hydraulics),
-
one external forced oil lubricated hydrodynamic thrust bearing,
-
one internal hydrostatic bearing located between the pump side and the turbine side, lubricated by handle water,
- only one low pressure labyrinth seal.
121
FEATURES . HYonoBTmc MARIND -THRUST BEAR116
-BARREL DESIGN - LAEYRINTH SEAL
-SURFACE TREATMENT
TPMDX
2)
- RELIABILITY
Flexibility of the design:
As often, the process duties change with time, or are just different than the one expected, it is important to have an adaptable system (membrane characteristics modifications, salinity or temperature slightly different from the design one...)
122 3)
Flexibility
For example: In MALTA both sea water and highly brackish water plants are equipped with the same TPMDX. (Same pump pressure and capacity). Only the turbine nozzles are different to meet the two different recovery ratios: 35% in sea water and 75% in B.W. plant.
MALTA TPMOX %I FOR S. W. AND B. W.
-e-
)
-
Therefore, the B.W. TPMDX can be retrofitted in a few hours to be installed in the sea water plant. 4)
Long range flexibility
As the pumping equipment has to be designed for a 20 years life, and as it is probable that the basic duties of the R/O process will be modified during the coming years, once again, long range flexibility is an important point. Whether or not there is an energy recovery system, the use of a gear increaser is definitely a great advantage on a long range basis.
x, LONO RMOE FLSXIULITY -UEEO MOOlFlCAT~ -
-
.n.
11.1
-e-
-
123
V.
COMPARISON 1)
BETWEEN
Equipment
SEPARATED
AND INTEGRATED
SOLUTIONS
size
The following
sketch
and energy recovery
shows a space comparison
systems
available
between
the different
pumping
~11 units are shown at
on the market.
the same scale.
‘--THE
ENERGY
RECOVERY PUMPING SYSTEMS SIZE DMPARISON
TRAIN OF
L = 7.6m
2)
Technical
L=S
m
comparison
The main causes of failure -
1 - mechanical
-
2 - bearings,
-
3 - wear rings
are:
seals,
(number of stages).
That is why all these elements comparison
in a turbo machine
of the equipment
have to be carefully
to be selected.
considered
in the technical
124
ENERGY
RECOVERY
PUMPING
-TECHNICAL
BEM'IIGS
fgpis SIWTSEAL
COHPARISONSEPARATED
1,NTEGRATED
FE4Tllm
SYSTEN
TPflDX
PELmNmEEL
mxustw
IlWRNAL
1
4 EXTERNAL
I
1 ~HYJRJSTA.
j
+ CLUTCH +6EARIFANY
I
/
$#ljljApDS 1LARYRINTH
I
RALLORSLEEVE
I
4 IEcpALs
2ILc. SEALS
6ullDPACK.
!?%#htis 1
pRSTA6ES
MI,& 3
I
w19: : ] ‘; ,:,,,
TURBINE
4
TO
6
WHEEL
The size and quantity of peripheral equipment (such as.electrical equipment, valves, control...) are two main factors in the cost of a plant. Therefore, such points also have to be included in the cost comparison before making a decision on the equipment to be chosen.
ENERGY
RECOVERY -TECHNICAL
FEAlluE
PUNPING
SEPARATED
INTEGRATED
PRTCNMEEL
REVERSEPlm
TPMDX KW
SYSTEM
CORPARISON-
MGD
KW
M6D
INSTALLED POWER
MAX. 1 SIZINO IS/ID CDNTROL VALVE
STARTIM
1:35 6.5
(268)
BY PASS 20 X TUR.CAP
DIRECT OPEN VALVE
':Z5
a
‘:Yi
10 (450)
10 (450)
&‘p”
TuR,
CAP
CLOSED OPEWINS
~&,p~&LATIDN
VALVE SEOUEMCE
+
125
3)
Efficiency
It is clear that a Pelton running -
pump, whether
1 - The range of high efficiency
the one of a Pelton -
turbine has a greater
2 - The maximum
reverse
efficiency
or not it is of the integral of a reverse
than a reverse
type, for two reasons:
running
pump is smaller
than
turbine. efficiency
of a Pelton
turbine
is higher
than the one of a
running pump.
Nevertheless: -
the difference
in efficiency
decreases
-
the difference
in efficiency
only affects
energy.
For example,
input power, using than the reverse
with increased
capacity.
the turbine recovered
part of the
if a turbine gives a power saving of about 40% of the
a Pelton wheel turbine with an efficiency
running
pump will give an overall
of 3 points higher
saving of about 1% of the
input power. Such a gain is neglegible or choosing
the best control
compared
to the one made by avoiding
maintenance,
system.
.
REVERSE RUNNING PUMP TURBINEB
TURBINE
Efficiency
range from
EFFICIENCY
Efficiency
range from
84 to 86% at design
75 to 85% at design
point.
point.
126 4)
Range of regulation
of turbines
REVERSE RUNNING PUMP TURBINE
PELTON WHEEL TURBINE
razi
RISK OF CAVITATION RANGE
Good adaptability
VI.
OF REGULATION
to capacity
OF TURBINES
Good adaptability
variations
but not to pressure
and pressure
variation,
which affects
technical
efficiency
and
length of life.
RANGE OF APPLICATION It is obvious
decision
It appears
versus
variation
sensibility,
with low but affecting
in both cases.
SYSTEMS
that the size of the needed
equipment
is a major point in the
to choose for the high pressure
pumping
items.
today that 3 ranges of capacities
systems;
solutions
efficiency
OF THE DIFFERENT
of the type of equipment
energy recovery
pumping
both
to both capacity
the following
diagram
define
3 types of high pressure
shows the relative
the range of capacities
interest
they can be applied
to.
TRAIN FRESH WATER PRODUCTION
RELATIVE INTEREST OF DIFFERENT SYSTEMS FOR ENERGY RECOVERY
of the three
117
Elsevier Science Publishers B.V.,Amsterdam-PrintedinThe Netherlands
ENERGY RECOVERY PUMPS IN REVERSE OSMOSIS DESALINATION PLANTS P. Goubeau, Pompes Guinard, 45, Av. du Pont, De Tasset, 74000 Annecy, France
INTRODUCTION
I.
With the fresh water supply critically low in many places, and with the quality and availability of fresh water decreasing, desalination is a vital solution to this major problem. Of the many desalting processes existing today, reverse osmosis (R/O) is growing fast, and although it is still being developed and improved, it is already a leading method of desalination. The reason for this is that R/O meets two of the most important requirements for desalination: low running cost and low energy consumption. These advantages of reverse osmosis can be further improved by using an energy recovery device. There are several ways of reducing running cost and energy consumption, and the choice of the right one is very important. There is now enough experience in the different aspects of energy recovery to allow comparison of the different systems. The following presentation will include, after a quick review of desalination requirements, a description of the integrated energy recovery pumping system and a comparison of the two major technologieswhich take advantage of the remaining energy of the concentrated brine of the R/O process.
II.
THE REQUIREMENTS OF DESALINATION BY REVERSE OSMOSIS
1) Desalination of sea water Desalination is a vital problem for the user countries. The local activity, whether it is industry or tourism, very often relies on the fresh water supply. Thus, the first priority is to produce fresh water reliably. The second point is that these plants are generally in very remote areas, so maintenance should be as infrequent and as simple as possible. Lastly, the users, except in the Middle East, generally have high energy costs. 2)
Advantages of reverse osmosis vs thermal process:
Lower running costs (especially energy consumption), shorter delivery time and some technical aspects like low temperature, and all the energy being in tha. form of pressure. In reverse osmosis, three main points have to be considered: a) salted water pretreatment: This problem is now well known and many companies have good experience in this matter. Improper pretreatment can
118 shorten the life of the membranes and reduce the quality of the produced fresh water. b) Membranes: There are several different kinds of membranes on the market now, some of which are new, and others which have been in use for a long time. The result of membrane failure is poor fresh water quality and membrane replacement costs. c) The high pressure pumping or energy recovery pumping system: The result of failure is non-production. Thus it is vital for the customers, consultants and contractors to choose the most suitable equipment for the high pressure pumping system. 3)
Requirements for reverse osmosis plant equipment
In the view to save, even to improve the advantages of the reverse osmosis vs thermal processes, all the equipment has to meet the following requirements Producing water "any way": high reliability.
: low maintenance
Low running cost
low energy consumption. Flexibility to adapt to the needs of the users, including winter-summer (intake water temperaturevariations) long term : especially for brackish water because of TDS variation and generally because of modification of the membrane characteristics, Possibility of modification to meet new data (as the pumping equipment is generally designed for a 20 years running time, one can expect that new membranes will be available by this time, and the pumping equipment should meet the new data requirements with as few modifications as possible.) Simple running procedure and regulation. Short deliveries.
REVERSE OSMOSIS DESALINATION
REQUIREMENTS
LOWRUNNING
,
HIGH EFFICIENCY LOW MAINTENANCE
FLEXISILITY
>
HYDRAULIC
DESIGN
LONG RANGE FLEXIBILITY
>
EVOLUTING
DESIGN
RELIABILITY
_ ..___
COST
ANSWERS
*
DESIGN CRITERIA
----.-
119 III. THE ENERGY RECOVERY PUMPING SYSTEMS There are two ways to meet the requirements of the reverse osmosis process: 1) to use standard water or petroleum pumping equipment for this particular application. 2) to design and develop a complete system exactly adapted to this application. Our experience in
standard energy recovery pumping system (we have
been supplying energy recovery equipments for petro-chemical industry for the past 20 years) showed that this standard systems may not be well adapted to all sizes of R/O plants, especially regarding cost, maintenance and flexibility. Then, POMPES GUINARD decided to put its experience in the service of the development of an adapted energy recovery pumping system, known under the name of "TPMDX".
INTEGRATED SYSTEM T?MDX
PUMP + TURBINE
SEPARATED UNITS
THE ENERGY
RECOVERY
PUMPING SYSTEMS
For that POMPES GUINARD used: 1)
Its nuclear experience for safety and reliability
Medium high speed (4000 to 9000 RMP) Oil lubrication systems Type of bearing (tilting pad oil lubrication or hydrostatic bearings). This experience is the result of
25
years
of development and technical impro-
vement, proven by 200 high pressure feed pumps or safety pumps class II running on about 50 nuclear sites and cautioned by the N stamp of the American Society of Mechanical Engineers.
120 2)
Its experience in the petroleum industry and water reinjection environmental conditions.
-
Labyrinth seal instead of mechanical seal
-
Choice of environmental equipment and instrumentation
-
Extra safety equipment (especially for lubrication)
We have 35 years of experience in petrochemical processes and 10 years in hi& pressure water reinjection. 3)
Its experience in'turbine design and regulation to design high
efficiency turbine hydraulics, and about 17 years of industrial applications. 4)
Its experience in sea water pumping for the choice and especially the
utilization /of the right materials and the design (40 years in the Middle East and Latin America including off-shore for reinjection, fire pumps, etc.)
IV. THE
1)
TPMDX
Description:
The TPMDX unit is composed of : -
the turbopump TPMDX,
-
the heat exchanger,
-
the gear increaser,
-
the complete lubrication system,
-
the high speed coupling,
-
the low speed coupling,
-
the set of instrumentation,
-
the common baseplate with or without motor,
-
the coupling guards.
The TPMDX turbopump is composed of.: -
one multistage pump (multi-bladenozzle hydraulics),
-
one multistage turbine (multi-bladenozzle hydraulics),
-
one external forced oil lubricated hydrodynamic thrust bearing,
-
one internal hydrostatic bearing located between the pump side and the turbine side, lubricated by handle water,
- only one low pressure labyrinth seal.
121
FEATURES . HYonoBTmc MARIND -THRUST BEAR116
-BARREL DESIGN - LAEYRINTH SEAL
-SURFACE TREATMENT
TPMDX
2)
- RELIABILITY
Flexibility of the design:
As often, the process duties change with time, or are just different than the one expected, it is important to have an adaptable system (membrane characteristics modifications, salinity or temperature slightly different from the design one...)
122 3)
Flexibility
For example: In MALTA both sea water and highly brackish water plants are equipped with the same TPMDX. (Same pump pressure and capacity). Only the turbine nozzles are different to meet the two different recovery ratios: 35% in sea water and 75% in B.W. plant.
MALTA TPMOX %I FOR S. W. AND B. W.
-e-
)
-
Therefore, the B.W. TPMDX can be retrofitted in a few hours to be installed in the sea water plant. 4)
Long range flexibility
As the pumping equipment has to be designed for a 20 years life, and as it is probable that the basic duties of the R/O process will be modified during the coming years, once again, long range flexibility is an important point. Whether or not there is an energy recovery system, the use of a gear increaser is definitely a great advantage on a long range basis.
x, LONO RMOE FLSXIULITY -UEEO MOOlFlCAT~ -
-
.n.
11.1
-e-
-
123
V.
COMPARISON 1)
BETWEEN
Equipment
SEPARATED
AND INTEGRATED
SOLUTIONS
size
The following
sketch
and energy recovery
shows a space comparison
systems
available
between
the different
pumping
~11 units are shown at
on the market.
the same scale.
‘--THE
ENERGY
RECOVERY PUMPING SYSTEMS SIZE DMPARISON
TRAIN OF
L = 7.6m
2)
Technical
L=S
m
comparison
The main causes of failure -
1 - mechanical
-
2 - bearings,
-
3 - wear rings
are:
seals,
(number of stages).
That is why all these elements comparison
in a turbo machine
of the equipment
have to be carefully
to be selected.
considered
in the technical
124
ENERGY
RECOVERY
PUMPING
-TECHNICAL
BEM'IIGS
fgpis SIWTSEAL
COHPARISONSEPARATED
1,NTEGRATED
FE4Tllm
SYSTEN
TPflDX
PELmNmEEL
mxustw
IlWRNAL
1
4 EXTERNAL
I
1 ~HYJRJSTA.
j
+ CLUTCH +6EARIFANY
I
/
$#ljljApDS 1LARYRINTH
I
RALLORSLEEVE
I
4 IEcpALs
2ILc. SEALS
6ullDPACK.
!?%#htis 1
pRSTA6ES
MI,& 3
I
w19: : ] ‘; ,:,,,
TURBINE
4
TO
6
WHEEL
The size and quantity of peripheral equipment (such as.electrical equipment, valves, control...) are two main factors in the cost of a plant. Therefore, such points also have to be included in the cost comparison before making a decision on the equipment to be chosen.
ENERGY
RECOVERY -TECHNICAL
FEAlluE
PUNPING
SEPARATED
INTEGRATED
PRTCNMEEL
REVERSEPlm
TPMDX KW
SYSTEM
CORPARISON-
MGD
KW
M6D
INSTALLED POWER
MAX. 1 SIZINO IS/ID CDNTROL VALVE
STARTIM
1:35 6.5
(268)
BY PASS 20 X TUR.CAP
DIRECT OPEN VALVE
':Z5
a
‘:Yi
10 (450)
10 (450)
&‘p”
TuR,
CAP
CLOSED OPEWINS
~&,p~&LATIDN
VALVE SEOUEMCE
+
125
3)
Efficiency
It is clear that a Pelton running -
pump, whether
1 - The range of high efficiency
the one of a Pelton -
turbine has a greater
2 - The maximum
reverse
efficiency
or not it is of the integral of a reverse
than a reverse
type, for two reasons:
running
pump is smaller
than
turbine. efficiency
of a Pelton
turbine
is higher
than the one of a
running pump.
Nevertheless: -
the difference
in efficiency
decreases
-
the difference
in efficiency
only affects
energy.
For example,
input power, using than the reverse
with increased
capacity.
the turbine recovered
part of the
if a turbine gives a power saving of about 40% of the
a Pelton wheel turbine with an efficiency
running
pump will give an overall
of 3 points higher
saving of about 1% of the
input power. Such a gain is neglegible or choosing
the best control
compared
to the one made by avoiding
maintenance,
system.
.
REVERSE RUNNING PUMP TURBINEB
TURBINE
Efficiency
range from
EFFICIENCY
Efficiency
range from
84 to 86% at design
75 to 85% at design
point.
point.
126 4)
Range of regulation
of turbines
REVERSE RUNNING PUMP TURBINE
PELTON WHEEL TURBINE
razi
RISK OF CAVITATION RANGE
Good adaptability
VI.
OF REGULATION
to capacity
OF TURBINES
Good adaptability
variations
but not to pressure
and pressure
variation,
which affects
technical
efficiency
and
length of life.
RANGE OF APPLICATION It is obvious
decision
It appears
versus
variation
sensibility,
with low but affecting
in both cases.
SYSTEMS
that the size of the needed
equipment
is a major point in the
to choose for the high pressure
pumping
items.
today that 3 ranges of capacities
systems;
solutions
efficiency
OF THE DIFFERENT
of the type of equipment
energy recovery
pumping
both
to both capacity
the following
diagram
define
3 types of high pressure
shows the relative
the range of capacities
interest
they can be applied
to.
TRAIN FRESH WATER PRODUCTION
RELATIVE INTEREST OF DIFFERENT SYSTEMS FOR ENERGY RECOVERY
of the three