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PCS — Preussag Conversion System® mobile floating seawater desalination plant
DESALINATION Desalination 114 (1997) 145-151
ELSEVIER
PCS - Preussag Conversion System ® Mobile floating seawater desalination plant Harald Lampe a, Thomas Altmann a*, Hans J. Giitjens b aSalzgitter Anlagenbau GmbH, Eisenhi~ttenstrasse 99, D-38239 Salzgitter, Germany Tel. +49 (5341) 214776; +49 (5341) 214565; E-mail: [email protected]; [email protected] bHowaldtsw erke-Deutsche Werft A G, D-24143 Kiel, Germany Received 5 November 1997; accepted 12 November 1997
Abstract
The PCS-Preussag Conversion System® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions. In the present design example, a standardized Preussag seawater desalination plant using reverse osmosis technology is preferably installed on a converted single shell oil tanker because this outdated tanker design concept will eventual~ be outlawed due to its potential ecological hazard in case of emergency. The PCSPreussag Conversion System~can offer a useful and economic alternative to conventional land-based desalination plants for a number of applications. Keywords: Seawater desalination plant; Shipbased; Mobil floating; Reverse osmosis process
1. I n t r o d u c t i o n
Frequently a sufficient potable water supply in arid coastal regions can only be ensured by operating seawater desalination plants. If consumers of potable water in such regions are located far away from each other, either many small or few large land-based seawater desalination plants with correspondingly extensive distribution networks are needed, both of which require large investments.
For these and other applications, a mobile floating seawater desalination plant installed on a ship can offer a useful and economic alternative to conventional land-based plants. The mobile seawater desalination plant can serve one or several consumers. The potable water produced on the ship is pumped into storage tanks on the coast via pipelines and is then pumped into the distribution networks supplying the potable water to the consumers.
*Corresponding author. 0011-9164/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S 0 0 1 1 - 9 1 6 4 ( 9 8 ) 0 0 0 0 6 - X
146
11. Lampe et al. / Desalination 114 (1997) 145-151
2. P C S - P r e u s s a g c o n v e r s i o n s y s t e m ®
The PCS - Preussag Conversion System ® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions and has resulted from a joint development by the Preussag companies Salzgitter Anlagenbau G m b H , Preussag Noell Wassertechnik G m b H and Howaldtswerke-Deutsche Werfi AG, an international shipbuilding company. The name Preussag Conversion System (PCS) represents b o t h the conversion o f seawater into potable water and the conversion o f a formerly conventional ship into a mobile floating seawater desalination plant. T h e ship can be equipped with optional seawater desalination technologies, e.g., reverse osmosis (RO), multi-stage flash evaporation (MSF), multi-effective distillation (MED) or mechanical vapour compression distillation (MVC). The size o f the ship will depend on the intended service concept o f the system in each specific application and on the desired production capacity o f the seawater desalination plant (Fig. 1; Tables 1-3).
Table 1 Possible applications of a mobile floating seawater desalination plant Potable water supply for arid coastal regions: • • • • • • • •
for islands for coastal places located far away from each other along a shoreline for remote communities without a well-developed infrastructure in case of limited land resources in case of adverse coast conditions in case of seasonal fluctuations in supply and demand of potable water temporarily, in case of trouble or maintenance of land-based seawater desalination plants temporarily, to supply large construction sites located near the coast
Table 2 Advantages ofPCS ® as compared to land-based seawater desalination plants • • • • • • •
Lower investment cost Lower water production costs Shorter delivery times Flexible and variable applications Saving of land resources High quality of workmanship Simplified Authority Engineering, Authorities Approval Procedures and customs advantages
Table 3 Reasons for the feasibility ofPCS ® • • • • Fig. 1. PCS - Preussag Conversion System®.
Saving of many smaller land-based plants involving site mobilization and civil work, e.g., foundations, buildings, roads, seawater intake structures. Conversion, assembly, commissioning and performance tests take place in a shipyard. Utilization of space and infrastructure already available on the ship, e.g., accommodation, offices, workshops, power generation, air conditioning, etc. Turnkey delivery of the complete system to the respective service area.
H. Lampe et al. / Desalination 114 (1997) 145-151
3. P C S ® design
In the present design example, a standardized Preussag seawater desalination plant using RO technology is preferably installed on a converted single shell oil tanker (Fig. 2). This outdated tanker design concept will eventually be outlawed due to its potential ecological hazard in case of emergencies. In cooperation with Howaldtswerke- Deutsche Werfl AG the required rebuilding measures were defined, considering the ship-building aspects and
Fig. 2. Single shell oil tanker, dead weight 140,000 tons.
147
the cost situation. RO technology was selected because it offers the following benefits as compared to thermal processes: • lower investment cost and operating costs • less space requirement • needs only electric energy, no heating steam The rebuilding work required on the oil tanker and the assembly of the seawater desalination plant are entirely performed in a shipyard. The former central oil tanks are cleaned and lined with a protective painting. The product water is
148
H. Lampe et al. /Desalination 114 (1997) 145-151
0
0
0
O
Fig. 3. Layout ofPCS - Preussag Conversion System®. 1 seawater intake; 2 chemical storage, preparation, dosing; 3 dual media filter; 4 fine filter; 5 reverse osmosis units; 6 permeate storage; 7 product water passivation; 8 potable water storage tanks; 9 backwash system; 10 control room; 11 motor control center; 12 chemical cleaning system; 13 main engine; 14 power generation compartment; 15 deckhouse with accommodation and mess; 16 navigator bridge. stored in four of the five tanks with a capacity of 18,000 m 3 each. The tank located at the bow will contain the seawater intake including screening and pumping facilities as well as the chemicals storage including preparation and dosing units. The RO plant comprising pretreatment facilities, RO units and post-treatment section is installed on the ship's deck and partly accommodated in a hall. The ship's superstructure contains accommodation, mess, sanitary and galley facilities, offices, workshops, a navigator bridge, etc. (Fig. 3; Tables 4 and 5). After commissioning and performance tests are finished in the shipyard, the complete system is delivered turnkey to the respective service area. Generation o f electric energy on board the ship: On board the ship, there are three diesel generators o f 8 0 0 k W each which generate the electric power for the normal ship service. The electric power o f approximately 16 M W required for operating the seawater desalination plant is provided by an additional generator located in the engine room and driven by the ship's main engine (Fig. 4).
Table 4 Technical characteristics of ship Length, m Breadth, m Depth, m Draught, m Deadweight, t Cargo capacity, m3 Main engine output, MW Service speed, kn
265 45 24 7-13 140,000 162,000 16.5 15
Table 5 Technical characteristics of seawater desalination plants Technology Plant capacity, m3/d Water type Salt content, ppm Power consumption, kWh/m3
Reverse osmosis process 50,000 Potable < 500 7
H. Lampe et al. / Desalination I14 (1997) 145-151
149
/ ......~Y
:
g t K K ~1
BI~S~L G E I ~ R ~ T O 2 3 X 000KW DECK4
F~,OOR INNE~T~
0
S
Fig. 4. Generation of electric energy on board the ship.
I0
A step-up gear will be installed between the main engine and the power generator in order to obtain the required synchronous speed. An additional tooth coupling allows to disconnect the propeller from the main engine while the generator works. This configuration offers the alternatives to use the main engine either as the ship's drive unit or, if the ship lies at anchor, for power generation for the seawater desalination plant. The option of operating the seawater desali-nation plant while the ship moves, e.g., from one place of service to another, is basically possible if a power generator with a dedicated drive engine is installed.
4. Seawater desalination osmosis process
by
the
reverse
The RO process includes the following three main stages: pretreatment, reverse osmosis, and post-treatment (Fig. 5).
4.1. Pretreatment
The seawater is taken in through sea chests at the bow of the ship and passes through a specially designed metal screen. The seawater supply pumps elevate the pressure of the seawater sufficiently to pass it through the pretreatment process. Here the suspended solids, which cause fouling of the RO membranes, are removed by inline coagulation and filtration. A coagulant is added to the acidified seawater, effectively mixing, and then immediately passing through a dual-media filter to remove the microflocs which have formed. Polyelectrolytes can be used in addition to coagulants to support the formation of stable, filterable flocs. A disinfectant is injected into the seawater to prevent microbiological activities in the pipes and filters. Acid is required to prevent carbonate scaling on the RO membranes and is also added upstream of the dual-media filter. The dual-media filters have to be regularly backwashed with filtrate or brine and scour air from the bottom to the top, the effluent being discharged into the sea.
150
H. Lampe et al. / Desalination 114 (1997) 145-151 STATICMtX£R
I
POLYE~.ECTROLYTE
DUMP
RECOVEI~
.......
D|SIN~E'CTANT CL~.ANINIG PUMP
CLEANING *rANK
MIXER : PIdMP
Fig. 5. Reverse osmosis process. The filtrate is polished by means of fine filters for the final protection of the RO membranes from suspended particles. A dechlorination agent is injected into the feed water stream to eliminate the residual disinfectant.
4.2. R e v e r s e osmosis
The feed water is pumped through the membranes with sufficient pressure, 35-45% of the feed water being converted into permeate and
H. Lampe et al. / Desalination 114 (1997) 145-151
the concentrate being passed through an energy recovery turbine and then partially transferred to the backwash tank and mainly discharged overboard. By passing the concentrate through the energy recovery turbine, the consumption of electric energy is cut by 35%. Chemical cleaning of the RO membranes will be performed regularly in order to reestablish the initial plant performance. 4.3. Post-treatment
Disinfectant and lime are added downstream of the permeate tank for disinfection, pH adjustment and passivation. After lime and disinfectant have been added, the permeate becomes potable water.
5. Conclusions
The PCS - Preussag Conversion System® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions. The ship can be equipped with optional seawater desalination technologies. The size of the ship will depend on the intended service concept of
151
the system in each specific application and on the desired production capacity of the seawater desalination plant. In the present design example, a standardized Preussag seawater desalination plant using RO technology is preferably installed on a converted single shell oil tanker because this outdated tanker design concept will eventually be outlawed due to its potential ecological hazard in case of emergencies. The PCS - Preussag Conversion System® can offer a useful and economic alternative to conventional land-based desalination plants for a number of applications.
References
[1] M. Fadel, K. Wangnick and N.M. Wade, Desalination, 45 (1983) 49. [2] K. Wangnick, Floating sea-water desalination plants--An economical alternative for providing drinking water in arid regions. Meerestechnik, No. 2, 1982. [3] G.F. Tusel, B. Ohlemann, D.K. Emmermann and I. Kamal, Desalination, 38 (1981) 147. [4] J.B. Rossiter, Mar. Eng. Rev., 82 (1982) 14. [5] V.I. Vasjukov, M.D. Klyikov, V.Yu. Podbereznyi and V.In. Shipilov, Desalination, 89 (1992) 21.
ELSEVIER
PCS - Preussag Conversion System ® Mobile floating seawater desalination plant Harald Lampe a, Thomas Altmann a*, Hans J. Giitjens b aSalzgitter Anlagenbau GmbH, Eisenhi~ttenstrasse 99, D-38239 Salzgitter, Germany Tel. +49 (5341) 214776; +49 (5341) 214565; E-mail: [email protected]; [email protected] bHowaldtsw erke-Deutsche Werft A G, D-24143 Kiel, Germany Received 5 November 1997; accepted 12 November 1997
Abstract
The PCS-Preussag Conversion System® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions. In the present design example, a standardized Preussag seawater desalination plant using reverse osmosis technology is preferably installed on a converted single shell oil tanker because this outdated tanker design concept will eventual~ be outlawed due to its potential ecological hazard in case of emergency. The PCSPreussag Conversion System~can offer a useful and economic alternative to conventional land-based desalination plants for a number of applications. Keywords: Seawater desalination plant; Shipbased; Mobil floating; Reverse osmosis process
1. I n t r o d u c t i o n
Frequently a sufficient potable water supply in arid coastal regions can only be ensured by operating seawater desalination plants. If consumers of potable water in such regions are located far away from each other, either many small or few large land-based seawater desalination plants with correspondingly extensive distribution networks are needed, both of which require large investments.
For these and other applications, a mobile floating seawater desalination plant installed on a ship can offer a useful and economic alternative to conventional land-based plants. The mobile seawater desalination plant can serve one or several consumers. The potable water produced on the ship is pumped into storage tanks on the coast via pipelines and is then pumped into the distribution networks supplying the potable water to the consumers.
*Corresponding author. 0011-9164/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S 0 0 1 1 - 9 1 6 4 ( 9 8 ) 0 0 0 0 6 - X
146
11. Lampe et al. / Desalination 114 (1997) 145-151
2. P C S - P r e u s s a g c o n v e r s i o n s y s t e m ®
The PCS - Preussag Conversion System ® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions and has resulted from a joint development by the Preussag companies Salzgitter Anlagenbau G m b H , Preussag Noell Wassertechnik G m b H and Howaldtswerke-Deutsche Werfi AG, an international shipbuilding company. The name Preussag Conversion System (PCS) represents b o t h the conversion o f seawater into potable water and the conversion o f a formerly conventional ship into a mobile floating seawater desalination plant. T h e ship can be equipped with optional seawater desalination technologies, e.g., reverse osmosis (RO), multi-stage flash evaporation (MSF), multi-effective distillation (MED) or mechanical vapour compression distillation (MVC). The size o f the ship will depend on the intended service concept o f the system in each specific application and on the desired production capacity o f the seawater desalination plant (Fig. 1; Tables 1-3).
Table 1 Possible applications of a mobile floating seawater desalination plant Potable water supply for arid coastal regions: • • • • • • • •
for islands for coastal places located far away from each other along a shoreline for remote communities without a well-developed infrastructure in case of limited land resources in case of adverse coast conditions in case of seasonal fluctuations in supply and demand of potable water temporarily, in case of trouble or maintenance of land-based seawater desalination plants temporarily, to supply large construction sites located near the coast
Table 2 Advantages ofPCS ® as compared to land-based seawater desalination plants • • • • • • •
Lower investment cost Lower water production costs Shorter delivery times Flexible and variable applications Saving of land resources High quality of workmanship Simplified Authority Engineering, Authorities Approval Procedures and customs advantages
Table 3 Reasons for the feasibility ofPCS ® • • • • Fig. 1. PCS - Preussag Conversion System®.
Saving of many smaller land-based plants involving site mobilization and civil work, e.g., foundations, buildings, roads, seawater intake structures. Conversion, assembly, commissioning and performance tests take place in a shipyard. Utilization of space and infrastructure already available on the ship, e.g., accommodation, offices, workshops, power generation, air conditioning, etc. Turnkey delivery of the complete system to the respective service area.
H. Lampe et al. / Desalination 114 (1997) 145-151
3. P C S ® design
In the present design example, a standardized Preussag seawater desalination plant using RO technology is preferably installed on a converted single shell oil tanker (Fig. 2). This outdated tanker design concept will eventually be outlawed due to its potential ecological hazard in case of emergencies. In cooperation with Howaldtswerke- Deutsche Werfl AG the required rebuilding measures were defined, considering the ship-building aspects and
Fig. 2. Single shell oil tanker, dead weight 140,000 tons.
147
the cost situation. RO technology was selected because it offers the following benefits as compared to thermal processes: • lower investment cost and operating costs • less space requirement • needs only electric energy, no heating steam The rebuilding work required on the oil tanker and the assembly of the seawater desalination plant are entirely performed in a shipyard. The former central oil tanks are cleaned and lined with a protective painting. The product water is
148
H. Lampe et al. /Desalination 114 (1997) 145-151
0
0
0
O
Fig. 3. Layout ofPCS - Preussag Conversion System®. 1 seawater intake; 2 chemical storage, preparation, dosing; 3 dual media filter; 4 fine filter; 5 reverse osmosis units; 6 permeate storage; 7 product water passivation; 8 potable water storage tanks; 9 backwash system; 10 control room; 11 motor control center; 12 chemical cleaning system; 13 main engine; 14 power generation compartment; 15 deckhouse with accommodation and mess; 16 navigator bridge. stored in four of the five tanks with a capacity of 18,000 m 3 each. The tank located at the bow will contain the seawater intake including screening and pumping facilities as well as the chemicals storage including preparation and dosing units. The RO plant comprising pretreatment facilities, RO units and post-treatment section is installed on the ship's deck and partly accommodated in a hall. The ship's superstructure contains accommodation, mess, sanitary and galley facilities, offices, workshops, a navigator bridge, etc. (Fig. 3; Tables 4 and 5). After commissioning and performance tests are finished in the shipyard, the complete system is delivered turnkey to the respective service area. Generation o f electric energy on board the ship: On board the ship, there are three diesel generators o f 8 0 0 k W each which generate the electric power for the normal ship service. The electric power o f approximately 16 M W required for operating the seawater desalination plant is provided by an additional generator located in the engine room and driven by the ship's main engine (Fig. 4).
Table 4 Technical characteristics of ship Length, m Breadth, m Depth, m Draught, m Deadweight, t Cargo capacity, m3 Main engine output, MW Service speed, kn
265 45 24 7-13 140,000 162,000 16.5 15
Table 5 Technical characteristics of seawater desalination plants Technology Plant capacity, m3/d Water type Salt content, ppm Power consumption, kWh/m3
Reverse osmosis process 50,000 Potable < 500 7
H. Lampe et al. / Desalination I14 (1997) 145-151
149
/ ......~Y
:
g t K K ~1
BI~S~L G E I ~ R ~ T O 2 3 X 000KW DECK4
F~,OOR INNE~T~
0
S
Fig. 4. Generation of electric energy on board the ship.
I0
A step-up gear will be installed between the main engine and the power generator in order to obtain the required synchronous speed. An additional tooth coupling allows to disconnect the propeller from the main engine while the generator works. This configuration offers the alternatives to use the main engine either as the ship's drive unit or, if the ship lies at anchor, for power generation for the seawater desalination plant. The option of operating the seawater desali-nation plant while the ship moves, e.g., from one place of service to another, is basically possible if a power generator with a dedicated drive engine is installed.
4. Seawater desalination osmosis process
by
the
reverse
The RO process includes the following three main stages: pretreatment, reverse osmosis, and post-treatment (Fig. 5).
4.1. Pretreatment
The seawater is taken in through sea chests at the bow of the ship and passes through a specially designed metal screen. The seawater supply pumps elevate the pressure of the seawater sufficiently to pass it through the pretreatment process. Here the suspended solids, which cause fouling of the RO membranes, are removed by inline coagulation and filtration. A coagulant is added to the acidified seawater, effectively mixing, and then immediately passing through a dual-media filter to remove the microflocs which have formed. Polyelectrolytes can be used in addition to coagulants to support the formation of stable, filterable flocs. A disinfectant is injected into the seawater to prevent microbiological activities in the pipes and filters. Acid is required to prevent carbonate scaling on the RO membranes and is also added upstream of the dual-media filter. The dual-media filters have to be regularly backwashed with filtrate or brine and scour air from the bottom to the top, the effluent being discharged into the sea.
150
H. Lampe et al. / Desalination 114 (1997) 145-151 STATICMtX£R
I
POLYE~.ECTROLYTE
DUMP
RECOVEI~
.......
D|SIN~E'CTANT CL~.ANINIG PUMP
CLEANING *rANK
MIXER : PIdMP
Fig. 5. Reverse osmosis process. The filtrate is polished by means of fine filters for the final protection of the RO membranes from suspended particles. A dechlorination agent is injected into the feed water stream to eliminate the residual disinfectant.
4.2. R e v e r s e osmosis
The feed water is pumped through the membranes with sufficient pressure, 35-45% of the feed water being converted into permeate and
H. Lampe et al. / Desalination 114 (1997) 145-151
the concentrate being passed through an energy recovery turbine and then partially transferred to the backwash tank and mainly discharged overboard. By passing the concentrate through the energy recovery turbine, the consumption of electric energy is cut by 35%. Chemical cleaning of the RO membranes will be performed regularly in order to reestablish the initial plant performance. 4.3. Post-treatment
Disinfectant and lime are added downstream of the permeate tank for disinfection, pH adjustment and passivation. After lime and disinfectant have been added, the permeate becomes potable water.
5. Conclusions
The PCS - Preussag Conversion System® is a mobile floating seawater desalination plant supplying potable water to arid coastal regions. The ship can be equipped with optional seawater desalination technologies. The size of the ship will depend on the intended service concept of
151
the system in each specific application and on the desired production capacity of the seawater desalination plant. In the present design example, a standardized Preussag seawater desalination plant using RO technology is preferably installed on a converted single shell oil tanker because this outdated tanker design concept will eventually be outlawed due to its potential ecological hazard in case of emergencies. The PCS - Preussag Conversion System® can offer a useful and economic alternative to conventional land-based desalination plants for a number of applications.
References
[1] M. Fadel, K. Wangnick and N.M. Wade, Desalination, 45 (1983) 49. [2] K. Wangnick, Floating sea-water desalination plants--An economical alternative for providing drinking water in arid regions. Meerestechnik, No. 2, 1982. [3] G.F. Tusel, B. Ohlemann, D.K. Emmermann and I. Kamal, Desalination, 38 (1981) 147. [4] J.B. Rossiter, Mar. Eng. Rev., 82 (1982) 14. [5] V.I. Vasjukov, M.D. Klyikov, V.Yu. Podbereznyi and V.In. Shipilov, Desalination, 89 (1992) 21.