- Email: [email protected]
Optimization of RO desalination systems powered by renewable energies. Part I: Wind energy
Desalination 160 (2004) 293-299
ELSEMER
Optimization of RO desalination systems powered by renewable energies. Part I: Wind energy Ignacio de la Nuez Pestana*, Francisco Javier Garcia Latorre, Celso Argudo Espinoza, Antonio G6mez Gotor School of Industrial Engineering, Vniversiv of Las Palmas de Gran Canaria, Spain Tel. +34 (92) 835-5789; Fax +34 (92) 835-1584; email: [email protected]
Received 30 April 2003; accepted 4 May 2003
Abstract Operation of an experimental RO plant connected directly to a wind system without energy storage was studied. The data obtained confirm the wide spectrum of operation of the plant with respect to the power available and the operation of the system. Keywords: Desalination; Renewable energy; Reverse osmosis; Simulation; Wind energy
1. Introduction
Water needs today have grown due to increasedconsumptionandto the contamination of aquifers. Initially other desalination systems have beenused, but at presentthe extensiveuse of the RO processpredominates.The flexibility in the dimensions of RO plants together with reducedenergyconsumptionandimprovementin membraneshavemadeRO the most efficient and economical process. Conventional sources of *Corresponding author.
energy have suffered important fluctuations in the last decades of the 20th century. Thus renewable energy sources are necessary for obtainingwater [ 11.Threedifferent methodsare: RO renewableenergy plants and alternative systems(diesel and storage) Small-scale RO plants that are connected accordingto the energyavailable [2,3] . RO plant - renewable energy without alternativeenergysources[4]. l
l
Within this framework,theOPRODESproject (JOR3-CT98-0274),has as one of its objectives
Presented at the European Conference on Desalination and the Environment: Fresh Waterfor All, Malta, 4-8 May 2003. European Desalination Society, International Water Association.
001 l-9164/04/$- See front matter 0 2004 Elsevier Science B.V. All rights reserved PII: SO01
l-9164(03)00669-6
294
I. de la Nuez Pestana et al. /Desalination
the study of RO membranessubjectedto flow and pressurefluctuations in desalinationplants poweredby renewableenergy.An RO plant has beendesignedto obtain this information. 2. Plant description The RO plant designedfor this project retains the philosophy of a conventional desalination plant, but it includesa seriesof importantmodifications [5,6] for the study of the membranes undergoing a variable regime due to colic and solar energy fluctuations. With this system the operationof the plant in variable regimeandwith stops and successive starts, depending on the availability of electric power in the system, is proved. 2.1. Technical characteristics Fig. 1 showsa conventionalschemeof anRO
Fig. 1..RO plant scheme.
160 (2004) 293-299
plant to which a seriesof modifications have beenmade: Pre-treatmentintakes: In order to study different pre-treatments,together or separately, there are three independent inputs for the addition of pre-treatmentproducts. . Pressuretube:The pressuretubewill taketwo inputsof productwaterthroughbothtube side ends.This system has been chosento check the quality of the product water in the different membranes.The collector ofproduct waterwill becoveredinsidethe tube so that it collects the product water coming only from the first membrane,or of the first and second ones,and so on. With this system,we will be ableto test, in a variable or invariable regime, whether it is necessaryto usen-membranes. . Cleaning tank: An automatedcleaning tank hasbeeninstalled sincedueto the automation of the plant, and the possibility to foresee shutdownsof long durationand outbursts,the
HI@ &sane Purr0
I. de la Nuez Pestana et al. /Desalination
cleaning will be carried out automatically, with the possibility of carrying it out manually in some cases. The high-pressure pump chosen for the project is a positive displacementpump with a stainlesssteelpiston pump in solid ceramic. The maximum flow is 13.62m3/hwith power ranges from 7-85 bar. The relationship between flow and pressure is lineal. A three-phaseelectric motor carriesthe haulage.The coupling between the motor-pump is carried out by means of a system of pulleys with a transmission relationship 4: 1. The combined(motor-pump)characteristics are given in Table 1. Theseparametersare the maximum and minimum that canbe obtained from the pump-motor with values higher than required by the membranes. A 6 m-long tube with six membranesis used in the project. The membranesare Koch Fluid Systems and the model TFC 2822-SSpremium polyamidespiral wound for seawaterdesalination and high rejection. Each membrane allows a permeationof 18.9 m3/d with a salt rejection of 99.8%, each with an areaof 27.9 m*. Once the
295
160 (2004) 293-299
Table 1
Characteristics of combined (pump-motor)
Motor, rpm
Pump,rpm Pressure, bar Flow, m3/h Power, kW
Min
Max
800 200 7 5.2 1.17
1500 375 85 9.8 26.43
Table 2 Functioning characteristics of the plant
Operating pressure, bar Recovery, % Electric motor, rpm Power consumption, kW
Min
Max
30 10 800 5.5
60 50 1500 21.5
membranetube is chosen and considering the selectionof the pump,the functioning characteristics of the plant aregiven in Table 2. The plant designedfor the project is shown in Fig. 2.
Fig. 2. Plant design.
296
I. de la Nuez Pestana et al. /Desalination
160 (2004) 293-299
Product Brine Seawater
Fig. 3. Instrumentation diagram. 2112Temperature transmitter (TT), 5.U7.1 Pressuretransmitter (PT) O-100 bar), 11.2 PT (pressuretransmitter) O-16 bar, 1 pH transmitter (PHT), lo,13 Conductivity transmitter (CT), 4 Pressurestat(PDSH) O-2.5 bar, 6 Pressurestat (PSDH) O-16 bar regularly, 5.2,7.2 Pressure indicators (PT) O-100 bar, 11.2 Pressureindicators (PI) O-6 bar, 14 Indicator and flow transmitter (FT, FI), 8 Monitorized regulating valve for seawater and high pressure.
2.2. Instrumentation and control Sincethe RO plant hasbeenbuilt for research, it has many instruments and monitors with an adequate control system, which operates the rejection valve and a speedvariator, simulating the different non-conventional energy power inputs. The basic instrumentationcharacteristics are shown in Fig. 3. All the instrumentation is connected to a programmableautomaton.The componentsofthe control systemare: Programmable automaton with 16 analogue inputs, 32 digital inputs/outputs,eight analogue inputs Telemecanique TSX 37, analogue programmablemonitorization software SCADA. 30 kW speedvariator TelemacaniqueAltivar ATV66D33N4S. Regulating valve (brine rejection), with an electro-hydraulic actuatorwith a monophase engine and pressurestatacting at the end of the cycle. l
addition of a PI regulatorin both control systems is necessary. 2.3. Software A programme that permits arbitrary and predefined functioning operationsof the plant was designed.The control programmeacts over thetwo control elements(control valve andspeed variator) and the information of the different instruments is stored in the PC simultaneously. The trials were carried out in 2001 and 2003, providing considerableinformation for the study of membranessubject to variable fluctuations. 3. Functioning methodology
l
l
The positive displacementpump was selected for independenceof the variables of flow and pressure. The flow will be controlled by the pressureof the pump, acting overthe speedin the electric motor that is working by the variator, thus a flow over the membranes.The pressurein the seawater system/circuit is obtained acting over the valve that closes the system and increasesthe pressure.Due to the relationship between the variables (flow and pressure),the
The plant has undergoneall the acceptable positions of pressureand flow that the manufacturer of membranes specifies. Jumps of power (abruptvariation of flow and/orpressure) havebeencarriedout. Different samplingperiods have been obtained to get the most relevant information in the RO process.For obtaining static dataperiods, 15s or more have beenused. For the transitory studies (stops and outbursts) periods of up to 1 s were used. The electric power obtainedby colic or solar systemis given to the RO plant by means of a speedvariator, which allows the continuousprogrammingof the energythat will consumethe high-pressurepump in an RO system. To the motor that drags the pump, the revolutions wanted are programmed,
I. de la Nuez Pestana et al. 1 Desalination 160 (2004) 293-299
obtaining in the pump a variable rather than a lineal flow. The different objectives are: Study of the membranebehaviour Optimum energystudy of an RO plant Study of the recovery subjected to fluctuations Aging processin plants of RO poweredwith renewableenergy Study of the RO plant that undergoesenergy pulses l l
297
Some authors have treated some of these points, but always on laboratory facilities or of reducedsize [7]. All these objectives are being developed as part of the investigations of the group.
l
4. Results
l
l
Dataobtainedin the operationof the plant are given in Table 3. The generateddata have been chosenwhen the electric engine is at 1500r-pm.
Table 3 Results obtained at 1500 rpm Pressure seawater, bar (PSI
Pressure Ampere, Temp., Flow Conduct. Flow brine, A “C seawater, seawater, brine, bar (4) (PB)
Conduct. brine, mS (GA
Flow product, m’/h (FP)
Conduct. Recovery, product, % mS (Cd
39 39 39 39 39 39 39 39 39
37 37 37 37 37 37 37 37 37
14 14 13.44 13.44 13.44 13.44 14 14 14
15 15 15 15 15 15 15 15 15
9.489 9.489 9.489 9.489 9.489 9.489 9.489 9.489 9.489
45,689 44,822 45,368 45,095 45,047 45,207 44,934 45,094 45,367
7.616 7.616 7.616 7.616 7.616 7.616 7.616 7.616 7.616
56,820 55,740 56,520 56,080 56,020 56,220 55,880 56,080 56,420
1.873 1.873 1.873 1.873 1.873 1.873 1.873 1.873 1.873
429 429 429 429 428 427 426 425 425
19.74 19.74 19.74 19.74 19.74 19.74 19.74 19.74 19.74
49 49 49 49 49 49 49 49 49 49
48 48 48 47 47 47 47 47 47 47
17.36 17.36 17.36 17.36 16.8 17.36 17.36 17.36 17.36 17.36
16 16 16 16 16 16 16 16 16 16
9.449 9.449 9.449 9.263 9.284 9.274 9.274 9.293 9.293 9.293
43,648 44,25 1 43,921 43,541 43,208 43,633 43,399 43,262 43,399 43,632
6.486 6.486 6.486 6.358 6.372 6.365 6.365 6.378 6.378 6.378
63,440 64,320 63,840 63,300 62,820 63,440 63,100 62,900 63,100 63,440
2.963 2.963 2.963 2.905 2.912 2.909 2.909 2.915 2.915 2.915
324 320 317 297 293 296 293 294 294 292
31.36 31.36 31.36 31.36 31.37 31.37 31.37 31.37 31.37 31.37
60 60 60 60 60 60 60 60 60 60
59 59 59 59 59 58 59 58 59 59
21.28 21.28 20.72 20.72 21.28 20.72 20.72 20.72 20.72 20.72
16 16 16 16 16 16 16 16 16 16
9.089 9.095 9.112 9.129 9.129 9.136 9.136 9.136 9.118 9.118
44,545 44,709 44,334 44,709 44,622 44,776 44,450 44,413 44,896 44,653
5.455 5.458 5.468 5.478 5.478 5.482 5.482 5.482 5.471 5.471
74,020 74,300 73,680 74,300 4,160 74,420 73,880 73,820 74,620 74,220
3.634 3.637 3.644 3.651 3.651 3.654 3.654 3.654 3.647 3.647
301 303 298 310 302 301 298 294 307 299
39.98 39.99 39.99 39.99 39.99 40.00 40.00 40.00 40.00 40.00
298
I. de la Nuez Pestana et al. /Desalination 160 (2004) 293-299
The data have beengeneratedduring 1 h (every 6 min) for three values of the pressurein the entranceof the tube of 40-50-60 bar, respectively. The pressuresto the entranceand exit of the tube correspond to the first and second columns of Table 3. Observe that the loss of pressure is smaller as the operation pressure increases.An increment in the consumption of amperes is observed in the function of the pressure,andthe seawaterflow is approximately the same. The two expressionsof the conservation have beenusedto complete Table 3.
The couplesof flow values and conductivity are shown for the input of the seawatermembrane and for the produce and brine. Usually the conductivity for this type of membrane is less than 500 mS. The recoveryis shown in eachone of the situations that varies from 19.74% to
1600RP.M.
0
20
40
60
80
Pressure
Fig. 4. Conductivity obtained (operating at 1500 rpm).
g
1 uuuuu 90000 80000 70000 60000 50000 40000 30000 20000 10000
1 mu 1000 800 600 400 200 0
0 0
20
40 Pressure
60
80
Fig. 5. Conductivity obtained.
40.00%.
The flow, that is a function of the rpm, remains almost constant. However, when you increasethe pressure, it increasesthe product flow andthe brine conductivity. An energystudy shows that the decreaseof the consumption is observedwhen the recovery increases.It goes from a consumption of 5.4 kW/m3 when the rejection is of 20%, to a consumptionof 4.2 kW1 m3whenthe rejection is of 40%. In Figs. 4 and5, the results obtained are shown for a day, operating at 1500 rpm. The fluctuations are shown when the pressures in the membranes vary. Observethat whenthe pressureis small, the behaviouris irregular becauseosmosis doesnot exist. The consumed intensity increasescompletely in this situation. In Fig. 5, the variations of conductivity are shown in the samesituation as the one obtained in Fig. 4. The specific energy consumptiondiminishes whenthe recoveryincreases.Whenrecoveryacts over the flow and pressure,we can concludethe
-1 6S.6 bu
s4 3.6. e
3. 2.6 2. 1.5
6
10
16 Power
20
26
30
kW
Fig. 6. Flow/power.
optimum results foreseenin this type of plant. The membranemanufacturerslimit the recovery being the objective of the control system,working around40-43% recovery. An increment of therecoverywill imply biggerpower,andin turn, the curve flow-pressure can increase.For the opposite, a decreaseof the recovery implies a decreaseof the curve flow-pressure.To achieve
I. de la Nuez Pestana et al. /Desalination
this type of control, Fig. 6 proposesthe necessity of instrumentalization of the flow product, as a necessarysign to re-feedthe system.Leaning on in this variable,you cancalculatethe installation recovery. Later, we show the most important valuesthat will allow definition of a control curve for this type of plant. The power that will consumethe installation is variable, shown in Fig. 6. 5. Conclusions
The developmentof an RO plant for variable chargesis presented.The plant hasbeenworking for more than 7000 h, generatinga history for analysing the behaviour of the plant. The membranes allow a variable functioning without deteriorating,althoughadditional information is neededfor the aging study. The resultsobtained reveal the optimum control for the reduction of the energy consumption in this type of design that consists of obtaining adequate recovery membranes(40-43%). The control systemmust take the plant to an adequaterecovery for each
160 (2004) 293-299
299
available power, this being possible by use of a simple programme. References
PI A. Hanati, Desalination using renewable energy sources,Desalination, 97 (1944) 339-352. PI D. Herold and A. Neskakis, A small PV-driven reverse osmosis desalination plant on the island of Gran Canaria, Desalination, 137 (2001) 285-292. 131 M.S. Miranda and D. Infield, A wind-powered seawater reverse-osmosissystem without batteries, Desalination, 153 (2002) 9-16. 141 C.K. Liu, J.-W. Park, R. Migita and G. Qin, Experiments of a prototype wind-driven reverse osmosis desalination system with feedback control, Desalination, 150 (2002) 277-287. PI G. Al-Enezi and N. Fawzi, Design consideration of RO units: casestudies,Desalination, 153 (2002)281286.
Fl A.J. Dababneh andM.A. Al-Nimr, A reverseosmosis [71
desalination unit, Desalination, 153 (2002) 265-272. M. Thomson, MS. Miranda and D. Infiel, A smallscaleseawaterreverse-osmosissystemwith excellent energy efficiency over a wide operating range, Desalination, 153 (2002) 229-236.
ELSEMER
Optimization of RO desalination systems powered by renewable energies. Part I: Wind energy Ignacio de la Nuez Pestana*, Francisco Javier Garcia Latorre, Celso Argudo Espinoza, Antonio G6mez Gotor School of Industrial Engineering, Vniversiv of Las Palmas de Gran Canaria, Spain Tel. +34 (92) 835-5789; Fax +34 (92) 835-1584; email: [email protected]
Received 30 April 2003; accepted 4 May 2003
Abstract Operation of an experimental RO plant connected directly to a wind system without energy storage was studied. The data obtained confirm the wide spectrum of operation of the plant with respect to the power available and the operation of the system. Keywords: Desalination; Renewable energy; Reverse osmosis; Simulation; Wind energy
1. Introduction
Water needs today have grown due to increasedconsumptionandto the contamination of aquifers. Initially other desalination systems have beenused, but at presentthe extensiveuse of the RO processpredominates.The flexibility in the dimensions of RO plants together with reducedenergyconsumptionandimprovementin membraneshavemadeRO the most efficient and economical process. Conventional sources of *Corresponding author.
energy have suffered important fluctuations in the last decades of the 20th century. Thus renewable energy sources are necessary for obtainingwater [ 11.Threedifferent methodsare: RO renewableenergy plants and alternative systems(diesel and storage) Small-scale RO plants that are connected accordingto the energyavailable [2,3] . RO plant - renewable energy without alternativeenergysources[4]. l
l
Within this framework,theOPRODESproject (JOR3-CT98-0274),has as one of its objectives
Presented at the European Conference on Desalination and the Environment: Fresh Waterfor All, Malta, 4-8 May 2003. European Desalination Society, International Water Association.
001 l-9164/04/$- See front matter 0 2004 Elsevier Science B.V. All rights reserved PII: SO01
l-9164(03)00669-6
294
I. de la Nuez Pestana et al. /Desalination
the study of RO membranessubjectedto flow and pressurefluctuations in desalinationplants poweredby renewableenergy.An RO plant has beendesignedto obtain this information. 2. Plant description The RO plant designedfor this project retains the philosophy of a conventional desalination plant, but it includesa seriesof importantmodifications [5,6] for the study of the membranes undergoing a variable regime due to colic and solar energy fluctuations. With this system the operationof the plant in variable regimeandwith stops and successive starts, depending on the availability of electric power in the system, is proved. 2.1. Technical characteristics Fig. 1 showsa conventionalschemeof anRO
Fig. 1..RO plant scheme.
160 (2004) 293-299
plant to which a seriesof modifications have beenmade: Pre-treatmentintakes: In order to study different pre-treatments,together or separately, there are three independent inputs for the addition of pre-treatmentproducts. . Pressuretube:The pressuretubewill taketwo inputsof productwaterthroughbothtube side ends.This system has been chosento check the quality of the product water in the different membranes.The collector ofproduct waterwill becoveredinsidethe tube so that it collects the product water coming only from the first membrane,or of the first and second ones,and so on. With this system,we will be ableto test, in a variable or invariable regime, whether it is necessaryto usen-membranes. . Cleaning tank: An automatedcleaning tank hasbeeninstalled sincedueto the automation of the plant, and the possibility to foresee shutdownsof long durationand outbursts,the
HI@ &sane Purr0
I. de la Nuez Pestana et al. /Desalination
cleaning will be carried out automatically, with the possibility of carrying it out manually in some cases. The high-pressure pump chosen for the project is a positive displacementpump with a stainlesssteelpiston pump in solid ceramic. The maximum flow is 13.62m3/hwith power ranges from 7-85 bar. The relationship between flow and pressure is lineal. A three-phaseelectric motor carriesthe haulage.The coupling between the motor-pump is carried out by means of a system of pulleys with a transmission relationship 4: 1. The combined(motor-pump)characteristics are given in Table 1. Theseparametersare the maximum and minimum that canbe obtained from the pump-motor with values higher than required by the membranes. A 6 m-long tube with six membranesis used in the project. The membranesare Koch Fluid Systems and the model TFC 2822-SSpremium polyamidespiral wound for seawaterdesalination and high rejection. Each membrane allows a permeationof 18.9 m3/d with a salt rejection of 99.8%, each with an areaof 27.9 m*. Once the
295
160 (2004) 293-299
Table 1
Characteristics of combined (pump-motor)
Motor, rpm
Pump,rpm Pressure, bar Flow, m3/h Power, kW
Min
Max
800 200 7 5.2 1.17
1500 375 85 9.8 26.43
Table 2 Functioning characteristics of the plant
Operating pressure, bar Recovery, % Electric motor, rpm Power consumption, kW
Min
Max
30 10 800 5.5
60 50 1500 21.5
membranetube is chosen and considering the selectionof the pump,the functioning characteristics of the plant aregiven in Table 2. The plant designedfor the project is shown in Fig. 2.
Fig. 2. Plant design.
296
I. de la Nuez Pestana et al. /Desalination
160 (2004) 293-299
Product Brine Seawater
Fig. 3. Instrumentation diagram. 2112Temperature transmitter (TT), 5.U7.1 Pressuretransmitter (PT) O-100 bar), 11.2 PT (pressuretransmitter) O-16 bar, 1 pH transmitter (PHT), lo,13 Conductivity transmitter (CT), 4 Pressurestat(PDSH) O-2.5 bar, 6 Pressurestat (PSDH) O-16 bar regularly, 5.2,7.2 Pressure indicators (PT) O-100 bar, 11.2 Pressureindicators (PI) O-6 bar, 14 Indicator and flow transmitter (FT, FI), 8 Monitorized regulating valve for seawater and high pressure.
2.2. Instrumentation and control Sincethe RO plant hasbeenbuilt for research, it has many instruments and monitors with an adequate control system, which operates the rejection valve and a speedvariator, simulating the different non-conventional energy power inputs. The basic instrumentationcharacteristics are shown in Fig. 3. All the instrumentation is connected to a programmableautomaton.The componentsofthe control systemare: Programmable automaton with 16 analogue inputs, 32 digital inputs/outputs,eight analogue inputs Telemecanique TSX 37, analogue programmablemonitorization software SCADA. 30 kW speedvariator TelemacaniqueAltivar ATV66D33N4S. Regulating valve (brine rejection), with an electro-hydraulic actuatorwith a monophase engine and pressurestatacting at the end of the cycle. l
addition of a PI regulatorin both control systems is necessary. 2.3. Software A programme that permits arbitrary and predefined functioning operationsof the plant was designed.The control programmeacts over thetwo control elements(control valve andspeed variator) and the information of the different instruments is stored in the PC simultaneously. The trials were carried out in 2001 and 2003, providing considerableinformation for the study of membranessubject to variable fluctuations. 3. Functioning methodology
l
l
The positive displacementpump was selected for independenceof the variables of flow and pressure. The flow will be controlled by the pressureof the pump, acting overthe speedin the electric motor that is working by the variator, thus a flow over the membranes.The pressurein the seawater system/circuit is obtained acting over the valve that closes the system and increasesthe pressure.Due to the relationship between the variables (flow and pressure),the
The plant has undergoneall the acceptable positions of pressureand flow that the manufacturer of membranes specifies. Jumps of power (abruptvariation of flow and/orpressure) havebeencarriedout. Different samplingperiods have been obtained to get the most relevant information in the RO process.For obtaining static dataperiods, 15s or more have beenused. For the transitory studies (stops and outbursts) periods of up to 1 s were used. The electric power obtainedby colic or solar systemis given to the RO plant by means of a speedvariator, which allows the continuousprogrammingof the energythat will consumethe high-pressurepump in an RO system. To the motor that drags the pump, the revolutions wanted are programmed,
I. de la Nuez Pestana et al. 1 Desalination 160 (2004) 293-299
obtaining in the pump a variable rather than a lineal flow. The different objectives are: Study of the membranebehaviour Optimum energystudy of an RO plant Study of the recovery subjected to fluctuations Aging processin plants of RO poweredwith renewableenergy Study of the RO plant that undergoesenergy pulses l l
297
Some authors have treated some of these points, but always on laboratory facilities or of reducedsize [7]. All these objectives are being developed as part of the investigations of the group.
l
4. Results
l
l
Dataobtainedin the operationof the plant are given in Table 3. The generateddata have been chosenwhen the electric engine is at 1500r-pm.
Table 3 Results obtained at 1500 rpm Pressure seawater, bar (PSI
Pressure Ampere, Temp., Flow Conduct. Flow brine, A “C seawater, seawater, brine, bar (4) (PB)
Conduct. brine, mS (GA
Flow product, m’/h (FP)
Conduct. Recovery, product, % mS (Cd
39 39 39 39 39 39 39 39 39
37 37 37 37 37 37 37 37 37
14 14 13.44 13.44 13.44 13.44 14 14 14
15 15 15 15 15 15 15 15 15
9.489 9.489 9.489 9.489 9.489 9.489 9.489 9.489 9.489
45,689 44,822 45,368 45,095 45,047 45,207 44,934 45,094 45,367
7.616 7.616 7.616 7.616 7.616 7.616 7.616 7.616 7.616
56,820 55,740 56,520 56,080 56,020 56,220 55,880 56,080 56,420
1.873 1.873 1.873 1.873 1.873 1.873 1.873 1.873 1.873
429 429 429 429 428 427 426 425 425
19.74 19.74 19.74 19.74 19.74 19.74 19.74 19.74 19.74
49 49 49 49 49 49 49 49 49 49
48 48 48 47 47 47 47 47 47 47
17.36 17.36 17.36 17.36 16.8 17.36 17.36 17.36 17.36 17.36
16 16 16 16 16 16 16 16 16 16
9.449 9.449 9.449 9.263 9.284 9.274 9.274 9.293 9.293 9.293
43,648 44,25 1 43,921 43,541 43,208 43,633 43,399 43,262 43,399 43,632
6.486 6.486 6.486 6.358 6.372 6.365 6.365 6.378 6.378 6.378
63,440 64,320 63,840 63,300 62,820 63,440 63,100 62,900 63,100 63,440
2.963 2.963 2.963 2.905 2.912 2.909 2.909 2.915 2.915 2.915
324 320 317 297 293 296 293 294 294 292
31.36 31.36 31.36 31.36 31.37 31.37 31.37 31.37 31.37 31.37
60 60 60 60 60 60 60 60 60 60
59 59 59 59 59 58 59 58 59 59
21.28 21.28 20.72 20.72 21.28 20.72 20.72 20.72 20.72 20.72
16 16 16 16 16 16 16 16 16 16
9.089 9.095 9.112 9.129 9.129 9.136 9.136 9.136 9.118 9.118
44,545 44,709 44,334 44,709 44,622 44,776 44,450 44,413 44,896 44,653
5.455 5.458 5.468 5.478 5.478 5.482 5.482 5.482 5.471 5.471
74,020 74,300 73,680 74,300 4,160 74,420 73,880 73,820 74,620 74,220
3.634 3.637 3.644 3.651 3.651 3.654 3.654 3.654 3.647 3.647
301 303 298 310 302 301 298 294 307 299
39.98 39.99 39.99 39.99 39.99 40.00 40.00 40.00 40.00 40.00
298
I. de la Nuez Pestana et al. /Desalination 160 (2004) 293-299
The data have beengeneratedduring 1 h (every 6 min) for three values of the pressurein the entranceof the tube of 40-50-60 bar, respectively. The pressuresto the entranceand exit of the tube correspond to the first and second columns of Table 3. Observe that the loss of pressure is smaller as the operation pressure increases.An increment in the consumption of amperes is observed in the function of the pressure,andthe seawaterflow is approximately the same. The two expressionsof the conservation have beenusedto complete Table 3.
The couplesof flow values and conductivity are shown for the input of the seawatermembrane and for the produce and brine. Usually the conductivity for this type of membrane is less than 500 mS. The recoveryis shown in eachone of the situations that varies from 19.74% to
1600RP.M.
0
20
40
60
80
Pressure
Fig. 4. Conductivity obtained (operating at 1500 rpm).
g
1 uuuuu 90000 80000 70000 60000 50000 40000 30000 20000 10000
1 mu 1000 800 600 400 200 0
0 0
20
40 Pressure
60
80
Fig. 5. Conductivity obtained.
40.00%.
The flow, that is a function of the rpm, remains almost constant. However, when you increasethe pressure, it increasesthe product flow andthe brine conductivity. An energystudy shows that the decreaseof the consumption is observedwhen the recovery increases.It goes from a consumption of 5.4 kW/m3 when the rejection is of 20%, to a consumptionof 4.2 kW1 m3whenthe rejection is of 40%. In Figs. 4 and5, the results obtained are shown for a day, operating at 1500 rpm. The fluctuations are shown when the pressures in the membranes vary. Observethat whenthe pressureis small, the behaviouris irregular becauseosmosis doesnot exist. The consumed intensity increasescompletely in this situation. In Fig. 5, the variations of conductivity are shown in the samesituation as the one obtained in Fig. 4. The specific energy consumptiondiminishes whenthe recoveryincreases.Whenrecoveryacts over the flow and pressure,we can concludethe
-1 6S.6 bu
s4 3.6. e
3. 2.6 2. 1.5
6
10
16 Power
20
26
30
kW
Fig. 6. Flow/power.
optimum results foreseenin this type of plant. The membranemanufacturerslimit the recovery being the objective of the control system,working around40-43% recovery. An increment of therecoverywill imply biggerpower,andin turn, the curve flow-pressure can increase.For the opposite, a decreaseof the recovery implies a decreaseof the curve flow-pressure.To achieve
I. de la Nuez Pestana et al. /Desalination
this type of control, Fig. 6 proposesthe necessity of instrumentalization of the flow product, as a necessarysign to re-feedthe system.Leaning on in this variable,you cancalculatethe installation recovery. Later, we show the most important valuesthat will allow definition of a control curve for this type of plant. The power that will consumethe installation is variable, shown in Fig. 6. 5. Conclusions
The developmentof an RO plant for variable chargesis presented.The plant hasbeenworking for more than 7000 h, generatinga history for analysing the behaviour of the plant. The membranes allow a variable functioning without deteriorating,althoughadditional information is neededfor the aging study. The resultsobtained reveal the optimum control for the reduction of the energy consumption in this type of design that consists of obtaining adequate recovery membranes(40-43%). The control systemmust take the plant to an adequaterecovery for each
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available power, this being possible by use of a simple programme. References
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