Transcript Optimization at higher pH and Sea water Temperature
Successful antiscalant field trial – Optimization at higher pH & Sea water Temperature
Larnaca Desalination Plant, Cyprus
Wiebo van der Wal & Filip Dutoy – thermPhos Belgium B.V.B.A
AWW 2013
Objectives
Sea Water Desalination process
– Produce drinking water using R.O. process to remove salts and impurities from sea water – Use Energy efficient systems – Water Quality complying with WHO guidelines (Boron < 1 ppm at Larnaca Desalination Plant) – Achieve contractual water Quantity requirements – Operate R.O. plant cost efficiently
Larnaca Desalination Plant Process
1
Sea Water Intake
2
Pre – Treatment
3
R everse O smosis
4
Post – Treatment
5
Storage & Distribution
The Boron issue
Boron Removal necessary due to: • Health effects • on mankind / infertility • Plants / vegetation • fruit yield • leaf damage • ripening process
Boron membrane rejection
Function of
:
Boron sea water concentration Sea Water Temperature Feed Water pH
Boron membrane rejection Larnaca Desalination Plant
• Mediterranean Sea Water typical value for boron: 5 ppm • Larnaca Desalination Plant - drinking water contractual value is < 1 ppm
Boron membrane rejection
Larnaca sea water temperature (5 year data) 29 °C
30,0 29,0 28,0 27,0 26,0 25,0 24,0 23,0 22,0 21,0 20,0 19,0 18,0 17,0 16,0 15,0 29 /1 2 28 /0 1 28 /0 2 31 /0 3 1/ 05 1/ 06 2/ 07 Date 2/ 08 2/ 09 3/ 10 3/ 11 3/ 12
15 °C Boron rejection is decreasing when temperature increases
Boron membrane rejection
Boron species in seawater versus pH
H
3
BO
3
H
H
2
BO
3 Not rejected Well rejected
Improve the Boron removal at Larnaca Desalination Plant • Monitor uncontrollable parameters such as Sea water temperature & Boron feed concentration • Innovative designs of Membrane Boron Removal • Increase Boron removal of membranes by increasing pH
Larnaca innovative RO design
Two pass design LWP (Cyprus) 80% - Permeate (front end)
Product Tank
Sea Water
1 st Pass 2
20%Permeate(back end)
nd Pass
Increasing water pH
Natural seawater pH Permeate Sea Water
1 st Pass
Permeate
2 nd Pass Product Tank
NaOH addition
First pass high pH
Necessary steps - LWP global improvement processes 1
Sea Water Intake Larnaca Desalination Plant 2001 & 2009
2
Pre – Treatment
3
R everse O smosis
4
Post – Treatment
5
Storage & Distribution EXITING PLANT - 2001
• Intake pipe • Screens • Pumping station • Coagulation / Flocculation • 12 Dual Media Filters • Booster pump • Micro filtration • 6 x High Pressure Pumps - Trains • Membrane Trains ( 1 st & 2 nd stage
)
• Turbine Energy Recovery • Antiscalant dosing • Chemical dosing • Limestone Reactors
EXPANDED PLANT - 2009
• New Intake pipe & suction system • Upgraded Screens • Extra Booster pumps • Additional Micro Filers • 6 x new ERIs linked with existing HP pump & turbine system ® IDE • Additional PVs • Replace membranes • No changes • Product tank • Chlorination • Pumping station (13km ) • Additional Pump system New upgraded SCADA system to incorporate the new systems for complete plant operation, monitoring & control
higher 1 st Innovative Operation RO stage pH no 2 nd pass for 6 months/ year Product Tank +8% more water
Sea Water
1 st Pass 2 nd Pass No 2 nd pass Less Energy More Water
Problems induced by increased pH
•
First pass
(natural Sea Water pH=8.2) – CaCO 3 precipitation •
Second pass
(pH > 9.0) – CaCO 3 precipitation – Mg(OH) 2 precipitation
Problems induced by increased pH
General parameters affecting plant operation • Seasonal temperature variability (15°c to 30°c) • LDP operational plant conditions versus time of the year • LDP seawater composition and pH
Problems induced by increased pH
Saturation index estimation
– First pass (pH=8.2) • Issue: CaCO3 precipitation • classical S&DSI calculation approach – Second pass ( pH > 9.0) • Issue: CaCO3 precipitation – classical LSI calculation approach • Issue: Mg(OH) 2 precipitation – brucite (highly insoluble) – laboratory scaling simulation approach
Problems induced by increased pH
Saturation index calculation
First pass: S&DSI
Problems induced by increased pH
Saturation index investigation
Second pass: • Laboratory investigation under typical LWP conditions
How to avoid problems induced by increased pH
Scaling potential statement
Both species are crystalline (SEM pictures) CaCO 3 Mg(OH) 2
How to avoid problems induced by increased pH
Scaling inhibition
Dose specific anti-scalants with their specific capabilities/limitations Phosphonate based technology How does antiscalant work ?
Scale formation phosphonate cation anion nucleation nuclei crystal growth small crystal agglomeration crystal agglomerate scale
Chelation Multivalent positive ions are made unavailable
Nucleation inhibition Competition between formation (K f ) and destabilization of (K d ) of nuclei
Nucleation inhibition Induction time f of K f , K d , [cation] n+ , [anion] n and [PhPh]
Nucleation inhibition Crystal growth
Crystal growth modification 100 001 010 Adsorption on crystalite: small size distorted crystalite
Crystal growth modification No inhibitor ATMP (5 ppm) 25 °C, pH 5.6 (0.25 mM BaSO4 – super-saturation ratio 25) Jones et al. CrystEngComm, 2001, 3, 165-167
Without phosphonate Dispersion E With phosphonate E Adsorption on particle: electrostatic repulsion
Inhibitor concentration effect
100 induction time 0 cc3>cc2>cc1 No inhibitor Inhibitor cc1 Inhibitor cc2 Inhibitor cc3 time
How to avoid problems induced by increase of pH
Antiscalant selection
SPE0111 selected from in-house phosphonate antiscalant solution
Improved performance to a level of -CaCO 3 : S&DSI to 2,6 without scaling formation -Mg(OH) 2 : increasing solubility by a factor of two
Antiscalant SPE0111 implementation
Trial data • Dose rate based on the high temperature and the most critical operational conditions • Monitoring – Plant operation follow up (DP, flows, …) – Historical data comparison – Product analysis (feed/brine) for loss detection – Membrane autopsies Results: No evidence of scaling during one year
Antiscalant SPE0111 optimization
Next steps Completion of 2 nd plant expansion (20% increase in production capacity) First stage SPE0111 dose rate optimization - rate calculation versus Modes and period of operation
Antiscalant SPE0111 optimization
Dose rate calculation versus mode of operation and period of the year 1,4 1,2 1 0,8 0,6 0,4 0,2 0 15 17 19 SPE0111 Dose rate (ppm feed) S&DSI 21 23 Temperature (°c) 25 27 29
Conclusions
• LDP meets all its contractual objectives operating at higher feed water pH – no evidence of membrane scaling.
• Required boron levels achieved using appropriate antiscalant in combination with correct membrane changes and adequate chemical cleaning • thermPhos is supporting successfully LDP in optimizing the dosing rate of the chosen antiscalant • Recent LDP +20% plant expansion makes boron rejection more critical - further work required for finer antiscalant dosing adjustments