1
Thermal Desalination Antiscalant
Indonesia Customer Seminar June 13 & 14 2012 Jakarta Indonesia
Overview
Scaling & Its Impact
Type of Scale in Thermal Desalination
Factors Influences Scale formation
Scale Inhibitor Technology Overview
PC-2040T Features Performance Comparison with other technology Advantages & Benefit
Why Scale Occur in Thermal Desalination?
Condition in thermal desalination generate supersaturated condition for some minerals salt in sea water
Factors:
Increasing of temperature Evaporative concentration Release of CO2 from the brine which induces further shift of bicarbonate ion to the carbonate to the hydroxide ion through the increase in pH 4HCO32- + Ca2+ + Mg 2+ CaCO CaCO3 (s) + Mg(OH)2 (s)+ 3CO2 (g)+ H 2 O
Scale Formation in MSF MP steam LP steam 5
3 ~30 C º
4
2
1-deaerator 2-brine heater 3-heat recovery 4-heat rejection 5-vacuum 6-brine recirculation pump Condensate
Seawater
Seawater
1 6
Distilled water Brine discharge
• Hard scale (CaSO4) and alkaline scale (CaCO 3 and MgOH2) in brine heater which has highest temperature • Calcium carbonate scale and sludge in flash chamber and demister
Scale Formation in MED
• Mainly alkaline scale (CaCO3) on tube surfaces where saturation index is the highest .
Effects of Scaling in the Brine Heater
Decreased brine temperature at a constant steam pressure
Increased steam pressure to maintain top brine temperature
Reduced flow rates for constant top temperature
Loss of production if no compensation has been made for 1 and 3
Effects of Scaling in the Heat Recovery Section
Lower temperature rise through the section and hence increased steam demand in the brine heater to maintain production levels
Effects of Scaling in the Demisters
Physical blocking of the mesh resulting in an increase in vapour pressure drop across the demister. This decreases the steam temperature in the recovery stage, reducing the heat transfer and so reducing the exit temperature of the brine and eventually reducing the inlet temperature to the brine heater.
Overall Effect of Scaling
Increased operational cost
Cost of cleaning
Decreased distillate production
Decreased system reliability
Effect of Scale on MSF Heat Consumption
Source: Effect of Scaling on Design and Opera tion of Thermal Seawater Desalination Plant, Dr. Rainer Gregg arath, SECRC COMO GmbH
Factors Influencing Scale
Water temperature
Alkalinity
Thermally dissolved solids
Type of dissolved products
Presence of nucleation particles
Silt from intake water
Flow and velocity
Time Alkaline scales (CaCO3, Mg(OH)2) will form more quickly than CaSO4 (Anhydride). CaSO 4 x ½ H2O (hemi-hydrate) will form very quickly.
Effect of Temperature on Scaling
80ºC
90ºC
120ºC
CaCO3
Mg(OH)2 CaCO3
CaSO4 Mg(OH)2 CaCO3
Increased hardness, more difficult to remove
Scale Type vs Temperature Deposit composition in sea water evaporator 100 e 90 l a c 80 s f 70 o n 60 o i t i 50 s o 40 p m 30 o C 20 10 0
CaCO3 Mg(OH)2 Nominal temperature difference - 27 C Concentration factor = 2 CaSO4
60
66
71
77
82
88
93
Evaporator water temperature, C
99
104
CaSO4 Scale Formation in MSF Operation 5 r 4 o t c a f 3 n o i t a r 2 t n e c n o 1 C
0
TDS 35
50
100 150 Temperature (ºC)
200
Data from:Mulford, Scale control in seawater evaporators
Scaling Tendency in MSF
Source: Fouling Phenomena in MSF Distiller, M, Abdul0Kareem Al-Sofi
Effect of Velocity - MSF (CaSO 4)
Effect of Flow - MED In the tubes, the hot vapors are continuously passing uniformly at the same mass and heat flow But if the on the outside tubes, if sea water flow has locally reduced , supersaturation of salts does occur -
evaporation of water
-
localized continued heating
-
removal of carbon dioxide)
Source: Effect of Scaling on Design and Operation o f Thermal Seawater Desalination Plant, Dr. Rainer Gregg arath, SECRC COMO GmbH
Effect of Flow – MED (No of Tubes Row)
Scaling Tendency MSF vs MED Parameter
Operating Temperature Operating Pressure Scaling/fouling potential
MSF
MED
90 – 120 0C
<80 0C
Sub-atmospheric
Sub-atmospheric
Low-Moderate
Moderate-High
It has been pointed out that higher scaling potential of MED compared to MSF is primarily due to the boundary layer characteristic of film boiling and flashing in MED process compared to bulk and surface flashing in MSF process
Scale Control in Thermal Desalination
CaCO3 scale control
Mg(OH)2 scale control
CaSO4 scale control
Dispersion capabilities
Scale Inhibitor Activity
Inhibition of crystal growth
Crystal modification
Crystal growth inhibition
Scale dispersion
Inhibit adherence
e s n e f e d f o s e d o M
Need Inhibitor that Work in All Fronts
22
Antiscalant Technology Development
Polyphosphate
Phosphonate/ Polyacrylate
Polymaleic Acid
Modified Polymaleic Acid
23
Antiscalant Performance Comparison Chemistry
T Tolerance
Phosphonate Polyacrylate
CaCO3
CaCO3 (Growth)
Mg(OH)2
CaSO4
(Deposition)
Disper sancy
Medium
Good
Mediocre
Poor
Poor
Poor
Medium
Good
Poor
Good
Fair
Poor
PMA Homopolymer
High
Poor
Good
Mediocre
Fair
Good
PMA Copolymer
High
Poor
Good
Good
Poor
Mediocre
PMA Terpolymer
High
Poor
Poor
Good
Good
Poor
24
Antiscalant: The Needs
Effective scale & deposition control for both “soft scale” (CaCO3 & Mg(OH)2) and “hard scale” (CaSO4)
Good dispersancy
High temperature and calcium tolerance
Easy to measure/detect
On line measurement & control capability
Cost-effective
Environmental friendly
25
Antiscalant Technology Development
Polyphosphate
Phosphonate / Polyacrylate
Polymaleic Acid
Modified Polymaleic Acid
Novel Antiscalant
26
27
PC-2040T: The Features
PC-2040T is antiscalant program for the control of soft scale (calcium carbonate and magnesium hydroxide) and hard scale (calcium sulfate) in all types of sea water distillation plants
It is specifically formulated for use in high “Top Brine Temperature” plants where the predominant scale potential is from calcium sulfate
PC-2040T is utilizing TRASAR® technology for easy detection, monitoring and control (future)
NSF Approved
28
PC-2040T: The Chemistry Blend of Nalco Patented:
Phosphino Carboxylic Acid -
Stable, reverse proof chemistry Excellent CaCO 3 and CaSO4 and deposition control Good Mg(OH)2 scale control Environmental friendly
High Stress Polymer (HSP®) - Terpolymer PAA - High stress tolerance dispersant for silt, iron, phosphate; etc
TRASAR® technology - “Tracer” material for easy detection & monitoring
29
PC-2040T: Performance
Laboratory Testing
SWCC Plant Trial
PC-2040T : Lab Testing CaSO4 Inhibition •
•
PC-2040 more effective than competitor A in CaSO 4 inhibition Especially at lower dose
70 PC-2040 Competitor A
n o i t i b i h n i % no effect 0
0.5 ppm
Effect PC-2040T on the Formation of CaSO 4 CaSO4 crystal
CaSO4 crystal grown PC-2040T
•
•
Dramatic decrease in crystal number (>100000 vs. 2 in treated sample) Decrease in crystal size and shape
32
SWCC
The Saline Water Conversion Corporation (SWCC) of Saudi Arabia is one of the most internationally recognized authority in the industry for evaluating thermal desalination antiscalant
The Research & Development Center (RDC) in Al-Jubail has been intensively involved in the evaluation of commercial scale inhibitor of most of recognized water treatment companies in the world
PC-2040T :SWCC Plant Evaluation
Phase #1
TBT : 110 0C
Dosage: 2 ppm
Phase #2
TBT : 110 0C
Dosage: 1 ppm
Phase #3
TBT : 119 0C
Dosage: 0.8 ppm
34
SWCC Plant Evaluation Certification
35
PC-2040T Dosage Guide Line (MSF)
36
PC-2040T Additional Dosage: Turbidity 1
) 0,8 m p p ( e0,6 s a e r c n0,4 i e s o0,2 D 0 0
1
2
3
4
5
6
Turbidity (NTU)
7
8
9
10
37
Antiscalant Dosage & Control
It is necessary to follow very closely the injection of the chemical by analysis or by feed flow rate control
Just few hours of under-dosage are enough to produce scale in the brine heater with resultant loss of production
Technology to measure & control antiscalant residual in “real time” basis is not available
38
PC-2040T: What is TRASAR®?
Patented Technology from Nalco
Use widely in boiler and cooling water system
A specifically chosen ingredient (a “tracer) is blended into Nalco product at precise concentration
Once the product is fed, the tracer is optically excited and easily detected in system water
The signal generated by this process is used to monitor and control chemical addition on a “real time” basis
39
PC-2040T: How Trasar® Work?
40
PC-2040T: How to Measure?
Pen Fluorometer
Hand Held
3DT Controller (Future)
41
PC-2040T: 3DT Automation (Future….)
PC-2040T
Summary PC-2040T Performance
Effective scale inhibitor & deposition control of CaCO3, Mg(OH)2 and CaSO4 at vary operating condition
Broad temperature range Broad range of concentration factors
Outperform antiscalant technology available in the market
Capability for having on-line measurement, “real time” & control (by Trasar®)
43
PC-2040T: Advantages
Effective scale & deposition control for all type of scales up to maximum operating condition of thermal desalination
Easy to monitor & control
NSF approved
44
PC-2040T: Benefits
Cleaner heat transfer surface
Lower steam consumption
Lower cleaning frequency
Higher plant efficiency
Higher plant reliability
Comply with SHE
