Post on 18-Aug-2018
Alternative Approaches to Design
Evaporator and Crystallizer
Systems using OLI Software
Ken Martins/CH2M HILL
October 17, 2012
Copyright 2012 by CH2M HILL, INC
Outline
• Key Drivers for Zero Liquid Discharge (ZLD) Processes
• Overview of Softener, Evaporator (EVAP) and
Crystallizer (CX) Processes
• Single Stream Analyzer® based Evaluation (with Excel)
• Iterative Stream Analyzer® Evaluation
• Aspen plus with OLI Chemistry Engine (Aspen OLI)
Evaluation
• CH2M HILL Process Modeler Tool “SOURCE”
Copyright 2012 by CH2M HILL, INC
Why ZLD is Becoming a More
Viable Option • Discharge permit water quality standards changing
– Lowered for certain parameters (e.g., metals, chlorides)
– New parameters added (e.g., TDS and Whole Effluent Toxicity
[WET])
• Regional water scarcity concerns driving internal
reuse, further increasing concentrations of all
dissolved salts
• EPA recommending ZLD (Steam Electric Power Generating Point Source Category: Final
Detailed Study Report, EPA 821-R-09-008)
Copyright 2012 by CH2M HILL, INC
Why ZLD is Becoming a More
Viable Option (con’t)
• Fewer alternatives for disposal in some regions
– Intensive permitting restrictions for deep well
injection and surface impoundments in California
• New wastewater streams (e.g., flue gas
desulfurization) more difficult to treat with
conventional technologies
Copyright 2012 by CH2M HILL, INC
Increasing Market trends for ZLD
• Global Water Intelligence, Dec 2009
– Total capital investment in ZLD systems around
the world is estimated to be between $100-200
million per year (2009)
– The predominance of ZLD projects has increased
from none in 1970 to about 100 in 2009
– Relatively few of these systems (a total of just over
100 worldwide), are designed purely as ZLD
systems (e.g., avoiding saline water discharge)
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Overview of ZLD Treatment Processes
Lime/Soda
Softener Evaporator Crystallizer
Distillate Distillate Waste Solids Waste Solids
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Softener Process with Post
Filtration
Evaporator Crystallizer
Distillate Distillate Waste Solids
Gravity Media
Filter
Reactor-
Clarifier
Sulfuric
Acid
Waste Solids to Dewatering
Influent
Hydrated Lime
Soda Ash
Sulfuric Acid
Antiscalant
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Softener Precipitation Chemistry
• KW = [H+][OH-]
• K2 = [10-pH][CO32-]/[HCO3
-]
• KSP(CaCO3) =[Ca2+][CO32-]
• KSP(Mg(OH)2) = [Mg2+][OH-]2
• KSP(CaF2) = [Ca2+][F-]2
• KSP(CaSO4) = [Ca2+][SO4]
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Softener Chemistry
Copyright 2012 by CH2M HILL, INC
2
Modeling Softener Chemistry in SA First Step: Add Lime, as Needed to Attain Target Soluble Mg
Second Step: Add Soda Ash, as Needed to Attain Target Soluble Ca
Copyright 2012 by CH2M HILL, INC
2
Lime Addition – 1st Step for
Softener Modeling
Copyright 2012 by CH2M HILL, INC
Soda Ash Addition – 2nd Step for
Softener Modeling
Copyright 2012 by CH2M HILL, INC
Vapor Recompression-driven
Evaporator
Lime/Soda
Softener Crystallizer
Distillate
Waste Solids
Waste Solids Recirc Pumps
Compressor
Evaporator Distillate
Preheater and Deaerator
not shown for clarity
Copyright 2012 by CH2M HILL, INC
CaSO4
Caustic
Key Design Factors for
Evaporators
• Soften water to avoid CaCO3 scale
– Adjust pH, strip CO2, N2, O2
– Add antiscalant
• For Mechanical Vapor Recompression
driven Evaporators, Limit Boiling Point
Rise to 5.5 to 6.5 F
• Seed evaporator liquor with CaSO4 solid
– Hold between 10-15% solids in slurry Copyright 2012 by CH2M HILL, INC
Use Stream Analyzer to Predict
Key Parameters of Interest
• Caustic dosage to achieve desired pH of
evaporator concentrate
• Composition and mass of solids
• Composition of liquid phase
– Boiling point of liquid phase
• Volume of distillate
Copyright 2012 by CH2M HILL, INC
Boiling Point Rise
Limit of 218.5 °F BPR
Developed using OLI’s StreamAnalyzer TM program
210
212
214
216
218
220
222
224
226
228
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Bo
ilin
g P
oin
t (º
F)
Brine (fraction of influent flow)
Boiling Point vs. Fraction Evaporated
5,000 mg/L Cl-, 10,000 mg/L TDS
10,000 mg/L Cl-, 20,000 mg/L TDS
15,000 mg/L Cl-, 25,500 mg/L TDS
20,000 mg/L Cl-, 40,000 mg/L TDS
Copyright 2011 by CH2M
HILL, INC
Prepare integrated mass balance, integrating
mass flows and chemistry calculations
• Use Stream Analyzer in tandem with Excel
– Start with design basis values of flows and
concentration in Excel
– Use Stream Analyzer to calculate chemistry and
phase changes for first unit operation
– Transfer Stream Analyzer output to Excel, Calculate
feed to next unit process
– Use Stream Analyzer to calculate chemistry and
phase changes for second unit operation and so on… Copyright 2012 by CH2M HILL, INC
Make Adjustments to Account for the
“Perfections” of Stream Analyzer
• Within integrated mass balance, we make
adjustments to account for :
– Lack of complete equilibrium
• Add excess to drive to near completion
– Equipment imperfections
• Floc carryover
• Undissolved lime
• Need to create methods and a tool to release to
others at CH2M HILL Copyright 2012 by CH2M HILL, INC
Sequential Process Steps
Modeled in SA
Copyright 2012 by CH2M HILL, INC
Example Screen Shot of Spreadsheet
Portion of Integrated Mass Balance
Copyright 2012 by CH2M HILL, INC
Vapor Recompression-driven
Crystallizer
Lime/Soda
Softener Evaporator
Distillate Waste Solids
Condensor
Multistage
Compressors
Crystallizer Distillate
Waste
Solids
Copyright 2012 by CH2M HILL, INC
Caustic
Key Design Factors for Crystallizers
• Soften water to avoid CaCO3 scale
– Adjust pH, strip CO2, N2, O2
– Add antiscalant
• For Mechanical Vapor Recompression driven
Crystallizer, Limit Boiling Point Rise to 6.5 F ,
otherwise steam-driven or vacuum crystallizer
designs
• Maintain crystallizer recirculated between 10-
15% solids in slurry Copyright 2012 by CH2M HILL, INC
Use Stream Analyzer to Predict
Key Parameters of Interest
• Composition and mass of solids
• Composition of liquid phase
– CaCl2 and NO3 often removed strictly as salt
cake moisture (Check by mass balance)
– Boiling point of liquid phase
• Mass of distillate
Copyright 2012 by CH2M HILL, INC
If Boiling Point Rise Too High for Mechanical
Recompression…..
• Can use vacuum
crystallizer • BP is reduced when
operated under vacuum
• Ca/Mg salt solubility
decreases as
temperature is lowered
• Can use steam fed
crystallizer
Salt
(CaCl2, MgCl2)
Hot Distillate
Compressor
Expansion Valve
Vacuum Pump
Copyright 2012 by CH2M HILL, INC
Alternative use of Stream
Analyzer as Iterative method
• Labor intensive method
• Replicates process as if starting up
• Water surveyed to create solids
– Take solids cut at 15% solids (normal design
point for CX
– Mix concentrate back with fresh influent 1:1
– Check solids with moisture for element balance
– Repeat Copyright 2012 by CH2M HILL, INC
First Concentration (Water
Survey) of Example Project
85% Aq phase
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20th Concentration (Water
Survey) of Example Project
85% Aq phase
Copyright 2012 by CH2M HILL, INC
Issues with iterative method
• Tedious - Each iteration requires
– Determine closest cut to 85% aqueous
– Save Aq phase, Check mass balance of solubles
– Blend with raw influent, Water survey again
• Prone to error
– Easy to select wrong percent liquids cut
• Time consuming
Copyright 2012 by CH2M HILL, INC
Speeding up the Iteration
Approach
• Method 1 – Mix 4 parts concentrate to a
part make-up for first couple iterations, then
just 1 part concentrate to 1 part make-up
• Method 2 – Water survey to dry salt,
Identify soluble species, artificially increase
those about 40 times, mix 1 part concentrate
to 1 part make-up
Copyright 2012 by CH2M HILL, INC
Aspen plus with OLI Engine
(Aspen OLI)
• Iterative method using Stream Analyzer
identified need to iterate and cycle-up
concentration to reach equilibrium
– Aspen plus does exactly that
Copyright 2012 by CH2M HILL, INC
Aspen OLI Model for Crystallizer Only
Copyright 2012 by CH2M HILL, INC
Aspen Output is Clunky
Copyright 2012 by CH2M HILL, INC
Aspen OLI Input and Output can
be Linked with Excel
Copyright 2012 by CH2M HILL, INC
Excel Allows use of Convenient
Graphics and Calculations
34
Copyright 2012 by CH2M HILL, INC
Future – CH2M HILL Software
SOURCE with OLI Engine • SOURCE is a CH2M HILL developed
process modeler similar to Aspen
– Unit processes are selected and linked together
– Chemistry is entered and the model calculates
the chemistry changes at each unit process
iteratively
• SOURCE has developed the ability to use
OLI’s chemistry engine (call basis)
• Strictly for internal CH2M HILL use
Copyright 2012 by CH2M HILL, INC
Future – CH2M HILL Source
with OLI Engine
• Current SOURCE unit processes
– Lime/Soda softeners, pH adjustment, Clarifiers,
Filters, Microfilters, Reverse osmosis,
Electrodeionization, Ion Exchange
• Future planned SOURCE unit processes
– Evaporators, Crystalyzers, Dewatering Systems
Copyright 2012 by CH2M HILL, INC
Screen Shot of SOURCE
Copyright 2012 by CH2M HILL, INC
Screen Shot of SOURCE
Copyright 2012 by CH2M HILL, INC
Screen Shot of SOURCE
Copyright 2012 by CH2M HILL, INC
Screen Shot of SOURCE
Copyright 2012 by CH2M HILL, INC
Questions?
Copyright 2012 by CH2M HILL, INC