Alternative Approaches to Design Evaporator and...

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”


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)


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


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)


Overview of ZLD Treatment Processes

Lime/Soda

Softener Evaporator Crystallizer

Distillate Distillate Waste Solids Waste Solids


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


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]


Softener Chemistry


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


2

Lime Addition – 1st Step for

Softener Modeling


Soda Ash Addition – 2nd Step for

Softener Modeling


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


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


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


Example Screen Shot of Spreadsheet

Portion of Integrated Mass Balance


Vapor Recompression-driven

Crystallizer

Lime/Soda

Softener Evaporator

Distillate Waste Solids

Condensor

Multistage

Compressors

Crystallizer Distillate

Waste

Solids


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


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


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


20th Concentration (Water

Survey) of Example Project

85% Aq phase


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


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


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


Aspen OLI Model for Crystallizer Only


Aspen Output is Clunky


Aspen OLI Input and Output can

be Linked with Excel


Excel Allows use of Convenient

Graphics and Calculations

34


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


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


Screen Shot of SOURCE


Questions?


Alternative Approaches to Design Evaporator and...

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