Modeling Lime-Soda Produced Water Softening Processes with Aspen Plus™/OLI

James Silva, Hope Matis, William Kostedt IV, and Vicki

Watkins

GE Global Research Center

Niskayuna, NY

ACKNOWLEDGEMENT

Funding for this project is provided by RPSEA through the “Ultra-Deepwater and Unconventional Natural Gas and Other Petroleum Resources” program authorized by the U.S. Energy Policy Act of 2005. RPSEA (www.rpsea.org) is a nonprofit corporation whose mission is to provide a stewardship role in ensuring the focused research, development and deployment of safe and environmentally responsible technology that can effectively deliver hydrocarbons from domestic resources to the citizens of the United States. RPSEA, operating as a consortium of premier U.S. energy research universities, industry, and independent research organizations, manages the program under a contract with the U.S. Department of Energy’s National Energy Technology Laboratory.

• 23% of domestic gas production • Pennsylvania Marcellus: 1750 new wells • Marcellus Produced Water: 24 MM bbl • Marcellus, Barnett:

- High TDS - High Group II metal concentrations (Ba, NORM)

Disposal options • Blendstock for reuse (93%) • UIC disposal in Ohio (7%) • Thermal water & salt recovery (still under development...but needed)

Objective: Identify Pretreatment Technologies...Economic Water & Salt Recovery for Ba-, NORM-containing Produced Water

US Shale Gas 2011...lots of high-TDS produced water

Produced Water Composition

Well-1 Well-2 Well-3 Well-4 Well-5 Well-6 Well-7** Design

County Bradford Bradford Bradford Butler Tioga Washington (Barnett)

TDS 96,792 154,855 202,255 68,405 149,149 123,043 127,766 132,460

Na+ 26,000 38,000 53,000 19,200 39,000 32,000 35,000 35,000

Mg++ 450 830 1,280 575 1,000 800 1,200 800

Ca++ 5,500 10,280 13,120 5,350 13,000 9,000 11,000 9,500

Sr++ 2,000 3,670 4,580 1,300 2,600 2,500 1,800 2,500

Ba++ 6,600 13,000 11,600 30 3,500 6,000 150 6,200

Fe++ 26 74 123 50 32 <10 50 50

Mn++ 1.5 2.5 3.4 1.7 2.7 <10 1.2 3

Cl- 56,199 88,988 118,534 41,842 90,014 72,725 78,534 78,407

SO4= <10 <10 <10 57 <10 <50 <100 0

SiO2 15 10 15 <50 39 18 30 0

226Ra* 5,400 7,600 4,000 4,900 5,400 350 2300 5,000

*pCi/L

Variable but High TDS, Ba, NORM

Pretreatment

Sludge Disposal:

- Suspended Solids

- Mg(OH)2

- Iron/Manganese

- NORM (?)

Distilled

Water

Product

Concentrate: ~300K ppm TDS (+Ba, NORM)

To UIC Disposal

0.56 bbl

0.44 bbl

1 bbl Produced Water

Thermal Water Recovery…Today

Design

Case, mg/L

TDS 132,000 Mg++ 800 Ca++ 9,500 Sr++ 2,500 Ba++ 6,200 TSS 200 226Ra (pCi/L) 5,000

Pretreatment-1

Produced Water

Evaporation

Mobile units or

Central Plant

Crystallization

Salt product (disposal or beneficial reuse)

Central plant Ba, Ra Removal

(option 2) Ba, Ra disposal

Sludge to RCRA-D or NORM disposal

Distilled water

Distilled water

Ba, Ra Removal (option 1)

Ba, Ra disposal

Thermal Water and Salt Recovery…Tomorrow

Produced Water Softening Options

Process Issue

Chelating Ion Exchange Resin Capacity

Nanofiltration Water Recovery

Sulfate coprecipitation Sludge disposal

Selective Ra adsorption Adsorbents not selective

Carbonate precipitation Sludge disposal

Modified carbonate precipitation Process complexity

MnO2 adsorption Adsorbent capacity

-Best Option depends on Produced Water Chemistry -Aspen/OLI enables process screening

0

2000

4000

6000

8000

10000

0 5 10 15 20 25 30

Aspen ELECNRTL

Aspen OLI

OLI Stream Analyzer

Marshall & Slusher (1966)

CaS

O4 S

olu

bili

ty, m

g/k

g

NaCl Concentration, wt%

Property Set/Source

Test Electrolyte Model for CaSO4-NaCl-H2O System

• ELECNRTL very inaccurate • OLI package excellent accuracy

0

1000

2000

3000

4000

5000

6000

7000

8000

0 5000 10000 15000 20000

25

50

100

200

500

Samples

Raw

pro

duced w

ate

r 2

26R

a a

ctivity, pC

i/L

Raw produced water [Ba], mg/L

Wet Sludge 226

Ra activity, pCi/gm(45 wt% solids)

DesignCase

Ba, Ra Removal Option: Sulfate Precipitation

• Radium, Barium coprecipitate: (Ba,Ra)SO4 • Simple material balance...calculate 226Ra activity in (Ba,Ra)SO4 sludge

• All Ba, Ra precipitate • No other Group II metals precipitate • 45 wt% solids in sludge

Disadvantages • Disposal may require NORM facility • $1.2-$2/bbl PW (design case) • Sulfate dosing needs Ba measurement

Seek Softening Process that Minimizes NORM Solids Disposal

Advantages • Coprecipitation efficiently removes Ra • (Ba,Ra)SO4 chemically stable • Na2SO4 is cheap ($0.15/bbl PW design) • Well-established process

Precipitation

Stage 1A

Precipitation

Stage 1B

Ca(OH)2

Mg(OH)2(s)

Fe(OH)3(s)

MnO2(s)

to RCRA-D

Na2CO3

CaCO3(s)/SrCO3(s)

to RCRA-D

Treated PW

to Thermal

H2O and NaCl

Recovery

Precipitation

Stage 2

Na2CO3

BaCO3(s)

RaCO3(s)

Produced

Water

(PW)

Feed

Redissolution HCl

BaCl2, RaCl2

Concentrate

to UIC

Oxidation

Oxidant

CO2

HCl

Modified Lime-Soda Process

Selectivity in Precip Stage 1B essential

Species Solubility*,

gm/100 gm H2O (20°C)

CaCO3 0.0015

SrCO3 0.0011

BaCO3 0.0022

*CRC Handbook of Chemistry & Physics

Model Prediction: No “interval” between CaCO3/SrCO3 and BaCO3 precipitation

Experimental: No selectivity...carbonate ppt contains NORM, Ba

0

5000

10000

15000

0 0.5 1 1.5

CaSrBa

pH

10.50

11.00

11.50

12.00

ppm

Hard

ness C

ation S

upern

ata

nt p

H

Fraction Stoichiometric Na2CO3 (vs. Ca+Sr+Ba)

2X

...Try the hydroxides

Carbonate Solubilities

Precipitation

Stage 1

NaOH

Fe(OH)3(s)

MnO2(s)

Mg(OH)2(s)

Ca(OH)2(s)

to RCRA-D

Treated PW

to Thermal

H2O and NaCl

Recovery

Precipitation

Stage 2

Na2CO3

SrCO3(s)

BaCO3(s)

RaCO3(s)

Produced

Water

(PW)

Feed

Redissolution HCl

BaCl2, RaCl2

Concentrate

to UIC

Oxidation

Oxidant

CO2

HCl

Modified NaOH-Soda Process

Species Solubility,

gm/100 gm H2O (20°C)

Mg(OH)2 0.0009*

Ca(OH)2 0.173**

Sr(OH)2 1.77**

Ba(OH)2 3.89**

*CRC Handbook of Chemistry & Physics **Wikipedia

10X

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.5 1.0 1.5

CalculatedMeasured

Fra

ction F

ee

d C

PM

Rem

ain

ing in S

olu

tio

n

Overall Stoichiometric Ratio

Hydroxide Solubilities

Potential for selectivity between Ca and Sr

0

5000

10000

15000

0 0.5 1 1.5

MgCaSrBa

pH

8.00

9.00

10.00

11.00

12.00

13.00

14.00

ppm

Hard

ness C

ation

Overall Stoichiometric Ratio:

(NaOH/2+Na2CO3)/(Mg+Ca+Sr+Ba)

Na2CO3/(Sr+Ba)o=4/1

NaOH Addition Na2CO3 Addition

Selectivity OK, but materials costs excessive ($3/bbl for design case)

Conclusions

Prediction accuracy OLI solubility predictions far superior to ELECNRTL

Aspen Plus modeling capability + OLI properties: tool for process evaluation

Suggestions for improvement: Simplify process for keeping track of components in Aspen - alphabetizing by component name - sorting by component type (solid, conventional)

Experiments: Carbonate-only system…no selectivity for Ca vs. Ba NaOH-Carbonate system: Good selectivity for Ca vs. Ba …experiment agrees with Aspen/OLI predictions