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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