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Development of a Highly Efficient Membrane-Based Wastewater Management System for Thermal Power Plants Xiao Wang, Palitha Jayaweera, Elisabeth Perea, Richard Callahan, and Indira Jayaweera*
Summary: The main goal of the proposed research is to introduce SRI-based polybenzimidazole (PBI) hollow-fiber membranes (HFMs) for flue gas desulfurization (FGD) wastewater (WW) treatment and Selenium (Se) release control. The PBI membranes are resistant to fouling and can be operated under substantially harsher conditions than those tolerated by commercial membranes. Success of this project will result in an effluent control system that reduces freshwater withdrawal by removing hazardous compounds and reusing the recovered water. Contact: Indira S. Jayaweera, Sr. Staff Scientist/ Sr. Program Manager, [email protected], +1-650-859-4042
Background of Flue Gas Desulfurization Wastewater (FGD WW) Treatment and Selenium (Se) Pollution Control
1. Water Requirements for Existing and Emerging Thermoelectric Plant Technologies. DOE/NETL, 2008. 2. Journal of the Air & Waste Management Association, 51 (2011) 1676-1688. 3. Journal AWWA, 100 (2008) 76-89.
Wet FGD
- Limestone-forced Oxidation - Limestone-inhibited Oxidation - Jet-bubbling Reactor - Lime - Magnesium-enhanced Lime - Dual Alkali - Seawater
Once-through
- Sodium Sulfite - Magnesium Oxide - Sodium Carbonate - Amine
Regenerable
Element/Ions in Untreated FGD
Wastewater Concentration (ppm)
Boron (B) 100 - 600 Calcium (Ca) 300 - 1000
Magnesium (Mg) 1000 - 4000 Potassium (K) 45 Sodium (Na) 500 Chloride (Cl-) 10000 - 25000 Nitrate (NO3
-) 1-400 Selenium (Se) 1-10 Sulfate (SO4 2-) 3000 - 20000
PC power plant with cooling and wet FGD 1
Comparison of the costs of MLD and ZLD.3
Minimum Liquid Discharge (MLD)3
• Membrane-based MLD is a more economical process than zero-liquid discharge (ZLD).
• The last 5% of ZLD is costly.
0 70 95 100 Water Recovery (%)
ZLD
Cost
of W
ater
Rec
over
y ($
/m3)
Primary Wastewater Reuse Minimal Liquid Discharge (MLD)
$12-13/1000 gal
$4-6.6/1000 gal
Selenium Chemistry 4-6
• For adults, the recommended daily Se intake is 55 mg, and the upper limit is 400 mg.
• Se toxicity: Se(+IV) < Se(+VI) < Se(-II). • Environmental Protection Agency (EPA) criterion: acute
concentration (20 ppb) and chronic concentration (5 ppb). • In FGD WW, Se is present as Se(+VI) and Se(+IV).
1 2 3 4 5 6 7 8 9 10 11 12 13 14
H2SeO3 HSeO3- SeO3
2-
HSeO4- SeO4
2-
pH
Se(+IV)
Se(+VI)
Speciation of Se in Aqueous Solution
H2Se HSe- Se(-II)
*In a nanofiltration (NF) membrane with negative surface charge, this area leads to higher rejection .
4. Talanta, 154 (2016) 474-480. 5. Aquatic Life Ambient Water Quality Criterion for Selenium – Freshwater, EPA, 2016. 6. Applied Geochemistry, 11 (1996) 797-802. 7. Science of the Total Environment 521–522 (2015) 246–260. 8. Water Research, 71(2015) 274-281. 9. Geochimica et Cosmochimica Acta, 206 (2017) 236–253. 10. Environmental Science and Pollution Research 22 (2015) 3127-3137. 11. Biotechnology Advances 34 (2016) 886–907. 12. Membrane Separation Technology in Carbon Capture, Chapter 3, 60. 13. Nature Communication, 4:2344 (2013).
Comparison of Technologies for Se Removal7
• Efficiency: ~100% removal, <10 ppb • Long resident time • pH and temperature dependent • High cost of chemicals and waste
disposal
Chemical Reduction8 Coagulation Ferrihydrite Precipitation9
• Efficiency: <5 ppb • Ineffective for SeO4 2-
• Influenced by other anions • pH dependent (4-6) • Extra cost for solid waste disposal
Electrocoagulation10
• Efficiency: ~ 98% removal • High energy consumption • Extra cost for electrolyzer construction
and electrode replacement
Biological Method11
• Efficiency: <10 ppb • Cheap and adaptable to various wastewaters • More energy to remove oxygen in wastewater • Remobilization of bio-reduced selenium • Interference of other oxyanions (e.g., nitrate,
sulfate)
• Efficiency: varies widely • Low cost • Not suitable for high levels of
contaminants • pH and temperature dependent • Ion-competitive effects • Extra cost for regeneration and disposal
of exhausted absorbents
Ion Exchange and Absorption12 Membrane Separation 13
• Efficiency: >95% • pH independent • Removes other pollutants
simultaneously • Operational cost is comparatively
high
Our Approach
FGD Recycle
FGD
Waste Heat 32oC to 70 oC
High Pressure RO
Low Pressure RO
Hydrocyclone
Concentration Disposal
Clean Water Recovery
Salt Precipitates Blowdown
Makeup water
Research focus
MLD Strategy Proposed by SRI
The main goal is to develop innovative effluent water management practices at coal-fired energy plants; we will also:
•Test the SRI seawater desalination PBI hollow-fiber membranes (HFMs) for separating sulfates and selenium from an FGD WW simulant and then from real-world FGD WW.
•Use the data to design and model the optimized membrane unit arrangement for reduced energy operation.
•Fabricate high-strength PBI HFMs suitable for processing high-salinity (high-osmotic pressure) brines at an industrial site.
Cooperative agreement grant with U.S. DOE: − Contract No. DE-FE0031552 Period of Performance: − 12/19/2017 – 06/18/2020 Funding: − U.S. Department of Energy: $639,949 − Cost share: $160,000 − Total: $799,949 NETL Project Manager: − Anthony Zinn: [email protected] Principal Investigator: − Indira Jayaweera: [email protected]
NETL • Funding and technology oversight SRI • PBI membrane development • Membrane testing Enerfex, Inc. • Membrane system modeling
PBI Performance Products, Inc. • PBI dope source Generon, IGS • Membrane fabrication site OLI Systems • Optional partner
Project Budget and Team
Membrane Separation Based on Polybenzimidazole Hollow-fiber Membranes (PBI HFMs)
http://diagram.premamaz.com/reverse-osmosis-diagram/
• Pressure driven process (200-1000 psi) to overcome osmosis pressure
• Solution diffusion mechanism: RO membrane is assumed to be nonporous, and transport is by diffusion between the interstitial space of polymer chains or polymer nodules
• Donnan effect: works in charged membranes • Reverse osmosis is the best known method for
removing dissolved hardness
Reverse Osmosis (RO) Technology
Repel
Hollow-fiber Membrane Spiral-wound Flat-sheet Membrane
Advantages of Hollow-fiber Membranes • No need for spacers • Self-supporting structure • Able to permeate channel • High surface area per unit of membrane module volume: spiral-wound packing density is 800 m2/m3
while hollow fiber is 6000 m2/m3 (reported by Lux Research, Inc.)
SRI PBI module
Hollow-fiber vs. Spiral-wound Membranes
J. Membr. Sci. 362 (2010), 202-210
PBI vs. Other Membrane Materials
N
N
N
N
H
H
n
PBI molecular structure
RO Membrane Materials Property Reference
PBI
Superior thermal stability: Tg=450oC, degradation at 450oC in air, continuous operating temperature up to 250oC
High mechanical strength Outstanding chemical resistance Excellent chlorine resistance.
Fire Mater. 26(2002),155–
168
Cellulose Triacetate
• Low thermal resistance (<30oC) • Low chemical resistance (working pH=2-8)
Poor chlorine resistance Desalination
326(2013), 79-95 Polyamide • Poor chlorine resistance
FGD and Advantages of Minimum Liquid Discharge (MLD)
PBI HFM
Fabrication of Polybenzimidazole Hollow-fiber Modules
550 µm
265 µm 100 µm 100 nm
100 nm
Nano open pores on shell surface
Interconnected porous structure in support layer
Barrier layer on lumen surface
1 µm
96.75
96.80
96.85
96.90
96.95
97.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
5000 7000 9000 11000 13000 15000
Reje
ctio
n (%
)
Flux
(LM
H)
TDS (ppm)
Test @ 400 psi
Flux (LMH)
Rejection (%)
Composition of Feed Solution (TDS=~1500)
Salt Concentration (ppm) Ions Concentration
(ppm)
CaSO4 2511 Ca2+ 3272
CaCl2 7029 Mg2+ 1908
MgCl2 7553 Na+ 681
NaCl 1731 Cl- 11191
Total 18824 SO4 2- 1773
Our PBI HFM is comparable to the best commercial product
Point Material Reference Do DowEX (cellulose triacetate) Desalination 102 (1995) 225-234
Du1 Permasep B-10 (polyamide) Desalination 126 (1999) 33-39 Du2 Permasep B-9 (polyamide) Desalination 48 (1983) 1-16 T-1 Hollosep MH10255 (Cellulose triacetate) Desalination 125(1999) 55-64
T2 Hollosep HA8130 (Cellulose triacetate) Journal of Membrane Science 236 (2004) 1—16
HF1 Dual layer (Polyethersulfone/polyamide) Environ. Sci. Technol. 46(2012), 7358−7365
HF2 Dual layer (Polyester/polyamide) Environ. Sci. Technol. 47(2013), 7430−7436
HF3 Electrospun fibers (polyacrylonitrile) Journal of Membrane Science 363 (2010) 195–203
Test with ~2000 ppm NaCl solution@400 psi at room temperature
Previous Test
Preliminary Test
Inside-out HF (Negatively-charged Barrier Layer)
100 µm 209 µm
496 µm
100 nm
1 µm 100 nm
Barrier layer on shell surface
Interconnected porous structure in support layer
Micro open pores on lumen surface
Test @ room temp (TDS=~5000)
Pressure Module #1 Module #2
Flux Rejection Flux Rejection 300 1.52 98.4 1.26 98.8 400 1.81 99.0 1.59 99.1
Test @ 50 oC (TDS=~5000)
Pressure Module #1 Module #2
Flux Rejection Flux Rejection 300 1.95 98.7 1.73 98.9 400 2.66 99.0 2.21 99.0
Outside-in HF (Positively-charged Barrier Layer)
100 nm
71.9 nm 84.4 nm
0.000
0.005
0.010
Reje
ctio
n (%
)
PBI HF (SRI)
Permeability
Perm
eabi
lity (L
/(m2 h
psi)
)
Hollosep (Toyobo)90
92
94
96
98
100
Rejection
-50
-40
-30
-20
-10
0
10
Per
cent
age
(%)
Change of water permeability Change of water-salt selectivity
PBI hollow fibers LCLE (DOW) BW30 (DOW)
86
87
88
89
90
91
92
93
94
95
96
97
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Reje
ctio
n (%
)
Flux
(L/m
2 hr
)
pH
Flux(L/m2 hr) Rejection (%)
4.9 6.9 9.2 10.0 9.9 7.9 4.9
Superior chlorine resistance 15
(Chlorine exposure: 4,000 ppm· h, pH=11, Feed solution: 2,000 ppm NaCl)
Ultra-thin PBI barrier layer Higher selectivity at low pH value
14. Desalination 125(1999) 55-64 15. J. Membr. Sci., 451(2014), 205-215
Performance is comparable to the commercial HF 14
Previous Test
Preliminary Test
Two Different Types of Hollow-fiber Membranes (HFMs) and Their Performance
Conclusions
Both operational cost and energy consumption will be significantly decreased by the use of reverse osmosis (RO) technology in flue gas desulfurization wastewater (FGD WW) management approaches.
Among the existing technologies, membrane separation, especially using RO, is the most promising way to remove Se and other heavy metals in FGD WW.
The hollow-fiber (HF) format reduces membrane module size and operational cost relative to spiral-wound membranes.
Inside-out HF can provide both high flux and rejection comparable to that of commercial flat-sheet membranes.
Outside-in HF can tolerate harsh operating conditions, and its separation performance is comparable to that of commercial membranes.
Acknowledgements The authors wish to acknowledge:
• The DoE Project Manager
• The SRI Team and Partners
• The DoE for current funding (DE-FE0031552)
• Previous Funding from, the KACST, Riyadh, National Energy Technology Laboratory (NETL) of the U.S. Department of Energy (Contract No. DE-FE0012963), and the Office of Naval Research (ONR) of the US Department of Defense (Contract No. N00014-10-C-0059).
Disclaimer This poster includes an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise does not necessarily constitute or imply endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
5. Large fiber module
2. Crosslinking
3. Post treatment
4. Potting
4” diameter module containing 10,000 fibers (Gas-separation PBI membrane elements are pictured)
1. Fiber Spinning