INSTRUCTIONS

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Co-production of Silica and Other Commodities
From Geothermal Fluids
William Bourcier, Carol Bruton, Elizabeth
Burton, Bill Ralph, and Mackenzie Johnson
Lawrence Livermore National Laboratory Pablo
Gutierrez California Energy Commission
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Objective Develop silica extraction process at
Mammoth Lakes (50MW) geothermal site

• Dual use
• Provides water to evaporative cooler for more
  electricity
• Marketable silica to offset the cost of producing
  electricity
• Favorable fluid for high-purity silica by-product

Resource value (M)
Silica 10 Lithium 1.5 Tungsten 2.6 Rubidium (90
) Cesium (100)
500 nm
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There are multiple commercial markets for
geothermal silica
Precipitated Silicas Current industrial
production - 6M lbs./day Potential geothermal
production - 3M lbs./day
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Manufacture of commercial silica begins with
water glass (sodium silicate)
Quartz Sand
Heat

Mineral acid and calcium salt
Ion Exchange
Mineral Acid
Precipitated
Soda Ash (Na2CO3)
Colloids
Gel
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Precision Colloids Inc. manufacturing facility in
Cartersville, Georgia
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• Agglomeration

Silica evolution in geothermal fluids

• Polymerization

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Silica in tire rubber is bound together by
polybutadiene polymers
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We process the geothermal fluid that exits the
heat exchanger
Turbine
Condenser
Geothermal fluid
Heat exchanger
Well
Isobutane
Re-injection pond
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We use reverse osmosis and ultra- filtration to
extract silica
To reinjection
Silica processing
Metals Extraction (ion exchange)
600-1000 ppm SiO2
1 ppm CsRb 6 ppm Li
Ultra filter
Geothermal fluid
50-100 ppm TDS
To evaporative cooler
1300 ppm TDS 250 ppm SiO2
Reverse osmosis
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There are many ways to get the silica out

• Additives
• Add salts (MgCl2, CaCl2)
• Commercial polyelectrolytes
• Cooling
• Increased residence time
• Raise pH (Ca(OH)2 , NaOH, NH4OH)
• Vary the silica concentration

The process can be tuned to harvest silica with
the desired properties
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Geothermal silica has favorable characteristics
Geothermal colloidal silica from Mammoth Lakes
Commercial colloidal silica
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Our pilot study will focus on a colloidal silica
by-product
Precipitated Silica

• No additives
• Lower cost
• No re-injection issues or permitting needed
• No post-processing
• Equivalent or higher price
• No need to remove trace metal impurities
• For precision casting application
• Sold as 30-50 wt. slurry
• Smaller market for colloidal solutions
• 24,000 MT/y in U.S.
• 1.5 MGD at MPLP would produce 1,000 MT/y

ADVANTAGES
20 microns
DISADVANTAGES
Colloidal Silica
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We produce clean water and commercially-pure
silica
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The economics of silica production at Mammoth
Lakes are favorable
Cumulative cash flow

• Estimated for 1.5 MGD flux
• Capital 2,300,00
• Includes all equipment, buildings, and design
  costs
• Operating 670,000/y
• Includes membrane cleaning and replacement,
  filtration maintenance, energy and manpower (2
  FTE)
• Income
• Silica 1,042,000/y
• Water 150,000/y
• Net 400,000/y
• For 20 year operating life
• Payout in year 7
• Rate of return 14

Net cash flow
Payout in year 7
Estimates based on WTCOST , a water treatment
cost estimation program (Mooch, 2003).
Reduces energy cost by 1.3 / kW-hour
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Our path forward at Mammoth Lakes

• Lab and preliminary field tests
• kinetics, silica composition and properties,
  extraction methods

Preliminary economic analysis
Full-scale production?
Economic analysis

• Pilot test
• Performance data
• Engineering design specs

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Geothermal systems show a wide range of
salinities and silica concentrations
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The future of resource extraction from geothermal
fluids looks good
Silica gel

• Commercially viable silica by-products can be
  produced
• Increase the amount of green geothermal energy
• Saves energy that would be needed for mining
• Can also apply methods to produced waters from
  oil and gas fields

Coso geothermal field
Need to develop new selective extraction
technologies to see maximum payback
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Evaporative cooling panels at Mammoth Lakes site
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Purpose Reduce the cost of geothermal
electricity by co-producing marketable by-products

• Produce additional revenue from marketable
  by-products
• Eliminate scaling and re-injection problems
• Extract more energy from the resource
• Allow additional downstream resource extraction
• Save energy spent and avoid waste generated in
  mining

500 nm
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Salton Sea
Geothermal energy production is plagued by
scaling and corrosion
Coso
Salton Sea
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Ridgecrest California needs more potable water

• Currently mining water that is 20-30 thousand
  years old
• Only available new sources are brackish water
  wells
• Zero liquid discharge requirement makes
  desalination expensive (1700/AF),
• 2/3 of that cost is for brine disposal
• What can they do?

Ridgecrest
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The Coso geothermal field may provide some novel
water supply solutions for Ridgecrest

• Use geothermal reservoir for concentrate
  re-injection
• Geothermal field needs additional water
• Avoid expensive zero-liquid-discharge technology
  stream

• Use waste heat for thermal desalination
• Unused steam can be used to power thermal
  desalination units
• Could be used to treat brackish waters from the
  North West Well Field

Requires pipeline to Coso
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Two possible treatment options using the Coso
geothermal field
I. Concentrate re-injected in Coso field
II. Thermal desalination of brackish wells

• Desalination using evaporator
• Re-inject brines

Concentrate to Coso for reinjection
PIPELINE
PIPELINES
Evaporator
Fe-Mn ox. RO or ED
North West Well Field
North West Well Field
To potable water supply
To potable water supply
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Where to go for additional water a list
prioritized by relative cost

• Water re-use
• Re-cycle water from treatment plants to aquifers
• Or have dual distribution systems
• Treatment of marginally impaired waters
• Need smart membranes for low-cost treatment
• Desalination of brackish waters
• U.S. uses 500 km3/year, brackish water reservoir
  in U.S. is 1,500,000 km3
• Sea water desalination
• Expensive using existing technologies

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Todays Desalination Technologies Reverse
Osmosis, Electrodialysis, and Distillation
Thermal methods use heat to distill water while
re-capturing heat from vapor condensation
Reverse osmosis uses pressure to drive water
through a membrane leaving the salt behind
20 nm polyamide nodules
Electrodialysis uses an electrical potential to
drive ions through a membrane leaving the water
behind
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Existing desalination technologies use too much
energy

• Reverse osmosis
• High energy use
• Uses pressure to remove water from salt

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• Electrodialysis
• High resistivity membranes
• Not modular

Energy Use, MJ/m3
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Energy Cost, /m3
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• Thermal methods
• Very high energy use
• 1,000 kW-h/AF theoretical minimum
• 800,000 kW-h/AF for heat of vaporization

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0
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Our goal is to create a new selective extraction
technology based on electrodialysis
Clean Water
Concentrate
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Nanopores can be permselective for ion transport
No Permselectivity
Permselectivity
Double layer
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• Double layer overlap results in ion
  permselectivity
• Negative surface charge allows transport of
  positive ions
• Positive surface charge allows transport of
  negative ions

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Pore

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Double layer overlap
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For brackish salinities, double layer thickness
is 3-8 nm
Ion flow
Water flow
6- to 16-nm pores provide permselectivity needed
for electrodialysis membranes
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Platinum coated nanoporous polycarbonate
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Nanoporous polycarbonate performs much better
than commercial ED membranes
Membranes will be tested in a 1 gpm Ionics ED unit
Pilot testing will begin soon using California
Prop 50 funding
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We can separate by functionalizing the membrane
surfaces to favor transport of targeted species
Coat membrane with functional group for target
species
Perchlorate preferentially passes through the
pore
Tune pore size for given ionic strength to
enhance surface diffusion
Functional groups
ED membrane now preferentially removes target
species
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Waste heat can provide a lot of water through
thermal desalination

• Total of almost 9 quads of waste heat from
  industrial and commercial sources in the U.S.
• Assume 20 is suitable for thermal desal (Tgt50oC)
• Can produce about 30 million AF using thermal
  desalination at 60 kWh per 1000gallons

The Jubail desalination plant in Saudi Arabia
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High throughput, selective membranes exist in
life ion channels and aquaporins

• Ion channel in pore wall
• Selective for Kover Na
• Mimic K hydration sphere

2003 Nobel Prize in chemistry went to Rod
MacKinnon of Rockefeller University for
determining the structure of the potassium ion
channel
Leverage off of work to understand functionality
of ion channels
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Separation technologies can be investigated using
computations

• Carbon nanotubes
• Water transport through hydrophobic carbon
  nanotubes believed unlikely
• MD simulations of Hummer et al., 2001 and Kalra
  et al. 2003 predict fast water transport through
  carbon nanotubes
• Holt et al., 2006 confirm their calculations with
  experiments

• Ions at air-water interface
• Gibbs adsorption equation predicts ions should be
  repelled from the air-water interface
• MD simulations of Jungwirth and Tobias (2001)
  predict that polarizable anions are concentrated
  at the interface
• Ghosal et al., 2005 confirm their calculations
  with ALS experiments

Discovery-based science can now be done on the
computer!
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Reversible hydrophilic-hydrophobic surfaces can
be electrically switched

• SAM stalks of alkanethiol with MHAE heads grown
  on gold surface layer
• Cleave heads to leave carboxylic acid group
• Applied positive charge - causes stalks to bend
  over
• Change from hydrophilic to hydrophobic surface

Use this method to synthesize self-cleaning
membrane surface
From Robert Langers group at MIT, Lahan et al.
(2003) Science, 299371.
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Fast water transport observed through aligned
carbon nanotubes

• Transport of water up to 8000 times faster than
  predicted by continuum hydrodynamics, resulting
  in lower energy and/or capital costs for
  desalination
• Fabricated from low-cost materials silicon,
  hydrocarbons, metal alloys, and vapor-deposited
  polymers/ceramics.

CNT-based membranes could greatly lower energy
costs for desalination