Boiling Water Using the Sun Water Chemistry Challenges for a

Solar Power Plant

Jeanette Shoemaker, P.E. (Ohio)

Senior Mechanical Engineer

Bechtel Power Corporation

CIVIL GOVERNMENT SERVICESMINING & METALSOIL, GAS & CHEMICALS POWER

Ivanpah Solar Electric Generating Facility

Overview

Thermal Solar Power Fundamentals

Water Chemistry

Challenges for Solar Power Plants– Water Availability– Water Treatment Options– Wastewater Discharge

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Ivanpah Solar Electric Generating Facility

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Located in CA ~45 miles southwest of Las Vegas Owned By: NRG Energy, Google and BrightSource Energy 3 Units totaling approximately 400 MW Project site over 3600 acres Approximately 173,500 heliostats (each with having 2 mirrors) 459-foot steel structure

– Solar receiver steam generator (SRSG) sits atop tower– Auxiliary equipment located within the tower

Solar Thermal – Power Tower Technology

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Water Chemistry

What are the water quality requirements?

• High-Purity• Deoxygenated• pH Controlled

Why is it important?

Damage to the turbine or SRSG from:• Deposition• Erosion• Corrosion

Parameter SRSGMakeup

Drinking Water

Chloride 0.003 ppm 250 ppm

Specific Conductivity

0.2 μS/cm NR

Copper 0.002 ppm 1.3 ppm

Iron 0.005 ppm 0.3 ppm

pH 9.2 – 9.6 6.5 – 8.5

Silica 0.01 ppm NR

Sodium 0.003 ppm NR

Sulfate 0.003 ppm 250 ppm

TDS 0.025 ppm 500 ppm

Dissolved Oxygen

< 0.007 ppm 6 – 9 ppm

NR = Not Regulated

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Water Chemistry Challenges

Challenge: Zero Liquid Discharge

• Limited Water Availability

• No Evaporation Ponds or Onsite Waste Discharge Options

Impacts:

• Need water to make power

• Mirrors require frequent cleaning for best performance

• Water consumption and waste generation from water treatment technologies

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Minimizing Water Consumption

• Utilize ‘dry cooling’ in lieu of cooling towers

• Air-Cooled Condenser requires no water supply

• Optimize mirror washing process to reduce frequency and minimize water consumption

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Water Treatment

• Limited Water Quality Data• Technologies Available:

• Reverse Osmosis (RO)• Membrane separation• Large waste/reject stream generated

• Ion Exchange (IX)• No waste stream generated from process• Frequent regeneration required

• Ultrafiltration (UF)• Used in combination with ion exchange or RO

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Wastewater Management

• Restrictions

• No evaporation ponds

• All wastewater must be recycled or shipped off-site

• Results

• Strict water management• Reduce water consumption

• Reuse process water to maximum extent

• 100% recycle of all waste streams

• Waste-minimizing treatment technology

• IX in lieu of UF/RO

• Offsite resin regeneration• Trailer – mounted rental equipment

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QUESTIONS?