SEAWATER DESALINATION USING RENEWABLE ENERGY: SOLAR, GEOTHERMAL, AND WIND Noreddine Ghaffour, Sabine Latteman, Thomas Missimer, Kim Choon Ng, Shahnawaz Sinha, Gary Amy Water Desalination and Reuse Center King Abdullah University of Science and Technology

Introduction Global goals for seawater desalination improvement: -reduce the cost -reduce the carbon footprint -reduce the energy consumption -encourage the use of renewable energy sources Saudi Arabia is the world’s largest user of desalinated seawater and uses mostly energy- intensive thermal processes (MSF).

Renewable Energy in the Kingdom of Saudi Arabia Renewable energy sources viable in the Kingdom of Saudi Arabia -Solar available in the entire country (daytime use only and not a continuous source) -Wind available in western region and at various times throughout the country (variable viability) -Geothermal available primarily in western Saudi Arabia (where viable it is a continuous source)

Applicability of Renewable Energy Use in Seawater Desalination Multi-stage flash distillation -requires electric grid powering to run high- heat requirement -could use solar collector system for direct heating Multiple-effect distillation -heating of the water could involve direct use of solar collectors Reverse osmosis -requires electric grid powering

Applicability of Renewable Energy Use in Seawater Desalination Adsorption desalination -primary heating can be provided by either solar or geothermal -solar energy can be provided by heat collectors (70-850 C) or at higher temperatures via solar collectors -“low grade” or high grade geothermal resources can be used -further discussion on combined cycle solar- geothermal powering concept

Adsorption Desalination Adsorption desalination is a promising new technology that has a high potential to significantly reduce the cost of desalination. Advantages: -can treat high salinity waters above the threshold of RO or near saturation (up to about 230,000 mg/L TDS) -feedwater temperature range of 55 to 100 0C with optimal temperature at 80 0C. -can operate on waste heat, solar heat, or geothermal heat -pilot plants have demonstrated feasibility (National University of Singapore 4 m3/day) and KAUST 10 m3/day) -desalts water and produces cooling -can be operated to maximize desalting or cooling depending upon need, which can be changed seasonally

Adsorption Desalination Adsorption desalination is a batch-operated cycle: It occurs when a hydrophilic silica gel adsorbs water vapor from saline or brackish water, causing the desalting process. The adsorbent is re-generated or hydrophobic by low temperature heating (55o to 85oC) in the second half cycle – desorbing the water vapor. The water vapor moves to cooler surfaces and condense into distilled water. Cooling is produced in evaporator, in response to the vapor uptake or adsorption

Adsorption Desalination Adsorption Desalination and Cooling Demonstration Facility at KAUST ( 10 m3/day capacity)

Adsorption Desalination Using Solar and/or Waste Heat Sources Use of solar energy provides a low cost energy source, particularly good for the areas with high intensity sunlight. However, the system requires heat storage to operate at nighttime or during very cloudy days.

Combined-Cycle Adsorption Desalination Adsorption desalination using combined-cycle solar and geothermal energy sources would be used on approximate 12-hour cycles with daytime use of solar and nighttime use of geothermal.

Advantages of Using Combined-Cycle Solar and Geothermal Energy Using a combined-cycle heat source has several advantages which are: -allows up-scaling of AD technology to almost any capacity -eliminates the necessity for heat storage at nighttime or other times -reduces the stress on the thermal reservoir allowing the upward or lateral transmission of heat to restore lowered temperature during the down cycle -operates at a lower minimum temperature because of the recovery cycle -reduces the required well depth because the minimum temperature is lower (less cost) -eliminates the need for reserve generators to produce a 95% reliability factor (or higher)

Hot Dry Rock (HRD) Geothermal Source Utilization

Hydraulic Fracturing of a Hot Dry Rock Heat Source Hydraulic fracturing of a DHR heat reservoir allows recirculation of water which allows: Pumping into the fracture zone through an injection well Flow through the fractured zone to gain heat Discharge into the recovery well Conveyance of captured heat to land surface

Example of High Heat Flow Area Where HDR Can be Used as an Energy Source The heat flow along the western margin of the Red Sea is associated with the active rift system and volcanism.

Geothermal Gradient-Western Red Sea Coastline of Saudi Arabia Average range of heat flow gradients along the western Red Sea coast High gradient Low gradient Heat flow along the Red Sea coast of Saudi Arabia is variable, but sufficient to meet the needs to power adsorption desalination. Much higher thermal gradients are found in some areas (e.g., Medina).

Vertical Heat Transmission and Capture with Circulating Water in Wells Upward moving heat flow replaces captured heat as cooler injected water warms. The cool water induced heat sink must not break through to the collection well or wells. Model created to assess balance of heat flow using one injection well and one recovery well. Heat Flow

Modeling of Heat Breakthrough in a Granitic DHR Fractured Heat Source Heat flow model for 50 m of fractured rock (granite) -assumed center flow in 10 m corridor -80 0C return flow temperature -106 0C equilibrium temperature in discharge well -could operate for many days continuously with no breakthrough -12-hour cycle use allows no breakthrough

Conclusions 1) Adsorption desalination is a promising technology that can be operated efficiently using solely renewable energy heat sources. 2) Using combined-cycle solar and geothermal energy sources would allow continuous operation of large-scale facilities without dependence on a single energy source (limits on solar energy source). 3) Use of geothermal energy in 12-hour cycles reduces the depth required to harvest the heat energy, thereby reducing cost of construction. 4) The addition of geothermal energy use eliminates the need to install heat storage mechanisms for nighttime and cloudy day operations. 5) Combined-cycle solar/geothermal use allows up-scaling of adsorption desalination to virtually any capacity.

KAUST: A Science & Innovation Gateway For Sustainable Prosperity Questions ? 19