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Technologies for desalination of sea or brakish water

The desalination of sea or brakish water is seen by many as one of the key challenges of mankind. Many say that this is the key for the solution of the drinking water problem worldwide.

Experiences in the past have also shown that huge centralised solution with all their benefits also have some major disadvantages. May it be large investment costs, maintenance costs, additional costs for large infrastructure or ecological problems.

The average salinity of the oceans is around 3.5%

The salt concentration is for the
* Atlantic: 3.54 %
* Indian Ocean: 3.48 %
* Pacific: 3.45 %
* Baltic sea: 0.8 %
* "Kieler Bucht": 1.5 %
* "Finnischer und Bottnischer Meerbusen": 0.1 %
* North sea:
  - Close to rivers: 1.5-2.5 %
  - Northern North sea: 3.2-3.5 %
* Mediterranean sea: 3.74 %
* Black sea 1.7 - 1.8%
* Persian Gulf: 4 %
* Red sea: 4 %

An all other seas the salinity is around 3 to 4 %.

Inland sea:
* Caspic sea: 1.3 %
* Death see: 27 %

General process overview for desalination

  • RO (Reverse Osmose)
  • EDR (Electrodialysis Reversal)
  • MD (Membran Distillation)

Thermal desalination

  • Simple stills - up to 1m³ per day production
  • MEH (Multi Effect Humidification) - 1m³/5m³/10m³ per day production
  • MED (Multi Effect Distillation)
  • MES (Multi Effect Solar Desalination) - 45m³ to 100.000m³ per day production
  • MSF (Multi Stage Flash)
  • MVC (Mechanical Vapour Compression) - 4-20m³ production per hour
  • Wind powered desalination using Reverse Osmosis - 100m³ to 3,000m³/day

A number of scalable smaller or medium sized systems that are running for years independently and redundently and are powererd by wind or solar prove that there are alternatives to large centralised systems. 

An increasing number of new, innovative and promising concepts are being developed and are coming to the market that also use any kind of waste heat to produce good drinking water out of salty water.

Simple stills are products or technologies that are using as little technology as possible in order to distill drinking water from any kind of raw water quality. Although the process itself might look simple it takes a lot of research and skills to develop as system that not only makes sense but is also affordable and using appropriate technolgies.

This product for example has been developed in Germany and has proven through many real time tests that it can help solving the growing water problem using solar energy only. (detailled information on the left hand navigation "Simple stills").

 

Simple stills producing smaller quantities per unit (up to 1,5 liters) but are very cheap, can be applied in larger numbers, easily transported and immediatly used.

MEH (Mulit Effect Humidification)

MEH, Multi Effect Humidification is based on natural principles

Apart from long working products that can produce up to 20 liters distilled water per day per unit (solar stills) there are new promising developments that can work with any kind of heat source and produce distilled water in larger quantities at cheaper prices.

A special process based on the MEH Principle (Multi-Effect-Humidification) was developed for many years and has successfully fulfilled many tests. The process is based on the evaporation of salt water and the subsequent condensation of the generated steam. The steam is completely clear and does not carry any solvent. After condensation you gain clear, healthy and sweet fresh water. Prototypes of this principle can be visited in real time and under realistic circumstances. The production per unit is flexible and can range from 1m³ per day water production to 5m³ per day or 10m³ per day.

Important questions for the planning of an ideal set up can be: 

Process description of a Multi Effect Humidification (MEH) Desalination Plant

Sea water is heated by the sun or by waste heat - transferred by highly corrosion protected heat exchangers. It enters an evaporation chamber produced from corrosion free materials ? very important for reliable long term operation. Here the seawater evaporates from efficient antibacterial fleece surfaces. The produced steam is transported to the condenser in a second step ? completely without any additional energy demand. Like in nature, natural convection enables the best performance in the water production process - optimized by the well engineered geometric collocation of surfaces within the module. During condensation, the main part of the energy used for evaporation is regained applying materials with extremely low heat flux resistance.

All components in contact with salt water are made from corrosion free materials. Condenser / Evaporator are made of taste-free, beverage-conform PolyPropylen material. Casing of the humidification chamber and collection basins are made of highly graded stainless steel.

Advantages of MEH Systems

  • Low temperature heat of 85° C is used for evaporation
  • No moving parts within the distillation chamber enables low maintenance demand
  • The self-controlling natural convection loop enables best energy recovery
  • Sophisticated geometrical design allows easy maintenance and optimum performance at the same time
  • No pre-treatment of raw water is needed. The process is insensitive to high salt contents.

MEH Sample Data

Specification of Raw Water quality

Any not turbid raw water of nearly any source as: Sea water, brackish water, water from polluted wells

TDS                  Max. 100 000 ppm
Conductivity     Max. 120 000 µS/cm
Turbidity           No suspended substances (mechanical filtration at 50 Micron)

 

Specification of product water

Re-mineralization of produced distillate using add. drinking water supply unit

Salinity (TDS)                                     < 50 ppm
Conductivity                                      < 20 µS/cm
Temperature                                     max. 40°C
Max. Bacteria (Colony count 36°C)    < 30/ml directly after production (permanent 5/ml with add. UV-disinfection system)

Installation in Jeddah/Kingdom of Saudi Arabia

Solar driven desalination unit supplies office building in Jeddah: Using the heat from 140m² solar collectors the system supplies around 5m³ of clear drinking water to a roof storage per day.

Installation south of Jeddah - Solar farm

This installation is located south of Jeddah, about 20 km south of the city and 10 km away from the coast. This installation takes brackish water which has nearly the same salinity as the sea water. It is designed to produce 10m³ a day. To view the installation via google earth please contact us.

MES (Multi Effect Solar Desalination)

Process Description of a Multi-Effect-Solar (MES) Desalination Plant

The MES Desalination Plant has been designed to solve most economically energy and drinking water problems in countries with arid zones by using solar energy. MES Plants are able to produce drinking water and water for irrigation with a daily fresh water production between 45 m³/d and 100.000 m³/d. The Plant consists of the following main elements 

Hot Water Storage (HWS)
The key technology of a MES Plant for collecting and storing solar energy lies in the Hot Water Storage (HWS). The hot water storage consists of basins filled with seawater, brackish water or effluent water with high salt concentration from oil fields. The ground of each basin is covered with a layer of plastic sheet. On top of the water surface swims the Transparent Heat Insulation Cover (TWD) safely fixed against storms. The solar radiation shines through the TWD and heats up the water inside the HWS. After initial filling, the heating up to the design temperature of 50°C to 70°C may take between two and six weeks depending on its depth and the intensity of the solar radiation.

Evaporator & Condenser
The hot water enters the evaporator where a certain part of the water flow is transferred to steam that is absorbed by the circulated air, while the rest of the hot water flow cools down and is pumped back to the HWS. The water is sprayed downward, while the air flow is upward in counter flow. The saturated air is leaving the evaporator, before entering the condenser. The steam contained in the humid air is converted in the condenser into distillate. The concentrated brine inside the HWS can either pumped back or disposed and converted to salt.

Air circulation system
The transport of humid air is provided by fans, which maintain a closed circulation system.

Cooling water system
The cooling water system provides the condenser with the necessary cooling for the production of sufficient condensate. In case of coastal or offshore locations the cooling water is provided from the sea. In case of desert locations, a forced draft evaporation cooling process will be used.

Drinking water treatment
Drinking Water Treatment In the water treatment plant, disinfection is carried out and minerals may be added to the distillate to produce best drinking water, if not used for irrigation purposes.

Discharge of high saline water
The discharge of high saline water into the oil fields or to ground water layers will be very much reduced due to its conversion into potable water.

MES Sample Data

Maximum Capacity in summer                680 m³/d
Design Capacity                                     500 m³/d
Minimum Capacity in winter                    400 m³/d
Salinity of raw water                          80.000 ppm
Raw water temperature (range)        15-30°C
Hot water temperature (range)         50-70°C
Drinking water quality                        better than WHO
Salinity of drinking water (TDS, max.) 150 ppm
Recovery rate (efficiency)                     71,0%
Solar area (flexible layout)                     2,5 ha
Electrical power demand                      54 kW
Electrical specific power demand           2,6kWh/m³