Multi-Effect Distillation

IDE's MED Highlights:

• Low Temperature Seawater Distillation
• Low Pressure Steam Driven (Optional: Cogeneration Scheme / Waste Heat Recovery)
• Simple and Economical Operation & Maintenance
• High Quality Product (5ppm)
• Capacities: 600 - 25,000 cubic-meter/day per unit

IDE's MED units are comprised of a train of evaporative-condensers with a heat rejection condenser at the end. The low temperature differential allowance on each evaporator (effect) in the train allows a large number of effects to be utilized while maintaining a low brine discharge temperature, thus significantly increasing the Gain Output Ratio (GOR - a measure of energy efficiency). MED units are powered by heat from very low pressure steam (0.25 to 0.35 ata) or hot water sources above 600C.
Where higher pressure steam is available (over 2.0 ata), the plant can be supplied with a thermal vapor compression (TVC) unit. Using a steam jet thermo-compressor to recycle part of the vapor in the unit further increases thermal efficiency.
MED units are available with capacities of up to 25,000 cu.m/day in a single unit, with larger plants being realized by multiple unit installations.

The Process
The combination of unparalleled thermal efficiency, low temperature operation, minimal scaling, easy capacity regulation, stable automated operation and the ability to utilize low grade, low cost energy sources makes IDE's MED the most cost efficient sea water desalination unit available.
The result is totally pure, fresh, potable and soft water, with an average of less than 10 ppm TDS.
The inherent load-following capability of IDE's MED allows automatic and proportional regulation of the system’s capacity to variations in motive steam input. In dual purpose installations (power and water production), the system is able to produce maximum quantities of fresh water during peak demand periods - up to 110% of the nominal rated output. During non-peak hours of electrical production, the IDE MED can be reduced to as little as 50% of nominal capacity without operator intervention.
 

Co-Generation Schemes
Energy Saving in Co-Generation Schemes.

The ability of low temperature distillation plants to make effective use of low cost, low grade heat, or, where available, even zero cost waste heat, maximizes the reduction of the energy cost component of these plants. Water production costs are consequently lower than any other sea water desalination system.

Low grade heat is available through cogeneration schemes with steam turbine, diesel generator and gas turbine power plants. This is obtained through waste heat recovery from industrial cooling waters and exhaust gases, from solid waste incinerators, solar ponds and geothermal waters.

The high quality water produced by both MED & MVC processes, is less than 10 ppm TDS, and in some cases even as low as 2 ppm TDS. This high purity water allows its use directly as BFW (Boiler Feed Water), with or without minor polishing processes. Where potable water is required, the pure product water can be blended with raw water in order to achieve adequate potable water at a low price.

The LT-MED Process for Combined Power Generation and Sewater Desalination:
The LT-MED process incorporates technological advantages resulting in large reductions in total power consumption. Consumption is as low as 1.0 kWh/ton, utilizing waste heat, and up to 5 kWh/ton when using prime energy.

IDE has developed a unique design falling-film horizontal-tube MED (evaporator/condenser) with high heat-transfer coefficient, superior thermodynamic efficiency (compared to MSF) and very low pressure drops at high volumetric vapor flows, as encountered in low temperature (30oC to 70oC) operation. The development of low temperature MED process, at a maximum brine temperature of less than 70oC, is also aimed at avoiding scale formation on heat transfer surfaces.
 

Below are examples of possible co-generation schemes implementation: 

Back Pressure Steam 
Combined Cycle 
Diesel Engine 
Gas Turbine