First published in Cleantech magazine, Volume 6 Issue 6. Copyright Cleantech Investor Ltd
Watersolutions AG has unveiled a patented thermal process for desalination based on the principle of low temperature distillation (LTD). The system offers an exciting new desalination option which is simple to install, yet robust and highly efficient with low running and maintenance costs – and offers an unprecedented opportunity in terms of reducing energy consumption. The LTD system was recognised with the prestigious H2O Water Award, which was presented in November 2012 to Watersolutions for the Best Water Project.The LTD system condenses water at low temperature and pressure, using low grade ‘waste heat’1 (50-110°C) derived from thermal processes, cooling processes (e.g. district cooling), incineration, industrial processes (e.g. cement, fertilisers, etc.), mining and geothermal sources. There is a strong correlation between electricity usage and water needs, and in theory enough waste heat would be available by tapping electricity production to desalinate sufficient water for the needs of most societies.
An LTD plant requires no steam, just low grade waste heat available either from cooling water or air (exhaust). The source of this heat is irrelevant – it needs only to be available in sufficient quantities (6-30MW or more) and with an ideal gradient of 20 kelvins between the heat source and re-cooling source. As low as <10 kelvins per stage is possible; the Watersolutions pilot plant at the El Gouna resort in Egypt operated as low as 3 kelvins. Typically, an LTD plant would use between 0.8–1.5 kWh (up to 3 with many stages and difficult re-cooling) of electricity per m3 of very clean water (<10 ppm of dissolved solids) produced.
A Cost-effective Solution
The investment costs for an LTD plant are competitive. The investment cost is comparable to reverse osmosis (RO) modules, and significant cost savings occur when several LTD modules are combined to produce larger volumes. It is also expected that, as more plants are installed, there will be significant economies of scale.
Further, an LTD plant has a very high conversion ratio, requiring about 1.5 m3 of seawater to produce 1 m3 of very clean water. (The corresponding number for RO is 2.5-3 m3.) This means that the peripheral investments (water intake, filtration, pre-treatment etc.) are much reduced, especially if RO brine is used as feed.
Since LTD utilises ‘free’ waste heat, electricity usage is low. Combined with less chemical usage (e.g. anti-scalants) and less maintenance, this means that the operating costs are half or less compared to other systems. Typically the (low) electricity consumption of an LTD plant makes up some 75-80% of the overall operating costs (excluding depreciation), the rest being manpower, chemicals and parts.
In contrast to desalination plants which require replacement of parts such as membranes, maintenance costs for LTD, which has no membranes and no interior pipe bundles, are very low. Given the simplicity of the design, the materials used and its ability to function at relatively low pressure, the expected lifetime of an LTD plant is 25–30 years.
The cost is dependent on the final specification (the amount and temperature of waste heat, the sources of heat extraction and re-cooling, the quality of the water and the number of stages).
Applications of LTD
The LTD technology can work as a stand-alone plant, but it is also an ideal complement to existing technologies. The LTD process is particularly suitable where the salt content is high, the price of electricity high, part load flexibility is desired, and/or where a minimum of maintenance is required. In addition, it can be used to treat industrial wastewater from sources such as produced water, mining or industrial waste. The technology can accommodate variations in the plant load, running efficiently from 10–110% of plant design capacity. The process is self-adjusting, with the amount of water produced proportional to the amount of waste heat provided.
LTD works efficiently over a broad range of salinity. The process can also handle brine concentrate from RO. Indeed, retrofitting an existing RO plant with an LTD system would be an efficient way to increase the plant’s capacity.
The brine from an LTD plant can be concentrated close to the saturation level of salt, thus making drying of salt and minerals easier and Zero Liquid Discharge (ZLD) a real opportunity. The LTD system is not intended as a Zero Liquid Discharge technology, but Watersolutions is developing an alternative drying technology.
The LTD system is modular and scalable. Units are available in two sizes – a large module that produces 1,000-2,000 m3/d and a medium module with capacity of 500-1,000 m3/d. These units can be combined to scale up production as needed.
A full scale plant in El Gouna, Egypt, with a design capacity of 500 cubic meters per day (m3/d), has proven the principle, with very pure water being produced reliably and efficiently.
Comparison of SWRO and WS LTD – Cost and Efficiency
|In 2010||By 2015||By 2030||Today|
|Cost of water||($/m3)||0.5-0.8||0.4-0.7||0.3-0.4||0.25-0.35|
|Membrane Usefule Life||(years)||41095||41189||42278||n.a.|
|Plant recovery ration||(%)||45-50||50-55||55-65||80|
(1) Source: Membrane Seawater Desalination: Overview and Recent Trends (Nikolay Voutchkov, 2010)
(2) Source: Own calculations, based on operational experiences from El Gouna Plant, Egypt.
(3) Source: GP Bullhound, Sector update, July 2012, page 11
Switzerland-based Watersolutions AG has pioneered the LTD system for desalinating seawater and other saline waters, which functions on the basis of the thermal principle of low temperature distillation (LTD). The company has received funding from the Orascom Group, headed by Egyptian entrepreneur Samih Sawiris, and has installed a full scale plant at El Gouna, Egypt (in addition to a number of pilot plants in Switzerland).
Contact Espen Mansfeldt, CEO: