Thermal desalination

Desalination has been practiced for many years, although the early large-scale industrial applications were in the 1960s in the Middle-East using thermal desalination technologies such as multistage flash or multi-effect distillation. These plants used sophisticated thermal or vacuum systems to effectively distil a portion... 

Metal in the discharge can come from the source water, or be a product of corrosion. Note that due to their operation at elevated temperatures, when compared with membrane desalination plants, thermal desalination plants are... 

Slesarenkov, V., and Shtim, A., "Comparative Analysis of the Efficiency of Thermal Desalination Plants,"... 

RO plants are, however, much more sensitive to insufficient feedwater pretreatment than thermal plants. For this reason, it is accepted technology to use well water from wells drilled at the seashore rather than surface water as in thermal desalination. 

Up to 30% higher production in thermal desalination plants because of increased top brine temperature. 

IDE Thermal Desalination Solutions, Mechanical Vapour Compression brochure, www.ide-tech.com. M. Bradford, I. Buchanan, I. Moore, Refinery and heavy oil production wastewater recycle and reuse, Proceedings 70th International Water Conference, Orlando, USA, October 2009. 

Membrane Distillation (MD) is a hybrid thermal-membrane process that could be applied in produced water volume reduction applications while simultaneously augmenting sustainable water production in Qatar. A consortium of ConocoPhillips - Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity Water Company (QEWC), was formed to assess the suitability of MD to treat high salinity brines from thermal desalination plants similar salinity levels could be found in produced water. The pilot scale results showed that MD could operate at 50% recovery and achieve a stable flux of 5 L/(m. h) at when treating thermal brine at 70,000 mg/L TDS. The effluent produced contained < 10 mg/L TDS. 

The primary objeetive of this research was to evaluate the performance of two different MD teehnologies at pilot scale in the treatment of brine from thermal desalination plants. This highly saline brine mimics the produced water streams from oil/gas operations. 

When operated at a feed thermal brine TDS of 70 g/L and a 50% recovery rate, pilot unit A was able to desalinate brines from thermal desalination plants and consistently produce a high quality distillate (conductivity < 10 pS/cm - >99.99% rejection). 

In thermal desalination, any possible leaks from the reactor circuit towards the desalinated water produced by the system, must be prevented by the correct choice of operating pressures in the various circuits and by the use of an intermediate circuit. 

A quick analysis of energy usage will indicate why reverse osmosis has replaced thermal desalination. First, Eq. [2.2] can be used to calculate the minimum work required to produce the first drop of pure water from seawater as [11] ... 

This largely explains why SWRO has supplanted distillation/evaporation for seawater desalination. In situations where waste heat is available, thermal desalination may still be economically attractive. It should be noted that, despite an eightfold reduction in energy required for SWRO separation since the 1970s, additional SWRO energy reductions wiU be harder to achieve because of proximity of current SWRO systems to the theoretical minimum [11,58]. 

Al-Sahali, M. Ettouney, H. 2007, Developments in thermal desalination processes Design, energy, and costing aspects. Desalination 214, 227-240. [11] Kakac, S. Liu, H. 2002, Heat exchanchers selection, rating and thermal design, CRC Press, Florida. 

Table 3.3.15 shows that thermal desalination of sea water or brackish water by multistage flash distillation is more energy intensive than membrane desalination, but can better deal with more saline water and delivers even higher permeate quality, although reverse osmosis usually fulfills the requirements of drinking water (Table 3.3.16). 

Hui Tong Chua (thermal desalination low grade heat driven multi-effect distillation), School of Mechanical and Chemical Engineering, University of Western Australia (UWA), Perth, WA... 

Mohammed Zahir Al-Abri (thermal desalination water and wastewater treatment nanotechnology). Petroleum and Chemical Engineering Department, Sultan Qaboos University (SQU), A1 Khoudh, Muscat... 

Hussain Al-Towaie (solar power for seawater desalination thermal desalination). Owner CEO at Engineering Office CE SD (Clean Environment Sustainable Development), Aden... 

Physical characteristics, such as electrical conductivity, thermal coefficient of expansion, and thermal conductivity, are important considerations for selection of materials. For instance, cupronickel (90-10 Cu-Ni) are excellent materials for heat exchanger tubes in thermal desalination plants employing raw seawater, because of their excellent conductivity and corrosion resistance. The choice of material is narrowed down by eliminating low conductivity and low corrosion resistant materials. 

A very significant fraction of desalination is achieved via thermal desalination processes such as multistage flash, multieffect distillation, etc. (Section 10.2.1) (primarily in older plants). Pretreatment processes include filtration, chlorination, deaeration and scale control via acid addition, antisealant treatment, etc. Post-treatment processes include building up the dissolved salt concentration to the level of 50 ppm via blending with brackish ground water or addition of lime, etc. (Howe, 1974), since distilled water is highly corrosive. 

The ubiquity of water and metals that are ever present in the water means that hydrolysis reactions are essential aspects of many areas of science, industry and nature. Hydrolysis is an important component in water purification and treatment. In water treatment, many metals are removed from solution by precipitation as solid hydroxide phases which, in turn, may remove other metals and metalloids via adsorption onto the formed solids. In many countries, arsenic is removed from groundwater recovered for drinking via adsorption onto solid iron hydroxide, and knowledge ofthe precipitation behaviour of magnesium hydroxide is important in thermal desalination processes. 

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