Desalination Operating temperature

The STAR-H2 balance of plant (BOP) is comprised of three cascaded cycles (water cracking Brayton cycle and desalination) operating at successively lower temperatures - and with the heat rejected from each cycle used to drive the succeeding cycle, see Fig. XXIV-4. The reactor supplies 400 MW(th) of heat between 800 and 650°C. The strategy for BOP plant design is to use that heat as follows ... 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

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... 

Membranes could now be cast with appropriate porous properties such that the previously mentioned "tailoring" operation could be carried out, i.e., the underwater heating of the membrane to a temperature which would provide adequate desalination. 

In summary, the FT-30 membrane is a significant improvement in the art of thin-film-composite membranes, offering major improvements in flux, pH resistance, and chlorine resistance. Salt rejections consistent with single-pass production of potable water from seawater can be obtained and held under a wide variety of operating conditions (ph, temperature, pressure, and brine concentration). This membrane comes close to being the ideal membrane for seawater desalination in terms of productivity, chemical stability, and nonbiodegradability. 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

Inhibition of the precipitation of calcium carbonate is one potential commercial application for 0-(carboxymethyl flnulin. The formation of calcium carbonate crystals is a major problem in boilers, heat exchangers, saltwater desalination, gas and oil production, laundry, and other fields. As the water temperature increases, the solubility of calcium carbonates decreases, resulting in crystalli-zation/scale formation/incrustation, decreasing the efficiency of the operation and increasing costs. 

IMaterials and Scaling Issues. Two aspects of the basically simple desalination process require special attention. One is the high corrosivity of seawater, especially pronounced in the higher temperature distillation processes, which requires the use of corrosion-resistant, and therefore expensive, materials. Typical materials in use are copper—nickel alloys, stainless steel, titanium, and, at lower temperatures, fiber-reinforced polymers and special concrete compositions (39). It is noteworthy that in quest of a lower initial cost, the use of inadequate materials of constmction in many locations combined with poor operation by virtually untrained hands led to rapid deterioration and failure of plants long before their estimated design life. Adequate experience suggests by now how to avoid such failures. The other aspect is scale formation (40,41), discussed in mote detail below. 

The RO system design has been for optimum water production at 28 C, while still maintaining the capability for water production within the design specification of the RO membranes when operating at ambient seawater temperature. Based on the design inputs specified above, the desalination plant, consisting of a UF pre-treatment system and the RO desalination S tem has the following characteristics ... 

---