Continuous deionization

Process Water Purification Boiler feed water is a major process apphcation of RO. Sealants and colloids are particularly well rejected by membranes, and TDS is reduced to a level that makes ion exchange or continuous deionization for the residual ions very economic. Even the extremely high quahty water required for nuclear power plants can be made from seawater. The iiltra-high quahty water required for production of electronic microcircuits is usually processed starting with two RO systems operating in series, followeci by many other steps. 

Electrodemineralization includes a number of subset technologies, including electrodialysis (ED), electrodialysis reversal (EDR), and electrodeionization (EDI). Electrodeionization is sometimes termed continuous electrodeionization (CEDI) or continuous deionization (CDI). 

AVT Barg BD BDHR BF BOF BOOM BOP BS W BSI BTA Btu/lb BW BWR BX CA CANDUR CDI CFH CFR CHA CHF CHZ Cl CIP CMC CMC CMC COC All-Volatile treatment bar (pressure), gravity blowdown blowdown and heat recovery system blast furnace basic oxygen furnace boiler build, own, operate, maintain balance of plant basic sediment and water British Standards Institution benzotriazole British thermal unit(s) per pound boiler water boiling water reactor base-exchange water softener cellulose acetate Canadian deuterium reactor continuous deionization critical heat flux Code of Federal Regulations cyclohexylamine critical heat-flux carbohydrazide cast iron boiler clean-in-place carboxymethylcellulose (sodium) carboxy-methylcellulose critical miscelle concentration cycle of concentration... 

Continuous electrodeionization is primarily used as an alternative to ion exchange. Because of the extensive pretreatment required by CEDI systems, the technology has grown into a polisher for RO (see Figure 16.18). Continuous deionization can achieve mixed-bed water quality of RO permeate without the need to store and... 

Another alternative for water deionization, is continuous deionization (GDI). This technologically innovative deionization process was developed by Millipore Corporation and is currently marketed by lonpure. It uses electricity across ion exchange membranes and resins to remove ions from a continuous water stream. No chemical regeneration is required. A waste stream, carrying the rejected ions, of less than 10% of the feed water is required. 

The equipment required for water treatment will be determined by the quality of the incoming water. Typically, a USP pharmaceutical grade system will require pretreatment (filters), deionization, reverse osmosis, and potentially a polishing step such as continuous deionization. Many systems now incorporate UV filters for sanitization, which kill micro-bials and also eliminate ozone. 

J. Wood, J. Gifford, J. Arba, M. Shaw, Production of ultrapure water by continuous deionization. Desalination 250 (3) (2010) 973-976. 

In the interim period before the new deionization equipment for the L and K basins was received, portable equipment was installed in July 1995 and used to lower the L basin water conductivity from 110 to below 8 pS/cm in 2.5 months. The equipment was then moved to the K basin, and within three months the conductivity was lowered to below 10 pS/cm. Continued deionization in both basins for two more months lowered the conductivity further, to less than 3 pS/cm, and the chlorides, nitrates and sulphates were lowered to about 0.5 ppm. The corrosion surveillance programme continued in the three reactor basins and in the RBOF while the basin and water quality improvements were being carried out, i.e. until mid-1996. Results of the component immersion tests through September 1997 (the last withdrawal) showed no pitting corrosion on any of the corrosion coupons. These coupons were exposed to a variety of conditions for 37-49 months as conditions improved in the basins. Table 1.1 presents a summary of component immersion tests for the period 1992-2000, when corrosion coupons accumulated exposure time in extremely high quahty water and withdrawal intervals were extended. 

Continuous deionization of the storage basin water softens the water, as it removes the calcium bicarbonate and other ions contributing to hardness. Godard, however, found that zeolite softened, deionized water influenced the pitting behaviour of aluminium to the same extent as untreated water [2.6]. 

Radionuclide activity in the basin water. Radionuclide activity in the basin water (leached from the spent fuel) should be monitored and controlled to levels deemed to be safe for personnel working in the surrounding area. Continuous deionization of the water removes a and p-y radioactivity from the water. Fission products such as Cs and other radionuclides may be found in the water where failed spent fuel elements or cladding breached fuels are stored. Spedal materials such as zeolite can be used in ion exchange type purification systems to specifically remove these radionuclides. 

Spoor, P.B., Koene, L., Ter Veen, W.R. Janssen, L.J.J. (2002a) Continuous deionization of a dilute nickel solution. Chemical Engineering Journal, 85, 127-135. 

Quite a few separation processes were barely touched upon. A number of separation processes could not be covered azeotropic distillation Calutron cell disruption coagulation continuous deionization expression extractive distillation forward osmosis gaseous diffusion ion retardation leaching membrane distillation nanofiltration pressure-swing distillation, etc. Many analytical techniques were also not covered. 

Ganzi, G. C., and Parise, P. L. (1990). The production of pharmaceutical grades of water using continuous deionization post-reverse osmosis. J. Parenter. Sci. Technol. Parenter. Drug Assoc., July/Aug, Volume 44, Issue 4, pp. 231-241. 

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