Reverse demineralization

The success of EDR ia water demineralization has appareatly resulted from its greater tolerance of particulate and fouling matter compared to reverse osmosis greater forgivingness of process upsets greater tolerance for unskilled operators simplicity ia desiga and constmction of EDR stacks compared to reverse osmosis modules the abiHty to iaspect, clean, or replace one membrane at a time the existence of a comprehensive global sales and... 

Suifate (S04>-2 Adds to solids content of water, but, in itself, is not usually significant combines with calcium to form calcium sulfate scale Demineralization, distillation, reverse osmosis, electrodialysis... 

Dissolved Solids None Dissolved solids is measure of total amount of dissolved matter, determined by evaporation high concentrations of dissolved solids are objectionable because of process interference and as a cause of foaming in boilers Various softening processes, such as lime softening and cation exchange by hydrogen zeolite, will reduce dissolved, solids demineralization distillation reverse osmosis electrodialysis... 

Indian Ion Exchange and Chemical Industries - Produces reverse osmosis and demineralization systems, base exchange softeners, clarifiers and filters, degassers and de-aerators, filtration and micro filtration systems, effluent treatment plant...http //www.indianionexchange.com. ... 

Over the past three decades, there has been a growing industrial interest in using reverse osmosis for several objectives such as water purification and demineralization as well as environmental plications (e.g.. Comb, 1994 Rorech and Bond, 1993, El-Halwagi, 1992). The first step in designing the system is to understand the operating principles and modeling of RO modules. 

Basically, the hardness salts of calcium and magnesium ions are ex changed for sodium ions in the dealkization process the carbonate and bicarbonate salts, which cause high levels of alkalinity, are replaced with chloride ions. Reverse osmosis can also be used to produce demineralized water. 

The electrical conductivity of the water is critical to the correct operation of this type of boiler, and the precise level varies with design and power requirements. However, the conductivity is always relatively low (often specifications require a level of below 15-50 p,S/cm), so demineralized or reverse-osmosis (RO) quality FW is usually specified. 

The pre-boiler, FW supply should normally be of demineralized quality, such as may be provided by ion exchange, reverse osmosis (RO), or similar process. Extremely efficient mechanical deaeration also is required because the path length from the FW tank to the boiler is usually quite short, and thus the contact time is generally inadequate for the sole use of chemical oxygen scavengers (even catalyzed scavengers). 

The use of reverse osmosis (RO), electrodialysis reversal (EDR) and other membrane techniques, and evaporation or demineralization may be applicable when a reduction in the TDS content of the MU water source is required. 

Provision of pretreatment The initial fill volume and MU supply is almost always pretreated in some manner. Because of the large volume of water in these systems, even low-hardness waters can produce sufficient quantities of calcium carbonate scale to severely impede heat transfer thus, for MTHW pretreatment, the use of ion-exchange softeners is the norm. For HTHW, some form of demineralization such as reverse osmosis (RO) or deionization by cation-anion exchange is typically preferred. 

Reverse osmosis is a process used by some plants to remove dissolved salts. The waste stream from this process consists of reverse osmosis brine. In water treatment schemes reported by the industry, reverse osmosis was always used in conjunction with demineralizers, and sometimes with clarification, filtration, and ion exchange softening. 

The most widely used techniques for removing dissolved inorganic solids are boiling, addition of washing soda, lime-soda softening, complexation, sodium ion exchange, demineralization, reverse osmosis, electrodialysis, adsorption onto suspended solids, and aeration. 

Polyamides and their analogue are also effective for the selective membranes and there have been developed many kinds of permselective membranes. In early 1960 s, du Pont started to investigate the membranes for demineralization of water by reverse osmosis. After screening polymers, aromatic polyamides and polyhydrazides were shown to have superior properties9-11. In the present review various polyamides and their analogue are in focus as barrier materials for membranes, and their permeative characteristics will be discussed from the view point of their chemical structures. 

EDR is typically used for demineralization of brackish water, which often contains poorly soluble minerals such as calcium bicarbonate and calcium sulfate, as well as colloids such as humic and fulvic acids and iron hydroxides The periodic reversal of the direction of the electric current avoids scaling and fouling of the membranes by such substances. 

Figure 6. Reverse osmosis sea water demineralization pilot plant...

Research began as an investigation of electrically induced ionic adsorption on porous "inert" electrodes. Electrode pairs based on carbon have been developed which will demineralize saline water at low voltage, and can be regenerated upon reversal of polarity. Various carbon electrodes have been conveniently classified into cation- and anion-responsive types. As received carbons are normally cation-responsive, but anion-responsive types have been made by chemical treatment. Laboratory demineralization cells based on this principle have been constructed and operated. Owing primarily to the low cost of basic construction materials, the process shows great promise for the economical conversion of saline waters. 

The basic elements of a new electrochemical approach to saline water demineralization under study at the University of Oklahoma for the past three years are two porous electrodes, one of which is responsive to cations and the other to anions. When an appropriate voltage is applied to such an electrode pair immersed in saline water, cations are removed by the former and anions by the latter. In the regeneration phase, reversal of voltage gives up these ions to a reject solution. 

Cell DC-2. Earlier demineralization studies by Lyon (9) employed cell DC-2. This was a sandwich-type cell with Lucite side plates bolted together with two epoxy resin-gasketed graphite electrodes separated by an anion-permeable membrane. The membrane was necessary because a suitable anion-responsive electrode was not then known. The principle of operation is that in the cathode compartment, after several current reversal conditioning cycles, sodium ions are removed by the cathode while chloride ions migrate from the cathode through the membrane to the anion chamber. In the anode chamber, sodium ions, from the previous half cycles, are rejected from the anode. The net result was salt depletion in the cathode chamber and a similar concentration increase in the anode chamber. 

Reverse osmosis is a demineralization process that relies on a semi-permeable membrane to effect the separation of dissolved solids from a liquid. The semipermeable membrane allows liquid and some ions to pass, but retains the bulk of the dissolved solids. Although many liquids (solvents) may be used, the primary application of RO is water-based systems. Hence, all subsequent discussion and examples will be based on the use of water as the liquid solvent. 

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