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Ionics Reverse Osmosis Unit
Water Treatment System The overall water treatment system is divided into the following sub-systems:
Well Water and Demineralizer Feed System The Well Water system supplies water to the Well Water Storage Tank. The Demineralizer Feed system supplies well water for the Demineralizer system and the Fire Water system. The Well Water Storage tank has a capacity of 480,000 gallons, of which 50% is reserved for on-site fire fighting capability. Reverse Osmosis System Reverse Osmosis is a process of the removal of dissolved ions from water in which pressure is used to force the water through a semi-permeable membrane element, which will pass the water but reject most other dissolved materials. To understand reverse osmosis, the naturally occurring phenomenon of osmosis must be understood. Osmosis can be defined as the spontaneous passage of a liquid solvent from a dilute solution across an ideal semi-permeable membrane element. The transfer of the solvent water – but not the solutes (dissolved solids) – will continue until the concentrations of the solution on either side of a membrane element are equal. The flow rate of the water is directly proportional to the concentrations of the two solutions.
This driving force, called the osmotic pressure, can be measure, and resulting flow can be halted by applying a pressure equal to osmotic pressure on the more concentrated solution side. If this external pressure is increased further, the flow of water will be reversed from its natural flowing direction and towards the more dilute solution. The reversing of the flow is the process of reverse osmosis. For example, if a variable pressure were applied on the more concentrated solution side of a semi-permeable membrane element, the following conditions could be realized:
Demineralizer System The purpose of the Demineralizer System is to produce an effluent at a rate of 130 gallons per minute (gpm) two bed flow and 30 gpm mixed bed flow with less than 1 micromho conductivity and 0.1 ppm maximum total dissolved solids with a 20 micromho maximum quality. The system consists of one carbon filter, one Cation/Anion train, and one mixed bed unit containing both Cation & Anion resin. The Demineralizer units are regenerated with Sulfuric Acid and Caustic Soda. Natural water supplies are never chemically pure and contain various dissolved and suspended materials. While most suspended matter can be removed with one or more filtration techniques, dissolved minerals remain. Water is an excellent solvent and when most materials dissolve in it they break down into electrically charge particles of atomic size called ions. An equal balance of positively charged ions, cations, and negatively charge ions, anions, is established. Commonly occurring dissolved minerals result in waters having many different cations and anions present which often include the more typical ones below: Cations Anions Calcium Bicarbonate Magnesium Carbonate Sodium Sulfate Potassium Chloride Nitrate These materials in the water supply are objectionable in Boiler feed water and NOx injection water. However, these materials can be removed utilizing Ion Exchange. As the term implies, ion exchange involves a process whereby the objectionable ions in the water are exchanged for others, which present no problem in the facility. The heart of the process is the ion exchange resin, plastic materials in fine bead or granular form to which chemically active groups have been "attached." These resins have the ability to take up certain ions from the water and release others. In Demineralization, an exchange of ions takes place so that cations are replaced by Hydrogen ions (H+), and anions are replaced by Hydroxide ions (OH-) – the components of pure water. After demineralization nearly all of the dissolved minerals are removed. When the resins have insufficient capacity remaining to remove the impurities to the desired level, they are "exhausted" and must be regenerated. This is accomplished by passing a strong acid, such as Sulfuric acid, through the cation resin, to reverse the process. Similarly, a donor of hydroxide ions, such as Caustic soda, is passed through the anion resin to regenerate it. The ions which were picked up by the both resins, calcium, sodium, sulfates, etc., are given up by the resin and neutralized for discharge. The resins are once again ready to do their work.
NOx Injection Water System The above system is a Two-Bed Demineralizer, meaning that the anion and cation resins are in two separate vessels. When the ultimate in high-purity is required, the product from the two bed demineralizer is passed through the Mixed Bed demineralizer. Mixed beds differ from two beds in that both the cation and anion resins are housed in the same vessel. This high purity water is injected into the Combustion Turbine Generator for reduction of NOx emissions. |
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