Carbon demineralization

Aikaiinity Bicarbonate (HCOs" ), carbonate (COs , and hydroxyl (OH ), expressed as CaCOs Foaming and carryover of solids with steam embrittlement of boiler steel bicarbonate and carbonate produce CO2 in steam, a source of corrosion Lime and lime-soda softening, acid treatment, hydrogen zeolite softening, demineralization, dealkalization by anion exchange, distillation, degasifying... 

Aikaliniry Bicarbonates (HCOd Carbonates (CO,) Hydroxyl (OH) as CaCO, Steam systems foaming and solid carry over Steel embrittlement (HCO,) and (CO,) Corrosion Distillation Demineralization I..ime and lime soda Dealkalization I lon exchange) Acid treatment liydrogcn zeolire... 

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. 

For higher-pressure boilers demineralization is necessary to minimize total dissolved solids in the boiler. This water is normally carried in steel pipework, but if condensate is returned and the condensate has become contaminated (for example, with carbon dioxide or copper ions) more corrosion-resistant materials such as copper are required. Downstream of the boiler, steam pipework is usually steel with steel or stainless steel expansion bellows. 

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. 

Demineralization by SAC(H)/WBA(OH) Removes virtually all TDS except silica and carbon dioxide. The weakly basic anion cuts operating costs through a significantly enhanced capacity and reduced regeneration demands. However any sodium slip from the cation unit passes through the anion and increases the conductivity of the treated water. 

Demineralization by SAC(H)/Degassing/WBA(OH) Removes virtually all ionic TDS and carbon dioxide, but not silica. It is a cost-effective process. 

Demineralization by SAC(H)/SBA(OH) Removes virtually all TDS, including carbon dioxide and silica. The TDS in treated water is normally below 2 to 4 ppm. Conductivity is below 10 to 15 pS/cm, but this depends on the degree of sodium slip from the cation. Any slip is converted to sodium hydroxide in the anion unit (salt splitting), causing a sharp increase in conductivity and increased silica solubility. The lack of a degasser drains the anion unit capacity and requires increased caustic for regeneration. 

Demineralization by SAC(H)/Degassing/SBA(OH) Removes virtually all TDS, including carbon dioxide and silica. The degasser reduces the loading on the anion exchanger. Silica is reduced to 0.02 to 0.15 ppm Si02. 

Demineralization by SAC(H)/Degassing/SBA(OH)/MB Removes all TDS, including carbon dioxide and silica. This is a standard process where the RW is high in alkalinity and silica. The MB acts as a polisher with infrequent regeneration. Silica and sodium are both reduced to below 0.02 ppm as CaC03. Conductivity is below 0.1 pS/cm. A schematic layout of this type of plant is shown in Figure 9.3c. 

Neutralizing capacity functionality is important in lower pressure plants because it is common for some carbon dioxide derived from alkalinity breakdown to be carried over into the steam. It is less important in high-pressure units where demineralized water (or water of similar high purity) is employed because the FW is assumed to be essentially free of alkalinity. 

The use of pretreatment equipment such as dealkalization or demineralization to remove bicarbonates and carbonates in the MU. 

A recent study in these laboratories (75) on calcium carbonate precipitation from Wyodak coal has confirmed the relationship between ion-exchangeable calcium and the appearance of calcium carbonates during liquefaction. These experiments were performed on samples of the subbituminous coal which had been demineralized, to ensure that all carboxylic acid groups were in the acidic form, and subsequently exchanged with varying amounts of calcium ions. 

Area 500 accepts or generates, then stores, all of the utilities within the facility. These include caustic, oxygen, demineralized and deionized water, hot water, primary cooling water, recycle water, potable water, secondary cooling water, steam, propylene glycol, hydrogen, instrument air, natural gas, nitrogen, and carbon dioxide. 

Water is the most common raw material used, and it is recommended that the manufacturer fully comply with the standards of at least purified water for inclusion in the formulation, though there is no requirement. Efforts should be made to provide as much microbial-free water as possible this can be readily achieved by installing a loop system in which the incoming water is first subjected to ultraviolet sterilizer, carbon filter, demineralizer, and a... 

Stop solution/glycine-carbonate buffer (pH 9.6) dissolve 12.8 g ammonia-free glycine (ICN Biomedicals, Eschwege, Germany) and 18.0 g dry Na2C03 (Merck) in 200 ml demineralized water. The solution can be stored at 4°C for up to 3 months. 

Steam produced from demineralized water is free of carbonates. Steam produced from lime-softened water will be contaminated with carbonates that decompose in the boiler to carbon dioxide. As the steam condenses in a reboiler, the C02 accumulates as a noncondensable gas. This gas will be trapped mainly below the channel head pass partition baffle shown in Fig. 8.6. As the concentration of C02 increases, the C02 will be forced to dissolve in the water ... 

The dissolved solids, such as calcium carbonates, are removed by hot-lime softening or demineralization.1 Demineralized water (also called deionized water) typically has essentially all anions and cations removed by ion-exchange resin. Demineralized water is preferable to hot-lime-softened water as boiler feedwater for several reasons. 

Note that it is okay to heat softened or demineralized water to 160°F. You should not, however, do this with raw water. Calcium carbonate salts will plate out and foul the heat-exchanger tubes. 

Demineralization, like the zeolite process, involves ion exchange. The metal ions are replaced with hydrogen ions by means of the process and equipment described for the hydrogcn-zcolitc system (see Hot Lime Zeolite—Split Stream Softening, previously described). In addition, the salt anions (bicarbonate, carbonate, sulfate and chloride) are replaced by... 

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