Condensate polisher

Condensate Polishing. Ion exchange can be used to purify or poHsh returned condensate, removing corrosion products that could cause harmful deposits in boilers. Typically, the contaminants in the condensate system are particulate iron and copper. Low levels of other contaminants may enter the system through condenser and pump seal leaks or carryover of boiler water into the steam. Condensate poHshers filter out the particulates and remove soluble contaminants by ion exchange. 

Condensate purification In some boiler systems the condensate returning is retreated using ion exchange to minimise corrosion and deposit accumulation. This particularly applies to once-through boilers (mainly nuclear) where there may be no water/steam separator and perhaps limited facilities for blow-down. Additionally, some high heat-flux boilers (oil-fired) have been fitted with condensate polishing plant (CPP). 

Overall, these features mean that chemical control standards are necessarily high. For example, supplementation of the water treatment plant by condensate polishing plant and periodic chemical cleaning are particularly important. In addition, before each period of operation, a clean-up of the cycle is applied to remove crud. Stringent attention must be paid to the feed-water conditioning. 

In very large boiler plants, the CR system may include a condensate polishing plant (the physical location of this plant may be pre- or post-boiler). 

As part of the overall boiler plant operational management process, various items of water treatment equipment must be periodically checked, tested, back-washed, regenerated, or otherwise maintained. Such equipment may include filters, ion-exchange softeners and demineralizers, the RO plant, chemical feed tanks, and condensate polishers. 

In some circumstances (say, where copper and iron pickup occurs), it may be appropriate to use post-boiler treatment equipment such as condensate polishers. 

Similarly, posttreatment refers to similar process equipment after the boiler section (such as condensate polishing). 

Where soluble iron is present in condensate, it often is associated with copper. When the problem is considered serious, it usually is removed by a condensate polisher. Soluble iron in MU often is associated with manganese and usually (but not totally) is removed either by ion-exchange resins (often inadvertently) or in an aeration tower, where the process employs a combination of air or chlorine oxidation, followed by precipitation and filtration. 

In small boiler systems, the use of CR system strainers and high-temperature-resistant bag filters are highly recommended to prevent this corrosion debris from entering the FW system. In larger plants, condensate polishers or electromagnetic separators may be employed. Condensate dumping may even take place, although this is a wasteful and expensive process because both water and heat are lost. 

Synthetic resins are extremely widely used, both pre-boiler and postboiler. Pre-boiler, they are employed for basic MU water treatment (e.g., softening) and various higher quality purification processes (e.g. dealkalization and demineralization). Post-boiler applications are for condensate polishing. 

Figure 9.4 (a) Basic pure MU water scheme CF/BX/RO (b) very pure MU water scheme UF/RO/MB (c) very pure, membrane only, MU water scheme UF/RO/EDI (d) mobile condensate polishing scheme bag filter SAC(H)/MB. 

There is a very wide range of condensate polishers available, and it is important to properly understand the background to the problem to make the correct selection and ensure the economic viability of the project. 

Essentially, condensate polishers are pressure vessels containing ion-exchange resins in some form and configuration. There are primarily two different types of duty performed ... 

Although condensate polishers mitigate corrosion problems in the condensate, FW, and boiler, it should be remembered that they do noth-... 

So far, the discussion has primarily centered around the contamination of condensate due to iron and copper. However, large process industries often produce condensate containing oil, grease, and other contaminants, and these must also be removed because they are not only damaging to the boiler plant waterside, but may can adversely affect condensate polisher components. 

Deep-bed condensate polishers are commonly used for nuclear reactor power plants. Due to the extreme operating conditions, the resin is sometimes taken out of service as frequently as every 3 weeks for ultrasonic cleaning. This process removes the iron oxides and other particulates filtered out by the resin media. 

Deep-bed condensate polishers also are used to provide protection against condenser in-leakage in fossil-fueled sub- and supercritical boilers. Where condenser in-leakage occurs, it results in contamination of the condensate by Na, Cl, Ca, and Mg. 

Where condenser in-leakage develops in nuclear reactor boilers, calcium hideout may occur in the reactor water, implying that some leakage of Ca and Mg may have occurred from the condensate polishers. There also may be some sodium or chloride leakage from the polishers (under good conditions, the polisher effluent usually contains below 0.1 ppb Na). 

The condensate polishing system must be in excellent working order and typically operating in the ammonia cycle. 

Effect on condensate polishing capacity due to amine loading... 

In systems where the steam and condensate systems are extensive, it is important that any contamination of returned condensate be controlled either by monitoring and dumping or by condensate polishing. 

Steam that has lost heat and condensed (reverted to liquid water). Condensate polisher ... 

Dow. A Guide to Condensate Polishing. Technical literature. Dow Chemical Company, USA, 1979. 

Kasper, Joel (Aquagenics). A Look at Steam Systems, Carbon Filters and Condensate Polishers. Ultrapure Water, Tall Oaks Publishing, Inc., USA, February 1998. 

Miller, William S. (Ecolochem, Inc.). Oxygen Removal By Catalyzed Carbon Beds. EPRI Condensate Polishing Workshop, Electric Power Research Institute, USA, October 1985. 

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