Internal softening

NOTE Condensate system corrosion was an inevitable result of old-style, carbonate cycle internal softening programs, commonly employed in HRT, economic, locomotive, Lancashire, and similar boilers. 

Carbon dioxide carryover also occurs following the deliberate addition of soda ash (sodium carbonate) directly to the boiler. Where boiler designs provide for a significant internal drum or shell, the use of soda ash and caustic soda to prevent calcium and magnesium scales by precipitation reactions (internal softening) may be employed. 

This form of internal softening is not recommended in higher heat-flux boilers, however, because the risk of complex silicate scales is inevitable. The risk of such scales is further increased by the presence of either iron or aluminum, and analcite, acmite, or similar minerals may result. Under... 

The quahty of feed water required depends on boiler operating pressure, design, heat transfer rates, and steam use. Most boiler systems have sodium zeohte softened or demineralized makeup water. Feed-water hardness usually ranges from 0.01 to 2.0 ppm, but even water of this purity does not provide deposit-free operation. Therefore, good internal boiler water treatment programs are necessary. 

Plastic Pipe In contrast to other piping materials, plastic pipe is free from internal and external corrosion, is easily cut and joined, and does not cause galvanic corrosion when coupled to other materials. Allowable stresses and upper temperature limits are low. Normal operation is in the creep range. Fluids for which a plastic is not suited penetrate and soften it rather than dissolve surface layers. Coefficients... 

Hardness Calcium, magnesium, barium and strontium salts expressed as CaCOa Chief source of scale in heat exchange equipment, boilers, pipe lines, etc. forms curds with soap interferes wKh dyeing, etc. Softening, distillation, internal boiler water treatment, surface active agents, reverse osmosis, electrodialysis... 

Elastomer-plastic blends without vulcanization were prepared either in a two roll mill or Banbury mixer. Depending on the nature of plastic and rubber the mixing temperature was changed. Usually the plastic was fed into the two roll mill or an internal mixer after preheating the mixer to a temperature above the melting temperature of the plastic phase. The plastic phase was then added and the required melt viscosity was attained by applying a mechanical shear. The rubber phase was then added and the mixture was then melt mixed for an additional 1 to 3 min when other rubber additives, such as filler, activator, and lubricants or softeners, were added. Mixing was then carried out with controlled shear rate... 

A failure to install a necessary softener is ultimately reflected in higher bills for maintenance, repairs, and water treatment chemical products and services. Scaling can still occur with soft, lean waters, and the cost of additional fuel over a year probably would pay for several water softeners. In addition, the control of internal water chemistry becomes more difficult than it might otherwise be, which places an additional operational burden upon the facility. 

NOTE The term pretreatment is generally assumed to refer to some form of permanently installed equipment employed to treat MU water or FW. Such equipment provides physical or physicochemical water conditioning processes (such as ion-exchange softening) and is employed prior to the application of any internal FW or BW chemical treatments. 

Thus, merely cleaning boiler internals of carbonate deposits, say, by the use of an acid wash will not prevent a recurrence. Does the boiler require the installation of a water softener, an improved chemical treatment program, or better testing and monitoring ... 

In practice, however, it is often the case that for small LP steam heating boiler systems with a very high percentage of CR, and in those regions of countries where soft water is supplied, no water softener is provided or deemed necessary. Instead there is merely a reliance on internal chemical treatments (or sometimes magnetic devices or other types of gadget ). A good rule of thumb is ... 

The demand for alkali, phosphate, and/or polymer internal chemical treatments becomes significant, and unless extremely good control over BW chemistry and boiler plant operations is provided, the result most likely will be a scaled boiler, higher fuel costs, and reduced efficiency. A softener is required under these circumstances. 

For all LP steam operations in which the total hardness of RW exceeds, say, 10 to 20 ppm CaC03, the use of a softener is preferable to control solely via internal precipitation treatment. Oxygen scavenging and other internal treatment programs should also be provided. Some MPHW/HPHW and lower pressure steam boiler designs may require additional purification beyond simple water softening. 

This type, made by the General Electric Co., is resistant to sodium vapour and is used in sodiiun vapour discharge lamps. It has a very high boric oxide content, a low softening temperature, and a low electrical resistance. It is used as an internal layer in soda glass tubing X.8. ... 

---