Partial softening

Waters of intermediate hardness frequently contain fair amounts of other constituents and there is often a tendency for the scale to be loosely attached, permitting corrosion to occur irregularly underneath. In most waters the bicarbonate content is less than the hardness, but a few natural waters are known where the reverse is the case. These waters have been partially softened by the zeolite process which occurs underground, and then contain sodium bicarbonate which, together with the high concentration of chloride and other minerals, may accelerate attack. 

Table 10.3 Carbonate-Cycle Coagulation and Precipitation Program. Recommended BW Control Limits for Non-Highly-Rated FT Boilers Employing Hard or Partially Softened FW...

Under these conditions, cooling water cycles of concentration are likely to be restricted to a maximum of only 2.5 to 4x without some innovative chemical treatment and operations programming. Sources of subsurface water with hardness and alkalinity contents much higher than those cited are likely to be unsuitable for cooling systems without some form of additional pretreatment, such as dealkalization, partial softening, use of RO, or blending with lower alkalinity/lower hardness supplies. 

When water is very hard it is sometimes partially softened by a preliminary treatment with lime and soda. In some eases the permutit plant fed with such treated waters has ceased to work satisfactorily after a number of years, the permutit becoming contaminated with chalk.1... 

The resultant cathodes must undergo a further refining step as small levels of tin and antimony can often be deposited along with the lead. These elements are removed by oxygen softening and/or caustic dressing from the remelted cathodes. To limit the level of cathode contamination, some lead refineries apply partial softening to the lead bullion before the anodes are cast. 

Aluminum and ferrosilicon anodes are suitable for the protection of hot water tanks. The use of aluminum anodes in a hot water apparatus has additional effects, an indirect protective action on subsequent piping, since a protective film (1-1.5 mm thick) is built up by anode-formed aluminum oxide hydrates. In addition to alkalization at the cathode, a shift in the calcium carbonate (CaCOj)-CO2 equilibrium leads to partial softening of water, with CaC03 being deposited at the cathode. 

In addition, the refinery consumes water for cooling, for boilers, and for domestic purposes, and according to the source (surface water, ground water, reused water), the makeup water needs a specific treatment such as sand filtration, iron removal, (partial) softening, desalination, dosing of chemicals to control corrosion, and biofouling. 

Soft Water. The soft water has the same analysis as the raw water except that all the Ca and Mg are replaced by sodium. This completely softened water is blended with raw water to give the blended partially softened water of SO ppm hardness that is used throughout the MTR site. 

Anodes are cast from smelter bullion after copper separation and partial softening if needed, either in flat open moulds on a casting wheel as a measured amount, or into closed book moulds . One critical aspect of the performance of the anode is that it should dissolve at a uniform rate and this can be influenced by the microstructure and uniformity of the anode as well as by the impurity content. In this regard the casting method and the cooling rate are most important, and the use of book moulds is preferable in achieving better control and uniformity of the surface structure. With an open mould as in wheel cast anodes, the upper and lower surfaces are quite different in terms of crystal structure, oxidation and flatness. 

With this method, carbonate removal plus partial softening (with a reduction in M alk and TH), can be associated with clarification plus coagulation (with elimination of suspended, organic and colloidal matter) in the same settler. 

Semicrystalline polymers show a more complicated DMA picture. It was indicated in Fig. 6.4 that the glass transition results only in a partial softening because of the high level of cross-linking due to the crystals. Only above the melting temperature is the fully liquid state reached. A typical torsion pendulum result, obtained with an instrument similar to that in the sketch of Fig. 6.18, is shown in Fig. 6.24 for linear polyethylenes of different crystallinity. Three regions of maxima in G and tan S can be found below the equilibrium melting temperature of 414.6 K. Customarily these relaxations are called a, p, and y. A detailed interpretation of such DMA data has been... 

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