Precipitators treatment

Fig. 29. Effects of time and temperature of precipitation treatments on yield strength of alloy 2036—T4 sheet. Numbers represent strength in MPa. To...

Scale and deposits are controlled through the use of phosphates, chelants, and polymers. Phosphates are precipitating treatments, and chelants are solubilizing treatments. Polymers are most widely used to disperse particulates but they are also used to solubilize contaminants under certain conditions. 

Comparison of Sulfate Removal in Samples of Nitrocellulose by Acid Boil and Precipitation Treatments... 

In particular, where polyphosphate is added either to the MU waterline (say, as a stabilizer against the risks of after-precipitation) or to the FW line or FW tank (as a precipitating treatment for residual hardness), there is some risk of FW line phosphate deposits developing. Such deposits are likely to be primarily composed of hard, intractable calcium phosphate [tricalcium phosphate Ca3(P04)2] scale, but they may include magnesium phosphate [Mg3(P04)2] and other insoluble phosphates and hydroxides. The risk of precipitation and subsequent deposition is increased where the pH is below 8.3, if the FW line is particularly long, or when the FW temperature is high. 

Phosphate precipitant treatments should almost always be added directly to the boiler shell or drum, or to the FW line as close as possible to the boiler. (The phosphate dosing pump should be interlocked with the FW pump when dosing to the FW line.)... 

Commonly, phosphate or carbonate may be purposefully present in many boilers as a result of the application of certain internal precipitating treatment programs. Rather than providing a benefit, they can add further to the risk of deposition if the correct operational conditions are not maintained because adherent scales are produced rather than free-flowing sludges that are amenable to boiler blowdown (BD). 

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. 

With high-hardness waters, the carbonate-cycle form of precipitation treatment is often preferred to the phosphate-cycle because it forms a less bulky and less dense sludge. The disadvantages of hard-water carbonate-cycle precipitation treatments include ... 

Dozens of phosphates are commercially available, supplied as anhydrous materials or with varying levels of water of crystallization, although only a limited number are employed for BW precipitating treatment programs. 

M. M. Jordan, K. S. Sorbie, P. Chen, P. Armitage, P. Hammond, and K. Taylor. The design of polymer and phosphonate scale inhibitor precipitation treatments and the importance of precipitate solubility in extending squeeze lifetime. In Proceedings Volume, pages 641-651. SPE Oilfield Chem Int Symp (Houston, TX, 2/18-2/21), 1997. 

The next stage is elution, in which the captured ions are displaced from their sites when a suitable chemical solution, called the eluant, is flushed through the column. With the completion of this operation, the resin sites are restored to their original state and the beads are stated to be regenerated. The new pregnant eluate is either stored or is administered a precipitating treatment the column is subjected to a further backwash to remove its residual eluant. It is then fit to go on stream once more. 

Other Inorganic Cell Wall Precipitation Treatments... 

As in the case of hydrated niobium and vanadium pentoxides, it is a difficult matter to remove traces of mineral acids from the precipitate. Treatment with water gives rise to a cloudy hydrosol which passes through an ordinary filter. This can be prevented by addition to the wash-water of a small quantity of ammonia or acetic acid.4 In the preparation of anhydrous tantalum pentoxide, traces of adds can be removed by igniting the gel in admixture with a small quantity of ammonium carbonate. 

In each case the crude calcium alginate obtained by identical hot aqueous acid extraction and precipitation treatments was dark brown in color. The final products were analyzed the results obtained, together with the yields found, are recorded in Table II. 

Many non-ferrous castings are used in an as-cast condition, but certain applications require higher mechanical properties than as-cast material. Possible treatments are annealing, controlled cooling, solution heat treatment, artificial ageing and precipitation treatment. 

Mg. 6.8 Precipitation treatment of wastewater from a zinc-lead smelter, [28]. 

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