Scale removal chemical method

Mechanical and biological methods are very effective on a large scale, and physical and chemical methods are used to overcome particular difficulties such as final sterilization, odor removal, removal of inorganic and organic chemicals and breaking oil or fat emulsions. Normally, no electrochemical processes are used [10]. On the other hand, there are particular water and effluent treatment problems where electrochemical solutions are advantageous. Indeed, electrochemistry can be a very attractive idea. It is uniquely clean because (1) electrolysis (reduction/oxidation) takes place via an inert electrode and (2) it uses a mass-free reagent so no additional chemicals are added, which would create secondary streams, which would as it is often the case with conventional procedures, need further treatment, cf. Scheme 10. 

In our own work, the effectiveness was examined of trace element removal by two chemical coal cleaning methods being studied for possible large-scale application. One method involved treatment with aqueous Na,C03 solutions, and the other involved treatment with molten NaOH/KOH mixtures. In each case, acid washes were used as subsequent cleaning steps to decrease the ash content, followed by water washes in the final step. Although the primary objective of these treatments was to remove sulfur and ash-forming minerals, the extraction of trace elements from these coals was examined as an additional benefit of chemical coal cleaning. 

The analysis of corrosion scale or product may be done by wet chemical methods such as spectrophotometry or atomic absorption spectrophotometry in cases where the removal of corrosion scale is permitted, or by surface analytical techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, electron microprobe analysis, by energy dispersive X-ray analysis in the case of samples which need to be preserved. 

Still, all of the required conditions are present to make the photolysis of pesticides in natural waters inevitable. It seems that final proof of its extent and significance must await either more sophisticated methods for detecting and measuring transient chemical species or the actual application of photochemical principles to the practical-scale removal of pesticides from water. 

Chemical Methods. Chemical methods include pickling, which can be used to remove scale and metal oxides. Sulfuric acid and hydrochloric acid are usually used to treat steel and zinc, while nitric acid, nitric acid-hydrofluoric acid, or sulfuric acid-hydrofluoric acid are used for aluminum. Although pickling in phosphoric acid is somewhat slower, it has the advantage that a thin conversion layer of the substrate phosphates is produced, which provides temporary corrosion protection... 

However, physical methods suffer from microscopic-level phase separation [155] between the two constituents. This occurs due to the removal of solvent molecules which not only cause the aggregation of nanocrystals to form super-crystals but also lead to partial crystallization of regioregular polymeric chains. In such type of hybrids, it is difficult to realize the intimacy between QCNs and CP at nanometer scale. The loose networks of QCNs scatter the electrons in electronic devices which in turn leads to poor device efficiency, e.g., in solar cells, it is responsible for low photoconversion efficiency due to deterioration of the efficiency at charge generation, separation, and transport steps. In order to overcome above limitations, efforts have been made to improve the intimacy between the phases by adopting chemical methods that involve means for realizing chemical linking between two partners. 

All oil, grease and other soluble contamination should be removed by solvent degreasing or alkaline cleaning. Rust, scale and other non-soluble contaminants should be removed by mechanical or chemical methods. Grit blasting is the most commonly used mechanical method, but wheel abrasion, grinding, wire brushing, emery cloth or steel wool can be used. Chemosil 211 primer should be applied as soon as possible after the surface preparation to reduce the risk of contamination or oxidation of the substrate. 

Unfortunately, not all scales are removable by chemical methods. For example, only calcium carbonate scale is readily removed by acid. Others, such as calcium sulfate, can be removed chemically, but inefficiently or only partially. Most scales require mechanical methods, such as milling, for complete removal. See chapter 14 for further discussion of scale removal. 

Chemical lysis, or solubilization of the cell wall, is typically carried out using detergents such as Triton X-100, or the chaotropes urea, and guanidine hydrochloride. This approach does have the disadvantage that it can lead to some denaturation or degradation of the produci. While favored for laboratory cell disruption, these methods are not typically used at the larger scales. Enzymatic destruction of the cell walls is also possible, and as more economical routes to the development of appropriate enzymes are developed, this approach could find industrial application. Again, the removal of these additives is an issue. 

It is possible to remove all solids from the make-up water, but it is much cheaper to check the concentration by other means. Two general methods are employed. The first relies on physical or chemical effects to delay deposition of scale on the hot surfaces the second restricts the concentration to a level at which precipitation will not occur. In both cases, the accumulation of solids is removed by bleeding off water from the circuit to drain, in addition to that which is evaporated (see Figure 6.8). 

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