Scale removal mechanical

Often heat removal causes design problems for scale-up. Mechanical agitation coupled with a metabolic heat from the growing biomass... 

From the corrosion point of view, it is very important to control the deposition of scale. Removal of deposited scale by mechanical means is the first step. Standard, industrial water-treating techniques can be used to control scale deposition in general. In deep, hot wells or geothermal wells it is best to avoid untreated makeup water (i.e., geothermal brines). 

Mechanism of Scale Removal from Steel with Acid... 

Fig. 11.3 Mechanism of scale removal with acid, (a) High-temperature scale and (b) low-...

The mechanisms of oxide dissolution and scale removal have been widely studied in recent years. This work has been thoroughly reviewed by Frenier and Growcock who concluded, in agreement with others", that oxide removal from the surface of steel occurs predominantly by a process of reductive dissolution, rather than by chemical dissolution, which is slow in mineral acids. 

In general there does not appear to be any direct correlation between the rate of the chemical dissolution of oxides and the rate of scale removal, although most work on oxide dissolution has concentrated on magnetite. For example, Gorichev and co-workers have studied the kinetics and mechanisms of dissolution of magnetite in acids and found that it is faster in phosphoric acid than in hydrochloric, whereas scale removal is slower. Also, ferrous ions accelerate the dissolution of magnetite in sulphuric, phosphoric and hydrochloric acid , whereas the scale removal rate is reduced by the addition of ferrous ions. These observations appear to emphasise the importance of reductive dissolution and undermining in scale removal, as opposed to direct chemical dissolution. 

For the subculture of adherent cells, removal of culture medium and the detachment of cells from the monolayer are necessary. This detachment is usually performed with trypsin, but other proteases, such as pronase, dispase, and collagenase, can be employed. In general, a chelating agent, such as EDTA, is also added to capture the Ca2+ ions involved in the cell adhesion process. Some cell lines bind weakly to surfaces and, in small-scale cultures, can be removed mechanically by gently tapping or hitting the culture flask by hand. 

As with cotton and other cellulosics, the use of the electron microscope has aided the evaluation of mechanical degradation and wear of wool fabrics. Scale removal and fibrillation were more representative of normal wear, whereas a variety of fiber faults were observed on wool fabrics abraded by laboratory testers such faults included longitudinal splitting, transverse fracture, and abraded fibrils (172). 

For passivation treatments other than scale removal following thermal treatment, less aggressive acid solutions are usually employed. The primary purpose of these treatments is to remove contaminants that may be on the component s surface and could prevent the formation of the oxide layer locally. The most common contaminant is imbedded or free iron particle from forming or machining tools. Mechanical polishing can be employed to provide a uniform surface finish and to remove these contaminants. The polishing materials should be used for stainless only as they can carry over small particulates from one part to the next. In addition, the work-hardened state of this fine particulate, even from a stainless vessel, can have a lower threshold for corrosion and act as an initiation site if not removed. A dilute (10%) solution of nitric acid is... 

On a large scale, particles (as well as gases) are moved through the atmosphere by advection and turbulence, i.e., horizontal and vertical winds (Wexler et al. 1994 Seinfeld and Pandis 1998). Simultaneous with these large-scale motions are the smaller-scale processes that can transport particles across surface boundary layers (e.g., at the Earth s surface) and thus remove them. As discussed earlier, diffusion is the dominant removal mechanism for small particles because of their high diffusion coefficients and low gravitational settling velocities. Because of their very small sizes, nanoparticles can slip... 

The free energy of reaction (a) is favorable, and the starting materials are easily prepared. However, high purity is not achieved because fluorides often retain water or oxygen that remains in the product, and because slags such as Cap2 are admixed with the product and must be removed mechanically. In research-scale reductions, high purity fluoride [from oxide treated with HF(g)] and Ca can achieve > 99.9% pure lanthanoid metals, if the metals are further purified by vacuum fusion or distillation -. ... 

SCALE REMOVAL - Waterside, removal of scale using either the mechanical, the water treatment or the acid cleaning process. 

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