Surface scraping

PHOSPHATATION A clarification process where phosphoric acid or a soluble phosphate is used with lime and heat. The impurities are removed by flocculation, flotation, and surface scraping. 

The temperature of the room in which the liquoring is performed should not vary much, ond should be at least 70°. The operation of liquoring is performed da follows —The crystallization is- complete in twenty, hours. The superficial crystalline crust is then removed from die base of each loaf with a trowel, and the surface is levelled. These surface scrapings—or rather those of a previous day s work —are added to sirup until the density becomes 67° Twaddell at 60°. , ... 

XRD results of the surface scrapings positively identified both litharge (PbO) and cerussite (PbC03). Differential weathering of the trace elements into similar oxides and carbonates would certainly change the apparent concentrations. Considering the small amount of lead available for analysis, the relatively non-destructive EMPA is likely the better technique. 

The sample submitted for analysis may be unrepresentative of the bulk material on site e.g. a surface scraping of a weathered cement product is likely to result in a high proportion of fibres compared to the actual cement product. 

Surface soil scrapings were taken from Plots A, C - Control, and D - Shaded on November 4, 1985. The results of TCDD analyses of these surface samples were 33 ppb, 66 ppb, and 121 ppb for Plots A, C - Control, and D - Shaded respectively. These surface TCDD concentrations are compared to the concentrations in the subsurface soil layers in Figures 3, 5, and 6. Since it is impossible to take a sample of zero thickness, the surface scraping data are plotted at a depth of 0.15 cm. 

For the dry and shaded control experiment (Plot D - Shaded) the surface scraping sample concentration falls within the 2 standard deviation limits about the mean. This implies that no statistically significant loss of TCDD occurred in the dry shaded plot. Therefore, the presence of water and/or sunlight are important environmental parameters affecting the mobility of TCDD in soils. 

Mechanical aids stir the fluid by mechanical means or by rotating the surface. Surface scraping, widely used for batch processing of viscous liquids in the chemical process industry, is applied to the flow of such diverse fluids as high-viscosity plastics and air. Equipment with rotating heat exchanger ducts is found in commercial practice. 

In another series, gold alloy A(Table I) was exposed in-vitro for 1 hr to the supernatant of saliva. After distilled water rinsing and air drying, the surface was viewed under the FT-IR microscope and surface scrapings made with a scapel tip at different locations across the surface. Organic material removed at the different sites was obtained as thin films on KBr discs. An Analect FT-IR was used to obtain the spectrum... 

High heat transfer coefficients, up to 1 kW m K, and hence high production rates, are obtainable with double-pipe, scraped-surface heat exchangers. Although mainly employed in the crystallization of fats, waxes and other organic melts (section 8.2.2) and in freeze concentration processes (section 8.4.7), scraped-surface chillers have occasionally been employed for crystallization from solution. Because of the high turbulence and surface scraping action, however, the size of crystal produced is extremely small. 

Remove a fresh adhesive-backed collection paper and fold it in half. Apply the paper close to the area to be tested. Using the coring tool, cut down into the surface. Scrape the paint from inside the circle and place it on the paper. Be sure to remove all layers. Thoroughly clean the coring tool. Transfer the paint from the paper to a plastic vial. Grind up the paint with a plastic rod for about 10 s. 

The Phillips process is a two-stage crystallisation process that uses a pulsed column in the second stage to purify the crystals (79,80). In the pulsed column, countercurrent contact of the high purity PX Hquid with cold crystals results in displacement of impurities. In the first stage, a rotary filter is used. In both stages, scraped surface chillers are used. This process was commercialized in 1957, but no plants in operation as of 1996 use this technology. 

The long leaf fibers contribute strength to the leaves of certain nonwoody, monocotyledonous plants. They extend longitudinally the hiU length of the leaf and are buried in tissues of a parenchymatous nature. The fibers found nearest the leaf surface are the strongest. The fibers are separated from the pulp tissue by scraping because there is Htde bonding between fiber and pulp this operation is called decortication. Leaf fiber strands are also multiceUed in stmcture. 

For discharge of the cake, a discharge door is provided at the edge and the cake is moved by the rotor toward the door, the stirrer blades gradually being lowered onto the surface so that a small depth of soHds is scraped away. Alternatively, the cake may be reslurried and pumped away. 

Precipita.tlon, In the simplest case, the solubihty of an impurity in the Hquid metal changes with temperature. Thus the impurity may precipitate as a sohd phase upon cooling. For instance, the removal of iron from tin and of copper from lead are achieved by precipitation. When the soHd is lighter than the Hquid, it floats as a dross on the surface of the melt where it is easily removed by scraping. The process is called dressing. 

Drum Drying. The dmm or roHer dryers used for milk operate on the same principles as for other products. A thin layer or film of product is dried over an internally steam-heated dmm with steam pressures up to 620 kPa (90 psi) and 149°C. Approximately 1.2—1.3 kg of steam ate requited per kilogram of water evaporated. The dry film produced on the roHer is scraped from the surface, moved from the dryer by conveyor, and pulverized, sized, cooled, and put iato a container. 

Industrial separations are conducted in gravity or bath separators for a coarse feed, and in centrifugal separators for a fine feed (2,6,10). In gravity-type separators the feed and medium are introduced to the surface of a large quiescent pool of the medium. The float material overflows or is scraped from the pool surface. The heavy particles sink to the bottom of the separator and are removed using a pump or compressed air. The dmm separator (Fig. 13), up to 4.6 m dia and 7 m long, processes approximately 800 t/h, and treats feed of size up to 30 cm dia, operates in the gravity or the... 

Evaporation Retardants. Small molecule solvents that make up the most effective paint removers also have high vapor pressure and evaporate easily, sometimes before the remover has time to penetrate the finish. Low vapor pressure cosolvents are added to help reduce evaporation. The best approach has been to add a low melting point paraffin wax (mp = 46-57° C) to the paint remover formulation. When evaporation occurs the solvent is chilled and the wax is shocked-out forming a film on the surface of the remover that acts as a barrier to evaporation (5,6). The addition of certain esters enhances the effectiveness of the wax film. It is important not to break the wax film with excessive bmshing or scraping until the remover has penetrated and lifted the finish from the substrate. Likewise, it is important that the remover be used at warm temperatures, since at cool temperatures the wax film may not form, or if it does it will be brittle and fracture. Rapid evaporation occurs when the wax film is absent or broken. 

Insofar as they are used to purify other products, several processes used in the refinery fall under the classification of dewaxing processes however, such processes must also be classified as wax production processes (2). Most commercial dewaxing processes utilize solvent dilution, chilling to crystallize the wax, and filtration (28). The MEK process (methyl ethyl ketone—toluene solvent) is widely used. Wax crystals are formed by chilling through the walls of scraped surface chillers, and wax is separated from the resultant wax—oil—solvent slurry by using fliUy enclosed rotary vacuum filters. 

One of the early column crystallizers was that iatroduced for the separation of xylene isomers (see Xylene and Ethylbenzene). In this unit, shown schematically ia Eigure 25, -xylene crystals are formed ia a scraped-surface chiller above the column and fed to the column. The crystals move downward counter-currenfly to impure Hquid ia the upper portion of the column and melted -xylene ia the lower part of the column. Impure Hquor is withdrawn from an appropriate poiat near the top of the column of crystals while pure product, xylene, is removed from the bottom of the column. The pulse unit drives melt up the column as reflux and iato a product receiver. 

A simple separator used to recover the magnetic particles consists of a series of disks mounted on a shaft. Each disk has a number of permanent magnets mounted flush with the surface at its perimeter. The disks rotate into and out of the Hquid containing the suspended magnetic material and lift the magnetic particles out of the stream. The magnets are then scraped clean (Eig. 10). Very low residence times are needed for removal of the particles compared to settling or flotation (142). 

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