Graded beds

Diesel HDT is carried out at temperatures between 310°C and 400°C, pressures from about 500 to 700psig, and 1—4h 1 of space velocity. Preferred catalyst may be CoMo or NiMo in a single bed or combined in graded beds, depending on the quality of the feed and on the specifications required for the product. 

Axens, Graded Bed Technology for Pressure Drop Control, in Company Brochure. 2003. 

Many turbidites found on the continental margins are characterized by graded bedding 13.8). This type of particle sorting is produced by the sequential deposition... 

Since these sediments contain only clay- and silt-sized particles, the graded bedding in these deposits is not as pronounced as in the nearshore turbidites. 

Graded bedding A type of sediment stratification in which each stratum displays a gradahon in grain size from coarse below to fine above. 

Graded bed filters. A conventional graded bed filter is usually a cylindrical vessel (horizontal or vertical) filled with about 3 ft of graded filter media. 

Graded bed filters are capable of treating waters with as little as 1 ppm of suspended solids Most particles down to 25-50 p will be removed... 

All the three systems employed graded bed in order to tackle the reactor pressure drop, especially at the front end where the operating temperatures are lower and catalyst encounters the virgin stock. 

Sedimentary phosphate rocks occur throughout the geological time scale. Most sedimentary deposits were apparently formed in offshore marine conditions on continental shelves. They exhibit a wide range of chemical compositions and great variations in physical form. Economic deposits usually occur as one or more thick high-grade beds that are unconsolidated and have a uniform granular texture and composition, shallow overburden, and a minimum of structural deformation. 

Beds of ash commonly show lateral variation as well as vertical. In other words, with increasing distance from the parent vent, the ash becomes finer and, in the second case, because the heavier material falls first, ashes frequently exhibit graded bedding, with coarser material occurring at the base of a bed, and becoming finer towards the top. Reverse grading may... 

Although graded bedding occurs in several different types of sedimentary rock, it is characteristic of greywacke. As the name suggests, the sedimentation unit exhibits a grading from coarser grain size at the bottom to finer at... 

Graded bedding—In a stream, as current velocity wanes, first the larger or denser particles are deposited followed by smaller particles. This results in bedding showing a decrease in grain size from the bottom of the bed to the top of the bed (fine sediment on top and coarse at the bottom). 

FIGURE 5.10 Reverse-flow sorption trap (a) and the chromatogram of a 42-component mixture in an air sample collected with the device (b). The three adsorption beds are graded bed A is the weakest absorber and C is the strongest (largest surface area) adsorber. The flow direction is reversed between sample collection and injection. Compounds are 1, acetaldehyde 2, methyl alcohol 3, n-pentane 4, isoprene 5, acetone 6, ethyl alcohol 7, 2-propyl alcohol 8, n-hexane 9, butanone 10, ethylacetate 11, 1-propyl alcohol 12, 2-butyl alcohol 13, trichloromethane 14, benzene 15, isooctane 16, n-heptane 17, 2-pentanone 18, 2,5-drmethylfuran 19, 1-butylalcohol 20, tolnene 21, n-octane 22, hexanal 23, butylacetate 24, ethylbenzene 25, m-xylene 26, n-nonane 27, o-xylene 28, cumene 29, a-pinene 30, -pinene 31, n-decane 32, 1,2,4-trimethylbenzene 33, benzaldehyde 34, d-limonene 35, 1,2,3-trimethylbenzene 36, 1,2-dichlorobenzene 38, n-dodecane 39, 3-pentanone 40, 1-pentyl alcohol 41, 2-heptanone 42, n-undecane. 

Hydrotreating catalyst particles are surprisingly small, with diameters of 1.5 to 3.0 mm and length/diameter ratios of 3 to 4. In many units, ceramic balls and/or successively larger catalyst particles are loaded on top of the first catalyst bed. This graded bed protects the bulk of the catalyst by filtering particulate matter out of the feed. 

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