Dense media, separation processes

The use of liquids of varying density in a simple float-sink test leads to separation of the raw coal into different density fi actions. In a heavy liquid (dense medium), particles having a density lower than the liquid will float, and those having a higher density will sink. The commercial dense-media separation process is based on the same principle. Since the specific gravity of coal particles varies... 

Dense-medium separators (sink and float processes)... 

Washing processes fall into three classes (I > hydraulic separation. (2) dense medium separation and (3) centrifugal icyclone) separation. 

Dense-Medium Separators (Sink and Fioat Processes)... 

In a heavy-medium separation process, coal particles whose density is higher than the medium sink while the lower-density coal particles float the separation efficiency and the through put of the separation device depend on the velocity of coal particles in a dense medium. The viscosity of a medium has little effect on the low-density coal particles or the high-density gangue particles, but becomes critical in the separation of material of a density equal to or near that of the medium hence, a low viscosity must be maintained to separate near-density material at a high rate of feed. 

Dense-Medium Washing. Dense-medium separations include processes that dean raw coal by immersing it in a fluid medium with a density intermediate between the density of clean coal and that of reject. Most dense-medium washers use a suspension of fine magnetite in water to achieve the desired density. The process is very effective in providing a sharp separation and is relatively low in capital and operating costs. 

More accurate separations are made in dense medium vessels. Coal is slurried in a medium with a specific gravity close to that at which the separation is to he made. The lighter coal lends to floai and the refuse io sink. The two fractions liien can he mechanically separated. Theoretically, any size panicle can be treated hy the dense medium process. Practically. 

Separator, the Falcon Concentrator, and the Knelson Concentrator. The development of advanced ultrafine dense-medium systems, such as Carefree Coal and MicroMag, also have the potential to improve cleaning of coal fines. However, none of these processes has yet achieved any significant degree of commercialization. 

Air separation by membranes to produce N2 or O2 is interesting especially for small to medium capacities and medium (up to 99%) purity. The highest purities of oxygen (>99%) are to be obtained with dense (non-porous) membranes. The economics of gas separation processes is discussed in detail by Spilman [7] together with a number of potentially interesting applications. 

An alternate to the concept of cluster renewal discussed above is the concept of two-phase convection. This second approach disregards the separate behavior of lean and dense phases, instead models the time average heat transfer process as if it were convective from a pseudo-homogeneous particle-gas medium. Thus h hcl, hh and hd are not... 

A semi-quantitative picture of positronium formation in a spur in a dense gas was developed by Mogensen (1982) and Jacobsen (1984, 1986). If the separation of the positron from an electron is r, and there is assumed to be only one electron in the spur (a so-called single-pair spur), then the probability of positronium formation in the spur, in the absence of other competing processes, can be written as [1 — exp(—rc/r)] here rc is the critical, or Onsager, radius (Onsager, 1938), given for a medium of dielectric constant e by... 

I have chosen to discuss three separate categories of black holes those that arise from stellar collapse, those that may come about from merging and accretion processes and are termed supermassive black holes (SMBH), and those which may be relics of the dense highly inhomogeneous medium in the early universe (primordial black holes—PBH). 

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