Leach-bed

Leach-bed The feedstock is loaded in a vertical bioreactor to form a bed through which a liquid stream percolates as a leachate and is recirculated to the top of the same reactor where it is produced (Biocel process). This process is implemented in Lelystad, The Netherlands (ten Brummeler, 1999). 

Lehtomaki, A., Huttunen, S., Lehtinen, T.M., Rintala, J.A., 2008. Anaerobic digestion of grass silage in batch leach bed processes for methane production. Bioresource Technology 99 (8), 3267-3278. 

Since the 1960s the commercial development of continuous countercurrent processes has been almost entirely accompHshed by using a flow scheme that simulates the continuous countercurrent flow of adsorbent and process Hquid without the actual movement of the adsorbent. The idea of a simulated moving bed (SMB) can be traced back to the Shanks system for leaching soda ash (58). 

Batch Extractors. Coarse soHds are leached by percolation in fixed or moving-bed equipment. Both open and closed tanks (qv) having false bottoms are used, into which the soHds are dumped to a uniform depth and then treated with the solvent by percolation, immersion, or intermittent drainage methods. 

Moving-bed percolation systems are used for extraction from many types of ceUular particles such as seeds, beans, and peanuts (see Nuts). In most of these cases organic solvents are used to extract the oils from the particles. Pre-treatment of the seed or nut is usually necessary to increase the number of ceUs exposed to the solvent by increasing the specific surface by flaking or rolling. The oil-rich solvent (or misceUa) solution often contains a small proportion of fine particles which must be removed, as weU as the oil separated from the solvent after leaching. 

Percolation Leaching. Ground material coarse enough to permit circulation of a solution through a bed of particles can be leached by percolation of the solvent through the material placed ia a tank or vat. The process usually takes several days. 

In some liquid-phase processes, catalyst components are slowly leached from the catalyst bed and eventually the catalyst must be replaced. The feasibility of this type of process involves economics, ie, the costs of catalyst maintenance and keeping a unit out of service for catalyst replacement, and product quality and safety, ie, the effects of having catalyst components in the product and their ease of removal. 

Combustible masking materials such as organic char may be partially or completely removed by periodic elevations of the catalyst bed temperature. Noncombustible masking materials may be removed by air lancing or aqueous washing generally with a leaching solution (20,21). 

Continuous Percolators Coarse sohds are also leached by percolation in moving-bed equipment, including single-deck and nmlti-deck rake classifiers, bucket-elevator contactors, and horizontal-belt conveyors. 

The regeneration of the resin bed is never complete. Some traces of calcium and magnesium remain in the bed and are present in the lower-bed level. In the service run, sodium ions exchanged from the top layers of the bed form a very dilute regenerant solution which passes through the resin bed to the lower portion of the bed. This solution tends to leach some of the hardness ions not removed by previous regeneration. 

Extraction (sometimes called leaching) encompasses liquid-liquid as well as liquid-solid systems. Liquid-liquid extraction involves the transfer of solutes from one liquid phase into another liquid solvent it is normally conducted in mixer settlers, plate and agitated-tower contacting equipment, or packed or spray towers. Liquid-solid extraction, in which a liquid solvent is passed over a solid phase to remove some solute, is carried out in fixed-bed, moving-bed, or agitated-solid columns. 

Sintered metal fibers with filaments of uniform size (2-40 (tm), made of SS, Inconel, or Fecralloy , are fabricated in the form of panels. Gauzes based on thicker wires (100-250 tm) are made from SS, nickel, or copper. They have a low surface area of about 10 m g. Several procedures are used to increase the surface area, for example, leaching procedures, analogous to the production of Ra-Nickel, and electrophoretic deposition of particles or colloid suspensions. The porosity of structures formed from metal fibers range from 70 to 90%. The heat transfer coefficients are high, up to 2 times larger than for random packed beds [67]. 

Vat leaching is a more complex technique as compared with the techniques described earlier. Here, the ore meant to be leached is loaded into vats that are typically made of concrete and are a few meters deep and several meters in horizontal dimensions. The vats are often fitted with filter-type bottom to facilitate solution flow through the ore bed. Usually, several vats are employed and leaching solution is pumped continuously from one tank to the top... 

The film diffusion stages (i) and (v) are similar to the external mass transfer stages in leaching and may be dealt similarly (see Section 2.1.3). Solution flow conditions for resin touching the fixed beds are likely to be in the laminar flow range. 

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