Recycle of solids

Promote a national research and development program for improved ntaitiigement techmques, more effective organizational arrangements, and new and improved methods of collection, separation. reco ery, and recycling of solid wastes, and Ute environmentally safe dispostil of nonTeco enibIe residues... 

When slurry feeding is impractical, recycling of solids product to mix with the feed, both to dry and to achieve a better-handling... 

B. Recycle of Solid Waste Products from the MCS Reaction... 1593... 

The recycling of solids causes a spread in the residence time, and hence in the conversion of the particles as some rise only once through the riser while otha s are recycled several times. Partly unreacted feed can hence be discharged, causing insufficient conversion. It can be demonstrated (Smolders et al. [8]) that the conversion in the product stream (X a ), is equal to ... 

Continuous leaching can also be carried out on a laboratory scale, with one or more tanks (in series or in parallel) and with recycling of solids, if necessary. The difficulties that arise in long-term operation of these systems are usually due to wear on the equipment due to the action of the mineral particles, problems in maintaining complete suspension and homogeneity of the mineral, and accurate transfer of relatively small volumes of mineral suspensions from the feed tank to the... 

Douglas,E Webb,M Daborn,G.R. Presented on "Treatment and Recycling of Solid Wastes", Manchester, Jan. 197. ... 

This process will allow the recycling of solid waste to produce a useful product. High pressure and temperature combined with hydrogen can convert most types of domestic and industrial wastes back into products that are currently obtained from fossil coal and oil. No volatile polluting chemicals will be vented into the atmosphere. The metals can be recovered for further use and the ceramic materials will be converted into a product difficult to distinguish from natural rocks. This type of process will not solve all the solid waste disposal problems, but will provide a potential method for recovery of valuable products from waste. When implemented, it will dramatically reduce the amount of solid waste placed in landfills. This process also has the potential to reduce the amount of oil and coal mined to provide the carbon compounds needed to manufacture all petrochemical derived materials. This waste reduction process is a variation on the Fischer-Tropsch process, mentioned on page 101, in use commercially to produce hydrocarbon materials from coal. 

A deep bed system that avoids hetch backwashing to clean the filter is lhe Dyan Sand" filler. The bed design is continuously claimed and regenerated by the internal recycling of solids from the bottom of the bed to the top through an air-lift pipe and a sand washer. This filter allows a constant pressure drop across the bed and avoids the need for a parallel filter to allow backwashing. 

Waste materials such as municipal solid waste, scrap tires, and waste plastics have traditionally been placed in sanitary landfills. However, with landfill space rapidly decreasing in the United States and worldwide, an alternative disposal method for these waste materials becomes imperative. The recycling of solid wastes is a challenging problem, with both economic and environmental constraints. Recently, two broad approaches have been attempted to reclaim solid wastes. The first approach relies on thermal or catalytic conversion of waste materials into fuel and valuable chemical feedstocks. Examples of this approach include gasification, pyrolysis, depolymerization, and liquefaction. The second approach relies on the physical recovery of valuable ingredients in the waste materials. 

Assessment, Symp. on Treatment and Recycling of Solid Wastes, Institute of Solid Wastes Management, Manchester, England, Jan., 1974. 

Units such as the Studsvik Energy or Ahlstrom license systems do not possess external heat transfer surfaces. In these cases the cost of the unit can be minimised by reducing the external recycle of solids. This is best served by design of a very abrupt exit (or even an internal separator) to maximise internal refluxing of particles. This requires a different exit design than the previous case, with no conflicting demands other than erosion tendencies of the increased internally refluxing stream. 

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