Applications fluidized beds

Corrective Action Application Fluidized bed incineration has been used to incinerate municipal wastewater treatment plant sludge, oil refinery waste, some pharmaceutical wastes, and some chemical wastes including phenolic waste, and methyl methacrylate. Heat recovery is piossible. 

Principles of ECT and the latest developments in the technology are highlighted with emphasis on the volume ECT (ECVT) for 3D imaging. The significance of ECT technique in process engineering is presented in the framework of industrial application. Fluidized beds, pneumatic solids conveying, and slurry bubble columns are examples of ECT s capability to provide quantitative and qualitative understanding of the internal process dynamics. 

Type of Reaction and Application. An increased emphasis on gas-solid reactions has been evident for about a decade. Three of the papers in this symposium treat gas-solid reactions, two (13,18) dealing with coal combustion and the other (11) with catalyst regeneration. Of the four papers which consider solid-catalysed gas-phase reactions, one (15) deals with a specific application (production of maleic anhydride), and one (12) treats an unspecified consecutive reaction of the type A B C the other two (14,16) are concerned with unspecified first order irreversible reactions. The final paper (17) considers a relatively recent application, fluidized bed aerosol filtration. Principles of fluid bed reactor modeling are directly applicable to such a case Aerosol particles disappear by adsorption on the collector (fluidized) particles much as a gaseous component disappears by reaction in the case of a solid-catalysed reaction. 

Chemical Applications. Fluidized bed processing has become widely used in the chemical industry. It is important in particular for the synthesis of polyethylene and polypropylene, key basic plastics used for packaging, textiles, and plastic components. Fluidized bed reactors are used also for the industrial production of monomers such as vinyl chloride or acrylonitrile, which are both used to make plastics. These reactors are also employed to produce polymers such as synthetic rubber and polystyrene. The advantages of uniform heat transfer, great surface interaction, and transportation as fluid, whether in liquid or gaseous form, have made fluidized bed processing very valuable for contemporary chemical industry processes. 

In large-scale applications, fluidized-bed boilers are now dominant on the market. Both bubbling fluidized beds (BFBs) and circulating fluidized beds (CFBs) are used for biofuel firing. BFBs were originally limited to a rather narrow specification of fuels but now flue-gas recycling is used in both types of boilers. Especially, CFBs are considered to be tolerant to varying fuel qualities and, if this type of boiler is chosen, there would be no need to combine it with a dryer [3,4]. 

Fig. 16. Typical distributor grid designs for fluidized-bed applications (a) porous plate, (b) cone, (c) perforated plate, (d) downward dish, (e) upward dish,...

Spouted Beds The spoutedT)ed technique was developed primarily for sohds which are too coarse to be handled in fluidized beds. Although their applications overlap, the methods of gas-sohds mixing... 

When heavier refractories are required because of operating conditions, insulating brick is installed next to the shell and firebrick is installed to protect the insulating brick. Industrial experience in many fields of application has demonstrated that such a hning will success-billy withstand the abrasive conditions for many years without replacement. Most serious refractory wear occurs with coarse particles at high gas velocities and is usually most pronounced near the operating level of the fluidized bed. 

There are many uses of fluidized beds. A number of applications have become commercial successes others are in the pilot-plant stage, and others in bench-scale stage. Generally, the fluidized bed is used for gas-solids contac ting however, in some instances the presence of the gas or sohd is used only to provide a fluidized bed to accomplish the end result. Uses or special (maracteristics follow ... 

Fluidized-bed opposed-jet mills Hosokawa Micron Powder Systems Div.) differ from the Majac mill in that powder is not fed into the jets, but the jets impinge into a chamber mich contains suspended powder. The powder is entrained into the jets. This ehminates wear on the nozzles, and reduces contamination. Otherwise, construction and appheations are similar to the Majac mill. The fluidized-bed level is maintained a few inches above the jets. The Fluidized-bed mill is available in 13 sizes with air volumes ranging from. 50 to 11,000 mVh. One application is for toner grinding. 

TABLE 25-46 Full-Scale Commercial Applications of Fluidized Bed Process... 

The anaerobic filter, UASB, and fluidized bed reac tors have all been used for anaerobic treatment of industrial wastes, as each is especially suited for use in anaerobic treatment. Table 25-44 presents results from these applications. 

Fluidized-Bed Combustion The principles of gas-solid fluidization and their application to the chemical process industry are treated in Sec tion 17. Their general application to combustion is reviewed briefly here, and their more specific application to fluidized-bed boilers is discussed later in this section. 

Miscellaneous Systems Many other systems have been proposed for transferring heat regeneratively, including the use of high-temperature hquids and fluidized beds for direct contact with gases, but other problems which hmit industrial application are encountered. These svstems are covered by methods described in Secs. 11 and 12 of this handbook. 

The previous example was a rather unique application and not a typical case for fluidization. Although some fluidized bed reactions are executed at elevated pressure, like the naphtha reforming, most are used at atmospheric or at low pressures. The proceeding conceptual sketch. Figure 8.2.4, gives the most important features of a fluid-bed, cataljdic reactor. 

Applicability/Limitations Fluidized beds require frequent attention for maintenance and cleaning purposes. This treatment is ideal for slurries and sludges but not for bulky or viscous wastes. The waste particles should be of a certain size and be homogeneous. Wastes must have a low sodium content and a low heavy metal content. Some refractory wastes may not be fully destroyed since these units operate at low combustion temperatures (750 to 1000°C). 

Corrective Action Application Circulating fluidized bed incinerators are ready for full-scale testing under the EPA SITE Program. A unit is now in the RCRA permitting process. 

Most plastics are now available as powders and can be applied as coatings by fluidized bed or spraying techniques. Nylon 11 and polyethylene have proved most useful for chemical plant applications. 

Howard, J. R. (ed.). Fluidized Beds Combustion and Applications, Applied Science Publishers, London (1983)... 

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