Solids bed

Solid-Bed Dehydration. Sihca gel, bauxite, activated alurnina, or molecular sieves can be used for removing dissolved water to meet propane specifications. The soHd-bed dehydrators are used in a cycHc adsorption process. After an adsorption cycle has completed, the bed is heated with a purge gas or a vaporized Hquid-product stream for regeneration. If the latter is used, the Hquid product is condensed, separated from the free water, and returned to the process. After the beds are regenerated, they are cooled and returned to the adsorption cycle. 

Solid-Bed Caustic Treatment. SoHd-bed caustic units utilizing methanol [67-56-1] injection into the LPG feed stream can be used for carbonyl sulfide removal. The methanol—caustic solution must be drained periodically from the beds and discarded. When the soHd bed is exhausted, the spent caustic must be discarded and replaced. The LPG from the treater has a low enough water content to meet the propane specification. 

Vibratory devices which constantly agitate the solids bed maintain a relatively constant value for such that... 

For heat transfer directly to solids, predictive equations give directly the volume V or the heat-transfer area A, as determined by heat balance and airflow rate. For devices with gas flow normal to a fluidized-solids bed,... 

In rotary devices, reradiation from the exposed shelf surface to the solids bed is a major design consideration. A treatise on furnaces, including radiative heat-transfer effects, is given by Ellwood and Danatos [Chem. Eng., 73(8), 174 (1966)]. For discussion of radiation heat-transfer computational methods, heat fliixes obtainable, and emissivity values, see Schornshort and Viskanta (ASME Paper 68-H 7-32), Sherman (ASME Paper 56-A-III), and the fohowing subsection. 

Fluidizing oir... hot or Cold... hurnid or dry Fluidized deep-solids bed... 

The material on solids drying is divided into two subsections, Solids-Drying Fundamentals, and Sohds-Drying Equipment. In this introductory part some elementary definitions are given. In solids-gas contacting equipment, the solids bed can exist in any of the following four conditions. 

Parallel flow. The direction of gas flow is parallel to the surface of the sohds phase. Contacting is primarily at the interface between phases, with possibly some penetration of gas into the voids among the solids near the surface. The solids bed is usually in a static-condition (Fig. 12-30). 

Direct Roto-Louvre dryer. This is one of the more important special types, differing from the direc t rotaiy unit in that true through circulation of gas through the solids bed is provided. Like the direct rotary, it is suitable for low- and medium-temperature operation. 

Design Methods for Calciners In indirect-heated calciners, heat transfer is primarily by radiation from the cyhnder wall to the solids bed. The thermal efficiency ranges from 30 to 65 percent. By utilization of the furnace exhaust gases for preheated combustion air, steam produc tion, or heat for other process steps, the thermal efficiency can be increased considerably. The limiting factors in heat transmission he in the conductivity and radiation constants of the shell metal and solids bed. If the characteristics of these are known, equipment may be accurately sized by employing the Stefan-Boltzmann radiation equation. Apparent heat-transfer coefficients will range from 17 J/(m s K) in low-temperature operations to 8.5 J/(m s K) in high-temperature processes. 

Granular Beds of Particulate Solids Beds of solids like sand or coal are used as filter media to clarify water or chemical solutions containing small quantities of suspended particles. Filter-grade grains of desired particTe size can be purchasea. Frequently beds will be constructed of layers of different materials and different particle sizes. 

The ferric oxide is impregnated on wood chips, which produces a solid bed with a large ferric oxide surface area. Several grades of treated wood chips are available, based on iron oxide content. The most common grades are 6.5-, 9.0-, 15.0-, and 20-lb iron oxide/bushel. The chips are contained in a vessel, and sour gas flows through the bed and reacts with the ferric oxide. Figure 7-3 shows a typical vessel for the iron sponge process. 

The zinc oxide process is similar to the iron sponge process. It uses a solid bed of granular zinc oxide to react with the H2S to form water and zinc sulfide ... 

This chapter discusses the design of liquid glycol and solid bed dehydration systems that are the most common methods of dehydration used... 

Solid bed dehydration systems work on the principle of adsorption. Adsorption involves a form of adhesion between the surface of the solid desiccant and the water vapor in the gas. The water forms an extremely thin film that is held to the desiccant surface by forces of attraction, but there is no chemical reaction. The desiccant is a solid, granulated drying or dehydrating medium with an extremely large effective surface area per unit weight because of a multitude of microscopic pores and capillary... 

Figure 8-21. Simplified flow diagram of a solid bed dehydrator.

Figure 8-22. Maximum design velocity for solid bed adsorbers.

The detailed design of solid bed dehydrators. should be left to experts. The general rules of thumb presented in this chapter can be used for preliminary design as shown in the following example ... 

The prepolymer is subjected to further condensation by heating for 4 hat 260° C while passing superheated steam at a pressure of 1 bar through the solid bed. The white PA-4,6 obtained has a ijrt,i of 4.6 as measured in 96% sulfuric acid. 

For larger particles, the nature of interparticle forces is still unresolved. A typical operating condition for most commercial gas solid beds is well beyond the point of minimum bubbling. It might be expected that... 

Wender, L., and Cooper, G. T., Heat Transfer Between Fluidized-Solids Beds and Boundary Surfaces-Correlation of Data, AIChE J., 4(1) 15-23 (1958)... 

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