Fluidized reactor characteristics

CO2 capture characteristics of dry sorbents in a fast fluidized reactor... 

One of the advanced concepts for capturing CO2 is an absorption process that utilizes dry regenerable sorbents. Pure sodium bicarbonate from Dongyang Chemical Company and spray-dried sorbents were used to examine the characteristics of CO2 reaction in a flue gas environment. The chemical characteristics were investigated in a fast fluidized reactor of 0.025 m i.d., and the effects of several variables on sorbent activity, including gas velocity (1.5 to 3.5 m/s), temperature (40 to 70 °C), and solid concentration (15 to 25 kg/m /s)], were examined in a fast fluidized-bed. Spray-dried Sorb NX30 showed fast kinetics in the fluidized reactor. 

The fluidized reactor can be a bubbling fluidized type or a fast fluidized type, depending on the gas velocity and the reactivity of the sorbents. We adopted a fast fluidized bed type reactor for carbonation and regeneration reactions in order to identify the chemical characteristics of sorbents in a fast fluidized reactor of 0.025 m i.d. 

In an Oak Ridge study [61] various types of fluidized-bed reactors were compared. Systems investigated were (a) a sodium-cooled fast reactor, (b) a gas-cooled system, (c) an organic-moderated reactor, (d) a heavy-water-moderated reactor, and (e) a light-water system. A detailed study of this latter system was carried out to compare its characteristics and performance with solid-fuel heterogeneous pressurized-water reactors. The results indicated that both the light-water-moderated and organicmoderated fluidized reactors showed promise, while the gas-cooled, the D20-cooled, and the fast (unmoderated) reactors were found to be less satisfactory for application of the fluidized-bed technique. 

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Distributors in industrial units typically have large numbers of injection points of quite diverse design characteristics, some of which are depicted in Eigure 16 for fluidized-bed appHcations. Flow variations through these parallel paths can lead to poor flow distributions within a reactor, thus reducing product yields and selectivity. In some circumstances, undesirable side products can foul portions of the distributor and further upset flow patterns. Where this is important, or where the possibiHties and consequences are insufficiently understood and independent means caimot be employed to assure adequate distribution, the pilot plant must be sized to accommodate such a distributor. Spacing should be comparable to those distributors that are anticipated to be... 

Fluidized bed catalytic reactors seem to have so many advantageous features that they were considered for many processes. One of the advantages is their excellent heat transfer characteristics, due to the large catalyst surface to volume ratio, so very little temperature difference is needed for heat transfer. This would make temperature control problem-free. The second is the uniformity of reaction conditions in the bed. 

Characteristic of fluidized bed reactors is the large wind box to equalize pressure. This is a primary requirement to get even flow through the bed. The expanding shell at the upper part is there to retain as much solid as possible in the reactor. 

The effectiveness of a fluidized bed as a ehemical reactor depends to a large extent on the amount of convective and diffusive transfer between bubble gas and emulsion phase, since reaction usually occurs only when gas and solids are in contact. Often gas in the bubble cloud complex passes through the reactor in plug flow with little back mixing, while the solids are assumed to be well mixed. Actual reactor models depend greatly on kinetics and fluidization characteristics and become too complex to treat here. 

To provide the pr equisite knowledge for designing the three-phase fluidized-bed reactors with new modes, the hydrodynamics such as phase holdup, mixing and bubble properties and heat and mass transfer characteristics in the reactors have to be determined. Thus, in this study, the hydrodynamics and heat and mass transfer characteristics in the inverse and circulating three-phase fluidized-bed reactors for wastewater treatment in the present and previous studies have been summarized. Correlations for the hydrod3aiamics as well as mass and heat transfer coefficients are proposed. The areas wherein future research should be undertaken to improve... 

W.J. Lee, Coal Gasification Characteristics in a Thermo-balance and Fluidized Bed Reactors, PhD Thesis, KAIST, Korea, 1995. 

Of these, fixed-bed adiabatic reactors are the cheapest in terms of capital cost. Tubular reactors are more expensive than fixed-bed adiabatic reactors, with the highest capital costs associated with moving and fluidized beds. The choice of reactor configuration for reactions involving a solid supported catalyst is often dominated by the deactivation characteristics of the catalyst. 

Since the catalysts employed in fluidized bed reactors have characteristic dimensions in the 10 to 300 micron range, the external surface... 

Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 11-24. After an introduction (Chapter 11) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21-24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions. 

Some contrasting characteristics of the main kinds of three- phase reactors are summarized in Table 8.3. In trickle bed reactors both phases usually flow down, the liquid as a film over the packing. In flooded reactors the gas and liquid flow upward through a fixed bed. Slurry reactors keep the solids in suspension mechanically the overflow may be a clear liquid or a slurry, and the gas disengages from the vessel. The fluidized three-phase... 

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