Liquid-solid riser

Roy, S. and Dudukovic, M.P. (2001) Flow mapping and modeling of liquid-solid risers, 8th Conference... 

The velocity and hold-up distribution of the solid phase in a liquid-solid riser has been studied with radioactive particle tracking and computed tomography (CT).[ 1 The goal of this research was the development of an understanding of the variables affecting the performance of liquid-solid risers, and of fundamentally-based scale-up rules. An improved PEPT system has recently been developed, capable of continuously following the 3D trajectory of a radiotracer particle (as small as 500/um) moving at 0.1 ms with a resolution of 5 mm. The system has been used to measure in situ flow patterns of solids in a gas-solids Interconnected Fluidised Bed reactor. 

Figure 1.6 Schematic of CARPT and CT (left) schematic of liquid-solid riser (right) (Roy,...

Roy S Quantification of two-phase flow in liquid—solid risers (Doctoral dissertation), St. Louis, MO, 2000, Washington University. 

Roy S, Dudukovic MP Flow mapping and modeling of liquid—solid risers, Ind Eng Chem Res 40 5440-5454, 2001. http //dx.doi.org/10.1021/ie010181t. 

Roy S, Chen J, Kumar SB, Al-Dahhan MH, Dudukovic MP (1997) Tomographic and particle tracking studies in a liquid-solid riser. Ind Eng Chem Res 36(11) 4666-4669... 

Advances in multiphase reactors for fuel industry are discussed in this work. Downer reactors have some advantages over riser reactors, but suffer from some serious shortcomings. The coupled reactors can fully utilize the advantages of the riser and the downer. For fuel industry that involves gas-liquid-solid system, slurry bed reactors especially airlift reactors are preferred due to their performance of excellent heat control and ease of seale up. For high-pressure processes, the spherical reactor is promising due to its special characteristics. 

Figure 7-4 Slurry reactor (left) for well-mixed gas-solid reactions and fluidized bed reactor (center) for liquid-solid reactions. At the right is shown a riser reactor in which the catalyst is carried with the reactants and separated and returned to the reactor. The slurry reactor is generally mixed and is described by the CSTR model, while the fluidized bed is described by the PFTR or CSTR models.

The fluidized bed reactor has been used for phenol removal instead of fixed bed as most of the products formed are insoluble. The operation in packed bed reactors would lead to clogging phenomena and undesirable pressure drop [47, 88]. When deactivation of biocatalysts occurs and regeneration is needed, the liquid-solid circulating fluidized bed is a worthy alternative, as demonstrated for phenol polymerization [89]. The continuous enzymatic polymerization was carried out in a riser section and a downcomer was used for the regeneration of the coated immobilized particles. 

Note, however, that liquid acids are still largely used in refinery and petrochemical processes. For example, HF alkylation (for isobutane alkylation with light olefins) is still among the top-ten refining processes licensed by UOP, with over 100 units installed worldwide. However, UOP introduced from 2002 the Alkylene process, which uses a liquid phase riser reactor with a solid acid catalyst for the isobutane alkylation. However, HF alkylation remains the best economic choice [223], notwithstanding environmental and corrosion problems. Also in this case, the conventional process has been improved, for example by HF aerosol vapor suppression. Other aspects of isobutane alkylation have been reviewed by Hommeltoft [224]. 

Prediction of gas solid flow fields, in processes such as pneumatic transport lines, risers, fluidised-bed reactors, hoppers and precipitators are crucial to the operation of most process plants. Up to now, the inability to accurately model these interactions has limited the role that simulation could play in improving operations. In recent years, CFD software developers have focused on this area to develop new modelling methods that can simulate gas-liquid-solid flows to a much higher level of reliability. As a result, process industry... 

Razzak SA, Baighi S, Zhu J-X, Mi Y (2009) Phase holdup measurement in a gas-liquid-solid drculating fluidized bed (GLSCFB) riser using electrical resistance tomography and optical fibre probe. Chem Eng J 147 210-218... 

Figure 3 shows the radial profile of the gas holdup in the riser with increasing superficial gas velocity under different solid holdups. The gas holdup increases with increasing superficial gas velocity at the different solid holdups. At a low superficial gas velocity, the liquid velocity... 

Figure 7.7b shows the essential features of a refinery catalytic cracker. Large molar mass hydrocarbon molecules are made to crack into smaller hydrocarbon molecules in the presence of a solid catalyst. The liquid hydrocarbon feed is atomized as it enters the catalytic cracking reactor and is mixed with the catalyst particles being carried by a flow of steam or light hydrocarbon gas. The mixture is carried up the riser and the reaction is essentially complete at the top of the riser. However, the reaction is accompanied by the deposition of carbon (coke) on the surface of the catalyst. The catalyst is separated from the gaseous products at the top of the reactor. The gaseous products leave the reactor... 

For small catalyst particles completely different reactor types are used. The catalyst is now suspended in the flowing reaction mixture and has to be separated at the reactor exit or is carried along with the fluid. Particle sizes are now from 10 fim up to 1 mm. In Figure 1.2 some of the common reactor types are shown. Figure 1.2(a) shows the fluid bed reactor, where the gaseous feed keeps the small catalyst particle in suspension. Catalyst carried over in the exit stream is separated, for example, in cyclones. For even shorter contact times, riser reactors are used in which the solid catalyst is transported in the gas stream. Fluid bed reactors are also used for feed mixtures of a liquid and a gas. 

The list is merely suggestive. Complexity of reactive flows may greatly expand the list of issues on which further research is required. Another area which deserves mention here is modeling of inherently unsteady flows. Most flows in engineering equipment are unsteady (gas-liquid flow in a bubble column reactor, gas-solid flow in a riser reactor and so on). However, for most engineering purposes, all the details of these unsteady flows are not required to be known. Further work is necessary to evolve adequate representation of such flows within the CFD framework without resorting to full, unsteady simulations. This development is especially necessary to simulate inherently unsteady flows in large industrial reactors where full, unsteady simulations may require unaffordable resources (and therefore, may not be cost effective). Different reactor types and different classes of multiphase flows will have different research requirements based on current and future applications under consideration. 

An airlift reactor is a column divided into two sections, a riser and a downcomer, interconnected at top and bottom (Fig. 5). Gas entering the bottom of the riser lifts the liquid and any accompanying solid particles... 

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