Three-phase slurry reactors scale

In this chapter, we have attempted to summarize the philosophy and procedural details for the design and scale-up of three-phase slurry reactors. First, the widespread use of three-phase slurry systems in the petroleum processing, chemicals, and process industry has been highlighted with suitable examples. The factors governing the performance of three-phase slurry... 

The general difficulties in design and scale-up of bubble column reactors concern reaction specific data, such as solubilities and kinetic parameters as well as hydrodynamic properties. The paper critically reviews correlations and new results which are applicable in estimation of hydrodynamic parameters of two-phase and three-phase (slurry) bubble column reactors. 

The use of a fluidized-bed reactor is possible only when the reactants are essentiaUy in the gaseous phase. Eluidized-beds are not suitable for middle distiUate synthesis, where a heavy wax is formed. Eor gasoline synthesis processes like the MobU MTG process and the Synthol process, such reactors are especiaUy suitable when frequent or continuous regeneration of the catalyst is required. Slurry reactors and ebuUiating-bed reactors comprising a three-phase system with very fine catalyst are, in principle, suitable for middle distiUate and wax synthesis, but have not been appHed on a commercial scale. 

Cybulski et al. [39] have studied the performance of a commercial-scale monolith reactor for liquid-phase methanol synthesis by computer simulations. The authors developed a mathematical model of the monolith reactor and investigated the influence of several design parameters for the actual process. Optimal process conditions were derived for the three-phase methanol synthesis. The optimum catalyst thickness for the monolith was found to be of the same order as the particle size for negligible intraparticle diffusion (50-75 p.m). Recirculation of the solvent with decompression was shown to result in higher CO conversion. It was concluded that the performance of a monolith reactor is fully commensurable with slurry columns, autoclaves, and trickle-bed reactors. 

Hybrid strategy for real time optimization with feasibility driven for a large scale three-phase catalytic slurry reactor... 

Hybrid Strategy for Real Time Optimization with Feasibility Driven for a Large Scale Three-Phase Catalytic Slurry Reactor... 

In the Shell Middle Distillates Synthesis (SMDS) process starting from natural gas, the reactor configuration chosen for the first commercial unit in Malaysia, successfully commercialized in 1993, is the multi-tubular downflow trickle bed with catalyst inside the tubes (Sie et al., 1991) see Fig. 30e. Because of the enormous exothermicity of the synthesis reaction and the relatively poor heat transfer an extremely large heat transfer area is required. The reactor volume is largely governed by the installable heat transfer area in a vessel of given volume. Use of the multi-tubular three-phase fluidized bed or slurry reactor (see Fig. 30k and 301) provides much better heat transfer characteristics (an improvement of a factor of five over fixed bed units) and could lead to considerably lower reactor volumes. However, the anticipated scale-up problems with three-phase... 

Three-phase fluidized beds and slurry reactors (see Figs. 30g-l) in which the solid catalyst is suspended in the liquid usually operate under conditions of homogeneous bubbly flow or chum turbulent flow (see regime map in Fig. 33). The presence of solids alters the bubble hydrodynamics to a significant extent. In recent years there has been considerable research effort on the study of the hydrodynamics of such systems (see, e.g., Fan, 1989). However, the scale-up aspects of such reactors are still a mater of some uncertainty, especially for systems with high solids concentration and operations at increased pressures it is for this reason that the Shell Middle Distillate Synthesis process adopts the multi-tubular trickle bed reactor concept (cf. Fig. 30e). The even distribution of liquid to thousands of tubes packed with catalyst, however poses problems of a different engineering nature. 

Most of the more recently proposed GTL concepts are based on the use of the LTFT three phase fluid bed reactor. This development can also overcome the fixed bed reactor limitations on the temperature control of the very exothermic FT reaction. Additionally, a higher catalyst utilisation efficiency is possible and, as mentioned previously, larger reactor capacities can be attained, compared with tubular fixed bed units. The first commercial scale LTFT slurry reactor, a 2 500 bpd unit, was commercialised by Sasol in 1993 and is in continuous operation using an iron FT catalyst. 

There are a large number of processes where solid catalysts are employed. The process streams are either gaseous or liquid, or a combination of these. The catalysts usually have a high porosity. Especially in the petroleum and petrochemical industries one encounters catalytic reactors of a great variety. Well known reactor types are fixed bed, moving bed, fluidized bed, entrained bed, slurry reactor and three phase packed column. The choice between these reactor types is mostly based on the relative requirements for mass transfer, degree of conversion and heat transfer. Heterogeneous catalysis is a well developed science, with its own specific literature. In this chapter some technical acpects will be presented, particularly those related to scale-up. 

For catalytic three-phase processes, batchwise operating slurry reactors are frequently used in kinetic experiments. The reactor can operate under atmospheric pressure, but a more common approach is to use a pressurized autoclave equipped with a stirrer and cata-lyst/solvent pretreatment units. The gas-phase pressure is kept constant by regulation. Another option is to use a shaking reactor, which does not require a stirrer, but the stirring is accomplished by vigorous shaking of the equipment. Typical laboratory-scale reactors are shown in Figure A9.8. 

Several textbooks are available which describe in detail how to design and scale-up slurry reactors, e.g., the book by Shah, which appeared in 1979 [2] and the new book (1984) of Doraiswamy and Sharma [l] For modelling catalytic three phase reactors, we also refer to the papers of Ramachandran and Chaudhari [3,156j. At a previous NATO ASI Conference (Cesme-Izmir, 1981) Hofmann [5] presented a description of the reactor models governing the design and scale-up of slurry reactors. We therefore will concentrate on some new developments only. 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

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