S.T. Sie

Design and scale-up of the Fischer-Tropsch bubble column slurry reactor

The Fischer-Tropsch (FT) synthesis on a large scale is of interest, as a means of conversion of remote natural gas to high-quality products, particularly, liquid transportation fuels. Recent developments have resulted in reactors of advanced design having production capacities of 2500 bbl/day or higher, which is more than two orders of magnitude higher than the productivity of classical reactors operated before or during World War II. Some fundamental aspects of these reactors, which belong to the classes of gas-solid fluidised beds, multi-tubular trickle-beds, and slurry bubble columns, are discussed to aid the selection and design of reactors for a specific application. Special attention is given to scaling up of slurry bubble columns. Published experimental work is carefully analysed, and procedures are recommended for the estimation of the necessary design and scale-up parameters. Model calculations of a commercial FT reactor are presented in order to underline various important design and operating issues.

Fundamentals and selection of advanced Fischer-Tropsch reactors

Fischer-Tropsch synthesis on a large scale is of interest as a means for conversion of remote natural gas to high-quality products, particularly liquid transportation fuels. Recent developments have resulted in reactors of advanced design having production capacities of 2500 bbl/day or higher, which is more than two orders of magnitude higher than the productivity of classical reactors operated before or during World War II. Some fundamental aspects of these reactors, which belong to the classes of gas-solid fluidized beds, multitubular trickle-beds, and slurry bubble columns are discussed to aid selection and design of reactors for a specific application. Special attention is given to scaling up of slurry bubble columns. A scaling-up strategy is proposed which might obviate the inclusion of a costly demonstration stage in the development of a novel process using bubble columns.

Strategies for multiphase reactor selection

Abstract The central theme addressed in this paper is: how do we arrive at the “ideal” reactor configuration meeting most closely with the process requirements? The problem of reactor selection is analyzed at three strategy levels. Decisions are made at each strategy level using the reactor ”wish” list. Combination of the individual decisions yields the final, ideal, reactor configuration. The three strategy levels are: Strategy level I:“Catalyst” design strategy. At this strategy level the ideal catalyst particle size, shape, porous structure and distribution of active material are determined. For gas-liquid systems, the appropriate decision concerns the choice of gas-dispersed or liquid-dispersed systems, and the provision of the appropriate ratio between liquid-phase bulk volume and volume of liquid-phase diffusion layer. Strategy level II:Injection and dispersion strategies. (a) Reactant and energy injection strategy: injection strategies examined include one-shot (batch), continuous, pulsed injection, reversed flow operation, and staged injection (in time or space), and the use of dispersionless contacting by keeping the reactants separated by a barrie (membrane). (b) Choice of the optimum state of mixedness for concentration and temperature: the proper choice of state of mixedness can influence selectivity and product properties. (c) Separation of product or energy in situ : product removal in situ helps to increase conversion by driving the reaction to the right and preventing undesirable side reactions. Removal of energy in situ by use of evaporating solvents has the function of a thermal flywheel. (d) Contacting flow pattern: here there is a choice between co-, counter- and cross-current contacting of phases. Strategy level III:Choice of hydrodynamic flow regime. Here the choice between the various “fluidization” regimes, e.g. dispersed bubbly flow, slug flow, churn-turbulent flow, dense-phase transport, dilute-phase transport, is made on the basis of the interphase mass transfer characteristics, heat transfer, mixing, etc. Combination of the decisions reached at the three strategy levels will yield the most suitable reactor configuration. In this paper it is argued that a systematic approach to reactor selection may lead to novel and innovative reactor configurations with a potential edge over existing and conventional technologies.

Process Development and Scale Up: III. Scale-up and scale-down of trickle bed processes

Trickle bed processes belong to the most widely used multiphase reactors and are applied on a large scale particularly for hydrotreatment of medium heavy and heavy oil fractions in the hydrocarbon processing industry. Laboratory scale reactors used in the development of new processes or in studies aimed at improving existing ones should therefore give accurate and meaningful test results which allow reliable upscaling. For reasons of efficiency in R&D, the size of the laboratory test units should be as small as possible without detracting from the meaningfulness of the data. The present paper discusses scaling rules of laboratory trickle bed reactors and the influence of scale parameters on residence time distribution and catalyst contacting under conditions that are typical for hydrotreatment of oils. The main limiting factors for downsizing of laboratory trickle-bed reactors are the distortion of the packing in the vicinity

Consequences of catalyst deactivation for process design and operation

Abstract Catalyst deactivation has important consequences for the design of a process and the way it is operated. The nature of the deactivation, and in particular the question whether it can be reversed under conditions which are compatible with the normal operation or whether a separate regeneration treatment of the catalyst is required to restore its activity, as well as the time-scale of the deactivation determine the type of technology that is feasible and process options like reactor type and process configuration. This relationship between deactivation behaviour and process lay-out forms the subject matter of the present paper. The general principles that guide the choices of process type and parameters are illustrated in more detail with examples from the fields of catalytic reforming of petroleum naphtha and hydroprocessing of petroleum residues. In these fields, different catalyst deactivation mechanisms are operative and catalyst deactivation rates can vary widely depending upon feedstock and process parameters. Consequently, different reactor technologies and process configurational choices are possible. The relation between catalyst deactivation behaviour and process design and operation can be viewed from two sides: on the one hand, the deactivation behaviour may dictate the choice between viable process options and may provide an incentive for the development of novel technology that can cope optimally with the demands set by the deactivation of the catalyst. On the other hand, the introduction of novel technological options may widen the scope of a process, e.g. by opening the possibilities to apply novel catalysts or to operate under unconventional conditions that lead to a more economic or otherwise better process, possibilities that were previously barred by catalyst deactivation.

Catalysts for second-stage deep hydrodesulfurisation of gas oils

Abstract The interest for new deep hydrodesulfurisation (HDS) processes is expected to rise since more stringent legislation for the maximum sulfur concentration in automotive diesel fuel has been proposed. A realistic option is the application of a separate deep HDS reactor following the existing HDS process in which alternative catalysts may be applied. It was shown that ASA-supported Pt and PtPd catalysts are very active in model feed deep HDS reactions. Moreover, in the deep HDS of a pre-hydrotreated straight-run gas oil (P-SRGO) under relevant industrial conditions, PtPd/ASA showed a very promising performance. The applicability of ASA-supported noble metal catalysts in practice will be largely determined by the H 2 S concentration in the second-stage reactor and the price of noble metals. In addition, NiW/γ-Al 2 O 3 is also considered to be a promising catalyst for second-stage deep HDS. From the differences in the relative performance between model and real feed experiments, it is found that the suitability of a catalyst for deep HDS of gas oils cannot be evaluated by single-component model studies alone. The H 2 S concentration and the presence of other competing reactants largely determine the outcome of model experiments and should therefore be chosen carefully.

Reactor development for conversion of natural gas to liquid fuels: A scale up strategy relying on hydrodynamic analogies.

Abstract Gas-solid fluidized beds and bubble column slurry reactors are very commonly encountered in processes for conversion of natural gas to liquid fuels and light olefins. This paper proposes a unified design and scale-up strategy for such “fluidized” multiphase reactors. The approaches uses hydrodynamic analogies as a basis. These analogies have been investigated in a variety of gas-solid and gas-liquid systems in several columns varying in diameters between 0.05 m and 0.63 m. It is argued that the appreciation of the hydrodynamic analogies will allow cross-fertilisation of concept and design data, thereby reducing process development costs.

Past, Present and Future Role of Microporous Catalysts in the Petroleum Industry

ABSTRACT Zeolitic catalysts are currently widely used in a variety of processes of the petroleum industry and represent a factor of very great economic importance. The present paper reviews the current trends in petroleum refining and examines the role of zeolitic catalysts against this background. The historical development and future perspectives of three major processes of the oil industry that apply zeolitic catalysts, viz., catalytic cracking, hydrocracking and paraffin isomerization are discussed in more detail within this context. Microporous materials offer many possibilities as catalysts to meet future demands in the catalytic process technology in petroleum refining and synthetic fuels production of the future.

A numerical comparison of alternative three-phase reactors with a conventional trickle-bed reactor. The advantages of countercurrent flow for hydrodesulfurization

Abstract A computer model was developed to compare a conventional cocurrent trickle-bed reactor with two novel countercurrent three-phase reactors: the three-levels-of-porosity reactor and the internally finned monolith reactor. The hydrodesulfurization of a vacuum gas oil was taken as a case study. It was found that the application of countercurrent flow in the novel reactors results in significant increase of conversion. Sensitivity for mass transfer and H2S inhibition were investigated. Reduced mass transfer compared to a conventional trickle-bed does not limit the reaction.

Selection, design and scale up of the Fischer-Tropsch reactor

Publisher Summary This chapter discusses the selection, design, and scale up of the Fischer–Tropsch reactor. Middle distillates can be directly distilled from crude oil but can also be produced by converting coal or natural gas using the Fischer–Tropsch reaction. During this process natural gas is first converted into synthesis gas. In the second step, syngas is converted into long chain hydrocarbons. Selective hydrocracking and hydro-isomerization of these long chain hydrocarbons yields marketable middle distillates. One of the most important subjects in the development of the Fischer–Tropsch process is the selection, design, and scale-up of the reactor for the heavy paraffin synthesis. The synthesis can be carried out in both trickle bed reactors and slurry bubble columns. Slurry bubble columns can be operated in two flow regimes—the homogeneous flow regime and the churn turbulent flow regime. In this chapter, the Fischer–Tropsch slurry reactor is simulated and optimized to make a comparison among operations in the homogeneous flow regime and churn turbulent operation. It also compares the performance of the slurry reactor with a simulated performance of the Fischer–Tropsch trickle bed reactor.