Hydroprocessing Reactor Design

This section will focus on the various hydroprocessing technologies that have been commercialized or are in a pilot stage near commercialization. Reactor design characteristics that differentiate the technologies will be highlighted. Included in this section is an overview of the properties and applications of commercial residuum hydroprocessing catalysts. 

Reactor design is a key element in each process listed in Table XX. The method of feed introduction, the arrangement of the catalyst bed, and the mode of operation have an impact on the ability to process residua. For this reason, classification by reactor type provides a convenient and appropriate distinction for discussing hydroprocessing technology. The most common reactor designs include fixed beds, ebullated or expanded beds and slurry beds, and moving-bed reactors. These classifications are discussed in more detail next. 

The initial focus for the application of hydroprocesses for the conversion of heavy feedstocks was the removal of sulfur. However, many recent processes have concentrated on the objective of achieving high feedstock conversion. The emphasis on sulfur removal, in these process designs, shifts from the primary hydroprocessing step to the secondary hydroprocessing reactor. 

Advances in hydroprocessing are driven by competitive forces and clean-fuel regulations. These advances include improved catalysts (Chapters 9-11), better reactor design (Chapters 7-8), advanced process control (Chapter 22), and online optimization (Chapter 23). As clean-fiiel regulations migrate from North America and the EU into the rest of the world, and as globalization of the oil industry continues apace, the need will continue for new (and better) hydroprocessing units. Hopefully, within a few years, this chapter will be obsolete and we ll have to write an update. 

Hydroprocessing reactors originally designed for low severity service t5q)ically are not adequate to handle increased severity with high activity catalysts or to achieve the operating efficiency demanded by the current and future fuels specifications. 

This chapter details the development of a hydroprocessing reactor model and its further application in the design and simulation of a heavy oil upgrading process developed by the Mexican Institute of Petroleum (IMP). The chapter includes a description of the case of study, the experimental studies, the mathematical formulation of the reactor model, reactor scale-up and design, and simulation results at different scales. 

With these criteria in mind, various reactors have been designed to satisfy the needs of the hydroprocesses, including hydrodesulfurization (McEvoy, 1996). Thus, reactors may vary from as little as 4 ft. in diameter to as much as 20 ft. in diameter and have a wall thickness anywhere from 4.5 to 10 in. or so. These vessels may weigh from 150 tons to as much as 1000 tons. Obviously, before selecting a suitable reactor, shipping and handling requirements (in addition to the more conventional process economics) must be given serious consideration. 

Reactions involving gas, liquid, and solid are often encountered in the chemical process industry. The most common occurrence of this type of reaction is in hydroprocessing operations, in which a variety of reactions between hydrogen, an oil phase, and a catalyst have been examined. Other common three-phase catalytic reactions are oxidation and hydration reactions. Some three-phase reactions, such as coal liquefaction, involve a solid reactant. These and numerous other similar gas-liquid solid reactions, as well as a large number of gas-liquid reactions, are carried out in a vessel or a reactor which contains all three phases simultaneously. The subject of this monograph is the design of such gas-liquid -solid reactors. 

Nigam, K.D.P. Design of trickle-bed reactors. In Hydroprocessing in Petroleum Refining Industry— A Compendium, Verma, R.P., Bhatnagar, A.K., Eds. Lovraj Memorial Trust Delhi, 2000 391. 

Reactors, Catalyst Beds and Quench Zones. As shown in Table 4, most hydroprocessing reactions are exothermic. The heat released in naphtha and kerosene hydrotreaters is relatively low, so units designed for these feeds may use just one reactor that contains a single catalyst bed. However, for heavier feeds and/or feeds that contain large amounts of sulfur, aromatics or... 

---