Reactors hydroprocessing units

Fig. 17. Schematic flow diagram of residuum hydroprocessing unit utilizing LC-Fining expanded-bed reactor (van Driesen and Fornoff, 1985).

A pre-treated Maya residue has been hydrotreated catalytically in a continuous hydroprocessing unit provided with a perfectly mixed reactor. A commercial catalyst, Topsoe TK-751, has been used and kinetic study of hydrodemetallation reactions has been performed. 

A pretreated (1) residue Maya has been hydrogenated in a hydroprocessing unit provided with a continuous stirred tank reactor (CSTR). 

In residue hydroprocessing units, heat release is high, but some licensors avoid using intra-reactor quench because residue feeds often form lumps of coked-bonded catalyst in fixed-bed units. In reactors with complex internals, such lumps are very hard to remove during a catalyst change-out. Therefore, fixed-bed residue units often comprise three or more 1-bed reactors in series with quench in between. In many cases, the first reactor is guard bed filled with one or catalysts designed to remove metals. 

Due to the presence of hydrogen, leaks in hydroprocessing units often cause fires. Such fires can be devastating, if not deadly. The replacement of a reactor and the reconstruction of other equipment damaged by the accident can take 12 months. The cost of lost production can exceed US 50 million. Safety concerns are responsible for several operating constraints, such as ... 

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. 

As stated before, the volume of catalyst per unit volume of reactor space, which is to be termed the fractional catalyst volume (equal to 1 minus the voidage) and the degree of utilization of this catalytic material are important factors in a high-pressure, relatively slow catalytic process, such as the hydroprocessing of oils. The effectiveness factor of catalyst particles of arbitrary shape can be correlated with a generalized Thiele modulus 4>gen, defined by... 

Figure 19-39 shows examples of gas-liquid-solid fluidized-bed reactors. Figure 19-39a illustrates a conventional gas-liquid-solid fluidized bed reactor. Figure 19-39h shows an ebuUating bed reactor for the hydroprocessing of heavy crude oil. A stable fluidized bed is maintained by recirculation of the mixed fluid through the bed and a draft tube. Reactor temperatures may range from 350 to 600°C (662 to 1112°F) and 200 atm (2940 psi). An external pump sometimes is used instead of the built-in impeller shown. Such units were developed for the liquefaction of coal. 

The ex-situ presulfided catalysts having an oxysulfide form of active metals can be converted into a sulfided form during the activation stage in a hydroprocessing reactor, providing a quick and convenient start-up of the commercial units. 

Industrially, hydrodesulfurization of oil fractions, like aU hydroprocessing, is carried out catalytically in a fixed bed trickle flow unit. The catalyst is stacked in a packed bed and gas (hydrogen) and liquid (oil) are fed downstream concurrently. The reactor operates in the trickle-flow regime, in which the catalyst pellets are fully wetted with the liquid and both gas and liquid flow along the external surface. 

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... 

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