A hydroprocessing units

A mixing tee for the hot and cold make-up hydrogen to a hydroprocessing unit leaked near the weld to the downstream piping. SEM examination indicated decarburization and Assuring along the internal surface of the tee. 

The conditions under which a hydroprocessing unit operates is a strong function of feedstock. Typical processing conditions are shown in Table 5.2-8 for a variety of hydroprocesses [60]. 

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

Figure 7.12 illustrates the recycle gas circuit throughout a hydroprocessing unit. First, the reaction product is sent to a HPS, where the liquid products are recovered from the gas mixture. Then the gas stream is sent to a scrubbing unit in order to remove hydrogen sulfide and ammonia by contacting with an amine. 

Sulfur is removed from a number of refinery process off-gas streams (sour gas) to meet the sulfur oxide emissions limits of the Clean Air Act and to recover salable elemental sulfur. Process off-gas streams, or sour gas, from the coker, catalytic cracking unit, hydrotreating units, and hydroprocessing units can contain high concentrations of hydrogen sulfide mixed with light refinery fuel gases. 

Wastewater reuse is a good way to reduce overall pollutant loadings. However, water quality is critical in water reuse. The contaminants present must be compatible with the reuse. For example, reuse waters with high solids content are not satisfactory for crude unit desalting. Stripped foul water containing low H2S and ammonia and high concentrations of phenols has essentially no solids. It is suitable for crude unit desalter wash water if the phenols extracted by the crude are subsequently converted by hydroprocessing units into nonphenolic compounds [36]. Some other examples include ... 

In order to minimize these problems, the refiners are often forced to operate at low conversion levels (ca. 50%). Despite its importance as a critical factor limiting the maximum conversion attainable in commercial residue hydroprocessing units, the problem of sediment... 

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. 

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. 

Due to the presence of a large excess of hydrogen, coke formation in hydroprocessing units is slow - so slow that it can be neglected in material balances for commercial units. However, coke formation is one of four major causes of catalyst deactivation. The other three are poisoning, fouling, and sintering (see Section 4.1). 

Most hydrotreaters and hydrocrackers are trickle-bed units. A classic article by Satterfield " describes the fundamental behaviour of such units, in which mixtures of liquid and gaseous reactants pass down over fixed beds of catalyst. In hydroprocessing units, the liquid reactants are petroleum fractions, and the gaseous reactant is hydrogen. 

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. 

With hydroprocessing units, most refiners try to maximize feed rate while (a) meeting other process objectives and (b) maintaining a high on-stream factor. Some try to maximize conversion, while others just want to hit a key process target at minimum cost. 

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. 

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