Operating hydroprocessing units

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]. 

In newer RDS applications the hydroprocessing unit is an integral part of the overall crude oil upgrading scheme to produce transportation fuels such as gasoline and kerosene. The RDS unit may operate independently of, or in combination with, other refinery conversion units, depending on the particular feedstock and product demand (Howell et al., 1985 Siewert etal., 1985). Hydroprocessing requirements and catalyst requirements are dictated by the processing route chosen. 

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... 

Throughput, operating pressure and process configuration - once-through or recycle of unconverted oil - are the major factors affecting construction costs for hydroprocessing units, which range from 1000 to 4000 per daily... 

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 ... 

PDU Operation - Current Study. This paper will present the results of several alternate processing modes utilizing the expanded catalyst bed (LC-Finer) for hydroprocessing coal extracts. Neither distillate yield nor C -C4 gas yield data from either the SRC unit or the SCT thermal step of the TSL process have been included in this analysis. The specific PDU runs are as follows ... 

Short contact time SRC can be upgraded via catalytic hydroprocessing into low sulfur boiler fuels. However, the solid SCT SRC feedstock requires solvent dilution to reduce its viscosity. Furthermore, even for a 50 wt % W. Kentucky SCR SRC blend, all pilot unit lines and valves have to be heat-traced above 350°F in order to achieve smooth mechanical operations. 

Catalysts currently employed in process development units for coal liquefaction are hydroprocessing catalysts developed for petroleum refining (5l6). They are composed of combinations of Mo or W with Co, Ni or other promoters dispersed on alumina or silica-alumina supports. When used in liquefaction, these catalysts deactivate rapidly f6-9i causing decreases in product yield and quality and problems with process operability. Thus the... 

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. 

Hydroprocessing - especially hydrocracking - is exothermic. Effective control of produced heat is the primary concern of designers, owners and operators of hydrocracking units. In modem units, a high flux of recycle gas provides a sink for process heat. It also promotes plug flow and the transport of heat through the reactors. Most licensors recommend that the ratio of recycle gas to makeup gas should exceed 4 1. 

In addition to scale-up difficulties, there are a number of problems related to the stable operation of a bubble column associated with hydrodynamics. For example, consider the important commercial application of bubble columns in hydroprocessing of petroleum resids, heavy oils and synthetic crudes. Hydrodynamic cold flow and hot flow studies on the Exxon Donor Solvent coal liquefaction process (Tarmy et al., 1984) showed that much of the literature correlations for the hydrodynamic parameters (holdup, interfacial area and dispersion coefficients) obtained with cold flow units, at ambient conditions, are not applicable for commercial units operating at relatively higher pressures. In addition, the flow pattern in commercial units was considerably different. In the hydroprocessing of petroleum residues by the H-Oil and LC-Fining processes, refinery operations have experienced problems with nonuniform distribution of gas and liquid reactants across the distributor, maintaining stable fluidization and preventing temperature excursions (Beaton et al., 1986, Fan, 1989 and Embaby, 1990). Catalyst addition, withdrawal and elutriation have also been identified as problems in these hydrotreaters. 

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