Process hydroprocessing units

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. 

Liquid products contain sulfur and nitrogen and must be hydroprocessed to improve quality. Separate hydroprocessing units for upgrading the naphtha, kerosene, and gas oil fractions can be used to optimize the overall process. Refined gas oil or diesel fuel is aromatic in character and contains more cycloparaffins than conventional crude oil. The resulting fuel is low in cetane number, high in density, and typically has very good low-temperature handling properties. 

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. 

Equipment. In designing the apparatus to be used for the hydro-treating and hydrocracking of SRC, heavy reliance was placed on the petroleum-processing experience in the Houdry Division of Air Products. A continuous process development unit was designed and constructed to catalytically hydroprocess nominally 1 L/hr of SRC liquid. A simplified flowsheet of the unit appears in Figure 1. 

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... 

For fixed-bed hydroprocessing units, the process conditions - pressure, temperature, space velocity, and catalyst - are determined by feed quality and process objectives. Table 12 shows typical process conditions for the hydrotreating of different feeds in fixed-bed hydrotreating units. The values shown are approximate. 

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... 

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. 

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. 

I 6 Predictive Modeling of the Hydroprocessing Units Process Model... 

Transition metal sulfide units occur in minerals in nature and play an important role in the catalytic activity of enzymes such as hydrogenase and nitrogenase. Industrial processes use transition metal sulfides in hydroprocessing catalysis. Both the metal and the sulfur sites in these compounds can undergo redox reactions which are an important part of their reactivity. Thus, the electronic situation of the ReS4 anion and related complexes is of considerable interest and has been evaluated applying quantum chemical methods. 

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 ... 

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... 

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