Plant hydroprocessing

Aromatic and Nonaromatic Hydrocarbon Separation. Aromatics are partially removed from kerosines and jet fuels to improve smoke point and burning characteristics. This removal is commonly accompHshed by hydroprocessing, but can also be achieved by Hquid-Hquid extraction with solvents, such as furfural, or by adsorptive separation. Table 7 shows the results of a simulated moving-bed pilot-plant test using siHca gel adsorbent and feedstock components mainly in the C q—range. The extent of extraction does not vary gready for each of the various species of aromatics present. SiHca gel tends to extract all aromatics from nonaromatics (89). 

Table I lists the categories of laboratory reactors used for catalyst testing and catalytic process studies, viz., in the order of decreasing size pilot-plant, bench-scale and microflow reactors. Table II compares the feed requirements of some representative examples of these three classes for a typical case of oil hydroprocessing. The large effect of scale is evident whereas the pilot plant consumes monthly amounts of liquid and gas that require supply on a periodic basis by tank car and tube trailers, the microflow needs can be covered by a small drum or can and a few gas bottles. The size of the test reactor does not only have consequences for the logistics of supply, storage and disposal of feeds and products, but can also dictate the scale of preparation of special feedstocks and catalysts.

Figure 13 A shows some calculated radial temperatures within catalyst beds for some typical cases of hydroprocessing of oils in either a gas phase or a trickle-flow process. In these calculations, effective radial thermal conductivities were used that have been determined from existing correlations involving both static and convective mechanisms of heat transfer. It can be seen that whereas deviations from true iso-thermicity are reasonably small for a bed diameter of 1 cm, isothermal operation is hardly possible at the diameters in the range of pilot-plants, especially if the reactor is relatively short and operated with gas only. Under the latter circumstances, the reactor may even be unstable and temperature may run away.

In the past few years the residue hydrodesulfiirization process has gone through a number of changes. Deeper desulfurization and more conversion to mid-distillate have become a primary target for several units. At the same time, heavier residues are being processed. To address these and other questions, Nippon Ketjen has developed a new series of resid catalysts, viz. the KFR series. The two most common modes of resid hydroprocessing applied on commercial scale, are illustrated with pilot plant test data and data from commercial units. 

Recovery of SCWO byproduct heat. This depends on the existence and needs of nearby processes and facilities. As an example, the HydroProcess-ing sewage sludge plant was to supply heat to a nearby clothing factory. 8... 

Sulfur Sulfur is present in all lube plant feedstocks fractionated from crude oil and its content may be up to several percentage points. Solvent refining removes some but not all, therefore such stocks with no further treatment can contain up to several mass percent of sulfur. Hydrofinishing of solvent refined stocks can reduce this level substantially. Base stocks from conversion processes will have sulfur levels in the low parts per million (ppm) range since sulfur is relatively easily removed in severe hydroprocessing. 

In 1983, Chevron s Richmond Lube Oil Project (RLOP), just outside San Francisco, came online producing 9000 bpd light, medium, and heavy lubes via an all-hydroprocessing route.24-25 The plant schematic is shown in Figure 10.12 and is described in more detail in Chapter 7. 

FIGURE 10.12 Schematic of Chevron all-hydroprocessing RLOP plant. 

The Secunda process scheme was conceived to maximize gasoline production - therefore, it includes hydroprocessing and catalytic reformers similar to those used in petroleum refineries. Due to the scale of operation, it includes facilities for the recovered of ethylene, alcohols, ketones, phenols, ammonia and other chemical products. Its twin plant at the same location, Sasol 3, has a very similar configuration. At present all the original Synthol reactors have been replaced by the more efficient Sasol Advanced Synthol (SAS) reactors, with capacities of up to 20 000 bpd per train. 

Paraskos [59] and Montagna [43,60] have tested the validity of these simplifications with hydroprocessing reactions of gas oils performed in pilot plant reactors. It resulted that log-log plots of (c/c ) versus 1/(LHSV) and versus L respectively some times gave straight lines for desulphurization, demetalization and de-nitrogeneation reactions, but with varying slopes and dependent additionally on the nature of feed, temperature and catalyst size i.e. an unsatisfying situation. 

A fuel gas long situation also provides the opportunity to recover valuable products from the fuel gas. For example, a refinery plant might consider recovery of hydrogen from a hydroprocessing gas source. Options for H2 recovery include pressure swing adsorption (PSA) and membrane systems based on the H2 purity requirement. Alternatively, ethane and ethylene could be recovered from certain fuel... 

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