Pilot plants, hydrotreating

If the SRC-II is hydrotreated at an intermediate or moderate severity, further processing will be necessary to upgrade the product to specification transportation fuels. A number of pilot plant tests have been made to determine the conditions and to demonstrate the feasibility of these processing steps. 

Only 5-6% of the hydrotreated SRC-II product boils above the jet boiling range. In this chapter, several possible refining routes for the production of distillate fuels from SRC-II process product are considered, based on results from several demonstration pilot plant tests. In all cases, the initial hydrotreating step is the key step in processing sequence. 

The Illinois H-Coal and SRC-II syncrudes contain large amounts of chloride, 32 parts per million (ppm) and 50 ppm, respectively. The Wyodak H-Coal syncrude contains only 3 ppm. Because the exit line from the pilot plants which processed the SRC-II syncrude occasionally plugged with ammonium chloride, we water washed the Illinois H-Coal syncrude prior to hydrotreating. It is our understanding that chloride will be removed by water washing at a commercial coal liquefaction facility. 

The syncrudes were hydrotreated in fixed bed, downflow pilot plants. They have high and low pressure product separators, recycle hydrogen facilities, and extensive control and... 

The feasibility of hydrotreating whole shale oil is demonstrated by means of several long pilot plant tests using proprietary commercial catalysts developed by Chevron. One such test was on stream for over 3500 hr. The rate of catalyst deactivation was very low at processing conditions of 0.6 LHSV and 2000 psia hydrogen pressure. The run was shut down when the feed supply was exhausted although the catalyst was still active. 

The 650°F+ fraction of the hydrotreated shale oil was processed in in FCC pilot plant, and the results show that it is an excellent feed for a conventional refinery. The resulting FCC yields, activity, and product qualities are quite similar to those derived from normal petroleum gas oils. 

The properties of the 650° F+ fraction of the hydrotreated shale oil also indicate that it will be an appropriate feed to an extinction recycle hydrocracker in situations where jet fuel is a desired product. Supporting pilot plant studies are described elsewhere (1,2,3). 

The FCC process is the most common conversion unit in use today. As such, it is important to determine the performance of an FCC when feeding hydrotreated shale oil. The two 650° F+ feeds shown in Table VI were evaluated in an FCC pilot plant operating in a fixed fluidized-bed mode. The catalyst was withdrawn from an operating commercial FCC unit. It is a zeolite catalyst, CBZ-1, produced by Davison Chemical Division of W. R. Grace and Company and is moderately active as well as contaminated with metals. 

Approximate yields for the hydrotreating and FCC processes are shown in Table X. The whole-oil hydrotreater data are based on results from the large-scale feed preparation run. The FCC data are described above. Since 41 LV % of the raw shale oil is fed to the FCC as hydrotreated 650° F+ bottoms, the FCC pilot plant yields were multiplied by 0.41 and reported as yield to raw shale oil. 

The first stock run was SRC filter feed obtained from the Pittsburg and Midway Coal Company SRC pilot plant at Ft. Lewis, Washington. This contains all of the recycle process solvent, ash, and unconverted coal. The stock was filtered prior to hydrotreating. (Table I compares inspections of the filter feed and filtrate.) Filtration upgraded the oil portion of the stock. 

In order to process SRC in the pilot plant equipment without using an extraneous solvent, a portion of the hydrotreated product was recycled to the feed reservoir as diluent. Recycle was essentially internal, and SRC and hydrogen were the only net feeds to the system. Pulverized SRC was added to the hot reservoir at a ratio of two parts SRC to three parts recycled product (combined feed ratio = 2.5). Vigorous stirring ensured that no undissolved solids were taken into the feed pump system. 

In a trickle bed reactor the gas and liquid flow (trickle) concurrently downward over a packed bed of catalyst particles. Industrial trickle beds are typically 3 to 6 m deep and up to 3 m in diameter and are filled with catalyst particles ranging irom to in. in diameter. The pores of the catalyst are filled with liquid. In petroleum refining, pressures of 34 to 100 atm and temperatures of 350 to 425°C are not uncommon. A pilot-plant trickle bed reactor might be about 1 m deep and 4 cm in diameter. Trickle beds are used in such processes as the hydrodesulfurization of heavy oil stocks, the hydrotreating of lubricating oils, and reactions such as the production of butynediol from acetylene and aqueous formaldehyde over a copper acetylide catalyst. It is on this latter type of reaction,... 

Figure 2. Hydrogen consumption vs. product nitrogen in the hydrotreating of whole shale oil with ICR 106. Small pilot plant (O), about 1850 psia. Large pilot plant (U), about 1550 psia (A, approximately 1800 psia and (V), about 1650 psia.

Essentially all of the conversion of 650°F plus bottom material to transportation fuel occurs in the hydrotreating step. Table II compares the overall material balance and yield and nitrogen levels obtained at Toledo with original pilot plant results. These data indicate that the denitrification activity of the catalyst was consistent with prior results, however the apparent yield structure was different. The differences in yields are attributed to two factors (1)... 

Figure 2. T.B.P. distillation comparison of pilot plant and refinery whole hydrotreated product...

Trickle-bed reactors have the following problems (i) In general they are complicated with respect to the mass transfer (gas-liquid and liquid-solid). In addition, proper hydrodynamic conditions (wetting of catalyst, distribution of gas and liquid phase) are hard to realize. Scale-up is therefore difficult and pilot plants are often still needed, (ii) The amount of H2 fed to the reactor - above all in the case of a second stage deep desulfurization of an already hydrotreated fuel - is much higher than the amount chemically needed. Therefore, a costly recycle compressor for the (unconsumed) hydrogen has to be installed. 

Researchers at Haldor Topsoe and their collaborators in academic institutions have contributed significantly to both the advances in research on fundamental aspects of catalytically active sites of transition metal sulfides and the development of new and more active commercial hydrotreating catalysts and processes . Haldor Topsoe has commercialized more active catalysts for HDS. Its TK-554 catalyst is analogous to Akzo Nobel s KF 756 catalyst, while its newer, more active catalyst is termed TK-574. For example, in pilot plant studies, under conditions where TK-554 produces 400 ppmw sulfur in SRGO, I K 574 will produce 280 ppmw. Under more severe conditions, TK-554 will produce 60 ppmw, while TK 574 will produce 30 ppmw, and similar benefits are found with a mixture of straight run and... 

Paraskos et al. [61], Montagna and Shah [54] and Montagna et al. [55] used a pilot plant for hydrotreating gas oil to test the various correlations. Log-plots of /Cg versus 1/(S.V.) or versus L gave straight lines for demetalization and denitrogenation reactions. On this basis, a generalized equation ... 

Bhaskar, M., Valavarasu, G., Sairam, B., Balaraman, K.S., Balu, K. 2004. Three-phase reactor model to simulate the performance of pilot-plant and industrial trickle-bed reactors sustaining hydrotreating reactions. Ind. Eng. Chem. Res. 43(21) 6654-6669. 

The hydrotreating scheme outlined in this paper has been used in Shell s commercial scale gas oil cracking plant at Houston for hydrogenation of the gasoline/gas oil pyrolyzate. The hydrotreater has been in operation for approximately 5 years on the initial catalyst charge. The Shell catalyst has been proven regenerable in both pilot and commercial scale operations. 

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