Feed quality liquid fraction

Equation 7.32 takes into account the variations in feed, vapour and liquid rates on the column vapour and liquid flows. The feed quality qF is assumed to remain constant (qF is the fraction of the feed which flows down the column as liquid). 

The SRC-II process, developed by Gulf Oil Corp., was an improved version of the SRC-I process, designed to produce more valuable liquid products, rather than a solid. The major difference between SRC-II and the typical process described above was the recycle of a portion of the fractionator bottoms to the slurry feed tank. This increased the ash content of the reactor feed. This ash, particularly the iron pyrites in the ash, acted as a catalyst and improved product yield and quality. 

As shown in Fig. 18.23, dry liquid feed containing olefins and isobutane is charged to a combined reactor-settler. In this example, the reactor uses the principle of a differential gravity head to circulate through a cooler before contacting a highly dispersed hydrocarbon feed in the reactor pipe. The hydrocarbon phase, generated in the settler, is sent to a fractionator, which separates LPG-quality propane, isobutane recycle, n-butane, and alkylate products. A small amount of dissolved catalyst is also removed from the propane product by a small stripper tower. 

The SO2 scrubbing tower described in Problem 4.26 is to be used to reduce the SO2 mole fraction in the waste gas to a level that meets air quality control regulations. The solvent feed rate must be large enough to keep the SO2 mass fraction in the exit liquid below a specified maximum value. 

Although the gasoline fraction is almost absent in this crude, it is nevertheless a valuable stock-feed for production of diesel fuel and of special kerosenes, also as source of high quality bitumens. In tests, this crude showed a shift in its limit of stress T, equal to 28 kg/cm, and on that basis, it was classified as a liquid of non-Newtonian type. 

In both the liquid- and vapor-phase extraction processes, the kerosene feed is typically prefractionated to narrow the feed to the desired four-carbon number range (either Cjo-Cu or C11-C14). This heartcut is hydrotreated to remove the majority of kerosene contaminants that may compromise the performance of life of the adsorbent or subsequent quality of the LAB or LAS properties. In some process flow schemes, the fractionation into the discrete n-paraffin cuts may be deferred until after the extraction process. 

An additional area of concern relates to the quality of the coke produced from hydrotreated vacuum resid feeds. For a variety of reasons, premature furnace fouling, inclusion of semi-coked liquids in the quenched coke drum, and carry-over of coke fines into the fractionator, the delayed coking of 100% hydrotreated feed has not been successfully achieved in commercial operations. 

Once a set of data has been obtained which correlates, the flocculant consumption, if used, needs to be optimised. Alternative polymers might be examined if centrate quality had been difficult to maintain or if the quantity needed was considered excessive. The relative flow rates of polymer solution, and feed, would be assessed to see whether the polymer concentration needs to be adjusted to make it minimum strength, without causing it to be a large fraction of the total flow. This should not be more than, say, 10 or 15%. Polymer tends to be most efficient when it is most dilute. Moreover it is easier to get a uniform mix of two liquids when they are both of comparable size. However the larger the volume the flocculant is, then the greater is the clarification capacity lost unnecessarily to the clean flocculant. The location for admitting the polymer may be questioned, and considered for introduction further upstream, if flocculation in the centrate has been observed, or if extra dryness is required at the expense of extra polymer in dry solids work. 

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