Hydrotreating handling

Fluid catalytic cracking units present formidable emission control problems. Contaminants are present in both reactor product gas and regenerator flue gas. The reactor product contains hydrogen sulfide, ammonia, and cyanides, plus combined sulfur and nitrogen in the liquid products. Hydrogen sulfide, ammonia and cyanides are handled as part of the overall refinery waste water cleanup. The combined sulfur and nitrogen may be removed by hydrotreating. 

Consider the oil-recycling plant shown in Fig. 3.16. In this plant, two types of waste oil are handled gas oil and lube oil. The two streams are first deashed and demetallized. Next, atmospheric distillation is used to obtain light gases, gas oil, and a heavy product. The heavy product is distilled under vacuum to yield lube oil. Both the gas oil and the lube oil should be further processed to attain desired properties. The gas oil is steam stripped to remove light and sulfur impurities, then hydrotreated. The lube oil is dewaxed/deasphalted using solvent extraction followed by steam stripping. 

A possible solution is to gasify the more dilute vacuum tower bottoms product in an oxygen blown gasifier and to convert the excess synthesis gas to methanol. In those cases where a Flexicoker is used the heavy scrubber liquids could be recycled to extinction. Therefore, the plant products are SNG, naphtha, 300-800°F distillate and methanol. All of these products are of high quality or can be hydrotreated to achieve high quality. As a result, they could be easily integrated into the utility fuel mix with a minimum amount of disruption or special product handling facilities. 

Koppers Tar creosote oil is comprised primarily of two-, three-, and four-ring polynuclear aromatic compounds. Only 4% of this solvent, which contains a sizable amount of fluoranthene (bp 723°F), boils over 850°F. Typical hydrotreated 420°-850°F distillate product from this feed material has a multitude of additional components in much smaller concentrations as determined by gas chromatography (GC). The major components of the feed contribute less to the total concentration in product than in feed. Therefore, product distillates are less pure than feed distillates and less likely to solidify than feed. Indeed, Koppers Tar is itself a solid-liquid mixture which upon observation suggests handling problems. In anticipation of pumpability problems for mixtures of SRC in Koppers Tar, a viscosity study was made on several different concen-... 

While this heavy LCO material could be shifted to other markets, this does not necessarily have to be the case. Under certain conditions, this material can be recycled to the FCC unit . For this to be feasible, the refiner must hydrotreat the FCC feed at a pressure sufficient to desulfurize the sterically hindered sulfur containing compounds and the feed hydrotreater must have sufficient excess capacity to handle the additional material. This material could also be sent to an existing hydrocracker, if sufficient capacity existed, and converted into gasoline blendstock. Alternatively, it could be hydrotreated separately under more severe conditions to remove the sulfur, such as with SynAlliance s SynShift process . This would entail higher hydrogen consumption per barrel of treated material because of some aromatic saturation. However, the amount of material being processed would... 

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