Vacuum bottoms processing

The heavy vacuum bottoms stream is fed to a Flexicoking unit. This is a commercial (125,126) petroleum process that employs circulating fluidized beds at low (0.3 MPa (50 psi)) pressures and intermediate temperatures, ie, 480—650°C in the coker and 815—980°C in the gasifier, to produce high yields of hquids or gases from organic material present in the feed. Residual carbon is rejected with the ash from the gasifier fluidized bed. The total Hquid product is a blend of streams from Hquefaction and the Flexicoker. 

Vacuum distillatiou is used to remove the residue from the distillate product. Additional heavy oil may be recovered from the vacuum bottoms by employing Exxon s Flexicoldng process. 

Process hydrogen is produced by steam reforming light hydrocarbon gases. An alternative method for hydrogen production is partial oxidation of the heavy vacuum bottoms stream or of coal. 

Experience indicates that an important part of a normal process development is definition of solutions to operability and reliability problems that have been identified. The EDS process development is no exception. Potential mechanical problems associated with feed slurry preheat, slurry pumping, high pressure letdown valves and vacuum bottoms pumping have been identified and will be addressed in the 250 T/D pilot plant program. In addition, several process problems associated with the variety of coals processed have been identified and solutions defined. The status of both pilot plant construction and definition of solutions to process problems is presented in this paper. 

ER E discussions with Texaco and with Shell on bottoms processing are summarized herein. Texaco has indicated that its partial oxidation process could be applied to coal liquefaction bottoms on a commercial scale and that operation of their 12 T/D pilot plant with coal liquefaction bottoms representative of a projected commercial feedstock would be adequate to set the design basis for a commercial facility. Texaco indicated that three to four years after successful operation of the 12 T/D unit a commercial facility could be ready for startup. In initial discussions, Shell has indicated that development of the Shell/ Koppers partial oxidation process for coal liquefaction bottoms would involve operations of both their 6 T/D pilot plant and their 150 T/D demonstration unit. It was estimated that the 150 T/D facility might become available in the late 1980/early 1981 time frame for possible operation on vacuum bottoms. 

Cince the first commercial H-Oil unit came on-stream at Lake Charles in 1963, a variety of feedstocks have been processed, including heavy cycle oils, atmospheric bottoms, vacuum bottoms, and cutback propane deasphalter bottoms. The unit has operated successfully with both microspheroidal and extrudate catalysts and has been expanded to 6000 bbl/day. 

The H-Oil imit was designed to convert 2500 bbl/day of West Texas sour vacuum bottoms into lighter products (J). Later it was found possible to process a heavier, lower value feedstock, cutback propane... 

The Kuwait atmospheric residual is the least expensive to process of the six stocks. The Venezuelan vacuum bottoms are the most expensive,... 

The solvent is first hydrogenated and then mixed with the fresh coal after which the slurry is passed through a preheater and into the reactor. The slurry product is separated by distillation into gas, naphtha, middle distillates, and a vacuum bottoms slurry this latter product is coked to produce additional liquid products. The process has the capability of producing high yields of low-sulfur liquids from bituminous (or subbituminous) coals and lignites (Table 19.4). 

Today s standard vacuum evaporators are far removed from open pans. The so-called grainer process actually is closer to the original vacuum-pan process [17,18]. It was displaced by developments in the vacuum-pan process. It survives as a minor source thanks largely to the unique particle characteristics of its product. These are due to slow rates of evaporation from large, quiescent brine surface areas. A flow of air across the brine surface keeps the evaporation temperature at 90-95°C. Surface tension keeps afloat the flakes that initially form. Growth continues, mostly on the underside, until the hollow, pyramidal particles reach a size where they sink to the bottom. The process obviously is energy-intensive, and this fact accounts for its commercial demise [2]. 

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