Flexicoking yields

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. 

Properties. Pilot-unit data indicate the EDS process may accommodate a wide variety of coal types. Overall process yields from bituminous, subbituminous, and lignite coals, which include Hquids from both Hquefaction and Flexicoking, are shown in Figure 14. The Hquids produced have higher nitrogen contents than are found in similar petroleum fractions. Sulfur contents reflect the sulfur levels of the starting coals ca 4.0 wt % sulfur in the dry bituminous coal 0.5 wt % in the subbituminous and 1.2 wt % sulfur in the dry lignite. 

Fig. 14. Preferred Hquefaction-coking Hquid yields in the EDS process for various coals where Hrepresents Flexicoking Hquids and , Hquefaction Hquids (124). A, Ireland (West Virginia) B, Monterey (Illinois) C, Burning Star (Illinois) D, Wyodak (Wyoming) and E, Big Brown (Texas).

Butylene yield Gas oil Residue Delayed coking Flexicoking Steam cracking of naphtha... 

Yields of liquid products from flexicoking are the same as from fluid coking, because the coking reactor is unaltered. As with fluid coking, the extent of desulfurization depends on the sulfur content of the feedstock as well as on the chemical nature of the sulfur in the feed stock. 

Exxon Donor Solvent, and SRC-II, reactors are run at high severities to maximize distillate yield. Then, in the case of the H-Coal and SRC-II processes all the vacuum tower residue is sent to a partial oxidation gasifier to produce hydrogen. The amount of residue is set by the amount of hydrogen to be generated. The Exxon Donor Solvent process differs in that all or part of the vacuum tower residue is processed in a Flexicoking unit to recover additional liquids and to produce low Btu fuel gas. Partial oxidation can be used to process the remainder of the bottom to produce hydrogen. 

The heavy bottoms from vacuum distillation may be sent to a FLEXICOKING unit along with air and steam to produce additional distilled liquid products and a low quality fuel gas for process furnaces. Light hydrocarbon gases coming from the distillation unit are steam reformed to produce hydrogen. The total liquid yield is thus a blend of streams from liquefaction and flexi-coking. 

Fluid coke is produced in a fluidized bed reactor where the heavy oil feedstock is sprayed onto a bed of fluidized coke. The oil feedstock is cracked by steam introduced into the bottom of the fluidized bed reactor. Vapor product is drawn off the top of the reactor while the coke descends to the bottom of the reactor and is transported to a burner where a portion of the coke is burned to operate the process. Fluid coke reactors are operated at about 510 - 540°C (950 - 1000 F). Flexicoke is a variant cm fluid coke, where a gasifier is added to the process to increase coke yields. Fluid coker installations tend to have yields that are lower than delayed coker installations, while flexicoker installaticms have yields that can be significantly greater than delayed coker installations. Fluid cokers produce layered and non-layered cokes. Both delayed and fluid coke installations produce amorphous, incipient, and mesophase cokes with the amorphous cokes having higher volatility and mesophase cokes having the lowest volatility. 

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