Coker

In the 1970 s, heavy fuel came mainly from atmospheric distillation residue. Nowadays a very large proportion of this product is vacuum distilled and the distillate obtained is fed to conversion units such as catalytic cracking, visbreaking and cokers. These produce lighter products —gas and gasoline— but also very heavy components, that are viscous and have high contaminant levels, that are subsequently incorporated in the fuels. 

Wang W, Nelson K A, Xiao L and Coker D F 1994 Molecular dynamics simulation studies of solvent cage effects on photodissociation in condensed phases J. Chem. Phys. 101 9663-71... 

Batista V S and Coker D F 1996 Nonadiabatic molecular dynamics simulation of photodissociation and geminate recombination of liquid xenon J. Chem. Phys. 105 4033-54... 

Ciccotti G and Ferrario M 1998 Constrained and nonequilibrium molecular dynamics Classical and Quantum Dynamics In Condensed Phase Simulations ed B J Berne, G Ciccotti and D F Coker (Singapore World Scientific) pp 157-77... 

Berne B J, Ciccotti G and Coker D F (ed) 1998 Classical and Quantum Dynamics In Condensed Phase S/mu/af/ons (Singapore World Scientific)... 

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. 

E. J. Coker and L. N. G. Filon, Treatise on Photoelasticity, Cambridge University Press, London, 1931. 

The vacuum residua or vacuum bottoms is the most complex fraction. Vacuum residua are used as asphalt and coker feed. In the bottoms, few molecules are free of heteroatoms molecular weights range from 400 to >2000, so high that characteri2ation of individual species is virtually impossible. Separations by group type become blurred by the sheer mass of substitution around a core stmcture and by the presence of multiple functionahties in a single molecules. Simultaneously, the traditional gc and ms techniques require the very volatiUty that this fraction lacks. 

Froth from the hot-water process may be mixed with a hydrocarbon diluent, eg, coker naphtha, and centrifuged. The Suncor process employs a two-stage centrifuging operation, and each stage consists of multiple centrifuges of conventional design installed in parallel. The bitumen product contains 1—2 wt % mineral (dry bitumen basis) and 5—15 wt % water (wet diluted basis). Syncmde also utilizes a centrifuge system with naphtha diluent. 

Thermal Cracking. Heavy petroleum fractions such as resid are thermally cracked in delayed cokers or flexicokers (44,56,57). The main products from the process are petroleum coke and off-gas which contain light olefins and butylenes. This stream also contains a considerable amount of butane. Process conditions for the flexicoker are more severe than for the delayed coker, about 550°C versus 450°C. Both are operated at low pressures, around 300—600 kPa (43—87 psi). Flexicokers produce much more linear butenes, particularly 2-butene, than delayed cokers and about half the amount of isobutylene (Table 7). This is attributed to high severity of operation for the flexicoker (43). 

The H-Coal process could operate in one of two modes, depending on the desired product slate. In the "syn-cmde" mode, a fluid-bed coking unit was employed to maximize recovery of distillate from the Hquefaction product (Fig. 7a). When operated in the fuel oil mode (Fig. 7b), no coker was used and the primary product was a coal-derived low sulfur fuel oil. Total hydrogen demand on the process was also reduced in the latter mode of operation. 

T. WiUiamson, G. Coker, K. J. Sims, L. Zhang, andD. Elyanow, 53 rd Annual Meeting, International Water Conference, Pittsburgh, Pa., Oct. 19—21, 1992. 

---