Flash hydrocracking

Rhenium is used in tungsten and molybdenum-based alloys. It is used for filaments for ion gages in mass spectrometers. Rhenium-tungsten alloys are used in thermocouples to measure temperatures up to 2,200°C. Rhenium wire is used in flash bulbs for photography. Rhenium compounds also are used as catalysts in hydrogenation and hydrocracking reactions in petroleum refining. 

The hydrocracker simulator was also converted to subroutine form for inclusion in the nonlinear programming model of the Toledo process complex. The subroutine was considerably simplified, however, to save computer time and memory. The major differences are (1) the fractionation section is represented by correlations instead of by a multi-stage separation model, (2) high pressure flash calculations use fixed equilibrium K-values instead of re-evaluating them as a function of composition, and (3) the beds in each reactor are treated as one isothermal bed, eliminating the need for heat balance equations. 

The flash of 27-multicomponent mixtures in the high pressure hydrocracking separator were calculated in this paper. To those polar components, special treatment were used. The properties M, Tc, Pc of petroleum fractions were calculated by Riazi and Daubeit [11](1980) correlations, and co was calculated by Lee and Keslefs correlation. A group of typical results... 

The reactor effluent leaving the air cooler is separated into hydrogen-rich recycle gas, a sour water stream, and a hydrocarbon liquid stream in the high-pressure separator. The sour water effluent stream is often sent to a plant for ammonia recovery and for purification so water can be recycled back to the hydrocracker. The hydrocarbon rich stream is pressure reduced and fed to the distillation section after light products are flashed off in a low-pressure separator. 

Properties of the base stocks (Table 7.22) compared with solvent extracted stocks show that the hydrocracked products have better colors, Vis, and flash points. Sulfur and nitrogen levels will be in the low parts per million range. 

Rigorous, flow-sheet-based models for hydrocrackers include sub-models for furnaces, pumps, compressors, reactors, quench zones, flash drums, recycle gas scrubbers, fractionation towers, and - importantly - economic data. As discussed in Chapter 23 by Mudt, et al., such models can comprise hundreds of reactions and hundreds of thousands of equations. The model grows when inequalities are included to ensure a feasible solution that honors process constraints. To solve such models in real time (i.e., in less than an hour), open-equation mathematics and high-powered solvers are used. 

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