Cavett Problem. A process having multiple recycle loops formulated by R.H. Cavett [Proc. Am. Petrol. Inst., 43, 57 (1963)] has been used extensively to test tearing, sequencing, and convergence procedures. Although the process flowsheet requires compressors, valves, and heat exchangers, a simplified ASPEN PLUS flowsheet is shown in Figure 7.33 (excluding the recycle convergence units). In this form, the process is the equivalent of a four-theoretical-stage, near-isothermal distillation (rather than the conventional near-isobaric type) for which a patent by A.Gunther [U.S. Patent 3,575,007 (April 13, 1971)] exists. For the specifications shown on the flowsheet, use a process simulator to determine the component flow rates for all streams in the process.

Figure 7.33:-

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Component lbmol/hr N 358.2 CO 4,965.6 V1 Partial Condenser Stage F1 FLASH2 100F, 814.7 psia HS 339.4 V2 L1 C 2,995.5 C 2,395.5 Feed Stage 2,291.0 Feed F2 FLASH2 120F, 284.7 psia iCA 604.1 120F, 284.7 psia nC 1,539.9 V3 12 iC, 790.4 nCs 1,129.9 nC6 1,764.7 nC 2,606.7 F3 FLASH2 Lower Stage 96F, 63.7 psia nCg 1,844.5 nCg 1,669.0 V4 13 RC 10 831.7 NC 12 1.214.5 F4 FLASH2 Partial Reboiler Stage 85F, 277 psia LA Figure 7.33 Near-isothermal distillation process.