DESIGN METHODOLOGY III RECYCLE STRUCTURE OF THE PROCESS GOAL --Determine alternate recycle structures for the process based on reactor operating requirements. 11/29/99 Recycle structure
11/29/99 Recycle Structure 1 DESIGN METHODOLOGY III: RECYCLE STRUCTURE OF THE PROCESS GOAL --Determine alternate recycle structures for the process based on reactor operating requirements
RECYCLE STRUCTURE FOR SINGLE REACTION SYSTEM Vapor phase recycle Purge Products fresh Reaction Separation eel System System B products Liquid phase recycle 11/29/99 Recycle structure
11/29/99 Recycle Structure 2 Reaction System Separation System Purge Products Byproducts Liquid Phase Recycle Vapor Phase Recycle Fresh Feed RECYCLE STRUCTURE FOR SINGLE REACTION SYSTEM
REASONS FOR RECYCLE Recycle unreacted reactants E Conversion limitations E Excess reactant to shift equilibrium ◆ Recycle diluent E Reactor heat management E Flammability constraints ◆ Recycle" to extinction” E Recycle byproduct to equilibrium- no net production 11/29/99 Recycle structure
11/29/99 Recycle Structure 3 REASONS FOR RECYCLE u Recycle unreacted reactants ð Conversion limitations ð Excess reactant to shift equilibrium u Recycle diluent ð Reactor heat management ð Flammability constraints u Recycle “to extinction” ð Recycle byproduct to equilibrium - no net production
EXAMPLE #1. EFFECT OF FEED COMPOSTION ON EQUILIBRIUM CONVERISION 07 06 0.5 03 02 0.1 0 0 3 fAO/fB0 A+B今C Delta=extent of reaction for Ky=Yc/rarb=2.0 fA0=feed rate of a, fB0 =feed rate of B=1.0 fC0=0. 11/29/99 Recycle structure
11/29/99 Recycle Structure 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 1 2 3 4 5 fA0/fB0 Delta EXAMPLE #1. EFFECT OF FEED COMPOSTION ON EQUILIBRIUM CONVERISION A + B Û C Delta = extent of reaction for Ky = Yc/YaYb = 2.0 fA0 = feed rate of A, fB0 = feed rate of B = 1.0 fC0 = 0
REACTOR CONSIDERATIONS ◆ Heat management E What is the adiabatic temperature change? E excessive(more than 25 C), must modify design Diluent >Heating(endothermic) or cooling(exothermic ◆ Equilibriun E Modify operating conditions Change temperature or pressure Use excess of one reactant in feed 11/29/99 Recycle structure 5
11/29/99 Recycle Structure 5 REACTOR CONSIDERATIONS u Heat management ð What is the adiabatic temperature change? ð If excessive (more than 25 C), must modify design ÿDiluent ÿHeating (endothermic) or cooling (exothermic) u Equilibrium ð Modify operating conditions ÿ Change temperature or pressure ÿ Use excess of one reactant in feed