Project ForgeChemical Reaction Engineering
Ideal Reactor Design
GATE 2020
Hard
A unit pulse of tracer is given to an ideal PFR operating at steady state with a recycle ratio R=1 (ratio of fluid volume returned to entrance vs. volume leaving the system). If τ is the (fresh-feed-based) space time of the PFR, the first four observed exit pulses t1,t2,t3,t4 satisfy
- At1=τ, t2=2τ, t3=3τ, t4=4τ
- t1=τ/2, t2=τ, t3=3τ/2, t4=2τ
- Ct1=τ/2, t2=τ/4, t3=τ/8, t4=τ/16
- Dt1=τ/3, t2=2τ/3, t3=τ, t4=4τ/3
Explanation
With R=1, the actual flow through the vessel is twice the fresh feed rate, so one pass through the reactor (of volume V) takes V/(2×fresh feed rate)=τ/2, not τ (τ is defined using the fresh feed rate alone). Each recirculation adds another τ/2, giving pulses at τ/2, τ, 3τ/2, 2τ.
Source: GATE CH 2020 (2020)
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