How this calculation works
Recycling unreacted material can increase overall reactant utilization, but it also returns inert material to the reactor. Without a route for inert removal, fresh inert cannot leave a steady process at the same rate it enters. This calculator closes separate reactant and inert balances around a simple recycle loop with a purge. Desired product is completely removed before the remaining gas is split into recycle and purge.
A_reactor=F(1−xI)/[1−(1−p)(1−X)]; I_reactor=F xI/pA worked example
For fresh flow one hundred with ten percent inert, fifty percent per-pass conversion and ten percent purge, reactor inert flow is one hundred. Reactor reactant flow is ninety divided by 0.55. The purge removes ten inert units per time, exactly matching fresh inert. Reducing purge increases inert circulation and can change reactor-feed composition even when fresh feed remains fixed.
Good to know
The model assumes one reactant, unaffected inert and complete product separation. It does not compute equilibrium conversion, reaction selectivity, incomplete condensation, energy use or compressor requirements. A small positive purge can produce a very large modeled recycle. That mathematical result is not a recommended operating condition or proof of feasible equipment capacity; process constraints require separate analysis.
Reference: NPTEL — material and energy balances with recycle and purge (opens in a new tab) ↗
What this calculation answers
Recycling unreacted material can increase overall reactant utilization, but it also returns inert material to the reactor. Without a route for inert removal, fresh inert cannot leave a steady process at the same rate it enters.
This calculator closes separate reactant and inert balances around a simple recycle loop with a purge. Desired product is completely removed before the remaining gas is split into recycle and purge.
The First order CSTR and plug flow conversion calculator predicts a per-pass ideal conversion. Recycling introduces a separate steady-state reactant and inert balance, with purge applied after complete product removal.
Use the right input conventions
Fresh feed is total molar flow in one consistent time unit. Its inert percentage sets the fresh reactant remainder. Conversion refers to reactant consumed in one reactor pass, not overall consumption of fresh reactant.
The purge percentage applies to the complete separator gas before recycle. It removes the same fraction of unreacted reactant and inert; it is not a selectively separated inert stream.
Interpret the result
The table lists fresh feed, reactor feed, separator gas, purge and recycle. Reactor feed can exceed fresh feed substantially because it includes returning material, which is not additional external supply.
At steady state, inert leaving in the purge equals fresh inert entering. Product formation plus purged reactant balances fresh reactant. These identities are useful checks when interpreting the larger internal circulation values.
Work through the example
For fresh flow one hundred with ten percent inert, fifty percent per-pass conversion and ten percent purge, reactor inert flow is one hundred. Reactor reactant flow is ninety divided by 0.55.
The purge removes ten inert units per time, exactly matching fresh inert. Reducing purge increases inert circulation and can change reactor-feed composition even when fresh feed remains fixed.
Where the model stops
The model assumes one reactant, unaffected inert and complete product separation. It does not compute equilibrium conversion, reaction selectivity, incomplete condensation, energy use or compressor requirements.
A small positive purge can produce a very large modeled recycle. That mathematical result is not a recommended operating condition or proof of feasible equipment capacity; process constraints require separate analysis.
A few questions, answered
Does ten percent purge mean ten percent of fresh feed?
No. It is ten percent of separator gas, whose flow includes circulating unreacted material and inert.
What changes in the comparison?
Increase the separator purge fraction and inspect lower inert circulation alongside greater reactant loss in the purge.