Process recycle and purge: In a continuous process with recycle, the main purpose of introducing a purge stream is to

Introduction / Context:
Recycle loops improve conversion and energy efficiency, but non-reactive or slowly removed components (inerts, impurities, byproducts) can accumulate. A purge stream prevents their runaway build-up, stabilising composition and safeguarding equipment.

Given Data / Assumptions:

• Steady-state continuous process with recycle.
• Presence of inert species or trace impurities in the loop.
• Primary aim is stable loop composition and controllability.

Concept / Approach:
The total mass balance with species accumulation in a loop shows that, without a purge, any unconsumed inert will trend upward toward 100% in the recycle. A small purge bleed ensures a finite residence time for inerts, establishing a steady-state concentration consistent with process targets.

Step-by-Step Solution:

Verification / Alternative check:
Typical ammonia and methanol loops include purges to limit argon, methane, and other inerts; operating data corroborate the necessity of purging to maintain catalyst performance and heat-integration targets.

Why Other Options Are Wrong:

• Increase yield/enrich product: Purging removes valuable reactants too; it is a compromise, not a yield booster.
• Conserve heat: Purge can penalise heat recovery rather than conserve it.

Common Pitfalls:
Oversizing the purge wastes reactants; undersizing allows inerts to accumulate and reduce loop effectiveness.

Final Answer:
Limit the build-up of inerts and unwanted species