Recently Patel and co workers analyzed processes by considering the mass, heat and work flows in and out of processes. They were able to determine targets of performance for the process and in particular were able to determine the minimum heat and work requirements for a given process mass balance. A reversible process, in other words one that operates such that the entropy change of the universe is zero, operates at this target. This target is important in that it allows us to determine, for example, what the minimum CO2 emissions are for a process.

Real process operate very far from this theoretical target. This caused us to ask why and where are the major irreversibilities generated? In order answer this we consider how we can synthesize a simple, but reversible reactor – separator – recycle system. We consider the heat and work flows in and out of the process and show where and how much work must be recovered or consumed by both the reactor and separator in order for the process to be reversible. We then consider various scenarios where we do not recover the all work and instead consider this work irreversibly lost. We show the impact of this on the work and energy requirements of the process and from this we can see the major causes for irreversibilities and thus inefficiencies in the process that result from our design and in particular in our handling of work recovery and integration.

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