Retrecir

Retrecir is a term used in process engineering to describe the intentional recirculation of a portion of an output stream back to an earlier point in a system. The goal is to improve mixing, temperature uniformity, concentration control, energy efficiency, or emissions. A typical retrecir arrangement comprises a bypass, a valve or pump to control the diverted flow, a recirculation line returning to the reactor inlet or feed point, and sensors to monitor relevant variables. Control strategies range from fixed-ratio flow splits to closed-loop PID or model-predictive controllers that adjust the recirculated fraction to maintain target temperature, composition, or pressure.

Common domains include chemical reactors, combustion systems where exhaust gas recirculation reduces NOx, HVAC systems to recover heat and regulate air quality, and water or wastewater treatment to maintain disinfectant residual and homogenize content, as well as fermentation or bioprocessing. Advantages include improved process stability, better heat or mass transfer, energy savings, and reduced emissions; limitations include increased system complexity, additional equipment cost, potential fouling or impurity buildup, and the need to manage backpressure and possible pressure drops.

Terminology varies by field; retrecir is used in some sources as a general term for recirculation, while other contexts prefer recirculation or recycle.