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The optimization of chemical processes has gained immense importance in the present day. This work is aimed at the on-line optimization of an industrial crude distillation unit (CDU). A nonlinear, steady-state CDU model has been developed in-house for this purpose. Model tuning parameters in the form of vaporization efficiencies were incorporated to minimize the discrepancy between the measured and simulated column parameters on-line. The crude feed composition, represented by the true boiling point (TBP) curve, is known to vary with time. A procedure was developed to back-calculate the TBP curve using on-line plant data. Finally, the objective function was formulated to simultaneously maximize the net achievable profit and set the product properties within a user-specified range. The entire scheme was tested using real plant data off-line, but the problem formulation is suitable for supervisory-level on-line optimization without further modifications. It is shown that substantial increases in profitability can be achieved using supervisory on-line optimization.

Loose shell syndrome (LSS) of farmed black tiger shrimp Penaeus monodon has been reported from Indian shrimp farms since 1998 and is recognized as a major disease problem causing significant economic loss to the shrimp aquaculture sector. Unlike the rapid mortalities associated with viral pathogens such as white spot syndrome virus and yellow head virus, progression of LSS is gradual, leading to low-level progressive mortalities. The signs of LSS include a flaccid spongy abdomen due to muscular dystrophy, space between the exoskeleton and muscle, and a shrunken hepatopancreas. The feed conversion efficiency is reduced, and shrimp have poor meat quality, caused by impairment of the hepatopancreatic functions such as digestion and absorption as evidenced by the atrophy of the hepatopancreas. Histopathological investigations on LSS-affected shrimp showed shrinkage of extensor and flexor muscles with occasional hemocytic infiltration. The hepatopancreas showed inflammation of hepatopancreatic tubules with enlargement of intertubular spaces, hemocytic infiltration, and low levels of lipid reserves in the R cells. In advanced stages of LSS, many tubules were in highly necrotic condition with a sloughed epithelium, reflecting the dysfunction of the digestive gland. LSS could be induced in healthy tiger shrimp by challenge studies using membrane-filtered LSS-affected shrimp tissues, suggesting involvement of a filterable infectious agent.

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