Maximization of propylene in an industrial FCC unit

YesThe FCC riser cracks gas oil into useful fuels such as gasoline, diesel and some lighter products such as ethylene and propylene, which are major building blocks for the polyethylene and polypropylene production. The production objective of the riser is usually the maximization of gasoline and diesel, but it can also be to maximize propylene. The optimization and parameter estimation of a six-lumped catalytic cracking reaction of gas oil in FCC is carried out to maximize the yield of propylene using an optimisation framework developed in gPROMS software 5.0 by optimizing mass flow rates and temperatures of catalyst and gas oil. The optimal values of 290.8 kg/s mass flow rate of catalyst and 53.4 kg/s mass flow rate of gas oil were obtained as propylene yield is maximized to give 8.95 wt%. When compared with the base case simulation value of 4.59 wt% propylene yield, the maximized propylene yield is increased by 95%

Conditions for which MPC fails to converge to the correct target

This paper considers the efficacy of disturbance models for ensuring offset free tracking and optimum steady-state target selection within linear model predictive control (MPC). Previously published methods for steady-state target determination can address model error, disturbances, and output target changes when the desired steady state is unconstrained, but may fail when there are active constraints. This paper focuses on scenarios where the most desirable target is unreachable, thus some constraints are active in steady state. Examples are given showing that the resulting feasible steady-state target can converge to a point which is not as close as possible to the true target. These failures have not been widely discussed in the literature. From the closed-loop behavior, hypotheses are put forward as necessary conditions for offset-free control. These hypotheses are then investigated through the use of Karush-Kuhn- Tucker (KKT) conditions of optimality

Mercury exposure in children with autistic spectrum disorder: Case-control study

Although mercury has been proven to be a neurotoxicant, there is a lack of data to evaluate the causal relationship between mercury and autism. We aim to see if there is increased mercury exposure in children with autistic spectrum disorder. We performed a cross-sectional cohort study over a 5-month period in 2000 to compare the hair and blood mercury levels of children with autistic spectrum disorder (n = 82; mean age 7.2 years) and a control group of normal children (n = 55; mean age 7.8 years). There was no difference in the mean mercury levels. The mean blood mercury levels of the autistic and control groups were 19.53 and 17.68 nmol/L, respectively (P = .15), and the mean hair mercury levels of the autistic and control groups were 2.26 and 2.07 ppm, respectively (P = .79). Thus, the results from our cohort study with similar environmental mercury exposure indicate that there is no causal relationship between mercury as an environmental neurotoxin and autism.link_to_subscribed_fulltex