1,721,324 research outputs found
Modelling long-term decisions to limit effects of market uncertainties
Full text linkThis paper proposes an alternative approach to handle uncertainties for both the plant-wide and the enterprise-wide optimization problems. Such an approach deals with the introduction of long-term policies and business strategies (e.g. tight supply contracts, take-or-pay agreements) into the classical supply chain problem. Contracts and agreements have more and more the task to reduce the effects of market demand and price volatilities and their integration in the typical mixed-integer models for supply chain optimization takes to reliable enterprise scheduling and planning. Technique validation and numerical comparison against status quo are proposed and discussed
Optimal cleaning cycle scheduling under uncertain conditions: A flexibility analysis on heat exchanger fouling
Full text linkFouling is a substantial economic, energy, and safety issue for all the process industry applications, heat transfer units in particular. Although this phenomenon can be mitigated, it cannot be avoided and proper cleaning cycle scheduling is the best way to deal with it. After thorough literature research about the most reliable fouling model description, cleaning procedures have been optimized by minimizing the Time Average Losses (TAL) under nominal operating conditions according to the well-established procedure. For this purpose, different cleaning actions, namely chemical and mechanical, have been accounted for. However, this procedure is strictly related to nominal operating conditions therefore perturbations, when present, could considerably compromise the process profitability due to unexpected shutdown or extraordinary maintenance operations. After a preliminary sensitivity analysis, the uncertain variables and the corresponding disturbance likelihood were estimated. Hence, cleaning cycles were rescheduled on the basis of a stochastic flexibility index for different probability distributions to show how the uncertainty characterization affects the optimal time and economic losses. A decisional algorithm was finally conceived in order to assess the best number of chemical cleaning cycles included in a cleaning supercycle. In conclusion, this study highlights how optimal scheduling is affected by external perturbations and provides an important tool to the decision-maker in order to make a more conscious design choice based on a robust multi-criteria optimization
Recurrent intrahepatic cholestasis
No full textIntrahepatic recurrent cholestasis (IRC), after its first description in 1959, has been sporadically reported from all parts of the world. In total, less than 50 cases have been published, 4 of them in Italy. In the present report, six new patients are described: their age ranged between 16 and 51 yr; two were women. Four of them had several attacks of cholestatic jaundice, ranging from 4 to more than 10; two patients had, up to now, only one episode of jaundice: they are reported because they presented with all the features of the syndrome and had close familial relationship with the other patients. Clinically, they were characterized by pruritus and in the cases of longest duration, by steatorrhea and loss of weight. The peak of serum bilirubin, mainly in the conjugated form, ranged from 15 to over 50 mg/100 ml; alkaline phosphatases and serum cholesterol were very high during the attack, while serum transaminases were constantly normal or near normal. In all patients, the biliary tree was normal as proved either by direct cholangiography obtained during laparotomy or laparoscopy, or by intravenous cholangiogram performed in the interval between the attacks. Histology was obtained in all patients and in all, it showed heavy pigment deposition, normal liver structure, slight increase of fibrous tissue in portal spaces, where inflammatory infiltrates were present. In the interval between the attacks of jaundice, all patients showed complete remission of clinical and biochemical signs. The most striking feature of these cases is that all are natives of a very small area of the Appennines and all but one are more or less closely related. In particular, the two patients who had only one episode of jaundice are respectively sister and first cousin of one of the more typical cases. Moreover one patient has two brothers now living in England, already described as having IRC
Multiple-Effect Evaporation
No full textMultiple-effect evaporation is the cheapest and simplest unit operation aimed to either recover the solvent from a solution or concentrate the solution itself. Several system configurations exist and the optimal one from a Net Income point of view can be selected for each specific case. By mean of a desalination case study cocurrent and countercurrent schemes are compared and advantages and disadvantages of both of them are highlighted and commented from an operability and an economic perspective
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