OPTIMUM OPERATION FOR DIFFERENT DESIGN CONDITIONS OF A SINGLE PRESSURE HEAT RECOVERY STEAM GENERATOR (HRSG) FOR MINIMUM ENTROPY GENERATION
Heat Recovery Steam Generator (HRSG) is the critical link between the “topping” gas and “bottoming” steam power cycle of a combined power plant. Depending on the mass flow and property of exhaust flue gas from the gas cycle, optimum design and operation, for minimum entropy generation in a single pressure HRSG generating superheated steam is reported in this paper. It shows that an optimum pressure of steam generation exists for minimum entropy generation. The interdependence between the physical size (and hence cost) of different heat transfer components of HRSG with the thermodynamic optimum operation for minimum entropy generation is presented. Optimum pressure of steam generation increases with greater size of super heater, economizer and evaporator up to certain limit, beyond which the increase in optimum saturation pressure is marginal with increase in size of the heat transfer units. However, increasing evaporator size and degree of superheat have the adverse effect of lesser steam generation for a given economizer and super heater for minimum entropy generation.
Heat-recovery steam generators: Understand the basics
Gas turbines with heat-recovery steam generators (HRSGs) can be found in virtually every chemical process industries (CPI) plant. They can be operated in either the cogeneration mode or the combined-cycle mode. In the cogeneration mode, steam produced from the HRSG is mainly used for process applications, whereas in the combined-cycle mode, power is generated via a steam turbine generator. Recent trends in HRSG design include multiple-pressure units for maximum energy recovery, the use of high-temperature superheaters or reheaters in combined-cycle plants, and auxiliary firing for efficient steam generation. In addition, furnace firing is often employed in small capacity units when the exhaust gas is raised to temperatures of 2,400--3,000 F to maximize steam generation and thus improve fuel utilization. This article highlights some of the basic facts about gas turbine HRSGs. This information can help plant engineers, consultants, and those planning cogeneration projects make important decisions about the system and performance related aspects.
Design and synthesis of water-soluble prodrugs of rifabutin for intraveneous administration.
Acinetobacter baumannii is a gram-negative bacterium causing severe hospital-acquired infections such as bloodstream infections or pneumonia. Moreover, multidrug resistant A. baumannii becomes prevalent in many hospitals. Consequently, the World Health Organization made this bacterium a critical priority for the research and development of new antibiotics. Rifabutin, a semisynthetic product from the rifamycin class, was recently found to be very active in nutrient-limited eukaryotic cell culture medium against various A. baumannii strains, including extremely drug-resistant strains, with minimal inhibitory concentrations as low as 0.008 μg/mL. Moreover, this in vitro potency translates into in vivo efficacy. Thus, rifabutin appears to be an attractive novel antibiotic against A. baumannii. In this work, our objective was to design and synthetize rifabutin prodrugs with increased aqueous solubility to allow intraveneous use. Synthetic methodologies were developed to selectively functionalize the hydroxyl group in position 21 and to afford 17 prodrugs. We measured the water solubility of the prodrugs, the stability in human and mouse plasma and their antimicrobial activity against A. baumannii after incubation in human serum. Finally, a pharmacokinetic release study of rifabutin was performed in CD1 mice with three selected prodrugs as a proof of concept.