Organic Rankine Cycle (ORC) is widely used in the field of low temperature waste heat recovery, including solar, biomass and geothermal energy, among others. Based on the thermodynamic model of ORC system built up in Matlab, this study employ Genetic Algorithm (GA) on ORC system for parametric optimization and select a ratio of heat transfer area to total net power output as the performance evaluation criterion to predict the economy of system. R11, R113, R123 and isopentane are choosed as the working medium. The results show that the ORC system with isopentane has the minimum objective function value of 0.429m2/kw. The corresponding condensing temperature and degree of supercooling are generally located at lower boundary over their parametric design ranges, and the corresponding pinch point temperature difference are located at upper boundary. For different working fluids, there exist an optimum evaporating temperature and degree of superheat.
Coal-fired power
plants produce flue gas desulfurization (FGD) gypsum as a byproduct
of the sulfur removal process. This gypsum is contaminated with trace
elements. Knowing the occurrence and release characteristics of trace
elements from the FGD gypsum is very important if the gypsum is to
be safely used in different applications. The sequential extraction
procedure proposed by the European Community Bureau of Reference (BCR)
can be used to provide mercury speciation information for FGD gypsum
samples. Many researchers have used the BCR sequential extraction
method to analyze the occurrence of mercury in FGD gypsum. Unfortunately,
the recovery ratio is low, around 50–60%. The recovery is low
because the BCR method does not include the portion of elemental mercury
(Hg0) lost during each leaching step. In this work, modifications
to the BCR method were made to more accurately determine the amount
of mercury lost during the extraction. Using this “improved
BCR method”, the Lumex RA-915+/PYRO-915 mercury analyzer measures
the mercury content in the residues at each extraction step. The difference
between the sample and residue concentrations is equal to the amount
of Hg released. This indirect measurement method was used to overcome
the shortcomings of the traditional BCR sequential extraction process.
The results show that the “improved BCR method” has
a recovery ratio of about 99%, which can more accurately evaluate
the environmental stability of mercury in gypsum. Thus, an improved
five-step sequential extraction procedure for analysis of mercury
was successfully applied to FGD gypsum samples in this study.
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