V.H. Rangel-Hernández

Second Law Analysis of a Mobile Air Conditioning System with Internal Heat Exchanger Using Low GWP Refrigerants

This paper investigates the results of a Second Law analysis applied to a mobile air conditioning system (MACs) integrated with an internal heat exchanger (IHX) by considering R152a, R1234yf and R1234ze as low global warming potential (GWP) refrigerants and establishing R134a as baseline. System simulation is performed considering the maximum value of entropy generated in the IHX. The maximum entropy production occurs at an effectiveness of 66% for both R152a and R134a, whereas for the cases of R1234yf and R1234ze occurs at 55%. Sub-cooling and superheating effects are evaluated for each one of the cases. It is also found that the sub-cooling effect shows the greatest impact on the cycle efficiency. The results also show the influence of isentropic efficiency on relative exergy destruction, resulting that the most affected components are the compressor and the condenser for all of the refrigerants studied herein. It is also found that the most efficient operation of the system resulted to be when using the R1234ze refrigerant.

Assessing the Exergy Costs of a 332-MW Pulverized Coal-Fired Boiler

In this paper, we analyze the exergy costs of a real large industrial boiler with the aim of improving efficiency. Specifically, the 350-MW front-fired, natural circulation, single reheat and balanced draft coal-fired boiler forms part of a 1050-MW conventional power plant located in Spain. We start with a diagram of the power plant, followed by a formulation of the exergy cost allocation problem to determine the exergy cost of the product of the boiler as a whole and the expenses of the individual components and energy streams. We also define a productive structure of the system. Furthermore, a proposal for including the exergy of radiation is provided in this study. Our results show that the unit exergy cost of the product of the boiler goes from 2.352 to 2.5, and that the maximum values are located in the ancillary electrical devices, such as induced-draft fans and coil heaters. Finally, radiation does not have an effect on the electricity cost, but affects at least 30% of the unit exergy cost of the boiler’s product.

Evaluating the Energy Requirements of Small-Scale Biodiesel Production From Raw Tallow of Tanning Industry

The study at hand provides an analysis of the energy input-yield ratios of a planned small-scale raw-tallow-fuelled biodiesel production plant. In the state of Guanajuato, the rendering activities generate roughly 150 tonnes of raw tallow that is refused into nearby pounds or rivers, a common practice that causes an irreversible environmental damage. So in order to make use of this residue, it is proposed here to use it as feedstock for a biodiesel production plant. The plant is assumed to be comprised of a separation process, an acid catalized pretreatment, a transesterification process, a steam generator and a storage zone. Hence a detailed energy analysis was carried out to evaluate the mass and energy transfer ratios of each subsystem as well as their energy efficiencies so as to decide whether the plant could be technical and economically feasible and competitive. The results of this former study must be seen as the base for an informed dialogue with important stakeholders and governmental organizations.Copyright

Extended exergy analysis applied to an offshore platform flare stack

An original procedure based on the EEA method (Extended Exergy Accounting) is described and implemented in this paper. The goal is the quantification of the environmental externality linked to the chemicals released by an offshore platform flare stack (SOX and NOX ). The extended exergy calculations provide a measure of both the exergy flux released into the environment by the offshore platform flare stack and its “cost” in primary resource equivalents. Idealized processes are assumed for the effluent treatment, and this bears a non-negligible influence on the final resource cost. As a further example of the application, it is shown that both the environmental damage and the product costs can be reduced if hot gas recycling is enforced.© 2009 ASME