Alejandro Zaleta-Aguilar

Optimal process of solar to thermal energy conversion and design of irreversible flat-plate solar collectors

Thermodynamic optimization based on the first and the second law is developed to determine the optimal performance parameters and to design a solar to thermal energy conversion system. An exergy analysis is presented to determine the optimum outlet temperature of the working fluid and the optimum path flow length of solar collectors with various configurations. The collectors used to heat the air flow during solar-to-thermal energy conversion, are internally arranged in different ways with respect to the absorber plates and heat transfer elements. The exergy balance and the dimensionless exergy relationships are derived by taking into account the irreversibilities produced by the pressure drop in the flow of the working fluid through the collector. Design formulas for different air duct and absorber plate arrangements are obtained.

Thermodynamic characterization of the power loss factor in steam turbines

Abstract Erosion, roughness, steam path damage etc., are factors that reduce the power capacity in a steam turbine (ST). Any power loss occurring locally in intermediate stages of a ST results in more available energy in the downstream stages. This effect is well known as the loss factor (LF) [Steam Turbines and Their Cycles, Krieger, NY, USA, 1974; Steam and Gas Turbines, McGraw-Hill, NY, USA, 1927; Steam Turbines Theory and Design, McGraw-Hill, NY, USA, 1984]. Currently, it is calculated by graphical methods [Evaluting and Improving Steam Turbine Performance, Gilson, NY, USA, 1993]. In this work, a new thermodynamic expression for the LF is introduced in order to improve applications to evaluate malfunctions in the first and intermediate stages of STs. The proposed thermodynamic expression for the LF is based on second law analysis and concepts like the internal parameter θ , and the dissipation temperature T d [Las Ecuaciones Caracteristicas, Doctoral Thesis, University of Zaragoza, 1992]. To show the main features and easiness of application of the proposed method, a 158 MW conventional power plant is analyzed, comparing the classical graphical method [Evaluating and Improving Steam Turbine performance, Gilson, NY, USA, 1993; Simplified Performance Test of Steam Turbines, ASME, NY, USA, 1970] and the proposed expression of the LF. Special emphasis is made on the thermoeconomical deviations that could arise by an imprecise application of the LF Method during an energy audit of the steam turbine internal parts.

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.

Numerical Analysis of a Gas Turbine Using Bio-Ethanol

The change of the fuel to a bio-fuel in a gas turbine combustor is a defiant challenge due to there is not enough information about the thermal behavior into the combustor, even there is not information about the change of conventional fuel used. In these sense, a numerical analysis using Natural Gas, Diesel and Bio-Ethanol is presented. The results show a significant reduction of the Turbine Inlet Temperature (TIT) when the diesel and bio-ethanol are used in the gas turbine combustor (TITNatural Gas = 1,262.24 K, TITDiesel = 1,204.67 K and TITBio-ethanol = 918.24 K). This leads to an increment of the diesel and bio-fuel mass flow rate in order to reach the allowable condition of the gas turbine combustor. As it is well known, the reduction of the TIT means a reduction of the output power of the gas turbine, thus to avoid this, the increase of bio-ethanol was about 255.5% and diesel was about 112.2% (considering 3.6 kg/s of fuel as the full load). This paper gives an attempt to discover the viability to use bio-fuels in gas turbines from the thermal-fluid dynamic standpoint.Copyright

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