Direct solar air heating in linear concentrating collectors assisted by a turbocharger for industrial processes: theoretical analysis and experimental characterization
- Autores: Antonio Famiglietti
- Directores de la Tesis: Antonio Lecuona Neumann (dir. tes.)
- Lectura: En la Universidad Carlos III de Madrid ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Eduardo Rincón Mejía (presid.), José González Aguilar (secret.), José M. Cardemil (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de Madrid
- Materias:
- Enlaces
- Tesis en acceso abierto en: e-Archivo
- Resumen
Energy demand of industry has a relevant share of global energy consumption. The larger portion of industrial demand is heating, mainly provided from fossil fuels. The concerns about pollutant and greenhouse gas emissions, together with the fossil fuels scarcity encourage the research efforts toward environmentally sustainable energy sources and among them, solar energy is widely available. Among solar thermal technologies, linear concentrating collectors represent a suitable solution for providing industrial process heat in the medium temperature range. A heat transfer fluid, as thermal oil, or water, is generally adopted to evacuate heat from the solar receivers and to deliver it to thermal processes, contributing to complexity, cost, and even environmental impact.
In this thesis the direct air heating inside concentrating solar collector is investigated as a promising solution for industrial processes requiring hot air in the medium temperature range, aiming at low installation and maintenance costs. Although uncommon, the theoretical analysis carried out revealed the feasibility of direct air heating at atmospheric pressure either in parabolic trough and linear Fresnel collectors within a limited range of design and operating conditions. The high pumping power required to blow air through the receivers arises as one of the main constraints, becoming unsustainable at medium and large scale. To overcome this limitation, an innovative layout is proposed using an automotive turbocharger to configure an original open-to-atmosphere solar Brayton cycle with null power efficiency. The compressor increases the air pressure before solar heating inside the receivers, minimizing the pumping power consumption. The turbine placed at the receiver outlet recovers the compressing and the pumping power, releasing hot air at between 300 °C and 400 °C for its usage in the thermal process. The maximum allowable temperature of evacuated standard receivers, indicated as 600 °C by most of the manufacturers, limits the inlet turbine temperature. No substantial mechanical excess of power at the common turbine and compressor shaft is expected. Instead, turbocharger freewheeling enables to blow air through the solar receivers without auxiliary energy consumption, eventually delivering the hot air with an overpressure for pumping to the user.
To support the proposal, a first small-scale experimental prototype of the turbo-assisted solar air heater is designed and installed, using Linear Fresnel collectors and a low-capacity turbocharger. The experimental results allow the thermal and mechanical characterization of the solar collector and the turbocharger, besides tuning and validating the numerical model implemented. They corroborate the practical viability of the concept and indicates relevant features and critical aspects for scaling up to industrial size. A detailed quasi-steady numerical model is developed, including technical features of commercial linear Fresnel collectors and off-the-shelf turbochargers. Daily and yearly assessments of several medium-scale facilities are obtained considering the typical meteorological year of the selected location. The results allow identifying the relevant design and operating parameters and their effect on the performances of the turbo-assisted solar air heater. By combining theoretical and experimental approaches this thesis establishes the framework for the development, design, optimization, and operation of the innovative technology proposed, opening the possibility to its application to several industrial sectors.
