276235 Concentrated Solar Energy Combined with Thermal Storage for 24/7 Operation of a High-Temperature Thermochemical Process

Monday, October 29, 2012: 4:30 PM
305 (Convention Center )
Anna S. Wallerand1, Zoran R. Jovanovic2 and Aldo Steinfeld1,3, (1)Department of Mechanical and Process Engineering, ETH Zürich, Zürich, Switzerland, (2)Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland, (3)Solar Technology Laboratory, Paul Scherrer Institute, Villigen, Switzerland

A concept of a high-temperature endothermal chemical reactor is modelled to assess its 24/7 operation utilizing concentrated solar energy as the source of process heat.  The concept is based on three main constituents: a concentrating solar tower system with high-temperature receiver, a thermal storage unit, and an endothermal chemical reactor. In this work, the chemical reactor is represented by an allothermal fluidized bed producing syngas via coal gasification with steam.

During daytime, absorbed heat is transferred to air flowing through a structured volumetric receiver exposed to concentrated solar radiation.  The hot air is split into two streams. One stream charges a thermal storage unit envisioned as a packed bed of spherical ceramic particles; the other stream is passed directly through a multitude of heat exchanger tubes immersed in the fluidized bed gasifier.  At night, cold air is heated by flowing through the packing in the thermal storage prior to being passed through the reactor heat exchanger tubes, thereby assuring 24/7 operation of the coal gasification and uninterrupted production of syngas.

The governing steady-state and transient mass and energy conservation equations are formulated and solved numerically for a 1 MW gasifier.  The system is examined in terms of the dimensions of the constituent components (storage/reactor volume, area of heliostat field), the influence of specific design parameters (heat transfer coefficients), its overall response to seasonal and daily variations in solar irradiance, scale-up potential (10, 50 MW), material strains (volumetric expansion due to high temperature differences), and the overall solar to chemical/electrical efficiencies.

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