Roberto Solimene

Directly irradiated fluidized bed reactors for thermochemical processing and energy storage: Application to calcium looping

Directly irradiated fluidized bed reactors are very promising in the context of concentrated solar power applications, as they can be operated at process temperatures high enough to perform thermochemical storage reactions with high energy density. Limestone calcination-carbonation is an appealing reaction for thermochemical storage applications due to the cheapness of the raw material, and the interesting value of the reaction enthalpy at fairly high process temperatures. Moreover, limestone calcination-carbonation is intensively studied in Calcium Looping (CaL) application for post combustion CO2 capture and sequestration. In this work, the dynamics of a directly irradiated 0.1 m ID fluidized bed reactor exposed to a 12 kWel simulated solar furnace is analyzed with specific reference to temperature distribution at the surface and in the bulk of the bed. Simulation of the solar radiation was performed through an array of three short arc Xe-lamps coupled with elliptical reflectors, yielding a peak flux of...

Power generation by Stirling engine during fluidized bed combustion of wood pellets

ABSTRACT A system consisting of a Stirling engine (SE) and a fluidized bed combustor (FBC) for combined heat and power (CHP) generation has been experimentally investigated. The heat generated by combustion of wood pellets is used as source for the SE that converts part of the thermal energy into mechanical and then electric energy. This system, having the heat exchanger of the SE located inside the sand bed of the FBC, presents several advantages: (1) very high bed-to-external surfaces heat exchange coefficients; (2) absence of fouling on the heat exchange surface due to the cleaning action exerted by the fluidized sand particles; and (3) FBCs are able to use a wide variety of biomass fuels. The FBC used in this investigation can develop a thermal power in the range 15–40 kW feeding wood pellets as fuel and changing fluidization conditions and fuel feeding rate. Bed operation temperature was varied in the range 750–850°C. The SE adopted is a γ-type with the heater in form of tube bundle. The performances of this integrated system have been assessed in terms of gaseous emissions and of SE efficiency varying the bed temperature and the pressure of SE working fluid. A mathematical model able to simulate the integration of the FBC with the SE for CHP generation has been developed to quantify the heat fluxes among the different components of the system.

Dynamic modeling of a solar receiver/thermal energy storage system based on a compartmented dense gas fluidized bed

Fluidized beds may be considered a promising option to collection and storage of thermal energy of solar radiation in Concentrated Solar Power (CSP) systems thanks to their excellent thermal properties in terms of bed-to-wall heat transfer coefficient and thermal diffusivity and to the possibility to operate at much higher temperature. A novel concept of solar receiver for combined heat and power (CHP) generation consisting of a compartmented dense gas fluidized bed has been proposed to effectively accomplish three complementary tasks: collection of incident solar radiation, heat transfer to the working fluid of the thermodynamic cycle and thermal energy storage. A dynamical model of the system laid the basis for optimizing collection of incident radiative power, heat transfer to the steam cycle, storage of energy as sensible heat of bed solids providing the ground for the basic design of a 700kWth demonstration CSP plant.

Controlling thermal properties of dense gas fluidized beds for concentrated solar power by internal and external solids circulation

Fluidization technology displays a long record of success stories, mostly related to applications to thermal and thermochemical processes, which are fostering extension to novel and relatively unexplored fields. Application of fluidized beds to collection and thermal storage of solar radiation in Concentrated Solar Power (CSP) is one of the most promising, a field which poses challenging issues and great opportunities to fluidization scientists and technologists. The potential of this growing field calls for reconsideration of some of the typical design and operation guidelines and criteria, with the goal of exploiting the inherently good thermal performances of gas-fluidized beds at their best. “Creative” and non-conventional design and operation of fluidized beds, like those based on internal and external solids circulation, may be beneficial to the enhancement of thermal diffusivity and surface-to-bed heat transfer, improving the potential for application in the very demanding context of CSP with thermal energy storage. This paper investigated: i) a fluidized bed configuration with an uneven distribution of the fluidizing gas to promote vortices in the scale of bed height (internal solids circulation); ii) a dual fluidized bed configuration characterized by an external solids circulation achieved by the operation of a riser and a bubbling fluidized bed. CFD simulations showed the hydrodynamics conditions under which the internal solids circulation was established. The hydrodynamic characterization of the external solids circulation was achieved by an experimental study carried out with different cold models. The dual fluidized bed system was optimized in terms of operating conditions and geometrical features of the connections between two fluidized beds.Fluidization technology displays a long record of success stories, mostly related to applications to thermal and thermochemical processes, which are fostering extension to novel and relatively unexplored fields. Application of fluidized beds to collection and thermal storage of solar radiation in Concentrated Solar Power (CSP) is one of the most promising, a field which poses challenging issues and great opportunities to fluidization scientists and technologists. The potential of this growing field calls for reconsideration of some of the typical design and operation guidelines and criteria, with the goal of exploiting the inherently good thermal performances of gas-fluidized beds at their best. “Creative” and non-conventional design and operation of fluidized beds, like those based on internal and external solids circulation, may be beneficial to the enhancement of thermal diffusivity and surface-to-bed heat transfer, improving the potential for application in the very demanding context of CSP with therm...