Conference Dates

May 22-27, 2016


Application of fluidized beds to collection and thermal storage of solar radiation is beneficial in Concentrated Solar Power (CSP) systems thanks to their well-known inherently good thermal performances. Non-conventional design and operation of fluidized beds based on uneven or unsteady (pulsed) fluidization (1), may further enhance their thermal performances improving the potential for applications in the very demanding CSP systems. Dense gas-fluidized beds have the potential to effectively accomplish three complementary tasks: the collection of incident solar radiation; the heat transfer of the incident power to immersed tube bundles of high-efficiency steam and/or organic Rankine cycles (ORC) and the thermal energy storage equalizing the inherent time-variability of the incident radiation for stationary CHP generation. A novel concept of solar receiver for CHP (combined heat and power) generation consisting of a compartmented dense gas fluidized bed has been proposed (2). The present study addresses the hydrodynamics of a dense gas-fluidized bed operated at ambient conditions and equipped with a compartmented windbox. Figure 1 outlines the experimental apparatus which consists of a nearly-2D fluidization column (2850x1860x200mm) equipped with two sparger-type gas distributors extending along 20 and 80% of the fluidized bed width. The regions of the bed above the two spargers were marked as compartments A and NA, respectively. The bed material was fine silica sand with a mean Sauter diameter of 145 µm. A pressure measurement system was used to monitor pressures and pressure gradients at different locations inside the fluidized bed. A pressure gradient exceeding a threshold of 0.11mbar/mm was assumed to mark the onset of local fluidization. A procedure was developed to draw the separation boundary (dashed line) between fluidized and non-fluidized regions for different bed heights (0.55, 0.95, 1.39 and 1.85m) as the gas superficial velocity was varied in either regions of the bed (UA and UNA=0-4Umf). Selected fluidization maps are shown in figure 2 where separation boundaries at different values of UA and UNA for a static bed height of 1.85 are reported. Figure 3 reports the fractional extension of the fluidized region at a level of 400mm for different values of UA e UNA as the static bed height was varied. Results indicate that a perfectly compartmented fluidized bed cannot be obtained simply using a compartmented windbox, but a proper choice of the operating conditions enables good control of the local fluidization conditions and of the gas cross-flow between the compartments.

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