Influence of Fluidised Bed Inventory on the Performance of Limestone Sorbent in Calcium Looping for Thermochemical Energy Storage

Abstract

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the “closed-loop” scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration).

Modeling of an Autothermal Process for Integrated Carbon Dioxide Capture and Methanation by Magnesium Looping (MgO/MgCO3) and Renewable Hydrogen

“…Finer and lighter particles featuring smaller terminal and fluidization velocities can indeed be transported to the reactor exit or segregated to the top of a fluidized bed. This allows selective particle circulation between the reactors R 1 and R 2 . − Alternatively, the catalyst could be anchored to reactor internal surfaces/walls, or packed-fluidized bed (i.e., confined fluidization) could be exploited to fluidize smaller sorbent particles in the void of a packed catalyst . The CH 4 -rich stream exiting R 2 is sent in series to two heat exchangers, HX 3 and HX 4 .…”

Partial Separation of Carbonated Material to Improve the Efficiency of Calcium Looping for the Thermochemical Storage of Solar Energy

“…Two threshold scenarios (no and total separation) were evaluated to identify the maximum and minimum energy and size requirements. Moreover, the potential separation of the carbonated material was experimentally assessed by Tregambi et al [45] and Di Lauro et al [53]. The difference in the minimum fluidization velocity between the calcined and carbonated particles evidenced the possibility of a potential partial separation between more and less carbonated particles.…”

“…A less intense sintering effect occurs in limestone-only beds. The high operating temperatures under calcination and carbonation cycles increase thermal sintering, leading to higher particle density and lower reactive porosity [53]. Moreover, the lower the sorbent conversion, the greater the amount of inert material circulating in the system [54].…”

“…The results show the potential segregation of less carbonated particles that, having a lower density, are characterized by a lower minimum fluidization velocity and tend to segregate to the upper part of the bed (flotsam). On the contrary, the more carbonated particles, characterized by higher minimum fluidization velocities, tend to segregate to the bottom of the bed (jetsam) [53]. However, the energy and size requirements of the CaL TCES system with the potential partial separation of the carbonated material still need to be addressed.…”