Fabio Serra

Experimental investigation of a packed bed thermal energy storage system

In this work experimental investigations on a thermal energy storage system with a solid material as storage media and air as heat transfer fluid will be presented. The experimental test rig, installed at the DIMCM of the University of Cagliari, consists of a carbon steel tank filled with freely poured alumina beads that allows investigations of heat transfer phenomena in packed beds. The aim of this work is to show the influence of the operating conditions and physical parameters on thermocline formation and, in particular, the thermal behaviour of the thermal energy storage for repeated charging and discharging cycles. Better charging efficiency is obtained for lower values of mass flow rate and maximum air temperature and for increasing aspect ratio. A decreasing influence of the metal wall with continuous operation is also highlighted. In conclusion, the analysis focuses on the thermal hysteresis phenomenon, which causes degradation of the thermocline and the reduction of the energy that can be stored by the accumulator as the repeated number of cycles increases.

Fixed-Bed Coal Gasifiers Integrated With MCFC-GT Hybrid Systems for Distributed Power and Heat Generation

In this paper, a performance assessment of coal gasification processes integrated with molten carbonate fuel cells (IG-MCFC) is reported on. The main aim of the study was to evaluate the performance of small and medium size IG-MCFC systems based on fixed-bed gasifiers for distributed power and heat generation. In particular, the plant configuration considered here was developed on the basis of the 700 kg/h fixed-bed up-draft coal gasifier located in the Sotacarbo Research Centre in Carbonia, Italy. The MCFC section is based on the DFC/T® hybrid system developed by FCE Inc., and includes a MCFC stack integrated with an indirectly heated gas turbine. Two different coals, namely a low and a high sulphur coal, were considered. Moreover, the performance of MCFC hybrid systems fuelled by natural gas and coal gas were also compared. The results of the performance assessment show that the optimum value of the gas turbine pressure ratio is around 3, which is very similar to that used by the DFC/T systems proposed by FCE Inc. and fuelled by natural gas. However, replacing methane with coal gases leads to a significant decrease in MCFC efficiency, on the order of 10–11 percentage points. On the whole, the performance assessment carried out in this paper demonstrates that IG-MCFC systems could be an interesting option for small- and medium-size power generation plants fuelled by coal as they can reach efficiencies of nearly 40%.Copyright

Energy and Cost Analysis of Small Size CHP Coal Gasification Plants Integrated With Syngas Storage Systems

This study evaluates the load modulation capabilities of small and medium size CHP systems based on integrated coal gasification and syngas storage (ICGSS) power plants. ICGSS systems can perform a load-following service since a portion of the produced syngas is stored during periods of low energy demand and used to increase power output during periods of peaking demand. In particular, the main energy and economic performance of ICGSS power generation plants were evaluated with reference to three different prime movers (gas turbines, internal combustion engines and hybrid fuel cell systems) and as a function of the required electrical load curve. Moreover, a preliminary economic analysis was also carried out to evaluate the energy production cost in comparison with base-load energy production cost.The results of the study show that ICGSS power plants offer considerable scope for enhancing operating flexibility and load modulation capabilities of CHP systems based on coal gasification. In comparison to coal gasification power plants designed to produce only base-load energy, ICGSS systems require a more powerful prime mover and a larger coal gasification section. In the field of duty-cycles of more likely interest, the coal gasification section needs to be enlarged by 5–50% and a fraction from 2% to 16% of the produced syngas needs to be stored. ICGSS plants based on hybrid fuel cells performed better in terms of electrical efficiency. Moreover, with respect to the corresponding base-load systems, electrical efficiency decreases by about 2–3 percentage points for ICGSS-GT and ICGSS-ICE, while it increases by about 1–2 percentage points for ICGSS-HFC. Finally, syngas storage can reduce energy costs in CHP systems, especially in the case high peaking electricity requirements, large useful heat productions and by using ICGSS based on ICE as prime movers.Copyright