مدل شبیه سازی از مذاب کربنات در سوخت سلولی میکرو توربین و سیستم های هیبریدی

A Hybrid System based on High Temperature Fuel Cells coupled to a Microturbine allows a high efficiency, low environmental pollution and it may be exploited as a CHP System producing heat and electricity both Grid Connected and Stand Alone; the overall electrical efficiency could reach a very high value (up to 60%) and total efficiency could be over 70% including the contribution due to heat recovery. In the context of wide research activities of ENEA on High Temperature Fuel Cells and Hybrid Systems – that involve materials, system BoP and fuels – a very great effort has been devoted to design and build, in the ENEA Research Centre of “Casaccia”, an experimental Test-Rig based on a Molten Carbonate Fuel Cells Emulator and a Microturbine, to evaluate components performance characteristics at different operating conditions. To obtain relevant and reliable data and to compare them to the future experimental test results, a careful numerical simulation analysis of an Hybrid System has been developed by the Authors and it is presented in this Article. The numerical models of the System components were implemented in IPSE Pro™; the performance characteristics have been derived by evaluating operational parameters at nominal and partial loads and, moreover, a sensitivity analysis – varying main working parameters – has been performed on steady state conditions. The simulations show in detail the behaviour of both the Hybrid System and the Subsystems varying the main parameters (output electrical power, inlet flow rates, working pressure, power density, etc.) including rotational speed configuration of Microturbine.

Fuel Cells are electrochemical devices suitable to direct conversion of chemical energy in electricity, with high efficiency and low pollution emissions. Among different Fuel Cells Technologies, High Temperature Fuel Cells (HTFC) operate from 600 °C to 1000 °C with more than 45% of electrical efficiency, also at partial load conditions; even when the contribution of thermal recovery is included the overall efficiency can be over 70% [1], [2] and [3]. A pressurized HTFC System allows the direct coupling with a Microturbine (μGT): it is a small gas turbine (some inches of diameter) which can drive an electric generator with a rated capacity of 25–200 kW and net efficiency typically about 25–30%, rotating at very high speed (about 100,000 rpm). Microturbines are very important for a distributed production of electricity and heat because, like HTFC Systems, they may operate on site, allowing also a general reduction of electrical transmission losses [4]. By coupling a Fuel Cell System and a Microturbine we can obtain a new Energy System which presents very high electrical efficiency with a strong reduction of pollution. The performance of an HTFC–μGT System is better than a simple HTFC System or a Gas/Steam Turbine Combined System; then, the effect of the high cost of a simple HTFC system can be mitigated and a Hybrid System (HS) can be more competitive, compared to other kinds of power plants. Therefore, the coupling between Microturbines and Fuel Cells is very interesting.

The paper deals with a Molten Carbonate Fuel Cells–Microturbine Hybrid System simulation, in the context of a wide research activity of ENEA on HTFC Systems; a numerical model has been implemented by using IPSE Pro 3.1 and detailed simulations have been conducted to provide a reliable analysis in order to evaluate the system performance. Each single model of devices and the whole system were duly validated by comparing literature data; the reliability of the whole simulation code has been validated also making a thorough sensitivity analysis. The behaviour of the components and of the HS shown by the numerical simulations is in accordance to the quoted papers; therefore, appropriate simplifications were introduced and moreover, in this work, cells electric resistance are well approximated with Ohm’s law. The steady state simulation of the Hybrid System shown that the efficiency both of the Electrochemical Unit and of the whole Hybrid System can be higher than that of gas–steam turbine conventional power plant. Indeed, at nominal load, the HS yield is about 135 kW of electric power (22 kW from Bottoming Cycle) while about 100 kW are available as thermal power and they can be recovered by thermal cogeneration; finally, the rate between the output electric energy and the inlet chemical energy of fuel is close to 60%. This result is well shared in literature and it is very interesting in relation to a possible commercial development of such CHP systems for distributed generation of electricity and heat. The result is also considerable for the choice of the Microturbine and it is also very important for the study of Microturbine by Emulator. Moreover, the simulation shows that pressure losses into reactors and into the piping must be minimized as much as possible.