Techno-energy-economic sensitivity analysis of hybrid system Solid Oxide Fuel Cell/Gas Turbine

Abstract

The paper presents a wide and deep analysis of the techno-energy and economic performance of a Solid Oxide Fuel Cell/Gas Turbine hybrid system fed by gas at different compositions of H2, CO, H2O, CO2, CH4, and N2. The layout of the system accounts for pressurizing of entering fluids, heat up to the set Solid Oxide Fuel Cell inlet conditions, Solid Oxide Fuel Cell thermo-electrochemical processing, Solid Oxide Fuel Cell—exhaust fluids combustion, turboexpansion after heat up, and final recovery unit for cogeneration purposes. An ad hoc numerical modeling is developed and then run in a Matlab calculation environment. The influence on the system is evaluated by investigating the change of the fuel composition, and by managing the main operating parameters such as pressure and the fuel utilization factor. The analysis reports on the specific mass flowrates necessary to the purpose required, by assessing the SOFC outlet molar compositions, specific energies (work) at main system elements, specific thermal energies at main system elements, energy and technical performance for Solid Oxide Fuel Cell energy unit; the performance such as electric and thermal efficiency, temperatures at main system elements. A final sensitivity analysis on the performance, Levelized Cost of Energy and Primary Energy Saving, is made for completion. The first simulation campaign is carried out on a variable anodic mixture composed of H2, CO, H2O, considering the H2/CO ratio variable within the range 0.5-14, and H2O molar fraction variable in the range 0.1-0.4; used to approach a possible syngas in which they are significantly high compared to other possible compounds. While other simulation campaigns are conducted on real syngases, produced by biomass gasification. The overall Solid Oxide Fuel Cell/Gas Turbine system showed a very promising electric efficiency, ranging from 53 to 63%, a thermal efficiency of about 37%, an LCOE ranging from 0.09 to 0.14 $-kWh-1, and a Primary Energy Saving in the range of 33-52%, which resulted to be highly affected by the H2/CO ratio. Also, real syngases at high H2/CO ratio are noticed as the highest quality, revealing electric efficiency higher than 60%. Syngases with methane presence also revealed good performance, according to the fuel processing of methane itself to hydrogen. Low-quality syngases revealed electric efficiencies of about 51%. Levelized Cost of Energy varied from 0.09 (for high-quality gas) to 0.19 (for low-quality gas) $-kWh-1, while Primary Energy Saving ranged from 44 to 52%.