Design and Optimization of an Innovative Solid Oxide Fuel Cell-Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

Distributed power generation and cogeneration is an attractive way toward a more rational conversion of fuel and biofuel. The fuel cell-gas turbine hybrid cycles are emerging as the most promising candidates to achieve distributed generation with comparable or higher efficiency than large-scale power plants. The present contribution is devoted to the design and optimization of an innovative solid oxide fuel cell-gas turbine hybrid cycle for distributed generation at small power scale, typical of residential building applications. A 5kW planar SOFC module, operating at atmospheric pressure, is integrated with a micro gas turbine unit, including two radial turbines and one radial compressor, based on an inverted Brayton cycle. A thermodynamic optimization approach, coupled with system energy integration, is applied to evaluate several design options. The optimization results indicate the existence of optimal designs achieving exergy efficiency higher than 65%. Sensitivity analyses on the more influential parameters are carried out. The heat exchanger network design is performed for an optimal configuration and a complete system layout is proposed. An example of hybrid system integration in a common residential building is discussed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design & Optimisation of an Innovative Solid Oxide Fuel Cell – Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

Emanuele Facchinetti, Daniel Favrat, François Maréchal

An attractive way toward a more rational conversion of fuel and biofuel is the decentralized power generation and cogeneration. The fuel cell-gas turbine hybrid cycles are emerging as the most promising candidates to achieve in decentralized generation comparable or higher efficiency than in large scale power plants. The present contribution is devoted to the design and optimization of an innovative concept of small scale Solid Oxide Fuel Cell – Gas Turbine hybrid cycle for residential applications. A 5kW planar SOFC module, operating at atmospheric pressure, is integrated with a micro gas turbine unit, including two radial turbines and one radial compressor, based on an inverted Brayton cycle. A thermodynamic optimization approach, coupled with system energy integration, is applied to evaluate several design options. The optimization results indicate the existence of realistic optimal designs achieving exergy efficiency higher than 66%. Sensitivity analyses on the more sensible parameters are carried out. The heat exchanger network definition is performed for an optimal configuration and a system layout is proposed. The cogeneration performance of the system and its integration in common residential buildings are discussed.

Wiley-Blackwell2014

The role of process integration techniques in the thermo-economic optimization of energy conversion systems

François Maréchal, Laurence Tock

Within the goal of reducing greenhouse gas emissions and supplying sustainable energy, complex integrated energy conversion systems have to be designed by taking into account thermodynamic, economic and environmental considerations simultaneously. The process performance highly depends on the quality of the process integration and on the energy conversion, in particular, on how the heat requirements are balanced and how the combined heat and power generation is integrated. In chemical processes, the heat requirements after heat recovery are typically satisfied by the energy conversion system, while for fuel and electricity producing processes, the requirements are balanced by waste and process streams available on-site. The optimal internal heat recovery and utility integration can be computed by applying heat cascade models that are solved by using mathematical programming techniques. The mass and energy balances of the process unit operations are therefore satisfied by the optimal energy conversion system integration without having to explicitly model the heat exchanger network. The presented thermo-economic optimization approach combines flowsheeting and process integration techniques with economic evaluation and life-cycle assessment in a multi-objective optimization framework. The advantage of including the process integration model in the design process is that the influence of the process design and operation is reflected on the thermo-environomic performance of an energy balanced system in which the heat supplied from energy resources is integrated. The methodology has been successfully applied to study CO2 capture concepts in power plants using natural gas, coal or biomass resources, to analyse thermo-chemical H2 production processes and to evaluate different biofuel processes producing Fischer-Tropsch fuel, methanol, dimethylether and H2 by biomass gasification. The potential performance improvement through process integration is revealed for each case. In particular, it is highlighted how the optimization of the combined cycle valorizing the excess heat and of heat pumping options improve the process efficiency by simultaneously maximizing the combined production of fuel, captured CO2, heat and power. This shows that this computer-aided process design strategy combining flowsheeting, energy integration, cost assessment and multi-objective optimization is a powerful tool to systematically generate different process options, assess trade-offs and reveal process improvements through process integration.

2013

Thermo-economic Optimization of a Solid Oxide Fuel Cell, Gas Turbine Hybrid System

Nordahl Autissier, Daniel Favrat, François Maréchal, Francesca Palazzi, Jan Van Herle

Large scale power production benefits from the high efficiency of gas-steam combined cycles. In the lower power range, fuel cells are a good candidate to combine with gas turbines. Such systems can achieve efficiencies exceeding 60%. High temperature Solid Oxide Fuel Cells (SOFC) offer good opportunities for this coupling. In this paper, a systematic method to select a design according to user specifications is presented. The most attractive configurations of this technology coupling are identified using a thermo-economic multi-objective optimization approach. The SOFC model includes detailed computation of losses of the electrodes and thermal management. The system is integrated using pinch based methods. A thermo- economic approach is then used to compute the integrated system performances, size and cost. This allows to perform the optimization of the system with regard to two objectives: minimize the specific cost and maximize the efficiency. Optimization results prove the existence of designs with costs from 2400

/kW for a 44% efficiency to 6700

/kW for a 70% efficiency. Several design options are analysed regarding, among others, fuel processing, pressure ratio or turbine inlet temperature. The model of a pressurized SOFC-microGT hybrid cycle combines a state-of- the-art planar SOFC with a high speed micro gas turbine sustained by air bearings.

2007