(180g) Analysis and Multi-Objective Optimization of Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle

Chemical process optimization problems often have multiple and conflicting objectives, such as profit, capital cost, operating cost, production cost, energy consumptions, environmental impacts and safety. In such cases, Multi-Objective Optimization (MOO) is useful in finding many optimal solutions, to understand the quantitative trade-offs among the objectives, and also to obtain the optimal values of decision variables. Natural gas, syngas or biogas can be converted into power, heat and electricity, using combustion engine, gas turbine or Solid Oxide Fuel Cell (SOFC). SOFC with Gas Turbine (GT) has shown higher thermodynamic performance, due to better heat integration. Hence, this hybrid conversion system leads to better utilization of natural resource, reduced environmental impacts, and more profit.

SOFC-GT system is divided into five sub-systems: (1) fuel processing using steam reformer, (2) SOFC, (3) anodic GT, (4) cathodic GT, and (5) CO₂ compression. The unconverted fuel from the anodic side of SOFC is combusted in a burner, and then it is used in anodic GT to produce electricity. The SOFC-GT has been simulated in BELSIM-Vali (version 4.7.0.3) flowsheeting software. This study optimizes performance of SOFC-GT system for minimization of both levelized electricity cost and annualized capital cost per kWh, simultaneously. The MOO problem has 12 decision variables, from all five sub-systems of SOFC-GT. The MOO of SOFC-GT system is performed using OSMOSE, which has four integrated parts: (1) stochastic MOO program which provides the values of decision variables, (2) to pass values of decision variables to BELSIM Vali for simulating SOFC-GT system, (3) to obtain temperatures and flow rates of important streams from BELSIM Vali and perform heat integration, and (4) performance evaluation or calculations of objective functions for SOFC-GT system. For optimal SOFC-GT designs, the composite curves for maximum amount of possible heat recovery indicate good performance of the system, and the optimal designs do not require any external hot utility. The SOFC-GT system separate the CO₂, which can be stored and used in other applications. Finally, first law energy and exergy efficiencies of optimal SOFC-GT system are significantly better compared to other conversion systems. The results of this study will be presented at 2016 AIChE Annual Meeting.

Keywords:

Multi-Objective Optimization, Solid Oxide Fuel Cell, Gas Turbine, Heat Integration.

References:

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