317103 Peaking Power With 100% CO2 Capture Through the Integration of Solid-Oxide Fuel Cells, Compressed Air Energy Storage and Real Time Optimization
In recent years, sustainable production of environmentally friendly electricity has become a major topic of discussion and research worldwide. One promising technology is the solid-oxide fuel cell (SOFC) power generation system [1]-[4]. An SOFC utilizes a carbonaceous fuel gas (synthesis gas, for example) and an oxidant (typically air) to efficiently produce electrical power through an electrochemical reaction across a solid oxide barrier. There are key advantages to using SOFCs for power production. For example, the anode exhaust is mainly H2O and CO2, which are easily separated if the anode and cathode streams are not mixed downstream, and the cathode exhaust is mostly N2, which can be used for additional power generation or heat recovery and then safely vented. However, a significant disadvantage of the SOFC system is that there are currently cost-prohibitive operational challenges associated with its dynamic use, which limits the usefulness of an SOFC system for following a typical diurnal demand profile for electrical power.
This work extends on the design of a natural gas-fuelled SOFC system for base load power production with a compressed air energy storage (CAES) plant for load-following capabilities described by Nease and Adams (2013) [5]. Real-time optimization (RTO) is used to improve load-following performance by minimizing the squared error between supply and demand over dynamic simulations of up to one year of operation. The RTO scheme uses real demand data available from the Independent Electricity Operator of Ontario (IESO) to avoid sudden drop-offs in performance of the SOFC/CAES plant stemming from system (such as stream flows) and compressed air storage (such as minimum/maximum storage pressures) constraints. The effect of prediction horizon on the RTO scheme's ability to improve load-following is investigated. Furthermore, real forecasting performance metrics from the IESO are used to incorporate realistic noise into the RTO predictions in order to quantify the effect of uncertainty on the load-following capabilities of the SOFC/CAES system. Calculations are performed using a combination of Aspen Plus v7.3 for pseudo steady-state model development and MATLAB for dynamic simulations.
Simulation results based on real market demand and pricing data show promising results for the SOFC/CAES system with regard to its ability to provide peaking power with 100% carbon capture at competitive market prices. The addition of CAES to a base-load SOFC plant provides significant load-following capabilities with relatively small penalties to efficiencies (1.1% HHV) and levelized costs of electricity (LCOE) (0.08-0.3 ¢ kW-1 h-1). Moreover, the addition of RTO to the SOFC/CAES plant reduces the sum of squared error (SSE) between plant supply and consumer demand by up to 68% when a realistic prediction horizon of 24 hours is used. Extending this prediction horizon further reduces SSE with diminishing marginal returns. The addition of pure random noise with a standard deviation of up to 10% does not have an adverse effect on load-following performance. However, consistent over- or under-prediction of demand causes significant increases in SSE due to error compounding (as much as a 100% increase over the case with no uncertainty). However, even under unrealistically high uncertainty conditions, the use of RTO still improves load-following by more than 50%. The integrated SOFC/CAES plant, with the addition of RTO, is hence a very exciting forward-looking energy strategy to provide affordable peaking power with zero CO2 emissions.
References
[3] Duan, L.; Yang, Y.; He, B.; Xu, G. Study on a novel solid oxide fuel cell/gas turbine hybrid cycle system with CO2 capture. Int. Journ. of Energy Res. 2012, 36, 139-152.
[4] Becker, W.L.; Braun, R.J.; Penev, M.; Melaina, M. Design and technoeconomic performance analysis of a 1 MW solid oxide fuel cell polygeneration system for combined production of heat, hydrogen, and power. Journal of Power Sources. 2012, 200, 34-44.
[5] Nease, J, Adams TA II. Systems for peaking power with 100% CO2 capture by integration of solid oxide fuel cells with compressed air energy storage. J. Power Sources. 2013; 228(15): 281-293.
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