Combined Cycle Power Plants with Chemical Looping Combustion

Abstract

The objective of this work is to study the dynamics of process configurations of combined cycle power plants with chemical looping combustion for CO₂ capture. The focus of this presentation is on plants that operate within uncertain/variable market power demand, which is the source of many challenges in the everyday operation of power plants. The fluctuation in power demand is the result of a number of external factors related to the time of day, the time of the year, the power plant location with regards to the surrounding use of competitive renewable energy sources and the overall market. Nonetheless, the real-time power demand in the United States is forecasted on a minute to minute basis by the Federal Energy Regulatory Commission (FERC), as shown for a given day in New England in Figure 1. Therefore, an opportunity exists for modern power plants to take advantage of model-based approaches for optimization and system design, within environmental constraints. In order to remain competitive in the future, power plants need to operate dynamically while capturing CO₂ at a minimal cost and energy penalty. The methodology proposed herein uses dynamic models of natural gas-fired, combined cycle power plants and chemical-looping for the combustion of the fuel with inexpensive CO₂ capture.

Figure 1: Forecasted Power Demand for a Given Day in New England from FERC

The increasing rate of CO₂ emissions from fossil fuel combustion draws urgency to the development of alternative and sustainable sources of energy [1,2]. While the implementation of alternative energy sources is ongoing, the slow rate of adoption leaves fossil fuels to remain the world leader in energy production for some time. The most practical solution to reduce anthropogenic CO₂ emissions in the short term is to deploy Carbon Capture and Storage (CCS) strategies [3]. Chemical-looping combustion (CLC) has emerged as one of the most promising, low-cost CCS technologies, [4-6] with the potential to reduce the cost of CO₂ capture by 50% [7]. Chemical looping is a two-step technology for the oxidation of fossil fuels in the absence of nitrogen, which results in a stream of CO₂ ready for sequestration. The two steps of chemical looping comprise the cyclic reduction and oxidation of a metallic oxygen carrier.

Figure 2 shows the structure of the integrated CLC combined-cycle power plant examined in this work. The CLC oxidizer replaces the traditional gas turbine combustion chamber of a conventional Brayton cycle, while the heat released during the CLC reduction step is used for heat recuperation within the plant. The exhaust heat of the gas turbine is used in a reheat Rankine cycle downstream to improve the overall efficiency of the plant. The power plant shown in Figure 2 was simulated in Dymola [8], using the Modelica [9] language. Several scenarios of varying fuel loads were simulated and the performance of the integrated plant was explored.

Figure 2: Combined cycle power plant with chemical-looping combustion

In summary, a combined cycle power plant with integrated for CO₂ capture using was simulated for various scenarios of variable market power demand. A proof of concept analysis of the dynamic model adjusting the fuel load based on predicted power demand will be presented. The overall efficiency of the plant was estimated under various scenarios. An analysis of the cost of capturing CO₂ in natural gas fired power plants will be presented and discussed. An outlook of the use of model-based approaches in modern power plants will be discussed.

Acknowledgements: This material is based upon work supported by the National Science Foundation under Grant No. 1054718.

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