Optimal design of combined cycle power plants with fixed‐bed chemical‐looping combustion reactors

Abstract

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Design and Scheduling of Semibatch Chemical-Looping Reactors

“…The CLC reactor is then again purged with inert gas, and the system restarts the cycle by repeating the reduction stage. As discussed in Chen and Bollas, all of the exhaust streams of the various CLC stages can be used for heat recuperation in the CLC reactor and the gas and steam turbines of the power plant. However, the stream that results in higher plant efficiency is the heat removal stream and that needs to be maximized in terms of total enthalpy produced per enthalpy of the fuel provided …”

“…This high-temperature air stream is expanded by the gas turbine of the combined cycle, while the other low-quality streams could be utilized by other components in the power generation system. Maximization of the heat removal stage enthalpy in the CLC island directly benefits the efficiency of the power plant (with which the CLC island is integrated) because it maximizes the power generation from the gas turbine, which is the highest efficiency component of a combined cycle power plant . The decision variables used for the optimization problem include the duration of the reduction stage, the time spent for the reduction/oxidation of each reactor moduleexpressed through time interval coefficients, the temperature and flow rate of the inlet air for heat removal and oxidation, and the oxygen carrier properties (e.g., active loading of the metal oxide), as summarized in Table .…”

“…The allowable ranges of the design variables of Table were as follows: 100 ≤ m ox (kg/s) ≤ 160; 350 ≤ m HR (kg/s) ≤ 470; 430 ≤ T in , ox (°C) ≤ 500; 480 ≤ T in , hr (°C) ≤ 550; 650 ≤ τ red (s) ≤ 760; 0 ≤ [ a , b ] (−) ≤ 1; and 20 ≤ ω(%) ≤ 40. In all the case studies discussed in the following sections, the oxygen carrier active weight content, ω, was found at the upper bound allowed, while the reduction stage time constant, τ red , was fixed to 730 s due to the scheduling pattern chosen for the CLC island …”

“…To address the issue of temperature gradients inside and at the outlet of the reactor, Spallina et al devised a control strategy balancing reduction and oxidation conditions so that the operation of fixed bed reactors can be tuned for integration with CC power plants. Furthermore, Chen et al , explored process intensification options for near-carbon-neutral, natural-gas-fueled combined cycle (CC) power plants, wherein the conventional combustor was replaced by a series of chemical-looping combustion (CLC) reactors. Dynamic modeling and optimization were deployed to design CLC–CC power plants with optimal configuration and performance, on the basis of validated reference power plant models. , …”

“…The advantages of a reverse-flow reactor concept were explored, first by reversing the flow direction of the feed in the fixed bed reactor undergoing oxygen carrier reduction . The design of integrating CLC–CC power plants was proven to be feasible by replacing the conventional combustor with a CLC island made up of a series of fixed bed reactors operating in parallel . In this work, a concept of a simulated moving bed (SMB) made up of multiple fixed bed reactors in cyclic arrangement is proposed for chemical-looping combustion.…”