Integration of a novel Chemical Looping Combustion reactor into a thermochemical energy storage system

Abstract

This study analyses the performance of a back-up power process that uses a novel chemical looping packed bed air reactor to oxidize a batch of reduced solids while heating high pressure flowing air. In this arrangement, the solids are slowly oxidized by a diffusionally-controlled flow of oxygen perpendicular to the main air flow, thus imposing very long oxidation times for all reacting particles. A decay in the thermal power output of the reactor can be expected with time due to the increasing resistance to O2 diffusion towards the unreacted oxygen carrier particles as the reaction progresses. In this work, integration of the dynamic system formed by the reactor and the power plant used to produce power from the exploitation of the variable thermal output of the reactor is investigated. Different case studies are assessed for decarbonization of energy production and storage of renewable energy. The reactor is rated at a maximum 50 MWth power output in all cases, employing iron- or nickel-based particles as oxygen carrier. A simplified model for mass and heat transfer in the proximity of the wall orifices allows the definition of operating windows and reactor dimensions. In the chosen case examples, each single reactor operates in discharge mode for around 4–5 h (depending on plant configuration) as a back-up power generator, heating up a compressed air stream up to ∼ 1000 °C and achieving an energy density between 816 and 2214 kWhth/m3. Gas turbines in recuperative, steam injected and combined cycle power plant architectures integrated in the novel chemical looping combustion (CLC) reactor are investigated. Cycle efficiencies up to 49% are calculated for systems that make use of a single reactor configuration and exploit the residual heat for power production through a organic Rankine cycle (ORC) bottomed system. A more flexible multi-reactor configuration is also investigated to address the unavoidable decay in power output during discharge and provide power output controllability. The levelized cost of electricity (LCOE) is estimated be comparable to system elements from the literature when H2 is used as reducing gas. The use of biogas to reduce the solids during the energy charge stage is found to be particularly advantageous, leading to LCOE values between ∼ 120 and 175 €/MWh for the reference reactor system using iron-based solids. This also allows achieving negative CO2 emissions if the captured CO2 generated during the reduction stage is stored.