Thermal Integration of a Flexible Calcium Looping CO₂ Capture System in an Existing Back-Up Coal Power Plant

Abstract

The CO 2 capture from back-up power plants by making use of calcium looping systems combined with large piles of Ca-solids has been studied in this work. A flexible CO 2 capture system based on a concept described in a previous work has been integrated into an existing power plant by including a small oxyfired calciner (that represents just 8% of the total thermal capacity) to steadily regenerate the sorbent and a carbonator reactor following the back-up power plant operation periods to capture 90% of the CO 2 as CaCO 3 and two large piles of rich CaO and CaCO 3 solids stored at modest temperatures. When the back-up plant enters into operation, the calcined solids are brought into contact with the flue gases in the carbonator reactor; meanwhile, the oxy-calciner operates continuously at a steady state. In order to improve the flexibility of the CO 2 capture system and to minimize the increase of CO 2 capture costs associated with the additional new equipment used only during the brief back-up periods, we propose using the steam cycle of the existing power plant to recover a large fraction of the heat available from the streams leaving the carbonator. This makes it possible to maintain the electrical power output but reducing the thermal input to the power plant by 12% and thus the size of the associated CO 2 capture equipment. To generate the auxiliary power required for the oxy-calciner block, a small steam cycle is designed by integrating the waste heat from the streams leaving this reactor. By solving the mass and heat balances and proposing a feasible thermal integration scheme by using Aspen Hysys, it has been calculated that the CO 2 emitted by long-amortized power plants operated as back-up can be captured with a net efficiency of 28%.

Part-Load Operation of a Novel Calcium Looping System for Flexible CO2 Capture in Coal-Fired Power Plants

“…Despite the reduced heat duty, the calciner has shown to guarantee stable operation at all investigated carbonator loads, both in terms of off-gas compositions (see Figure ) and hydrodynamic conditions (see Figure ). The latter observations are in line with the conclusions drawn by Arias et al in a recent study, which characterized a flexible CaL system for the power sector with a high temperature sorbent storage . The authors postulated that the CaL calciner can be operated continuously in steady-state mode when the load-following power plant enters into operation.…”

“…The latter observations are in line with the conclusions drawn by Arias et al in a recent study, which characterized a flexible CaL system for the power sector with a high temperature sorbent storage. 46 The authors postulated that the CaL calciner can be operated continuously in steady-state mode when the loadfollowing power plant enters into operation. Furthermore, the resulting decrease in oxygen flow required to burn supplementary fuel at part-load conditions can be compensated by recirculated flue gas to maintain constant solid entrainment (i.e., gas superficial velocity) in the calciner.…”

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

“…734 The calcium looping process can be designed flexibly such that it is suitable for the CO 2 capture from power plants with large load fluctuations. 735,736 The economic attractiveness of the calcium looping process (or oxide/ carbonate looping processes in general) increases further if (besides CO 2 capture) products are generated that have a certain value, e.g., hydrogen (sorption-enhanced reforming or water−gas shift) 737−746 or thermal energy (thermochemical energy storage), 747−756 and may therefore accelerate the implementation at the industrial scale (see section 6.4). What is certainly missing currently for high-temperature CO 2 capture applications in general are demonstration units that prove that the different processes employing metal oxide sorbents for CO 2 work reliably at the industrial scale.…”

CO2 capture using solid sorbents: Fundamental aspects, mechanistic insights and recent advances

“…the cement industry [40], [637]- [643], even though current prices of CO2 are low [644]. The calcium looping process can be designed flexibly such that it is suitable for the CO2 capture from power plants with large load fluctuations [645], [646]. The economic attractiveness of the calcium looping process increases further if (besides CO2 capture) products are generated that have a certain value, e.g.…”