Design and Experimental Testing of a 1.9MWth Calcium Looping Pilot Plant

Assessing CO2 sources and sinks in and around Taiwan: Implication for achieving regional carbon neutrality by 2050

Taiwan has pledged to achieve net-zero carbon emissions by 2050, but the current extent of carbon sinks in Taiwan remains unclear. Therefore, this study aims to first review the existing nature-based carbon sinks on land and in the oceans around Taiwan. Subsequently, we suggest potential strategies to reduce CO2 emissions and propose carbon dioxide removal methods (CDRs). The natural carbon sinks by forests, sediments, and oceans in and around Taiwan are approximately 21.5, 42.1, and 96.8 Mt-CO2 y-1, respectively, which is significantly less than Taiwan's CO2 emissions (280 Mt-CO2 y-1). Taiwan must consider decarbonization strategies like using electric vehicles, renewable energy, and hydrogen energy by formulating enabling policies. Besides more precisely assessing both terrestrial and marine carbon sinks, Taiwan should develop novel CDRs such as bioenergy with carbon capture and storage, afforestation, reforestation, biochar, seaweed cultivation, and ocean alkalinity enhancement, to reach carbon neutrality by 2050.

Carbon capture for decarbonisation of energy-intensive industries: a comparative review of techno-economic feasibility of solid looping cycles

Carbon capture and storage will play a crucial role in industrial decarbonisation. However, the current literature presents a large variability in the techno-economic feasibility of CO2 capture technologies. Consequently, reliable pathways for carbon capture deployment in energy-intensive industries are still missing. This work provides a comprehensive review of the state-of-the-art CO2 capture technologies for decarbonisation of the iron and steel, cement, petroleum refining, and pulp and paper industries. Amine scrubbing was shown to be the least feasible option, resulting in the average avoided CO2 cost of between $$62.7\;\mathrm{C}\!\!\!\!{\scriptstyle{{}^=}\,} \cdot {\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}^{\;\;\;\;\;\;\;\; - 1}$$ for the pulp and paper and $$104.6\;\mathrm{C}\!\!\!\!{\scriptstyle{{}^=}\,} \cdot {\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}^{\;\;\;\;\;\;\;\; - 1}$$ for the iron and steel industry. Its average equivalent energy requirement varied between 2.7 (iron and steel) and $$5.1\;\;{\rm{M}}{{\rm{J}}_{{\rm{th}}}} \cdot {\rm{kg}}_{{\rm{C}}{{\rm{O}}_2}}^{\;\;\;\;\;\;\;\; - 1}$$ (cement). Retrofits of emerging calcium looping were shown to improve the overall viability of CO2 capture for industrial decarbonisation. Calcium looping was shown to result in the average avoided CO2 cost of between 32.7 (iron and steel) and $$42.9\;\mathrm{C}\!\!\!\!{\scriptstyle{{}^=}\,} \cdot {\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}^{\;\;\;\;\;\;\;\; - 1}$$ (cement). Its average equivalent energy requirement varied between 2.0 (iron and steel) and $$3.7\;\;{\rm{M}}{{\rm{J}}_{{\rm{th}}}} \cdot {\rm{kg}}_{{\rm{C}}{{\rm{O}}_2}}^{\;\;\;\;\;\;\;\; - 1}$$ (pulp and paper). Such performance demonstrated the superiority of calcium looping for industrial decarbonisation. Further work should focus on standardising the techno-economic assessment of technologies for industrial decarbonisation.

Development of Thermochemical Heat Storage Based on CaO/CaCO3 Cycles: A Review

Due to the inconsistency and intermittence of solar energy, concentrated solar power (CSP) cannot stably transmit energy to the grid. Heat storage can maximize the availability of CSP plants. Especially, thermochemical heat storage (TCHS) based on CaO/CaCO3 cycles has broad application prospects due to many advantages, such as high heat storage density, high exothermic temperature, low energy loss, low material price, and good coupling with CSP plants. This paper provided a comprehensive outlook on the integrated system of CaO/CaCO3 heat storage, advanced reactor design, heat storage conditions, as well as the performance of CaO-based materials. The challenges and opportunities faced by current research were discussed, and suggestions for future research and development directions of CaO/CaCO3 heat storage were briefly put forward.

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

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

Calcium Looping: On the Positive Influence of SO2 and the Negative Influence of H2O on CO2 Capture by Metamorphosed Limestone-Derived Sorbents

The CO₂ capture performance of sorbents derived from three distinct limestones, including a metamorphosed limestone, is studied under conditions relevant for calcium looping CO₂ capture from power plant flue gas. The combined and individual influence of flue gas H₂O and SO₂ content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO₄ accumulation on the sorbents' capture performance were examined using bubbling fluidized bed reactor systems. The metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H₂O negatively influences CO₂ capture performance, while limited sulfation can positively influence CO₂ capture, with space time significantly impacting CO₂ and SO₂ co-capture performance. The morphological characteristics influencing sorbents' capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented. This insight into the morphology responsible for metamorphosed limestone-derived sorbent's anomalous capture behavior can guide future sorbent selection and design efforts.

CO2 Capture, Use, and Storage in the Cement Industry: State of the Art and Expectations

The implementation of carbon capture, use, and storage in the cement industry is a necessity, not an option, if the climate targets are to be met. Although no capture technology has reached commercial scale demonstration in the cement sector yet, much progress has been made in the last decade. This work intends to provide a general overview of the CO2 capture technologies that have been evaluated so far in the cement industry at the pilot scale, and also about the current plans for future commercial demonstration.

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

The CO₂ 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 CO₂ capture system based on a concept described in a previous work has been integrated into an existing power plant by including a small oxy-fired 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 CO₂ as CaCO₃ and two large piles of rich CaO and CaCO₃ 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 CO₂ capture system and to minimize the increase of CO₂ 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 CO₂ 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 CO₂ emitted by long-amortized power plants operated as back-up can be captured with a net efficiency of 28%.

Kinetics of Solid-Gas Reactions and Their Application to Carbonate Looping Systems

Reaction kinetics is an important field of study in chemical engineering to translate laboratory-scale studies to large-scale reactor conditions. The procedures used to determine kinetic parameters (activation energy, pre-exponential factor and the reaction model) include model-fitting, model-free and generalized methods, which have been extensively used in published literature to model solid-gas reactions. A comprehensive review of kinetic analysis methods will be presented using the example of carbonate looping, an important process applied to thermochemical energy storage and carbon capture technologies. The kinetic parameters obtained by different methods for both the calcination and carbonation reactions are compared. The experimental conditions, material properties and the kinetic method are found to strongly influence the kinetic parameters and recommendations are provided for the analysis of both reactions. Of the methods, isoconversional techniques are encouraged to arrive at non-mechanistic parameters for calcination, while for carbonation, material characterization is recommended before choosing a specific kinetic analysis method.

Characterization of a Marl-Type Cement Raw Meal as CO2 Sorbent for Calcium Looping

The use of cement raw meals as sorbent precursors for CO₂ capture can reinforce the synergies between the cement production process and calcium looping CO₂ capture technology. In this work, we measure the CO₂-carrying capacity of different calcined samples of a particular marl, which were obtained under very different calcination conditions and setups (a thermogravimetric analyzer, a drop tube furnace, and an industrial calciner). We find that the reactivity toward CO₂ of these calcined materials displays a strong sensitivity to the calcination conditions, in particular to calcination time. A pronounced competition between the belite (Ca₂SiO₄) formation reaction and the formation of free CaO needed for CO₂ capture is detected. As the calcination of the raw meal approaches flash conditions (i.e., >90% calcination conversion in less than 10 s), the belite formation is shown to be minimized, leading to sorbents with CO₂-carrying capacities of approximately 0.4 mol CO₂/mol CaO.