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- Modeling the deactivation of CaO-based sorbents during multiple Ca-looping cycles for CO2 post-combustion capturePublication . Abreu, Miguel; Teixeira, Paula; Filipe, Rui; Domingues, Luís; Pinheiro, Carla; Matos, Henrique A.A novel model is presented for the estimation of natural CaO-based sorbents carbonation reactivity decay during Calcium Looping carbonation-calcination cycles. The model consists of a cyclic framework of two sub-models, the Overlapping Grain Model and the novel proposed modified Rate Theory for the Pore Size Distribution model. The model was implemented in gPROMS ModelBuilder (R) and parameter estimation was used for model validation using experimental data from three CaO-based sorbent precursors. The carbonation profile for the three sorbents was simulated with average deviations under 5%. The calcination sub-model predicted the evolution of total porous volume and total surface area for the calcination and sintering of dolomite, with an error of 3%. The cyclic framework successfully predicted the carbonation behavior of dolomite for 20 carbonation-calcination cycles. The model can be used for other CaO-based sorbents and the flexible modular structure allows the integration of other modules or approaches.
- Multi-scale modelling and simulation of Ca-looping cycle process for CO2 post-combustion capturePublication . Pinheiro, Carla; Filipe, Rui; Torres, Miguel Abreu; Silva, João; Matos, Henrique A.The present work focuses on one of the more promising new post-combustion technologies using calcium-based materials, known as the “Ca-looping cycle” process, which endeavors to scrub CO2 from flue gases and syngases by using natural lime-based sorbents and which appears to potentially offer limited CO2 capture costs. So, the major driving force is to improve overall efficiency, reduce the cost, and minimize adverse environmental impacts of post-combustion Ca-looping cycle CO2 capture, as compared to more conventional technologies (e.g., amine-based solvent scrubbing). There is a large energy penalty with amine scrubbing, the closest to market technology. The main objective of this work is to develop a first principles model to simulate different natural sorbents looping cycle performance in a fixed bed reactor laboratory scale system. A rigorous non-linear dynamic model of the looping cycle process was developed in gPROMS, based on the multiscale concept. The multiscale modeling is an emerging technique, where the characteristic length for each phenomena that occurs is taken into consideration, leading to a set of submodels with different scale lengths. These submodels when coupled together allow the simulation of a macrosystem (Hangos and Cameron, 2001). After the identification of the characteristic dimensions involved in the models, the first step is the development of a single particle model, which takes into account the energy and material transport, undergoing reactions (carbonation and calcination) and structural changes inside the particle. The material and heat transport inside the particle take into account the structural changes. Detailed models of single particle undergoing cycles of calcination and carbonation are developed. An improved decay approach is introduced in the model for those sorbents exhibiting carbonation decay with the number of cycles. The experimental characterization of the samples gave vital information on the physicochemical changes occurring during testing that need to be described in the model in the carbonation decay function. The conversion decay does not only depend on the number of cycles, but also on the conditions of the previous cycles, temperature, pressure, gas phase composition and characteristics of the material used for the carbonation. Model parameters are estimated from experimental results obtained for different sorbents tested (Santos et al., 2012)(Pinheiro et al., 2016). Several simulations for different sorbents and operating conditions were performed and the model was validated with experimental data obtained in a fixed bed reactor. It was also important to ensure that the model is numerically stable within a large range of values.
- Analysis of integrated calcium looping alternatives in a cement plantPublication . Amorim, Ana; Filipe, Rui; Matos, Henrique A.Calcium looping is a promising post-combustion CO2 capturing technology, highly compatible with the cement industry, one of the major industrial sources of CO2 emissions. Limestone, a raw material for clinker, forms lime, a calcium looping adsorbent. Thus, it is possible to maximize the synergies between a cement plant and a calcium looping unit by establishing an integrated configuration. Nevertheless, the integration of calcium looping in cement plants has not yet been thoroughly studied. This study examines different integration alternatives, developing models for the preheater and calciner using Aspen Plus, validated with operational data, alongside an entrained-flow carbonator model considering adsorbent deactivation. By combining these models, six integrated configurations are proposed and compared with the tail-end calcium looping configuration. The integrated configurations show a reduction in fuel consumption and net energy consumption for the same CO2 avoided emissions. The most promising configuration was identified and a comparative techno-economic analysis was conducted.