Emerging CO2 Capture Research Articles

Bayesian Symbolic Learning to Build Analytical Correlations from Rigorous Process Simulations: Application to CO2 Capture Technologies.

Process modeling has become a fundamental tool to guide experimental work. Unfortunately, process models based on first principles can be expensive to develop and evaluate, and hard to use, particularly when convergence issues arise. This work proves that Bayesian symbolic learning can be applied to derive simple closed-form expressions from rigorous process simulations, streamlining the process modeling task and making process models more accessible to experimental groups. Compared to conventional surrogate models, our approach provides analytical expressions that are easier to communicate and manipulate algebraically to get insights into the process. We apply this method to synthetic data obtained from two basic CO2 capture processes simulated in Aspen HYSYS, identifying accurate simplified interpretable equations for key variables dictating the process economic and environmental performance. We then use these expressions to analyze the process variables' elasticities and benchmark an emerging CO2 capture process against the business as usual technology.

Study on the performance of CO2 capture from flue gas with ceramic and PTFE membrane contactors

Excessive CO2 emissions contribute to global warming, which may cause potential threat to survival of humans and other creatures, and it is necessary to take effective measures to curb CO2 emissions. Gas-liquid membrane contact CO2 separation technology is an emerging CO2 capture technology that combines advantages of membrane separation and chemical absorption. In this paper, differences of CO2 capture performance between ceramic and polytetrafluoroethylene (PTFE) membranes with pore size of 10 nm and 100 nm are investigated comprehensively. The morphological structure, pore size distribution, wettability and membrane flux of ceramic and PTFE membranes are analyzed by membrane characterization. Moreover, with monoethanolamine (MEA) as absorbent, CO2 capture performance under different operating parameters (e.g., absorber flow rate and temperature, gas flow rate and pressure) is investigated through experiments based on ceramic and PTFE membrane modules. The CO2 capture efficiency of ceramic and PTFE membrane is 94.7% and 99.3%, respectively. However, the mass transfer rate of ceramic membrane is much higher than that of PTFE membrane. The results show that ceramic membrane exhibits favorable CO2 capture performance under appropriate operation parameters. This paper will provide theoretical and technical references for subsequent industrial CO2 capture applications.

CO2 capture in existing power plants using second generation Ca-Looping systems firing biomass in the calciner

Abstract Calcium looping (CaL) is an emerging CO2 capture technology that uses high temperature circulating fluidized beds, CFB, with CaO particles as functional material and that can be retrofitted to existing power plants. Its similarity to existing CFB combustion technology has made it possible to demonstrate its feasibility at MW scale and to obtain an accurate estimation of its energy efficiency and cost. This work analyzes a novel CaL system that incorporates recent developments tested at large pilot scale, where the calciner operates under an oxygen-rich atmosphere and the sorbent is reactivated by recarbonation allowing a reduction in the thermal input needed in the calciner. It has been shown that, when this 2nd generation CaL system is coupled to existing large sources of flue gases and biomass is used as fuel in the calciner, the full system becomes carbon-negative, with CO2 emissions as low as −245.3 kgCO2/MWhe since the biomass source is carbon-neutral. The net electric efficiencies achieved for the entire system including CO2 capture are higher than 33%. Moreover, the total investment required for this CaL system can be reduced by more than 30% compared to conventional CaL systems due to the reduced footprint of the calciner-related equipment when the calciner is fired with pure oxygen.

CO2 Carrying Capacities of Cement Raw Meals in Calcium Looping Systems

Calcium looping, CaL, is an emerging CO2 capture technology that is of special interest for use in cement plants, as it offers the possibility of exploiting several energy and material synergies. In this work, the CO2 carrying capacity of calcined raw meal materials for cement plants has been investigated with thermogravimetric equipment in a wide range of testing conditions. When calcination was carried out at high temperatures and over long times, some raw meals display a sharp decrease in their subsequent CO2 capture capacity compared to their limestone counterparts, while others perform as expected from their CaO content. XRD observations of calcined samples confirmed the formation of Ca2SiO4, i.e., belite, as the main deactivation agent, since belite formation removes active CaO for CO2 capture during the carbonation stage. The extent of belite formation was found to be greatly influenced by the nature of the raw meal (in particular by the level of aggregation of Ca and Si atoms in the material), by ...

Economic feasibility of calcium looping under uncertainty

An emerging calcium looping process has been shown to be a promising alternative to solvent scrubbing, which is regarded as the most mature CO2 capture technology. Its retrofits to coal-fired power plants have the potential to reduce both energy and economic penalties associated with the mature CO2 capture technologies. However, these conclusions have been made based on the deterministic outputs of the economic models that have not considered uncertainties in the model inputs. Therefore, this study incorporates a stochastic approach into the economic analysis of the retrofit of such emerging CO2 capture technology to the coal-fired power plant. The stochastic analysis revealed that levelised cost of electricity (LCOE) and specific total capital requirement were highly affected by the uncertainty in the input variables to the process and economic models. The most probable values for these key economic performance indicators were shown to fall between 75 and 115 €/MWelh, and 2100 and 2300 €/kWel,gross, respectively. Interestingly, the most probable LCOE values for the coal-fired power plant will fall between 50 and 150 €/MWelh. This indicated that the calcium looping retrofit scenario can become economically favoured, mainly due to the high economic penalties incurred by unabated coal-fired power plant associated with carbon tax. Importantly, the outputs of the stochastic economic assessment aligned well with the deterministic results reported in the literature. As the latter were generated using different sets of assumptions regarding the process and economic models, the stochastic approach to the economic assessment can minimise the impact of the model assumptions on estimates of the key economic parameters. Moreover, by indicating the probability of particular outputs, as well as ranking the model input variables according to their influence on the key economic performance, such analysis would allow making more insightful decisions regarding further funding and development of the calcium looping process. Finally, use of the stochastic approach in the economic feasibility assessment enables a more profound and reliable comparison of the different calcium looping retrofit configurations, as well as benchmarking different CO2 capture technologies.

Chemical looping combustion of hard coal and torrefied biomass in a 1 MWth pilot plant

Chemical looping combustion (CLC) is an emerging CO2 capture technology utilizing two interconnected circulating fluidized beds (CFB). An oxygen carrier is oxidized in the air reactor and reduced in the fuel reactor. In comparison to a classic oxyfuel process, no air separation unit is required to provide the oxygen needed to burn the fuel. The solid fuel, such as coal or biomass, is gasified in the fuel reactor, and the products from gasification are oxidized by the oxygen carrier. This work presents results of 110h autothermal and partial autothermal CLC operation with ilmenite and iron ore as oxygen carriers. Hard coal and a fuel blend of hard coal and torrefied biomass were used as fuels. The results show that the oxygen demand of the fuel reactor required for a complete conversion of unconverted gases was in the range of 27%. At the same time, the carbon capture efficiency was low in the present configuration of the 1 MWth pilot. This means that unconverted char left the fuel reactor and burned in the air reactor. The reason for this is that no carbon stripper unit was used during these investigations. Some possible modifications like an oxygen carrier with oxygen uncoupling, a lower fuel feeding point or a secondary fluidization of the fuel reactor could significantly enhance the carbon capture efficiency.

The Value of CO2-Bulk Energy Storage to Reducing CO2 Emissions

Carbon-dioxide (CO2) bulk energy storage (CO2-BES) is an emerging CO2 capture, utilization, and storage (CCUS) approach that stores CO2 that is captured from large point sources (e.g., fossil-fuel power plants) to time-shift electricity generated from variable renewable energy technologies so that it matches demand. Excess electricity can be used to compress and inject CO2 into sedimentary-basin geothermal resources, which stores the excess electricity as pressure and directly reduces CO2 emissions. The stored energy can be produced and used when electricity demand exceeds supply. CO2-BES indirectly reduces CO2 emissions if this time-shifting displaces electricity that would otherwise be produced by power plants that emit CO2. As a result, CO2-BES can have direct and indirect value to reducing CO2 emissions. In this study we applied a linear optimization program that we developed to determine the indirect and direct value that CO2-BES could have to reducing CO2 emissions over a day, and used the Electricity Reliability Council of Texas (ERCOT) electricity system as a case study. Using a CO2 price of $13/tCO2, we found that CO2-BES has an indirect value of 1.98 tCO2/MWh and reduced CO2 emissions through two mechanisms: (1) enabling a greater utilization of electricity generated by wind energy technologies, and (2) enabling natural gas power plants to displace electricity generated by coal-fired power plants. CO2-BES did not have a direct value to reducing CO2 in this study because a CO2 price of $13/tCO2 is less than the ∼$50/tCO2 to ∼$70/t CO2 cost of directly capturing CO2 from fossil-fueled power plants.

Calcium looping combustion for high-efficiency low-emission power generation

High-temperature solid looping technologies, such as calcium looping and chemical looping combustion are regarded as emerging CO2 capture technologies with potential to reduce the net efficiency penalties associated with CO2 separation. Importantly, high-temperature operation of these technologies allows utilisation of the high-grade heat for power generation. Building on these emerging technologies, this study intended to establish a new class of high-temperature solid looping combustion technologies for high-efficiency low-emission power generation called calcium looping combustion. Such combustion technology comprises a combustor, as a primary source of heat for indirect heating in a calciner, and a carbonator where CO2 is separated from flue gas leaving the combustor; hence high-grade heat, which can be used for power generation, and a concentrated CO2 stream, which can be either utilised or permanently stored, are generated. The techno-economic performance of calcium looping combustion was comparable to a conventional coal-fired power plant. Depending on whether the concentrated CO2 stream is utilised elsewhere or permanently stored, calcium looping combustion was characterised with a net efficiency gain of 0.7%HHV points or a net efficiency penalty of 2.4%HHV, respectively. Additionally, the cost of CO2 avoided for calcium looping combustion was estimated to be 10.0 €/tCO2 and 33.9 €/tCO2, respectively. Therefore, similarly to chemical looping combustion, calcium looping combustion introduced in this study is a viable high-efficiency low-emission power generation technology that produces a concentrated CO2 stream with no efficiency penalty associated with CO2 separation.

Calcium looping with supercritical CO2 cycle for decarbonisation of coal-fired power plant

State-of-the-art integration scenarios of calcium looping (CaL), which is an emerging CO2 capture technology, assume that excess heat is used to raise steam for the steam cycle and result in a net efficiency penalty of 6.0–8.0% points. In this study, a concept using the supercritical CO2 cycle (s-CO2) instead of the conventional steam cycle is proposed. Retrofit of CaL with recompression s-CO2 cycle to the 580 MWel coal-fired power plant was found to result in a net efficiency penalty of 6.9%HHV points. This is 1%HHV point lower than that for the same system linked with the steam cycle having the same turbine inlet conditions (593.3 °C/242.3 bar). A further reduction of the net efficiency penalty to 5.8%HHV points was achieved through considering a pump instead of a first CO2 compression stage and increasing the turbine inlet temperature to 620 °C and pressure to 300 bar. As the s-CO2 cycle's specific capital cost is up to 27% lower than that of the equivalent steam cycle, CaL with s-CO2 cycle is a viable option for the coal-fired power plant decarbonisation. Moreover, it can be expected that this cycle can be successfully implemented in other high-temperature looping cycles, such as chemical looping combustion.

Emerging CO2 capture systems

In 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range of emerging CO2 capture technologies that promised to deliver lower energy penalties and cost. These included new energy conversion technologies such as chemical looping and novel capture systems based on the use of solid sorbents or membrane-based separation systems. In the last 10 years, a substantial body of scientific and technical literature on these topics has been produced from a large number of R&D projects worldwide, trying to demonstrate these concepts at increasing pilot scales, test and model the performance of key components at bench scale, investigate and develop improved functional materials, optimize the full process schemes with a view to a wide range of industrial applications, and to carry out more rigorous cost studies etc. This paper presents a general and critical review of the state of the art of these emerging CO2 capture technologies paying special attention to specific process routes that have undergone a substantial increase in technical readiness level toward the large scales required by any CO2 capture system.

Influence of Steam Injection during Calcination on the Reactivity of CaO-Based Sorbent for Carbon Capture

Calcium looping is an emerging CO2 capture technology based on cyclic calcination/carbonation reactions using calcium-based sorbents. Steam is typically present in flue/fuel gas streams from combustion or gasification and in the calciner used for sorbent regeneration. The effect of steam in the calciner on sorbent performance has received little attention in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. Two Canadian limestones, Cadomin and Havelock, were tested, and various levels of steam (up to 40%) were injected in the sorbent regeneration process for 15 calcination/carbonation cycles. All concentrations of steam examined were found to increase sorbent reactivity for carbonation for both sorbents. In these experiments, 15% steam concentration with calcination had the largest impact on carrying capacity for both sorbents. Steam changes the morphology of the ...

Reactivation of calcium-based sorbent by water hydration for CO2 capture

Calcium looping is an emerging CO2 capture technology in which CO2 is captured at high temperature using a calcium-based sorbent, which however suffers from a well-known problem of loss-in-capacity after a few cycles. Water hydration is a potential method that can be applied to reactivate the sorbent on-site. The present work confirmed the effectiveness of periodic water hydration on the reactivation of a limestone and a synthetic CaO/cement sorbent. Furthermore, it was found that the water hydration of calcined limestone was independent of the factors, such as particle size, hydration duration, hydration temperature, and pre-calcination temperature. Also the conversion of hydrated limestone cannot be further enhanced by ultrasonic hydration. In contrast, the synthetic CaO/cement sorbent showed strong dependence on those factors. In addition, the CaO conversion of the synthetic CaO/cement sorbent can be recovered to more than 80% by ultrasonic hydration.

Prospects for CO2 capture in European industry

PurposeThe aim of this study is to assess the role of CO2 capture and storage (CCS) technologies in the reduction of CO2 emissions from European industries.Design/methodology/approachA database covering all industrial installations included in the EU ETS has been created. Potential capture sources have been identified and the potential for CO2 capture has been estimated based on branch‐ and plant‐specific conditions. Emphasis is placed here on three branches of industry with promising prospects for CCS: mineral oil refineries, iron and steel, and cement manufacturers.FindingsA relatively small number (∼270) of large installations (>500,000 tCO2/year) dominates emissions from the three branches investigated in this study. Together these installations emit 432 MtCO2/year, 8 percent of EU's total greenhouse gas emissions. If the full potential of emerging CO2 capture technologies was realized, some 270‐330 MtCO2 emissions could be avoided annually. Further, several regions have been singled out as particularly suitable to facilitate integrated CO2 transport networks. The most promising prospects for an early deployment of CCS are found in the regions bordering the North Sea.Research limitations/implicationsReplacement/retrofitting of the existing plant stock will involve large investments and deployment will take time. It is thus important to consider how the current industry structure influences the potential to reduce CO2 in the short‐ medium and long term. It is concluded that the age structure of the existing industry plant stock and its implications for the timing and deployment rate of CO2 capture and other mitigation measures are important and should therefore be further investigated.Practical implicationsCCS has been recognized as a key option for reducing CO2 emissions within the EU. This assessment shows that considerable emission reductions could be achieved by targeting large point sources in some of the most emission‐intensive industries. Yet, a number of challenges need to be resolved in all parts of the CCS chain. Efforts need to be intensified from all stakeholders to gain more experience with the technological, economical and social aspects of CCS.Originality/valueThis study provides a first estimate of the potential role for CO2 capture technologies in lowering CO2 emissions from European heavy industry. By considering wider system aspects as well as plant‐specific conditions the assessment made in this study gives a realistic overview of the prospects and practical limitations of CCS in EU industry.

Electric swing adsorption as emerging CO2 capture technique

Abstract The application of Electric swing adsorption (ESA) as a successful second generation technique to capture CO 2 was evaluated. The objective of this work is to demonstrate that under certain conditions, ESA can be used in CO 2 capture from flue gases of power plants. A process with seven steps was developed and tested for CO 2 capture from a flue gas from a natural gas power station with emission levels of 1 Gton of CO 2 per year with a content of 3.5%. The seven steps employed are: feed, rinse with hot gas, internal rinse, electrification, depressurization and two purge steps. Using this process we could obtain CO 2 -rich streams with purities of 89.7% keeping recovery around 70% and energy consumption of 1.9 GJ/ton of CO 2 captured.