CO2 Capture System Research Articles

Performance of Na2CO3-CaO sorbent in sorption-enhanced steam methane reforming

The addition of alkali molten salts has been reported as a strategy to overcome the sintering problem presented by calcium oxide in CO2 capture systems. In this work, the influence of sodium doping in a CaO sorbent was investigated in the sorption enhanced steam methane reforming process (SE-SMR). The goal was to increase the stability of the sorbent and, consequently, the efficiency of the process. For that, a Na-containing sorbent was prepared using the precipitation technique and a pure calcium oxide was obtained by calcination of CaCO3. The sorbents were physically mixed with 10 % Ni/Al2O3 catalyst and tested in 10 cycles of SE-SMR at 600 °C and CH4:H2O equals to 4. In general, both materials showed 100 % of CH4 conversion and H2 molar fraction of 93.5 vol.%. However, regarding the stability over the SE-SMR cycles, it was evidenced that the addition of sodium decreased the duration of pre-breakthrough comparing with the non-doped material. The XRD, SEM, and TGA results allowed us to observe an inverse relationship of particle diameter and CO2 capture performance. Na2CO3-CaO presented a larger average crystallite size compared to the pure CaO which led to a higher probability of the CaCO3 layers to inactivate the calcium oxide and, consequently, caused a strong sintering effect. Besides the presence of sodium, the precipitation method and the synthesis conditions could have favored the low initial CO2 uptake and poor stability of the Na2CO3-CaO sorbent.

Process simulation development of a clean waste-to-energy conversion power plant: Thermodynamic and environmental assessment

Waste-to-energy (WTE) conversion technologies for generating renewable energy and solving the environmental problems have an important role in the development of sustainable circular economy. This paper presents a novel high-efficiency WTE power plant using refuse-derived fuel (RDF) as feedstock by integrating torrefaction (T) pretreatment with plasma gasifier (PG), solid oxide fuel cell (SOFC), and combined heat and power (CHP) system. The combined impacts of torrefaction conditions (i.e. temperature and residence time) and steam-to-fuel (S/F) ratio on the energy and environmental performances of the proposed T-PG-SOFC-CHP power plant without CO2 capture (System I) is first evaluated. Results show that torrefaction of RDF prior to plasma gasification provides better syngas quality and therefore the system electrical efficiency (SEE) and CHP efficiency (CHPE) of System I can be markedly boosted compared to that of untreated RDF. However, the integration of torrefaction unit shows a negative effect on the energy return on investment (EROI) due to high energy demands for torrefaction and plasma gasification. Overall, the values of CHPE of System I range from 47.25% to 55.39% when the torrefaction temperatures of 200 and 250 °C are adopted. In contrast, the torrefaction of RDF at 300 °C is not a recommended condition for operation in the T-PG-SOFC-CHP power plant because of noticeably negative energy and environmental impacts. Moreover, to prevent the risk of carbon deposition on the SOFC anode, a recirculation ratio (RR) of the anode off-gas of 30% is required. Finally, the introduction of oxy-fuel combustion technology into the T-PG-SOFC-CHP system for CO2 capture (System II) allows to achieve a zero direct CO2 emission WTE power plant. However, this results in an energy penalty of about 5.40–6.77% associated with the CO2 capture and compression process.

Key CO2 capture technology of pure oxygen exhaust gas combustion for syngas-fueled high-temperature fuel cells

Integrated gasification fuel cells (IGFCs) integrating high-temperature solid oxide fuel cell technology with CO2 capture processes represents highly-efficient power systems with negligible CO2 emissions. Flame burning with pure oxygen is an ideal method for fuel cell exhaust gas treatment, and this report describes experimental and numerical studies regarding an oxy-combustor for treating the exhaust gas of a 10 kW IGFC system anode. The applied simulation method was verified based on experiments, and the key performance indices of the combustor were studied under various conditions. It was determined that 315 K was the ideal condensation temperature to obtain flame stability. Under these pure oxygen flame burning conditions, CO was almost completely converted, and the dry mole fraction of CO2 after burning was ≥ 0.958 when there was up to 5% excess O2. Overall, 5% excess O2 was recommended to maximize CO2 capture and promote other environmental considerations. Additionally, the optimal tangential fuel jet angle to control the liner temperature was approximately 25°. The total fuel utilization had to be high enough to maintain the oxygen flame temperature of the anode exhaust gas below 1800 K to ensure that the system was environmentally friendly. The results presented herein have great value for designing IGFCs coupled with CO2 capture systems.

Experimental and Numerical Study of CO2/CH4 Separation Using SAPO-34/PES Hollow Fiber Membrane

The poor compatibility between polymeric matrix and inorganic filler in mixed matrix membrane (MMM) generates interfacial defects that reduce the gas selectivity. In this work, the defects in poletherysulfone (PES)/silicoaluminophosphate (SAPO)-34 zeolite mixed matrix membrane was prepared by dry–wet spinning technique for the separation of CO2/CH4 mixtures. In this regard, the synthesized PES/SAPO-34 mixed matrix membranes (MMMs) were characterized via FESEM, TGA and DSC analyses. The response surface methodology (RSM) was applied to find the relationships between several explanatory variables such as air gap distance, jet strech ratio and zeolite content and CO2 permeance as responses. The results were validated with the experimental data, which the model results were in good agreement with the available experimental data. The effects of feed temperature and feed pressure on permeation and CO2/CH4 selectivity of membranes were investigated. The MMMs showed better performance than the neat PES membrane. Two dimensional countercurrent mathematical model for membrane separation has been incorporated with Aspen HYSYS as a user defined unit operation in order to optimize and design the membrane system for CO2 capture from natural gas. Parameter sensitivities, along with process economics, have been studied for different design configurations (including recycle streams and multiple stages). It has been observed that double stage with permeate recycle system gives the optimum design configuration due to minimum process gas cost involved with it. Permeation results manifested that the PES/SAPO-34 fabricated at optimum conditions has incredible worth from the prospective of industrial separations of CO2 from flue and natural gas.

Depressurization of CO2-N2 and CO2-He in a pipe: Experiments and modelling of pressure and temperature dynamics

To design and operate safe and efficient CO2-transportation systems for CO2 capture and storage (CCS), engineers need simulation tools properly accounting for the fluid and thermodynamics of CO2. As the transportation systems evolve into networks, it becomes important that these tools also account for impurities in the CO2, which may significantly affect the thermophysical properties, directly impacting system design and safety. Tube-depressurization experiments provide crucial data to develop and validate models describing transient multiphase multicomponent flow in pipes. In this work, we perform experiments in a new facility with dense and fast instrumentation for both pressure and temperature. One experiment is for CO2 with 1.8 mol % N2, and one has 1.92 mol % He, both starting from 12 MPa and 25 ∘C. In order to quantify the effect of impurities, the experiments are compared to results for pure CO2 and analysed on the background of simulations. We employ a homogeneous equilibrium model (HEM) augmented in this work to account for the appearance of solid CO2 in CO2 mixtures. We observe that the moderate amounts of impurities significantly influence both pressure and temperature dynamics. In particular, the ‘pressure plateau’, a key quantity for the assessment of running-ductile fracture, increases as much as 4 MPa for CO2-He compared to pure CO2. A further insight is that models must account for solid CO2 in order to capture the correct temperature development as the pressure decreases towards atmospheric conditions.

Advanced Coal Technologies for sustainable power sector in India

In India, more than two-thirds of the total electricity is generated from coal-based power plants. The country will be heavily dependent on coal for electricity generation at least for a few more decades. A low carbon scenario for 2030 is projected and the results show that coal-based power plant will contribute to 58 % of electricity generated. This paper reports the sustainability assessment of several Advanced Coal Technologies (ACT), with and without a CO2 capture system, for application in Indian coal-based power plants. In order to assess sustainability quantitatively, an index called Sustainability Index is estimated using a sequential combination of the Analytic Hierarchy Process and a multi-criteria decision-making method. The results show that ACTs like supercritical and ultra supercritical power plants with a carbon capture system have higher sustainability indices. These ACTs will help in reducing the CO2 emissions and combat climate change. This study helps academicians, industrialists, policymakers, and other stakeholders to develop a technology roadmap for sustainable development in India.

Risk Assessment of a Post-Combustion and Amine-Based CO2 Capture Ready Process

CO2 Capture Ready Process, as a part of Carbon Capture and Storage (CCS) technology, is a response to international political pressure and the priority of the European Commission to reduce anthropogenic CO2 emissions since it is connected with concerns regarding global warming. This is currently considered as an option for lessing CO2 emissions into the atmosphere. Many laboratory experiments, as well as pilot projects, have been carried out using different capture systems, but until now no experience from the one-to-one size operational installation has been gained. The energy industry must meet several challenges associated with the start-up of the new full-scale project. This paper investigates the problems that can occur while linking a new technology like the CO2 Capture Ready Process to a working fossil fuel power plant. A Hazard and Operability study (HAZOP) has been used, as it is a structured and systematic examination of a planned or existing process or operation, in order to identify and evaluate problems that may represent risks to personnel or equipment. A case study of a post-combustion CO2 capture system with an aqueous monoethanolamine as a solvent is presented, as it is the most likely system to be used in Polish power plants. Basic problems in the analysis as well as the parameters that should be considered to determine vulnerabilities of the process were successfully identified. Gaining experience about the installation’s behaviour while connected to the existing equipment of any power plant is critical for future CCS projects.

Scaling CO2 Capture With Downstream Flow CO2 Conversion to Ethanol

To prevent the global average temperature from increasing more than 1.5°C and lower the concentration of greenhouse gases (GHGs) in the atmosphere, most emissions trajectories necessitate the implementation of strategies that include both GHG mitigation and negative emissions technologies (NETs). For NETs, there are unique research challenges faced by both CO2 capture and utilization to scale in an economically feasible manner. Starting with incumbent methods, wherein CO2 is recovered from a high concentration source, and moving toward CO2 capture from more widely available dilute sources, we outline how CO2 capture systems interface with downstream utilization in flow reactors. To provide a real-world point of comparison, we analyze CO2 sourcing for Air Company's CO2-to-alcohols pilot and demonstration scale deployments in Brooklyn, New York, USA and Calgary, Alberta, Canada as case studies. The degree of reduction in atmospheric CO2 depends on product alcohol usage; for example, use as a fixed chemical feedstock provides longer term emissions reduction than as a fuel, which is eventually oxidized. Lastly, we discuss the barriers that are present for economic scale-up of CO2 capture and utilization technologies broadly.

Calcium looping for power generation with CO2 capture: The potential of sorbent storage for improved economic performance and flexibility

Abstract The aim of this work is to investigate the potential of calcium looping (CaL) CO2 capture system for power plants with sorbent storage, for flexible and low-emission power generation from coal. Two different CaL systems have been analyzed for CO2 capture from a reference pulverized coal power plant: (i) a Baseline CaL system and (ii) a FlexiCaL system with sorbent storage. The sorbent storage systems can be exploited in two ways: the primary storage system allows to decouple the carbonator and the calciner load and reduce the size of the calciner island; the secondary storage unit allows to increase/reduce the maximum/minimum power output of the plant for improved grid services. Heat and mass balances have been computed at different loads with process simulation software, considering the off-design operation of the main plant components. A simplified economic analysis has been carried out to compute the cost of electricity and estimate the economic benefits of the primary sorbent storage system for a given power generation profile. The method used in this work allowed to compute the off-design behaviour of the CaL power plant the with the highest accuracy among the literature studies and to understand the potential of the secondary solids storage to provide grid services for the first time. The part-load analysis provided insights on the design of the carbonator reactor, that should limit the heat transfer surface in the riser to avoid excessive reactor cooling at part-load. Conversely, reaction heat should preferably be extracted from the external heat exchangers, where the heat transfer rate can be controlled more easily. From the thermodynamic standpoint, the two CaL plants feature similar efficiency on weekly cycling basis. The secondary storage allows increased operativity of the FlexiCaL plant on the secondary market, thanks to +2% of maximum power and -5% of minimum power output. The primary storage system allows reducing the capital cost of the CaL system, leading to LCOE reduction by 4-5% compared to the Baseline case, in a wide range of carbon tax and plant availability.

Dynamic model and performance of an integrated sorption-enhanced steam methane reforming process with separators for the simultaneous blue H2 production and CO2 capture

An integrated sorption-enhanced steam methane reforming (SESMR) process for simultaneous blue H2 production and CO2 capture is developed on the semi-central scale of ~ 48 ton H2/day. The developed SESMR process consists of a cyclic fluidized-bed (CFB) system, heating and pretreatment systems, CO2 capture system, a H2 pressure swing adsorption (PSA) system, compressors, and a combustor. To analyze the CFB system consisting of a bubbling fluidized-bed (BFB) reactor and fast fluidized-bed (FFB) regenerator, a dynamic model is formulated using the conservation equations combined with the Lagrange and Eulerian approaches and gas-velocity prediction. After a validation with reference, the developed CFB model is integrated with the dynamic model of the PSA and the algebraic equations for the other units to analyze the dynamic behavior and performance of the integrated SESMR process. The energy efficiency (82.2%) and H2 production cost of the SESMR process (12% reduction from that of the SMR process) are close to the prediction by the United States Department of Energy, let alone CO2 capture. According to the sensitivity analysis, the temperature of the BFB reactor is the most important factor because it considerably affects the production rate, product quality, CO2 capture, H2 cost, and energy efficiency. Since the CFB model has been shown to accurately predict the performance and reasonably explain the dynamic behaviors, it can be applied not only to the SESMR process but also to other CFB-related processes. The SESMR process contributes to the design, optimization, control, and decision-making processes relating to centralized or semi-central blue H2 production.

Exergoenvironmental analysis of a combined cycle power plant fueled by natural gas from an offshore platform

This study presents a detailed, disaggregated Life Cycle Assessment for natural gas obtained from an offshore area in Rio de Janeiro/Brazil, based on the Eco-indicator 99 method. The stages of production, transmission, purification, distribution, and final use of natural gas are considered. Environmental data are used to develop an exergoenvironmental assessment, which unravels the formation of environmental impacts throughout the energy system. The results of the Life Cycle Assessment indicate that the environmental impacts associated with offshore natural gas are quantified as 336 mPts/kg, where the majority of impacts are related to purification at the refinery (249) mPts/kg, followed by extraction at the platform (59.3 mPts/kg) and distribution (19.5 mPts/kg). The results of exergy and exergoenvironmental assessments quantified the environmental impacts associated with electricity production from natural gas in a combined cycle power plant as 61.9 mPt/kWh. These impacts can be reduced by considering a 50% decrease in flaring/venting as well as air and liquid emissions, resulting in 59.8 mPt/kWh. These findings are applicable to the assessment of natural gas power plants and the exploration of alternative abatement options (such as CO2 capture systems).

Treatment of Flue Gas in a CO2 Capture Pilot Plant for a Commercial CFB Boiler

The problem of reducing carbon dioxide emissions from flue gas, particularly from flue gas originating from coal-firing CFB systems, is currently an important challenge. Many centers around the world have tested post-combustion CO2 capture systems. One of these systems, operated using DR-VPSA adsorption technology (dual-reflux vacuum pressure swing adsorption), was tested under the Strategic Project in Poland. The flue gas in this study originated from a supercritical CFB boiler (460 MWe). An important problem involved in capturing CO2 from flue gas is the occurrence of SO2 and NOx. These substances have a negative effect on the CO2 adsorption process. In this study, commercial impregnated activated carbon was used to remove SO2 and NOx from CFB flue gas in the pre-treatment section during the tests of a pilot CO2 capture unit in a large-scale CFB boiler at the Lagisza Power Plant (Poland). The spent activated carbon was analyzed using several different methods (N2 adsorption–desorption isotherms, SEM-EDX, XRD, FTIR, and TG) to evaluate the efficiency of the operation and life span of the adsorbent used in the SO2 and NOx removal unit. The results demonstrate that using commercial impregnated activated carbon in the pre-treatment section ensures sufficient flue gas purification and the removal of sulfur oxides but remains insufficient for nitrogen oxides.

Performance analysis and comparison of cryogenic CO2 capture system

ABSTRACT Excessive energy requirement for the cryogenic condition is still the challenge for the current cryogenic CO2 capture system. In this work, the capture performance is investigated for the aim of energy savings on different cryogenic CO2 capture system, based on the combination of pressure recovery and cold energy utilization on the process residual gas. Based on this, two novel energy saving CO2 capture processes are proposed, which are defined as the post-expansion and the pre-cooled processes, respectively. The study presents a detailed comparison of the proposed process with conventional one regarding CO2 recovery and energy consumption. Also, the energy saving potential of two proposed processes is analyzed by varying the operating parameters, including process temperature, compression pressure, and inlet gas CO2 concentration. The simulation results show that the specific energy consumption can be decreased by 3.9% and 7.4% in the proposed post-expansion and pre-cooled process due to the effect of less cooling energy and compression work consumption, respectively.

Technoeconomic Feasibility Study of Cement Plants as Reference Facilities for Centralized CO2 Capture in Industrial Sites

The proposed concept connects industrial sites with significant heat demands (self-produced in natural gas or coal-fired boilers) with a cement plant through the implementation of a calcium looping carbon capture system which uses the kiln furnace as calciner for both the cement and the capture plant. This new concept includes a carbonator reactor fed by CaO from the cement plant in each one of the industry sites to capture the CO2 content of their own flue gas. After carbonation reaction, the exhaust sorbent is transported back to the cement plant for regeneration in the kiln furnace. The aim of this project is to carry out a techno-economic feasibility study of the integration proposed. An introduction about the state of the art of the technologies involved, with particular regard to Ca-looping and to Oxy-fuel combustion in cement manufacturing, is presented to establish the context of the study. In order to analyse various operation conditions of the proposed CO2 capture system, different levels of integration are described. The three studied scenarios are (i) the integration of the coal-fired industrial boiler and the cement plant, (ii) the integration of the natural gas-fired industrial boiler and the cement plant and (iii) the integration of both industrial boilers and the cement plant. An economic study is carried out to assess the feasibility of the centralized carbon capture system. The assumptions of carbon tax equal to 30 €/tCO2 and CaO cost of 20 €/tCaO were considered in the economic analysis. Under these conditions there are room for economic feasibility of both, the small industries and the cement plant as saving are obtained when the scenarios are integrated. It must be pointed out that the economic feasibility of the proposed concept will strongly depend on the policies of emissions taxation.

Hydrodynamic mechanism study of the diameter-varying spray tower with atomization impinging spray

Our group proposed a diameter-varying spray tower and a new spray mode of dual-nozzle opposed impinging spray method to achieve the low-energy-consumption and environmentally-friendly CO2 capture process and some meaningful results have been obtained by experiments. However, the detailed information about the hydrodynamics (like liquid and gas phase distribution, gas-liquid contacting area and gas-liquid contacting time causing by impinging spray) inside the proposed tower is hard to be obtained by experimental work. In this work, to specifically explain the hydrodynamic mechanism with impinging spray inside the proposed spray tower, ANSYS Fluent18.0 and Euler-Lagrange approach were used to simulate the complex gas-liquid two-phase flow based on experimental results. The effects of nozzle location, nozzle number, spray angle, liquid injection velocity and gas intake mode were investigated, and the optimal design scheme of the spray tower was proposed. Simulation results indicated that the dual-nozzle opposed impinging spray method (DOSM) showed better absorption performance compared with the single-nozzle side spray method (SSSM) and single-nozzle middle spray method (SMSM). Spray angle of 60 degrees had efficient gas-liquid distribution. The liquid inlet velocity of 8 m·s−1 was suggested under the experimental conditions. The double-sided gas intake mode intensified gas-liquid absorption performance. The simulation results were well verified by experiments. The relationship between flow field optimization and CO2 absorption performance enhancing was also discussed comprehensively. Finally, it was concluded that both the numerical simulation and experimental results proved that the diameter-varying spray tower with the impinging spray method is a promising reactor for the CO2 capture system.

Flexible Calcium Looping System for CO2 Capture From Coal-Fired Power Plants: A Comprehensive Modelling Study on Part-Load and Dynamic Performance and Economic Optimization of the Sorbent Storage System

In this work, an advanced Calcium looping (CaL) power plant with thermochemical energy storage system is assessed. The CaL system is equipped with two solids storage silos storing calcined solids from the calciner and carbonated solids from the carbonator. The presence of the solids storage allows to design and operate the CaL calciner line (calciner, ASU, CPU) on the average load of the existing power plant, while the carbonator can follow the load of the conventional power plant with air-blown boiler. The economic analysis carried out shows that the optimal size of the storage system from an economic and logistical point of view is on the daily cycle, which shows a cost of CO2 avoided (CCA) of 31 €/tCO2, about 16% less than the case without storage. In addition, the adoption of the storage system allows the CaL steam cycle to operate with a higher average daily electrical efficiency than without storage, limiting the operation at partial load. Moreover, by exploiting the secondary storage it is possible to have an increase of about 20 MWe respect to the nominal condition, and a reduction of about 56 MWe below the minimum load. As demonstrated by studying the dynamics of the system, the increase in power output can be produced in a relatively short time (40% within 40s and the remaining 60% within 300s) by boosting the hot CaO flow through the sorbent cooling line.

Novel Fluidized Bed Particle Classifier for Application in Calcium Looping With Indirect Heat Transfer – Experiments and Simulations

This article summarizes a detailed scientific study of a particle classification system to be used in a fully integrated regenerative calcium looping (FICaL) system for CO2 capture. In conventional calcium looping, the required calcination heat is provided by a separate oxyfuel combustor, which needs an air separation unit (ASU) to provide the required oxygen for the process. The ASU demands a considerable amount of power, which gives an energy penalty of typically 5 % to the power plant. However, in the FICaL system, the required heat for the calcination is instead supplied indirectly from the main combustor in the power plant, so there is a no need for an ASU in the system. Based on process simulation studies done with Aspen Plus®, this may reduce the energy penalty to values in the order of 1-2 %. The indirect heat transfer is done by using inert heat transfer (HT) particles that are heated up in the combustor and then transferred to the calciner where the sorbent material is heated up after mixing with the hotter inert particles. Thereby the sorbent material is calcined. However, after calcination, the sorbent and heat transfer particles have to be separated. Hence, an efficient classifier is required. The current work has therefore focused on designing, constructing and doing experiments in a novel particle classification system. A novel cross-flow fluidized bed classifier was designed, using computational fluid dynamics (CFD) simulations as a tool, in order to separate the sorbent and HT particles exiting from the calciner. The classifier, which has no mechanical moving parts exposed to very high temperature, can be operated under the required high-temperature conditions prevailing in a full-scale plant. Two different cold-flow lab-scale versions of the classifier was built and used for a large number of experiments. In the classification, the aim is to minimize the loss of sorbent particles via the bottom exit from the classifier, and also to minimize the loss of HT particles via the top exit from the classifier. The second and improved version was able to classify very well a mixture of down-scaled sorbent particles (zirconia) and down-scaled HT particles (steel). The experiments with the improved classifier version gave particle losses in the order of 2-3 %, values that are close to what can be seen as acceptable in a full-scale hot-flow system. Extensive CFD simulations were carried out with the commercial software Barracuda® 17.1 to investigate in detail how the different particle types behave in the classifier. Even if the exact particle losses were not well predicted, Barracuda was able to predict the general gas-solids flow behavior and proved to be a useful tool in the design process. Different drag models were used to reproduce the experimental findings and validate the CFD model. Barracuda was also used to simulate the classification process under hot-flow conditions and indicated that the classifier will also perform well under such conditions. The results of the corresponding research work are promising as the classifier is able to give a high degree of purity of the particle streams leaving the classifier. The iterative design and modelling effort from this research work has produced a functional, high-efficiency classification concept.

Toward Improved Guidelines for Uncertainty Analysis of Carbon Capture and Storage Techno-economic Studies

Uncertainty analysis is a key element of sound techno-economic analysis (TEA) of CO2 capture and storage (CCS) technologies and systems, and in the communication of TEA results. Many CCS technologies are novel concepts, that are still in the early (pre-commercial) stages of development. Therefore, uncertainties in their technology performance and cost are often substantial, making it imperative that they be characterized, and their impacts reported. Although uncertainty analysis itself is not novel, with some methods already frequently used by the CCS TEA community, a document that provides a comprehensive overview of methods and approaches, as well as guidance on their selection and use, is still lacking. Given its importance, we seek to fill this gap by providing a critical review of uncertainty analysis methods along with guidance on the selection and use of these methods for CCS TEAs, highlighting good practice and examples from the CCS literature. There are many opportunities to bring the use of uncertainty analysis to a higher level than currently practiced. This review of and guidance on available methods is intended to help accelerate continued methods development and their application to more robust and meaningful CCS performance and cost studies.

Efficient design of heat exchange for CFB reactors in CO2 capture system regarding geometry-induced secondary flow

CO2 capture technology using temperature-swing adsorption faces many obstacles for commercialization. Circulating fluidized bed systems have high capture performance, but an energy-efficient design is essential to reduce the CO2 capture cost. In this study, thermal-fluid characteristics of circulating fluidized bed with two-phase flow are analyzed, and thermal design is implemented. First, a laboratory-scale circulating fluidized bed system was used to investigate the relationship between hydrodynamics and heat transfer in experiments and numerical simulations. Numerical method predicted well the pressure fluctuations and local bed-to-wall heat transfer. Particle behaviors affected greatly the heat transfer. Accordingly, to control solid particle flow, the effect of reactor geometry on hydrodynamics and heat transfer was analyzed. Compared with the conventional circular reactor, the rectangular reactor had a secondary flow of solid particles in the horizontal section. Flow toward the narrow wall, and rotational flow near the corners, were identified. Intensity of the secondary flow depended on the aspect ratio. It was firstly reported that the geometry-induced secondary flow affected significantly heat transfer. Due to the strong secondary flow in the rectangular reactor, the local heat transfer was more than doubled. Ultimately, thermal design was carried out by analyzing the minimum temperature difference (MTD) according to the reactor geometry. The rectangular reactor showed an MTD of 67% compared to the circular reactor and 45% compared to the square reactor. Because MTD decreased and the coolant amount increased simultaneous with increasing aspect ratio, the rectangular reactor with an aspect ratio of 4:1 was the most energy-efficient design. Finally, through thermal design, the pilot-scale rectangular reactor is designed and under-constructed in order to evaluate the CO2 capture system performance and the potential for commercialization.

Techno-economic feasibility and sustainability of an integrated carbon capture and conversion process to synthetic natural gas

Carbon Capture Utilization and Storage (CCUS) technologies are receiving increasing interest and its implementation at world scale appears to be crucial to reduce CO2 emissions. In this context, Power-to-Gas technologies (PtG) are very promising, allowing to store renewable electricity and valorize captured CO2 to produce Synthetic Natural Gas (SNG), among other. The present work simulates an integrated CO2 capture and conversion process to SNG, and investigates its techno-economic and environmental performances. Different scenarios are defined considering the application to a cement plant flue gas and the production of renewable hydrogen. An advanced CO2 capture unit is implemented, considering a configuration (Rich Vapor Compression and Inter Cooling) and a solvent (MDEA + PZ) allowing to minimize its specific energy consumption (35 % regeneration energy savings in comparison with a conventional amine-based CO2 capture system). The excess heat released by the catalytic conversion is recovered for the solvent regeneration maximizing the amount of captured CO2. From the scenarios analyses, it is shown that integrating the CO2 capture and conversion steps is beneficial for reducing both the net CO2 emission to the atmosphere, by 45 %, and the contribution to fossil depletion, by 81 %, in comparison with the non-integrated one, as the production of fossil-based natural gas is replaced by renewable SNG. The proposed process leads to a cost of 2.39 € per kg Raw-SNG, with expected revenues of 0.87 € per kg Raw-SNG. Significant subsidies and incentives would thus be needed to compete with conventional energy prices for natural gas (0.55 € per kg).