Ruikai Zhao | Tianjin University (original) (raw)
Papers by Ruikai Zhao
Journal of Thermal Science, 2019
As a huge reserve for potential energy, natural gas hydrates (NGHs) are attracting increasingly e... more As a huge reserve for potential energy, natural gas hydrates (NGHs) are attracting increasingly extra attentions, and a series of researches on gas recovery from NGHs sediments have been carried out. But the slow formation and dissociation kinetics of NGHs is a major bottleneck in the applications of NGHs technology. Previous studies have shown that nanobubbles, which formed from melt hydrates, have significant promotion effects on dissociation and reformation dynamics of gas hydrates. Nanobubbles can persist for a long time in liquids, disaccording with the standpoint of classical thermodynamic theories, thus they can participate in the hydrate process. Based on different types of hydrate systems (gas + water, gas +water +inhibitors/promoters, gas + water + hydrophilic/hydrophobic surface), the effects of nanobubble evolution on nucleation, dissociation, reformation process and "memory effect" of gas hydrates are discussed in this paper. Researches on the nanobubbles in hydrate process are also summarized and prospected in this study.
Renewable and Sustainable Energy Reviews, 2019
Carbon dioxide capture from the post-combustion flue gas via temperature swing adsorption is supp... more Carbon dioxide capture from the post-combustion flue gas via temperature swing adsorption is supposed to be a valid technology to mitigate carbon emissions. With regard to the adsorbent development and process improvement , the technologies of temperature swing adsorption for post-combustion carbon dioxide capture have been reviewed and compared in terms of fixed bed, fluidized bed and moving bed. A comprehensive evaluation framework of fixed-bed temperature swing adsorption for CO 2 capture has been established. In a four-step fixed-bed cycle, a shortcut model has been utilized. Four typical adsorbent materials, such as activated carbon, zeolite 13X, zeolite NaUSY and Mg-MOF-74, have been chosen in this assessment. The comparative study has been conducted under the same operating conditions, from four aspects using eight performance indicators. Results indicate that Mg-MOF-74 and zeolite 13X reveal excellent performance among the four selected adsorbents. Thereinto, Mg-MOF-74 performs well at four indicators including purity, productivity, specific thermal energy consumption and second-law efficiency; zeolite 13X excels in the other four indicators such as selectivity, recovery , minimum separation work and capture cost. Future work will complete a thorough assessment criterion in evaluating the TSA process for CO 2 capture.
Energy Conversion and Management, 2019
Abrupt climate change such as the loss of Arctic sea-ice area urgently needs negative emissions t... more Abrupt climate change such as the loss of Arctic sea-ice area urgently needs negative emissions technologies. The potential application of direct air capture of carbon dioxide from indoor air and outdoor air in closed buildings or crowded places has been discussed in this paper. From the aspects of carbon reduction and indoor comfort, the ventilation system integrating a capture device is of great value in practical use. For ultra-dilute carbon dioxide sources, many traditional separation processes have no cost advantages, but adsorption technologies such as temperature vacuum swing adsorption is one of suitable methods. Thermodynamic exploration has been investigated regarding minimum separation work and second-law efficiency at various concentrations in the air. The influence of concentration, adsorption temperature, desorption temperature and desorption pressure on the energy efficiency has also been evaluated. Results show that the minimum separation work for the level of 400 ppm is approximately 20 kJ/mol. The optimal second-law efficiencies are 44.57%, 37.55% and 31.60%, respectively for 3000 ppm, 2000 ppm and 1000 ppm. It means that a high energy-efficiency capture device in buildings merits attention in the exploration of the possibility of approaching negative carbon buildings.
Journal of Cleaner Production, 2019
This paper presents a techno-economic study to seek the feasibility about the proposed system tha... more This paper presents a techno-economic study to seek the feasibility about the proposed system that integrating solar-assisted pressure-temperature swing adsorption (PTSA) into an 800MWe coal-fired power plant. Solar energy has the potential to supply thermal energy demand for carbon capture, which can avoid the energy consumption of the traditional method such as the steam extraction. The performance of the proposed system is largely affected by the climatic conditions and solar collector's types. The assessment criteria include carbon emission intensity (CEI), levelized cost of electricity (LCOE) and cost of CO2 avoidance (COA). By the parametric analysis, the results show that CEI of the novel system with solar thermal collectors is approximately 2g/kWh lower than that of the referenced power plant with CO2 adsorption capture. In addition, CEI of the novel system can be further decrease with the decline of desorption temperature, adsorption pressure and desorption pressure. For the sake of lower LCOE and COA, the prices of the power plant capacity, adsorbents and solar collectors should be reduced. Specifically, LCOE of the system with evacuated tube collector will be lower than that of the reference system with CO2 capture as the price of solar field is lower than 46.08 USD/m2.
Energy Procedia, 2014
As an end user of energy products, carbon dioxide capture and storage (CCS) system commonly requi... more As an end user of energy products, carbon dioxide capture and storage (CCS) system commonly requires a significant amount of energy to sustain a steady operation. As a renewable energy source, solar energy can supply plenty of thermal energy in different grades through various types of solar collector. Between the demand and supply sides, several technologies of solar thermal engineering can be applied as a bridge for an energy efficient design. In this paper, a technological framework for the energy efficiency in post-combustion CO 2 capture is further discussed as a second section of the two-part study. Based on existing research, several possible options of alternative energy supply to CCS system are analyzed, particularly for solar thermal energy. Moreover, some key design issues for the solar-assisted CCS system, such as integrated solar reactor with the regeneration component, are discussed as well.
Energy Procedia, 2014
Representative carbon dioxide capture and storage (CCS) system of the post-combustion, no matter ... more Representative carbon dioxide capture and storage (CCS) system of the post-combustion, no matter it employs adsorption, absorption or cryogenics separation technologies, commonly requires significant amounts of energy for the fundamental operation. Thus, energy consumption and related cost rise are primary challenges for the promotion of post-combustion technology. Solar thermal energy has already been widely used as an effective and clean energy source in industrial applications for drying, heating and even cooling since the last century. Various options of solar collector, such as flat plate type, evacuate tube type, and parabolic trough type, facilitate a comprehensive energy supply in different energy quality grades. In this paper, a technological framework for the energy efficiency in post-combustion CO 2 capture is briefly presented for a connection between the energy demand of a CCS system and the energy supply of solar thermal engineering. The match performance between solar thermal utilization systems and CCS system is discussed in terms of energy form of the demand side (CCS), energy grades of supply sides (solar collector), and possible dynamic adjustment.
Energy Procedia, 2014
Solvent-based Post-combustion Carbon Capture (PCC), which can reduce CO 2 emissions from coal-fir... more Solvent-based Post-combustion Carbon Capture (PCC), which can reduce CO 2 emissions from coal-fired power plants, is one of the most advanced mature Carbon Capture and Storage (CCS) technologies at present. Two problems limit its development. One is the output reduction of power plant due to the steam extraction from turbine. The other is a large amount of water consumption for the evaporation of the solution in the absorber and desorber. In this paper we propose an integrated system to reduce the steam extraction from turbine and to produce freshwater by using solar thermal energy. The new system produces more electricity and freshwater during the daytime, and uses the steam extraction to reduce CO 2 emissions at night. A techno-economic feasibility study is performed as a case study for a 300 MWe coal-fired power plant assisted by solar desalination. As for the potential impact parameters, the local climatic conditions and CO 2 capture rate are discussed. Low-cost collectors and desalting equipment would make the technology more cost-effective.
Applied Energy, 2018
The carbon capture by adsorption (CCA) is regarded as an available engineering technology because... more The carbon capture by adsorption (CCA) is regarded as an available engineering technology because of its low energy-consumption, easy to control, and possible integration with renewable energy. The recent advances in CCA research comprises mainly about the performance improvement of adsorbents, design and optimization of engineering process. However, considering the time-consuming and intensive funding required for experimental investigation, the numerical simulation has been widely applied in CCA. In numerical simulation field of CCA, the adsorption process is commonly simplified into mathematical models group comprised of adsorption kinetics model, the adsorption equilibrium model, pressure drop model and heat transfer model. However, few studies’ focus is to provide a detailed review of the research methodology of mathematical modeling in CCA simulation.
This paper presents a pathway map on CCA mathematical modeling through literature review and case study. An overview of model screening and modeling method of CCA is provided in the review part. This part also provides a short guided tour on how to combine the fundamental models about heat and mass transfer together to form a model group for various application scenarios in CCA. Then the pathway map on CCA modeling, which is summarized based on the review, is applied to a case study. In this part, the adsorption of CO2/N2 mixtures on activated carbon under the conditions of high temperature and low pressure is numerically investigated based on the established models. The performance indicators comprise gas temperature, mole fraction, and adsorbate amount of the fixed bed, are applied in the evaluation performance of CCA. Based on the proposed methodology, the CCA modeling demonstrates a more fluent design process relative to the real physical scenario, with a possible access to further optimization. Particularly, the simulation results showed that the optimized dimensionless velocity for the highest utilization efficiency of the fixed bed can be obtained and thus is proposed as 1.2–1.4 for the most suitable feed velocity to fit different size of fixed bed and different types of adsorbents for the engineering design.
Renewable and Sustainable Energy Reviews, 2017
Traditional technologies of carbon capture and storage (CCS) are being focused on capturing CO 2 ... more Traditional technologies of carbon capture and storage (CCS) are being focused on capturing CO 2 in large-scale demonstrations, which has been proved to result in the high cost and energy penalty. Meanwhile, typical innovative measures, commonly defined as the second generation CCS technologies, elude conventional ones by integrating with solar energy and thus contributing to a more energy-efficient conversion of CO 2. However, few reviews pay attention to thermodynamic processes and parameters of these novel technologies, and there is a lack of systematic evaluation and comparison among them. This paper firstly presents a guided tour on the state-of-art of typical and innovative CCS technologies integrated with solar energy. An overview on thermodynamic processes, including chemical reactions, operating conditions and efficiency indexes of five typical technologies is presented so that the current development level can be clarified. Since the high energy requirement and related operating cost are the main barriers to the application of existing CCS technologies, the minimum work and second-law efficiency are applied as the main indicators in the second part of this paper which relates to performance evaluation. In addition, the performance windows for innovative technologies are illustrated for the comparison of technological maturity. The results show that energy requirement of innovative CCS technologies from the flue gas is avg. 100–200 kJ/mol CO 2 and the second-law efficiency of them is only 5– 12%. Therefore, the maturity and popularity of these novel technologies are still relatively low. But the well-integrated systems and diversified output of these technologies can benefit existing energy infrastructures in a long period.
Journal of CO2 Utilization, 2018
This study explores the impacts of materials, such as adsorbents and electrodes, on the energy ef... more This study explores the impacts of materials, such as adsorbents and electrodes, on the energy efficiency of a 4-step ESA cycle for CO 2 capture. Three types of adsorbents including activated carbon honeycomb monolith (ACHM) and two hybrid adsorbents are compared, and two kinds of electrodes such as aluminum and brass are combined for comparative analysis. Process description of ESA cycle, including feed, electrification, elec-trification with purge and cooling, is presented via the adsorption isotherm diagram. By the theory of ther-modynamic carbon pump, sensitivity analysis of cycle parameters is evaluated in terms of the second-law efficiency (Eff 2nd) and the electrical heating efficiency (Eff ele). The results show that Eff 2nd of the employed adsorbents is in the range of 1.17%–6.15%, and Eff ele of the selected electrodes is between 27.46% and 60.91%. Among the three adsorbents, Eff 2nd of ACHM is the lowest one compared to the others. Similarly, Eff ele of the combination with brass is superior to that of the groups with aluminum. However, the actual efficiency of ESA cycle is the production of both Eff 2nd and Eff ele , which is approximately 1.03%–3.66%. Typical measures are proposed to reduce the heat loss of the adsorbents and electrodes as well for future work.
Solar Energy Materials and Solar Cells, 2018
Because of the ability to utilize the low-grade solar thermal energy for regeneration, a CO 2 cap... more Because of the ability to utilize the low-grade solar thermal energy for regeneration, a CO 2 capture system characterized by solar-assisted pressure temperature swing adsorption (SOL-PTSA) is studied on the effects of adsorbent materials. A detailed cycle description is firstly presented within the diagram of adsorption isotherm for the energy-efficiency analysis. Typical adsorbent materials, including zeolites and chemical adsorbent, are assessed in terms of sensible heat and latent heat, etc. Then, the energy consumption and the second-law efficiency , which can be considered as lumped indicators from such material parameters, are chosen as performance indicators as well. The influence of separation temperature, desorption temperature, CO 2 concentration and CO 2 adsorption pressure on system performance are finally obtained. For the chosen three adsorbent materials, the energy consumption of SOL-PTSA system is at the range of 25.96–87.76 kJ/mol, and the corresponding second-law efficiencies are at the range of 9.18–26.89%. The effect of adsorbent materials on the energy-efficiency of SOL-PTSA system mainly depends on specific heat, CO 2 working capacity and cycle design. In addition, the integration options of solar energy into PTSA technology are also discussed from the standpoint of the utilization of solar grade heat due to two energy loads required for PTSA's operation.
Applied Thermal Engineering, 2018
This paper presents a comprehensive thermodynamic research on energy efficiency of vacuum-pressur... more This paper presents a comprehensive thermodynamic research on energy efficiency of vacuum-pressure swing adsorption (VPSA). The study examined the influence from four types of typical adsorbent materials on the energy efficiency of VPSA by cycle parameters. The selected adsorbent materials are activated carbons, zeolite 5A, zeolite 13X, silica gels, and metal-organic frameworks (MOFs). The study also analyzes the effects of separation temperature, adsorption pressure, desorption pressure, CO2 concentration and percent of unused bed on the energy-efficiency of VPSA cycle. The examined performance parameters are CO2 working capacity, proportionality factor, energy consumption and second-law efficiency. The results show that the energy consumption is approximately 2.0-4.5MJ/kg and the second-law efficiencies are 4%-7% for VPSA cycles using the five adsorbent materials. The effect of adsorbent materials on the energy efficiency mainly depends on the proportionality factor of CO2 working capacity (β) of VPSA cycle, which is important to screen materials at the fixed cyclic boundary conditions and preliminary calculation of second-law efficiency for VPSA cycles. For existing adsorbent materials which are Type I commonly, the lower values of β would lead to the higher second-law efficiencies. The development of new adsorbents of Type III would be extremely urgent in near future.
Energy Conversion and Management , 2017
A single-stage 4-step pressure-vacuum swing adsorption (PVSA) process, capable of CO 2 separation... more A single-stage 4-step pressure-vacuum swing adsorption (PVSA) process, capable of CO 2 separation from the prepared flue gas, is experimentally studied on a fresh perspective of energy-efficiency analysis. The major contribution of thermodynamic carbon pump, which includes the minimum CO 2 separation work and the second-law efficiency, is to establish the relationship between energy consumption and separation difficulty. Adsorption/desorption cycles utilizing a fixed bed of an adsorbent material made of zeolite 13X are performed. Not only the recovery target, but also the second-law efficiency is considered as the main performance criteria in this paper. Thereby, the performance analysis of experimental apparatus is conducted over a range of process parameters, namely 10–20% CO 2 concentration, 1.0–3.0 sl/min flow rate, 10–30 s time duration of pressur-ization with feed, 80–120 s time duration of feed and 40–80 s time duration of purge. The results show that the specific energy consumption for the 4-step PVSA experiments is varied from 2719.31 kJ/kg to 9334.21 kJ/kg, the corresponding range of second-law efficiency calculated by thermodynamic carbon pump is 1.83–4.27%. The efficiency of vacuum pump affects the specific energy consumption of CO 2 capture process. The second-law efficiency in experimental studies of this paper is strongly dependent on the mechanical work performance of vacuum pump.
Applied Thermal Engineering, 2017
The present work describes the theoretical research frameworks mainly for the thermodynamic prope... more The present work describes the theoretical research frameworks mainly for the thermodynamic properties of adsorbed phase, which is applied in the field of temperature swing adsorption (TSA) for CO2 capture. The heat of adsorption and specific heat capacity of the adsorbed phase are quantitatively analyzed based on the adsorption isotherm data of CO2 on activated carbon at the temperature ranging from 273K to 358K. Employing such thermodynamic properties of adsorbed CO2, the effect of four cyclic parameters on the energy-efficiency performance of 4-step TSA processes is evaluated based on the thermodynamic carbon pump theory including the minimum separation work and the second-law efficiency. The results show that the regeneration heat has been increased with considering adsorbed phase, and the amount of sensible heat for the adsorbed phase accounts for approximately one-sixth to one-fourth of the total thermal energy consumption. However, the corresponding second-law efficiencies just drop 1.43%-7.21%. Although the total thermal energy consumption is higher than the traditional absorption technologies, the second-law efficiencies are slightly higher due to lower heating requirements and auxiliary power.
Energy, 2017
Currently, the significant energy penalty and performance limitation of energy consumption are th... more Currently, the significant energy penalty and performance limitation of energy consumption are the main technical barriers to the large-scale applications of CO 2 capture. Carbon pump, which realizes an enrichment of CO 2 from carbon source to carbon sink, is applied in a modeling for energy-efficiency analysis of CO 2 capture technologies. In this study, two adsorption technologies, including vacuum-pressure swing adsorption (VPSA) and pressure-temperature swing adsorption (PTSA), are compared in terms of the minimum separation work and the second-law efficiency. Based on carbon pump, two adsorption cycles can be presented through the process expression in the adsorption isotherm diagram, which is an easy pathway to show CO 2 adsorbed amounts for each step. The influence of process parameters for VPSA and PTSA were studied as well. Results show that the maximum values of the second-law efficiency are 24.30% and 19.09%, respectively for VPSA and PTSA with the change of CO 2 concentration from 5% to 25%. However, the second-law efficiency for VPSA and PTSA decreases with the increase of the other three factors, including desorption temperature, pressure of the feed and percent of unused bed. Parameters of component in cycle should also receive more attention for energy-efficiency analysis.
Energy, 2017
Currently, significant energy consumption is one of the main technical barriers to the large-scal... more Currently, significant energy consumption is one of the main technical barriers to the large-scale application of CO 2 capture technology. A novel conceptdcarbon pumpdis proposed in this paper to analyze the energy-efficiency of these technologies. The analysis model, which embodies the carbon pump concept, includes the minimum CO 2 separation work and the second-law efficiency. Based on this model, the proposed method is applied to comparative analysis of current capture technologies considering both the quantity of energy consumption and the grade of difficulty level for CO 2 separation. The analyzed results show that the second-law efficiencies of the statistical cases are below 35%. For post-combustion technologies with CO 2 concentrations ranging from 5% to 15%, the higher group of second-law efficiency is approximately above 15%, and the lower is approximately 10% or lower. It can be concluded that a great energy-saving potential still exists in post-combustion technologies through improving the efficiency of heat exchanger and pump, developing new materials, and network optimization. Additionally, integrating renewable energy into capture technologies is an important measure for reducing the consumption of primary energy and the carbon footprint of the whole system.
Renewable and Sustainable Energy Reviews, 2015
Since 2000, solar thermal utilization (STU) has a great process in China, not only with a large s... more Since 2000, solar thermal utilization (STU) has a great process in China, not only with a large scale commercial development, but also with an increasing number of scientific publications and patent applications. In this paper, several representative technologies of STU in China are studied based on an analysis of the relationship between patents and policies. Patent information of STU is collected and analyzed in terms of the time distribution, type distribution and technical trends. The main driving factor—energy policy—was discussed through the patent analysis. STU patents took off after the millennium and 85.8% of them came from the solar water heater. For conventional technologies, 94.2% of the granted patents were from companies and individuals, and the patents proposed by various research institutions were mainly in the technological beginning and technological maturity. Advanced technologies are still at a growth stage in China, and they have 412 patents in all and 70.5% of the patents were from systematic design and test method. Energy policies have played a significant role in promoting the progress of STU in China. Based on a patent analysis, it can be expected that STU will enter the age of medium-high temperature in China.
Energy Conversion and Management, 2015
One of main technical barriers to a large-scale application of carbon capture and storage (CCS) t... more One of main technical barriers to a large-scale application of carbon capture and storage (CCS) technology is a significant amount of required energy, e.g., regeneration heat of solvent in the chemical absorption system. Thus, energy consumption and corresponding high operation cost become two primary challenges for the promotion of CCS technology. Meanwhile, energy from the solar source in various forms has already been successfully used as an effective alternative supply in the industrial section for drying, heating and even cooling. Thus, integrating solar energy utilization into the CCS process could be a reasonable option for a sustainable development. A comparative analysis of CCS integrated with solar energy was presented in this paper based on the existing researches. The current status on typical configuration structure, feature and energy-efficiency performance of integrating options is reviewed for post-combustion, pre-combustion and oxygen-combustion systems. Based on these typical CO 2 capture systems, a theoretical analysis is conducted for an energy-efficient comparison. Then four typical structures of the post-combustion system, which are highlighted in the review, are chosen as comparative objects for energy-saving and techno-economic evaluation. The results show that systems with a solar-assisted thermal energy and power generation have comparative advantages in term of carbon emission intensity, but the economic cost is increased under the current conditions of the equipment price. Compared to that of baseline case, carbon emission intensity of the case integrated with solar Organic Rankine Cycle can be reduced with a maximum decline of 9.73%, meanwhile the levelized costs of electricity increases 0.01 USD/kW h correspondingly.
International Journal of Greenhouse Gas Control, 2014
A novel system integrating solar Organic Rankine Cycle (ORC) into a power plant with amine-based ... more A novel system integrating solar Organic Rankine Cycle (ORC) into a power plant with amine-based chemical absorption for CO 2 capture is proposed. The condensation heat of ORC provides the required heat for solvent regeneration, which avoids the energy penalty caused by the steam extraction traditionally. The cascade utilization of solar energy is realized through a combined supply of power generation and condensation heat. From the aspects of technology and economics, a performance analysis is presented to compare the proposed system and three other systems based on a 300 MWe power plant. The proposed system shows better performance than that of reference systems in the power generation and emission reductions. Economic evaluation was conducted in terms of levelized costs of electricity (LCOE) and cost of CO 2 removed (COR). In order to achieve lower LCOE and COR compared to the power plant integrated with solar assisted post-combustion CO 2 capture (PCC), the price of ORC has to be lower than 1284.46 USD/kW under the conditions that the price of the solar field is 120 USD/m 2. It is believed that the proposed system has a satisfied potential to meet the thermal demand for the solvent regeneration in the power plant with PCC.
Journal of Thermal Science, 2019
As a huge reserve for potential energy, natural gas hydrates (NGHs) are attracting increasingly e... more As a huge reserve for potential energy, natural gas hydrates (NGHs) are attracting increasingly extra attentions, and a series of researches on gas recovery from NGHs sediments have been carried out. But the slow formation and dissociation kinetics of NGHs is a major bottleneck in the applications of NGHs technology. Previous studies have shown that nanobubbles, which formed from melt hydrates, have significant promotion effects on dissociation and reformation dynamics of gas hydrates. Nanobubbles can persist for a long time in liquids, disaccording with the standpoint of classical thermodynamic theories, thus they can participate in the hydrate process. Based on different types of hydrate systems (gas + water, gas +water +inhibitors/promoters, gas + water + hydrophilic/hydrophobic surface), the effects of nanobubble evolution on nucleation, dissociation, reformation process and "memory effect" of gas hydrates are discussed in this paper. Researches on the nanobubbles in hydrate process are also summarized and prospected in this study.
Renewable and Sustainable Energy Reviews, 2019
Carbon dioxide capture from the post-combustion flue gas via temperature swing adsorption is supp... more Carbon dioxide capture from the post-combustion flue gas via temperature swing adsorption is supposed to be a valid technology to mitigate carbon emissions. With regard to the adsorbent development and process improvement , the technologies of temperature swing adsorption for post-combustion carbon dioxide capture have been reviewed and compared in terms of fixed bed, fluidized bed and moving bed. A comprehensive evaluation framework of fixed-bed temperature swing adsorption for CO 2 capture has been established. In a four-step fixed-bed cycle, a shortcut model has been utilized. Four typical adsorbent materials, such as activated carbon, zeolite 13X, zeolite NaUSY and Mg-MOF-74, have been chosen in this assessment. The comparative study has been conducted under the same operating conditions, from four aspects using eight performance indicators. Results indicate that Mg-MOF-74 and zeolite 13X reveal excellent performance among the four selected adsorbents. Thereinto, Mg-MOF-74 performs well at four indicators including purity, productivity, specific thermal energy consumption and second-law efficiency; zeolite 13X excels in the other four indicators such as selectivity, recovery , minimum separation work and capture cost. Future work will complete a thorough assessment criterion in evaluating the TSA process for CO 2 capture.
Energy Conversion and Management, 2019
Abrupt climate change such as the loss of Arctic sea-ice area urgently needs negative emissions t... more Abrupt climate change such as the loss of Arctic sea-ice area urgently needs negative emissions technologies. The potential application of direct air capture of carbon dioxide from indoor air and outdoor air in closed buildings or crowded places has been discussed in this paper. From the aspects of carbon reduction and indoor comfort, the ventilation system integrating a capture device is of great value in practical use. For ultra-dilute carbon dioxide sources, many traditional separation processes have no cost advantages, but adsorption technologies such as temperature vacuum swing adsorption is one of suitable methods. Thermodynamic exploration has been investigated regarding minimum separation work and second-law efficiency at various concentrations in the air. The influence of concentration, adsorption temperature, desorption temperature and desorption pressure on the energy efficiency has also been evaluated. Results show that the minimum separation work for the level of 400 ppm is approximately 20 kJ/mol. The optimal second-law efficiencies are 44.57%, 37.55% and 31.60%, respectively for 3000 ppm, 2000 ppm and 1000 ppm. It means that a high energy-efficiency capture device in buildings merits attention in the exploration of the possibility of approaching negative carbon buildings.
Journal of Cleaner Production, 2019
This paper presents a techno-economic study to seek the feasibility about the proposed system tha... more This paper presents a techno-economic study to seek the feasibility about the proposed system that integrating solar-assisted pressure-temperature swing adsorption (PTSA) into an 800MWe coal-fired power plant. Solar energy has the potential to supply thermal energy demand for carbon capture, which can avoid the energy consumption of the traditional method such as the steam extraction. The performance of the proposed system is largely affected by the climatic conditions and solar collector's types. The assessment criteria include carbon emission intensity (CEI), levelized cost of electricity (LCOE) and cost of CO2 avoidance (COA). By the parametric analysis, the results show that CEI of the novel system with solar thermal collectors is approximately 2g/kWh lower than that of the referenced power plant with CO2 adsorption capture. In addition, CEI of the novel system can be further decrease with the decline of desorption temperature, adsorption pressure and desorption pressure. For the sake of lower LCOE and COA, the prices of the power plant capacity, adsorbents and solar collectors should be reduced. Specifically, LCOE of the system with evacuated tube collector will be lower than that of the reference system with CO2 capture as the price of solar field is lower than 46.08 USD/m2.
Energy Procedia, 2014
As an end user of energy products, carbon dioxide capture and storage (CCS) system commonly requi... more As an end user of energy products, carbon dioxide capture and storage (CCS) system commonly requires a significant amount of energy to sustain a steady operation. As a renewable energy source, solar energy can supply plenty of thermal energy in different grades through various types of solar collector. Between the demand and supply sides, several technologies of solar thermal engineering can be applied as a bridge for an energy efficient design. In this paper, a technological framework for the energy efficiency in post-combustion CO 2 capture is further discussed as a second section of the two-part study. Based on existing research, several possible options of alternative energy supply to CCS system are analyzed, particularly for solar thermal energy. Moreover, some key design issues for the solar-assisted CCS system, such as integrated solar reactor with the regeneration component, are discussed as well.
Energy Procedia, 2014
Representative carbon dioxide capture and storage (CCS) system of the post-combustion, no matter ... more Representative carbon dioxide capture and storage (CCS) system of the post-combustion, no matter it employs adsorption, absorption or cryogenics separation technologies, commonly requires significant amounts of energy for the fundamental operation. Thus, energy consumption and related cost rise are primary challenges for the promotion of post-combustion technology. Solar thermal energy has already been widely used as an effective and clean energy source in industrial applications for drying, heating and even cooling since the last century. Various options of solar collector, such as flat plate type, evacuate tube type, and parabolic trough type, facilitate a comprehensive energy supply in different energy quality grades. In this paper, a technological framework for the energy efficiency in post-combustion CO 2 capture is briefly presented for a connection between the energy demand of a CCS system and the energy supply of solar thermal engineering. The match performance between solar thermal utilization systems and CCS system is discussed in terms of energy form of the demand side (CCS), energy grades of supply sides (solar collector), and possible dynamic adjustment.
Energy Procedia, 2014
Solvent-based Post-combustion Carbon Capture (PCC), which can reduce CO 2 emissions from coal-fir... more Solvent-based Post-combustion Carbon Capture (PCC), which can reduce CO 2 emissions from coal-fired power plants, is one of the most advanced mature Carbon Capture and Storage (CCS) technologies at present. Two problems limit its development. One is the output reduction of power plant due to the steam extraction from turbine. The other is a large amount of water consumption for the evaporation of the solution in the absorber and desorber. In this paper we propose an integrated system to reduce the steam extraction from turbine and to produce freshwater by using solar thermal energy. The new system produces more electricity and freshwater during the daytime, and uses the steam extraction to reduce CO 2 emissions at night. A techno-economic feasibility study is performed as a case study for a 300 MWe coal-fired power plant assisted by solar desalination. As for the potential impact parameters, the local climatic conditions and CO 2 capture rate are discussed. Low-cost collectors and desalting equipment would make the technology more cost-effective.
Applied Energy, 2018
The carbon capture by adsorption (CCA) is regarded as an available engineering technology because... more The carbon capture by adsorption (CCA) is regarded as an available engineering technology because of its low energy-consumption, easy to control, and possible integration with renewable energy. The recent advances in CCA research comprises mainly about the performance improvement of adsorbents, design and optimization of engineering process. However, considering the time-consuming and intensive funding required for experimental investigation, the numerical simulation has been widely applied in CCA. In numerical simulation field of CCA, the adsorption process is commonly simplified into mathematical models group comprised of adsorption kinetics model, the adsorption equilibrium model, pressure drop model and heat transfer model. However, few studies’ focus is to provide a detailed review of the research methodology of mathematical modeling in CCA simulation.
This paper presents a pathway map on CCA mathematical modeling through literature review and case study. An overview of model screening and modeling method of CCA is provided in the review part. This part also provides a short guided tour on how to combine the fundamental models about heat and mass transfer together to form a model group for various application scenarios in CCA. Then the pathway map on CCA modeling, which is summarized based on the review, is applied to a case study. In this part, the adsorption of CO2/N2 mixtures on activated carbon under the conditions of high temperature and low pressure is numerically investigated based on the established models. The performance indicators comprise gas temperature, mole fraction, and adsorbate amount of the fixed bed, are applied in the evaluation performance of CCA. Based on the proposed methodology, the CCA modeling demonstrates a more fluent design process relative to the real physical scenario, with a possible access to further optimization. Particularly, the simulation results showed that the optimized dimensionless velocity for the highest utilization efficiency of the fixed bed can be obtained and thus is proposed as 1.2–1.4 for the most suitable feed velocity to fit different size of fixed bed and different types of adsorbents for the engineering design.
Renewable and Sustainable Energy Reviews, 2017
Traditional technologies of carbon capture and storage (CCS) are being focused on capturing CO 2 ... more Traditional technologies of carbon capture and storage (CCS) are being focused on capturing CO 2 in large-scale demonstrations, which has been proved to result in the high cost and energy penalty. Meanwhile, typical innovative measures, commonly defined as the second generation CCS technologies, elude conventional ones by integrating with solar energy and thus contributing to a more energy-efficient conversion of CO 2. However, few reviews pay attention to thermodynamic processes and parameters of these novel technologies, and there is a lack of systematic evaluation and comparison among them. This paper firstly presents a guided tour on the state-of-art of typical and innovative CCS technologies integrated with solar energy. An overview on thermodynamic processes, including chemical reactions, operating conditions and efficiency indexes of five typical technologies is presented so that the current development level can be clarified. Since the high energy requirement and related operating cost are the main barriers to the application of existing CCS technologies, the minimum work and second-law efficiency are applied as the main indicators in the second part of this paper which relates to performance evaluation. In addition, the performance windows for innovative technologies are illustrated for the comparison of technological maturity. The results show that energy requirement of innovative CCS technologies from the flue gas is avg. 100–200 kJ/mol CO 2 and the second-law efficiency of them is only 5– 12%. Therefore, the maturity and popularity of these novel technologies are still relatively low. But the well-integrated systems and diversified output of these technologies can benefit existing energy infrastructures in a long period.
Journal of CO2 Utilization, 2018
This study explores the impacts of materials, such as adsorbents and electrodes, on the energy ef... more This study explores the impacts of materials, such as adsorbents and electrodes, on the energy efficiency of a 4-step ESA cycle for CO 2 capture. Three types of adsorbents including activated carbon honeycomb monolith (ACHM) and two hybrid adsorbents are compared, and two kinds of electrodes such as aluminum and brass are combined for comparative analysis. Process description of ESA cycle, including feed, electrification, elec-trification with purge and cooling, is presented via the adsorption isotherm diagram. By the theory of ther-modynamic carbon pump, sensitivity analysis of cycle parameters is evaluated in terms of the second-law efficiency (Eff 2nd) and the electrical heating efficiency (Eff ele). The results show that Eff 2nd of the employed adsorbents is in the range of 1.17%–6.15%, and Eff ele of the selected electrodes is between 27.46% and 60.91%. Among the three adsorbents, Eff 2nd of ACHM is the lowest one compared to the others. Similarly, Eff ele of the combination with brass is superior to that of the groups with aluminum. However, the actual efficiency of ESA cycle is the production of both Eff 2nd and Eff ele , which is approximately 1.03%–3.66%. Typical measures are proposed to reduce the heat loss of the adsorbents and electrodes as well for future work.
Solar Energy Materials and Solar Cells, 2018
Because of the ability to utilize the low-grade solar thermal energy for regeneration, a CO 2 cap... more Because of the ability to utilize the low-grade solar thermal energy for regeneration, a CO 2 capture system characterized by solar-assisted pressure temperature swing adsorption (SOL-PTSA) is studied on the effects of adsorbent materials. A detailed cycle description is firstly presented within the diagram of adsorption isotherm for the energy-efficiency analysis. Typical adsorbent materials, including zeolites and chemical adsorbent, are assessed in terms of sensible heat and latent heat, etc. Then, the energy consumption and the second-law efficiency , which can be considered as lumped indicators from such material parameters, are chosen as performance indicators as well. The influence of separation temperature, desorption temperature, CO 2 concentration and CO 2 adsorption pressure on system performance are finally obtained. For the chosen three adsorbent materials, the energy consumption of SOL-PTSA system is at the range of 25.96–87.76 kJ/mol, and the corresponding second-law efficiencies are at the range of 9.18–26.89%. The effect of adsorbent materials on the energy-efficiency of SOL-PTSA system mainly depends on specific heat, CO 2 working capacity and cycle design. In addition, the integration options of solar energy into PTSA technology are also discussed from the standpoint of the utilization of solar grade heat due to two energy loads required for PTSA's operation.
Applied Thermal Engineering, 2018
This paper presents a comprehensive thermodynamic research on energy efficiency of vacuum-pressur... more This paper presents a comprehensive thermodynamic research on energy efficiency of vacuum-pressure swing adsorption (VPSA). The study examined the influence from four types of typical adsorbent materials on the energy efficiency of VPSA by cycle parameters. The selected adsorbent materials are activated carbons, zeolite 5A, zeolite 13X, silica gels, and metal-organic frameworks (MOFs). The study also analyzes the effects of separation temperature, adsorption pressure, desorption pressure, CO2 concentration and percent of unused bed on the energy-efficiency of VPSA cycle. The examined performance parameters are CO2 working capacity, proportionality factor, energy consumption and second-law efficiency. The results show that the energy consumption is approximately 2.0-4.5MJ/kg and the second-law efficiencies are 4%-7% for VPSA cycles using the five adsorbent materials. The effect of adsorbent materials on the energy efficiency mainly depends on the proportionality factor of CO2 working capacity (β) of VPSA cycle, which is important to screen materials at the fixed cyclic boundary conditions and preliminary calculation of second-law efficiency for VPSA cycles. For existing adsorbent materials which are Type I commonly, the lower values of β would lead to the higher second-law efficiencies. The development of new adsorbents of Type III would be extremely urgent in near future.
Energy Conversion and Management , 2017
A single-stage 4-step pressure-vacuum swing adsorption (PVSA) process, capable of CO 2 separation... more A single-stage 4-step pressure-vacuum swing adsorption (PVSA) process, capable of CO 2 separation from the prepared flue gas, is experimentally studied on a fresh perspective of energy-efficiency analysis. The major contribution of thermodynamic carbon pump, which includes the minimum CO 2 separation work and the second-law efficiency, is to establish the relationship between energy consumption and separation difficulty. Adsorption/desorption cycles utilizing a fixed bed of an adsorbent material made of zeolite 13X are performed. Not only the recovery target, but also the second-law efficiency is considered as the main performance criteria in this paper. Thereby, the performance analysis of experimental apparatus is conducted over a range of process parameters, namely 10–20% CO 2 concentration, 1.0–3.0 sl/min flow rate, 10–30 s time duration of pressur-ization with feed, 80–120 s time duration of feed and 40–80 s time duration of purge. The results show that the specific energy consumption for the 4-step PVSA experiments is varied from 2719.31 kJ/kg to 9334.21 kJ/kg, the corresponding range of second-law efficiency calculated by thermodynamic carbon pump is 1.83–4.27%. The efficiency of vacuum pump affects the specific energy consumption of CO 2 capture process. The second-law efficiency in experimental studies of this paper is strongly dependent on the mechanical work performance of vacuum pump.
Applied Thermal Engineering, 2017
The present work describes the theoretical research frameworks mainly for the thermodynamic prope... more The present work describes the theoretical research frameworks mainly for the thermodynamic properties of adsorbed phase, which is applied in the field of temperature swing adsorption (TSA) for CO2 capture. The heat of adsorption and specific heat capacity of the adsorbed phase are quantitatively analyzed based on the adsorption isotherm data of CO2 on activated carbon at the temperature ranging from 273K to 358K. Employing such thermodynamic properties of adsorbed CO2, the effect of four cyclic parameters on the energy-efficiency performance of 4-step TSA processes is evaluated based on the thermodynamic carbon pump theory including the minimum separation work and the second-law efficiency. The results show that the regeneration heat has been increased with considering adsorbed phase, and the amount of sensible heat for the adsorbed phase accounts for approximately one-sixth to one-fourth of the total thermal energy consumption. However, the corresponding second-law efficiencies just drop 1.43%-7.21%. Although the total thermal energy consumption is higher than the traditional absorption technologies, the second-law efficiencies are slightly higher due to lower heating requirements and auxiliary power.
Energy, 2017
Currently, the significant energy penalty and performance limitation of energy consumption are th... more Currently, the significant energy penalty and performance limitation of energy consumption are the main technical barriers to the large-scale applications of CO 2 capture. Carbon pump, which realizes an enrichment of CO 2 from carbon source to carbon sink, is applied in a modeling for energy-efficiency analysis of CO 2 capture technologies. In this study, two adsorption technologies, including vacuum-pressure swing adsorption (VPSA) and pressure-temperature swing adsorption (PTSA), are compared in terms of the minimum separation work and the second-law efficiency. Based on carbon pump, two adsorption cycles can be presented through the process expression in the adsorption isotherm diagram, which is an easy pathway to show CO 2 adsorbed amounts for each step. The influence of process parameters for VPSA and PTSA were studied as well. Results show that the maximum values of the second-law efficiency are 24.30% and 19.09%, respectively for VPSA and PTSA with the change of CO 2 concentration from 5% to 25%. However, the second-law efficiency for VPSA and PTSA decreases with the increase of the other three factors, including desorption temperature, pressure of the feed and percent of unused bed. Parameters of component in cycle should also receive more attention for energy-efficiency analysis.
Energy, 2017
Currently, significant energy consumption is one of the main technical barriers to the large-scal... more Currently, significant energy consumption is one of the main technical barriers to the large-scale application of CO 2 capture technology. A novel conceptdcarbon pumpdis proposed in this paper to analyze the energy-efficiency of these technologies. The analysis model, which embodies the carbon pump concept, includes the minimum CO 2 separation work and the second-law efficiency. Based on this model, the proposed method is applied to comparative analysis of current capture technologies considering both the quantity of energy consumption and the grade of difficulty level for CO 2 separation. The analyzed results show that the second-law efficiencies of the statistical cases are below 35%. For post-combustion technologies with CO 2 concentrations ranging from 5% to 15%, the higher group of second-law efficiency is approximately above 15%, and the lower is approximately 10% or lower. It can be concluded that a great energy-saving potential still exists in post-combustion technologies through improving the efficiency of heat exchanger and pump, developing new materials, and network optimization. Additionally, integrating renewable energy into capture technologies is an important measure for reducing the consumption of primary energy and the carbon footprint of the whole system.
Renewable and Sustainable Energy Reviews, 2015
Since 2000, solar thermal utilization (STU) has a great process in China, not only with a large s... more Since 2000, solar thermal utilization (STU) has a great process in China, not only with a large scale commercial development, but also with an increasing number of scientific publications and patent applications. In this paper, several representative technologies of STU in China are studied based on an analysis of the relationship between patents and policies. Patent information of STU is collected and analyzed in terms of the time distribution, type distribution and technical trends. The main driving factor—energy policy—was discussed through the patent analysis. STU patents took off after the millennium and 85.8% of them came from the solar water heater. For conventional technologies, 94.2% of the granted patents were from companies and individuals, and the patents proposed by various research institutions were mainly in the technological beginning and technological maturity. Advanced technologies are still at a growth stage in China, and they have 412 patents in all and 70.5% of the patents were from systematic design and test method. Energy policies have played a significant role in promoting the progress of STU in China. Based on a patent analysis, it can be expected that STU will enter the age of medium-high temperature in China.
Energy Conversion and Management, 2015
One of main technical barriers to a large-scale application of carbon capture and storage (CCS) t... more One of main technical barriers to a large-scale application of carbon capture and storage (CCS) technology is a significant amount of required energy, e.g., regeneration heat of solvent in the chemical absorption system. Thus, energy consumption and corresponding high operation cost become two primary challenges for the promotion of CCS technology. Meanwhile, energy from the solar source in various forms has already been successfully used as an effective alternative supply in the industrial section for drying, heating and even cooling. Thus, integrating solar energy utilization into the CCS process could be a reasonable option for a sustainable development. A comparative analysis of CCS integrated with solar energy was presented in this paper based on the existing researches. The current status on typical configuration structure, feature and energy-efficiency performance of integrating options is reviewed for post-combustion, pre-combustion and oxygen-combustion systems. Based on these typical CO 2 capture systems, a theoretical analysis is conducted for an energy-efficient comparison. Then four typical structures of the post-combustion system, which are highlighted in the review, are chosen as comparative objects for energy-saving and techno-economic evaluation. The results show that systems with a solar-assisted thermal energy and power generation have comparative advantages in term of carbon emission intensity, but the economic cost is increased under the current conditions of the equipment price. Compared to that of baseline case, carbon emission intensity of the case integrated with solar Organic Rankine Cycle can be reduced with a maximum decline of 9.73%, meanwhile the levelized costs of electricity increases 0.01 USD/kW h correspondingly.
International Journal of Greenhouse Gas Control, 2014
A novel system integrating solar Organic Rankine Cycle (ORC) into a power plant with amine-based ... more A novel system integrating solar Organic Rankine Cycle (ORC) into a power plant with amine-based chemical absorption for CO 2 capture is proposed. The condensation heat of ORC provides the required heat for solvent regeneration, which avoids the energy penalty caused by the steam extraction traditionally. The cascade utilization of solar energy is realized through a combined supply of power generation and condensation heat. From the aspects of technology and economics, a performance analysis is presented to compare the proposed system and three other systems based on a 300 MWe power plant. The proposed system shows better performance than that of reference systems in the power generation and emission reductions. Economic evaluation was conducted in terms of levelized costs of electricity (LCOE) and cost of CO 2 removed (COR). In order to achieve lower LCOE and COR compared to the power plant integrated with solar assisted post-combustion CO 2 capture (PCC), the price of ORC has to be lower than 1284.46 USD/kW under the conditions that the price of the solar field is 120 USD/m 2. It is believed that the proposed system has a satisfied potential to meet the thermal demand for the solvent regeneration in the power plant with PCC.