Hydrogen production from solar energy powered supercritical cycle using carbon dioxide

A hydrogen production method is proposed, which utilizes solar energy powered thermodynamic cycle using supercritical carbon dioxide (CO₂) as working fluid for the combined production of hydrogen and thermal energy. The proposed system consists of evacuated solar collectors, power generating turbine, water electrolysis, heat recovery system, and feed pump. In the present study, an experimental prototype has been designed and constructed. The performance of the cycle is tested experimentally under different weather conditions. CO₂ is efficiently converted into supercritical state in the collector, the CO₂ temperature reaches about 190 °C in summer days, and even in winter days it can reach about 80 °C. Such a high-temperature realizes the combined production of electricity and thermal energy. Different from the electrochemical hydrogen production via solar battery-based water splitting on hand, which requires the use of solar batteries with high energy requirements, the generated electricity in the supercritical cycle can be directly used to produce hydrogen gas from water. The amount of hydrogen gas produced by using the electricity generated in the supercritical cycle is about 1035 g per day using an evacuated solar collector of 100.0 m² for per family house in summer conditions, and it is about 568.0 g even in winter days. Additionally, the estimated heat recovery efficiency is about 0.62. Such a high efficiency is sufficient to illustrate the cycle performance.     

Use of solar energy to reduce carbon dioxide

It is thermodynamically possible to decompose carbon dioxide to carbon and oxygen by means of thermochemical cycles analogous to cyclic processes for decomposing water. Highly concentrated solar energy can supply the necessary energy at temperatures that permit short, efficient cycles. The reduced carbon can be converted to fuels that are dense, convenient, and require no major changes in the consuming sector of the economy.     

Thermodynamic analysis of a novel energy storage system with carbon dioxide as working fluid

Recently, energy storage system (ESS) with carbon dioxide (CO₂) as working fluid has been proposed as a new method to deal with the application restrictions of Compressed Air Energy Storage (CAES) technology, such as dependence on geological formations and low energy storage density. A novel ESS named as Compressed CO₂ Energy Storage (CCES) based on transcritical CO₂ Brayton cycle is presented in this paper. The working principle of CCES system is introduced and thermodynamic model is established to assess the system performance. Parametric analysis is carried out to study the effect of some key parameters on system performance. Results show that the increase of turbine efficiency is more favorable for system optimization and the effect of minimum pressures on system performance is more significant compared with maximum pressures. A simple comparison of CCES system, liquid CO₂ system and Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) system is conducted. It is shown that the system efficiency of CCES is lower than that of AA-CAES system but 4.05% higher than that of liquid CO₂ system, while the energy density of CCES system is 2.8 times the value of AA-CAES system, which makes CCES a novel ESS with potential application.     

A solar energy storage and power generation system based on supercritical carbon dioxide

This paper proposes a new type of solar energy based power generation system using supercritical carbon dioxide and heat storage. The power generation cycle uses supercritical carbon dioxide as the working fluid and integrates the supercritical carbon dioxide cycle with an efficient high-temperature heat storage. The analysis shows that the new power generation system has significantly higher solar energy conversion efficiency in comparison to the conventional water-based (steam) system. At the same time, the heat storage not only overcomes the intermittent nature of solar energy but also improves the overall system efficiency. The study further reveals that the high temperatures and high pressures are favorable for solar energy storage and power generation. Moreover the expander and the heat storage/regenerator are found to be the key components that determine the overall system performance.     

Integrated biomass energy systems and emissions of carbon dioxide

Electric Power Research Institute (EPRI) and the US Department of Energy (DOE) have been funding a number of case studies under the initiative entitled “Economic Development through Biomass Systems Integration”, with the objective of investigate the feasibility of integrated biomass energy systems, utilizing a dedicated feedstock supply system (DFSS) for energy production. This paper deals with the full fuel cycle for four of these case studies, which have been examined with regard to the emissions of carbon dioxide, CO₂. Although the conversion of biomass to electricity in itself does not emit more CO₂ than is captured by the biomass through photosynthesis, there will be some CO₂ emissions from the DFSS. External energy is required for the production and transportation of the biomass feedstock, and this energy is mainly based on fossil fuels. By using this input energy, CO₂ and other greenhouse gases are emitted. However, by utilizing biomass with fossil fuels as external input fuels, we would get about 10–15 times more electric energy per unit fossil fuel, compared with a 100% coal power system. By introducing a DFSS on former farmland the amount of energy spent for production of crops can be reduced, the amount of fertilizers can be decreased, the soil can be improved and a significant amount of energy will be produced compared with an ordinary farm crop. Compared with traditional coal-based electricity production, the CO₂ emissions are in most cases reduced significantly by as much as 95%. The important conclusion is the great potential for reducing greenhouse gas emissions through the offset of coal by biomass.     

Thermodynamic analysis of a novel compressed carbon dioxide energy storage system with low-temperature thermal storage

Research projects on new electrical energy storage (EES) systems are underway because of the role of EES in balancing the electric grid and smoothing out the instability of renewable energy. In this paper, a novel compressed carbon dioxide energy storage with low-temperature thermal storage was proposed. Liquid CO₂ storage was employed to increase the storage density of the system and avoid its dependence on geological formations. Low-temperature thermal energy storage technology was utilized to recycle the heat of compression and reduce the challenges to system components. The system configuration was introduced in detail. Four evaluation criteria, the round trip efficiency (RTE), exergy efficiency (η_Ex), thermal efficiency (η_TE), and energy density (ρ_E) were defined to show the system performance. Parametric analysis was carried out to examine the effects of some key parameters on system performance and the genetic algorithm was adopted for system optimization. The calculated results show that, for the novel EES under the basic working condition, its RTE is 41.4%, η_TE is 59.7%, η_Ex is 45.4%, and ρ_E is 15 kWh m⁻³. The value of ρ_E increases with the increasing pump outlet pressure for a fixed value of pressure ratio, and the changes of RTE, η_TE, and the total exergy destruction of the system (E_D,total) with pump outlet pressure are complicated for different values of pressure ratio. When both pressure ratio and pump outlet pressure are high, the values of RTE and ρ_E can be maximized whereas the value of E_D,total can be minimized. Besides, no matter how pump outlet pressure and pressure ratio change, the exergy destruction of the system mainly come from compressors and regenerators, which accounts for about 50% of the total exergy destruction.     

Analysis and forecast of the Tianjin industrial carbon dioxide emissions resulted from energy consumption

This paper analyses the carbon dioxide emissions caused by industrial energy consumption of Tianjin from 2005 to 2012. The carbon emissions decomposition illustrated that the scale of production factor played a major role in the growth of Tianjin industrial carbon emissions and the average contribution of carbon emissions is up to 220.8975% in the statistical period; the intensity of energy factor played an important role in slowing down the growth of industrial carbon dioxide emissions. The average contribution of carbon emissions was ?136.1994% in the statistical period. The prediction model based on carbon emissions data from industrial energy consumption from 2003 to 2012 reached a high accuracy, with an average error of 1.78% for stochastic impacts by regression on population, affluence, and technology (STIRPAT) model, 2.41% for the Logistic regression model and an average error of 1.54% for the grey model. This research can contribute to predict the carbon emission and through it some suggestions can be made.     

Analytical model of carbon dioxide emission with energy payback effect

An analytical model is proposed to account for carbon emission behaviour during replacement of power source from fossil fuel to renewable energy in which sustainability of energy supply is stressed. Logistic function of time is assumed for producing renewable power sources. Analyses show that energy payback time (EPT) should be much shorter than the doubling time of manufacturing cycle to secure adequate available energy during, as well as after, the replacement. A nuclear plant, small hydropower plant, wind power plant and photovoltaic cell are taken as representative candidates and investigated as options to replace fossil power until toward the end of this century. Nuclear or small hydropower plants are promising candidates but the photovoltaic cell needs further development efforts to reduce EPT and avoid energy expense after the replacement.     

Negative carbon intensity of renewable energy technologies involving biomass or carbon dioxide as inputs

Conventional fossil fuel-based energy technologies can achieve efficiency in energy conversion but they are usually completely inefficient in carbon conversion because they generate significant CO₂ emissions to the atmosphere per unit energy converted. In contrast, some renewable energy technologies characterized by negative carbon intensity can simultaneously achieve efficiency in the conversion of energy and in the conversion of carbon. These carbon negative renewable energy technologies can generate useful energy and remove CO₂ from the atmosphere, either by direct capture and recycling of atmospheric CO₂ or indirectly, by involving biofuels. Interestingly, the deployment of carbon negative renewable energy technologies can offset carbon emissions from conventional fossil fuel-based energy technologies and thus reduce the overall carbon intensity of energy systems.The current review analyzes two groups of renewable energy technologies involving biomass or CO₂ as inputs. The discussions focus on useful techniques which enable to achieve negative carbon intensity of energy while being technologically promising in near-term as well as cost-effective. These analyzes include advanced carbon sequestration concepts such as soil carbon sequestration and CO₂ recycling to useful C-rich products such as fuels and fertilizers. The 'drop-in' of renewable energy is achieved by allowing bioenergy and renewable energies in the form of renewable electricity, renewable thermal energy, solar energy, renewable hydrogen, etc. The carbon negative renewable energy technologies are analyzed and perspectives and constraints of each technology are expounded.     

Study of solar energy powered transcritical cycle using supercritical carbon dioxide

In this paper, the performance of solar energy powered transcritical cycle using supercritical carbon dioxide for a combined electricity and heat generation, is studied experimentally. The experimental set‐up consists of evacuated solar collectors, pressure relief valve, heat exchangers and CO₂ feed pump. The pressure relief valve is used to simulate operation of a turbine and to complete the thermodynamic cycle. A complete effort was carried out to investigate the cycle performances not only in summer, but also in winter conditions. The results show that a reasonable thermodynamic efficiency can be obtained and COP for the overall outputs from the cycle is measured at 0.548 and 0.406, respectively, on a typical summer and winter day. The study shows the potential of the application of the solar energy powered cycle as a green power/heat generation system. Copyright © 2006 John Wiley & Sons, Ltd.     

Analysis of energy and carbon dioxide emission caused by power consumption

The main objective of this on‐site study is to use a full‐scale Heating, Ventilating, and Air‐Conditioning (HVAC) system installed in an office building in Taiwan for comparing the power consumption, energy‐saving, and carbon dioxide (CO₂) reduction of two different strategies for controlling the HVAC. These strategies are the Constant Volume (CV) system [Constant Air Volume+Constant‐flow], and the Variable Volume (VV) system [Variable Air Volume +Variable‐flow]. The on‐site experimental results indicate that average power consumptions are 164 kW for the CV system, and 88 kW for the VV system; the average electric current drops from 469 A for the CV system to 258 A for the VV system. Approximately 46% of the average energy‐saving can be achieved if the HVAC system is operated as a VV system. Additionally, the reduced quantity of accumulated CO₂ emission varies from 67 to 3687 kg with 0.637 kg CO₂ kwh^?1 emission factor during the office hours of 08:30 (a.m.)–17:00 (p.m.). The results demonstrate that switching the operation of an office building HVAC system from CV to VV will significantly enhance energy‐savings and CO₂ reduction. This studywill offer useful information for evaluating an indoor environmental policy with respect to energy‐savings and CO₂ emission reduction for office HVACs used in subtropical regions. Copyright © 2010 John Wiley & Sons, Ltd.     

Secure energy supply in 2025: Indonesia's need for an energy policy strategy

Indonesia as an emerging country with one of the fastest growing economies requires sufficient supply with energy for national development. Domestic energy production cannot satisfy the domestic demand, and the deficiency necessitates growing imports. The present energy mix consists of 96% from non-renewable sources, i.e. fossil fuels, less than 4% from renewables. Government Regulation 5/2006 aims at increasing the proportion of renewable sources to 17%. Two scenarios for the energy situation in 2025 have been elaborated and are discussed. An overall energy policy strategy and regulatory framework covering non-renewable and renewable resources are crucial for securing energy demand.     

利用环境再冷的二氧化碳储能热电联产系统及其热力学分析

为提升光电出力特性及灵活性,构建光储协同系统成为改善光电可调度性与减少弃光的主流趋势.本文基于光伏电场运营环境特点,提出一种利用夜间环境冷量再冷的二氧化碳储能热电联产系统,重点分析了不同运行模式下系统性能随关键参数的变化规律.结果表明:太阳能集热系统单独工作模式下,增大蓄冷回热器最小温差、夜间环境温度和低压罐压力会导致...     

太阳能技术对我国未来减排CO2的贡献

1世界对可再生能源减排作用的估计可再生能源不但是重要的后续能源,而且对未来减排CO2将发挥重要作用。国际上许多组织和国家预测,本世纪中叶可再生能源在一次性能源消耗中将超过50%。最近20年来,各种可再生能源技术的日趋成熟和生产规模的不断扩大,对能源的贡献也日渐增大。可以预料,随着可再生能源的快速发展,对未来CO2减排的贡献会越来越大。为加速发展中国家可再生能源的发展,1996年世界银行通过全球环境基金(GEF)项目,对未来CO2的排放作了如下估计:如果不采取措施,50年后,大气中CO2的含量就是现在的3.5倍,如果积极采取各种清洁能…     

Hydrate-based removal of carbon dioxide and hydrogen sulphide from biogas mixtures: Experimental investigation and energy evaluations

This paper presents an experimental study on the application of gas hydrate technology to biogas upgrading. Since CH₄, CO₂ and H₂S form hydrates at quite different thermodynamic conditions, the capture of CO₂ and H₂S by means of gas hydrate crystallization appears to be a viable technological alternative for their removal from biogas streams. Nevertheless, hydrate-based biogas upgrading has been poorly investigated. Works found in literature are mainly at a laboratory scale and concern with thermodynamic and kinetic fundamental studies. The experimental campaign was carried out with an up-scaled apparatus, in which hydrates are produced in a rapid manner, with hydrate formation times of few minutes. Two types of mixtures were used: a CH₄/CO₂ mixture and a CH₄/CO₂/H₂S mixture. The objective of the investigation is to evaluate the selectivity and the separation efficiency of the process and the role of hydrogen sulphide in the hydrate equilibrium. Results show that H₂S can be captured along with CO₂ in the same process. The maximum value of the separation factor, defined as the ratio between the number of moles of CO₂ and the number of moles of CH₄ removed from the gas phase, is 11. In the gas phase, a reduction of CO₂ of 24.5% in volume is achievable in 30 min.Energy costs of a real 30-min separation process, carried out in the experimental campaign, are evaluated and compared with those obtained from theoretical calculations. Some aspects for technology improvement are discussed.     

Some studies on reducing carbon dioxide emission from a CRDI engine with hydrogen and a carbon capture system

The increased use of fossil fuels in the transportation sector has led to an exponential rise of carbon dioxide in the atmosphere. The carbon dioxide (CO₂) is the major cause of global warming resulting in climate change and extreme weather conditions. This study explores the ways of reducing the CO₂ emission from the exhaust of a common rail engine. The reduction in CO₂ emissions were achieved by a combination of methods. It includes the use of low carbon biofuels (cedarwood oil (CWO), and wintergreen oil (WGO)), induction of zero-carbon, hydrogen in the intake manifold and a zeolite-based after-treatment system. In diesel, CWO and WGO were blended 20% by volume and experiments were conducted at different load conditions. The results shows that 20% blending of winter green oil resulted in maximum CO₂ reduction of 20% as compared to diesel. The emission was further reduced with the induction of hydrogen along with the after-treatment system. It is seen that a maximum of 54% reduction in CO₂ emission could be achieved with the combination for WGO in comparison to diesel without much affecting the other emissions and performance parameters.     

超临界二氧化碳布雷顿循环发电系统热力学分析

为了对超临界二氧化碳布雷顿循环发电系统热力学进行分析,首先构建了分流再压缩和一次再热耦合的超临界二氧化碳布雷顿循环系统主要关键部件的数学分析模型,并基于Matlab软件进行计算分析。分别讨论了系统主要关键参数对系统循环效率的影响。从仿真结果可以看出存在最佳的分流系数,最优的压缩机入口温度、压力和再热压力,使得循环系统具有较高的循环效率。最后为能够全面地反映系统综合性能,引入了遗传算法作为优化分析方法,研究多参数对系统循环效率的综合影响,得到最高效率点的最优关键参数。     

超临界二氧化碳再压缩布雷顿循环系统动态特性研究

超临界二氧化碳(S-CO₂)布雷顿循环因其环保性与高热电转换效率而被视为核能发电未来发展的重要方向。借助Simulink软件平台,建立了S-CO₂再压缩布雷顿循环闭环动态仿真系统,通过模拟结果与Sandia实验数据的比较,验证了系统模型的有效性。研究搭建的超临界CO₂再压缩布雷顿循环系统在稳态设计点条件下的预测热效率为31.85%,此外,还获得了热源功率和流量扰动条件下系统热力学参数的响应特征,发现热源功率的变化促使系统效率单调提升或降低,而改变系统流量未呈现类似变化趋势;扰动施加过程中,循环系统的参数对热源功率的变化非常敏感,热源功率减小15.00%,循环效率从31.85%降低到22.00%。最终基于仿真结果,获得多参量耦合关联下的变化规律与调控策略,可为S-CO₂再压缩布雷顿工程应用奠定基础。     

Study on solidification of carbon dioxide using cold energy of liquefied natural gas

The present paper deals with solidification characteristics of carbon dioxide around the gas feed nozzle of the flue gas from a thermal energy power plant. The present experiment was carried out under dioxide contents between 3 and 50 vol%. The results obtained indicate that the solidification fraction of carbon dioxide increased with a decrease in cooling temperature. The solidification fraction of carbon dioxide was expressed as a function of the nondimensional temperature and concentration of the carbon dioxide. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 249–268, 2000     

The energy efficiency of carbon dioxide fixation by a hydrogen-oxidizing bacterium

Fixing carbon dioxide (CO₂) with solar hydrogen (H₂) is a novel alternative to conventional photosynthesis of plants and microalgae. The energy efficiency of CO₂ fixation by a hydrogen-oxidizing bacterium was investigated in a closed reactor system. The molar ratio of consumed H₂ and CO₂ was measured under mass transfer limitation in atmospheres of sufficient H₂, low CO₂, and a broad range of O₂. The energy efficiency, ranging from 10% to 60%, was primarily affected by the oxygen concentration (6–30 mol%). The research revealed a clear trend that a low oxygen concentration gave high energy efficiency, but slow gas consumption. A high energy efficiency of 50% was measured under a moderate oxygen concentration (10 mol%). Based on 10% solar hydrogen efficiency, a 5% overall efficiency from solar energy to biomass can therefore be achieved.