Simulation Modelling and Techno-Economics of Supercritical Carbon Dioxide Recompression Closed Brayton Cycle

In recent years, there has been global interest in meeting targets relating to energy affordability and security while taking into account greenhouse gas emissions. This has heightened major interest in potential investigations into the use of supercritical carbon dioxide (sCO2) power cycles. Climate change mitigation is the ultimate driver for this increased interest;other relevant issues include the potential for high cycle efficiency and a circular economy. In this study, a 25 MWe recompression closed Brayton cycle (RCBC) has been assessed, and sCO2 has been proposed as the working fluid for the power plant. The methodology used in this research work comprises thermodynamic and techno-economic analysis for the prospective commercialization of this sCO2 power cycle. An evaluated estimation of capital expenditure, operational expenditure, and cost of electricity has been considered in this study. The ASPEN Plus simulation results have been compared with theoretical and mathematical calculations to assess the performance of the compressors, turbine, and heat exchangers. The results thus reveal that the cycle efficiency for this prospective sCO2 recompression closed Brayton cycle increases (39% - 53.6%) as the temperature progressively increases from 550˚C to 900˚C. Data from the Aspen simulation model was used to aid the cost function calculations to estimate the total capital investment cost of the plant. Also, the techno-economic results have shown less cost for purchasing equipment due to fewer components being required for the cycle configuration as compared to the conventional steam power plant.

Configuration Consideration for Expander in Transcritical Carbon Dioxide Two-Stage Compression Cycle

To investigate the configuration consideration of expander in transcritical carbon dioxide two-stage compression cycle, the best place in the cycle should be searched for to reinvest the recovery work so as to improve the system efficiency. The expander and the compressor are connected to the same shaft and integrated into one unit, with the latter being driven by the former, thus the transfer loss and leakage loss can be decreased greatly. In these systems, the expander can be either connected with the first stage compressor (shortened as DCDL cycle) or the second stage compressor (shortened as DCDH cycle), but the two configuration ways can get different performances. By setting up theoretical model for two kinds of expander configuration ways in the transcritical carbon dioxide two-stage compression cycle, the first and the second laws of thermodynamics are used to analyze the coefficient of performance, exergy efficiency, inter-stage pressure, discharge temperature and exergy losses of each component for the two cycles. From the model results, the performance of DCDH cycle is better than that of DCDL cycle. The analysis results are indispensable to providing a theoretical basis for practical design and operating.

System design and analysis of the trans-critical carbon-dioxide automotive air-conditioning system

As an environmentally harmless and feasible alternate refrigerant, CO 2 has attracted worldwide attention, especially in the area of automobile air conditioning (AAC). The thermal property of CO 2 and its trans critical refrigeration cycle is very different from that of the traditional CFC or HCFC system. The detailed process of CO 2 system thermal cycle design and optimization is described in this paper. System prototype and performance test bench were developed to analyze the performance of the CO 2 AAC system.

Second Law of Thermodynamics Analysis of Transcritical Carbon Dioxide Refrigeration Cycle

In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy analysis model is applied. The effects of heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures on the exergy loss, exergy efficiency and the coefficient of performance (COP) of the expansion turbine cycle are analyzed. It is found that the great percentages of exergy losses take place in the gas cooler and compressor. Moreover, heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures have strong influence on the exergy efficiency, COP and the exergy loss of each component. The analysis shows that there exists an optimal heat rejection pressure corresponding to the maximum exergy efficiency and COP, respectively. The results are of significance in providing theoretical basis for optimal design and the control of the transcritical carbon dioxide system with an expansion turbine.

Study of optimal discharge pressure of compressor in CO_2 refrigerating trans-critical cycle

In this paper, a carbon dioxide trans-critical refrigerating system which is different from a conventional subcritical refrigerating cycle was studied. The trans-critical carbon dioxide refrigerating systems are based on the Gustav Lorntzen cycle. Emphasis was focused on how to determine the optimal discharge pressure of compressor in CO2 trans-critical cycle. The factors related with the optimal discharge pressure were analyzed. A formula was developed based on cycle simulation, which could be used to predict the optimal discharge pressure of a basic CO2 trans-critical cycle. After further studies on CO2 trans-critical cycles with a regenerator or expander, two more formulas were also developed. These formulas could provide an access to improve the COP of CO2 trans-critical cycle.

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Metal-organic frameworks （MOFs） have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I（also named Cu-BTC or MOF-199） was chemically reduced by doping it with alkali metals （Li, Na and K） and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction （XRD）, thermo-gravimetric analysis （TGA） and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li＋, Na＋ and K＋, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.

A Review of the Life Cycle Analysis for Plastic Waste Pyrolysis

Pyrolysis is a rapidly expanding chemical-based recyclable method that complements physical recycling. It avoids improper disposal of post-consumer polymers and mitigates the ecological problems linked to the production of new plastic. Nevertheless, while there is a consensus that pyrolysis might be a crucial technology in the years to come, more discussions are needed to address the challenges related to scaling up, the long-term sustainability of the process, and additional variables essential to the advancement of the green economy. Herein, it emphasizes knowledge gaps and methodological issues in current Life Cycle Assessment (LCA), underlining the need for standardized techniques and updated data to support robust decision-making for adopting pyrolysis technologies in waste management strategies. For this purpose, this study reviews the LCAs of pyrolytic processes, encompassing the complete life cycle, from feedstock collection to end-product distribution, including elements such as energy consumption, greenhouse gas emissions, and waste creation. Hence, we evaluate diverse pyrolysis processes, including slow, rapid, and catalytic pyrolysis, emphasizing their distinct efficiency and environmental footprints. Furthermore, we evaluate the impact of feedstock composition, process parameters, and scale of operation on the overall sustainability of pyrolysis-based plastic waste treatment by integrating results from current literature and identifying essential research needs. Therefore, this paper argues that existing LCA studies need more coherence and accuracy. It follows a thorough evaluation of previous research and suggests new insights into methodologies and restrictions.

CARBON CYCLE OF MARSH IN THE SANJIANG PLAIN

The Sanjinag Plain of China is a low plain. Its total area is 10. 89 × 104 km2 and marsh area takes up 10. 20%. Marsh is a kind of vegetation type with strong carbon-fixing ability among the terrestrial areystam and carbon cycle performing in the form of carbon dioxide. This paper discusses the fixation of atmospheric CO2 by marsh plant; the transfer of carbon from marsh to atmosphere; the change of CO2 and vertical transfer of CO2 near atmosphere of the earth; the carbon floW among marsh plants, soil and atmosphere. Some scientific data about the biological production, carbon content of marsh plants and the capacity for releasing and fixing are used to explain the carbon cycle of marsh in the Sanjiang Plain.

Study on the Separation,Extraction of Lycopene and Its Effects on Cell Cycle

The separation, extraction of lycopene and its effects on the proliferation and cells cycle of the chemical-induced cells were investigated in order to research on its extraction method and the mechanism in inhibiting neoplastic transformation. The best extraction condition of lycopene with super-critical carbon dioxide was under the pressure of 25MPa, the temperature of 50℃ and duration of 3. 0h. Lycopene could inhibit cell growth rate and cells proliferation significantly, while increase the cell numbers of G1 -phase and decrease that of S-phase and G2+M-phase. The potency of the effects of lycopene on cells cycle might be one of the important reasons for inhibiting neoplastic transformation.

The role of new energy in carbon neutral

Carbon dioxide is an important medium of the global carbon cycle,and has the dual properties of realizing the conversion of organic matter in the ecosystem and causing the greenhouse effect.The fixed or available carbon dioxide in the atmosphere is defined as"gray carbon",while the carbon dioxide that cannot be fixed or used and remains in the atmosphere is called"black carbon".Carbon neutral is the consensus of human development,but its implementation still faces many challenges in politics,resources,technology,market,and energy structure,etc.It is proposed that carbon replacement,carbon emission reduction,carbon sequestration,and carbon cycle are the four main approaches to achieve carbon neutral,among which carbon replacement is the backbone.New energy has become the leading role of the third energy conversion and will dominate carbon neutral in the future.Nowadays,solar energy,wind energy,hydropower,nuclear energy and hydrogen energy are the main forces of new energy,helping the power sector to achieve low carbon emissions."Green hydrogen"is the reserve force of new energy,helping further reduce carbon emissions in industrial and transportation fields.Artificial carbon conversion technology is a bridge connecting new energy and fossil energy,effectively reducing the carbon emissions of fossil energy.It is predicted that the peak value of China’s carbon dioxide emissions will reach 110×10^(8) t in 2030.The study predicts that China’s carbon emissions will drop to 22×10^(8) t,33×10^(8) t and 44×10^(8) t,respectively,in 2060 according to three scenarios of high,medium,and low levels.To realize carbon neutral in China,seven implementation suggestions have been put forward to build a new"three small and one large"energy structure in China and promote the realization of China’s energy independence strategy.

基于S-CO_(2)布雷顿循环的太阳能发电储能一体化系统性能分析

设计了一种以S-CO_(2)和石英石为储能介质、再压缩S-CO_(2)布雷顿循环为动力循环的塔式太阳能热发电储能一体化系统。基于Gensystem计算平台,建立了动力循环、太阳能集热系统、S-CO_(2)斜温层储热罐的数学模型,研究了集热系统性能和S-CO_(2)斜温层储热罐的储、释热动态特性。在此基础上,分析了一体化系统的热力性能和经济性能。结果表明:经过13次循环储、释热过程,斜温层储热罐出口温度趋于稳定。释热结束时,斜温层储热罐热流体出口温度下降了63 K,储热结束时,冷流体出口温度升高了46 K。与配置双储热罐的塔式太阳能热发电系统相比,一体化系统夏至日和冬至日日均发电效率分别提高了1.8%和1.7%,系统总投资降低了9.46%,平准化度电成本下降了9.45%,投资回收期缩短了1.8 a。

风量对跨临界CO_(2)驻车空调系统性能的影响

为研究风量变化对跨临界CO_(2)驻车空调系统性能的影响,控制室内外风量在最优风量以降低总能耗,获得最高的能效比。通过搭建系统样机,在焓差室测试其性能并研究风量对系统性能的影响。结果表明:样机在名义制冷工况下,取系统理想制冷性能系数C_(OP)最大时对应的排气压力为最优排气压力(9 MPa)。在最优排气压力下探究风量的影响。室内风量固定时,随着室外风量的增加,排气温度先快速下降后趋于稳定。室外风量固定时,排气温度与室内风量的关系取决于室外风量的大小,当室外风量低于1500 m^(3)/h时,排气温度随着室内风量的增加而增加;当室外风量高于1500 m^(3)/h时,排气温度随着室内风量的增加呈现先减小后增大的趋势,且在室内风量为300 m^(3)/h时排气温度达到最小值。室内、外风量增加时,系统制冷量先增加后降低,总功耗先降低后升高,系统C_(OP)呈现先上升后下降的趋势。最优风量为室内风量300 m^(3)/h,室外风量1750 m^(3)/h,此时系统C_(OP)达到最大2.26,为跨临界CO_(2)驻车空调系统的设计与安全高效运行提供参考。

生物炭替代煤粉/焦炭高炉炼铁碳减排技术研究进展

钢铁行业是能源消耗和碳排放大户,因此在碳中和背景下寻求可替代传统煤的零碳原料是钢铁行业重点发展的碳减排技术。生物炭具有碳中性特征,碳含量和热值与煤接近,是煤粉和焦炭理想的替代原料。本文系统介绍了生物炭在炼焦、烧结、高炉炼铁中的潜在利用途径,并进一步聚焦生物炭应用于高炉炼铁时所需具备的理化特性,阐述了生物炭碱金属、强度、粒度与比表面积在替煤代焦时的影响及机理。针对碱金属降低焦炭强度等问题,介绍了酸洗等脱矿方法降低生物炭碱金属含量;针对生物炭机械强度差难以入炉问题,总结了焦炭强度形成机理和生物炭成型增强工艺;针对生物炭导致炼焦煤混合物流动性变差问题,通过调控生物炭粒度和比表面积以降低对焦炭的负面影响。最后,总结了生物炭替代煤粉和焦炭高炉炼铁的国内外进展及预期CO_(2)减排效果。通过分析生物炭替煤代焦目前工业应用中存在的挑战以及生命周期评价的相关研究情况,为未来钢铁行业实现碳中和提供技术支撑。

S-CO_(2)部分膨胀循环余热利用系统热力学特性研究

针对通过热力循环实现余热利用的系统,解决循环热效率与热源利用率之间的相互制约问题是构建高效余热吸收系统的关键。以超临界二氧化碳循环为例,为拓宽余热吸收温区从而提高余热利用效率,构建了新型循环即部分膨胀循环,耦合燃气轮机排气后,余热利用系统的发电效率为28.62%,循环热效率34.03%,热源利用率84.11%。为论证部分膨胀循环的优势,进一步构建了基于单回热布雷顿循环与再压缩布雷顿循环的余热利用系统,并对3种循环进行对比,通过热力学第一定律、第二定律计算分析,发现部分膨胀循环的发电效率均高于其他2种经典循环;通过分析循环流程,揭示了部分膨胀循环效率较高的原因,即部分膨胀结构拓宽了吸热温区,使得热源利用率大幅升高,从而提高了发电效率。

集成塔式太阳能的新型超临界压缩二氧化碳储能系统性能分析

随着可再生能源快速发展,储能技术在实现可再生能源大规模并网中起着至关重要的作用。与压缩空气储能系统相比,压缩超临界二氧化碳储能系统具有体积小、储能密度高的优势。该文提出集成塔式太阳能的简单回热压缩循环和再压缩循环的两种超临界压缩二氧化碳储能(supercritical compressed carbon dioxide energy storage,SC-CCES)系统,并进行热力学分析和经济性分析。相较于集成塔式太阳能的SC-CCES参比系统,集成塔式太阳能的简单回热压缩和再压缩循环SC-CCES系统更有利于提高太阳能利用率,其光电转换效率分别为23.56%和28.77%,分别比参比系统高出2.63%和7.84%。提高储能压力和释能压力都可以有效提高系统的能量效率、光电转换效率、㶲效率和单位体积储存能量。此外,集成塔式太阳能的再压缩SC-CCES系统具有较好的经济性能,动态投资回收年限约6到7年,20年净现值(net present value,NPV)为23456.16×10^(3)美元,比耦合简单回热压缩系统高7956.69×10^(3)美元,内部收益率(internal rate of return,IRR)为17.55%。

超临界二氧化碳布雷顿循环系统关键参数对循环效率的影响研究

超临界二氧化碳(S-CO_(2))布雷顿循环具有热能利用率高、结构紧凑、布置简单等优点,耦合反应堆容易实现集成化,适用于小型模块堆的研发。本文建立了简单回热、分流再压缩、再热再压缩及间冷再压缩循环的4种循环布局模型,针对设备等熵效率采用了一种无量纲效率计算方法,计算了不同设备尺寸和工作压比下的设备效率,深入分析了压缩机和涡轮机入口参数及其效率随工况改变对系统循环效率的影响。结果表明:4种循环布局针对不同工况变化趋势相似。其中,主压缩机和涡轮机入口焓值、中间压缩机入口压力及再热涡轮机入口压力都存在对应循环效率最高的最佳值;以分流再压缩循环为例给出了不同功率等级及不同系统最高温度下循环效率随系统压比的变化,并与采用恒定设备效率计算结果进行对比,其结果能更全面客观的反应S-CO_(2)布雷顿循环的特征。

矩形通道内超临界压力CO_(2)流动换热数值研究

针对高马赫数发动机热防护和机载设备长航程供电问题,基于超临界二氧化碳布雷顿循环提出了热防护与发电一体化系统。采用数值模拟方法探究了单侧受热矩形通道内超临界压力下CO_(2)的对流传热特性,并且分析了不同热流密度时入口温度、冷却流量和加热长度对冷却性能的影响。研究发现单侧受热矩形通道内SCO_(2)的流动换热存在周向不均匀性,增大冷却剂流量可以有效降低壁面温度。但对周向壁面温差影响较小并且温差随热流密度增大单调上升,由0.5 MW‧m^(-2)的最大温差75 K增加至2.0 MW‧m^(-2)的最大温差297 K。二次流在通道拐角处形成回流,局部扰流使传热增强。当流体温度高于拟临界温度时,定压比热容随入口温度的升高而减小,但是雷诺数的增大弥补了这一缺陷并使得换热能力增强。不同加热长度的冷却性能受传热特性影响,不发生传热恶化时,相同冷却流量条件下加热长度越大冷却后的壁面最高温度越高。但是当发生传热恶化时,不同加热长度冷却后的壁面最高温度分为相同和随加热长度增大两种情况。

炼化一体化型企业产品碳足迹核算研究

以ISO/TS 14067、GHG Protocol和PAS 2050为依据,描述了炼化一体化型企业全厂碳排放和炼化产品碳足迹的核算方法。通过建立炼化一体化型企业单装置核算模型和全厂核算模型,分析了如何将间接排放分摊到各炼化产品中以及不同碳排放分配方式的适用范围,并对未来炼化一体化型企业产品碳足迹核算的发展进行了讨论。

CO_(2)跨临界制冷系统新型分布式压缩循环研究

为了对CO_(2)跨临界蒸气压缩循环进行高效冷却并提升系统性能,提出分布式压缩循环系统(distributed compression cycle system,DCCS)。在DCCS中,气冷器出口的超临界CO_(2)不再被进一步过冷而是进行二次增压,并在常规热汇条件下进行放热冷却。通过热力学计算DCCS在不同工况下的性能随二次增压比变化情况。结果表明:相对于基础系统,DCCS可有效提升系统性能,在气冷器出口温度不变时,最大制冷COP增幅在8.2%~10.76%之间,制冷量的增幅最高可达约26%。在蒸发温度不变时,最大制冷COP增幅在8.57%~13.51%之间。DCCS中理想的二次增压比要求并不高,且对于二次增压所增加的系统功耗相对于基础系统不会超过20%。相对于目前仅采取单一过冷技术的系统,DCCS在系统性能系数上仍具有优势。DCCS的提出为跨临界CO_(2)蒸气压缩循环系统的性能提升与完善提供了全新的方向。

航空发动机热防护超临界CO_(2)闭式循环方案设计

针对航空飞行器高速飞行时发动机热环境严峻、冷源有限的问题,提出了一种应用于航空发动机热防护、以超临界CO_(2)为工质的闭式布雷顿冷却循环方案。采用能量分析法构建布雷顿循环的数学模型,对比分析了简单循环、回热循环与间冷循环3种循环结构的优劣,比较了高温部件冷却通道的串并联结构对循环性能的影响。结果表明:回热循环能够提高系统热效率约4%,但热沉利用率降低50%;间冷循环能够降低系统热沉消耗8%,但会导致系统总质量增大;超临界CO_(2)简单循环是最符合发动机中间工质冷却循环工作需求的循环结构。对于简单循环而言,高温部件冷却通道并联结构的热效率比串联结构的高6%,但需要的碳氢燃料质量流量提高了2.7%,在碳氢燃料质量充足的条件下,并联结构的性能更优。