Coupling effect of evaporation and condensation processes of organic Rankine cycle for geothermal power generation improvement

Organic Rankine cycle(ORC)is widely used for the low grade geothermal power generation.However,a large amount of irreversible loss results in poor technical and economic performance due to its poor matching between the heat source/sink and the working medium in the condenser and the evaporator.The condensing temperature,cooling water temperature difference and pinch point temperature difference are often fixed according to engineering experience.In order to optimize the ORC system comprehensively,the coupling effect of evaporation and condensation process was proposed in this paper.Based on the laws of thermodynamics,the energy analysis,exergy analysis and entropy analysis were adopted to investigate the ORC performance including net output power,thermal efficiency,exergy efficiency,thermal conductivity,irreversible loss,etc.,using geothermal water at a temperature of 120℃as the heat source and isobutane as the working fluid.The results show that there exists a pair of optimal evaporating temperature and condensing temperatures to maximize the system performance.The net power output and the system comprehensive performance achieve their highest values at the same evaporating temperature,but the system comprehensive performance corresponds to a lower condensing temperature than the net power output.

A survey of geothermal power generation combined with renewable energy for low carbon emissions

At present,industrial development is heavily dependent on traditional fossil energy,which has had an increasingly serious impact on the environment.Clean and renewable energy has received extensive attention and its proportion in daily life has gradually increased.As a clean and renewable energy source that is not affected by changes in weather and seasons,geothermal energy has developed rapidly in recent years and has received increasing attention.According to reports,the total installed capacity of geothermal power generation in the world in 2020 was 15950 MW-an increase of~27%over 2015.At the end of 2019,the total installed capacity for global geothermal direct use was 107727 MW-an increase of 52.0%compared with 2015;the total annual energy use was 1020887 TJ(283580 GWh)-an increase of 72.3%over 2015.Through the investigation of geothermal power generation technology in recent years,the characteristics and shortcomings of various power generation methods are analysed.At the same time,this review analyzes the characteristics of geothermal energy and other renewable-energy(solar energy,water energy)coupling power generation,and analyzes the principles and characteristics of geothermal energy and various new-energy coupling power generation methods.Through investigation and analysis,this review provides a complete understanding of various geothermal power generation technologies and provides insights into the future development direction.

Renewable Energy:Wind Turbines,Solar Cells,Small Hydroelectric Plants,Biomass,and Geothermal Sources of Energy

In this paper,we present five basic types of renewable energy sources,namely:wind turbines,solar cells,small hydroelectric plants,biomass,and geothermal sources of energy.Wind turbines transform energy of wind into electrical energy,solar cells transform energy of sun into electric energy,hydroelectric plants transform energy of water into electric energy,devices or machines can be constructed to transform energy of biomass into heat energy,and geothermal energy into some form of energy.In this paper we present basic information and reasons why there is need today to use these forms of energy—called green energies,we present how these devices or machines function,and we propose for future work design of typical devices or machines that will satisfy basic functional needs.

Two stages power generation test of the hot dry rock exploration and production demonstration project in the Gonghe Basin,northeastern Qinghai-Tibet plateau,China

The Hot Dry Rock(HDR)is considered as a clean and renewable energy,poised to significantly contribute to the global energy decarbonization agenda.Many HDR projects worldwide have accumulated valuable experience in efficient drilling and completion,reservoir construction,and fracture simulation.In 2019,China Geological Survey(CGS)initiated a demonstration project of HDR exploration and production in the Gonghe Basin,aiming to overcome the setbacks faced by HDR projects.Over the ensuing four years,the Gonghe HDR project achieved the first power generation in 2021,followed by the second power generation test in 2022.After establishing the primary well group in the initial phase,two directional wells and one branch well were drilled.Noteworthy progress was made in successfully constructing the targeted reservoir,realizing inter-well connectivity,power generation and grid connection,implementing of the real-time micro-seismic monitoring.A closed-loop technical validation of the HDR exploration and production was completed.However,many technical challenges remain in the process of HDR industrialization,such as reservoir fracture network characterization,efficient drilling and completion,multiple fracturing treatment,continuous injection and production,as well as mitigation of induced seismicity and numerical simulation technology.

Performance analysis and improvement of geothermal binary cycle power plant in oilfield

In order to improve the efficiency of a geothermal power plant, oil wells in the high water cut stage were used as geothermal wells, thereby improving the recovery ratio and economic benefit. A new function that reflects both the technical and economic performances was put forward and used as the objective function. An organic Rankine cycle (ORC) was analyzed through the energetic and exergetic analyses, and the reasons for low efficiency were pinpointed. Results indicate that geothermal water directly transferring heat to the working fluid reduces energy dissipation and increases cycle efficiencies. The net power output with an internal heat exchanger (IHE) is averagely 5.3% higher than that without an IHE. R601a and R601 can be used to replace R123 for geothermal water below 110℃. Moreover, the modified ORC dramatically outperforms the actual one.

Figure of Merit Analysis of a Hybrid Solar-geothermal Power Plant

Figure of merit analysis is a general methodology used to evaluate whether a hybrid power plant could produce more power than two stand-alone power plants. In this paper, the assessment methodology using figure of merit analysis was re-examined for a hybrid solar-geothermal power plant. A new definition of the figure of merit was introduced specifically for a solar boosted geothermal plant to include both the technical and economic factors. The new definition was then applied in a case study of a hypothetical demonstration hybrid solar-geothermal power plant in Australia. The power plant was considered to have a typical net power output of 2.2 MW with a solar energy fraction of 27%. The analysis was performed to compare the power output and capital cost of the hybrid plant with the state-of-the-art (SoA) and existing stand-alone solar and geothermal plants. Based on the new definition, the hybrid plant was found to generally outperform the two existing stand-alone plants. Moreover, at an ambient temperature of 5 °C, the hybrid plant was found to outperform the SoA stand-alone plants when the geothermal temperature was greater than 150 °C. For geothermal temperature of 180 °C on the other hand, the hybrid plant outperformed the SoA stand-alone plants at ambient temperatures lower than 33 °C.

Status in quo and future of geothermal energy in China

Energy saving and CO2 emissions reduction are critical tasks currently,and great effort has been made by Chinese government. Renewable energy consumption and CO2 emissions and reduction plan in China are introduced in this paper. Analysis is also made on present status and prospect of geothermal power generation and direct use in China respectively. Now,there is a new understanding of geothermal resources,and hot dry rock,considered as the future of geothermal resources,is likely used to generate electricity.

Determination of Curie Point Depth, Heat Flow and Geothermal Gradient from High Resolution Aeromagnetic Data around Lamurde Area, Adamawa State, North-Eastern Nigeria

Analysis of high resolution of aeromagnetic data was carried out over Lamurde, Adamawa state north-eastern Nigeria to determine the Curie point depth (CPD), heat flow and geothermal gradient. The aeromagnetic data used for this work was obtained at Nigerian geological survey agency, the total magnetic intensity was processed to produce the residual magnetic map which was divided into 4 overlapping blocks, each block was subjected to spectral analyses to obtain depths to the top boundary and centroid, while depth to bottom of the magnetic sources was calculated using empirical formula. The depths values obtained were then used to assess the CPD, heat flow and geothermal gradient in the area. The result shows that the CPD varies between 9.62 and 10.92 km with an average of 10.45 k, the heat flow varies between 150.73 and 132.78 mWm−20⋅°C−1 with an average of 139.12 mWm−20⋅°C−1 and the geothermal gradient in the study area varies between 12.16 and 15.67 °C/km with an average of 13.39 °C/km. In view of the above results, the high heat flow may be responsible for maturation of hydrocarbon in Benue Trough as well as responsible for the lead Zinc Mineralization. Again by implication, Lamurde area can be a good area for geothermal reservoir exploration for an alternative source for power generation.

Working fluids of a low-temperature geothermally-powered Rankine cycle for combined power and heat generation system

A novel combined power and heat generation system was investigated in this study. This system consists of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The advantages of the novel combined power and heat generation system are free of using additional cooling water circling system for the power generation subsystem as well as maximizing the use of thermal energy in the low-temperature geothermal source. The main purpose is to identify suitable working fluids (wet, isentropic and dry flu-ids) which may yield high PPR (the ratio of power produced by the power generation subsystem to power consumed by the heat pump subsystem) value and QQR (the ratio of heat supplied to the user to heat produced by the geothermal source) value. Parameters under investigation were evaporating temperature, PPR value and QQR value. Results indicate that there exits an optimum evaporating temperature to maximize the PPR value and minimize the QQR value at the same time for individual fluid. And dry fluids show higher PPR values but lower QQR values. NH3 and R152a outstand among wet fluids. R134a out-stands among isentropic fluids. R236ea, R245ca, R245fa, R600 and R600a outstand among dry fluids. R236ea shows the highest PPR value among the recommended fluids.

Thermo-economic analysis of a direct supercritical CO_(2) electric power generation system using geothermal heat

A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrated model,thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity(LCOE).Specifically,in geothermal heat extraction simulation,an integrated wellbore-reservoir system model(T2Well/ECO_(2)N)was used to generate a database for creating a fast,predictive,and compatible geothermal heat mining model by employing a response surface methodology.A parametric study was conducted to demonstrate the impact of turbine discharge pressure,injection and production well distance,CO_(2) injection flowrate,CO_(2) injection temperature,and monitored production well bottom pressure on LCOE,system thermal efficiency,and capital cost.It was found that for a 100 MWe power plant,a minimal LCOE of$0.177/kWh was achieved for a 20-year steady operation without considering CO_(2) sequestration credit.In addition,when CO_(2) sequestration credit is$1.00/t,an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.

地热能有机朗肯循环系统设计与动态仿真

针对地热能利用,根据地热井口条件通过热力学计算和设备选型设计了对应的ORC机组,并对该机组动态特性进行了仿真;研究了热源温度和流量、冷却水温度以及工质流量4种参数变化对ORC机组关键运行参数和性能的影响规律。结果表明:机组输出性能对冷却水温度变化最为敏感,冷热源温度增大10℃,轴功分别减小16%和增大7%;热源温度和流量增大都会使过热度、蒸发压力和轴功显著升高,热效率略有下降,但其对机组冷端传热的影响有限,对热端传热的影响很小,过热度和蒸发压力几乎不变;相比冷热源参数的变化,工质流量变化时机组关键参数的波动最小,机组能很快恢复稳定。

CO_(2)Plume Geothermal(CPG)Systems for Combined Heat and Power Production:an Evaluation of Various Plant Configurations

CO_(2) Plume Geothermal(CPG)systems are a promising concept for utilising petrothermal resources in the context of a future carbon capture utilisation and sequestration economy.Petrothermal geothermal energy has a tremendous worldwide potential for decarbonising both the power and heating sectors.This paper investigates three potential CPG configurations for combined heating and power generation(CHP).The present work examines scenarios with reservoir depths of 4 km and 5 km,as well as required district heating system(DHS)supply temperatures of 70℃ and 90℃.The results reveal that a two-staged serial CHP concept eventuates in the highest achievable net power output.For a thermosiphon system,the relative net power reduction by the CHP option compared with a sole power generation system is significantly lower than for a pumped system.The net power reduction for pumped systems lies between 62.6%and 22.9%.For a thermosiphon system with a depth of 5 km and a required DHS supply temperature of 70℃,the achievable net power by the most beneficial CHP option is even 9.2%higher than for sole power generation systems.The second law efficiency for the sole power generation concepts are in a range between 33.0%and 43.0%.The second law efficiency can increase up to 63.0%in the case of a CHP application.Thus,the combined heat and power generation can significantly increase the overall second law efficiency of a CPG system.The evaluation of the achievable revenues demonstrates that a CHP application might improve the economic performance of both thermosiphon and pumped CPG systems.However,the minimum heat revenue required for compensating the power reduction increases with higher electricity revenues.In summary,the results of this work provide valuable insights for the potential development of CPG systems for CHP applications and their economic feasibility.

中国新能源资源潜力及前景展望

随着中国经济的快速发展,国内常规油气的开发已不能满足经济发展的需要。预计到2020年,中国石油缺口约2.8×108t,天然气缺口800×108m3。世界各国都很重视新能源的开发和利用,煤层气、油砂、油页岩、地热、燃料乙醇和生物柴油等已经在部分国家实现了有效开发。中国新能源资源丰富,发展新能源对中国具有重要的战略意义。为此,分析了中国煤层气、油砂、油页岩等非常规油气资源及地热、太阳能等可再生能源的资源基础和进展;目前,中国石油已经在煤层气、燃料乙醇、地热、油砂和油页岩等新能源方面积极开展工作,为下一步新能源业务加快发展奠定了良好的基础;分析认为:中国新能源要实现真正意义上的替代作用道路还很漫长,提出了"建立新理论找到新资源"、"应用新技术取得新突破"等新能源发展建议。

煤矿低温热源利用技术研究与应用

针对低温热源蕴藏量大且可再生的特点,在分析国内外低温热源利用现状的基础上,指出了煤矿低温热源利用的优势及存在的问题。根据煤矿各种低温热源的特点,在阐述热泵原理的基础上,研究了矿井回风源热泵技术、电厂冷却水热能回收技术、矿井水热能提取技术。结合煤矿低温热源多种形式并存的特点,提出了煤矿低温热源综合利用技术。冀中能源集团所属矿井的低温热源利用效果表明,煤矿低温热源应用具有广阔的发展前景。

有机朗肯循环-喷射式制冷功冷联产系统热力分析

为充分利用地热能资源,在有机朗肯循环(ORC)基础上,结合喷射式制冷系统(ER),提出了一种新型有机朗肯循环-喷射式制冷功冷联产系统.以110℃饱和地热水为热源,采用R123为循环工质,基于热力学第一、第二定律建立了联产系统热力学理论模型,编制计算程序并以能源利用率为评价指标进行了系统热力性能分析.结果表明,抽汽份额α在0~0.7内,能源利用率随蒸发压力p3增加而增加,而抽汽份额α在0.8~1之间时,能源利用率随蒸发压力增加而逐渐减小;能源利用率随抽汽压力p6增大而增大,且抽汽份额α越大增幅越高;随冷凝压力p10增加能源利用率不断减小,当p10为0.3 MPa,α为1时,能源利用率达到最大值为74.1%;制冷蒸发温度T8越高能源利用率越大,且抽汽份额α越大能源利用率增幅越大.

中国低碳地热发电的回顾与展望

一个国家地热产业的发展程度主要是以地热发电的装机容量来衡量的。中国自20世纪70年代开始进行地热发电以来,装机容量一直徘徊在25MWe左右,在世界上进行地热发电的24个国家中排名为第18位。本文分析了中国地热发电裹足不前的国内外的原因,讨论了中国地热资源的潜力和可能利用高温地热资源进行地热发电的区域,展望了地热发电的前景。

银川市地埋管地源热泵系统利用潜力分析

根据银川市浅层地温能资源赋存条件,综合考虑地埋管地源热泵开发利用的各地层影响因素,结合层次分析法对地埋管地源热泵系统的开发利用进行适宜性分区。结果表明,银川市地埋管地源热泵开发利用只有适宜区与较适宜区,无不适宜区,说明地埋管地源热泵系统在银川市具有较好的开发利用地质条件。通过对研究区浅层地温能资源量的计算及经济、社会效益的分析,发现研究区浅层地温能具有相当可观的开发利用量,对其开发利用可减少大量大气污染物的排放。

可再生能源发电介绍

介绍了小水电、风力发电、太阳能发电、地热能发电、生物质能发电、海洋能发电等可再生能源发电的发展概况,分析了可再生能源发电存在的问题以及相应对策,阐述了可再生能源发电的发展前景与规划,得出可再生能源发电产业能解决我国西部及边远地区的供电问题的结论。

湖南省浅层地温能资源调查与评价

为了推动湖南省的浅层地温能开发,针对湖南省13个地级城市开展了地质、水文地质、地热地质勘察、钻探和相关实验,对浅层地温能的赋存条件、资源量、开发适宜性进行了调查评价。结果表明,湖南省平均大地热流值为59.31 mW/m^2,低于全国平均值。空间分布为南高北低、东高西低,中部为高低相间,局部有异常圈闭的区段,显示出复杂构造的影响。湘中南的瓦屋塘—白马山岩浆岩带和湘南姑婆山—金鸡岭—骑田岭—热水岩浆岩带热流密度大于80 mW/m^2。湖南省绝大部分地区适宜建设地埋管地源热泵系统。仅在常德、岳阳、益阳、株洲等松散岩类孔隙水的分布地区有地下水地源热泵适宜区。湖南省13个地级城市规划区浅层地温能总热容量为6.93×10^15 kJ/℃,冬季总换热功率为1.00×10^8 kW,夏季总换热功率为1.39×10^8 kW。建议湖南省发达地区尤其是长株潭城市群新建城区建设地埋管地源热泵系统,大力发展浅层地温能。

欧洲地热资源开发利用现状及启示

欧洲地热资源开发利用发展迅速,在全球地热市场占据重要地位。在国家大力推进地热能开发利用的背景下,欧洲地热利用的发展趋势和经验对我国地热开发利用具有重要的借鉴意义。本文在跟踪欧洲地热发展现状的基础上,对欧洲地热市场和地热能开发利用技术,以及欧盟为支持地热发展所采取的行动和财政支持政策进行了梳理总结。针对当前我国地热资源开发利用存在的问题,提出加强我国地热资源开发的建议:开展地热资源开发利用现状普查与监测;加强重点地区的地热资源勘查评价;因地制宜地发展多种地热利用方式;加大对地热资源开发的政策支持力度;引进和创新地热利用的理论和技术方法;建立全国性地热发展联盟和平台。