Thermodynamic analysis and optimization of various power cycles for a geothermal resource

In this study, geothermal resources in Kutahya-Simav region having geothermal water at a temperature suitable for power generation is considered. The study is aimed to yield the method of the most effective use of the geothermal resource and a rational thermodynamic comparison of various cycles for a given resource. Maximum first law efficiencies vary between 6.9 to 10.6% while the second law efficiencies vary between 38.5 to 59.3% depending on the cycle considered. The maximum power output, the first law, and the second law efficiencies are obtained for Kalina cycle followed by combined cycle and binary cycle.     

Preliminary studies of some geothermal areas in India

In order to assess the geothermal resources of the hot springs located in different tectonic regions of India, preliminary geophysical, geochemical and tritium studies were undertaken in Puga valley (Ladakh), Ratnagiri and Kolaba Districts (West Coast) and Bhimbandh (Bihar) areas. The studies indicate that out of the three areas investigated, the Puga valley is the most promising because of its higher geothermal gradient, association of spring waters with magmatic components, its higher estimated reservoir temperature (≥ 200°C) and probable larger available supply of groundwater.     

Geothermal electric power generation in Iceland for the proposedIceland/United Kingdom HVDC power link

A review is given of the geothermal electric power potential in Iceland which could economically be developed to supplement hydro power for the proposed HVDC power link to the United Kingdom and supply the power-intensive industries in Iceland which are currently envisioned for development. Technically harnessable energy for electricity generation, taking account of geothermal resources down to an assumed base depth, temperature distribution in the crust, probable geothermal recovery factor, and accessibility of the field, has been assessed. Nineteen known high-temperature fields and nine probable fields have been identified. Technically harnessable geoheat for various areas is indicated. Data on high-temperature fields suitable for geothermal electric power generation and on harnessable energy for electric power generation within volcanic zones are presented     

地热发电的投资经济分析

地热能是一种清洁的可再生能源,越来越多的国家宣布支持地热开发。地热发电必须考虑到影响成本的各种因素,地热发电的成本主要由初始投资和电力生产运行及维护成本两部分组成。地热项目具体的投资成本与资源特征和现场条件有着非常密切的关系,资源的温度、深度、化学特性和渗透性是影响发电成本的主要因素。与传统化石燃料发电相比,地热发电已具有相当的竞争力,在生命周期内地热发电厂的平均成本大大低于传统燃料发电厂。另外,地热发电还有抵消化石燃料价格波动对电力市场影响的作用,有利于促进农村和偏远地区经济发展,有利于能源供应多元化。当然,地热能发展也面临着一些障碍,包括钻井的成功率、地热技术尚不够完善以及项目启动成本高等。建议今后地热资源的利用不再仅局限于极少数高温地热项目中,而是尽可能发掘地热资源的所有潜力。     

地热资源的开发利用及可持续发展

地热资源作为一种新型能源矿产,具有分布广泛、易于开发等特点,其利用方式主要有地热发电和地热直接利用两种.我国具有良好的地热资源条件,主要为中低温地热资源.据计算,我国12个主要沉积盆地的地热可开采资源量为7500×1018J,相当于2560×108t标煤.当前,我国地热资源利用方式主要以供暖、洗浴、种植等直接利用为主;地热发电发展缓慢,主要分布在西藏;利用热泵技术开发地热资源得到了快速发展;油区地热资源的开发利用也取得了良好的经济和社会效益.但同时我国地热资源产业也面临着一些问题,包括大部分地区尚未开展地热资源勘查评价,影响了地热资源规划的制订及地热产业的发展;防腐、防垢技术还需要进一步加强研究;地热回灌率普遍过低;增强型地热系统研究有待加强等.为了促进地热资源的可持续发展,建议在加大地热资源勘查力度的同时,应以浅层地温能和热水型地热资源为主,发挥热泵技术的优势,开展地热资源的综合利用及梯级利用;重视和加快油气区地热资源的利用;在西藏等适宜地区加大高温地热能发电利用;集中全国优势技术力量,在一两个有利区域开展增强型地热系统技术探索;此外,走回灌开发道路是地热资源开发利用的必然选择.     

Thermodynamic analysis and performance optimization of organic rankine cycles for the conversion of low‐to‐moderate grade geothermal heat

The present study considers a thermodynamic analysis and performance optimization of geothermal power cycles. The proposed binary‐cycles operate with moderately low temperature and liquid‐dominated geothermal resources in the range of 110°C to 160°C, and cooling air at ambient conditions of 25°C and 101.3 kPa reference temperature and atmospheric pressure, respectively. A thermodynamic optimization process and an irreversibility analysis were performed to maximize the power output while minimizing the overall exergy destruction and improving the First‐law and Second‐law efficiencies of the cycle. Maximum net power output was observed to increase exponentially with the geothermal resource temperature to yield 16–49 kW per unit mass flow rate of the geothermal fluid for the non‐regenerative organic Rankine cycles (ORCs), as compared with 8–34 kW for the regenerative cycles. The cycle First‐law efficiency was determined in the range of 8–15% for the investigated geothermal binary power cycles. Maximum Second‐law efficiency of approximately 56% was achieved by the ORC with an internal heat exchanger. In addition, a performance analysis of selected pure organic fluids such as R123, R152a, isobutane and n‐pentane, with boiling points in the range of ?24°C to 36°C, was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n‐pentane, were recommended for non‐regenerative cycles. The regenerative ORCs, however, require organic fluids with lower vapour specific heat capacity (i.e. isobutane) for an optimal operation of the binary‐cycle. Copyright © 2015 John Wiley & Sons, Ltd.     

Exergetic analysis of various types of geothermal power plants

Based on available surveys, it has been shown that Iran has substantial geothermal potential in the north and north-western provinces, where in some places the temperature reaches 240 °C. In order to better exploit these renewable resources, it is necessary to study this area. Thus, the aim of this paper is a comparative study of the different geothermal power plant concepts, based on the exergy analysis for high-temperature geothermal resources. The considered cycles for this study are a binary geothermal power plant using a simple organic Rankine cycle (ORC), a binary geothermal power plant using an ORC with an internal heat exchanger (IHE), a binary cycle with a regenerative ORC, a binary cycle with a regenerative ORC with an IHE, a single-flash geothermal power plant, a double-flash geothermal power plant and a combined flash-binary power plant. With respect to each cycle, a thermodynamic model had to be developed. Model validation was undertaken using available data from the literature. Based on the exergy analysis, a comparative study was done to clarify the best cycle configuration. The performance of each cycle has been discussed in terms of the second-law efficiency, exergy destruction rate, and first-law efficiency. Comparisons between the different geothermal power plant concepts as well as many approaches to define efficiencies have been presented. The maximum first-law efficiency was found to be related to the ORC with an IHE with R123 as the working fluid and was calculated to be 7.65%. In contrast, the first-law efficiency based on the energy input into the ORC revealed that the binary cycle with the regenerative ORC with an IHE and R123 as the working fluid has the highest efficiency (15.35%). Also, the maximum first-law efficiency was shown to be given by the flash-binary with R123 as the working fluid and was calculated to be 11.81%.     

Research on the generation of electricity from the geothermal resources in Simav region, Turkey

One of the greatest problems in using renewable energy sources is the great variability of energy level, both in the short and long term. Geothermal energy, by nature, has high availability because the source is not dependent on weather conditions, so it is among the most stable renewable energy sources. Geothermal energy has the potential to play an important role in the future energy supply of Turkey. Although Turkey has the second-highest geothermal energy potential in Europe, electricity generation from geothermal energy is rather low.This study examines the use of geothermal energy in electricity generation and investigates the applicability of the existent geothermal energy resources to electricity generation in the Kütahya–Simav region, Turkey. The binary cycle is used in the designed power plant for electricity generation from geothermal fluid in which the percentage of liquid is high and which is at lower temperature. In this power plant, R134a is chosen as the secondary fluid, whose boiling point temperature is lower than that of water, and is used instead of geothermal fluid in a second cycle. The thermal efficiency of the designed power plant is measured to be 12.93%.     

Determination of·fouling factors for shell-and-tube type heat exchangers exposed to los azufres geothermal fluids

According to the latest estimates, there are about 1500 geothermal sites in Mexico, ninety percent of which can probably produce low enthalpy fluids only. Hot water discarded from geothermal flash plants adds to this stock which represents a considerable source of thermal energy. Its utilization for direct industrial applications or electricity generation through binary cycles requires heat exchangers.The IIE, with the financial support and technical cooperation of CFE, has for some time been experimenting with heaters of different types subject to geothermal brines. This paper describes the work done to date and the preliminary results obtained.     

Ideal thermal efficiency for geothermal binary plants

The Carnot cycle is reviewed as to its appropriateness to serve as the ideal model for geothermal binary power plants. It is shown that the Carnot cycle sets an unrealistically high upper limit on the thermal efficiency of these plants. A more useful model is the triangular (or trilateral) cycle because binary plants operating on geothermal hot water use a non-isothermal heat source. The triangular cycle imposes a lower upper bound on the thermal efficiency and serves as a more meaningful ideal cycle against which to measure the performance of real binary cycles. Carnot and triangular cycle efficiencies are contrasted and the thermal efficiencies of several actual binary cycles are weighed against those of the ideal triangular cycle to determine their relative efficiencies. It is found that actual binary plants can achieve relative efficiencies as high as 85%. The paper briefly discusses cycles using two-phase expanders that in principle come close to the ideal triangular cycle.     

Efficiency improvement for geothermal power generation to meet summer peak demand

Geothermal power is an important part of New Zealand's renewable electricity supply due to its attractive cost and reliability. Modular type binary cycle plants have been imported and installed in various geothermal fields in New Zealand, with plans for further expansion. Power output of these plants deteriorates in the summer because plant efficiency depends directly on the geothermal resource and the ambient temperature. As these plants normally use air-cooled condensers, incorporating a water-augmented air-cooled system could improve the power output in summer thereby matching the peak air-conditioning demand. In this work, power generation for the Rotokawa plant was characterized using a similar plant performance and local weather. The improved performance was modelled for retrofit with a wet-cooling system. Maximum generation increase on the hottest day could be 6.8%. The average gain in power over the summer, November–February, was 1.5%, and the average gain for the whole year was 1%. With current binary unit generation capacity at the Rotokawa plant of 35 MW, investment in a water-augmented air-cooled system could provide 2 MW of peak generation on the hottest days. This investment in efficiency is found to compare favourably to other supply options such as solar PV, wind or gas.     

Life cycle assessment of geothermal binary power plants using enhanced low-temperature reservoirs

Geothermal binary power plants that use low-temperature heat sources have gained increasing interest in the recent years due to political efforts to reduce greenhouse gas emissions and the consumption of finite energy resources. The construction of such plants requires large amounts of energy and material. Hence, the question arises if geothermal binary power plants are also environmentally promising from a cradle-to-grave point of view. In this context, a comprehensive Life Cycle Analysis (LCA) on geothermal power production from EGS (enhanced geothermal systems) low-temperature reservoirs is performed. The results of the analysis show that the environmental impacts are very much influenced by the geological conditions that can be obtained at a specific site. At sites with (above-) average geological conditions, geothermal binary power generation can significantly contribute to more sustainable power supply. At sites with less favorable conditions, only certain plant designs can make up for the energy and material input to lock up the geothermal reservoir by the provided energy. The main aspects of environmentally sound plants are enhancement of the reservoir productivity, reliable design of the deep wells and an efficient utilization of the geothermal fluid for net power and district heat production.     

地热资源发电技术特点及发展方向

地热资源是一种清洁无污染、可再生的新型能源,对于发展低碳经济、实现可持续发展具有积极的作用.目前地热发电技术主要包括干蒸汽发电、扩容式蒸汽发电、双工质循环发电和卡琳娜循环发电等.其中干蒸汽发电系统工艺简单,技术成熟,安全可靠,循环效率可达20％以上,是高温地热田发电的主要形式;扩容式发电技术已在地热发电领域得到广泛应用,尤其是中高温地热田,二级扩容系统循环效率约为15％～20％;针对中低温地热资源,双工质循环发电技术是较为适用的,它由地热水系统和低沸点介质系统组成,循环效率较扩容式蒸汽发电技术可提高20％～30％;卡琳娜循环在低温地热资源应用领域中有其独特的优越性,通过调整氨和水的比例,可以适应低温地热水的发电特性,卡琳娜循环发电技术的循环效率比朗肯循环的效率高20％～50％.在低温地热资源的开发利用过程中,双工质循环和卡琳娜循环技术具有广阔的发展前景.作为一种新型地热资源,干热岩具有很高的开发利用价值.新型的联合循环发电技术是地热发电技术的发展方向.在浅层地热能得到大规模开发后,中深层地热资源和干热岩资源将成为地热发电技术新的资源,我国应注重中深层地热资源和干热岩资源的开发.     

Development and role of geothermal resources in India

The geothermal resources discovered in India consist of warm/hot water systems. Medium-temperature waters and reversal of temperature at depth were observed in Puga, Manikaran and the West Coast geothermal areas after exploratory drilling. Such resources can be utilized only for non-electrical applications after detailed technical—economic feasibility studies. The presence of medium-temperature (90–140°C) springs in the cold, remote and steep Himalayan terrains and of lower temperature springs (100°C) in the hot and variable climate of the Peninsular and Coastal regions further restrict full utilization of these resources, with the exception of Cambay, West Coast and Tatapani—Jhor areas. After careful study a list of direct utilizations is proposed for future consideration and the development of the main geothermal resources in India.     

Fifty years of geothermal power generation at Wairakei

The challenges and changes that have occurred over the last 50 years of remarkable service from the Wairakei Geothermal Power Project are reviewed. The project was initially constructed during the 1953–1963 period. Plant changes including the decommissioning of the high-pressure turbine generators, the installation of a 3.5-MW intermediate-low pressure steam turbine at the Wairakei Power Station in 1996, the commissioning of the 55 MW Poihipi Power Station in 1997, the 14 MW binary power plant at the Wairakei Power Station in 2005, and a proposed new station to be constructed in the Te Mihi area in 2011–2016 are briefly discussed. Also reviewed are steamfield aspects including steam separation processes, a pilot scheme that was designed to carry hot geothermal water some distance before flash steam generation by pressure reduction, steam production from vapor-dominated regions in the Wairakei reservoir, geothermal water injection, and cascade and direct heat uses. Finally, various aspects of the Wairakei development that have contributed to its success are described. It is anticipated that the geothermal resource will be producing beyond 2028 at generation levels 50% above the current (2008) level.     

Geothermal energy potential for power generation in Turkey: A case study in Simav,Kutahya

Geothermal energy and the other renewable energy sources are becoming attractive solutions for clean and sustainable energy needs of Turkey. Geothermal energy is being used for electricity production and it has direct usage in Turkey, which is among the first five countries in the world for the geothermal direct usage applications. Although, Turkey is the second country to have the highest geothermal energy potential in Europe, the electricity production from geothermal energy is quite low. The main purpose of this study is to investigate the status of the geothermal energy for the electricity generation in Turkey. Currently, there is one geothermal power plant with an installed capacity of 20.4 MWe already operating in the Denizli–Kizildere geothermal field and another is under the construction in the Aydin–Germencik field.This study examines the potential and utilization of the existing geothermal energy resources in Kutahya–Simav region. The temperature of the geothermal fluid in the Simav–Eynal field is too high for the district heating system. Therefore, the possibility of electrical energy generation by a binary-cycle has been researched and the preliminary feasibility studies have been conducted in the field. For the environmental reasons, the working fluid used in this binary power plant has been chosen as HCFC-124. It has been concluded that the Kutahya–Simav geothermal power plant has the potential to produce an installed capacity of 2.9 MWe energy, and a minimum of 17,020 MWh/year electrical energy can be produced from this plant. As a conclusion, the pre-feasibility study indicates that the project is economically feasible and applicable.     

基于全生命周期的地热发电系统环境影响评价

为明确不同类型地热发电系统“获取、转化”环节的钻井、建设、运行、退役等不同过程对地热发电系统的环境影响贡献,本文建立了基于热力学优化模型的闪蒸/双工质地热发电系统全生命周期环境影响评价模型。进而,选取西藏羊八井、广东丰顺、华北油田及青海共和四种典型地热热储,整理和收集了我国地热发电系统的环境影响全生命周期环境影响清单,分析了地热发电站六个不同过程对三个主要环境影响潜值评价指标：酸化潜值、富营养化潜值和全球变暖潜值的影响规律。发现钻井完井过程分别平均占到地热电站酸化潜值、全球变暖潜值和富营养化潜值的46.28%、45.90%和27.52%,地下系统和地上系统的环境影响贡献相当;地热梯度与地热电站的全生命周期环境影响潜值有着负相关关系,梯度越大,环境影响潜值越低。。     

低温地热发电有机朗肯循环的优化

采用(火用)分析方法及PR状态方程,建立了低温地热发电有机朗肯循环的工质优选及主要参数优化热力学方法.比较计算了以10种干流体有机工质为循环工质的低温地热发电有机朗肯循环的输出功率、(火用)效率及其余主要热力性能.结果表明,低温地热发电有机朗肯循环的性能极大地受工质的物性及蒸发温度的影响.总体来看,随着工质临界温度的升...     

Comparative analysis of natural and conventional working fluids for use in transcritical Rankine cycle using low‐temperature geothermal source

Theoretical analyses of natural and conventional working fluids‐based transcritical Rankine power cycles driven by low‐temperature geothermal sources have been carried out with the methodology of pinch point analysis using computer models. The regenerator has been introduced and analyzed with a modified methodology considering the considerable variation of specific heat with temperature near the critical state. The evaluations of transcritical Rankine cycles have been performed based on equal thermodynamic mean heat rejection temperature and optimized gas heater pressures at various geothermal source temperature levels ranging from 80 to 120°C. The performances of CO₂, a natural working fluid most commonly used in a transcritical power cycle, have been indicated as baselines. The results obtained show: optimum thermodynamic mean heat injection temperatures of transcritical Rankine cycles are distributed in the range of 60 to 70% of given geothermal source temperature level; optimum gas heater pressures of working fluids considered are lower than baselines; thermal efficiencies and expansion ratios (Exp_r) are higher than baselines while net power output, volume flow rate at turbine inlet (V₁) and heat transfer capacity curves are distributed at both sides of baselines. From thermodynamic and techno‐economic point of view, R125 presents the best performances. It shows 10% higher net power output, 3% lower V₁, 1.0 time higher Exp_r, and 22% reduction of total heat transfer areas compared with baselines given geothermal source temperature of 90°C. With the geothermal source temperature above 100°C, R32 and R143a also show better performances. R170 shows nearly the same performances with baselines except for the higher V₁ value. It also shows that better temperature gliding match between fluids in the gas heater can lead to more net power output. Copyright © 2010 John Wiley & Sons, Ltd.     

Geothermal energy utilization trends from a technological paradigm perspective

The use of geothermal energy and its associated technologies has been increasing worldwide. However, there has been little paradigmatic research conducted in this area. This paper proposes a systematic methodology to research the development trends for the sustainable development of geothermal energy. A novel data analysis system was created to research the geothermal energy utilization trends, and a technological paradigm theory was adopted to explain the technological changes. A diffusion velocity model was used to simulate and forecast the geothermal power generation development in the diffusion phase. Simulation results showed that the development of installed capacity for geothermal generation had a strong inertia force along with the S-curve. Power generation from geothermal power sources reached a peak in 2008 and is estimated to be saturated by 2030. Geothermal energy technologies in hybrid power systems based on other renewable energy sources look to be more promising in the future.