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.     

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.     

Performance and parametric investigation of a binary geothermal power plant by exergy

Exergy analysis of a binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy diagram, and compared to the energy diagram. The sites with greater exergy destructions include brine reinjection, heat exchanger and condenser losses. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The energy and exergy efficiencies of the plant are 4.5% and 21.7%, respectively, based on the energy and exergy of geothermal water at the heat exchanger inlet. The energy and exergy efficiencies are 10.2% and 33.5%, respectively, based on the heat input and exergy input to the binary Rankine cycle. The effects of turbine inlet pressure and temperature and the condenser pressure on the exergy and energy efficiencies, the net power output and the brine reinjection temperature are investigated and the trends are explained.     

Modified exergoeconomic modeling of geothermal power plants

In this study, a modified exergoeconomic model is proposed for geothermal power plants using exergy and cost accounting analyses, and a case study is in this regard presented for the Tuzla geothermal power plant system (Tuzla GPPS) in Turkey to illustrate an application of the currently modified exergoeconomic model. Tuzla GPPS has a total installed capacity of 7.5 MW and was recently put into operation. Electricity is generated using a binary cycle. In the analysis, the actual system data are used to assess the power plant system performance through both energy and exergy efficiencies, exergy losses and loss cost rates. Exergy efficiency values vary between 35% and 49% with an average exergy efficiency of 45.2%. The relations between the capital costs and the exergetic loss/destruction for the system components are studied. Six new exergetic cost parameters, e.g., the component annualized cost rate, exergy balance cost, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy production cost rate and the overall unavoidable system exergy production cost rate are studied to provide a more comprehensive evaluation of the system.     

World geothermal power generation in the period 2001–2005

A review has been made of all the country update papers submitted to the World Geothermal Congress 2005 (WGC2005) from countries in which geothermal electricity is currently being generated. The most significant data to emerge from these papers, and from follow-up contacts with representatives of these countries, are: (1) a total of 24 countries now generate electricity from geothermal resources; (2) the total installed capacity worldwide is approximately 8930 MW_e, corresponding to about 8030 MW_e running capacity and electric energy production is nearly 57,000 GWh (early 2005 data); (3) Costa Rica, France (Guadeloupe), Iceland, Indonesia, Italy¹, Kenya, Mexico, Nicaragua, Russia, and the USA have increased the capacity of their power plant installations by more than 10% with respect to the year 2000; (4) the new members of the geothermal electricity generating community comprise Austria, Germany and Papua New Guinea; (5) the installed capacity in Argentina and Greece is now null since their geothermal power plants have been dismantled; (6) nineteen countries have carried out significant geothermal drilling operations since 2000, with 307 new wells drilled.     

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%.     

Power generation from geothermal resources in Turkey

This study provides information on power generation via geothermal resources and sector development. The first instance of power generation from geothermal resources was performed by a state-owned power plant at Kızıldere-Denizli, whereas the first private sector investment was the Dora-I power plant, commissioned in 2006. Legislation regulating rights ownership and certification laws was issued in 2007. The installed capacity of the geothermal resources is 311.871 MW for 16 power plants, and power generation licenses were issued for 713.541 MW at the end of 2012. The total potential geothermal power that can be generated in Turkey is estimated to be approximately 2000 MW. The geothermal fields in Turkey produce high levels of greenhouse gases, which have been deemed highly responsible for global warming. Due to high CO₂ emissions, the geothermal energy sector risks a carbon tax in the near future. For certain geothermal resources, multiple investors produce electricity from the same resource. The sector will inevitably experience severe damage unless permanent solutions are devised for problems related to sustainably managing geothermal resources and environmental problems.     

Modelling of hydrogen production from hydrogen sulfide in geothermal power plants

Geothermal power plants emit high amount of hydrogen sulfide (H₂S). The presence of H₂S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. There is an increasing interest in developing suitable methods and technologies to produce hydrogen from H₂S as promising alternative solution for energy requirements. In the present study, the AMIS technology is the invention of a proprietary technology (AMIS^® - acronym for “Abatement of Mercury and Hydrogen Sulfide” in Italian language) for the abatement of hydrogen sulphide and mercury emission, is primarily employed to produce hydrogen from H₂S. A proton exchange membrane (PEM) electrolyzer operates at 150 °C with gaseous H₂S sulfur dimer in the anode compartment and hydrogen gas in the cathode compartment. Thermodynamic calculations of electrolysis process are made and parametric studies are undertaken by changing several parameters of the process. Also, energy and exergy efficiencies of the process are calculated as % 27.8 and % 57.1 at 150 °C inlet temperature of H₂S, respectively.     

Dual-fluid-hybrid power plant co-powered by low-temperature geothermal water

Three variants of power plants fuelled or co-fuelled by geothermal water have been assessed, with the aim of making the best use of the energy contained in a stream of 80–120 °C geothermal water. Heat-flow calculations for three power plant types, namely an Organic Rankine Cycle (ORC) power plant, a dual-fluid-hybrid power plant and a single-fluid hybrid-fuelled power plant, are presented. The analysis shows the thermodynamic benefits, in terms of the extent of using the thermal energy of low-temperature geothermal water, that arise from utilizing hybrid and dual-fluid-hybrid power plants rather than ORC power plants. The dual-fluid plant optimizes the use of the geothermal water, but the hybrid plant makes the best overall utilization of the energy compared to separate ORC and fuel-fired plants.     

Exergy analysis of a dual-level binary geothermal power plant

Exergy analysis of a 12.4 MW existing binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram, and compared to the energy flow diagram. The causes of exergy destruction in the plant include the exergy of the working fluid lost in the condenser, the exergy of the brine reinjected, the turbine-pump losses, and the preheater–vaporizer losses. The exergy destruction at these sites accounts for 22.6, 14.8, 13.9, and 13.0% of the total exergy input to the plant, respectively. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The exergetic efficiency of the plant is determined to be 29.1% based on the exergy of the geothermal fluid at the vaporizer inlet, and 34.2% based on the exergy drop of the brine across the vaporizer–preheater system (i.e. exergy input to the Rankine cycle). For comparison, the corresponding thermal efficiencies for the plant are calculated to be 5.8 and 8.9%, respectively.     

Investment cost for geothermal power plants

Stepwise development strategy is considered a suitable method for securing a cost-effective way for the development of geothermal power plants. This strategy has been in use in Iceland for the last decade. Geothermal high-temperature fields are developed in steps of 20–30 MW. About 6 years are required for each step in the development. Parallel development of several fields in a country might be preferable, especially when a rapid increase of the generation capacity is required in that country. The capacity factor of geothermal power plants depends on the mix of power plants serving the electricity grid. Where geothermal power plants can be operated as base load, the capacity factor is usually in excess of 0.9. The investment cost of geothermal power plants is divided into the cost of surface equipment and activities and the cost of subsurface investment. The surface costs include the cost of surface exploration, and the plant and steam-gathering system, while the cost of subsurface investment is that of drilling. Surface equipment costs can be estimated with the same accuracy as other construction works at the surface (buildings, roads, bridges), whereas higher uncertainty might be associated with the cost of drilling. Analyses of the surface costs of five power plants in Iceland show that the investment cost of the surface equipment is linear with size, in the range 20–60 MW. Surface costs were found to be about 1000 USD/kW with a relative error of 10%. Stefánsson (Stefánsson, V., 1992. Success in geothermal development. Geothermics 21, 823–834) published a statistical study of the drilling results in 31 high-temperature fields in the world. Using these results, it is possible to estimate the expectation value and its limits of error for the subsurface investment in an arbtitrary geothermal field. The results obtained for the range 20–60 MW are summarized as follows:

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Electrolyzer-fuel cell combination for grid peak load management in a geothermal power plant: Power to hydrogen and hydrogen to power conversion

This study provides comprehensive energy, exergy, and economic evaluations and optimizations of a novel integrated fuel cell/geothermal-based energy system simultaneously generating cooling and electricity. The system is empowered by geothermal energy and the electricity is mainly produced by a dual organic cycle. A proton exchange membrane electrolyzer is employed to generate the oxygen and hydrogen consumed by a proton exchange membrane fuel cell utilized to support the network during consumption peak periods. This fuel cell can be also used for supplying the electricity demanded by the network to satisfy the loads at different times. All the simulations are conducted using Engineering Equation Solver software. To optimize the system, a multi-objective optimization method based on genetic algorithm is applied in MATLAB software. The objective functions are minimized cost rate and maximized exergy efficiency. The optimum values of exergy efficiency and cost rate are found to be 62.19% and 18.55$/h, respectively. Additionally, the results reveal that combining a fuel cell and an electrolyzer can be an effective solution when it comes to electricity consumption management during peak load and low load periods.     

Performance improvement of a single-flash geothermal power plant in Dieng,Indonesia, upon conversion to a double-flash system using thermodynamic analysis

We investigated proposed design of a double-flash system and compared it to the existing single-flash power plant in Dieng, Indonesia, which uses waste brine from a high pressure separator. The performance of the double-flash system was evaluated using the second law of thermodynamics, and this was based on energy and exergy analyses. The Engineering Equation Solver (EES) was used to solve the relevant mathematical equations.Our results indicate that the double-flash design is interesting for application in Dieng since the power output would increase by 19.97%. Moreover, the precipitation system to avoid silica deposition in the injection well does not have to change much. Therefore, the building costs associated with the new double-flash system would be minimal. The available exergy from the reservoir is 66,204 kW based on the enthalpy determined by TFT (Tracer Flow Test) measurements. The single-flash power plant has a net power output of 23,400 kW with a second law efficiency of 36.7%. In the double-flash design, components such as a LPS, a second purifier and an HPT would be added to the plant. Furthermore, our calculations indicate that the power plant's output and second law efficiency would increase to 29,155 kW and 44.04%, respectively. The waste brine disposed of using this precipitation system would decrease by 8.22% at 5443 kW.     

The reliability of distributed solar in critical peak demand: A capital value assessment

Generation is most valuable when demand is highest. As electricity can't yet be cheaply stored, generation and transmission infrastructure must be built to meet the highest expected demand, plus a margin of error. Reliably producing power at times of critical demand not only offsets the need to use expensive liquid fuels such as diesel or condensate, but also removes the need to build backup power stations and transmission infrastructure that would only be used for a small fraction of the year. Under the most extreme demand conditions, solar has reduced the peak demand seen by retailers and wholesale energy markets. This study compares the capital cost of critical peak availability from gas turbines to the capital cost of critical peak availability from distributed solar in the Australian National Electricity Market (NEM). When compared on this basis, 10–22% of the cost of installing the solar system can be attributed to the capital value of critical peak generation. North–west and west facing PV is worth a further 3–6% of system installation costs when compared to generally north facing PV. Finally, southern states, with longer summer days and more sunshine in the afternoon are found to benefit more from peak supply of solar PV.     

Experimental investigation on heat extraction using a two-phase closed thermosyphon for thermoelectric power generation

An experimental investigation on heat extraction using a two-phase closed thermosyphon charged with water (a filling ratio of 40%) for thermoelectric power generation was conducted to study the temperature gradients on the thermosyphon and the thermoelectric conversion characteristics. Results showed that the thermosyphon had a relatively stable working state at 100–300°C, and the maximum output power increased exponentially with temperature difference, being 20 W at a temperature difference of 210°C. The power generation efficiency increased in Hill function with increasing heating power input, the maximum value being approximately 0.01924.     

垃圾焚烧热电联产蒸汽参数选择

针对垃圾焚烧热电联产时,采用中温中压及中温次高压蒸汽参数对全厂投资及经济性的影响进行研究。以日处理规模为600 t·d^-1的生活垃圾焚烧设施作为研究对象,从主机设备参数、主机设备投资额、经济指标、营业收入及投资回收期等5个方面进行分析。研究结果表明,采用中温次高压参数时,垃圾焚烧设施热电联产全厂热效率较采用中温中压参数时提高1.7%,热电联产时全年总收入较采用中温中压参数时提高11.5%,且经济性更好,静态投资回收期约为4.73年。     

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。。     

生物质直燃和混燃发电环境效益分析

利用生物质代替矿物燃料发电可以减少CO2和SO2的排放量。确定了燃煤机组CO2和SO2排放量基准,建立生物质发电的CO2和SO2的排放量模型及其偏差模型;计算不同发电方式下CO2和SO2的生成量及减排量;分析了气化炉气化效率对生物质发电CO2和SO2生成量的影响。结果表明,提高生物质发电效率和气化效率可以显著降低CO2和SO2的排放;生物质发电的环境效益明显优于燃煤发电,而生物质气化合成气与煤混燃发电的环境效益优于生物质直燃发电。     

Investigation of hydrogen production performance of chlor-alkali cell integrated into a power generation system based on geothermal resources

In present study, hydrogen production performance of chlor-alkali cell integrated into a power generation system based on geothermal resource is studied. The basic elements of the novel system are a separator, a steam power turbine, an organic Rankine cycle (ORC), an air cooled condenser, a saturated NaCl solution reservoir tank and a chlor-alkali cell. To enhance the performance of the cell, the saturated NaCl solution is heated by the waste heat from the ORC. So, this integrated system generates significant amount of electricity for the city grid and also yields three main products those are hydrogen, chlorine and sodium hydroxide. According to the parametric study, when the temperature of a geothermal resource varies from 140 to 155 °C, the electrical power generation increases from nearly 2.5 MW to 3.9 MW and hydrogen production increases from 10.5 to 21.1 kg-h. Thus, when the geothermal resource temperature of 155 °C, the energy efficiency of the system is 6.2% and the exergetic efficiency is 22.4%. As a result, the geothermal energy potential plays a key role on the integrated system performance and the hydrogen production rate.