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The conversion efficiency of geothermal energy is very low. For low-temperature resources, such as geothermal energy, a supercritical organic Rankine cycle (ORC) has been shown to be more efficient than an ORC. Recuperative supercritical ORCs have been proven to yield even higher efficiencies for cases where the heat source is limited above the ambient temperature. Most studies on these cycles have focused on turbine inlet temperatures between 80 and 130 °C. Only a few studies have explored other working fluids between 180 and 350 °C but did not analyze optimum turbine inlet pressures. Turbine inlet temperatures ranging from 170 to 240 °C were tested with the heat source provided by a medium temperature geothermal reservoir. A parametric analysis was performed for various turbine inlet pressures and temperatures. Numerous environmental and nontoxic fluids were analyzed. Temperatures and pressures were selected for each tested fluid to achieve the maximum plant efficiency and net work. The best performing binary cycle fluid was R1233zd(E) with a plant efficiency of 16.2% and a second law efficiency of 52.3% for a turbine inlet temperature of 240 °C. This cycle was compared to a single flash plant. The binary cycle plant produced over double the work and had significantly less exergy destruction. • A recuperative supercritical ORC was compared to current binary systems. • Various environmental and nontoxic fluids were analyzed. • Performance of the best performing fluid was compared to a single flash plant. • R1233zd(E), butane, isopentane, pentane, and neopentane performed the best. [ABSTRACT FROM AUTHOR] more...

The design of plant-wide control system to optimize electricity production in geothermal power plant is proposed in this research. The objective is to overcome the deficiency due to changes in the characteristics of production well and fluctuation in electricity demand load. The proposed plant-wide control system has two main tasks; to maintain production process at optimum value and to increase efficiency. The pressure in separator and condenser is maintained at the respective set points under electrical load fluctuations in order to ensure optimum efficiency. The control system also reduce the usage of auxialiary electrical power and increase efficiency. The task was performed by controlling inlet cooling water temperatures to the condenser. It was concluded that the proposed control structure was able to increase efficiency and maintain production. more...

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This method of combining thermodynamic and silica scaling analysis aims to improve efficiency, power output and sustainability in geothermal power plants which suffer from high concentration of silica. The proposed method was employed in an analysis of the Dieng geothermal power plant. The process starts with a performance evaluation of the existing power plant system, which is comprised of many components where losses of both energy and exergy occur. Once the performance of the existing plant has been evaluated, optimization of operating parameters can be applied to maximize its power output without the expensive addition of any new components. The process then continues with the development of scenarios with the power plant’s design, seeking potential methods to improve its performance. In these scenarios, the plant is expanded into a double flash system, single flash-binary and double flash-binary. Silica scaling behavior models are then applied to determine which is the best scenario for development. It was found that a double flash system is the best expansion scenario for Dieng Geothermal Power Plant. This scenario produces a high power output of 29,155 kW and the lowest excess deposit of silica at 899 ppm. Although this scenario produces lower power output than the double flash-binary system, it has less negative impact from silica scaling. By introducing this system, the company can obtain additional power output of 4855 kW. [ABSTRACT FROM AUTHOR] more...

This paper addressed the performance of single flash combined with a binary system that was proposed in the Dieng geothermal power plant by applying thermodynamic assessment methods. A set of mathematical equations from the plant was developed and solved iteratively using engineering equation solver. The results showed that the available exergy of the produced fluid from production wells is 66,204 kW. The performance of an existing single-flash power plant indicated 24,300 kW of net power output. The proposed design of single flash combined with a binary system improves the power output by 17.16% to 27,786 kW. The second law efficiency increases from 36.7% to 41.97% while the first law efficiency increases from 11.62% to 13.61%. [ABSTRACT FROM AUTHOR] more...

A reformulation of the USGS volumetric “heat in place” method is presented. More specifically, expressions for “recoverable heat” are derived by considering specific power cycles, i.e., single-flash and binary. The latter approach eliminates the ambiguities associated with specifications of a reference temperature and the utilization efficiency. Since the use of an arbitrarily low reference temperature such as the ambient temperature yields too optimistic an estimate for the recoverable heat, the abandonment temperature instead of the ambient (or condenser) temperature should be assumed as the reference temperature in order to obtain realistic estimates of recoverable heat. The standard USGS method will, however, yield a non-zero available work for temperatures between the ambient (or condenser) and abandonment temperatures; in this case, the only way to conform the USGS method to reality is to require conversion (utilization) efficiency to also tend to zero. The probable range for the thermal recovery factor is considered, and it is argued that in the early exploration stage prior to deep drilling and well testing, the proper lower limit for the recovery factor is zero. An illustrative example of the standard USGS method vs. the present reformulation of the USGS method for resource estimation is presented using previously published data from the Sumikawa geothermal field. A Monte Carlo procedure was employed to predict the megawatt capacity at Sumikawa for three cases: (1) the reformulated USGS method, (2) the effect of a zero minimum recovery factor, and (3) the standard USGS method. A total of 100,000 Monte Carlo simulations were used in each case to compute the cumulative probability distribution. Comparing Cases 1 and 3, it is apparent that the original USGS method predicts a much larger capacity than the new formulation. The main effect of a zero minimum recovery factor (Case 2) is to yield a considerably smaller capacity at the 90% confidence level compared to Case 1. In a certain sense, a zero minimum recovery factor encodes a lack of knowledge regarding the productivity of as yet undrilled wells. [ABSTRACT FROM AUTHOR] more...

Purpose: This paper presents a life cycle inventory (LCI) describing the material and energy demands for constructing and operating a geothermal combined heat and power (GCHP) plant as well as direct emissions of gases, waste water, and waste heat. The data are based on a newly constructed GCHP plant in Iceland, representing the design of both single flash (SF) and double flash (DF) power plants that currently produce the majority of electricity from geothermal plants worldwide. Methods: Primary data were collected for the construction, operation, and maintenance of a GCHP plant. As the design and operation of geothermal flash power plants is site-specific due to the different nature of geothermal resources, a method of scaling data to a site specific parameter is proposed to make the LCI available as representative secondary data for such plants. These parameters along with other data identified as site-specific serve as the minimum data to be collected for adjusting the presented data to represent other flash power plants with or without combined heat production. Results: The construction stage dominates the material burdens for the electricity and heat production. For the life cycle of electricity, it includes 80 % of diesel fuel use (whereof 96 % originates from well drilling), while 99 % of groundwater is used during the operational stage. The use and composition of geothermal fluid is site-specific but accounts for all direct emissions from the electricity production. The main materials in terms of mass used for the construction of the GCHP plant are water, diesel, steel, cement, asphalt, bentonite, and silica flour. Mineral wool and aluminum were also among the main material contributors. Material and energy burdens per functional unit are generally higher for a SF plant compared with DF plants. For heat production, 1.7 MJ of waste heat from power generation is used to produce 1 MJ of usable heat. Conclusions: By presenting LCI data scaled with site-specific parameters, the flexibility of its use is increased as secondary data. However, the collection of primary data for the composition of geothermal fluid and values for site specific parameters is always required to represent local conditions. Thus, the LCI for Hellisheiði GCHP can be regarded as representative data for electricity and heat from geothermal flash power plants. [ABSTRACT FROM AUTHOR] more...

Highlights: [•] The conversion efficiency of geothermal power plants is lower than all thermal plants. [•] Worldwide review of published data gave an average conversion efficiency of 12%. [•] A generic conversion relation was developed based on the total produced enthalpy. [•] Correlations are presented for single flash/dry steam, double flash and binary plants. [Copyright &y& Elsevier] more...