共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperature geothermal heat sources is presented. The ratio of the total heat exchanger area to net power output is used as the objective function and was optimized using the steepest descent method. Evaporation and condensation temperatures, geothermal and cooling water velocities are varied in the optimization method. The optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. The optimization method converges to a unique solution for specific values of evaporation and condensation temperatures and geothermal and cooling water velocities. The choice of working fluid can be greatly affect the objective function which is a measure of power plant cost and in some instances the difference could be more than twice. Ammonia has minimum objective function and maximum geothermal water utilization, but not necessarily maximum cycle efficiency. Exergy analysis shows that efficiency of the ammonia cycle has been largely compromised in the optimization process than that of other working fluids. The fluids, HCFC 123 and n-Pentane, have better performance than PF 5050, although the latter has most preferable physical and chemical characteristics compared to other fluids considered. 相似文献
3.
One of the methods of generating geothermal power is to use a suitable working fluid which extracts heat from geothermal fluids and generates power in a closed cycle. This paper presents a discussion of an improvement of the basic closed cycle with isobutane as a working fluid. A regenerative heat exchanger is added for heating the cold condensate of isobutane with the highly superheated exhaust. The addition of this heat exchanger can result in a significant reduction in the size of heat rejection equipment. Furthermore, the waste brine of the improved system is at such a high temperature that the waste heat can be economically utilized for desalting water for industrial uses. 相似文献
4.
以CO_2为工质的高温闭式布雷顿循环具有高效、简单和紧凑的特点。其高效率的实现有赖于回热器内良好的温度滑移匹配以充分回收乏气的热量。提高回热器温度滑移匹配性的关键是使流经回热器的高低压力流体的热容相接近。本文从超临界CO_2的热物性特点出发,分析了部分冷却的再压缩超临界CO_2布雷顿循环对温度滑移匹配的优化效果。根据对物性的分析结果,提出了流量调节应该覆盖高低压流体物性变化剧烈的所有温区,通过模拟计算对其进行了优化分析,认为对于一定的高低温热源,存在最优的透平进、出口压力。 相似文献
5.
LIU Ruijian GAO Fengling LIANG Kunfeng WANG Lin WANG Moran MI Guoqiang LI Yachao 《热科学学报(英文版)》2021,30(3):869-879
The non-linear temperature glide in the supercritical CO_2 cooling process makes the heat transfer pinch point of heat exchanger show multiplicity,like size,location distribution and quantity,which makes the thermodynamic performance of the CO_2 transcritical cycle more complex and eventually affects the evaluation of the optimal operating state of the system.Based on the second law of thermodynamics and the constraints of heat transfer pinch,a thermodynamic evaluation method of CO_2 transcritical heat pump system was proposed according to the degree of temperature matching.The influence mechanism of multi-characteristic change of heat transfer pinch point on temperature matching degree and the effect of temperature matching degree on thermodynamic performance of CO_2 transcritical heat pump system were discussed.The relationship between temperature matching degree,COP and exergy efficiency of the system was analyzed.It is considered that the change of temperature matching index value can clearly characterize the change trends of COP and exergy efficiency.That is,the smaller the temperature matching degree is,the closer the temperature distribution of heat transfer fluids on both sides of the heat exchanger is to Lorenz cycle,and the greater the COP and exergy efficiency are.Furthermore,by monitoring the outlet temperature of the CO_2 cooler,which has an essential relationship with the temperature matching degree during the heat exchange process,the deviation between actual and optimal working condition can be judged online,which is beneficial to real-time evaluation of the working state of the system. 相似文献
6.
This paper describes a one-dimensional mathematical model that allows simulating the heat exchange in a steam generator working with water at supercritical pressure. The model has been developed in order to simulate the full and part load behaviour of heat recovery steam generators (HRSGs) of combined cycle gas turbine (CCGT) power plants. It takes into account the strong variation of some of the thermal and transport properties of fluids at supercritical pressure and discusses what parameters may be considered as constant along the heat exchanger.On the one hand, the model is useful because going supercritical is considered a way to further improve the efficiency of CCGT power plants and, on the other hand, because part load operation is the most usual operation mode in power plants. 相似文献
7.
8.
According to fluid critical temperature and heat source temperature, organic Rankine cycle (ORC) is recognized in two categories: subcritical ORC and supercritical ORC. For a given heat source, some organic fluids not only can be used in subcritical ORC, but also can be used in supercritical ORC. For heat source with temperature of 90 °C, HFC125, HFC143a and HF218 can be used in both ORCs. Performance of the three substances in both cycles, especially in near-critical conditions is studied with expander inlet temperature of 85 °C and hot water mass flow rate of 1 kg/s. The results show that when fluids go in supercritical ORC from subcritical ORC, cycle thermal efficiency varies continuously, while mass flow rate and net power generation vary discontinuously. Maximum net power generation in near-critical conditions of subcritical ORC is higher than that of supercritical ORC. For HFC125 and HFC143a, outlet temperature of hot water decreases with the increase of heating pressure ratio. For HF218, outlet temperature of hot water increases firstly and decreases secondly with the increase of heating pressure ratio, which leads to an increase of net power generation with the increase of heating pressure ratio in high heating pressure ratio conditions. 相似文献
9.
《Applied Thermal Engineering》2007,27(11-12):2074-2078
This paper presents a method of increasing the power output of a geothermal power plant based on organic working fluid. The power is raised by increasing the flow of geothermal water supplied to the evaporator by means of returning the stream of geothermal water from downstream of the evaporator for a repeated passage through that heat exchanger. Such arrangement increases the flow of the working fluid in the circuit. Analyses have been conducted for a power plant using several types of organic fluids. The results obtained show that there is one optimum evaporation temperature of the working fluid, which depends on the quantity of the recycled geothermal water, at which the capacity of the Clausius–Rankine is the highest. 相似文献
10.
This study involves the design of a single flash cycle which comprises a separator, steam turbine, condenser and pump combined with Organic Rankine Cycle (ORC). The ORC has a three-stage heat exchanger. The mass flow rate of the organic fluid varies depending on the type of organic fluid. The system is heated by geothermal water. The effect of changing the geothermal water temperature [200–260°C] on performance parameters including the power output and overall efficiency has been studied. Four working fluids (n-Butane, Isobutane, R11 and R123) were chosen depending on their properties. The results show that a drop in the source temperature (T1) by 10% will result in 9.7% and 25.3% drop in overall efficiency and net power output for Isobutane. Also, Isobutane has a drop of 4.2% in both; overall efficiency and net power output for a 10% drop in pressure ratio (rp). R11 shows the highest overall efficiency and net power output (18.76% and 24.887 MW) respectively at the design point. 相似文献
11.
12.
Huijuan Chen D. Yogi Goswami Elias K. Stefanakos 《Renewable & Sustainable Energy Reviews》2010,14(9):3059-3067
This paper presents a review of the organic Rankine cycle and supercritical Rankine cycle for the conversion of low-grade heat into electrical power, as well as selection criteria of potential working fluids, screening of 35 working fluids for the two cycles and analyses of the influence of fluid properties on cycle performance. The thermodynamic and physical properties, stability, environmental impacts, safety and compatibility, and availability and cost are among the important considerations when selecting a working fluid. The paper discusses the types of working fluids, influence of latent heat, density and specific heat, and the effectiveness of superheating. A discussion of the 35 screened working fluids is also presented. 相似文献
13.
Thermodynamic analysis and performance optimization of organic rankine cycles for the conversion of low‐to‐moderate grade geothermal heat
下载免费PDF全文
![点击此处可从《国际能源研究杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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. 相似文献
14.
In this study the option of combined heat and power generation was considered for geothermal resources at a temperature level below 450 K. Series and parallel circuits of an Organic Rankine Cycle (ORC) and an additional heat generation were compared by second law analysis. Depending on operating parameters criteria for the choice of the working fluid were identified. The results show that due to a combined heat and power generation, the second law efficiency of a geothermal power plant can be significantly increased in comparison to a power generation. The most efficient concept is a series circuit with an organic working fluid that shows high critical temperatures like isopentane. For parallel circuits and for power generation, fluids like R227ea with low critical temperatures are to be preferred. 相似文献
15.
In the present study, an integrated system is proposed and thermodynamically analyzed to reduce greenhouse gas (GHG) emissions while improving overall system performance. The integrated system is comprised of a supercritical carbon dioxide (CO2) Rankine cycle cascaded by an Organic (R600) Rankine cycle, an electrolyzer, and a heat recovery system. It is designed to utilize a medium-to-high temperature geothermal energy source for power and hydrogen production, and thermal energy utilization for space heating. Therefore, parametric studies for the supercritical CO2 cycle, the Organic (R600) cycle, and the overall system are conducted. In addition, the effect of various operational conditions, such as geothermal source, ambient and cooling water temperatures on the performance of each cycle and the integrated system, is illustrated. It is found that increasing geothermal source temperature results in slight increases of the exergetic efficiency of the overall system. The energy efficiencies of the CO2 and Organic Rankine cycles do not considerably vary with source temperature changes. The decay of the cooling water temperature leads to a decrease in the overall system exergetic efficiency. The system configuration, which is introduced, is capable of producing about 180 kg/h for the geothermal source of mass flow rate of 40 kg/s and a temperature of 473 K. 相似文献
16.
17.
Organic Rankine Cycle (ORC) is a promising technology for converting the low-grade energy to electricity. This paper presents an investigation on the parameter optimization and performance comparison of the fluids in subcritical ORC and transcritical power cycle in low-temperature (i.e. 80–100 °C) binary geothermal power system. The optimization procedure was conducted with a simulation program written in Matlab using five indicators: thermal efficiency, exergy efficiency, recovery efficiency, heat exchanger area per unit power output (APR) and the levelized energy cost (LEC). With the given heat source and heat sink conditions, performances of the working fluids were evaluated and compared under their optimized internal operation parameters. The optimum cycle design and the corresponding operation parameters were provided simultaneously. The results indicate that the choice of working fluid varies the objective function and the value of the optimized operation parameters are not all the same for different indicators. R123 in subcritical ORC system yields the highest thermal efficiency and exergy efficiency of 11.1% and 54.1%, respectively. Although the thermal efficiency and exergy efficiency of R125 in transcritical cycle is 46.4% and 20% lower than that of R123 in subcritical ORC, it provides 20.7% larger recovery efficiency. And the LEC value is relatively low. Moreover, 22032L petroleum is saved and 74,019 kg CO2 is reduced per year when the LEC value is used as the objective function. In conclusion, R125 in transcritical power cycle shows excellent economic and environmental performance and can maximize utilization of the geothermal. It is preferable for the low-temperature geothermal ORC system. R41 also exhibits favorable performance except for its flammability. 相似文献
18.
For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, experiments were carried out on cooling heat transfer of supercritical pressure fluids flowing in a plate heat exchanger (PHE). Using two refrigerants of HFC134a and HCFC22 as the test fluids, heat transfer coefficient data were obtained at different pressure, flow rate, and heat load conditions. The heat transfer coefficient generally had a maximum in the vicinity of the pseudocritical point and showed seven- to ninefold values compared with tube flow. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure fluids in the PHE were clarified and a correlation of heat transfer coefficient was developed. 相似文献
19.
In consideration of the high-temperature characteristic of engine's waste heat and stricter environmental regulations, natural substance, including CO_2 and hydrocarbons, have been treated as promising working fluid for diesel engine waste heat recovery due to its environment friendly and excellent physical and chemical properties. This paper presented a comprehensive performance analysis on transcritical Rankine cycles for diesel engine multiple waste heat recovery using hydrocarbons and CO_2 as working fluid. The optimal turbine inlet pressures corresponding to maximum net power output, maximum exergy efficiency and minimum electricity production cost(EPC) were obtained. The effect of working fluid on these optimal pressures has been discussed. For fluids with low critical temperature, the optimal pressure corresponding to maximum net power output is lower than the one for maximum exergy efficiency, while the opposite results can be found for fluid with high critical temperature. Then, the effect of various working fluid properties in transcritical cycle performance is discussed. Comparison results show that CO_2 obtains only more power output than Ethane, Propane and Propene, but CO_2 is capable of absorbing more energy from engine coolant and regeneration heat with comparable total heat transfer areas and has an advantage in turbine size, particularly for hydrocarbons with high critical temperature. 相似文献
20.