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.

Geothermal Power Generation Potential in the Eastern Linqing Depression

China has been the leading country worldwide in direct geothermal utilization for a rather long time, which has contributed significantly to reducing carbon emissions. But the installed capacity of geothermal power generation in China is very small, and there are only a few geothermal power plants in China, specifically in Tibet, including the well-known Yangbajing geothermal power plant. Therefore, it is anticipated that more high-temperature geothermal resources will be discovered in order to promote China’s power generation. There is potential for high-enthalpy geothermal in the Eastern Linqing Depression in Shandong Province, where geothermal energy is stored in Ordovician and Cambrian carbonate strata. Based on the geothermal gradient in Cenozoic strata and the depth of the target geothermal reservoir, the temperature distribution pattern of the reservoir was analyzed, and two "sweet points" were identified in the Yucheng geothermal field and the Guanxian geothermal field, where the reservoir temperature is predicted to be higher than 200°C at a depth of less than 8000 m. Due to the low karst fissure ratio and the insufficient geothermal fluid in the geothermal reservoir, it is recommended that an enhanced geothermal system be set up, to increase the permeability of the natural fracture system in the carbonate formations and provide sufficient fluid for power generation through reinjection of used geothermal fluid. The power generation capacity of the two geothermal fields was estimated using a volumetric method, revealing a power generation capacity of 1621.02 MWe for the Yucheng geothermal field, and 1287.19 MWe for the Guanxian geothermal field.

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.

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.

Induced Earthquake Hazard by Geothermal Power Plants: Statistical Evaluation and Probabilistic Modeling

This study statistically evaluated the characteristics of induced earthquakes by geothermal power plants(GPPs)and generated a probabilistic model for simulating stochastic seismic events.Four well-known power plant zones were selected worldwide from the United States,Germany,France,and New Zealand.The operational condition information,as well as the corresponding earthquake catalogs recorded in the vicinity of GPPs,were gathered from their commencement date.The statistical properties of events were studied elaborately.By using this proposed database,a probabilistic model was developed capable of generating the number of induced seismic events per month,their magnitude,focal depth,and distance from the epicenter to the power plant,randomly.All of these parameters are simulated as a function of power plant injection rate.Generally speaking,the model,introduced in this study,is a tool for engineers and scientists interested in the seismic risk assessment of built environments prone to induced seismicity produced by GPPs operation.

Characteristics and prospect of geothermal industry in China under the“dual carbon”target

Geothermal energy utilization in China had been promoted actively during the 13^(th)Five-Year Plan period(2016-2020),with resultant achievements showing unique Chinese characteristics.Buildings(measured by areas)heated/cooled by intermediate-to-deep geothermal energy increased more rapidly than those by shallow geothermal energy.Geothermal power generation was restricted by the distribution of the resource and the sufficiency of local power supply.With the proposition of“dual carbon goal”by the central government of China and the coming era of great development of renewable energy,geothermal energy will be provided more development opportunities in room heating/cooling and power generation in the country ever than before.However,tackling technology bottlenecks and introduction of appropriate policy support are still urgently needed for nurturing a healthy environment for geothermal industry.Analysis suggests that a near-to medium-term development of geothermal energy shall be focused on a comprehensive and efficient utilization both through heating/cooling and power generation.Room heating/cooling by intermediate-to-deep and shallow geothermal energy shall be promoted nationwide according to local resource endowment and economic conditions.Geothermal power generation in Yunnan and Tibet shall be pushed forward in an orderly way.For medium-and long-term development,focus shall be put on power generation by using low to medium temperature geothermal energy and hot dry rocks.The"hot spring+"model shall be adapted in steps on a regular basis.To achieve these,measures including attaching importance to tackling key technologies,promoting standards for geothermal energy development and utilization,strengthening geothermal energy exploration and evaluation,and seeking for necessary policy support shall be taken.