Heat Extraction and Recover of Deep Borehole Heat Exchanger: Negotiating with Intermittent Operation Mode Under Complex Geological Conditions

2021 ◽  
Author(s):  
Yongqiang Luo ◽  
Guozhi Xu ◽  
Shicong Zhang ◽  
Nan Cheng ◽  
Zhiyong Tian ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Operation Mode ◽  
Heat Extraction ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Geological Conditions ◽  
Intermittent Operation

Heat extraction model and characteristics of coaxial deep borehole heat exchanger

2021 ◽  
Vol 169 ◽  
pp. 738-751
Author(s):  
Ji Li ◽  
Wei Xu ◽  
Jianfeng Li ◽  
Shuai Huang ◽  
Zhao Li ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Extraction ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Extraction Model

scholarly journals Simulations of Heat Supply Performance of a Deep Borehole Heat Exchanger under Different Scheduled Operation Conditions

Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 121
Author(s):  
Jiaqi Zhang ◽  
Xinli Lu ◽  
Wei Zhang ◽  
Jiali Liu ◽  
Wen Yue ◽  
...  
Keyword(s):  
Heat Supply ◽  
Operation Mode ◽  
Continuous Operation ◽  
Heat Extraction ◽  
Formation Temperature ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Electricity Cost ◽  
Mode 2 ◽  
Mode 3

With the changing world energy structure, the development of renewable energy sources is gradually accelerating. Among them, close attention has been given to geothermal energy because of its abundant resources and supply stability. In this article, a deep borehole heat exchanger (DBHE) is coupled with a heat pump system to calculate the heat supply and daily electricity consumption of the system. To make better use of the peaks and valleys in electricity prices, the following three daily operating modes were studied: 24-h operation (Mode 1), 8-h operation plus 16-h non-operation (Mode 2), and two cycles of 4-h operation and 8-h non-operation (Mode 3). Simulation results show that scheduled non-continuous operation can effectively improve the outlet temperature of the heat extraction fluid circulating in the DBHE. The heat extraction rates of Mode 1 is 190.9 kW for mass flowrate of 9 kg/s; in Mode 2 and Mode 3 cases, the rates change to 304.7 kW and 293.0 kW, respectively. The daily operational electricity cost of Mode 1 is the greatest because of 24-h operation; due to scheduled non-continuous operation, the daily operational electricity cost of Mode 3 is only about 66% of that of Mode 2. After an 8-month period without heating, the formation-temperature can be restored within 4 °C of its original state; 90% recovery of the formation-temperature can be achieved by the end of the second month of the non-operation season.

Analysis of heat extraction performance and long-term sustainability for multiple deep borehole heat exchanger array: A project-based study

2021 ◽  
Vol 289 ◽  
pp. 116590
Author(s):  
Wanlong Cai ◽  
Fenghao Wang ◽  
Shuang Chen ◽  
Chaofan Chen ◽  
Jun Liu ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Extraction ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Extraction Performance

scholarly journals Sustainability of the Exploitation of Campi Flegrei Geothermal Area Using a Zero-mass Extraction Device

2020 ◽  
Author(s):  
Claudio Alimonti ◽  
Elena Soldo ◽  
Gennaro Sepede ◽  
Salvador Ángel Gómez-Lopera
Keyword(s):  
Heat Exchanger ◽  
Coupled Model ◽  
Heat Extraction ◽  
Campi Flegrei ◽  
Geothermal System ◽  
Volcanic Area ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Zero Mass ◽  
Extraction Device

Abstract In this paper, the use of a zero-mass extraction device has been simulated in the volcanic area of CampiFlegrei (Italy),one of the most promising geothermal districts of Italy.The sustainability of the heat extraction has been studied with a coupled model of the geothermal reservoir and the deep borehole heat exchanger. The reservoir model has been built using the SHEMAT software, the heat transfer in the deep borehole heat exchanger has been simulated using GEOPIPE, a pure conductive semi-analytical model. An iterative approach has been used to couple the two simulators. The work has demonstrated that the area of CampiFlegrei is a promising candidate to produce sustainable geothermal energy with a zero-mass extraction device. It is also demonstrated that the coupled model of reservoir and deep borehole heat exchanger is the best modelling approach when convective structures are present in the geothermal system, which can generate heat recovery effects.

Performance Evaluation and Operation Mechanism of Deep Borehole Heat Exchanger with Different Types of Boundary Conditions

2020 ◽  
Author(s):  
Wanlong Cai ◽  
Chaofan Chen ◽  
Fenghao Wang ◽  
Jun Liu ◽  
Olaf Kolditz ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Boundary Conditions ◽  
Urban Areas ◽  
Geothermal Energy ◽  
Heat Fluxes ◽  
Heat Extraction ◽  
Neumann Condition ◽  
Deep Borehole ◽  
Borehole Heat Exchanger ◽  
Different Types

<p>Due to its sustainability, continuity and low carbon emissions, the utilization of geothermal energy is gaining more attention all around the world. Shallow geothermal energy is usually extracted through borehole heat exchangers (BHE) with a maximum length up to 150 m. Such systems typically require large space areas, thus limiting its application in built-up urban areas. This study presents a case where deep borehole heat exchanger (DBHE) with a depth down to 2500 m was constructed to extract geothermal energy for building heating purposes. A double-continuum finite element based numerical model was set up to simulate the heat transport process within and around the DBHE. The model has been validated by the experimental data in a demonstration project located in Fengxi, Xi’an China. The heat extracting performance of DBHE under different types of boundary conditions (including the Dirichlet condition and Neumann condition) are evaluated. The amount of thermal recharges from top, sides and bottom of the domain were differentiated and quantified. It is found that different types of boundary conditions will lead to deviations in the simulated heat fluxes and corresponding thermal recharge. The numerical simulations also suggest that the sustainable heat extract capacity of DBHE is mainly determined by the stored heat from the surrounding subsurface, and thermal recharge takes only a limited contribution. According to the calibrated modelling results, the proper heat extraction rate of DBHE in the long-period operation modes is analyzed.</p>

Deformations and permeability variations in fine sediments induced by freezing-thawing cycles caused by borehole heat exchangers

2021 ◽  
Author(s):  
Giorgia Dalla Santa ◽  
Simonetta Cola ◽  
Antonio Galgaro
Keyword(s):  
Heat Exchanger ◽  
Pore Size ◽  
Heat Exchangers ◽  
Heat Extraction ◽  
Water Salinity ◽  
Cohesive Sediments ◽  
Borehole Heat Exchanger ◽  
Freeze Thaw ◽  
Vertical Permeability ◽  
Borehole Heat Exchangers

<p>In closed-loop Ground Source Heat Pump system, the circulation of a heat-carrier fluid into the heat exchanger provides the thermal exchange with the underground.</p><p>In order to improve the heat extraction from the ground, the fluid temperature is often lowered down to subzero temperatures; as a consequence, the thermal alteration induced in the ground is more intense and can cause freezing processes in the surroundings. In sediments with significant clay fraction, the inner structure and the pore size distribution are irreversibly altered by freezing-thawing cycles.</p><p>A wide laboratory program has been performed in order to measure the induced deformations and the permeability variations under different conditions of mechanical loads/depth [1], interstitial water salinity [2] and soil plasticity [3]. In addition, vertical deformations and permeability variations induced by freeze-thaw cycles have been measured also in Over-Consolidated silty clays at different OCR [4].</p><p>The results suggest that, despite the induced frozen condition is quite confined close to the borehole [5], in Normal-Consolidated silty clay layers the freezing-thawing-cycles induce an irreversible settlement up to 16%, gathered cycle-after cycle depending on sediment plasticity, pore fluid salinity and applied load. In addition, despite the overall contraction of the soil, the vertical hydraulic conductivity may increase by about 8 times due to a remarkable modification of the soil fabric with increases in pore size, pores connectivity and orientation [6].</p><p>The OC silty-clays show an opposite behavior. Experimental results point out that, in case of OC deposits, higher the OCR lower the freeze-thaw induced settlement. In case of OCR > 15, the settlement turns to a slight expansion. Conversely, the observed augment in vertical permeability increases with the OCR degree [4].</p><p>These occurrences are significant and irreversible and could affect the functionality of the system as well as lead to environmental effects such as local settlements, negative friction on the borehole heat exchangers or interconnection among aquifers in the probe surroundings.</p><ul><li>[1]. Dalla Santa G*, Galgaro A, Tateo F, Cola S (2016). Modified compressibility of cohesive sediments induced by thermal anomalies due to a borehole heat exchanger. <strong>Engineering Geology</strong> 202, 143-152.</li> <li>[2]. Dalla Santa G*, Galgaro A, Tateo F, Cola S (2016). Induced thermal compaction in cohesive sediments around a borehole heat exchanger: laboratory tests on the effect of pore water salinity. <strong>Environmental Earth Sciences</strong>, 75(3), 1-11.</li> <li>[3]. Cola S, Dalla Santa G, Galgaro A (2020). Geotechnical hazards caused by freezing-thawing processes induced by borehole heat exchangers. <strong>Lecture Notes in Civil Engineering</strong>, 40, pp. 529–536</li> <li>[4]. Dalla Santa G, Cola S, Galgaro A (2021). Deformation and Vertical Permeability Variations Induced by Freeze-Thaw Cycles in Over-Consolidated Silty Clays. <strong>Challenges and Innovations in Geomechanics</strong>, 117</li> <li>[5]. Dalla Santa G*, Farina Z, Anbergen H, Rühaak W, Galgaro A (2019). A Comparative Study on the Relevance of Computing Freeze-Thaw Effects for Borehole Heat Exchanger Modelling. <strong>Geothermics</strong> 79, 164-175.</li> <li>[6]. Dalla Santa G*, Cola S, Secco M, Tateo F, Sassi R, Galgaro A (2019). Multiscale analysis of freeze-thaw effects induced by ground heat exchangers on permeability of silty-clays. <strong>Geotechnique</strong> 2019, 69(2).</li> </ul>

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