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Geothermal heat mining simulations using supercritical CO2 (sCO2) were performed in this research. Working fluid selection criteria for power generation using sCO2 from a geothermal reservoir are then presented for subcritical, superheated and supercritical organic Rankine cycles (ORCs). Meanwhile, method of working fluid classification for ORC is proposed. To get the most feasible ORC design, this study introduces the concept of “turning point” for isentropic and dry working fluids, as well as minimum turbine inlet temperature for wet working fluids. A thermodynamic model was developed with capabilities to obtain the optimal working fluid mass flow rate, evaporation temperature, superheated temperature, and supercritical pressure, to evaluate the thermal performance of the three ORC approaches using hot produced sCO2. With this model, thirty potential working fluids with critical temperatures in the range from 50 to 225 °C were screened for utilizing hot produced sCO2 considering physical properties, environmental and safety impacts, and thermodynamic performances. Finally, the thermodynamic results were compared for all possible working fluids.

The concept of injecting supercritical CO2 (sCO2) into a geothermal reservoir was computationally investigated to assess its performance in terms of the benefit of using CO2 captured from fossil power plants for geothermal heat mining. A coupled wellbore-reservoir system was simulated considering the flow of pure sCO2 in an injection well, the interaction of sCO2 and water in a permeable reservoir, and the flow of the two-phase mixture of sCO2 and water in a production well. Results of simulations indicate that this CO2 application is capable of providing a good source of renewable energy. It was found that for a reservoir with a 0.08 km3 volume, about 8-9 MWth could be extracted in a steady state fashion for a 30-year lifetime operation. This is approximately equivalent to 100 MWth/km3. A sensitivity analysis provided information on the impact of certain parameters on the performance of the integrated system. The injection flowrate, the distance between the production and injection wellbores and the penetrating depth of the production wellbore into the reservoir have a first order impact on the pressure management of the reservoir. Additionally, CO2 injection temperature has a large effect on the thermosiphon characteristics of the system.

Process monitoring plays an essential role in ensuring the safe and efficient operation of multi‐unit plantwide industrial processes. However, complicated nonlinear dynamics of these processes pose enormous challenges to the plantwide process monitoring approaches. In this paper, a novel distributed temporal–spatial neighbourhood enhanced variational autoencoder (DTS‐VAE) monitoring scheme is proposed. The scheme selects the temporal and spatial neighbourhood sets of a current sample from a local unit. Time‐series correlation is utilized to construct temporal representative samples to obtain process dynamic characteristics. Likewise, spatial similarity is employed to construct spatial representative samples to obtain spatial patterns in the data. Then the reconstructed and current samples serve as the inputs for a variational autoencoder to extract features from the current sample and its neighbourhoods. Subsequently, a distributed monitor that considers the temporal–spatial characteristics is established for each unit. Finally, a comprehensive evaluation index is developed using Bayesian fusion strategy to improve monitoring performance. The proposed DTS‐VAE monitoring scheme was effectively verified on the Tennessee Eastman benchmark process and a wastewater treatment plant. [ABSTRACT FROM AUTHOR]

A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO2 turbine expansion electric power generation system was proposed in this paper. Assisted by this integrated model, thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity (LCOE). Specifically, in geothermal heat extraction simulation, an integrated well-bore-reservoir system model (T2Well/ECO2N) was used to generate a database for creating a fast, predictive, and compatible geothermal heat mining model by employing a response surface methodology. A parametric study was conducted to demonstrate the impact of turbine discharge pressure, injection and production well distance, CO2 injection flowrate, CO2 injection temperature, and monitored production well bottom pressure on LCOE, system thermal efficiency, and capital cost. It was found that for a 100 MWe power plant, a minimal LCOE of $0.177/kWh was achieved for a 20-year steady operation without considering CO2 sequestration credit. In addition, when CO2 sequestration credit is $1.00/t, an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t. [ABSTRACT FROM AUTHOR]

Summary: Supercritical CO2 (sCO2) has been proven to be a promising working fluid for geothermal heat mining, and the produced hot sCO2 can be directly used for power generation. However, the sCO2 produced from a brine‐based reservoir may contain a certain amount of water, preventing direct power‐cycle utilization. In this paper, an axial vane separator was designed to address the separation problem of sCO2 and water produced from geothermal reservoirs. First, the influences of operational and structural parameters on the separation performance were analyzed through numerical simulations. Five factors were selected to develop separation performance regression models by the response‐surface method (RSM). Finally, geometrical parameter optimization was applied to these RSM models. The results show that the guide vane area and the exhaust inlet are the main locations impacting the system pressure drop. The separation performance can be affected by many factors, including the guide blade outlet angle, number of vanes, hub diameter, length of the vortex tube, droplet size, and inlet velocity. The water‐droplet size and the number of vanes are the most critical factors affecting the separation efficiency. The inlet velocity, the number of vanes, and the hub diameter have a larger influence on the pressure drop of the separator. The optimization results indicate that the separation efficiency can reach 100% under certain operating conditions with a pressure drop no greater than 100 kPa. [ABSTRACT FROM AUTHOR]