Organic Rankine Cycle Cycle Research Articles

4E Assessment of an Organic Rankine Cycle (ORC) Activated with Waste Heat of a Flash-Binary Geothermal Power Plant.

In this paper, the 4E assessment (Energetic, Exergetic, Exergoeconomic and Exergoenvironmental) of a low-temperature ORC activated by two different alternatives is presented. The first alternative (S1) contemplates the activation of the ORC through the recovery of waste heat from a flash-binary geothermal power plant. The second alternative (S2) contemplates the activation of the ORC using direct heat from a geothermal well. For both alternatives, the energetic and exergetic models were established. At the same time, the economic and environmental impact models were developed. Finally, based on the combination of the exergy concepts and the economic and ecological indicators, the exergoeconomic and exergoenvironmental performances of the ORC were obtained. The results show higher economic, exergoeconomic and exergoenvironmental profitability for S1. Besides, for the alternative S1, the ORC cycle has an acceptable economic profitability for a net power of 358.4 kW at a temperature of 110 °C, while for S2, this profitability starts being attractive for a power 2.65 times greater than S1 and with a temperature higher than 135 °C. In conclusion, the above represents an area of opportunity and a considerable advantage for the implementation of the ORC in the recovery of waste heat from flash-binary geothermal power plants.

Thermodynamic simulation and optimization of natural gas liquefaction cycle based on the common structure of organic rankine cycle

In this paper, using Aspen HYSYS and two different structures of an organic Rankine cycle (ORC), thermodynamic and environmental improvements are made in the common process of a natural gas liquefaction process based on the PRICO method. According to the analyses, in the PRICO process, the total exergy efficiency, power consumption, and carbon dioxide (CO2) emission are 43.9%, 278.47 kWh/ton, and 0.17 kgCO2/kgLNG, respectively. Results showed that heat recovery by the ORC cycle results in decreasing the exergy loss, increasing the exergy efficiency, lowering the power consumption, and reduction in the CO2 emission. The total exergy efficiency of the PRICO process coupled with the modified ORC and ORC increases to 54.1% and 53.68%, respectively. Besides, the amount of consumed power is reduced to 225.42 kWh/ton and 227.26 kWh/ton, respectively. From the environmental aspect, it is demonstrated that the CO2 emission of the PRICO plus modified ORC process in comparison with PRICO and PRICO plus ORC is lower by 23.53% and 7.14%, respectively. Finally, comparing the results with previous papers revealed that the proposed scheme in this paper (PRICO plus modified ORC), regarding the energy and exergy efficiencies, has a better performance than technologies such as SMR, DMR, C3MR, and PRICO.

Adaptation of residential solar systems for domestic hot water (DHW) to hybrid organic Rankine Cycle (ORC) distributed generation

Among the portfolio of energy systems for local power generation, Organic Rankine cycles (ORCs) for residential applications are an opportunity for local cogeneration based on synergies with existing thermal heating and storage systems. They can be highly competitive for isolated installations and the refurbishment of existing solar heating installations based on solar domestic hot water. This article evaluates the potential for hybrid solar ORC integration in residential buildings. The analyses focus on the annual yields of a domestic 1 kW ORC cycle to assess the advantages and disadvantages of the variation of demand and the availability of solar resources. The models are developed, integrating TRNSYS and EES to allow a detailed evolution characterisation. Performance and impact of CHP adaptation are considered based on demand, storage volume-collectors area ratio, and production strategies. The analysis is completed with a thermo-economic analysis under different ranges of thermodynamic parameters. Positive IRR results of 8.61% are obtained for the installation located in Seville, Spain, operating the ORC 15% of the year. It also reduces the overheating associated with the lack of heat demand and excess solar irradiation in the solar system for the warm months by 20%.

Mapping the potential for a combined generation of electricity and industrial process heat in the northeast of Brazil - Case study: Bahia

Industrial Process Heat represents a large part of the energy demands of industries. A parabolic trough solar plant with cogeneration can meet the thermal and electric demand of these industries, mainly at medium and low temperatures.In this work, a linear parabolic solar plant for generation of electricity (1 MWe) and industrial process heat (1 MWt) were simulated at a small industry situated in the State of Bahia. The levelized costs of heat (LCOH) for an evacuated tube solar plant resulted, for extensive regions west and north (Carinhanha (IGR 10, Guanambi), Barra (IGR 4, Feira de Santana), Bom Jesus da Lapa (IGR 10, Guanambi), Santa Rita de Cássia (IGR 8, Barreiras), Paulo Afonso (IGR 3, Paulo Afonso), Remanso (IGR 6, Juazeiro) and Correntina (IGR 8, Barreiras) of the State of Bahia, in the range of 2.85–2.97 ¢/kWh-t. When compared to the medium LCOH produced by the combustion of natural gas in the United States (2.8 ¢/kWh-t) and in European Union (between 3.5 and 5.9 ¢/kWh-t), have shown to be quite competitive. Even in the case of using non-evacuated tubes collectors, the region mentioned has a LCOH in the range of 3.93 ¢/kWh-t to 4.19 ¢US$/kWh-t and still competes with costs in Europe.The levelized costs of electricity (LCOE), considering a linear parabolic solar power plant with evacuated tube collectors and ORC cycle, resulted in minimum and maximum values of 0.225 US$/kWh-e and 0.591 US$/kWh-e for the State of Bahia. In 2019, commercial enterprises of CSP technology reached LCOE values in the range of 0.10 US$/kWh-e to 0.243 US$/kWh-e and, therefore, the LCOE for the most promising regions of Bahia (west and north) have shown to be competitive in the current market. The study also showed that is indifferent to the use of Organic Rankine Cycle (ORC) or Vapour Rankine Cycle (VRC) for the generation of solar energy in the promising regions identified in the State of Bahia. The explanation is that, although the ORC is more efficient than the VRC for operational temperatures of this power plant, its cost is still very high, both for still being under development and for its small scale of production. As consequence, the recommendation of this study is the use of VRC turbines, which are already manufactured in the country and are routinely used to convert biomass to electricity.

Analysis of Organic Rankine Cycle efficiency and vapor generator heat transfer surface in function of the reduced pressure

In the paper presented is analysis of the influence of reduced pressure on efficiency and heat transfer area of vapor generator of Organic Rankine Cycle (ORC) in case of subcritical and supercritical parameters of operation. Compared are two cases of subcritical and supercritical ORC featuring a similar arrangement of heat source supply and heat removal, that is featuring the same temperatures of working fluid before the turbine, and the same condensation temperature in the respective cycles. The analysis is helpful in selection of the appropriate pressure in the vapor generator. In accomplished analyses a selection of wet ORC working fluids are scrutinized for a given range of heat source temperatures with respect to influence on efficiency of thermodynamic cycle and vapor generator area of heat transfer on installation and operation costs to illustrate the issue. Investment cost of a vapor generator in the ORC cycle accounts for a main share of expenditure alongside the cost of the expanding machine. Results of calculations show that from the point of view of cycle efficiency and size of vapor generator the pressures close to critical fluid pressure are usually optimal. Some working fluids feature even an optimal pressure. For the region close to critical point authors elaborated own method for heat transfer coefficients elaboration, which is useful in more exact estimations of heat transfer process in vapor generator. In case of a heat source with a relatively high temperature, it is better to consider a thermodynamic cycle with supercritical parameters even if as a result the vapor generator is slightly larger than for the case of a subcritical cycle. There will always be a more pronounced gain in efficiency compared to the expense induced by the heat transfer surface area of vapor generator.

Process synthesis for the valorisation of low-grade heat: Geothermal brines and industrial waste streams

The increasing demand of power and the need to reduce our dependency on fossil resources represent an opportunity to valorise low-to-medium grade heat streams such as mild hot streams from industry and natural brines into electricity. A systematic approach is required for the simultaneous selection of thermodynamic cycle which includes its configuration, the thermal fluid, and the optimal operating conditions. A methodology that integrates heuristics, for pre-screening, machine learning, to include rigorous thermodynamics, and mathematical optimization, for process flowsheet design is proposed. The pre-screening yields three fluids, benzene, toluene and 1,1,1,2,3,3,3-heptafluoropropane (R227ea) and two promising cycles, dual pressure organic Rankine cycle (ORC) and organic flash Rankine cycle (OFRC). The mathematical optimization shows that for temperatures over 120 °C, the OFRC using Benzene is the configuration of choice in terms of thermodynamic performance, but the ORC provides the most economical electricity. For hot resources below 120 °C, the efficiency of both cycles converges, but the best fluid turns out to be R227ea alongside the dual ORC cycle showing better performance and lower cost. The cooling costs present a minimum at ΔTmin equal to 8 °C. The results on process design are used to evaluate a exploitation of geothermal resources across Spain.

Comparing the profitability of waste heat electricity generation of internal combustion engines: An exergoeconomic analysis through optimization of two different organic Rankine cycle scenarios

• Two heat recovery scenarios from ICE with the aim of using in ORC cycle is studied. • The scenarios were designed based on heat recovery from exhaust and jacket water. • A comprehensive program based on energy and exergoeconomic analysis is developed. • The effects of refrigerant type and thermodynamic conditions for each scenario is studied. • The optimum scenario based on higher electricity generation or efficiency is introduced. The increasing consumption of fossil fuels has caused the emission of an enormous amount of greenhouse gases it has led to the problem of global warming and other damages to the environment. Therefore, heat recovery has become very important in recent years. In this paper, two different scenarios of the Organic Rankine cycle (ORC) are proposed to heat recovery of an internal combustion engine with two heat loss levels (stack and jacket water). The novelty of this paper is the comparison of the application of two different scenarios for the use of two available heat sources that have not been studied in previous research. Three different types of organic fluids including dry (n-butane and R245fa), wet (R134a) and isentropic (R123) were studied by energy, exergy and economic analysis. In addition, the parameters of pressure and the inlet temperature of the turbine and the superheat temperature value of the inlet flow to the turbine were optimized by the multi-objective optimization. The optimization results showed that the parameter influencing the thermodynamic and economic indicators most is the ORC pressure ratio. The optimized results of the two scenarios were compared according to thermodynamic and economic analysis and the best results were obtained for scenario 2 and fluid R123. For this case, the levelized cost of electricity (LCOE), Total Investment Cost (TIC) and electricity generation are 0.05776 $/kWh, 317,528 $ and 202.5 kW, respectively. Moreover, studying 20 countries in all the five continents, showed that developed countries were the ones with the minimum and maximum payback periods.

Techno-Economic Optimization of a Low-Temperature Organic Rankine System Driven by Multiple Heat Sources

This study presents the optimization of organic Rankine cycle (ORC) which utilizes low temperature waste heat from the aluminum production process and two low temperature renewable energy sources, solar thermal energy and geothermal energy. As geothermal energy is present at lower temperature level compared to the other two heat sources, two separate ORC cycles are considered. Optimization of the proposed system is performed based on a non-linear programming (NLP) formulation by maximizing the thermodynamic and economic performance of the system. The main variables considered in the model include temperature, pressure, flowrate, mass enthalpy, and energy flows of all the streams in the system. To optimize the variables in the system, correlations were developed, which were formulated as NLP models and optimized by minimizing the sum of least squares. The results show that most of the generated power output can be provided by the waste heat, while the lowest by the solar energy due to the relatively low average solar irradiance at considered location. When monthly time periods are considered, the highest electricity production is generated by the working fluid R1245fa in June, and amounts to 830.4 kW from waste heat, 246.5 kW from geothermal energy and 149.4 kW from solar energy. The proposed system is economically feasible for all three studied working fluids and the discount rates of 2% and higher. The final conclusions indicate that the proposed ORC system utilizing waste heat, geothermal and solar thermal energy, can generate power in a more sustainable way.

Thermodynamic analysis and optimization of the organic Rankine and high-temperature Kalina cycles for recovering the waste heat of a bi-fuel engine

Global warming is currently one of the biggest concerns worldwide; hence, addressing this issue is a trending topic among the research community. Escalating global warming through the wasted energy (30% of its input chemical energy) from internal combustion engines (ICEs) by exhaust emission is a major issue that should be considered. One way to reduce the waste of energy from ICEs is to recover the heat using a thermodynamic cycle. Using this method, not only does the engine power increase but also the fuel consumption decreases. Toward this end, and in this study, the organic Rankine cycle (ORC) and high-temperature Kalina cycle (HTKC), which have been previously used for other purposes, for the first time are utilized for waste heat recovery from the exhaust gases of a Bi-fuel engine. Also, a comprehensive comparison between the performance of the cycles and the limitation of industrialization is considered. The overall goal is to study and optimize these two cycles' overall performance in different operational modes using thermodynamic relationships and sensitivity analysis. In the developed thermodynamic model, the results obtained from the experiment on the Bi-fuel engine are used as the input data. The analysis indicates that the HTKC and ORC can recover 10–25 kW and 2–7 kW power, respectively. Under the investigated operational modes, the efficiency of the HTKC is around 25–40%, and the efficiency of the ORC is between 8 and 13%. Also, the HTKC and ORC cycle can reduce fuel consumption by 20%–30% and 8–10%, respectively. Comparing the performed analysis, it is observed that the performance of the HTKC for waste heat recovery is significantly better than the ORC.

Energy, exergy and economic analysis of combined solar ORC-VCC power plant

Abstract A renewable energy source, especially solar energy, is one of the best alternatives for power generation in rural areas. Organic Rankine cycle (ORC) can be powered by a low-grade energy source, suitable for small-scale power production in rural areas. This study investigates the combined power generation and cooling system using the combination of ORC and vapor compression cycle (VCC), where ORC is powered by a parabolic trough solar collector. Thermodynamic and economic simulation of the system is conducted for four different working fluids, which are R245fa, R114, R600 and R142b. It can be concluded that the thermal efficiency of the power plant increases by using the combined ORC-VCC system. The effect of thermodynamic parameters such as turbine inlet temperature and pressure on the system performance is also discussed, and the optimal design values are provided. The results show that the power plant uses R245fa as the minimum exergy destruction rate. The study indicates that R114 gives minimum cost function (PCEU) for 137°C turbine inlet temperature while the minimum PCEU for R142b is obtained at a turbine inlet pressure of 2500 kPa. Finally, the study indicates that the inlet pressure of the turbine has a significant impact on the system cost and thermal efficiency.

ORC and sCO2 cycle for high temperature WHR applications

This article suggests a suitable closed thermodynamic cycle for waste heat from a cement plant by using alternative working fluids. A pair of closed working cycles is compared: supercritical CO2 cycle (sCO2) and the Organic Rankine Cycle (ORC). In the case of ORC, it was necessary to choose a suitable working fluid. The goal is to minimize the ODP (Ozone Depletion Potential) and GWP (Global Warming Potential), to maximize the thermal efficiency and to optimize the minimum working temperature difference (pinch points, approach points), the temperature profiles of the heat exchangers and their working pressure and temperature, which affects the cost. Both cycles (ORC and sCO2) including a detailed component analysis are calculated using Python in Spyder IDE, which includes all the libraries for this task. According to the results of the calculations, the ORC cycle was chosen for further calculations of the components (condenser and turbine). The most suitable working fluids with high efficiency are hexamethyldisiloxane (MM), ethylbenzene and toluene, from which toluene was selected.

Multi-objective optimisation of supercritical CO<SUB align=right>2 combined cycles based on energy-exergy-economy balanced analysis

In this paper, the supercritical CO2 (sCO2) recompression cycle combined cycles are analysed, where the bottom cycles include transcritical CO2 (tCO2), organic Rankine cycle (ORC) or trilateral flash cycle (TFC). The working fluid for the ORC and the TFC can be R123, R245fa, or n-Pentane. We implemented four sub-models in our calculation: 1) thermodynamic model; 2) heat transfer model; 3) economic model; 4) exergoeconomic model. The specific exergy costing (SPECO) method is utilised in the exergoeconomic model, and the multi-objective genetic algorithm is adopted to give the Pareto front of total unit exergy cost of the product (cPtot) and the thermal efficiency. Our model has been validated with the existing literature. The results show that the thermal efficiency standalone CO2 achieved 41.66% while attaching the tCO2, ORC, or TFC bottom cycle could improve the thermal efficiency by 1.1%, 1.68%, or 0.05%, respectively. In the meantime, the (cPtot, which is the representation of the cost, decreased by 0.2$/GJ for ORC and increased by 0.06$/GJ and 1.05$/GJ for tCO2 and TFC respectively. The influence of different working fluids for ORC and TFC is not obvious. Therefore, attaching the ORC as the bottom cycle will bring about the best performance and lowest cost.

Thermodynamic analysis of refrigerants used in ORC-VCC combined power systems for low temperature heat sources

Fossil resources are largely used for energy supply. This situation causes environ?mental pollution. In recent years, studies in the field of more environmentally friend?ly and sustainable energy conversion technologies have increased. In this context, organic Rankine cycle (ORC) technology is combined with RES. In this study, combined ORC and vapor compression cycle (VCC) were investigated. The electricity produced in the combined ORC-VCC system was used both in the compressor of the VCC system and in the plant. The main factor affecting the efficiency of the combined ORC-VCC system is the refrigerant. Therefore, it is necessary to examine the selection of the most suitable refrigerant for an ORC-VCC based system. Fifteen different refrigerants were optimized with the enginering equation solver program, and energy and exergy analyzes of the systems were made separately. According to the results, the best energy efficiency and COP values among the refrigerants was found to be R40 (?ORC = 0.1206) for the ORC system and R113 (COP = 4.405) for the VCC system. For all system components in the VCC, the most exergy destruction occurs in the evaporator, followed by the compressor, condenser, and throttle, respectively. In ORC, the most exergy destruction is in the evaporator, followed by the condenser, tube and pump, respectively. The total efficiency was found to be (? = 0.53) for the combined ORC-VCC system. The total exergetic efficiency was found to be (?glob = 0.26) for the combined ORC-VCC system.

Thermodynamic Investigation of a Solar Energy Cogeneration Plant Using an Organic Rankine Cycle in Supercritical Conditions

In the present work, a novel Organic Rankine Cycle (ORC) configuration is used for a low-grade heat source cogeneration plant. An investigation is conducted accordingly into the simultaneous production of electricity and cold. The proposed configuration relies on concentrated solar power (as heat source) and ambient air (for cooling). Furthermore, two gas ejectors are added to the system in order to optimize the thermodynamic efficiency of the organic Rankine cycle. The results show that the thermodynamic and geometric parameters related to these ejectors have an important effect on the overall system performances. In order to account for the related environmental impact, the following working fluids are considered: HCFC-124, HFC-236fa, HFO-1234yf and HFO-1234ze. As shown by the numerical simulations, the fluid R1234yf presents the minimal heat consumption and therefore provides an optimal thermal efficiency for the ORC cycle (which is around 29%). However, the refrigerant R236fa displays the highest refrigeration performances with a performance coefficient reaching a value as high as 0.38.

Maximizing the power output and net present value of organic Rankine cycle: Application to aluminium industry

This study presents an integrated design and optimization of an Organic Rankine Cycle (ORC) for the recovery of waste heat from aluminium production. Non-Linear Programming (NLP) models were developed, with the objectives of maximizing electricity production and the Net Present Value (NPV) of the system. The models account for optimizing the operating conditions and changes in thermodynamic features of the system. The developed models are applied to a case study of Slovenian aluminium company where the performance of three different working fluids (R245fa, R1234yf and R1234ze) are compared. The optimization is performed considering different temperatures and prices of produced hot water and electricity, minimum approach temperature (ΔTmin), concentration of CO2 in flue gas and temperature and flowrate of flue gas. Results show that the selected working fluids for the proposed waste heat-based ORC system have the potential to substitute up to about 830 kW of electricity in a sustainable and economic manner. Out of the three working fluids considered, R245fa showed up to 7.9% efficiency of the ORC cycle and was identified as the best performing working fluid considering both economic viability and the amount of electricity produced by the system, however the refrigerant inherently has higher GHG footprint.

Direct integration of an organic Rankine cycle into an internal combustion engine cooling system for comprehensive and simplified waste heat recovery

Cogeneration systems based on internal combustion engines (ICE) provide decent efficiency and flexibility. In order to further improve the efficiency, organic Rankine cycle (ORC) can be used to convert high temperature (waste) heat from flue gas to electricity. There is a large amount of heat in jacket cooling at lower temperatures for which there is often no demand so it has to be rejected into the ambient. Previous systems trying to utilise this heat in the ORC cycle end up as too complex and expensive. This study introduces an innovative jacket cooling method. In the cooling system of an ICE, instead of typical water or oil-based heat transfer fluids, the working fluid of an ORC is used as the engine coolant, recovering the low-potential heat. Preheated organic fluid is then directly used in the bottoming ORC with further heat input from the flue gas. This concept allows utilising both low and high potential heat from the cooling of the ICE and from the flue gas recovery, while omitting the intermediate heat-transfer circuits commonly found in ORC waste heat recovery applications. Presented thermodynamic analysis shows a strong dependency of the ORC utilisation efficiency on cooling fluid allowed pressure in the ICE jacket and on the heat flow ratio between the coolant and the flue gas of the ICE. A baseline study with a specific 83 kWe ICE with the novel configuration provides an improvement of nearly 10 kW in comparison with 7 kW of an ORC utilising only flue gas. More general parametric analysis has shown the potential of the ORC power output improvement by more than 60% for specific ICE types and higher pressures and temperatures in the engine cooling circuit. In a cogeneration regime, these benefits in electrical power output come at the cost of a very slight decrease in overall efficiency.

Performance Assessment and Working Fluid Selection for Novel Integrated Vapor Compression Cycle and Organic Rankine Cycle for Ultra Low Grade Waste Heat Recovery

This paper presents the performance assessment and working fluid selection for a novel integrated vapor compression cycle-organic Rankine cycle system (i-VCC-ORC), which recovers ultra-low-temperature waste heat rejected (50 °C) by the condenser of a vapor compression cycle (VCC). The analyses are carried out for a vapor compression cycle of a refrigeration capacity (heat input) of 35kW along with the component sizing of the organic Rankine cycle (ORC). The effects of the operational parameters on integrated system performance were investigated. The integrated system performance is estimated in terms of net COP, cycle thermal efficiency and exergy efficiency by completely utilizing and recovering the heat rejected by the condenser of the VCC system. R600a-R141b with COPnet (3.54) and ORC thermal efficiency (3.05%) is found to be the most suitable VCC-ORC working fluid pair. The integration of the vapor compression refrigeration cycle with the organic Rankine cycle increases the COP of the system by 12.5% as compared to the standalone COP of the vapor compression system. Moreover, the sensitivity analysis results show that there exists an optimum operating condition that maximizes the thermal performance of the integrated system.

Artificial neural network grey-box model for design and optimization of 50 MWe-scale combined supercritical CO2 Brayton cycle-ORC coal-fired power plant

Supercritical CO2 (sCO2) Brayton cycle is a promising technology for coal-fired power generation with high efficiency and compact equipment size. However, its sophisticated construct and high-temperature waste heat rejection require a systematic design to maximize its performance. Herein, we develop a combined sCO2 Brayton cycle-organic Rankine cycle (ORC) design for coal-fired power plant. A novel glass-box model that considers the specific designs of sCO2 boiler, recuperators, coolers, and turbomachinery is formulated to optimize the power plant. A high-accuracy artificial neural network model is also developed to estimate the system’s pressure drop to reduce model complexity. As a result, the glass-box model is reformulated into a grey-box model. The model is applied to three different combined cycles’ design problem to evaluate their performance. Result shows that the grey-box model saves more than 50% of CPU time. With the turbine inlet at 620 °C/25 MPa and the main compressor inlet at 35 °C/7.38 MPa, the proposed combined cycle reaches a thermal efficiency of 45.73%, thereby achieving a 2.75 percentage point improvement compared with the standalone design. Sensitivity analysis is also carried out to evaluate the effects of ORC working fluid, flue gas temperature at the cooling wall outlet, main compressor inlet pressure, and evaporating temperature of ORC, on the system’s performance.

Thermodynamic Investigation of a Trigeneration ORC Based System Driven by Condensing Boiler Hot Water Heat Source Using Different Working Fluids

This study conducts thermodynamic analysis on three trigeneration cycles including Organic Rankine Cycle (ORC), Liquefied Natural Gas (LNG) cold energy, and absorption refrigeration cycle in order to select appropriate working fluids. Different types of ORC cycles including simple ORC, regenerative, and ORC with Internal Heat Exchange (IHE) were investigated. For those types, the operation of six working fluids with different thermodynamic behaviors (R141b, R124, R236fa, R245fa, R600, and R123) was evaluated. In power plants, a low-grade heat source was provided by condensing boiler hot water energy while the thermal sink was prepared by cold energy of LNG. The effect of boiler temperature variation on energy and exergy efficiencies was investigated. According to the derived results, regenerative ORC-based systems possessed maximum energy and exergy efficiencies, while simple ORC and ORC with internal heat exchanger exhibited approximately the same quantities. Also, among these analyzed working fluids, R141b had the maximum energetic and exergetic efficiencies, while R124 and R236fa had minimum performance.

Energy recovery from wastewater in deep-sea mining: Feasibility study on an energy supply solution with cold wastewater

Deep-sea mining has been regarded as one of the most promising technologies to meet the increasing demands for minerals and metals. The exploration of renewable energy supply solutions should be prioritized because the current solutions are highly dependent on fossil fuels. In this study, recognizing that the wastewater transported with minerals to the production support vessel is a potential cold source, the wastewater energy recovery is proposed for the first time. Focusing on exploring an efficient and cost-effective solution for wastewater energy recovery, the organic Rankine cycle (ORC) using six working fluids and Kalina cycle are investigated, and a multi-objective optimization for the levelized cost of electricity (LCOE) and exergy efficiency is presented. Based on the design criteria and measured data of the Solwara 1 Project of Nautilus Minerals, optimization results show that R601 with the highest critical temperature used in ORC performs best in terms of LCOE (0.102$/kWh) and exergy efficiency (40.2%), compared with 0.125$/kWh and 42.5% of ammonia-water mixer (0.966/0.034) used in Kalina cycle. In addition, the discounted payback periods of ORC and Kalina cycle are 12.71 years and 18.95 years respectively, indicating that ORC is economically more feasible than Kalina cycle. Moreover, the feasibility of the proposed system is validated by its economic benefits, good performance compared with ocean thermal energy conversion systems, and high flexibility and compatibility. The wastewater energy recovery is expected to provide a sustainable and low-carbon energy supply idea for deep-sea mining.