Reduction Of Exergy Losses Research Articles

Thermodynamic analysis of a solar-driven supercritical water gasification-oxidation system for ammonia production and heat supply from chicken manure

Faced with the dual challenges of energy shortage and environmental pollution, researchers are turning to extracting clean energy from waste resources. The coupled system of solar energy and supercritical water gasification offers a novel solution to these issues. In this study, a solar-driven supercritical water gasification-oxidation system for ammonia production and heat supply from chicken manure was simulated. Additionally, the effects of temperature of supercritical water gasification, chicken manure slurry concentration, water-dry matter ratio, and pressure of supercritical water gasification and oxidation on the system's products, efficiency, and device exergy losses were examined. Under typical working conditions (the temperature of supercritical water gasification: 750 °C, chicken manure slurry concentration: 50 wt%, water-dry matter ratio: 5, the pressure of supercritical water gasification and oxidation: 25 MPa), and the system had a treatment capacity of 5 t/h of dry chicken manure. The system yielded 2604.04 kg/h of NH3 and 23763.9 kg/h of heating steam. It demonstrated an energy efficiency of 68.38% and an exergy efficiency of 46.85%. The total exergy losses of the system amounted to 34704.73kw, with the solar collector accounting for the largest share at 49.6%. The temperature of supercritical water gasification and water-dry matter ratio significantly impacted the system efficiency. Conversely, chicken manure slurry concentration and the pressure of supercritical water gasification and oxidation exerted minimal influence. The solar collector and gasification reactor emerged as the primary contributors to exergy losses in the entire system. Notably, the lower temperatures of supercritical water gasification, chicken manure slurry concentrations, pressures of supercritical water gasification and oxidation, and water-dry matter ratios can reduce exergy losses in both the solar collector and the gasification reactor.

Exergy efficiency and sustainability indicators of forced convection mixed mode solar dryer system for drying process

The study investigates the effectiveness of a mixed-mode solar dryer (MSD) featuring two double-pass solar air collectors in series, with a focus on dehydrating cluster figs characterized by high moisture content and rapid deterioration. Exergy analysis is a powerful tool to assess the efficiency and sustainability of drying systems. The study involves experimental data obtained from the drying process under different air mass flow rates (0.018–0.062 kg/s). The solar radiation intensity ranged from 120 W/m2 to 750 W/m2 during these experiments. The solar air collectors and mixed mode dryer exergy efficiency is found to be dependent on solar radiation intensity, showing increased efficiency with higher air mass flow rates due to enhanced heat removal and reduced losses to the surroundings. The findings reveal that the optimal air mass flow rate of 0.062 kg/s yields the highest exergy efficiency in the solar air collectors. The overall exergy efficiency of the mixed-mode solar drying chamber increases with higher air mass flow rates, ranging from 18.8 % to 41.4 %. Improvement potential (IP) analysis indicates that, as the air mass flow rate increases, the potential for reducing exergy losses decreases. The sustainability index (SI), measures the environmental impact, and it ranges from 1.26 to 1.71, with higher values associated with higher exergy efficiency.

Enhancing heat exchanger performance with perforated/non‐perforated flow modulators generating continuous/discontinuous swirl flow: A comprehensive review

AbstractHeat exchangers are crucial in transferring heat and finding applications across various industries. Numerous strategies have been devised to improve and optimize the heat transfer process within these systems. Among these, passive methods have garnered significant attention for their ability to operate without external power consumption. This article examines the recent experimental and computational studies conducted by researchers since 2018 on passive enhancement techniques, especially twisted tape, wire coil, swirl flow generator, and others, to boost the thermal efficiency of heat exchangers and aid designers in adopting passive augmentation methods for compact heat exchangers. Recently, researchers' new class of flow maldistribution devices, referred to as swirl flow devices, has gained attention; which enhances convective heat transfer by introducing swirl into the main flow and disrupting the boundary layer at the tube surface through alterations in surface geometry. Twisted tape inserts are devices that demonstrate better performance in laminar flow compared to turbulent flow. Conversely, other passive techniques like ribs, conical nozzles, and conical rings are generally more effective in turbulent flow than laminar flow. A recent research trend is the utilization of nanofluids in combination with other passive heat transfer enhancement techniques like turbulators, ribs, and twisted tape inserts in heat exchangers, which can reduce exergy losses and improve overall convective heat transfer coefficient and effectiveness of heat exchanger.

Functional ventilation building envelope integrated photovoltaic modules and phrase change material in subtropical climate: An in-depth numerical investigation

Most of existing solar ventilation envelope systems adopt a single structure including a glass cover a massive wall, which possesses the drawbacks of low thermal efficiency and poor stability. In recent decades, auxiliary power generation devices, led by photovoltaic (PV), have made epochal achievements in integrated building applications, while the superior thermal regulation capability of thermal storage materials, represented by phrase change materials (PCM), has further helped to improve the thermal environment of buildings, and the above two technologies have demonstrated great energy conservation potential. In order to explore the application and synergistic effect of the above two energy-conservation technologies in passive ventilation envelopes, a novel functional ventilation building envelope (FVBE) integrated with PV panel and PCM is proposed in this paper. A comprehensive exploration of the influence of various key parameters on the thermal performance of the FVBE-PV/PCM system. The electrical and thermal performance of the system is explored based on different seasonal climates. Specifically, effects of thickness as well as the melting temperature of PCM and the air channel width has been provided in this study. Taking the inner wall surface temperature (Tinner_wall), equivalent indoor load (Qload) and electrical efficiency (ηe) as evaluation indexes, the thermal efficiency, electrical performance and the coupling mechanism was assessed. Specifically, the coupling mechanism between the thermal performance and electrical performance of the FVBE-PV/PCM system was analyzed from the perspective of combined heat and power, revealing the functional characteristics of the system. Meanwhile, the article conducted a comparative study on the thermal and electrical performance of a typical building integrated PV (BIPV), FVBE-PV system FVBE-PV/PCM system. In particular, energy and exergy analysis is carried out to characterize the energy utilization of the FVBE-PV/PCM system in different structural systems. The research found that increasing the thickness of both the PCM and air channel leads to lower indoor temperature and heat flux, with different optimal phase transition temperatures for summer and winter. Although the FVBE-PV system exhibited a maximum 3.12 % reduction in power generation efficiency compared to the BIPV system due to increased PV temperature caused by air layer insulation, incorporating PCM can reduce exergy losses by an average of 31.731 % to mitigate this drawback and improve energy efficiency. Additionally, the analysis revealed varying coupling correlations between thermal performance and power generation based on two key parameters. This study could contribute to the functional improvement of the building envelope and simultaneous indoor thermal regulation.

Thermoradiative coupling graphene-based thermionic solar conversion

Thermionic conversion, due to its simple solid-state structure capable of converting heat to electricity directly, is promising for concentrated solar power. However, because of the extremely high cathode temperature, a large portion of the heat is lost to the environment. The paper introduces a novel concept of selective thermoradiative-graphene thermionic conversion (STR-GTI) that involving a combined control of photon and electron emission to modify the radiation dissipation. A detailed thermodynamic model is developed to evaluate the energy transfer irreversibility of STR-GTI solar conversion. The results demonstrate that the selective themoradiative photon emission and graphene thermionic electron emission effects synergistically reduce internal irreversible losses in the STR-GTI system, leading to a maximum energy efficiency of 34.34 % at a concentration ratio of 425, cathode work function of 1.8 eV and thermoradiative bandgap of 0.2 eV. The STR-GTI system outperforms both individual GTI and STR converters in terms of exergy efficiency and entropy production minimization. It exhibits a remarkable 102.03 % increase in exergy efficiency compared to the STR & GTI system at a thermoradiative voltage of −0.14 eV, accompanied by a 28.56 % reduction in exergy loss and a 37.83 % decrease in entropy production. The combination of narrowing the spectral radiation bandwidth and significant electron emission capabilities of graphene contribute to the system’s resilience against solar radiation fluctuations.

Experimental study and process evaluation of coproduction graphene, acetylene and hydrogen from methane pyrolysis by thermal plasma

This paper developed a process for the coproduction of graphene, acetylene and hydrogen from methane pyrolysis by thermal plasma. Bench-scale tests under three specific energy input (SEI) were carried out to investigate the morphology of carbon nanomaterials and the product selectivity. The process was evaluated by exergy and exergoeconomic analyses. Results indicated that a higher SEI improved the selectivity of graphene nanoflakes (GNFs) and reduced their defects. The product selectivity of GNFs played a critical role in the decrease of total fuel exergy per unit of GNFs as the SEI increased. The plasma reactor exhibited the highest exergy loss ratio in the entire process due to heat dissipation. The quenching device exhibited the second-highest exergy loss ratio in the process, stemming from irreversible entropy increase causing exergy loss. Improving the design of the plasma reactor to enhance thermal efficiency and implementing a feasible waste heat recovery system were identified as effective strategies to enhance exergy efficiency. Excluding consideration of co-products, GNFs with high SEI had the lowest cost of 199.41 CNY/kg, when co-products were considered, the lowest cost decreases by 30%, and the low SEI had the lowest GNFs cost at 140.71 CNY/kg. This indicated that there was enough investment potential to tailor the properties of GNFs produced by such processes for application scenarios. The unit exergy cost of GNFs decreased from 0.89 CNY/MJ to 0.80 CNY/MJ as the SEI of the plasma reactor increased. Subsequently, it rose to 1.16 CNY/MJ. Prioritizing the increase in investment costs for the plasma reactor to reduce exergy loss costs should be considered first, and optimizing the waste heat recovery process was also a key direction to minimize exergy loss costs.

An efficient methanol pre-reforming gas turbine combined cycle with integration of mid-temperature energy upgradation and CO2 recovery: Thermodynamic and economic analysis

An innovative design has been developed to optimize the performance of the gas turbine combined cycle (GTCC) by integration with a decarbonized methanol steam reforming (MSR-deCO2) system based on the principle of the cascade utilization of chemical and thermal exergy. In the integrated system, the primary fuel is reformed with the steam extracted from GTCC and decarbonized before combustion. The reforming process leads to a significant reduction of exergy loss in the combustor. Introducing methanol as a viable turbine fuel presents an opportunity for recuperating mid-temperature heat as chemical energy through endothermic MSR and redeeming it as high-grade thermal energy in the combustor. By such incorporation, the power generation of the mid-temperature heat in the bottoming cycle is significantly enhanced, and most of the CO2 is removed as the liquid phase. Based on a 530 MW GTCC plant, thermodynamic analysis reveals a 4.6% energy efficiency increase, a 4.3% exergy efficiency boost, and an 82.2% CO2 recovery with a 0.354 MJ/kgCO2 energy penalty. The proposed design yields 454.4 M$ more profit than the reference power plant throughout its lifespan. Additionally, sensitivity analysis indicates optimal conditions for MSR at approximately 250 °C, a 1:1 water-to-methanol ratio, and a higher reaction pressure preference.

Enhancing performance of multi-pressure evaporation organic Rankine Cycle/Supercritical Carbon Dioxide Brayton cycle through genetic algorithm and Machine learning optimization

The Supercritical Carbon Dioxide Brayton combined cycle is one of the most important ways to enhance the performance of the cycle. Since the considerable exergy loss resulting from large temperature differences in the heat exchangers of combined cycles, the multi-pressure evaporation concept was adopted from Organic Rankine cycle research. Two novel multi-pressure evaporation configurations, namely parallel evaporation Brayton combined cycle and series evaporation Brayton combined cycle, are designed with the purpose of enhancing SCO2 Brayton cycle performance. The performance of the two new cycles was compared with that of the baseline cycle. Moreover, Printed Circuit Heat Exchangers were employed to improve the overall compactness of the cycles. The results from model calculations were utilized to train an Artificial intelligence neural network model using machine learning techniques which allowed to simplify the cycle and improves the computational speed. Subsequently, genetic algorithm was employed to conduct multi-objective optimization on the three cycles. Finally, a detailed exploration was conducted from the perspective of thermal and exergy to elucidate the reasons for the advantages and differences between the two new cycles compared to the baseline cycle. The results indicate that the series Brayton combined cycle exhibits the highest performance, and the combined cycle of multi-pressure evaporation helps to improve the performance of the combined cycle. Compared to the baseline cycle, the combined cycle efficiency of both series and parallel combined cycles has increased from 45.54% to 46.18% and 46.29%, respectively, while the bottom cycle efficiency has improved from 3.81% to 4.93% and 5.03%. The ratio of heat exchange area to net output power increased from 0.6051 to 0.6614 and 0.6740 for the parallel and series cycles, respectively. Thermal analysis shows that, the fundamental purpose of changing the layout is to improve the specific power per unit of working medium in the cycle. Exergy analysis shows that, the two new combined cycles improve cycle efficiency by reducing exergy losses in the intermediate heat exchanger. Compared to the parallel version, the series version's staged compression allows for a lower temperature difference in intermediate heat exchanger 1, resulting in smaller exergy losses and higher cycle efficiency. This work will contribute to an enhanced understanding of Supercritical Carbon Dioxide combined cycles within the academic community and the introduction of multi-pressure evaporation will further improve the performance of these important cycles.

Exergy and environmental analysis of SOFC-based system including reformers and heat recovery approaches to establish hydrogen-rich streams with least exergy loss

Building total CO2 emissions must decline by more than 95 % from 2020 to 2050. Statistical studies affirm that 84 % of the fuel cell applications in the world are attributed to the residential market and are limited to the range of 0.5–5 kW. In this study, defining a building-based fuel cell, the first and second law of thermodynamics were approved for the hybrid system consisting of SOFC enhanced with an internal reformer and microturbine. In addition, an external reformer along with two heat recovery systems are integrated to change methane to hydrogen. Based on the exergy balance equation, 37 The installation of heat recoveries was very effective in hybrid system irreversibility reduction so they were able to reduce exergy losses by 38 %. The most irreversibility was related to chemical reactions that occurred in the external reformer (share of 37.3 %) and combustion chamber (share of 32 %) while the share of the fuel cell was only 10.7 %. The calculations of the second law showed that the hybrid system with heat recovery can convert 57.6 % of the input exergy into useful work. The environmental analysis revealed that establishing a hybrid system with a higher temperature is more effective than that with higher pressure. The CO2 emissions of the hybrid system at the lowest and highest temperature were 1.946 kg/kW and 0.81 kg/kW.

The exergy analysis of low carbon or carbon free fuels: Methane, methanol, and hydrogen under engine like conditions

The carbon dioxide (CO2) emitted from the combustion of fossil fuels is considered the main contributor to the warming of the climate system. Low carbon or carbon free fuels like methane, methanol, and hydrogen have gained a lot of attention on their ability of CO2 reduction in Internal Combustion (IC) engines. In this context, improving thermal efficiency at reduced levels of emissions by adopting low carbon fuels is meaningful in the current situation. However, the exergy loss of unconstrained combustion degrades the exergy work transform in IC engines. The present study focuses on the exergy loss and the thermomechanical exergy of these low carbon or carbon free dual fuels blended with high reactive n-heptane as the diesel surrogate under engine like conditions. Results reveal that these fuels lower the exergy loss by reducing the rate of n-heptane dehydrogenation and isomerization reaction. In addition, hydrogen in blends shows more influence on exergy loss reduction than methanol and methane. Using low carbon or carbon free fuels in blends improves the thermomechanical exergy distribution at 1000–2000 K combustion range. This is due to the fact that the reactions concerning radicals are more active than a traditional isooctane/n-heptane mixture, especially under low initial temperature and rich mixture conditions. Methanol in blend promotes the thermomechanical exergy at 1500–2000 K temperature range due to its highly intense H2O2-OH, CH2O-CO oxidation reaction, especially for the rich mixture. Furthermore, with regard to these low carbon fuels, one unit increment of thermomechanical exergy leads to approximately 0.65–1.2% improvement of second law efficiency. In conclusion, the optimization of low carbon fuels on exergy is mainly reflected in the low temperature and rich mixture combustion conditions, thus, the use of low carbon fuels does improve exergy use in combustion processes where the mixture is not uniformly distributed.

Exergy and Energy Analysis of the Shell-and-Tube Heat Exchanger for a Poultry Litter Co-Combustion Process

Increasing production of poultry litter, and its associated problems, stimulates the need for generating useful energy in an environmentally friendly and efficient energy system, such as the use of shell-and-tube heat exchangers (STHE) in a fluidized-bed combustion (FBC) system. A holistic approach which involves the integration of the First Law of Thermodynamics (FLT) and Second Law of Thermodynamics (SLT) is required for conducting effective assessment of an energy system. In this study, the STHE designed by the CAESECT research group, which was integrated into the lab-scale FBC, was investigated to determine the maximum available work performed by the system and account for the exergy loss due to irreversibility. The effects of varying operating parameters and configuration of the space heaters connected to the STHE for space heating purposes were investigated in order to improve the thermal efficiency of the poultry litter-to-energy conversion process. Exergy and energy analysis performed on the STHE using flue gas and water media showed higher efficiency (75–92%) obtained via energy analysis, but much lower efficiency (12–25%) was obtained when the ambient conditions were factored into the exergy analysis, thus indicating huge exergy loss to the surroundings. From the obtained experimental data coupled with the simulation on parallel arrangement of air heaters, it was observed that exergy loss increased with increasing flue gas flow rate from 46.8–57.6 kg/h and with increasing ambient temperature from 8.8 °C to 25 °C. To lower the cost of STHE during final design, a larger temperature difference between the hot and cold flue gas is needed throughout the exchanger, which further increases the exergetic loss while maintaining an energy balance. In addition, this study also found the optimal conditions to reduce exergy loss and improve energy efficiency of the designed STHE. This study shows the possibility to evaluate energy systems using integration of exergy and energy analysis.

Experimental study for improving photovoltaic thermal system performance using hybrid titanium oxide-copper oxide nanofluid

Overheating of photovoltaic (PV) cell is one of the most common issues that cause the degradation of their function and reduce conversion efficiency. This work investigates the effect of using a novel TiO2-CuO hybrid nanofluid to improve the energy and exergy of photovoltaic thermal (PVT) systems by reducing PV cell temperature. Serpentine tubes soldered on an absorbing plate attached behind the PV module were proposed to improve heat removal of the PV module with volume concentrations of 0.2 vol% and 0.3 vol%, with a flow rate of 1.16 L/min. Improving the thermophysical properties of the hybrid nanofluid has reduced the temperature of the PV module by 39% more than the uncooled PV module. The PVT system's electrical power and overall efficiency improved by 77.5% and 58.2%, respectively, at increased volume concentration to 0.3 vol% compared with the uncooled PV module. The exergy analysis indicated an increase in the overall exergy efficiency by 14.97 %, with thermal exergy dropping because of the closer the outlet nanofluid temperature to ambient temperature. Hybrid nanofluid cooling has improved exergy efficiency to 14.97%, reducing exergy losses by 37.9% and entropy generation by 69.6% at 0.3 vol%. The economic analysis shows a better payback period of 21 months when cooling with a hybrid nanofluid compared with the uncooled PV module.

Exergy Efficiency and COP Improvement of a CO2 Transcritical Heat Pump System by Replacing an Expansion Valve with a Tesla Turbine

The heat pump system has been widely used in residential and commercial applications due to its attractive advantages of high energy efficiency, reliability, and environmental impact. The massive exergy loss during the isenthalpic process in the expansion valve is a major drawback of the heat pump system. Therefore, the Tesla turbine exergy analysis in terms of transiting exergy efficiency is investigated and integrated with the transcritical heat pump system. The aim is to investigate the factors that reduce exergy losses and increase the coefficient of performance and exergy efficiency. The contribution of this paper is twofold. First, a three-dimensional numerical analysis of the supercritical CO2 flow simulation in the Tesla turbine in three different geometries is carried out. Second, the effect of the Tesla turbine on the coefficient of performance and exergy efficiency of the heat pump system is investigated. The effect of the rotor speed and disk spacing on the Tesla turbine power, exergy loss, and transiting exergy efficiency is investigated. The results showed that at a lower disk spacing, the turbine produces higher specific power and transiting exergy efficiency. In addition, the coefficient of performance (COP) and exergy efficiency improvement in the heat pump system combined with the Tesla turbine are 9.8% and 28.9% higher than in the conventional transcritical heat pump system, respectively.

A comparative evaluation of alternative optimization strategies for a novel heliostat-driven hydrogen production/injection system coupled with a vanadium chlorine cycle

This paper introduces an innovative and cost-effective multi-generation plant, driven by the central receiver-based concentrated solar systems, to facilitate the desired global green-transition process. The vanadium chlorine thermochemical cycle, which uses hydrogen instead of natural gas in the combustion chamber, is used as an innovative approach for reducing greenhouse gas emissions. The proposed system also includes a thermoelectric generator (TEG) for excess power generation and a multi-effect desalination (MED) unit to reduce exergy loss. The suggested system's technological, economic, and environmental metrics are analyzed and compared to a similar system that stores the created hydrogen rather than burning it in the combustion chamber. Furthermore, the viability of the studied model is investigated under the optimal operating condition, using the example of Sevilla in order to make the conclusions more reliable. According to the findings, the suggested novel configuration is a better alternative in terms of cost and environmental impact owing to decreased product energy costs and CO2 emissions. The outcomes further indicate that the substitution of the condenser with TEG leads to considerably higher power production. According to the optimization findings, the multi-objective grey wolf algorithm is the best optimization strategy compared to the non-dominated genetic and particle swarm approaches. At the best optimization point, 2.5% higher exergy efficiency, 1 $/GJ cheaper product energy cost, and 0.12 kg/kWh lower levelized CO2 emission are achieved compared to the operating condition. The Sankey diagram indicates that the solar heliostat system has the highest irreversibility. The exergy analysis results further reveal that the flue gas condensation process through the Rankine cycle and MED unit lead to a 53.2% reduction in exergy loss. Finally, considerable CO2 emission reductions show that the suggested new method is an effective solution for cleaner energy production in warmer climate countries.

Exergy analysis of vacuum ice production device by solid adsorption

This paper proposes a vacuum ice production device by solid adsorption. An analysis model related to exergy loss and exergy efficiency is established in each component of the vacuum flash ice making system. By comparing the exergy analysis results of adsorption vacuum ice production device and condensing vacuum ice production, this paper has drown an effective method to reduce exergy loss. It has been found that the exergy efficiency of the adsorption vacuum ice production device is 9.64% higher than that of the condensing vacuum ice production device. The exergy efficiency of water vapor adsorption in the adsorption chamber is the highest, while the exergy efficiency of water vapor adsorption in the condensation chamber is the lowest. In order to reduce the energy demand of the device, the heat released by the condenser should be fully utilized to reduce the exergy loss of the condenser. At the same time, the heat and mass transfer of the flash evaporation process should be enhanced when designing the flash chamber, such as optimizing the ice making working fluid to improve the exergy efficiency of the flash chamber.

Exergy Analysis of Coal-Based Series Polygeneration Systems for Methanol and Electricity Co-Production.

This paper quantifies the exergy losses of coal-based series polygeneration systems and evaluates the potential efficiency improvements that can be realized by applying advanced technologies for gasification, methanol synthesis, and combined cycle power generation. Exergy analysis identified exergy losses and their associated causes from chemical and physical processes. A new indicator was defined to evaluate the potential gain from minimizing exergy losses caused by physical processes—the degree of perfection of the system’s thermodynamic performance. The influences of a variety of advanced technical solutions on exergy improvement were analyzed and compared. It was found that the overall exergy loss of a series polygeneration system can be reduced significantly, from 57.4% to 48.9%, by applying all the advanced technologies selected. For gasification, four advanced technologies were evaluated, and the largest reduction in exergy loss (about 2.5 percentage points) was contributed by hot gas cleaning, followed by ion transport membrane technology (1.5 percentage points), slurry pre-heating (0.91 percentage points), and syngas heat recovery (0.6 percentage points). For methanol synthesis, partial shift technology reduced the overall exergy loss by about 1.4 percentage points. For power generation, using a G-class gas turbine decreased the overall exergy loss by about 1.6 percentage points.

Using synthesis gas heat to produce work via an externally fired gas power cycle

Synthesis gas production requires significant amounts of energy. Efficiency improvements and introduction of renewable or non-carbon energy sources are needed to reduce carbon dioxide emissions. Downgrading of high level heat in synthesis gas cooling trains contributes significantly to exergy losses. Recently, turbine expansion of synthesis gas was investigated by various authors, as one method to reduce exergy losses. However, using synthesis gas as a working fluid poses risks to rotating machinery. Thus an externally fired gas power cycle is proposed, which also allows flexibility to incorporate various types of renewable energy sources. In this study helium is the working fluid and nuclear energy the heat source. A helium-steam combined cycle arrangement is simulated and analysed using energy, exergy and cost analysis. Hot synthesis gas is used to provide additional heat to the helium-steam combined cycle via indirect heat exchange, thereby allowing a close match between the temperatures. Further cooling of the synthesis gas via steam generation is also employed. The work output of the integrated system versus a standalone case was increased by at least 19%. The specific exergy destruction in kW/MW work output was reduced by 38% and the specific equipment cost in $/MW work output increased by 22%.

Opportunities for renewable electricity utilization in coal to liquid fuels process: Thermodynamic and techo-economic analysis

Renewable electricity has been developed very fast to reduce both the reliance on fossil energy and CO2 emission, and its utilization for the sustainable production of chemical products is of increasingly interest. In this work, opportunities for renewable electricity utilization in coal to liquid fuels process are studied through thermodynamic and techo-economic analysis. Three CPtL (coal and renewable power to liquid fuels) processes are investigated, namely Case GSP + E, Case Shell + E and Case Texaco + E. Exergy losses of the subsystems are quantitatively analyzed, and measures to reduce exergy losses are proposed. By integration with renewable electricity, carbon efficiency could be improved by 69.09–99.44%, and life cycle CO2 emission could be reduced by 37.81–44.85%; however, the production cost is raised by 54.18–94.07% due to the high cost of electricity and electrolyzer. Sensitivity analysis shows that electricity price has the most significant impact on the production cost. At present market conditions, CPtL is incompetent with coal to liquid fuels (CtL) process yet from the viewpoint of economics, but it might become viable in the future by decreasing electricity price (0.07–0.01 $/kWh), electrolyzer cost (1150–640 $/kW) and electricity consumption of electrolysis (4.70–4.05 kWh/Nm3 H2).

Thermodynamic analysis of a tri-generation system driven by biomass direct chemical looping combustion process

Chemical looping process (CLP) is a promising technology for in-situ CO2 capture without energy penalty. Direct CLP has more compact structure, favorable economic competitiveness, and larger reduction of exergy loss compared to syngas CLP. In this work, a novel biomass direct chemical looping combustion (CLC) driven tri-generation system for the production of cooling, heating, and power is proposed. The proposed system contains a direct CLC section as the prime mover, two gas turbines and an organic Rankine cycle for power generation, an absorption chiller for cooling production, and two heat exchangers to generate heat. First, a thorough thermodynamic analysis is implemented to assess the energy and exergy efficiencies of the proposed system under evaluated design conditions, as well as identify the exergy loss distribution. Second, Sensitivity analysis is conducted to investigate the effects of major operating parameters on the system performances. Third, the performances of the proposed system are compared to syngas CLC based tri-generation system. Thermodynamic analysis results show that the proposed system has high energy efficiency of 90.92% and exergy efficiency of 33.82%. The largest exergy loss takes place in the air reactor, accounting for 34.42% of total exergy loss, followed by fuel reactor and absorption chiller, which are 30.09% and 15.37%, respectively. Besides, the proposed system has better thermodynamic performances than syngas CLC driven tri-generation, whose energy and exergy efficiencies are 69% and 23.4%, respectively.

A novel working fluid selection and waste heat recovery by an exergoeconomic approach for a geothermally sourced ORC system

A novel working fluid selection methodology is proposed for organic Rankine cycles (ORCs) coupled with low-grade geothermal sources by employing an existing dataset of an operating binary geothermal plant that works with n-pentane. Thermodynamic and thermoeconomic aspects of power production are combined to evaluate 29 different single-component working fluid candidates from different chemical branches in four-step elimination methodology. In terms of working fluid classification from physical point of view, results indicate that there is a direct relationship between vapor expansion ratio (VER) and net work output for dry working fluids. On the other hand, it is shown that isentropic fluids behave differently from dry fluids. Based on the proposed methodology, R113 is selected as a new working fluid for the existing plant instead of n-pentane. Results indicate that by applying the proposed methodology, it is possible to increase first and second law efficiencies of plant 0.59% and 3.18%, respectively, while reducing the levelized electrical cost (LEC) around 11% in comparison to base plant outputs with n-pentane. Furthermore, a case study is presented in addition the plant level analysis by implementing a hypothetical waste heat recovery cycle, configurated with proposed methodology, in order to reduce exergy losses originating from brine re-injection. It is shown that it may be possible to further reduce the LEC around 1% and increase the overall efficiencies 0.1% for the first law and 0.26% for the second law. However, it is necessary to be deliberate about these final results since they also demonstrate the sensitivity of LEC to the increases in second law efficiency rather than levelized capital investments.