Exergy Loss Research Articles

Thermodynamic and environmental analysis of integrated supercritical water gasification of sewage sludge for power and hydrogen production

Supercritical water gasification is a promising process for treating sewage sludge (SS) to obtain hydrogen and electrical energy. Here, a novel thermodynamic equilibrium model for supercritical water gasification of sewage sludge was developed and the thermodynamic and environmental effects of operating parameters on the system were investigated. The sensitivity analysis revealed that the optimum reaction condition for the system was: reaction temperature of 750 °C, preheated water to SS ratio of 1, and SS concentration of 25 %. Under this condition, the system energy efficiency and exergy efficiency were 44.74 % and 46.51 %, respectively, with H2 production of 103.19 kg/h and power generation of 2526.2 kW. The energy and exergy efficiencies could be improved by reducing the preheated water to SS ratio and increasing the reaction temperature and SS concentration. The heat exchangers and the heater were the key units causing exergy losses, accounting for 40.3 % and 19.5 % of the total exergy losses, respectively. When utilizing carbon capture and storage (CCS), the global warming potential (GWP) value was only 0.31 kg CO2-eq under the optimal operating parameters, which was 61.44 % less than without CCS.

Exergy analysis of ejector‐enhanced dual‐evaporator cycle using effective temperature method

AbstractThis study compares the exergy of an ejector‐based two evaporator cycle (EB‐TEC) with a conventional two evaporator cycle (C‐TEC). The analysis utilizes a modified Gouy–Stodola equation, which provides a more accurate insight of the system irreversibility compared to the standard Gouy–Stodola formulation. Furthermore, the comparison includes three working fluids, that is, R134a, R1234ze, and R600 in both the cycles. The study examines the effects of varying evaporators and condenser temperatures and the dryness fraction at the exit of Evaporator 1. The data is analyzed using an Engineering Equation Solver. The findings indicate that increasing the temperature of the low‐temperature evaporator leads to a drop in exergy losses and enhancement in exergy efficiency in both the cycles. When the temperature of Evaporator 1 is increased, the total exergy of the EB‐TEC is decreased but for the C‐TEC, it is increased. Furthermore, increasing the condenser temperature results in higher exergy destruction in both EB‐TEC and C‐TEC. Notably, the maximum exergy destruction is 49.44 kW for R600, whereas the minimum exergy destruction is 14.42 kW for R1234ze in the EB‐TEC.

Energy and exergy analysis for advanced air-conditioning: Comparative evaluation of electrodialysis and aerodynamic thermal methods in liquid-desiccant reconcentration

A comprehensive exploration into the efficiency thresholds of electrodialysis (ED) and conventional aerodynamic thermal (AT) methods for reconcentrating high-concentration solutions is absent in current discourse. To address the gap, this study undertakes explicit derivations and experimental investigations to discern the divergences in energy and exergy performances between these two methods. The experimental results reveal that the ED method exhibits 6.9 times higher energy output/input ratio than the AT method, yet its exergy efficiency is 2.1 times lower in the baseline scenario due to the oversight of spent solution restoration costs. Moreover, the exergy loss of each component is identified by comparing the maximum exergy efficiency with the experimental exergy efficiency. These results help pinpoint measures to address significant exergy loss in key components, thereby boosting system performance. For the ED method, innovation and advancement in membrane technology and materials should be prioritized due to the significant limitations imposed by imperfect membranes. While for the AT method, utilizing renewable energy sources like solar energy to power the heater can greatly enhance system efficiency, considering that exergy loss within the heater is the primary limiting factor.

Sustainable energy storage solutions for coal-fired power plants: A comparative study on the integration of liquid air energy storage and hydrogen energy storage systems

With the majority of the world's energy demand still reliant on fossil fuels, particularly coal, mitigating the substantial carbon dioxide (CO2) emissions from coal-fired power plants is imperative for achieving a net-zero carbon future. Energy storage technologies offer a viable solution to provide better flexibility against load fluctuations and reduce the carbon footprint of coal-fired power plants by minimizing exergy losses, thereby achieving better energy efficiency. This work focuses on developing two such energy storage technologies: Liquid Air Energy Storage (LAES) and Hydrogen Energy Storage (HES), and their integration strategies with a sub-critical coal-fired power plant. The performance of the integrated systems is analyzed based on key parameters like energy storage capacity, net unit power output during charging and discharging, round-trip efficiencies, and net unit efficiencies at different operating load conditions of the plant. Our results show that during the charging cycles, by increasing the air flow rate in LAES and the hydrogen production rate in HES, the net unit efficiency of the integrated plant decreases by 3–10% at different load conditions, while the energy-based round-trip efficiency increases with increasing liquid air and hydrogen flow rates during the discharge cycles. For the HES system, utilization of the produced hydrogen in the fuel cells gives 40–50% better roundtrip efficiencies than co-firing hydrogen in the boiler at full and minimum load and it increases with increasing hydrogen flow rates. While HES has shown a better overall net unit efficiency (41.5%, in fuel cell scenario) of the integrated unit than the LAES system (40%) for the base case operation, LAES shows superior round-trip efficiencies when operated at higher liquid air discharge flow rates (>80 kg/s). The results provide insights into the system modeling of LAES and HES integrated with a sub-critical coal power plant, contributing to the advancement of sustainable energy storage solutions.

Design of an innovative system for hydrogen production by electrolysis using waste heat recovery technology in natural gas engines

This research proposes designing and implementing a system to produce hydrogen, utilizing the thermal energy from the exhaust gases in a natural gas engine. For the construction of the system, a thermoelectric generator was used to convert the thermal energy from the exhaust gases into electrical power and an electrolyzer bank to produce hydrogen. The system was evaluated using a natural gas engine, which operated at a constant speed (2400 rpm) and six load conditions (20 %, 40 %, 60 %, 80 %, and 100 %). The effect of hydrogen on the engine was evaluated with fuel mixtures (NG + 10 % HEF and NG + 15 % HEF). The results demonstrate that the NG + 10 % HEF and NG + 15 % HEF mixtures allow for a decrease of 1.84 % and 2.33 % in BSFC and an increase of 1.88 % and 2.38 % in BTE. Through the NG + 15 % HEF mixture, the engine achieved an energy efficiency of 34.15 % and an exergetic efficiency of 32.84 %. Additionally, the NG + 15 % HEF mixture reduces annual CO, CO2, and HC emissions by 9.52 %, 15.48 %, and 13.39 %, respectively. The addition of hydrogen positively impacts the engine's economic cost, allowing for a decrease of 1.56 % in the cost of useful work and a reduction of 3.32 % in the cost of exergy loss. In general, the proposed system for hydrogen production represents an alternative for utilizing the residual energy from exhaust gases, resulting in better performance parameters, reduced annual pollutant emissions, and lower economic costs.

A hybrid MCDM optimization for utilization of novel set of biosynthesized nanofluids on thermal performance for solar thermal collectors

Recent advancements in solar technology have spurred researchers to develop a precise and cost-effective method for monitoring solar radiation across diverse environmental conditions. This study focuses on optimizing performance parameters by replacing conventional nanofluids, produced through chemical and physical processes, with biosynthesized counterparts. Biosynthesized nanoparticles, derived from biological sources like microorganisms or plants, offer a promising avenue for enhancing solar panel efficiency. Through the construction and testing of an integrated photovoltaic thermal system, varying operating parameters have been explored to maximize photovoltaic efficiency. The highest overall efficiency, reaching approximately 62 %, was achieved with biosynthesized Graphene oxide nanofluid under higher Direct Normal Irradiance (DNI) levels, while the lowest was observed with Aluminum oxide nanofluid at lower DNI values. Employing Multi-Criteria Decision methods such as Analytical Hierarchical Process (AHP) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), nanofluids were ranked based on criteria including Exergy loss, Surface temperature, Overall efficiency, and Electrical efficiency, with weights of 49.58 %, 28.43 %, 13.45 %, and 8.54 % respectively. TOPSIS prioritized Graphene Oxide as the most favorable nanofluid, followed by Copper-Oxide and Cerium-Oxide, while Aluminum-Oxide received the lowest priority in optimizing PV panel performance.

Comparative analysis of water cooler for different working fluids: Energy and exergy approach

Enhancing the performance of traditional vapor compression cooling cycles is an important aspect in the quest to minimize global energy consumption, to own sustainable energy systems soon, and to preserve the environment. This study performed a comparative analysis of the performance of a water cooler with different working fluids to replace R143a and improve system performance. A mathematical model derived from energy and exergy analysis is developed for the evaluation of the effect of operating conditions on the system COP, exergetic losses, and exergetic efficiency. The evaluation has been conducted for evaporation and condensation temperatures ranging between -30°C to 15°C and 25°C to 55°C, respectively. Results showed that the cycle with R510A has the maximum COP. The average system COP with R510A, RE170, and R152a are 19.54%, 13.53%, and 9.36 % higher than that with R134a, respectively. The highest value of exergy loss takes place in the compressor. At different working fluids, exergy losses decrease as evaporation temperatures increase and condensation temperatures decrease. The system with R510A has the minimum exergy losses. The average exergy losses for systems with R510A, RE170, and R152a are 34.62%, 28.33%, and 18.64% lower than that of R134a, respectively. The system with R510A has higher exergy efficiency and R134a has the minimum values of exergy efficiency. Generally, the water cooler provided better performance with R510A and RE170 than with R152a and R134a. Therefore, R510A can be considered as the best replacement for R134a and R152a.

Sensitivity and sustainability analysis of combined cycle plant with integrated LNG pressure energy recovery

Although combined cycle power plants (CCPPs) and liquefied natural gas (LNG) have arisen as solutions to the intermittent nature of renewable energy sources, they still need creative methods for performance enhancement and sustainability of the energy systems. Moreover, the energy efficiency of CCPPs is negatively impacted by environmental conditions, higher specific fuel consumption and a large quantity of waste heat released into the ambient. On the other hand, using seawater as a heating medium in LNG regasification circuits has a detrimental effect on the marine ecosystem. In this context, the LNG pressure energy recovery system through a direct expansion cycle (DEC) integrated with CCPP is proposed to improve sustainability, enhance exergetic performance and to reduce the heat recovery steam generator (HRSG) exhaust loss. To improve the cycle performance, low grade heat harnessed from CCPP is used as the heat source in the DEC rather than seawater. The system performance is analyzed by the energy and exergy method through a mathematical model. Moreover, the sensitivity analysis of the combined system is accomplished to examine the influence of LNG flow rate and ambient temperature on various performance indicators of the total system. It is observed that the integration of DEC boosts the HRSG performance by reducing the stack exergy loss and the efficiency is sensitive to LNG flow rate. The total integrated system energy efficiency ηtot, enhanced to 1.55% compared to the base case. Whereas, for ambient temperature in range of 15 – 45 °C, the system minimum and maximum exergetic efficiency ηex,tot is found to be 54.52 % and 55.94 %. Furthermore, the comparison of exergetic sustainability indicators is calculated and presented for three different simulation cases. The results demonstrate that increase in ηex,tot, affects the environment impact factor, ref and the sustainability index, θsi and improved 2.09 % compared to base case combined cycle.

Comparative investigation on the thermodynamic performance of coal-fired power plant integrating with the molten salt thermal storage system

One of the most critical challenges facing China is enhancing the operational flexibility of coal-fired power plants (CFPPs), given the increasing reliance on renewable energy for power generation. This study focuses on analyzing and comparing the molten salt thermal storage systems integrated in CFPP in consideration of peak-shaving capacity, equivalent round-trip efficiency, heat consumption rate, and exergy efficiency. Five charging schemes integrating thermal energy storage (TES), power to heat (P2H) and combination of TES and P2H are proposed and tested via their thermodynamic models. Results show that all five integrated molten salt thermal storage systems can enhance the peak shaving capability of the CFPP. When integrating P2H system, CFPP has the potential to achieve a zero-power output. Furthermore, comparing to the other four schemes, P2H-only integrating scheme has the highest equivalent round-trip efficiency of 36.23 % and the lowest heat consumption rate of 8288.87 kJ·(kW·h)−1. However, its exergy efficiency decreases to 36.51 % due to the electric heater experiencing the highest exergy loss of 132.56 MW, in contrast to the TES-coupled system which shows a higher exergy efficiency of 39.58 %. The P2H-only scheme boasts the largest investment of $33,353,100 and the longest repayment time, while also earning the highest compensation for peak shaving. This study provides a promising approach for molten salt thermal storage system designs in enhancing flexibility for CFPPs.

Performance analysis of a compressed air energy storage incorporated with a biomass power generation system

Compressed air energy storage technology is recognized as a promising method to consume renewable energy on a large scale and establish the safe and stable operation of the power grid. To improve the energy efficiency and economic performance of the compressed air energy storage system, this study proposes a design for integrating a compressed air energy storage system with a biomass power generation system. In the energy storage process, the feedwater from the biomass power generation system is used to cool the compressed air in the compressed air energy storage system. In the energy release process, the flue gas from the biomass power generation system is used to heat the compressed air. Besides, the compressed air from the compressed air energy storage system first works in the expander and then goes to the biomass power generation system for combustion. Based on the system simulation, the proposed system is assessed from the energy, exergy, economy, and environment perspectives. The results show that the round-trip efficiency and the energy storage density of the compressed air energy storage subsystem are 84.90 % and 15.91 MJ/m3, respectively. The exergy efficiency of the compressed air energy storage subsystem is 80.46 %, with the highest exergy loss in the throttle valves. The total investment of the compressed air energy storage subsystem is 256.45 k$, and the dynamic payback period and the net present value are 4.20 years and 340.48 k$. Besides, the proposed system’s CO2 emission is 258 kg/GWh. This study provides a new option for enhancing the performance of compressed air energy storage through the system integration.

Thermodynamic and optimization analysis of a fuel cell-based combined cooling, heating, and power system integrated with LNG-fueled chemical looping hydrogen generation

Chemical looping combustion technology is essential to achieve efficient decarbonized electricity generation for fossil-fueled power plants. However, the existing chemical looping hydrogen generation (CLHG)-driven cogeneration systems have complex refrigeration units and energy-consuming carbon capture. This study proposes a novel solid oxide fuel cell (SOFC)-based combined cooling, heating, and power (CCHP) system, which is integrated with the CLHG and fueled by a liquid natural gas (LNG) regasification process. The system is designed to enhance the overall performance by directly recovering LNG cold energy for cooling and liquefying the resulting CO2. The energy and exergy performance of the system under the baseline design case are evaluated. Subsequently, we discuss the impact of key design parameters on system performance and weigh between cooling/heating power and net power generation for the system dominated by the combined heat and power (CHP)/combined cooling and power (CCP) mode. Our findings reveal that the proposed system exhibits an electrical efficiency of 66.92 % and an exergy efficiency of 53.94 % under the baseline design case. The exergy loss ratio for condenser1 is identified as the highest among all components, accounting for 29.50 %. The constituent unit with the largest exergy loss contribution is the LNG regasification unit, followed by the SOFC unit, CLHG unit, transcritical CO2 cycle unit, and heating unit. More hydrogen needs to be replenished when fuel flow in the CLHG and fuel utilization in the SOFC are used to improve system performance. The optimal electrical and exergy efficiencies of the system predominantly designed in CCP mode surpass those in CHP mode by 4.27 % and 0.57 %, respectively. The results can guide potential applications of CLHG-based cogeneration systems.

Optimization of High-Alumina Blast Furnace Slag Based on Exergy Analysis

Raw material with a high Al2O3 content has led to an increase in the Al2O3 content in blast furnace slag, which has affected the normal operation of a blast furnace. The exergy analysis method is an important method for studying the energy utilization of high-alumina blast furnace smelting. In this paper, to investigate the impact of slag composition on exergy efficiency and optimize exergy efficiency during the smelting process of high Al2O3 iron ore, a gray box exergy analysis model of blast furnace smelting and an objective function for minimizing the total exergy loss were developed. The results indicated that the blast furnace smelting process had an exergy efficiency (η) of 28.29% for hot metal and slag; the exergy efficiency of the blast furnace did not significantly increase with the increasing w(MgO)/w(Al2O3) and R (w(CaO)/w(SiO2)), but the exergy efficiency of the blast furnace declined with increasing w(Al2O3). The regional optimal solution for the objective function method was 7129.42 MJ with slag compositions of R = 1.295, w(MgO)/w(Al2O3) = 0.545, and w(Al2O3) = 15%.

Numerical investigation on mixed convection for laminar molten salt in horizontal square tubes

Molten salts are the key working media in nuclear and new energy fields. However, the mixed convection of molten salt is rarely investigated. The mixed convection of laminar flow in horizontal square tubes with constant heat flux is analyzed using Fluent software for the first time. The effects of heat flux, inlet temperature and Reynolds number on the flow and heat transfer performances are evaluated. It is found that as the buoyancy force increases, the friction factor, flow entropy generation rate, Nusselt number, and exergy efficiency increase, while the heat transfer entropy generation rate and exergy loss decrease. Compared to the forced convection, the maximum local friction factor, flow entropy generation rate, mean Nusselt number and mean exergy efficiency for mixed convection increase by 25.8%, 50.5%, 109.0% and 7.6%, respectively. Moreover, the maximum mean heat transfer entropy generation rate and exergy loss decrease by 56.1% and 57.3%, respectively. In addition, approximately 42% of the friction factor predicted by Fluent and 30% of the heat transfer predicted by Fluent exceed 20.0% uncertainties of conventional correlations. Therefore, an accurate friction factor correlation with 12.9% uncertainty and an accurate heat transfer correlation with 9.1% uncertainty are proposed.

Exergy Analysis of Tita nium Dioxide (TiO2) Suspended with R290/R600 as a Substitute for R134a

Synthetic refrigerants are being phased out gradually in accordance with international environmental protection protocols because of global warming and ozone layer depletion. Adopting R290/R600 refrigerant, an environmentally friendly refrigerant, to replace R134a, a high global warming potential refrigerant, provides one of the solutions. In this study, exergy analysis of R134a and TiO2 suspended with lubricant and R290/R600 with a composition of 60% R290 and 40% R600 (60:40) was investigated in vapour compression system (VCRS) using R290/ R600 in TiO2 nanomixture lubricant and compared with R134a and R290/ R600 in pure lubricant. At the inlets and outlets, the main components of the VCRS are connected to temperature and pressure sensors to measure the inlet and outlet temperatures and pressures. The results obtained were used to analyses the exergy losses at various VCRS components (compressor, condenser, evaporator, expansion valve) were investigated to determine the refrigerator’s total exergy destruction (E·xdest.Total) and efficiency (ηex). The E·xdest.Total of R290/R600 in pure lubricant and R290/R600 TiO2 nanomixture lubricant was reduced by 26.9% and 42.3%, respectively, and system ηex increased by 27.7% and 38.9% respectively when compared to R134a in the system. Hence, TiO2 suspended with R290/R600 is potential a substitute for R134a.

Multiparameter optimization of the acid gas removal process using self-heat recuperation technology in IGCC system based on genetic algorithm

The acid gas removal (AGR) process in the integrated gasification combined cycle (IGCC) system consumes a large amount of heat and reduces the generation efficiency. Process modification of self-heat recuperation (SHR) technology based on vapor compression heat pumps is expected to reduce the energy consumption of the AGR process. On this basis, this paper conducted a comprehensive and parametric analysis of the AGR process integrated with a vapor compression heat pump. Wherein, two key parameters, the stripper pressure (P1) and the heat pump heat exchanger inlet pressure (P2), were analyzed in detail to understand the energy consumption characteristics of each module of the system. By establishing the optimization objective functions of minimizing system operating cost and exergy loss respectively, the system multi-parameter optimization was conducted based on the genetic algorithm by coding and solving in HYSYS and MATLAB. The corresponding parameter variables for the optimal cases of the two optimization objectives are also comparatively derived. The results showed that P1 mainly changes the SHR capacity of the system by changing the allowable flow rate of the SHR mass under different working conditions, while P2 mainly affects the SHR capacity of the system by changing the heat of the fraction at the top of the stripper. The minimum operating cost of the system decreased to 0.0655 $/kgH2S, which is 1.50 % lower compared to the original case. The minimum exergy loss of the system is reduced from 7788.89 kW to 7398.59 MW, which is about 5.01 % lower than that of the original case.

Multimode thermoacoustic system for heating and cooling

Thermoacoustic technology emerges as a sustainable and low-carbon method for energy conversion, leveraging environmentally friendly working mediums and independence from electricity. This study presents the development of a multimode heat-driven thermoacoustic system designed to utilize medium/low-grade heat sources for room-temperature cooling and heating. We constructed both a simulation model and an experimental prototype for a single-unit direct-coupled thermoacoustic system, exploring its performance in heating-only, cooling-only, and hybrid heating and cooling modes. Internal characteristic analysis including an examination of internal exergy loss and a distribution analysis of key parameters was first conducted in the hybrid cooling and heating mode. The results indicated a positive-focused traveling-wave-dominant acoustic field within the thermoacoustic core unit, enhancing energy conversion efficiency. The output system performance was subsequently tested under different working conditions in the heating-only and cooling-only modes. A maximum output heating power of 2.3 kW and a maximum COPh of 1.41 were observed in the heating-only mode. Meanwhile, a cooling power of 748 W and a COPc of 0.4 were obtained in the typical cooling condition at 7 °C when operating in cooling-only mode. These findings underscore the promising potential of thermoacoustic systems for efficiently utilizing medium/low-grade heat sources for cooling and/or heating applications in the future.

Comparative study on the organic rankine cycle off-design performance under different zeotropic mixture flow boiling correlations

Zeotropic mixture utilization enhances the performance of the Organic Rankine cycle (ORC) significantly. For geothermal ORC power plants, the zeotropic mixture flow boiling correlation plays a vital role in both evaporator design and system performance evaluation. Based on the screened zeotropic mixture R1224yd(Z)/R1234ze(E) (0.452/0.548), a comparative analysis of 4 flow boiling correlations is performed to assess their impact on both evaporator design and system performance under off-design conditions. The results underscore a substantial impact of these correlations on determining the plate length, with the largest relative difference being 53.8%, consequently resulting in uncertainties of 31.7% and 23.4% for the evaporator exergy loss and cost, respectively. Under off-design working conditions, the relative difference in net power output varies from 16.43% to 7.67%. The exergy efficiency variation is up to 11.82% and the electricity production cost (EPC) uncertainty is up to 11.2% at the working condition with the maximum difference in net output work. This study provides valuable insights for selecting the appropriate zeotropic mixture flow boiling correlation in practical evaporator design and evaluating the off-design performance of ORC systems.

Design and optimization of a combined supercritical CO2 recompression Brayton/Kalina cycle by using solar energy and LNG cold energy

Solar energy and LNG cold energy have broad application scenarios as two renewable sources, but their complementary potential has not been fully explored. To fill this gap, this paper constructs a novel combined cycle that utilizes solar energy and recovers LNG cold energy to generate power. This combined cycle consists of a supercritical carbon dioxide recompression Brayton cycle, an ammonia-water mixture Kalina cycle, and an LNG cryogenic power system. A systematic evaluation was conducted on the thermodynamics and exergoeconomic of the model, and the simulation results under basic operating conditions show that the first law efficiency, second law efficiency, net power output and total unit cost reach 55.73 %, 47.72 %, 13.709 MW and 27.44 $·GJ−1 respectively. The genetic algorithm and elitist non-dominated sorting genetic algorithm are used to optimize the system performance. By using the parallel direct search method, the maximum first law efficiency, as well as second law efficiency and a minimum total unit cost of 59.45 %, 52.23 % and 24.81 $·GJ−1 are obtained respectively. The optimal first law efficiency, second law efficiency, and total unit cost of the system, which are 53.52 %, 50.33 % and 26.44 $·GJ−1 respectively, are searched simultaneously from the multi-objective optimization results by LINMAP decision-making method. Furthermore, this paper analyzes the exergy flow rate of the system and heat transfer processes of the heat exchangers under optimal operating condition. A total of 23,059.35 kW of LNG cold energy is fully utilized by the system in the LNG gasification process. The exergy loss ratio and cost ratio of each equipment analysis demonstrates that the heat exchangers (HX) have the largest percentage both exergy loss ratio and cost ratio, especially the HX4.

Modeling and analysis method for carbon emission flow in integrated energy systems considering energy quality

AbstractWhile proposing dual carbon strategy goals, research on carbon reduction in integrated energy systems (IESs) has become a focus of attention. Traditional IES carbon emission flow is mostly based on energy flow, without considering the differences in energy quality. Exergy can be used as a reasonable measure of energy quality. Combining the theory of exergy flow and carbon emission flow, a modeling and analysis method for IES carbon emission flow considering energy quality is proposed. First, exergy flow models for electric and natural gas systems, equivalent exergy flow models for heat systems, and exergy hub models are introduced. Afterward, the exergy branch losses are allocated to the nodes at both ends. A networked modeling method for the carbon emission flow of energy stations is proposed. A unified matrix calculation model for IES carbon emission flow considering energy quality is established. On this basis, an IES carbon emission flow calculation method considering energy quality is proposed. Finally, this method is applied to the test IES, and the results show that the carbon emission flow calculation results reflect the distribution of carbon emissions borne by the effective energy supplied by the source and consumed by the load in the system, taking into account both the quantity and quality of energy. The reasonable allocation of new energy is conducive to synchronously improving the energy efficiency, exergy efficiency, and cleanliness of the system.

Extended exergy analysis of a novel integrated absorptional cooling system design without utilization of generator for economical and robust provision of higher cooling demands

The focus of this study is on designing a novel system for the provision of high-capacity cooling and heating loads (4000 kW) with the utilization of absorption technology to increase economic viability and COP value of existing cooling plants via lower-grade waste heat sources (70 °C-90 °C). To achieve this aim, in the novel system, an integration including the LiBr-water solution based absorptional heat transformer (AHT), and absorptional cooling cycle (ACC), and flat plate solar collector (FPSC) systems was proposed. In the integration, the utilization of the generator in the cooling cycle was avoided with the interaction of the high-temperature LiBr-water solution (120 °C-150 °C) from the AHT system and ACC system evaporator. In this way, both the additional cost of the boiler and heat source and the enhancement of economic viability and COP value were achieved. Energy, economic, traditional, and extended exergy, sustainability, and environmental analyses were implemented in this novel system. The COP value for the cooling system was determined to be 3.10 from energy analysis. This result forms a significant indicator for achieving of the main focus of the current study with the proposed novel system. The annual heating and cooling duty generations with this novel system were computed as 52.37 GWh and 52.40 GWh, respectively. In the context of economically comparing the proposed system to other plants with similar scale that already exist, the initial overall expenditure, yearly operational expenses, and the time it takes to recover the investment for the proposed system were set at $4.56 million, $3.12 million, and 1.75 years, respectively. It is worth noting, though, that these figures fall within the range of $6–8 million, $5–7 million, and 5–10 years, respectively, for the currently operational plants. This result indicated that the proposed system provides a robust alternative to the existing cooling-heating cogeneration systems in terms of main output generation and is more economically viable. Also, the novel system gained annually US$3.89 million in energy costs. The conventional exergy analysis results were summarized by forming an exergy flow and loss diagram, namely, the Grassmann diagram. In addition, in this current study, the novel extended exergy flow diagram indicating extended exergy content components, energy carriers of the proposed system, and exergy product rate streams was also proposed and drawn for the proposed system.