Net Electrical Efficiency Research Articles

Efficiency enhancement of a combined cycle power plant by thermal integration of multiple waste heat streams with organic Rankine cycle

AbstractThe study investigated the efficiency improvement of a 9.5 MW gas engine‐based combined cycle power plant utilizing multiple waste heat streams in an organic Rankine cycle. Four different waste heat sources were considered: I) boiler stack gas, II) engine jacket water, III) boiler steam, and IV) engines' exhaust gas. Besides, three different organic fluids; R245fa, R134a, and R1234ze(Z) were employed to find the best working fluid in the given operating conditions. The performance analysis of the ORC revealed that R245fa is a suitable potential fluid for cases I and II, whereas R134a performs better for cases III and IV. Integrating the ORC with the boiler stack using R245fa at 8 barg provided an additional 16.5% waste gas heat recovery. It increased the net electric efficiency of the existing plant by 0.7%. The jacket water heat recovery further improved the net electric efficiency by 2.1%. By integrating both streams with the ORC in the existing system, the net electrical efficiency was increased from 42.6% to 45.3%. The estimated payback period for the jacket water heat recovery scenario utilizing Chinese ORC equipment was 9.3 years. However, this period was significantly reduced to 4.6 years for general industry applications, rendering it economically viable.

Thermodynamic and economic analysis of a novel solid oxide fuel cell, two level thermoelectric generator and double effect parallel absorption chiller integrated system

This study presents a comprehensive thermodynamic and economic analysis of a novel hybrid energy system integrating a Solid Oxide Fuel Cell (SOFC) with a Two-Level Thermoelectric Generator (TTEG) and a Double-Effect Parallel Absorption Chiller (DEPAC) for enhanced waste heat recovery. The primary objective is to maximize energy utilization and overall efficiency by leveraging the synergetic effects of these components. Unlike previous studies, this research uniquely evaluates the effectiveness of the integrated system and examines the impact of different Absorption Chiller configurations and the number of TTEG elements, filling a critical gap in the literature. The proposed system achieves a net electrical efficiency of 42.88 %, an energy efficiency of 44.61 %, and an exergy efficiency of 57.16 % under optimal conditions. This marks a significant improvement compared to standalone SOFC systems, with the TTEG effectively harnessing waste heat and contributing an additional 0.680 kW/m2 to the overall power output. The integration of the DEPAC system further enhances performance by providing cooling with a Coefficient of Performance (COP) of 1.351. The economic analysis reveals a positive Net Present Value (NPV) of $1,993,136, a Dynamic Payback Period (DPP) of 6.7 years, and a Levelized Cost of Electricity (LCOE) of $59/MWh, underscoring the system's financial viability. These findings demonstrate that the hybrid system offers a sustainable and efficient solution for power generation and waste heat recovery, aligning with the broader goals of advancing renewable energy technologies and setting a new benchmark in hybrid energy system design and optimization.

Effects of regulating the cathode gas properties on the ammonia-fueled solid oxide fuel cell. Part I. Parasitic power consumption and electrical efficiency after increasing O2 and H2O

This study designed and simulated a kW-scale SOFC system equipped with liquified O2 and NH3 tanks for unmanned underwater vehicles (UUVs). Optimizing the parasitic power consumption and electrical efficiency was performed via using oxygen-enriched cathode gas, in-cell cracking of ammonia and adding steam into cathode gas coupled with phase change of recycle steam. The results show increasing O2 concentration helps improve the net system electrical efficiency from 47.9% at simulate air to 51.7% at pure O2. The use of in-cell cracking increases the net system electrical efficiency by 1.3% on this basis. Interestingly, substitution of O2 to H2O would slightly reduce the net electrical efficiency of the system with O2-enriched cathode gas (e.g., decreased by 0.2% when using 40% H2O); however, substitution of N2 to H2O would help improve the net electrical efficiency of the system with simulated air as cathode gas (e.g., increased by 1.2% when using 40% H2O).

Thermodynamic analysis of the air separation unit and CO2 purification unit in the semi-closed supercritical CO2 cycle with nearly zero emission

The natural gas-fired semi-closed supercritical CO2 cycle is an efficient oxyfuel combustion power generation technology featuring nearly zero emissions. This study investigated the interaction of the semi-closed supercritical CO2 power unit with the air separation unit (ASU), which supplies O2 for combustion and adiabatic compression heat for the heat recovery process in the power unit, and the CO2 purification unit (CPU), which refines the CO2 in the exhaust gas to 99.97% for enhanced oil recovery (EOR) applications. The detailed thermodynamic models of the power unit, ASU, and CPU have been constructed to explore the impact of variations in oxygen purity and excess oxygen coefficient on the overall thermodynamic performance of the system. The results demonstrate that the net electric efficiency peaks at an oxygen purity of 98%, and a one percent decrease in oxygen purity reduces the net electrical efficiency by approximately 0.36% to 0.97% points. Moreover, the net electric efficiency decreased by 0.10% points when the excess oxygen coefficient increased from 3.00% to 13.67%. These findings may offer valuable guidance for developing oxyfuel combustion power generation technologies.

Turning Data Center Waste Heat into Energy: A Guide to Organic Rankine Cycle System Design and Performance Evaluation

This study delves into the adoption of the organic Rankine cycle (ORC) for recovering waste heat from data centers (DCs). Through a literature review, it examines energy reuse with a focus on electric power generation, the selection of working fluids, and system design principles. The objective is to develop a thorough framework for system design and analysis, beginning with a quantity and quality investigation of waste heat available. Air cooling systems, chosen often for their simplicity, account for about 70% of used cooling methods. Water cooling demonstrates greater effectiveness, albeit less commonly adopted. This study pays close attention to the selection of potential working fluids, meticulously considering the limitations presented by the available sources of heat and cold for vaporization and condensation, respectively. It reviews an ORC-based system setup, incorporating fluid streams for internal processes. The research includes a conceptual case study where the system is designed and simulations are conducted in the DWSIM environment. The simulation model considers hot air or hot liquid water returning from the data center cooling system for ORC working fluid evaporation. Ambient water serves for condensing, with pentane and isopentane identified as suitable organic fluids. Pentane assures ORC net electric efficiencies ranging between 3.1 and 7.1% when operating pressure ratios increase from 2.8 to 6.4. Isopentane systems, meanwhile, achieve efficiencies of 3.6–7.0% across pressure ratios of 2.7–6.0. Furthermore, the investigation provides key performance indicators for a reference data center in terms of power usage effectiveness (PUE), energy reuse factor (ERF), energy reuse effectiveness (ERE), and greenhouse gas (GHG) savings. This study concludes with guidelines for system analysis, including exergy considerations, and details the sizing process for evaporators and condensers.

System simulation and parametric analysis of low-concentration coal mine gas fed SOFC-CHP with deoxygenation and enrichment pretreatment

Solid oxide fuel cell (SOFC) combined heat and power (CHP) can efficiently convert low-concentration coal mine gas (LC-CMG) into clean energy, avoiding the greenhouse effect of LC-CMG. Deoxygenation and methane enrichment pretreatment of LC-CMG can prevent explosion and anode oxidation risk. Herein, a chemical process model of LC-CMG fed SOFC-CHP system with the pretreatment was established to predict the performances under different operating conditions. Performance evaluation and exergy analysis were performed considering the use of oxygen-rich gas from the pretreatment at SOFC cathode. The effects of key operation parameters on system performances were investigated in terms of residual oxygen concentration, inlet methane concentration, fuel flow and fuel utilization. The results indicated that net electrical efficiency and heat supply efficiency can respectively reach 49.13 % and 23.90 % using LC-CMG of 15 % CH4 with enhancing effect of oxygen-rich gas at cathode. The decrease of methane concentration and the increase of residual oxygen concentration and flow rate caused the decreased electrical efficiency but the increased heat supply efficiency due to the enlargement of concentration polarization and heat supply. The optimal operation parameters were recognized by comprehensively considering diverse performance indicators. This work can guide system integration and operation optimization of LC-CMG fed SOFC-CHP.

Thermodynamic Analysis and Comparison of Power Cycles for Small Modular Reactors

Small nuclear power plants can provide a stable, carbon-free energy supply to civil infrastructure and industrial enterprises in remote regions isolated from unified energy systems. More than 70 projects of small modular reactors are currently being developed by IAEA member countries; several low-power power units are already supplying thermal and electrical energy to consumers. One of the main limitations standing in the way of widespread dissemination of this technology is the high specific capital cost of a low-power nuclear power plant; therefore, new scientific and technical solutions are needed in this industry. Increasing the thermodynamic efficiency of power cycles of small modular reactors can become a driver for reducing the cost of supplied electrical energy. This paper presents the results of a comprehensive thermodynamic analysis of existing and promising power cycles for small modular reactors. In addition to traditional steam power cycles, cycles using non-traditional working fluids, including carbon dioxide, freons, and helium cycles, are considered. Optimal sets of thermodynamic parameters were determined to ensure maximum net efficiency of electricity production. For water-cooled reactor plants, a maximum efficiency of 33.5% at an initial temperature of 300 °C could be achieved using a steam turbine cycle. It was revealed that for reactor plants with liquid metal and liquid salt coolant in the range of initial temperatures above 550–700 °C, the maximum thermal efficiency was provided by the Brayton recompression cycle with a carbon dioxide coolant: the net electrical efficiency exceeded the level of steam turbine plants, with intermediate superheating of the steam, and could reach a value of 49.4% at 600 °C. This makes the use of these cycles promising for low-power nuclear power plants with a high initial temperature. In small gas-cooled reactor plants with a helium coolant, the use of a binary cycle consisting of a helium Brayton cycle and a steam-powered Rankine cycle provided an efficiency of 44.3% at an initial helium temperature of 700 °C and 52.9% at 1000 °C. This was higher than in the Brayton cycle with a recuperator, with a minimum temperature difference in the heat exchanger of 20 °C: the efficiency was 40.2% and 52%, respectively. Also, the transition to power cycles with non-traditional working fluids will lead to a change in the operating conditions of turbomachines and heat exchangers.

Techno-economic assessment of the modified Allam cycle configurations with multi-stage pump/compressor for efficient operation in hot regions

The Allam cycle is renowned for its zero-carbon power generation and high efficiency. However, it faces challenges in hot regions where there is no available cold source for carbon dioxide liquefaction, leading to deterioration in its performance. In this study, a multi-stage pump/compressor is introduced, aiming to enhance the net electric efficiency of the conventional Allam cycle. Various potential enhancement methods are explored and analyzed through comprehensive thermodynamic and economic analyses. Among the configurations under consideration, the Allam cycle combined with two-stage pump/compressor and bypass compressor exhibits the best performance, achieving a 6.71 % increase in the efficiency of the conventional cycle. For the conventional Allam cycle, the efficiency decreases by 0.42 % for every 1 ℃ increase in ambient temperature, however, it is 0.17 % for the Allam-MPC cycle, which indicates it is less responsive to changes in ambient temperature. Moreover, the economic performance of the proposed cycle is better than that of the conventional cycle, which has higher revenue and lower levelized cost of electricity. The capital costs of the modified equipment represent around 1.43 % of the total capital costs of the conventional Allam cycle, and the investment-increment payback period is less than 0.5 years when the ambient temperature exceeds 30 ℃. Sensitivity analyses suggest that the proposed cycle will be more economically viable in hot regions with lower natural gas prices and higher electricity prices. Overall, this study provides a promising approach to improving the performance of Allam cycle in hot regions and offering valuable references for its practical implementation.

Design, modeling, and optimization of a novel 6 kWe hybrid solid oxide fuel cell high temperature-proton exchange membrane fuel cell system

This work investigates a novel approach in terms of design, configuration, heat integration and optimization of a 6 kWe total energy system fueled with natural gas. Specifically, a Solid Oxide Fuel Cell (SOFC) is used for both electricity generation and fuel reforming, since its exhaust stream fuels a polybenzimidazole (PBI)-based, High Temperature-Proton Exchange Membrane Fuel Cell (HT-PEMFC). The study investigates the possible advantages of such a system in both technical and economic terms. After modeling each component/subsystem, the total system model is optimized with the objective function aiming to maximize the net electrical efficiency of the total hybrid system. The system is optimized with a genetic algorithm-based optimization strategy, reaching a net electrical efficiency of 43.6 %. In comparison to standalone fuel cell systems with the same net electrical power output, the proposed hybrid system outperforms both an HT-PEMFC system and an SOFC system, which perform at net electrical efficiencies of 23.2 % and 40.7 %, respectively. Also, the lifecycle cost for the proposed system is $64,097, which is lower than both standalone HT-PEMFC and SOFC systems. Therefore, with the current high rising costs for natural gas, such highly efficient systems are likely to become important elements of the future energy infrastructure.

Numerical Study on Effects of Flow Channel Length on Solid Oxide Fuel Cell-Integrated System Performances

The structural dimensions of the SOFC have an important influence on the solid oxide fuel cell (SOFC)-integrated system performance. The paper focuses on analyzing the effect of the flow channel length on the integrated system. The system model includes a 3-D SOFC model, established using COMSOL 6.1, and a 1-D model of the SOFC-integrated system established, using Aspen Plus V11. This analysis was conducted within an operating voltage range from 0.4 V to 0.9 V and flow channel length range from 6 cm to 18 cm for the SOFC-integrated system model. Performance evaluation indicators for integrated systems are conducted, focusing on three aspects: net electrical power, net electrical efficiency, and thermoelectric efficiency. The purpose of the paper is to explore the optimal flow channel length of SOFC in the integrated system. The results indicate that there is inevitably an optimal length in the integrated system at which both the net electrical power and net electrical efficiency reach their maximum values. When considering the heat recycling in the system, the integrated system with a flow channel length of 16 cm achieves the highest thermoelectric efficiency of 65.68% at 0.7 V. Therefore, there is a flow channel length that allows the system to achieve the highest thermoelectric efficiency. This study provides optimization ideas for the production and manufacturing of SOFCs from the perspective of practical engineering applications.

Techno-economic evaluation of CO2 capture and storage retrofit in decarbonizing different thermal power plants: A case study in China

Given that thermal power plants are the dominant mode of power generation in China, decarbonization from thermal power plants is significant to protect the global climate from further warming. CO2 capture and storage (CCS) is one of the most promising approaches for mitigating CO2 emissions; therefore, studies evaluating the effect of CCS retrofit on thermal power plants are urgently required. This study selected coal-fired power plant (CFPP) and natural gas combined cycle power plant (NGCC) as the representative technologies for thermal power plants, and proposed system models for their integrations with CCS. A comprehensive evaluation system was established using different metrics such as specific CO2 emission (CO2 emission per kWh), net electric efficiency, levelized cost of electricity (LCOE), and cost of avoiding CO2 emission (COAE). The detailed effects of fuel price fluctuations, technological advances, and different technology combinations on key metrics were analyzed, in order to propose policy recommendations for the decarbonization of China's thermal power plants using CCS technology. The following results were obtained: (1) The use of CCS to reduce CO2 emissions from thermal power plants will lead to a significant increase in LCOE. Each 100 g/kWh reduction in specific CO2 emission will result in 11 %–14.5 % increase in LCOE for CFPP + CCS, and 9.5 %–13.5 % increase for NGCC + CCS. (2) Technological advances toward reducing specific heat consumption for CO2 capture should be strongly promoted to reduce LCOE. Each 0.4 GJ/t reduction in specific heat consumption will result in an approximately 0.066 CNY/kWh reduction in LCOE for CFPP. (3) Both CFPP + CCS and NGCC + CCS exhibit potential for decreasing COAE below 600 CNY/t, although the technologies to meet this threshold are not currently realistic at higher fuel prices.

Thermodynamic Evaluation of a Combined SOFC-PEMFC Cycle System

Solid oxide fuel cell (SOFC) technology offers a promising way to reduce maritime greenhouse gas (GHG) emissions.Integration with a proton exchange membrane fuel cell (PEMFC) allows unreacted hydrogen, produced in the SOFC stack, to be reused and increase the electrical efficiency of the system. In this study, the Cycle Tempo software is used to model a SOFC-PEFMC combined cycle system operating on methane. The system is thermodynamically analysed to reveal the influence of SOFC fuel utilisation, cell voltage, operating temperature and PEMFC cell voltage on the system performance. A multivariable parametric analysis is applied to generate contour plots of net electrical efficiency and fraction of total power produced by the PEMFC. The analysis shows that increasing the cell voltage of both the SOFC and PEMFC has a positive influence on efficiency, whereas increasing the fuel utilisation reduces the system efficiency. Efficiencies in the range of 50-68% can be achieved. Model assumptions for PEMFC operating parameters are verified to exert little influence on the system efficiency, which confirms the assumption of constant values for these parameters. This study highlights the high-efficiency potential of the combined system and the difficulties that arise from thermally integrating an SOFC with a PEMFC.

Energy integration of light hydrocarbon separation, LNG cold energy power generation, and BOG combustion: Thermo-economic optimization and analysis

To recover boil-off gas (BOG) and liquefied natural gas (LNG) cold energy, this paper proposes three systems integrating light hydrocarbon separation (LHS), BOG combustion, organic Rankine cycle (ORC) with different structures and natural gas (NG) direct expansion. Both single and multi-objective optimizations are implemented to find the best system performance. Meanwhile, two multi-objective decision methods are also used to refine this work. Single objective optimization depicts that the system with parallel ORC has the highest net electric power (NEP), exergy efficiency, and net present value (NPV) of 6.85 MW, 29.07%, and 31.08 × 107 $ respectively. Multi-objective optimization results indicate the NEP, exergy efficiency, and NPV of the system with parallel ORC still outperform the other two systems. From the energy analysis, it is found that the system with parallel ORC achieves 81.07% utilization of LNG cold energy, which is the highest among the three systems. The exergy analysis indicates that the combustion chamber and heat exchanger (HX) with the highest exergy destruction in any system. Moreover, economic analysis demonstrates that the three systems are more sensitive to fluctuations in interest rates than in electricity prices.

Spectrally Efficient Integrated Silicon Photonic Phase‐Diverse DD Receiver with Near‐Ideal Phase Response for C‐Band DWDM Transmission

AbstractIn this paper, a spectrally efficient silicon photonics phase‐diverse direct‐detection receiver based on asymmetric self‐coherent detection is proposed. The receiver is hardware efficient and composed of only two photodiodes and two analog‐to‐digital channels to accurately recover complex double‐sideband signals by leveraging an optimized integrated silicon racetrack resonator with near‐ideal phase responses. Moreover, the periodicity of the resonator response enables the receiver to support multi‐channel transmission such as dense wavelength‐division multiplexing. The receiver circuit is fabricated and characterized. In 40‐km transmission experiments, a record net electrical spectral efficiency of 7.10 bit s−1 Hz−1 per wavelength and per polarization is achieved, where a net 208‐Gb s−1 32QAM transmission is demonstrated using 29.3‐GHz electrical bandwidth. Furthermore, the receiver achieves net 220‐Gb s−1 16QAM transmissions in 14 channels from 1527 to 1550 nm with 205‐GHz spacing, and a maximum 240‐Gb s−1 net capacity at a single channel. Such a performance is reached with only standard coherent digital signal processing stacks including all‐linear equalization.

Design, optimization, and technical evaluation of coking dry gas chemical looping hydrogen generation systems coupled with solid oxide fuel cell

Coking dry gas from delayed coking processes is rich in light hydrocarbons, making it a comparative ideal feedstock for hydrogen production. Current steam reforming processes have the disadvantages of high energy consumption and carbon emissions, whereas chemical looping hydrogen generation produces high-purity hydrogen with inherent carbon capture and a low energy penalty. Therefore, this study proposes a coking dry gas chemical looping process for hydrogen production, considering two schemes (external-heating and self-heating) and optimizes key parameters of the systems in detail. The optimal molar ratios of the oxygen carrier, steam, and air to coking dry gas for the externally heated and self-heated schemes were 8.62, 4.90, 2.27 and 8.62, 3.78, 4.07, respectively. The energy efficiencies of the two systems can reach 76.55% and 77.93% with carbon capture rates of 76.29% and 100%, 3.26% and 5.13% higher than efficiency of the steam reforming system. The self-heated system had the highest hydrogen production of 2.67 kmol/kmol coking dry gas. Based on a self-heated hydrogen system, a chemical looping hydrogen generation system was coupled with a solid oxide fuel cell. This integrated system achieved the better power generation performance with an anode recycling ratio of about 0.7. The net electrical efficiency of the system was 58.79%, which is 3.34% higher than that of a steam reforming system coupled with a solid oxide fuel cell. The results reveal that the chemical looping systems are suitable for the clean utilization of dry gas and provide a strategy for efficient hydrogen production and power generation.

Energy efficiency enhancement of a thermal power plant by novel heat integration of Internal Combustion Engine, Boiler, and Organic Rankine Cycle

AbstractThe utilization of waste energy contributes to reducing carbon emissions and mitigating global warming. A novel heat integration system comprising an Internal Combustion Engine (ICE), Boiler, and Organic Rankine Cycle (ORC) coupling is techno‐economically examined in this study. The feasibility of waste heat recovery from industrial boilers of a thermal power plant (Gadoon Textile Mills Limited, Pakistan) having 2.66‐MW capacity was assessed. This was done by efficiently harnessing the waste heat from boiler exhaust gas by coupling an existing system with an ORC. A steady‐state simulation model of the ICE‐Boiler‐ORC system was developed through Power Plant Simulator and Designer (PPSD) software to perform a multiparametric study. Additional heat power (3710 kW) was extracted from the boilers' waste gases through ORC. Consequently, the overall plant thermal efficiency was enhanced from 61.84% to 82.68% and the overall net electric efficiency of the existing system was increased by 0.9%. The average payback period was found 4.2 years based on different plant operation scenarios and equipment prices (Chinese or European origin). Therefore, the proposed system holds significant technical and economic potential for enhancing energy efficiency through low‐grade waste heat and proves to be economically viable with a short payback period.

Techno-Economic Analysis of the Solid Oxide Semi-Closed CO2 Cycle and Comparison With Other Power Generation Cycles With CO2 Capture

Abstract This work presents the techno-economic analysis of the solid oxide semi-closed CO2 cycle (SOS-CO2), a hybrid semi-closed cycle with solid oxide fuel cells (SOFC) recently developed by Politecnico di Milano for power generation from natural gas with near-zero CO2 emissions. According to previous studies, the cycle is able to achieve an outstanding net electric efficiency of 75.7%. while capturing more than 99% of the generated CO2. All the cycles components, including the fuel cell and the turbine, have been designed and sized with the aim of assessing the performance and the capital cost. The energy and economic key performance indicators are compared with those of two benchmark cycles with CO2 capture: the Allam cycle and a combined cycle with amines. Moreover, a sensitivity analysis is performed on the forecasted cost of the natural gas and the SOFC stacks. The results indicate that the specific total capital requirement of the SOS-CO2 cycle (2504 €/kWel) is considerably higher than the Allam cycle (1926 €/kWel) and combined cycle with amines (1981 €/kWel). On the other hand, the SOS-CO2 cycle benefits from its far higher efficiency (74.0% versus 53.9% of the Allam cycle and 52.8% of the combined cycle with amines) which makes the cycle less sensitive to the fuel cost and CO2 tax. In terms of cost of electricity, the SOS-CO2 cycle turns out to be the best technology for natural gas prices above 8 €/GJ, while the Allam cycle appears to be the preferred option at lower fuel prices. For a fuel cost of 12 €/GJ, the SOS-CO2 cycle features a cost of electricity of 106.2 €/MWh, lower than the Allam cycle (119.1 €/MWh) and the combined cycle with amines (126.9 €/MWh).

Feasibility and Performance Analysis of a Dual‐Regulation System in the Process of Methanol and Electricity Coproduction by Coal Gasification

The traditional coal‐gasification process has many problems, such as low yield, large loss of syngas, and large carbon emission. Herein, a novel dual‐regulation system is established. Natural gas is used as the supplemental feed to add hydrogen‐ to coal‐gasification syngas, which is the primary regulation process. Water–gas shift process with calcium looping is treated as the secondary regulation process to regulate the ratio of H2 to CO and CO2 subtly. The potential feasibility of the system is verified through thermodynamic perspective by Aspen Plus. Under the simulation condition, the final methanol product amount is 3485.12 kmol h−1 with 97.2% concentration and 33.47 MWe net electricity is generated. As a result, the methanol efficiency and net electricity efficiency are 60.55% and 3.22%, respectively. For investigating the effectiveness of regulation, the effects of mass ratio of natural to coal feedstock on materials and performances are discussed.

Energy efficiency analysis and optimization of a pressurized oxy-fuel circulating fluidized bed combustion system

The commercial application of oxy-fuel combustion technology is limited by energy deduction which is caused by addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). Pressurized circulating fluidized bed (CFB) oxy-fuel combustion technology is one option to improve the net electric generation efficiency. In this research, a series of simulations and optimizations were carried out to analyze the energy efficiency of a pressurized oxy-fuel combustion system. The boiler structure and heat exchange surface arrangement under different pressure were calculated. The cross-sectional area of the furnace and tail flue were both reduced up to 10 % of the original size and the floor space of the boiler was considered to be the lowest at 1.1 MPa. The energy efficiency and exergy analysis were used to explore the influence of pressure on the net efficiency and the optimization potential of system. The net electric generation efficiency reached a maximum value of 24.16 % at 1.1 MPa, which is 5.4 % higher than that at atmospheric pressure. Finally, four parameters, i.e. preheat temperature, oxygen concentration, ASU outlet oxygen purity and CPU compressor outlet pressure, were optimized to improve the system net efficiency to 26.67 %, 29.04 %, 25.87 % and 24.36 %, respectively.

Performance analysis of a CO2 near-zero emission integrated system for stepwise recovery of LNG cold energy and GT exhaust heat

Combined cooling, heating and power (CCHP) system can further improve energy utilization efficiency while meeting diversified energy demands, and the rational use of the CCHP system is an effective way to alleviate the energy crisis. An innovative cascaded CCHP system based on the transcritical carbon dioxide cycle (TRCC) and organic Rankine cycle (ORC) has been proposed, which is designed to recover the cold energy of liquefied natural gas (LNG) and the exhaust heat from the gas turbine (GT), while achieving near-zero CO2 emissions. The simulation result demonstrates that the system achieves energy utilization efficiency, exergy efficiency and net electrical efficiency of 87.3%, 56.9% and 55.39%, respectively, with a CO2 capture rate of 79.2 kg/h under the design condition. Compared to the mentioned cogeneration systems that recover LNG cold energy and GT waste heat, the proposed system exhibits improvements in energy utilization efficiency, exergy efficiency and net electrical efficiency by 9.84%, 4.37% and 3.4%, respectively. The parameter sensitivity analysis reveals that increasing the pressure ratio of the TCO2 turbine and ORC turbine or reducing the air compressor feed temperature can improve the overall performance of the system. If the focus is solely on energy utilization efficiency and exergy efficiency, appropriately increasing the air compressor pressure ratio or reducing the gas turbine pressure ratio would be beneficial. The proposed system in the study is environmentally friendly and energy-saving, which especially suggests a direction for cold energy cascade utilization in LNG stations integrated with CCHP.