Air Compressor Pressure Ratio Research Articles

Exergoeconomic Analysis and Optimization of a Biomass Integrated Gasification Combined Cycle Based on Externally Fired Gas Turbine, Steam Rankine Cycle, Organic Rankine Cycle, and Absorption Refrigeration Cycle.

Adopting biomass energy as an alternative to fossil fuels for electricity production presents a viable strategy to address the prevailing energy deficits and environmental concerns, although it faces challenges related to suboptimal energy efficiency levels. This study introduces a novel combined cooling and power (CCP) system, incorporating an externally fired gas turbine (EFGT), steam Rankine cycle (SRC), absorption refrigeration cycle (ARC), and organic Rankine cycle (ORC), aimed at boosting the efficiency of biomass integrated gasification combined cycle systems. Through the development of mathematical models, this research evaluates the system's performance from both thermodynamic and exergoeconomic perspectives. Results show that the system could achieve the thermal efficiency, exergy efficiency, and levelized cost of exergy (LCOE) of 70.67%, 39.13%, and 11.67 USD/GJ, respectively. The analysis identifies the combustion chamber of the EFGT as the component with the highest rate of exergy destruction. Further analysis on parameters indicates that improvements in thermodynamic performance are achievable with increased air compressor pressure ratio and gas turbine inlet temperature, or reduced pinch point temperature difference, while the LCOE can be minimized through adjustments in these parameters. Optimized operation conditions demonstrate a potential 5.7% reduction in LCOE at the expense of a 2.5% decrease in exergy efficiency when compared to the baseline scenario.

Assessment of a combined heating and power system based on compressed air energy storage and reversible solid oxide cell: Energy, exergy, and exergoeconomic evaluation

The electricity grid with high-penetration renewable energy sources has urged us to seek means to solve the mismatching between electricity supply and demand. Energy storage technology could accomplish the energy conversion process between different periods to achieve the efficient and stable utilization of renewable energy sources. In this paper, a hybrid energy storage system based on compressed air energy storage and reversible solid oxidation fuel cell (rSOC) is proposed. During the charging process, the rSOC operates in electrolysis cell (EC) mode to achieve the energy storage by converting the compression heat to chemical fuels. During the discharging process, the cell operates in fuel cell mode for electricity production and the gas turbine is conducted to recover the waste heat from cell. To evaluate the comprehensive performance of the proposed system, the energy, exergy, and exergoeconomic studies are conducted in this paper. Under the design condition, the results indicated that the proposed system is capable of generating 300.36 kW of electricity and 106.28 kW of heating; in the meantime, the energy efficiency, exergy efficiency, and total cost per unit exergy of product are 73.80%, 55.70%, and 216.78 $/MWh, respectively. The parametric analysis indicates that the increase in pressure ratio of air compressor, steam utilization factor of rSOC stack under EC mode and current density of the rSOC stack under EC mode reduce exergy efficiency and total cost per unit exergy of product simultaneously, while the increment of operating pressure of rSOC stack under FC mode enhances the exergy efficiency and decreases total cost per unit exergy of product. The multi-objective optimization is carried out to improve the comprehensive performance of the proposed system, and the results expressed that the best optimal solution has the exergy efficiency and total cost per unit exergy of product of 65.85% and 187.05 $/MWh, respectively. Compared to the basic operating condition, the improvement of the proposed system has led to the maximum enhancement of 20.32% in exergy efficiency and 18.60% in total cost per unit exergy of product.

Exergy analysis of thermodynamic performance of a gas turbine unit

BACKGROUND: Gas turbine units are the most widespread type of power plants used in almost all industries. Such a wide distribution in combination with a high level of energy characteristics, high specific power and flexibility determine the relevance of research in the field of assessing their operating parameters.
 AIM: Determining the exergy characteristics (exergy efficiency and exergy dissipation factor) of a gas turbine plant and evaluation the efficiency of energy use in a gas turbine plant, as well as analysis of the influence of ambient temperature on the selected parameters.
 METHODS: The paper presents the results of an exergy analysis of the gas turbine plant as part of the Jandar Thermal Power Plant, Syria. To evaluate the described parameters, the method of exergy analysis of the thermodynamic characteristics of a gas turbine plant based on the first and second laws of thermodynamics in conjunction with the laws of conservation of mass and energy was used. An important feature of the study, which also emphasizes its novelty, is taking into account the chemical exergy of combustion gases during the exergy analysis.
 RESULTS: Based on the results of the study, it was found that the maximum exergy efficiency was 92.8% and was typical for a turbine as part of a gas turbine, while the highest exergy dissipation was observed in the process of fuel combustion in the combustion chamber and was equal to 80% (117.3 MW). The lowest exergy values corresponded to the compressor — 6.0% (9 MW). For the gas turbine unit as a whole, the total exergy dissipation was 147.3 MW and the exergy efficiency was 53.3%. In this case, the main sources of irreversibility in the gas turbine unit are the combustion chamber and combustion gases.
 CONCLUSION: Exergy analysis is a convenient method for evaluating the thermodynamic perfection of gas turbine units. As a further line of the study, it is necessary to evaluate the effects of various conditions, such as air humidity or compressor pressure ratio, on the exergy characteristics of the gas turbine fuller.

Economic and environmental assessment and bi-objective optimization of a novel biomass-powered co-generation system: Impact of design parameters

Organic flash cycle facilitates high heat recovery and seamless integration with refrigeration cycle. Moreover, the use of a two-phase ejector in the organic flash cycle enables operation at temperatures below zero and enhances cooling/power production. A parametric study is conducted to scrutinize the influence of key design variables gas turbine inlet temperature (T3), flash tank inlet temperature (T14), and air compressor pressure ratio (P2/P1) on plant outputs. P2/P1 is a crucial design factor affecting overall performance, optimizing efficiencies and reducing levelized cost of product at a ratio of 5. Additionally, T3 has positive effects on several performance indices, but higher values lead to decreased system-generated cooling from 910.2 kW to 774.1 kW. Meanwhile, T14 has mixed effects, improving system-generated electricity, sustainability index, levelized cost of product, CO2 emission rate, and exergy efficiency, but negatively impacting system-generated cooling, energy efficiency, and total investment cost rate. The optimization process has a positive impact on system-generated electricity, emitted CO2 rate, sustainability index, exergo-environmental index, energy efficiency, and exergy efficiency, leading to their respective values reaching 5945 kW, 0.9648 kg/kWh, 1.511, 0.6158, 10889 kW, 42.37%, and 33.82. Meanwhile, system-generated cooling, total investment cost rate, and levelized cost of product show performance degradation.

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.

Development of an innovative high-performance poly-generation plant for efficient multi-level heat recovery of a biogas-powered micro gas turbine: Environmental and Multi-criteria analysis

Nowadays, the biogas-powered gas turbine cycles in poly-generation systems play a crucial role due to increasing fuel prices, declining renewable energy sources, and environmental concerns associated with fossil fuels. Concerning the high temperature of expanded gas, a novel high-performance poly-generation plant is achievable by intelligently selecting different subsystems. This paper presents a novel biogas-fueled poly-generation plant for producing electricity, refrigeration load, distilled water, and hydrogen simultaneously using multi-level heat recovery. An extended assessment of the devised plant output is performed based on energy-exergy, environmental, and exergoeconomic criteria, in which the plant’s gas turbine inlet temperature, preheated air temperature, air compressor pressure ratio, as well as turbine inlet pressure, are considered as variables. In the following, to demonstrate the advantages of using a Stirling engine, this study investigates two scenarios to reveal its superiority, and a bi-objective optimization is performed, where the objective functions comprise minimizing the poly-generation unit products cost and maximizing the sustainability index. When the plant is operated with a Stirling engine, the plant produces 986 kW of electricity, 137.5 kW of refrigeration load, 8.39 m3/h of distilled water, and 2.96 kg/h of hydrogen. In this case, the energetic and exergetic efficiencies of the proposed system are enhanced by 2.96% and 7.89%, respectively compared to non-Stirling engine mode. Also, the carbon dioxide emissions and sustainability index are ameliorated from 606.2 kg/MWh to 588.6 kg/MWh and from 1.47 to 1.5, respectively. In addition, the sensitivity analysis indicates that in a certain ratio of PRAC, the plant's performance reaches its optimal mode. Moreover, the unit cost of products and sustainability index are improved by 9.9% and 8%, respectively, compared to the base design case with the SE.

Comprehensive analysis and multi-objective optimization of an innovative power generation system using biomass gasification and LNG regasification processes

The biomass-based systems have considerable feasibility to design a co-generation with different subsystems. This paper presents a novel biomass-based gas turbine with a modified Kalina cycle, supercritical-CO2 cycle, and LNG regasifying subsystems. A turbine is installed in the LNG regasifying subsystems to produce more power. Energy, advanced exergy, including thermal and mechanical exergies, and economic analyses are applied to assess the system's performance. Three double-objective and two triple-objective optimizations are carried out to obtain the system's operation mode at the optimum state. The results reveal that the combustion chamber and supercritical-CO2 cycle's condenser have the highest exergy destruction. Also, the compressors and turbines have the main portion of the investment cost rate of about 79.91%. The design system provides 7560 kW net power, 41.75% exergy efficiency, and 6.2 years payback period. Regarding the parametric study, the system's performance indexes are mainly affected by the air compressor's pressure ratio. Furthermore, considering the net power-sum unit cost of production as the optimization goal represents the best performance of 7830 kW net power, 42.97% exergy efficiency, and 7.262 $/GJ sum unit cost of products.

A proposed configuration of biomass based combined power and cooling plant and its 6E analyses

The paper reports 6E analyses (energy, exergy, economic, environmental, exergo-economic and exergo-environmental) of a biomass based combined power and cooling plant that uses sawdust as its fuel, steam as its sole gasifying agent. The gasification model includes tar in the producer gas and yields maximum hydrogen content when steam-to-biomass ratio (STBM) and reactor temperature are set to 2 and 800 °C respectively. The performance of the cogeneration plant is assessed by varying different input parameters viz. air compressor pressure ratio (pr) and turbine inlet temperature (TIT). Simulation results show that the optimum performance is achieved when TIT is 1100 °C and pr is in the range of 6 to 8. The exergo-economic factor and exergo-environmental factor are evaluated by considering these optimised conditions. Exergy analysis suggests that the gasifier is subjected to maximum exergy destruction. From economic analysis, the computed effective price of electricity (EPOE) is 0.064 USD/kWh with the discounted payback period of the plant being 8.5 years. The exergo-economic and exergo-environmental factors obtained are 51.5 % and 0.0288 % respectively at the favourable operating conditions.

Techno-economic and environmental assessment of a novel polygeneration system based on integration of biomass air-steam gasification and solar parabolic trough collector

Renewable energy-based polygeneration energy systems, in addition to providing a variety of products, can effectively improve this planet's environmental conditions and reduce emissions. Therefore, in the present work, a novel polygeneration system has been proposed to produce power, heat, freshwater, and hydrogen-based on biomass and solar energy. In the present system, the Kalina cycle, Gas turbine cycle, double-pressure steam cycle, and organic Rankine cycle are used to produce power, Multi-effect desalination and reverse osmosis are used to produce freshwater, and the PEM electrolyzer is used to produce hydrogen. Also, the exhaust syngas from the gasification process has been used to supply steam to the gasifier reactor. Considering the determination of environmental laws and the need to transform Kish Island into a green island for residents and tourists, a proposed system has been defined for Kish Island in Iran. In the proposed system, the feasibility of three biomass fuels, Municipal Solid Waste (MSW), Mixed Paper Waste (MPW), and Date Palm Waste (DPW), was studied from a technical, economic, and environmental point of view. Air and steam agents have been used for the gasification of mentioned fuels. To evaluate the performance of the system in terms of thermodynamics, economics, and environment during the year, the analysis of the average monthly solar for the studied system has been used. MED has been analyzed using artificial intelligence techniques. Finally, a sensitivity analysis is performed for the main operational parameters. The results of the proposed system modeling show that MSW is the most economical fuel and the use of DPW has the least environmental impact on the system, but in terms of operating conditions, MPW with overall energy and exergy efficiency of 41.68% and 34.19% compared to other fuels perform better. The overall results of the 4E analysis for MSW fuel show that the overall energy and exergy efficiency of the polygeneration system is 39% and 32.01%, respectively. Power generation costs and environmental impacts for MSW biomass are 0.014 $/kWh and 0.002 Pts/kWh, respectively. The monthly analysis of the studied system for all three fuels shows that the net power generation decreases in the summer months. The results of the sensitivity analysis of the studied system show that the optimal design of gasification temperature, air compressor pressure ratio, condenser pressure, and the number of MED effects play a key role in the objective functions of the studied system.

Biomass possessing toward an efficient arrangement using a novel framework of waste-to-useful products: MOPSO optimization and comprehensive thermodynamic and cost analyses

The maximum use of the potential of biomass-fed power plants through an efficient waste-to-useful products framework ameliorates the performance resulting in better applicability. The current study suggests a novel multi-heat recovery for multiple productions aimed at simultaneous power, liquefied hydrogen, natural gas for urban usage, and freshwater generation. Meanwhile, the main system is made of a biomass processing unit using a gasifier, a Brayton cycle, a carbon dioxide power cycle, a Kalina cycle, a multi-effect desalination, and a Claude cycle attributed to hydrogen liquefaction, and a liquefied natural gas cold energy recovery-based power cycle. The system is examined from the viewpoints of thermodynamic and economic profitability and is optimized in four different scenarios employing a MOPSO (multi-objective particle swarm optimization) technique. Additionally, the sensitivity of the profitability measured by the NPV (net present value) is also evaluated at different prices of input fuel and products. Moreover, the scenarios of the MOPSO include exergyefficiency(εcycle)/NPVtotal, εcycle/freshwaterproductivity(m˙fw), NPVtotal/m˙fw, and εcycle/NPVtotal/m˙fw. Regarding the highest sensitivity impact of the inlet air compressor's pressure ratio on the performance variables and hydrogen liquefaction price on the NPVtotal, the last optimum case stated εcycle=37.1%,NPVtotal=1.635M$,andm˙fw=29.9kg/s.

The investigation of an SGT5-2000E gas turbine power plant performance in Benin City based on energy analysis

• The effect of change in ambient air temperature on the performance of the SGT5 -2000E Gas turbine Power Plant was analyzed for this location. • The average net power output was 97.33% of the guaranteed value. • For this location, a 1 0 C rise in ambient air temperature, there are drops of 1.16% in net power output and 1.58% net thermal efficiency, a 1.58% increase in SFC and HR, and a 0.64% decrease in WR. • This study has suggested efficient ways of overcome drawbacks observed. In order to address the growing global energy demand and save energy from operating gas turbine power plants, the performance and losses from existing gas turbine power plants need to be studied. In view of this, this research work aims at carrying out the energy analysis of the SGT5-2000E Gas Power Plant for off-design conditions. The energy analysis was conducted using operating data collected from the power plant to evaluate the thermal efficiencies, specific fuel consumption (SFC), heat rate (HR), work ratio (WR) and energy losses with the aid of MATLAB software. The effects of ambient air temperature and compressor pressure ratio on the thermodynamic performance were carried out. Energy analysis results obtained showed that the average net thermal efficiency of the SGT5-2000E Gas Power Plant was found to be 30.21% at the ambient air temperature range from 21 to 35 0 C, the compressor pressure ratio of 10.73 to 10.96, the net power output of 148.92MW to 160. 70MW, and 60.16% of the fuel energy input was lost to the power plant surroundings as waste heat. Also, the results obtained revealed that for a 1 0 C rise in ambient air temperature, there are drops of 1.16% in net power output and 1.58% net thermal efficiency, a 1.58% increase in SFC and HR, and a 0.64% decrease in WR. Furthermore, the results obtained showed that there was a lower performance of the plant at high ambient air temperature and a lower compressor pressure ratio and the exhaust gas waste heat can be utilized for a combined heat and power system. Accordingly, the study has provided an understanding of suitable information about the power plant that can be used for efficient operation and waste minimization as ways of performance enhancement of the SGT5-2000E Gas Turbine Power Plant in Benin City.

Performance evaluation and multi-objective optimization of a novel UAV propulsion system based on PEM fuel cell

The present study has developed and optimized a novel hybrid propulsion system for unmanned aerial vehicles (UAVs). This system has two independent power generation sources which are the proton exchange membrane fuel cell (PEMFC) and a single-stage turbocharged engine. Each of these two systems can be used independently or simultaneously to generate power and thrust. To study the performance of the proposed hybrid propulsion system, a comprehensive thermodynamic analysis has been performed. In order to find the best working condition for the system, the effect of various design parameters on system performance has been analyzed. Multi-objective optimization of the hybrid system using the NSGA-II algorithm has been carried out to maximize the generated thrust of the propulsion system while minimizing fuel consumption rate. These will be ideal conditions for long-endurance missions. The results revealed that fuel consumption rate and the generated thrust in optimized point are equal to 34.58 (mg/s) and 69.56 (N), respectively. Also, we achieved 62.41% thermal efficiency for the new proposed propulsion system. To study system reactions to deviation from design parameters, a sensitivity analysis has been performed which revealed that an increase in air compressor pressure ratio doesn’t change the thrust but increases the flight duration by decreasing the fuel consumption rate. Also, increasing the number of cells increases the generated thrust and efficiency of the system, however, this will increase the fuel consumption rate which lowers the flight duration. So, it is a compromise between two contradicting features and design objectives to select the characteristics of the system. System performance in different altitudes has been also investigated. By increasing the altitude, the overall efficiency drops, and the fuel consumption rate will increase.

Single-column cryogenic air separation: Enabling efficient oxygen production with rapid startup and low capital costs—application to low-carbon fossil-fuel plants

The rapid integration of intermittent renewable sources into the electricity grid is driving the need for more flexible, low-carbon fossil-fuel plants with lower capital costs. This then drives the need to improve the cryogenic air separation unit (ASU). To address this changing landscape, we explore a Praxair single-column ASU (PSC-ASU) design with the goal of reducing costs and improving flexibility, compared to a conventional double-column ASU. The PSC-ASU incorporates partial air condensation and air pre-separation in the bottom reboiler with a phase separator as well as N2-enriched vapor condensation in the upper reboiler to decrease energy consumption, as compared to Linde’s single-column ASU. All three of the above-mentioned ASU designs are simulated in Aspen Plus and analyzed. An economic analysis is applied to evaluate the relative cost savings of the PSC-ASU compared to the double-column ASU. Results suggest that the specific energy consumption of the PSC-ASU is significantly lower than that of Linde’s single-column ASU due to a drastically improved oxygen recovery rate. Although this improved oxygen recovery rate is still lower than that of the double-column ASU, the required pressure ratio of the main air compressor is 21% lower than that of the double-column ASU. As a result, the specific energy consumption of the PSC-ASU is only 1.9% greater than that of the double-column ASU for producing 95.1 mol% O2. However, the PSC-ASU reduces the hourly capital cost by 19% due to the elimination of a high-pressure column. This would effectively decrease the total hourly cost of the ASU, and thus the total hourly cost of low-carbon, fossil-fuel power plants that require oxygen.

Multi-objective optimization of a biomass gasification to generate electricity and desalinated water using Grey Wolf Optimizer and artificial neural network

In the current research, an innovative biomass-based energy system is proposed for power and desalinated water production. The plant's primary components consist of a gasifier, a compressor, a heat exchanger, a gas turbine, a combustion chamber, and a Multi-effect desalination with thermal vapor compression (MED-TVC) unit. A comprehensive thermodynamic and thermoeconomic assessment is conducted on the proposed system. Besides, a parametric study is conducted to determine the effect of primary decision variables on the system performance. Multiple objective optimization using the multi-objective grey wolf optimizer (MOGWO) algorithm is applied to obtain the optimal solution with the highest exergy efficiency and the minimum amount of total cost rate. The artificial neural network (ANN) has an intermediary role in the optimization process to decrease computational time and enhance optimization speed. The relation between the objective function and decision variables is investigated, employing ANN to determine the energy system's optimum point. The generation rate for power and freshwater at the optimal point is equal to 5127 kW and 38.6 kg/s, respectively. Besides, the optimum value of the exergy efficiency and total cost rate are computed as 15.61% and 206.78 $/h, respectively. The results also revealed that the number of effects of the desalination unit does not affect the carbon dioxide emissions. Moreover, the scatter distribution of the key decision variable indicates that the air compressor pressure ratio is not a sensible variable, and their optimum points are distributed across the entire domain.

Simulation of a new biomass integrated gasification combined cycle (BIGCC) power generation system using Aspen Plus: Performance analysis and energetic assessment

A new biomass integrated gasification combined cycle (BIGCC), which featured an innovative two-stage enriched air gasification system coupling a fluidized bed with a swirl-melting furnace, was proposed and built for clean and efficient biomass utilization. The performance of biomass gasification and power generation under various operating conditions was assessed using a comprehensive Aspen Plus model for system optimization. The model was validated by pilot-scale experimental data and gas turbine regulations, showing good agreement. Parameters including oxygen percentage of enriched air (OP), gasification temperature, excess air ratio and compressor pressure ratio were studied for BIGCC optimization. Results showed that increase OP could effectively improve syngas quality and two-stage gasification efficiency, enhancing the gas turbine inlet and outlet temperature. The maximum BIGCC fuel utilization efficiency could be obtained at OP of 40%. Increasing gasification temperature showed a negative effect on the two-stage gasification performance. For efficient BIGCC operation, the excess air ratio should be below 3.5 to maintain a designed gas turbine inlet temperature. Modest increase of compressor pressure ratio favored the power generation. Finally, the BIGCC energy analysis further proved the rationality of system design and sufficient utilization of biomass energy.

Optimization of a combined cooling, heating, and power (CCHP) system with a gas turbine prime mover: A case study in the dairy industry

A proposed system consists of a combined cooling, heating, and power (CCHP) system driven by a gas turbine prime mover and an auxiliary boiler (CCHP-Boiler) system in a dairy factory. The CCHP-Boiler system optimized based on three different objective functions. In the 1st method, the system is considered as the combined CCHP-Boiler system. However, in the 2nd and 3rd methods, the optimization process has been carried out to the combined CCHP-Boiler system which has power transfer with the central power plant (CPP). The first objective function in the 1st method is the exergy efficiency of the CCHP-Boiler system. The second objective function is the annual total cost of the CCHP-Boiler system. In the 2nd and 3rd methods, the comprehensive objective function (CO), is the single-objective function. The results indicate that the base design requires a higher pressure ratio of air compressor (RP), which is equal to 14.79, and consequently, the existence of APH and LPG2 is recommended. But, optimization with all the methods for the CCHP-Boiler system leads to low RP values, which is approximately equal to 6. Meanwhile, it can be concluded that the existence of air pre-heater (APH) is not necessary and it should be removed.

Integration of biomass gasification with a supercritical CO2 and Kalina cycles in a combined heating and power system: A thermodynamic and exergoeconomic analysis

A novel cogeneration system based on a combination of a gas turbine cycle, a supercritical CO2 cycle, and a Kalina cycle is devised for heating and power generation. Energy, exergy, and exergoeconomic analysis are performed to assess the system’s performance and feasibility. According to the findings, the energy and exergy efficiencies of the system are obtained by 78.15% and 40.97%, respectively. In addition, heating capacity enhanced with the increment of air preheater’s terminal temperature difference (ΔTAP), air compressor’s pressure ratio (r1p), and pressure ratio of S–CO2 compressor (r2p). The system’s sum unit cost of the product (SUCP) decreased with the increment of ΔTAP and with the decrement of ammonia concentration. Besides, the minimum value of SUCP is obtained at the air compressor pressure ratio of r1p=13.24 and r2p=2.63. The maximum value of exergy efficiency is evaluated at ΔTAP=262K, r1p=14.5, and r2p=4.21. Moreover, the maximum net output power is obtained where the design parameters are set as ΔTAP=262K, r1p=14.5, and r2p=3.5. Furthermore, the economic analysis revealed that the payback period and net present value are evaluated to be 6.9 years and 5.374×10+6 $, respectively, for the electricity price of 0.07 $/kWh and fuel cost of 2 $/GJ.

Emergy-based exergoeconomic and exergoenvironmental evaluation of a combined power and cooling system based on ORC-VCR

Ensuring efficient operation of energy conversion systems in terms of economics and ecology is a prime objective that should be addressed within the design, optimization, and development stages of such systems. Adopting appropriate measures for accurate assessment and comprehensive evaluation of thermodynamic systems is a sheer necessity for accomplishing this purpose. In this study, the newly developed emergy-based exergoeconomic (i.e., emergoeconomic) and emergy-based exergoenvironmental (i.e., emergoenvironmental) analyses have been employed to assess a combined power and cooling system, including a gas turbine cycle, a steam Rankine cycle, and an integrated organic Rankine cycle-vapor compression refrigeration (ORC-VCR) subsystem serving as a waste heat recovery unit. The merit of emergy-based methods is that they can evaluate and express results by an identical unit of measurement (i.e., sej) which enables us to undertake a fair and accurate comparison between the methods in question. The results showed that the combustion chamber, with the total economic emergy rate of 6.83E13 (sej h−1) and the total ecological emergy rate of 6.05E14 (sej h−1), was the most critical component in the entire system from both the economic and ecological viewpoints. Moreover, a parametric study was carried out on the entire system, as well as the ORC-VCR unit, to examine the effect of design parameters on the emergy-based monetary and ecological performances. Increasing the air compressor pressure ratio from 6 to 11 enhanced the entire system’s both emergy-based performances by almost 8%, followed by improvements made by the gas turbine isentropic efficiency and combustor inlet temperature, with 6.5% and 5.5%, respectively. However, other design parameters exerted limited impact. Regarding the ORC-VCR, raising the ORC turbine inlet temperature and the isentropic efficiencies associated with the ORC turbine and VCR compressor improved the emergy-based performances, while the reverse was observed for the ORC condenser and evaporator temperature rise.

The use of waste heat recovery (WHR) options to produce electricity, heating, cooling, and freshwater for residential buildings

In recent years, there is a growing attention drawn to the area of building-integrated CCHP systems, due to its high capability in cost and energy saving. In this study, a residential scale multigenerational system is proposed to generate power by using solid oxide fuel cell and gas turbine (hybrid SOFC/GT), heating (by using HRSG), cooling (by using a double-effect absorption chiller) and freshwater (by using a Revers osmose plant). The system is modeled in engineering equation solver and studied from energy, exergy, economic and environmental standpoints. A parametric study is conducted in order to define the crucial decision variables in the system, and their effect on the overall exergy efficiency and unit product cost, along with the rate of freshwater production is observed. Results of the parametric study demonstrated that fuel utilization factor, stack temperature difference, current density, and the pressure ratio of air compressor have the most substantial influence on the behavior of the proposed system. Moreover, obtained results revealed that the energy and exergy efficiency of the system reaches 86.32% and 69.06%, respectively. In addition, the rate of freshwater production and unit product cost of the entire system becomes 256 L/day and 37.78 $/GJ.hr. Furthermore, the emission of the proposed system becomes 0.225 ton/MW.hr, which faces a 31% reduction compared to the standalone power generation system.

Air mass flow and pressure optimisation of a PEM fuel cell range extender system

In order to eliminate the local CO2 emissions from vehicles and to combat the associated climate change, the classic internal combustion engine can be replaced by an electric motor. The two most advantageous variants for the necessary electrical energy storage in the vehicle are currently the purely electrochemical storage in batteries and the chemical storage in hydrogen with subsequent conversion into electrical energy by means of a fuel cell stack. The two variants can also be combined in a battery electric vehicle with a fuel cell range extender, so that the vehicle can be refuelled either purely electrically or using hydrogen. The air compressor, a key component of a PEM fuel cell system, can be operated at different air excess and pressure ratios, which influence the stack as well as the system efficiency. To asses the steady state behaviour of a PEM fuel cell range extender system, a system test bench utilising a commercially available 30 kW stack (96 cells, 409 cm2 cell area) was developed. The influences of the operating parameters (air excess ratio 1.3 to 1.7, stack temperature 20 °C–60 °C, air compressor pressure ratio up to 1.67, load point 122 mA/cm2 to 978 mA/cm2) on the fuel cell stack voltage level (constant ambient relative humidity of 45%) and the corresponding system efficiency were measured by utilising current, voltage, mass flow, temperature and pressure sensors. A fuel cell stack model was presented, which correlates closely with the experimental data (0.861% relative error). The air supply components were modelled utilising a surface fit. Subsequently, the system efficiency of the validated model was optimised by varying the air mass flow and air pressure. It is shown that higher air pressures and lower air excess ratios increase the system efficiency at high loads. The maximum achieved system efficiency is 55.21% at the lowest continuous load point and 43.74% at the highest continuous load point. Future work can utilise the test bench or the validated model for component design studies to further improve the system efficiency.