Rankine Cycle Power Generation Research Articles

Aerodynamic design and optimization analysis of a 200 kW radial-inflow turbine

Abstract In low-temperature waste heat recovery for organic Rankine cycle (ORC) power generation, the radial-inflow turbine (RIT) plays a crucial role. This study focuses on the preliminary design, three-dimensional simulations, and optimization of a 200 kW RIT for R245fa working fluid. The turbine’s preliminary design relies on selected empirical coefficients, leading to performance uncertainty. The performance of the turbine obtained from the initial design was evaluated using computer simulations, indicating that achieving outstanding isentropic efficiency and power targets solely relying on the design of empirical coefficients can sometimes be challenging. Design of Experiments (DOE) on five variables was performed using the Isight platform, highlighting rotor inlet blade height as crucial for turbine performance. The optimized RIT showed a 10.5% efficiency increase and 45.6 kW power gain. Entropy production analysis confirmed substantial improvement. Systematic theoretical calculations followed by DOE optimization effectively enhance turbine efficiency, providing valuable and innovative insights for satisfactory design solutions.

Thermodynamic analysis of a cascade organic Rankine cycle power generation system driven by hybrid geothermal energy and liquefied natural gas

The combination of renewable energy and liquefied natural gas (LNG) cold energy can effectively improve energy utilization efficiency and achieve the goal of energy conservation and emission reduction, which is one of the important directions of future development. This work proposed a cascade organic Rankine cycle (ORC) driven by a geothermal heat source and an LNG heat sink. Seven organic fluids are chosen as candidates to form different working fluid pairs. The effects of the main design parameters on system performance are carried out through the thermodynamic analysis. Then, the optimal design conditions and fluid selection schemes are searched based on the single-objective optimization results. Finally, the exergy destruction study is conducted under the optimal design conditions and working fluid pair. Results showed that the cascade ORC system using the working fluid pair of R601/R290 had the highest exergy efficiency, which could reach 20.02%. At the same time, under the optimal design conditions, the secondary cycle condenser and LNG direct expansion brought high exergy destruction, which was respectively 29.3% and 25.8%, and followed by the two turbines in the cascade ORC system, which were 16.1%, 11.2% and 7.7%.

Integration and Optimization of a Waste Heat Driven Organic Rankine Cycle for Power Generation in Wastewater Treatment Plants

The study focuses on achieving energy self-sufficiency in Wastewater Treatment Plants by proposing a comprehensive model for integrating, sizing, and optimizing an Organic Rankine Cycle system. The Organic Rankine Cycle system is designed to utilize waste heat from the gensets at As Samra Wastewater Treatment Plant in Jordan, where it will contribute to the overall electrical energy supply of the plant. Real data from As Samra Wastewater Treatment Plant is used to model and calculate the available waste heat using TRNSYS® software. The Organic Rankine Cycle model is then developed using ASPEN PLUS® software to explore the impact of operational parameters and determine their optimal values for maximizing the plant's energy profile. An economic analysis is conducted to assess the feasibility of the proposed model, considering system components, installation, operation, and maintenance costs. To optimize the Organic Rankine Cycle system, the study employs the Multi-Output Support Vector Regression technique to capture nonlinear relationships between independent variables (fluid type, turbine inlet pressure, turbine inlet temperature, turbine outlet pressure, and mass flow rate) and dependent variables (pump power input, waste heat input, and turbine specific work). The Osprey optimization algorithm is used to address the multi-objective optimization problem, with the proposed Pareto-based Osprey Optimization Algorithm and the Multi-Objective Particle Swarm Optimization technique being employed to evaluate critical performance and economic parameters such as system thermal efficiency, net power output, and the levelized cost of electricity. The results of the optimization strategies indicate that the M-SVR model's prediction accuracy is significantly improved after parameter optimization, with the model returning high R2 and low Mean Square Error values of 0.991 and 0.00216, respectively. The Pareto-Based Osprey Optimization Algorithm optimizer identifies the best working fluid as Isobutane/Isopentane in a ratio of 66:34, with optimal turbine inlet pressure and temperature of 15 bars and 218 °C, respectively. The Organic Rankine Cycle model at these optimal conditions achieves a cycle efficiency of 19.93 % and an Levelized Cost of Electricity value of 0.0353 USD/kWh.

Investigation of a new holistic energy system for a sustainable airport with green fuels

The advancement of sustainable solutions through renewable and clean energy sources is considered crucial to mitigate carbon emissions. This study reports a novel system developed for an airport utilizing geothermal, biomass, and PV solar energy sources. The proposed system is capable of producing five useful outputs, including electrical power, hot water, hydrogen, kerosene, and space heating. The system proposed in the study is further considered for the Vancouver Airport in British Columbia, Canada using the most recent available data. The geothermal sub-system introduced in this study is also unique, which utilizes the carbon dioxide captured from biomass gassification as the heat transfer medium for geothermal heat to the Rankine cycle for power generation and heating. The present system is modeled and analyzed using thermodynamic method through energetic and exergetic approaches to determine the variation in system performance based on different annual environmental conditions. The biomass gasification and kerosene production are evaluated based on the Aspen Plus models and simulation. The efficiencies of the geothermal system with the carbon dioxide reservoir are found to have energetic and exergetic efficiencies of 78% and 37% respectively. The total hydrogen production is potentially estimated to be 452 tons on an annual basis. The kerosene production mass flow rate is reported as 0.112 kg/s. The overall energetic and exergetic efficiencies of the system are found to be 41.8% and 32.9% respectively. Moreover, this study offers crucial information for the aviation sector to adopt sustainable solutions more effectively.

Review on the development of solar geothermal complementary power generation system

Nowadays, due to the burning of fossil energy has many negative impacts on the environment, people are looking for new sustainable energy sources that can replace fossil energy, and among them, geothermal energy and solar energy are more prominent, but the two energy sources alone have certain shortcomings, and since complementary solar geothermal energy systems compensate for some of the shortcomings of the two energy sources, much research has been done in this field. This essay summarizes the conclusion from those studies and identify the shortcomings. The largest losses in the system are always in the solar power system. The component with the highest losses may be the evaporator or the trough solar collectors with over 50%. In a solar-geothermal complementary power system, the two energy sources promote each other and the system is more efficient in the summer than in the winter. In a solar-geothermal Organic Rankine Cycle power generation system, Supercritical Organic Rankine Cycle can be a better option than subcritical Organic Rankine Cycle for solar geothermal hybrid power production and cost control. And hybrid power plants benefits will increase over time

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

Numerical Investigation of the Influence of Different Suction and Discharge Ports on Scroll Expander Performance

Background: With the rapid consumption of non-renewable energy such as coal, oil and natural gas, the growing demand for environmental protection, the re-utilization of low-grade waste heat energy has become an important approach to improve energy utilization efficiency. As a new technology, organic Rankine cycle (ORC) power generation technology can make full use of and convert heat waste. Objective: Both the suction and discharge pressures of the scroll expander have a certain influence on the output and motion characteristics of the orbiting scroll. By studying the position and arrangement of the suction and discharge ports of the expander, a theoretical basis can be provided for the design of these ports. Methods: For the scroll expander using working fluid R134a, establishing the geometrical and three-dimensional models of the suction and discharge ports of the scroll expander with different positions and structures, based on the Computational Fluid Dynamics (CFD) method. Results/Discussion: Through comprehensive comparison, it was found that the structure of the original suction pipe outperformed any of the other structures; the fluid flow in the original discharge pipe was more complicated, and the simplified model of the commonly used scroll mechanical discharge pipe had the optimal performance. Conclusion: Compared with the original prototype SEI2, the suction port area is increased, and the suction port pulsation intensity coefficient and the suction pressure loss coefficient of the prototype SEI4 are reduced by 34.833% and 5.264% respectively, which can make the suction process of the expander more stable. Since the unilateral discharge ports Outlet3 and Outlet5 are located in the moving and static regions, respectively, there is a difference in the perturbation of the outlet fluid by the movable scroll, so that the gas pulsation intensity at Outlet3 is nearly double that of Outlet5.

Design and multi-objective optimization of combined air separation and ORC system for harnessing LNG cold energy considering variable regasification rates

Regasification of liquefied natural gas (LNG) releases significant cooling potential, but improper usage can easily lead to wastage of resources and environmental pollution. The study developed an integrated air separation system and Organic Rankine Cycle (ORC) power generation system to effectively harness the inherent cold energy within LNG. Two distinct optimization algorithms, the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) and the Particle Swarm Optimization (PSO), were employed to determine the optimal operational parameters. The results showed the superior performance of PSO over NSGA-II, as demonstrated by the exergy efficiency, net output power, and levelized cost of energy at 78.12 %, 2.29*1011 kW, and 0.0665 $/kWh, respectively. Additionally, an assessment of various factors influencing the system's performance was conducted. The performance of both conventional and proposed systems was studied under varying regasification rates. The findings indicated that incorporating the cold recovery and storage unit enhanced the efficient utilization of LNG cold energy, resulting in an increased valley-to-peak ratio of the total power output from 0.03 in the conventional system to 0.5. The proposed system exhibits alignment with the energy consumption demands of users, and this study is anticipated to furnish a theoretical foundation for harnessing the cooling capacity of liquid hydrogen.

Thermal performance study of a solar-coupled phase changes thermal energy storage system for ORC power generation

The current solar organic Rankine cycle power generation (ORC) system cannot run smoothly under the design conditions due to the shortcomings of solar fluctuations, and thermal energy storage (TES) can effectively buffer the fluctuations of solar energy. Cascaded heat storage (CLTES) has been shown to be more suitable for solar heat storage than single-stage heat storage (LTES). The main objective of this study is to analyze the thermal storage characteristics of thermal storage systems under real-time solar energy fluctuations, and to improve the thermal storage efficiency and total thermal storage capacity of solar phase change thermal storage systems in distributed scenarios. The current research on solar CLTES system needs to focus on the heat storage characteristics under the actual solar fluctuations to provide guidance for the design and practical operation of CLTES system. Analyzing the effect of solar fluctuations on thermal storage performance is the focus of solar thermal storage research, which can provide guidance for the design and actual operation of CLTES systems. However, the current research on solar CLTES system lacks the analysis of thermal storage characteristics under typical solar energy fluctuations. Therefore, a simplified two-dimensional enthalpy-dynamic model of heat transfer for shell-and-tube latent heat storage system is developed in this paper to simulate the heat storage characteristics of single-stage and cascade heat accumulators containing different phase change materials (PCMs) at a fixed temperature of the heat source, and the heat storage performance of the system is simulated based on the solar fluctuations of typical four seasons. Finally, based on the shortcomings of large-capacity thermal storage, a dual-tank recirculation thermal storage model is proposed and the thermal storage characteristics of the improved recirculation model are analyzed. The results show that the optimized cycle heat storage mode can bring about a minimum of 10 % and a maximum of 17.2 % thermal efficiency improvement. On a typical summer day with the most abundant solar energy resources, four times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 81.83 %), and on a typical winter day with the least solar energy resources, two times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 75.81 %). The maximum difference of heat storage between them is 45.38 %.

Thermo-economic assessment and multi-objective optimization of organic Rankine cycle driven by solar energy and waste heat

An organic Rankine cycle (ORC) power generation system driven by integrated solar energy and waste heat is proposed based on the concept of multi-energy complementarity. Three types of solar collectors, two different heat source integration schemes and nine different candidate organic fluids are studied and compared. The effects of main operating parameters on thermo-economic performance are analyzed. A multi-objective optimization framework with a competitive mechanism based multi-objective particle swarm optimizer (CMOPSO) as the core is constructed and the system is optimized. The results of the multi-objective optimization guide the design of the multi-heat source ORC and the selection of the working fluid. When the temperature difference between two heat sources is greater than 50 °C, the heat exchangers are recommended to be connected in series for better overall performance. Besides, the series scheme favors the working fluid with a higher critical temperature, whereas the working fluid with a lower critical temperature is appropriate for the parallel scheme.

Impacts of energy-saving and emission-reduction on sustainability of cement production

How energy saving and emission reduction measures influence the interrelationship between carbon emissions and environmental sustainability of cement industry is not very clear, and this could lead to trade-off. This study investigates effects of three representative energy saving and emission reduction measures (steam Rankine cycle power generation (SRC), organic Rankine cycle power generation (ORC) and carbon capture and utilization (CCU)) on environmental performance of cement production using an improved emergy analysis and carbon emissions amounting. The proposed approach can investigate resource efficiency and emissions' impact as well as carbon footprint of a system in study simultaneously. A cement enterprise, in Jilin Province in China, as a case, is explored using the proposed combined approach based on scenario analysis. The results illustrate that combination of SRC + ORC can promote environmental sustainability of cement production and carbon emission reduction by 4.61 % and 4.28 % respectively, mainly derived from SRC application (by 4.06 % and 3.81 %), (2) CCU can promote carbon emission reduction by 3.97 % but weaken the environmental sustainability by 2.10 % due to enhancing share of purchased nonrenewable electricity, and (3) combination of SRC + ORC + CCU can promote the environmental sustainability (by 2.43 %) and carbon emission reduction by 8.25 %. In addition, due to strong dependence on nonrenewable resources, combination of SRC + ORC + CCU is still limited in improvement of environmental performance of the industry. In the future, China's cement industry should further enhance environmental performance of CCU and efficiency of ORC, as well as improve the resource structure of this industry.

Thermodynamic and thermo-economic analysis, performance comparison and parameter optimization of basic and regenerative organic Rankine cycles for waste heat recovery

In order to recycle the sinter waste heat efficiently, the possibility of taking the low temperature flue gas emitted from sinter waste heat boiler as heat source of organic Rankine cycle for power generation is investigated in the current study. The thermodynamic and thermo-economic models of basic organic Rankine cycle (BORC) and regenerative organic Rankine cycle (RORC) were constructed, and R236ea, R245fa and R601a were selected as the working fluids of BORC and RORC. Subsequently, the parametric effects on the thermodynamic and thermo-economic performances under various working fluids for BORC and RORC were analyzed and compared, and then the suitable thermal parameters of BORC and RORC were established through the multi-objective optimization. The results show that, the thermal efficiency of RORC is apparently greater than that of BORC for the given thermal parameters, while the levelized energy cost of RORC is a little bigger than that of BORC. The net output power of R236ea is the largest in the whole optimal conditions, and the flue gas waste heat recovery rate of R236ea for BORC is also the largest at a respectable 65.07 %, while the levelized energy cost of R601a is the smallest for BORC and RORC, showing better thermo-economic performance.

A Novel Cascade Utilization System of Liquid Hydrogen Cold Energy: Energy, Exergy, and Economic Analysis

In order to effectively improve the cold energy recovery efficiency and thermodynamic performance of liquid hydrogen regasification process, a novel type of liquid hydrogen cold energy cascade utilization (RC-HT-AS-DI-CS-AC) system is proposed, which includes Rankine cycle power generation (RC), hydrogen turbine power generation (HT), air separation (AS), production of dry ice (DI), cold storage (CS) and air conditioning (AC). A comprehensive energy, exergy and economic analysis is carried out to compare the proposed system with a comparison system scheme (CSS). For RC-HT-AS-DI-CS-AC system, the energy efficiency of overall system is 79.74%. The cold energy provided by the hydrogen stream achieve 182.31 kW, which is 61.18% increase compared with the CSS. The acquired exergy and exergy efficiency of the RC-HT-AS-DI-CS-AC system increase by 119.6% and 115.9% compared with the CSS. It reveals the importance of liquid hydrogen pressurization to improve exergy efficiency for overall system. However, in the economic analysis, the total annual cost (TAC) of the system of RC-HT-AS-DI-CS-AC system is 278,400 US $, which is significantly higher than TAC of CSS. As a result, the IRR of CSS and RC-HT-AS-DI-CS-AC systems are 87.39% and 15.10% respectively. Therefore, from a commercial point of view, CSS is more worthy of industrialization.

Potential development of organic Rankine cycle (ORC) power generation system by utilizing heat from natural hot-spring in Malaysia

Organic Rankine Cycle (ORC) is widely used because of its ability to work with low and medium-grade heat resources. ORC basically operate by using organic working fluid which allows the application of Rankine Cycle to be operate at various range of heat resources depend on the properties of working fluid. This allows wide application of ORC power cycle at temperature below 370 °C where the steam-based Rankine Cycle are no longer efficient. This present paper discusses the potential development of micro power generation based on the ORC concept by utilizing heat from natural hot spring in Malaysia. The performance of the systems is analysed based on three different working fluids which are R134a, R410a and R245-fa. The comparison was done by the variation of hot water inlet temperatures in the range of 50 °C to 75 °C at the evaporator and 25 °C of ambient water at the condenser. The results indicates that R245-fa had 9 % thermal efficiency when the hot water inlet temperature is 75 °C which is the highest among the other working fluids in the similar condition. Meanwhile, the ideal power output of turbine is also analysed. The R410 can generate 2.38 kW power output when the input temperature of hot water is 75 °C which is the highest as compared to other working fluid at similar condition. Therefore, it can conclude that the micro-scale power generation systems can be developed based on ORC power cycle by utilizing heat resources by natural hot spring in Malaysia.

Evaluation of Multi-Utility Models with Municipal Solid Waste Combustion as the Primary Source under Specific Geographical and Operating Conditions

Developments in waste incineration technology in terms of efficient fuel preparation, combustion, and emissions reduction, as well as the growing needs of the community in terms of electricity, water, and air conditioning loads, are the prime motive for this study. This study presents a novel approach, in which three models of the fluidized bed combustion of municipal waste for simultaneous power generation, freshwater production, and district cooling are analyzed for their energy and exergy performance. The three simultaneously evaluated utility models are different configurations of a fluidized bed combustion system with Rankine cycle power generation, cooling with a vapor absorption refrigeration system, and fresh water production using multiple effect desalination. The output from the turbine, cooling system, and desalination system is determined using the Engineering Equations Solver for different boiler operating pressures. Energy and exergy analysis data for different pressures are used to identify the best configuration. Two variants of the absorption cooling system, namely, single effect and double effect, are considered. The variants of the multiple-effect desalination are the three-stage and five-stage methods. Input parameters used in this study are municipal solid waste generation and composition data collected for an urban community in an arid climate zone with high demand for electric power, cooling, and fresh water. Model 2, which contains two turbines with the reheating and cooling systems connected to a high-pressure turbine and water desalination connected to a low-pressure turbine, gave the best overall performance. Significant savings in terms of the replacement of conventional energy were observed from these waste conversion plants with greater benefits in arid weather conditions. The results obtained by different models under different operating criteria constitute a guideline for municipal planners for the selection of appropriate waste utilization technology, as well as the appropriate operations.

Enhancing geothermal ORC power generation with SOFC: A comprehensive parametric study on thermodynamic performance

Geothermal energy is a promising renewable energy source due to its abundant global reserves. However, most geothermal resources are of low grade, severely restricting their power generation capacity and efficiency. In this study, the geothermal organic Rankine cycle power generation system is combined with a solid oxide fuel cell-gas turbine system to improve the overall power supply and heat utilization efficiency. The heat source and cycle temperature are upgraded using high-temperature solid oxide fuel cell waste gas, and the combined system’s efficiency is further improved through cascade heat utilization. Electrochemical-thermodynamic models are developed for the proposed system, and energy-exergy analysis is carried out. The effects of fuel cell current density, operating temperature and geothermal grade on the combined system’s performance are comprehensively analyzed. Compared to the standalone geothermal system, the energy efficiency and output power of the organic Rankine cycle increase by 8.11% and 7.95% respectively in the baseline case. Under the lowest geothermal temperature condition, the cycle output power is improved by 22.64%. The net power of the combined system can vary from 358 kW to 846 kW by adjusting the fuel cell current density from 1000 A m−2 to 8000 A m−2, demonstrating a flexible power supply capability. The optimal solid oxide fuel cell operating temperature is 1023.15 K, resulting in the highest system overall energy efficiency of 14.85%. The presented work provides essential guidelines for improving geothermal power generation performance and designing applicable combined systems.

A CFD-based study of twin-screw expander performance and inlet structure optimization

Twin-screw expanders are widely used for small to medium-sized organic Rankine cycle (ORC) power generation. In order to improve the performance of twin-screw expanders in ORC, this study aims to improve the inlet efficiency and reduce the inlet pressure loss by changing the geometry of the inlet and shell. The CFD transient simulation is used to study the pressure, gas flow conditions and other parameters in the working chamber that are not easily obtained through experiments. The effects of improved size, speed, pressure ratio and internal volume ratio on the performance of the expander are analyzed based on the results. The results show that for the three expanders with different internal volume ratios, the optimized expander power and filling factor increases by 2%-14%. Isentropic efficiency of the expander reaches a maximum value of 0.73 when the pressure ratio is slightly greater than the internal volume ratio.

Utilizing CO2 from refinery for methanol and electricity coproduction: System assessment

As one of the major energy-consuming and high-emission industries, the refineries account for 10% of global industrial carbon emissions, of which about 25% is emitted by fluid catalytic cracking (FCC) process. Therefore, CO2 capture from FCC flue gas create the possibility for low-carbon refineries. We developed a novel CO2 utilization process to methanol production modeling using Aspen Plus. Meanwhile, organic Rankine Cycle (ORC) power generation technology was coupled to recover the waste heat of the system. A five-million-ton FCC unit in China was selected as a case study. We conducted some analysis for the process, the results show that the developed system boosts the energy efficiency of the FCC unit by 2.8%. The annual capacity of the waste heat power generation unit is 4.8 GWh, with a thermal efficiency of 5.9%.

Techno-economic optimization of a biomass gasification energy system with Supercritical CO2 cycle for hydrogen fuel and electricity production

Biomass is considered a carbon–neutral fuel and can play a significant role in obtaining sustainable energy generation. This study aims to raise the exergy efficiency and reduce costs in a novel energy system that is employed to generate power, heating, cooling, fresh water, and hydrogen fuel. Based on this, municipal solid waste (MSW), wood, and paper are considered as biomass fuels of the examined system and the system performance is evaluated from a thermodynamic and thermo-economic point of view through a parametric study. In the considered system, the generated gas in the gasifier supplies the energy required to run an externally fired gas turbine module. The waste heat of the gas turbine cycle is used to run a supercritical CO2 (S-CO2) power generation cycle coupled with a heat exchanger to supply hot water and run an organic Rankine cycle (ORC) power generation cycle, as well as an absorption chiller cycle equipped with an ejector to produce cooling. In addition, the waste heat of the ORC is employed to produce fresh water through a humidification-dehumidification (HDH) desalination unit, a part of which is used to supply a proton exchange membrane electrolyzer (PEME) and the remaining is for other purposes. By considering the exergy efficiency and the levelized cost of energy (LCOE) as objective functions, a multi-objective optimization based on the genetic algorithm has been applied. An artificial neural network (ANN) plays an intermediating role in the optimization process to reduce the calculation time and raise the optimization speed. The relationship between the objective function and decision variables was analyzed using the ANN to determine the optimal point in this energy system. The results show that under optimal operating conditions, the exergy efficiency of the system with the biomass fuels of MSW, wood, and paper is equal to 41.21 %, 40.25 %, and 39.33 %, respectively. The LCOE values ​​under the same conditions are 30.77 $/MWh, 32.06 $/MWh, and 33.6 $/MWh, respectively. Furthermore, at the optimum point, the amount of fresh water and hydrogen production in the system with the biomass fuels of MSW, wood, and paper is equal to 1.128 kg⁄s, 1.058 kg⁄s, 0.991 kg⁄s, and 9.355 g/s, 9.038 g⁄s and 8.438 g⁄s, respectively. Overall, the proposed system with the biomass fuel of MSW has shown good performance in terms of thermodynamics and cost-effectiveness.

A feasibility study of using the organic Rankine cycle for power generation from the flue gases of recovery boilers

ABSTRACT: Almost 415 tons/h of flue gases with a temperature of 160°C are released to the atmosphere from the recovery boiler of a pulp mill with capacity of 1000 air dried (a.d.) metric tons of pulp per day. This is a large waste heat stream that can be used to generate power, to decrease the operating costs of a pulp mill, and to save carbon dioxide (CO2) emissions. In this work, the feasibility of using an organic Rankine cycle (ORC) with ammonia as the working fluid to generate power from the flue gases of recovery boilers is studied. CHEMCAD and Taguchi methods are used for simulation of the process and for optimization of operating conditions, respectively. The temperature of the ammonia and flue gases at the exit of evaporator, exit pressure of the pump and turbine, and the degree of subcooling of ammonia at the exit of the condenser are five operating parameters that are manipulated to optimize the process. Three different scenarios are defined: minimizing the net power cost, maximizing the ORC efficiency, and maximizing the net profit. Different aspects of these scenarios, such as net power generation, cost, efficiency, and CO2 emission savings are discussed, and optimum operating conditions are reported.