ORC Unit Research Articles

Analysis and Optimization of Operating Modes of Mini-CHP on Local Fuels in Conditions of Surplus Electric Power Capacities in the Unified Energy System of Belarus. Part 1

The paper presents the results of a study to determine the rational structure of mini-CHP (Cogeneration Heat and Power Plant) using local fuels types (LFT) for operation as part of the United Energy System (UES) of Belarus with a surplus of electricity generating capacity and dominance of imported types of energy resources (natural gas and nuclear fuel) in the fuel balance. When optimizing the operating modes of mini-CHPs using LFT and operating in parallel with the UES, which has a significant surplus of electricity generating capacity, it is necessary to separate options for existing stations and options for newly built ones. In the first case, due to the fact that the power of the equipment is known, it is advisable to consider two extreme options, i.e., the operation of the heating unit according to an electrical or thermal load schedule. In this case, in order to maintain the daily consumption traffic it is necessary to provide for the accumulation of thermal or electrical energy, respectively. In the case of new construction, the optimized parameter is the power of the generating equipment, so it is advisable to give preference to the option with the maximum number of hours of use of the rated power. In order to increase the economic attractiveness of mini-CHP, options for developing the structure of mini-CHP using LFT with the transition to multi-generation technologies and adaptation to the existing operating conditions of the UES of Belarus have been considered. The results of an analysis of commercially available technologies for storing excess electrical energy are presented in accordance with current and projected (until 2030) cost and operational indicators. For adapting mini-CHP to operate in the UES in conditions of a surplus of electrical power capacity, an electrical energy storage system using hydrogen as an intermediate energy carrier is of greatest interest. To utilize the excess electrical energy consumption from a mini-CHP with a heating ORC unit during the daily dips, a structural diagram configuration using an alkaline electrolysis module for hydrogen production is proposed. The efficiency of energy storage and use technology is considered depending on the specific energy intensity for various electrical energy storage technologies. The use of the two most energy-intensive energy storage technologies is proposed: accumulation based on electrochemical batte-ries and the “electricity-hydrogen” type. During the study, an analysis of the functioning of the ORC-installation Turboden 14 CHP ORC-installation operating as part of a mini-CHP using LFT was carried out. It was revealed that today the installation operates in a wide range of load changes (from 17 to 87 % of the rated electrical power), while the generation of electrical energy from thermal consumption varied in the range from 0.20 to 0.026 MW/MW. Due to the fact that the ORC installation under study is a component of the energy source with a high installed peak thermal power, in the current state there is no direct correlation between the outside air temperature and the generation power of the ORC installation. This circumstance indicates the need to continue the study of heat load trends to build functional models for short- and medium-term forecasting of heat load depending on the time of day and average hourly outside air temperature, which was implemented in the second part of the work.

Combined Supercritical CO2 Brayton Cycle and Organic Rankine Cycle for Exhaust Heat Recovery

Abstract In order to reduce energy consumption and related CO2 emissions, waste heat recovery is considered a viable opportunity in several economic sectors, with a focus on industry and transportation. Among different proposed technologies, thermodynamic cycles using suitable organic working fluids seem to be promising options, and the possibility of combining two different cycles improves the final recovered energy. In this paper, a combination of Brayton and Rankine cycles is proposed: the upper cycle has supercritical carbon dioxide (sCO2) as its working fluid, while the bottomed Rankine section is realized by an organic fluid (organic Rankine cycle (ORC)). This combined unit is applied to recover the exhaust energy from the flue gases of an internal combustion engine (ICE) for the transportation sector. The sCO2 Brayton cycle is directly facing the exhaust gases, and it should dispose of a certain amount of energy at lower pressure, which can be further recovered by the ORC unit. A specific mathematical model has been developed, which uses experimental engine data to estimate a realistic final recoverable energy. The model is able to evaluate the performance of each recovery subsection, highlighting interactions and possible trade-offs between them. Hence, the combined system can be optimized from a global point of view, identifying the most influential operating parameters and also considering a regeneration stage in the ORC unit.

A newly application of Organic Rankine Cycle for building energy management with cooling heating power hydrogen liquefaction generation- South Korea

This research revolves around the modeling and optimization of an innovative geothermal system powered by geothermal energy. The system incorporates a modified Organic Rankine Cycle to efficiently produce electricity, hydrogen, cooling, and heating. The study is specifically tailored for South Korea, with a focus on the city of Ulsan. The primary objective of this geothermal system is to generate essential products for residential buildings without contributing to carbon emissions or environmental pollution. The modeling aspect of this research is conducted using EES software, while optimization efforts are aimed at enhancing performance by optimizing the exergy efficiency and reducing costs. The response surface method (RSM) and Design Expert optimization software are employed for this purpose. The optimal results demonstrate that, in its most efficient state, the system can achieve an impressive exergy efficiency of 45.382 % and operate at a cost rate of 50.414 $/h. The economic analysis underscores that the modified ORC unit bears the highest system cost, amounting to 49.47 $/h. The findings reveal that the suggested geothermal system performs exceptionally well in cities with weather conditions akin to Ulsan. In other regions across the globe, it has the potential to significantly enhance cost-effectiveness and exergy efficiency. The research concludes by evaluating the system's capacity to provide electricity, heating, and cooling for residential complexes within the study areas, highlighting its potential for addressing diverse energy needs in urban settings while prioritizing sustainability and environmental responsibility. The results showed that the study system can produce 3,982,413.6 kWh of heating, and 4,555,440 kWh of cooling during the year. The environmental results showed that by producing 4088.72 MWh of electricity annually in the city of Ulsan, South Korea, it is possible to help the expansion of 4 hectares of green space per year. Also, by reducing carbon dioxide emission by 834.09 tons of CO2, the proposed system avoids the cost of 20,018.3 $ on the environment. The proposed geothermal system can supply the electrical needs of 401 people in Ulsan city during the year.

Theoretical and experimental analysis of the impact of a recuperative stage on the performance of an ORC-based solar microcogeneration unit

Microgeneration ORC-based units driven by solar energy, which enable combined heat and power generation (CHP), are a promising solution for decarbonizing the domestic sector. However, the intermittent availability of solar energy, coupled with the variability in user demand for domestic hot water (DHW), can lead the system to frequent off-design conditions and a less reliable energy supply. Consequently, increasing attention has recently been focused on the technological and design solutions for improving plant performance and ensuring its continuous operation. This paper presents the results of an experimental campaign carried out to investigate the possible advantages – in terms of efficiency and savings of thermal energy in the upper source – of introducing a recovery heat exchanger (RHX) in the basic configuration of a solar ORC-based system. Tests were conducted on a fully instrumented ORC-based plant with two 12 kW electric heaters providing the thermal power recovered through the solar collectors. The RHX is introduced into a recuperative branch that can be bypassed by closing a dedicated three-way valve. The study aims to investigate the behavior of the ORC unit in the absence of solar radiation (with the electric heaters switched off) when the recovery unit is powered only by the hot water stored in the Thermal Energy Storage (TES) tank. Another purpose of the present work is to evaluate the benefits introduced by the RHX in reducing the temperature decrease of the TES hot water and, consequently, maximizing the operating time of the ORC-based unit. In order to support the experimental analysis, a comprehensive theoretical model of the unit was developed and validated against experimental data. The model was used as a software platform to optimize the plant design and recuperative branch configuration. The theoretical model was developed in the GT-Suite™ environment thus integrating a mono and zero-thermo-fluid-dynamic approach. In this way, a physical representation of the entire ORC-based unit is performed allowing also to define an optimal control strategy for maximizing plant performance under severe off-design and transient conditions.

Thermodynamic analysis of a hybrid energy system coupling solar organic Rankine cycle and ground source heat pump: Exploring heat cascade utilization

The demand for efficient utilization of renewable energy is growing and the hybrid energy system driven by solar and geothermal energy is a significant way to achieve carbon neutrality. This paper presents a hybrid energy system coupling solar organic Rankine cycle (S-ORC) with ground source heat pump (GSHP) for heating and power supply to explore the heat cascade utilization. In the hybrid energy system, the ground heat exchanger (GHE) is shared by the S-ORC and GSHP systems and the waste heat from the condenser of S-ORC is recovered to enhance the coefficient of performance (COP) of GSHP. A mathematical model is optimized to analyze the parametric effects on thermodynamic performance. The results indicate that the COP of the hybrid energy system can be improved up to 6.5 which shows the obvious advantage compared to 2.8 of the stand-alone GSHP system. Furthermore, the hybrid energy system can obtain optimum exergy efficiency by matching ground source temperature and condensation temperature in the ORC unit. For a building of 3000 m2 with heating and power supply, multi-objective optimization is carried out to obtain the optimal design performance that the net power output, thermal efficiency and exergy efficiency are 180.0 kW, 27.5%, and 9.2% respectively.

Comparative study on operating strategies of the organic Rankine cycle under transient heat source

An effective operating strategy is crucial to the adaptive operation of the ORC unit driven by the transient heat source. The dynamic model of a small-scale ORC prototype is established and validated by the tested data in this study. Three operating strategies are proposed and compared: the constant vapor superheat operation, constant evaporation temperature operation, and optimal evaporation temperature operation. It is found that PI controllers can satisfy the control of the ORC system with evaporation temperature controlled at ±1 °C and vapor superheat at ± 3 °C. The expander output power varies more significantly than the system thermal and exergy efficiencies under heat source fluctuation. The constant evaporation operation is sensitive to the transient heat source and is only recommended for the expander with a strict constraint on vapor temperature and pressure. The optimal evaporation temperature operation is recommended as it has the highest system performance and enables the ORC unit to be adaptive to the transient heat source. The constant vapor superheat mode can achieve close-to-optimal performance by carefully setting the rotating speed of the expander. Thus, it can also be preferred considering its performance, simplicity, and the unique advantage of power supply with a stable frequency.

Assessment of thermodynamic performance of a novelty solar-ORC configuration based hydrogen production: An experimental study

In this study, a solar-Organic Rankine Cycle (ORC) assisted hydrogen production system was experimentally investigated. An evacuated tube heat pipe solar collector (ETHPSC) was used for thermal energy generation. The tubes used in this study were produced differently from the tubes of the conventional heat pipe. The condenser area of the vacuum tubes used was made of glass instead of copper. Moreover, acetone was used as the fluid in the tube. The thermal energy obtained from the collector was used as a heat source for electrical energy in the ORC system. A uniquely designed ORC system is modeled and manufactured. The electrical energy obtained from the ORC unit was used for hydrogen production by means of the proton exchange membrane electrolyzer (PEMe). As a result of the study, two different efficiency analyses were made. If all of the electricity produced in the S-1 scenario was spend on hydrogen production, the energy and exergy efficiency were calculated as 3.45% and 2.15%, respectively. In the S-2 scenario, if some of the electricity produced was spend on hydrogen production, the energy and exergy efficiency of the whole system were found to be 0.01446% and 0.002146% respectively. In addition, 0.000004433 kg/s hydrogen production was obtained from the presented system.

Theoretical study of a downdraft gasifier, microturbine, and organic Rankine cycle fuelled by date molasses waste for distributed generation applications in Iraq

AbstractThe main objective of this work is the modeling of a combined heat and power (CHP) system that transforms waste from manufacturing date molasses in the Babylon province in central Iraq into electrical and thermal energy. A compact CHP facility that uses date waste (pomace and pits) as a feedstock is the subject of theoretical modeling and simulation research. The planned power plant consists of a downdraft gasifier, a microturbine (MT), and an organic Rankine cycle engine (ORC) as a bottom unit to maximize electric generation by recovering the MT exhaust gas heat and achieving a maximum electric output. The net electric production is 361.68 kW (280 kW from the MT unit and 81.68 kW from the ORC unit). To determine the best‐working fluid for the ORC system as a whole, three working fluids, including isopentane, benzene, and R113, were investigated. The temperature difference between the heat source and the fluid's boiling point is a key factor in choosing a more appropriate ORC working fluid. Isopentane is the most suitable working fluid for CHP applications, according to the findings of the simulation. The electric efficiency achieved is 30%, and the overall efficiency of the CHP plant was 56.87% from the gasification of date pits. The simulation results showed a satisfactory producer gas lower calorific value of 3.92 MJ k‐g‐1 for date pomace and 4.65 MJ k‐g‐1 for date pits, and cold gasification efficiencies of 73% and 76% for pomace and pits, respectively. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Techno-economic evaluation of an organic rankine cycle-based multi-source energy system for 100%-renewable power supply: A rural case study

In remote areas, providing electricity through grid-connected energy systems or transferring fossil fuels would be economically infeasible. A stand-alone hybrid renewable energy system is considered as an effective solution to supply electricity to remote areas' populations. In this study, the techno-economic feasibility of a solar-driven ORC/Photovoltaic/Wind Turbine/Battery system is investigated to electrify a 927-household remote village. To this end, first, the annual performance of a solar-driven ORC unit including parabolic trough collectors, an ORC, and a heat storage bank is optimized by MATLAB software. Based on the results of Genetic Algorithm optimization process, the yearly average efficiency of this unit reaches more than 15.06%, 22.64%, and 30.23% at the collector areas of 1000m2, 1500m2 and 2000m2, respectively. Then, the annual generated power output of the solar-driven ORC unit is imported into the HOMER algorithm to find the most appropriate hybrid renewable solution according to the geographical and financial characteristics of the remote village. The optimum configuration comprises the ORC/PV/WT/Battery when the collector area is 1000 m2; the energy cost is obtained as low as 0.275 $/kWh. The proposed system also shows compatibility with the environment since it prevents more than 1000 ton/year of CO2 emissions compared to the Iranian power grid.

Scaling up a woodchip-fired containerized CHP ORC unit toward commercialization

Microcogeneration utilizing organic Rankine cycle technology has seen challenges in commercialization, despite its vast application potential. The market is large, but so is the competition from standard boilers. This was also the case for a previously developed biomass-fired 50 kWth 2 kWe unit intended for large buildings and small industries. Therefore, a scaled-up 120 kWth and 6.2 kWe unit has been proposed with better commercialization prospects.This paper discusses the process of scaling up, designing, assembling and operation of this system. It includes innovative modifications of previously applied technologies regarding the boiler, expander and the overall system configuration. Both units utilize a rotary vane expander as a specific feature of the design. A comparison with the previous smaller unit is performed on several thousand hours of experimental data. The larger unit reaches higher net combined heat and power production efficiency, reaching 89.3%, even though the expander nominal isentropic efficiency slightly drops to 56%. Economic considerations and market feasibility are discussed with respect to the scaling-up from the laboratory scale unit towards commercialization. Thanks to the simplification of the unit, regardless of the scale-up, the absolute cost remains nearly the same for both units.

Assessment of the differential impact of scroll and sliding vane rotary expander permeability on the energy performance of a small-scale solar-ORC unit

Organic Rankine Cycle ORC-based power unit is a suitable solution for combined heat and power (CHP) generation in the residential sector currently responsible for an average 28 % energy-related CO2 emissions. The ability to tolerate seasonal daily and hourly fluctuations of the available thermal energy without significant performance compromission – i.e. efficiency of electricity generation and domestic hot water (DHW) fulfillment – is crucial. The need for the plant to work under severe off-design conditions affects the expander selection which for such plants are generally of volumetric technology. The most up-to-date literature addresses scroll-type and sliding vane rotary (SVRE) expanders as the most effective options. For such reason the present paper deals with the experimental assessment of the energy performance of an ORC-based plant equipped with both a custom-design SVRE and a scroll expander. The ORC unit assumes the same plant configuration in the two cases except for the expander layout. SVRE is connected through a mechanical joint to the electric generator whereas the scroll expander shares the same shaft and casing with the electric machine. The former approach ensures to control the expander speed which is set by the dynamic equilibrium in the latter case. The comparative analysis provides useful insights on the relative advantage of both technologies and configuration and a clear indication on the different operating strategy required in each case. SVRE leads to an electric output of the power unit in the 200–700 W range with a 2–6% efficiency whilst scroll expander is associated with a 100–500 W power range and a 2–4% efficiency partly compensated with a shorter starting time and a larger operability range (17–60 g/s). Despite SVRE is regulated in revolution speed its efficiency (20–40 %) is lower than the scroll one (40–60 %). The experimental assessment of the power unit was coupled with an in-depth modeling activity to address the impact of the expander operating conditions mainly on the inlet expander pressure which is close to the upper pressure of the thermodynamic cycle. The model derived from a theoretical analysis of the expander permeability focuses on the effect of the expander revolution speed – variable in the SVRE case constrained in the scroll case – and provides good accuracy with a Root Mean Square Error below 4 % in both cases.

Energy and Exergy-Based Screening of Various Refrigerants, Hydrocarbons and Siloxanes for the Optimization of Biomass Boiler–Organic Rankine Cycle (BB–ORC) Heat and Power Cogeneration Plants

The cogeneration of power and heat was investigated for Biomass Boiler–Organic Rankine Cycle (BB–ORC) plants with the characteristics of typical units, such as the 1 MWel Turboden ORC 10 CHP. The thermodynamic analysis of the ORC unit was undertaken considering forty-two (42) dry and isentropic candidate pure working fluids. Only subcritical Rankine cycles were considered, and the pinch point temperature differences for the evaporation and condensation heat exchangers were kept constant at 10 °C in all cases. The study provides an original and unique screening of almost all pure working fluids that are considered appropriate in the literature under the same operation and optimization conditions and compiles them into a single reference. In its conclusions, the study provides useful fluid selection and design guidelines, which may be easily followed depending on the optimization objective of the ORC designer or operator. In general, hydrocarbons are found to lie in the optimum middle range of the fluid spectrum, between the siloxanes that maximize the production of mechanical power and the refrigerants that maximize the production of heat. Specific hydrocarbon fluids, such as cyclopentane, heptane, hexane, benzene, and toluene, are found as rational options for maximum mechanical efficiency when operating with practically feasible condensation pressures between 10 and 200 kPa. At condensation pressures below 10 kPa, ethylbenzene, o-xylene, m-xylene, p-xylene, and nonane are also found to be feasible options. Finally, cyclopentane, hexane, and MM (hexamethyldisiloxane) are selected as the most appropriate options for cogeneration plants aiming simultaneously at high mechanical power and maximum temperature water production.

Dynamic Modeling and Comparison Study of Control Strategies of a Small-Scale Organic Rankine Cycle

The control strategy is crucial for the effective and safe operation of the ORC system. A transient model of the ORC system was developed in the present work and validated by the experimental data of a 4 kW ORC prototype. Then, the effect of heat source temperature on the dynamic response and operation characteristics of the ORC system were analyzed. Five control strategies were compared: the constant working fluid mass flow rate mode, constant vapor superheat mode, constant vapor temperature mode, constant evaporation pressure mode and constant output power load mode. Under the constraint that the working fluid at the expander inlet should be superheated, we found that the constant vapor superheat mode enabled the safe operation with the largest range of heat source temperature, while the other four modes were only available for a certain temperature range. Apart from the constant output power mode, the constant evaporation pressure mode can also provide a relatively stable performance for the ORC unit. The variation of the thermal efficiency was limited when the heat source temperature was higher than 125 °C, except for the constant vapor temperature mode. Considering the high performance and stable operation of the ORC system, it is necessary to have different operation modes combined in the control strategy according to the specific working scenarios.

High-efficient and carbon-free biomass power generation hybrid system consisting of chemical looping air separation and semi-closed supercritical CO2 cycle with a bottoming organic Rankine cycle

Herein, a novel biomass power generation system, comprising of CO2-assisted gasification unit, chemical looping air separation (CLAS) unit, semi-closed supercritical CO2 (sCO2) cycle with the bottoming ORC unit, was proposed to overcome the problems of low-efficiency and high-pollution rendered by traditional biomass utilization method. And the heat integration between those subunits was well designed based on the principle of energy cascade utilization. The sensitive analysis was carried out to clarify the reasons behind thermodynamic performance variation, and the optimized net power efficiency reached 38.76% when the CO2/C ratio was 0.25, gasification temperature was 830 °C, sCO2 turbine inlet temperature and pressure were 1200 °C and 300 bar respectively, which was superior to 28.01% of biomass integrated gasification combined cycle system. In addition, the exergy analysis found that modification efforts should be exerted on CLAS and sCO2 compression pump, whose exergy destruction were 7.58 MW and 5.15 MW, respectively. Besides, its environmental and economic merits were obvious with the CO2 specific emission at 0.31 kg/MWh, and the levelized cost of electricity at 57.38 $/MWh. Furthermore, three typical biomasses were examined for the proposed system, the results showed that the dryer and carbon-richer biomass could benefit system thermodynamic and economic performance.

Influence study of bottom cycle ratios and superheat for vessels waste heat cascade recovery based on TEG-ORC combined cycle system employing R245fa

ABSTRACT The vessel’s waste heat has the characteristics of a large temperature gradient, huge recoverable volumes, and various properties. TEG-ORC combined cycle is a promising method for multiple vessels waste heat cascade utilization. Keeping the evaporation pressure at 0.7Mpa, R245fa of low toxicity and environmental friendly is employed for the research under the conditions of different bottom cycle ratios(₣) and superheating. The interaction between essential parameters and system performance is explored. As the ₣ gets larger, the system net power output (W net ), the system thermal efficiency (η s ) and the waste heat utilization of main engine flue gas (f g ) gradually increase, the power-production cost (C g ) of the system gradually decreases. When the degree of superheat increases from 3.36K to 9.23K, the output power of the expander increases synchronously. The results show that superheating improves the combined cycle W net and f g while reducing theC g . The stability and safety of the ORC unit are further enhanced by expanding the ₣. When the ₣ is 0.885 and superheat is 11.28 K, W net is 965.18 W, η s is 8.74%, and the C g of the system is 0.5363 $ k Wh−1, and the rate of f g is 85.07%.

Development of a 10 kW class axial impulse single stage turboexpander for a micro-CHP ORC unit

Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly.

Design, exergy analysis, and optimization of a hydrogen generation/storage energy system with solar heliostat fields and absorption-ejector refrigeration system

In the current work, a solar-based energy plant that includes an organic Rankine cycle, an NH3−LiNO3 operated refrigeration system, reverse osmosis desalination, and hydrogen production device are integrated, modeled, and optimized. A parametric examination is designed with Matlab software to show the impact of varying primary system variables on outputs like system total energy, exergy efficiency, and total exergy output. All processes have been carried out for different working fluids, namely iso-butane, Propane, n-octane, and the results are compared. Parametric analysis reveals that at solar radiation of 800 W/m2, which is reasonable for the sun in most of the Middle East, selecting n-Octane as a working media results in an increase in the hydrogen production rate of about 150%. This also confirms the importance of selecting the right working fluid for the ORC unit. Moreover, the influence of substantial decision variables on the hydrogen production, net out pout power, exergy efficiency indicated that multi-criteria optimization is necessary. The multi-objective optimization strategy suggests the TIP = 1753 kPa, Toil = 99°C, ηistur = 0.9, ηispump = 0.87, and AHeliostat = 2800 m2, for the optimum state of the studied system. Additionally, the scatter distribution and sensitivity analysis for optimum point introduced by multi-criteria optimization utilized for better understanding the optimization process.

The IRC-PD Tool: A Code to Design Steam and Organic Waste Heat Recovery Units

The Algerian economy and electricity generation sector are strongly dependent on fossil fuels. Over 93% of Algerian exports are hydrocarbons, and approximately 90% of the generated electricity comes from natural gas power plants. However, Algeria is also a country with huge potential in terms of both renewable energy sources and industrial processes waste heat recovery. For these reasons, the government launched an ambitious program to foster renewable energy sources and industrial energy efficiency. In this context, steam and organic Rankine cycles could play a crucial role; however, there is a need for reliable and time-efficient optimization tools that take into account technical, economic, environmental, and safety aspects. For this purpose, the authors built a mathematical tool able to optimize both steam and organic Rankine units. The tool, called Improved Rankine Cycle Plant Designer, was developed in MATLAB environment, uses the Genetic Algorithm toolbox, acquires the fluids thermophysical properties from CoolProp and REFPROP databases, while the safety information is derived from the ASHRAE database. The tool, designed to support the development of both RES and industrial processes waste heat recovery, could perform single or multi-objective optimizations of the steam Rankine cycle layout and of a multiple set of organic Rankine cycle configurations, including the ones which adopt a water or an oil thermal loop. In the case of the ORC unit, the working fluid is selected among more than 120 pure fluids and their mixtures. The turbines’ design parameters and the adoption of a water- or an air-cooled condenser are also optimization results. To facilitate the plant layout and working fluid selection, the economic analysis is performed to better evaluate the plant economic feasibility after the thermodynamic optimization of the cycle. Considering the willingness of moving from a fossil to a RES-based economy, there is a need for adopting plants using low environmental impact working fluids. However, because ORC fluids are subjected to environmental and safety issues, as well as phase out, the code also computes the Total Equivalent Warming Impact, provides safety information using the ASHRAE database, and displays an alert if the organic substance is phased out or is going to be banned. To show the tool’s potentialities and improve the knowledge on waste heat recovery in bio-gas plants, the authors selected an in-operation facility in which the waste heat is released by a 1 MWel internal combustion engine as the test case. The optimization outcomes reveal that the technical, economic, environmental, and safety performance can be achieved adopting the organic Rankine cycle recuperative configuration. The unit, which adopts Benzene as working fluid, needs to be decoupled from the heat source by means of an oil thermal loop. This optimized solution guarantees to boost the electricity production of the bio-gas facility up to 15%.

Development of a Fuzzy Logic Controller for Small-Scale Solar Organic Rankine Cycle Cogeneration Plants

Solar energy is widely recognized as one of the most attractive renewable energy sources to support the transition toward a decarbonized society. Use of low- and medium-temperature concentrated solar technologies makes decentralized power production of combined heating and power (CHP) an alternative to conventional energy conversion systems. However, because of the changes in solar radiation and the inertia of the different subsystems, the operation control of concentrated solar power (CSP) plants is fundamental to increasing their overall conversion efficiency and improving reliability. Therefore, in this study, the operation control of a micro-scale CHP plant consisting of a linear Fresnel reflector solar field, an organic Rankine cycle unit, and a phase change material thermal energy storage tank, as designed and built under the EU-funded Innova Microsolar project by a consortium of universities and companies, is investigated. In particular, a fuzzy logic control is developed in MATLAB/Simulink by the authors in order to (i) initially recognize the type of user according to the related energy consumption profile by means of a neural network and (ii) optimize the thermal-load-following approach by introducing a set of fuzzy rules to switch among the different operation modes. Annual simulations are performed by combining the plant with different thermal load profiles. In general, the analysis shows that that the proposed fuzzy logic control increases the contribution of the TES unit in supplying the ORC unit, while reducing the number of switches between the different OMs. Furthermore, when connected with a residential user load profile, the overall electrical and thermal energy production of the plant increases. Hence, the developed control logic proves to have good potential in increasing the energy efficiency of low- and medium-temperature concentrated solar ORC systems when integrated into the built environment.

Experimental Assessment of a Multi-Variable Control Strategy of a Micro-Cogeneration Solar-ORC Plant for Domestic Application

Suitability to off-design operation, applicability to combined thermal and electrical generation in a wide range of low temperatures and pressures and compliance with safety and environmental limitations qualify small-scale Organic Rankine Cycle plants as a viable option for combined heat and power generation in the residential sector. As the plants scale down, the electric and thermal output maximization has to account for issues, spanning from high pump power absorption, compared to the electric output of the plant, to intrinsically low plant permeability induced by the expander, to the intermittent availability of thermal power, affected by the heat demand for domestic hot water (DHW) production. The present paper accounts for a flat-plate solar thermal collector array, bottomed by an ORC unit featuring a sliding vane expander and pump and flat-plate heat exchangers. A high-temperature buffer vessel stores artificially heated water – electric heaters, simulating the solar collector - and feeds either the hot water line for domestic use or the ORC evaporator, depending on the instantaneous demand (i.e., domestic hot water or electric power), the temperature conditions inside the tank and the stored mass availability. A low-temperature receiver acts like the heat sink of the ORC unit and harvests the residual thermal power, downstream the expander: a dedicated control, modelled to properly modulate the mass addition/subtraction to this storage unit allows to restore the operating points of the cycle and to limit the incidence of off-design operation, via real-time adjustment of the cycle operating parameters. Indeed, the possibility of continuous ORC generation depends on (i) the nature of the demand and (ii) the amount of hot water withdrawn from the high-temperature buffer vessel. The time-to-temperature for the mass stored inside the buffer affects the amount of ORC unit activations and eventually the maximum attainable generation of electric energy. The plant energy performance is experimentally assessed, and various characteristic operating points are mapped, based on test runs carried out on a real-scale ORC pilot unit.