Bottoming Organic Rankine Cycle Research Articles

Thermo-economic assessment and systematic comparison of combined supercritical CO2 and organic Rankine cycle (SCO2-ORC) systems for solar power tower plants

Solar power towers (SPTs) integrated with thermal energy storage are promising solutions for solar energy utilisation. Supercritical CO2 power cycles are acknowledged as an attractive option for dry-cooling SPT plants. However, abundant low-grade waste heat exists in the SCO2 gas cooler, which is directly dissipated to the ambient. In order to further improve the performance of SCO2-based SPT plants, organic Rankine cycle (ORC) systems can be introduced as a bottoming cycle subsystem. In this paper, an ORC subsystem is added to four different SCO2 cycle layouts, i.e., recuperated (RE), recompression (RC), intercooling (IC), and partial cooling (PC) cycles, to form combined cycle systems for SPT applications. A parametric study reveals that the thermal efficiency of the power block (i.e., the whole power cycle system), and the salt temperature difference across the receiver are the determining factors of the thermo-economic performance of SPT-SCO2-ORC plants. Design optimisation and annual performance evaluations are implemented using actual weather data in Delingha, China. Compared to the SPT plant with a standalone recuperated SCO2 cycle system, the annual electricity generation is increased by 19 % by integrating a bottoming ORC subsystem. The SPT-RC-ORC system produces the maximum electricity generation of 123 GW·h/year, while the SPT-RE-ORC system achieves the lowest levelised cost of electricity (LCOE) of 0.12 $/kW·h and the minimum payback time of 8.8 years. A wide range of solar irradiance conditions is further considered to generalise the performance evaluation of such combined cycle systems, with results showing that with the highest solar irradiance investigated (3700 sunshine hours, 1000 W/m2·h), the LCOE of the SPT-RE-ORC plant can be as low as 0.07 $/kW·h and the payback time is as short as 6 years. This study investigates optimal SCO2-ORC configurations for SPT applications based on annual performance evaluations, and presents preliminary assessments of the thermo-economic potential of ushc SPT-SCO2-ORC plants across a variety of solar resource conditions.

Thermo-economic assessment of hybrid Kalina cycle and organic Rankine cycle system using a parabolic trough collector solar field

This study presents a solar powered hybrid power system consisting the Kalina cycle (KC) and a bottoming organic Rankine cycle (ORC). LS-2 parabolic trough collector (PTC) is modeled in solar field with two different kinds of working fluid: Syltherm 800 and MXene/Syltherm 800 nanofluid. MXene particle (Ti3C2) is used with 0.1 wt% due to their outstanding thermal absorption properties. The use of MXene-based nanofluid has shown remarkable thermophysical properties, resulting in a significant increase in the useful heat generated by 11.10%. The hybrid system utilizing the MXene-based nanofluid demonstrates a substantial improvement in work utilization. Moreover, the maximum energetic and exergetic efficiency achieved with the MXene-based nanofluid are 6.095% and 6.55%, respectively, indicating its superior performance in converting solar energy into usable power with greater efficiency. When considering the overall cost of the MXene-based solar field, it was found to be approximately 7.63% higher compared to the Syltherm 800-based parabolic trough collector system. However, the Levelized cost of electricity (LCOE) for the Syltherm 800-based solar field was calculated as 0.1351 $/kW-hour, while for the MXene/Syltherm 800-based solar field, it was slightly lower at 0.1324 $/kW-hour. Additionally, the Payback period was reported as 5 years and 9 months for the Syltherm 800-based solar field, and 5 years and 7 months for the MXene/Syltherm 800-based solar field.

Comparative sensitivity analysis of micro-scale gas turbine and supercritical CO2 systems with bottoming organic Rankine cycles fed by the biomass gasification for decentralized trigeneration

In this article, the performance of a micro gas turbine (mGT) and a supercritical CO2 (sCO2) system fuelled by a biomass gasifier and with similar nominal net power output is compared. Both plants include a bottoming organic Rankine cycle system to maximise the electrical power output. Using a component-oriented, off-design modelling approach a sensitivity analysis is performed by varying the main operating parameters. In addition, the integrated systems are also evaluated in combination with a network of residential apartments to assess their adaptability to variable users' thermal and electrical demands.Results have shown that at full load and ambient temperature of 15 °C, the average net electric power of the whole integrated sCO2 system is around 126 kWe which is approximately 25% higher than the one of the mGT system, but with a lower net electric efficiency resulting in 75% higher biomass consumption. Nonetheless, the net thermal power production of the integrated sCO2 system is almost 355 kWt which is 4.35 times higher than the mGT system resulting in higher overall efficiency. When combined with residential apartments, the sCO2 system proves to be suitable for 140 apartments operating with higher overall efficiency compared to the mGT system coupled with 30 apartments.

Assessing sustainable operational conditions of a bottoming organic Rankine cycle using zeotropic mixtures: An energy-emergy approach

In this work, an Organic Rankine Cycle system is used to produce electricity from the waste heat of an internal combustion engine (ICE). The toluene, and cyclohexane, are the selected pure fluids to be compared with the zeotropic mixtures. The zeotropic mixtures used as working fluids are cyclohexane/R11 (0.2/0.8), cyclohexane/R11 (0.25/0.75), and cyclohexane/R11 (0.3/0.7). An energy, exergy and emergy analysis was conducted to assess the sustainability of the whole system and the viability of the zeotropic mixture from the environmental point of view. Finally, a multi-objective optimization was carried out. The results showed that the zeotropic mixtures have better performance compared with the selected pure fluids when the net power and the exergy efficiency are considered. The pure fluids had a better Emergy Sustainability Index (ESI) index by 10% on average, there is not a big difference on this parameter so the advantages of using zeotropic mixtures as working fluids for this type of system cannot t be ignored. However, using the mixture the system obtained a lower Environmental load Ratio (ELR) value compared to cyclohexane and toluene. Finally, the multi-objective optimization was able to maximize the exergy efficiency for the working fluids by about 9.7% and reduce the ESI by 50.94%. This study intends to show the advantage and disadvantage of using zeotropic mixtures as working fluid on waste heat recovery systems that uses Organic Rankine cycle from the environmental point of view and using emergy as a way to asses the sustainability of the whole system.

Parametric and economic analysis of high-temperature cascade organic Rankine cycle with a biphenyl and diphenyl oxide mixture

High-temperature organic Rankine cycle (ORC) systems have the potential to improve the heat-to-power conversion efficiency and expand the temperature range for heat recovery, heat battery and solar power generation. Restricted by the critical temperature of the commonly used organic working fluids, the current ORC technology has a maximum working temperature of around 300 °C. This paper proposes a high-temperature cascade organic Rankine cycle (CORC) system using a biphenyl and diphenyl oxide (BDO) mixture as the top cycle fluid and conventional organic fluids for the bottom cycle. The BDO mixture has excellent heat stability over a wide operation condition from 12 °C to 400 °C in single-phase and binary-phase states. However, at present a detailed study on the ORC using the mixture is lacking. In this paper, a parametric analysis of the high-temperature CORC system is conducted. A mathematical model based on the equivalent hot side temperature is built to simulate the ORC efficiency. The thermodynamic and exergetic performances of the novel CORC system under different bottom ORC working fluids, mixing chamber temperatures, evaporation temperatures, and condensation temperatures are investigated. The results show the maximum thermal efficiency of the CORC system is 38.74 % and 40.26 % at top ORC evaporation temperatures of 360 °C and 400 °C. The largest exergy destruction takes place in the heat exchanger between the top and bottom ORCs. Besides, the heat regenerators have a significant impact on the thermodynamic performance and can elevate the CORC efficiency by about 4 %. The proposed system has a higher efficiency and a lower equipment cost than conventional steam Rankine cycle at 400 °C while eliminating the challenges of wet steam turbines.

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.

A multi-generation system for hydrogen production through the high-temperature solid oxide electrolyzer integrated to 150 MW coal-fired steam boiler

A multi-generation system including power generation, domestic hot water, and H2 production was designed for the waste recovery of a 150 MW coal-fired power plant. A high-temperature electrolyzer was integrated into the present system to produce H2. The second product of O2 from the electrolyzer was used to enrich the combustion process. The required power for the electrolyzer was obtained from a bottoming organic Rankine cycle (ORC). In this regard, a supercritical ORC was designed in which cyclopentane was used as the working fluid. The required heat of the electrolyzer was obtained by a heat exchanger located in the combustion chamber to reach the required temperature level. The designed system was analyzed by the energy and exergy method for different temperatures and current densities. It is determined that it is available to produce H2 in an amount of 0.0739 to 0.0762 kmol/s for the optimal current densities at every single handled temperature. The energy efficiency of the overall system was determined in the range of 27.19% and 27.36%. The exergy efficiency of the overall system was determined in the range of 35.05% and 35.25%. An increase of 15.78–16.53% in energy efficiency was achieved. This increase was achieved as 20.43–21.16% in the exergy efficiency.

Zeotropic working fluid selection for an organic Rankine cycle bottoming with a marine engine

Organic Rankine cycle (ORC) is an effective approach for low-grade energy utilization. It is important to improve the efficiency of an ORC when the heat source temperature varies. In this study, a method of selecting zeotropic mixture for a bottoming ORC with changeable heat source temperature is presented. The effects of the operation conditions of the marine engine and the ambient temperature are investigated. First, the optimal performances of the ORC using 40 pure working fluids are determined and compared. Then, two zeotropic mixtures benzene/m-xylene and cyclopentane/toluene are selected and the mechanism of temperature match with the heat source and sink is explored. Finally, the performance improvement with benzene/m-xylene using the composition adjustment method is evaluated. The results indicate that the suitable pure working fluids are isopentane and R245ca for a low exhaust temperature while toluene and m-xylene are the best when the exhaust temperature is high. Using the zeotropic mixtures benzene/m-xylene and cyclopentane/toluene can obtain a high performance over the operation range of the marine engine. When the exhaust temperature is 225 °C, the net power and exergy efficiency of benzene/m-xylene are improved by 6.9%–21.9% and 6.5%–22.0%, respectively, compared with the pure fluids benzene and m-xylene. When the exhaust temperature increases to 380 °C, these improvements decrease to 1.9%–6.8%. If a zeotropic mixture is used, the critical temperature of the component with a high-boiling point should be close to the maximum operation temperature of the heat source, and the temperature glide should first match with the temperature increase of the heat sink. If the heat sink temperature is fixed, it is impossible to enhance the ORC performance using the composition adjustment method. However, the composition adjustment method is effective when the temperature of the heat sink varies with the ambient temperature. The net power and exergy efficiency of the ORC are improved by up to 21.9% and 22% in winter using benzene/m-xylene. However, these improvements are less than 6.8% in summer.

Innovative small axial multistage turbine with partial admission for bottoming ORC

The expander is the key element of an organic Rankine cycle (ORC) and has a significant influence on the cycle efficiency. Therefore, in this study, an innovative small axial multistage turbine with partial admission for a bottoming ORC (ORBC) is investigated. The ORBC was used for the waste heat utilization of exhaust gases and jacket cooling water from a 537 kW biogas internal combustion engine (ICE) .The initial design of the turbine flow part was developed using a mean diameter two-dimensional (2D) preliminary design (PD) method. The high rotational speed of the axial turbine, which is its most critical characteristic, was overcome by employing partial admission. To achieve high isentropic efficiency, new (nonstandard) profiles of the nozzle and moving blades were designed using an analytical method. The initial full flow part of the turbine was further investigated by three-dimensional (3D) computational fluid dynamics (CFD) simulations, with the aim of improving its design. The simulations also provided a better insight into the physics of flow than the mean diameter 2D method. Both the 2D PD calculations and 3D CFD simulations were performed using real gas properties.The innovative axial action–reaction turbine with partial admission has 8 stages, a mean diameter of 140 mm, and a rotational speed of 9000 rpm. According to the CFD simulation results, a mass flow of isopentane as the working fluid of 1.171 kg/s achieves an effective power of 60.35 kW and isentropic efficiency of 74.8%. These represent an 11.2% increase in the overall power and a 4.5% increase in the overall thermodynamic efficiency by employing an ORBC on a 537 kW biogas ICE.Therefore, the new turbine is competitive with other expanders in this power range.

Integrated Vapor Compression Chiller with Bottoming Organic Rankine Cycle and Onsite Low-Grade Renewable Energy

The present study offers a scheme to improve the performance of existing large-scale chillers. The system involves raising the temperature of the chiller’s cooling water stream using renewable energy sources by incorporating an organic Rankine cycle (ORC). The thermal analysis was conducted by raising the temperature of one-third of the approximately 200 ton chiller’s cooling water. The investigation was considered for ORC evaporator inlet temperature of 90~120 °C by the step of 10 °C. Various working fluids for the different ORC evaporator inlet temperatures were examined. Sensitivity analyses conducted on the degree of superheating, degree of subcooling, condenser saturation temperature, pinch point temperature differences of the ORC evaporator and condenser, and the mass flowrates of the heating and cooling streams were also reported. Genetic algorithm was employed to carry out the optimization. The best options for the ORC working fluid at the heating source ORC evaporator inlet temperatures of 90 °C was found to be DME, presenting an improvement of 48.72% in comparison with the rated coefficient of performance (COP) value of the VCC, with a renewable energy input requirement of 710 kW. At the heat source temperatures of 100 °C and 110 °C, butene, which presented an improvement in the COP equal to 48.76% and 68.85%, respectively, with the corresponding renewable energy requirements of 789.6 kW and 852 kW, was found to be the ideal candidate. Meanwhile, at the heat source inlet temperature of 120 °C, R1233zd (E), representing an improvement of 140.88% with the renewable energy input of around 1061 kW, was determined to be the most favorable ORC working fluid candidate.

Performance analysis of a dual-loop bottoming organic Rankine cycle (ORC) for waste heat recovery of a heavy-duty diesel engine, Part I: Thermodynamic analysis

In this paper, which is the part 1 of this study, the energy and exergy characteristics of a dual-loop organic Rankine cycle (ORC) combining with a heavy-duty diesel engine were investigated. The proposed cycle is driven by the waste heat of the exhaust gases, intake air, and the coolant. Central composite design (CCD), which is a standard response surface methodology (RSM) technique, was applied to design of experiments (DoE) and to investigate the influence of both the engine and cyclic parameters such as the engine speed, the start of injection (SOI), the higher pressure of the high-temperature loop, and the higher pressure of the low-temperature loop. Adequacy of the developed RSM models has been evaluated by the ANOVA tables. The results revealed an increase in whether the engine or cycle parameters led to an enhance in the produced power of the system. As a comparison, the variation in engine variables has more impact on the produced power. On the opposite side, a change in the engine speed and SOI have a minor effect on the thermal efficiency of the system. The maximum produced power of the dual-loop ORC system was identified as 310 kW, which was resulted at the engine speed of 1800 RPM, and 0.0 degrees of CA bTDC for SOI; while the higher pressures of the HT and LT loops were in 2400 and 2100 kPa, respectively. This obtained power is 31% of the engine brake power. The maximum values for the thermal and exergy efficiencies were observed as 9.5% and 43%, respectively. Also, the exergy analysis demonstrated that the highest exergy destruction rate of the system is determined to be 500 kW.

A Comprehensive Perspective of Waste Heat Recovery Potential from Solar Stirling Engines

Despite the higher efficiency advantage, the cost reduction of PV technology has been more successful compared to the dish Stirling engine (DSE) due to the large market volume and sturdy competition. Irrespective of the types of source, there exists a potential of waste heat recovery from Stirling engines operating at higher temperature regime. Accordingly, to make DSE commercially viable and efficient, innovative ways such as hybridization (combing a bottoming cycle), Co-generation, Tri-generation etc. need to be explored. In this paper, the techno-economic feasibility of hybridization of a typical solar DSE with a bottoming organic Rankine cycle (ORC) via. a heat recovery vapour generator (HRVG) is explored. The overall energetic and exergetic efficiency of the DSE has been improved by 5.79% and 5.64% while recovering the waste heat through a bottoming ORC. The design and effective incorporation of the HRVG with cooler side of the Stirling engine is identified to be crucial for the overall exergetic performance of solar Stirling-ORC. Further, the economic feasibility of a solar String-ORC combination is evaluated in terms of levelized cost of electricity (LCOE) and payback period. Both LCOE and payback period are found to be in comparable range with the PV technology.

Increasing the Energy Efficiency of an Internal Combustion Engine for Ship Propulsion with Bottom ORCs

The study examines the option of adding a bottom Organic Rankine Cycle (ORC) for energy recovery from an internal combustion engine (ICE) for ship propulsion. In fact, energy recovery from the exhaust gas normally rejected to the atmosphere and eventually from the cooling water circuit (usually rejected to the sea) can significantly reduce the fuel consumption of a naval ICE during its operation. In the paper, different possible bottom ORC configurations are considered and simulated using the Aspen® code. Different working fluids are taken into account, jointly with regenerative and two-temperature levels designs. The energy recovery allowed by each solution is evaluated for different engine load, allowing the identification of the most suitable ORC configuration. For the selected case, the preliminary design of the main heat exchangers is carried out and the off-design performance of the whole combined propulsion plant (ICE + ORC) is evaluated, leading to a preliminary analysis of cost saving during normal ship operation. The results of this analysis show an increase in power output of about 10% and an expected Payback Time of less than 6 years.

A comparative study of the energy, exergetic and thermo-economic performance of a novelty combined Brayton S-CO2-ORC configurations as bottoming cycles

This paper presents a comparative study on the energy, exergetic and thermo-economic performance of a novelty thermal power system integrated by a supercritical CO2 Brayton cycle, and a recuperative organic Rankine cycle (RORC) or a simple organic Rankine cycle (SORC). A thermodynamic model was developed applying the mass, energy and exergy balances to all the equipment, allowing to calculate the exergy destruction in the components. In addition, a sensitivity analysis allowed studying the effect of the primary turbine inlet temperature (TIT, PHIGH, rP and TC) on the net power generated, the thermal and exergy efficiency, and some thermo-economic indicators such as the payback period (PBP), the specific investment cost (SIC), and the levelized cost of energy (LCOE), when cyclohexane, acetone and toluene are used as working fluids in the bottoming organic Rankine cycle. The parametric study results show that cyclohexane is the organic fluid that presents the best thermo-economic performance, and the optimization with the PSO method conclude a 2308.91 USD/kWh in the SIC, 0.22 USD/kWh in the LCOE, and 9.89 year in the PBP for the RORC system. Therefore, to obtain technical and economic viability, and increase the industrial applications of these thermal systems, thermo-economic optimizations must be proposed to obtain lower values of the evaluated performance indicators.

Parametric optimisation of a combined supercritical CO2 (S-CO2) cycle and organic Rankine cycle (ORC) system for internal combustion engine (ICE) waste-heat recovery

Supercritical CO2 (S-CO2) power-cycle systems are a promising technology for waste-heat recovery from internal combustion engines (ICEs). However, the effective utilisation of the heat from both the exhaust gases and cooling circuit by a standalone S-CO2 cycle system remains a challenge due to the unmatched thermal load of these heat sources, while a large amount of unexploited heat is directly rejected in the system’s pre-cooler. In this paper, a combined-cycle system for ICE waste-heat recovery is presented that couples an S-CO2 cycle to a bottoming organic Rankine cycle (ORC), which recovers heat rejected from the S-CO2 cycle system, as well as thermal energy available from the jacket-water and exhaust-gas streams that have not been utilised by the S-CO2 cycle system. Parametric optimisation is implemented to determine operating conditions for both cycles from thermodynamic and economic perspectives. With a baseline case using a standalone S-CO2 cycle system for an ICE with a rated power output of 1170 kW, our investigation reveals that the combined-cycle system can deliver a maximum net power output of 215 kW at a minimum specific investment cost (SIC) of 4670 $/kW, which are 58% and 4% higher than those of the standalone S-CO2 cycle system, respectively. A range of ICEs of different sizes are also considered, with significant performance improvements indicating a promising potential of exploiting such combined-cycle systems. This work motivates the pursuit of further performance improvements to waste-heat recovery systems from ICEs and other similar applications.

Parametric analysis on the low temperature wet air waste heat recovery through an organic Rankine cycle

Removing moisture in the wet farm products through the open air ventilation is a traditional postharvest treatment method. However, its overall energy consumption is high and the drying time is long. Here, a combined system is proposed through integrating a bottom organic Rankine cycle (ORC) to a top closed farm products air drying cycle to save energy and decreasing the drying time. Based on a steady state thermodynamic model without any losses, a theoretical work on thermal performance the proposed system has been conducted. The key operation parameters and suitable operation conditions for both the prominent energy saving ratio and high moisture extraction characteristics have been analyzed. The calculation results showed both the prominent energy saving and high moisture extraction performances can be achieved at the low ORC evaporating pressure condition, but the optimal energy saving performance and the moisture extraction performance could not be achieved simultaneously. Increasing dew point temperature of the humid air leaving the drying chamber improves both the energy saving and moisture extraction performances of the drying system significantly. Under the working conditions in this research, with the dew point temperature value of the humid air leaving the drying chamber over 323 K, the optimal energy saving performance is achieved at a fixed low ORC evaporation pressure. But, the prominent energy saving and high moisture extraction performances could not be accomplished simultaneously, with the dew point temperature value of the humid air leaving the drying chamber lower than 323 K.

Performance improvement of the bottoming steam Rankine cycle (SRC) and organic Rankine cycle (ORC) systems for a triple combined system using gas turbine (GT) as topping cycle

In the present study, performance improvement of SRC and ORC systems used as a bottoming system in a GT based triple combined system was evaluated for varying turbine inlet temperature and pressure. In the first step, SRC was parametrically optimized for a varying pressure (from 10 bar to 100 bar) and temperature (from saturated steam temperature to 480 °C). In the second step, a parametric optimization is performed to comprehensively evaluate the effects of acetone, R113, R141b, R152a, R245fa and R365mfc on thermodynamic performances of ORC (Organic Rankine Cycle) with the increasing turbine inlet pressure and temperature. Along with the optimization, the ORC turbine inlet pressure was heightened from 7.5 bar to the critical pressures of the working fluids with the increments of 2.5 bar. The ORC turbine inlet temperature was varied between saturation temperature and the maximum working temperature of selected working fluids. Finally, energy and exergy efficiencies of the overall triple combined system (GT-SRC-ORC) was calculated by depending on pressure, temperature and working fluids. As a result, the best working fluids among the selected fluids was found as R141b. Maximum net thermal efficiency, exergy efficiency and a net power of the ORC with R141b were calculated as 22.6%, 64.76% and 780.35 kW at 40 bar and 225 °C, respectively. Net thermal and exergy efficiency of the overall system (GT-SRC-ORC) with R141b was found 47.65%, 67.35%, respectively. By this way, the waste heat recovery corresponding to 734.57 kg/h natural gas which is equivalent to 2203.73 kg-CO2/h emissions was carried out.

Electric power conversion of exhaust waste heat recovery from gas turbine power plant using organic Rankine cycle

In this study, an examination of a bottoming organic Rankine cycle for power conversion of the flue gases from a 5.75 MW gas turbine power plant was carried out. First law of thermodynamics was applied to the four major components of the system and simulated using developed MATLAB codes, while the thermo-physical properties at each state were supplied by engineering equation solver database. Five organic working fluids were compared based on selected performance indices. Toluene exhibited the best performance at full and partial electric generator load conditions with net power outputs of 532.70 kW at full load and 412.95 kW at partial load of 75%, while at 50% partial load, R245fa has the highest net power output of 469.09 kW. The cycle efficiency of the organic Rankine cycle system was improved from 34.67% at full load to 40.51% with exhaust gases from the power plant considered as sources of low-grade heat. R245fa showed the best adaptability at 50% partial load but at excessively high mass flow rate of 13.62 kg/s. It is evidently shown from this study that, waste heat recovery technologies can effectively generate about 16.8% of the nominal power of a gas turbine power plant and hence, reduce emissions per kW generated, suitable for sustainable environment as well as promoting energy security.

Integrating biomass gasification with a steam-injected micro gas turbine and an Organic Rankine Cycle unit for combined heat and power production

Proper integration of different energy systems is one of the most effective strategies to achieve higher conversion efficiencies and to reduce emissions in power systems. Hence, in this study a biomass-fuelled Steam Injected micro Gas Turbine (SImGT) coupled to a bottom Organic Rankine Cycle (ORC) unit is investigated to better exploit the primary energy use while lowering the environmental impact. In the proposed integrated system configuration, a Heat Recovery Steam Generator (HRSG) produces steam for both the gasification process and the SImGT. To conduct a realistic simulation, several gas conditioning units are included in the configuration of the integrated system to purify the produced syngas to the allowable limit of mGTs. The impacts of both the mass flow rate of the injected steam and the S/B ratio on the performance of the integrated system have been assessed. Results of the analysis have shown that the produced electrical power increases as the mass flow rate of the injected steam increases, while the net electrical efficiency of the integrated system is penalized marginally. At its maximum net electricity production, the integrated system has an output of 127.6 kWel and 78.7 kWth with 23.6% electrical efficiency when the mass flow rate of the injected steam to the combustion chamber is 25 g/s, which corresponds to the maximum of the investigated range in this study.

Design and CFD Analysis of a Radial-Inflow Turbine for Small Scale ORC Applications

In recent years, Organic Rankine Cycle (ORC) technology has received growing interests, thanks to its high flexibility and to the capability to exploit energy sources at temperature levels difficult to be approached with conventional power cycles. These features allow exploiting renewable and renewable-equivalent energy sources, by either improving the energy conversion efficiency of existing plants or using waste heat from industrial process. As far as the expander is concerned, a high potential solution is represented by turbo-expanders, which allow reduction of plant clutter and complexity, so enhancing the potential impact on the diffusion of small power ORC-based plants. The present work concerns the design of a RadialInflow Turbine for a bottoming Organic Rankine Cycle in the tens of kW scale. Design boundary conditions are retrieved by a zero-dimensional model of a solar-assisted micro gas turbine in cogenerating mode. The design process is started by means of an in-house mean-line design code accounting for real gas properties. The code is used to carry out parametric analyses to investigate the design space for several working fluids encompassing different classes, namely refrigerants and siloxanes. The program is used to assess the effect of design variables and working fluid on the turbine performance and turbine design characteristics. Subsequently, the most promising design candidates are selected and three-dimensional first guess stator and rotor geometries are built on these preliminary designs. Stationary and rotating passages are then meshed and analyzed by means of RANS CFD based solution of the stator – rotor interaction.