Thermodynamic comparison and dynamic simulation of direct and indirect solar organic Rankine cycle systems with PCM storage

A thermodynamic comparison between a novel direct solar ORC system (DSOS) and indirect solar ORC system (ISOS) is carried out in this study. A phase change material (PCM) heat storage unit is integrated with both systems to ensure the stability of power generation. Water and R245fa are selected as a heat transfer fluids (HTFs) for ISOS and DSOS respectively. However, R245fa is used as working fluid for both systems. Weekly, monthly and annual dynamic simulations are carried out to compare the performance of both systems using hourly weather data of Islamabad, Pakistan. ISOS has shown 1.71% system efficiency and able to provide 34.02 kW/day power while DSOS has shown 4.5 times higher system efficiency and 2.8 times higher power on annual basis. Numerical model for the PCM storage is developed and validated with the previous experimental data. Average annual amount of energy stored by PCM during charging phase for ISOS is 4.24 MW/day higher than DSOS. However, in comparison with ISOS, DSOS has delivered 33.80 kW/day more power to HTF during discharging phase of the PCM on annual basis. Maximum benefits of PCM storage are observed during the summer season compared to the winter season at selected operating conditions. Furthermore, average annual increment in capacity factor by using PCM storage are found to be 21.71% and 17% for DSOS and ISOS respectively

Modelling, simulation and comparison of phase change material storage based direct and indirect solar organic Rankine cycle systems

The thermodynamic performance of a novel direct solar organic Rankine cycle system and conventional indirect solar organic Rankine cycle system is compared in this study. The working fluid is vaporized directly in the solar collectors in direct solar organic Rankine cycle system while heat transfer fluid is used to vaporize the working in indirect solar organic Rankine cycle system. The evacuated flat plate collectors array covering a total aperture area of 150 m2 is employed as a heat source and a phase change material tank having a surface area of 25.82 m2 is used as thermal storage for both configurations. R245fa and water are chosen as heat transfer fluids for direct and indirect solar organic Rankine cycle systems, respectively. However, R245fa is used as a working fluid for both configurations. The performance of both configurations is compared by carrying out weekly, monthly and annual dynamic simulations in MATLAB by using hourly weather data of Islamabad, Pakistan. The direct solar organic Rankine cycle system outperforms the indirect solar organic Rankine cycle system in terms of thermal efficiency and net power. The annual system efficiency and an annual average net power of the direct solar organic Rankine cycle system are 71.96% and 64.38% higher than indirect solar organic Rankine cycle system respectively. However, average annual heat stored by phase change material during charging mode of indirect solar organic Rankine cycle system is 4.24 MJ more than direct solar organic Rankine cycle system. Conversely, direct solar organic Rankine cycle system has provided annual daily average power of 33.80 kW extra to heat transfer fluid during the discharging mode of phase change material storage. Furthermore, with phase change material storage, the capacity factor is increased by 17 % and 21.71 % on annual basis for direct and indirect solar organic Rankine cycle systems, respectively

Effect of Phase Change Material Storage on the Dynamic Performance of a Direct Vapor Generation Solar Organic Rankine Cycle System

Solar energy is a potential source for a thermal power generation system. A direct vapor generation solar organic Rankine cycle system using phase change material storage was analyzed in the present study. The overall system consisted of an arrangement of evacuated flat plate collectors, a phase-change-material-based thermal storage tank, a turbine, a water-cooled condenser, and an organic fluid pump. The MATLAB programming environment was used to develop the thermodynamic model of the whole system. The thermal storage tank was modeled using the finite difference method and the results were validated against experimental work carried out in the past. The hourly weather data of Karachi, Pakistan, was used to carry out the dynamic simulation of the system on a weekly, monthly, and annual basis. The impact of phase change material storage on the enhancement of the overall system performance during the charging and discharging modes was also evaluated. The annual organic Rankine cycle efficiency, system efficiency, and net power output were observed to be 12.16%, 9.38%, and 26.8 kW, respectively. The spring and autumn seasons showed better performance of the phase change material storage system compared to the summer and winter seasons. The rise in working fluid temperature, the fall in phase change material temperature, and the amount of heat stored by the thermal storage were found to be at a maximum in September, while their values became a minimum in February

Performance Assessment and Working Fluid Selection for Novel Integrated Vapor Compression Cycle and Organic Rankine Cycle for Ultra Low Grade Waste Heat Recovery

This paper presents the performance assessment and working fluid selection for a novel integrated vapor compression cycle-organic Rankine cycle system (i-VCC-ORC), which recovers ultra-low-temperature waste heat rejected (50 °C) by the condenser of a vapor compression cycle (VCC). The analyses are carried out for a vapor compression cycle of a refrigeration capacity (heat input) of 35kW along with the component sizing of the organic Rankine cycle (ORC). The effects of the operational parameters on integrated system performance were investigated. The integrated system performance is estimated in terms of net COP, cycle thermal efficiency and exergy efficiency by completely utilizing and recovering the heat rejected by the condenser of the VCC system. R600a-R141b with COPnet (3.54) and ORC thermal efficiency (3.05%) is found to be the most suitable VCC-ORC working fluid pair. The integration of the vapor compression refrigeration cycle with the organic Rankine cycle increases the COP of the system by 12.5% as compared to the standalone COP of the vapor compression system. Moreover, the sensitivity analysis results show that there exists an optimum operating condition that maximizes the thermal performance of the integrated system

Analysis of a novel solar electricity generation system using cascade Rankine cycle and steam screw expander

© 2015 Elsevier Ltd. A novel solar electricity generation system (SEGS) using cascade cycle is proposed. The top and the bottom are steam Rankine cycle (SRC) and organic Rankine cycle (ORC). Particulary, screw expander (SE), which is characterized by good applicability in power conversion with steam-liquid mixture, is employed in the SRC. Steam is generated directly in the parabolic trough collectors (PTC) and expands in the SE. The heat released by steam condensation is used to drive the ORC. This type of SEGS has the advantages of avoidance of superheated steam, moderate operating temperature and pressure, low technical requirements in heat collection and storage, and suitableness for distributed power generation. Simulation of the system performance is conducted on the use of ten ORC fluids. Four hot/cold side temperatures of 473/313 K, 473/293 K, 523/313 K and 523/293 K are exemplified. The results indicate the ORC evaporation temperature corresponding to theoretical maximum solar power efficiency fails to provide a pressure ratio (PR) that matches the SE built-in PR. Off-design operation of the SE is recommended for the purpose of higher system efficiency and simpler ORC turbine. Efficiency of 13.68-15.62% for the proposed system can be achieved

Effect of working fluids on the performance of a novel direct vapor generation solar organic Rankine cycle system

© 2015 Elsevier Ltd. All rights reserved. A novel solar organic Rankine cycle (ORC) system with direct vapor generation (DVG) is proposed. A heat storage unit is embedded in the ORC to guarantee the stability of power generation. Compared with conventional solar ORCs, the proposed system avoids the secondary heat transfer intermediate and shows good reaction to the fluctuation of solar radiation. The technical feasibility of the system is discussed. Performance is analyzed by using 17 dry and isentropic working fluids. Fluid effects on the efficiencies of ORC, collectors and the whole system are studied. The results indicate that the collector efficiency generally decreases while the ORC and system efficiencies increase with the increment in fluid critical temperature. At evaporation temperature of 120°C and solar radiation of 800 Wm-2, the ORC, collector and overall thermal efficiencies of R236fa are 10.59, 56.14 and 5.08% while their values for Benzene are 12.5, 52.58 and 6.57% respectively. The difference between collector efficiencies using R236fa and Benzene gets larger at lower solar radiation. The heat collection is strongly correlated with latent and sensible heat of the working fluid. Among the fluids, R123 exhibits the highest overall performance and seems to be suitable for the proposed system in the short term

Performance Assessment of Direct Vapor Generation Solar Organic Rankine Cycle System Coupled with Heat Storage

Phase change materials employed as thermal energy storage can aid in maximizing the use of stored solar energy. The current research examined the impact of three kinds of phase change materials (PCMs) on the dynamic performance of a solar organic Rankine cycle (ORC) system based on a direct vapor production. A number of evacuated flat plate collectors, a condenser, an expander, and an organic fluid pump make up this system. The thermodynamic cycle model of the direct vapor generation (DVG) solar ORC system was combined with the finite difference model of a phase change material heat storage tank created in MATLAB. The effect of PCMs (Organic, Inorganic and Eutectic PCMs) on the collector, ORC, and system efficiency, net power output, PCM temperature, and heat stored was studied weekly, monthly, and annually. Among the selected PCMs, Mg(NO3)2.6H2O had the highest system efficiency at 9.34%; KNO3-NaNO2 had the highest net power output at 33.80 kW; and MgCl2.6H2O stored the maximum energy of 20.18 MJ annually. Under the given operational and boundary conditions, the spring and fall were preferable to the summer and winter months for storing heat from phase change materials

Modelling of organic Rankine cycle efficiency with respect to the equivalent hot side temperature

© 2016 Elsevier Ltd An indicator, namely equivalent hot side temperature (TEHST) is proposed for the organic Rankine cycle (ORC). TEHST is derived from ideal thermodynamic process, but can denote the efficiency of irreversible ORC. Study on 27 fluids shows that given the operating conditions, fluid of higher TEHST generally offers higher ORC efficiency. This relationship is stronger and more universal than those established with respect to the critical temperature, boiling point temperature, Jacobs number and Figure of Merit. An ORC model by the method of error transfer and compensation is further built, in which the efficiency is quantitatively correlated with TEHST. Unlike the conventional ORC efficiency model, this one consists of thermodynamic parameters on the liquid/vapor curve and is independent on fluid properties at superheated state, and hence is more convenient. It has high accuracy especially for basic ORC and the relative deviation of the estimated efficiency from that calculated by the conventional model is from −0.7% to 3.4%. The novel model is applied for the thermodynamic performance prediction of a recently developed fluid of HFO1336mzzZ based on the phase equilibrium data. The results indicate HFO1336mzzZ is more efficient than R245fa on the conditions of high evaporation temperature and low pump efficiency

ESTIMATION OF TOTAL FACTOR PRODUCTIVITY GROWTH IN AGRICULTURE SECTOR IN PUNJAB, PAKISTAN: 1970-2005

Pakistan being an agricultural country has large resources of biomass in the form of crop residues like wood, wheat straw, rice husk, cotton sticks and bagasse. Power generation using biomass offers an excellent opportunity to overcome current scenario of energy crises. Of the all biomass resources, bagasse is one of the potential energy sources which can be successfully utilized for power generation. During the last decade, bagasse fired boilers attained major importance due to increasing prices of primary energy (e.g. fossil fuels). Performance of a bagasse fired boiler was evaluated at Shakarganj Sugar Mill, Bhone-Jhang having steam generation capacity of 80 tons h -1 at 25 bar working pressure. The unit was forced circulation and bi-drum type water tube boiler which was equipped with all accessories like air heater, economizer and superheater. Flue gas analyzer and thermocouples were used to record percent composition and temperature of flue gases respectively. Physical analysis of bagasse showed gross calorific value of bagasse as 2326 kCal kg -1 . Ultimate analysis of bagasse was performed and the actual air supplied to the boiler was calculated to be 4.05 kg per kg of bagasse under the available resources of the plant. Performance evaluation of the boiler was carried out and a complete heat balance sheet was prepared to investigate the different sources of heat losses. The efficiency of the boiler was evaluated on the basis of heat losses through boiler and was found to be 56.08%. It was also determined that 2 kg of steam produced from 1 kg of bagasse under existing condition of the boiler. The performance evaluation of the boiler was also done on the basis of total heat values of steam and found to be 55.98%. The results obtained from both the methods were found almost similar. Effects of excess air, stack and ambient temperature on the efficiency of boiler have also been evaluated and presented in the manuscript