Mathematical modelling of operation modes and performance evaluation of an innovative small-scale concentrated solar organic Rankine cycle plant

In this paper an innovative small-scale concentrated solar 2 kWe organic Rankine cycle plant coupled with a phase change material storage tank equipped with reversible heat pipes is investigated using a simulation analysis. The plant, intended for residential applications, is going to be built and tested under the European funded H2020 Innova MicroSolar project executed by the consortium of several Universities and industrial organizations, led by Northumbria University. The authors of this work used the design of the integrated system, developed by the consortium, to preliminary estimate the overall performance of the system in order to provide useful information for its forthcoming real operation. In particular, according to the varying ambient conditions, the influence of different operation modes of the prototype plant are evaluated. The dynamic simulation analysis has shown an interesting performance of the system in terms of annual operating hours, power production and conversion efficiencies. More precisely, the organic Rankine cycle unit is able to operate for more than 3100 h/year, achieving the design performance when solar power is sufficiently high, producing about 5100 kWhe/year. For the considered operating set-point temperatures of the thermal energy storage, the plant is able to reach high conversion efficiency also when the organic Rankine cycle unit is supplied by discharging the energy stored in the storage tank, for about 800 h/year. Hence, the work has provided some useful insights into the best working conditions of such micro combined heat and power system to be integrated in residential buildings. Moreover, the analysis could serve as a general guide for the design and optimization of the mutual interactions of the different subsystems in small-scale concentrated solar organic Rankine cycle plants

Energy flexible CHP-DHN systems: Unlocking the flexibility in a real plant

The purpose of this paper is to identify and analyze the impact of flexibility enablers in cogeneration and district heating network (CHP-DHN) plants by means of a real case study located in central Italy. A wider definition of energy flexibility applicable to the entire energy supply chain (i.e. production, transport and usage) is used in this analysis. In particular the flexibility is intended as the capability of each part of the system to produce a variation in its load curve, while ensuring the required performance. In this sense energy efficiency technologies, the use of energy storage and advanced control techniques can be seen as flexibility enablers potentially available in each section of the energy system. The innovative contribution of this work is to propose flexibility strategies in compliance with the constraints imposed by both the managers and users. The study aims to show possible ways to activate flexibility services to be used with known instruments and to quantify their impact with a simulation-based approach. In particular, three different flexibility instruments are identified in different sections of the plant: (i) the use of a thermal energy storage (TES) in the generation side, (ii) the optimal management of the DHN supply temperature (energy distribution side) and (iii) the management of the thermostatically controlled loads (TCLs) of the final users (demand side) connected to the network. Through the implementation of simulation models calibrated with available measurements, the influence of these flexibility instruments on the energy/environmental performance is evaluated in comparison to the current configuration of the plant. Results confirm the great impact of the TES to increase the CHP working hours and, as a consequence, a primary energy saving increase is obtained in mid-season and in summer season. Whereas the optimal management of the water supply temperature in the DHN allows to obtain 1% fuel reduction in a typical winter week and 2% in a typical summer week. As far as the activation of the demand side flexibility is concerned, the effect of the management of TCLs on energy conservation is demonstrated: 1 °C reduction of the setpoint of all the residential users during a typical winter day produces a 7.3% reduction of the DHN thermal demand. However, its impact on the generation side (i.e. to reduce the electricity/thermal production of the CHP at specific times) is limited due to the characteristics of the considered CHP plant (the CHP engine is sized to cover only the thermal baseload and it scarcely affected by thermal demand variations). The analysis proposed helps to obtain valuable hints on unlocking the energy flexibility in CHP-DHN plants useful for a better management of such systems

Computersimulatie van geotabs-systemen

Geotabs is een recent afgerond Europees onderzoeksproject gericht op de verbetering van installatieontwerp en -regeling van kantoorgebouwen voorzien van geothermische warmtepompen en betonkernactivering. Het uiteindelijke doel is een betere energieprestatie en een eenvoudigere commissioning-procedure terwijl het thermisch comfort gewaarborgd blijft. Gebouwsimulatie was één van de onderzoeksmethoden. De belangrijkste conclusies worden in dit artikel beschreven

Second virial coefficients for dimethyl ether

Dimethyl ether (DME) is a clean and economical alternative fuel. In addition, it is also an ozone-friendly refrigerant. Burnett measurements were carried out at temperatures from (344 to 393) K and at pressures from (0.055 to 4.015) MPa. A total of 138 experimental points, taken along 15 isotherms and 12 different temperatures, were obtained. The apparatus was calibrated by helium. The derived second coefficients were compared with the selected correlations and with literature data

innovative coupling of cogeneration units with fire tube boilers thermo fluid dynamics of the fire tubes

Nowadays the thermal energy demand in the industrial sector is usually satisfied by means of fire tube boilers while electricity is supplied from the grid. Alternatively cogeneration units could be adopted for thermal and electrical energy self-production, whilst installing boilers only as back-up units. However, even when cogeneration is profitable, it is not widespread because industries are usually unwilling to accept cogeneration plants for reliability and high investment costs issues. In this work a system aimed at overcoming the above mentioned market difficulties is proposed. It consists of an innovative coupling of a combined heat and power unit with a modified fire tube boiler. In particular, a CFD analysis was carried out by the authors in order to address the most critical aspects related with the coupling of the two systems. More precisely, the following aspects were evaluated in detail: (i) pressure losses of the exhausts going from the prime mover to the boiler due to the sudden cross-section area variations; (ii) thermal power recoverable from the exhausts in the tubes of the boiler; (iii) dependence of the system on the final users' specification

Liquefied natural gas for the UK: a life cycle assessment

PURPOSE: Liquefied natural gas (LNG) is expected to become an important component of the UK’s energy supply because the national hydrocarbon reserves on the continental shelf have started diminishing. However, use of any carbon-based fuel runs counter to mitigation of greenhouse gas emissions (GHGs). Hence, a broad environmental assessment to analyse the import of LNG to the UK is required. METHODS: A cradle to gate life cycle assessment has been carried out of a specific but representative case: LNG imported to the UK from Qatar. The analysis covers the supply chain, from gas extraction through to distribution to the end-user, assuming state-of-the-art facilities and ships. A sensitivity analysis was also conducted on key parameters including the energy requirements of the liquefaction and vaporisation processes, fuel for propulsion, shipping distance, tanker volume and composition of raw gas. RESULTS AND DISCUSSION: All environmental indicators of the CML methodology were analysed. The processes of liquefaction, LNG transport and evaporation determine more than 50% of the cradle to gate global warming potential (GWP). When 1% of the total gas delivered is vented as methane emissions leakage throughout the supply chain, the GWP increases by 15% compared to the GWP of the base scenario. The variation of the GWP increases to 78% compared to the base scenario when 5% of the delivered gas is considered to be lost as vented emissions. For all the scenarios analysed, more than 75% of the total acidification potential (AP) is due to the sweetening of the natural gas before liquefaction. Direct emissions from transport always determine between 25 and 49% of the total eutrophication potential (EP) whereas the operation and maintenance of the sending ports strongly influences the fresh water aquatic ecotoxicity potential (FAETP). CONCLUSIONS: The study highlights long-distance transport of LNG and natural gas processing, including sweetening, liquefaction and vaporisation, as the key operations that strongly affect the life cycle impacts. Those cannot be considered negligible when the environmental burdens of the LNG supply chain are considered. Furthermore, the effect of possible fugitive methane emissions along the supply chain are critical for the impact of operations such as extraction, liquefaction, storage before transport, transport itself and evaporation

Black box modelling of a latent heat thermal energy storage system coupled with heat pipes

This paper presents black box models to represent a LHTESS (Latent Heat Thermal Energy Storage System) coupled with heat pipes, aimed at increasing the storage performance and at decreasing the time of charging/discharging. The presented storage system is part of a micro solar CHP plant and the developed model is intended to be used in the simulation tool of the overall system, thus it has to be accurate but also fast computing. Black box data driven models are considered, trained by means of numerical data obtained from a white box detailed model of the LHTESS and heat pipes system. A year round simulation of the system during its normal operation within the micro solar CHP plant is used as dataset. Then the black box models are trained and finally validated on these data. Results show the need for a black box model that can take into account the different seasonal performance of the LHTESS. In this analysis the best fit was achieved by means of Random Forest models with an accuracy higher than 90%

PVT properties of an alternative biofuel: dimethyl ether

Dimethyl ether is an important chemical material and it has many engineering applications. It is a clean and economical alternative fuel and an ozone-friendly refrigerant. In this work, its PVT properties have been object of study. In particular, the experimental work was performed both in the two-phase region and in the superheated vapor region phase by means of the isochoric method. The isochoric measurements were carried out at temperatures from 219 K to 363 K and at pressures from 22 kPa up to 1,740 kPa. A total of 159 points, both in the two phase (71 points) and in the superheated vapor region (88 points) were obtained. The present experimental PVT data contribute to the deeper knowledge of the behaviour of the fluid both in the superheated vapour and in the saturation pressure region and to the development of a new equation of state

Increasing the Operation Efficiency of Air Conditioning System for Integrated Power Plant on the Base of Its Monitoring

Increasing the Operation Efficiency of Air Conditioning System for Integrated Power Plant on the Base of Its Monitoring / E. Trushliakov, A. Radchenko, S. Forduy, A. Zubarev, A. Hrych // Advances in intelligent systems and computing. – 2020. – Т. 1113 AISC . – P. 351–360Abstract. The efficiency of reciprocating gas engines of integrated energy systems (IES) for combined electricity, heat and refrigeration generation is strictly influenced by their cyclic air temperatures. To evaluate the effect of gas engine cyclic air deep cooling, compared with conventional its cooling, the data on dependence of fuel consumption and power output of gas engine JMS 420 GS-N.L on its inlet air temperature at varying ambient air temperatures at the entrance of the radiator for scavenge air cooling were received. The results of treatment of gas engine efficiency monitoring proved non-effective operation of conventional chilling all the ambient air, coming into the engine room, because of increased air temperature at the inlet of turbocharger (TC), caused by heat influx from surroundings in the engine room. A new method of gas engine inlet air two-stage cooling at increased ambient air temperatures and advanced cyclic air cooling system with absorption lithium-bromide chiller and refrigerant ejector chiller was proposed. With this chilled water from absorption lithiumbromide chiller is used as a coolant in the first high-temperature stage of engine inlet air cooler and boiling refrigerant of ejector chiller in the second lowtemperature stage