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Abstract Liquefied Natural Gas (LNG) is becoming vital in relation to energy transition and fighting climate change. Because of its cryogenic temperature (111 K), LNG is an exergy “mine” that can be exploited in the regasification process for multiple industrial applications. But this exergy is usually wasted. This research presents a Combined Cold and Power (CCP) system with exergy recovery from LNG-regasification. This exergy is exploited for the combined production of electricity and low-temperature refrigeration distributed through a CO 2 District Cooling Network. These systems entail many benefits, but also pending challenges. The CCP system is modelled using real operation data, and its performance is analyzed and benchmarked against that of a cryogenic power plant, both at design and off-design operating conditions. The proposed CCP system reports an equivalent electricity saving of 139 kWh/t-LNG with an exergetic efficiency of 40%, turning into useful energy up to 64% of the maximum cold recoverable in the regasification process. The performance enhances as the heat source temperature rises. Higher LNG flow rates contribute to increase the electricity and refrigeration production, but irreversibilities also increase. Finally, findings show that a low LNG regasification pressure is preferable in spite of the negative effect on the power generation.

Abstract In this paper a thermoeconomic analysis of a novel hybrid Renewable Polygeneration System connected to a district heating and cooling network is presented. The plant is powered simultaneously by solar and geothermal sources, producing electricity, desalinated water, heat and cooling energy. System layout includes Parabolic Through Collector (PTC) field, geothermal wells, Organic Rankine Cycle (ORC) unit and a Multi-Effect Desalination (MED) system. Cooling and thermal demands are calculated by suitable building dynamic simulation models, calibrated for Pantelleria Island. Electrical demand is obtained by measured data. A detailed control strategy has been implemented in order to prevent any heat dissipation, to match the appropriate operating temperature levels in each component, to avoid a too low temperature of geothermal fluid reinjected in the wells and to manage the priority of space heating and cooling process. A 1-year dynamic simulation has been performed and results analyzed on daily, monthly and yearly basis. The system achieved an SPB equal to 8.50 and it resulted capable to cover the energy demands of a small community. Moreover, the plant is capable to cover the fresh water demand of the Pantelleria Island.

Abstract The paper presents the validation of a 1D compressor model (1DCM) applied to the simulation of deep-surge operation. The compressor is described following an enhanced map-based approach, where proper "virtual pipes" are placed upstream and downstream the compressor to deal with the mass and energy storage and wave propagation effects. The proposed methodology, which takes into account main flow and thermal loss mechanisms, is based on the employment of "extended" compressor maps obtained through a steady version of the 1DCM. The tuning and validation of the 1DCM have been carried out comparing its results with the experimental data. Preliminarily, the steady version of the 1DCM is tuned against to the measured map for various rotational speeds. Subsequently, it is used to derive the extended map, including both direct and reverse flow branches. Finally, the unsteady version of the 1DCM is validated against experimental data denoting a satisfactory agreement, especially in terms of pulse frequency, amplitude and global shape. Summarizing, the proposed model, combining the reduced computational effort typical of 1D simulation with the adoption of advanced features such as "virtual pipe" and extended compressor map, shows the capability to capture the phenomenology of the compressor surging.

Abstract The results of experiments in oxygen/graphite, steam/ graphite, and water/graphite systems provide information on aerosol formation in case of hypothetical accidents in high temperature reactors. The particle mass concentrations and size distributions were measured over a temperature range for the different corrosive media. The aerosol parameters are discussed in terms of the physical phenomena that occur during the aerosol forming corrosion process.

Abstract Liquefied Natural Gas (LNG) is a valuable exergetic source due to its low-temperature (−162 °C). However, LNG is regasified using seawater as heat source and without exergy recovery in most of LNG terminals worldwide. In this paper we model a polygeneration plant that recovers the low-temperature and pressure exergy from LNG-regasification to generate simultaneously power and refrigeration in a District Cooling network at three different temperature levels. The plant is divided into different subsystems arranged in cascade. The objective of this research is the selection of the most suitable working fluids and heat transfer fluids for operating in each subsystem. The performance of the system is analyzed from the thermodynamic and environmental point of view. Although neither of the candidate fluids satisfies all the desirable features, the selected fluids are: methane, carbon dioxide and propane. The plant achieves an equivalent electricity production of 125 kWh for metric ton of LNG regasified with an exergetic efficiency of 40.6%. Besides, the seawater utilized in the plant is 60% lower than the required by the common LNG regasification process and an annual emission of 75 thousand tons of CO2 is avoided.

Waste heat recovery from the exhaust gases of gas turbines, geothermal resources, and from industrial plants offers a great opportunity for rational energy usage by productively converting the waste energy. In the present communication we report a systematic study starting with the hydrocarbons for the different temperature ranges at which the waste heat is available from high, medium, or low temperature heat sources (viz., 773.15, 623.15 and 523.15 K). In the present work hydrocarbons from n-pentane to n-dodecane were investigated in comparison to water, benzene and toluene. Model calculations have been performed at various boiler pressures. Higher efficiencies are achieved at higher boiler pressures. In the low temperature range (523.15 K) hydrocarbons such as n-hexane, n-pentane are promising. If the heat is available at higher temperature (773.15 K) n-dodecane and toluene are the suitable fluids. In the case studies for the intermediate temperature range (623.15 K), it turns out that for many conditions, octane, heptanes and water are well suited working fluid for cogeneration systems. The results for the total heat recovery efficiency and the surface area of the heat exchanger have been discussed. T–H Diagrams were used to select the best possible conditions.

Abstract A steady-state simulation model of a commercial 3-ton ammonia/water absorption chiller is developed and validated using the flow-sheeting software Aspen-Plus. First an appropriate thermodynamic property model for the ammonia/water fluid mixture is selected. To this purpose nine methods from the software library are pre-selected and tested, but none of the methods predicts the VLE (vapour–liquid equilibrium) with sufficient accuracy. The interaction parameters of these models are then determined by fitting the equations of state (EOS) to VLE data. It is finally found that the Boston–Mathias modified Peng–Robinson EOS with fitted parameters predicts most accurately the VLE for the temperature and pressure ranges encountered in commercial chillers. A simulation model of the machine is then developed. The simulation results are found to be in good agreement with data from literature at a cooling air temperature of 35 oC. The heat transfer characteristics ( UA ) of the various heat exchangers of the machine are then determined and the model modified to make it accept these ( UA ) as input parameters. The comparison of the simulation predictions at cooling air temperatures of 26.7 and 38 oC with the bibliographical data showed good concordance. The proposed model could be very useful for the analysis and performance prediction of the commercial absorption chiller.

Abstract Photovoltaic (PV) systems transform solar irradiation into electricity, thereby substituting for traditional energy sources and reducing environmental pollution. The present work evaluates a developed market (Italy) in which subsidies have been re-introduced for PV plants with a nominal capacity above 20 kW through the FER1 (renewable energy sources) Decree. The discounted cash flow (DCF) methodology is applied to several cases of PV plants in public buildings, in order to determine the value of several critical variables (i.e. level of insolation, plant size, share of self-consumption, investment cost, electricity purchase price). In particular, differences in net present value (NPV) and discounted payback time (DPBT) between subsidy and no-subsidy scenarios are quantified. Break-even point (BEP) analysis is used to define the share of self-consumed energy for which NPV is positive. This share is found to range from 9 to 28% in 105 kW plants and from 10 to 35% in 25 kW plants. In addition, the results verify profitability in almost all of the baseline case studies and only half of the alternative scenarios (involving no subsidies). The estimated profits are consistent with investments aimed at increasing the share of self-consumed energy.