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Abstract A Triangle Cycle with a piston engine expansion unit is used to convert low temperature heat into electrical energy. In this process, the isentropic efficiency of the expansion unit is considered to be unknown, and a theoretical approach for the calculation of isentropic efficiency is presented. A number of influences are taken into account – dead volume, residual mass, liquid injection performance and wall heat transfer. Various working fluids are investigated in a wide range of temperatures (333K–573K), engine speeds (5 Hz–30 Hz) and stroke volumes (0.1 L–50 L). The isentropic efficiency of water as working fluid is in the range of 0.75–0.88 and drops significantly for high stroke volumes and engine speeds. In general, injection mass has the most impact on isentropic efficiency because it influences dead volume and injection performance. The injection mass increases with vapor density and therefore is significantly influenced by working fluid and temperatures. The Triangle Cycle is compared with Organic Rankine Cycles by using determined isentropic efficiency. The exergetic efficiency of the Triangle Cycle using water is up to 35–70% higher than that of supercritical Organic Rankine Cycles in situations with a heat source temperature of up to 450K.

Abstract A total heat recovery system performances are analysed by monitoring building–plant system long term behaviour. Some of the installed chillers offer in fact the possibility of a total recovery of the heat rejected by condenser. The results are very satisfactory both in energy and economic–financial terms. The experimental test takes advantage of the supervisor just existing in the building. Therefore it is an example of how these control systems can be used not only for safety and management needs, but also for a detailed performance analysis able to permit an easy simulation of the effects of different design and control options.

The availability of wet biomass as waste from a lot of industrial processes, from agriculture and farms and the need to meet the environmental standards force to investigate all options in order to dispose this waste. The possible treatments usually strongly depend on biomass characteristics, namely water content, density, organic content, heating value, etc. In particular, some of these wastes can be burnt in special plants, using them as energy supply for different processes. The study carried out with this paper is concerned with the promising utilization of the organic wastes from an existing poultry industry as fuel. Different plant configurations have been considered in order to make use of the oil and of the meat and bone meal, which are the by-products of the chicken cooking process. In particular, the process plant can be integrated with an energy supply plant, which can consist of an indirectly fired gas turbine. Moreover, a steam turbine plant or a simplified system for the supply of the only technological steam are investigated and compared. Thermodynamic and economic analysis have been carried out for the examined configurations in order to outline the basic differences in terms of energy savings/production and of return of the investments.

Today, coal is responsible for 40% of annual CO2 emissions. At the same time, global warming causes climate changes accompanied with catastrophic meteorological phenomena all over the world. After the 2015 Paris Agriment many countries set ambitious energy policy to reduce the annual greenhouse gas emission. The 2021 UN Climate Change Conference, COP26 - Glasgow, ended with the adoption of a less stringent resolution than some anticipated: countries only agreed to “phase down” rather than “phase out” coal. Is possible the realization of the Paris Agreement after COP-26? For achieving this ambitious targets in such conditions, the support of the multi-disciplinary scientific knowledge is needed. Since 2002 a series of SDEWES Conferences were founded. This paper presents an overview of published researches in special issues of leading journals dedicated to the series SDEWES Conferences, including also the papers in current special issue presented on Conferences held in 2020: 2nd LA SDEWES Conference - Buenos Aires, 1st AP SDEWES Conference - Gold Coast, 4th SEE SDEWES Conference - Sarajevo and 15th SDEWES Conference - Cologne. The focus is on five main fields: (1) energy system analysis ; (2) energy savings in the building sector ; (3) district heating ; (4) electrification of transport and (5) water-energy nexus. Undoubtedly, the researches presented in this special issue as well as in previous ones, will contribute to the achievement of the goals of the Paris Agreement in difficult conditions after COP26.

International audience

Abstract An industrial ammonia synthesis loop is a complex interconnected system. With the synthesis reactor operated at high-pressure levels and with synthesis gas made of hydrogen and nitrogen, a highly efficient process design is necessary in order to meet the requirements in terms of cost-efficiency and environmental impact. The evaluation and optimization of different designs in the process synthesis phase are generally done by considering mass and energy balances. However, the conclusions drawn from such an analysis can be misleading and provide, if any, little useful information with respect to system improvement. In order to address these issues, an exergy analysis is used to identify the real thermodynamic inefficiencies of a system and its components. Furthermore, a subsequently conducted advanced exergy analysis provides the means to determine the structural interactions within a system and the thermodynamic improvement potential of its components. In this context, two different ammonia synthesis loop configurations are analyzed. The first concept consists of a three-staged adiabatic reactor with intermediate quench cooling, whereas the second design features a cooled reactor.

Abstract The effect of co-digesting sludge with bio-waste was investigated using an experimental apparatus set for reproducing the operating conditions of a full-scale digester in an existing wastewater treatment plant of 90,000 PE (population equivalent). An increase in the organic loading rate from 1.46 kgVS/m3 day to 2.1 kgVS/m3 day obtained by introducing 40 kg of biowaste per m3 of sludge in the digester caused an increase in the specific methane generation from 90 NL/kgVS to 435 NL/kgVS. These results were used to assess the energetic potential of digesters in eight existing wastewater treatment plants operating in an Italian province with 28,000 PE to 90,000 PE. Results showed that these facilities were able to co-digest globally about 2900 tonnes per year of bio-waste and to generate about 3400 MWh/year of electricity.

Abstract This paper presents experimental and modelling results of fuel gas obtained in a steam-oxygen blown fluidised bed pilot scale (500 kW th ) coal gasifier that is part of the ZECOMIX (Zero Emission of CarbOn with MIXed Technologies) research infrastructure run by ENEA. As there is poor information about start up and steady state operation of fluidised bed gasifiers at such a scale, in this work we investigated the influence of some important parameters such as coal ignition temperature, feeding rate of particulate bed material (olivine sand) and transition from oxidant to reducing environment. The experimental runs confirmed the crucial importance of S/O (steam/oxygen) ratio on the product gas composition. High quality syngas (low content of methane, below 1.0 v/v %, and high content of H 2 and CO: CO + H 2 61.0 v/v%) was obtained with S/O = 1.1. A shortcut model of the gasifier was also formulated, considering instantaneous coal pyrolysis, kinetics of coke steam reforming reactions in the fluidised bed, and achievement of thermodynamic equilibrium for the water gas shift reaction. The model takes into consideration the average residence time of coke particles into the gasifier: since this is a characteristic parameter of the reactor, the performance of different fluidised bed gasifiers can be simulated.