Worldwide escalating energy consumption of recent years, due to the earth population growth and the spreading of industrialization, has resulted in an increased concern about the environmental impact ...of energy conversion systems. Heavy exploitation and extensive use of fossil fuels have indeed also led to envisage their foreseeable depletion, thus opening the way to the use of alternative fuels as biomass. Among thermo-chemical treatments of biomass, gasification is particularly attractive for its release of syngas (or producer gas), suitable of being used in various combustion systems, including internal combustion engines. In principle, biomass contaminants and heavy hydrocarbons can be removed during syngas cleaning, before the actual combustion process, thus leading to an overall cleaner conversion process. At present, demonstrating operational feasibility and effectiveness of gasification technologies and proving long term sustainability, also through the enhancement of fuel flexibility, are recognized as key elements for the development and market diffusion of biomass energy systems. In fact, although gasification has been known for a long time, its control has long requested serious efforts by researchers and manufacturers. Nowadays, new perspectives are imaginable thanks to the use of simulation tools that may reveal particularly useful to improve gasification efficiency and increase the quality of the producer gas.
In recent years, several numerical models have been indeed proposed to characterise and predict such a complex process, where drying, pyrolysis, gasification and combustion take place simultaneously. This article presents a general overview of gasification models available, with emphasis on those based on the stoichiometric method. Although this last may seem too restrictive under some circumstances, equilibrium models are useful to predict the maximum yield attainable by a reagent system, since they reproduce an ideal gasification performance. Due to their simplicity and the reduced computational time, these models are suitable of being employed in a first stage of an analysis or within optimization procedures, where the influence of a number of parameters has to be investigated or a choice of the optimal biomass to be treated for a certain scope is to be made.
•A method to assess energy performance of wastewater treatment plants is proposed.•Energy performance indicators are coupled with pollution removal efficiencies.•The method is applied to a large ...database of wastewater treatment plants.•Some classes of energy performance are introduced.
Wastewater treatment is a high energy consuming process, and its energy demand is considerably increasing due to the introduction of more restrictive standards on the quality of water effluents, that require advanced technologies for pollutant removal. Energy audits are carried out in order to improve energy efficiency of wastewater treatment plants, by introducing some measures, such as adjustments of the treatment scheme, or optimization of existing operational units. At the same time, energy recovery from wastewater treatment and its by-products is being implemented in order to reduce economic costs and environmental impact of the process. In order to assess the benefits resulting from implementation of these interventions, procedures for evaluation of energy performance of wastewater treatment plants are being developed.
In this work, a novel method is proposed for assessing energy performance of wastewater treatment plants by coupling simple energy performance indicators with specific pollution removal efficiencies. This procedure is applied to a large database of wastewater treatment plants, in order to define some classes of energy performance depending on removal efficiency. The method is also used to analyse some Italian plants, representative of different design and management conditions. As a result, only 8.2% of around 300 plants presents the highest class of performance, considering the energy consumption related to the organic matter removal.
Direct use of Waste Vegetable Oil (WVO) as fuel is very attractive to reduce fossil fuels utilization and increase sustainability. WVO incorrect disposal causes serious damages to sewage systems and ...wastewater treatment plants. Moreover, if WVO reaches natural ecosystems, such as rivers, aquifers or subsoil, the environmental consequences can be severe. In recent years, the main reuse of WVO has been in biodiesel production, which is remunerative under current tax allowance policies. However, biodiesel production requires complex physical–chemical treatments, while direct use of WVO just needs mechanical treatment. As a consequence, WVO direct use in energy conversion systems lower the impact, from the economic, energetic and environmental points of view, with respect to biodiesel production. Moreover, as concerns the environmental impact, it should be considered that the direct use of WVO as fuel produces less polluting emissions when considering the whole life cycle: carbon dioxide produced during combustion, in fact, can be partially absorbed by crops used for oil production.
This paper presents a comprehensive review of the work done to evaluate the effects of direct use of WVO in internal combustion engines. Many authors have shown the advantages of using straight vegetable oils or biodiesel produced from WVO as fuel, while the benefits of WVO direct use have not yet been clearly presented. The available literature still presents few papers about this topic, therefore also the use of vegetable oil, that presents physical chemical characteristics very similar to those of WVO, has been taken into account. After a brief introduction, the characteristics of WVO most affecting its use as fuel have been studied. Then several applications of WVO direct use in internal combustion engines and the available fuel supply technologies have been considered. Finally, the energetic performance and the pollutant emissions reported in literature have been deeply analyzed.
•A review of micro combined heat and power bioenergy systems is presented.•Features of an innovative bioenergy system (20kWe and 40kWth) are shown.•An experimental characterization of the bioenergy ...system is realized.•Global energy balance and Sankey diagram are presented.•The effects of users' temperature on efficiencies of the bioenergy system are shown.
The present paper describes an experimental characterisation of a biomass powered micro-cogeneration system based on the coupling between a gasifier and an internal combustion engine. The ECO 20 unit is sized to deliver a maximum electrical and thermal power of 20 kWe and 40 kWth, respectively. In order to highlight possible inefficiencies along the biomass-to-energy conversion chain, the global energy balance of the system under real working conditions is derived. Ultimate and proximate analyses of the processed biomass are performed, accompanied by temperature and mass flow rate measurements and gas chromatograph characterization of collected samples of the produced syngas. The greatest inefficiency is found in the gasification section with a value of the cold gas efficiency in the range of 57–60%. The low quality of the syngas (lower heating value equal to 3731 kJ/Nm3) affects the engine combustion efficiency, hence its electrical efficiency that does not exceed 22.5%. The global electrical efficiency of the plant is equal to about 13.5%. As a further analysis, waste heat recovery is considered under different conditions by decreasing the temperature of the water flowing in the secondary circuit from 68.35 °C to 20.50 °C for the use of the provided thermal energy. This determines an increase of the thermal efficiency of the engine from 11.3% to 56.2%, while the global thermal efficiency increases from 6.46% to 33.72%. A feature of the ECO 20 system is the cooling of the syngas delivered to the engine by its same cooling water, for a considerable advantage on volumetric efficiency with respect to other analogous systems, also in the cases the thermal power is not utilised.
This paper presents an economic and energy feasibility analysis of a renewable energy system for a small city in southern Italy to convert it to zero greenhouse gas city by 2030. The proposed energy ...infrastructure utilises different technologies: wind turbine, photovoltaic panels and biogas cogeneration plants to produce electric energy, and thermal solar panels, cogeneration and heat pumps to meet the thermal energy demand of the city. The electrification of transport sector is also considered. The whole city energy system is analysed by the EnergyPLAN software to evaluate streams combination and potential synergies between the different sectors. In order to improve the analysis, PhotoVoltaic technology has been simulated in TRNSYS environment, to obtain detailed prediction of this component of the energy infrastructure. The system behaviour was analysed considering different time bases: daily, weekly and yearly. The EnergyPLAN outputs include the aggregated yearly production and demands of all modelled energy conversion systems, as well as hourly values useful to identify the measures to make Altavilla Silentina nearly zero carbon city. Every measure identified becomes a new input in EnergyPLAN to evaluate its effect on city energy balance. The economic analysis has been performed to evaluate the electricity and thermal energy costs.
Abstract
Using Ground Coupled Heat Pump (GCHP) systems in urban areas can be particularly difficult due to space or legislative constraints, other than excessive costs due to drilling. To overcome ...these problems, the authors proposed to use Artificial Ground Freezing (AGF) probes, used for tunnel excavation, as Ground Heat Exchangers (GHE). It is a widespread practice to seal the probes in the tunnel after the completion. The conversion of existing AGF probes into GHE for GCHP allows us to avoid additional drilling costs, and other space or legislative constraints associated with the use of GCHP systems in urban areas. Such systems could be developed to use underground urban transportation tunnels for heating and cooling in smart cities. These systems were tested after the construction of two tunnels, as part of the GeoGRID project, in Piazza Municipio, Naples, Italy. The data obtained from the experimental setup have been analysed and used for validation of a finite element model developed by the authors to simulate heat transfer between the probes and the surrounding ground. A simplified pipe flow model was introduced, in combination with a 3D model of the ground, to reduce the complexity and computational effort to solve the discretized equations. The simulation results have been compared with experimental data, showing a good agreement, and observing differences in the range of 2 – 5 %. The model can therefore be used as a predictive tool for the development of this type of innovative heat exchanger.
Wastewater treatment plants are high energy-consuming systems, and their electric energy consumption contributes to 25–30% of the total operating costs. A significant part of thermal energy is needed ...for management of the sludge produced during the process. Sludge drying by Combined Heat and Power (CHP) systems is attractive to obtain substantial economic and energy savings, especially if all the waste heat can be used. Since biogas production, where available, is insufficient for sludge drying, the direct use of the exhaust gases of a CHP system fuelled with syngas derived from sludge gasification and waste vegetable oil, is proposed. The profitability of this system is comparable with that of the systems currently employed in advanced wastewater treatment plants. The economic convenience derives from the reduction of sludge to be disposed and the overall energy saving in the plant. The simple payback of the proposed system, equal to 6.8 years, is only one year higher than that found for of an analogue conventional system, while the Net Present Value is 30% higher than that calculated for a conventional system. In terms of environmental impact, the layout presented is more efficient as biomass-derived fuels are used instead of fossil fuels.
•A feasibility study of an integrated system for sludge drying is presented.•Sludge drying is made by WHR from a CHP system made of a gasifier and an ICE.•ICE fuelling is considered through WVO and syngas from dried sludge gasification.•Sub-models for drier, gasifier, ice and the WHR system are presented.•Profitability is assessed through comparison with a conventional system.
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•The feasibility of using waste vegetable oil for energy production is analyzed.•An engine powered by diesel and waste vegetable oil is experimentally investigated.•The results are ...applied to the case study of a real wastewater treatment plant.•A feasibility analysis of the proposed system is carried out.•The system appears to be economically and environmentally feasible.
Waste vegetable oil is generated from different sources, such as domestic, commercial and industrial activities, and it requires proper management. Due to the increase in the generation of waste vegetable oil, concern for its management has intensified.
The most common management option for waste vegetable oil is the conversion into biodiesel, which improves the chemical-physical characteristics of raw waste vegetable oil for its use but is characterized by significant energy consumption and environmental impact. Therefore, straight waste vegetable oil as fuel, after mechanical pre-treatments and with suitable operational strategy, is suggested in the available literature.
In this work, waste vegetable oil from the separate collection is proposed as a source to fuel a combined heat and power unit producing energy for wastewater and sludge treatment plants, which is high energy-demanding.
The operation of the combined heat and power unit is analyzed considering data from an experimental campaign carried out to investigate the performance of internal combustion engines powered by waste vegetable oil. Such experimental data are used to carry out the feasibility analysis of a combined heat and power system for an actual wastewater treatment plant located in the Campania region, southern Italy.
The system appears to be economically feasible with a simple payback around 3.44 years, a net present value higher than 19.0 M€ and an interest rate of return of 26.7%. Moreover, it produces 70.0% less equivalent carbon dioxide emissions, with respect to a similar system powered by fossil fuels.
Therefore, waste vegetable oil as a locally available and renewable energy source may contribute to realize smart and resilient communities, since it improves securing domestic energy supply and waste valorization.
This paper presents a new methodology that allows to define a 100% renewable smart energy system in a sustainable manner. The authors integrate the EnergyPlan with a mathematical model that analyzes ...the energy system from an exergetic point of view taking into account the exergy of the whole energy system and its components. Once multiple scenarios are obtained by EnergyPLAN, the exergetic model identifies the scenario characterized by the highest exergetic efficiency and the lowest energy wasting. This approach is a novelty since the “exergetic” optimization criterion coupled with EnergyPLAN software has never been utilized. Since the best energy system could not be economically attractive, this methodology might support Municipalities in setting up focused incentives to make the sustainable solutions the most cost effective too.
The authors present a case study by applying the new methodology to the city of Pompeii. The results show that the best solution provides 21.0 MWe capacity of PV plant, integrated to 8.10 MWe of CHP plant. Due to a high value of critical excess electricity production, 10 MWe heat pumps must be installed. Finally, a solar thermal plant is installed. The proposed system could be only realized if new incentives are provided.
•A 100% renewable energy system is carried out through a new methodology.•Energy, exergetic and economic analyses of the case study proposed are presented.•A tool to define types of RES plants must be incentive to convert territory in 100% renewable energy.
Abstract
Thermoacoustics is a promising technology for energy conversion purposes. Among the bottlenecks limiting a large diffusion of thermoacoustic devices, there are heat exchangers, whose ...behaviour in oscillatory flows is rather different than those working in stationary flows. Furthermore, the classical linear acoustic theory in the frequency domain cannot predict with high-fidelity the thermo-fluid dynamics of such heat exchangers. In this article, a CFD model based on a standing wave device including a parallel plate heat exchanger is proposed. The setup is inspired by a similar prototype of a thermoacoustic engine in which the performance of the ambient heat exchanger was tested. The results of the CFD model are therefore compared, in terms of the temperature difference between fluid and solid wall in the heat exchanger, average heat flux and Nusselt number, with experimental data showing a satisfying agreement.
