1,721,026 research outputs found
Application of environmental performance assessment of CHP systems with local and global approaches
No full textThis paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario. Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the "Avoided Heat Generator" is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact. Numerical evaluations of the CHP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for several CHP systems with different technologies and electric power sizes, in order to provide a comprehensive overview of current CHP prime mover environmental performance and to serve as an application reference example of the two methods potential use, in the framework of the CHP units authorization procedure. The significant effect of the reference comparative scenario is also highlighted
COMBINING WASTE-TO-ENERGY STEAM CYCLE WITH GAS TURBINE UNITS
No full textIn recent years, interest has been growing in developing new possibilities to maximize the conversion of waste into energy. Technologies allowing for efficient Waste-To-Energy (WTE) conversion are supported in the EU, by the European Waste Framework Directive, suggesting an efficiency criteria aimed at introducing a reference quality standard. Nevertheless, current state-of-the-art WTE plants are typically characterized by low efficiency values, compared to conventional steam power plants using fossil fuels. This is mainly due to limitations in the WTE steam cycle design parameters, in comparison with large fossil fuelled power plants.
This paper focuses on an innovative and promising strategy to improve waste conversion through integration of a conventional WTE power plant with a Gas Turbine (GT). The resulting WTE-GT integrated plant requires to conceive a redesign and an optimization of the steam-gas cycle. In particular, this study investigates the feasibility of utilizing the hot gases leaving the GT to superheat the steam leaving the WTE steam generator, as well as heating the feed water returning to the steam generator of the WTE condenser. Parametric analysis of the effect of the GT discharged heat on the steam mass flow production is carried out and the optimum plant match condition in terms of plants capacity ratio is identified. Detailed modifications to the WTE cycle and the resulting enhancement of its performance are presented.
Numerical results of a representative WTE plant integrated with different GT commercial units are shown and discussed. Results of the study suggest issues and useful guidelines to: (i) create new advanced WTE-GT integrated power plants or to (ii) repower existing low-performing WTE power plant, in order to increase waste conversion into energy
Performance Indexes and Output Allocation for Multi-fuel Energy Systems
No full textAbstractIn this paper we take into account the concept of conversion efficiency by exploring Multi-Fuel (MF) energy systems. A MF system can be defined as a system with various fuel energy input and useful product output. The difficult task in defining a performance index for MF systems consists in quantifying the contribution of each input fuel to the total output energy.This paper intends to make few proposals and start a discussion that would be helpful to assess the MF system performance.The conventional first law efficiency, normally used to assess performance of Single-Fuel (SF) system, can be applied but it provides incomplete information for a MF system. The electric equivalent efficiency, the relative and overall MF synergy index concepts are introduced as most significant performance indexes; these new performance indexes are presented with the aim to evaluate the MF performance compared to reference SF scenarios. Proposed performance indexes are analyzed, discussed and compared from a general point of view, identifying aspects of relation and main differences. The introduced conversion efficiency indexes are applied and discussed to a specific co-combustion power plant case. The influence of the reference scenarios, as it is highlighted in the paper, results of key importance. The evaluation of the proposed indexes is of relevant interest with the goal of formulating a specific and unified theory about MF power energy systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Performance Assessment of Smart District Heating Networks: The Influence of Distributed (Co)Generation on the Network Primary Energy Consumption
No full textInfluence of the Prosumer Allocation and Heat Production on a District Heating Network
Full text linkTo face the climate change and global warming issues, European countries have set new targets in order to reduce the CO2 emissions to 40% by 2030 and to 80% by 2050. The district heating networks, and in particular low-temperature networks, due to their efficient heat supply and distribution represent a key point for meeting these goals, as well as the renewable sources integration. Nowadays, in fact, about 40% of the energy consumed in Europe is for heating, most of which is provided by fossil fuels employment. This article concerns the smart district heating, namely, the possibility of a bidirectional energy exchange between the district heating network and the connected users. The main purpose of this study is to evaluate the possibility of including a prosumer-that is, a customer who can both consume and produce heat-in an existing small/medium district heating network. To this purpose, an in-house-developed software has been applied to analyze whether and which user of the district heating network is more suitable to be set as prosumer and the effect of the installed distributed generation system on the network. The results show how the choice of a prosumer over another and how the amount of exchanged thermal power affect the performance of the network, with a consequent need of a modification in its operation and management
Preliminary Investigations on a Test Bench for Integrated Micro-CHP Energy Systems
No full textAbstractMicro-CHP (Combined Heat and Power) energy systems are potentially suitable for residential and tertiary utilities, typically characterized by low-grade heat demand and limited electric-to-thermal energy demand ratio values. Different innovative and under development CHP technologies are currently investigated in small scale units, but a standard has not been identified till now. Moreover, depending on the load request, the produced electricity can be used, stored in electric accumulator or in the external net, or integrated with other external sources. Contextually, the available heat can be used, accumulated inside the system or dissipated. The actual convenience of small size CHP systems depends on the demand profiles and the operation management logic.A test facility is being developed, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies (such as Organic Rankine Cycles and Proton Exchange Membrane Fuel Cells), a battery and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles.This report describes the main characteristics of the implemented test bench, the selection procedure of the adopted micro-CHP unit and expected performance
Repowering existing under-utilized WTE power plant with gas turbines
Full text linkSeveral Northern European countries are facing an incineration plant capacity larger than national generation
of waste, mainly caused by a reduced availability of waste, economic crisis and over-investments.
This is causing several WTE power plants to operate at reduced or under-utilized waste input capacity. In
the aforementioned context, this paper focuses on two repowering options to improve waste conversion
efficiency of an existing under-utilized Waste-To-Energy (WTE) power plant with a Gas Turbine (GT). In
particular, this study investigates the feasibility of middle pressure repowering strategies: additional
steam is produced in a simplified Heat Recovery Steam Generator (HRSG) fed by the GT exhaust gas.
The proposed repowering options are quite simple and easy to adapt to mid-size under-utilized types
of WTE power plant.
A thermodynamic evaluation of the system feasibility is presented for a typical WTE. For each investigated
repowering option, minimum GT size is identified along with optimum plant match condition in
terms of plants capacity.
A complete thermodynamic simulation of the steam cycle is performed and different plant configurations
are examined under different GT commercial units. Detailed modifications to the WTE cycle and the
resulting performance improvements are presented for both analyzed repowering options.
Furthermore, different key performance indicators have been taken into account to evaluate, for each
investigated configuration, the integrated dual-fuel system performance enhancement in comparison
with the under-utilized and the original WTE plant.
Both power output and efficiency of the repowered WTE plant compare favorably with those of the
original stand-alone system: repowered system power output rise up to three times the original one
and first law efficiency can reach up to 36%. Furthermore, the integration with GT can enhance the waste
utilization, achieving positive synergy effects, as quantified in this study
Advanced Waste-to-energy Steam Cycles
No full textAbstractThis paper focuses on possibilities to maximize waste conversion through integration of a Waste-To-Energy (WTE) plant with a gas turbine (GT). In particular, this study investigates the feasibility of utilizing the hot gases leaving the GT mainly to superheat the steam leaving the WTE steam generator. A parametric investigation on the steam production is carried out and the optimum plant match condition in terms of plants capacity ratio is identified and discussed. Detailed modifications to a typical WTE cycle arrangement are presented, in order to evaluate the resulting performance enhancement. Numerical results of a conventional reference WTE plant repowering with different GT commercial units are shown and discussed. Performance indexes, specifically introduced in order to assess the proposed integrated configuration and to allocate power output to each input fuel are illustrated and applied on the considered plant. Results of the study suggest possibilities to create new advanced WTE-GT integrated power plants or to repower existing WTE plants, in order to increase waste to energy conversion
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