effects of uncertainties on the stability of the results of an optimal sized modular cogeneration plant

Abstract In the last decades, the growing concerns about global warming and climate changes effects led to specific Directive, especially in Europe, promoting the use of primary energy saving techniques. In particular, a more widespread adoption of cogeneration systems has been obtained. However, distributed energy systems do not ensure the achievement of primary energy and cost savings without a proper sizing and operation of the plant. Therefore, vector optimization algorithms could play a key role to identify optimal solutions even when conflicting goals are pursued. The potential of the proposed methodology is demonstrated showing the results achieved from a specific application

Pre-lift Valve Actuation Strategy for the Performance Improvement of a DISI VVA Turbocharged Engine

Abstract Modern internal combustion engines (ICEs) are becoming more and more complex in order to achieve not only better power and torque performance, but also to respect the pollutant emissions and the fuel consumption (CO 2 ) limits. The turbocharger, advanced valve actuation systems (VVA) and the EGR circuit allow the ICE's load control together with the traditional throttle valve and spark advance. Thus, an higher number of operating parameters are available for the calibration engineer to achieve the required performance target (minimum fuel consumption at part load, maximum power and torque at full load, etc.). On the other hand, the increased degrees of freedom may frustrate the potentialities of so complex systems because of the effort needed to identify the optimal engine control strategies. The development of proper numerical models may assist and direct the experimental activity in order to reduce the related times and costs. Although VVA solutions could bring a reduction in the specific fuel consumption thanks to an important de-throttling of the intake system, unfortunately they can simultaneously lead to higher noise levels radiated by the intake mouth. In fact, in this case, the pressure waves travelling through the intake ducts are not properly damped by the throttle valve. In this paper a numerical methodology is developed to define the engine calibration and the intake valve lift profile that simultaneously minimize the BSFC and the noise at part load. The engine object of the study is a turbocharged Spark-Ignition Direct Injection (SIDI) ICE equipped by a lost motion valve actuation system for the intake valves. In this study, the commercial 1D thermo fluid-dynamic code GT-PowerTM is provided with user routines for the description of the combustion process and the handing of variable valve lift profiles. The engine model is thus integrated with a commercial optimization code (modeFRONTIERTM) to identify the optimized load control strategies to achieve the set objectives. The proposed methodology is also used for the definition of unconventional valve lift profiles. Particularly, the advantages related to the use of a small pre-lift before the main valve lift profile are estimated compared to a conventional EIVC strategy

CRITERI DI OTTIMIZZAZIONE DI SISTEMI COGENERATIVI: APPROCCIO MULTIOBIETTIVO

Il conseguimento di risultati energeticamente “ottimi” mediante il ricorso alla produzione combinata di energia termica ed elettrica costituisce un problema complesso. Non è possibile, infatti, quantificarne i benefici prescindendo da una conoscenza accurata dei carichi dell’utenza in esame. Il numero di variabili che intervengono nel problema è tale, inoltre, da stravolgere completamente i margini di risparmio energetico ed economico al mutare del quadro normativo, tariffario o dello scenario energetico di riferimento. La dipendenza dalla configurazione impiantistica e dalla relativa logica di gestione è altrettanto significativa. Lo studio, ad esempio, ha messo in luce come per una stessa unità cogenerativa il vantaggio energetico globale del sistema può variare nell’intervallo 0÷19%. Un’analisi di previsione del tipo di quella proposta è fondamentale, quindi, per cercare una soluzione impiantistica (taglia del cogeneratore, schema d’impianto, logica di gestione, taglia dell’eventuale macchina frigorifera ad assorbimento, numero di cogeneratori, etc.) che si avvicini alla soluzione energetica più valida pur garantendo un adeguato profitto. A tal fine, la determinazione delle configurazioni di ottimo è stata perseguita attraverso gli strumenti propri dell’analisi multiobiettivo e ricorrendo, in particolare, all’algoritmo evolutivo di tipo genetico MOGA II implementato nel software di ottimizzazione modeFRONTIER®. Lo studio mostra come la ricerca di configurazioni orientate alla massimizzazione del risparmio energetico complessivo conduce verso risultati peggiorativi per quanto concerne il tempo di ritorno del capitale investito. L’impossibilità di definire un chiaro trade-off fra il Risparmio di Energia Primaria ed il Simple Payback, a conferma della complessità con cui le diverse variabili concorrono a determinare i risultati, ribadisce la sostanziale impossibilità di condurre un’analisi predittiva che prescinda dal ricorso all’ottimizzazione vettoriale. Il potenziale della produzione combinata di energia termica ed elettrica in termini di risparmio energetico è tale da giustificare le attenzioni rivolte alla tecnologia cogenerativa basata su motori a combustione interna alternativi alimentati a gas naturale. Configurazioni impiantistiche e logiche di gestione dei gruppi come quelle analizzate nel presente lavoro, suscettibili di ulteriore ottimizzazione e affinamento, sono tali da configurare risparmi di energia primaria che si avvicinano al 20% in applicazioni ad utenze del settore ospedaliero. Il risultato è ancora più interessante se si considera che la variabilità dei carichi nel settore civile è spesso tale da inficiare, almeno in parte, i potenziali vantaggi della produzione combinata. Per quanto concerne l’utenza dell’Ospedale S.Paolo in esame, ad esempio, particolarmente interessanti potrebbero risultare tutte quelle soluzioni che prevedono il ricorso a tre cogeneratori, caratterizzate da valori del risparmio energetico intorno al 18%, valori di SPB di circa 4 anni e livelli di potenza elettrica erogata compresi nell’intervallo 225÷240 kW per cogeneratore. Queste, infatti, sembrano costituire un valido compromesso in termini di flessibilità di esercizio, semplificazione impiantistica e sicurezza dell’approvvigionamento energetico nell’eventualità di black out elettrici brevi o prolungati. Una volta individuata la soluzione cercata (taglia e numero di cogeneratori) sulla base di opportuni vincoli decisionali, una serie di analisi supplementari possono essere condotte, ad esempio, in merito alla valutazione delle prestazioni energetiche del sistema a carico parziale, in merito a configurazioni impiantistiche ottimizzate, etc. Lo studio, infatti, mostra come la modellazione termo fluidodinamica monodimensionale dell’intero cogeneratore, comprensivo del circuito di recupero termico, possa costituire un valido strumento di ausilio alla progettazione, permettendo di simulare il comportamento del sistema al variare delle condizioni operative, oppure fornire uno strumento di analisi dei risultati attesi al variare della configurazione impiantistica, in risposta a mutate esigenze dell’utenza, o della logica di esercizio del sistema (es. modalità di esercizio heat tracking)

Optimization Criteria for Cogeneration Systems: Multi-Objective Approach and Application in an Hospital Facility

Cogeneration is commonly recognized as one of the most effective solutions to achieve the increasingly stringent requirements in primary energy consumption reduction and greenhouse emissions reduction. The potential of cogeneration led to the adoption of specific directives promoting this technique. In addition, distributed generation plays a strategic role in power reliability. The study and prototyping of cogeneration plants has thus involved many research centers. Similar activities were carried out by DiME (University of Naples). These activities highlighted the need to study the cogeneration system-user interaction to estimate the real energetic and economic benefits. The paper develops a specific methodology that is used to conduct an analysis on the loads of a specific hospital facility. The energetic and economic benefits generated by CHP plants depend on plant and user characteristics, plant layout, management strategies, and economic variables. Therefore, the potential benefits that have attracted the attention of the scientific community are not always granted. For this reason, a predictive analysis is needed to find the optimum configuration of the plant (i.e., engine size, plant configuration, management strategies, absorption chiller size, engine number) that approaches the best energetic solution while ensuring a reasonable profit. Therefore, this study attempts to determine the optimal configuration through a multi-objective approach. The achievement of optimal energetic and economic results through combined heat and power plants is a complex problem. In fact, it is not possible to quantify the benefits even with an accurate knowledge of the user load profiles. The number of variables involved in the problem could also completely change energetic and cost savings with changes in regulation, tariffs or reference energetic scenarios. Equally significant is the dependence on the plant configuration and its management strategy. The study, for example, has revealed that the overall energy savings can vary in the range of 0???19% for a specific CHP gas engine. Therefore, a predictive analysis such as the one proposed in this study is important in determining a plant solution (engine size, plant configuration, management logic, possible absorption chiller size, engines number, etc.) that approaches the best energetic solution while ensuring a reasonable profit. For this reason, the determination of the plant optimal configuration has been pursued through a multi-objective approach, specifically through the genetic evolutionary algorithm MOGA II implemented in the optimization software modeFRONTIER. The study shows how the search for configurations aimed at maximizing the global energy saving leads to the Simple Payback worsening results. The configuration of a trade-off between primary energy saving and Simple Payback confirms the inability to conduct any predictive analysis that disregards the use of vector optimization. The potential energy savings of combined heat and power justifies the attention given to the cogeneration technology based on reciprocating internal combustion gas engines. The plant configurations and management strategies analyzed in this work, which require further optimization and refinement, indicate primary energy savings approaching 20% for hospital facilities. The result is even more interesting when you consider that the load variability in the civil sector often affects, at least partially, the potential benefits of combined heat and power. With regard to the S. Paolo Hospital in Naples, for example, solutions that use three gas engines are particularly interesting and are characterized by energy savings of approximately 18%, SPB of approximately 4 years and electric power output in the range 225???240 kW for each engine. These solutions seem to represent a good compromise of operational flexibility, plant simplification and power reliability in the case of short or long power outages

Regulation Problems of Combined Cycle Gas-Steam Turbine Power Plant in a Liberalized Market: Part II - Thermodynamic Analysis

This paper addresses the thermodynamic analysis performed with reference to a 760 MW Combined Cycle Gas-Steam Power Plant, built in Sparanise (Italy) and went into service in September 2007. The analysis is based on the experimental analysis already described in Part I of the work. The new Italian legislation revealed a number of technical and economic issues for Combined Cycle Power Plants designed to reach out their maximum efficiency in the operation at the nominal point, thus affecting its efficiency, operations and maintenance costs. In fact, this Plant does not operate at constant maximum load (Base Load) but it is forced to continuous load variations facing the problem of Frequency Regulation. For the evaluation of these aspects, thermodynamic analyses have been performed. This activity is used to identify the combinations of control parameters that maximize the overall performance and enable the evaluation of different system configurations. An application of the tool developed for the thermodynamic analysis has also been proposed to evaluate the effect of the Inlet Fogging Technique on the global efficiency and significant quantities

Experimental Development, Thermo-Fluid Dynamics Simulation and Energetic Analysis of a 15 kW Micro-CHP Plant

Cogeneration is commonly recognized as one of the most effective solutions to achieve the increasingly stringent reduction in primary energy consumption and greenhouse emissions. This characteristic led to the adoption of specific directives promoting this technique. In addition, a strategic role in power reliability is recognized to distributed generation. The study and prototyping of cogeneration plants, therefore, has involved many research centers. This paper deals with energetic aspects of CHP referring to the study of a 15 kW micro-CHP plant based on a GPL reciprocating engine designed, built and grid connected. The plant consists of a heat recovery system characterized by a single water circuit recovering heat from exhaust gases, from engine coolant and from the energy radiated by the engine within the shell hosting the plant. Some tests were carried out at whole open throttle and the experimental data were collected. However it was needed to perform a 1D thermo-fluid dynamics simulation of the engine to completely characterize the micro-CHP. As the heat actually recovered depends on the user's thermal load, particularly from the required temperature's level, a comparison of the results for six types of users were performed: residential, hospital, office, commercial, sports, hotel. Both Italian legislative indexes IRE and LT were evaluated, as defined by A.E.E.G resolution n. 42/02 and subsequent updates, as well as the plant’s total Primary Energy Saving. Keywords: Micro-CHP, Heat Recovery System, Primary Energy Saving (PES), Reciprocating Internal Combustion Engine (RICE), 1D Thermo-Fluid Dynamics simulatio

Regulation Problems of Combined Cycle Gas-Steam Turbine Power Plant in a Liberalized Market: Part I - Experimental Investigation and Energetic Analysis

This paper addresses the experimental and energetic analysis of the performance of a 760 MW Combined Cycle Gas-Steam Turbine Power Plant, built in Sparanise (Italy) and went into service in September 2007. The Plant object of the study faces the problem of Frequency Regulation in the restructured Italian power system which, following the European deregulating process, has been moving from a vertically integrated structure to a new scenario, with several private hold companies competing on the generation side. Bound by electricity market price and dispatching regulations, the power plant does not operate at constant maximum load (Base Load), but it is forced to continuous load variations. The new legislation revealed a number of technical and economic issues for Combined Cycle Power Plants designed to achieve its maximum efficiency in the operation at the nominal point, thus affecting its efficiency as well as operations and maintenance costs. For the partial evaluation of these aspects, in this part of the work experimental investigations and energetic analyses of current performance have been carried out. Subsequently, the main results from the proposed research activity will be used in Part II of the article, to perform thermodynamic analyses

Experimental Development, 1D CFD Simulation and Energetic Analysis of a 15 kW Micro-CHP Unit based on Reciprocating Internal Combustion Engine

Cogeneration is commonly recognized as one of the most effective solutions to achieve the increasingly stringent reduction in primary energy consumption and greenhouse emissions. This characteristic led to the adoption of specific directives promoting this technique. In addition, a strategic role in power reliability is recognized to distributed generation. The study and prototyping of cogeneration plants, therefore, has involved many research centers. This paper deals with energetic aspects of CHP referring to the study of a 15 kW micro-CHP plant based on a LPG reciprocating engine designed, built and grid connected. The plant consists of a heat recovery system characterized by a single water circuit recovering heat from exhaust gases, from engine coolant and from the energy radiated by the engine within the shell hosting the plant. Some tests were carried out at whole open throttle and the experimental data were collected. However it was needed to perform a 1D thermo-fluid dynamics simulation of the engine to completely characterize the micro-CHP. As the heat actually recovered depends on the user's thermal load, particularly from the required temperature's level, a comparison of the results for six types of users were performed: residential, hospital, office, commercial, sports, hotel. Both Italian legislative indexes IRE and LT were evaluated, as defined by A.E.E.G resolution n. 42/02 and subsequent updates, as well as the plant???s total Primary Energy Saving

Study of a New Mechanical VVA System. Part II: Estimation of the Actual Fuel Consumption Improvement through 1D Fluid Dynamic Analysis and Valve Train Friction Estimation

It is commonly recognized that one of the most effective ways to improve Brake-Specific Fuel Consumption (BSFC) in a spark-ignition engine at partial load is the adoption of VVA strategies, which largely affect the pumping work. Many different solutions have been proposed, characterized by different levels of complexity, effectiveness and costs. VVA systems currently available on the market allow for variable valve timing and/or lift (VVA). The design of a new mechanical VVA system has been discussed in Part I of this article. That study led to the development of a four-element VVA mechanism. Now, to estimate the potential advantages of the studied system on engine performances, one-dimensional thermo-fluid dynamic analyses were conducted, considering both full load and partial load operating conditions. For this reason, this article addresses the definition of the one-dimensional model of a 638-cm3 single-cylinder engine under development, which will be equipped with the four-element VVA system. The findings from the one-dimensional study will be discussed in detail. In particular, the parametric analyses, which concern the engine power at wide open throttle and the SFC at partial load, will be presented. These results, however, are only theoretical results because the one-dimensional simulation is not able to take into account the increased friction losses due to the complexity of the VVA system. Therefore, to correctly quantify the actual fuel consumption allowed by the studied system (net of the generally increased power dissipated by friction when compared to a conventional valve train), a specific methodology, discussed in Part I, has been adopted

Ottimizzazione Multivariabile-Multiobiettivo di Sistemi Cogenerativi: Applicazione ad un’Azienda Ospedaliera. Parte A: Metodologia

La cogenerazione è comunemente riconosciuta come una delle soluzioni più efficaci per far fronte alla necessità di conseguire una riduzione dei consumi di energia primaria e delle emissioni di sostanze clima-alteranti. Nel presente lavoro si riferisce dello sviluppo di una specifica metodologia di calcolo, utilizzata per condurre una serie di analisi quantitative con riferimento alle curve di carico di un’utenza ospedaliera di riferimento e attraverso lo studio dell’interazione impianto-utenza. 55 MULTIVARIABLE AND MULTIOBJECTIVE OPTIMIZATION FOR COGENERATION PLANTS. PART A: METHODOLOGY Combined heat and power plants are recognized as very effective solutions to achieve the increasingly stringent requirements in primary energy saving. The paper addresses the use of a specifically developed methodology to conduct several analyses on the basis of the loads of a specific hospital facility and through the study of the cogeneration system-user interaction