A new thermoeconomic methodology for energy systems

Thermoeconomics, or exergoeconomics, can be classified into the three fields: cost allocation, cost optimization, and cost analysis. In this study, a new thermoeconomic methodology for energy systems is proposed in the three fields. The proposed methodology is very simple and clear. That is, the number of the proposed equation is only one in each field, and it is developed with a wonergy newly introduced in this paper. The wonergy is defined as an energy that can equally evaluate the worth of each product. Any energy, including enthalpy or exergy, can be applied to the wonergy and be evaluated by this equation. In order to confirm its validity, the CGAM problem and various cogenerations were analyzed. Seven sorts of energy, including enthalpy and exergy, were applied for cost allocation. Enthalpy, exergy, and profit were applied for cost optimization. Enthalpy and exergy were applied for cost analysis. Exergy is generally recognized as the most reasonable criterion in exergoeconomics. By the proposed methodology, however, exergy is the most reasonable in cost allocation and cost analysis, and all of exergy, enthalpy, and profit are reasonable in cost optimization. Therefore, we conclude that various forms of wonergy should be applied to the analysis of thermoeconomics.     

A thermoeconomic analysis of biomass energy for trigeneration

The principal objective of this study is to formulate a calculation process, based on the second law of exergy, for evaluating the thermoeconomic potential of a steam-turbine plant for trigeneration. The plant employs biomass, namely, waste wood as its energy source. Four different plant configurations are presented and assessed. ‘Their cost effectiveness is evaluated with varying economic and operating parameters’, because only the fuel price and electricity price are varied. In case 1, high pressure superheated steam generated is supplied to meet the demand for process heat as well as chilled water production in an absorption chiller. In cases 2 and 3, steam is extracted at appropriate stages of the turbine and supplied to meet the demand for process heat and chilled water production in an absorption chiller. Steam generated in case 2 produces sufficient power to meet internal demands while case 3 generates excess electricity for sale back to the utility. In case 4, low pressure saturated steam is generated to meet the demand for process heat and electricity is bought from the utilities, including those used to power an electric vapour-compression chiller. For all cases, it was found that exergy destruction is most extensive in the furnace, amounting to nearly 60%. Exergy destruction in the steam drum is the next most extensive ranging from 11% to 16%. It was also observed that the overall production cost decreases with steam pressure and increases with steam temperature.     

A fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems

An enthalpy formulation based fixed grid methodology is developed for the numerical solution of convection-diffusion controlled mushy region phase-change problems. The basic feature of the proposed method lies in the representation of the latent heat of evolution, and of the flow in the solid-liquid mushy zone, by suitably chosen sources. There is complete freedom within the methodology for the definition of such sources so that a variety of phase-change situations can be modelled. A test problem of freezing in a thermal cavity under natural convection is used to demonstrate an application of the method.     

A thermoeconomic model of a photovoltaic heat pump

In this paper the model of a heat pump whose evaporator operates as a photovoltaic collector, is studied. The energy balance equations have been used for some heat pump components, and for each layer of the photovoltaic evaporator: covering glaze, photovoltaic modules, thermal absorber plate, refrigerant tube and insulator. The model has been solved by means of a program using proper simplifications. The system input is represented by the solar radiation intensity and the environment temperature, that influence the output electric power of the photovoltaic modules and the evaporation power. The model results have been obtained referring to the photovoltaic evaporator and the plant operating as heat pump, in terms of the photovoltaic evaporator layers temperatures, the refrigerant fluid properties values in the cycle fundamental points, the thermal and mechanical powers, the efficiencies that characterize the plant performances from the energy, exergy and economic point of view. This study allows to realize a thermoeconomic comparison between a photovoltaic heat pump and a traditional heat pump under the same working conditions.     

A critical comparison between thermoeconomic and emergy analyses algebra

Both thermoeconomic accounting and emergy analysis methodologies deal with energy systems and are aimed at allocating costs of input resources among system products. They have, however, different goals and fields of application. The former focuses on energy systems converting the energy of fuel/s into the desired product/s. The latter amplifies the perspective by extending it to the wider level of biosphere, by including all the processes that are involved in the formation of system inputs, either devices or material and energy flows.     

Finite size thermoeconomic optimization for irreversible heat engines

An optimization analysis for an irreversible heat engine has been carried out based on a new thermoeconomic optimization criterion. The thermoeconomical objective function has been taken as the power output per unit total cost. In the analysis, the irreversibility effects due to heat transfer across finite temperature differences, the heat leak loss between the external heat reservoirs and internal dissipation of the working fluid are taken into account. The maximum of the objective function and the corresponding optimal conditions has been derived analytically. The effects of technical and economical parameters on the global and optimal performances have been investigated.     

A new multibody modelling methodology for wind turbine structures using a cardanic joint beam element

This paper presents a new multibody modelling methodology for wind turbine structures. The methodology is based on the hybrid multibody system being composed of rigid, flexible bodies, force elements and joints. With a cardanic joint beam element based on the Timoshenko beam theory, the flexible bodies, e.g. rotor blades and tower, shafts, are modelled by a set of rigid bodies connected by cardanic joints geometrically and constrained by spring forces elastically, thus a whole wind turbine structure can be represented by a discrete system of rigid bodies, springs, and dampers. Using some concepts of the differential geometry, the Lagrange's motion equations of the multibody system are represented in explicit form. With this model, the global natural vibrations of a wind turbine structure of 600 kW are analysed.     

Hybrid Fuel Impact Reconciliation Method: An integral tool for thermoeconomic diagnosis

This paper proposes a method of thermoeconomic diagnosis based on the concepts of the fuel impact formula and the analytical reconciliation method. Such a method is able to detect, isolate and quantify individually the causes in terms of the additional fuel consumption, when internal malfunctions or control deviations occur. Commonly, any diagnosis method requires the definition of a Test State Condition (TEC), a Reference State Condition (REC), and a comparison technique. In the proposed method the technique is based on the reconciliation procedure, however the common factor consists in maintaining the overall production of a steady operating plant. This will determine the term-by-term fuel impact due to each malfunction. The results obtained allow a comparison between the methods mentioned earlier. The keys of the proposed method are the modification of the reference state, the integration of a modified fuel impact formula and the introduction of a filtering technique for the effects induced by the control and regulation system. In order to validate the mathematical model, this is applied to a combined cycle power plant. Comparisons between the proposed model and the results from the other two methods are studied. The diagnosis error was less than 0.2%.     

Framework for the quantitative modelling of the European methodology for qualification of non-destructive testing

The European methodology for qualification of non-destructive testing has been adopted as the basis of inspection qualifications for nuclear utilities in many European countries. According to this methodology, the inspection qualification is based on a combination of technical justification and practical trials. The methodology is qualitative in nature, and it does not give explicit guidance on how the evidence from the technical justification and results from trials should be weighted. This article discusses the quantification of the methodology. A structured and quantified approach to combine evidence from technical justifications and practical trials would provide improved transparency in the qualification process. A Bayesian framework for the quantification process is presented and examples of possibilities to combine technical justification and trial results are given. The article also identifies the areas needing further development.     

Validation of a methodology for determining the PEM fuel cell complex impedance modelling parameters

In this paper, we present a new methodology for determining the complex impedance parameters for a Proton Exchange Membrane (PEM) Fuel Cell in order to have a general model for embedded diagnosis. The modelling of Fuel Cells is a very important phase because it contributes to a better understanding and representation of the internal phenomena in this type of generator. After obtaining the experimental results of the complex impedance using a realized test bench for Proton Exchange Membrane (PEM) Fuel Cell using an electrochemical method which is the electrochemical impedance spectroscopy (EIS), we treat these results with an identification algorithm based on least squares method in the objective to determine the variations laws of the complex impedance parameters then implement in a PEM Fuel Cell model with Matlab/Simulink software. The established model of the complex impedance is based on electrical components and takes into account the mathematical equations of the different elements. The simulation results of this implemented model inform us about the state of the PEM Fuel Cell and validate the choice of the parameters. The validation of this choice is done by a comparative study using residual analysis method between the experimental and the simulation results. The general model is obtained from the superposition of the measured and theoretical results.     

Design methodology and thermal modelling of industrial scale reactor for solid state hydrogen storage

In this study, a novel set of comprehensive arithmetic correlations has been proposed to design an industrial scale cylindrical reactor with embedded cooling tubes (ECT) for metal hydride (MH) based hydrogen storage and thermal management applications. Based on ASME standards, different nominal pipe sizes were imparted into a cylindrical reactor design with ECT to accommodate 50 kg of LaNi_4.7Al_0.3 alloy. A three dimensional numerical model has been developed using COMSOL Multiphysics 4.3a to predict the hydriding performance of designed reactors, which was further experimentally validated as well. At an absorption condition of 30 bar supply pressure and 298 K absorption temperature with 60 lpm volumetric HTF flow rate, 6 inch reactor with 99 ECT portrayed better heat transfer characteristics. From the parametric investigation, it is observed that the variation of supply pressure has predominant effect followed by the variation of the HTF flow rate on hydriding (absorption) kinetics of the device. However, the variation of absorption temperature has minuscule influence on the hydriding performance. At a supply condition of 30 bar and 298 K with water flow rate of 30 lpm, a hydrogen storage capacity (HSC) of 1.29 wt% was achieved within 2060 s.     

A methodology for modelling synthetic daily sequences of hourly power demand for villages and small towns, based on stochastic processes

A model to generate daily sequences of hourly power demand values is described. Inputs are the daily values of energy consumption and load-factors (the ratio between mean and peak load). The whole model covers three independent first-order autoregressive models to generate data sequences of, respectively, daily energy consumption, daily load-factor and hourly power demand. The analysis of a power demand data set reveals that energy consumption and load-factor are independent variables; two independent time series of daily values of energy consumption and load-factor are built; their statistical and sequential properties can be described with first-order autoregressive models. Assuming a villlage’s consumption-structure as characterized by load curves with a peak load at night, the load-factor is taken as a shape-factor for these curves. A frequency distribution is built on daily load factors. The data sequence is, then, sorted into groups of daily curves, each one characterized by a load-factor-class. A daily average load curve is estimated for each class, along with its daily standard deviation curve. An analysis of each group of daily curves shows that the statistical and sequential properties of each one can be also described with first-order autoregressive models. For modelling purposes, the autocorrelation coefficient is determined for each load-factor class. Thus, energy and power relate to each other under different load-factors. Application examples are offered, for design purposes.     

Thermal management for a hydrogen-fueled 1-kW PEMFC based on thermoeconomic analysis

Thermal management is a critical issue in optimizing the performance of proton exchange membrane fuels cells (PEMFC). The heat balance between the heat generation in fuel cell stack (FCS) and the heat removal by coolant liquid determines the operating temperature of the PEMFC and the dehydration or flooding condition in FCS. In this study, the amount of water condensed among all the water produced during the electrochemical reaction in FCS of a hydrogen-fueled 1-kW PEMFC at various conditions was determined using a thermoeconomic method called modified productive structure analysis (MOPSA) and the calculated results were compared with observed ones. The amount of the condensed water which should be removed through the cathode channel is dependent crucially on the cooling rate of FCS, which indicates that thermal management for FCS can be done by controlling of the cooling rate of FCS.     

Performance analysis and optimization of heat exchangers: a new thermoeconomic approach

A thermoeconomic performance optimization has been carried out for a single pass counter-flow heat exchanger model. In the considered model, the irreversibilities due to heat transfer between the hot and cold stream are taken into account and other irreversibilities such as pressure drops and flow imbalance are ignored. The objective function is defined as the actual heat transfer rate per unit total cost considering lost exergy and investment costs. The optimal performance and design parameters which maximize the objective function have been investigated. The effects of the technical and economical parameters on the general and optimal thermoeconomical performances have been also discussed.     

A proposal for a new US oil policy

This article proposes the substitution of more involvement by the US government in international oil trade for less government regulation of the domestic oil business. The proposal attempts to isolate the domestic oil business from the international distortions caused by OPEC. In particular, an enlarged government role is suggested, in setting the volumes and prices at which oil is imported. In return, it is recommended that all US oil be deregulated. This can be achieved at no direct increase in cost to the US consumer. The proposal does not call for confrontation with OPEC governments, but would partially rest on their cooperation. The plan offers a more easily administered, less bureaucratic control of US crude oil prices and the prospect of producing more US oil.     

City carbon budgets: A proposal to align incentives for climate-friendly communities

Local governments can have a large effect on carbon emissions through land use zoning, building codes, transport infrastructure investments, and support for transportation alternatives. This paper proposes a climate policy instrument – city carbon budgets – that provides a durable framework for local governments to reduce greenhouse gas emissions. Local governments would be assigned an emissions “budget”, and would be required to keep annual local transport and buildings emissions within this budget. This policy framework could be implemented and managed by a higher-level government, or might be used in awarding funds to developing country cities from international climate funds. The state of California has enacted a version of this policy. In this paper, we identify and evaluate options for creating an effective and acceptable institutional structure, allocating emission targets to localities, measuring emissions, providing flexibility and incentives to local governments, and assuring compliance. We also discuss the likely costs of such a policy.     

Quick-E-scan: A methodology for the energy scan of SMEs

This paper introduces the Quick-E-Scan methodology that has been developed to achieve the operational energy efficiency of small & medium enterprises (SMEs), characterized by being scarcely disposed to long energy audits and by a limited budget for energy management programs. On one side, through dividing the firm into functional units – either service (lighting, HVAC, etc.) or production units – the main consuming areas are identified and a criticality index is defined; conversely, an enhancement index highlights the gap of each unit towards the best available techniques (BATs) in energy management programs. Finally, a priority index, created with the junction of the two indexes, points out the most profitable areas in which energy saving measures should be implemented. The methodology, particularly quick and simple, has been successfully tested in 38 SMEs in Northern Italy.     

The iterative contribution and relevance of modelling to UK energy policy

This paper discusses the iterative provision of modelling insights on long-term decarbonisation scenarios for UK energy policy makers. A multi-year model construction process of the UK MARKAL-Macro-hybrid energy-economic model, and four subsequent major policy analyses illustrates the scope of this interaction. The initial set of modelling runs focused on the technical feasibility of long-term 60% carbon dioxide (CO₂) reduction scenarios, the role of key technologies, and the underlying uncertainties. Furthermore subsequent modelling studies were aimed to generate insights on more stringent targets, and on issues and uncertainties that may make targets harder to achieve. Hence, this paper analyses the large number of long-term UK CO₂ reduction scenarios through a clustering approach on target stringency and barriers to implementation. Robust findings and key uncertainties are highlighted, including the critical role of the power sector, trade-offs between resources, sectors, key energy technologies and behavioural responses, and the increasing level and spread of CO₂ marginal prices and GDP impacts. The relevance and use of modelling insights to the UK energy policy process is shown in the continuation of the energy modelling–policy interface. This constitutes both ongoing model development, and nuanced scenario analysis designed to further explore key uncertainties in evolving policy issues.     

S109E联合循环机组热电冷联产的热经济性分析

简要介绍了武昌热电公司利用天然气的改扩建工程;着重分析了S109E联合循环热电冷联产的热经济性,结果表明,这一联产形式实现了能源梯级利用,使能源转换效率高达70%.