Maria da Graça Carvalho

Multi-criteria assessment of new and renewable energy power plants

The multi-criteria evaluation of new and renewable technologies demonstrates the potential analysis of complex systems. Every energy system under consideration is an entity by itself, defined by the respective number of parameters which are deterministically interrelated according to the physical laws. Sustainability indicators take into account the economic and environmental resources parameters. This paper presents selection of criteria and options for the new and renewable energy technologies assessment based on the analysis and synthesis of parameters under the information deficiency method. In order to present an evaluation of the new energy technologies, a number of options featuring some of the characteristics measured by the selected sustainability indicators are taken into consideration. For each option under consideration, the sustainability indicators are defined in order to verify their rating under the specific constraints and to obtain the generalised index of sustainability rating of all options. The aim of this paper is to define energy indicators used in the assessment of energy systems which meet the sustainability criterion. In this respect, the following indicators are taken into consideration: energy resources, environment capacity, social indicators and economic indicators.

Energy system assessment with sustainability indicators

Abstract The paper presents an attempt to select, define and apply a set of sustainability indicators for the energy system assessment. Starting from the general sustainability concept, a set of indicators is defined reflecting specific criteria for the energy system evaluation. Particular attention is devoted to the resource, environment, social and economic criteria. Among these groups of criteria there are individual indicators emphasising respective aspect of the sustainability concept. This approach has its limitation due to the lack of data for serious consideration of the system. But it should be anticipated that these excises might serve as the guidance for the eventual future application. Also, this methodology for the assessment of energy system will become an useful tool only if it proves useful in the engineering practice. The example under consideration is an island with only individual consumption to be satisfied with solar, wind, biomass and oil-fired power plant which represent four options under consideration. The set of indicators is defined and determined with the aim to demonstrate the method of decision making procedure in selecting the option which meet selected indicators numerical values and constrain reflecting the non-numeric information of weighting factor for the determination of general criteria for the selection of appropriate option.

Optimisation of MSW collection routes for minimum fuel consumption using 3D GIS modelling.

Collection of municipal solid waste (MSW) may account for more than 70% of the total waste management budget, most of which is for fuel costs. It is therefore crucial to optimise the routing network used for waste collection and transportation. This paper proposes the use of geographical information systems (GIS) 3D route modelling software for waste collection and transportation, which adds one more degree of freedom to the system and allows driving routes to be optimised for minimum fuel consumption. The model takes into account the effects of road inclination and vehicle weight. It is applied to two different cases: routing waste collection vehicles in the city of Praia, the capital of Cape Verde, and routing the transport of waste from different municipalities of Santiago Island to an incineration plant. For the Praia city region, the 3D model that minimised fuel consumption yielded cost savings of 8% as compared with an approach that simply calculated the shortest 3D route. Remarkably, this was true despite the fact that the GIS-recommended fuel reduction route was actually 1.8% longer than the shortest possible travel distance. For the Santiago Island case, the difference was even more significant: a 12% fuel reduction for a similar total travel distance. These figures indicate the importance of considering both the relief of the terrain and fuel consumption in selecting a suitable cost function to optimise vehicle routing.

Sustainable Energy Development

In order to reach the goals indicated by the sustainable energy development the efficiency in the energy conversion use has to meet several criterions [1]. The potential for the efficiency improvement is generally underestimated. Most of the energy conversion systems consider the efficiency improvement as a separate process and their analysis reflects only the potential improvement of the process but not the potential for the efficiency improvement obtained by an exergy analysis of the energy system. Fossil fuel energy resources use is mostly conversion to heat by the combustion processes. Since the combustion process is taking place at temperatures between 900 — 1300°C and over 40% of heat is used a low temperature heat, it is indispensable to take into consideration the thermodynamic assessment of the efficiency in order to bring in line energy conversion processes and energy demand to obtain the optimum fuel utilization.

A Conservative Formulation of the Discrete Transfer Method

The discrete transfer method, often employed to calculate radiative heat transfer in combustion chambers, is not conservative. The reason for this behavior is examined and a conservative formulation is proposed and evaluated. A simple treatment of isotropic scattering media is also presented. The original and the conservative formulation of the method are applied to two-dimensional and three-dimensional enclosures containing a participating medium.

3-D numerical model for predicting NOx emissions from an industrial pulverized coal combustor

The paper describes a three-dimensional computer simulation developed to predict the behaviour of industrial pulverized coal furnaces. The model was applied to a 300 MWe front-wall fired boiler under different operating conditions. The main characteristics of the current model are the use of the Lagrangian framework to describe the particulate phase, the discrete transfer model to handle the radiation transmission, and the standard k−e model for turbulence treatment. The turbulent dispersion of particles is described by a new stochastic self-stable strategy. The NOx formation mechanism is calculated in a post-processor routine. Measurements of NOx emissions were made in the flue gases; the results agree well with those obtained by the simulations.

Flue gas recirculation in a gas-fired laboratory furnace: Measurements and modelling

This paper presents an experimental and numerical study of the effect of flue gas recirculation (FGR) on flame characteristics and pollutant emissions. The experimental study was performed in a small-scale laboratory furnace fired by a gas swirl burner of industrial type. The data reported include simultaneous flue gas concentrations of O 2, CO, CO2, unburnt hydrocarbons (UHC) and NOx. In addition, detailed in-flame data for major gas-phase species concentrations and gas temperatures were obtained in the near-burner region for two representative operating conditions. For these conditions, a mathematical model based on the numerical solution of the equations governing conservation of mass, momentum and energy and the transport equations for scalar quantities was used. The flue gas data show a marked decrease of NOx emissions with FGR without significant effects on flame stability, overall combustion efficiency and CO and UHC emissions. The transition between yellow and blue flame occurs at higher FGR rates as the excess air increases. The detailed in-flame data suggest that prompt NOx is an important mechanism of NOx formation for the present flow configuration without FGR and that FGR is an effective method for reducing it. These trends are correctly predicted by the mathematical model. However, discrepancies between the predicted and measured temperature and species concentrations, including NOx, were found, especially close to the burner. These may be due to the shortcomings of the turbulence model in the prediction of swirling flows.

Spray characterization: numerical prediction of Sauter mean diameter and droplet size distribution

A simplified equation of the Nukiyama-Tanasawa type for droplet size distribution in sprays is obtained from the synergetic concept of entropy information, assuming spherical droplets and zero and infinity as their limit sizes. The introduction of Sauter mean diameter (SMD) definition in that equation yields a new distribution function dependent solely on SMD, which is calculated from available correlations for pressure-jet and pre-filming airblast atomizers. For plain-jet airblast atomizers a new and dimensionally consistent correlation is determined. Several droplet size distributions are then predicted. Experimental data are compared with predictions of SMD; the agreement is satisfactory.

Modelling of radiative heat transfer in enclosures with obstacles

Radiation models suitable for incorporation in reactive fluid flow codes are extended to calculate radiation in enclosures containing obstacles of very small thickness. The discrete transfer, the discrete ordinates and the finite volume method are employed to predict the heat transfer in two-dimensional enclosures and the results are compared with zone method calculations, with the total exchange areas determined by the Monte-Carlo method. All the methods predict similar heat fluxes, but the computational requirements are different. The discrete ordinates and the finite volume method are the most economical oneis. An application to a utility boiler is also presented. 0 1997 Elsevier Science Ltd.

A case study of fuel savings through optimisation of MSW transportation routes

Purpose – The high costs of collection and transportation of municipal solid waste (MSW) on the overall waste management budget (sometimes more than 75 per cent) makes it an issue to be urgently addressed for improvement. The paper aims to focus on the optimisation of routing networks for waste collection/transportation.Design/methodology/approach – The paper proposes herein the application of geographic information system (GIS) 3D route modelling for waste collection/transportation to optimise the route according to the minimum fuel consumption criterion to different municipalities of the island of Santo Antao of Cape Verde.Findings – The optimisation for the lowest fuel consumption yields 52 per cent savings in fuel, when compared to that for the shortest distance, even travelling a 34 percent longer distance, which shows the importance of considering simultaneously the relief of the territory and the lowest fuel consumption criterion when optimising vehicle routes.Practical implications – With such a s...