Caratterizzazione numerica e sperimentale del processo di conversione dell'energia in un impianto di termovalorizzazione in scala reale alimentato a CDR di eventuale derivazione da biomasse

Responsabili di progetto

Michela Costa, Chang-tang Chang

Accordo

TAIWAN - NSTC - National Science and Technology Council

Bando

CNR/NSC 2012-2013

Dipartimento

Energia e Trasporti

Area tematica

Ingegneria, ICT e tecnologie per l'energia e i trasporti

Stato del progetto

Nuovo

Proposta di ricerca

Italy and Taiwan are united by a lack in self-produced energy and a strong energy dependence on other countries. Italy is 78% reliant on imports for its primary energy, Taiwan is 98%. The use and development of renewable energy sources and the improvement of energy utilization efficiency, therefore, are essential parts of the energy policies of both these countries.
Another common problem affecting the daily life in Italy and Taiwan is waste disposal, especially exacerbated by the growing quantities of municipal solid waste (MSW) and industrial waste (IW), rapidly declining availability of sanitary landfill sites, increasing costs for treatment and disposal, and more strict environmental regulations.
A solution to face with the aforementioned problems is converting waste to energy. Bioconversion, incineration or thermo-chemical conversion processes are viable routes. Among these, incineration is a particularly useful measure for waste management since it has the advantage of energy recovery, volume reduction and complete disinfection. In particular, the refuse derived fuel (RDF) approach gives the possibility to also solve fuel shortage issues. Non-combustibles are removed from waste and combustibles are processed to RDF as a combustible product with a more uniform particle size distribution and a higher heating value than untreated waste.
The National I-Lan University of Taiwan has a long term experience in the characterization of RDF derived from industrial wastes including biomasses as carbon black, wood and bamboo. The Istituto Motori of CNR and the University Parthenope in Naples, Italy, on the other hand, gained a certain experience in both the experimental and the numerical characterisation of incineration plants. The three-dimensional numerical simulation of the processes occurring in a waste-to-energy plant burning RDF of defined composition, in particular, offers the possibility of fully characterising the thermo-fluidynamic field in the combustion chamber, and, in particular, the temperature, velocity and chemical species distribution. The detail achieved by means of simulations allows overwhelming the lack of information resulting from the impossibility of effecting in-situ measurements with high spatial and temporal resolution. Data collected on real scale plant under real operating conditions, indeed, are preferred to data collected on pilot scale plants, since simple velocity or residence time-scaling laws often do not apply to complicated combustion problems.
The present research project is aimed to carry out an analysis of a waste incineration plant of real scale, burning RDF derived principally from biomasses. The analysis will be done by proposing a numerical model that takes account the strong interdependence between the sub-processes in which the incineration can be divided, namely the waste bed treatment, the combustion in the gas phase and the energy recovery. The research activities of the two Italian proposers and the Taiwan unit are essential and closely interdependent.
Combustion problems are among the most complex to deal with by means of Computational Fluid Dynamics (CFD) since they usually involve complicated geometries and fluid dynamics, heat transfer including nonlinear thermal radiation, and chemical activity. Many industrial combustors have very different length scales. The combustor may be relatively large, while the length scale required to simulate properly the individual flames may be several orders of magnitude smaller. Therefore, the computational domain for large-scale problems may require hundreds of thousands, or millions of cells, even in the case the simplest methods for turbulent flows description are used. Within the present project particular care will be devoted in building the computational domain.
A simulation model of the processes interesting the solid phase will be developed at the University of Naples Parthenope. The waste bed will be treated as a saturated porous medium, the consumption of which is strongly dependent on the thermo- fluidynamic conditions of the gaseous phase in the secondary combustion chamber. The coupling between the two phases will be fundamental. The results of the model for the solid phase, in fact, will furnish the input to the computational domain for the gas phase and will give form to the inlet surface. The Istituto Motori, which will deal with the simulation of the gas phase processes into more detail, will continuously interact with the University Parthenope. This will also provide boundary conditions as the radiative heat transfer. Effects due to the plant operation, such as wall fouling, will be considered. The contribution of the University I-Lan in Taiwan will be also crucial for two reasons. The experimental work conducted in Taiwan will provide the data necessary to calibrate the calculation code. In a second phase, when the predictability of the code will be considered as acceptable, the results of the numerical simulations will serve to better target the experimental sampling.
The model will serve to perform sensitivity analyses of the plant operation, in terms of both energy efficiency and environmental impact, to changes in the governing parameters. Effects deriving from, say, the variation of the initial composition of the waste, the air mass flow rate, the mass flow rate of additional gaseous hydrocarbons, will be investigated. Possible sources of combustion inefficiencies or pollutants formation increase will be pointed out.

Obiettivi della ricerca

Objective of the research project is the assessment of a comprehensive numerical model able to simulate the energy conversion process occurring in a waste-to-energy real scale plant. The model will lead to a complete characterization of the plant from both an energetic and an environmental point of view. The use of RDF of given composition, eventually including biomasses will be considered.
The solid fuel will be assumed as a saturated porous medium of defined chemical and macroscopic composition, whose thermo-physical properties will be evaluated on a case by case basis by the Taiwan unit. The various mechanisms of heat and mass transfer between the RDF bed, the entering air and the combustion products will be modeled by the University of Naples Parthenope. The gas phase will be treated as a turbulent reacting flow. The gas kinetics will be simulated by using schemes of different detail able to describe the oxidation process of the fuel volatile compounds and the influence of turbulence. The experience of the CNR - Istituto Motori on the matter will be exploited. Models of formation of nitrogen oxides, carbonaceous particulate and dioxins will be introduced. The validation of the proposed code will be done by comparing the obtained results with available reference data (benchmarks), and on the ground of measurements effected on a real working plant.
The proposed model will be exploited to highlight possible sources of combustion inefficiencies or pollutants formation increase, hence it could represent the first step towards developing an innovative procedure for the management and control of waste-to-energy systems during their exercise.

Ultimo aggiornamento: 08/06/2025