FLUIDIZED COMBUSTION OF LIQUID FUELS: PIONEERING WORKS, PAST APPLICATIONS, TODAY’S KNOWLEDGE AND OPPORTUNITIES

The use of liquid fuels for fluidized bed (FB) combustion is gaining importance for co-firing, waste incineration, switch to renewable energy sources or during plant start-up. The design of a suitable liquid injection system is a key requirement to ensure that all of heat is released within the bed of a bubbling fluidized combustor or the riser of a circulating system. The scientific literature has revealed around 100 papers dealing with FB combustion of liquid fuels since the pioneering work in 1975. This paper conveys an effort to review the relevant aspects of FB combustion of liquid fuels, with the exclusion of mixtures of solid fuels in liquids, which were left out of this work. Following a logical path that goes from early investigations toward a more sound knowledge, it is organized in four sections: Fuels, Fuel Feeding, Combustion Results and Emissions. The Conclusions summarize the main aspects and draw prospective for future research and application of liquid fuel FB combustion

Fluidized Bed Combustion of Liquid Bio-Fuels: Application of Integrated Diagnostics for Micro-Explosions Characterization

A novel integrated diagnostic technique has been developed for the analysis of the “regime with microexplosions” that may be established during the low-temperature (T < 800 °C) fluidized bed combustion of liquid fuels. It consists of the comparison among three analogue data series: (i) pressure signals measured in the freeboard and high-pass filtered, (ii) oxygen molar fractions measured by zirconia-based probes at two elevations in the bed and in the splash region, and (iii) video frames of the bed surface recorded and purposely worked out. The integrated technique has been applied to the combustion of biodiesel at minimum fluidization and has proven to be a valid tool to provide the fingerprints of the mechanism of the low-temperature fluidized combustion of liquid fuels. The time series generated from the measured data sets have been analyzed with the aid of the Hurst’s rescaled range analysis, the V-statistic, and the Lyapunov exponents’ evaluation. The issue of localizing micro-explosions throughout bed, bubbles, and splash zone has been tackled by the V-statistic analysis, which has proven that the location of micro-explosions is just at the bed surface when T = 650 °C and moves deeper and deeper into the bed when its temperature increased to about 800 °C. The values found for the largest Lyapunov exponent in the time series demonstrate that the investigated system is not only dynamic but also chaotic in its nature

AN INVESTIGATION ON LOW-TEMPERATURE FLUIDIZED COMBUSTION OF LIQUID FUELS

ABSTRACT Presently, the combustion at low temperature is receiving a great deal of interest because emissions of micro-and nanopollutants are expected to be greatly reduced. Following previous studies on the low temperature combustion behavior, the authors report results and discussion of steady-state experiments on an atmospheric, pre-pilot scale, 140 mm ID, FB reactor, equipped with an under-bed, airassisted, liquid-fuel injector. The experimental program was focused on the operation at temperatures lower than the classical value for FBC of solid fuels (i.e., 850°C). The data series taken into consideration are the concentrations of the main unburned species in the splash zone, those of oxygen measured in the bed and in the splash zone as well as the freeboard pressure. The interpretation of the results is mainly based on the statistical analysis in the time domain. The combustion pattern of bio-diesel is compared to that of the diesel fuel under varying operating conditions (e.g., bed temperature, dispersion air velocity at the fuel nozzle, injector height in the bed). Conclusions that were previously published on the base of labscale results are checked against new data obtained on the pilot scale. An innovative technique for the analysis of the micro-explosive regime is presented. It consists in the comparison of oxygen concentration measured by the zirconia-based probes at different heights in the bed and in the splash region, pressure signals measured in the freeboard and purposely filtered, and video-recordings of the bed surface phenomena. INTRODUCTION From a viewpoint directed at application of fluidized bed combustion (FBC), conventional, petroleum-derived liquid fuels are usually not taken into consideration. Vice versa, the cheap biomass-derived liquid fuels are worth of being exploited, at least for some specific applications. The combustion at low temperature is presently receiving a great deal of interest in view of depressing emission of micro-and nano-pollutants. The operation of a fluidized bed combustor (FBC) at a temperature lower than the classical value for FBC of solid fuels (i.e., 850°C) presents a number of interesting issues the mechanisms of which are not completely revealed yet. The combustion of a liquid fuel in a fluidized bed can be considered as the result of a number of serial stages: atomization, vaporization, pyrolysis, mixing with air and oxidation, formation of pollutant. They occur in an ideal sequence moving from the fuel inlet port to the bed exit, provided that the residence time in the bed is long enough [2] at the laboratory scale, i.e., with an 80 mm ID fluidized combustor. They identified a combustion behavior at a bed temperature below 750°C that was described as &quot;regime with micro-explosions&quot;. Because of the periodic eruption of air bubbles the properties of th

Recovery and Valorization of Tomato By-products in R&D EU-funded Projects

In the last years, the European Commission has been funding numerous projects regarding the valorization of food wastes. Tomato by-products received great attention especially in Spain, Italy, Greece, and Portugal due to high volumes and high concentration of valuable compounds. Among 40 funded projects about the management of tomato wastes in general, 14 projects are strictly connected to the valorization and exploitation of the tomato residues/by-products after processing and are of great interest for their scientific, technical, and economical outcomes. They received an overall budget of around 37 M€ over 35 years, involving 20 European and 4 non-European countries, with project coordinators located in Germany, the Netherlands, and Italy in most of the cases. This chapter delivers general information about these projects, assessing and reporting scientific and technical results. Moreover, the interconnection is highlighted among them by focusing on the contribution they gave to the European know-how, the management of the by-products and the progress they reached in waste minimization and valorization. Finally, the industrial and environmental outcomes of these projects have been reported by highlighting issues and problems that are still to be overcome

Solution to Agricultural Machinery Powering Problems Using DIY Photovoltaics

The contribution of this work is the realization and the field testing of a photovoltaic system in agriculture following the Do-It-by-Yourself (DIY) approach, i.e., a system easy to be assembled from commercially available components, portable off-site and recharging the battery directly when working. This solution allows the daily work of a simple agricultural machine to be carried out with the advantage of no interruption and, in addition, the saving of any electricity cost associated to battery recharging. The design and the realization of the DIY photovoltaic apparatus are described, which turns out quite cheap. The resulting economic advantages are analyzed, with reference to a geographical collocation and the typical agricultural practice in Sicily

Fluidized Bed Design and Process Calculations for the Continuous Torrefaction of Tomato Peels with Solid Product Separation

This work reports the Authors’ concept idea and the gross design of a plant system capable of continuously separating the torrefied solids from the inert bed material downstream from a fluidized bed reactor, where biomass torrefaction is performed in a continuous operation mode. It is constituted of three units that process solids: i. a bubbling fluidized bed, equipped with a heat exchanging tube bundle, acting as a torrefaction reactor; ii. an inclined plate sieve separator for collection of the torrefied product as oversize solids; iii. a loop-seal for reinjection of undersize particles, i.e., the inert solids, back into the bed.A simple model of the torrefaction reactor as a well-stirred system has been devised to predict the conversion of feedstock (i.e., tomato peel particles) on the basis of an empirical correlation previously established by the Authors under batch conditions; the variability of biomass particle residence time in the bed as induced by the fluidization of inert solids has been accounted for by introducing a distribution function of the biomass residence time, and this latter has been suitably incorporated within the equations yielding the bed inventory of biomass. The recycling system of undersize inert solids back into the bed through a standpipe and a loop-seal for reinjection has been simply designed according to literature.The resulting set of equations is easily handled and smoothly provides the plant design variables and the relevant process calculations

Binary mixtures of biomass and inert components in fluidized beds: experimental and neural network exploration

Considering the little understanding of the hydrodynamics of multicomponent particle beds involving biomass, a detailed investigation has been performed, which combines well-known experimental and theoretical approaches, relying, respectively, on conventional pressure drop methods and artificial neural network (ANN) techniques. Specific research tasks related to this research work include: i. to experimentally investigate by means of visual observation the mixing and segregation behavior of selected binary mixtures when varying the biomass size and shape as well as the properties (size and density) of the granular solids in cold flow experiments; ii. to carry out a systematic experimental investigation on the effect of the biomass weight and volume fractions on the characteristic velocities (e.g., complete fluidization velocity and minimum slugging velocity) of the investigated binary mixtures in order to select the critical weight fraction of biomass in the mixtures beyond which the fluidization properties deteriorate (e.g., channeling, segregation, slugging); iii. to analyze the results obtained in about 80 cold flow experiments by means of ANN techniques to scrutinize the key factors that influence the behavior and the characteristic properties of binary mixtures. Experimental results suggest that the bed components’ density difference prevails over the size difference in determining the mixing/segregation behavior of binary fluidized bed, whereas the velocities of minimum and complete fluidization increase with a growing biomass weight fraction in the bed. The training of ANNs demonstrated good performances for both outputs (Umf and Ucf); in particular, the best predictions have been obtained for Umf with a MAPE1 <4% (R2=0.98), while for Ucf the best ANN returned a MAPE of about 7% (R2=0.93). The analysis on the importance of each individual input on ANN predictions confirmed the importance of particle density of the bed components. Unexpectedly, results showed that morphological features of biomass have a limited importance on Ucf

Codice di simulazione e potenzialità predittive per la stagionatura di salami tradizionali

Riassunto Gli Autori discutono le ipotesi ed i passi necessari allo sviluppo di un modello matematico “a principi primi” di essiccazione del salame in corso di stagionatura. L’articolo compara i dati sperimentali ottenuti da svariate lavorazioni industriali e pilota con i dati ottenuti dal modello matematico. I risultati ottenuti indicano una soddisfacente corrispondenza tra i valori teorici del calo peso ed i dati sperimentali, con un errore percentuale dell’ordine del 10% e mai superiore al 25%. Risulta pertanto disponibile un codice di calcolo snello e user friendly in MS Visual Basic 6.0, con documentate potenzialità predittive in termini di perdita di peso in corso di lavorazione e finale, contenuto d’acqua e temperatura di lavorazione del salame. Abstract The assumptions and the steps needed to develop a "first principles" mathematical model during sausage maturation are discussed. This article compares the experimental data obtained from a variety of industrial and pilot-scale processes with the data obtained by the mathematical model. The results obtained show a satisfactory correspondence between the theoretical values of weight loss and the experimental data, with a percent error of the order of 10% and never higher than 25%. It therefore provides a manageable and user friendly calculation code in MS Visual Basic 6.0, with documented predictive potentials in terms of weight los

Liquid and gaseous fuels conversion (Chapter 8)

Fluidized bed combustion (FBC) is a valuable conceptual option for gaseous or liquid fuels by virtue of the advantages of this technology with respect to fuel flexibility and emissions. However, the plant design experience and the practical application of FBC for gaseous or liquid fuels is quite limited. Liquid fuels have been considered for start-up or during co-firing in solid-fuelled FBC plant of various size; some liquid wastes have been proposed or are actually treated in FBC for incineration. More recently, new openings to liquid fuel FBC have been provided by the increasing interest in biomass- and waste-derived fuels, as a consequence of the Kyoto protocol, the need of energy source diversification and the on-going development of innovative combustion solutions with inherent CO2 capture possibilities (Hoteit et al., 2009), like Chemical Looping Combustion (CLC). This subject will be dealt with more details in Chapter 20. Further, since the combustion at low temperature is presently receiving a great deal of interest in view of depressing emission of micro- and nano-pollutants, the option of carrying out liquid fuelled FBC at a temperature lower than the classical value for solid fuels (i.e., 850°C) may offer a number of advantages. Since the fluidized bed technology is effective for burning high-volatile fuels, the extension to liquid fuels is rather straightforward, in particular if benefits are obtained, for instance burning liquid wastes with medium heating value and raw vegetable oils without any preventive chemical treatment. The search of the scientific literature revealed around 120 papers dealing with FB combustion of liquid fuels, after the exclusion of mixtures or suspensions of solid fuels in liquids, which are left out of this book, but were covered by a review work in a past presentation by Greco et al. (1999). Nevertheless, no dedicated reviews are available on this matter. So far, both options of bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) have been considered in liquid fuel combustion studies. In an application perspective, industrial fluidized bed furnaces operating with natural gas can be considered in specific applications such as foundry sand reconditioning, incineration of sludge with a high moisture content, cleaning of metallic parts and calcination of solid particles (Dounit et al., 2001). Thus, FBC of natural gas has received some investigation interest since the early developments of FBC, particularly in the former Soviet Union. The FBC of gaseous fuels is presently restricted to a scientific curiosity and fundamental investigations. However, also for gaseous fuels the new CO2–free combustion technologies may revalue this option: actually, CLC was originally conceived for gas combustion. The survey of the scientific literature revealed around 30 research papers dealing with FB combustion of gaseous fuels