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

The leading non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure

Using Numerical Stochastic Perturbation Theory within three-dimensional pure SU(3) gauge theory, we estimate the last unknown renormalization constant that is needed for converting the vacuum energy density of this model from lattice regularization to the MSbar scheme. Making use of a previous non-perturbative lattice measurement of the plaquette expectation value in three dimensions, this allows us to approximate the first non-perturbative coefficient that appears in the weak-coupling expansion of hot QCD pressure.Comment: 16 pages. v2: published versio

Renormalization of infrared contributions to the QCD pressure

Thanks to dimensional reduction, the infrared contributions to the QCD pressure can be obtained from two different three-dimensional effective field theories, called the Electrostatic QCD (Yang-Mills plus adjoint Higgs) and the Magnetostatic QCD (pure Yang-Mills theory). Lattice measurements have been carried out within these theories, but a proper interpretation of the results requires renormalization, and in some cases also improvement, i.e. the removal of terms of O(a) or O(a^2). We discuss how these computations can be implemented and carried out up to 4-loop level with the help of Numerical Stochastic Perturbation Theory.Comment: 7 pages, 4 figures, talk presented at Lattice 2006 (High temperature and density

New Perspectives on Catalytic Hydrogen Production by the Reforming, Partial Oxidation and Decomposition of Methane and Biogas

The article provides a short review on catalyst-based processes for the production of hydrogen starting from methane, both of fossil origin and from sustainable processes. The three main paths of steam- and dry-reforming, partial oxidation and thermo-catalytic decomposition are briefly introduced and compared, above all with reference to the latest publications available and to new catalysts which obey the criteria of lower environmental impact and minimize the content of critical raw materials. The novel strategies based on chemical looping with CO2 utilization, membrane separation, electrical-assisted (plasma and microwave) processes, multistage reactors and catalyst patterning are also illustrated as the most promising perspective for CH4 reforming, especially on small and medium scale. Although these strategies should only be considered at a limited level of technological readiness, research on these topics, including catalyst development and process optimization, represents the crucial challenge for the scientific community

Unquenched Numerical Stochastic Perturbation Theory

The inclusion of fermionic loops contribution in Numerical Stochastic Perturbation Theory (NSPT) has a nice feature: it does not cost so much (provided only that an FFT can be implemented in a fairly efficient way). Focusing on Lattice SU(3), we report on the performance of the current implementation of the algorithm and the status of first computations undertaken.Comment: 3 pages, 3 figures, Lattice2002(algor

High-loop perturbative renormalization constants for Lattice QCD (I): finite constants for Wilson quark currents

We present a high order perturbative computation of the renormalization constants Z_V, Z_A and of the ratio Z_P/Z_S for Wilson fermions. The computational setup is the one provided by the RI'-MOM scheme. Three- and four-loop expansions are made possible by Numerical Stochastic Perturbation Theory. Results are given for various numbers of flavours and/or (within a finite accuracy) for generic n_f up to three loops. For the case n_f=2 we also present four-loop results. Finite size effects are well under control and the continuum limit is taken by means of hypercubic symmetric Taylor expansions. The main indetermination comes from truncation errors, which should be assessed in connection with convergence properties of the series. The latter is best discussed in the framework of Boosted Perturbation Theory, whose impact we try to assess carefully. Final results and their uncertainties show that high-loop perturbative computations of Lattice QCD RC's are feasible and should not be viewed as a second choice. As a by-product, we discuss the perturbative expansion for the critical mass, also for which results are for generic n_f up to three loops, while a four-loop result is obtained for n_f=2

3-d Lattice QCD Free Energy to Four Loops

We compute the expansion of the 3-d Lattice QCD free energy to four loop order by means of Numerical Stochastic Perturbation Theory. The first and second order are already known and are correctly reproduced. The third and fourth order coefficients are new results. The known logarithmic divergence in the fourth order is correctly identified. We comment on the relevance of our computation in the context of dimensionally reduced finite temperature QCD.Comment: 8 pages, 3 figures, latex typeset with JHEP3.cl

Two and three loops computations of renormalization constants for lattice QCD

Renormalization constants can be computed by means of Numerical Stochastic Perturbation Theory to two/three loops in lattice perturbation theory, both in the quenched approximation and in the full (unquenched) theory. As a case of study we report on the computation of renormalization constants of the propagator for Wilson fermions. We present our unquenched (N_f=2) computations and compare the results with non perturbative determinations.Comment: Lattice2004(improv), 3 pages, 4 figure

ATTRITION OF BED MATERIALS AND FUEL PELLETS FOR FLUIDIZED BED GASIFICATION APPLICATION

This paper reports on a study of the attrition/fragmentation behavior of different bed materials and fuel pellets for application in fluidized bed gasification. Three different bed materials displaying catalytic activity, namely fresh and sintered dolomite and a Ni-alumina catalyst, were tested for their resistance to fragmentation and attrition in fluidized bed. The fresh dolomite displayed extensive particle breakage upon calcination and a large production of attrited fines during fluidized bed operation. The other two materials were much more resistant to attrition and appeared to be suitable for further long-term operation testing. The attrition/fragmentation resistance of three pelletized fuels, one based on wood and the other two on a mixture of wood and coal, was also characterized under both inert and gasification conditions. Pellet breakage by primary fragmentation upon devolatilization appeared to be rather limited for all fuels. On the contrary, attrition of carbon fines from the char particles during gasification was extensive, due to a gasification-assisted attrition mechanism