Three weeks ago Monday (MNM Week 26) we reported the very successful 6th Annual EuroFlam Seminar, organised at Cardiff University on Wednesday 23rd and Thursday 24th June. There, Visiting Investigators from the three EuroFlam members, ENEL SPI, IFRF and Cardiff University, met together during the two days to present their reports on the projects that they had carried our during the previous year.

This group was augmented by a small number of visiting investigators, who are presently in residence and have carried out a substantial part of their project.

This week, in this  Volume 3, we are continuing the publication of abstracts of the presentations made at the Seminar.

Abstract
In 1997 and 1998 the IFRF carried out furnace trials to test the excess enthalpy combustion. The trails resulted in characterisation of the flow field and mixing in a furnace equipped with the Low-NOx regenerative burner of Nippon Furnace Kogyo Co.. While in 1997 the high potential of excess enthalpy combustion was demonstrated by using natural gas similar technical work was done for Light Fuel Oil (LFO) and Heavy Fuel Oil (HFO) in 1998.

The Laser Sheet Visualisation (LSV) technique was used to characterise the mixing of fuel, air and hot combustion products because significant characteristics like flame length, flame contour, stability and combustion intensity depend primarily on this mixing. Both the fuel jet and the central jet are visualised. LSV is based on the Mie-Scattering at tracer particles which are added to one of the flow. The obtained concentration data is used to determine the mixing quality and mixing regions of the flows. A Continuum Nd-YAG laser is used to generate light pulses at 25 Hz with a wavelength of 532 nm. The light is directed into the furnace and is expanded by an optical system to a sheet. An intensified CCD-camera is placed perpendicular to the flow and collects the light scattered by the seeding particles. The images recorded on videotape are transferred to a computer. Large sequences of instantaneous planar Mie scattering images are processed to derive various mean parameters. For each of the jets the average concentration, RMS-concentration, intermittency, unmixedness, dissipation and normalised jet intensity are calculated. The RMS-concentration indicates where the mixing is the most intense, while the unmixedness and intermittency describe the extend of mixing between the two flows and the fuel jet boundary, respectively. The 50% normalised mean scalar lines can be used to define the jet half width.

The laser sheet showed high intensity fluctuations in the near burner zone. These fluctuations are probably caused by light absorption by clouds of soot and recirculating particles. The flame length is underestimated since the assumption is made that the mixing is perfect and that the combustion speed is infinite compared to the mixing. There is also an influence of the large recirculating flow on the flame length. Since the fuel is reacting with the mixture of flue gas and hot air the oxygen concentration will be substantially lower than for air only. Consequently the air requirement is higher, resulting in a underestimation of the flame length. The jets show an expansion half angle of around 5° which are slightly lower than predicted for a turbulent free jet (6.5°).

Abstract
Burning velocity is one of the most important parameter used to value the performance of a combustion system.

It has been predicted that an aerosol containing droplets within the so-called ‘transition’ range, typically between 7-15 um, may burn faster than a vapour/air mixture. Other models predict that the burning velocity attained for a gaseous mixture is the maximum attainable.

No experimental data exists against which such predictions can be appraised. There is then the need to provide reliable experimental data in well-controlled facilities in which single aerosol generation and combustion mechanisms can be controlled independently.

This EuroFlam project is part of a more complex research work in progress in Cardiff University whose aim is to characterise two-phase liquid fuel generation and combustion. Particularly, this project has the aim to appraise suitable Vapour Fuel/Air ratio quantification techniques in aerosol mixtures generated in controlled environments.

Various diagnostic techniques have been analysed. Particularly:

1. Malvern MasterSizer X: this uses the diffraction properties of laser-light to esteem the size of fuel droplets. It can also be used to quantify the liquid-phase fuel concentration by measuring the laser-beam obscuration. Besides, knowing the total amount of fuel injected in the rig, the fuel vapour concentration can be easily obtained.
2. The Laser Induced Fluorescence Technique (LIF). In this technique, the laser light is formed into a sheet which enter in the rig and excite the fuel, making possible to map the fuel distribution within the chamber. Besides, using the LIF exciplex methodology it would be possible to discriminate between liquid and vapour-phase fuel concentrations.
3. The Near-Infrared Absorption Technique (NIR). This is a novel method developed in 1996 by Shell Research and has shown to be capable to provide fuel vapour concentration measurements in heterogeneous fuel mixtures. This technique relies on the fact that carbon-hydrogen bonds absorb infrared radiation. The concentration of a fuel vapour can be determined by measuring the amount of infrared light that the sample absorbs and applying Beer-Lambert law.

Several measurements have been taken using Malvern Mastersizer X. The results are that Malvern Mastersizer seems suitable for quantitative measure of liquid phase AFR at low levels of laser obscuration, but can only give qualitative indications at high levels of laser obscuration.

NIR absorption technique seems to be a better solution to quantify fuel vapour fraction in liquid two-phase combustors. A Novel NIR absorption facility has been built during this EuroFlam project. Preliminary calibration results will be obtained by the end of this project.

Abstract
The proposed research activity aims to investigate the formation and destruction of trace organic pollutants under pyrolysis conditions from different types of coal, and two other poor fuels: toluene diisocyanate, known as TDI and poly (ethylene terephthalate) known as PET.

Several classes of organic compounds can be generated during combustion under locally reducing conditions. Some of them, owing to their high specific toxicological potential, can represent a risk for the environment and human health. The production of these compounds can be significantly enhanced when undesired poor combustion efficiency conditions or techniques requiring fuel rich conditions (i.e. staged combustion for NO_x reduction) are applied. The Polynuclear Aromatic Hydrocarbons (PAH) represent a class of relevant environmental concern for several industrial combustion processes; their emission is regulated by laws imposing very stringent limits both on concentration in flue gases and emission factors.

Particular attention has been devoted in this study to identify and quantify compounds belonging to this class in order to provide basic data for the development of a simple kinetic model of PAH formation from coal, TDI and PET under fuel rich conditions. The study involves other organic compounds, as Monocyclic Aromatic Hydrocarbons (MAC), and n-alkanes which can be considered as PAH precursors or intermediates.

The chemical characterisation of the species produced during the process have been made by using analytical pyrolysis combined with gas chromatography and mass spectrometry (Py-GC-MS). The tests will be carried out on a commercial apparatus (CDS Pyroprobe 1000) which has been modelled and characterised in a previous work.

The behaviour of Ashland, bituminous coal, South African, also a bituminous coal, lignite, TDI and PET has been studied by applying different pyrolysis temperatures, in the range from 200 to 1400°C. The total organic gaschromatographable volatile material has been studied in a range from 25 to 400 u.m.a (molecular weight). The formation of 32 PAH and n-alkanes from C₁₂ to C₃₆ has also been followed.

The volatile products obtained during pyrolysis have been studied using GC-MS (in mode scan). An identification of each compound through its mass spectrum has been done, comparing the spectrum with the ones of NBS library.

The profiles of PAH which were originally present in the coals as "mobile phase", extractable with an organic solvent, will be compared with those of PAH evolved during the pyrolysis process. PAH evolved from coals having different rank and geographical origin (from lignite to anthracite) will be investigated to assess the influence of coal nature and rank.

Finally, a preliminary study of the formation kinetic of a set of reference PAH from one selected bituminous coal will be carried out to provide basic data for the development of a simple kinetic model.

Abstract
During my presentation at the EuroFlam meeting in Cardiff, I’ll try to summarise the experimental results obtained at ENEL about the measurement, by means of microwave, of carbon (UCC) presents in ashes, mainly fly ashes from power plants fired by coal.

I’ll show the diagrams of an apparatus (MITER 1600) already available in ENEL for this aim, its performances and its main problems:

1. Response strongly dependent on the technique used to fill the test cell
2. Response dependent on coal used in the power plant
3. Low reproducibility of the results
4. To obtain the calibration curve, several chemical analysis are required
5. Sensitivity is good enough only in a narrow range (0%à ~ 7%UCC typically)

Power plants are particularly interested in ashes containing 5%UCC: around this value the low reproducibility of the data means uncertainty about the measurement of some percent UCC. During my work was possible to find out a particular setting of the apparatus that allowed moving the narrow range of good sensitivity in order to include 5%. Unfortunately, the one-to-one relationship of the calibration curve is not more valid in this case.

So many problems convinced me about the necessity of a completely new measurement technique without any strong variation of the already-existing instrument. For this reason a microwave resonator replaced the coaxial termination presents in MITER 1600. Along the axis of the cavity was plugged a movable quartz tube containing the sample. This resonator and the antenna inside, were projected in order to obtain two eigen-frequency (modes TM 010 & TE 111) near one to the other. In this way two frequency markers, very independent form the thermal drift, were available. The reflection coefficient vs. frequency was detected and the results will be shown. For measurements, I chose the TM mode because its spatial distribution. The parameters characterising the resonance curve were plotted vs. UCC: width and central frequency show a very linear dependence on UCC up to 36% (max value available in lab) and allowed, independently, to easily measure UCC. The accuracy is ~ 1‰. Independence on coal could be reached by means of these parameters. A third one has not a so linear calibration curve. A linear calibration curve is important because it need only two point (this means only two chemical analysis) to be fixed. In any case measurements are very highly reproducible. All these experimental results will be shown.

So the above-mentioned problems do not affect the new microwave spectrometer, apart from #2, and a constant-performances apparatus is usable in lab. Moreover three independent calibration curves are available. Obviously, another apparatus to be used in field is under construction.

At the end of this abstract let me thank the EuroFlam and the TMR-program for the opportunity that they have offered me: I hope to be involved in other researches in the future. Special acknowledgements to Laura Botti that, now, continues my researches: she took her degree working in the same lab where I was because my Ph.D. thesis, so I’m sure about her capabilities. Is a pleasure for me to thank ENEL and, particularly, Ing. Mario Graziadio, for the possibility to work at its research centre in Pisa-IT. As in this centre did not exist a microwave lab, Mario Graziadio engaged himself hardly to collect the instruments and to obtain a room where I could work independently and freely. In my own lab, following alone my own research program was easy to flatter myself to be a genuine (T. M.) researcher!

This periodical forms part of the group of publications owned by the IFRF
The IFRF Monday Night Mail is published by:
IFRF NET, P O Box 10,000, The Netherlands
Edited: Peter Roberts
ISSN 1562-4781