With the evolution of oxy-combustion technologies from pilot-scale to  demonstration plants, Computational Fluid Dynamics (CFD) has become a fundamental tool for their development at the industrial scale.  Indeed, one of the main research topics in oxy-combustion is the development of suitable models for the CO2-enriched atmosphere. 

In this context, IFRF ongoingly investigates, both numerically and experimentally, oxy-combustion flames in pilot furnaces and semi-industrial systems following the Verification & Validation approach.  Whilst FOSPER (Furnace #1) tests the semi-industrial flames on which to validate comprehensive approaches (refer to the relevant IFRF published reports on the website at Current Reports and the notes in the CFD Forum from the Workshop in Renfrew last June), simpler devices, such as the IFRF’s drop tube pilot furnace for solid fuel characterisation – the Isothermal Plug Flow Reactor, enable us to fill the gap on particles’ thermal histories and their behavior toward ignition in different O2/CO2 atmospheres.

The IPFR, now completely refurbished and operative at Livorno experimental area, can manage coal and biomass devolatilization and char combustion tests with different atmospheres (e.g. O2/N2, O2/CO2) ensuring particle temperatures up to 1600 K with high heating rates (103-4 K/s).

Last week, in the frame of a collaboration with ENEA (Italian Agency for Energy and Environment), IFRF, University of Pisa and ENEA researchers tested the performances of the ODC system (Optical Diagnostic of Combustion), developed by ENEA for diagnostics of turbulent flame fluctuations, in tracking the signals emitted by coal and char particles during devolatilisation, ignition and char combustion in different atmospheres.

The ODC system consists of a photodiode, a computer that performs data analysis, a DAQ and a charge amplifier.  The photodiode samples the radiant energy and  chemiluminescence emitted by the particles and surrounding gases as they travel along the drop tube.  The sampled brightness spectrum contains information related to thermal history and chemistry as well, because radiant energy is sampled at very high frequency, i.e., 500 kHz (order of MHz can be easily reached and at low cost), and turbulence dynamics.  This technique is on-line, very economical and absolutely not intrusive because it needs only the holes through the system to introduce the optic fibers. 

Four sensors are used along the reactor to detect the signal coming from clouds of coal and biomass particles reacting in the IPFR.  On the basis of the in-phase analysis of the signal coming from the four sensors, additional information can be ascertained on different features of coal combustion in oxy-flame conditions, like particle velocity and residence times, ignition delay, burn-out times, etc.  

During last week’s tests, the technique was also employed to successfully monitor the transition from conventional diffusion air flame to oxy-flameless combustion in the burner feeding hot gases to the  IPFR.   A report is in preparation on the preliminary results on the application of ODC techniques in furnace N.1 and the AASB burner.

Anyone who wishes to have further information on the tests should contact Leo Tognotti.

Next week the IFRF Events Calendar will be updated with information about the Validation Workshop  which will take place in Turku, Finland on 16 and 17 June.  Watch MNM for details – also regarding reports to be published  on solid fuel characterisation and IPFR.