| OCR Text |
Show 1. EXPERIMENTAL METHOD The experimental apparatus is shown schematically on figure 1 . The grid ( A ) is made of stainless steel, fine mesh grating and has a rectangular shape (8 x 22 m m ) ; it is fitted horizontally in the experimental cell and heated to a constant grid temperature (T ) by a low vol-tage electric circuit . A small amount (mg order) of solid fuel is placed on the support (D) which, by rotation, may drop it on the grid when the gas flow through the cell ha s been established. The evolution of the temperature of the grid (T ) and of the pulverized fuel (T ) is § s followed by thermocouple recording, the thermo-element (C) being fixed to the grid and imbedded into the solid particles. The temperature shown by the thermocouple depends on its diameter; therefore, in order to correct for heat losses, a series of couples of increasing diameter (between 50 and 200 microns) has been utilized and the temperatures recorded have been extrapolated to zero mass. Comparison with temperature measurements performed by an emission pyrometer (in the range of temperatures beyond 700 °C) has shown that the thus obtained , extrapolated thermocouple readings agree with the pyrometer readings -within an error of about ten degrees C. The gas flow fed through the reactor is either pure nitrogen or nitrogen containing a variable percent of oxygen; the flow rate is kept 3 -1 below 10 cm s ; under this condition there is no measurable cooling effect on the grid. Inlet and outlet gas is analysed for CO, CO and oxygen content by on-line N. D.I.R. analysers, respectively paramagnetic analyser. A sealed window extending over the whole front side of the cell allows direct observation of the phenomena such as smoke release. light emission due to ignition, presence of flame in the gas phase (either of the "premix" type or of the "sooting" type) and end of fast combustion of the solid by disappearance of light emission. This may be done either by visual observation or, for fast events, by a photomultiplier cell. 7-3 |
