Enhancement of char reactivity by rapid heating of precursor coal

Abstract

Char reactivity is generally higher the (a) lower the rank of the precursor coal’3*, (b) lower the temperature to which the char has been taken prior to reaction133, (c) shorter the soak time at maximum heat treatment temperature (HTT)3, and (d) smaller the char particle size’, We have now found another variable which can affect subsequent char reactivity, that is the heating rate to maximum HTT. Chars were produced from a 70 x 100 U.S. mesh North Dakota lignite having the following ASTM analysis: ash (dry), 7.3%; VM (daf), 47.1%; and fixed carbon (daf), 52.%. Chars were prepared by heating the lignite in nitrogen to maximum temperature either in a fluidized bed at 10” C/min or in a laminar-flow unit at about 8 x 103”C/s 4. In both cases, soak time at maximum temperature was under 1 s. Subsequently, char reactivity in 0.1 MPa of air was measured at 500°C in a TGA apparatus as previously described’. The char sample was heated in the TGA unit at lO”C/min to 500°C in N2 and soaked for 15 min prior to studying reactivity. Reactivity was expressed as