PHENOMENOLOGICAL MODELS OF CELLULOSE PYROLYSIS

Using yields vs. residence time and temperature from 50 to 1000 ms and 650-900 degrees C, measured with the ultra pyrolysis system at the Un iversity of Western Ontario (UWO) we establish an approximate total ga seous yield function Y(t,T). With UWO data, we also establish approxim ate correlations between individual gaseous yields (CO, CO2, C2H4, CH4 , C2H2, C2H6 and C3H6) and the total gaseous yield that could be used to give Y-i(t,T) for individual gases. We further extend Y(t,T) using shock tube pyrolysis measurements from 0.3 to 2 ms and 900 to 2100 deg rees C made at Kansas State University (KSU). In doing so, we develop a global decay model that gives analytical time and temperature depend encies for cellulose, activated cellulose, tar, prompt total gas and l ate total gas. We next examine the impact of heating rates and heat tr ansfer upon pyrolysis of cellulose using slow pyrolysis data obtained by thermogravimetric analysis at the Colorado School of Mines (CSM). I n this effort, we first develop an accurate general relationship for B oltzmann integrals. Then using an analytically convenient Arrhenius re action rate (ARR) we examine data taken at varying heating rates and w ith three Biot numbers. We find some phenomenological analytical relat ionships giving ARR parameter dependencies on heating rate and particl e size that appear indicative of heat transfer impacts. If adequate da ta becomes available these relationships might be applied to hemicellu lose and lignin. Then the pyrolysis rates of any plant species might b e predicted in terms of the pyrolytic characteristics of their cellulo se, hemicellulose and lignin components. (C) 1997 Elsevier Science Ltd .