Effects of Pyrolysis conditions and air-oxidation of coals on characteristics of chars

摘要

For coping with entrained-bed gasification, we consider what are the properties of chars which are obtained from various kind of coals on the basis of pore-structure and some measured values. Chars are prepared by three pyrolysis-conditions: normal pyrolysis or slow heating (NP: heating at rates of 5K/min. and holding a temperature of 1273K for one minute), rapid pyrolysis (RP: heating at rates of about 500K/sec. and holding a temperature of 1273K for 5 min.), and flash pyrolysis (FP: droping test, 1 min. holding at a temperature of 1273K). In rapid pyrolysis, the specific surface area of the char increases due to CO_2 adsorption therein. Such a phenomena is notable in chars with smaller C%. However, when N_2 adsorption, the chars prepared by slow heating is larger than the chars prepared by rapid pyrolysis in specific surface area, which makes a conclusion that measurable pores when N_2-adsorption differ from those when CO_2-adsorption in radius and shape. A close correlation is found between the reactivity of char and the specific surface area when CO_2-adsorption. Considerations are made as to effects of air-oxidizing (at 393K/423K for 7 hours) on pore-structure and reactivity of chars. Oxidization increases yield, specific surface area, and true density of the char. The effects are found to be more and more remarkable as C% lowers. It is thought that reactivity of char seems to be affected in complicated fashion by the components such as Inertinite and Ash.