OXIDATION RATES OF A SINGLE CHAR PARTICLE IN AN ELECTRODYNAMIC BALANCE

The changes in reaction rate of a carbon char with conversion in the t emperature range 500-1200 K are followed by using an electrodynamic ba lance (EDB). This device allows, in a temperature range wider than in other apparatus, in situ measurements of mass, diameter, density, surf ace area, rate of reaction, and temperature for a single, suspended su bmillimeter particle as the reaction takes place. A synthetic char (Sp herocarb) has been used because of its low ash and volatile matter con tents and its spherical shape. The results on oxidation kinetics obtai ned in an EDB are compared with low-temperature reaction rate data, ob tained by conventional thermogravimetric apparatus on Spherocarb, and with the data obtained in an entrained-flow reactor at temperatures ty pical of pulverized-fuels combustors. The correlation between all the data in the temperature range 500-2300 K is examined. EDB data can be combined with entrained-flow data to depict a sharp change in reaction regime from a chemical kinetic to an internal diffusion control. A si mple Thiele analysis, considering different classes of pores, yields r esults that suggest pores in the 100-1000 nm range are responsible for diffusional constraints that cause the kinetic data to depart from th e chemical regime.