OXIDATION RATES OF A SINGLE CHAR PARTICLE IN AN ELECTRODYNAMIC BALANCE

The changes in reaction rate of a carbon char with conversion in the temperature range 500-1200 K are followed by using an electrodynamic balance (EDB). This device allows, in a temperature range wider than in other apparatus, in situ measurements of mass, diameter, density, surface area, rate of reaction, and temperature for a single, suspended submillimeter particle as the reaction takes place. A synthetic char (Spherocarb) has been used because of its low ash and volatile matter contents and its spherical shape. The results on oxidation kinetics obtained in an EDB are compared with low-temperature reaction rate data, obtained by conventional thermogravimetric apparatus on Spherocarb, and with the data obtained in an entrained-flow reactor at temperatures typical 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 simple Thiele analysis, considering different classes of pores, yields results that suggest pores in the 100-1000 nm range are responsible for diffusional constraints that cause the kinetic data to depart from the chemical regime

MORPHOLOGICAL-CHANGES DURING OXIDATION OF A SINGLE CHAR PARTICLE

The e v o l u t i o n of pore s i z e d i s t r i b u t i o n d u r i n g t h e o x i d a t i o n of s i n g l e Spherocarb c h a r p a r t i c l e s has been measured u n d e r c h e m i c a l c o n t r o l l e d c o n d i t i o n s . E l e c t r o d y n a m i c a l l y l e v i t a t e d p a r t i c l e s were heated t o r e a c t i o n t e m p e r a t u r e u s i n g a l a s e r and t h e weight and s i z e changes m o n i t o r e d . The l a s e r h e a t i n g was i n t e r r u y p t e d a t s e l e c t e d c o n v e r s i o n s and t h e C 0 2 a d s o r p t i o n determined at ambient c o n d i t i o n s . A s r e a c t i o n p r o c e e d s , p a r t i c l e s a r e found t o s h r i n k , t h e macropore volume d e c r e a s e s i n p r o p o r t i o n t o t h e t o t a l p a r t i c l e volume, m a i n t a i n i n g a c o n s t a n t m a c r o p o r o s i t y . The micropore volume, however, d e c r e a s e s w i t h i n c r e a s i n g c o n v e r s i o n whereas t h e n o r m a l i z e d p o r e size d i s t r i b u t i o n remains unchanged, s u g g e s t i n g t h a t t h e d e n s i f i c a t i o n of t h e microporous volume which l e a d s to. p a r t i c l e s h r i n k a g e r e s u l t s from pore e l i m i n a t i o n . A t t h e same time t h e mesopore volume i n c r e a s e s with i n c r e a s i n g c o n v e r s i o n i n d i c a t i n g t h a t t h e mesopores play a dominant r o l e i n t h e c h a r r e a c t i o

STUDY OF ADSORPTION DESORPTION OF CONTAMINANTS ON SINGLE SOIL PARTICLES USING THE ELECTRODYNAMIC THERMOGRAVIMETRIC ANALYZER

The isothermal adsorption and desorption of organic vapors on a single soil particle was studied with the aid of the electrodynamic thermogravimetric analyzer (EDTGA). Toluene and carbon tetrachloride were tested at room temperature during their adsorption on Spherocarb, montmorillonite, and Carbopack particles. The maximum amount of either organic compound adsorbed was comparable to that required for one monolayer coverage of the particle surface area. Significant differences among various pairs of solid-organic vapor examined were identified and correlated to differences in solid pore structure and chemical affinity between the organic compound and the solid

INCINERATION OF CONTAMINATED SOILS IN AN ELECTRODYNAMIC BALANCE

Understanding contaminant evolution from landfill soils is important in several in-situ remediation processes as well as in thermal treatment and incineration of contaminated top soils. To delineate the rate-limiting processes in the absence of interparticle effects, single surrogate soil particles are examined in this work. The adsorption-desorption characteristics of toluene and carbon tetrachloride on single, surrogate soil particles have been studied using an electrodynamic balance (EDB) under ambient conditions (P = latm; T = 298K). The EDB offers high mass sensitivity (DELTA-m approximately 10(-9)g) in the absence of external mass transfer limitations and interparticle effects. In this work, three types of solid particles, 100-170-mu-m in diameter, were examined, namely montmorillonite, a clay, and two synthetic chars, Spherocarb and Carbopack, of very different pore structures. Three different values of relative pressures, P/P(o), were tested for each liquid by changing the saturator bath temperatures. Significant differences were identified among the various solid-organic compound pairs examined in adsorption-desorption sequences in the EDB. These are strongly correlated with differences in the solid pore structures