The rarefied gas effect occurs inside the sulfur product layer of limestone in oxy-fuel fired flue gas.To obtain the micro-structure of the limestone and investigate the rarefied gas effect and gaseous reactant diffusion law inside the limestone sulfur product layer

experiments were carried out by thermogravimetric analyzer(TGA)and scanning electron microscope(SEM)and mercury injection apparatus.The limestone with average diameter of 31.4μm was used as the sample

and the experimental was conducted at 750 ℃ with low CO2 concentration.The results showed that

through partial micro-breakage on surface of the limestone particle

the limestone particle was reunited with many small grains.The pore size among the limestone particles was from 5nm to 1 000nm

and the one that smaller than 50nm accounted for above 75%.Theoretical analysis indicated that the rarefied gas effect varied with the gas pressure and temperature

especially as the pressure increasing

the gas diffusion transited from free molecular flow region to continuous medium region.Moreover

the gaseous SO2 diffusion coefficient in the limestone sulfur product layer was obtained by calculation.For pore size with different fractal dimensions

the gaseous SO2 had different diffusion coefficients

which ranged from 0.016 2cm2/min to 0.125 9 cm2/min.