The sulfation reaction of half-calcined dolomite particles at high CO2
partial pressures (around 1 bar) was investigated. The experiments we
re carried out in two different reactors: (a) a thermogravimetric anal
ysis system (slow heating rates) and (b) a shock-microreactor (rapid h
eating rates). The experiments were carried out under isothermal condi
tions at temperatures between 650 and 875 degrees C. A natural dolomit
e sample was used. Different particle sizes were tested: 26, 128, 256
and 512 mu m. Under reaction conditions employed in the experiments (P
-CO2 approximate to 1 atm and T < 900 degrees C), half-calcination of
dolomite particles takes place and the sulfation reaction occurs betwe
en CaCO3 . MgO and SO2. The CaCO3 is the only active species during su
lfation. The particle size and temperature have a strong influence on
the variation in extent of conversion with time. Two different stages
can be distinguished in the sulfation of half-calcined dolomite partic
les; chemical control at the onset of reaction and diffusional control
at longer reaction times. When the sulfation reaction is carried out
under conditions similar to those existing in a boiler (high heating r
ates and simultaneous calcination and sulfation), the measured reactio
n rates are higher than those observed from thermogravimetric experime
nts. At X = 0.1 an activation energy of 34 kcal mol(-1) (142 kJ mol(-1
)) was measured. This value suggests that the process is controlled by
a solid state diffusion mechanism.