| Carbon dioxide（CO2） emissions have received public focus. The third generation of oxyfuel technology（Oxy-steam） and OCCSS zero emissions system as the latest CO2 emission reduction technology has broad prospects. O2/H2 O combustion as a new combustion technology has brought many fundamental questions which need to conduct in-depth research. In this paper, Zhun Dong coal was used. Acid treatment was used to prepare ultra clean coal, UCC, whose ash content is less than 0.2%. Then, two char（ZD-raw-char/ZD-d-char） were made in High temperature drop tube（HTDP）. And, the combustion test was also conducted in drop tube. Under different temperatures and oxygen concentration, two atmospheres（O2/H2O、O2/N2） was compared to analysis the raw char and demineralized char combustion characteristic and char construct. Kinetic analysis was conducted to analysis the influence mechanism of H2 O on combustion.Under 1200℃, compared O2/H2 O and O2/N2 combustion characteristic at 21% O2 concentration, it is interesting that ZD-d-char and ZD-raw-char behavior different trend in two atmosphere, the raw char has faster burning rate in O2/H2 O, but the demineralized char O2/H2 O burning rate is lower than in O2/N2. The main difference comes from the presence of ash has changed the competition relations between char-H2 O reaction and char-O2 reaction. When the temperature reaches 1400℃, the combustion rate of ZD-d-char in O2/H2 O is significantly great than in O2/N2, it‘s because the diffusion becomes the constraint factor at high temperature, where O2 diffusion velocity in H2 O is faster in N2. In addition, steam gasification rate increase much at high temperature which cannot be ignored.Under different atmosphere, ZD-d-char and ZD-raw-char samples were get in different conversion rate, XPS test was made to analysis the carbon and oxygen element occurrence. The results show that in the combustion process, the proportion of C-C in char surface declines and C-O/C=O/O-C=O proportion gradually increased, it’s because the O2 molecules damages the carbon layer structure, Where this trend has been weakened under H2 O atmosphere. On the other hand, ZD-d-char has different tread, under O2/H2 O and O2/N2, the surface element of carbon and oxygen keep stable proportion. Raman analysis was also conducted, results show that H2 O promotes the consumptions of amorphous carbon during combustion, the degree of structural ordering of raw char in O2/H2 O and O2/N2 increases along with the combustion process, which means the char combustion reactivity deceases. Where, ZD-d char experienced different trend. Under O2/N2, the structural order keeps stable during the combustion process, where under O2/H2 O, H2 O promote the graphite process.Applying the intrinsic kinetic model which considers the internal and external diffusion to calculate the kinetic parameters under different atmosphere, compared the internal and external efficiency coefficient and the intrinsic reaction rate at the beginning of combustion reaction, it is found that the intrinsic reaction rate in O2/H2 O is significantly greater than in O2/N2. But, due to che diffusion constraint, the actual increase in the reaction rate is limited. ZD-d char under O2/H2 O atmosphere, has a lower intrinsic reaction rate than in O2/N2, where, due to the higher diffusion rate in H2 O, the internal and external factor in O2/H2 O are greater than in O2/N2, which made the actual overall reaction in O2/H2 O is slightly larger than in O2/N2. |
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