Effect Of Steam On The Thermal Transformation Of Pyrite

Oxy-fuel combustion continues to be of great interest all round the word because of the enormous pressure on carbon dioxide reduction. During the technology is applied to industrial application, ash deposition and slagging is a desiderate problem for coal-fired boilers on the heat exchanger. The transformations of iron-bearing minerals have long been recognized as an important factor for ash deposition and slagging. In further pyrite the main iron-bearing mineral in coal. So lots of studied have been done on the transformation of pyrite and its relationship with ash deposition and slagging under air combustion. The transformation model has also been built under air combustion. However, under oxy-fuel combustion, the transformation of pyrite and its relationship with ash deposition and slagging has little been investigated. Compared to conditional air combustion, high concentration of steam would impact the transformation of pyrite, which will further influence impact the characteristic of deposition and slagging on the heat exchanger. Therefore, it is urgent to study the conversion of pyrite and its mechanism under steam containing atmosphere to offer theoretical and experimental basis for the tendency of ash deposition under oxy-fuel wet recycle combustion.In this work, the conversion behavior of pyrite in steam containing atmosphere is investigated. Pure pyrite is used as raw material on the TGA under different experimental conditions. And XRD and XRF are used to analysis the composition of conversion products and the results show that steam promotes the decomposition of pyrite at lower temperature. With the increasing of temperature, the ability of steam to oxidize pyrrhotine becomes stronger. Pyrrhotine is oxidized to form magnetite first and further to be oxidized to hematite by steam. The kinetic model of pyrite transformation is also investigated and the results indicate that the model that described the decomposition process was shrinking core and three-dimensional diffusion, almost the same with that in nitrogen. But apparent activation energy was 16.83 k J/mol and 18.51 k J/mol respectively lower than that in nitrogen atmosphere. At last, the transformation behavior of pyrite under simulant oxy-fuel atmosphere is studied. It is revealed that the final products of pyrite under 3%O2 and O2/H2 O atmosphere are hematite. But the transformation process is not the same. Under 3%O2 atmosphere, pyrite first to form iron sulfate and then to form hematite(high purity nitrogen as balance gas). While under O2/H2 O atmosphere, pyrite is oxidized to form hematite directly. Steam dominates the promoting of pyrite decomposition under CO2/H2 O at low atmosphere and they have almost the same ability to oxidize pyrrhotine. The effect of CO2 on pyrite transformation is not obvious under O2/CO2/H2 O atmosphere compared with O2/H2 O.