Preliminary experimental study on the affect of water of the hydrogen reduced hematite pellet
Abstract: Global warming is one of the most important challenges that we are facing today. Since carbon dioxide (CO2) is by far our most common green house gas pollutant, most large corporations need to reconsider how their production is performed to keep the global warming below 2 ◦C. Today the steel production in Sweden accounts for 10% of its total annual emission of CO2. HYBRIT (Hydrogen Breakthrough Ironmaking Technology) is a joint venture between LKAB, SSAB and Vattenfall which aims to develop a new iron making route by reducing iron ore pellets with hydrogen gas, producing water as off-gas instead of CO2. Due to the endothermic nature of the reduction between iron oxide and H2 the reaction requires energy to proceed. During the reduction of a spherical pellet the reduction proceeds through dif- ferent stages, where all of them contains the reaction product of water vapor. This thesis will present and discuss the effect of water vapor during the reduction of a single hematite pellet at 700 ◦C and 900 ◦C, this report also includes a description of the making of an ex- perimental setup to control the H2O partial pressure in the reaction gas. Both temperatures includes three experiments each consisting of different amount of water vapor in the reduction gas, namely, 0% (pure H2), 5.5% and 10% H2O, all reductions were carried out for 60 minutes. The first experiment with pure H2 is used as a reference experiment as comparison to the latter, to be able to discuss the effect of the water vapor. The mass loss during reduction is measured using a thermogravimetric method to calculate the degree of reduction. The results showed that higher temperature led to higher rate of reduction. Further, increasing amount of water vapor decreased the reduction rate. The effect of water was found substantial. The 900 ◦C experiments reached 100% reduction during the 60 minutes. The 900 ◦C experiments reached a reduction of 95% after: 19.6 minutes (pure H2), 23.7 minutes (5.5% H2O) and 38.6 minutes (10% H2O). The 700 ◦C experiments only reached a reduction of around 90%. They reached 85% reduction after 40.6 minutes (pure H2), 45.1 minutes (5.5% H2O) and 53.2 minutes (10% H2O). At 900 ◦C, the reduction with 10% H2O needs double the time compared to 0% H2O to reach the same degree of reduction. The results show that water vapor affect the mass transfer of hydrogen in the gas phase and to the reaction sites as well as the driving force of the reaction.
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