Preliminary experimental study on the affect of water of the hydrogen reduced hematite pellet

University essay from KTH/Materialvetenskap

Author: Henrik Welander; [2021]

Keywords: ;

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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