Ilmenite with addition of NiO as oxygen carrier for chemical-looping combustion

• The naturally occurring mineral ilmenite, FeTiO3, has been examined as oxygen carrier for chemical-loopingcombustion. NiO-based particles have been used as an additive, in order to examine if it is possible toutilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactivecombustion intermediates such as CO and H2. Firstly, ilmenite was examined by oxidation and reductionexperiments in a batch fluidized-bed reactor. These experiments indicated moderate reactivitybetween ilmenite and CH4, which was used as reducing gas. However, adding 5 wt.% of NiO-based particlesto the ilmenite improved the conversion of CH4 greatly, resulting in an increase in combustion efficiencywith a factor of 3. Secondly, 83 h of chemical-looping combustion experiments were conducted ina small circulating fluidized-bed reactor, using ilmenite as oxygen carrier and natural gas as fuel. A widerange of process parameters and different levels of NiO addition were examined. Occasionally, there wereproblems with the circulation of solids between the air reactor and fuel reactor, but most of the time theexperiments worked well. The products were mostly CO2, H2O and unconverted CH4. Adding smallamounts of NiO-based particles to the reactor increased the conversion of the fuel considerably. Forthe base case conducted at 900, the combustion efficiency was 76% for pure ilmenite and 90% for thecorresponding experiments with 1 wt.% NiO-based particles added to the reactor. The properties ofilmenite were found to change considerably during operation. Used particles had lower density, weremore reactive and more porous than fresh particles. These changes appear to have been physical, andno unexpected chemical phases could be identified.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

Ilmenite

Natural Gas

Chemical-looping combustion

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